USGS-OFR-91-367 USGS-OFR-91-367

UNITED STATES DEPARTMENT OF THE INTERIOR

GEOLOGICAL SURVEY

Denver, Colorado

SEISMICITY AND FOCAL MECHANISMS FOR THE SOUTHERN GREAT BASINOF NEVADA AND CALIFORNIA IN 1990

Stephen C. Harmsen

Open-File Report 91-367

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CONTENTS

Page

mu- r OQUC t-ion j^Acknowledgements jCalibrations of instruments------------------------- ------ ----------- 3Overview of seismicity in the SGB for 1990 - 3Notable southern NTS seismicity, 1990 - 7Silent Canyon, northwest NTS, seismicity, in 1990 11Death Valley and vicinity seismicity in 1990- - 11Northwestern SGB seismicity, 1990 15Sarcobatus Flat, Oasis Valley, and caldera seismicity, 1990 15Yucca Mountain seismicity, 1990---------------- ------------------------ 19D"*vaj-Ues » j^ySome comments on regional stresses and SGBSN focal mechanisms 22nummary and cQjjcj.usions 2.1~Oo,fc\ vonr>oo r--i + a/1 OCI\C -LcjTcIlCCb 1_1UCU ^Q

Appendix A. SGB earthquake locations for the year 1990, and quadrangleTI'^m/^riwwMH.wwwwwMwww Qf\II cl lilt: o -«-« -. .-. ju

Appendix B. Chemical explosion locations for the year 1990 59Appendix C. Nuclear device tests and low-frequency shallow

seismicity in tne JMlo, 1990 /IAppendix D. Earthquake focal mechanisms for 1990 77Appendix E. Station codes, locations, and instrumentation-------- ----- 96Appendix F. Input parameters to HYP071 101

FIGURES

Page Figure 1.--SGBSN station locations and physiographic features of the

southern Great Basin - 22. --Seismicity in the southern Great Basin, 1990---------------- 43.--Scattergrams of standard error of depth versus nearest

station distance and versus azimuthal gap - 64. --Seismicity and focal mechanism in vicinity of Cane Spring

fault, southern NTS, in 1990 85.--Epicentral scatter and RMS travel time residual graphs

for three Cane Spring hypocenters of January, 1990-------- 96. Seismicity in the vicinity of Cane Spring fault, southern

NTS, 1978 through 1990 107. --Seismicity in vicinity of Silent Canyon caldera during

8. Earthquakes in vicinity of Death Valley, California, (a)in 1990, and (b) in 1978-1989 14

9. Seismicity in the northwestern SGB during 1990- 1610. --Seismicity in the northwestern SGB, 1978 through 1989 1711. --Focal mechanisms in eastern Sarcobatus Flat and western

NTS for 1990 1812. Seismicity in eastern Sarcobatus Flat and western NTS,

1978 through 1990 2013. Seismicity in vicinity of Yucca Mountain, 1990- -- 2114. --Individual and average P and T axes for 1990 focal

mechanisms ^ o

iii

Page Figure 15. Intersected P quadrants and intersected T quadrants for

1990 focal mechanisms - 26 A1-A4. Quadrangle names in:

Al.--northeast quarter of the southern Great Basin 31 A2.--southeast quarter of the southern Great Basin 32 A3.--northwest quarter of the southern Great Basin--- - 33 A4. southwest quarter of the southern Great Basin 34

Bl. Epicenters for detected chemical explosions in thesouthern Great Basin for 1990 - -- --- -- ----- -- 60

Cl. Epicenters for announced NTS nuclear device tests and somepreliminary induced earthquake epicenters- - --- -- 72

C2. Seismograms from four SGBSN stations for an aftershock ofthe test Tenabo 73

D1-D17. Focal mechanism for:Dl.--Skull Mtn. (Cane Spring, Nevada quadrangle)

earthquake 1990-01-26 79 D2. Scrugham Peak, northern NTS, earthquake 1990-02-15 80 D3.--Scrugham Peak, northern NTS, earthquake 1990-02-27 81 D4.--Bonnie Claire SE, Nevada, earthquake 1990-04-21 82 D5.--Bonnie Claire SE, Nevada, earthquake 1990-05-13 83 D6.--Springdale, Nevada, earthquake 1990-06-04 84 D7.--Oasis Valley, Nevada (Black Mountain SW quadrangle)

earthquake 1990-06-25 85 D8.--Jackass Flats, NTS, earthquake 1990-07-22 86 D9. Tucki Mtn. (Stovepipe Wells, Calif, quadrangle)

earthquake 1990-07-25 87 D10.--Springdale, Nevada, earthquake 1990-08-02 88 Dll.--Springdale, Nevada, earthquake 1990-08-03 89 D12.--Stonewall Pass, Nevada, earthquake 1990-08-21 90 D13.--Springdale, Nevada, earthquake 1990-09-05 91 D14.--Springdale, Nevada, earthquake 1990-09-06 92 D15. Springdale, Nevada, earthquake 1990-10-29 93 Dl6.--Mellan, Nevada, earthquake 1990-11-01 94 D17.--Gold Point, Nevada, earthquake 1990-12-13 95

Fl.--The two P and S velocity models used for preliminaryhypocenter determination in the SGB----------- -- 103

TABLES

PageTable 1.--Selected statistical properties of SGBSN catalog for 1990 5

2. Focal mechanism parameters for SGB earthquakes of 1990 24 Cl. Announced NTS nuclear device test hypocenter parameters for

1990 71 El. Seismographic systems in use in SGBSN in 1990- 96

IV

Seismicity and Focal Mechanisms for the Southern Great Basin of Nevada and California in 1990

Abstract

For the calendar year 1990, the Southern Great Basin seismic network (SGBSN) recorded about 1050 earthquakes in the SGB, as compared to 1190 in 1989. Local magnitudes, ML, ranged from 0.0 for various earthquakes to 3.2 for an earthquake on April 3,1990 5:47:58 UTC, 37.368° North, 117.358° West, Mud Lake, Nevada quadrangle. 95% of those earthquakes have the property, ML < 2.4. Within a 10 km radius of the center of Yucca Mountain, the site of a potential national, high-level nuclear waste repository, one earthquake with ML = 0.6 was recorded at 40-Mile Wash. The estimated depth of focus of this earthquake is 3.8 km below sea level. Other, smaller events may have also occurred in the immediate vicinity of Yucca Mountain, but would have been below the detection threshold (ML » 0.0 at Yucca Mountain). Focal mechanisms are computed for seventeen earthquakes in the Nevada Test Site (NTS) and in the SGB west of the NTS for the year 1990. Solutions are mostly strike-slip, although normal slip is observed for a hypocenter at Stonewall Flat, Nevada, and reverse slip is observed for a hypocenter at Tucki Mountain, California. The average direction of the focal mechanism P-axes is North 47° East, with nearly horizontal inclination, and the average direction of the T-axes is North 42° West, with nearly horizontal inclination, consistent with a regional tectonic model of active northwest extension during the Holocene epoch.

Introduction

The SGBSN has operated continuously since August, 1978, with the current complement of 54 stations in place by mid-1981. Horizontal-component seismographs were added in 1984, and a vertical-component seismograph south of Boulder City, Nevada, was added in August, 1988. Figure 1 shows the current station locations, along with some of the major physiologic features. Stations CPX and EPN were moved to less noisy sites in August and September, 1990, and renamed CPY and EPM, respectively.

The primary purpose of the network is to investigate the seismotectonic environment in the vicinity of Yucca Mountain, Nevada, the potential site of a high-level, national nuclear waste repository. Also, the network provides information on seismically active regions within about 160 km radial distance of Yucca Mountain. Seismic signals from the network are continuously teleme­ tered to the USGS data processing center in Golden, Colorado, where preliminary hypocenter determination is performed, along with research on focal mechanisms and faulting, on fluid- induced seismicity, on attenuation of seismic waves, on velocity structure, and on other topics of importance to the Yucca Mountain Project.

Operation of the seismic network is funded under an interagency agreement with the De­ partment of Energy, which provides Quality Assurance guidelines for the collection, analysis, interpretation, and reporting of data. The seismic network data are collected as permanent records to support site characterization. Because seismicity data in the SGB come from sources and crustal paths that are, at best, approximately known, the hypocenters and analyses that are presented in open-file format are necessarily preliminary. Any "final" report of seismicity in the SGB should integrate information from all relevant sources, whereas the open-file reports of SGB seismicity periodically published by the U.S.G.S., such as this one, are less comprehensive. All hypocenters and focal mechanisms discussed in this report are preliminary.

Acknowledgments

Maintenance and periodic calibration of seimic stations and related field equipment is per­ formed by D. E. Overturf of the U. S. Geological Survey, and by contract technicians. Preliminary

118 117 116 115

ZS SO 100

MR-Montezuma Range SF-8ar cobatus Ft at OV-Oaala Val I ey LCR-Last Chance Range GVM-Qr apevln* Mtns.

V SHSUOCKAPH STATION

a cmr OR TOTTN TM-Timber Mtn. CF-Crater Flat

SR-Specter Range YM-Yucca Mtn. BM-Bare Mtn.

PM-Pahute Mesa YF-Yucca Fl at RM-Ralnler Mesa LVV-Las Vegas ValleyMV-Mercury Valley LM-Lake Mead EM-EI dorado Mtns. FF-Frenchman F!ai

NTS-Nevada Test Site

Figure 1.- Map of SGBSN seismograph station locations, cities and towns, and major physio­ graphic features of the southern Great Basin.

seismic event catagorizations, phase arrival time determinations, and hypocenter determinations were performed by Miles Weida and Joel Duggar, also of the U. S. Geological Survey.

Helpful reviews of this report were provided by Joan Gomberg and Margaret Hopper of the U.S. Geological Survey, Branch of Geologic Risk Assessment.

Calibrations of Instruments

All seismographic systems in the SGBSN are periodically calibrated as specified in the Qual­ ity Assurance document, YMP-USGS Seismic Procedure 11. Seismometers are visited and cal­ ibrated every six months, or as needed. Calibration results are deemed acceptable when the amplitude response of a seismographic system lies within a ±30% range of a nominal response, in the frequency band 2 < / < 10 Hz. In actual field calibrations, systems are tested in the frequency band 0.1 < / < 20 Hz. In these calibrations, the S13 systems generally display an amplitude response within 10% of the nominal level at all measured frequencies, while the L4C systems display responses within 25% of their nominal levels for frequencies 1 < / < 10 Hz. For / < 2 Hz, the true system magnifications are rarely required, because wavelet periods corre­ sponding to peak-amplitude S-waves observed on seismograms of local SGB earthquakes, which are scaled to obtain ML estimates, are almost always < 0.5 seconds.

Overview of Seismicity in the SGB for 1990

Epicenters for all earthquakes occurring during the calendar year 1990 in the SGB for which preliminary hypocenters could be determined are listed in Appendix A and shown in Figure 2. The southwestern part of the region is better covered by the Caltech seismic network at Pasadena, California, and any study of strain and seismicity rates in the southwestern SGB would benefit by merging data from their catalog with the SGBSN catalog. Many other portions of the SGB shown in Figure 1 are extremely sparcely covered by SGBSN stations, or not covered at all, except for short-duration special studies conducted by other networks or laboratories. The SGBSN also archives regional and teleseismic data and regularly provides it to interested investigators. Epicenters for chemical explosions and probable explosions that were located by the SGBSN are listed in Appendix B, and are shown in Appendix B, Figure Bl. Epicenters for nuclear device tests at Nevada Test Site (NTS) are listed in Appendix C, and are shown in Figure Cl. Some probable nuclear device detonation aftershock epicenters and cavity-collapse related activity, located in the Silent Canyon Caldera, are denoted by "L" (low-frequency event) in Figures 2, 7, and Cl. They are also listed in Appendix C. Focal mechanism solutions derived from data collected by the SGBSN for 17 earthquakes of 1990 are shown in the figures of Appendix D. Appendix E contains station information, and Appendix F contains information about input parameters to the hypocenter location program HYPO71.

The earthquake data base whose hypocenters are listed in Appendix A is derived from SGBSN seismic signals that were captured by a computer dedicated to seismic monitoring, and from data read from 16 millimeter develocorder films, which serve as a backup to the computer detection system. Events read from the develocorder are labeled with a D in the "quality" field of each hypocenter record of Appendix A. Measurements made from seismograms recorded on the computer are generally more reliable, with impulsive P and S arrivals being determined to an accuracy better than 0.02 sec (digitizing rate=104.167 sps/channel), versus 0.10 sec for arrivals read from develocorder film. Hypocenters derived from computer-recorded events are labeled "I" in the quality field. Seismograms from all SGBSN stations that display a usable signal for a given local earthquake are written to computer magnetic tapes for permanent archiving. Copies of these tapes are periodically distributed to the U.S.G.S. Local Records Center, and are available to interested investigators after annual seismicity reports are published.

118 West 117 116 115

37.6

- 36.6

11825 50 100 km

iYM-Yucca Mta

V SEISMOGRAPH1C STATION D CITY OR TOWN

mag < 1.0 o 2.0 5 mng < 3.0o 1.0 i mag < 2.0 O 3.0 £ mag

114.5

Figure 2.- Earthquake epicenters in the SGB for the year 1990. Boxes indicate regions discussed in subsequent text and figures.

As many as five magnitude estimates are determined per event, (1) coda-average magnitude, Mca , (2) duration magnitude, Mp, (3) local magnitude from horizontal component instruments ML°T ) (4) local magnitude from vertical component instruments, MLer , and (5) local magnitude from clipped records, M£*P . These are discussed in previous SGBSN data reports (for example, Rogers and others, 1987). Standard error estimates in the hypocentral parameters are routinely calculated in the program HYPO71 (Lee and Lahr, 1975), and some of these are listed in Appendix A. Table 1 summarizes some of the hypocentral parameters computed by HYPO71 for the digitally recorded earthquake data of 1990. In Table 1, JRMS is the average traveltime residual, # P+S Phases is the number of phases used by the algorithm, Gap is the maximum azimuthal angle without a station, Depth is the depth of focus estimate, Err(z) is the estimate of standard error in depth, and Amjn is the minimum source-to-station epicentral distance.

Table 1. Selected statistical characteristics of a subset of the 1990 SGBSN seismicity catalog. 1

Statistic

MeanMedian

MaximumMinimumN# obs.

RMS (sec)0.1540.13 2.160.00946

Phases15.113 564

946

Mca

1.541.48 3.800.66736

McLltp

1.671.60 4.000.80358

MD

1.301.27 2.500.4033

Mr1.491.44

3.74s0.10528

Mr1.311.25 3.230.02909

Gap (deg.)157.8147 33242.879

Depth 2

(km)3.963.31

20.22-2.0

879

Err(z) (km)2.481.30 28.70.0879

(km)16.4712.3

141.00.2879

1 Only events captured by digital monitoring system are included. Also, only events with Err(z)< 30 km are included in the tabulations for Gap, Depth, Err(z), and Am»n .2 Depth of focus is relative to sea level (0.0 km), positive below.3 One-station estimate, NEIC ML = 3.1 for this earthquake.

The average magnitude for SGB hypocenters of 1990 is about 1.5. Furthermore, 95% of those hypocenters have ML < 2.4. To further illustrate statistical properties of the hypocenter catalog, plots of err(z) versus Am»n and err(z) versus source-to-station gap are shown in Figure 3. Although err(z) correlates positively with these two parameters, the scattergrams show that the correlation is weak, and many events having no nearby stations and/or poor coverage nevertheless are reported with relatively low err(z) estimates (< 2 km). This tendency of HYPO71 to underestimate uncertainty in depth estimates is shared by many currently available hypocenter determining algorithms. This point is discussed by Gomberg and others (1990).

Earthquake hypocenter determination requires that the investigator make a number of sim­ plifying assumptions about the nature of rock being sampled by seismic rays. In this report and all prior SGBSN data reports, the earth models are assumed to be a sequence of horizontal layers with constant P-wave and S-wave velocities are constant. The ratio of P to S velocity is assumed constant in the medium, implying that the raypaths for those two body waves are identical. Appendix F shows the two standard models, one for the immediate vicinity of Yucca Mountain and the other for the rest of the southern Great Basin. Even for a fixed earth model, variations in hypocenters may result from varying initial conditions (e.g., starting hypocenter) and data weighting schemes. Some of these factors are discussed in the 1987 through 1989 seismicity report (in preparation). To reduce the chance of HYPO71 iterations converging to a local rather than the global RMS minimum, starting depths of both zero and seven km are used; the reported hypocenter in Appendix A is the one having the minimum RMS. In the case of equal RMS values, the hypocenter resulting from the seven km starting depth is (arbitrarily) reported. No algorithm is known that "finds" the true earth model;

1990

(A)

DO %o

20 40 60 80 100 120 140

Mm. Epicentral distance (km)

10 20 30 40

Mm. epicentral distance (km)

30 60 90 120 150 180 210 240 270 300 330

Maximum angular gap (degrees)

Figure 3.- (a) HYPOTl's estimated standard error in depth of focus (km) of SGB earthquakes for 1990 versus distance in km to nearest station with a usable P or S phase arrival time reading, (b) Close-up of inner 50 km of the data plotted in (a), (c) Estimated standard error in depth of focus of SGB earthquakes for 1990 versus source to station gap in degrees.

all available computer codes tend to smooth the earth's roughness, and thereby probably bias hypocenters in ways that defy simple error-statistic estimation. One may infer a strong appar­ ent horizontal velocity anisotropy from SGB P-wave traveltimes from Rainier Mesa and western Yucca Flat nuclear device sources. Although these observed variations correspond to very shallow crustal depths (probably not exceeding five to ten km below the earth's surface), and may not be representative of local earthquake source-to-station raypaths, they are strong enough to result in epicenter errors of three km for Rainier Mesa tests recorded at SGBSN stations when using standard, horizontally isotropic, earth models and HYPO71 to determine the hypocenter. Most NTS tests are located to within about one km of the true epicenter, however.

The multiple sources of hypocenter estimate uncertainty need to be considered when making generalizations about the spatial distribution of SGB seismicity. Redetermination of hypocenters using a variety of plausible earth models should be performed to discover the range of hypocenters that could be associated with a given earthquake's phase arrival time data before one concludes that the data unequivocally demonstrate the validity of some favorite hypothesis. Revisiting the data in this way should result in the development of a more viable data base of hypocenters, which is less dependent on vagaries of computer programs and model biases than the current catalog.

Notable Southern NTS Seismicity, 1990

Microearthquakes occur sporadically in the SGB, with detection rates varying from zero per day to a few dozen per day. The first relatively concentrated seismicity for 1990 began on January 26, at the northernmost end of Skull Mountain, Nevada Test Site. A focal mechanism was prepared for the mainshock of January 26, 1990, 10:34:15 UTC, having ML = 2.5, Am»n = 6.4 km, depth about 5 km below sea level. The solutions indicate predominantly right-lateral strike slip motion on an east-dipping, nearly north-south oriented fault, or predominantly left-lateral strike slip motion on a north-dipping, east-west oriented fault (Figure Dl). The mainshock is one of about two dozen late January microearthquakes loosely distributed under the northern end of Skull Mountain. The most prominant fault in the vicinity is the Cane Spring fault, a left-lateral strike-slip fault trending w North 50° east, which may define the south-eastern boundary of Skull Mountain (Poole and others, 1965, Ekren and Sargent, 1965). The focal mechanism solutions for this Skull Mountain earthquake are not consistent with motion on the Cane Spring or en echelon Skull Mountain faults in its vicinity. Depth sections of the Skull Mountain series hypocenters, shown in Figure 4, show that events extend from near-surface to a depth of about six km below sea level. Examination of the behavior of the root-mean-square travel-time residual (RMS} as a function of assumed focal depth indicates that for some of these events the shallowest hypocenters are poorly resolved. Figure 5 shows that RMS does not increase significantly with focal depth until about six km below sea level. (This ambiguity could be reduced by increasing near-source station density which may be possible by deploying a temporary portable seismic net.) Figure 6 is a map of all preliminary epicenters in the same region as those of Figure 4 for the time period August, 1978, through December, 1990. The average number of microearthquakes detected and located by the SGBSN in this map region per year prior to 1990 is 42. For 1990, the number is 72.

Seismicity in the vicinity of the Cane Spring fault is examined here because the suggestion has been advanced (Ken Fox, written communication) that a semi-continuous belt of seismicity monitored by the SGBSN may illuminate a fault zone that extends northeast from the Amargosa Desert of California and Nevada to the Pahranagat Shear Zone, southeast of Alamo, Nevada (see Figure 1 for locations). If such a fault zone exists, it is difficult to find major surface-breaking faults in the NTS that align with the zone and with seismicity concentrations. Gomberg (1991) explores plane

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116.25 116.00

Figure 4.- Preliminary epicenters and depth sections of hypocenters in the vicinity of Skull Moun­ tain and Cane Spring fault, Nevada Test Site, for the year 1990. The concentration of epicenters north of the fault, in the northernmost part of Skull Mountain, occurred in late January, 1990.

0.7_ _ CANE SPRING9 900126 9 55 56

DBA

0> Q

0--

-0.2

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587

3

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4 2 3 n C 9081-7:

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CD »Pha-55 Gap- 47 Dmin- 6.6 C in -,

BB M

-0.7l l l

11 13 15

Delta X(km) Fixed H (km)

Figure 5.- Left Side: Plots of variations in epicenter with assumed depth of focus for the mainshock and two very shallow hypocenters in the Skull Mountain series of late January, 1990. The letters correspond to depth: 0, 1,2,..., A, B, C, ... are zero, one, two, ..., 10, 11, 12, ... below sea level (hexadecimal notation). "M" refers to the epicenter for the solution with depth fixed at one km above sea level. "S" and "Z" refer to free depth epicenters, with z0 = 1 and 0 km, respectively. Right Side: Plots of RMS travel time residual as a function of assumed depth of focus corresponding to the same earthquake data. The letters above the (z,y) points are HYPOTl's "grades," which are always assigned to hypocenters, and are frequently used to assess their relative accuracy. The velocity model used in hypocenter determinations for these plots has Vp = 4.9 km/sec in the shallowest layer, and Vp = 6.0 km/sec in the second layer.

.0

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00 O0 e

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116.2536.7

0 1 2.5I I I

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11D V SEISMOGRAPHIC STATION

mag < 1.0 o 2.0 £ mag < 3.0 o 1.0 £ mag < 2.0 O 3.0 ^ mag

Figure 6.- Earthquake epicenters in the same part of southern NTS as shown in Figure 4 for the period August, 1978, through December, 1990. The extended catalog shows concentrations of activity at several places away from the Cane Spring fault, but none on the fault, which is mapped as vertical by Poole and others (1965).

10

strain boundary element models to show that major faults in the SGB may modify a regionally uniform shear strain field to distribute concentrations of shear strain away from the major fault traces. Concentrations of shear strain are found where faults bend and terminate. Therefore, the relative absence of seismicity between Frenchman Flat and the Pahranagat shear zone may not indicate the lack of northeast-trending faults connecting these two zones of relatively high seismicity. Instead, such faults, if they exist, may be unusually long and straight. Alternate interpretations of the low levels of seismicity between southern NTS and the Pahranagat Shear Zone cannot be ruled out. Because SGBSN station coverage is at its sparsest at Nellis Air Force Range, east of NTS, with a resulting higher-than-average detection threshold magnitude, the SGBSN catalog provides little information to corroborate various hypotheses about crustal deformation there.

Silent Canyon, Northwest NTS, Seismicity, in 1990

A series of earthquakes in the southern Silent Canyon Caldera (SCC), northern Nevada Test Site, occurred in mid-February through late February, 1990, with sporadic tremors in later months. A map of epicenters for Silent Canyon Caldera activity for 1990 is presented in Figure 7. The hypocenters are concentrated at a depth of about seven km below sea level, with few less than six km. Depth sections (not shown) indicate the possibility of a northeast-dipping seismically active plane, although patterns such as this may be due to depth-epicenter tradeoffs associated with hypocentral uncertainty rather than to structure. Graphs of the S-wave traveltime versus the P-wave traveltime for several SCC events ("Wadati diagrams") suggest that locally, Vp/Vs = 1.81 ± 0.03, somewhat higher than the regional average (1.71). Inputting the 1.81 ratio into HYPO71 results in SCC event hypocenters being about one km shallower than those reported here.

Typically, source spectra S-wave corner frequencies, /c , for SCC events, especially those associated in time and space with nuclear device tests, are low, with fc < 5 Hz. The February seismicity is unusual for SCC in that its frequency content is more typical of most SGB subregions, with observed source corner frequencies, fc > 10 Hz, that one expects for micro earthquakes. SCC is geologically complex, and variation in frequency content of seismic coda for events in different parts of the caldera may indicate strong local variations in Q as well as variations in seismic source properties.

