Disaster Monitoring and Warning System by the Niigata Prefectural Government after the Mid Niigata Prefecture Earthquake

摘要

At 5:56 p.m. on October 23, 2004, an earthquake with a magnitude of 6.8 shook Ghuetsu area of Niigata Prefecture. The epicenter was located in the vicinity of Kawaguchi Town. The maximum seismic intensity of 7.0 was recorded. A lot of aftershocks occurred repeatedly; many of them recorded seismic intensity of over 6.0. The earthquake killed more than fifty people and cut off the supply of essential utilities. The area's infrastructures including public facilities were almost completely destroyed, and numerous landslides caused blockage in river channels and formed natural dams. In particular, two large natural dams were formed due to blockage in the Imo-river and affected the communities of Higashitakezawa and Terano in Koshi-Nagaoka. In Kogomo, upstream of the Higashitakezawa natural dam, some houses were submerged. There was high possibility of debris flow occurrence in the downstream area originating from the collapse of natural dams. In order to protect the downstream areas such as Ryuko (101 households: 436people) in Uonuma from successive possible sediment disasters, the prefecture undertook to manage disaster mitigation using monitoring measures. The authors would like to introduce the disaster monitoring and warning system planned by Niigata prefectural government and report on counter measures undertaken during critical seasons (rainy season, typhoon season, and early spring when snow melts) following the 2004 earthquake.