Upload
jackie
View
105
Download
1
Tags:
Embed Size (px)
DESCRIPTION
Hebrew University of Jerusalem. Paleoseismology. Elisa Kagan Hebrew University of Jerusalem & the Geological Survey of Israel July 23, 2008 (PhD advisors: Amotz Agnon, Moti Stein, Mira Bar-Matthews). Paleoseismology is the study of the timing, location, and size of ancient earthquakes. - PowerPoint PPT Presentation
Citation preview
Elisa KaganHebrew University of Jerusalem& the Geological Survey of Israel
July 23, 2008
(PhD advisors: Amotz Agnon, Moti Stein, Mira Bar-Matthews)
Hebrew University of Jerusalem
Paleoseismology is the study of the timing, location, and size of ancient earthquakes.
San Andeas Fault, California
plates
Interested in knowing:•Recurrence of earthquakes•Location•Magnitude•Local Intensities, site effects
•Mechanisms•Segmentation•Fault interactions•Directivity•Etc…………..
TOOLS:•Instrumental Record•Historical Record•Paleoseismic Record(Faults, deformed sedimentse.g. lake sediments, speleothems)
Instrumental is so precise!BUT… way too short
Historical…. Quite detailed….BUT, not totally reliable and also TOO SHORT (up to 2000 years)
Long, detailed, and well-dated paleoseismic record needed10’s-100’s of thousands of years
largest quakes may not be included in
historical records
more seismic cycles
insight into long-term recurrence times and
patterns (G&R, clustering…)
Surface rupture is recorded in the landscape and the sediments
$$$
Modeling
Paleoseismic Datapre-instrumental
caveats• Site specific• Data sets CAN be small, sparse, analog (changing in a continuous manner relative to another quantity )
• Quantification of uncertainty - major challenge
We need:
•Earthquake-induced geological evidence (on-fault or off-fault)
•Preserved evidence
•Accessibility
•Dateable material
•Preferably continuous record
•Preferably multi-site, multi-archive
Different paleoseismic techniques
Fault scarp created by the 1959 Hebgen Lake, Montana, earthquake
San Andreas, 1600 earthquakeBet Zayda (near the Kinneret)
Across Seattle Fault
ON-FAULT STUDIES
Trenching across faults
ON-Fault:
•Fault-specific• Can measure rupture• Can measure recurrence •Can differentiate different segments•Can interpret magnitude
Example Fault Database from California (CDMG)
Need to “trench” each and every one!
Slip Rates (mm/yr)By Segment
Very detailed information!
At MeasurementSites
Average Recurrence Interval(years)
On-Fault not always available
May be covered by soil, alluvium, lake, ocean
Japan: Fault scarp, hidden deep within a black spruce thicket...
This includes basically all subduction zone quakes (e.g. majority of devastating tsunami-triggering earthquakes)
PRO & CON: Can include evidence of earthquakes from various faults
TECTONICSETTING
Off-fault evidence can record earthquakes from various locations and distances
Paleo-tsunami deposits
Chile
Jody Bourgeois
Fallen Boulders
MSc Mor KanariKiryat Shemona
A stream channel offset by the San Andreas fault, Carrizo Plain, central California (photo by Robert E. Wallace)
Geomorphology
deformed landforms
Dendroseismology – tree-ring analysis, earthquake-damaged trees
New Madrid Seismic Zone -Intraplate
Clastic Dikes
in Lisan Fm., PhD - Zafrir Levy
Nahal Mishmar, Deformed Lake Sediment
Soreq Cave (Bet Shemesh), Fallen Stalagmite
Speleoseismology
Archaeoseismology
Ateret - Vadum Iacob - N. Wall
Susita
Nimrod crusader fortress offset
Cross correlation of data types:
•Paleoseismicity
•Plate tectonics
•GPS
•Instrumental
Modified Mercalli Intensity Scale
• Gives a local characteristic of the earthquake at a site.
• Based on response of people and structures.• MMI is generally larger near the epicenter of an
earthquake, and decreases with distance.• However, site effects can cause anomalies in
this trend.
