Abstract
The Niigata-ken-Chuetsu earthquake of October 23, 2004 caused widespread liquefaction in the alluvial plain of the Shinano River and southwestern coastal lowlands facing the Sea of Japan in Niigata Prefecture. We conducted reconnaissance investigations immediately following the earthquake, focusing on soil liquefaction and associated damage to structures. In addition to the field reconnaissance, we interpreted aerial photographs taken after the earthquake to determine the spatial extent of liquefaction. Sand boiling was more frequent and severe in Yoita, Mitsuke, Nagaoka and Ojiya in the northern region of the epicenter bordering the Shinano River, and Kashiwazaki and Kariwa in southwestern coastal lowlands. The liquefied soils classified into four types: fluvial sand deposits of the Shinano River and its tributaries, backfill on gravelly deposits, fill and/or backfill on soft cohesive or organic soil deposits, and natural dune sand on lower slope of coastal dune.
