Waveform inversion of shallow repetitive long period events at Villarrica Volcano, Chile
Waveform inversion of shallow repetitive long period events at Villarrica Volcano, Chile
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智利比亚里卡火山浅层重复长周期事件的波形反演
DOI：
10.1002/jgrb.50354
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
G. Waite
中科院分区：
文献类型：
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作者：
J. Richardson;G. Waite
比利亚里卡火山目前的特点是在山顶火山口有一个活跃的熔岩湖，有温和的斯特龙博利风格的玄武岩安山岩产品喷发。熔岩湖作为一个可渗透的屏障，其中富含气体的岩浆释放挥发物，然后通过管道对流过程下降到深层储存库。我们使用匹配滤波器在三年的时间内识别出数千个重复的长周期（LP）地震事件;发现每个事件都与次声发射有关，因此从熔岩湖中放气。使用该事件目录进行计时，我们在2010 - 2012年的三年部署期间叠加信号，以产生代表性的地震和次声特征，并使用网络中的九个台站进行全波形地震反演。数据可以很好地用一个单一的水平力源-时间函数表示，方向为N75°E，从水平方向倾斜7°W，最大振幅为34.4 MN。该源在时间上是稳定的，并且可以通过由熔岩湖中的破裂气泡产生的力偶系统和熔岩晃动的响应拖曳力来解释，以填充由不对称火山口中的气体排放产生的空隙。路径效应随着距离震源的增加而延长了事件的尾波，导致在遥远的地震仪上出现类似震颤的信号。由于LP事件的发生与震颤强度相关，我们认为大部分震颤是离散LP叠加的结果。
Villarrica volcano is presently characterized by an active lava lake in the summit crater, with mild strombolian style eruptions of basaltic‐andesitic products. The lava lake acts as a permeable barrier where gas‐rich magma releases volatiles and then descends through the process of conduit convection to a deep storage reservoir. We identified thousands of repetitive long‐period (LP) seismic events within a three‐year time period using a matched filter; each was discovered to be associated with an infrasonic emission, and hence outgassing from the lava lake. Using this catalog of events for timing, we stacked signals over the three‐year deployment from 2010‐2012 to produce representative seismic and infrasonic signatures, and performed a full‐waveform seismic inversion using nine stations from the network. The data are well represented by a single horizontal force source‐time function, oriented N75°E and dipping 7°W from horizontal, with a maximum amplitude of 34.4 MN. The source is stable in time, and can be explained by a force couple system produced by a bursting bubble in the lava lake and the responsive drag force of the lava sloshing to fill in the void produced by the gas emission in an asymmetrical crater. Path effects lengthen the coda of the events with increasing distance from the source, resulting in emergent tremor‐like signals at distant seismometers. Since the occurrence of LP events correlates with tremor intensity, we suggest much of the tremor results from the superposition of discrete LPs.