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.
　Two dimensional effective stress analysis are conducted for two kinds of quaywalls. One is analysis for Ohama No.2 Wharf that was seriously damaged by the earthquake. Another is for Ohama No.1 wharf that was not damaged at all. The effective stress model used in this analysis consists of a multiple virtual simple shear mechanisms in arbitrary directions.
　The results of the effective stress analysis-of both quaywalls indicate that a fundamental pattern of the deformation of the quaywall is reasonably simulated by
the present approach. In particular the results obtained from the analysis of the damaged quaywall indicate that a fundamental mechanism of the deformation of the quaywall is due to the reduction of the initial stress caused by liquefaction. This mechanism of deformation is quite different from that indicated by conventional Newmark's sliding block concept.