Journal of Japan Society of Civil Engineers, Ser. A1 (Structural Engineering & Earthquake Engineering (SE/EE)), Vol. 68, No. 4, I_20-I_30, 2012.

FINITE FAULT MODELING OF FUTURE LARGE EARTHQUAKE FROM NORTH FAULT IN ,

Meghdad SAMAEI1, Masakatsu MIYAJIMA2, Hamid SAFFARI3, Masato TSURUGI4

1 Doctoral Student, Graduate School of Natural Science and Technology, Kanazawa University (Kakuma-machi, Kanazawa, Ishikawa 920-1192, Japan) E-mail: [email protected] 2 Member of JSCE, Professor, Graduate School of Natural Science and Technology, Kanazawa University (Kakuma-machi, Kanazawa, Ishikawa 920-1192, Japan) E-mail: [email protected] 3 Doctoral Researcher, Graduate School of Natural Science and Technology, Kanazawa University (Kakuma-machi, Kanazawa, Ishikawa 920-1192, Japan) E-mail: [email protected] 4 Senior researcher, Geo-Research Institute (4-3-2, Itachibori, Nishi-ku, Osaka, Japan) E-mail: [email protected]

The main purpose of this study is to predict strong ground motions from future large earthquake for Karaj city, the capital of province of Iran. This city is an industrialized city having over one million populations and is located near several active faults. Finite fault modeling with a dynamic corner frequency has adopted here for simulation of future large earthquake. Target fault is North Tehran fault with the length of 110 km and rupture of west part of the fault which is closest to Karaj, assumed for this simulation. For seven rupture starting points, acceleration time series in the site of Karaj Caravansary –historical building- are predicted. Peak ground accelerations for those are vary from 423 2 2 cm/s to 584 cm/s which is in the range of 1990 Rudbar earthquake (Mw=7.3) . Results of acceleration simulations in different distances are also compared with attenuation relations for two types of soil. Our simulations show general agreement with one of the most well known world attenuation relations and also with one of the newest attenuation relation that hase developed for Iranian plateau.

Key words: Strong ground motion prediction, Finite fault modeling, Karaj, North Tehran fault

1. INTRODUCTION Strong ground motion will be predicted in the site of Karaj Shah Abbasi Caravansary which is a Karaj city, the capital of the with historical building located in the down town and is the population of 1,377,450 in the 2006 census, is one of the oldest structures in the city. This the fifth-largest city in Iran. However, this city is caravansary belongs to and built increasingly becoming an extension of metropolitan between 1688 to 1698 A.C. It is one of the hundreds Tehran. Karaj, Tehran and surrounding faults are caravansaries along the Silk Road. Caravansaries shown in Fig. 1. As it is seen; the west part of the had been roadside inns where travelers could rest North Tehran fault passes through Karaj. So it is and recover from the day's journey. They supported important to estimate the earthquake ground motion the flow of commerce, information, and people caused by this fault in the city. across the network of trade routes. North Tehran fault with the length of 110 km Results of strong motion simulations in different which is counted as a thrust fault (Tchalenko et al.1) distances will also be compared with an attenuation and Berberian et al.2)) is the target fault in this study. relation that has developed for Iran plateau and also The devastating earthquakes of 855 to 856 (exact one of the most popular attenuation relations that year is uncertain) and 1177 could have been caused has developed for world. This comparison will by this fault (Berberian3)). carried out for two types of soil.

I_20 Journal of Japan Society of Civil Engineers, Ser. A1 (Structural Engineering & Earthquake Engineering (SE/EE)), Vol. 68, No. 4, I_20-I_30, 2012.

