Mega-thrust and Intra-slab Earthquakes beneath Tokyo Metropolitan Area around subduction and collision zones in JAPAN

HR: 10:50h
AN: T42A-03 [Abstracts]
TI: Mega-thrust and Intra-slab Earthquakes beneath Tokyo Metropolitan Area around subduction and collision zones in JAPAN
AU: * Hirata, N
EM: hirata@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo, 113-0032, Japan
AU: Kasahara, K
EM: kkasa@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo, 113-0032, Japan
AU: Hagiwara, H
EM: hagiwara@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo, 113-0032, Japan
AU: Satow, H
EM: satow@eri..u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo, 113-0032, Japan
AU: Shimazaki, K
EM: nikosh@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo, 113-0032, Japan
AU: Koketsu, K
EM: koketsu@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo, 113-0032, Japan
AU: Wu, F
EM: francis@binghamton.edu
AF: Dept Geological Sciences, Binghamton University, P.O. Box 6000, Binghamton, NY 13902-6000, United States
AU: Okaya, D
EM: okaya@usc.edu
AF: Dept Earth Sciences Univ. Southern California, University Park, Los Angeles, 90089-074, United States
AB: In central Japan the Philippine Sea plate (PSP) subducts beneath the Tokyo Metropolitan area, the Kanto region, where it causes mega-thrust earthquakes, such as the 1703 Genroku earthquake (M8.0) and the 1923 Kanto earthquake (M7.9). The vertical proximity of this down going lithospheric plate is of concern because the greater Tokyo urban region has a population of 42 million and is the center of approximately 40 % of the nation's economic activities. A M7+ earthquake in this region at present has high potential to produce devastating loss of life and property with even greater global economic repercussions.The M7+ earthquake is evaluated to occur with a probability of 70 % in 30 years by the Earthquake Research Committee of Japan.We started the Special Project for Earthquake Disaster Mitigation in Tokyo metropolitan areas, a project to improve information needed for seismic hazards analyses of the largest urban centers. Under the project we will deploy a 400-sation dense seismic array in metropolitan Tokyo and Kanto, referred to as the Metropolitan Seismic Observation network (MeSO-net) in next 4 years. The target area of the present project is unique in tectonic setting because two oceanic plates, Philippine Sea plate (PSP) and Pacific plate (PAC), are subducting beneath the Kanto and also a volcanic arc, Izu-Bonin arc, is colliding with Honshu arc. The situation makes the tectonics complicated: there are both zones of smooth subduction and collision of the oceanic plate with the landward plate, either the Eurasian plate or the North American plate. Furthermore, the PSP encounters the PAC at shallow depth in the eastern Kanto region. The newly developing MeSO-net will contribute to understand the generation mechanism associated with the plate subduction and collision. Assessment in Kanto of the seismic hazard requires identification of all significant faults and possible earthquake scenarios and rupture behavior, regional characterizations of the PSP geometry and the overlying Honshu arc physical properties. Our study addresses (1) improved regional characterization of the PSP geometry based on new deep seismic reflection profiles (Sato etal.,2005), reprocessed off-shore profiles (Kimura et al.,2005), and a dense seismic array in the Boso peninsula (Hagiwara et al., 2006) and (2) identification of collision of internal heterogeneity (Wu et al., 2007). We compile these results and present a new model which will be verified by data from the planned MeSO-net. We present a relatively high resolution tomographic image from so far obtained data to show a low velocity zone which suggests a possible internal failure of the slab; a source region of the M7+ intra-slab earthquake. Our study contributes a new assessment of the seismic hazard in the Tokyo metropolitan area.
UR: http://www.eri.u- tokyo.ac.jp/shuto/EN/index.html
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
DE: 7218 Lithosphere (1236)
DE: 7270 Tomography (6982, 8180)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
DE: 8180 Tomography (6982, 7270)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting