Elevated time-dependent strengthening rates observed in San Andreas Fault drilling, samples
Elevated time-dependent strengthening rates observed in San Andreas Fault drilling, samples
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DOI：
10.1016/j.epsl.2016.06.036
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发表时间：
2016-09-15
影响因子：
5.3
通讯作者：
Kopf, Achim J.
中科院分区：
文献类型：
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作者：
Ikari, Matt J.;Carpenter, Brett M.;Kopf, Achim J.
位于加州的中央圣安德烈亚斯断层被称为蠕动断层，然而最近的研究表明，它可能正在积累滑动赤字，因此应认真考虑其孕震潜力。我们进行了实验室摩擦实验，测量随时间变化的摩擦加强（愈合）的断层带和围岩样品在钻井过程中恢复在圣安德烈亚斯断层观测站在深度（SAFOD），位于南部边缘附近的蠕变部分和直接附近的三个重复的微地震集群。我们发现，对于保持时间高达3000 s，摩擦愈合遵循对数线性依赖于保持时间，并且愈合率对于活跃剪切断层岩心的样品非常低，与先前的结果一致。然而，考虑到保持时间更长，高达350，000 s，愈合速率加快，使得所有样品的数据都更好地由幂律关系描述。通常，具有较高含量的页硅酸盐矿物的样品表现出低的对数线性愈合速率，并且当包括较长的保持时间时，显著地富含粘土的断层带样品也表现出强的幂律愈合。我们的数据表明，弱断层，如圣安德烈亚斯断层的蠕动部分，可以积累地震间的剪切应力比预期的更快，从以前的摩擦数据。利用摩擦愈合对保持时间的幂律依赖性，基于我们的数据的复发间隔和应力降的计算精确地匹配了圣安德烈亚斯断层上离散蠕变事件和重复M-W = 2地震的观测。(C)2016爱思唯尔B. V.保留所有权利。
The central San Andreas Fault in California is known as a creeping fault, however recent studies have shown that it may be accumulating a slip deficit and thus its seismogenic potential should be seriously considered. We conducted laboratory friction experiments measuring time-dependent frictional strengthening (healing) on fault zone and wall rock samples recovered during drilling at the San Andreas Fault Observatory at Depth (SAFOD), located near the southern edge of the creeping section and in the direct vicinity of three repeating microearthquake clusters. We find that for hold times of up to 3000 s, frictional healing follows a log -linear dependence on hold time and that the healing rate is very low for a sample of the actively shearing fault core, consistent with previous results. However, considering longer hold times up to 350,000 s, the healing rate accelerates such that the data for all samples are better described by a power law relation. In general, samples having a higher content of phyllosilicate minerals exhibit low log -linear healing rates, and the notably clay-rich fault zone sample also exhibits strong power -law healing when longer hold times are included. Our data suggest that weak faults, such as the creeping section of the San Andreas Fault, can accumulate interseismic shear stress more rapidly than expected from previous friction data. Using the power -law dependence of frictional healing on hold time, calculations of recurrence interval and stress drop based on our data accurately match observations of discrete creep events and repeating M-w = 2 earthquakes on the San Andreas Fault. (C) 2016 Elsevier B.V. All rights reserved.