IDENTIFICATION AND MODELING OF EARTHQUAKE GROUND RESPONSE .2. SITE LIQUEFACTION

Downhole records of seismically-induced soil liquefaction are a valuab le source of information on the associated mechanisms of stiffness deg radation and lateral spreading. In this paper, free-held downhole arra y seismic records are employed to identify and model the recorded resp onse at Wildlife Refuge (California, USA) and Port Island (Kobe, Japan ) sites. The Wildlife Refuge site was instrumented in 1982 with a two- accelerometer array and six piezometers that recorded a case of seismi cally induced site liquefaction. At Port Island, a four-accelerometer downhole array recorded strong motion during the recent 1995 Hyogoken- Nanbu earthquake. This earthquake resulted in widespread liquefaction and major ground deformations at Port Island. Using the recorded downh ole accelerations at these two sites, the actual seismic shear stress- strain histories are directly evaluated. These histories provide valua ble insight into the mechanisms of site liquefaction and associated lo ss of stiffness and strength. Based on the identified dynamic soil beh aviors, computational simulations of the observed seismic response are performed. Optimization techniques are employed to estimate the neces sary computational modeling parameters. This document constitutes the second part of a set of two companion papers about site amplification and liquefaction. Copyright (C) 1996 Elsevier Science Limited.