Weakness of the San Andreas Fault revealed by samples from the active fault zone
Weakness of the San Andreas Fault revealed by samples from the active fault zone
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DOI：
10.1038/ngeo1089
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发表时间：
2011-04-01
影响因子：
18.3
通讯作者：
Saffer, D. M.
中科院分区：
文献类型：
--
作者：
Carpenter, B. M.;Marone, C.;Saffer, D. M.
了解构造断层的强度和滑动行为是地震物理学和地震危险性评估的中心问题（1-8）。许多主要断层，包括圣安德烈亚斯断层，与周围的岩石相比是脆弱的，但这种脆弱的原因是有争议的（1）。先前对圣安德烈亚斯断层岩石摩擦强度的测量值太高，无法解释观察到的弱点（1，9 -13）。然而，这些测量依赖于在离活动断层一定距离处采集的样本或风化表面样本。最近对圣安德烈亚斯断层（9）的钻探提供了来自孕震深度活动滑动断层的材料。在这里，我们提出了系统的测量的摩擦性能和组成的圣安德烈亚斯断层在2.7公里的深度，包括围岩和活动断层。我们发现，断层相对于围岩是软弱的，断层岩石表现出稳定的滑动摩擦行为。断裂带含有弱矿物蒙皂石，并且没有表现出摩擦愈合-材料中的键在断裂后不愈合。综合考虑，断裂带材料的低固有强度和缺乏愈合可以解释为什么圣安德烈亚斯断层的滑动是由加州中部的地震蠕变和小地震造成的，而不是由大的破坏性地震造成的。
Understanding the strength and slip behaviour of tectonic faults is a central problem in earthquake physics and seismic-hazard assessment(1-8). Many major faults, including the San Andreas Fault, are weak compared with the surrounding rock, but the cause of this weakness is debated(1). Previous measurements of the frictional strength of San Andreas Fault rocks are too high to explain the observed weakness(1,9-13). However, these measurements relied on samples taken at a distance from the active fault or from weathered surface samples. Recent drilling into the San Andreas Fault(9) has provided material from the actively slipping fault at seismogenic depths. Here we present systematic measurements of the frictional properties and composition of the San Andreas Fault at 2.7 km depth, including the wall rock and active fault. We find that the fault is weak relative to the surrounding rock and that the fault rock exhibits stable sliding friction behaviour. The fault zone contains the weak mineral smectite and exhibits no frictional healing-bonds in the material do not heal after rupture. Taken together, the low inherent strength and lack of healing of the fault-zone material could explain why the San Andreas Fault slips by aseismic creep and small earthquakes in central California, rather than by large, destructive earthquakes.