STRONG GROUND MOTION SIMULATION BASED ON STOCHASTIC FINITE FAULT MODELING FOR TABRIZ, A CITY IN THE NW OF IRAN

摘要

Tabriz, a city in the north west of Iran, has experienced several large destructive historical earthquakes in the past. North Tabriz Fault as an active fault in Tabriz region, with a clear surface expression has caused these large destructive earthquakes in the past. It has an average strike of NW-SE over a length of about 150 km and appears to be generally close to the vertical direction in dip. North Tabriz Fault has been seismically inactive during the last two centuries and due to the absence of ground motion records in Tabriz region, simulation of future events based on regional seismicity information and ground motion model is necessary. In this regard, seismic hazard deaggregation is performed for 10% and 2% probability of exceedance in 50 years and earthquake simulation is done based on the deaggregation results. Attenuation equations developed by Sadigh (1997), Atkinson-Silva (2000) and Campbell-Bozorgnia (2003), have been considered to model epistemic uncertainty having potential errors in the physical description of seismic wave attenuation and equal weights are considered for these attenuation equations. Seismic hazard deaggregation and uniform hazard spectra are computed based on these attenuation equations. The mean magnitudes and distances for PGA and different spectral accelerations are calculated using seismic hazard deaggregation for return periods of 475 and 2475 year. Strong ground motions due to the activation of North Tabriz Fault have been simulated based on stochastic finite fault modeling considering the calculated mean magnitude for return period of 475 year. In order to be taken the stress drop uncertainty in account, stress drops of 20, 40 and 60 bars have been considered in the simulations. Based on these different stress drops, firstly, suites of ground motions have been simulated for return period of 475 year and secondly, their spectral accelerations have been compared with the corresponding uniform hazard spectra. Regarding this comparison, it can be concluded that for the return period of 475 year, a stress drop of about 60 bars generates more compatible spectral accelerations with the corresponding uniform hazard spectra.