The rise and fall of periodic ‘drumbeat’ seismicity at Tungurahua volcano, Ecuador
The rise and fall of periodic ‘drumbeat’ seismicity at Tungurahua volcano, Ecuador
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厄瓜多尔通古拉瓦火山周期性“鼓声”地震活动的升降
DOI：
10.1016/j.epsl.2017.07.030
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发表时间：
2017
影响因子：
5.3
通讯作者：
Santiago Aguaiza
中科院分区：
文献类型：
--
作者：
A. Bell;S. Hernández;H. Gaunt;P. Mothes;M. Ruiz;Daniel Sierra;Santiago Aguaiza
高周期性的“鼓声”长周期（LP）地震已被描述从几个安山质和英安质火山，通常伴随着增量上升和渗出的粘性岩浆。然而，控制鼓声和LP地震的发生和特征的过程仍然存在争议。在这里，我们使用新的定量工具来描述2015年4月在厄瓜多尔安山质通古拉瓦火山的鼓声LP地震活动的出现，演变和退化。这些信号是在一次轻微的爆炸活动和火山灰排放期间记录的，没有熔岩渗出，并且是在通古拉瓦持续17年的喷发期间首次报告的。在连续四天的高水平和“脉冲”震颤之后，高周期LP地震首次出现在4月10日。在接下来的四天里，事件间时间和事件振幅通过一系列稳定行为之间的逐步过渡而演变，每个过渡都涉及周期性程度的降低。类似波形的家庭持续之前，期间和之后的鼓声活动，但不同的家庭的活动水平的变化与事件率，振幅和周期性的转变。一个复杂的微震活动的“启动”序列显示脉冲状和逐步变化的事件间的时间和振幅在几个小时前的鼓声活动，表明事件的大小和速率之间的部分解耦。观测结果增加了鼓声LP地震的现象，并表明，在通古拉瓦，它们是由上升的岩浆柱边缘的剪切破坏控制的气体通量和快速降压造成的。
Highly periodic ‘drumbeat’ long period (LP) earthquakes have been described from several andesitic and dacitic volcanoes, commonly accompanying incremental ascent and effusion of viscous magma. However, the processes controlling the occurrence and characteristics of drumbeat, and LP earthquakes more generally, remain contested. Here we use new quantitative tools to describe the emergence, evolution, and degradation of drumbeat LP seismicity at the andesitic Tungurahua volcano, Ecuador, in April 2015. The signals were recorded during an episode of minor explosive activity and ash emission, without lava effusion, and are the first to be reported at Tungurahua during the ongoing 17 yrs of eruption. Following four days of high levels of continuous and ‘pulsed’ tremor, highly-periodic LP earthquakes first appear on 10 April. Over the next four days, inter-event times and event amplitudes evolve through a series of step-wise transitions between stable behaviors, each involving a decrease in the degree of periodicity. Families of similar waveforms persist before, during, and after drumbeat activity, but the activity levels of different families change coincidentally with transitions in event rate, amplitude, and periodicity. A complex micro-seismicity ‘initiation’ sequence shows pulse-like and stepwise changes in inter-event times and amplitudes in the hours preceding the onset of drumbeat activity that indicate a partial de-coupling between event size and rate. The observations increase the phenomenology of drumbeat LP earthquakes, and suggest that at Tungurahua they result from gas flux and rapid depressurization controlled by shear failure of the margins of the ascending magma column.
影响因子：
2.8
作者：
A. Bell;J. Greenhough;M. Heap;I. Main
通讯作者：
A. Bell;J. Greenhough;M. Heap;I. Main