Development of hydrothermal high-velocity rotary shear apparatus in Kochi, Japan: towards understanding fault slip behavior in the seismogenic zone environment

In Kochi, JAMSTEC, Japan, we have developed rotary shear apparatuses to understand fault slip behavior of geologic materials at coseismic slip rates. However, coseismic fault behavior under hydrothermal conditions has remained challenging to reproduce in the laboratory. To address this issue, we developed a novel apparatus (HDR: hydrothermal rotary shear apparatus) in 2017, which is capable of high-velocity slip (~2 m/s) at temperatures of up to 600 ℃ and pore fluid pressures of up to 120 MPa. Using this apparatus, we have successfully carried out hydrothermal high-velocity friction experiments on various types of materials, including bare gabbro surfaces and gouges derived from quartz, gabbro, granite, olivine, calcite, and clay minerals under a wide range of pressure-temperature-velocity conditions. The experimental data obtained under hydrothermal conditions are sometimes markedly different from those typically observed in room-temperature experiments due to dynamic changes in fluid properties and chemical reactions in supercritical water. Further understanding of coupled interactions between fault slip, frictional heat, fluid properties, chemical reactions, etc. under hydrothermal conditions will be essential for constraining fault slip behavior in seismogenic-zone settings. In this presentation, we introduce some of our latest results obtained using HDR.