Japan Geoscience Union Meeting 2015

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Oral

Symbol M (Multidisciplinary and Interdisciplinary) » M-IS Intersection

[M-IS35] Why is this planet to be the Earth? -the role of water

Sun. May 24, 2015 2:15 PM - 4:00 PM 201A (2F)

Convener:*Nobukazu Seama(Department of Planetology, Graduate School of Science, Kobe University), Yoshiyuki Tatsumi(Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology), Keiji Ohtsuki(Graduate School of Science, Kobe University), Takashi Nakagawa(JAMSTEC/MAT), Ikuo Katayama(Department of Earth and Planetary Systems Science, Hiroshima University), Gou Fujie(Japan Agency for Marine-Earth Science and Technology), Akiko Nakamura(Graduate School of Science, Kobe University), Chair:Ikuo Katayama(Department of Earth and Planetary Systems Science, Hiroshima University), Nobukazu Seama(Department of Planetology, Graduate School of Science, Kobe University)

3:45 PM - 3:48 PM

[MIS35-P01] A resistivity model of the back arc region in the NE Japan arc based on marine and island MT data

3-min talk in an oral session

*Hiroshi ICHIHARA1, Noriko TADA1, Kiyoshi BABA2, Takafumi KASAYA1, Masahiro ICHIKI3, Toshiki KAIDA3, Yasuo OGAWA4 (1.Japan Agency for Marine-Earth Science and Technology, 2.Earthquake Research Institute, the University of Tokyo, 3.Research Center for Prediction of Earthquakes and Volcanic Eruptions, Tohoku University, 4.Volcanic Fluid Research Center, Tokyo Institute of Technology)

Keywords:NE Japan arc, Japan Sea, Back arc, magnetotelurics, resisitivity, Geofluid

Distribution of physical properties in the back-arc in NE Japan subduction zone have not been understood because the area is mostly located beneath the sea floor. In this study, we estimated electrical resistivity distribution in this area based on electromagnetic data obtained on the seafloor and islands in the eastern part of Japan Sea. The ocean bottom EM data were obtained with 6 ocean bottom electro-magnetometers (OBEMs) between April and August 2013 by MR13-02A and NT13-18 JAMSTEC scientific cruises. The island data were acquired in the 3 islands in the Japan Sea (Tobishima, Awashima and Sado islands) between April and October 2013. These recorded time-series data were converted to a frequency-domain impedance tensor based on the BIRRP program (Chave and Thomson, 2004). As results, high-quality MT responses and geomagnetic tippers in both the trench and back-arc areas. The phase tensor ellipses (Caldwell et al. 2004) indicates high Φmax (>65 degrees) and Φmin (>50 degrees) in the long periods (>8000 seconds) implying conductive zone in the deep area. The ellipses in the short period show strong contrast between western part (Yamato basin) and eastern part of study area, which indicate heterogeneity in crustal structure. Then we also inverted the MT impedances into resistivity distribution based on the 3-D inversion code (Tada et al., 2012) after the correction local topographic effect. The inversion result shows a significant conductor above the subducting Pacific plate. A surface conductor is also estimated beneath the Yamato Basin. These features are consistent to the phase tensors discussed above. The deep conductor may be related to dehydration in subducting Pacific Plate and convention in the mantle wedge. The surface conductor may reflect sediments rocks formed during back-arc opening in Miocene.