Japan Geoscience Union Meeting 2016

Presentation information


Symbol S (Solid Earth Sciences) » S-CG Complex & General

[S-CG63] Dynamics in mobile belts

Mon. May 23, 2016 5:15 PM - 6:30 PM Poster Hall (International Exhibition Hall HALL6)

Convener:*Yukitoshi Fukahata(Disaster Prevention Research Institute, Kyoto University), Norio Shigematsu(Research Institute of Earthquake and Volcano Geology, Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology), Aitaro Kato(Graduate School of Environmental Studies, Nagoya University), Hikaru Iwamori(Geochemical Evolution Research Program, Japan Agency for Marine-Earth Science and Technology), Yasutaka Ikeda(Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo), Toru Takeshita(Department of Natural History Sciences, Graduate School of Science, Hokkaido University)

5:15 PM - 6:30 PM

[SCG63-P03] Electrical conductivity change in a brine-saturated granitic rock under uni-axial compression

*Ryo Sawaki2, Misaki Morimoto2, Tohru Watanabe1 (1.Gradudate School of Science and Engineering, University of Toyama, 2.Faculty of Science, University of Toyama)

Keywords:electrical conductivity, stress, anisotropy

Geophysical observations have shown that fluids exist pervasively within the crust. Fluids fill intergrain cracks (open grain boundaries) and intra-grain cracks at the upper and middle crust conditions. Since the opening of cracks strongly depends on the stress state, electrical conductivity should be anisotropic under a stress state. We have conducted uni-axial compression tests on brine-saturated granitic rocks and studied the change in electrical conductivity in the directions parallel and perpendicular to the compression.
The loading system is composed of a hand press (Maximum load: 20 kN), a load cell and stainless steel end-pieces. A fine grained (100-500 mm) biotite granite (Aji, Kagawa Pref., Japan) was selected as a rock sample for its small grain size and textural uniformity. A cube sample with the edge length of 25 mm was filled with 0.1 M KCl aqueous solution and loaded up to 20 MPa. Electrical impedance was continuously monitored during a compression test with two-electrode method (Ag-AgCl electrodes).
Electrical conductivity decreased with increasing axial stress in the directions parallel and perpendicular to the compression. When the axial stress was increased from 0 MPa to 5 MPa, the magnitude of decrease in conductivity was 2% and 4% in the direction parallel and perpendicular to the compression, respectively. The decrease in conductivity was much smaller than that observed in hydrostatic compression tests (e.g., Watanabe and Higuchi, 2015). The decrease in conductivity must be caused by the closure of cracks, which were perpendicular or subperpendicular to the compression.