Doctoral Dissertation 2004

Strong Motion Simulation of the 1999 Earthquakes in Western Turkey:STtochastic Green's Function Technique with Characterized Source Model and Phase Dependent Site Response

Gülüm Birgören

This thesis discusses the improvement of simulation of high frequency strong ground motion at basin sites by the Stochastic Green's Function Method using a new empirical site response estimation technique. Traditional approaches to calculating the site response in places underlain by sedimentary layers do not effectively take into account the phase properties of a signal. However, the phase part of the signal which keeps the arrival time information becomes essential when the basin induced waves are considered. It is well known that extended duration of ground motion is associated with the damage in flexible structures at the sites underlain by deep basins. The site response estimation technique proposed in the present study preserves both the amplitude and phase parts of the site response in the analysis so that the extended duration of the seismic motion can be simulated realistically for the regions whose velocity structure information is limited. As an application of the proposed methodology the 1999 Düzce and Kocaeli, Turkey Earthquakes have been analyzed.

First, source characterization of the 1999 Düzce Earthquake has been performed by applying the multi-time window linear waveform inversion method to low-frequency ground motions. Source models of the Düzce and Kocaeli Earthquakes obtained from the waveform inversion have been improved applying the Empirical Green's Function Simulation Technique to broad frequency ground motions. The existance of supershear rupture velocity of eastern propagation during the Düzce Earthquake pointed out in a previous study was also investigated based on the inverse and forward simulation results.

Next, development of an empirical method to estimate the phase-dependent site response in time domain using Wavelet Analysis has been introduced. This method has been applied to the Düzce and Adapazari Basins in Turkey using the aftershock data set of the 1999 Düzce and Kocaeli Earthquakes recorded at those regions.

Finally, acceptability of the Stochastic Green's Function Method to prediction of strong ground motion is examined with the phase dependent site response. Simulations of the ground motions in forward modeling for the 1999 Düzce and Kocaeli Earthquakes indicated that the main features of the observed records were almost confirmed by the simulated ones both in time and frequency domains. Based on the findings of this research, it can be concluded that the phase dependent site response estimation method is a promising tool to reproduce the ground motion at basin sites.