HR: 1340h
AN: S23A-1121    [Abstracts]
TI: Marine magnetotelluric survey of the crustal structure, off the Tokai region, Japan
AU: * Sakata, G
EM: genki@t03.mbox.media.kyoto-u.ac.jp
AF: Geophysics Lab, Department of Civil and Earth Resources Engineering, Faculty of Engineering, Kyoto University, Kyotodaigaku-katsura, Nishigyo-ku, Kyoto, 615-8540, Japan
AU: Goto, T
AF: Japan Agency for Marine-Earth Science and Technology, 2-15, Natsushima, Yokosuka, Kanagawa, 237-0061, Japan
AU: Kasaya, T
AF: Japan Agency for Marine-Earth Science and Technology, 2-15, Natsushima, Yokosuka, Kanagawa, 237-0061, Japan
AU: Kinoshita, M
AF: Japan Agency for Marine-Earth Science and Technology, 2-15, Natsushima, Yokosuka, Kanagawa, 237-0061, Japan
AU: Onishi, K
AF: Geophysics Lab, Department of Civil and Earth Resources Engineering, Faculty of Engineering, Kyoto University, Kyotodaigaku-katsura, Nishigyo-ku, Kyoto, 615-8540, Japan
AU: Mikada, H
AF: Geophysics Lab, Department of Civil and Earth Resources Engineering, Faculty of Engineering, Kyoto University, Kyotodaigaku-katsura, Nishigyo-ku, Kyoto, 615-8540, Japan
AB: Resistivity structure below the sea floor has useful information on the characteristics in the generation mechanism of earthquake, and it also has a key to investigate the distribution of natural resources such as oil and methane hydrate since they all could be related to interstitial fluid migration. To clarify the crustal and mantle resistivity structures around the Enshu Basin, off the Tokai region, Japan, marine magnetotelluric(MT) soundings were carried out. The Enshu Basin is located where unconsolidated sediments on the subducting Philippine Sea plate are underplated to the southwest Japan arc above a mega-thrust seismogenic zone. Five ocean bottom electro- magnetometers (OBEM) and four ocean bottom electrometers (OBE) were used in this survey to measure two marine electromagnetic field data sets over the subducting Philippine Sea plate for a couple of periods, one from January to February and the other April to July in 2007. Both time series data of horizontal electric and magnetic fields were obtained at five sites, and only horizontal electric field data were obtained four sites. In this survey, we recorded raw electromagnetic signals with 8 Hz sampling rate and estimated MT responses at the region after resampling the time series data with 0.1 Hz sampling rate. Careful de-spiking and noise reduction to maximize the coherence of the data at the five sites led us to obtain apparent resistivity structure. Our two-dimensional inversion model demonstrates the electrical resistivity structure in both the crust and mantle, and resembles to a seismic reflection section. In this study, we performed TE-mode MT inversion. The preliminary result taking in geographical features illustrates outlines of the characteristic resistivity structure. This result gives us explanations by what the elements and conditions the earthquake is caused in the region.
DE: 0629 Inverse scattering
DE: 0925 Magnetic and electrical methods (5109)
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3006 Marine electromagnetics
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
SC: Seismology [S]
MN: 2007 Fall Meeting