Shallow resistivity structure of Asama Volcano and its implications for magma ascent process in the 2004 eruption
Shallow resistivity structure of Asama Volcano and its implications for magma ascent process in the 2004 eruption
复制标题
DOI：
10.1016/j.jvolgeores.2008.01.016
复制
发表时间：
2008-06-10
影响因子：
2.9
通讯作者：
Kagiyama, Tsuneomi
中科院分区：
文献类型：
--
作者：
Aizawa, Koki;Ogawa, Yasuo;Kagiyama, Tsuneomi
浅间火山是一座活火山，历史上有许多火山喷发的记录。最近一次喷发发生在 2004 年，地点是山顶火山口。在本文中，我们论证了通过密集大地电磁勘探获得的浅于 3 km 的电阻率结构。大地电磁数据主要在横跨火山的 4 条测线沿线的 74 个测量点获得。通过二维反演获得的电阻率剖面的特征在于电阻表面层和下面的导电层。剖面的主要特征是在几百米到几公里的深度范围内存在电阻体，周围是高导电区域。考虑到电阻体的位置对应于古老的喷发中心（一个对应于24 ka塌陷火山口，另一个对应于21 ka熔岩穹顶），电阻体意味着低孔隙度的古老且凝固的侵入岩浆区。由于地热活动存在于电阻体附近，因此封闭的高导电区域被解释为由古老凝固岩浆的热量驱动的热液系统。通过火山构造地震研究和全球定位系统（GPS）连续观测推断，在塌陷火山口下的电阻体下方有岩浆侵入，这意味着火山内部岩浆活动受到结构控制。在这项研究中，我们提出，岩浆上升受到古老且凝固的残余岩浆的阻碍，部分向东水平迁移，最终上升到山顶，导致了2004年的火山喷发。 (C) 2008 Elsevier B.V. 保留所有权利。
Asama volcano is an active volcano with many historical records of Vulcanian eruptions. Its most recent eruptions occurred in 2004 at the summit crater. In this paper, we argue the resistivity structure shallower than 3 km obtained by a dense magnetotelluric survey. The magnetotelluric data were obtained at 74 measurement sites mainly along the four survey lines across the volcano. The resistivity profiles obtained by two-dimensional inversions are characterized by a resistive surface layer and an underlying conductive layer. The dominant feature of the profiles is the existence of resistive bodies at a depth range of a few hundred meters to a few kilometers surrounded by a highly conductive region. Considering that the location of resistive bodies correspond to the old eruption centers (one corresponds to the 24 ka collapse caldera and the other to the 21 ka lava dome), the resistive bodies imply zones of old and solidified intrusive magma with low porosity. Because geothermal activities exist near the resistive bodies, the enclosing highly conductive regions are interpreted as a hydrothermal system driven by the heat from the old solidified magma. Beneath the resistive body under the collapsed caldera, intrusion of magma is inferred from the studies of volcano-tectonic earthquakes and continuous global positioning system (GPS) observation, implying the structural control of magma activity within the volcano. In this study, we propose that the magma ascent was impeded by the old and solidified remnant magma and partly migrated horizontally to the east and finally ascended to the summit, resulting in the 2004 eruptions. (C) 2008 Elsevier B.V. All rights reserved.