Focal mechanism solutions for two of the February, 1990 SCC series earthquakes are shown in Appendix D, Figures D2 and D3. Both focal mechanisms indicate oblique strike-slip, normal-slip motion, although details of nodal plane orientations differ. Earthquakes having these sorts of focal mechanisms might be expected in a region having &H & 0"«> with &H oriented in a WSW-ENE direction, if a Coulomb yield criterion with a coefficient of friction, /i w 0.75, is required, and prin­ cipal horizontal compressive stresses having magnitudes, GH w 4<7^, are locally present (Morrow and Byerlee, 1984; Harmsen and Rogers, 1986). The February, 1990 SCC series is well modeled by the standard double-couple focal mechanism, and the distribution of P-wave first motions nei­ ther suggests nor requires the presence of a substantial component of an isotropic (volumetric) component to the source moment, unlike the almost exclusively dilatational distribution of P- wave polarities for a few SCC earthquakes following BENHAM and other Silent Canyon Caldera nuclear device tests.

Death Valley and Vicinity Seismicity in 1990

Death Valley is considered to be one of the most tectonically active regions of the southern Great Basin. Hamilton (1988) states that "Death Valley is now being widened obliquely as the ranges to the west move relatively northwestward away from those to the east. ... The northwest- trending [Furnace Creek and Death Valley] strike-slip faults are thus transform faults to the

11

1 16.55

1990 Seismicity 116.45 116.35

116.65

10 km V SEISMOGRAPHIC STATION

116.2537.4

37.3

BlackMountainCaldera

Silent Canyon Caldera

Sleeping /Butte /Segment /

Timber Mountain

i\ I I Resurgent

-37.2

1116.25

1 ' ' ' « mag < 1.0 o 2.0 £ mag < 3.0o 1.0 S mag < 2.0 o 3.0 < mag

Figure 7.- Preliminary epicenters in the vicinity of Silent Canyon Caldera for high-coda-frequency earthquakes (shown as hexagons) and low-coda-frequency probable nuclear-testing induced events (shown as "L"s) recorded in 1990. Focal mechanism solutions for two earthquakes that occurred in February, 1990, are plotted near their epicenters. Caldera complex boundaries are shown (W. J. Carr, written communication).

12

extension recorded by the oblique slip on the north-trending Black Mountains frontal faults" (p72- 73). The SGBSN geographic coverage was designed to permit monitoring of seismicity having ML > 1.5 in the vicinity of central and northern Death Valley. During the period 1979 through 1990, the central part of Death Valley has been relatively quiet, although activity localized at Tucki Mountain and in the eastern Panamint Mountains, bounding Death Valley to the west, are notably elevated relative to the regional levels. Figure 8a shows all earthquake epicenters for 1990 in the vicinity of the central part of Death Valley, and Figure 8b shows all epicenters for previous years of SGBSN monitoring, 1978 through 1989 (stations shown in Figure 8 define the western perimeter of the network; west of the stations seismic monitoring is far less complete). The central valley has a nearly complete absence of earthquake epicenters. Other faults known to have had surface movement in the last two to three million years are also shown in Figure 8; correlation of epicenters with some of these faults is evidently much better than with the main Death Valley fault or the Furnace Creek fault. Hamilton goes on, "the continuing Quaternary extension of this [central] section of Death Valley may be accomodated by slip on a fault that dips westward from the west base of the Black Mountains, ..., the continuation of that fault beneath the west side of the valley and the Panamint Mountains is at a very gentle angle ..." (Hamilton, 1988, p. 76-77). The SGBSN may be monitoring seismicity on a detachment fault, perhaps at its intersection with other faults, or on other complicated structures in Death Valley, rather than seismicity on the main strike-slip faults. Slip on the Furnace Creek and Death Valley faults must be episodic, with the seismic network monitoring a quiescent moment in its evolution, or slip is aseismic, occurring primarily by creep. The former alternative may be plausible if rock of the central valley is experiencing significantly lower fluid pore pressures than that of the region to the west. A study of the spatial correlation of microseismicity levels (number of events; cumulative moment) with hydrologic parameters in the vicinity of Death Valley should be informative.

The focal mechanism shown in Figure 8(a) (also in Appendix D, Figure D9) for an earthquake at Tucki Mountain, California, that occurred on July 25, 1990, 00:52:50 UTC, is the only example of a reverse-slip solution for data analysed in this report. (A focal mechanism for an earthquake on March 16, 1982, at northern Tucki Mountain, California, one of whose nodal planes also displays a large component of reverse slip, is discussed in Harmsen and Bufe (1991).) The epicenter of that lone 1990 earthquake is at the southeast end of a northwest-trending lineation of earthquakes that occurred sporadically over several years of monitoring. The northeast dipping nodal plane of the focal mechanism, if the fault plane, indicates that the rock of Death Valley is pushing over a possible mountain-bounding fault in eastern Tucki Mountain. If the alternate nodal plane is the fault plane, then the rock of Death Valley is pushing under Tucki Mountain. From the principal of minimum energy, the work required against gravity favors slip on the former nodal plane. That the SGBSN observes reverse slip in what some geologists claim is the most actively extending region within the SGB may appear ironic; however, if Tucki Mountain is an obstacle to that extension, then reverse slip may be a required component of the total crustal deformation response in its vicinity. Furthermore, thrust at Tucki Mtn. is predicted by models of strike-slip along a curved fault, in this case, from the Furnace Creek fault to the Death Valley fault. There is excellent agreement between the deformation implied by the Tucki Mtn. focal mechanism and "secondary structure" predicted by a laboratory-scale photoelastic model of stress along a curved fault (Freund, 1974, his Figure 27).

Because of the extremely low rate of occurrence of small-magnitude earthquakes in central Death Valley, a more complete picture of current crustal deformation there is difficult to obtain. It is plausible that the rock of the central valley has greater hydraulic conductivity, and consequently lower pore pressure, than the rock of the surrounding mountain ranges, resulting in greater effective normal stress across the major faults than exists across the secondary faults in the

13

(A)

1990

seis

mic

ity

117

(B)

Pre

-1990 s

eis

mic

ity

117

36.5

-

117.

511

6.5

117.

5

- 3

6.5

116.

5

1020

30

km

V

SEIS

MO

GR

APH

IC

STA

TIO

N

mag

<

1.0

o 1.

0 ^

mag

<

2.0

O

D

CIT

Y O

R T

OW

N

2.0

^ m

ag

< 3.

0 3.

0 ^ m

ag

Fig

ure

8.-

(a)

Pre

lim

inar

y ep

icen

ters

in

the

vici

nity

of

Dea

th V

alle

y, C

alif

orni

a, f

or e

arth

quak

es

duri

ng t

he

cale

ndar

yea

r 19

90,

and

faul

ts t

hat

may

hav

e ha

d su

rfac

e m

ovem

ent

in t

he

last

tw

o to

th

ree

mil

lion

yea

rs.

Foc

al m

echa

nism

, w

ith

com

pres

sion

al q

uad

ran

t da

rken

ed,

is f

or a

n ea

rthq

uake

of

Jul

y 25

, 19

90,

0:52

UT

C.

(b)

Pre

lim

inar

y ep

icen

ters

in

the

sam

e re

gion

as

Fig

ure

8(a)

for

the

peri

od A

ugus

t, 1

978

thro

ugh D

ecem

ber,

198

9.

mountain ranges surrounding Death Valley. It is also possible that the Death Valley-Furnace Creek fault system is experiencing a quiescient moment in its evolution, or that deviatoric stress levels are low (Rogers and others, 1991), or that the northwest trend of the Furnace Creek fault is not suitable to permit slip in the current stress field.

Northwestern SGB seismicity, 1990

In the northwestern section of the southern Great Basin, several small series of earthquakes occurred in 1990, and four earthquakes in the region were analysed for focal mechanisms (Figure 9). On April 21, 17:55:52 UTC a strike-slip earthquake having ML = 2.0 occurred at the western edge of Sarcobatus Flat, about 16 km south of Scottys Junction, Nevada (mechanism labeled "1" in Figure 9; Appendix D, Figure D4). The estimated depth of the earthquake is 7.2 ± 1.4 km below sea level. On May 13, 00:48:11 UTC, an oblique normal-slip, strike-slip earthquake having ML = 1.9 occurred about 2.7 km east of the April 21 earthquake (mechanism labeled "2" in Figure 9; Appendix D, Figure D5). The estimated depth of the May 13 earthquake is 6.3± 1.5 km below sea level. On November 1, 07:51:46 UTC, a normal-slip earthquake having ML = 2.4 occurred in Stonewall Flat about 18 km ESE of Goldfield, Nevada (mechanism labeled "3" in Figure 9; Appendix D, Figure D16). The estimated depth of the earthquake is 6.0± 1.4 km below sea level. On December 13, 01:01:00 UTC, a strike-slip earthquake having ML = 2.8 occurred about 1 km east of the town of Gold Point, 14 km SE of Lida, Nevada, in an unnamed alluvial valley west of Mt. Dunfee (mechanism labeled "4" in Figure 9; Appendix D, Figure D17). The estimated depth of the December 13 earthquake is 2.8 ± 1.0 km below sea level.

The northwestern SGB has been perennially seismically active, and listings and discussions of preliminary hypocenters from the SGBSN may be found in Rogers and others (1987), Harmsen and Rogers (1987), and Harmsen and Bufe (1991). Figure 10 shows all epicenters determined by the SGBSN prior to 1990. Besides the areas seismically active in 1990, notable concentrations of seismicity may be discerned in previous years' monitoring in the Montezuma Range, in the Palmetto Mountains west of Lida, Nevada, in the Last Chance Range, at Gold Mountain and the Grapevine Mountains, in northern Death Valley, and in various other mountains and valleys. The strike-slip focal mechanism for the earthquake of December 13 contrasts with predominantly normal-slip mechanisms for earthquakes about 5 to 10 km east of the December 13, 1990, epi­ center, reported in the three just-cited open-file reports. This close proximity of strike-slip and dip-slip styles of deformation argues for the local presence of an axially symmetric stress field in the vicinity of Slate Ridge, Nevada.

Sarcobatus Flat, Oasis Valley, and caldera seismicity, 1990

Central and eastern Sarcobatus Flat also have been seismically active during the period of operation of the SGBSN. Seismicity at Sarcobatus Flat for the period 1978 through 1983 is reviewed in Rogers and others (1987), and listings of subsequent seismicity are given in Harmsen and Rogers (1987) and Harmsen and Bufe (1991). Many clusters of seismicity continued to be observed in eastern Sarcobatus Flat during 1990. Predominantly strike-slip focal mechanisms for five earthquakes in eastern Sarcobatus Flat are shown in Figure 11 (mechanisms 2, 5, 7, 8, and 9, respectively; Appendix D, Figures D6, D10, D13, D14, and D15, respectively). Magnitudes for these Sarcobatus Flat events range from ML = 1.1 for an earthquake of August 2, 1990, 05:15:02 UTC to ML = 2.6 for an earthquake of October 29, 1990, 02:37:27 UTC. Depth estimates range from 0.5 ± 0.5 km below sea level for an earthquake of September 6, 1990, 10:32:18 UTC, to about 5.0 ± 1.4 km for earthquakes in September and October. Figure 11 also shows two focal mechanisms (numbers 3 and 6) near the western edge of the volcanic calderas that form the western part of NTS, one (number 3) an oblique strike-slip, normal slip mechanism for an

15

SYLVANIA MTOS

117.7

117.5

1990 seismicity

117.3 117.1

GOLDFIELD D

STONEWALL FLAT

LJDA D V

D ' SCOTTYS JUNCTION

37.75

37.6

37.4

37.2

11737

0 2 5 10 kmill I

V SEISMOGRAPHIC STATION D CITY OR TOWN

mag < 1.0 ° 2.0 £ mag < 3.0 1.0 < mag < 2.0 o 3.0 < mag

Figure 9.- Seismicity recorded in the northwestern part of the SGB during 1990, with four focal mechanisms plotted near their corresponding epicenters.

16

Seismicity 8/78 through 12/89

117.5 117.3 117.1

GdLDFIELDD

STONEWALL FIAT

o . 8"

SCOTTYS JUNCTION

r

37.75

37.6

37.4

37.2

117.7 11737

0 2 5 10 kmIII I

V SEISMOGRAPHIC STATION D CITY OR TOWN

mag < 1.01.0 < mag < 2.0

° 2.0 ^ mag < 3.0 o 3.0 < mag

Figure 10.- Seismicity recorded in the northwestern part of the SGB during the period August, 1978, through December, 1989, i.e., during the recording period of the SGBSN prior to 1990.

17

Sarcobatus

Flat

Olack Mtrt

V Caldera

^^.Sfeeplng

/ Butte y/ Segment

Oasis Valley \ Segment

D

BEATTY.I \j x /Segment Yucca( v l [

<

NTS

D V

AMARGOSA VALLEY

37.5

11736.5

086 10 km ill i

116.25 V SEI3MOGRAPH1C STATION D CITY OR TOWN

o mag < 1.0

O 1.0 £ mag < 2.0

O 2.0 i mag < 3.0 O 3-0 £ mag

Figure 11.- Map of eastern Sarcobatus Flat and western NTS, showing caldera boundaries (W. Carr, written communication, 1990) and focal mechanisms for earthquakes of 1990, labeled "1" through "9." The inner and outer dashed rings surrounding the resurgent dome of the Timber Mountain Caldera represent minimum and maximum estimates of its extent, respectively.

18

earthquake on June 24, 1990, 23:55:38 UTC, west of the Black Mountain Caldera, having ML = 1.9 (Appendix D, Figure D7), and one (number 6) a strike-slip mechanism for an earthquake on August 3, 1990, 20:23:55 UTC having ML = 2.3 with epicenter at the western edge of the Oasis Valley segment of the Timber Mountain-Oasis Valley caldera complex (W. Carr, written communication, 1990) (Appendix D, Figure D9). Figure 11 displays another predominantly strike-slip focal mechanism solution for a ML = 1.1 earthquake at Little Skull Mountain on July 22, 1990, 08:17:14 UTC (mechanism 4; Appendix D, Figure D8). Seismicity recorded by the SGBSN for the period August 1, 1978 through December 31, 1990 in the same map region as Figure 11 is plotted in Figure 12. This plot shows that Yucca Mountain, a seismically quiet place, is surrounded by zones of variable - but generally higher - seismicity levels. The western edges of the volcanic caldera complexes appear to help define a diffuse, but distinctly visible, north-south trending seismicity zone having length in excess of 50 km, which we designate as the "Oasis Valley lineament" (A. M. Rogers and others, 1989, written communication).

Much of the diffuse seismicity in the interior of the Silent Canyon Caldera is low-frequency activity associated with the Department of Energy's nuclear device testing program (e.g., cavity collapses), but most other seismicity shown in Figure 12 is natural (epicenters from a few mining blasts may have been misidentified as earthquake epicenters). The concentrations of seismicity at some caldera and resurgent dome boundaries (e.g., Sleeping Butte segment boundary with Timber Mountain caldera segment, labeled A in Figure 12; northeastern edge of Timber Mountain caldera segment, labeled B; southern edge of Timber Mountain resurgent dome, labeled C) are spatially similar to concentrations of seismicity along the southern edge of the Long Valley caldera (Savage and Cockerham, 1984) which were widely held to be associated with dike intrusion. However, I do not wish to imply that these Timber Mountain seismicity patterns suggest the possibility of an active volcanic process, only the possibility that caldera boundaries may continue to act as stress concentrators some 9.5 million years after active volcanism occurred. Alternatively, one may argue that zones or pockets of concentrated seismicity are observed throughout the SGB, and the coincidence of some of them with caldera boundaries is not sujGEicient evidence to conclude a causal relationship between the two. The spatial relationship between seismicity and caldera structure is not new to the SGBSN data set. McKeown (1975) also noted that aftershocks of the megaton-yield series of Pahute Mesa nuclear explosions of the late 1960s were mostly confined to caldera faults and caldera-bounding faults ("ring fractures"). Aftershock distributions rarely extended away from the calderas along basin-and-range faults.

Yucca Mountain Seismicity, 1990

No earthquakes were detected by the SGBSN at Yucca Mountain in 1990; the nearest earth­ quake occurred in 40-Mile Wash four km east of Yucca Mountain Jan 14, 1990, 14:57:54 UTC, ML 0.6 (Figure 13a). The depth of focus was well constrained at about 3.8 km below sea level using the velocity model of Appendix F, Figure F2 (the Yucca Mountain model) (Figure 13b). Polarities of P-wave first motions were too ambiguous to usefully constrain focal mecha­ nism nodal planes. A temporary portable microearthquake network installed by the University of Nevada, Reno, Nevada, in the vicinity of Yucca Mountain during the last quarter of 1990, capable of recording earthquakes having magnitudes as low as ML 1.0, also showed that Yucca Mountain is seismically quiet (Brune and others, 1991). Microseismicity at Yucca Moun­ tain recorded by the SGBSN in previous years is discussed in Rogers and others (1987), Harmsen and Rogers (1987), and in an upcoming report on SGB seismicity for 1987 through 1989.

b-values

This report does not intend to provide a comprehensive analysis of b-values for SGBSN data.

19

117.0

37.5

025 10ill i

CP Q I 36.5 116.25

V SElSMOGRAPfflC STATION D CITY OR TOWN

o mag < 1.0 O 2.0 Z mag < 3.0

O 1.0 £ mag < 2.0 O 3-0 £ mag

Figure 12.- Seismicity in eastern Sarcobatus Flat and western NTS during the period August, 1978, through December, 1990, showing caldera boundaries (W. Carr, written communication, 1990). A concentration of seismicity at the Timber Mountain Caldera-Sleeping Butte segment boundary is labeled "A." Another concentration, at the northeastern boundary of the Timber Mountain Caldera, is labeled "B," and a third, at the southeastern edge of the resurgent dome of the Timber Mountain Caldera, is labeled "C." A few other seismicity concentrations at caldera boundaries are evident, but unlabeled. No attempt was made prior to about 1982 to exclude seismicity, either aftershocks or cavity collapses, that resulted from the Department of Energy's nuclear device testing program. After 1982, reporting of such phenomena was gradually phased out of the SGBSN catalog. Such activity may comprise the majority of epicenters shown in the Silent Canyon Caldera.

20

IA)

o o

cV)CO

Crater Flat

37

118.3536.75

10 kmV SEISMOGRAPH1C STATION

O mag < 1.0

O 1 - 0 ^ niog < 2.0

(B)0.8 T0P0PAH SPRING SV M

-

'E I>~ ~<o --^ 0-

0>Q -

-n P

900114 14 57

123ZD B

78

4

: E

54

aBcD

K B «Pha-19 Gap- 60 Dmin- 0.8 B

CD

(f) <">-UJ O QL

U)

-0.6 0.6 -1 1n i i i 9 11 13 15

Delta X(km) Fixed H (km)

Figure 13.- (a) Seismicity detected by the SGBSN in the immediate vicinity of Yucca Mountain, Nevada, during the calendar year 1990 is confined to one earthquake at Forty-Mile Wash, shown with filled-in epicenter. A few earthquakes at Bare Mountain are also shown, (b) Left. Epicentral variation with assumed focal depth for the 40-Mile Wash earthquake shown in Figure 13(a), with letters having the same meanings as in Figure 5. Right. Variation in RMS residual as a function of assumed depth of focus. Note the much improved definition of the depth estimate (relative to the RMS criterion) when nearby station data are present when compared to the RMS graphs of Figure 5. Letters above and below the (x, y) points again correspond to HYPO71 "grades" assigned to the hypocenters.

21

However, because b-values are frequently considered when seismologists attempt to characterize the seismotectonic framework of a region, a few estimates are provided here. Only SGBSN data for the calendar year 1990 are used in the following determinations, also, only local magnitudes are considered.

The goal is to estimate the coefficient b in the relationship,

log AT; = a + bMLi,

where N^ is the number of earthquakes in each "magnitude bin," within which the hypocenter magnitudes have the property \MLJ ML+\ < dM, where MLJ is the jth magnitude reading, and » the »th bin, with midpoint Mn t and dM is the half-interval width. Various estimation methods (least-square, maximum likelihood, and others) are used to estimate 6. For vertical-component instrument derived magnitudes, data partitioning in the magnitude range 1.375 < MLer < 3.375, in magnitude intervals of 0.25, was observed to provide a sufficiently linear relation between log AT and ML- The resulting preliminary b- value estimates are 6 = -1.03 (Aki method), 6 =

A A

1.01 (Page method), 6 = 1.01 (Karnik maximum likelihood method), 6 = 0.92 (Perkins minimum x2 fit), and b = 1.01 (Bender correction to Aki value). For horizontal-component magnitudes, the magnitude range 1.375 < M£°r < 3.875, in magnitude intervals of 0.25, provides

^^ A

an approximately linear log AT versus ML. The resulting b-value estimates are b = 0.93 (Aki method), b = -0.93 (Page method), 6 = -0.92 (Karnik maximum likelihood method), 6 = -0.88 (Perkins minimum x2 method), and 6 = 0.92 (Bender correction to Aki value). These various estimates are discussed in Bender (1983). The consistently lower estimates for b when using horizontal instrument ML data when compared to vertical instrument ML data may result from the lower gain settings of the horizontal instruments, which allow them to record larger magnitude events on scale; also, the horizontal component magnitudes for ML > 2.5 are, on average, higher than corresponding vertical component magnitudes, further discussed in the 1987 to 1989 SGB seismicity report. An area for future research might be the assessment of local variations in b-value, and the comparison of 6-values for SGBSN data with those of adjacent parts of Nevada, California and Utah. Variations are, according to frequently espoused dogma, significant because many seismologists believe that 6-value varies inversely with regional stress,

In particular, we may wish to compare 6-values within the SGB with that of the Central Nevada Seismic Belt, which has experienced several ML > 6 earthquakes in the twentieth century.

Some Comments on Regional Stresses and SGBSN Focal Mechanisms

The nature of the regional crustal stress tensor, how it varies laterally, vertically, temporally, and how smooth or rough it is are all topics of great interest and great uncertainty both in the SGB and in most continental crust. Earthquake focal mechanisms could theoretically provide constraints on the range of plausible stress tensors, especially if more were known about local material and fault properties, e.g., whether new faults are being formed or old faults are being reactivated, if the latter, whether a Coulomb-Mohr criterion of failure is appropriate (Mogi, 1974), and if so, the range of coefficients of friction, /i, that are present (Morrow and Byerlee, 1984), the local pore pressure, and the thermal regime. A commonly invoked assumption in stress field determinations is that sliding occurs in the direction of maximum shear stress on a given plane. This assumption is plausible for smooth planes of weakness; it is less plausible for corrugated or

22

undulating surfaces, on which motion is probably parallel to the direction of corrugation. In the same vein, if /z has directional variation (i.e., if /z is a second order tensor rather than a scalar), the underlying physics may require a revision of the standard assumptions.

The focal mechanism solutions for SGBSN data are themselves somewhat ambiguous, both as a result of the regional character of the station distribution and the uncertainty in the source-to- station raypaths. Some of these uncertainties are discussed in the 1987 to 1989 SGB seismicity report. P-wave first motions are modeled as direct or refracted by HYPO71, depending on assumed focal depth (some cases well constrained, other cases poorly constrained) and source-to- station distance (on average, a much better-constrained parameter). If wrongly modeled, raypath take-off angles may affect the range of permissible double-couple mechanisms. Amplitudes of first motions vary strongly with source radiation pattern as well as with path effects, and thus provide ambiguous guidelines to the analyst trying to determine whether a particular arrival is direct or refracted. With this uncertainty, focal mechanisms are nevertheless reported in Appendix D as a preferred solution and, optionally, one or two alternate solutions. The alternate mechanisms of Appendix D at tempt to display the range of the most-poorly constrained parameter, which could be the strike, dip, or rake angle of one of the nodal planes. When fitting a potential stress tensor to a population of earthquake focal mechanisms, the analyst must consider both nodal planes of a given "preferred" solution, and should also consider the nodal planes from alternate solutions. Thus, an exponential growth in computer time is indicated by the permutations and combinations: each earthquake may have a preferred solution and two (or more) solutions exhibiting the maximum plausible variation in strike, dip, and rake angles. For a population of n earthquakes, one may wish to consider > 6n permutations of nodal planes when analysing the appropriateness of a given stress tensor, and must consider a wide range of initially plausible stress tensors. Michael (1987) reviews various algorithms for stress tensor determination, in which the algorithm either preselects the preferred plane or uses both nodal planes; pre-selection is biased by the relative importance the algorithm places on various slip criteria, and no pre-selection generally widens the confidence regions for principal compressive stress directions and relative amplitudes. Whether stress field inversions should be performed for the set or some subset of focal mechanisms computed from 1979 through 1990 by analysis of SGBSN data is debatable, but what the focal mechanisms can do is to provide a data base that may generally support or contradict the hypothesis that some specific uniform stress tensor, determined by other means in the vicinity of Yucca Mountain, extends regionally through some portion of the southern Great Basin.

Two less computer-intensive and assumption-dependent ways of describing the focal mecha­ nism data are to compute the average P-axis and T-axis directions, and to intersect compression dihedra and tension dihedra, respectively. These analyses have been performed for mechanisms reported in prior SGBSN data reports (e.g., Rogers and others, 1987). Table 2 presents 17 focal mechanism solutions for SGB earthquakes of 1990, without consideration of plausible alternate solutions. For 16 of these solutions (solution 10 excluded), the average P-axis, as determined by Watson statistics (Schuenemeyer and others, 1972), trends North 46.6° East, with inclination -6.8°, and the average T-axis trends North 41.9° West, with inclination -3.0°. Figure 14 is a plot of those 17 P and T axes, with arrows in the directions of the just-noted average values. The intersection of 16 P-dihedra of those focal mechanisms (the reverse-slip solution shown in Figure D10 is again excluded) yields a pair of small area patches on the lower hemisphere, one in the northeast quadrant, and a small sub-horizontal one in the southwest quadrant; the T-dihedra intersect in larger patches centered in the northwest and southeast directions, in cones having radius about 15° (Figure 15). These regions of intersection are plausible areas to search for the directions of maximum and minimum principal compressive stresses when seeking a uniform

23

Tab

le 2

. Pr

elim

inar

y So

uthe

rn G

reat

Bas

in F

ocal

Mec

hani

sms

for

1990

St,

stri

ke o

f nod

al p

lane

; D

p, d

ip o

f nod

al p

lane

; R

k, r

aie

of s

lip v

ecto

r, T

r, tr

end

of

axis

; PI

, pl

unge

of

axis

. C

onve

ntio

n fo

r ra

ke a

ngle

sig

n:

180

° <

Rk

< 0

° fo

r m

echa

nism

s ha

ving

a c

ompo

nent

of

norm

al s

lip,

and

0° <

Rk

< 1

80°

for

mec

hani

sms

havi

ng a

com

pone

nt o

f re

vers

e sl

ip.

ML

, lo

cal

(SG

B)

mag

nitu

de;

Tsm

, ty

pe o

f sou

rce

mec

hani

sm:

1, s

ingl

e ev

ent

foca

l m

echa

nism

; 2,

com

posi

te fo

cal

mec

hani

sm.

Nod

al p

lane

s: N

o in

ferr

ed

faul

t pl

anes

for

the

se f

ocal

mec

hani

sms

are

pres

ente

d he

re,

alth

ough

for

man

y of

the

mec

hani

sms,

inf

eren

ces

abou

t th

e pr

efer

red

noda

l pl

ane

base

d on

lin

eatio

ns o

f ep

icen

ters

and

/or

on t

he s

tate

of

tect

onic

cru

stal

str

ess

are

poss

ible

. Fo

r ex

ampl

e, i

f th

e m

axim

um h

oriz

onta

l co

mpr

essi

onal

str

ess

is

orie

nted

at

abou

t N

orth

20°

to

30°

Eas

t, th

en r

ight

-lat

eral

str

ike

slip

may

be

expe

cted

on

stee

ply

dipp

ing,

nor

th-t

rend

ing

faul

t pl

anes

wit

h gr

eate

r lik

elih

ood

than

lef

t-la

tera

l str

ike

slip

on

east

-tre

ndin

g fa

ult

plan

es,

othe

r m

echa

nica

l co

nditi

ons

bein

g eq

ual.

Rm

k: R

emar

ks,

desi

gnat

ed b

y *,

mea

ns

that

(SV

/P)g

am

plit

ude

rati

os w

ere

used

to

cons

trai

n or

hel

p de

term

ine

the

foca

l m

echa

nism

. A

lter

nate

foc

al m

echa

nism

s: d

ashe

d-lin

e so

luti

ons

in

the

figu

res

of A

ppen

dix

D r

epre

sent

equ

ally

pla

usib

le f

ocal

mec

hani

sm s

olut

ions

for

the

sam

e da

ta.

Alt

erna

te s

olut

ions

are

not

sho

wn

in t

his

tabl

e.

Figu

re

Inde

x

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Ori

gin

time

(UT

C)

Dat

e T

ime

9001

2690

0215

9002

2790

0421

9005

1390

0604

9006

2490

0722

9007

2590

0802

9008

0390

0821

9009

0590

0906

9010

2990

1101

9012

13

10:3

411

:49

8:16

17:5

50:

488:

4723

:55

8:17

0:52

5:15

20:2

322

:00

4:58

10:3

22:

377:

511:

01

Foca

l G

eolo

gic

dept

h M

agni

tude

Q

uadr

angl

e (k

m)

(ML

)

5.06

7.03

6.46

6.64

6.20

0.97

4.79

2.62

8.05

5.00

-1.0

32.

385.

000.

774.

965.

982.

72

2.4

2.3

2.0

2.0

1.9

1.5

1.9

1.1

2.2

1.1

2.3

1.9

2.0

2.2

2.6

2.6

2.8

Can

e Sp

ring

, N

ev.

Scru

gham

Pea

k, N

ev.

Scru

gham

Pea

k, N

ev.

Bon

nie

Cla

ire

SE,

Nev

.B

onni

e C

lair

e SE

, N

ev.

Spri

ngda

le,

Nev

.B

lack

Mou

ntai

n, N

ev.

Cal

ico

Hill

s. N

ev.

Stov

epip

e W

ells

, C

al.

Spri

ngda

le,

Nev

.Sp

ring

dale

, N

ev.

Ston

ewal

l Pa

ss,

Nev

.Sp

ring

dale

, N

ev.

Spri

ngda

le,

Nev

.Sp

ring

dale

, N

ev.

Mel

lan,

Nev

.G

old

Poi

nt,

Nev

.

T s m 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

Nod

al p

lane

s 1s

t 2n

d P

St 12.

284.

211.

87.

240.

15.

288.

198.

314.

355.

75.

181.

94.

89.

355.

290.

150.

Dp

66.

85.

64.

77.

73.

90.

73.

84.

40.

88.

87.

57.

76.

85.

89.

77.

90.

Rk

-147

.-3

0.-1

36.

16.

-58.

-175

.-4

2.14

1.82

.17

5.-1

0.-1

14.

-43.

-19.

-165

.-3

8.-1

60.

St 267.

16.

98.

353.

356.

285.

33.

293.

144.

85.

165.

41.

197.

181.

265.

30.

60.

Dp

61.

61.

51.

75.

36.

85.

50.

51.

50.

85.

80.

40.

48.

71.

75.

53.

70.

Rk

-28.

-174

.-3

4.16

7.-1

49.

0.-1

57.

8. 97.

2.-1

77.

-58.

-161

.-1

75.

-1.

-164

.0.

Tr

232.

236.

70.

220.

187.

240.

243.

252.

230.

40.

30.

42.

47.

43.

221.

243.

17.

Pri

ncip

al a

xes

T

BPI 40

.24

.49

.2. 52

.4. 42

.22

.5. 2. 9. 68

.40

.17

.11

.36

.14

.

Tr

139.

334.

331.

310.

307.

150.

346.

148.

95.

310.

120.

288.

152.

136.

129.

345.

283.

PI 3. 17.

8. 20.

21.

3. 14.

31.

83.

5. 5. 9. 17.

10.

10.

15.

14.

Tr

45.

95.

235.

125.

50.

20.

90.

10.

320.

150.

240.

195.

260.

255.

360.

94.

150.

PI

50.

60.

40.

70.

30.

85.

45.

50.

5. 85.

80.

20.

45.

70.

75.

50.

70.

R

m

k * * * *

SGB Focal Mechanism P and T axes 1990

O

P axis

T axis

Figure 14.- Inclinations (plunges) and azimuths of 17 focal mechanism preferred solution P axes and T axes for 1990 data reported in Appendix D are plotted on the equal area lower hemisphere projection. The inward-directed tabs represent the orientation of the average P-axis for all but one those data, and the outward-directed tabs represent the orientation of the average T-axis for all but one of those data (the exceptional Tucki Mtn. reverse-slip mechanism, whose T-axis has an arrow pointing towards it, is excluded from the averaging computations). Dashed circles represent inclinations of 25°, 45°, and 65°, respectively.

25

Intersection of P & T Dihedra N

! k + f

+ +

«

1

s

(I1990 SGBSN FOCAL MECHSNumber of mechanisms =16

(7 1 region 024 inconsistencies resp: x \ <7 3 region 024 inconsistencies resp: <> /Min & max depths (km) -1.0 7.0

Figure 15.- Intersection of compressional first motion quadrants, containing the T axes of 16 of the 17 focal mechanisms of 1990, may constrain the location of minimum principal compressive stress direction, cr3 , in a region where the stress tensor is uniform. The zones of intersection of the T quadrants of those 16 focal mechanisms are shown surrounded by diamonds. Similarly, the zones of intersection of the 16 focal mechanism P quadrants, which may constrain the location of the maximum principal compressive stress direction, o^, are shown surrounded by x symbols. Regions where all but one and all but two quadrants intersect are also shown in this figure.

26

stress tensor that attempts to fit this set of focal mechanisms. The average P and T directions, and the zones of quadrant intersection, agree fairly well with those of focal mechanism data presented in previous SGBSN reports. For example, the average P-axis for SGB earthquake focal mechanisms for the period 1987 through 1989 trends North 38° East, with inclination 5°, and the average T axis for those data trends North 57° West, with inclination 2.8°. The differences between the two data set averages result from a few anomalous solutions and from the broader geographic region sampled in the 1987-1989 report. Individual and average focal mechanism data for a much broader region, including all of Nevada and adjacent parts of California, are presented in Rogers and others (1991).

Summary and Conclusions

Yucca Mountain continues to exhibit very low rates of seismicity, but is surrounded by many zones of relatively elevated, but low-magnitude, seismicity, such as Sarcobatus Flat, southern Nevada Test Site (Rock Valley-Cane Spring fault zones), and Timber Mountain.

Caldera boundaries should be considered as controlling structures for seismicity in the vicinity of Yucca Mountain and Timber Mountain.

Although no swarms, clusters, or magnitude 3+ earthquakes have been recorded in the Oasis Valley west of the calderas of western NTS, more than a decade of seismic monitoring by the SGBSN reveals an approximately linear north-south trending epicenter pattern with length w 50 km in that valley. This epicenter trend is about 25 km west of the center of Yucca Mtn.

The fact that predominantly strike-slip seismicity is observed in at least equal abundance to predominantly normal-slip seismicity during the monitoring period 1979-1990 suggests that seismically active portions of the southern Great Basin enjoy a stress field having relatively large maximum horizontal compressive stress, <7#, comparable or even slightly greater than the vertical crustal stress, av w pgz.

The nearly complete absence of seismicity on Death Valley and Furnace Creek faults during the monitoring period 1979 through 1990, coupled with the presence of seismicity on the east side of the Panamint Mountains, suggest that the local seismically active structures may be rangefront faults, perhaps at their intersection with gently dipping faults spanning central Death Valley from the western Black Mountains to the eastern Panamint Mountains.

27

References Cited

Bender, B,, 1983, Maximum likelihood estimation of 6 values for magnitude grouped data: Seis- motogicaL Society of America Bulletin, v. 73, p. 831-851. (NNA.920211.0029)

Brune, J. M., Nicks, W., and Aburto, A., 1991, Microearthquakes at Yucca Mountain: Nevada, abs., Seismological Research Letters, v. 62, no. 1, p. 51. (NNA.920211.0030)

Christiansen, R. L., Lipman, P. W., Carr, W. J., Byers, F. M., Orkild, P. P., and Sargent, K. A., 1977, Timber Mountain-Oasis Valley caldera complex of southern Nevada: Geological Society of America Bulletin, v. 88, p 943-959. (NNA.990329.0044)

Ekren, E. B. and Sargent, K. A., 1965, Geologic Map of the Skull Mountain quadrangle, Nye County, Nevada: U. S. Geological Survey map GQ-387. (HQS.880517.1181)

Freund, R., 1974, Kinematics of transform and transcurrent faults: Tectonophysicst v. 21, p. 93-134. (NNA.920211.0031)

Gomberg, J., 1991, Seismicity and shear strain in the southern Great Basin of Nevada and Cali­ fornia: J. Geophysical Research, v. 96, p. 16,383-16,400. (NNA.920211.0032)

Gomberg, J., Shedlock, K. M., and Roecker, S., 1990, The effect of S-wave arrival times on the accuracy of hypocenter estimation: Seismological Society of America Bulletin, v. 80, p. 1605- 1628. (NNA.920211.0033)

Hamilton, Warren B., 1988, Detachment faulting in the Death Valley region, California and Nevada, an Geologic and Hydrologic Investigations of a Potential Nuclear Waste Disposal Site at Yucca Mountain, Southern Nevada, Michael D. Carr and James C. Yount, eds., p. 51-86. (NNA.920211.0034)

Harmsen, S. C., and Rogers, A. M., 1986, Inferences about the local stress field from focal mech­ anisms: applications to earthquakes in the southern Great Basin of Nevada: Seismological Society of America Bulletin, v. 76, p. 1560-1572. (NNA.920211.0035)

Harmsen, S. C., and Rogers, A. M., 1987, Earthquake location data for the southern Great Basin of Nevada and California: 1984 through 1986: U.S. Geological Survey Open-File Report 87-596, 92 p. (NNA.870821.0046)

Kisslinger, C., Bowman, J. R., and Koch, Karl, 1981, Procedures for computing focal mechanisms from local (SV/P) Z data: Seismological Society of America Bulletin, v. 71, p. 1719-1729. (NNA.920211.0036)

Kisslinger, C., Bowman, J. R., and Koch, Karl, 1982, Errata to procedures for computing focal mechanisms from local (SV/P) Z data: Seismological Society of America Bulletin, v. 72., p. 344. (NNA.920211.0037)

Lee, W. H. K., and Lahr, J. C., 1975, HYPO71 (revised): A computer program for determining hypocenter, magnitude, and first-motion pattern of local earthquakes: U.S. Geological Survey Open-File Report 75-311, 116 p. (NNA.920211.0038)

Lee, W. H. K., and Stewart, S. W., 1979, Principles and applications of microearthquake networks: New York City, N. Y., Academic Press, 293 p. (NNA.920211.0039)

McKeown, F. A., 1975, Relation of geological structure to seismicity at Pahute Mesa, Nevada Test Site: Seismological Society of America Bulletin, v. 65, p. 747-764. (NNA.920211.0040)

Michael, A. J., 1987, Use of focal mechanisms to determine stress: a control study: J. Geophysical Research, v. 92, p. 357-368. (NNA.920211.0041)

Mogi, K., 1974, On the pressure dependence of strength of rocks and the Coulomb fracture criterion: Tectonophysics, v. 21, p. 273-285. (NNA.920211.0042)

28

Morrow, C., and J. Byerlee, 1984, Fractional sliding and fracture behavior of some Nevada Test Site tuffs: Proc. U.S. Symp. Rock Mech., 25th, p. 467-474. (HQS.880517.1676)

Poole, F. C., Elston, D. P., and Carr, W. J., 1965, Geologic map of the Cane Spring Quadrangle, Nye County, Nevada: U. S. Geological Survey map GQ-455. (NNA.920219.0010)

Rogers, A. M., Harmsen, S. C., and Meremonte, M. E., 1987, Evaluation of the seismicity of the southern Great Basin and its relationship to the tectonic framework of the region: U. S. Geological Survey Open-File Report 87-408, 196 p. (HQS.880517.1409)

Rogers, A. M., Harmsen, S. C., Corbett, E. J., Priestley, K., and DePolo, D., 1991, The seismicity of Nevada and some adjacent parts of the Great Basin, in Neotectonics of North America, Slemmons, D. B., Engdahl, E. R., Black wall, D., and Schwartz, D., eds., Geological Society of America, vol. DMV, p. 153-184. (NNA.920211.0043)

Savage, J. C., and Cockerham, R. S., 1984, Earthquake swarm in Long Valley Caldera, January, 1983: Evidence for dike inflation, in Active tectonic and magmatic processes beneath Long Valley Caldera, Eastern California, vol. II: U. S. Geological Open-File Report 84-939, pp. 541-583. (NNA.920211.0044)

Schuenemeyer, J. H., Koch, G. S., and Link, R. F., 1972, A computer program to analyze directional data, based on the methods of Fisher and Watson: J. Mathematical Geology, v. 4, p. 177-202. (NNA.920211.0045)

Snoke, J. A., Munsey, J. W., Teague, A. G., and Bollinger, G. A., 1984, A program for focal mech­ anism determination by combined use of polarity and SV-P amplitude ratio data: Earthquake Notes, v. 55, p. 15. (NNA.920211.0046)

NOTE: Parenthesized numbers following each cited reference are for U.S. Department of -Energy OCRWM Records Management purposes only and should not be used when ordering the publication.

29

Appendix A

Earthquake locations for the year 1990 and quadrangle map names to which locations are keyed

The local hypocenter summary column headings are for the most part self-explanatory. UTC is Universal Coordinated Time. Horizontal error equals \fadx2 + sdy 2 , where sdx and sdy refer to the HYPO71 standard errors in longitude and latitude, respectively. Vertical error is the HYPO71 standard error in depth (sdz). "AZI GAP" is the azimuthal gap, that is, the largest angle subtended by the epicenter and any two circularly adjacent stations with positive phase weight. "Ql" and "Q2" represent two HYPO71 hypocenter quality estimates as defined by Lee and Lahr (1975). "DS" is a code for data source: A for analog seismograms, (data scaled from develocorder films, starting depth, 2o> at 7 km for iterations), I for data scaled from digital seismograms. Various values are tried for ZQ, the initial hypocenter guess. XQ and yo are always taken to be near the earliest-reporting station. When equal final RMS values occur for solutions having different 2o> the solution derived from the ZQ = 7.0 km starting value is reported (although the choice is arbitrary).

Mca is the coda-average magnitude, Md is the duration magnitude estimate, MLh is local mag­ nitude from horizontal-component instruments, MLv is local magnitude from vertical-component instruments, MLc is the maximum of station magnitudes from overdriven (clipped) records. Am­ plitudes recovered from vertical-component data are multiplied by 1.75 to provide an approximate horizontal-equivalent amplitude. The depths may be followed by one or two stars. One star means that the depth-of-focus standard error estimate was very large (> half crustal thickness). Two stars imply that the depth was fixed by HYPO71 during the last several iterations for hypocenter, because the data lacked resolving power for that parameter. DELMIN is the minimum source to station distance in km, and RMS RES. is the root-mean-square travel time residual, defined in the text of this report. #N PH. is the number of (P+S) phases having positive weight in the solution. Finally, U.S.G.S. quadrangle is the name of 7| or 15 minute topographic quadrangle in which the epicenter lies.

Appendix A excludes all "low-frequency" seismicity associated with NTS nuclear device tests. Such phenomena include aftershocks at ultra-shallow hypocentral depths and cavity collapses. Such events, though having a tectonic significance, are strongly associated in time and space with testing, and their inclusion in the Appendix A seismicity catalog would probably bias any effort to determine natural seismicity rates in the northern NTS from this catalog. See Appendix C of this report for further details on these "low-frequency" events.

30

^

<f

115.25038.500

^

- "*

4V38.000

* -V

&

4- *-

N.T.J

37.000116.250 114.500

SEISMOGRAPH STATION

Figure Al.- Quadrangle names in the northeast quarter of the southern Great Basin.

31

115.250

N.T.S.

/,* */ 4

<fr> >\

116.250

V SEISMOGRAPH STATION ) ' --.- __

Figure A2.- Quadrangle names in the southeast quarter of the southern Great Basin.

114.500

32

117.00038.500

4*<#-.

38.000

,^

.N/V

,^

<y

, \ */*

-N.T.S.-H^9-

*

37.000118.000

7 SEISMOGRAPH STATION

Figure A3.- Quadrangle names in the northwest quarter of the southern Great Basin.

116.250

33

118.000

117.000

-

"

A

V SEISMOGRAPH STATION

o>

37.000

36.500

4*

116.2!5.500

Figure A4.-~ Quadrangle names in the southwest quarter of the southern Great Basin.

34

1990

LO

CA

L H

YPO

CEN

TER

SU

MM

AR

Y -

SGB

EA

RTH

QU

AK

ES

STAND

LO

Ul

DATE

- TIM

E(UTC)

JAN

2 2 3 3 4 5 6 6 6 6 6 7 7 7 7 7 8 9 10 10 10 10 11 12 12 12 12 12 12 12 12 12 13 13 13 13 14 14 14 14 14 14 15 15

12:28:37

17:45:21

1:40:47

20:4

1:44

21:50:23

17:40:39

12:11:36

16:43:54

18:12:

118:57:42

20:21:24

1:53:15

4:41

:23

14:30:18

18:46:30

18:45:27

21:

4:52

7: 7:42

9:21

:36

11:20:56

11:38:53

17:43:44

3: 5:

210:

9:20

0:27:15

0:38:

81:

47:3

53:

43:2

33:

47:1

711:48:29

14:19:25

17:29:57

3:44

:34

4:59

:32

5:31

:15

16:56:

1

0:28

:41

3:40

:15

12:2

8:51

14:57:55

19:49:34

23:15:58

4:52

:54

11:32:37

LATI

TUDE

(DEG

. N)

36.712

36.943

36.778

37.3

4136.713

36.722

38.441

36.756

38.285

36.962

37.1

4037.883

37.019

35.771

37.115

37.113

37.324

36.797

36.495

36.737

37.444

36.222

37.320

37.314

37.256

35.473

37.295

37.305

37.435

37.303

36.340

37.309

37.403

37.310

36.800

37.313

37.455

37.854

37.113

36.850

37.116

36.852

36.4

6136

.360

LONGITUDE

(DEG

. W)

115.555

114.514

115.647

115.369

116.253

118.040

115.394

116.627

117.

515

114.649

115.

041

114.903

117.503

117.577

117.

031

117.036

118.382

115.920

117.263

115.

911

115.085

115.103

117.557

117.335

115.035

115.605

117.339

117.336

115.

081

117.347

116.869

117.337

117.515

117.326

116.307

117.327

114.098

114.918

117.034

116.393

117.033

116.183

116.162

115.822

ERRO

RH(KM)

0.4

4.4

0.9

2.9

0.6

3.8

4.3

2.2

2.2

3.6

2.6

0.7

1.1

0.3

0.3

2.2

0.6

0.7

0.4

0.4

. .

0.6

0.6

0.4

2.6

0.4

0.7

0.6

0.3

0.7

0.4

0.4

0.4

0.4

0.7

8.4

2.9

0.3

0.3

0.3

0.8

0.3

0.6

DEPT

H(K

M) 1.69

-1.5

4-0.36

5.00

*5.49

-1.02

3.80

*2.97

26.23

-0.88

3.06

*0.19

3.05

*8.

090.64

0.95

2.97

6.97

0.16

-1.9

40.46

6.85

0.46

7.24

-1.65

-1.13

6.04

6.54

2.67

1.93

9.89

7.00

7.92

8.51

1.77

7.70

2.55

*-1.99

7.54

2.44

5.34

1.71

10.9

95.

01

ERROR

Z(KM

)

2.7

1.8

1.5

. .

0.9

2.6

2.3

2.4

.

2.5

__

1.0

0.5

0.5

4.7

1.4

0.7

0.5

0.4

0.9

1.1

0.2

2.2

0.9

1.1

0.9

1.2

2.2

1.0

0.6

0.6

2.5

1.0

^^_

2.3

1.6

0.6

2.2

1.0

0.4

4.8

GAP

(DEG

)

110

299

169

179

123

278

260

147

274

228

265

245

162

296

127

104

282

256

191

148 84 213 71 148

223

238 75 135 81 74 106 71 97 146

107

149

313

227

104 61 105

138 77 228

12S MA

GNIT

UDE

Mca

BCA

CDI

BCI

1.67

CDA

ABI

1.16

CDI

1.84

CDU

1.97

BCI

1.42

ADD

2.20

BDI

2.36

CDI

CDI

CCI

1.03

BDI

1.92

BCI

ACI

1.59

BDU

ADA

ADI

1.62

ACI

1.38

BBI

2.62

DDI

1.08

BCI

2.37

ACI

0.76

ADI

1.57

DDU

2.09

ABI

1.47

ACI

AAI

2.09

BBI

1.88

BCI

BBI

2.04

ABI

1.81

ACI

1.26

BBI

1.16

ACI

1.34

DDI

2.10

CDI

1.97

ABI

1.14

AAI

1.20

BCI

1.10

ACI

1.16

AAI

1.28

BDI

1.70

Md 2.55

1.10

1.76

0.97

1.68

1.32

0.97

1.29

1.76

2.03

0.45

0.94

0.96

ESTI

MATE

SMLh

3.74

1.57

2.27

0.78

1.94

1.68

3.51

1.11

0.81

1.27

2.26

1.11

1.33

1.27

2.25

2.02

0.80

1.62

MLv

0.87

1.26

1.71

1.82

0.99

1.97

2.17

0.89

0.61

0.90

1.57

1.03

2.86

1.09

1.39

-0.0

9

1.04

2.06

1.08

2.12

1.79

1.07

2.03

1.20

1.20

0.71

1.32

2.11

2.13

1.20

0.61

1.11

0.85

1.54

1.35

MLc 1.3

1.8

1.8

1.1

1.7

1.5

STAND

AZI

QQD

DEL-

RM

S |N

MIN

RES.