Fig. 1 Karaj, Tehran and surrounding faults

Fig. 2 Karaj Shah Abbasi Caravansary

2. FINITE FAULT MODELING WITH subfaults with unique dimensions. For each subfault DYNAMIC CORNER FREQUENCY ground motion is being produced by stochastic source point method with an ω 2 model. By One of the most useful methods to simulate considering the effects of path and site, the ground motion for a large earthquake is based on the produced motions for all subfaults are summed in simulation of several small earthquakes as subevents the observation point with a proper time delay to that comprise a large fault-rupture event. This idea obtain the ground motion acceleration from the for the first time was introduces by Hartzell4); when entire fault: he used this method to model the El Centro displacement record for the 1940 Imperial Valley ∑∑ ∆ (1) earthquake. In this method a large fault is divided into N subfaults and each subfault is considered as a where is relative delay time for the radiated small point source. The contributions of all point Δtij sources are summed in the observation point and wave from the ijth subfault to reach the observation large event is produced. point and aij is the subevent (motion) which One of the simple solutions for this method was 5) coincides with the ijth subfault. Each aij(t) is proposed by Beresnev and Atkinson . In this calculated by the stochastic point-source method of solution target fault is divided to nl × nw (=N) Boore6),7). In Boore’s method the acceleration

I_21 Journal of Japan Society of Civil Engineers, Ser. A1 (Structural Engineering & Earthquake Engineering (SE/EE)), Vol. 68, No. 4, I_20-I_30, 2012. spectrum for a subfault at a distance Rij is modeled subfaults are not identical the seismic moment of as a point source with an ω2 shape. The acceleration each subfault is expressed as: spectrum of shear wave of the ijth subfault, Aij(f), is described by: (4) ∑ ∑ ∑∑ // where Sij is the relative slip weight of the ijth subfault. (2) It should be noted here that in this method, a subevent is produced with just one set of random numbers. (unlike the other methods that might use where M0ij, f0ij, and Rij are the ijth subfault seismic several sets of random numbers for producing moment, corner frequency, and distance from the several small earthquakes and use the average of observation point, respectively. The constant them as a subevent.) C=θφ4FV/(4πρβ3), where θφ is radiation pattern (average value of 0.55 for shear waves), F is free surface amplification (2.0), V is partition onto two horizontal components (0.71), ρ is density, and β is shear wave velocity. f0ij is the corner frequency of the ijth subfault. D(f) is the site amplification and the term exp(-πfκ0) is a high-cut filter to model near surface κ0 effects. The quality factor, Q(f), is inversely related to anelastic attenuation. The implied 1/R geometric attenuation term is applicable for body-wave spreading in a whole space. The approach of the stochastic point-source model is to generate a transient time series that has a stochastic character, and whose spectrum matches a specified desired amplitude spectrum such as that given by Equation (2). Steps for doing this are illustrated in Figure 3. First, white Gaussian noise is generated for the duration of the motion (Fig. 3a). Duration of the motion can generally be represented as: T(R)=T0 +dR, where T0 is the source duration and d is the coefficient controlling the increase of duration with distance which is derived empirically (Atkinson and Boore8)). This noise is then windowed (Fig. 3b); the windowed noise is transformed into the frequency domain (Fig. 3c); the spectrum is normalized by the square-root of the mean square amplitude spectrum (Fig. 3d); the normalized spectrum is multiplied by the ground motion spectrum Y (Fig. 3e); the resulting spectrum is transformed back to the time domain (Figure 3f). Fig. 3 Basis of the time-domain procedure for simulating ground motions using the stochastic method. (From The corner frequency of the ijth subfault, f0ij(t), is 7) defined as: Boore ) / ∆ 4.910 Despite all advantages of the presented approach by Beresnev and Atkinson5), Motazedian and ∆ / 9) 4.910/ (3) Atkinson showed that the received energy at the observation point is very sensitive to subfault sizes e.g. as the subfault sizes are increased, the energy at where the average seismic moment of subfaults is low frequency is decreased and the energy at high M0ave= M0/N. In identical subfaults, the moment of frequencies is increased. They overcame this each subfault is controlled by the ratio of its area to problem by introducing a “dynamic corner the area of the main fault (M0ij = M0/N, where M0 is frequency“. In their model, the corner frequency is a the seismic moment of the entire fault). If the

