STRONG GROUND MOTION SIMULATION BY HYBRID GREEN'S FUNCTION METHOD
(Thesis Supervisor: Eser Durukal)
This study discusses the effectiveness of hybrid Green's function method in simulating near field strong ground motions from a future large earthquake. Hybrid Green's function (HGF) method starts with calculating Green's functions which are a combination of deterministically calculated, coherent, low frequency motion and stochastically simulated, incoherent, high frequency motion. Following the hybrid Green's function calculation, summation of the Green's functions using the numerical framework of the empirical Green's function (EGF) method gives the large earthquake synthetics. The study is divided into two parts. Part 1 is a generic study, which aims at investigating the availibility of the method when there are no records from previous small earthquakes, as it is the case of EGF approach. It focuses on testing the method for uniform simulation of strong ground motion for a region. Simulation is carried out for a strike slip fault ,and 32 stations are selected, located at lkm to 30km fault distances. In simulating large earthquake motions, the essence of the method is to sum the Green's functions to follow the d law, whether they are real or simulated. The summation of Green's functions is the same process as in the EGF method. The advantage of the HGF method is that, it can be used when there are no recorded small earthquakes near the source area of the large earthquake. Based on the comparisons of the results with empirical attenuation relations and response spectra from several other similar magnitude earthquakes, it can be stated that the method works well in the distance range 5- 30km. There are unrealistically large amplitude differences between the two horizontal ground motion components at sites at 1 krn fault distance, which is mainly caused by discrete wave number method (DWNM). Part 2 of the thesis aims to test the reliability of the method on the basis of a recorded event. For that purpose, we have choosen the Mw 6.0, 2004 Parkfield earthquake because it produced a wealth of high quality near-fault ground motion data. We have carried out simulation for seven rock stations and one soil site station. The preliminary source model determined by Ji (2004) using seismic data, has been used and subsequently modified, applying HGF method. The comparisons of simulated motion in time and frequency domain proved the efficiency of the method in broadband simulation.