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Electromagnetic Research on Structure of Graben and its implication to Volcanism

地堑结构的电磁研究及其对火山作用的意义

基本信息

批准号：
09640504
负责人：
KAGIYAMA Tsuneomi
金额：
$ 1.41万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1998
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-09640504/
关键词：
Graben Resistivity Structure Kyushu Volcanism 九州

项目摘要

We carried out magnetotelluric survey at 26 sites along East-West lines across the southern Kyushu in 1997, and 13 sites in the northern part of Miyazaki Prefecture in 1998. Simultaneous magnetic and electric field variations were measured in the ULF, ELF and VLF band. The experiment found some anomalous regions suggesting magmatic activity. Volcanic area is characterized by a simple four-layer structure ; relatively resistive overburden, very conducting second layer at the depth of a few hundred meters, resistive basement, and deep conductor. On the other hand, a rather resistive second layer and lack of deep conductor characterize non-volcanic region. The low-resistivity second layer (Shallow Low Resistivity Region) is distributed around Kirishima volcanic region and other volcanoes, which have gold mines or geothermal areas. This evidence indicates that SLRR is a water-saturated porous layer or altered layer. The deep conductor (Deep Low Resistivity Region) appears about a few tens km below the surface in average, but shallower beneath the presently active volcanoes. These SLRR and DLRR mainly distribute from Kushikino to Kirishima volcanic region via Miyanojo and Okuchi Basins, which have volcanic activity within several million years, but partly elongates to the non-volcanic such as Hitoyoshi Basin in the NE direction. This direction may correspond to the direction of the trend of the depression region or old graven.

1997年，我们在九州南部沿东西线的26个站点和1998年在宫崎县北部的13个站点进行了大地电磁测量。在ULF、ELF和VLF频段同时测量了磁场和电场变化。实验发现了一些异常区域，表明存在岩浆活动。火山区的特点是简单的四层结构；相对电阻性覆盖层、数百米深度处导电性良好的第二层、电阻性基底和深层导体。另一方面，第二层电阻相当大且缺乏深层导体，这是非火山区域的特征。低电阻率第二层（浅低电阻率区）分布在雾岛火山区和其他火山周围，有金矿或地热区。这一证据表明 SLRR 是水饱和多孔层或蚀变层。深层导体（深层低电阻率区域）平均出现在地表以下约几十公里处，但在目前活火山下方较浅。这些SLRR和DLRR主要分布于串木野至雾岛火山区，经宫之条盆地和大口盆地，这些盆地在几百万年内有火山活动，但部分向NE方向延伸至人吉盆地等非火山区域。这个方向可能对应于凹陷区域或旧坟墓的走向方向。