Seismic precursors to volcanic explosions during the 2006 eruption of Augustine Volcano
Seismic precursors to volcanic explosions during the 2006 eruption of Augustine Volcano
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2006 年奥古斯丁火山喷发期间火山爆发的地震前兆
DOI：
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发表时间：
2010
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影响因子：
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通讯作者：
M. West
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作者：
H. Buurman;M. West
2006年阿拉斯加奥古斯丁火山爆发，在长达一个月的时间内引发了3,500多次地震，这是火山活动最具爆炸性的时期。我们研究了两种定量工具，在回顾性分析中，是即将爆发的良好指标。第一种工具，称为频率指数（FI），是基于地震记录中高频和低频能量的简单比率。它是一个度量标准，使我们能够量化典型的高频，混合和低频火山地震之间的差异。FI值大于-0.4表明地震通常被称为高频或火山构造事件。小于-1.3的FI值对应于通常被称为低频地震的事件。因为FI是基于一个比率而不是一个谱峰，所以混合地震被成功地分配到介于这两类之间的FI值。在这次喷发中，我们发现FI小于-1.8的事件与爆发性喷发之间存在显著的相关性。我们研究的第二种工具是基于通过波形互相关识别的重复地震波形。虽然绝大多数的地震在这次喷发有独特的波形，事件的子集表现出高度的相似性发生，并密切相关的爆炸性喷发事件。在这13次大爆炸事件中，有7次发生在高度相似的地震群之前。我们一起应用FI和相关工具来识别高频和低频地震发生的变化，并研究它们与喷发的爆发性，爆炸性和连续性阶段的关系。我们发现，具有低FI值的地震和具有高度相似性的地震几乎完全发生在爆炸性喷发的几个小时内，并假设它们是由于火山建筑物中岩浆的最终上升而发生的。由于这两种方法都不需要分析师审查地震位置，我们相信它们作为自动化实时火山监测工具具有相当大的潜力。
The 2006 eruption of Augustine Volcano, Alaska, generated more than 3,500 earthquakes in a month-long time frame bracketing the most explosive period of activity. We examine two quantitative tools that, in retrospective analysis, were excellent indicators of imminent eruption. The first tool, referred to as the frequency index (FI ), is based on a simple ratio of highand low-frequency energy in an earthquake seismogram. It is a metric that allows us to quantify the differences between the canonical high-frequency, hybrid, and low-frequency volcanic earthquakes. FI values greater than -0.4 indicate earthquakes classically referred to as highfrequency or volcano-tectonic events. FI values less than -1.3 correspond to events usually referred to as low-frequency earthquakes. Because the FI is based on a ratio and not a spectral peak, hybrid earthquakes are successfully assigned FI values intermediate to these two classes. In this eruption, we find a remarkable correlation between events with FI less than -1.8 and explosive eruptions. The second tool we examine is based on repeating seismic waveforms identified through waveform cross-correlation. Although the vast majority of earthquakes during this eruption have unique waveforms, subsets of events exhibiting a high degree of similarity occur and are closely tied to explosive eruption events. Of the 13 large explosion events, seven were preceded by clusters of highly similar earthquakes. We apply the FI and correlation tools together to identify changes in highand low-frequency earthquake occurrences and examine their relations to the precursory, explosive, and continuous phases of the eruption. We find that earthquakes that have low FI values and earthquakes exhibiting high degrees of similarity occur almost exclusively within hours of explosive eruptions and postulate that they occur as a result of the final ascent of magma in the volcanic edifice. Because neither of these methods requires analyst-reviewed earthquake locations, we believe that they have considerable potential as automated real-time volcano monitoring tools.