Triggered earthquakes suppressed by an evolving stress shadow from a propagating dyke
Triggered earthquakes suppressed by an evolving stress shadow from a propagating dyke
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DOI：
10.1038/ngeo2491
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发表时间：
2015-07
影响因子：
18.3
通讯作者：
R. Green;T. Greenfield;R. White
中科院分区：
文献类型：
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作者：
R. Green;T. Greenfield;R. White
大地震可以在静态应力中产生微小的变化：增加会引发余震群，或者减少会产生一个地震减少的区域——应力阴影。然而，来自大地震的地震波也会引起可能引发地震活动的瞬态动应力。这使得很难区分静应力和动应力变化对余震的相对影响。堤防侵入不会产生动应力，因此为应力阴影假说提供了一个明确的测试。在这里，我们使用GPS和地震数据重建了2014年8月冰岛中部Bárðarbunga火山下长46公里、宽5米的火成岩岩脉的侵入。我们发现，在堤坝就位期间，在距离5至15公里的地方首先触发了地震活动爆发，然后随着堤坝尖端向远离火山的方向传播而突然停止。我们计算了堤防扩展过程中不断变化的静应力变化，并表明在堤防附近的三个不同区域，应力速率既控制着地震率的触发，又控制着地震率的抑制。我们的研究结果表明静应力的变化有助于控制地震聚集。类似的小的静态应力变化对于触发地热区附近的地震活动可能是重要的，这些地区是水力压裂和压缩油气田。
Large earthquakes can generate small changes in static stress: increases that trigger aftershock swarms, or reductions that create a region of reduced seismicity—a stress shadow,. However, seismic waves from large earthquakes also cause transient dynamic stresses that may trigger seismicity,. This makes it difficult to separate the relative influence of static and dynamic stress changes on aftershocks. Dyke intrusions do not generate dynamic stresses, so provide an unambiguous test of the stress shadow hypothesis. Here we use GPS and seismic data to reconstruct the intrusion of an igneous dyke that is 46 km long and 5 m wide beneath Bárðarbunga Volcano, central Iceland, in August 2014. We find that during dyke emplacement, bursts of seismicity at a distance of 5 to 15 km were first triggered and then abruptly switched off as the dyke tip propagated away from the volcano. We calculate the evolving static stress changes during dyke propagation and show that the stressing rate controls both the triggering and then suppression of earthquake rates in three separate areas adjacent to the dyke. Our results imply that static stress changes help control earthquake clustering. Similar small static stress changes may be important for triggering seismicity near geothermal areas, regions being hydrofractured and deflating oil and gas fields.