Low-frequency earthquakes in Shikoku, Japan, and their relationship to episodic tremor and slip
Low-frequency earthquakes in Shikoku, Japan, and their relationship to episodic tremor and slip
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DOI：
10.1038/nature04931
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发表时间：
2006-07-13
期刊：
影响因子：
64.8
通讯作者：
Nakamula, Sho
中科院分区：
文献类型：
--
作者：
Shelly, David R.;Beroza, Gregory C.;Nakamula, Sho
在日本西南部的南海海槽俯冲带发现了非火山地震震颤（1），随后在卡斯卡迪亚俯冲带发现了非火山地震震颤（2）。在这两个位置，观测到的震颤与孕震区板块界面下倾的大的缓慢滑动事件在时间上一致（2-7）。然而，地震和地震滑动之间的关系仍然不确定，这主要是由于难以限制地震的震源深度。在日本西南部，一个高质量的钻孔地震网络允许识别震颤中的相干S波（有时是P波）到达，其震源被归类为低频地震。由于低频地震至少包括一部分震颤，因此了解其机制对于了解整体震颤至关重要。在这里，我们提供了强有力的证据表明，这些地震发生在板块界面上，与推断的缓慢滑动区一致。这些事件的位置和特征表明，它们是由剪切滑移产生的，而不是由流体流动产生的。我们对地震P波和S波速度的估计暗示，附近的高孔隙流体压力可能会促进这种瞬态失效模式。低频地震可能有助于地震灾害预测，因为它提供了一种监测深度缓慢滑动的新手段。
Non-volcanic seismic tremor was discovered in the Nankai trough subduction zone in southwest Japan(1) and subsequently identified in the Cascadia subduction zone(2). In both locations, tremor is observed to coincide temporally with large, slow slip events on the plate interface downdip of the seismogenic zone(2-7). The relationship between tremor and aseismic slip remains uncertain, however, largely owing to difficulty in constraining the source depth of tremor. In southwest Japan, a high quality borehole seismic network allows identification of coherent S-wave ( and sometimes P-wave) arrivals within the tremor, whose sources are classified as low-frequency earthquakes. As low-frequency earthquakes comprise at least a portion of tremor, understanding their mechanism is critical to understanding tremor as a whole. Here, we provide strong evidence that these earthquakes occur on the plate interface, coincident with the inferred zone of slow slip. The locations and characteristics of these events suggest that they are generated by shear slip during otherwise aseismic transients, rather than by fluid flow. High pore-fluid pressure in the immediate vicinity, as implied by our estimates of seismic P- and S-wave speeds, may act to promote this transient mode of failure. Low-frequency earthquakes could potentially contribute to seismic hazard forecasting by providing a new means to monitor slow slip at depth.