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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Repeating coupled earthquakes at Shishaldin Volcano, Alaska
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Repeating coupled earthquakes at Shishaldin Volcano, Alaska

机译：在阿拉斯加的希沙尔丁火山重复耦合地震

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Since it last erupted in 1999, Shishaldin Volcano, Aleutian Islands, Alaska, has produced hundreds to thousands of long-period (1-2 Hz; LP) earthquakes every day with no other sign of volcanic unrest. In 2002, the earthquakes also exhibited a short-period (4-7 Hz; SP) signal occurring between 3 and 15 s before the LP phase. Although the SP phase contains higher frequencies than the LP phase, its spectral content is still well below that expected of brittle failure events. The SP phase was never observed without the LP phase, although LP events continued to occur in the absence of the precursory signal. The two-phased events are termed "coupled events", reflecting a triggered relationship between two discrete event types. Both phases are highly repetitive in time series, suggestive of stable, non-destructive sources. Waveform cross-correlation and spectral coherence are used to extract waveforms from the continuous record and determine precise P-wave arrivals for the SP phase. Although depths are poorly constrained, the SP phase is believed to lie at shallow ( < 4 km) depths just west of Shishaldin's summit. The variable timing between the SP and LP arrivals indicates that the trigger mechanism between the phases itself moves at variable speeds. A model is proposed in which the SP phase results from fluid moving within the conduit, possibly around an obstruction and the LP phase results from the coalescence of a shallow gas bubble. The variable timing is attributed to changes in gas content within the conduit. The destruction of the conduit obstacle on November 21, 2002 resulted in the abrupt disappearance of the SP phase.
机译：自从1999年上一次爆发以来，阿拉斯加阿留申群岛的Shishaldin火山每天产生数百至数千次长周期（1-2 Hz; LP）地震，而没有其他火山爆发的迹象。在2002年，地震还表现出一个短周期（4-7 Hz； SP）信号，发生在LP相之前的3至15 s之间。尽管SP相包含的频率高于LP相，但其频谱含量仍远低于预期的脆性破坏事件。没有LP阶段就从未观察到SP阶段，尽管在没有前驱信号的情况下LP事件继续发生。两阶段事件称为“耦合事件”，反映了两个离散事件类型之间的触发关系。这两个阶段在时间序列上都是高度重复的，这表明稳定，无损的来源。波形互相关和频谱相干用于从连续记录中提取波形，并确定SP相位的精确P波到达。尽管深度控制不力，但据信SP阶段位于Shishaldin峰顶以西的浅层（<4 km）深度。 SP和LP到达之间的可变时间表明相之间的触发机制本身以可变速度运动。提出了一种模型，其中SP相是由流体在导管内（可能围绕障碍物）移动引起的，而LP相则是由浅气泡的合并引起的。可变的定时归因于导管内气体含量的变化。 2002年11月21日，导管障碍物的破坏导致SP阶段突然消失。

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