Zafarani Hassani 2013 Site Amplification Earthquakes Zagros

ORIGINAL ARTICLE

Site response and source spectra of S waves in the Zagrosregion, Iran

H. Zafarani & B. Hassani

Received: 27 February 2012 /Accepted: 4 November 2012 /Published online: 20 November 2012# Springer Science+Business Media Dordrecht 2012

Abstract S wave amplitude spectra from shallowearthquakes with magnitudes ranging between 4.2and 6.2 in the Zagros region of Iran that occurredbetween 1998 and 2008 are used to examine sourceparameters and site response of S waves. A general-ized inversion scheme has been used to separate thesource, propagation path, and local site effects from Swave spectra. For removing the trade-off betweensource and site terms and propagation effects (includ-ing geometric and anelastic attenuation), the spectralamplitudes of the records used were corrected forattenuation and geometrical spreading function usinga path model proposed by Zafarani and Soghrat (BullSeism Soc Am 102:20312045, 2012) for the region.We assume a Brunes point source model to retrievesource parameters like corner frequency, momentmagnitude, and high-frequency fall off coefficient,for each event. When the source spectra are interpretedin terms of Brunes model, the average stress drops

obtained are about 7.1 and 5.9 MPa (71 and 59 bars),respectively for the eastern and western Zagros regions.Stress drops range from1.4 to 35.0MPa (14 to 350 bars),with no clear dependence on magnitude. The results interms of stress drop and S wave seismic energy indicatethat the Zagros events are more similar to interplateearthquakes of western North America than to intraplateevents of eastern North America. The method also pro-vides us with site responses for all 40 stations individ-ually and is an interesting alternative to other methods,such as the H/V method. A new empirical relationshipbetween body-wave magnitudes and moment magni-tude has been proposed for the Iranian plateau usingderived seismic moment from the inversion.

Keywords Brunesmodel . Stressdrop . Site response .

Interplate earthquake . Zagros

1 Introduction

The factors influencing earthquake ground motionshave been separated into source, path, and site effects.This separation has proven to be useful for under-standing the physical process of strong-motion gener-ation and predicting future seismic motions (see, e.g.,Boore 2003). An accurate and reliable quantitativeprediction of earthquake strong motions cannot beachieved without understanding the source, site, andpath effects. Obtaining source parameters (e.g., stressdrop and corner frequency) is challenging because

J Seismol (2013) 17:645666DOI 10.1007/s10950-012-9344-1

H. Zafarani (*)International Institute of Earthquake Engineeringand Seismology (IIEES), No. 26, Arghavan St.,North Dibajee, Farmanieh,PO Box 19395/3913, Tehran, Irane-mail: [email protected]

B. HassaniDepartment of Earth Sciences, Western University,Biology & Geological Sciences Bldg.,London, Ontario, Canada N6A 5B7e-mail: [email protected]

they require analysis of the higher-frequency parts ofthe spectrum, where attenuation, scattering, and otherpath effects have a significant effect. Also, groundmotions in the frequency range of 0.515 Hz, whichare of most engineering interest, are strongly affectedby local site conditions, such as complex surface ge-ology and irregular topography. Therefore, the practi-cal way of estimating site effect and source parametersin this frequency range is an empirical approach (Shojiand Kamiyama 2002).

In recent years, ground-motion prediction equationsfor the Iranian plateau have been successfully devel-oped (Zafarani et al. 2008; Soghrat et al. 2012;Zafarani and Soghrat 2012) based on the stochasticmodeling approach of Boore (2003), but yet there arelimited number of studies which have focused on theregion-specific seismic source and wave propagationparameters of major seismotectonic provinces of Iran(e.g., Nowroozi 2010; Zafarani et al. 2008, 2009,2012; Hassani et al. 2011; Mousavi et al. 2007;Motazedian 2006). Here, the Zagros region, one ofthe most seismically active regions in Iran has beenselected for investigating the source and site terms.The Zagros Mountains in southwestern Iran are alinear intracontinental seismically active fold-and-thrust belt, accommodating nearly one third of thepresent-day convergence rate between Arabia andEurasia (Berberian 1995; Vernant et al. 2004). Thebelt extends for about 1,800 km from northern Iraq,through south-western Iran, to the Strait of Hormuz(Fig. 1). Seismic activity is widely distributed in theregion (see Fig. 1), with many destructive earthquakes.However, fault rapture at depth usually does not prop-agate to the Earths surface in the Zagros, apparentlydue to the presence of a thick salt layer above thebasement, preventing ruptures reaching the surface(e.g., Berberian 1995). The Zagros range can be sub-divided into two main subregions that are distinct intheir topography, geomorphology, exposed stratigra-phy, and seismicity. The elevation of the mountains inthe 100-km-wide north-eastern zone, called the HighZagros (Fig. 1) range from 1,500 to 2,000 m, thetallest mountains reaching up to an elevation of over4,000 m and exposing stratigraphic levels in theMesozoic and Palaeozoic. The 100- to 200-km-widesouth-western zone, called the Simply Folded Belt(SFB), rises from sea level in the SW to 1.5 km inthe NE (Fig. 1) and exposes Palaeozoic strata onlyrarely (except for the Hormuz salt plugs). The SFB is

dominated by the large, open, linear folds for whichthe range is famous (e.g., Berberian 1995; Ramsey etal. 2008). The southern margin of the High Zagros liesalong the High Zagros fault (Figs. 2 and 3), which isusually the southern limit of exposure of Palaeozoicrocks (Berberian 1995). Most of the present-day de-formation determined by GPS (e.g., Vernant et al.2004) and seismicity occurs in the SFB (Fig. 1), inwhich shortening within young sedimentary rocks isaccommodated as folding along anticlines (e.g.,Berberian 1995; Ramsey et al. 2008). The Zagrosregion frequently experiences small to moderate earth-quakes. However, though the historical catalog of theregion contains events as large as M7.4 (the Silakhorearthquake of 1909; see Ambraseys and Melville1982), there are few strong-motion records of earth-quakes with a magnitude greater than M6 that wouldallow to take an empirical approach for determinationof ground-motion characteristics. The largest earth-quakes (shown in Fig. 1) occurred in the region duringthe instrumental era (i.e., the M7.4 Silakhor earth-quake of 22 January 1909, the M6.7 Ghir earthquakeof 10 April 1972, and the M 6.7 Khorgu earthquake of

Fig. 1 Seismicity of the Zagros region (M>5.0), 19642010.Major active faults are also shown with solid lines. The boxedregions are the areas shown in Figs. 2 and 3. Hexagram in box 1denotes the location of the Silakhor earthquake of 22 January1909 (M=7.4). The Ghir earthquake of 10 April 1972 (M=6.7),and the Khorgu earthquake of 21 March 1977 (M=6.7), are alsoshown by two pentagrams in box 2. HZ High Zagros zone, SFBsimple fold belt

646 J Seismol (2013) 17:645666

21 March 1977). Unfortunately, there is no strong-motion record from these three large events.

Therefore, the appropriate method of predictingground motions for future earthquakes in the Zagros

47oE 30 48oE 30 49oE 3033oN

20

40

34oN

20

40

35oN

Asr

ArnBtn

Bod

CCnDAa

Drd

Ljb

NAd

Sld

Snr

Ann

CaiDsh

Dhr

Km1

Shh

TAd

Markazi

Hamedan

Kermanshah

Lorestan54~5

M

1

HighZagros F.