I_22 Journal of Japan Society of Civil Engineers, Ser. A1 (Structural Engineering & Earthquake Engineering (SE/EE)), Vol. 68, No. 4, I_20-I_30, 2012. function of time, and the rupture history controls the implement the concept of “pulsing area”. Pulsing frequency content of the simulated time series of area is the active area on the fault that contributes to each subfault. The rupture begins with a high corner the dynamic corner frequency at a given moment in frequency and progresses to lower corner time, and therefore the passive area does not affect frequencies as the ruptured area grows. the dynamic corner frequency. The cumulative In this approach the acceleration spectrum of the number of pulsing subfaults (NR in Equation (6)), shear wave of the ijth subfault, Aij(f), is described by would increase with time at the beginning of rupture but become constant at a fixed percentage of the total rupture area which is “the percentage of the pulsing area”. This is in agreement with generally accepted idea that the rise time of subfaults are (5) much smaller than the duration of fault rupture. where the dynamic corner frequency, f0ij(t), is 3. ANALYSIS AND RESULTS defined as a function of the cumulative number of ruptured subfaults, NR(t), at time t: As it pointed earlier, the target fault for our simulation is North Tehran fault. The location of the / ∆ / 4.9 10 / (6) fault is decided based on the map of major active faults of Iran, published by IIEES10). The thrust dip of this fault is highly variable from 10 to 80 degrees Hij is a scaling factor for conserving the total area towards north (Tchalenko et al.1)). In the west part under the spectrum of subfaults as the corner dip is roughly estimated to be about 35˚ (Berberian frequency decreases with time which is: et al. 2)) As it is seen in the Fig. 1, North Tehran Fault is / divided into 3 segments; A, B and C. These 3 segments are Karaj-, Kan and Lashgarak ∑ / ∑ (7) segments respectively. In this study earthquake accelerograms are predicted for rupture of “A” Stochastic finite fault modeling based on a segment of the fault which is closest to Karaj. The dynamic corner frequency is adopted in this study so upper depth and lower depth are decided from the success of the simulation is not dependent to the recorded events (with M>2.5) of Institute of subfault size any more. This new model can also Geophysics, (IGTU) and also

Table 1 Recorded data on North Tehran Fault Row Ref Date Time Latitude N Longitude E Depth Magnitude 1 IGTU 2/21/1998 20:5:37 35.714 51.173 10 2.5 (Mn) 2 IGTU 8/26/1999 20:50:1 35.755 51.243 17.2 2.7 (Mn) 3 IGTU 11/4/2000 13:16:42 35.736 51.171 16.4 2.5 (Mn) 4 IGTU 1/24/2001 6:18:3 35.79 51.542 16 2.9 (Mn) 5 IIEES 2/10/2001 2:19:44 35.84 50.97 13 2.5 (Ml) 6 IGTU 10/2/2002 20:37:37 35.834 51.713 7.9 2.5 (Mn) 7 IIEES 9/9/2004 1:36:49 35.82 51.26 6 2.9 (Ml) 8 IGTU 8/15/2005 16:41:20 35.802 51.705 10.5 2.6 (Mn) 9 IGTU 12/18/2005 7:51:31 35.792 51.6 11.4 2.5 (Mn) 10 IIEES 8/15/2006 0:33:53 35.79 51.57 15 2.6 (Ml)

