Temporal change in permeability of the rock estimated from repeated water injection experiments near the Nojima fault in Awaji Island, Japan

Three boreholes with depths of 500, 800, and 1800 m were drilled near the Nojima fault, which is one of the 1995 Hyogoken‐Nanbu earthquake faults. In order to research the structure and its temporal change of the active fault, the water injection experiments were conducted from the 1800‐m borehole in 1997 and 2000. Then, the discharge changes at the 800‐m borehole were observed during the water injections. Considering the permeable zone near the fault as simple two‐dimensional layer with an uniform thickness, we estimated the permeability of the permeable zone near the Nojima fault from the discharge changes associated with the water injections. It is found that the permeability of the permeable zone in 2000 became lower than that in 1997.