Japan Geoscience Union Meeting 2019

Presentation information

[E] Oral

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

[S-CG48] Science of slow earthquakes: Toward unified understandings of whole earthquake process

Thu. May 30, 2019 10:45 AM - 12:15 PM Convention Hall A (2F)

convener:Satoshi Ide(Department of Earth an Planetary Science, University of Tokyo), Hitoshi Hirose(Research Center for Urban Safety and Security, Kobe University), Kohtaro Ujiie(Graduate School of Life and Environmental Sciences, University of Tsukuba), Takahiro Hatano(Earthquake Research Institute, University of Tokyo), Chairperson:Kohtaro Ujiie(Graduate School of Life and Environmental Sciences, University of Tsukuba), Simon Wallis(Nagoya University)

12:00 PM - 12:15 PM

[SCG48-27] Frictional properties of opal gouge at low-temperature hydrothermal conditions and their implications for seismogenic faulting along subduction-zone megathrusts

*Kyuichi Kanagawa1, Tomoya Nakanishi2, Morito Kuwana3, Michiyo Sawai1, Takehiro Hirose4 (1.School of Science, Chiba University, 2.Graduate School of Science and Engineering, Chiba University, 3.Faculty of Science, Chiba University, 4.Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology)

Keywords:frictional properties, opal gouge, low-temperature hydrothermal conditions

We conducted a series of triaxial friction experiments on opal gouge at low-temperature (≦200°C) hydrothermal conditions, in order to address the change in frictional stability along subduction-zone megathrusts. The results revealed frictional properties of opal gouge dependent on temperature (T), displacement (V) or pore water presure (Pp), as described below.

When fitted by the rate- and state-friction constitutive law, friction parameter a does not change much with T, V or Pp, while friction parameter b increases, and resultantly (a b) value decreases with increasing T, decreasing V or increasing Pp. Microstructural observations revealed that densification and coalescence of gouge particles occurred at higher T, suggesting the operation of pressure solution. Thus increasing activity of thermally activated pressure solution with increasing T, decreasing V or increasing Pp promotes gouge lithification to increase frictional strength, by which (a b) value decreases to <0, and thereby the transition from aseismic faulting to seismic faulting along subduction-zone megathrusts. Our results also imply that increasing Pp at that transition region where (a b) ≈0 would decrease (a b) value to <0, and hence promote slow seismic faulting with small negative (a b) values, which is consistent with highVP/VS ratios observed in the regions of slow earthquakes.