11 IGTU 8/15/2006 0:33:54 35.788 51.53 3.7 2.6 (Mn)

12 IGTU 7/31/2007 3:8:1 35.783 51.686 4 2.9 (Mn)

13 IGTU 7/31/2007 3:18:27 35.825 51.645 8.4 2.6 (Mn) 14 IIEES 7/31/2007 6:20:9 35.77 51.66 16 2.9 (Ml)

15 IGTU 7/31/2007 7:9:44 35.808 51.686 1.5 2.6 (Mn)

16 IGTU 10/22/2008 6:12:44 36.006 51.107 3.5 2.5 (Mn) 17 IIEES 8/21/2010 19:41:17 35.93 51.06 14 2.6(Ml)

18 IGTU 4/1/2011 2:40:59 35.796 50.999 5 2.5 (Mn)

I_23 Journal of Japan Society of Civil Engineers, Ser. A1 (Structural Engineering & Earthquake Engineering (SE/EE)), Vol. 68, No. 4, I_20-I_30, 2012. International Institute of Earthquake Engineering assumed as rupture starting points and acceleration and Seismology (IIEES) from 1998 to 2011. This time histories for those points are drawn in Fig. 5. data is shown in Table 1. All the recorded events The soil condition of Caravansary estimated to be have the hypocenteral depth between 3 to 18 type II of Iranian code of practice for seismic kilometers so the siesmogenic depth decided to be resistant design of buildings, standard 2800 18) site from 3 to 18 kilometers. classes (With the average shear wave velocity of In finite fault method, modeling of the finite 560 m/s). The site amplification factors employed source requires the orientation and dimensions of here are those of Boore and Joyner19) for various the fault plane, the dimensions of subfaults and the sites which are characterized by the average shear location of the hypocenter. The parameters used in wave velocity. this study are listed in Table 2. Moment magnitude is calculated from empirical relationships of Wells Table 2 Modeling parameters 11) and Coppersmith for reverse faults by considering Fault orientation Strike 305˚; Dip 35˚ rupture area. Stress parameter, percentage of pulsing Fault dimensions along strike 46 by 26 km area, Q value and high cut filter are based on the and dip work by Motazedian12) for earthquakes in northern Fault depth range 3 – 18 km Iran. Geometric spreading used here is trilinear Moment magnitude 7.1 relationship that proposed by Kanamori and Subfault dimensions 2 by 2 km Anderson13) which is widely used in Iran and other Stress parameter 68 bars 5),8),14),15) Number of subfaults 299 regions of the world . Crustal shear wave 1.147 velocity and crustal density are taken from the work Q (f) 87f Geometrical spreading 1/R, R ≤ 70 km of Radjaee et al16). They determined a model of the 1/70, 70 < R ≤ 130 km crust for the central Alborz Mountains using teleseismic receiver functions from data recorded on 1 130 , R > 130 a temporarily network. Rupture velocity is 70 R considered to be 0.8 times of shear wave Windowing function Saragoni-Hart velocity12),16),17). Kappa factor (High-cut filter) 0.05 We don’t have information of slip distribution on Pulsing area 50% the fault; therefore unity slip rate for all subfaults Crustal shear-wave velocity 3.5 km/sec Rupture velocity 0.8 × shear wave velocity has been used. 3 In Fig. 4, geometry of the fault and location of Crustal density 2.8 g/cm Karaj Caravansary are shown. Seven points are

Fig. 4 Geometry of the fault

I_24 Journal of Japan Society of Civil Engineers, Ser. A1 (Structural Engineering & Earthquake Engineering (SE/EE)), Vol. 68, No. 4, I_20-I_30, 2012.

Fig. 5 Predicted acceleration time histories for one horizontal direction for different rupture starting points and observed record of L component, Rudbar Earthquake (R (i, j) implies the location of rupture starting point in ijth subfult)

There is no recorded earthquake with a big 40,000 to 50,000 people were killed and extensive magnitude on the North Tehran Fault; so here we damage and landslides observed in the show acceleration time history of Rudbar --Zanjan area. The shown accelerogram earthquake of 1990/06/20 with Mw=7.3 (Berberian is the L component of the record at Abbar station of and Walker20), Sarkar et al21)) beside time histories BHRC ground motion stations. Average shear wave of our simulations in Figure 5. This earthquake was velocity of upper 30 meter in this station; is 621 chosen because it was one of the devastating m/sec as Sinaeian et al. 22) (2007) report; therefore it earthquakes that occurred in the last decades in Iran is also characterized as type II of Iranian code of and its accelerogram is available. In this earthquake practice for seismic resistant design of buildings18)

I_25 Journal of Japan Society of Civil Engineers, Ser. A1 (Structural Engineering & Earthquake Engineering (SE/EE)), Vol. 68, No. 4, I_20-I_30, 2012.