עוצמהThe real measure of the "badness" of the earthquake
Based on human observations of damage and effects of earthquakes, not any measurement by a machine.
examples:
• IV. Felt indoors by many, outdoors by few.
• Awakened few, especially light sleepers.Frightened no one, unless apprehensive from previous experience.Vibration like that due to the passing of heavy or heavily loaded trucks.Sensation like heavy body striking building or falling of heavy objects inside.Rattling of dishes, windows, doors; glassware and crockery clink and clash.Creaking of walls, frame, especially in the upper range of this grade.Hanging objects swung, in numerous instances.Slightly disturbed liquids in open vessels. Rocked standing motor cars noticeably.
• VIII. Fright general -- alarm approaches panic.
• Disturbed persons driving motor cars.Trees shaken strongly -- branches, trunks, broken off, especially palm trees.Ejected sand and mud in small amounts.Changes: temporary, permanent; in flow of springs and wells; dry wells renewed flow; in temperature of spring and well waters.Damage slight in structures (brick) built especially to withstand earthquakes.
• Considerable in ordinary substantial buildings, partial collapse: racked, tumbled down, wooden houses in some cases; threw out panel walls in frame structures, broke off decayed piling.Fall of walls.Cracked, broke, solid stone walls seriously.Wet ground to some extent, also ground on steep slopes.Twisting, fall, of chimneys, columns, monuments, also factory stacks, towers.Moved conspicuously, overturned, very heavy furniture.
Borah Peak Earthquake
Oct 28, 1983
Ms=7.3
Modified Mercalli Intensity Map
INQUA SCALE
“A global catalogue and mapping of earthquake environmental effects"
Using the present to interpret the past
Calibrate the scale: modern, measured earthquakes & geological effectsThen: use paleoseismic evidence and calibrate to magnitude etc…
Request: report to them ALL geological effects after an earthquake
Damaged cave deposits as
paleoseismological markers
Forti & Postpischl, 1984. Marine Geology
Postpischl et al, 1991. Tectonophysics
Lacave et al., 2004 J. Earthquake Engineering
Kagan et al., 2005. Geology
Gilli, 2005. Comptes Rendus Geoscience
Seismological studies show enhancement of amplitudes (x6 and more) may occur at depths (but also at times reduction)
due to interference of upcoming and downgoing waves
(e.g. Bard and Tucker, 1985)
Site effect is yet unknown
Soreq Caves
Eshtaol
Beit-Shemesh
N
ToJerusalem
Soreq Cave
Har-Tuv Cave
Map bet-
shemesh
Location Map
עבודות קודמות בנושא פלאואקלים, קארסט, והידרולוגיה* במערת שורק:
Asaf, 1975; Even, 1983; Frumkin et al., 1994; Kaufman et al., 1998; Ayalon et al., 1998,1999,2002; Bar-Matthews et al., 1991,1996,1997,1999,2000,2001, 2002.
>kyr 185 רציפההשקעה •
דמיון רב בין שתי המערות•
התמוטטויות ותופעות נזק רבות•
מיקום מאפשר רישום רעידות אדמה מהעתק ים • ואולי מהעתקים נוספים המלח
של רעידות קטנות סינון•
איך יודעים שרעידות אדמה?גרמו לנזקים במערות אלו
?מה לא גרם לנזקים
נזק אנתרופוגני? נזק מבעלי ?חיים
לא!! אין כניסות טבעיות!!
רק במאה האחרונהחציבה
תיארוך התופעות פותר את בעיית
החציבה
anthropogenic
פרמה-פרוסט?
תנועת קרח?
לא במרכז ישראל!תקופות קרח לא היו קרות מספיק
ולא היה כיסוי קרחנהרות תת-קרקעים?
השתפלות?
לא היו במערות המחקר
Perma-frost
אירועים אקלימיים?
לא נמצאה קורלציה•
? עומס סטטי
רעידת אדמה תהיה •
ה"טריגר"
זקיפים גם נשברו•
תרומה לרקורד הפלאוסייסמי של אזור המרוחק מההעתק •הפעיל, רקורד של הרעידות הגדולות
* פיתוח השיטה
* קביעת גילי התמוטטויות, והארכת
185 (מהליסן) ל- 70kyמ- הרקורד הקיים
ky
קורלציה עם הרקורד הפלאוסייסמי * הקיים
מה
עשינו?
