Basin Effects on Ground Motion Characteristics: A Numerical Study

Abstract

Basin effects is the entrapping and reverberation of the waves of earthquake in the deposits of soft sedimentary soils atop convex depressions in the underlying bedrock, causing considerable changes in frequency content, amplitude, and duration. In previous earthquakes, this had a significant impact on the duration and severity of the shaking. During the earthquakes, significant disparities in structural damage in the basin relative to surrounding exposed rocks, or even inside the basin itself, were noted. The amplitude of shaking in the basin can be 10 times that of the surrounding rocks. When exposed to ground movements induced by earthquake loading, it is widely known that each soil type behaves differently. In general, depending on geotechnical qualities, depth, and arrangement of soil layers, the soil layers over the hard bedrock may attenuate or enhance the bedrock earthquake motion. The main basin effects are impedance contrast, soil damping, resonance, basement focusing, basin-edge induced surface waves and trapping of waves. The major reason for the cause of various destruction patterns in the basin is edge-induced surface waves. Several numerical studies and experiments have been conducted on the effects of basin edge on the generation of surface waves, influence and characteristics of these waves. The propagation of the seismic waves inside the basin are greatly influenced by the mechanical and geometrical features of the soil in the basin. In the present study, numerical analysis has been carried out using finite difference method to investigate the response of buildings to the BGL-waves. For the simulation of the SH wave, fourth order staggered grid wave FD program given by Narayan and Kumar, 2013 is used for getting response in the rock, homogeneous soil and basin models. The validation of the numerical model has been carried out and the results have been compared with the analytical results.