Aftershocks halted by static stress shadows
Aftershocks halted by static stress shadows
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DOI：
10.1038/ngeo1465
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发表时间：
2012-06
影响因子：
18.3
通讯作者：
S. Toda;R. Stein;G. Beroza;D. Marsan
中科院分区：
文献类型：
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作者：
S. Toda;R. Stein;G. Beroza;D. Marsan
地震给周围的地壳带来静态和动态的应力变化。断层的突然滑动会引起小而持久的静态应力变化，而通过的地震波会引起大而短暂的动态应力变化。由于静应力和动应力都能在主震的几个破裂尺度内触发地震，因此很难区分它们对触发过程的贡献。然而，只有动应力才能在远离震源的地方触发地震，只有静应力才能产生应力阴影，在那里，地震后阴影区的应力和地震活动率下降，。在这里，我们计算的应力施加的6.1级约书亚树和附近的7.3级兰德斯地震发生在加州，分别在1992年4月和6月，并通过时间来测量地震活动。我们表明，在第一次地震的余震区受到静应力增加，从第二，地震活动率跳跃。相反，第一次地震的余震区落在第二次地震的应力阴影下，静应力下降，地震活动停止。地震活动的停止意味着静应力是大地震空间聚集的必要因素，应该成为危险性评估的一个组成部分。
Earthquakes impart static and dynamic stress changes to the surrounding crust. Sudden fault slip causes small but permanent—static—stress changes, and passing seismic waves cause large, but brief and oscillatory—dynamic—stress changes. Because both static and dynamic stresses can trigger earthquakes within several rupture dimensions of a mainshock, it has proven difficult to disentangle their contributions to the triggering process,,. However, only dynamic stress can trigger earthquakes far from the source,, and only static stress can create stress shadows, where the stress and thus the seismicity rate in the shadow area drops following an earthquake,,,. Here we calculate the stress imparted by the magnitude 6.1 Joshua Tree and nearby magnitude 7.3 Landers earthquakes that occurred in California in April and June 1992, respectively, and measure seismicity through time. We show that, where the aftershock zone of the first earthquake was subjected to a static stress increase from the second, the seismicity rate jumped. In contrast, where the aftershock zone of the first earthquake fell under the stress shadow of the second and static stress dropped, seismicity shut down. The arrest of seismicity implies that static stress is a requisite element of spatial clustering of large earthquakes and should be a constituent of hazard assessment.