Response of a Soft Basin to Incident Rayleigh Wave Considering Hysteresis Behavior of Soil

The topography of an area, i.e., the physical features and their arrangement, largely modifies the intensity of earthquake ground motion there. It is widely recognized that a basin can significantly amplify or reduce motions at the ground surface. Naturally, the response of a soft basin to an incident Rayleigh wave has received much attention in the area of seismic site effects. However, previous studies, using boundary element method and its variants, have to resort to the assumption of linear elastic behavior of soil. This idealized assumption does not reflect the true soil behavior and can lead to an overestimate or an underestimate of the surface ground motion. Accordingly, this study aims to analyze the response of a trapezoidal soft basin to incident Rayleigh wave, considering the hysteresis behavior of soil where shear modulus and damping ratio vary with shear strain. The novel use of time-domain finite element method in simulating the propagation of Rayleigh wave enables the numerical model to incorporate such nonlinear behavior of soil. The obtained ground motions are subsequently compared with those from a simulation using linear elastic behavior of soil. The comparison illustrates the effect of soil hysteresis characteristics on the ground motions at locations inside the basin, in which the shaking level can be noticeably increased or reduced.