HR: 13:50h
AN: S53A-02 INVITED     [Abstracts]
TI: Multi-Fault System of the 2004 Mid-Niigata Prefecture Earthquake and its Aftershocks
AU: * Hirata, N
EM: hirata@eri.u-tokyo.ac.jp
AF: The Earthquake Research Institute, the University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Sato, H
EM: satow@eri.u-tokyo.ac.jp
AF: The Earthquake Research Institute, the University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Kato, A
EM: akato@eri.u-tokyo.ac.jp
AF: The Earthquake Research Institute, the University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Sakai, S
EM: coco@eri.u-tokyo.ac.jp
AF: The Earthquake Research Institute, the University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Kurashimo, E
EM: ekura@eri.u-tokyo.ac.jp
AF: The Earthquake Research Institute, the University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AB: The 2004 Mid-Niigata Prefecture Earthquake (Japan Metrological Agency; JMA), central Japan, was a damaging event that destroyed up to 10 000 dwellings, with 40 fatalities and leaving 3000 injured. The earthquake occurred at 17:56 (JST) on October 23, 2004 with a local body wave magnitude (MJMA) of 6.8. The hypocenter was located at a relatively shallow depth of 13 km in an active fault-and-fold system overlain by thick sediments. Data recorded by a seismic network deployed the day after the mainshock are used to determine the major source faults responsible for the mainshock and major aftershocks. Using this high-resolution seismic data, three major source faults are identified: two parallel faults dipping steeply to the west located 5 km apart, and the other dipping eastward and oriented perpendicular to the west-dipping faults. The analysis also reveals that the lateral variation in seismic velocity observed at the surface extends to a depth of 15 km, encompassing the source area of the mainshock. This strong heterogeneity of the crust, related to the complex geological and tectonic evolution of the area, is considered to be responsible for the prominent aftershock activity following the 2004 Niigata event
UR: http://www.eri.u-tokyo.ac.jp/hirata/chuetsu/0401104yotiren1.htm
DE: 7299 General or miscellaneous
SC: Seismology [S]
MN: 2005 Joint Assembly