Resistivity Structure of Izu-Oshima Volcano Revealed by the ELF-VLF Magnetotelluric Method
Resistivity Structure of Izu-Oshima Volcano Revealed by the ELF-VLF Magnetotelluric Method
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ELF-VLF大地电磁法揭示伊豆大岛火山电阻率结构
DOI：
10.5636/jgg.42.169
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发表时间：
1990
期刊：
影响因子：
--
通讯作者：
Takafumi Shimomura
中科院分区：
文献类型：
--
作者：
H. Utada;Takafumi Shimomura
应用甚低频和极低频大地电磁(MT)方法研究了伊豆-大岛火山的电阻率分布。我们将17.4 kHz的人工电磁信号用于VLF方法，并将三个基波舒曼共振频率用于ELF方法。1984年和1985年在57个测点进行了测量，其中包括中央火山口底板上的30个测点，并根据测量结果确定了一维电阻率模型。模拟结果清楚地表明，在海拔几百米的深度处，火山口下的水库占主导地位。在中央圆锥体宫原山的火山口底部，在四个地点进行了测量。结果表明，宫原山的导体很浅，其电阻率小于10Ω·m，而且宫原山的建筑物有向东向西延伸的趋势，南部的导电性要强于北部。重要的是，在一维近似范围内，这个异常导电层只存在于火山口底部以下200-300米处。我们得出的结论是，这个导电层直接反映了宫原山中央锥体目前的热活动。此外，在火山口边缘的北部和南部，导电层的深度往往较浅。这显示了破火山口边缘下地下水分布的一种特殊特征。
The VLF and ELF magnetotelluric (MT) methods have been applied to study the electrical resistivity distribution in the Izu-Oshima volcano. We utilized a 17.4kHz artificial electromagnetic signal for the VLF method, and three fundamental Schumann resonance frequencies for the ELF method. Measurements were made in 1984 and 1985 at 57 sites including 30 on the central caldera floor, and one-dimensional resistivity models were determined from the results. The modeling results clearly indicate the dominance of a water reservoir beneath the caldera at the depth of a few hundred meters above the sea level.On the crater floor of the central cone Mihara-yama, measurements were carried out at four sites. The result shows a very shallow conductor with a resistivity of less than 10Ω·m. We also found that the edifice of Mihara-yama tends to be more conducting in the southern part than in the northern part, extending in the east-west direction. The important thing is that, within the one-dimensional approximation, this anomalously conducting layer exists only 200-300m below the crater floor. We concluded this conducting layer directly reflects the present thermal activity in the central cone of Mihara-yama. Furthermore, the depth of the conducting layer tends to be shallow at the northern and southern parts of the caldera rim. This shows a peculiar feature of the groundwater distribution beneath the caldera rim.