Permeability Changes Of Fault Gouge While Frictional Sliding Under High-Temperature And High-Pressure Conditions

Recently, measurements of permeability of fault rocks become one of the important test items to understand the fluid flow properties in the vicinity of the faults. Previous studies have clarified general permeability profile of the fault rock. While fault gouge, due to its smaller grain size, shows low permeability and becomes a seal to prohibit fluid flow across the fault, the fault breccia including numerous connecting fractures becomes the high permeable conduit along the fault. However, most of previous studies did not address these transport properties while the faults are moving, becouse they have investigated the permeability of fault rocks under hydrostatic pressure. Here, to reveal the evolution of transport properties of various fault rocks during fault moving, the high-temperature and high-pressure triaxial testing machine was employed to investigate the permeability changes of artificial/natural fault gouge during the fault sliding. Experimental apparatus at AIST is a triaxial gas-rig which can produce high temperature of 800 degree C and high confining pressure of 200 MPa in maximum. Artificial gouge (Na montmorillonite powder) and natural fault gouge sampled from a normal fault with ca. 5 m of fault displacement in sandstone at Katuura, Japan were sandwiched by pre-cut surfaces of sandstone angled 30 degree to the cylindrical axis. We used the pore pressure oscillation method to measure the permeability, which is advantageous to measure the permeability dynamically. We would like to compare the patterns of permeability change with the degree of the deformation localization varied as gouge, cataclasite, breccia and protolith. It will be of particular interests in the estimation of pore pressure increasing/decreasing in the vicinity of the fault, caused by porosity change during fault sliding. This kind of research would be a key to deduce the mechanism of abnormal pore pressure occurrence at faulting, considered as a trigger of seismic event.