1D finite element artificial boundary method for transient response of ocean site under obliquely incident earthquake waves

Abstract

Ocean site consisting of seawater-seabed-bedrock system is modeled as horizontally layered fluid-poroelastic-solid media. Earthquake wave is assumed as a plane P or SV wave of oblique incidence from the solid bedrock into the site. A time-domain numerical method called one-dimensional finite element artificial boundary (1D-FE-AB) method is proposed to effectively and accurately calculate the transient response of the ocean site under the obliquely incident earthquake waves. In this method, a horizontally line-shaped AB is firstly introduced in the solid bedrock to divide the whole site into the fluid-poroelastic-solid layer and the remaining homogenous solid half space. The former is semi-discretized by FE method along depth, and the latter with the incident earthquake wave is simulated by an exact AB condition. The resulting semi-discrete system with AB is then transformed into a spatially 1D dynamic equation along depth by using the Snell's law of plane body wave propagation in multilayer media. The 1D equation can be solved by the time integration algorithm such as Newmark method. Numerical examples are finally given to demonstrate the effectiveness of the proposed 1D-FE-AB method.