Fast-moving dislocations trigger flash weakening in carbonate-bearing faults during earthquakes.
Fast-moving dislocations trigger flash weakening in carbonate-bearing faults during earthquakes.
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DOI：
10.1038/srep16112
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发表时间：
2015-11-10
影响因子：
4.6
通讯作者：
Di Toro G
中科院分区：
文献类型：
--
作者：
Spagnuolo E;Plümper O;Violay M;Cavallo A;Di Toro G
破裂锋可以引起断层位移，在几毫秒内达到几ms−1的速度，在距离地震成核区的任何距离。在含硅酸盐岩石的情况下，突然的滑动加速导致粗糙接触处的熔融，从而导致断层摩擦强度的大幅降低（即，闪光减弱）。在含碳酸盐岩的实验中也观察到闪变弱化，但缺乏熔融的证据。为了揭示碳酸盐岩闪变弱化的微观物理机制，采用旋转剪切仪对预切卡拉拉大理石圆柱体进行了与地震传播相关的实验。在第一个5毫米的滑动的剪切应力降低到30%和CO2被释放。聚焦离子束，扫描和透射电子显微镜调查的滑动区揭示了方解石纳米颗粒和无定形碳的存在。我们解释的CO2释放，纳米颗粒和无定形碳的形成是一个冲击式的应力释放与快速移动的位错的迁移的结果。无定形碳，由于其低摩擦系数，是负责闪光减弱，并促进地震破裂的传播碳酸盐断层补丁。
Rupture fronts can cause fault displacement, reaching speeds up to several ms−1 within a few milliseconds, at any distance away from the earthquake nucleation area. In the case of silicate-bearing rocks the abrupt slip acceleration results in melting at asperity contacts causing a large reduction in fault frictional strength (i.e., flash weakening). Flash weakening is also observed in experiments performed in carbonate-bearing rocks but evidence for melting is lacking. To unravel the micro-physical mechanisms associated with flash weakening in carbonates, experiments were conducted on pre-cut Carrara marble cylinders using a rotary shear apparatus at conditions relevant to earthquakes propagation. In the first 5 mm of slip the shear stress was reduced up to 30% and CO2 was released. Focused ion beam, scanning and transmission electron microscopy investigations of the slipping zones reveal the presence of calcite nanograins and amorphous carbon. We interpret the CO2 release, the formation of nanograins and amorphous carbon to be the result of a shock-like stress release associated with the migration of fast-moving dislocations. Amorphous carbon, given its low friction coefficient, is responsible for flash weakening and promotes the propagation of the seismic rupture in carbonate-bearing fault patches.