Fig. 6 A seismotectonic map of the region of Rudbar earthquake from Sarkar et al21). Earthquake epicenter is shown with a star (*). The meisoseismal area, three fault segments, viz. Baklor (B), Kabateh (K) and Zard Goli (ZG), locations of the Abbar accelerograph station and the three completely devastated towns of Rudbar, Manjil and Lowsan are also identified. The regions near Lahijan from where soil liquefaction was reported are marked with L

(standard 2800) site classes like the site of Karaj total length of 80 km20),21),23). These three segments Caravansary. The seismotectonic map of the region are Baklor, Kabateh and Zard Goli and are shown in of Rudbar earthquake is shown in Fig. 6. Fig. 6. These segments are arranged in right- There are some similarities between Rudbar stepping en-echolon pattern and are separated by earthquake and our simulations. We have similar gaps in the observed surface rupture. Three main moment magnitude (7.1 and 7.3) and similar subevents that can be seen in seismic body waves hypocentral distance (The seismogram recorded in are correspond to these three main segments of Rudbar earthquake has hypocenter distance of 43 surface rupture20),21). km and our simulations have hypocentral distances We should point out here that the difference of of 20 – 44 kilometers). The similarity is also with the PGAs for different cases is mostly because of the amplification of the site; as it pointed before, the stochastic process of generating the wave. both sites are characterized as type II of Iranian Directivity effect also plays an important role on the code of practice for seismic resistant design of produced PGA. Directivity effect for the point buildings18). R(20,8) is quiet obvious; Although we have a These similarities in input data have lead to further hypocentral distance (33 km) for this point similar output which here is PGA. As it can be seen compared to points R(1,13), R(4,9), R(8,10), in the Figure 5, we have the peak accelerations from R(12,7) and R(16,9), we see a bigger PGA on the 423 cm/s/s to 584 cm/s/s which are in the range of time series of acceleration. This is because as Rudbar earthquake (505 cm/s/s). s-waves travel from this point as rupture starting The important difference between our simulations point along the fault, they are reinforced by waves and Rudbar earthquake is the time duration of the generated by newly ruptured segments. Accordingly motion. Our simulations have the time duration of we observe bigger acceleration despite the further 15 to 25 seconds while this for Rudbar earthquake is distance. This is also considerable for the point more than 50 seconds. The reason for big difference R(23,13) which is the furthest rupture starting point in time duration is the difference between the size (with 44 km of distance) but yields the second and shape of the faults. We have generated motions biggest PGA. This issue can also be noticed trough for rupture of a rectangular fault with the length of time duration of generated motions. Generated 46 km while Rudbar earthquake has been associated motions of R(20,8) and R(23,13) have shorter by three segment discontinues surface rupture with durations compared to R(1,13), R(4,9) and R(8,10)

I_26 Journal of Japan Society of Civil Engineers, Ser. 10000 A1 (Structural Engineering & Earthquake Engineering (SE/EE)), Vol. 68, No. 4, I_20-I_30, 2012.

1000

SA(cm/s/s) 100

10 0.01 0.1 1 10 Natural Period (s)

Fig. 7 5% damped of acceleration response spectra for estimated time series (black lines) and one of Rudbar earthquake (blue line) which shows that, for R(20,8) and R(23,13) horizontal components of motion in different generated waves for different subfaults reach to the distances for two types of soil conditions. Soil receiver rather together. conditions we considered here are soil type II and For further comparison, 5% damped of III of Iranian code of practice for seismic resistant 18) acceleration response spectra of estimated time design of buildings (standard 2800) with VS30 series and observed record of Rudbar earthquake is =560 m/s and VS30 =275 m/s respectively. (VS30 is also shown in Fig. 7. The figure shows that response the time-averaged shear-wave velocity in the top 30 spectra of our simulations are very close to the m of the site profile.) Site amplification curves response spectra of observed Rudbar earthquake. versus frequency for these types of soil are derived Therefore the effects of simulated earthquakes on from Boore and Joyner19) curves of NEHRP regular buildings are the same as Rudbar (National Earthquake Hazard Reduction Program) earthquake. site classes by linear interpolation. A unity slip Comparison shows similarity of peak acceleration distribution is assumed and the same seven locations and response spectra of our simulation with the of the hypocenter on the fault plane of Figure 4 are actual earthquake of Rudbar. This similarity of considered. We simulate records for distances from results is in company with similarity of input factors surface projection of the fault ranging from 1 to 400. like magnitude, hypocentral distance and soil (Note, the actual distances from surface projection condition of the site. Based on this comparison we of the fault are as follows: 1, 2, 5, 10, 15, 20, 30, 40, can conclude that an earthquake which occurs in 50, 60, 70, 80, 100, 120, 150, 200, 250, 300 and 400 Karaj can be as destructive as Rudbar earthquake so km.) Eight lines at equally spaced azimuths considering this hazard of earthquake for spreading out from a point above the center of the construction of new structures and also retrofitting top of the fault plane were defined to capture the of historical buildings like Karaj Caravansary is average effect of directivity; the geometry of the necessary. simulated points is shown in Fig. 8.

