Soufrière Hills Eruption, Montserrat, 1995–1997: Volcanic earthquake locations and fault plane solutions
Soufrière Hills Eruption, Montserrat, 1995–1997: Volcanic earthquake locations and fault plane solutions
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DOI：
10.1029/98gl00858
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发表时间：
1998-09
影响因子：
5.2
通讯作者：
Willy P Aspinall;A. D. Miller;Lloyd Lynch;J. Latchman;R. C. Stewart;Randall A. White;John A. Power
中科院分区：
文献类型：
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作者：
Willy P Aspinall;A. D. Miller;Lloyd Lynch;J. Latchman;R. C. Stewart;Randall A. White;John A. Power
自1995年7月蒙特塞拉特火山爆发以来，共记录了9242次地震事件，并根据台站走时校正进行了统一重新定位。早期的地震活动在蒙特塞拉特南部通常是分散的，而且大多局限于7公里以下的深度。然而，在火山的东北侧翼下出现了一群火山构造地震（VT）的NE - SW排列的震中，随后在火山下方和圣乔治山下的一个独立位置形成了VT震源巢。震源的整体空间分布表明，任何实质性岩浆体的最小深度约为5公里。与通往地表的管道打开相关的活动变得越来越浅，震源集中在火山口下方，1995年秋季圆顶建筑开始后，VTs减少，重复的“混合”地震事件群成为主导。到1996年末，随着岩浆喷发速率的上升，大多数地震事件都发生在直径约2公里的范围内，这些范围从大约3公里的深度延伸到地表——剪切破坏地震的减少表明岩浆喷发的途径实际上已经变得不受限制。对于一些更大的地震，已经确定了单独的和复合的断层解。我们假设，由于与上覆岩石圈板块的应力相互作用，在线性VT活动附近的局部伸展应力条件可能会促进正常断层的生长，并促进火山的板块弱点。
A total of 9242 seismic events, recorded since the start of the eruption on Montserrat in July 1995, have been uniformly relocated with station travel‐time corrections. Early seismicity was generally diffuse under southern Montserrat, and mostly restricted to depths less than 7 km. However, a NE‐SW alignment of epicentres beneath the NE flank of the volcano emerged in one swarm of volcano‐tectonic earthquakes (VTs) and later nests of VT hypocentres developed beneath the volcano and at a separated location, under St. George's Hill. The overall spatial distribution of hypocentres suggests a minimum depth of about 5 km for any substantial magma body. Activity associated with the opening of a conduit to the surface became increasingly shallow, with foci concentrated below the crater and, after dome building started in Fall 1995, VTs diminished and repetitive swarms of ‘hybrid’ seismic events became predominant. By late‐1996, as magma effusion rates escalated, most seismic events were originating within a volume about 2 km diameter which extended up to the surface from only about 3 km depth ‐ the diminution of shear failure earthquakes suggests the pathway for magma discharge had become effectively unconstricted. Individual and composite fault plane solutions have been determined for a few larger earthquakes. We postulate that localised extensional stress conditions near the linear VT activity, due to interaction with stresses in the overriding lithospheric plate, may encourage normal fault growth and promote sector weaknesses in the volcano.