Very Low Frequency Earthquakes in Between the Seismogenic and Tremor Zones in Cascadia?
Very Low Frequency Earthquakes in Between the Seismogenic and Tremor Zones in Cascadia?
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DOI：
10.1029/2021av000607
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发表时间：
2022-04-01
期刊：
影响因子：
8.4
通讯作者：
Okuwaki, Ryo
中科院分区：
文献类型：
--
作者：
Fan, Wenyuan;Barbour, Andrew J.;Okuwaki, Ryo
巨型逆冲断层地震和与之相关的海啸会导致一些最严重的自然灾害。除了地震之外，俯冲带还存在广泛的滑动行为，包括跨越多个空间和时间尺度的慢地震。了解这些事件可能有助于了解巨型逆冲断层的应力或强度条件。在所有类型的慢地震中，极低频地震（VLFE）是最神秘的，因为它们很难可靠地检测到，而且对VLFE的物理性质知之甚少。在这里，我们显示了三个VLFE在卡斯卡迪亚，是动态触发的2009年MW 6.9运河德巴列纳斯地震在加州湾。VLFEs可能位于孕震区和卡斯卡迪亚幕式震颤和滑动（ETS）带之间，包括一个矩震级为5.7的事件。这是迄今为止报道的最大的VLFE，产生了清晰的大地测量信号。我们的研究结果表明，卡斯卡迪亚巨型逆冲断层可能会在这个间隙区的某些地方迅速滑动，这种允许的滑动行为对沿海社区，也许进一步内陆有直接的地震危险影响。此外，观测到的震源可能代表了一类新的滑动事件，其特征不符合目前对缓慢或规则地震的理解。
Megathrust earthquakes and their associated tsunamis cause some of the worst natural disasters. In addition to earthquakes, a wide range of slip behaviors are present at subduction zones, including slow earthquakes that span multiple orders of spatial and temporal scales. Understanding these events may shed light on the stress or strength conditions of the megathrust fault. Out of all types of slow earthquakes, very low frequency earthquakes (VLFEs) are most enigmatic because they are difficult to detect reliably, and the physical nature of VLFEs are poorly understood. Here we show three VLFEs in Cascadia that were dynamically triggered by a 2009 Mw 6.9 Canal de Ballenas earthquake in the Gulf of California. The VLFEs likely locate in between the seismogenic zone and the Cascadia episodic tremor and slip (ETS) zone, including one event with a moment magnitude of 5.7. This is the largest VLFE reported to date, causing clear geodetic signals. Our results show that the Cascadia megathrust fault might slip rapidly at some spots in this gap zone, and such a permissible slip behavior has direct seismic hazard implications for coastal communities and perhaps further inland. Further, the observed seismic sources may represent a new class of slip events, whose characteristics do not fit current understandings of slow or regular earthquakes.