4. COMPARISON WITH ATTENUATION RELATIONS

Since in recent years no earthquake of target moment has happened around Karaj and thus no strong-motion recordings are available to compare the results of the simulation with actual data, we chose to draw a comparison with attenuation laws developed for Iranian plateau or similar regions. Attenuation relationships estimate ground motion as a function of magnitude and distance. Fig. 8 Geometry of sites for producing synthesized earthquakes. Using the stochastic finite-fault model of Locations of sites step out from a point above the center 9) of the fault plane, along eight lines equally spaced in Motazedian and Atkinson with the model azimuth. Only one half of the focal sphere is shown in parameters listed in Table 2, we generated random the figure.

I_27 Journal of Japan Society of Civil Engineers, Ser. A1 (Structural Engineering & Earthquake Engineering (SE/EE)), Vol. 68, No. 4, I_20-I_30, 2012.

Soil type II (Vs30 =560 m/s) Soil type III (Vs30 =275 m/s) 1000 1000

100 100 PGA (cm/s/s) PGA (cm/s/s)

10 10 1 10 100 1 10 100 Distance (Km) Distance (Km)

Soil type II (Vs30 =560 m/s) Soil type III (Vs30 =275 m/s)

100 100

10 10 PGV (cm/s) PGV (cm/s)

1 1 1 10 100 1 10 100 Distance (km) Distance (km)

Fig. 9 Maximum acceleration and velocity from simulations versus closest distance to the rupture of the fault (dots) in comparison with two attenuation models; first: Campbell and Bozorgnia (blue line), second: Saffari (red line)

Fig. 9 plots PGA and PGV from simulations starting points). Saffari et al’s curve is not versus closest distance to the rupture on the fault in recommended for distances below 15 km because comparison with the two empirical attenuation they had few data for regression in those distances, models. First attenuation model we chose here is but we have brought it here for a better comparison. well known model of Campbell and Bozorgnia24) (The curve is shown with dashed line in this range.) which is developed for world earthquakes. Second It should be noted here that our definition of one is model of Saffari et al25) which is newest distance here is M4 of the distances defined by model that has developed for Iranian plateau. Joyner and Boore26). Curves are drawn for two types of soil profile with As can be seen in the Figure 9, our simulations VS30=560 and VS30=275 and for every soil profile show a general agreement with both curves total number of 1064 simulations have done (19 especially with the one of Campbell and Bozorgnia, distances 8 azimuthally equal lines 7 rupture although the shapes of the curves are different. The

