Abstract
The Kushibiki fault, which runs northwest-southeast and dips southwest, is an active fault in the western part of the Kanto plane, Japan. Earth resistivity by direct current method, self-potential gradient and geomagnetic total intensity are measured in this area.
Analyses of the Schlumberger and Wenner soundings show that the resistivity structure in the fault zone in striking contrast to the surrounding layers. The relatively high resistivity layer of 300 to 500 ohm-m is restricted to the fault zone, and the layer dips more steeply southwest in the center than at the edge. A very low resistivity layer of 10 ohm-m or less appears at a depth of about 100 m outside of the fault zone, but in the fault zone the layer appears at a depth of 10 to 30 m just under the highly resistive layer.
An anomalous field of geomagnetic total intensity in the range of 60 to 100 nT is found along the fault with a width of about 100 m. The distributions of the self-potential gradients on the two lines across the fault do not support the theory that the anomalous magnetic field originates in a current generated by a streaming potential. So the origin is considered to be magnetized bodies. It can be explained that the high resistivity layer in the fault zone is magnetized to an intensity of 1.5×10-3emu/cc, whereas the magnetization of the surroundings is 5×10-4emu/cc.