מיפוי •
)בעיקר ע"י קידוח גלעינים( של דיגום • התמוטטויות, וזיהוי המגעים 70כ-
הפלאוסייסמייםTh/234U230 בשיטת תיארוך • פיענוח•
עם מחקרים פלאוסייסמים נוספיםהשוואה •
Mapping
N
כיוונים מעודפיםהתמוטטויותשל ה
מיפוי
אחרי התמוטטות
לפני התמוטטות
diagrams
נפול
regrowth
נפול
regrowth
תקרות ממוטטות
שכבות של התמוטטויות במשקע
זרימה)שמהווה את
רצפת המערה(
After Gilli, 1999.
Collapse layers in flowstone
שכבות של התמוטטויות במשקע זרימה
Core in flowstone
Pre-collapse
Post-collapse
חתך: נטיף נפול, לכוד במשקע זרימה
~10cm
מעל ומתחת למגע הפלאוסייסמי בעזרת הלמינותתיארוך •איזוטופים
(U/Th) אורניום ותוריום - רדיאואקטיביים (מס-ספקטרומטר )מדידת האיזוטופים השונים בעזרת
דיוק בתיארוך רעידות אדמה )או כל אירוע גיאולוגי אחר(
)שיטת התיארוך שגיאה אנליטיתהאבסולוטי(
)234U/230Th [MCICPMS]: 1-2 % )שגיאה של
:שגיאה גיאולוגיתקירבת הדוגמא למגע הפלאוסייסמי )מספר השנים שהדוגמא מייצגת )תלוי בגודל וקצב השקעה )?האם הגילים הם "מינימום" או "מקסימום" או שניהם )רווח
Fallen macaroni stalactites and fallen ceiling pieces embedded in floor
flowstone lamina
U2
Sample SO-57
MC= 53.5 ± 1.1 ky
MC= 82.2 ± 1.6 ky
MC= 108.1 ± 1.7 ky
U/Th (Multi Collector) and d18O dating,
MC= 129 ± 2.8 ky
Y
X
V
W
Z
T
S
U1
PRE
PREPOST
POST
POST
PRE
PRE
Flowstone has slow growth rate usually
CB
POSTB=40.1 ± 0.2 ka PRE
C=40.9 ± 1.4 ka
Sample SO-1-6
Fast growth rate
התמוטטויות, 70 דגימה: • גילי 70 יותר מ- •
MCICPMS זמן חזרה של בערך •
שנה10,000
שאלות / בעיות פתוחות
המקומית לגרימת הנזק המתועד ומתוארך עוצמת הסף.א. מהי 1
במערות?
" של השפעת רעידות LIVE - פתרון ע"י ניסויים הנדסיים ותצפיות "
אדמה עכשוויות
הצפויה לגרום אותם נזקים?המגניטודה המינימאלית.ב. ומכאן מהי 1
- פתרון ע"י ניסויים
אילו תגובות אתר ישפיעו על העוצמות המקומיות? (איזו
מגניטודה תביא לאיזו עוצמה מקומית?).... ומכאן מה
המגניטודה הנדרשת?
Threshold Intensity ? מהי עוצמת הסף
1996דוג' מצרפת
M 5.2
VI (MSK) ק"מ מהמוקד, באזור עוצמה 10נזק במערה
בעיקר נטיפי קש שבורים
כנראה היתה תגובת אתר בעקבות טופוגרפיה
Gilli et al., 1999
Marco and Agnon, 1995; Marco et al,., 1996; Agnon et al., 2006
Faulting & Paleoliquefaction in the Lisan Fm.
