Interseismic Coupling, Megathrust Earthquakes and Seismic Swarms Along the Chilean Subduction Zone (38A°-18A°S)
Interseismic Coupling, Megathrust Earthquakes and Seismic Swarms Along the Chilean Subduction Zone (38A°-18A°S)
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DOI：
10.1007/s00024-016-1280-5
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发表时间：
2016-05-01
影响因子：
2
通讯作者：
Socquet, A.
中科院分区：
文献类型：
--
作者：
Metois, M.;Vigny, C.;Socquet, A.
最近，密集的 GPS 网络在板块边界上的扩展使得能够非常精确地绘制沿活动断层的震间耦合图。震间耦合系数与震间期断层上的滑动速度与长期板块速度之比有关，但从断层力学行为角度对耦合的解释仍不清楚。在这里，我们研究了智利俯冲带的耦合与地震活动之间的联系，该俯冲带在过去 5 年中发生了 3 次大地震破裂（2010 年的莫莱 Mw 8.8、2014 年的伊基克 Mw 8.1 和 2015 年的伊拉佩尔 Mw 8.4）。我们将最近在边缘（38A 度 - 18A 度 S）上获取的 GPS 数据与较早的数据相结合，以获得俯冲界面上震间耦合变化的第一张几乎连续的图像。在这里，我们表明至少有六个低耦合区（LCZ），即相对于邻近的高耦合段耦合较低的区域。我们还发现，对于最近的三个 Mw > 8 事件，同震粗糙体与高度耦合的段有很好的相关性，而 LCZ 则充当屏障并阻止了破裂。事件发生前震间期的耦合与背景地震活动之间的关系尚不清楚。然而，我们注意到，群序列容易出现在LCZ与邻近段过渡处的中间耦合区，并且背景地震活动往往集中在发震锁定区的下倾部分。因此，高度耦合的段通常表现出低背景地震活动性。在这一整体背景下，在 2015 年伊拉佩尔地震中部分破裂的大都会段似乎是一个异常值，因为破裂前耦合和背景地震活动都很高，从而引发了这个人口非常稠密地区剩余地震危险的问题。
The recent expansion of dense GPS networks over plate boundaries allows for remarkably precise mapping of interseismic coupling along active faults. The interseismic coupling coefficient is related to the ratio between slipping velocity on the fault during the interseismic period and the long-term plates velocity, but the interpretation of coupling in terms of mechanical behavior of the fault is still unclear. Here, we investigate the link between coupling and seismicity over the Chilean subduction zone that ruptured three times in the last 5 years with major earthquakes (Maule Mw 8.8 in 2010, Iquique Mw 8.1 in 2014 and Illapel Mw 8.4 in 2015). We combine recent GPS data acquired over the margin (38A degrees-18A degrees S) with older data to get the first nearly continuous picture of the interseismic coupling variations on the subduction interface. Here, we show that at least six low coupling zones (LCZ), areas where coupling is low relatively to the neighboring highly coupled segments can be identified. We also find that for the three most recent Mw > 8 events, co-seismic asperities correlate well with highly coupled segments, while LCZs behaved as barriers and stopped the ruptures. The relation between coupling and background seismicity in the interseismic period before the events is less clear. However, we note that swarm sequences are prone to occur in intermediate coupling areas at the transition between LCZ and neighboring segments, and that the background seismicity tends to concentrate on the downdip part of the seismogenic locked zone. Thus, highly coupled segments usually exhibit low background seismicity. In this overall context, the Metropolitan segment that partly ruptured during the 2015 Illapel earthquake appears as an outlier since both coupling and background seismicity were high before the rupture, raising the issue of the remaining seismic hazard in this very densely populated area.