HR: 15:30h
AN: S54A-01    [Abstracts]
TI: Landslide Distribution, Damage and Land Use Interactions During the 2004 Chuetsu Earthquake
AU: * Sidle, R C
EM: sidle@slope.dpri.kyoto-u.ac.jp
AF: Slope Conservation Section, Geohazards Division, Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto, 611-0011 Japan
AU: Trandafir, A C
EM: atrandafir@yahoo.com
AF: Slope Conservation Section, Geohazards Division, Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto, 611-0011 Japan
AU: Kamai, T
EM: kamai@slope,dpri.kyoto-u. ac.jp
AF: Slope Conservation Section, Geohazards Division, Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto, 611-0011 Japan
AB: A series of earthquakes struck Niigata Prefecture, Japan, on 23 October 2004 killing about 40 people and injuring about 3000. These earthquakes were characterized by a shallow focal depth (13 km) that generated strong levels of ground motion, resulting in extensive damage and thousands of landslides throughout the region. Most landslides on natural slopes occurred in the regional geological structure consisting of sandy siltstone and thin-bedded alternations of sandstone and siltstone. Earthquakes exacerbate such potential instabilities by the ground motion induced and the enhancement of pore water pressure in wet regoliths. The three strongest earthquakes occurred within a period of less than 40 minutes, and had sequential magnitudes (JMA) of 6.8, 6.3, and 6.5. The highest density of landslides (12/km²) was mapped within a 2.9 km radius of the M6.5 epicenter near Yamakoshi village; about 4 times higher density compared to the other epicenters located to the east and west. This higher density may be a consequence of the cumulative shaking effects associated with the two earlier earthquakes of M6.8 and 6.5, in addition to the topographic and geologic factors controlling the stability of the region. Roads, residential fills, agricultural terraces on hillslopes, and other earthworks increased the susceptibility of sites to slope failure. Numerous earthquake-induced failures in terraces and adjacent hillslopes around rice paddy fields occurred near Yamakoshi village. A housing development in Nagaoka city constructed on an old earthflow suffered from severe damage to fill slopes during the earthquake. Nearly saturated conditions in these deep fills together with poor drainage systems contributed to the landslide damages. Clearly, land use activities in rural and urban areas exacerbated the extent of earthquake-triggered landslides.
DE: 5470 Surface materials and properties
DE: 7212 Earthquake ground motions and engineering
DE: 7299 General or miscellaneous
SC: Seismology [S]
MN: 2005 Joint Assembly