Sahneh F.

Main ZagrosReverse F.

Nahavand F.

Fig. 2 Epicenter location ofthe earthquakes analyzed forthe present study (circles),strong-motion stations (tri-angles), and paths (solidline) in subregion 1 (areaoutlined in solid box inFig. 1). Major active faultsare also shown with solidlines

51oE 52oE 53oE 54oE 55oE 56oE26oN

27oN

28oN

29oN

30oNGom

HAdJhm

Krn

Zdr

Bah

Kes

KenRci

Rgn

Persian Gulf

Be1Be2

Ber

Dbn

Gmh

Jum

Ken

Ner

Qsm

SuaTalTmn

5

M

4~5

Fars

Kerman

Hormozgan

2

Lar F.

Beriz F.

Sarvestan F.

Bakhtegan F.

Zagros MountainFront F.

MFF.

MFF.

SabzPushan F.

HZF.

HZF.

Zagrosforedeep F.

MountainFrontal F.

Karebas F.

ZFF.

Borazjan F.

Qir F.

HighZagros F.

Main ZagrosReverse F.

Fig. 3 Epicenter location ofthe earthquakes analyzed forthe present study (circles),strong-motion stations (tri-angles), and paths (solidline) in subregion 2 (areaoutlined in solid box inFig. 1). Major active faultsare also shown with solidlines. MFF mountain frontfault, ZFF Zagros foredeepfault, HZF High Zagros fault

J Seismol (2013) 17:645666 647

region should be based on an assumed seismologicalmodel of source and propagation processes, takinginto account that physical models calibrated to the dataof limited magnitude and distance ranges can be usedwith reasonable confidence in predicting motions be-yond those distance and magnitude ranges. To theextent of our knowledge, this study is the first effortto address this problem with strong-motion data forthe Zagros region. In this paper, the generalized inver-sion (GI) of the S wave amplitude spectra from thestrong-motion network data in this region is used toestimate source and site effects. This technique wasfirst presented by Andrews (1986) by recasting themethod of spectral ratios into a generalized inverseproblem and simultaneously solving of the data ofmultiple-recorded events. Since after, the approachhas been used and developed by numerous authors(e.g., Iwata and Irikura 1988; Castro et al. 1990;Boatwright et al. 1991; Hartzell 1992; Harmsen1997; Dutta et al. 2001, 2003; Salazar et al. 2007;Drouet et al. 2008; Tramelli et al. 2010). Here, a largenumber of significant earthquakes in the region wereanalyzed, considering the events that occurred from1998 to the end of 2008. Furthermore, this is the firstsystematic study on the determination of momentmagnitude from strong-motion records for the region.

2 Data

We collected three-component waveforms recordedat 40 stations of the Iranian strong-motion network,which have been installed and maintained by theBuilding and House Research Center (BHRC;Mirzaei Alavijeh et al. 1998, 2007). All of the sta-tions are equipped with a digital accelerometer(Kinemetrics model SSA-2). We analyzed 148waveforms from 35 events which occurred fromAugust 1998 to December 2008 and ranged in mag-nitude from 4.2 to 6.2 with a focal depth of less than30 km. The epicentral distances ranged from 10 to100 km. The list of earthquakes used in this studyis given in Appendix A, along with the event num-ber, seismic characteristics, and recording stationsfor each event. Also, the name, geographic coordi-nates, and a three-letter abbreviation, for strong-motion stations is provided in Appendix B. Theregion under study consists of two subregions asdepicted in Fig. 1. As it is clear, subregion 1

completely belongs to the High Zagros and subre-gion 2 is completely located in the SFB. Figures 2and 3 show a distribution of stations and events usedhere, and also a visual concept of different paths andlinked records is provided using line between sta-tions and corresponding earthquakes. To obtain thefinal database, following steps were performed: (1)earthquakes with reported seismic characteristics,since 1998 installation up to the end of 2008, wereselected in the Zagros region of Iran. (2) Three-component records with only one correctable hori-zontal component were excluded from the database.(3) Earthquakes with at least three, stations with atleast two records, which are linked to the referencesites, compose the final database. As mentioned insimilar studies (e.g., Harmsen 1997), a key factor toachieve reliable results using the GI method is theavailability of adequate number of recorded groundmotions for each event which are distributed invarious directions in order to reduce the directivityeffects and also sufficient number of recorded eventsfor each site. Both of the abovementioned con-straints were applied to the selected dataset. Themagnitude-distance distribution of the dataset usedfor this study is shown in Fig. 4. For the sake ofcompleteness, it should be noted that here, we try todetermine the source spectra of each event separate-ly (see Table 1 below), and therefore the lack orscarcity of data at some magnitude-distance bins isnot a serious/crucial obstacle. We should keep inmind that the path effect (Q factor) has been adoptedfrom an independent study (Zafarani and Soghrat2012). In other words, since we try to investigatesource spectrum of each event individually, we donot need to have a rich catalog in all magnitudes andsince we have taken the Q factor from a separatestudy, we believe that the scarcity/lack of data insome distances is not a great deal. For the sake ofcompleteness, it should be noted that the GI formu-lation is based on the linear assumption and siteamplification (site effects) have been assumed tobe independent of strong-motion level.

The uncorrected acceleration time series recorded bya given station were corrected for the instrument re-sponse and baseline, following a standard algorithm(Trifunac and Lee 1973). Multiresolution wavelet anal-ysis (Ansari et al. 2010) has been conducted in order toremove undesirable noise from the recorded signals.The data were processed to obtain the Fourier spectra

648 J Seismol (2013) 17:645666

of the S wave windows which contain the strongest partof the shaking (Soghrat et al. 2012). We first determinedthe onset times of S waves on the records using theHusid plot of energy buildup (Husid 1967). Also, toestimate the time of the last arrival of the direct S wave,cumulative root mean square function (McCann andShah 1979) has been used. We then extracted the Swave trains with a cosine-tapered window applied atthe beginning and the end of each window. The lengthof each of these tapers will be 5 % of the total tracelength. The spectrum was smoothed using a 5-pointmoving average filter and interpolated at 20 points,which are equally spaced on the logarithmic scale, be-tween 0.4 and 15 Hz. The Fourier amplitude spectrum(FAS) of horizontal ground motion was computed as theresultant geometric mean of the orthogonal componentsof motion. Figure 5 shows an example of the algorithmused here for determination of S wave window (seeSoghrat et al. 2012 for more details).

3 Method of analysis

We use the GI technique of Andrews (1986),implementing the singular value decomposition(SVD) algorithm. Here, we provide a methodoutline. For further details and a complete de-scription of the method, we refer the reader tothe works of Andrews (1986), Harzell (1992),Salazar et al. (2007), and Hassani et al. (2011).Suppose the database contains J stations overwhich I earthquakes have been recorded, thenfollowing Andrews (1986), the shear-wave

spectrum of the ith event recorded at the jth siteYij () can be written in the frequency domain asa product of a source term Ei(), a path termPij(,R), and a site-effect term Gj():

Yijf Eif Pij f ;R Gjf 1This factorization implicitly accepts the validity of

the principle of superposition, which in turn makes itpossible to treat each of these terms as an independentfilter (Salazar et al. 2007). This general representationof the problem also assumes that directional effects inthe source are averaged out by observations at differ-ent azimuths (Hartzell 1992). Here, the path term isrepresented by geometrical spreading (Z(Rij)) and an-elastic attenuation (Q()):

Pij f ;R Z Rij

: expp fR ijQsf :bs

2

where Rij is the hypocentral distance between theith event and the jth station, Qs() and s are Swave frequency-dependent quality factor and ve-locity, respectively. Because of the trade-off be-tween path attenuation and the high-frequencyfalloff of the spectrum, no attempt was made inthe current study to independently determine Q()(Hartzell 1992). Instead, a propagation term (in-cluding geometric and anelastic attenuation), hasbeen adopted from Zafarani and Soghrat (2012),which is represented as follow:

ZRij / Rij1 ;Rij < 40 km

Rij0:5 Rij 40 km

3

101 1023

3.5

4

4.5

5

5.5

6

6.5

7

7.5

Mw

Distance (Rhypo, Km)

Eastern ZagrosWestern Zagros

Fig. 4 Magnitude-distancedistribution of records usedin this study

J Seismol (2013) 17:645666 649

Qf 153f 0:83 4A site effect Gj() representing combination of site

amplification and the diminution function (path-inde-pendent loss of energy) terms was also considered as:

Gj f Aj f exp pk0f 5

where Aj()is the jth station amplification function and0 represents the diminution parameter or zero-distance kappa factor (Anderson and Hough 1984).

We first determined for all accelerometric stationsthrough the conventional technique based on the esti-mate of the spectral decay of the Fourier amplitudespectra at higher frequencies, generally more than

Table 1 List of source parametersseismic moment (Mo), moment magnitude (Mw), stress drop (), corner frequency ( fc), radius (r),and radiated energy (Es) estimated from the inversion of S wave spectra

Event No. Mo (Nm) Mw (MPa) fc (Hz) Es (J) r (km)

1 2.51E+16 4.9 3.2 0.86 2 2.52E+11 1.5

2 1.58E+18 6.1 4.5 0.24 2 1.10E+13 5.4

3 2.82E+17 5.6 1.4 0.29 2 8.07E+11 4.5

4 4.31E+15 4.4 4.4 1.73 2 7.94E+10 0.8

5 1.21E+16 4.7 7.1 1.43 2 2.52E+11 0.9

6 4.80E+15 4.4 6.5 1.90 2 9.66E+10 0.7

7 7.63E+15 4.6 12 1.99 2 2.78E+11 0.7

8 5.01E+16 5.1 4 0.74 2 6.15E+11 1.8

9 1.52E+16 4.8 22.4 1.95 2 9.23E+11 0.7

10 4.52E+15 4.4 6.4 1.93 2 1.14E+11 0.7

11 2.00E+17 5.5 2.4 0.39 2 1.38E+12 3.3

12 2.13E+16 4.9 1.7 0.74 2 1.17E+11 1.8

13 8.50E+15 4.6 4.1 1.35 2 1.34E+11 1.0

14 1.32E+16 4.7 6.8 1.37 2 2.63E+11 0.9

15 5.01E+16 5.1 1.7 0.56 2 2.52E+11 2.3

16 3.65E+15 4.3 2.6 1.53 2 3.86E+10 0.9

17 7.76E+17 5.9 13.4 0.44 2 3.41E+13 2.9

18 5.62E+17 5.8 12.8 0.49 2 3.83E+13 2.7

19 5.01E+16 5.1 15.6 1.16 2 3.94E+12 1.1

20 7.66E+17 5.9 3.7 0.29 2 7.92E+12 4.5

21 9.24E+15 4.6 15.4 2.03 2 4.34E+11 0.6

22 4.50E+16 5.1 9.6 1.02 2 1.34E+12 1.3

23 1.12E+18 6.0 14.5 0.40 2 3.69E+13 3.2

24 1.19E+16 4.7 6.4 1.40 2 2.72E+11 0.9

25 3.55E+16 5.0 9.3 1.10 2 1.05E+12 1.2

26 8.13E+14 3.9 35 6.01 2 6.60E+10 0.2

27 2.87E+15 4.3 8.9 2.50 2 8.03E+10 0.5

28 6.26E+17 5.8 3 0.29 2 5.17E+12 4.5

29 1.00E+17 5.3 11.7 0.84 2 3.73E+12 1.6

30 2.24E+18 6.2 8.9 0.27 2 6.15E+13 4.8

31 5.01E+16 5.1 12.5 1.08 2 2.15E+12 1.2

32 7.00E+16 5.2 8.9 0.86 2 3.09E+12 1.5

33 2.00E+17 5.5 6.4 0.54 2 4.60E+12 2.4

34 6.59E+16 5.2 5.4 0.74 2 1.65E+12 1.7

35 2.63E+16 4.9 6.1 1.05 2 5.71E+11 1.2

650 J Seismol (2013) 17:645666

5 Hz, in a log-linear plot (Anderson and Hough 1984).An average for each station is obtained from thegeometric mean of the Fourier spectra (see Fig. 6).Then, the zero-distance kappa factor was determinedfrom the best-fitted line (=rR+0) through the dis-tribution of kappa factors as a function of distances(Anderson and Hough 1984). The best-fit regressionline is =0.0002R+0.043, which suggests a value of0.043 for 0. The kappa factor of 0.024 for the verticalcomponent is estimated based on the same procedure(Fig. 7). The high dispersion here, which is also com-mon in almost all kappa determination studies (see,e.g., Motazedian 2006) is due to the fact that such asimple factor could not explain/represent the complexphenomena of wave propagation in the earths crustand near-surface soil-sedimentary layers. Also, thestatistical uncertainty is estimated as the 1 standarddeviation range of the linear regression.

Substituting Eqs. 2, 4, and 5 into Eq. 1, the model isthen linearized by taking the natural logarithms. If weconsider a total number of recordings (N), correspondingto a number of earthquakes (I) recorded at a total number

of stations (J), then a compact matrix formulation forEq. 6 can be represented as follows:

Y A path source1; ::::::i; I

site1; ::::::j; J

X 6

where [Y] represents a vector containing theground-motion amplitude corrected by the geomet-rical spreading and the diminution functions; inaddition, the last seven rows stand for predefinedvalues for seven reference sites (see below), andeach of its member represents a vector with nrows, when n is the number of selected points indesired frequency range; [A] denotes a sparse ma-trix containing only three nonzero elements ineach row (from rows 1 to n). The first columncontains a nonzero vector with n rows while othercolumns represent an nn diagonal matrix. [X]represents a matrix holding I+J+1 terms, namely,the vector solution containing the path term Q f ,source effect In(Ei()) and the site amplificationterm In(Aj()) when each of its members represents

0 10 20 30 40 50 60 70 80100

0100

Event No.30, Station No.37, Comb1x(cm

/s2)

0 10 20 30 40 50 60 70 805

0

5

N(cm

/s2)

0 10 20 30 40 50 60 70 80100

0100 t1 t2

x(cm

/s2)

Corr

e cte

d

0 10 20 30 40 50 60 70 800.05

0.5

1

E/E t

0 10 20 30 40 50 60 70 800

50

100

e(cm

/s2)

0 10 20 30 40 50 60 70 800

10

20t2

c(cm/

s2 )

0 10 20 30 40 50 60 70 80100

0

100

t(sec)

Swav

e

(cm/s2

)

101 100 101 102100

101

102Event No.30, Station No.37, Comb1

f(Hz)

acce

lera

tion

spec

trum

(cm/s)

t1

Fig. 5 An example of selecting the direct shear-wave windowfor an event that occurred on 10 Sep. 2008 recorded in the LenjAb station. Symbols t1 and t2 denote the estimated arrival andend times of the direct S wave, respectively. Left (from top tobottom), the uncorrected acceleration record, extracted noise

identified by the wavelet de-noising method, the wavelet de-noised signal, and its Husid plot, acceleration envelope function,cumulative RMS function, the S wave portion of the correctedsignal; right, the acceleration Fourier amplitude spectrum of Swave window

J Seismol (2013) 17:645666 651

a vector with n rows. Equation 6 is solved for (X)in the frequency range of interest, using a SVD

algorithm (Andrews 1986) which provides a nu-merically robust solution to the problem.

