Japan Geoscience Union Meeting 2018

Presentation information

[JJ] Oral

S (Solid Earth Sciences) » S-SS Seismology

[S-SS15] Fault Rheology and Earthquake Physics

Mon. May 21, 2018 10:45 AM - 12:15 PM A07 (Tokyo Bay Makuhari Hall)

convener:Hideki Mukoyoshi(Department of Geoscience Interdisciplinary Graduate School of Science and Engineering, Shimane University), Wataru Tanikawa(Japan Agency for Marine-Earth Science and Technology, Kochi Instutute for Core Sample Research), Takanori Matsuzawa(国立研究開発法人 防災科学技術研究所, 共同), Keisuke Yoshida(Tohoku University), Chairperson:Tanikawa Wataru, Yoshida Keisuke(東北大学大学院理学研究科 地球物理学専攻)

11:30 AM - 11:45 AM

[SSS15-15] Effects of dissolution−precipitation creep on the frictional properties of opal gouge at low-temperature hydrothermal conditions

*Nakanishi Tomoya2, Kyuichi Kanagawa1, Michiyo Sawai1 (1.Graduate School of Science, Chiba University, 2.Faculty of Science, Chiba University)

Keywords:frictional properties, opal gouge, low-temperature hydrothermal conditions, dissolution−precipitation creep

In order to examine the effects of dissolution−precipitation creep on the frictional properties at low-temperature hydrothermal conditions, we conducted triaxial friction experiments on opal gouge at a confining pressure of 150 MPa, a pore water pressure of 50 MPa, and temperatures (T) ranging from room T to 200°C, and at displacement rates (V) changed stepwise among 0.1155, 1.155 and 11.55 μm/s. We then fitted the friction data for each step change in V by the rate- and state-dependent friction constitutive law, and obtained the optimized (ab) value, i.e., an indicator of frictional stability, at each V.

The results show that steady-state friction coefficient μss increases with increasing T, from 0.64 at room T to 0.67 at 200°C, which is consistent with slip hardening behavior observed at higher Ts. Microstructural observations reveal that significant grain interlocking and porosity reduction occur in the gouge layer sheared at higher Ts. Thus increasing gouge lithification with increasing T, which is promoted by thermally activated dissolution–precipitation creep, is likely responsible for increasing μss with increasing T.

Our results also show that (ab) value tends to decrease with increasing T or decreasing V at T ≧50°C. Decreasing (ab) value with decreasing V at a given T is likely due to increasing gouge lithification and hence μss with decreasing V, which is promoted by dissolution−precipitation creep favored at lower Vs. At a given V, a value does not change much while b value increases with increasing T, which results in decreasing (ab) value with increasing T. Increasing b value with increasing T implies that more strength recovery occurs when V is stepped down, which is also ascribed to increasing activity of dissolution−precipitation creep. Because (ab) value does not change with V at room T, dissolution−precipitation creep was not active at room T.

At a given V, the transition from ab > 0 to ab < 0 occurs with increasing T, but the transition T is also dependent on V, because (ab) value is dependent on both T and V as described above; T <50°C at V = 0.1155 μm/s, 50°C< T <100°C at V = 1.155 μm/s, and T >100°C at V = 11.55 μm/s. Our results suggest that increasing activity of dissolution−precipitation creep with increasing T or decreasing V promotes decreasing (ab) value and hence the transition from stable aseismic faulting with ab > 0 to unstable, possible seismic faulting with ab < 0.