LIQUEFACTION OF RECLAIMED ISLAND IN KOBE, JAPAN

Widespread liquefaction occurred in Kobe, Japan, during the 1995 Hyogo ken-Nanbu earthquake. At the reclaimed Port Island in Kobe, the observ ed large-scale liquefaction was documented by acceleration records fro m a downhole seismic array. Four accelerometers recorded the soil stra tum response, from the ground surface down to a depth of 83 m. These r ecorded accelerations are used here to obtain direct estimates of the corresponding seismic shear stress and strain histories within the Soi l layers, which shed light on (1) the site seismic response during liq uefaction and associated loss of soil stiffness at shallow depths near the ground surface; and (2) the virtually linear site response at dee per elevations. Response of the liquefied upper layer is characterized by cycles of large shear strain and very small shear stress. Converse ly, the lower strata exhibited no sign of stiffness degradation throug hout the earthquake. A computational simulation of this case history i s performed in order to assess the mechanisms of site amplification an d excess pore-pressure buildup. The results of this study demonstrate that acceleration histories recorded by downhole arrays represent a va luable direct source of information on site response during seismic ex citation.