Revealing the cascade of slow transients behind a large slow slip event
Revealing the cascade of slow transients behind a large slow slip event
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揭示大型慢滑事件背后的慢速瞬变级联
DOI：
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发表时间：
2017
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通讯作者：
M. Campillo
中科院分区：
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作者：
W. Frank;Baptiste Rousset;C. Lasserre;M. Campillo
慢滑事件能够达到与大型逆冲地震（Mw bbbb70）相似的震级，在调节构造运动中起主要作用。这些滑动瞬态是沿板块边界根部缓慢释放的累积构造应力，被认为是沿板块界面发生的主要地震破裂，在时间和空间上都是平滑的。我们在这里证明，大的慢滑动事件实际上是一个复杂的级联短的慢瞬变。利用密集的低频地震目录作为指导，我们研究了2006年发生在墨西哥Guerrero地下40公里俯冲界面上的Mw7.5慢滑事件。我们表明，虽然GPS记录的长周期地表位移表明持续时间为6个月，但构造释放方向的运动仅在<60天内零星发生，其表面特征因板块界面的快速重新锁定而减弱。这些结果表明，我们目前的缓慢和连续破裂的概念模型是过时的，是小的、聚集的滑动事件叠加的低分辨率大地测量观测的产物。我们提出的慢滑动作为慢瞬态级联的模型对慢滑动事件的标度有重要的影响，因为它意味着我们高估了持续时间T，低估了大慢滑动事件的矩量M。
Capable of reaching similar magnitudes to large megathrust earthquakes (Mw > 7), slow slip events play a major role in accommodating tectonic motion. These slip transients are the slow release of built-up tectonic stress along the roots of plate boundaries and are thought to represent a predominantly aseismic rupture along the plate interface that is smooth in both time and space. We demonstrate here that large slow slip events are in fact a complex cascade of short slow transients. Using a dense catalog of low-frequency earthquakes as a guide, we investigate the Mw7.5 slow slip event that happened in 2006 along the subduction interface 40 km beneath Guerrero, Mexico. We show that while the long-period surface displacements as recorded by GPS suggest a six month duration, motion in the direction of tectonic release only sporadically occurs over <60 days and its surface signature is attenuated by rapid relocking of the plate interface. These results demonstrate that our current conceptual model of slow and continuous rupture is outdated and is an artifact of low-resolution geodetic observations of a superposition of small, clustered slip events. Our proposed model of slow slip as a cascade of slow transients has important consequences for the scaling of slow slip events as it implies that we overestimate the duration T and underestimate the moment magnitude M of large slow slip events.