Study of Basin-edge Effects on the Ground Motion Characteristics Using 2.5-D Modelling

Abstract

This paper presents the role of basin-edge geometry in the generation of surface waves using 2.5-D modelling. The simulated responses of various basin-edge models revealed surface wave generation near the basin edge and their propagation normal to the edge. Seismic responses of basin-edge models using different fundamental frequency of soil along with spectral analysis of differential ground motion confirmed that surface waves start generating near the basin edge when body-wave frequency exceeds the fundamental frequency of soil. Spectral analysis of differential ground motion also confirmed the generation of high frequency surface wave. An increase of surface-wave amplitude with soil thickness was obtained. Large ground displacement observed near the basin edge may be due to the interference of surface/diffracted waves with the direct waves and their multiples. The effect of edge roughness on the surface-wave characteristics was found to be negligible as compared with the edge geometry. Simulated results revealed a decrease of surface-wave amplitude with edge slope, particularly in the case of surface waves caused by S waves. Surface wave generation near the basin edge was obtained for all four considered angles of incidence. At the same time, it was also inferred that the characteristics of these surface waves depend on the angle of incidence to some extent. The findings of this paper reveal that basin-edge effects deserve a particular attention for the purpose of earthquake-resistant design and seismic microzonation.