0 20 40 60 80 100 120 140 160 180 2000

0.02

0.04

0.06

0.08

0.1Horizental Components

0 20 40 60 80 100 120 140 160 180 200

0

0.05

0.1

0.02

R(km)

Vertical Components

= (0.00030.00003)R +(0.0240.0016)

= (0.00020.00003)R +(0.0430.0014)

Fig. 7 The distribution of kappa factor versus distance for horizontal (top) and vertical (bottom) components. Gray lines denote the 1standard deviation range

0 10 20 30 40102

101

100

101Event No.10, Station No.8

FAS(

cm/s)

0 10 20 30 40102

101

100


FAS(

cm/s)

0 10 20 30 40102

100


0 10 20 30 40104

102

100


0 10 20 30 40102

101

100


0 10 20 30 40102

101

100


0 10 20 30 40104

102

100


FAS(

cm/s)

Frequency(Hz) 0 10 20 30 40104

102

100


Frequency(Hz)0 10 20 30 40

101

100

101


Frequency(Hz)

=0.046

=0.040

=0.051

=0.032=0.064

=0.041

=0.068 =0.058 =0.044

Fig. 6 Determination of kappa factor for average of horizontal components. The straight lines show the regression fits to logarithm ofspectral amplitude versus frequency

652 J Seismol (2013) 17:645666

Andrews (1986) pointed out the presence of oneundetermined degree of freedom in this system ofequations which can be removed by specifying theamplification at selected reference sites to approx-imately be a constant value or by assuming pre-defined shapes for source spectra (e.g., 2 model).In the current study, the database contains fiveseparate groups of data (see Figs. 2 and 3); there-fore, we need to select at least five reference sites(i.e., one for each group). The inversion analysishas been done for each network/subsets of data(no for the whole set of data). This is due to thefact that the formulation of the GI method (seeEq. 6) needs the connectivity of data for each network.This requirement is fulfilled by considering five separatesubsets of data (see Figs. 2 and 3). The main assumptionabout reference site, is surmising a frequency indepen-dent site response (see Hassani et al. 2011 for moredetails). Here, a preliminary inversion has been doneto investigate relative site responses, assuming that themean of the whole set of stations is free of site effect ateach frequency (Drouet et al. 2008).

The shear-wave velocity values in the upper-most 30 m (30) values were available at 31strong-motion stations of the studied area. Thesestations with their corresponding shear-wave ve-locity are tabulated in Appendix B. Taking intoaccount the 30 values, surface geological condi-tions, if available, the H/V ratios and the resultingresponses of this inversion, stations with the low-est relative values of response have been consid-ered as reference stations and those showingamplification peaks or troughs compared withthe mean have been removed from the set ofreference stations. Chen and Atkinson (2002),Siddiqqi and Atkinson (2002), and Sokolov etal. (2005) showed that the H/V ratios for rocksites, when averaged over many recordings, arecorrelated with the general geological conditionsand may be used as a simple and useful estimateof an amplification effect. Here, the H/V ratios atthe reference sites with necessary modificationshave been used as a constraint to remove theabovementioned undetermined degree of freedomand a second inversion was performed using thisreference condition. Following Drouet et al.(2008), we finally checked on the final resultsthat the stations used in the reference still havea flat transfer function not too far from a

theoretical rock-site response (i.e., a flat ampli-tude response in the frequencies of engineeringinterest).

4 Inversion results

Applying the inversion method to the selected data-base, the source spectra, site responses, and S wavequality factors were obtained simultaneously. Theresults are presented and discussed in the followingsections.

4.1 Source model

The source term Ei() of ith event derived from theinversion can be written as

Eif C4p2f 2 M 0i 7and

C RVF=4psbs3R0 8where R=0.55 is the average shear-wave radiation pat-

tern, F=2 is the free surface amplification, V 1= 2p isintroduced to account for the partition of total shear-waveenergy into two horizontal components, s=2.8 g/cm

3 ands=3.5 km/s are the mass density and the shear-wavevelocity in the vicinity of the earthquake source, R0=1 km is a reference distance, and M0i() is the momentrate spectrum that can be expressed in the form

M 0if M0i1 f =fcig i 9

where M0i(), 0i, and i respectively are the scalarmoment, corner-, and the high-frequency spectral fall-off coefficient associated with the ith earthquake. Themost commonly used model of the earthquake sourcespectrum is the theoretical 2 model introduced byAki (1967) using Brune (1970, 1971) source scaling.Since for small to moderate events, the source issmall, and likely to be simple, it is valid to ignorefinite-source effects and assume a single-corner-frequency point source to model the spectral ampli-tudes of S waves. Here, we assume that the sourcespectra for all events are approximated by an 2

source model (i.e., i=2). In the second stage ofinversion, we visually estimated the initial corner

J Seismol (2013) 17:645666 653

frequency (0in) from resultant source spectra, andused low- and high-frequency level of the sourcespectra to estimate the initial guess of the scalarmoment (M0in(), consequently MWin). A gridsearch analysis was carried out to estimate theoptimal values of abovementioned parameters foreach event computed from M0in() values of Eq. 9,so that residuals between estimated and observedspectral amplitudes become minimum. The follow-ing ranges of parameters have been considered:MWin 0.1 MWi MWin + 0.1 for events withreported moment magnitude and M(b, L, S) 0.5MM(b, L, S)+0.5 for events without reported mo-ment magnitude, and 0.2

2003, Eq. 12). The value of i in general does notdepend on earthquake size, and this led to the scaling ofearthquakes in terms of source dimensions and averageslip. Aki (1967) has shown that for constant stress dropM0c3 is a constant, and this dependence of the cornerfrequency c on the moment M0 controls the scaling ofthe spectral shapes. Repeating the regression analysiswith the slope fixed at 3, corresponding to similarity inthe earthquake source and constant stress drop, we get

logM0 16:52 0:056 3 log fc 13The plot of the relation in Eq. 13 is shown by a thick

solid line in Fig. 10, and the shaded area in the same

figure shows 1 standard deviation of the mean value.Equation 13 can be rewritten as M0c3=3.311016Nm1s3 corresponding to a constant stress drop of6.6 MPa. The results (comparison of Figs. 7 and8) show that there is no significant difference andstrong deviation from similarity assumption. Thisfact is of utmost important in the point-sourcestochastic simulations which will be performingto predict ground motions from the future largeearthquakes in the region. Hassani et al. (2011)obtained a relation M0c3=2.481016Nm1s3 forsmall to moderate earthquakes in the Central-Eastern region of Iran. Also, Zafarani et al.(2012) have found a relationship M0c3=6.811016Nm1 s3 for events in the Alborz region,Northern Iran. Taking to account the estimatedstress drops of the two subregions (areas 1 and2) separately, Eq. 13 can be rewritten as M0c

3=2.971016Nm1s3 corresponding to a constantstress drop of 5.9 MPa for the western Zagros (area 1in Fig. 1 belongs to the High Zagros region) andM0c

3=3.561016Nm1s3 corresponding to a constant stressdrop of 7.1 MPa for the eastern Zagros (area 2 inFig. 1 belongs to the SFB region). The plot ofboth relations are shown by a thick solid line inFig. 11, and the shaded area in the same figureshows 1 standard deviation of the mean value. Asit is clear, there is no significant difference be-tween source characteristics of two the subregions.This was expected because both subregions belongto the Zagros seismotectonic zone, having an inter-plate regime (Zafarani and Soghrat 2012).

