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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Resistivity and self-potential changes associated with volcanic activity: The July 8, 2000 Miyake-jima eruption (Japan)
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Resistivity and self-potential changes associated with volcanic activity: The July 8, 2000 Miyake-jima eruption (Japan)

机译：与火山活动有关的电阻率和自电位变化：2000年7月8日三宅岛喷发（日本）

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摘要

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.
机译：经过17年的静默，三宅岛火山于2000年7月8日突然爆发，并诞生了一个直径1公里，深250 m的火山口。在1995-2000年间，通过电磁方法，包括直流电阻率测量和自电位（SP）测量，对这种预期的动荡进行了监视。在1997-98年产生的2500年历史的Hatcho-Taira山顶破火山口音频-大地电磁测深仪之下，发现了一种导电介质，其厚度为200-500 m（在等值线50Ωm之内），位于数百米的深度。它与活跃的稳态热液系统有关，该系统以靠近1940圆锥体为中心并向南延伸。在斯伦贝谢阵列中设置的直流电阻率仪具有600、1000和1400 m长的注入管线，从1999年9月至2000年7月3日，在新形成的火山口附近，电阻率发生了强烈变化。视电阻率在1400 m长线上已达到其初始值的三倍左右，在600 m线上已降至约20％。就在2000年7月8日，在Hatcho-Taira火山口内的喷发SP测绘之前，揭示了负异常，在过去的几十年中出现了正异常。最大的负异常，幅度为-225 mV，主要发生在1940年的圆锥上方，该圆锥在火山口形成中坍塌。贯穿火山口的一条1公里长的永久SP线表明在喷发前的3个月中加速变化。在更大范围内，1995年和2000年调查之间的比较表明，火山下方的热液活动在全球范围内有所增加。它的源头可能是火山口以南250 m。这些观察结果表明，在火山喷发前的几个月中，热液系统受到了缓慢的扰动，而在山顶坍塌之前的两周内，当出现构造和火山群时，发生了剧烈的变化。

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