Solution of problem on SIP (Shear-induced Polarization) in fault gouges and the development to the field observations.

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An experimental study on the electrical potential induced in fault gouge materials accompanying with their shear deformation have been carried out. Some electrical polarizations could be observed in common saturated fine aggregates, such as clay during the shear deformation test in laboratory. This phenomenon is called SIP (Shear-induced Polarization). This phenomenon of SIP can be interpreted in terms of physicochemical interaction between fine particle and interstitial water with electrolyte. However, the SIP was not detected in the remolded clay for handicraft-use which treated with some non-dipole oil.The plane shear strain test was performed to clarify the relation of the polarity of induced potential with deformation and the sense of strain. Sign of electric charge generated on the plane of maximum strain axis (tensional) was plus, that on the plane of minimum strain axis was minus and that on the plane of intermediate strain axis was neutral. This characteristic property was confirmed in gouge sample by the other kind of deformation test.We observed SIP at sites of landslide by measurement of the spontaneous potential. The sites locate at large scale of landslide areas of Busuno landslide area in Jouetsu City, Niigata Prefecture, Northeast Japan and Nuta Yone landslide area in Nagaoka, Kochi Prefecture, Shikoku, Japan. The spontaneous potential changes with increasing the displacement of landslide. The large discontinuity of the electric potential distribution was observed at the boundary of landslide blocks. The senses of electric potential observed at landslide fields coincided with those senses obtained from the model experiments in the laboratory.