After correction for all known path and siteeffects, including geometrical spreading, attenuation,and site amplifications (including kappa), the radi-ated S wave energy ESi for the ith event wascalculated using the following relation (Vassiliouand Kanamori 1982)

ESi AZ1

12pf M oif j j

2

df 14

where A 15pa51 10pb5S1

and is the Pwave velocity near the source region. The obtainedvalues of ESi may be underestimated to someextent because the frequency band limited of thespectral data was used to evaluate Eq. 14. The

101 100 101 1021012

1014

1016

1018

1020Se

ismic

mom

ent(N

.m)

fc(Hz)

Mofc

2.54 = 3.47x1016 N.m/s3

Fig. 9 Plot of seismic moment versus corner frequencyobtained from S wave spectral analysis. The regression line(solid) is shown with the 1 standard deviation range (shaded)

101 100 101 1021012

1014

1016

1018

1020

Seism

ic m

omen

t(N.m

)

fc(Hz)

= 3.5 MPa

= 16.1 Mpa

Mofc

3 = 3.31x 10 16 N.m/s3

= 6.6 MPa

Fig. 10 Plot of seismic moment versus corner frequencyobtained from S wave spectral analysis by fixing the slope inEq. 12 at 3. The regression line (solid) is shown with the 1standard deviation range (shaded)

J Seismol (2013) 17:645666 655

relation between Es and M0 obtained in this studycan be expressed as

logEs 4:68 0:061 logM0 15A comparison between this study and similar

studies is depicted in Fig. 12. The dashed line istaken from Hassani et al. (2011) obtained for theCentral-Eastern region of Iran, and the solid lineis the result of Zafarani et al. (2012) for theAlborz region, Northern Iran. The results showthat earthquakes in the Northern part of Iran havehigher energy and higher stress drops than Zagros

and Central-Eastern parts of Iran. According toScholz et al. (1986), an earthquake that occurson a well-defined plate boundary such as, say, the SanAndreas fault, is clearly an interplate earthquake,and one that occurs in a midplate region far fromany known plate boundary is clearly intraplate.The Zagros region is situated on the deformednorthern margin of the Arabian continental plate,near the boundary of Arabian and southernEurasian plate (Talebian and Jackson 2004), andtherefore the characteristics of these events aremore like interplate earthquakes of western NorthAmerica (see also Silva et al. 1997). The resultsof this study also show the similarity of theZagros earthquakes with the western USA thaneastern North America from the view point ofsource characteristics like spectral amplitudes andlocal stress drops. In contrary, Northern Iran is farmore away from the plate boundary and its earth-quakes clearly can be described as intraplate/mid-plate events (Zafarani and Soghrat 2012). Already,Shoja-Taheri and Niazi (1981) have shown thatthe seismicity pattern of intraplate subregions ofAlborz and Central-Eastern Iran is diffuse, and thecumulative strain release is about one order ofmagnitude below the two interplate boundariesrepresenting Zagros and Hindukush.

Finally, using derived seismic moment from thesecond-stage inversion in the current study and theprevious studies by Hassani et al. (2011) and Zafaraniet al. (2012), the body-wave magnitudes (mb), for 46events in the Iranian plateau which were reported by

101 100 1011012

1014

1016

1018

1020

fc(Hz)

Eastern Zagros

101 100 1011012

1014

1016

1018

1020

Seism

ic m

omen

t(N.m

)

fc(Hz)

Western Zagros

Mofc

3 = 2.97x 10 16 N.m/s3

= 5.9 MPa = 7.1 MpaM

ofc

3 = 3.56x 10 16 N.m/s3

Fig. 11 Plot of seismic mo-ment versus corner frequen-cy obtained from S wavespectral analysis by fixingthe slope in Eq. 12 at 3obtained for the Western(Fig. 2) and Eastern (Fig. 3)Zagros regions. The regres-sion line (solid) is shownwith the 1 standard devia-tion range (shaded)

1014 1015 1016 1017 1018 1019 1020109

1010

1011

1012

1013

1014

1015

Ener

gy(E

s), N

.m

Seismic Moment(M0), N.m

Es/M

o = 2.11x 10 5

(Zagros region)

Es/M

o = 8.2x 10 5

(Northern part of Iran)

Es/M

o = 2.5x 10 5

(CentralEast part of Iran)

Fig. 12 Plot of seismic energy versus moment. The regressionline (solid) corresponds to a constant stress drop is shown alongwith the 1 standard deviation range (shaded). The result ofZafarani et al. (2012) for the Alborz region, Northern part ofIran is also shown. The broken line is taken from Hassani et al.(2011) obtained for the Central-Eastern part of Iran

656 J Seismol (2013) 17:645666

NEIC, has been used to obtain a relationship betweenmb andMw. The relation can be expressed as follow andis shown in Fig. 13.

Mw 0:81 0:11mb 0:86 0:50 16

An empirical global relationship converting mb toMw proposed by Scordilis (2006) has also been shownfor comparison. Using data from Central-Eastern Iran(i.e., 13 events taken from Hassani et al. 2011), leadsto very similar results

Mw 0:79 0:08mb 0:87 0:35 17

4.2 Site response

The next outcome of this study is the site ampli-fication, Aj f for 40 stations which was obtainedin the defined frequency range of 0.4 to 15 Hz.Thick and thin solid lines in Fig. 14 represent themean site amplification factors estimated from theGI at each station and 1 standard deviation, re-spectively. Figure 14 also shows comparisons ofamplification spectra at each site between the GImethod and the earthquake H/V method of Lermoand Chvez-Garca (1993). The method assumesthat the local site conditions do not significantlyinfluence the vertical component of the groundmotion and the H/V spectral ratios may be usedas an indicator of site effects. Here, similar to what

has been done in Chen and Atkinson (2002) andMotazedian (2006), a combination of amplificationthrough the crustal profile and near-surface atten-uation, kappa, was applied in order to model theH/V ratios. In order to clarify the differences in theestimates of site amplifications, site amplificationfactors for both methods at each station were av-eraged over ten frequency bins with central valuesequally spaced on the logarithmic scale (f=1.13,2.59, 4.05, 5.51, 6.97, 8.43, 9.89, 11.35, 12.81,and 14.27 Hz). The averaged amplification factorsat each frequency bands were plotted for the re-spective methods (Fig. 15). As it is clear, compar-ison of site response values of inversion and thoseof H/V shows that the results are more scattered inhigher frequencies (f>5 Hz). A similar trend canbe found in other studies (e.g., Shojia andKamiyama 2002). Also, comparison of the H/Vresults with the inversion technique reveals thatboth methods practically represent the same shapeof site response.

