Low friction and fault weakening revealed by rising sensitivity of tremor to tidal stress
Low friction and fault weakening revealed by rising sensitivity of tremor to tidal stress
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DOI：
10.1038/ngeo2419
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发表时间：
2015-05-01
影响因子：
18.3
通讯作者：
Houston, Heidi
中科院分区：
文献类型：
--
作者：
Houston, Heidi
在俯冲带，板块边界断层深部的摩擦水平控制着应力的积累和释放，从而控制着应力向较浅的断层锁定部分的转移，该断层可能在大逆冲地震中滑动。在一些俯冲带，深断层滑动缓慢，速度远低于较浅的常规地震，并且经常伴随着称为震颤的微弱地震波。海洋或固体潮汐引起的微小应力变化可能会引发地震和缓慢滑动。在这里，我使用地震数据结合潮汐应力计算来确定潮汐对 2007 年至 2012 年间卡斯卡迪亚六次大型慢滑移事件产生的 31,000 次地震的影响。我发现，随着断层上每个点的滑移累积，地震对潮汐应力的敏感度在每次滑移事件期间都会上升。具体来说，震颤率是潮汐应力的指数函数，并且这种指数敏感性会持续几天增长，这意味着断层在滑动过程中减弱。我利用潮汐应力与震颤之间的关系计算了断层的内摩擦系数，发现其值为0到0.1，这表明深部断层本质上是脆弱的。
At subduction zones, the level of friction on the deep part of the plate boundary fault controls stress accumulation and release, which govern the transfer of stress to the shallower, locked part of the fault that can slip in a megathrust earthquake. In some subduction zones, the deep fault slips slowly, at speeds far less than shallower, regular earthquakes, and is often accompanied by weak seismic waves called tremor. Tremor and slow slip can be triggered by small stress changes induced by ocean or solid Earth tides. Here I use seismic data combined with calculations of tidal stress to determine the influence of tides on 31,000 tremors generated by six large slow-slip events in Cascadia between 2007 and 2012. I find that the sensitivity of tremor to tidal stresses rises during each slip event, as slip at each spot on the fault accumulates. Specifically, tremor rate is an exponential function of tidal stress, and this exponential sensitivity grows for several days, implying that the fault weakens during slip. I use the relationship between tidal stress and tremor to calculate a coefficient of intrinsic friction for the fault and find values of 0 to 0.1, which indicate that the deep fault is inherently weak.