Experimental studies on coupled deformation and chemical reactions

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The main purpose of the present studies has been to investigate the role of pore fluids on rock rheology and earthquake initiation processes. We selected Median Tectonic Line, Nojima fault, Neodani fault, Kannawa fault, Yanagase fault and Hanaore fault as representative faults and have measured permeability and storage capacity under deep crustal conditions using an oscillation method and a constant flow method with a deformation and fluid flow gas apparatus. There were only several papers reporting internal and permeability structures when the present studies started, but we have collected over 5,000 permeability data for about 500 specimens collected from those faults. Thermal pressurization (TP), i.e., pore pressure rise due to frictional heating, has been proposed as a mechanism for the weakening of faults at the initiation of earthquakes for over the last three decades, but its significance has remained to be evaluated due to the lack sufficient data on fault-zone permeability. Our data clearly shows that fault zones are variable in permeability structures and that TP will occur for some faults, but not for others. Analyses of TP processes have also shown that the slip weakening distance, D_c, of fault is on the order of several fractions of 1 meter. There has been several orders of magnitude difference in D_c between seismically-determined and laboratory measured D_c for nearly 20 years (D_c paradox). TP processes yield D_c values on the same order of magnitude as determined seismically and high-velocity frictional studies may solve D_c paradox.