HR: 0800h
AN: S51A-0136    [Abstracts]
TI: Dense passive seismic survey of Mt. Fuji, Japan during 2002-2004
AU: * Nakamichi, H
EM: hnakamichi@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AU: Watanabe, H
EM: watanabe@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, Univ. Tokyo, 1-1-1 Yayoi, Bunkyo, Tokyo, 113-0032 Japan
AU: Ohminato, T
EM: takao@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, Univ. Tokyo, 1-1-1 Yayoi, Bunkyo, Tokyo, 113-0032 Japan
AB: Mt. Fuji, the most famous and highest volcano in Japan, has a larger eruption rate than most other island-arc volcanoes by one order of magnitude. Mt. Fuji has erupted mostly basaltic products, although it is an island-arc type volcano. These features may be due to the unique tectonic setting of Mt. Fuji, which is located near three converging plates, including the Philippine Sea (PHS) plate. The volcanic front and plate boundary cross near Mt. Fuji. In addition, the region around Mt. Fuji is a zone of crustal collision where the Izu block collides with the Honshu block. The existence of the PHS plate beneath Mt. Fuji has not been determined. Low frequency (LF) earthquakes intensively occurred in September - December 2000 and April - May 2001 at depths of 10 - 20 km beneath Mt. Fuji. However, no other associated volcanic unrest was observed at that time. A passive seismic survey of Mt. Fuji has been conducted to clarify the source mechanisms of the LF earthquakes and to conduct 3D seismic imaging of the subsurface structure. A dense seismic network was deployed around Mt. Fuji in September - December 2002 by scientists and technicians from 6 national universities of Japan. The network includes 28 temporary and 138 permanent seismic stations. Temporary seismic stations are equipped with three-component seismometers including 6 CMG-3T, 7 Trillium and 15 L4-3D. Half of permanent stations are as a part of the Hi-net of NIED. The seismic stations are deployed 2 - 10 km apart with a gradual increase in station spacing away from Mt. Fuji and also densely distributed in the direction NE-SW across Mt. Fuji. We will show an outline of the passive seismic survey of Mt. Fuji and preliminary results of velocity tomography beneath Mt. Fuji. The between the Izu and Honshu blocks, the PHS plate, and volcanic brief results are as follows: (1) High-frequency seismic activity is clearly seen in several regions, including zones of collision activity of the Izu Peninsula; (2) LF earthquakes are also captured with the network and located at depths of 12 - 16 km beneath Mt. Fuji; (3) A shallow high velocity anomaly is seen at depths of 0 - 5 km beneath Mt. Fuji; (4) A low velocity anomaly is seen at depths of 10 - 20 km beneath Mt. Fuji, corresponding to the LF locations.
DE: 8180 Tomography
DE: 8499 General or miscellaneous
DE: 7230 Seismicity and seismotectonics
DE: 7280 Volcano seismology (8419)
DE: 8150 Plate boundary--general (3040)
SC: Seismology [S]
MN: 2004 AGU Fall Meeting