PH.

U.S.

G.S.

(KM) (SEC)

QUADRANGLE

22.9

0.

13 19 HEAVENS WELL

64.9

0.

17 13 RO

X NE

17

.4 0.

19 21

QUARTZ PE

AK SW

29.1

0.

20 5 BADGER SPRING

3.7

0.14

13 ST

RIPE

D HILLS

57.4 0.

20 11 ***QUAD. NO

T LI

STED

*

53.9

0.

13

9 FO

REST

HO

ME4.5

0.26

11 BARE MTN

93.7

0.

02

4 OUTLAW SPRINGS SE

53.1 0.

30 17 RO

X13.3 0.

27

8 LO

WER

PAHRANAGAT LA

KE

14.6

0.

14

6 DEADMAN

SPRING

14.1 0.

25 20

LAST CHANCE RANGE

67.5

0.

20 27 MOUNTAIN SPRINGS CANYON

14.8

0.

15 21

BONNIE CLAIRE SE

14.6 0.

12 24

BONNIE CLAIRE SE

43.6

0.

15 16 ***QUAD. NO

T LI

STED

* 15.6 0.

08 11 FR

ENCH

MAN

FLAT

16.8

0.

14 21

PA

NAMI

NT BUTTE

9.6

0.13

15

MERCURY

5.1

0.16

40

ALAMO NE

44

.8 2.

16

4 LA

S VEGAS

NE

12.6 0.

16 13

MAGRUDER MTN

7.0

0.10

9 GOLD POINT

16.6 0.01

6 ALAMO SE

88

.0 1.03 18 ***QUAD. NO

T LISTED*

7.3

0.14

20

GOLD POINT

7.0

0.07

9 GOLD PO

INT

4.1

0.13

19 ALAMO NE

7.

9 0.

15 26 GO

LD POINT

21.6

0.

15 10

FU

RNAC

E CREEK

7.1

0.17

37 GOLD POINT

4.5

0.10

12 MAGRUDER MTN

6.2

0.08

13 GO

LD POINT

7.1

0.11 13 JA

CKAS

S FL

ATS

6.3

0.14

13 GOLD POINT

59.0 0.

08

8 ***QUAD. NO

T LISTED*

13.7

0.

39 12

WHEATGRASS SPRING

14.5

0.

13 23

BONNIE CLAIRE SE

1.0

0.11 18

TOPOPAH

SPRING SW

14.9 0.11 18 BONNIE CLAIRE SE

1.3

0.10

14

SKULL

MTN

5.7

0.09

21

AMARGOSA FL

AT

26.8

0.

10 19 MT

ST

IRLI

NG

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e R£ :UJUI.

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36

1990

LOCA

L HYPOCENTER SUMMARY -

SGB

EARTHQUAKES

STAN

DSTAND

AZI

QQD

DEL-

RMS

|NDA

TE-

TIME

(UTC)

JAN

23 23 24 24 24 25 25 25 25 26 26 26 26 26 26 26 26 26 26 26 26 263

26 26 26 26 26 26 26 26 26 26 26 26 26 26 27 27 27 27 27 27 27 27

22:

7:54

23:2

6:52

5:28

:38

16:10:16

19:58:14

19:39: 8

19:41: 5

20:1

2:26

23:3

4: 0

2:41

:47

3:13

: 7

3:17

:26

3:20

:41

3:48

:34

9: 9:56

9:55

:56

9:56

:27

10:

1:26

10:

2:36

10:

3:20

10:21:34

10:2

2:41

10:34:16

10:55:56

11:10:10

11:14: 3

11:17:36

11:23:56

11:55:27

12:28:51

13:4

7:51

16:25:42

17:17:40

17:31:53

17:52:37

17:56:10

2:11

:51

2:15

:11

2:35:29

2:35

:34

3:27

:38

3:44

:34

9: 3:

2211:29:56

LATI

TUDE

(DEC.

N)

36.4

7937.495

37.118

37.000

37.803

37.736

37.747

37.770

37.172

37.072

36.810

36.790

36.805

38.488

37.555

36.8

0936.815

36.808

36.818

36.813

36.806

37.107

36.812

36.806

36.805

36.807

36.798

36.808

36.804

36.807

36.811

36.805

36.808

36.811

36.811

36.806

36.810

36.824

36.786

36.805

36.814

36.813

38.514

37.297

LONG

ITUD

E(D

EC.

W)

116.249

115.278

115.148

116.215

114.938

114.664

114.637

114.658

116.207

116.168

116.118

116.

091

116.114

115.369

117.168

116.116

116.113

116.114

116.113

116.115

116.115

116.863

116.120

116.107

116.112

116.118

116.

121

116.120

116.115

116.114

116.117

116.117

116.112

116.123

116.116

116.116

116.114

116.138

116.105

116.110

116.107

116.113

115.349

115.

371

ERROR

H(KM)

0.4

1.4

1.3

0.9

10.2 3.6

1.9

2.5

0.4

1.0

0.4

0.5

0.4

4.7

0.6

0.3

0.5

0.4

0.5

0.6

0.3

0.3

0.4

0.5

0.2

0.3

0.4

0.7

0.5

0.5

0.4

0.3

0.3

0.4

0.4

0.5

0.3

1.1

0.7

0.5

0.4

0.7

5.7

0.7

DEPTH

(KM) 7.08

4.36*

6.89

-1.33

3.05*

-1.4

0

1.67

1.32

-1.5

73.31

4.01

5.23

0.22

-1.1

30.20

0.69

4.36

0.45

4.21

5.10

4.76

0.65

5.17

5.94

1.75

1.51

0.31

3.52

0.16

2.78

4.37

1.46

0.65

5.44

4.55

3.83

0.86

6.75

4.02

1.25

5.03

5.77

1.09*

10.6

7

ERROR

Z(KM)

1.5

1.0

0.7

2.6

3.5

5.2

0.6

1.3

2.7

1.9

0.7

4.1

0.9

0.5

1.0

0.6

2.2

2.4

1.0

0.5

1.4

0.8

0.7

1.0

0.7

1.7

0.8

1.4

1.7

0.9

0.5

1.5

2.5

1.1

0.5

0.6

2.8

5.9

1.4

1.9

___

5.5

GAP

(DEC

)

90 130

243

241

232

270

278

272 56 282 87 129

119

266

124 87 154 88 95 88 93 102 47 289 95 50 51 155 87 51 88 155 95 47 88 156 88 272

174

121 97 186

285

146

12S MA

GNIT

UDE

Mca

Md

ABI

1.34

CCI

1.79

BDI

1.74

ADI

1.14

DDI

1.41

CDI

1.68

BDI

CDI

BCI

2.51

ADI

0.82

BBI

1.74

ABI

ABI

1.28

DDU

2.26

BCI

1.03

BBI

1.46

ACI

BBI

1.51

1.

37

BBI

1.56

BBI

1.64

ABI

ACI

1.59

BBI

2.25

ADI

ABI

1.38

BBI

1.43

BBI

1.38

BCI

1.42

BBI

1.60

BBI

1.65 1.

07

BBI

1.43

ACI

ABI

0.78

BBI

1.86

BBI

1.98

ACI

BBI

1.68

BDI

BCI

CBI

ABI

1.29

ADI

1.25

DDI

2.25

CCI

1.54

ESTIMATES

MLh

MLv

1.14

1.20

1.20

1.49

0.54

1.90

1.31

1.43

1.10

1.19

2.60

2.39

0.92

2.02

1.

510.64

0.86

2.05

1.48

1.38

1.04

0.79

1.23

0.96

1.28

1.33

1.02

1.10

2.46

2.31

0.51

1.00

1.68

1.24

1.14

1.35

1.36

1.29

1.24

0.66

2.38

2.06

1.93

1.90

0.74

1.26

1.39

0.30

0.80

0.95

1.15

0.73

2.18

1.98

1.16

1.08

MLc 1.6

2.3

1.0

1.3

1.8

1.8

1.8

1.3

2.5

MIN

RES. PH

. U.S.G.S.

(KM)

(SEC)

QUAD

RANG

LE

13.6

0.

12 15 AMARGOSA

FLAT

22.3

0.1

2 7 HANCOCK

SUMMIT

6.6

0.13 10 LO

WER

PAHR

ANAG

AT LA

KE15

.8 0.

15 13

TIP

PIPA

H SP

RING

14.5 0.80

5 WH

EATG

RASS

SP

RING

15.8

0.17

7 CALIENTE NW

18.0

0.08

6 CALIENTE NW

19.5

0.07

6 THE

BLUFFS

11.4 0

.23

40 R

AINI

ER M

ESA

6.7

0.12

13 T

IPPI

PAH

SPRING

6.7

0.17 28 CAN

E SP

RING

9.9

0.11 14 CANE

SPRI

NG

7.4

0.11 15

CAN

E SP

RING

59.5

0.51

21 FOREST H

OME

25.0 0

.23

19 GOLDFIELD

6.9

0.17

29

CANE SPRING

6.6

0.12

19 C

ANE

SPRING

7.1

0.19

32

CAN

E SPRING

6.4

0.17 20

CANE

SPRI

NG6.6

0.25 28 C

ANE SPRING

7.2

0.08 14 CANE SPRING

13.0

0.11

20 S

PRIN

GDAL

E6.4

0.22

55 CAN

E SPRING

7.7

0.04

7 CANE SPR

ING

7.5

0.12

24

CANE SPRING

6.9

0.19

38

CAN

E SPRING

7.5

0.18 3

6 CA

NE S

PRIN

G6.8

0.19

22 C

ANE SPRING

7.4

0.29

36

CAN

E SP

RING

7.1

0.23 35

CANE

SPRI

NG

6.7

0.18 29 C

ANE SP

RING

7.2

0.08

17 CAN

E SPRING

7.2

0.13 24 CAN

E SP

RING

6.3

0.21 35 CAN

E SPRING

6.7 0.

18 29

CANE SPRING

7.1

0.09

14 CANE SPRING

7.0

0.16 33 CAN

E SPRING

4.3

0.04

5

SKULL MTN

9.5

0.08

6 CANE S

PRIN

G7.6

0.13

7 CA

NE S

PRING

7.1

0.11

17 CANE SP

RING

6.8

0.10

9 CANE SPRING

62.8 0.

29

7 ***QUAD. NOT

LISTED*

21.7

0.0

7 6 BA

DGER

SPRING

8

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1990

LOCAL HYPOCENTER SU

MMAR

Y - SG

B EA

RTHQ

UAKE

S

Ln

DATE

- TIME

(UTC)

MAY

8 8 8 9 9 11 11 12 12 13 14 14 15 15 16 16 16 16 16 17 17 17 17 17 17 18 18 18 18 18 19 19 20 20 20 20 21 21 21 23 23 24 24 25

1:18

: 5

9:46

:43

17:27:36

0: 7:

1012:55:58

1:11:34

19:21:53

11:

0:28

17:38:26

0:48

:12

5:28

: 1

17:4

7:41

1:23:

819:25:52

6:54:38

7:50

:37

10:17:36

13:49:19

21:3

2:17

0:50:

511:58:19

12:44:27

12:45:47

14:48:57

19:

3:44

0:27

:12

1:26:13

6:44

:24

18:40:16

18:40:54

2:21

:13

3: 3:12

1:27

: 3

15:57:38

19:13:27

23:31:34

11:12:28

21:32:53

23:1

8:23

6:38

:56

8:11

:27

3:30

:50

15:52:35

7:56

:10

LATI

TUDE

(DEC

. N)

37.

36.

37.

36.

36.

36.

35.

37.

37.

37.

37.

37.

37.

36.

37.

37.

37.

36.

36.

36.

37.

36.

36.

37.

37.

37.

37.

36.

37.

37.

35.

37.

36.

36.

37.

37.

36.

37.

37.

37.

37.

36.

37.

36.

114

625

303

205

443

838

999

158

026

117

477

243

729

367

115

114

370

608

666

880

635

619

616

395

215

118

643

741

262

259

851

025

152

578

138

415

836

073

204

218

230

681

249

670

LONGITUDE

(DEC

.

117.

W) 940

116.260

115.

117.

116.

117.

117.

117.

116.

117.

114.

114.

115.

114.

117.

117.

115.

117.

116.

115.

117.

116.

116.

117.

115.

117.

117.

116.

117.

117.

117.

116.

117.

115.

118.

115.

115.

117.

115.

116.

116.

116.

115.

116.

481

907

967

503

896

609

298

035

618

966

977

913

030

034

207

004

655

982

334

260

259

890

792

029

331

194

521

519

764

455

814

887

013

612

394

003

011

514

505

277

032

660

ERRO

RH(KM)

2.0

0.9

1.5

1.2

1.2

0.8

3.1

0.5

0.5

0.3

1.6

1.4

1.4

1.0

0.3

0.3

1.0

0.4

0.8

0.3

1.4

0.2

0.5

0.9

0.7

0.4

0.8

0.4

0.4

0.3

7.3

0.4

1.5

0.3

1.5

0.8

0.6

0.4

0.6

0.3

0.3

0.2

1.2

0.5

DEPTH

(KM)

-1.02

3.40

1.55

6.14

11.0

12.

48

3.50*

8.91

2.73

6.28

-2.02

2.93

4.53

-1.5

46.59

1.51

6.62

10.05

-0.7

60.

64-0

.16

4.59

4.32

8.86

9.86

4.11

0.42

2.14

9.10

9.59

-1.02

9.35

7.00

7.20

2.46

-0.36

-0.44

6.15

6.58

-0.33

8.89

-0.63

3.41

3.85

ERRO

RZ(

KM)

2.1

3.5

11.0 1.4

1.9

1.0

__

0.5

0.7

1.5

1.3

4.8

1.8

1.9

1.8

1.5

3.2

1.5

0.8

0.4

1.0

0.4

1.3

0.8

1.3

4.1

1.1

1.1

0.9

0.6

11.6 0.6

1.3

1.0

6.7

1.1

0.8

2.2

2.3

0.4

0.7

0.2

3.4

3.3

GAP

(DEG

)

258

142 91 254 88 200

292

191

149 50 272

221

199

179

105 86 132 80 221

123

154

147

150

188

86 128

159

117 85 103

295

140

293

109

241

124

124 95 161

146

157

147

195

156

12S

BDI

BCI

CCI

BDI

CBA

ADI

CDU

ADI

AC I

AC I

BDI

BDI

BDA

BCI

AC I

AC I

BDI

ABI

ADI

ABI

BCI

AC I

ACI

BDI

BBI

BCI

ACI

ABI

ABI

ABI

DDI

ACI

BDI

ABI

GDI

BCI

BCI

BBI

BCI

ACI

ACI

ACI

BDI

BCI

MAGN

Mca

1.55

1.09

1.37

2.38

1.34

1.85

1.19

1.14

1.84

1.45

1.48

1.72

1.51

1.56

1.57

1.23

1.34

1.24

0.88

0.99

1.30

1.62

1.30

0.82

0.96

0.92

1.70

0.95

0.88

1.79

1.55

2.22

1.14

1.80

1.31

1.11

1.27

2.05

1.02

STAND

STAND

AZI

QQD

DEL-

RMS

|N

UDE

ESTI

MATE

S MIN

RES. PH

. U.

S.G.

S.Md

ML

h ML

v ML

c (KM) (S

EC)

QUADRANGLE

1.74

1.67

1.63

2.54

0.87

1.90

1.60

1.09 .79

.44

.56

.15

1.53

0.44

1.31

1.41

1.78

0.64

1.40

1.22

1.00

0.93

2.24

1.53

1.75

1.69 .27

.11

.14

.04

1.81

1.46

0.71

1.41

2.58

1.96

0.90

0.72

1.87

1.51

1.40

1.69

1.42

1.53

0.95

1.45

0.73

1.07

1.15

0.56

0.70

1.33

1.81

0.85

1.20

0.51

0.86

0.79

1.72

0.61

1.50

0.79

1.80

1.49

2.16

1.10

1.83

0.95

0.75

0.91

1.8

1.7

2.7

1.41

1.

52

1.5

1.5

0.8

1.8

1.8

1.8

1.8

1.3

1.3

1.8

1.5

1.9

1.6

2.1

29.2

0.

14 13

WAUCOBA

SPRING

7.5

0.16

11

STRIPED HILLS

, 26.1 0.

20

8 CU

TLER

RESE^.V<^

74.6

0.

20 25

HA

IWEE

RESERVOIR

13.2

0.31 14

FU

RNAC

E CREEK

9.5

0.10 13

DR

Y MT

N

83.8

0.32 10 LITTLE LA

KE

8.9

0.07

10 LA

ST CHANCE

6.2

0.07

11

BUCKBOARD M{?^ _,

14.9

0.13 31

BO

NNIE

CLAIffe &

17.8

0.

04

8 EL

IGN

NE

, 19

.7 0.11

8 DELAMAR

3 N^/

4.3

0.14

9 WHITE BLOTCH

SPRINGS

27.0

0.

16 12 DRY

LAKE

14.7

0.13 24

BO

NNIE

CLAIRE SE

14

.6 0.

10 23 BO

NNIE

CLAIRE SE

14

.4 0.

07

5 ALAMO

20.0

0.12 21

STOVEPIPE WELLS

14.7

8.7

0.09

0.11

15 BI

G DU

NE21

PLUTONIUM VALLEY

8.5

0.16

12

MONTEZUMA

PEAK

7.7

0.02 10

LATHROP WELLS

7.9

0.07

13

LATHROP WELLS

3.7

0.17 15 SOLDIER

PASS

13.2

0.

17 18

PA

POOS

E LA

KE

15.1

0.

08 10 BO

NNIE

CLAIRE SE

8.

0 0.12

9 MONTEZUMA

PEAK

6.9

0.10 17 SPECTER

RANGE

11.6

0.

10 13

MA

GRUD

ER MTN

11.7

0.06 11

MAGRUDER MTN

81.9

0.

25 13

LITTLE LAKE

6.1

0.09 18 TI

MBER

MTN

69.4

0.

20 17 HA

IWEE

RE

SE

11.3

0.

07 14 MER

CURY

SW

33

.2 0.17 15 **

*QUA

D. NOT

LIST

ED

16.8 0.

20 15 GROOM RANGE NE

40.4

0.

24 29

DO

G BO

NE LA

KE SOUTH

10.4

0.

14 17

BO

NNIE

CLAIRE SE

2.0

16.2

0.12 13 LOWER

PAHRANAGAT LA

KE

13.9

0.

09 20 THIRSTY CANYON NE

13.8 0.

06 16 THIRSTY CANYON

0.8

6.8

0.06

15 ST

RIPE

D HILLS

1.98

1.85

1.8

16.4

0.

23 15 LOWER PAHRANAGAT LA

KE

0.50

11

.6 0.

06 16 BI

G DU

NE

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47

1990

LO

CA

L H

YPO

CEN

TER

SU

MM

AR

Y -

SGB

EA

RTH

QU

AK

ES

.£-

oo

DATE

- TIME

(UTC)

JUN

28 28 29 29 29 29 29 30 30 30 30 30

JUL

1 1 1 2 2 2 2 4 5 6 6 6 7 7 8 8 8 9 10 12 12 13 13 16 17 18 18 19 19 19 19 19

10:16:45

10:49:17

6:48

: 6

9:19

:29

9:54

:55

13:21:43

21:2

2:47

5:10

:31

5:30

:18

11:53:27

12:50:33

15:47:13

12:30:60

14:5

6:31

17:19:

15:

8:

5511:21:17

11:24:36

16:25:18

17:

7:21

11:42:14

0:26

:44

8:10

:16

19:52:18

11:1

1:34

22:5

5:40

0:21

:24

6:41

: 4

20:20: 5

20:3

4:40

7:50

: 4

6:10:37

10:26:33

13:4

5:48

15:3

0:59

1:24:20

20:14: 2

12:40:23

17:21: 4

11:11:13

14:37:40

18:35:44

20:42: 0

21:1

2:42

LATI

TUDE

(DEC.

N)

36.097

37.204

38.1

6136.102

36.843

37.484

36.719

38.182

37.059

37.337

37.347

37.094

37.945

37.260

37.257

37.447

37.237

37.237

37.325

37.052

36.559

37.113

37.130

37.808

38.155

37.530

36.666

37.249

36.933

36.817

36.024

37.779

37.202

37.240

36.4

5135.689

36.459

37.4

7137.080

38.428

38.458

35.894

38.523

37.897

LONG

ITUD

E(DEC.

W)

114.642

117.552

114.

951

117.

701

116.257

114.814

115.

951

117.804

116.305

115.429

114.829

117.358

117.448

116.425

116.426

117.185

114.842

114.

851

115.420

117.

461

116.828

115.179

115.177

115.220

114.

961

115.322

116.378

114.810

115.

611

116.266

117.374

116.127

117.554

116.570

114.493

116.618

116.165

117.957

114.912

117.909

117.910

117.846

117.935

117.477

STAND

ERRO

RH(

KM)

2.3

0.5

2.3

1.0

0.5

1.1

0.9

3.0

0.2

0.7

1.0

0.5

3.5

0.5

0.6

0.4

0.9

1.6

0.7

0.5

0.3

0.4

0.9

0.5

2.6

0.5

0.4

2.2

0.5

0.3

1.4

0.3

0.6

0.3

1.5

3.4

0.3

2.2

1.0

7.6

2.4

7.7

3.0

0.6

DEPT

H(K

M)

-1.9

42.74

-1.02

5.94*

8.98

1.97

1.77

-1.02

-0.19

0.27

1.85

0.90

3.38

*0.

90-1.78

0.93

1.33

3.21

*

3.21

*1.75

7.12

0.07

0.36

0.64

-1.54

4.23

4.84

7.00

*3.

03*

3.78

3.70

*5.17

2.95

1.59

3.14

6.30

*

10.65

5.59

3.26

*-0

.46

3.46

4.72

3.02

*3.

04*

STAND

ERROR

Z(KM

)

1.7

1.0

1.7

0.9

3.9

2.8

2.3

0.1

1.0

2.3

0.7

^^^

0.8

0.7

0.6

2.0

^^^

1.8

1.2

0.3

0.5

0.9

2.4

5.5

0.6

0.9

^^^

2.6

1.2

0.8

4.0

0.5

2.0

6.3

2.3

5.4

^^^

AZI

GAP

(DEG

)

211

132

250

276

109

221

155

261

115 57 195

114

238 84 78 141

200

242 83 147 72 167

166

118

248

166

167

246 90 97 260 93 129 47 220

278 78 247

193

300

301

311

304

225

000

12S MAGNITUDE

ESTIMATES

Mca

Md

MLh

BDI

1.69

ABI

1.26

BDI

2.20

GDI

2.01

ABI

0.84

BDI

1.14

BCI

GDI

1.83

ABI

1.13

BCI

1.39

BDI

1.04

ACI

1.63

CDI

1.63

ACI

0.88

BCI

1.76

ACI

1.09

ADI

1.37

CDU

1.20

CCI

.39

BCI

.53

ABI

0.92

ACI

.48

BCI

.34

BCI

.43

CDI

1.48

CCI

1.06

ACI

1.25

CDU

1.53

CCI

1.92

ABI

1.26

CDI

1.87

BCI

1.69

ABI

1.09

ABI

1.42

BDI

1.68

CDI

1.62

AAI

1.16

BDI

1.62

CDI

2.20

DDI

1.39

BDI

1.86

DDI

1.84

CDI

1.75

CDI

1.41

1.41

1.91

1.87

1.09

1.99

1.71

1.17

1.19

1.51

1.91

1.02

1.44

1.65

1.73

0.98

1.83

1.37

1.70

1.08

1.82

1.74

1.18

1.94

1.03

2.39

1.67

1.38

2.19

1.65

2.19

1.87

1.75

MLv

1.71

1.29

2.08

1.82

0.44

1.05

0.78

2.02

0.62

1.41

1.08

0.98

1.49

0.95

1.46

1.17

1.45

1.26

1.43

1.63

0.92

1.60

1.21

1.49

1.52

1.24

0.90

1.58

1.94

0.83

2.00

1.81

0.74

1.31

1.59

1.81

1.02

1.61

2.24

1.56

2.12

2.12

1.87

1.58

MLc 0.8

2.3

1.8

1.4

1.3

1.5

1.8

1.9

1.1

2.2

2.0

1.3

1.1

1.4

2.0

DEL-

RMS

|N

MIN

RES. PH

. U.