Figure 16 shows the obtained amplification val-ues which have been averaged over the entirefrequency band (0.415 Hz) in comparison withthe results of H/V method. For comparison, theaverage amplification over all frequencies obtainedfor Central-Eastern (Hassani et al. 2011) andNorthern Iran regions (Zafarani et al. 2012) arealso shown. In conclusion, it can be said that inan average sense over all frequencies, there is agood agreement in not only dominant period butalso amplification factor between the GI schemeand the H/V method. In order to examine theresult of the inversion method, against the sitecondition, sites were classified in two categoriesas rock and soil. Sites with 30500 m/sare categorized as rock (Zare et al. 1999).The average of site response obtained by inver-sion is shown in Fig. 17, for both categories.A band width of 0.6 Hz was used for the low-frequency band=0.41.0 Hz, and 3.5 Hz forthe high-frequency band = 2.56.0 Hz. Thesolid line shows the best-fitted line between theresults of the current study. Dashed and dottedlines show the similar quantities for East-Central Iran and the Alborz region, NorthernIran, respectively. It can be concluded that site

3 3.5 4 4.5 5 5.53

3.5

4

4.5

5

5.5

mb

Mw

Mw = (0.81 0.11) mb + (0.86 0.50)(This study)

Mw = (0.85 0.11) mb + (1.03 0.23)3.5 mb 6.5(Scordilis, 2006)

Fig. 13 The results of regression analysis between Mw and mb.The solid lines show the results of regression and 1 standarddeviation

J Seismol (2013) 17:645666 657

amplification at low frequencies have a strongercorrelation with the 30, compared with the am-plification at higher frequencies. A similar trendhas been seen for East-Central Iran by Hassani et

al. (2011). It is clear also that site response in theAlborz region, Northern Iran, has a weak correla-tion with the 30, compared with the two otherregions.

100 101101

100

101

AM

PLIF

ICA

TIO

N 1Asr

100 101101

100

1012Arn

100 101101

100

1013Ann

100 101101

100

1014Bah

100 101101

100

101

AM

PLIF

ICA

TIO

N 5Be1

100 101101

100

1016Be2

100 101101

100

1017Ber

100 101101

100

1018Btn

100 101101

100

101

AM

PLIF

ICA

TIO

N 9Bod

100 101101

100

10110Cai

100 101101

100

10111CCn

100 101101

100

10112Dsh

100 101101

100

101

AM

PLIF

ICA

TIO

N 13Dhr

100 101101

100

10114DAa

100 101101

100

10115Dbn

100 101101

100

10116Drd

100 101101

100

101

AM

PLIF

ICA

TIO

N 17Gmh

100 101101

100

10118Gom

100 101101

100

10119HAd

100 101101

100

10120Jhm

100 101101

100

101

Frequency(Hz)

AM

PLIF

ICA

TIO

N 21Jum

100 101101

100

101

Frequency(Hz)

22Krn

100 101101

100

101

Frequency(Hz)

23Kes

100 101101

100

101

Frequency(Hz)

24Ken

Fig. 14 Site-amplification spectra at 40 stations obtained from performed inversion (solid), arrived from H/V method (dashed), and 1standard deviation range (shaded)

658 J Seismol (2013) 17:645666

Already, Dutta et al. (2003) have reported a similartrend for S wave site response in Anchorage, Alaska,from weak-motion data using the GI method. Theresults of Fig. 17 show that the transition from soilto rock category (dashed line along the ordinate) cor-responds to amplification factor of 2.2 and 3, re-spectively at low and high frequencies.

4.3 Residuals

If a prediction model is not biased at any fixedpoint (i.e., at a specific frequency, distance, ormagnitude), the residuals between the observedand predicted values should be distributed normal-ly with a mathematical expectation of zero andwith different variances. Here, we examined thecomputed residuals, defined as the natural log of

observed FAS minus the natural log of predictedFAS, as a function of distance and magnitude, tobe sure that the results are not biased. Table 2summarizes the model parameters which are eitherchosen or obtained in the inversion. Residuals forfrequencies from 0.4 to 15 Hz over all records arecalculated using the model parameters as listed inTable 2. The distribution of residuals was plottedagainst distance and magnitude to explore possibletrends in the results. Figure 18a shows the histogramof the residuals which show a normal distribution with asmall variance of about 0.26. Figure 18b, c shows thesame residuals but as a function of hypocentral distanceand magnitude, respectively. As it can be concludedfrom Figs. 18 and 19, there is no apparent bias and trendin the residuals; all the residual plots examined show noobvious dependence of the scatter on distance or

100 101101

100

101A

MPL

IFIC

ATI

ON 25Ken

100 101101

100

10126Km1

100 101101

100

10127Ljb

100 101101

100

10128Ner

100 101101

100

101

AM

PLIF

ICA

TIO

N 29NAd

100 101101

100

10130Qsm

100 101101

100

10131Rci

100 101101

100

10132Rgn

100 101101

100

101

AM

PLIF

ICA

TIO

N 33Shh

100 101101

100

10134Sld

100 101101

100

10135Snr

100 101101

100

10136Sua

100 101101

100

101

Frequency(Hz)

AM

PLIF

ICA

TIO

N 37Tal

100 101101

100

101

Frequency(Hz)

38Tmn

100 101101

100

101

Frequency(Hz)

39TAd

100 101101

100

101

Frequency(Hz)

40Zdr

Fig. 14 (continued)

J Seismol (2013) 17:645666 659

magnitude and in conclusion, the model is fitting thedata rather well.

5 Summary and conclusions

S wave spectra of earthquakes recorded by theBHRC strong-motion stations at regional scale aremodeled as the product of source, propagation(including geometric and anelastic attenuation),and site effects. SVD algorithm is employed tosolve the inverse problem and retrieve these dif-ferent terms, because it provides a numericallyrobust solution to the least squares problem. Inthis study, 148 three-component records were usedwhich contain 35 earthquakes of magnitude M4.2to M6.2. These earthquakes were recorded at 40stations in the hypocentral distance range from10 to 100 km. We constrained the inversion usingthe H/V ratio at seven reference sites which have arelatively flat response.

In the moment (M0) range of 1015NmM0

1018Nm, accepting the similarity assumption, thepresent study of source parameters yielded therelation M0c3=3.311016Nm1 s3, where fc iscorner frequency. The Brune stress drop ()

101 100 101101

100

101G

ener

aliz

ed in

vers

ion

1.13 Hz

101 100 101101

100

1012.59 Hz

101 100 101101

100

1014.05 Hz

101 100 101101

100

1015.51 Hz

101 100 101101

100

101

Gen

eral

ized

inve

rsio

n

6.97 Hz

101 100 101101

100

1018.43 Hz

101 100 101101

100

101

H/V method

9.89 Hz

101 100 101101

100

101

H/V method

11.35 Hz

101 100 101101

100

101

H/V method

Gen

eral

ized

inve

rsio

n

12.81 Hz

101 100 101101

100

101

H/V method

14.27 Hz

Fig. 15 Comparisons of amplification spectra between the GI and direct spectral ratio that were averaged over ten frequency bands

101 100 101101

100

101

Ave

rage

site

resp

onse

by

GI m

etho

d

Average site response by H/V method

Zagros

CentralEeastNorthern Iran

1:1

1:2

2:1

Fig. 16 The comparison of average site response calculated byinversion versus that obtained from the H/Vmethod. The dashedlines in the figure indicate 1:2 and 2:1 correspondence. Whitecircles the Zagros stations used in the current study, crossesNorthern Iranian stations obtained from Zafarani et al. (2012),and triangles the site effects estimated for the stations in theCentral-Eastern Iran by Hassani et al. (2011)