I_28 Journal of Japan Society of Civil Engineers, Ser. A1 (Structural Engineering & Earthquake Engineering (SE/EE)), Vol. 68, No. 4, I_20-I_30, 2012. difference of the shapes is expected because our North Tehran fault because this fault has not been simulations are based on a seismological model that active in recent decades and we have no strong which is a theoretical issue while the attenuation or middle sized earthquake from this fault (Ashtari relations are based on regression of observed data et al. 28)). which are empirical. This is shown by other researches too8),17),27). For PGA, our simulations show a bit of smaller ACKNOWLEDGMENT: Thank to Dr. Dariush amounts in distances less than 70 kilometers Motazedian for sharing his code “EXSIM”, with us. compared to both attenuation models; this difference is more pronounced in distances between 10 and 70 km. However for PGV, simulations with finite fault REFERENCES modeling show very good agreement with 1) Tchalenko, J.S., Berberian, M., Iranmanesh, H., Baily, M. attenuation models in distances less than 70 km. and Arsovsky, M.: Tectonic framework of the Tehran It can be noticed that geometrical spreading has region, Geological Survey of Iran, Rep. 29, pp. 7-46. 1974. an important effect on the shape of the arrangement 2) Berberian, M., Qorashi, M., Arzhangravesh B., and of dots in Figure 9. The constant value of PGA or Mohajer-Ashjai, A.: Recent tectonics, seismotectonics, and PGV can almost be seen clearly between the earthquake-fault hazard study of the region distances 70 to 130 km. A better estimation of (Contribution to the Seismotectonics of Iran, Part V), geometric spreading in Iran can make the results of Geological Survey of Iran, Report No. 56, p. 316. 1985. (in finite fault simulation closer to attenuation models. Persian) 3) Berberian, M.: Natural hazards and the first earthquake

catalog of Iran, Vol. 1: historical hazards in Iran prior 1900,

I.I.E.E.S. Report. 1994. 5. CONCLUSIONS 4) Hartzell, S.: Earthquake aftershocks as Green’s functions, Geophysical Research letters. Vol. 5, pp. 1-14, 1978. Acceleration time series of strong ground motion 5) Beresnev, I. A. and Atkinson, G. M.: Modeling finite-fault are predicted for Karaj city in the site of Karaj radiation from the ω 2 spectrum, Bulletin of Caravansary. Finite fault modeling with a dynamic the Seismological Society of America, Vol. 73, pp. 67-84, corner frequency adopted for simulation. Target 1997. fault is North Tehran fault with the length of 110 km 6) Boore, D. M.: Stochastic simulation of high-frequency and the rupture of west part of it which is closest to ground motions based on seismological models of the Karaj, assumed for this simulation. For seven radiated spectra, Bulletin of the Seismological rupture starting points acceleration time series are Society of America, Vol. 73, pp. 1865-1894, 1983. predicted. Peak ground accelerations for those are 7) Boore, D. M.: Simulation of ground motion using a vary from 423 cm/s2 to 584 cm/s2 which are in the stochastic method. Pure applied geophysics, Vol. 160, pp. range of recorded Rudbar earthquake at Abbar with 635-676, 2003. the similar magnitude, hypocentral distance and soil 8) Atkinson, G. M. and Boore, D. M.: Ground motion relations characteristics of the site. 5% damped response for Eastern North America, Bulletin of the Seismological spectra of those simulated accelerograms are also Society of America, Vol. 85, pp. 17-30, 1995. compared with the one of Rudbar earthquake. 9) Motazedian, D., and Atkinson, G. M.: Stochastic Finite-Fault Modeling Based on a Dynamic Corner Frequency, Similarity of response spectra shows that effect of Bulletin of the Seismological Society of America, Vol. 95 pp. earthquake from North Tehran fault on the buildings 995-1010, 2005. in Karaj and its surrounding area can be as 10) Hessami, K., Jamali, F. and Tabbasi, H.: Major Active destructive as Rudbar earthquake on the buildings in Faults of Iran, International Institute of Earthquake . Engineering and Seismology, 2003. We also compared results of our simulations in 11) Wells, D. L. and Coppersmith, K. J.: New empirical different distances with attenuation relationships. relationships among magnitude, rupture length, rupture We showed that PGAs and PGVs of finite fault width, rupture area and surface displacement Bulletin of simulations are in general agreement with the Seismological Society of America, Vol. 84, pp. attenuation models. 974–1002. 1994. In this study a unity distribution of slip for all 12) Motazedian, D.: Region-specific key seismic parameters for subfaults considered for simulation. Further studies earthquakes in Northern Iran, Bulletin of the Seismological should be done by modeling asperities of the fault or Society of America, Vol. 96, pp. 1383–1395, 2006. by considering proper slip distribution over the fault. 13) Kanamori, H. and Anderson, D.L.: Theoretical baisis of This is possible with the inversion analysis of some empirical relations in seismology, Bulletin of middle sized earthquakes caused by rupture of the the Seismological Society of America, Vol. 65, pp. target fault. Doing this has been difficult so far for 1073–1095, 1975.