בקרקעית נוצר נוף מדורגת הרבדה
שלבים ביצירת
שכבת רסק
Breccia Layer
b-וניזול במים גלים יצירתcהרחפה-
c- הרחפהd- התרחיף ושקיעת
e- השקעה המשך
1996, JGR
U-Th dating70 000 year recordLongest worldwide at the time
Different sites show somewhat different records
Holocene lake sediment paleoseismology
Nahal Ze’elim
Ken-Tor et al., JGR, 2001; Ken-Tor et al., Radiocarbon, 2001
31 B.C.
? 64 B.C.? ?
נחל צאלים- מחשוף outcrop
Agnon et al., 2006Ken-Tor et al., 2001
2 sigma, until 8 meters depth
66
07
49
41
93
63
17
53
3
-14
0
-52
5
-75
0
14
56
y = -0.2946x + 472.14
R2 = 0.9829
0
100
200
300
400
500
600
700
800
900
-1500 -1000 -500 0 500 1000 1500
Age BC/AD
De
pth
, m
C14 calibrated ages
seismites, historicalcorrelation
Linear (C14 calibratedages)
צאלים גם, אבל "עמוק", אין היאטוסיםדוקטורט שלי
1997 coring campaign
Migowski et al., 2004
מבחן לשיטה
מגניטודה
מופיעבחתך
נעדרבחתך
עוצמה מקומית
קח
מר
Agnon et al., 2006עוצמה מקומית
מגניטודה
מק”
ר ט
צנפי
אק
חמר
במשך מפורט רישום שנה אלפים עשרת
אנו חיים בתקופה פעילה
Migowski et al., 2004
Identifying the Largest Earthquakes in Lisan Lacustrine Breccias
by Correlation with Cave Seismites and Asphalt-bearing Breccias
זיהוי רעידות האדמה החזקות ביותר ברקורד הסייסמיטים ע"י קורלציה עם ספליאוסייסמיטים וברקציות בתצורת ליסן
המכילות אספלט
Lake Lisan deformed varves
Soreq Cave deformed speleothems
15,000-75,000 yr BP
Late Pleistocene earthquake history of Dead Sea Basin and Judea Mt. area
Documented by: Lake Lisan & stalagmite cave archives
Massada Plain (M1b)Perazim Valley (PZ)Nahal Tovlan (NT)Nahal Tamar (TM)
Nahal Mishmar (MR)
Soreq Cave
Searching for matching
events in the different archives
compare seismites from various types of sediments & locations
Lake
• Different number/type/thickness of seismites
•Location, source distance •Water depth•Lithology•Sediment compaction•Slope & basin structure
Cave
• Different number/type of seismites
•Location, source distance •Depth underground•Size of cave room•Type of speleothem
Paleoseism records.
Normally lucky to find one suitable site
Records and recurrence rates are typically based on one site
Multi-archive study :
different medium (dif. response to EQ)
different location (dif. distance to EQ)
different physical conditions (e.g. water depth)
site effects (amplification)
Motivation
(Modified after Garfunkel et al., 1981)
Dead Sea basin, central Dead Sea Transform
sites
Lisan maximum extent (LGM)
Massada
Perazim
SoreqCaves
Tovlan
Tamar
Site locations
Mishmar
Sea level
+200 m
+400 m
-200 m
-400 m
Lake Lisan levels
Soreq caves
Massada, Mishmar & Tovlan
Perazim & Tamar
40 km (filters out smaller events)
60 m
consequences for seismite formation
Dea
d S
ea T
ran
sfo
rm
LGM ~26 ka
eg: 35 ka
eg: 46 ka
(Marco, Agnon et al. 1995, 1996, 2005; Ken-Tor et al., 2001; Migowski et al., 2004;Agnon et al., 2006; Kagan et al., 2006)
Lacustrine intraclast brecciasSEISMITES
Brecciated, homogenated, folded, faulted
Association of Asphalt Inclusions and Breccias in Lisan
• Observed in many sites• May represent asphalt or oil
discharge into lake before strong
earthquake•Turbulence after quake may cause
floating asphalt/oil to be trapped in
sediment before oxidation takes
place
Association of Asphalt Inclusions and Breccias in
Lisan
Historical accounts of asphalt floating on Dead Sea
after earthquakes
(Arie Nissenbaum, 1977)
(1) Field : Lacustrine section- detailed description, sampling for dating
