Geophysical Research Letters
American Geophysical Union
Analyses of rocks from the Active Fault Survey Tunnel (AFST) provides insight into the structure and hydrogeology of the northeast-trending Mozumi-Sukenobu fault, an active strike-slip fault with 125 to 500 m of right-lateral slip in central Japan. Interlayered regions of sub-vertical permeability zones formed by cataclasis and slip on clay-rich foliated zones. Core samples range from 10−19 m2 to almost 10−13 m2. CFC analyses of waters from the fault zone show that water entering the tunnel is 27–36 years old, yielding a bulk fault permeability of 10−14 to 10−15 m2. The data support a fault zone model of a fluid-saturated, low-velocity zone with a sharp velocity contrasting with the protolith. Pore-fluid pressures could build and dissipate in isolated high permeability pods 10's–100's m in dimension.
Forster, C. B., Evans, J. P., Tanaka, H., Wantanabe, K., Jeffreys, R., and Nohara, T., 2003, Near-surface hydrologic structure of an Active Fault: The Mozumi Fault, Japan, Geophysical Research Letters. 30 (6), 8010, doi:10.1029/2002GL014904.