In 1983, Nihonkai Chubu Earthquake of magnitude 7.7 hit northern part of Japan. The earthquake caused damage to quaywalls at Akita Port located about 100 km from the epicenter. The damage was associated with the liquefaction of backfill sand. In order to analyze the mechanism of the damage, soils are taken from the site for laboratory tests. The record of the earthquake motion is digitized. Based on these investigations, a two dimensional effective stress analysis is conducted. The model used in this study consists of a multiple virtual simple shear mechanisms oriented in arbitrary directions. The results of the effective stress analysis indicate that a fundamental mechanism in producing deformation of the soil and the structure is due to the initial stress and its release in accordance with the progress of cyclic mobility. This mechanism of deformation is quite different from that indicated by the conventional Newmark\u27s sliding block concept