S.G.

S.(K

M) (S

EC)

QUADRANGLE

22.0

0.

16

9 HO

OVER

DAM

8.9

0.15

25

LAST

CHA

NCE

32.7

0.19 14

SIL

VER

KING M

TN62.9 0.

10 15

COSO

PEAK

5.7

0.09 11

JACKASS

FLATS

15.1 0.

09

6 DELAMAR

6.6

0.10

10 M

ERCURY

51.8 0.17 14 C

OALDALE

NE7.2

0.06 14

BUCKBOARD MES

A28.4 0

.25

18 CUT

LER

RESE

20.7

0.

11

9 GREGERSON

BASIN

10.5

0.

14 17 UBEHEBE CR

ATER

56.2

0.29 13 PAYMASTER CANYON

10.3

0.11 13 SILENT B

UTTE

10.2 0.21 23 SI

LENT

BUTTE

17.4

0.1

1 14 STONEWALL PAS

S26.4 0

.13

11 DE

LAMA

R 3 NE

25.9

0.

13

7 DE

LAMA

R 3 NE

27.0

0.20 14

CUTLER

RESERVOIR

11.8

0.

18 2

2 UBEHEBE CR

ATER

9.6

0.12 2

6 CH

LORI

DE CLI

FF6.2

0.08

12 LOWER

PAHRANAGAT LA

KE4.4

0.17

13 LOWER

PAHRANAGAT LAKE

15.3

0.15 12

SEAMAN WAS

H

31.7 0

.15

9 SILVER K

ING MTN

16.9

0.

13 12

MT

IRIS

H4.2

0.08 14 LATHROP WELLS

27.6 0

.11

7 DE

LAMA

R 3 NE

32.0 0.

26 3

9 QU

ARTZ

PEA

K6.9

0.10 19 JACKASS

FLATS

46.1

0.

23 18 M

ATURANGO

16.4

0.15 25 R

EVEILLE PEAK

8.9

0.10

14 LA

ST CHANCE

RANGE

8.4

0.11

31

TH

IRST

Y CA

NYON

60.1 0.

18 13 **

*QUA

D. NOT

LIST

ED55.3 0

.22

14 LEACH

LAKE

5.8

0.11

21 AMARGOSA FLAT

6.8

0.23

15 S

OLDIER PASS

26.4 0

.21

19 D

ELAMAR 3

SW

79.7

0.32 11

**

*QUA

D. NOT

LIST

ED83

.0 0.

19 12 **

*QUA

D. NOT

LIST

ED141.0

0.37

9

LITTLE LA

KE

90.4 0

.19

10 **

*QUA

D. NOT

LIST

ED23

.3 0.

10 13 PAYMASTER CA

NYON

617

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1990

LO

CA

L H

YPO

CEN

TER

SU

MM

AR

Y -

SGB

EA

RTH

QU

AK

ES

Ln

O

DATE

- T

IME

(UTC)

AUG

13 13 13 13 14 14 14 14 14 15 15 15 15 17 17 18 18 18 18 19 20 20 20 20 21 21 22 22 23 23 23 23 23 23 24 24 25 25 25 25 26 27 27 27

15:47: 9

16:30:36

19:56:58

23:54:46

5:37

:34

13:

5:37

15:

4:27

15:23:20

18:33:24

4:32

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19:22:34

20:50:48

23:2

5: 7

10:56:55

12:16: 6

17:54:48

18:50:47

18:51:55

18:5

4:37

2:16

: 1

7:58:20

10:47:12

14:

7:33

21:

7: 5

2:10

: 6

22:

0:24

1:42:40

2:34

: 4

0: 7: 4

2:10:14

4:38

:36

9: 7:40

19:32: 6

22:24:11

9:51

:42

22:18:36

3:37

:10

5: 5:51

8:27

: 5

23:58:35

6:54:

34:

3:26

4:52

:50

22:4

0:15

LATI

TUDE

(DEC.

N)

37.325

38.164

36.364

37.547

37.352

38.474

38.406

37.353

37.144

36.633

37.556

37.3

52

37.110

37.353

36.789

37.133

37.2

9137

.290

37.126

36.955

37.3

1136

.613

36.340

37.9

09

37.9

1137

.440

35.649

35.996

37.098

37.100

37.1

2937

.404

35.900

35.759

36.8

2938

.424

37.229

36.008

36.5

2137

.313

36.775

37.438

35.6

5936

.717

LONG

ITUD

E(D

EG.

W)

117.

680

114.

953

115.

834

117.

173

115.

265

116.545

116.496

117.676

117.

393

117.170

117.168

117.668

116.

961

117.672

115.

812

117.316

116.735

116.

737

117.

323

117.

771

116.

038

116.

273

117.458

116.

412

116.415

117.229

116.328

117.818

117.

197

117.199

117.

314

115.223

117.659

117.979

116.

030

117.387

116.

507

117.085

117.886

116.035

116.103

115.846

115.929

116.

401

STAN

D ER

ROR

H(KM)

0.2

1.9

0.2

0.3

0.4

1.9

4.6

0.3

0.3

0.8

0.6

0.5

0.3

0.3

3.8

0.5

0.2

0.2

0.4

1.5

0.4

0.3

0.8

0.5

0.3

0.2

4.5

2.1

0.4

0.5

0.4

0.4

4.2

1.6

0.5

.

0.5

1.5

1.0

0.6

0.5

2.9

0.3

DEPT

H(K

M) 0.78

7.00

7.00

0.18

4.02

8.40

5.00

*0.

930.

407.99

2.41

0.36

0.56

0.99

8.81

0.86

0.57

0.25

4.70

3.07

*-6.19

4.70

5.23

5.32

5.72

0.86

-1.02

10.0

0**

1.54

4.90

4.96

0.89

1.17*

7.00

9.83

11.6

6

0.00

11.8

27.

00*

-0.86

10.1

4-1

.13

2.06*

6.11

STAND

ERRO

RZ(

KM)

0.4

3.8

1.2

0.5

8.6

2.0

. _ .

0.6

0.6

1.9

5.8

0.8

0.5

0.5

3.3

0.7

0.4

0.5

3.1

0.9

0.7

5.6

4.7

2.0

0.4

3.7

2.2

1.4

3.7

2.1

0.5

2.0

1.1 -

0.8

1.4

1.0

0.8

___

0.6

AZI

GAP

(DEG)

135

250

111 88 106

244

250

122

112

111

124

126

106

121

256 98 53 53 104

211 74 159

237 97 102 64 264

265 94 117 99 127

276

293

165

259 85 238

251

126

143 61 217

148

QQD

12S MAGNITUDE

ESTIMATES

Mca

Md

MLh

ACI

1.29

BDI

2.26

ACI

1.68

BCI

1.96

CCI

1.59

BDI

2.02

CDI

1.72

ACI

1.26

ACI

1.48

ABI

0.69

CCI

ACI

BCI

1.24

ACI

CDI

1.14

BCI

1.22

ABI

2.39

ABI

2.32

BCI

1.10

CDI

BCI

1.59

ACI

1.18

CDI

BCI

1.52

ACI

1.48

ACI

1.87

CDI

1.64

BDI

1.59

ACI

0.99

BCI

1.00

BCI

1.41

ACI

1.26

CDI

1.90

BDI

2.10

ACI

0.86

ADI

ACI

ADI

CDI

1.89

BCI

ACI

1.39

CCI

2.46

CDI

1.97

ACI

1.00

2.39

1.55

2.07 .39

.99

.59

.48

.40

0.87

1.30

0.87

1.19

0.80

2.37

2.46

1.37

1.42

1.53

1.10

1.83

1.95

0.93

0.99

1.69

1.38

2.12

2.47

1.11

2.05

1.52

2.72

MLv

1.17

2.45 .48

.95

.05

2.17 .73

.43

.34

0.60 .20

.09

1.07

1.12

0.98

1.17

2.35

2.33

0.99 .57

.73

0.83 .52

.63

.56

.89

.62

.77

0.90

0.89

1.41

0.97

1.98

2.22

0.50

1.63

1.03

0.44

2.09

1.61

0.93

2.50

1.92

0.67

DEL-

RMS

|N

MIN

RES.

PH

. U.

S.G.

S.MLc

(KM) (S

EC)

QUADRANGLE

10.7

0.0

7 14 MAGRUDER MTN

2.7

32.9

0.2

7 18 SILVER

KING

1.6

22.7 0

.08

23 M

T STIRLING

2.2

25.3

0.1

7 41

GOLDFIELD

20.0

0.0

7 8 BADGER SPRING

28.3

0.20

16 **

*QUA

D. NOT

LIST

ED

1.8

74.4

0.28

13 **

*QUA

D. NOT

LISTED*

13.6 0

.12

16 MAGRUDER MTN

16.6 0.13 2

1 UBEHEBE CRATER

9.8

0.07 11

STOVEPIPE WELLS

25.1 0.

14 13 G

OLDFIELD

13.4

0.11

9 MAGRUDER M

TN

15.6 0.16 30

SPR

INGD

ALE

13.5

0.10 14 MAGRUDER MTN

10.5 0

.27

11 FRENCHMAN

LAKE

1.3

15.2

0.15

19 U

BEHE

BE CRATER

2.6

8.4

0.13

53

BLAC

K MTN

SW2.7

8.6

0.13

48

BLAC

K MTN

SW

14.3

0.1

1 12 UBEHEBE CRA

TER

32.7 0

.22

15 WAUCOBA WAS

H1.6

12.6

0.16 2

6 OAK

SPRING

7.0

0.08

21

LATH

ROP WELLS

32.5 0.17 18 P

ANAMINT

BUTTE

1.6

18.7 0

.22

22 K

AWICH

PEAK

19.0

0.10

18 K

AWICH

PEAK

2.1

15.7 0

.14

40 S

TONEWALL P

ASS

55.3

0.25

10 A

VAWATZ P

ASS

78.2 0.28 17 LITTLE LA

KE17

.2 0.

14 18 B

ONN IE C

LAIRE

SW17

.3 0

.14

16 BO

NN IE CLAIRE S

W

1.4

14.7 0.18 3

2 UB

EHEB

E CR

ATER

15.3

0.08

8 ASH

SPRINGS

71.8

0.2

0 14 MOUNTAIN SP

RING

102.

9 0.

17 14 LITTLE LA

KE12

.7 0

.09

14 CAN

E SP

RING

80.3 0.08

4 SAN ANTONIA

13.8 0

.15

16 THIRSTY CANYON

20.2

0.15

4 TELESCOPE

PEAK

53.3

0.20 2

4 NEW YORK BUTTE

12.8

0.29

14 OAK S

PRIN

G BUTTE

10.6

0.1

0 11

CANE S

PRING

2.5

25.0

0.3

0 42

GROOM MINE

NE

55.8 0

.20

8 KINGSTON PE

AK1.2

7.8

0.07

17 LA

THRO

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SGB

EA

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AK

ES

STA

ND

STA

ND

A

ZI

00

0

DE

L-

RMS

|N

tn

DATE

- T

IME

(UTC

)

SEP

27 27 27 27 27 27 27 28 28 28 29 29 29 30 30 30 30 30 30 30 30OCT

1 1 1 1 1 2 2 2 2 2 3 4 4 5 5 5 5 5 5 5 6 6 6

0: 6:13

10:30:59

10:4

3: 2

12:19:58

15:5

6:34

18:

2:47

22:53:22

4:41:59

11:2

9:57

14:1

8:14

6: 7:

1

9:38

:21

19:2

1:41

2: 5:58

2:21:35

10:

9:46

10:18:15

10:5

3:36

17:

9:16

17:14:33

19:5

9: 8

2:12:21

4:43:20

10:5

3:28

13:28:11

13:5

6:37

1: 9:51

2:38

:24

5:42

:16

6: 8:29

8:30

:47

20:

6:58

9: 8:

3711

:54:

0

1:49

:56

3:18

:44

6: 4:19

6:31

: 8

7:41

: 3

11:31:44

21:4

0:20

7:44:32

11:46:14

13:

1:35

LATI

TUDE

(DEG.

N)

37.1

1936

.607

38.201

36.640

36.7

0037.004

37.2

6936.696

36.747

38.2

3835.997

36.028

37.5

0637

.369

36.6

3636.921

36.931

36.9

26

36.9

2037

.309

36.014

38.2

1636

.632

38.2

27

37.381

37.2

5638

.165

38.1

4736

.029

36.775

35.907

36.500

35.9

9537

.153

37.9

1935

.999

37.0

5537.171

36.694

37.3

0837

.874

37.088

36.7

4936

.743

LONG

ITUD

E(DEG.

W)

117.200

116.277

116.208

116.283

115.767

116.053

114.969

115.

761

116.027

116.170

114.

794

116.096

118.439

115.204

116.232

117.588

117.

571

117.579

117.587

117.316

116.082

116.

221

116.236

116.183

115.203

116.416

116.143

116.217

116.060

115.789

116.

721

116.568

116.070

117.377

117.766

115.

663

122.032

114.935

116.

271

117.568

116.128

116.875

116.

011

116.012

ERRO

RH(KM)

0.6

0.4

9.0

4.7

0.4

0.6

1.6

1.4

0.3

1.1

0.8

0.8

6.6

1.1

0.4

0.7

1.2

1.0

1.1

0.7

0.7

2.0

0.6

2.1

1.4

2.8

2.0

4.8

2.4

1.4

5.0

0.5

1.7

0.4

1.2

1.0

1.7

0.5

0.7

0.7

0.3

0.4

0.4

DEPT

H(K

M) 0.16

0.70

1.88

*-1

.82

0.09

1.70

-2.0

0-0.09

0.97

5.84

-1.4

2-1

.55

0.10

10.75

10.0

18.66

6.50

6.25

0.60

9.61

4.75

3.13

*8.75

-1.02

11.0

5-1.60

-1.13

2.43

*-1.97

-1.0

8

0.30

-0.4

7-0.19

-0.8

53.

06*

1.05

11.0

04.

656.47

-1.9

0-0

.47

-0.16

0.97

-0.1

3

ERROR

Z(KM

)

0.9

0.7

3.7

0.3

1.5

1.6

0.8

0.5

8.0

1.1

1.4

5.4

2.4

0.9

1.5

6.4

4.6

1.0

1.1

2.3

1.2

2.0

2.6

2.7

2.5

2.1

1.2

3.5

0.8

1.6

0.5

2.8

2.8

0.6

0.8

1.1

0.4

0.7

0.5

GAP

(DEG)

110 62

211

253

120

175

201

205

115

204

166

169

314

173

124

195

187

188

195

147

237

264

137

200

114

116

186

269

212

215

263 55 217

170

266

172

165

249

202 92 110

173

152

155

12S MA

GNIT

UDE

Mca

Md

BCI

BBI

2.06

2.24

DDI

1.50

CD I

BBI

1.74

ACI

1.96

BDI

2.01

BDI

ACI

1.51

CDI

2.16

ACI

2.01

BCI

2.20

DDU

2.52

BCI

ABI

1.16

ADU

2.81

CDI

1.59

BDI

1.80

BDI

1.16

ACI

BDI

1.66

CDI

2.19

ACI

0.89

CDI

1.39

BBI

1.23

CBU

1.19

CDI

1.87

DDU

DDI

2.18

BDI

1.22

CDI

1.93

BCI

1.57

CDI

1.86

ACI

1.26

CDI

DDI

2.03

BCI

3.80

BDI

1.32

ADI

BCI

BCI

1.65

ACI

1.22

ACI

2.14

ACI

1.39

ESTIMATES

MLh

2.45

1.22

1.95

1.90

1.24

1.00

1.64

1.62

1.58

1.15

1.49

MLv

0.82

1.91

1.53

0.64

1.73

1.67

1.95

0.83

1.51

1.95

2.12

1.97

0.96

0.81

1.51

1.63

1.10

0.85

1.79

1.74

0.47

1.58

1.31

1.83

1.99

0.99

1.36

1.50

1.98

1.13

1.81

1.73

3.90

1.48

0.45

0.84

1.44

1.09

1.44

1.23

MLc 2.3

1.4

1.7

1.2

1.5

2.4

2.2

2.7

1.4

2.3

1.8

1.9

2.1

1.1

2.2

2.1

1.8

1.6

1.1

1.5

MIN

RES. PH

. U.S.G.S.

(KM)

(S

EC)

QUAD

RANG

LE

18.7

0.18 11

BO

NN IE CL

AIRE

7.0

0.21 35

LATHROP WELLS

20.4 0

.46

15 TWIN SPRINGS

SLOUGH

5.1

0.15

9

STRIPED HI

LLS

4.0

0.17

29 MERCURY

NE8.3

0.13

14

YUC

CA FL

AT

22.3

0.23 13 D

ELAMAR LA

KE4.5

0.19

11

ME

RCUR

Y NE

11.2 0.11 23

CAM

P DESERT ROCK

23.3 0.22 16

TWIN

SPRINGS

SLOUGH

9.0

0.06

13 BOULDER CIT

Y12

.2 0.

19 22 S

TEWA

RT VALLEY

47.9

0.10

7 LONG V

ALLE

Y REGION

14.2 0.

09

7 AL

AMO

9.7

0.07 11

SP

ECTE

R RANGE

20.8 0.

09 10 D

RY MTN

20.4 0.17 11

DRY MTN

20.5 0.

20 15

DRY MTN

20.7

0.

14

9 DRY MTN

5.3

0.05

6 GO

LD PO

INT

14.1 0.13 16 S

TEWA

RT VAL

LEY

54.4

0.2

6 12 TWIN S

PRINGS SLOUGH

9.4

0.09

13

SPE

CTER

RANGE N

W22

.2 0.33 12

TWIN

SPRINGS

SLOUGH

13.7

0.

23 13 ASH S

PRINGS

8.0

0.28

6 SI

LENT

BUT

TE26.8 0.50 16

TWIN S

PRINGS SLOUGH

47.2

0.

65 11

TW

IN SPRINGS

SLOUGH

13.8

0.

54 2

4 ST

EWAR

T VA

LLEY

9.2

0.25 15 FRENCHMAN

LAKE SE

31.3 0.36 11

CO

NFID

ENCE

HILLS

14.1

0.19 19

BIG

DUNE

16.5 0.

38 27

TECOPA

17.3 0.14 18 U

BEHEBE CRATER

22.9

0.21 18 R

HYOL

ITE RIDGE

36.2

1.23 4

SHEN

ANDO

AH P

EAK

372.5

0.30

14 R

egio

nal

(NEI

C)22

.4 0

.20

10 D

ELAMAR 3

NW

5.4

0.06 10 S

TRIP

ED H

ILLS

10.8 0.22 15

MAG

RUDE

R MTN

20.9

0.

29 19

REV

EILL

E PEAK

14.8 0.09 14 S

PRIN

GDAL

E

10.7 0.

09 13

CAM

P DESERT ROCK

10.2

0.08 13 CAM

P DESERT ROCK

1990

LO

CA

L H

YPO

CEN

TER

SU

MM

AR

Y -

SGB

EA

RTH

QU

AK

ES

DATE - T

IME

(UTC

)

OCT

7 8 8 8 8 10 10 10 11 11 12 13 13 13 13 14 14 14 15 15 15 16 16 16 17 17 17 17 17 17 18 18 20 20 20 21 21 22 23 24 24 24 25 25

12:

3:38

2:29

:28

15:4

7:18

18:39:17

18:51: 7

5:50

:44

11:24:48

18:37:22

4:48

:25

14:39:49

7:30

: 8

1:44:47

11:26: 8

11:44: 7

19:52:38

0:26

:49

14:40: 2

19:4

3:43

7:43:

220:

4:35

23:48:15

8:14

:41

13:58:19

14:

2:43

0:23

:41

2:55

:42

15:41:55

15:55:49

17:26:51

20:18:24

19:2

5:51

22:

1:57

0:29

:35

5:27

:28

20:49:15

14:

2:27

21:19:55

10:43:56

22:55:21

5: 4: 6

8:38

:55

18:59:49

0:15

:11

21:5

7:37

LATITUDE

(DEC.

N)

35.9

9037.863

36.2

1836

.440

37.3

0736

.955

37.2

5037

.918

37.6

2535

.696

37.4

5836

.709

36.6

9636

.500

36.764

37.2

5237.240

36.0

05

37.6

9536

.625

37.7

0236

.922

37.241

37.2

47

36.2

8235

.897

36.154

35.7

7036

.143

37.552

37.091

35.9

6635.682

35.8

9836.683

36.2

99

36.174

37.234

36.294

37.3

4736

.744

36.0

57

35.7

1736

.119

LONG

ITUD

E (D

EC.

W)

117.223

116.128

117.580

116.985

116.037

116.386

114.

611

117.723

114.627

115.867

115.273

115.879

117.223

115.950

116.237

116.499

117.903

116.068

117.392

116.440

117.383

116.762

117.519

117.

521

117.578

116.882

117.

891

116.536

117.902

114.097

116.209

116.893

115.659

115.702

116.286

117.548

117.916

117.548

117.554

117.880

116.217

116.793

115.733

115.

361

STAN

D ERROR

H(KM)

9.5

0.8

3.4

1.4

0.1

0.3

5.9

1.2

0.9

2.4

1.4

0.9

0.4

0.7

1.2

0.5

2.1

1.5

1.3

0.8

1.8

0.3

0.5

0.6

2.3

5.2

2.7

2.3

2.0

2.7

0.9

5.0

4.5

0.5

4.2

2.0

0.7

2.8

0.6

2.7

10.3 1.9

DEPTH

(KM)

0.00*

0.88

-1.02

13.5

34.34

7.63

-1.02

3.15*

-1.36

3.62

*0.34

6.98

8.36

10.8

44.36

1.82

-1.23

5.80

-1.50

4.27

5.73

0.45

10.8

78.66

5.19*

0.70

-0.33

-1.0

24.07

2.45

*

7.61

20.22

7.00

2.61

*1.44

-1.02

3.02*

10.48

2.81*

11.0

26.

82-1

.02

5.00

3.34*

STAN

D ERROR

Z(KM)

____

1.1

2.6

1.8

0.9

0.6

4.4

0.4

1.6

1.4

0.7

1.7

0.7

1.6

2.2

2.7

1.9

1.8

1.5

0.4

0.8

1.4

__^

4.4

2.3

1.8

2.2

1.8

11.7

1.9

3.9

__^

0.8

0.9

6.1

8.6

AZI

GAP

(DEC)

313

111

260

190

113 76 276

262

291

268

192

163 85 125

239

123

241

215

181

266

213 96 191

138

256

272

288

251

286

326

117

244

281

289

134

252

289

148

253

267

206

131

124

159

QQD

12S MA

GNIT

UDE

Mca

Md

DDI

1.11

BCI

1.58

CDI

1.97

CDI

1.15

ACI

1.14

ABI

0.99

DDI

1.68

CDI

1.56

BDI

1.19

CDI

2.11

BDU

ACI

1.40

AAI

1.41

ABI

1.33

BDI

1.45

ACI

2.66

BDI

1.57

BDI

2.99

BDI

1.23

ADI

1.67

BDI

1.32

BCI

1.46

ADI

1.03

ACI

CDI

1.82

DDI

1.51

CDI

2.00

BDI

2.03

BDI

1.88 0

.64

DOU

1.80 1.63

BBI

1.26

ADI

DDI

1.66

CDI

1.77

ABI

1.77

CDI

1.81

CDI

1.63

ACI

0.99

CDI

1.44

ADI

1.48

ADA

0.63

CCI

DBI

1.93

CCI

1.94

ESTIMATES

MLh

MLv

MLc

0.91

1.70

1.92

0.89

1.66

0.75

1.04

2.28

2.17

2.37

1.33

1.63

2.63

2.03

1.88

0.95

1.79

1.09

0.88

1.54

1.58

1.38

1.97

0.94

1.21

0.65

1.65

1.86

1.8

1.00

1.90

1.18

1.27

1.50

1.08

0.9

1.9

1.67

3.4

1.24

1.6

1.52

1.4

1.13

0.9

0.98

0.93

1.5

1.85

1.45

1.1

2.07

2.09

2.1

1.91

2.08

1.01

1.3

0.88

1.56

1.71

1.66

0.9

1.80

1.78

1.11

1.44

0.90

0.67

0.87

1.82

DEL-

RMS

|N

MIN

RES. PH.

U.S.G.S.

(KM)

(S

EC)

QUAD

RANG

LE

97.4 0

.26

7 MA

NLY PE

AK20.1 0.

17

9 RE

VEIL

LE PEAK

47.3

0.41

21 CO

SO PEAK

11.6

0.31

20 FURNACE CREEK

12.1 0.

03 10 O

AK S

PRING

BUTTE

8.8

0.11 22

TOPOPAH

SPRING NW

41.0

0.

37 12

EL

GIN

23.6

0.1

4 10 SI

LVER

PE

AK10

.1 0.18

7 CALIENTE NW

54.4 0

.36

18 KINGSTON P

EAK

20.5 0.

