3D conductive structures and crustal activities beneath Japan islands

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In 1993, magnetotelluric surveys in the frequency range from VLF to ULF were carried out in the northern part of Miyagi prefecture, north-east Japan. The result showed that microseismicity is clearly active in the zone just above an electrically low resistive block located at the depth of about 10km.In 1994, similar MT surveys were carried out around Kakuto caldera situated in the southern part of Kyushu district, Japan. It was concluded that Ebino earthquake swarms likely occurred within the electrically resistive zone.In 1995, we examined the electrical resistivity structure beneath Nojima fault which was recognized to be moved at the same time when Hyougoken-Nanbu earthquake occurred in January, 1995. This investigation is aimed to monitor the recovery process of the fault for a long time.In addition to these investigations, Network-MT measurements utilizing the telephone company cables were conducted in a number of districts in Japan to obtain the basic structure of electric resistivity until the bottom of the earth crust.