The 2005 Zarand earthquake occurred on February 22 at 02:25:26, according to local time in Kerman province in Iran. The main Shock measured 6.5 on moment magnitude scale. Finding causative fault properties and parameters of this earthquake to get reliable values is priority of most researchers. Earthquake source parameters serve as a noteworthy database for synthesizers in seismology and as an essential starting point for the applied theoreticians. Determination of source parameters could make feasible a new level of understanding in many seismological studies that can be used with reported earthquake locations simultaneously to demonstrate boundaries of tectonic plates. It can provide critical information for earthquake hazard assessment and for improved understanding of the earthquake process. Moving towards exact and precise determination of source parameters is essential to reduce uncertainty at other desired stages. The primary purpose of this study is to ameliorate estimation of source parameters and computer simulations of earthquakes, examine the effect of a two sets of rupture parameters on synthesized strong ground motion via forward modelling and checking that which set parameters can be used to predict very realistic source parameters confirmed with Finite fault method. Source parameters of the 2005 Zarand earthquake have already been computed using diverse studies, including seismicity, the earth’s surface deformation field, and rupture characteristics. Each of these studies proposes different mechanisms for this earthquake.
Methodology
Satellite SAR data can gather different information of fault’s physical and geometric situation, because of imagery of two different geometry (ascending and descending), that this lead to optimum extraction of any causative fault parameters. InSAR has become a commonly used technique to measure surface deformation. Measurements by the SAR satellites are made obliquely below the satellite during both ascending orbits (where observations are made from the west) and descending orbits (where observations are made from the east). Two pairs of ascending and descending ENVISAT/ASAR images are available to study the coseismic deformation field of the Zarand 2005 earthquake. We can reconstruct earthquake causative fault parameters using combination of SAR observations and elastic displacement modelling (Okada, 1985). (Feigl, 2002) demonstrated the principles of obtaining earthquake causative fault parameters through elastic displacement modelling using SAR observations.
Though the source parameters are assumed completely unknown, we must set, for each parameters, a range of values between a lower and upper values. In fact, the basic premise for calculating source parameters of an earthquake using SAR observations in inversion processing will be some numbers with appropriate variation ranges.
Strong ground motion data provides researchers with very important information about the simulation of ground motion, rupture processes of earthquakes and consequently source parameters of an earthquake. Finite-fault modeling is widely used for the prediction of ground motion near the epicenters of large earthquakes. In the stochastic model, a large fault is divided into N subfaults, and each subfault is considered as a point source. A random slip distribution is assumed by using a random number as the basis to assign a relative slip to each subfault. Ground motions due to subfaults are calculated by the stochastic point-source method and are summed with an appropriate delay time to produce the motion due to the whole rupture. We have used the extended earthquake fault simulation program EXSIM (Motazedian & Atkinson, 2005) to simulate ground motion.
The study is based on data recorded by the Iranian Strong Motion Network which is run by the Building and Housing Research Center (BHRC). The data are recorded by three-component SSA-2 accelerometers with a threshold of 10 Gals at a sampling rate of 200 samples per second. This earthquake is recorded at the Zarand, Chatrud, Ravar, Horjand, Dasht-e-Khak, Davaran, Kerman1, Kerman2, Hinaman, Baghin, Tarz, Rafsanjan, Bardsir, Sirch, Kuhbanan, Shahr-e-Babak, Bayaz, Anar, Bahadoran, Bahabad, Pariz, Bafgh, Molla Esmaeil, Nayband, Mehriz, Cheshme Sabz, Saadat Abad and Darbehesht stations. In the next step, accelerograms simulation using estimated causative fault parameters in each satellite orbit is done, using stochastic finite fault method. Then results of both ascending and descending orbit are compared to observed values in each station.
Results and discussion
We use the maximum values recorded in each station and obtain results of simulated satellite data to final assessment. The results are demonstrated that the lowest difference in maximum values recorded in each orbit, belong to obtained results of satellite descending orbit data modelling with 5.36% accuracy in comparison to ascending orbit with 7.51% accuracy. Finally, the width, length, strike, dip, rake, depth, slip and coordinates of center causative fault of Zarand earthquake are 6.5 km, 15 km, 279 deg, 90 deg, 55 deg, 5 km, 2.9 m, 483333.4 easting and 3406437 northing, respectively. This procedure allows us to move forward from results with less accuracy to greater one for fault parameters.
Conclusion
The maximum absolute value of accelerograms is used for comparing between synthetic and observed peak ground acceleration in time series. We can say that estimated causative fault parameters for 2005 Zarand earthquake of descending orbit data is more accurate in comparison to ascending orbit data. Finally, we compare our results with Building and Housing Research Centre (BHRC) of Iran, Iranian Seismological Center(IGUT), USGS, IIEES, ISC, CMT catalogue, Talebian et al. (2006), Nicknam et al. (2007), Rouhollahi et al. (2012) reports. Our obtained depth is more similar to Talebian et al. (2006) report. The length of our fault is similar to Nicknam et al. (2007), Rouhollahi et al. (2012) reports. Our width of fault is differ from other studies. Our obtained strike is exactly similar to USGS one’s. Our dip and rake is differ from other studies. Our slip for Zarand causative fault is very similar to Rouhollahi et al. (2012) one’s.