Foreshock Activity Promoted by Locally Elevated Loading Rate on a 4‐m‐Long Laboratory Fault
Foreshock Activity Promoted by Locally Elevated Loading Rate on a 4‐m‐Long Laboratory Fault
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DOI：
10.1029/2021jb023336
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发表时间：
2022-02
期刊：
影响因子：
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通讯作者：
F. Yamashita;E. Fukuyama;S. Xu
中科院分区：
文献类型：
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作者：
F. Yamashita;E. Fukuyama;S. Xu
我们报告了实验室实验结果，以揭示控制前震发生和震级的因素。我们使用可以剪切4米长的岩石试样的设备进行岩石摩擦实验。我们观察到许多粘滑事件，以及在这些主要事件之间非常缓慢（几十μm/s）但持续时间很长的滑动。这些长期的缓慢滑动分别从断层的前缘和后缘开始，并不断向彼此稳定地传播。这种稳定滑动不会立即引发任何地震事件，无论累积的滑动量如何。在两个长期慢滑前缘合并后，在中部地区开始了第二阶段的慢滑，其滑动速率较高（几百μm/s），称为前兆慢滑，并伴有小地震事件（前震）的发生。随后，主快速破裂最终形成。我们认为承载前震的岩石大小与局部临界成核长度相似；当局部加载率较低时，土石体滑动稳定，但当局部加载率较高时，土石体也会发生不稳定滑动并辐射地震波。我们进一步发现，前震震级与局部滑动率之间存在明显的正相关关系。这些结果表明，局部加载率对前震的发生和震级有显著影响。因此，在研究地震成核过程和其他类似现象（如间歇性震颤和滑动（ETS）、冰震和重复地震）时，应考虑到它的影响。
We report laboratory experimental results to reveal the factors that control the occurrence and magnitude of foreshocks. We conducted rock friction experiments using an apparatus that can shear 4‐m‐long rock specimens. We observed many stick‐slip events, as well as very slow (several tens of μm/s) but long‐lasting slips between those main events. These long‐term slow slips individually initiated from both the leading and trailing edges of the fault, and kept propagating steadily toward each other. Such steady slips did not immediately trigger any seismic events, regardless of the accumulated slip amount. After the coalescence of the two long‐term slow slip fronts, a second phase of slow slip with higher slip rate (several hundreds of μm/s)—called precursory slow slip, began at the central area and was accompanied by the occurrence of small seismic events (foreshocks). Subsequently, the main fast rupture eventually developed. We propose that the asperities that hosted foreshocks had similar size to the local critical nucleation length; the asperities slipped stably when the local loading rate was low, but could also slip unstably and radiated seismic waves when the local loading rate became high. We further found a clear positive correlation between foreshock magnitude and local slip rate. These results suggest that local loading rate has a significant influence on the occurrence and magnitude of foreshocks. Therefore, its effect should be taken into account during the studies of earthquake nucleation process and other similar phenomena such as Episodic Tremor and Slip (ETS), icequakes, and repeating earthquakes.