5:15 PM - 7:15 PM
[SCG45-P02] Torque-controlled shearing experiments on smectite gouge under normal stress loading
Keywords:Friction experiment, Torque control, Smectite
The low friction strength of smectite minerals (e.g. montmorillonite) is believed to have a significant role in the control of the rheology and stability of faults that contain a high proportion of clay. Smectite is abundant in the upper part of the upper crust, and it is known to be present in the slip plane of faults. Specifically, IODP drilling has recovered the shallow part of the plate boundary fault in the Japan Trench, and it has been revealed that smectite accounts for 60-80% of this plate boundary fault. The frictional strength of smectite is commonly understood to be weaker than that of other rock-forming minerals. Consequently, it has been correlated with the weakness of some faults, including shallow subduction plate boundaries. Nevertheless, it is recognised that, in a hydrated state and under low confining pressure, smectite exhibits thixotropic properties as a clay suspension, and its macroscopic strength is time-dependent. This property has been well confirmed in tests using a rheometer, but studies under confining pressure have not been sufficient, and in general, the behaviour in the in situ environment where earthquakes occur is not clear.
In this study, we focus on the unique characteristics of smectite and conduct shearing experiments using a torque-controlled friction apparatus. The high-speed/low-speed rotary friction apparatus installed in JAMSTEC Kochi can conduct friction experiments under conditions of increased temperature and pressure. It has recently been upgraded to include a mode that controls the rotation speed, rotation position and torque. This development has enabled experiments to be conducted under normal stress loading that involve increasing or maintaining torque, such as in a rheometer, which was previously challenging to perform. The experiments are conducted using a sample composed of smectite and quartz, with the addition of water. The temperature is maintained at room temperature, and the pressure conditions are set to 5 MPa of fluid pressure and an effective normal pressure range of 1 MPa to 5 MPa. The experiments are conducted under speed-controlled and torque-controlled conditions. In the former test, the rotation speed (slip velocity) is varied between ~micrometer/sec to millimeter /sec, and the torque is measured at each velocity. In the latter test, the torque is varied in steps and the resulting shear rate development is measured. In the presentation, we will report on the preliminary results of these experiments.
In this study, we focus on the unique characteristics of smectite and conduct shearing experiments using a torque-controlled friction apparatus. The high-speed/low-speed rotary friction apparatus installed in JAMSTEC Kochi can conduct friction experiments under conditions of increased temperature and pressure. It has recently been upgraded to include a mode that controls the rotation speed, rotation position and torque. This development has enabled experiments to be conducted under normal stress loading that involve increasing or maintaining torque, such as in a rheometer, which was previously challenging to perform. The experiments are conducted using a sample composed of smectite and quartz, with the addition of water. The temperature is maintained at room temperature, and the pressure conditions are set to 5 MPa of fluid pressure and an effective normal pressure range of 1 MPa to 5 MPa. The experiments are conducted under speed-controlled and torque-controlled conditions. In the former test, the rotation speed (slip velocity) is varied between ~micrometer/sec to millimeter /sec, and the torque is measured at each velocity. In the latter test, the torque is varied in steps and the resulting shear rate development is measured. In the presentation, we will report on the preliminary results of these experiments.