Changes in the geomagnetic total intensity observed before the eruption of Oshima Volcano in 1986.
Changes in the geomagnetic total intensity observed before the eruption of Oshima Volcano in 1986.
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1986年大岛火山喷发前观测到的地磁总强度变化。
DOI：
10.5636/jgg.42.277
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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：
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作者：
T. Yukutake;H. Utada;T. Yoshino;H. Watanabe;Y. Hamano;Y. Sasai;E. Kimoto;K. Otani;Takafumi Shimomura
1986年11月15日大岛火山喷发前，有5台质子磁力仪在火山上工作。其中一个安装在火山口中心以南约500米处，记录了火山爆发前总强度的异常变化。异常变化始于1981年左右。总强度以-5.3nT/年（-0.44nT/月）的速度逐渐下降，5年内下降了27 nT。在爆发前6个月左右，总强度的下降速度加快。估计下降率约为-2.2nT/月。在爆发时，观察到非常快速和显著的变化。总强度在1分钟内下降4 nT。在中央锥喷发后，11月21日发生了裂缝喷发。在中央锥东南2公里处也观测到总磁场强度下降了约7 nT。在喷发前观测到的磁场变化被认为是由于岩浆侵入时火山体被加热所引起的，在最初阶段通过主喷口，在后期阶段通过一条新的路径到达新形成的火山口，称为A火山口。火山爆发时的变化被认为是由于火山内部的孔隙和裂缝中气体和液体的灾难性流出导致磁性材料的定向混乱。
Before the eruption of Oshima Volcano on November 15, 1986, 5 proton magnetometers were operating on the volcano. One of them, installed about 500m south from the center of the central crater, recorded anomalous changes in the total intensity preceding the eruption. The anomalous variation began around 1981. The total intensity decreased gradually at a rate of -5.3nT/year (-0.44nT/month), amounting to a 27nT decrease in 5 years. The decrease of the total intensity accelerated about six months before the eruption. The rate of decrease was estimated to be about -2.2nT/month. At the time of the eruption, a very fast and significant variation was observed. The total intensity decreased 4nT in one minute. Following the eruption from the central cone, fissure eruptions took place on November 21. A decrease in the total intensity of about 7nT was also observed at this time at a site 2km southeast of the central cone.The observed magnetic changes preceding the eruption are supposed to have been caused by the volcanic body being heated during the intrusion of magma, at the initial stage through the main vent, and at the later stage through a new path toward the newly formed crater, called A crater. The variation at the time of eruption is considered due to the disorientation of magnetic materials by the catastrophic outflow of gases and liquids through pores and cracks inside the volcano.