Geodetic Evidence for a Near-Fault Compliant Zone along the San Andreas Fault in the San Francisco Bay Area
Geodetic Evidence for a Near-Fault Compliant Zone along the San Andreas Fault in the San Francisco Bay Area
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旧金山湾区圣安德烈亚斯断层沿线近断层顺从区的大地测量证据
DOI：
10.1785/0120010110
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发表时间：
2002
影响因子：
3
通讯作者：
J. Freymueller
中科院分区：
文献类型：
--
作者：
Qizhi Chen;J. Freymueller
利用1996年和1997年的全球定位系统测量以及20世纪70年代和80年代在加利福尼亚州北部圣安德烈亚斯断层沿线五个小口径大地测量网络站点的电子测距数据来确定近断层应变率。博德加-托马莱斯、圣安德烈亚斯湖和黑山无线电设施网络(从北到南)的张量剪切应变率(1轴平行于断层，2轴垂直于断层的坐标系)分别为0.339±0.025，0.366±0.095和0.316±0.060μ应变/年。黑山无线电设施和圣安德烈亚斯湖地震台网中断层附近的剪切应变率既可以用低刚性柔顺带集中应变的二维不均匀模型来解释，也可以用8公里的很浅的锁定深度来解释。其他证据表明锁定深度大于10公里，因此我们倾向于第一种解释。断裂带和围岩之间的刚性差异似乎从南部开始变得更强，大约从博德加湾萨利安地块的北部开始，这表明断层两侧的物质和累积的断层错动在顺应断裂带的发展中发挥了作用。根据远场大地测量数据估计的断层滑移率对顺应带的存在只有微弱的敏感性，但如果顺应带存在且未建模，则对锁定深度的估计可能偏向较浅的值约10%。
Global Positioning System measurements in 1996 and 1997 and Electronic Distance Measuring data from the 1970s and 1980s at sites in five small-aperture geodetic networks along the San Andreas fault in northern California were used to determine the near-fault strain rate. The tensor shear strain rate \({\dot{{\varepsilon}}}_{12}\) (referred to a coordinate system with the 1 axis parallel to the fault and the 2 axis normal to the fault) in the Bodega–Tomales, Lake San Andreas, and Black Mountain–Radio Facility networks (from north to south) are 0.339 ± 0.025, 0.366 ± 0.095, and 0.316 ± 0.060 μstrain/yr, respectively. The shear strain rate near the fault in the Black Mountain–Radio Facility and Lake San Andreas networks can be explained either by a 2D inhomogeneous model in which a low-rigidity compliant zone concentrates strain near the fault or by a very shallow locking depth of 8 km. Other evidence points to a locking depth greater than 10 km, so we prefer the first explanation. The contrast in rigidity between the fault zone and the surrounding rock appears to become stronger to the south, starting at approximately the northern extent of the Salinian block at Bodega Bay, suggesting that both the materials on either side of the fault and the cumulative fault offset play a role in the development of a compliant fault zone. Estimates of fault slip rates from far field geodetic data are only weakly sensitive to the presence of a compliant zone, but estimates of locking depths can be biased by approximately 10% toward shallower values if a compliant zone is present and unmodeled.