3D conductive structures and crustal activities beneath Japan islands

1993年，在日本东北部宫城县北部进行了甚低频至极低频频率范围内的大地电磁测量。结果表明，微震活动在深度约10km的低阻块体上方明显活跃。1994年，在日本九州地区南部的角户火山口附近进行了类似的MT调查。由此得出结论，埃比诺地震群可能发生在电阻带内。1995年，我们对野岛断裂带下的电阻率结构进行了探测，发现该断裂带在1995年1月发生小古根-南部地震的同时发生了移动。本次调查的目的是对故障恢复过程进行长时间的监测。除了这些调查之外，利用电话公司电缆在日本的一些地区进行了Network-MT测量，以获得直到地壳底部的电阻率基本结构。

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.