HR: 1340h
AN: S13B-0207    [Abstracts]
TI: Two Different Earthquake Source Faults Caused Great Kanto Earthquake Disaster of 1923
AU: * Ishikawa, M
EM: ishikawa@ynu.ac.jp
AF: Yokohama National University, Graduate School of Environment and Information Sciences, Tokiwadai 79-7, Hodogaya-ku, Yokohama, 2408501 Japan
AB: The Kanto earthquake of 1 September 1923 in Japan is one of the most destructive earthquakes in the world, and over 100,000 people were sacrificed in the disaster. The source of the 1923 Kanto earthquake is a megathrust between Philippine Sea plate and Honshu plate. In this research, the geometry of the Philippine Sea slab at Izu collision zone was identified using GIS analysis for earthquake catalogue of the Japan Meteorological Agency, and a new hypothesis for the seismogenesis of the Kanto earthquake in Greater Tokyo Area is proposed. The GIS analysis for hypocenter database indicates the existence of an N-S trending slab tear beneath the Tanzawa Mountain. The Philippine Sea slab beneath western half of the Tanzawa Mountain is much deeper than the slab depth beneath eastern half of the Tanzawa Mountain. In the 1923 Kanto earthquake, some M7 class aftershocks occurred immediately after the M7.9 main shock. The M7.3 earthquake of 1 September in eastern region of Yamanashi Prefecture has been considered to be one of biggest aftershocks of the 1923 Kanto earthquake (Takemura, 2003). Although the M7.9 earthquake at 11:58 (Tokyo local time) and the M7.3 earthquake at 12:03 occurred near to each other within five minutes, the two earthquakes were generated on two different earthquake source faults in the slab tear model that I proposed to explain hypocenter distribution. The M7.9 earthquake occurred on the megathrust fault beneath eastern half of Tanzawa Mountain to Tokyo-Yokohama metropolitan region, and the M7.3 earthquake occurred on another earthquake source fault beneath western half of the Tanzawa Mountain. Therefore, the M7.3 earthquake should be considered to be another main shock. The 1923 Kanto earthquake generated slope failures extensively in western region of Greater Tokyo Area e.g. Hakone volcano and Tanzawa Mountain. The GIS-based spatial analysis for slope failures in Kanagawa Prefecture shows that slope failures took place at about 20,000 locations, and the total area reached about 58.5 square kilometer. This disaster resulted in about 800 victims, which is the maximum as slope failure disaster in Japan in the last100 years. Takemura (2003) indicates that this disaster was triggered by the ground motion of the M7.3 earthquake. Because two main shocks attacked within five minutes in the Greater Tokyo Area and results in the Great Kanto Earthquake Disaster, seismic hazard in the Greater Tokyo Area should be evaluated by consideration of the two different earthquake source faults.
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8036 Paleoseismology (7221)
DE: 8123 Dynamics: seismotectonics
SC: Seismology [S]
MN: Fall Meeting 2005