Stochastic modeling of Iranian earthquakes and estimation of ground motion for future earthquakes in Greater Tehran

Strong-motion data from eight significant well-documented earthquakes in Iran have been simulated using a stochastic modeling technique for finite faults proposed by Beresnev and Atkinson [Bull Seismol Soc Am 87 (1997) 67–84; Seism Res Lett 69 (1998) 27–32]. The database consists of 61 three-component records from eight earthquakes of magnitude ranging from M 6.3 to M 7.4, recorded at hypocentral distances up to 200 km. The model predictions are in good agreement with available Iranian strong-motion data as evidenced by near-zero average of differences between logarithms of the observed and predicted values for all frequencies. The strength factor, sfact, a quantity that controls the high-frequency radiation from the source is determined, on an event-by-event basis, by fitting simulated to observed response spectra.The calibrated model has been used in the second part of this study to predict ground motions in the Tehran metropolitan area from future large earthquakes along three faults in the Alborz seismic zone (ASZ), which are the most active and hazardous faults near the city. Peak horizontal accelerations (PHA) from our scenario earthquakes exceed 0.7 g, with the highest PHA in the North West parts of the city. Potentially damaging ground motions of 0.1 g and greater extend along the west and south of the city at distances of 10–35 km from the city border. A sensitivity analysis was performed to determine how the most critical input parameter (i.e. sfact) influences the PHA distribution for each scenario. Comparisons have been made between the results obtained with the above model and empirical attenuation models developed for Iran and other similar regions. Results are also validated to the extent possible using the modified Mercalli intensity (MMI) observations from the 1830 earthquake in the ASZ. The calibrated model can produce the distribution of intensities documented from historical reports and the simulated motions are consistent with MMI observations.