HR: 10:20h
AN: T31H-01    [PDF]
TI: Marine Magnetotelluric Experiment for the Mariana Subduction System
AU: Seama, N
EM: seama@kobe-u.ac.jp
AF: Research Center for Inland Seas, Kobe University, 1-1 Rokkodai, Nada, Kobe, 657-8501 Japan
AU: * Baba, K
EM: kiyoshib@jamstec.go.jp
AF: Institute for Frontier Research on Earth Evolution, Japan Marine Science and Technology Center, 2-15, Natsushima, Yokosuka, Kanagawa, 237-0061 Japan
AU: Goto, T
EM: tgoto@jamstec.go.jp
AF: Deep Sea Research Department, Japan Marine Science and Technology Center, 2-15, Natsushima, Yokosuka, Kanagawa, 237-0061 Japan
AU: Ichiki, M
EM: ichiki@jamstec.go.jp
AF: Institute for Frontier Research on Earth Evolution, Japan Marine Science and Technology Center, 2-15, Natsushima, Yokosuka, Kanagawa, 237-0061 Japan
AU: Kasaya, T
EM: tkasa@jamstec.go.jp
AF: Deep Sea Research Department, Japan Marine Science and Technology Center, 2-15, Natsushima, Yokosuka, Kanagawa, 237-0061 Japan
AU: Nogi, Y
EM: nogi@nipr.ac.jp
AF: National Institute of Polar Research, 1-9-10 Kaga Itabashi, Tokyo, 173-8515 Japan
AU: Schwalenberg, K
EM: katrin@physics.utoronto.ca
AF: University of Toronto, 60 St.Geogre St., Toronto, ON M5S 1SA Canada
AU: Iwamoto, H
EM: 022s403n@y02.kobe-u.ac.jp
AF: Graduate School of Science and Technology, Kobe University, 1-1 Rokkodai, Nada, Kobe, 657-8501 Japan
AU: Tada, N
EM: noriko@kobe-u.ac.jp
AF: Graduate School of Science and Technology, Kobe University, 1-1 Rokkodai, Nada, Kobe, 657-8501 Japan
AU: Matsuno, T
EM: 021s421n@y02.kobe-u.ac.jp
AF: Graduate School of Science and Technology, Kobe University, 1-1 Rokkodai, Nada, Kobe, 657-8501 Japan
AU: Syehiro, K
EM: suyehiro@jamstec.go.jp
AF: Deep Sea Research Department, Japan Marine Science and Technology Center, 2-15, Natsushima, Yokosuka, Kanagawa, 237-0061 Japan
AU: Utada, H
EM: utada@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1, Yayoi, Bunkyo, Tokyo, 113-0032 Japan
AB: A marine magnetotelluric (MT) experiment was carried out in the central Mariana area from 2001 to 2002 to elucidate electrical structure of the subduction-arc-back arc system. The electrical conductivity is mainly subject to temperature, partial melt, and volatiles such as water in the mantle. 10 ocean bottom electromagnetometers (OBEMs) were deployed along the line crossing the central Mariana trough during the cruise YK01-11 in October 2001. This OBEM array covers from the Pacific plate to Parece-Vela basin through Mariana trough. 5 of them were successfully recovered during the cruise using R/V M. Ewing in April 2002 and during the cruise KR02-14 in October 2002. The MT analysis has been carried out using the data at the 5 sites and another 3 sites. These additional data were collected by past experiments (Filloux, 1983; Seama et al., 2003) and the sites locate near the survey line of our experiment. Goto et al. (2003) analyzed 3 MT data sets around Marina islands and showed no thick conductive layer in the mantle wedge beneath the arc and fore arc region. In this study, we analyzed the 5 MT data sets in Mariana trough and Parece-Vela basin, so far. The MT responses were first corrected for the topographic effect which is significant especially for marine MT data. Then, the corrected responses are separated to TE and TM modes and then inverted in two-dimensional (2-D) model space independently. The responses for the each mode is sensitive to electric current flowing either parallel or perpendicular to the 2-D strike. Obtained 2-D models for both modes have common feature that the mantle resistivity decrease from several hundreds or more to several tens or less ohm-m at the depth of 60-70 km. The mantle below 60-70 km is, however, more conductive for the model of the TM inversion than that of the TE inversion. This may indicate anisotropy that is more conductive in the direction along the profile. These features are seen in the mantle beneath southern East Pacific Rise and interpreted that the upper resistive mantle is result from drying out of olivine due to partial melting and lower conductive and anisotropic feature is manifestation of the alignment of olivine crystals to the mantle flow direction in wet condition (Baba et al., 2003). The same interpretations may be possible for the Mariana back arc basin. In addition, further analysis is now on going, which we invert all the data to obtain the model for the whole 2-D transection. The result will be presented in the meeting.
DE: 1515 Geomagnetic induction
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 3914 Electrical properties
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8150 Plate boundary--general (3040)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting