Interseismic Strain Localization in the San Jacinto Fault Zone
Interseismic Strain Localization in the San Jacinto Fault Zone
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DOI：
10.1007/s00024-013-0753-z
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发表时间：
2014-11
影响因子：
2
通讯作者：
E. Lindsey;V. Sahakian;Y. Fialko;Y. Bock;S. Barbot;T. Rockwell
中科院分区：
文献类型：
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作者：
E. Lindsey;V. Sahakian;Y. Fialko;Y. Bock;S. Barbot;T. Rockwell
我们研究了加利福尼亚州安扎圣哈辛托断层的震间形变，之前的大地测量观测表明该断层存在异常高的剪切应变率。我们提出了一组来自 GPS 和 InSAR 观测的更新的长期速度，这些速度揭示了 2-3 公里宽的剪切带变形速度超过背景应变率两倍以上。 GPS 占据了 1990 年安装在 Anza 断层轨迹上的对准阵列，使我们能够排除浅层蠕变对观测到的应变率的可能影响。使用异质弹性半空间中的位错模型，我们发现断层带内的剪切模量减少了 1.2–1.6 倍，如 AllamandBen-Zion（Geophys J Int 190:1181–1196, 2012）的断层扫描成像所示，可以解释观测到的异常应变率的大约 50%。然而，本例中的最佳拟合锁定深度（10.4 ± 1.3 km）明显小于当地地震活动深度范围（14-18 km）。我们表明，假设锁定深度为 15 公里，则需要剪切模量减少至少 2.4 倍的深断层带才能完全解释大地应变率。两种替代可能性包括深部微震活动区域内断层蠕变占长期滑移率的很大一部分，或者上断层带内屈服强度降低导致震间期期间的分布式塑性破坏。
We investigate interseismic deformation across the San Jacinto fault at Anza, California where previous geodetic observations have indicated an anomalously high shear strain rate. We present an updated set of secular velocities from GPS and InSAR observations that reveal a 2–3 km wide shear zone deforming at a rate that exceeds the background strain rate by more than a factor of two. GPS occupations of an alignment array installed in 1990 across the fault trace at Anza allow us to rule out shallow creep as a possible contributor to the observed strain rate. Using a dislocation model in a heterogeneous elastic half space, we show that a reduction in shear modulus within the fault zone by a factor of 1.2–1.6 as imaged tomographically byAllamandBen-Zion(Geophys J Int 190:1181–1196, 2012) can explain about 50 % of the observed anomalous strain rate. However, the best-fitting locking depth in this case (10.4 ± 1.3 km) is significantly less than the local depth extent of seismicity (14–18 km). We show that a deep fault zone with a shear modulus reduction of at least a factor of 2.4 would be required to explain fully the geodetic strain rate, assuming the locking depth is 15 km. Two alternative possibilities include fault creep at a substantial fraction of the long-term slip rate within the region of deep microseismicity, or a reduced yield strength within the upper fault zone leading to distributed plastic failure during the interseismic period.