Stress-induced seismic velocity anisotropy and physical properties in the SAFOD Pilot Hole in Parkfield, CA
Stress-induced seismic velocity anisotropy and physical properties in the SAFOD Pilot Hole in Parkfield, CA
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DOI：
10.1029/2003gl019020
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发表时间：
2004-07-29
影响因子：
5.2
通讯作者：
Zoback, MD
中科院分区：
文献类型：
--
作者：
Boness, NL;Zoback, MD
SAFOD 导向孔从深度 775 m 至 2150 m 的高度裂隙萨里尼亚花岗岩中收集了一套全面的地球物理测井数据。导向孔穿过许多宏观裂缝和断层，方向极其不同。尽管裂缝和断层的方向变化很大，但剪切波的快速偏振方向与井眼破裂和钻井引起的拉伸裂缝确定的最大水平压缩方向非常一致。至少三个主要剪切带与钻孔相交，其特征是异常低的速度和电阻率、异常高的剪切速度各向异性以及不存在应力引起的井眼破裂（这表明异常低的差应力）。我们认为，在先导孔中观察到的地震速度各向异性的物理机制是响应各向异性应力状态而优先闭合裂缝。
A comprehensive suite of geophysical logs was collected in the SAFOD Pilot Hole from a depth of 775 m to 2150 m in highly fractured Salinian granite. The Pilot Hole intersected numerous macroscopic fractures and faults with extremely varied orientations. Despite the highly variable orientation of the fractures and faults, the fast polarization direction of the shear waves is very consistent with the direction of maximum horizontal compression determined from wellbore breakouts and drilling induced tensile fractures. At least three major shear zones were intersected by the borehole that are characterized by anomalously low velocity and resistivity, anomalously high shear velocity anisotropy and an absence of stress-induced wellbore breakouts ( which suggests anomalously low differential stress). We argue that the physical mechanism responsible for the seismic velocity anisotropy observed in the Pilot Hole is the preferential closure of fractures in response to an anisotropic stress state.