660 J Seismol (2013) 17:645666

estimates for individual earthquakes range fromabout 1.4 to 35.0 MPa and the average value isaround 6.6 MPa for the magnitude range of eventsconsidered in this study. The 1 standard deviationof the stress drop parameter corresponds to 16.1and 3.5 MPa, respectively. Using data from west-ern and eastern parts of the Zagros region, thestress drop has been estimated as 7.1 and 5.9 MPafor these regions, respectively. There is no significantdifference between source characteristics of two subre-gions. This was expected because both subregionsbelong to the Zagros seismotectonic zone, havingan Interplate regime. The relation between Es andMo can be expressed as log(Es)=(4.680.061)+logM0. To reduce the trade-off effects, thedistance-dependent kappa factors were indepen-dently determined from the slope of the amplitude

of Fourier acceleration spectrum at higher frequen-cies of generally more than 5 Hz. The kappa forhorizontal and vertical components was found tobe 0.043 and 0.024, respectively. Also, no attemptwas made to estimate the path effects in the cur-rent study; instead, a path model was adoptedfrom previous studies. The site spectrum resultedin the current study was compared with the H/Vmethod. Due to the shortcomings of the H/V ratiotechnique, we do not expect the H/V site responseestimates to perfectly match the general inversionresults in amplitude, although a better match inshape was obtained and generally, comparison ofresults reveals that the H/V ratios successfullymatch the shapes of the transfer functions obtainedby the inversion technique. A comparison of siteamplification values obtained by the inversion

102 103101

100

101

Soil Rock

s(m/s)

Am

plifi

catio

nLow frequency band

102 103101

100

101

RockSoil

s(m/s)

High frequency band

ln(Amp)=(0.410.18)ln(s)+(4.211.23)

ln(Amp)=(0.480.18)ln(s)+(4.051.20)

Fig. 17 The site response values at low (left) and high (right)frequency bands are plotted with respect to the average S wavevelocity of the uppermost 30 m (circles); solid line current study,dashed line East-Central Iran (Hassani et al. 2011), dotted line

the Alborz region, Northern Iran (Zafarani et al. 2012). Thedotted vertical line marks the transition from soil to rock sitecondition as defined by Zare et al. (1999)

Table 2 Seismological parame-ters as obtained from its calibra-tion in this study or adoptedfrom previous studies

Parameter Parameter value

Crustal shear-wave velocity 3.5 (km/s)

Crustal density (g/cm3) 2.8

Q f Q f =153f 0.83Geometric spreading R1 (R40 km), (R=0.40)1/2, and (R>40 km)Site amplification Generalized inversion results (this study)

Source spectrum Generalized inversion results (this study)

Kappa (parameter of high-cut filter (s)) 0.043

J Seismol (2013) 17:645666 661

method shows that both methods practically repre-sent a same shape for site response spectra, but,amplification values obtained from H/V ratios forsome of the sites are different from those obtained fromthe general inversion, and also there is a weak correla-tion between two methods in higher frequencies.Finally, for two frequency bands, the average of site

response spectra were computed and related to theshear-wave velocity in logarithmic scale. It can be con-cluded that site amplification at low frequencies have astronger correlation with the 30, compared with theamplification at higher frequencies. A similar trend hasbeen seen for East-Central Iran by Hassani et al. (2011).It was also concluded that site response in the Alborz

2 1 0 1 20

100

200

300

400

500

600

700

800

residual

nu

mbe

r of v

alue

s

101 1022

0

2

hypocentral distance (Km)

resid

ual

3.5 4 4.5 5 5.5 6 6.52

0

2

Mw

resid

ual

Fig. 18 Histogram of the residuals of the logarithms of Fourier amplitude spectra (left). Residuals as a function of hypocentral distanceand magnitude (right top and bottom), respectively

101 1022

0

2

ln(O

bs/Si

m) f=1.0 Hz

101 1022

0

2

ln(O

bs/Si

m) f=7.0 Hz

3 3.5 4 4.5 5 5.5 6 6.5 72

0

2

3 3.5 4 4.5 5 5.5 6 6.5 72

0

2

3 3.5 4 4.5 5 5.5 6 6.5 72

0

2

Mw101 102

2

0

2

ln(O

bs/Si

m)

rhypo(Km)

f=12.4 Hz

f=1.0 Hz

f=7.0 Hz

f=12.4.0 Hz

Fig. 19 Residuals of FAS at frequencies of 1.0, 7.0, and 12.4 Hz, plotted as a function of log10(hypocentral distance; left) andmagnitude (right)

662 J Seismol (2013) 17:645666

region, Northern Iran, has a weak correlation with the30, compared with the East-Central Iran and Zagrosregions.

Acknowledgment The authors acknowledge the Building andHousing Research Centre of Iran for providing them with theaccelerograms and shear-wave velocities used in the currentstudy.

Appendix A

Table 3 List of earthquakes used in this study

E. No. yyyy/mm/dd hh:min Latitude(deg)

Longitude(deg)

Depth(km)

Numberof records

Magnitude Stations(distance in km)

References

mb Ms Mw

1 1998/08/21 05:13 34.22 48.18 25 3 4.9 4.5 5 NAd(36) Bod(69) Asr(47) E2006

2 1999/05/06 23:00 29.54 51.93 7 5 5.7 6.3 6.2 Gmh(48) Ken(28) Bah(29)Gom(56) Ken(26)

E2006

3 1999/05/06 23:13 29.43 51.93 10 3 5.2 5.7 5.7 Bah(18) Gom(64) Ken(36) E2006

4 1999/05/21 19:17 29.37 51.99 15 4 4.2 3.3 4.2 Kes(25) Bah(18) Rgn(22)Rci(28)

E2006

5 1999/05/30 00:15 29.46 51.95 25 4 4.5 4.2 4.5 Rgn(34) Rci(34) Kes(33)Ken(39)

E2006

6 1999/05/31 19:11 29.32 52.05 15 4 4.3 3.8 4.3 Rgn(19) Rci(28) Kes(24)Bah(19)

E2006

7 1999/06/11 03:05 29.37 51.99 25 4 4.4 3.9 4.4 Rgn(30) Rci(34) Ken(45)Kes(32)

E2006

8 1999/10/31 15:09 29.37 51.85 15 4 4.9 4.9 5.2 Gmh(60) Rgn(34) Ken(36)Bah(19)

E2006

9 1999/12/05 00:06 29.52 51.77 15 3 4.6 4.4 4.6 Ner(21) Bah(34) Rgn(44) E2006

10 2002/04/24 19:43 34.53 47.36 25 5 4.8 4.6 4.8 Ann(26) Shh(39) Snr(43)Btn(31) Ljb(46)

E2006

11 2002/04/24 19:48 34.60 47.40 25 6 5.3 5.1 5.4 Ljb(40) Btn(35) Snr(37)Shh(39) Ann(25) Arn(58)

E2006

12 2002/04/24 20:10 34.49 47.35 25 4 4.8 4.3 4.8 Ann(28) Arn(58) Shh(39)Snr(47)

