Earthquake simulation studies for the Marmara region using empirical green's functions method

The main purpose of this article is to simulate three mid-sized earthquakes that occurred in Marmara Sea region, which has complex geologic and tectonic characteristics resulting in heterogeneous crustal structure. In the calculation of earthquake simulations, the method based on empirical Green's function (EGF) developed by Hutchings and Wu (1990) is used. In this way, we evaluate the achievements in simulating ground motion waveforms using empirical Green's function method especially for Marmara region where complex geologic structure exists. The main assumption of the method that simple rupture models and small sized earthquakes (impulsive point source event) recorded in the region can be used as an empirical Green's functions to simulate earthquake ground motions. Accurate estimation of strong motion time history simulation is essential to establishing the recent technology of the earthquake-resistant design and performance based design of structure to reduce earthquake damage. The main reason of this, non-linear dynamic analysis of structures in time domain needs synthetic accelerograms as an input. We simulate three earthquakes (Mw≈5) that occurred along three different extensions of the North Anatolian Fault Zone (NAFZ) inside of the Marmara Sea. The first one occurred on the northern branch of the NAFZ, in northern part of the Marmara Sea, the second one was along the mid-branch of NAFZ that bissects the Gulf of Gemlik and the last one took place on the southern branch of NAFZ in the vicinity of Kus Lake south of the terrestrial areas of the Marmara Sea. Earthquakes used in the study were recorded by broadband seismometer network operated by Kandilli Observatory and Earthquake Research Institute (KOERI). Modelling was made for each earthquake using by five stations, each of which recorded at least one after shock and one main shock, in total ten stations. The distance between recording stations and earthquake hypocenters ranged from 17 km to 121 km. The distance between the simulated earthquake hypocenter and EGF hypocenter ranged from 0.73km to 1.64 km. Similarities between recorded and simulated waveforms were investigated in terms of different parameters such as first arrivals of P waves, time differences between S and P wave arrivals, recording duration, maximum ground velocity, Fourier spectrum and energy distribution. The results confirm that empirical Green's function method is an appropriate method to obtain ground motion simulations especially in areas such as Marmara region which has a heterogeneous crust structure.