A fault‐zone conductor beneath a compressional inversion zone, northeastern Honshu, Japan

[1] A resistivity section based on magnetotelluric data was obtained for the Shonai Plain fault in northeastern Honshu, Japan. Faults in this area were created as normal faults during the opening of the Japan Sea in the Miocene but are now reactivated as high-angle reverse faults under compressional tectonics. Geological interpretations of the resistivity section support the proposed fault reactivation. An estimated east-dipping conductor along a deep part of the Shonai Plain fault system probably represents a fluid-rich zone around the fault zone. The high 3He/4He ratio near the fault indicates transportation of mantle fluid through this fluid-rich zone. These evidences may reflect the development of pronounced fracture permeability after fault rupturing, as in the fault-valve hypothesis.