[S-CG58] New Developments in fluid-rock Interactions: From Surface to Deep Subduction Zone

[SCG58-P12] Experimental study on Kinetically Controlled Stick-slip Behaviors of Simulated Gypsum Gouges with Dehydration

*Jun Muto¹, Mikihiro Kawabata¹, Hiroyuki Nagahama¹, Rei Shiraishi¹, Yuto Sasaki², Masaaki Iwasaki³ (1.Department of Earth Sciences, Tohoku University, 2.Kaijo Junior and Senior High School, 3.Dia Consultants Co., Ltd)

Keywords:dehydration instability, hydrous minerals, pore fluid pressure, kinetics, dehydration embrittlement

Pore fluid pressure generated by dehydration of hydrous minerals can trigger deep and intermediate-depth earthquakes. Therefore, it is essential to investigate its effect on frictional behaviors. We conducted friction experiments on simulated bassanite gouges (hemihydrate gypsum) and observed the stress drops and recurrence intervals of stick-slip events decreased over time under 200 MPa and 110 °C. Microstructural observations indicates that gouges deformed under room temperature shows the development of numerous shear bands including Riedel shears. On the other hand, a sample deformed under 200 MPa and 110 °C had few Riedel shear planes, indicative of the elevated pore fluid pressure suppressing the development of shear planes in the experiment. Additionally, assuming pore fluid pressure, frictional coefficients were estimated to be approximately 0.6, consistent with previous experimental study. We derived time function of dehydration-driven pore fluid pressure evolution using Avrami kinetics. Because of the mathematical similarity of Avrami equation on the fractal geometry on the surface of reaction products (water and anhydrate) to Weibull cumulative distribution function of failure rate, we discuss the kinetics-driven pore fluid pressure evolution controlled the stick-slip behaviors of the gypsum gouges under dehydration.