I_29 Journal of Japan Society of Civil Engineers, Ser. A1 (Structural Engineering & Earthquake Engineering (SE/EE)), Vol. 68, No. 4, I_20-I_30, 2012.

14) Nicknam, A., Yaghmaei Sabegh, S. and Yazdani, A.: accelerometric stations. The 5th International Conference Estimating the strong motion of the December 26, 2003 on Seismology and Earthquake Engineering (SEE5), Bam (Iran) earthquake using stochastic techniques, IUST International Institute of Earthquake Engineering and International Journal of Engineering Science, Vol. 19, pp. Seismology. (IIEES), Tehran, Iran, 2007. (In Persian) 45–55, 2008. 23) Berberian, M., Qorashi, M., Jackson, J. A., Priestley, K. and 15) Lam, N., Wilson, J. and Hutchinson, G.: Generation of Wallace, T.: The Rudbar-Tarom Earthquake of 20 June synthetic earthquake accelerograms using seismological 1990 in NW Persia: Preliminary field and seismological modeling: A review, Journal of Earthquake Engineering, observations, and its tectonic significance, Bulletin of Vol. 4, pp. 321–354, 2001. the Seismological Society of America, Vol. 82, pp. 16) Beresnev, I. A. and Atkinson, G. M.: Generic finite fault 1726-1755, 1992. model for ground-motion prediction in Eastern North 24) Campbell, K. W. and Bozorgnia, Y.: NGA Ground motion America, Bulletin of the Seismological Society of America, model for the geometric mean horizontal component of Vol. 89, pp. 608-625, 1999. PGA, PGV, PGD and 5% damped linear elastic response 17) Atkinson, G. M. and Boore, D. M.: Earthquake ground spectra for periods ranging from 0.01 to 10 s. Earthquake motion prediction equations for Eastern North America, Spectra. Vol. 24:1. pp. 139-171. 2008. Bulletin of the Seismological Society of America, Vol. 96, 25) Saffari, H., Kuwata, Y., Takada, S., and Mahdavian, A.: pp. 2181–2205, 2006. Updated PGA, PGV and spectral acceleration attenuation 18) Building and Housing Research Center (BHRC): Iranian relations for Iran, Earthquake spectra, 28, pp. 257-276, Code of Practice for Seismic Resistant Design of Buildings 2012. (standard 2800)”, Building and Housing Research Center 26) Joyner, W. B., Boore, D. M.: Measurement, characterization, (BHRC), p. 465, 2005. and prediction of strong ground motion, Proceedings of 19) Boore, D. M. and Joyner, W. B.: Site Amplification for Earthquake Engineering and Soil Dynamics II, 1988. Generic Rock Sites, Bulletin of the Seismological 27) Atkinson, G. M. and Boore, D. M.: Modification of existing Society of America, Vol. 87, pp. 327 – 341, 1997. ground-motion prediction equations in light of new data,

20) Berberian, M. and Walker, W.: The Rudbar Mw 7.3 Bulletin of the Seismological Society of America, Vol. 101, earthquake of 1990 June 20; seismotectonics, coseismic and pp. 1121–1135, 2011. geomorphic displacements, and historic earthquakes of the 28) Ashtari, M.; Hatzfeld, D.; Kamalian, N.: Microseismicity in western “High-Alborz”, Iran, Geophysical Juornal the region of Tehran, Tectonophysics, No. 395: pp. 193–208, International, Vol. 182, pp. 1577-1602, 2010. 2005. 21) Sarkar, I., Hamzeloo, H., and Khattri, K. N.: Estimation of (Received December 16, 2011 causative fault parameters of the Rudbar earthquake of Revised March 2, 2012 june 20, 1990 from near field SH-wave data, Accepted March 6, 2012) Tectonophysics, 364, pp. 55-70, 2003. 22) Sinaeian, F., Zare, M., Mirzaei Alavijeh, H., and Farzanegan, E.: Study of site amplification and soil characterizing of

I_30