Numerical Modeling of Near Fault Seismic Ground Motions for Strike slip and Dip slip faults

Abstract

Strong ground motion plays a vital role in engineering for design of important structures such as dams and nuclear power plants. The site of construction seldom contains past strong motion records, which is a major constraint in earthquake resistant design. Simulated strong motion records at such sites serve the purpose of safe design criteria. Researchers have been producing ground motions using analytical models, for the earthquakes that have occurred in the past. In the area of ground motion analysis, numerical studies on actual field conditions are quite few. Proposed research is to generate ground motions in near fault regions for both strike-slip and dip-slip faults. For this purpose, these faults are modeled to simulate the ground motion records using numerical approach. Semi-empirical approach is used to validate the characteristics of ground motions of both the earthquakes. It is found that the PGA values follow attenuation with respect to epicentral distance. It is observed that the simulated ground motions are in good agreement with the observed ground motions along FN and FP directions. Further the analysis has been carried out to derive and propose geophysical parameters such as ground motion prediction equation, stress drop, kappa parameter and frequency dependent quality parameter for Alaskan region. These parameters are important and play vital role in generating synthetic ground motions. The variation in magnitude of these parameters is significantly changed the peak ground acceleration and spectral acceleration. For this purpose, a study has been carried out on effect of geophysical parameters on ground motion. It is observed that there is no effect of quality factor on spectral acceleration in high period range, but slight effect is seen in low period range. Significant increase in spectral acceleration and PGA values is observed with increase in stress drop. As shear wave velocity increases, the rupture velocity increases as well and consequently the fault will be fractured more rapidly.