EFFECT OF TOPOGRAPHY ON THE STRONG GROUND MOTION CHARACTERISTICS: A NUMERICAL STUDY

Abstract

Various weathered and non-weathered ridge models have been simulated in time domain using double-couple point shear dislocation sources to evaluate the significance of topographic effects on the seismic response. Analysis in frequency domain has been performed using spectral ratio method. 2.5-D finite difference modelling for calculating 3-D elastic wavefields in media varying in two dimensions is adopted for simulating the strong ground motion. Parsimonious staggered grid finite difference method has been used in the computations instead of standard staggered grid scheme since it facilitates the computation of slip pattern as well as the ground displacement. The computed results reveal more amplification of motion at the crest of a ridge as compared to the base of the ridge. It was also found that with the increase in slope of ridge the peak amplification at the crest increases for radial and transverse components and decreases for vertical component. The effect of weathering of ridge mass on the characteristics of surface waves generated is also studied using various weathered ridge models. The analysis of responses of weathered and non-weathered ridge models reveals that surface waves have been generated near the top of the ridge. This study supports the use of numerical simulations for estimation of purely topography-induced amplification on ridge tops. Studies are performed on a complete range of slope angles between 19.98° and 45° to produce a set of generalized result.