HR: 1340h
AN: GP33B-1255    [Abstracts]
TI: Preliminary Report on Seafloor Electromagnetic Observations off Tottori in the Sea of Japan
AU: Oshiman, N
EM: osman@eqh.dpri.kyoto-u.ac.jp
AF: Disaster Prevention Research Institute, Kyoto University, Gokasyo, Uji, 611-0011, Japan
AU: Hiroaki Toh, H
EM: toh@sci.u-toyama.ac.jp
AF: University of Toyama, Gofuku 3190, Toyama, 930-8555, Japan
AU: Kasaya, T
EM: tkasa@jamstec.go.jp
AF: JAMSTEC, Natsushima 2-15, Yokosuka, 237-0061, Japan
AU: * Yoshimura, R
EM: ryokei@eqh.dpri.kyoto-u.ac.jp
AF: Disaster Prevention Research Institute, Kyoto University, Gokasyo, Uji, 611-0011, Japan
AU: Shimoizumi, M
EM: mshimo@kyushu-pc.ac.jp
AF: Kyushu Polytechnic College, hii 1996-1, Kokuraminami, Kitakyushu, 802-0985, Japan
AU: Shiozaki, I
EM: shiozaki@cv.tottori-u.ac.jp
AF: Tottori University, Koyama 4-101, Tottori, 680-8553, Japan
AU: Fujii, I
EM: fujii-kanda@met.kishou.go.jp
AF: The Kakioka Magnetic Observatory, JMA, Kakioka 595, Ishioka, 315-0116, Japan
AU: Shingai, M
EM: mshimo@kyushu-pc.ac.jp
AF: Kyushu Polytechnic College, hii 1996-1, Kokuraminami, Kitakyushu, 802-0985, Japan
AU: Yamaguchi, S
EM: yanchi@kobe-u.ac.jp
AF: Kobe University, Rokkodai 1-1, Nada-ku, Kobe, 657-8501, Japan
AU: Murakami, H
EM: murakami@cc.kochi-u.ac.jp
AF: Kochi University, Akebono 2-5-1, Kochi, 780-8520, Japan
AU: Yamazaki, A
EM: ayamazak@mri-jma.go.jp
AF: Meteorological Research Institute, JMA, Nagamine 1-1, Tsukuba, 305-0052, Japan
AU: Uyeshima, M
EM: uyeshima@eri.u-tokyo.ac.jp
AF: ERI, University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo, 113-0032, Japan
AB: Seafloor electromagnetic observations were made off Tottori in the Sea of Japan together with MT measurements in the land region, in order to investigate the rsistivity structure in the San-in region, the Tottori and surrounding region in the northern part of Chugoku district, southwestern Japan, where epicenters of microearthquakes are remarkably distributing within a line belt with a width of about 4-9 km along the coastal line of the Sea of Japan. The depths of the hypocenters are located up to about 10km depths. In the seismic belt, several large earthquakes of M6.2-7.4 took place in 1943, 1983 and 2000. Moreover, quaternary volcanoes, such as Daisen volvano and Oginosen volcano are also located in the seismic belt. Wide-band magnetotelluirc (MT) observations have been made along survey profiles of almost N-S direction in the San-in region since 1998, to investigate heterogeneity in the crustal electrical resistivity structure. Through those wide-band MT measurements we found the low resistive region beneath seismogenic zone of the high seismicity belt on each MT profile line, and that the upper resistive crust corresponds to the seismogenic zone in the Tottori and northern Hyogo region. The low resistive region found along each wide-band MT profile seems to form a conductive zone extending in the almost E-W direction beneath the seismic belt extending in the almost same direction of the conductor. This result strongly suggests the existence of crustal fluid beneath the seismogenic zone in the focal area. The survey lines should be extended toward the Sea of Japan and longer period MT data on the land area should be obtained, in order to investigate deeper resistivity structure and clarify the relationship between subducting Philippine Sea plate and the deeper resistivity structure beneath the San-in region. Therefore, we carried out seafloor and longer period MT surveys on land . It is important to analyze both data sets to obtain high accuracy resistivity strucure. OBEMs and OBEs were deployed and recovered in 2006 and 2007 to obtain seafloor geoelectromagnetic data beneath the off-Tottori of the Sea of Japan in the San-in region. High-quality MT data from the seafloor array, together with those of three additional land sites in the San-in region, is analyzing now. We will show the outlines of the observation and the preliminary results along the first survey line in presentation.
DE: 1515 Geomagnetic induction
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting