Simulation of historical earthquakes on 1st January 958 A.D., Mw = 6.3 and 1st Apr. 1150 A.D., Mw = 6.1 using the aftershocks data of 27 Nov. 2017 with Mw=7.3 by Empirical Green's Function Method

Zagros is very active in terms of seismicity and is the most seismic region of Iran. In the book on the history of earthquakes in Iran, two major earthquakes have been reported on 1st January 958 Mw 6.3, and 1st April 1150 Mw 6.1 (Ambraseys & Melville, 1982). It is well-known that the historical earthquakes consist of valuable information for identifying the hazard of earthquakes, completing the earthquake catalogs, better understanding the Zagros area, and better preparing for this natural phenomenon; on 12th November 2017, an earthquake with a magnitude of 7.3 occurred at a distance of 10 km from the Ezgleh and about 37 km northwest of Sarpolzahab city in Kermanshah province, located at the Iran-Iraq border. The earthquake location was close to historical earthquakes. In this regard, we used the empirical Green's function method to simulate the historical earthquake. Empirical Green's function evaluates parameters of strong ground motion such as time history, frequency content, effective duration, P and S wave arrival time, the Earth response spectrum, and the maximum acceleration of the earth that occurred during the earthquake. Empirical Green's function method is one of the most common and simple simulation methods for generating strong ground motion with geological heterogeneity effects, which is used to model ground motions using foreshocks and aftershocks. In this study, the simulation of one of the Sarpolzahab earthquake aftershocks was conducted by small aftershocks recorded in the Ezgeleh region, using the empirical function method. The temporary network data of the International Institute of Seismology and Earthquake Engineering was used for this study. The simulation results show that there is a good similarity between the waveforms, the Fourier amplitude spectra, and the simulated response spectra observed at the existing stations and that the errors are acceptable. The parameters of the acquired model consist of rupture velocity of 2.6 to 3.5 km/sec equivalent to 0.8 to 0.9 times the S-wave speed and healing velocity equal to 0.95 times the rupture velocity. The dimensions of the fault grids were 0.05x0.05 and the scalar seismic moment of the aftershock was 1.04×1023 Nm. In the simulation, asperities were not considered. The source time function was Kostrov-ramp and fault roughness was taken into account. Furthermore, the waveforms, Fourier amplitude spectra, and response spectra for the mentioned historical earthquakes were constructed with the results obtained from the reference earthquake for simulation. The results are reasonable; however, some errors are unavoidable.