17

8 HANCOCK

SUMM

IT6.4

0.11

10 M

ERCURY

7.4

0.07

14 S

TOVEPIPE WEL

LS15

.4 0

.09

8 MERCURY

SW3.9

0.07

8 SKULL MTN

13.2

0.0

6 7

SILE

NT BUTTE

20.5

0.19

11 WAUCOBA SPRING

15.6

0.1

5 14 S

TEWART V

ALLEY

29.8

0.14

8 SPLIT MTN

9.2

0.08

13

LATHROP WELLS

NW0.2

0.15

8

SPLIT

MTN

18.4

0.1

7 25 B

ULLFROG

11.4 0.0

5 8

LAST

CHANCE

RANGE

11.2

0.09

9 LAST CHA

NCE

RANGE

44.6

0.27

12 DARWIN

7.5

0.30

9 WINGATE WASH

75.8

0.

16 14 H

AIWEE RESERVOIR

36.8

0.22 16 C

ONFI

DENC

E HILLS

77.1

0.

20 12 HAIWEE RESERVOIR

56.9

0.

15

8 ***QUAD. NOT

LISTED*

6.2

0.21

12

TI

PPIP

AH S

PRIN

G2.3

0.14

4 WINGATE WA

SH71.1 0.

29

7 CL

ARK MTN

47.9 0.

20 10 SHENANDOAH PEAK

6.4

0.08

11

STRIPED

HILL

S41

.5 0

.22

8 DA

RWIN

77.2 0.21 10 HAIWEE RESERVOIR

8.8

0.08

8 LA

ST CHA

NCE

RANGE

42.1 0.

15

7 DA

RWIN

41.40.01

4 SOLDIER

PASS

5.0

0.11 14

SPECTER R

ANGE N

W12

.3 0

.35

7 BE

NNET

TS WELL

80.2

0.

19

6 CA

-NV BO

RDER

30.1 0.

36 11

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1990

LOCAL HY

POCE

NTER

SU

MMAR

Y - SGB

EART

HQUA

KES

00

DATE(u

DEC

18 18 18 19 19 20 21 21 22 24 24 24 24 24 25 25 25 25 26 27 27 31 31 31

- TI

METC) 2:

7:57

2:21

:29

6:24:53

5:36

:59

12:51:43

9:18:16

1:18:

821:24:27

5:53:15

4:15:21

7: 9:

5813

:33:

0

19:36:60

21:57:31

3:19

:39

9:11:

317

:23:

2413

:56:

6

15:4

9: 9

3:35:25

22:

4:46

11:24:24

15:36:30

18:56:28

LATITUDE

(DEG.

N)

36.690

36.696

36.677

37.231

37.122

36.880

36.807

36.916

36.735

37.018

36.610

37.268

36.906

37.123

36.968

36.898

36.673

36.632

36.7

6636.697

36.722

37.925

37.2

2737.120

LONG

ITUD

E(D

EG.

W)

115.877

115.869

115.

872

116.498

115.

810

116.

231

115.785

116.

827

116.

208

116.

235

115.939

117.009

116.831

117.

180

117.558

116.009

116.402

116.

016

116.200

116.268

116.202

116.135

117.545

117.

181

STAND

ERROR

H(KM

)

0.2

1.2

0.7

1.1

4.0

0.6

. __

0.7

0.2

0.7

0.4

0.8

1.2

0.6

1.2

1.5

0.8

0.4

1.5

0.6

0.5

0.4

0.6

0.6

DEPT

H(K

M)

10.39

10.35

9.86

4.34

15.95

4.92

1.65

14.5

15.36

5.65

0.35

10.3

9

0.86

9.83

8.92

3.50

10.46

5.20

3.87

-0.4

010.59

0.93

11.30

8.97

STAND

ERRO

RZ(KM)

0.3

1.2

0.8

6.7

5.3

1.5

_ _

0.9

0.6

0.8

0.6

1.7

1.6

1.8

3.4

3.0

1.0

0.7

3.1

0.6

1.0

0.7

1.0

1.9

AZI

GAP

(DEG

)

130

149

147

154

219

107

251

170

119

108

168

196

159

114

186

223

209

131

207

126

128

120

129

114

QQO

12S

1 1

ABI

BCI

AC I

CCI

CD I

ABA

ADI

(AC I

ABI

ABI

AC I

ADI

BCI

AC I

BDI

BDI

ADI

ABI

1

BDI

<ABI

tABI

1BCA

ABI

tAC I

MAGN

ITUD

Etea

Md

1.28

1.00

1.04

1.56

1.34

0.86

9.96 .13

.68

.22

.12

.46

.09

.10

.29

0.40

.12

.18

5.89

).90 .15

1.80

5.88

ESTI

MAMLh

1.06

0.44

1.95

1.14

2.12

0.38

1.03

1.26

0.93

1.42

1.07

0.88

TES MLv

MLc

1.34

1.5

0.84

0.98

1.15

1.7

1.09

1.00

0.78

1.24

2.0

0.99

0.65

0.8

1.04

0.59

1.09

1.30

1.5

0.88

0.12

0.87

0.9

0.51

0.47

0.76

1.2

1.03

0.76

DEL-

RMS

MIN

RES.

(KM)

(S

EC)

5.9

0.03

5.2

0.13

5.8

0.10

14.2 0

.17

20.3

0.1

45.

1 0.11

12.8 0

.07

19.9 0

.08

5.8

0.05

2.3

0.11

6.0

0.05

22.4 0

.10

20.0 0

.17

20.1 0.14

19.1 0.18

5.6

0.11

6.3

0.09

5.8

0.08

6.9

0.22

5.0

0.15

6.6

0.12

25.2 0

.21

9.1

0.10

19.9 0

.14

IN PH.

U.S.G.S.

QUADRANGLE

11 MERCURY

9 MERCURY NE

12 MER

CURY

NE

13 S

CRUGHAM PEAK

10 P

APOOSE LAKE S

E11

MINE MTN

4 FR

ENCH

MAN

LAKE

SE

12 B

ULLF

ROG

14 S

PECT

ER RANGE N

W13 T

IPPI

PAH

SPRING

8 ME

RCUR

Y SW

12 S

COTT

YS J

UNCT

ION

10 B

ULLFROG

14 B

ONN IE CLAIRE

SW10 D

RY MTN

7 YU

CCA

LAKE

9 LATHROP WELLS

NW14 C

AMP

DESERT RO

CK

11 SK

ULL

MTN

11 ST

RIPE

D HI

LLS

14 S

PECT

ER RANGE N

W12 R

EVEILLE PEAK

10 LAST C

HANCE

RANG

E11

BONN IE CLAIRE S

W

31

19:2

6:42

36.902

116.

856

0.6

13.5

91.8

132

ABI

1.18

0.63

18.3 0.

13 15 BULLFROG

Appendix B

Chemical explosion location data for the year 1990

The southern Great Basin of Nevada is seismically active from both natural and man-made sources. Chemical explosion seismic data acquired by -the SGBSN have been scaled to provide information on the accuracy of the crustal model and location algorithm used by the SGBSN. The following companies have been contacted and have provided helpful information on source locations, times, and in some cases, TNT-equivalent source size:

(1) Bond International Gold, Denver, Colorado. Blasting at Ladd Mountain, Nev. (Bullfrog Hills quadrangle), approximately daily (weekdays, 4 PM to 5 PM).

(2) Chemstar, Inc., Las Vegas, Nevada. Blasting at two limestone quarries, one in the Dry Lake, Nevada, quadrangle, and one in the Sloan, Nevada, quadrangle. The Dry Lake quarry coordinates are 36.361° North latitude, 114.915° West longitude.

(3) Cyprus Tonopah Mining, Tonopah, Nevada. Blasting in the San Antonia Mountains (San Antonia Ranch quadrangle), usually in the AM.

(4) Frehner Construction, North Las Vegas, Nevada. Blasting at limestone quarry in Sloan, Nevada, quadrangle.

(5) Saga Exploration Co., Beatty, Nevada. Blasting at Bare Mountain, Nevada, usually early to late afternoon.

A number of other organizations are also known to be engaged in blasting in the southern Great Basin of Nevada, but have not been contacted.

Column headings for this Appendix are identical to those for Appendix A. The depth of all blasts is at the surface (plus < 100 feet, usually), but in many instances, hypocenters have been located with depth as a free parameter, to examine the location algorithm and velocity model. If the hypocenter depth is reported as -1.00, it was fixed at that value during hypocenter determination. All other depths are freely determined. If the letters "PB" follow the depth estimate, the event is a probable blast, but just enough ambiguity was present in the seismograms to prevent a certain judgment. Far more hypocentral data from chemical explosions than are presented in this Appendix have been detected and archived by the SGBSN, especially for years proceeding 1989. The decision was made in late 1988 to scale data and to include all resulting hypocenters for known and probable blasts into the catalog, but to flag them as blasts (or probable blasts).

59

1 17 116 115.0 W

36.6-

35.6 N25 50 100 km V SEISMOGRAPH1C STATION D CITY OR TOWN

» mag < 1.0 a 2.0 £ mag < 3.0o 1.0 A ma( < 2.0 O 3.0 £ mag

Figure Bl. Epicenters for known and suspected chemical explosions detected by the SGBSN for the calendar year 1990 are plotted in map view.

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64

1990

LOCAL HYPOCENTER SUMMARY - SGB CHEMICAL EXPLOSIONS

Ui

DATE

- TIME

(UTC)

MAY

31 31JU

N 1 1 1 4 4 5 5 5 6 6 7 7 8 8 11 11 11 12 12 12 12 12 13 14 15 15 17 18 18 19 19 20 21 21 22 25 25 27 27 27 29 30

22:

1: 2

22:23:12

0:28

:11

22:4

7:34

23:3

4: 9

18:34:24

23:3

2:19

18:

9: 2

22:2

6:31

23:2

9:39

21:4

7: 3

23:2

3:41

22:5

2:30

23:11:57

0:19

:39

22:

3:52

22:2

3: 4

22:2

6:33

22:26:33

0:48

: 5

0:59:

310

:39:

1919:38: 2

19:38: 5

23:3

7:32

22:

7:32

23:1

6:34

23:2

4:58

21:58:12

22:41:28

23:

7:43

21:4

4:33

22:2

2:10

22:2

5:18

17:18:40

22:38:38

22:5

4:35

15:4

3: 6

22:34:32

0:27

:31

17:

4:45

22:1

8:26

22:27:29

19:46:45

LATITUDE

(DEC.

N)

36.8

9338

.353

36.9

4236

.893

35.6

1536.897

35.5

8936

.942

36.890

35.601

36.9

0036

.896

36.8

9035.594

37.241

36.8

9238.364

36.8

93

36.8

9336

.067

36.098

37.041

36.2

6236.291

36.901

36.8

9736

.892

35.7

1036

.100

36.8

89

36.9

3636

.898

38.3

0236

.899

37.0

1436

.895

36.891

36.941

36.8

9336

.888

36.9

0236

.893

36.8

9236

.913

LONG

ITUD

E(D

EC.

W)

116.814

117.342

116.885

116.814

115.561

116.814

115.568

116.885

116.813

115.569

116.

809

116.810

116.817

115.573

116.401

116.810

117.326

116.815

116.815

115.816

117.910

115.939

114.859

115.

121

116.816

116.810

116.814

115.659

117.705

116.816

116.888

116.823

117.

291

116.815

116.599

116.807

116.819

116.887

116.814

116.820

116.654

116.811

116.814

116.824

STAND

ERRO

RH(

KM)

0.5

3.9

0.5

0.4

2.8

0.5

3.8

0.4

0.4

2.0

0.3

0.3

0.4

2.4

0.3

0.3

3.4

0.3

0.3

6.3

3.8

0.7

1.8

3.8

0.6

0.9

0.5

6.7

2.1

0.5

0.5

0.5

4.3

0.3

0.4

0.8

0.3

0.4

0.4

0.4

0.3

0.5

0.4

0.9

STAND

DEPTH

ERRO

R(K

M)

Z(KM)

_ _ _ -f - _

.00BL

1.3

.00BL 30.0

.00B

L 1.

1.00BL

1.0

.00BL

30.0

.00BL

16.3

.00BL 30.0

.00B

L 1.3

.00B

L 1.4

.00BL 30.0

.00B

L 7.5

.00B

L 9.

4

.00BL

0.9

.00BL 30.0

J.20PB

0.3

.00B

L 9.0

.00BL 30

.0.00BL

0.8

.00B

L 0.8

.00BL 30.0

0.00

BL

4.0

0.00

BL

1.4

-1.43PB

1.3

7.00

*

0.20

BL 2.

80.

20BL

2.8

-1.0CBL

2.0

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30.0

0.00

BL

2.0

-1.0CBL

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Appendix C

Nuclear device tests and low-frequency shallow seismicity in the NTS, 1990

Hypocenter data for announced Nevada Test Site nuclear device tests occurring in 1990 are listed in Table Cl. Hypocenter parameters are listed as they are reported to the National Earth­ quake Information Center (NEIC) by the U. S. Department of Energy. Magnitude estimates are provided by Berkeley Seismographic Laboratory or by the NEIC. NTS nuclear detonation ground motions recorded at SGBSN stations are generally well beyond the seismograph dynamic range; thus, only initial P-wave arrival times can be reliably scaled from SGBSN seismograms of nuclear tests. The epicenters of the tests listed in Table Cl are plotted as octogons in Figure Cl, along with epicenters of located induced seismicity, plotted with the symbol "L."

Relatively high levels of seismicity are regularly recorded by SGBSN stations for periods ranging from hours to days following NTS nuclear device tests. The seismicity listed in Appendix C consists of events having characteristically lower-frequency seismic P coda and S coda than that of the vast majority of earthquakes in the SGB. Most of the low-frequency activity can be associated with nuclear device testing at Pahute Mesa, Yucca Flat, and in a few instances, at Rainier Mesa. Some of these events may be identified as the cavity collapses of given tests, although, in general, the heightened level of post-test seismicity often continues for days, with no single event having clearly greater magnitude, as determined from SGBSN seismograms, than many others in its vicinity. The grouping of these post-test events into Appendix C is based on the visual appearance of their seismic coda, and on their spatial and, to a lesser degree, temporal association with tests. Figure C2 is an example of four SGBSN seismograms of an aftershock (or collapse) at Silent Canyon Caldera. A working hypothesis for the lower-than-average frequency content for NTS test aftershock seismograms is that all of the aftershocks originate at very shallow depths, where the seismic attenuation of rock is very high, due to relatively low confining pressure.

The majority of post-test seismicity is not routinely located by SGBSN staff, but the seimic data are permanently archived on magnetic tapes. A list of event times for archived low-frequency NTS seismicity that has not been analysed for hypocenter parameters is also included in the latter part of Appendix C.

A few low-frequency events that are not located at NTS are included in Appendix C, because their seismic coda appears more similar to post-test, collapse-like seismicity than to earthquake coda. Many of these are undoubtedly blasts in unconsolidated alluvium or intensely fractured tuff. The verification that other explanations of these phenomena are invalid is left to future investigation.

Table Cl. Announced nuclear device tests at Nevada Test Site in the calendar year 1990.

YRMODA

900310900613900621900725 901012901114

HR MN SECND UTC

16 00 0.8316 00 0.0118 15 0.0015 00 0.06 17 30 0.0819 17 0.71 »

ML (SRC) 1

5.1 BRK5.6 BRK4.1 BRK4.8 NEIC 5.4 BRK5.1 BRK

Latitude (°N)

37.112537.261636.992837.2069 37.247937.2274

Longitude(°w)116.0552116.4201116.0045116.2143 116.4942116.3712

Depth (km)-0.77-1.28-0.90-1.84 -1.30-1.46

NAME

METROPOLISBULLIONAUSTIN

MINERAL QUARRY TENABO

HOUSTON

1 SRC: BRK=Seismographic Laboratory, Berkeley, California; NEIC= National Earthquake In­ formation Center, Golden, Colorado.

71

0 10 20 30 kmI I I I

V

D

BEATTY

V

V \ f.L

V

V

V

C^\ AMARGOSA VALLEY

37.6

116.9 YM-Yucca Mtn. V SEISMOGRAPHIC STATION

115.7536.5

D CITY OR TOWN

mag < 3.0 O 4.0 ^ mag < 5.0 O 5.0 ^ mag

Figure Cl. Epicenters for announced NTS nuclear device tests detonated during the calendar year 1990 are shown in map view (octogon symbols), along with some nuclear-testing-induced activity ("L" symbols). Location uncertainty of the "Ls" is high, due to low signal-to-noise ratios in the seismograms of SGBSN instruments that record the collapses.

72

1990 11 14 224 BGB

1990 11

14 224 BMTN

600

1800

900

-600

- -900

-1800

1990 11 14 224 CDH1

30

0

150

o S o

-15

0

19

90

11

14 2

24

TM

BR

-300

1.0

se

c

1400

700

-70

0

53.2

68.5

83

.7

98.9

T

ime (

se

c)

11

4.2

-1400

1.0

sec I

53

.268.5

83.7

9

8.9

Tim

e (

sec)

114.2

12

9.4

Fig

ure

C2.

Sei

smog

ram

s fr

om S

GB

SN

sta

tion

s B

GB

, B

MT

N,

CD

Hl,

and

TM

BR

for

a s

eism

ic

dist

urba

nce

at S

ilen

t C

anyo

n, N

TS

, ab

out

33 h

ours

aft

er t

he d

eton

atio

n of

"T

enab

o."

Eac

h pl

ot

also

dis

play

s ab

out

one

seco

nd o

f po

st-P

rec

ord

on a

n ex

pand

ed t

ime

axis

. P

-wav

e fi

rst

arri

vals

ar

e in

dica

ted.

T

hese

sei

smog

ram

s ha

ve d

omin

ant

freq

uenc

y in

the

nei

ghbo

rhoo

d of

3 H

z, a

bout

on

e-th

ird

the

dom

inan

t fr

eque

ncy

of s

eism

ogra

ms

from

typ

ical

SG

B e

arth

quak

es h

avin

g th

e sa

me

mag

nitu

de.

The

y al

so d

ispl

ay p

rom

inan

t re

verb

erat

ions

or

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ing,

an

d di

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ult-

to-o

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ve

S on

sets

. N

eith

er o

f th

ese

feat

ures

is

typi

cal

of m

ost

eart

hqua

ke s

eism

ogra

ms.

1990

LOCAL

HYPO

CENT

ER SUMMARY - SGB

LOW-

FREQ

UENC

Y PH

ENOM

ENA

DATE - TI

ME

(UTC)

FEB

18

17:

8: 9

MAR

4 15:47:51

4 15

:53:

4922 22 22 22 22 26 27

APR

29JUN

13 13 13 13 13 16 17 19 19 21 21 21 24

JUL

11 11 11 24 24 26 26 29 29 26 26 29

7:46

:41

9: 8:53

13:

8:46

13:1

7:14

14:36:

112:58:26

15:3

4:23

19:1

4:35

16:

9:37

18:1

1:15

18:21 :27

18:29:27

20:1

2: 9

1:25

:50

17:16:28

12:49:36

13:

0:13

18:25:30

18:2

6:44

18:33:48

14:

0:11

7:27

:57

8:22

: 6

8:26

:56

0:11:36

4:43

: 6

18:26:34

23:2

6:32

6:26

:56

11:1

4:48

18:26:34

23:26:32

6:26

:56

LATITUDE

(DEC.

N)

37.2

58

37.2

86

37.2

8137

.300

37.3

2437

.321

37.277

37.2

9337

.294

37.3

2937

.626

37.282

37.2

7337

.293

37.2

8737

.275

37.2

6837

.340

37.2

7137

.265

37.0

0037

.005

37.0

0237

.009

37.2

4937

.264

37.2

7337

.273

37.2

5437

.231

37.2

3137

.272

37.2

7237

.231

37.2

3137

.272

LONGITUDE

(DEC

. W)

116.

421

116.

481

116.510

116.

407

116.375

116.359

116.

402

116.385

116.495

116.380

116.966

116.

421

116.

410

116.

407

116.406

116.

398

116.425

116.364

116.414

116.

421

116.

007

116.

000

116.

001

116.

025

116.

496

116.

411

116.

408

116.404

116.426

116.

424

116.

383

116.394

116.

419

116.424

116.

383

116.

394

STAND

ERROR

H(KM)

2.1

5.0

0.7

1.0

2.7

2.2

0.9

3.9

1 .0

2.2

11.3

0.7

0.3

1.8

3.0

2.1

0.5

2.5

0.4

0.4

0.4

0.5

0.4

0.9

0.4

1 .1

0.7

0.6

0.6

1.6

1.7 .6 .0 .6 .7 .6

DEPTH

(KM)

-1.35

11.17*

0.46

*3.

006.27

10.78

2.49

7.12

-0.4

4*6.37

10.8

5*0.71

0.27

6.57

4.37

6.83

-1.14

8.86

- .0

0- .4

6- .6

0-0.92

- .62

- .2

5

-1.2

8*-0

.02

2.41

6.70

-1.88

-1 .24

-0.7

24.

074.

24-1.24

-0.72

4.07

STAN

D ER

ROR

Z(KM)

2.3

3.6

2.3

1.4

2.4

2.7

1.9

1.3

0.6

2.7

7.3

3.6

0.5

9.9

0.3

0.6

1.1

0.9

0.5

1.2

__

3.4

1.9

1.4

0.7

1.9

1.5

5.0

3.7

1.9

1.5

5.0

AZI

GAP

(DEC)

179

207

186

201

258

263

173

239

195

259

140

107 46

231

227

170

115

307

161 75 176

179

178 95 94 88 129

131

115 70 183

135

124

70 183

135

QQD

12S

BCI

DDI

GDI

BDI

GDI

BDI

BCI

GDI

GDI

BDI

DCI

BCI

AC I

BDI

CD I

BCI

AC I

GDI

AC I

BCI

AC I

AC I

AC I

BBI

CCI

BBI

BBI

BBI

BCI

DBI

BDI

CBI

BCI

DBI

BDI

CBI

MAGN

ITUD

E ES

TIMA

TES

Mca

Md

MLh

MLv

1.43

1.

39

1.37

1.77

1.81

2.01

1.31

0.97

1.78

1 .6

0

1.87

2.20

1.88

1.89

1.65

1.92

1.64

1.44

1.25

1.89

1.68

1.37

1.30

1.84

1 .53

1.81

2.20

1.66

1.42

1.65

1.57

2.11

1.20

1.44

1.57

2.11

1.20

1.96

1.75

0.92

1.13

1.43

1.69

1.13

1.81

2.32

1.53

1.82

1.42

0.93

1.45

1 .4

01.

331.

471.

201.21

1.19

1.11

1.36

1.21

1.19

1.11

MLc 2.2

2.1

1.4

1.4

2.0

1.8

1.9

1.5

1.5

1.5

DEL-

RM

S #N

MIN

RES. PH

. U.S.G.S.

(KM) (S

EC)

QUADRANGLE

9.9

0.28

10 SI

LENT

BU

TTE

14.1

0.29

8 SI

LENT

BUTTE

11.6

0.11 14 TR

AIL

RIDG

E12

.1 0.

07

8 SI

LENT

BU

TTE

13.0

0.12 10

SILENT BU

TTE

12.2

0.

13 11 DE

AD HO

RSE

FLAT

9.9

0.18

16

SILENT BU

TTE

10.3

0.11

8 SI

LENT

BU

TTE

12.9

0.

15 15

SI

LENT

BUTTE

13.7

0.09

7 SILENT BU

TTE

44.3

2.

16 15 CA

CTUS

SPRING

11.5

0.

18 14

SI

LENT

BU

TTE

10.0

0.

12 29

SILENT BU

TTE

11.5

0.19

9 SILENT BU

TTE

10.9

0.

17

8 SI

LENT

BU

TTE

9.5

0.27

12

SILENT BUTTE

10.8

0.

13 15 SILENT BU

TTE

33.9 0.

22

6 DE

AD HO

RSE

FLAT

10.2

0.

09 18

SILENT BU

TTE

10.3

0.

15 24

SILENT BUTTE

8.6

0.09 16 YUCCA

FLAT

9.4 0.

10 16 YUCCA

FLAT

9.1

0.07

10

YUCCA

FLAT

8.9

0.23

11 YUCCA

FLAT

13.6 0.

17 13 SC

RUGH

AM PE

AK9.5

0.24

11 SI

LENT

BUTTE

9.9

0.18

14 SI

LENT

BU

TTE

9.7

0.16

15 SI

LENT

BUTTE

10.1

0.

16 15 SI

LENT

BU

TTE

9.1

0.66

17 SC

RUGH

AM PE

AK

5.5

0.21 14 SC

RUGH

AM PE

AK8.

9 0.

37 15

SILENT BUTTE

10.6

0.

24 15

SI

LENT

BU

TTE

9.1

0.66

17

SC

RUGH

AM PE

AK5.

5 0.21 14 SCRUGHAM PE

AK8.

9 0.

37 15 SILENT BUTTE

29

11:14:48

37.2

72116.419

1.0

4.24

3.7

124

BCI

1.44

1.36

10.6

0.

24 15

SI

LENT

BU

TTE

19

90

LO

CA

L H

YP

OC

EN

TER

SU

MM

ARY

-

SGB

LOW

-FR

EQ

UE

NC

Y

PHEN

OM

ENA

DATE

- TI

ME(UTC)

AUG

5 11 12 14 28 29

SEP

5 7 7 12 16 19 29 30

OCT

3 11 12 12

10:50:42

4:12:17

9:26:

410:25:21

23:47:18

15:3

1:30

5:59:50

5:54

:20

7:14

:41

6:31

:21

8:28

:45

20:4

0: 6

1:56:5

611

:19:

39

16:34:46

13:5

6:20

16:43:53

18:57:23

LATI

TUDE

(DEC.

N)

37.2

6037

.265

37.379

37.2

6737

.321

37.276

37.3

0737

.274

37.266

37.3

0337

.306

37.315

37.0

6837

.293

37.5

4237

.100

37.2

1637

.251

LONGITUDE

(DEC

. W)

116.428

116.

411

116.360

116.420

116.

462

116.410

116.

381

116.

416

116.418

116.

393

116.

399

116.360

116.

898

116.

495

116.276

116.

509

116.326

116.

497

STAN

D ERROR

H(KM)

0.3

1.0

2.6

0.5

3.5

0.4

2.9

4.8

1.3

3.8

7.0

1.6

12.4

8.9

7.4

0.3

DEPTH

(KM)

-1.73

5.58

4.75

4.28

5.92*

-1.41

5.73

-0.6

6*-1.65

5.75

10.92

8.24

4.01*

11.8

6*

12.45

1.26

*10

.79*

4.04

STAND

ERRO

RZ(KM)

0.4

2.0

10.1 2.4

0.4

4.3

1.1

8.8

5.3

2.8

6.0

1.8

AZI

GAP

(DEC

)

81 84 166 56

210

133

248

187

206

241

241

255

345

134

248

134

146

147

QQD

12S

MAGNITUDE

ESTI

MATE

SMca

Md

MLh

MLv

AC I

BBI

CCI

BCI

GDI

ACI

1.38

GDI

GDI

1.51

BDI

GDI

1.35

DDI

2.23

BDI

DDI

DBI

1.99

DDI

2.13

DCI

1.09

DDI

ACI

2.04

1.96

11.74

11.

62

11.60

1

1.32

0

1.61

1 1 1 1 1 1 0

.10

.19

.23

.62

.94

.04

.01

.11

.03

.36

.51

.47

DEL-

RM

S |N

MIN

RES. PH

. U.

S.G.

S.ML

c (KM) (S

EC)

QUADRANGLE

10.5

0.11 21

SILENT BUTTE

9.6

0.23

17

SILENT BU

TTE

18.5

0.

29 12

SILENT CANYON NE

10.4 0.

15 19 SILENT BUTTE

16.1 0.

38

8 SILENT BU

TTE

1.4

10.30.05

7 SILENT BUTTE

11.5

0.

12

7 SILENT BUTTE

10.5 0.

27

6 SILENT BU

TTE

10.1

0.

07

7 SILENT BUTTE

11.6

0.21

7 SILENT BU

TTE

1.6

12.2 0.

37

8 SILENT BUTTE

1.5

11.7 0.

08

6 DE

AD HO

RSE

FLAT

40.4

2.

00

5 SPRINGDALE

1.5

12.9

1.51

8 SILENT BUTTE

36.7

0.

87 14 QUARTZITE MTN

13.0

1.67 14

TH

IRST

Y CANYON SE

0.2

7.18

5 AM

MONI

A TANKS

1.4

13.5

0.

14

6 SILENT BUTTE

Ln

DEC

23

20:1

4:1

5

37.2

47

11

6.4

97

0.8

5.2

42.9

17

0 B

CI

1.7

42.31

1.50

1.

4 14

.6 0.

15 14 SCRUGHAM PE

AK

1990 SGB LOW-FREQUENCY EVENTS WITHOUT HYPOCENTER DETERMINATIONS

MONTH DA HR:MN DA HR:MN DA HR:MN DA HR:MN DA HR:MN DA HR:MN DA HR:MN

MARCH

APRIL

MAY

JUNE

JULY

10 10

28

6

13 13 13

14 26 26

16:13 17:04

19:17

19:13

16:16 16:38 19:39

17:10 19:01 18:17

10 16:18 10 17:06

13 16:18 13 16:41 17 23:52

26 2:26 26 20:34 26 19:01

10 10

13 13 21

26 26 26

16:28 17:10

16:17 17:11 18:38

9:19 2:26

20:34

10 10

13 13 21

26 26

16:34 17:14

16:23 18:13 19:09

11:22 9:19

10 10

13 13 21

26 26

16:38 17:26

16:27 18:36 19:32

12:44 11:22

10 16:41

13 16:29 13 19:29 21 19:35

26 12:53 26 12:44

10 16:49

13 16:34 13 19:31

26 18:17 26 12:53

SEPTEMBER 15 5:43 20 0:09 26 0:04 28 11:00 29 0:08 29 0:10 29 6:23

OCTOBER

NOVEMBER

5 0:0812 18:2213 0:2313 3:4713 12:2614 3:0514 10:0114 13:2214 15:1214 18:2014 19:1014 21:4414 23:1114 23:2815 0:4715 1:4715 3:4515 4:5715 6:2815 8:4916 8:4217 23:2720 2:0821 10:2826 16:42

1 1:478 0:4613 14:1814 2:2414 20:1214 23:2017 5:5322 15:14

7121313131414141414141414141515151515151618202229

113131414141725

2:5519:061:115:0113:504:3110:0513:3215:3518:3519:1921:5423:1423:390:532:273:575:016:3019:0410:1312:4711:054:3111:13

15:355:50

23:212:5521:1023:265:589:07

71213131314141414141414141415151515151516182022

213131414142025

4:0420:001:265:2316:456:0710:0813:4015:5018:3719:4922:1123:1823:510:552:374:115:076:38

20:2113:0212:5311:1113:23

0:437:58

23:262:5721:1223:342:5811:28

101213131314141414141414141415151515151516182023

313131414142123

7:3120:181:576:2316:486:1310:1813:4516:3718:3920:0523:0023:2023:591:122:464:175:186:42

20:3414:4620:1918:320:05

14:549:00

23:474:25

22:1223:3516:336:29

121213131314141414141414141515151515151517182023

513141414162227

0:2021:171:597:29

23:517:4411:2414:0817:0018:4320:1923:0223:210:031:282:554:305:326:47

20:5610:4522:0022:4913:02

21:229:240:114:35

22:3016:182:2510:03

12 16:4312 23:0513 2:2013 8:5814 0:3414 8:1614 11:4514 14:2514 17:2014 18:5914 20:5814 23:0514 23:2415 0:3715 1:4015 3:1515 4:4115 5:4915 7:4415 21:2817 13:1418 23:5321 0:3425 0:02

7 15:1613 9:3714 0:3714 19:3414 23:1016 20:0922 8:5029 23:48

121213131414141414141414141515151515151617192126

813141414162230

18:0323:152:2410:432:599:0113:0814:4317:4619:0721:1823:0723:260:441:443:284:536:158:403:4919:5721:160:501:19

0:449:452:2319:4223:1420:1215:0815:20

30 15:40 30 16:00

DECEMBER 4 15:33 6 2:08 8 13:15 10 2:39 10 5:22 14 15:24 19 0:4819 15:25

76

Appendix D/

Earthquake focal mechanisms for 1990

The focal mechanisms of Appendix D were obtained by selecting the best-fitting solution(s) from the application of the computer program "FOCMEC" (Snoke and others, 1984) to the ray data generated by HYPO71, and in some instances, to amplitude data. We plot data on the lower focal hemisphere using the equal-area projection (Lee and Stewart, 1979). The symbols represent first-motion P polarities, and their positions represent the points where the HYPO71-determined raypaths intersect the focal hemisphere. The darkened circles represent impulsive compressional arrivals, the -f- symbols represent emergent compressionals, the open circles represent impulsive dilitationals, the symbols represent emergent dilatationals, and the x symbols represent indeter­ minate or nodal readings. The -f- symbol at the center of each mechanism is not a compression; it is a point of reference for readers who may wish to search for alternative solutions using a Schmidt (equal area) net. SGBSN station names are printed adjacent to the first-motion symbol for many of the solutions presented in Appendix D. In the following figures the P and T symbols represent the pressure and tension axes, respectively. The X and Y symbols represent slip vectors for each nodal plane, and B is the null axis. Primed P and T symbols are the respective vectors for alternate (dashed) solutions when they are presented. Some mechanisms from previous SGB data reports are composited using data from several events that are clustered in time and space. Composite solutions are not present in the 1990 data set.

~ For several mechanisms, the information contained in P-wave polarities was not adequate to effectively constrain the range of permissable nodal planes. In these instances, first motion P- and SV- amplitude data were gathered at selected stations, indicated by a large square around the polarity symbol. The observed and theoretical log10 (5V/P)a ratios and the difference between the logarithms of observed and theoretical ratios are computed for hundreds of potential solutions whose nodal planes conform to P-wave first-motion polarities. The theoretical values shown in each figure are for the "optimum" solution shown, having the lowest rms error and fewest polarity inconsistencies. If the difference between observed and theoretical values is greater than a specified limit, errmax , that station's amplitude data are not used in the solution and an asterisk is placed by its name in the solution table. We always set errmoa; < 0.3, corresponding to a maximum factor between theoretical and observed amplitude ratios of 2.0.

Kisslinger and others (1981 and 1982) and Rogers and others (1987) discuss several assump­ tions that must be satisfied for the (SV /P}z amplitude ratio method to be valid. Their comments and observations are included herein by reference. For completeness, the actual formula used to compute the theoretical (SV /P) amplitude ratio, as coded in /ocmec./or, is explicitly stated (from Kisslinger and others, 1981 and 1982). The formula for the ratio of SV to P wave displacement amplitude in the far field for elastic waves leaving a shear dislocation point source may be written

, (cot 8 tan 8} sin A tan 0 sin A + 2 sin A + esc 6 cos A tan 0 cos A.11 - ' ^ J

whereD = cos A cos A sin 0[ sin 0 sin A sec S -f- cos 0 esc 8]

-f- sin A sin 0 cos 0 sin A(cot5 tan 5) + sinA(cos2 0 sin 0sin A).

77

In this formula, Vp is the compressional wave velocity at the source, Va is the shear wave velocity, <f> is the takeoflF angle of the ray, measured upward from the z axis, which points downward, 8 is the angle between the fault plane normal and the z axis, A is the rake angle, measured in the fault plane, and A is the source-to-station azimuth. While this formula is used to constrain focal mechanism solution sets, we recognize that it is written for a point source in a homogeneous, isotropic medium. For example, it would not be appropriate for fault zones having strongly contrasting rock properties in the hanging wall and foot wall. If the reader is uncomfortable with the assumptions required by the (SV/P) Z method, he should give little weight to the focal mechanisms constrained by such data in his assessments of SGB seismicity.

78

CANE SPRINGDATE&TIME: 900126 10 34 15.61LAT: 36.811 LONG: 116,121DEPTH, km: 5.06 +/- 1.5 ML: 2.5DMIN (km)= 6.4

This Is the nolnshook oP a series oFearthquakes SE of Lookout Peak.NTS. an January 26 and 27. 1990.fl moderate constraint on the solutionset Is Imposed by the (SV/P)z amplituderatio at station VCT. wherethe observed log!0CSV/P)zequals 1.540. host nearby etatlonseismograns uere olipped Par this earthquake.

^P axis T axis B axis X axis Y axis

Soln 1 Var 2' Var 2"

azi 231.51 138.83 44.99

282.26 177.39 strike

267.39 265.72 266.70

plunge 39.82 3.21

50.00 24.40 29.50

dip 60.50 51.61 63.05

rake -28.34 -12.25 -13.71

Figure Dl. The focal mechanism solutions for this earthquake at Skull Mountain, Nevada Test Site, indicate predominantly right-lateral strike-slip motion on a north to north-northeast trending fault, or predominantly left-lateral strike-slip motion on an east-west trending, north-dipping fault. Some constraint on the range of solutions is imposed by the (SV/P)z amplitude ratio at station WCT. The small mechanism in the upper right of this figure (and all other figures of Appendix D) is a copy of the large mechanism's preferred solution, with compressional quadrants darkened, shown here to help the reader identify this mechanism when discussed in the main text of this report.

79

SCRUGHAM PEAKDATE&TIME: 900215 11 49 57.83LAT: 37.193 LONG: 116.379DEPTH, km: 5.80 +/- 0.4 ML: 2.3DlflN (km)= 5.4

This earthquake may be the nainshook of o short-lived series that occurred near Echo Peak. Nevada Test Site, on February 15. 1990. This hupooenter obtained from

a velocity node I in which vp/vs-l.Bl, following a Vodati diagram for the horizontal-oomp S-uave arrivals.

x"^P axisT axis8 axisX axisY axis

Soln 1Var 2*

azi232.39337.26100.00286.51193.83strike

283.83283.22

plunge29.5024.4050.0039.813.21dip

86.7984.28

rake-39.89-34.59

Figure D2. The focal mechanism solutions for this southern Silent Canyon caldera mainshock of February 15, 1990, indicate right-lateral strike slip motion on a north-northeast trending, east dipping fault, or oblique motion on a nearly vertically dipping, east-southeast trending fault.

80

^^P axis T axis B axis X axis Y axis

Soln 1

azi70.34

331.47 235.00 120.77

7.55 strike 97.55

plunge 48.98 7.64

39.99 26.07 38.87

dip 51.13

rake -34.36

SCRUGHAM PEAKDATE&TIME: 900227 8 16 59.24LAT: 37.197 LONG: 116.379DEPTH, km: 6.46 +/- 0.6 ML: 2.0DlflN (km)= 5.3

This earthquake nay be the2nd largest shook oF o short-livedseries That occurred nearEcho Peak. Nevada Test Site.on February 27. 1990.This hypooenter obtained From

a velocity node I In which vp/vs-1.81.

Figure D3. The focal mechanism solution for this southern Silent Canyon caldera earthquake of February 27, 1990, indicates oblique normal-slip strike-slip motion on nodal planes trending northeast-southwest and east-west, respectively.

81

BONNIE CLAIRE SEDATE&TIME: 900421 17 55 52.77LAT: 37.124 LONG: 117.062DEPTH, km: 6.64 +/- 1.9 ML: 2.0DMIN (km)= 16.0

Loql0CS/P)z Rmplltudes for Rbove SolutionsDashed CExtensional) Solid (ConprJ

STfl Observed Theoretical Difference Theor. DiFP. VCT 0.1127 0.0295 0.1132 0.1299 0.0128 MZP 0.5206 0.5935 -0.0729 0.5168 0.0038 RMS overage error ExtensIonal 0.10 Compress. 0.01

*^P axisT axisB axisX axisY axis

Soln 1Var 2'

azi219.65310.28124.92263.19356.70strike86.70

264.50

plunge1.72

19.9469.9815.2112.70

dip77.3087.90

rake15.60

-24.70

Figure D4. The focal mechanism solutions for this earthquake in northwest Sarcobatus Flat (Bonnie Claire SE quadrangle), Nevada indicate predominantly right-lateral strike slip on a north trending fault or left-lateral strike slip on an east trending fault. Solutions are constrained by two (SV/P)Z amplitude ratios, but include members having a small component of reverse slip and others having a small component of normal slip.

82

BONNffi CLAIRE SEDATE&TIME: 900513 0 48 11.70LAT: 37.117 LONG: 117.035DEPTH, km: 6.20 +/- 1.0 ML: 1.9

This Sonoobotus Flat earthquake Is the First and largest of several that ooourrod In May. 1990 at this looatfon. First notion constraint Is not great, but provides only extentionaI to strike-slip possibilities.

^P axis T axis B axis X axis Y axis

Soln 1 Var 2' Var 2"

azi 187.06 306.85 49.93

266.10 150.30 strike

240.30 234.30 251.60

plunge 51.75 21.39 30.02 54.41 17.30

dip 72.70 31.60 50.10

rake -58.40 -36.30 -22.90

Figure D5. The focal mechanism for this Sarcobatus Flat earthquake is not well constrained, but solutions are all predominantly strike slip to predominantly normal slip, with T axes oriented west-northwest to east-southeast.

83

SPRINGDALEDATE&TIME: 900604 8 47 13.69 LAT: 37.096 LONG: 116.876 DEPTH, km: 0.97 +/- 0.5 ML:DMIN (km): 14.5

1.5

*^P axis T axis B axis X axis Y axis

Soln 1 Var 2' Var 2"

azi 53.91

145.60 287.97 99.50

190.00 strike

280.00 285.00 290.20

plunge 8.41

11.28 75.86 13.99 2.00 dip

88.00 85.00 80.30

rake 14.00 -0.44 2.60

The 8:17 UTC event Is one oP the largeroF several shallow earthquakes at SoroobatusFlats, early June. 1990.The compressIonaI (O inconsistencyat station TMO Is noisy.

Figure D6. The focal mechanism solutions for this Sarcobatus Flat earthquake are all predomi­ nantly strike-slip on steeply dipping nodal planes. Sense of slip is right lateral on the approximately north-south trending nodal planes, and is left lateral on the approximately east-west trending nodal planes.

84

^^P axis T axis B axis X axis Y axis

Soln 1

azi 242.72 345.52 89.95

303.36 19B.20 strike

28B.20

plunge 41.65 14.00 45.00 39.86 17.39

dip 72.61

rake -42.19

BLACK MTN SWDATE&TIME: 900624 23 55 38.93LAT: 37.291 LONG: 116.738DEPTH, km: 4.79 +/- 1.3 ML: 1.9DMIN (km)= 8.6

Polarity Inconsistencies at LOP [Lookout Peak) and DCS (Queen City Sunn It) are for stations at epI centra I distances .gt. 70 kn.

Figure D7. The focal mechanism for this northern Oasis Valley earthquake, whose epicenter lies just west of the Black Mountain Caldera, indicates oblique strike-slip normal-slip motion. The strike slip component of motion is right lateral on the northeast-southwest trending nodal plane, and is left lateral on the west-northwest trending nodal plane.

85

JACKASS FLATSDATE&TIME: 900722 8 17 14.02 LAT: 36.863 LONG: 116.318 DEPTH, km: 2.62 +/- 0.4 ML: DlflN (km)= 0.2

These so IutTons ore fairlywell constrained using P arrivaldata only, for this earthquakealnoat direct Iy under the Calloo Hi I Isseismometer (CDHD .

1.1

azi plungeP axis 251.87 21.62T axis 147.85 31.43B axis 10.41 50.32X axis 107.95 6.21Y axis 203.00 39.00

strikeSoln 1 293.00 Var 2' 290.00 Var 2" 291.00

dip rake51.00 8.0041.00 12.0060.00 2.90

Figure D8. The focal mechanism solutions for this Jackass Flats earthquake indicate predominantly strike-slip motion, oblique right lateral on the north-northeast trending nodal planes, or left-lateral on the north-dipping, west-northwest trending nodal planes.

86

STOVEPIPE WELLS DATE&TIME: 900725 LAT: 36.556 LONG:

0 52 50.39117.044

DEPTH, km: DMIN (km)=

8.0518.8

+/- 0.7 ML: 2.2

x^

P axis T axis B axis X axis Y axis

Soln 1

azi 229.56 94.89

320.00 54.18

224.07 strike

314.07

plunge 4.98

82.93 5.00

39.82 49.74

dip 40.26

rake 82.25

The earthquake epicenter Is at the eastern edge oF Tuck I Mountain. California. The earthquake IB at the southeast end of a series that occurred over a several year period, uhose epicenters define a northwest-southeast I I near trend para I IeI to the Furnaoe Creek Fault.

Figure D9. The focal mechanism solutions for this Sarcobatus Flat earthquake indicate right lateral strike slip on north trending, steeply dipping nodal planes or left lateral strike slip on west trending, steeply dipping nodal planes. Some constraint on the range of solutions is provided by (SV/P)Z ratios at stations SGV and GMN.

87

SPRINGDALEDATE&TIME: 900802 5 15 2.68LAT: 37.147 LONG: 116.982DEPTH, km: 5.00 +/- 3.2 ML: 1.1DMIN (km)= 18.9

Two station ratios showing distinctly larger P amplitude than S amplitude uere used to constrain the set oP acceptable nodal planes for this Saroobatus Flat earthquake.

x^P axisT axisB axisX axisY axis

Soln 1Var 2'

azi40.07

309.93149.97264.91355.08strike85.0884.01

plunge1.714.70

85.002.114.53dip

85.4779.45

rake2.12

-10.73

Figure DIO. The focal mechanism for this earthquake at the western edge of Death Valley indicates almost pure reverse slip motion on the two northwest trending nodal planes. Reverse faulting is almost never observed by the SGBSN for SGB earthquakes.

88

azi plungeP axisT axisB axisX axisY axis

Soln 1Var 2'

29.64120.40239.9475.24

344.80strike74.8074.90

8.694.99

79.969.692.60dip

87.4088.30

rake-9.70-9.85

SPRINGDALEDATE&TIME: 900803 20 23 55.89LAT: 37.087 LONG: 116.754DEPTH, km: -1.03 +/- 0.4 ML: 2.3DMIN (km)= 7.1

These two solutions ore found by foomeo. using siip vector increments of 5 degrees In azimuth and plunge. One polarity error at etatlon HCY (distance 85-km] Is present.

Figure Dll. The focal mechanism solutions for this Sarcobatus Flat earthquake are predominantly strike slip, right lateral on the north-northwest trending nodal plane, or left lateral on the west- southwest trending nodal plane. The depth-of-focus estimate is at the earth's surface, which is an unlikely depth for earthquakes. A deeper-focus hypocenter would yield a wider range of acceptable focal mechanism solutions from the same first-motion polarities when compared to the two solutions shown in this figure.

89

STONEWALL PASS DATE&TIME: 900821 22 0 24.17 LAT: 37.439 LONG: 117.229 DEPTH, km: 2.38 +/- 1.1 ML: DlflN (km)= 15.6

1.9

Piercing points for this solution at 96and 71 degrees due to shallow-Focus hypooenter.The constraint on these fooal mechanismsolutions is provided, in part, by GVN's* and HCR & THO's - P waves, all very emergent.

aziP axis 42.16 T axis 288.42 B axis 194.97 X axis 91.48 Y axis 311.00

strikeSoln 1 41.00 Var 2' 31.70 Var 2" 41.50

plunge 67.73 9.36

20.02 32.64 50.30

dip 39.70 41.00 58.70

rake-57.60-74.70-60.40

Figure D12. The focal mechanism solutions for this earthquake at Stonewall Flat, Nevada, indicate predominantly normal slip on north trending and northeast trending nodal planes. The velocity model used for preliminary hypocenter and focal mechanism determination has an interface at 12 km below sea level, below which Vp = 6.5 km/sec, to a depth of 24 km.

90

SPRINGDALEDATE&TIME: 900905 4 58 34.41 LAT: 37.092 LONG: 116.876 DEPTH, km: 5.00 +/- 1.2 ML: DMIN (km)= 14.7

2.0

^^P axis T axis 6 axis X axis Y axis

Soln 1

azi 46.60

151.75 259.99 107.24

4.43 strike 94.43

plunge 39.86 17.38 45.00 41.64 14.00

dip 76.00

rake -43.22

The obove hypooenter hoa depth Fixed at Five km be I ou sea I eve I. R sma I I i improvement in RMS travel time residual occurs For a Free-depth solution at about one km below sea level (0.12 see vs 0.14 seo). but the Initial P-uave arrivals at most SGB stations appear to be direct rather than refracted, suggest I no that the true depth oF Foous IB greater tKan one km.

Logl0(SV/P)z For 5 km hypooenter: Observed Theoretical DlFFerenoe Station 0.4599 0.6136 -0.1537 GVN 0.6881 0.7213 -0.0329 FMT

Figure D13. The focal mechanism for this Sarcobatus Flat earthquake indicates predominantly right lateral strike slip on a north-south trending, west dipping nodal plane, or oblique normal slip strike slip on an east-west trending, steeply dipping nodal plane. (SV/P)Z amplitude ratios were collected at stations GVN and FMT to constrain the range of acceptable focal mechanism solutions.

91

o o

X

- . _ ;

O

0 _o

V

01 ©H--^===--t\ - r

i yf jFPL x^ \\f +^\^\\\\\\v\

y\ \ ^~~*\ P axis

' T a-y\a

SPRINGDALE i " DATE&TIME: 900906 10 32 18.73 Z IT?, LAT: 37.094 LONG: 116.877 £ «Y£ DEPTH, km: 0.77 +/- 0.5 ML: 2.2DMIN (km)= 14.7 0 , ,

^ ' Soln 1Var 2*

T' K'

azi43.33

136.30 254.80 90.72

359.00 strike 89.0085.00

This Sarcobatus Flat earthquake VQT 2" 270.00

___-.. """*'«y^- i -

/plunge16.929.65

70.38 18.92 5.00 dip

85.0089.0087.00

rake -19.00-15.0015.00

has predominantly strike-alipFooal mechanism BOIutIons, somewith a snolI normal slip component.some with a smalI reverse siIp component.

Figure D14. The focal mechanism solutions for this shallow Sarcobatus Flat earthquake all indicate right-lateral strike slip on north trending nodal planes, or left-lateral strike slip on west trending nodal planes.

92

SPRINGDALEDATE&TIME: 901029 2 37 27.24LAT: 37.188 LONG: 116.959DEPTH, km: 4.96 +/- 1.0 ML: 2.6DMIN (km)= 21.3

This is the largest SGB earthquake Tor Ootober 1990. fill solutions ore predominantly strike slip, some having a nodest oonponent of thrust or normal siIp.

Figure D15. The focal mechanism solutions for this 5 km below sea level Sarcobatus Flat earthquake all indicate right-lateral strike slip on approximately north trending nodal planes, or left-lateral strike slip on west trending nodal planes.

*^P axisT axisB axisX axisY axis

Soln 1Var 2'Var 2"

azi220.95129.00359.83265.14174.80strike

264.80260.99263.26

plunge11.419.60

75.001.26

14.94dip

75.0679.4581.70

rake-1.3010.72

-23.70

93

^P axis T axis B axis X axis Y axis

Soln 1 Var 2* Var 2"

azi 243.31 344.70 93.94

299.97 200.00 strike

290.00 289.00 120.00

plunge 35.68 15.37 50.16 36.86 13.00

dip 77.00 87.00 90.00

rake -38.00 -35.00 35.00

MELLANDATE&TIME: 901101 7 51 46.78LAT: 37.531 LONG: 116.521DEPTH, km: 5.98 +/- 1.4 ML: 2.4DMIN (km)= 22.8

This Gold Flat earthquake Is the nalnshoak oF a three-event series that ooourred In on otherwise seisnloallu quiet area during 1990. The epicenters lie In a featureless part of Gold Flat, about 16 km west oP the Kami oh Range. The RMS travel-tine reel duo I graph for This earthquake Is essentially Plat For Plxed-depth hypooenters ranging Pron eurPaoe Poous to six km be Iou sea leva I.

Figure D16. The focal mechanism solutions for this Gold Flat, Nevada, earthquake indicate oblique normal (or reverse) slip - strike slip on the west-northwest trending, almost vertical-dipping nodal planes, or right lateral strike slip on the east-northeast trending, southeast dipping nodal planes. The depth of focus is poorly resolved for this earthquake, with a virtually flat minimum in the RMS travel time residual function from surface focus to 6 km below sea level.

94

azi plunge

GOLD POINTDATE&TIME: 901213 1 1 0.36LAT: 37.368 LONG: 117.357DEPTH, km: 2.72 +/- 0.6 ML: 2.8DMIN (km)= 11.6

Rep I eked several P-cnsets.QCS polarity Is questionable. SH 2/28/91

P axis 15.95 T axis 284.00 B axis 154.84 X axis 60.13 Y axis 329.80

strikeSoln 1 59.80 Var 2' 59.08 Var 2" 60.60

11.38 9.57

75.04 1.26

14.90dip

75.1070.7170.30

rake-1.30-5.38 3.60

Figure D17. The focal mechanism solutions for this earthquake about 8 km north of Slate Ridge, Nevada indicate predominantly strike slip deformation on all nodal planes, with right lateral motion on the north-northwest trending, near vertical dipping planes, or left lateral motion on the west- southwest, steeply southeast-dipping planes.

95

Appendix E

Station codes, locations, and instrumentation

Appendix E contains a list of SGBSN station names, coordinates, and other descriptive infor­ mation. Instrument codes refer to the seismometer, amplifier/VCO, and discriminator packages for each station. For the current network, codes 1 through 7 are valid. Any other codes are for systems having unknown frequency response, which are no longer operating in the SGBSN. The following table shows the major components comprising the seven current seismographic systems.

Table El. Major components in seismographic systems comprising the SGBSN during 1990. All seismometers have natural frequency, / = 1.0 Hz. The (analog) output of the discriminators is digitized on a PDF 11/34 computer, with sampling rate = 104.167 sps/channel.

KIND1 2 3 4 5 6

- 7

SEISMOMETERMark L4C

Teledyne S13 Teledyne S13

Mark L4C Mark L4C

Teledyne S13 Ranger RR-1

Motionvertical vertical

vert., horiz. vertical

horizontal vertical vertical

Amplifier/VCOTricom 649 Tricom 649 Teledyne Geotech 42.50 Teledyne Geotech 42.50 Teledyne Geotech 42.50 Teledyne Geotech 42.50 Teledyne Geotech 42.50

DiscriminatorTricom 642 Tricom 642

Teledyne 4612 Tricom 642

Teledyne 4612 Tricom 642

Teledyne 4612

Magnification curves for representative seismograph systems in the SGBSN may be found in Rogers and others (1987) and in Harmsen and Bufe (1991).

96

STAT

ION

INFO

RMAT

ION

- SOUTHERN G

REAT BASIN

SEIS

MOGR

APHI

C NE

TWOR

K

CODE

AMR

APK

APK

APKW

AP

KW

BGB

BLT

BMT

BMTN

BRO

CDH1

CDH1

CDH5

CPX

CPX

CP2

CPY

CTS

DIM

EMN

EPN

EPN

EPM

EPNH

HE

PN

HEPM

EPR

FMT

STAT

ION

Amar

gosa

, Ca

t.

Angels P

eak,

Ne

v.

Angels P

eak,

Ne

v.

Big

Butte, Nev.

Belted R

ange,

Nev.

Black

Moun

tain

, Ne

v.

Black

Moun

tain

, Nev.

Bare

Mou

ntai

n, Nev.

Calico H

ills,

Nev.

Calico H

ills,

Nev.

CP-1,

Nev.

CP-1.

Nev.

CP-1,

Nev.

Cactus P

eak,

Ne

v.

Delamar

Mountains, Nev.

Eldorado M

tns.

, Nev.

Echo

Peak, Ne

v.

Echo

Peak, Ne

v.

East

Pa

hranagat Rn

g, Nv

Fune

ral

Mountains, Ca

l.

PERI

OD OF

OPERATION

(YR/

MO/D

A-YR

/MO/

DA)

78/0

7/24

-pre

sent

75/0

6/15

-81/

03/2

1 81

/03/

21-8

3/08

/04

83/0

8/05

-88/08/10

88/0

8/11

-pre

sent

79/01/23-pre

sent

79/0

5/30

-pre

sent

80/02/26-83/

04/0

1

83/0

4/01

-pre

sent

78/1

1/28

-81/04/08

80/02/06-81/11/18

81/1

1/18

-pre

sent

80/02/06-81/11/18

77/ / 80/03/01 *

80/0

8/05

-90/

08/2

9

90/0

8/29

-91/

01/1

5 91/01/15-pre

sent

79/0

4/24

-pre

sent

78/06/08-pre

sent

88/08/11-pre

sent

75/09/02-80/04/25

80/0

4/25

-90/

09/2

6 90/09/26-p

rese

nt

84/0

6/06

-86/

01/2

8 86

/01/

29-9

0/09

/26

90/0

9/26

-present

79/0

1/23

-present

78/1

1/28

-present

LATITUDE

(DEC

MINUTES)

36 23

36 19

36 19

37 02

37 28

37 17

37 17

36 45

36 5

1

36 5

1

36 55

36 55

36 5

5

37 3

9

37 3

6

35 5

5

37 12

37 13

37 12

37 13

37 10

36 3

8

.85

.17

.19

.24

.98

.02

.50

.76

.82

.82

.94

.73

.73

.37

.35

.31

.84

.57

.84

.57

.12

.27

N N N N N N N N N N N N N N N N N N N N N N

LONG

ITUD

E (DEC M

INUT

ES)

116

115

115

116

116

116

116

116

116

116

116

116

116

116

114

114

116

116

116

116

115

116

28 34 35 13 07 38 38 37 18 18 03 03

03 43 44 45 19

20 19

20 11 47

.56

.46

.25

.75

.41

.74

.41

.52

.97

.97

.26

.53

.53

.59

.27

.33

.43

.08

.43

.08

.23

.00

W W W W W W W W W W W W W W W W W W W W W W

ELEVATION

(METER

S)

690

2680

2600

1730

1854

2191

2040 920

1353

1055

1258

1368

1368

1868

1730 846

2260

2408

2260

2408

1305

1025

SEIS

MOME

TER

MODE

L/CO

MP.

L-4C

S-13

L-

4C

L-4C

L-4C

L-4C

L-4C

L-4C

L-4C

L-4C

L-1-3DS

(vert.)

L-4C

L-1-3DS

horzntl

NGC-

21

L-4C

L-4C

L-4C

L-4C

L-4C

Ranger SS

-1

S-13

L-4C

L-4C

L-4C ho

rizo

ntal

L-

4C ho

rizo

ntal

L-4C ho

rizo

ntal

L-4C

L-4C

GAIN

(DB) 84 84

84 84

84 84 84 84 84 84 90

84 108 ? 84 84 84 84 84 84 84

84

84 78

60

60 84 84

INST

CODE 1 2 1 1 4 1 1 1 1 1 1 1 1 8 1 1 4 1 1 7 2 4 4 5 5 5 1 1

. S L * * * * * * * * * * * * * * * * * * * * * * *

oo

6LR

GMN

GMNH

GMR

GMRH

GVN

GWV

GWY

HCR

JON

JONH

KRN

KRNA

LCH

LOP

LSM

LSM

LSMN

LS

MN

LSMN

LS

MN

LSME

LS

ME

LSME

LSME

MCA

MCY

MTI

MZP

NMN

Groom

Lake

Ro

ad,

Nev.

Gold

Mo

unta

in,

Nev.

Gold

Mountain.

Nev.

Groom

Range, Nev.

Groo

m Ra

nge,

Nev.

Grap

evin

e, Cal.

Gree

nwater Va

lley

, Ca

l.

Greenwater Va

lley

, Ca

l.

Hot

Creek

Rang

e, Nev.

Johnnie,

Nev.

Johnnie, Nev.

Kawi

ch Range, Nev.

Kawi

ch Range, Ne

v.

Last Ch

ange

Ra

nge,

Ca

l.

Look

out

Peak

, Nev.

Little Sk

ull

Mt., Ne

v.

Little Sk

ull

Mt.,

Nev.

Litt

le Sk

ull

Mt..

Nev.

Marb

le Canyon,

Cal.

Merc

ury,

Nev.

Magruder Mountain,

Nev,

Moun

t Irish, Nev.

Montezuma

Peak

, Nev.

Nasa

Mountain,

Nev.

75/1

1/20

-pre

sent

79/07/13-present

84/0

7/30

-pre

sent

79/0

1/23

-pre

sent

84/0

9/09

-p res

ent

78/11/28-present

78/07/24-88/02/16

88/0

4/01

-pre

sent

81/07/21-present

78/07/24-present

84/06/22-present

79/0

5/30-80/04/22

80/0

4/23

-p res

ent

79/07/13-present

79/01/23-present

79/1

2/13

-84/07/20

84/07/20-present

84/0

7/17

-85/

07/0

2 85

/07/

02-8

6/01

-28

86/0

1/28-86/06/24

86/0

6/24

-pre

sent

84/0

7/17

-85/

07/0

2 85

/07/

02-8

6/01

-28

86/0

1/28-86/06/24

86/0

6/24

-pre

sent

79/01/23-present

80/0

3/07

-pre

sent

79/07/13-present

79/0

6/08

-pre

sent

79/0

7/13

-pre

sent

78/1

1/28

-83/

11/0

1

37 37 37 37 37 36 36 36 38 36 36 37 37 37 36 36 36 36 36 36 37 37 37 37

11.94

18.04

18.0

4

20.02

20.0

2

59.9

4

11.1

1

11.15

14.0

1

26.3

9

26.39

42.3

7

44.5

3

13.95

51.27

44.55

44.5

5

44.55

38.77

39.6

4

26.4

4

40.68

42.03

04.8

5

N N N N N N N N N N N N N N N N N N N N N N N N

116

117

M7

115

115

117

116

116

116

116

116

116

116

117

116

116

116

116

117

115

117

115

117

116

01.0

1

15.44

15.4

4

46.3

6

46.3

6

20.7

8

40.22

40.2

1

26.20

06.2

8

06.2

8

20.0

7

22.89

38.7

8

10.11

16.33

16.33

16.3

3

16.69

57.6

7

29.9

3

16.72

23.1

0

49.0

9

W W W W W W W W W W W W W W W W W W W W W W W W

1432

2192

2192

1528

1528 812

1530

1540

2040 910

910

2570

1963

1404

1648

1113

1113

1113 270

1303

2075

1540

2353

1500

L-4C

L-4C

L-4C

L-4C

L-4C

L-4C

L-4C

L-4C

L-4C

L-4C

L-4C

L-4C

L-4C

L-4C

L-4C

L-4C

S-13

L-4C

L-4C

L-4C

S-13

L-4C

L-4C

L-4C

S-13

L-4C

S-13

L-4C

L-4C

L-4C

L-4C

hori

zont

al

hori

zont

al

hori

zont

al

hori

zont

al

hori

zont

al

hori

zont

al

hori

zont

al

horizontal

hori

zont

al

hori

zont

al

hori

zont

al

84 84 78 84 78 84 84 84 84 84 78 84 84 84 84 84

84 78

72

60

38 78

72

60

38 84 84 84 84 84 84

1 4 5 4 5 1 1 1 1 4 5 1 1 1 1 4 6 5 5 5 3 5 5 5 3 1 2 1 1 1 1

* * * * * * * * * * * * * * * * * * *

NOP

MOP

NPN

PAN

PANH

PGE

PGEH

PPK

PRN

PRN

PRNH

QCS

QSM

SDH

SGV

SGV

SGV

SHRG

SPRG

SRG

SSP

SSP

SVP

TCN

TMBR

TMBR

TMO

TPU

WCT

WCT

WCT

WRN

Nopa

h Rang

e, Ca

l.

North

Pah roc

Rg,

Nev.

Panamint Range, Ca

l.

Panamlnt Range, Cal.

Panamint Range, Ca

l.

Panamlnt Range, Cal.

Pipe

r Mountain,

Cal.

Pahroc R

ange

, Nev.

Pahroc Range, Nev.

Queen

City Su

mmit

, Nev.

Queen

of Sh

eba

Mine.

Ca

Stri

ped

Hill

s, Nev.

Sout

h Grapevine

Mts, Ca

Sheep

Range, Ne

v.

Spotted

Range, Nev.

Seaman R

ange,

Nev.

Shos

hone

Pea

k, Nev.

Stiver P

eak

Rang

e, Ne

v.

Thir

sty

Canyon,

Nev.

Timb

er M

t..

Nev.

Tin

Moun

tain

, Ca

l.

Temp

iute

Mou

ntai

n, Ne

v.

Wildcat

Mountain,

Nev.

78/07/24-80/04/25

80/04/25-p res

ent

79/06/08-present

88/0

4/01

-pre

sent

88/0

4/01

-pre

sent

78/1

1/28

-88/

02/1

3

84/1

0/11

-88/

02/1

3

79/0

7/13

-pre

sent

72/0

1/21

-80/06/19

80/06/19-present

84/0

8/28

-pre

sent

79/0

6/08

-prese

nt

78/1

1/28

-pre

sent

78/0

7/24

-pre

sent

78/1

1/28

-81/06/15

81/06/15-82/06/16

82/06/15-present

79/0

5/22

-pre

sent

79/05/28-present

79/0

6/08

-pre

sent

73/1

0/10

-80/05/25

80/0

5/27

-pre

sent

79/0

7/13

-pre

sent

84/11/02-present

82/0

2/19

-87/05/05

87/0

5/05

-pre

sent

78/11/28-present

79/06/08-present

81/04/08-88/01/05

88/0

1/05

-88/

03/1

1 88/03/11-present

Wort

hing

ton

Mts.

. Nev.

79/0

6/08

-pre

sent

36 07

.63

N

37 39.12

N

36 23

.59

N

36 23.59

N

36 20.93

N

36 20.93

N

37 25.51

N

37 24.40

N

37 24.40

N

37 45

.39

N

35 57.85

N

36 38.72

N

36 58.92

N

36 30.33

N

36 41

.64

N

37 52.93

N

36 55.53

N

37 42.89

N

37 08.80

N

37 02.11

N

36 48.29

N

37 36.27

N

36 47.79

N

37 58

.89

N

116

09.26 W

114

56.2

1 W

117

06.05 W

117

06.05 W

117

03.95 W

117

03.95 W

117

54.4

2 W

115

03.0

5 W

115

03.05 W

115

56.5

8 W

116 52

.05 W

116

20.38 W

117

02.1

1 W

115

09.6

1 W

115

48.63 W

115

04.15 W

116

13.26 W

117

48.2

0 W

116 43.52 W

116

23.2

1 W

117

24.30 W

115

39.06 W

116 37.62 W

115 35

.58 W

911

1660

1690

1690

1850

1850

1851

1402

1402

1914 450

1050

1550

1590

1191

1640

2021

2595

1469

1754

2113

1910

930

1725

L-4C

S-

13

L-4C

L-4C

L-4C

ho

rizo

ntal

L-4C

L-4C

ho

rizo

ntal

L-4C

NGC-

21

S-13

L-4C

ho

rizo

ntal

L-4C

L-4C

L-4C

L-4C

S-

13

L-4C

L-4C

L-4C

L-4C

NGC-

21

L-4C

L-4C

L-4C

L-4C

S-13

L-4C

L-4C

L-4C

L-

4C

L-4C

L-4C

84

84 84 84 78 84 78 84 ? 84 78 84 84 84 84

84

84 84 84 84 ? 84 84 84 84

84 84 84 84

66

84 84

1 2 1 4 5 4 5 1 8 6 5 1 1 1 1 2 1 1 1 1 8 1 1 1 1 6 1 1 1 1 1 1

* * * * * * * * * * * * * * * * * * * * * * * * * * * * *

YMT1

YMT2

YMT3

YMT4

YMT4

YMT4

YM4N

YM4S

NYM4

YM4E

YM4W

EYM4

YMT5

YMT5

YMT5

YMT6

YM

T6

YMT6

Yucca

Mountain,

Nov.

Yucca

Mountain,

Nev.

Yucca

Mountain,

Nev.

Yucca

Moun

tain

, Nev.

Yucc

a Mountain,

Nev.

Yucc

a Mountain,

Nev.

Yucc

a Mountain,

Nev.

Yucc

a Mountain,

Nev.

81/03/05-p res

ent

81/03/05-present

81/03/05-present

81/0

4/01

-81/

10/1

3 81/10/13-83/07/01

83/07/02-present

84/06/29-85/05/23

85/0

5/24

-86/

01/2

8 86/01/28-present

84/06/29-85/05/23

85/0

5/24

-86/

01/2

8 86/01/28-present

81/04/01-81/10/13

81/1

0/13

-83/

07/0

2(7)

83/07/02-p res

ent

81/04/01-81/10/13

81/1

0/13

-83/

07/0

2(7)

83/0

7/02

-prese

nt

36 5

1.22 N

36 47.14 N

36 47

.21

N

36 5

0.99

N

36 5

0.99

N

36 5

0.99 N

36 53

.91

N

36 51.36

N

116 31.86 W

116 29.22 W

116

24.75 W

116

27.18 w1

116

27.18 W

116

27.18 W

116

27.2

5 W

116

24.02 W

1006

1006

1060

1248

1248

1248

1355

1090

S-13

S-13

S-13

S-13

S-13

S-13

L-4C

ho

rizo

ntal

L-4C

ho

rizo

ntal

L-4C

ho

rizo

ntal

L-4C

ho

rizo

ntal

L-4C

ho

rizo

ntal

L-4C

ho

rizo

ntal

S-13

S-13

S-13

S-13

S-13

S-13

84 84 84 84 72 84 78 72 60 78 72 60 84 72 84 78 66 84

3 *

3 *

3 *

3 *

3 *

3 *

5 *

5 *

5 *

5 *

5 *

5 *

3 *

3 *

3 *

3 *

3 *

3 *

o o

NOTES: All

instru

ment

s are

verticaI compone

nt unless otherwise

noted.

If one

horizontal

-component in

stru

ment

ex

ists at

a

site

, it

has

north-south

polarity;

If tw

o ho

rizo

ntal

s exist

at a

site

, they have north-south

and

east-west

pola

riti

es,

resp

. The

polarity is su

gges

ted

by the

station

name

. A

* in th

e final

column indicates

satellite-determined station

coordinates,

Elev

atio

ns of

st

atio

ns w

ith

*s in

the

fina

l column were obtained using

altimeters calibrated against

neares

t US

GS benchmark. Locations

are

preliminar

y.

Appendix F

Input parameters to HYPO71

HYPO71.FOR, version 1.001, was baselined for use by the Yucca Mountain Project, with CID YMP-USGS/GDD0001.02, on October 22, 1990. This version of HYPO71 requires a minimum of three input files, (1), a header file, containing crustal velocity information, weighting scheme information, iteration-controlling parameters, and I/O-controlling parameters, (2), a station file, containing most of the information shown in Appendix E, above, and (3), a phase file, containing P and S phase arrival times and information for determining earthquake magnitude. The data of item (1) are presented in Appendix E, and will not be repeated here. The data of item (3) are too bulky for inclusion in this report, but are available on request.

Two header files are used, depending on the source zone. For most earthquakes occurring in the SGB, the file nvhead.dat, having the velocity model shown in Figure Fl (a) is input. For earthquakes occurring in the immediate vicinity of Yucca Mountain, the file nvhead.ymt, having the velocity model shown in Figure Fl (b), is input. Copies of these two files are shown below. For meanings of the "Control Card" parameters, the reader should consult Lee and Lahr (1975).

101

The below lines are a listing of nvhead.dat, used as an input file to HYP071.

HEADRESET TEST 1)- RESET TEST 2)- RESET TEST 3 RESET TEST 4 RESET TEST 5 RESET TEST 6 RESET TEST 7 RESET TEST 8 RESET TEST 9 RESET TEST 10 RESET TEST 11 RESET TEST 12 RESET TEST(13 RESET TEST(14 RESET TESTM5 RESET TEST(16,- RESET TEST(17)-

.38000000E+01

.59000000E+01

.61500000E+01

.65000000E+01

.69000000E+01

.78000000E+01

.00000000E+00 7. 10. 220.

0.550020.00000.50000.05005.00001.0000

-1.276001.66600

0.00227 100.0000 12.00000.50001.0000

-2.05000.00000.852-1.766.00000000E+00 .10000000E+01 .30000000E+01 .15000000E+02 .24000000E+02 .32000000E+02 .00000000E+00

1.71 3 0

(max | of iterations/solution

1 1111 0 0.00 0 0.00

The-below lines are a listing of nvhead.ymt, used as an Input file to HYP071.

HEAD ~ - RESET TEST RESET TEST RESET TEST RESET TEST RESET TESTRESET TEST( 6RESET TEST 7RESET TEST 8RESET TEST 9RESET TEST 10RESET TEST 11RESET TEST 12RESET TEST 13RESET TEST 14RESET TEST 15RESET TEST 16RESET TEST 17

.32000000E+01

.46000000E+C1

.57000000E+31

.62000000E+01

.65000000E+01

.78000000E+01

.00000000E+007. 5. 90.

0.100030.00000.50000.05005.00001.0000

-1.276001.66600

0.00227 100.00008.00000.50001.0000

-1.20000.00000.852-1.766.00000000E+00 .05000000E+01 .25000000E+01 .40000000E+01 .15000000E+02 .32000000E+02 .00000000E+00

1.71 3 0 1 1111 0 0.00 0 0.00

In this file, a slightly different weighting scheme with respect to distance is invoked than in nvhead.dat. above. In the former file, weights taper from 1. to 0. in a linear manner for epicentral distances between 10 and 220 km. In the latter file, weights taper from 1. to 0. for distances between 5 and 90 km.

102

(a) 0 1 234567(b)01 234567

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20

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VEL0CITY (KM/SEC) VEL0CITY (KM/SEC)

Figure Fl. (a) Primary (P) and secondary (S) wave velocities as a function of depth (0.0 = sea level) for the standard model used to locate southern Great Basin earthquakes. The interface at 15 km is optional, (b) P and S wave velocities as a function of depth for the Yucca Mountain region, being an idealization of the model proposed by Hoffman and Mooney (1984).

103