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Here, the generalized inversion of S-wave amplitude spectra is employed for deriving the site response and S-wave attenuation (quality factor) in the northwest region of Iran. A total of 279 strong-motion accelerograms recorded at distances below 200 km from 41 earthquakes with moment magnitudes ranging from M w 3.8 to 6.5 are used to determine the region-specific attenuation model. The site responses have been determined for all 54 stations individually. The bulk of strong-motion data (i.e., 184 records) comes from the 2012 Ahar-Varzaghan dual earthquakes in northwest Iran and their aftershocks. Also, the modified finite-fault method, which is able to model nonuniform stress distribution on the fault plane, is employed to investigate the coseismic stress parameter for the first and second Ahar-Varzaghan dual earthquakes by minimizing the difference between the synthesized and observed pseudospectral accelerations for 5% damping. Results denote a concentration of stress drops on the northwestern part of the first event's fault and on the central and eastern part of the second fault. Stochastic simulations, using the calibrated stress distribution have been performed on a regular grid covering the study area for both rock-and soil-site conditions (in total, 651 points). The results show that the maximum of peak ground accelerations (PGAs) during the Ahar-Varzaghan dual earthquakes for the rock-site condition reached 557 cm=s=s, and the largest peak ground velocities (PGVs) were estimated around 76 cm=s. In general, comparisons between simulated data and empirical ground-motion prediction equations (GMPEs) show that the stochastic predictions (PGAs and PGVs) are higher than those predicted by the empirical GMPEs for distances less than 30 km and are smaller for distances more than 30 km. The simulated data are also consistent with the modified Mercalli intensity observations and show reasonable agreement. This can be considered as another validation of the method.

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In this study Probabilistic Seismic Hazard Analysis is carried out for Tabriz region and results are presented by spectral isoacceleration maps and Uniform Hazard Spectra (UHS) for two levels of hazard. To achieve this goal, at first a catalog of all the historical and instrumentally recorded earthquakes covering timeline from 858 up to 2010, in a radius of 200 km around Tabriz city, has been gathered and processed for elimination of the aftershocks and foreshocks from main occurrences list and then seismicity parameters have been obtained by Kijko (2000) method. The seismic sources of the considered region have been studied and modeled. Probabilistic seismic hazard analysis is implemented for 22*17 grid points over Tabriz region and it's vicinity using SEISRISK III (1987) software by employing four attenuation relationships and two relationships between earthquake maximum magnitude and fault rupture length. The Results are combined using logic tree method and shown by spectral acceleration maps and Uniform Hazard Spectra with 2 and 10% probability of exceedence (PE) in 50 years for two types of soil.