HR: 0800h
AN: V11B-1430    [Abstracts]
TI: Seismic exploration of Fuji volcano with active sources in 2003
AU: * Oikawa, J
EM: oikawa@eri.u-tokyo.ac.jp
AF: ERI, Univ. Tokyo, 1-1 Yayoi 1, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Kagiyama, T
EM: kagiyama@eri.u-tokyo.ac.jp
AF: AVL, Kyoto Univ., Choyo-cho, Aso-gun, Kumamoto, 869-1404 Japan
AU: Tanaka, S
EM: tanaka@aob.geophys.tohoku.ac.jp
AF: Graduate School of Science, Tohoku Univ., Aramaki, Aoba, Aoba-ku, Sendai, Miyagi, 980-8578 Japan
AU: Miyamachi, H
EM: miya@seis.kagoshima-u.ac.jp
AF: Faculty of Science, Kagoshima Univ., 1-21-35, Gunmoto, Kagoshima, Kagoshima, 890-0065
AU: Tsutsui, T
EM: tom@geophys.mine.akita-u.ac.jp
AF: Faculty of Engineering and Resource Science, Akita Univ., 1-1 Tegata Gakuenmachi, Akita, Akita, 010-8502 Japan
AU: Ikeda, Y
EM: yasushi.ikeda-a@met.kisho.go.jp
AF: Japan Meteorological Agency, 1-3-4 Otemachi, Chiyoda-ku, Tokyo, 100-8122 Japan
AU: Katayama, H
EM: hkatayama@met.kishou.go.jp
AF: Japan Meteorological Agency, 1-3-4 Otemachi, Chiyoda-ku, Tokyo, 100-8122 Japan
AU: Matsuo, N
EM: matsuwo@sevo.kyushu-u.ac.jp
AF: SEVO, Kyushu Univ., 2-5643-29 Niiyama, Shimabara, Nagasaki, 855-0843 Japan
AU: Oshima, H
EM: oshima@uvo.sci.hokudai.ac.jp
AF: UVO, Hokkaido Univ., 142 Tachika, Sobetsu-cho, Usu, Hokkaido, 052-0106 Japan
AU: Nishimura, Y
EM: nishi@eos.hokudai.ac.jp
AF: UVO, Hokkaido Univ., 142 Tachika, Sobetsu-cho, Usu, Hokkaido, 052-0106 Japan
AU: Yamamoto, K
EM: yamamoto@svo.dpri.kyoto-u.ac.jp
AF: SVO, Kyoto Univ., 1722-19, Yokoyama, Tsurusaki, Sakurajima, Kagoshima, 891-1419 Japan
AU: Watanabe, T
EM: watanabe@seis.nagoya-u.ac.jp
AF: Graduate School of Environmental Studies, Nagoya Univ., Furo-cho, Chikusa-ku, Nagoya, Aichi, 464-8602 Japan
AU: Yamazaki, F
EM: yamazaki@seis.nagoya-u.ac.jp
AF: Graduate School of Environmental Studies, Nagoya Univ., Furo-cho, Chikusa-ku, Nagoya, Aichi, 464-8602 Japan
AB: Fuji volcano (altitude 3,776 m) is the largest basaltic stratovolcano in Japan. In late August and early September 2003, seismic exploration was conducted around Fuji volcano by the detonation of 500 kg charges of dynamite to investigate the seismic structure of that area. Seismographs with an eigenfrequency of 2 Hz were used for observation, positioned along a WSW-ENE line passing through the summit of the mountain. A total of 469 observation points were installed at intervals of 250-500 m. The data were stored in memory on-site using data loggers. The sampling interval was 4 ms. Charges were detonated at 5 points, one at each end of the observation line and 3 along its length. The first arrival times at each observation point for each detonation were recorded as data. The P-wave velocity structure directly below the observation line was determined by forward calculation using the ray tracing method [Zelt and Smith, 1992]. The P-wave velocity structure below the volcano, assuming a layered structure, was found to be as follows. (1) The first layer extends for about 40 km around the summit and to a depth of 1-2 km. The P-wave velocity is 2.5 km/s on the upper surface of the layer and 3.5 km/s on the lower interface. (2) The second layer has P-wave velocities of 4.0 km/s on the top interface and 5.5 km/s at the lower interface. The layer is 25 km thick to the west of the summit and 1-2 km thick to the east, and forms a dome shape with a peak altitude of 2000 m directly below the summit. (3) The third layer is 5-12 km thick and has P-wave velocities of 5.7 km/s at the top interface and 6.5 km/s at the lower interface. This layer reaches shallower levels to the east of the summit, corresponding to the area where the second layer is thinner. Mt. Fuji is located slightly back from where the Philippine Sea Plate subducts below the Eurasian plate in association with collision with the Izu Peninsula. Matsuda (1971) suggested that Mt. Fuji lies on the same uplifted body as the Tanzawa Range to the east. This uplifted body is formed by plate subduction and collision with the Izu Peninsula, and is believed to have influence at significant depth. This is considered to be the reason for the change in the geologic structure beneath Fuji volcano from west to east. The dome structure of the bedrock layer (second layer) directly beneath the summit is considered to have formed in the initial period of volcanic activity that formed Mt. Fuji, leading to the subsequent formation of Komitake volcano, Ko-Fuji volcano and the present day Fuji volcano.
DE: 8180 Tomography
DE: 8499 General or miscellaneous
DE: 9320 Asia
DE: 7280 Volcano seismology (8419)
DE: 8150 Plate boundary--general (3040)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting