Variations in the thermal conductivities of surface sediments in the Nankai subduction zone off Tokai, central Japan
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ORIGINAL RESEARCH PAPER
Variations in the thermal conductivities of surface sediments in the Nankai subduction zone off Tokai, central Japan Shusaku Goto • Tomonobu Mizoguchi Ryo Kimura • Masataka Kinoshita • Makoto Yamano • Hideki Hamamoto
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Received: 26 December 2011 / Accepted: 23 July 2012 Ó Springer Science+Business Media B.V. 2012
Abstract We investigated the relationship between variations in the thermal conductivity of surface sediments and the topography in the Nankai subduction zone off Tokai, central Japan, the easternmost part of the Nankai subduction zone, which has an accretionary prism with varied topography. We analyzed sediment thermal conductivity data obtained from the trough floor and accretionary prism. Variations in the thermal conductivity of sediments were related to the topographic features formed by accretionary prism development. Thermal conductivities of 1.1 W/m K were measured on the trough floor where thick terrigenous turbidites have been deposited. The thermal conductivity of Nankai Trough floor sediments decreases from northeast to southwest along the trough, probably because of the decreased grain size and/or changes in sediment mineral composition. High thermal conductivities (C1.0 W/m K) were measured in fault scarps on the accretionary prism. A landward increase in these values on the prism may be
explained by decreased porosity of the sediments attributable to tectonic deformation during accretionary prism development. At the base of the fault scarp of the frontal thrust, low thermal conductivities (\0.9 W/m K) were measured, likely reflecting the high porosity of the talus deposits. Low thermal conductivity (0.9 W/m K) was also measured in slope basins on the accretionary prism, likely also related to the high porosity of the sediments. Our results demonstrate that, for accurate heat flow measurement in an area of varied topography, the geothermal gradient and the thermal conductivity of the sediments must be measured within regions with similar topographic features. Keywords Thermal conductivity Topographic feature Nankai subduction zone Nankai Trough Accretionary prism Turbidite Heat-pulse method
S. Goto (&) Institute for Geo-Resources and Environment, National Institute of Advanced Industrial Science and Technology, AIST Tsukuba Central 7, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8567, Japan e-mail: [email protected]
Present Address: M. Kinoshita Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, 200 Monobe-otsu, Nankoku, Kochi 783-8502, Japan
T. Mizoguchi System Intech Co., Ltd., 3-20-8 Shibaura, Minato-ku, Tokyo 108-0023, Japan
M. Yamano Earthquake Research Institute, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan
R. Kimura Global Ocean Development Inc., 1-13-8 Kamiookanishi, Konan-ku, Yokohama, Kanagawa 233-0002, Japan
H. Hamamoto Center for Environmental Science in Saitama, 914 Kamitanadare, Kazo, Saitama 347-0115, Japan
M. Kinoshita Institute for Research on Earth Evolution, Japan
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