HR: 0800h
AN: S31A-0196    [Abstracts]
TI: Crustal heterogeneities deduced from wideband and Network MT measurements around the Niigata-Kobe Tectonic Zone, Chubu District, Japan
AU: * Yoshimura, R
EM: ryokei@eqh.dpri.kyoto-u.ac.jp
AF: Disaster Prevention Research Institute, Kyoto University, Gokasyo, Uji, Kyoto, 611-0011, Japan
AU: Uyeshima, M
EM: uyeshima@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, the University of Tokyo, 1-1-1 Yayoi, Bunkyo, Tokyo, 113- 0032, Japan
AU: Oshiman, N
EM: osman@eqh.dpri.kyoto-u.ac.jp
AF: Disaster Prevention Research Institute, Kyoto University, Gokasyo, Uji, Kyoto, 611-0011, Japan
AU: Toh, H
EM: toh@sci.u-toyama.ac.jp
AF: Department of Earth Sciences, University of Toyama, 3190, Gofuku, Toyama, 930-8555, Japan
AU: Ogawa, Y
EM: oga@ksvo.titech.ac.jp
AF: Volcanic Fluid Research Center, Tokyo Institute of Technology, 2-12-1, Ookayama, Meguro, Tokyo, 152-8551, Japan
AU: Ogawa, T
EM: ogawa@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, the University of Tokyo, 1-1-1 Yayoi, Bunkyo, Tokyo, 113- 0032, Japan
AU: Yamaguchi, S
EM: yanchi@kobe-u.ac.jp
AF: Department of Earth and Planetary Sciences, Kobe University, 1-1, Rokkodai, Nada, Kobe, 657-8501, Japan
AU: Resistivity structure in the NKTZ, R G
EM: ryokei@eqh.dpri.kyoto-u.ac.jp
AB: Wideband magnetotelluric (MT) soundings were carried out around the concentrated deformation zone, Chubu District, Japan (NKTZ: Niigata-Kobe Tectonic Zone, e.g. Sagiya et al., 2000). The NKTZ becomes one of important target areas in "the 2nd new Program of and Observation for Earthquake Prediction" (Hirata, 2004). A multidisciplinary research around the NKTZ, especially the Atotsugawa fault, using dense GPS, seismological observations and investigation of crustal resistivity structure has been started since 2004. In Oct. 2004, we obtained the MT data at 30 sites across the central part of the NKTZ in which the Ushikubi, Mozumi-Sukenobu, Atotsugawa, Takayama-Oppara faults are located. Apparent resistivity and phase in TM mode, phase in TE mode and tipper were used for two-dimensional inversions. Obtained model shows following inhomogeneities in the middle and lower crust. (A) Beneath the NKTZ, an almost 10km thick resistive block is detected. (B) This resistive block gets thin gradually to approximately 5km thickness at the Atotsugawa and Mozumi-Sukenobu faults which are centrally located in the NKTZ. (C) In the lower crust, beneath these faults, conductors are found, respectively. These conductors may represent fluids-filled week zones (e.g. Iio et al., 2002). To reveal heterogeneity along the fault plane, we carried out MT survey along the Atotsugawa fault in Oct. 2005. A seismic gap and a creep-like crustal movement were observed along the Atotsugawa fault (e.g. Ito et al., 2007; Geographical Survey Institute, Japan, 2002). Obtained preliminary inversion result shows lateral inhomogeneity correlated with heterogeneity in seismicity along the fault. The relatively low seismicity region on the Atotsugawa fault plane seems to be imaged as resistive body. In addition to these conventional wideband MT surveys, we have performed Network-MT surveys across and along the NKTZ since Dec. 2005, in order to determine the deeper structure down to the upper mantle in the wider area of Chubu district. The EM response functions across the NKTZ from Noto Peninsula to the south of Nagano prefecture show remarkable phase value enhancements in the longest period range (about 10000 s) in Noto area and in the shortest period range (about 10 s) in the NKTZ. The former and the latter probably indicate upper mantle and middle crust conductors, respectively. A 2-D inversion result along the Atotsugawa Fault indicates that seismogenic zone shallower than 10km is relatively resistive and the slipping zone beneath it down to 20km is relatively conductive. This feature is almost the same as that obtained from the conventional MT survey. Beneath the conductive zone, a moderately resistive layer is revealed.
DE: 0925 Magnetic and electrical methods (5109)
DE: 1209 Tectonic deformation (6924)
DE: 5109 Magnetic and electrical properties (0925)
SC: Seismology [S]
MN: 2007 Fall Meeting