and chemical analysis Cave- core drilling & hand samples for dating and chemical
analysis, description of seismites, spatial analysis
(2) Chronology : U-Th on calcite cave deposits and on Lisan aragonite (MC-ICP-MS at Geological Survey of Israel)
Methods
MC-ICP-MS
From these different and distant paleoseismic sites, three to four events
stand out(~ 10% of total)
70 ka-15 ka - 27 damaged speleothems dated - Define minimum 6 tectonoseismic events
Speleoseismite age ranges
15 20 25 30 35 40 45 50 55 60 65 70 75
1000's of years
sam
ple
pre
post
RESULTSspeleoseismites
Sei
smit
e
Findings Lisan Lake sediment field work and dating
• Massada: 21 seismites, thinner
seismites
• Perazim: 29 seismite ages
recalculated, very thick seismites
(data from Marco et al., 2006; ages
recalculated after Haase-Schramm et
al., 2004)
• Tovlan: ONE seismite
• Tamar: small part of section studied
• Mishmar: 2/3 of entire Lisan (10
seismites, in period when PZ has 19
and M1b has 9)Tovlan
Massada
Massada - west
38.4 ka (ss) Mas-2
34.8 kaMas-3
34.1 ka Mas-1
34.8 kaMas-6
36.2 kaMas-4
38.7 kaMas-5
Massada - east
36.2 kaTas-24
36.8 kaTas-21
32.6 kaTas-22
34.9 kaTas-20
Nahal Tamar
Legend
aad layer
breccia layer
asphalt
dating sample
conglomerate
Schematic diagram of outcrops of asphalt-bearing breccia layers at Massada and Nahal Tamar, all yielding ages from approximately 33 to 39 ka. Ages given are isochron ages, except for the one marked ss (single sample).
50 cm
RESULTS (preliminary)
Chronology of Asphalt in breccias
(detrital contamination)
3
6
9
12
15
18
21
24
27
30H
ei gh t ( m)
Top Gypsum Unit
The WhiteCliff
Three Gypsum Unit
Additional Gypsum Unit
Top
Mem
ber
Mid
dle M
emb
erB
ottom
Mem
ber
Samra-Lisan transition
Gypsum 5
Broken Gypsum Unit
Small Gypsums Unit
Massada Section
Dating of Massada Lisan site(multi-sample isochrons)
Almost complete
Torfstein, Kagan, in progress
RESULTS
Tovlan
Tamar
Perazim
Massada
Soreq Cave
HIATUS
COMPARISON
seismites
ABS: asphalt-bearing seismites
Recurrence Interval
IN LAKE & CAVE
- 3-4 earthquakes show at most sites in 55 kyr
- 14-18 kyr recurrence interval for the largest events expected for DST
Such long recurrence intervals are rarely reported in the literature, but probably because such long paleoseismic records have rarely been dated and most existing ones don’t actually include full seismic cycles.
But according to Marco et al., 1996:
Mean recurrence interval for largest events: M 7.9 is 50,000 yrs M M 7.5 is 20,000 yrs
May accommodate slip deficit
Calculation:Assume Guttenberg Richterlog10N = 2.66 – 0.93 M (from 1983-1993 (Shapira & Shamir, 1994)
According to the Lisan mixed layer record a M 6.3 event will occur once in 1600 yrs and from here M 7.9 is 50,000 yrs and M 7.5 is 20,000 yrs
Summary & Conclusions
1. Differences in records can shed light on how different media and
environmental conditions affect recording of earthquakes
2. Different locations and different media record earthquakes differently but the
large earthquakes show through most medium
3. Asphalt Bearing Seismites may be ancient precursors to large earthquakes
4. Distinctive large earthquakes occurred at central DST at ~ 38-40, 52, 71 ka
5. These are probably the largest earthquakes on the DST
Work in Progress
1. Similar Analyses in Holocene Records
2. Small-scale spatial analyses (on order of meters) of seismite variability
3. Lithological, grain-size analysis
4. Detailed analysis of lake levels correlation to seismite record