INVESTIGATION INTO THE PULSE OF DIRECTIVITY IN NEAR FIELD RECORDS OF IRAN USING STOCHASTIC FINITE FAULT SIMULATION

There are few actual records of near fault ruptures with features dierent from those of far elds. These features are mostly aected by forward directivity in near eld earthquakes. So, investigation into this eld of study by using methods such to simulate records would be essential Until now, dierent methods have been used by researchers to simulate strong ground motion. Stochastic simulation is a method widely used for simulating high frequency ground motion in recent years. This method, which considers a point source, was presented by Boore (1983). The seismic source is considered to be a rectangular fault plane divided by some sub-faults in its longitudinal and traversal directions. Bersneve and Atkinson (1998) have introduced earthquake stochastic simulation based on nite fault modeling. In such simulations, each subfault is considered a point source, using the source model presented by Brune, with a corner frequency and a constant stress drop. The target accelerogram is obtained by summation of accelerograms generated by each subfault and by considering their corresponding delay times. This new modeling considers rupture geometry and the directivity eect; therefore, its results will be more appropriate. The stress drop parameter is one of the most important parameters in stochastic simulation that has a high uncertainty. This parameter is studied here, based on both stochastic point source and nite fault modeling. For this purpose, the stress drop is calculated for 7 Iranian earthquakes with at least one near eld record. Then, these earthquakes have been simulated by using the results of the stress drops. Finally, several parameters, such as nu, t0, gamma, and the impulse peak, which affect near eld records and directivity pulses, have been investigated.