E2006

13 2002/04/24 20:11 34.53 47.16 25 3 4.5 0 4.5 Snr(55) Shh(54) Ann(32) E2006

14 2002/05/17 15:52 29.48 51.96 25 3 4.8 4.2 4.8 Ken(37) Bah(33) Ner(26) E2006

15 2002/12/24 17:03 34.56 47.48 20 6 5.1 4.6 5.2 Ann(24) Arn(48) Btn(28)Shh(29) Snr(34) Ljb(44)

E2006

16 2002/12/24 22:17 34.49 47.40 28 3 4.6 0 4.6 Snr(46) Shh(38) Ann(31) E2006

17 2003/07/10 17:06 28.31 54.17 10 4 5.8 5.5 5.8 Zdr(60) Jum(21) Jhm(64)HAd(27)

E2006

18 2003/07/10 17:40 28.25 54.08 15 4 5.7 5.4 5.7 HAd(38) Jhm(61) Jum(18)Zdr(63)

E2006

19 2003/11/28 23:19 28.33 54.05 25 3 5.2 4.3 5 HAd(44) Jum(27) Dbn(30) E2006

20 2005/11/27 10:22 26.77 55.90 12 6 6.1 5.8 5.9 Be2(62) Qsm(45) Krn(61)Ber(39) Be1(62) Sua(21)

HRVD

21 2006/03/30 16:17 33.55 48.71 10 3 4.8 4.8 CCn(25) Cai(22) Bod(39 NEIC

22 2006/03/30 19:36 33.65 48.78 20 8 5.2 5.1 CCn(24) Bod(34) Drd(37)Km1(47) Cai(29) Sld(67)TAd(31) Dhr(40)

HRVD

23 2006/03/31 01:17 33.62 48.91 12 9 5.7 6 6.1 CCn(13) Cai(35) Km1(54)Drd(23) Sld(56) Dhr(26)TAd(38) NAd(101) Asr(67)

HRVD

24 2006/03/31 01:31 33.71 48.65 10 4 4.7 4.7 NEIC

J Seismol (2013) 17:645666 663

Appendix B

Table 3 (continued)

E. No. yyyy/mm/dd hh:min Latitude(deg)

Longitude(deg)

Depth(km)

Numberof records

Magnitude Stations(distance in km)

References

mb Ms Mw

CCn(27) Bod(24) Km1(38)Cai(14)

25 2006/03/31 11:54 33.73 48.75 26 6 4.9 4.3 5.1 Km1(52) Sld(78) TAd(31)Drd(47) Bod(32) Cai(33)

HRVD

26 2006/04/02 01:59 33.76 48.91 15 3 4.2 4.2 DAa(22) Dsh(18) CCn(19) NEIC

27 2006/04/12 11:47 33.72 48.79 11 3 4.6 4.6 DAa(21) CCn(17) Dsh(11) NEIC

28 2006/06/28 21:02 26.77 55.81 12 4 5.8 5.8 5.8 Tmn(13) Ber(33) Qsm(52)Be2(68)

HRVD

29 2008/05/05 21:57 28.19 53.99 12 3 5.4 5.2 Dbn(33) Jum(14) Zdr(65) HRVD

30 2008/09/10 11:00 26.65 55.72 12 5 6.1 6.1 6.1 Ber(38) Tmn(23) Sua(40)Tal(17) Krn(66)

HRVD

31 2008/09/11 02:16 26.93 55.63 7 3 5.2 5.2 Tmn(30) Sua(47) Tal(22) HRVD

32 2008/09/17 17:43 26.75 55.96 12 3 5.3 5 5.2 Be1(60) Sua(17) Qsm(41) HRVD

33 2008/12/07 13:36 26.82 55.74 12 4 5.7 5.4 5.4 Ber(25) Be1(70) Sua(35)Tal(14)

HRVD

34 2008/12/08 14:41 26.83 55.76 12 6 5.5 5.3 5.1 Be1(68) Sua(33) Tal(15)Qsm(54) Be1(68) Tal(15)

HRVD

35 2008/12/09 15:09 26.75 55.80 14 3 5.2 5 5 Sua(30) Qsm(55) Tal(16) HRVD

Mw moment magnitude, E2006 Engdahl et al. (2006), HRVD Harvard Seismology, NEIC National Earthquake Information Centre

Table 4 Tabulations of stations with their corresponding shear-wave velocity

St. No. Station name Latitude (deg) Longitude (deg) Number of records V30 (m/s) Abbreviation

1 Aleshtar 33.871 48.259 2 621 Asr

2 Aran 34.41 47.92 3 Arn

3 Armanijan 34.61 47.35 6 390 Ann

4 Balaadeh 29.291 51.935 7 1,380 Bah

5 Bandar-e-Abbas 1 27.193 56.293 5 337 Be1

6 Bandar-e-Abbas 2 27.19 56.298 2 Be2

7 Bandar-e-Khamir 26.952 55.582 4 679 Ber

8 Bistoon 34.38 47.43 3 Btn

9 Boroojerd 33.891 48.754 5 579 Bod

10 Chaghalvandi 33.664 48.553 5 616 Cai

11 Chalan Choolan 33.659 48.913 6 428 CCn

12 Darbastaneh 33.701 48.817 2 1,103 Dsh

13 Darreh-Asbar 33.45 49.06 2 935 Dhr

14 Deh Azna 33.611 48.929 2 450 DAa

15 Doobaran 28.411 54.182 2 1,363 Dbn

16 Dorood 33.491 49.059 3 771 Drd

17 Ghaemiyeh 29.846 51.59 2 617 Gmh

18 Gooyom 29.829 52.4 2 598 Gom

19 Haji Abad 28.35 54.42 3 561 HAd

20 Jahrom 28.503 53.554 2 Jhm

664 J Seismol (2013) 17:645666

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Table 4 (continued)

St. No. Station name Latitude (deg) Longitude (deg) Number of records V30 (m/s) Abbreviation

21 Jouyom 28.259 53.982 4 1,244 Jum

22 Kahoorestan 27.216 55.564 2 807 Krn

23 KarehBas 29.45 52.17 4 Kes

24 Kazeroon 29.62 51.67 2 Ken

25 Khan zeynioun 29.671 52.147 5 773 Ken

26 Khoram Abad1 33.491 48.359 4 Km1

27 Lenj Ab 34.87 47.28 3 Ljb

28 Narges Zar 29.447 51.891 2 983 Ner

29 Noor Abad 34.072 47.972 2 758 NAd

30 Qeshm 26.962 56.275 5 757 Qsm

31 Richi 29.5 52.18 4 1,050 Rci

32 Romghan 29.371 52.162 6 1,362 Rgn

33 Sahneh 34.47 47.68 6 Shh

34 Shool Abad 33.184 49.192 3 1,084 Sld

35 Sonqor 34.78 47.6 6 1,477 Snr

36 Suza 26.782 56.07 7 1,334 Sua

37 Tabl 26.758 55.725 6 931 Tal

38 Tomban 26.766 55.863 3 778 Tmn

39 Tooshk-e-Ab-e-Sard 33.773 48.569 3 891 TAd

40 Zahedshahr 28.742 53.805 3 390 Zdr

Stations set in italics are the selected reference sites

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Site response and source spectra of S waves in the Zagros region, IranAbstractIntroductionDataMethod of analysisInversion resultsSource modelSite responseResiduals

Summary and conclusionsAppendix AAppendix BReferences

Documents

Zafarani Hassani 2013 Site Amplification Earthquakes Zagros