Resistivity and self-potential changes associated with volcanic activity: The July 8, 2000 Miyake-jima eruption (Japan)
Resistivity and self-potential changes associated with volcanic activity: The July 8, 2000 Miyake-jima eruption (Japan)
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与火山活动相关的电阻率和自电位变化：2000 年 7 月 8 日三宅岛喷发（日本）
DOI：
10.1016/s0012-821x(02)01025-7
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发表时间：
2003
影响因子：
5.3
通讯作者：
G. Donnadieu
中科院分区：
文献类型：
--
作者：
J. Zlotnicki;Y. Sasai;P. Yvetot;Y. Nishida;M. Uyeshima;F. Fauquet;H. Utada;Y. Takahashi;G. Donnadieu
三宅岛火山在沉寂了17年之后，于2000年7月8日突然爆发，形成了一个直径1公里、深250米的火山口。在1995-2000年期间，通过电磁方法，包括直流电阻率测量和自然电位测量，对这一预期的动乱进行了监测。在2500年历史的Hatcho-Taira山顶下，1997-98年进行的音频大地电磁测深确定了一个导电介质，厚度为200-500 m（在50 Ω m等值线内），位于几百米深的地方。它与中心靠近1940年锥体并向南延伸的活跃稳态热液系统有关。一个直流电阻率计设置在斯伦贝谢阵列与600，1000和1400米长的注入线证明强电阻率变化之间的1999年9月和2000年7月3日在附近的新形成的火山口。在1400 m长的测线上，视电阻率已达到其初始值的约3倍，而在600 m测线上已降低到约20%。就在2000年7月8日喷发之前，在山顶Hatcho-Taira破火山口内进行的SP绘图显示了在过去几十年中发生的正异常的负异常。最大的负异常，振幅为-225 mV，主要发生在1940年火山锥上方，该火山锥在火山口形成时坍塌。一个永久性的1公里长的SP线横跨破火山口表明加速变化在3个月前爆发。在更大的范围内，1995年和2000年调查的比较表明，火山下面的热液活动在全球范围内增加。它的源头可能在火山口以南250米处。这些观测结果表明，热液系统在喷发前的几个月里受到缓慢的干扰，而在山顶坍塌前的两周内发生了剧烈的变化，当时出现了构造和火山群。
The Miyake-jima volcano abruptly erupted on July 8, 2000 after 17 years of quiet and gave birth to a crater, 1 km in diameter and 250 m deep. This expected unrest was monitored during the years 1995–2000 by electromagnetic methods including DC resistivity measurements and self-potential (SP) surveys. Beneath the 2500 yr old Hatcho-Taira summit caldera audio-magnetotelluric soundings made in 1997–98 identified a conductive medium, 200–500 m thick (within the 50 Ω m isoline) located at a few hundred metres depth. It was associated with the active steady-state hydrothermal system centred close to the 1940 cone and extending southward. A DC resistivity meter set in a Schlumberger array with 600, 1000 and 1400 m long injection lines evidenced strong resistivity changes between September 1999 and July 3, 2000 in the vicinity of the newly formed crater. The apparent resistivity has reached about three times its initial values on the 1400 m long line and has lowered to about 20% on the 600 m line. Just prior to the July 8, 2000 eruption SP mapping made inside the summit Hatcho-Taira caldera revealed negative anomalies where positive ones had occurred during the previous tens of years. The largest negative anomaly, −225 mV in amplitude, mainly took place above the 1940 cone which collapsed in the crater formation. A permanent 1 km long SP line across the caldera suggests accelerating changes during the 3 months preceding the eruption. On a larger scale, the comparison between 1995 and 2000 surveys has shown a global increase of the hydrothermal activity beneath the volcano. Its source could have been 250 m to the south of the crater. These observations suggest that the hydrothermal system was slowly disturbed in the months preceding the eruption while drastic changes have occurred during the 2 weeks before the summit collapse when tectonic and volcanic swarms have appeared.