Nonlinear ground response at Lotung LSST site

A fully nonlinear finite-element (FE) model is developed to investigate the impact of hysteretic and viscous material behavior on the downhole motion recorded by an array at a large-scale seismic test site in Lotung, Taiwan, during the earthquake of May 20, 1986. A stick model with the same spatial interpolation accuracy as a three-dimensional FE model is used for vertical wave propagation analysis. The constitutive model is based on a three-dimensional bounding surface plasticity theory with a vanishing elastic region, and accounts for shear stiffness degradation right at the onset of loading. The model is cast in a time-domain nonlinear FE code SPECTRA and is used to analyze the 1986 earthquake data. It is shown that the recorded downhole motion of Lotung was dominated by nonlinear response. Results of the fully nonlinear analysis are compared with the predictions of the program SHAKE so that the performance of the nonlinear model may be assessed relative to that of an equivalent linear model.