Geometry and mechanics of secondary fracturing around small three‐dimensional faults in granitic rock
Geometry and mechanics of secondary fracturing around small three‐dimensional faults in granitic rock
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DOI：
10.1029/98jb01393
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发表时间：
1998-09
影响因子：
--
通讯作者：
S. Martel;W. Boger
中科院分区：
文献类型：
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作者：
S. Martel;W. Boger
沿天然小断层观察到的次生裂缝的方向、位置、大小和相对丰度可以用三维弹性模型来解释。在加利福尼亚州内华达山脉的块状花岗岩中，沿着近垂直的左旋走滑小断层的次生裂缝(1)从其宿主断层沿逆时针方向一致地走向25°±10°，倾角大于80°；(2)沿着断层迹线的中央部分通常没有；(3)在一些断层迹线的末端附近有许多，但沿着其他断层迹线没有；以及(4)在极少数情况下，沿着断层迹线中心或恰好越过断层迹线末端形成梯形阵列。这些观察结果与次生裂隙是一致的，这些裂隙沿着高滑动阻力的“粘性边缘”在椭圆形断层周长附近成核，并沿垂直于局部最大拉应力的三维方向传播。断裂相对于断层的方向反映了断层滑动过程中的小应力降。这些观测和模型共同对断层如何生长和传导流体产生了直接的影响。次级裂缝可能在小走滑断层的末端更大，而不是在它们的顶部和底部。因此，如果走滑断层以不受限制的方式增长，它们更有可能是端到端的连接，而不是自上而下的连接，特别是在滑动较小的地方。在断层之间的连接处，水力传导性可能会增强，因此沿着相连的走滑断层的高传导性区域更有可能是垂直的，而不是水平的。
The orientations, locations, sizes, and relative abundances of secondary fractures observed along small natural faults can be accounted for by a three-dimensional elastic model. Secondary fractures along small subvertical left-lateral strike-slip faults in massive granitic rock of the Sierra Nevada of California (1) consistently strike 25°±10° counterclockwise from their host faults and dip at angles greater than 80°; (2) generally are absent along the central portions of the fault traces; (3) are numerous near the ends of some fault traces but absent along others; and (4) in rare cases form echelon arrays either centered along a fault trace or just past the fault trace ends. These observations are consistent with secondary fractures that nucleated near the perimeter of an elliptical fault along a “cohesive rim” of high slip resistance and propagated in three dimensions normal to the local most tensile stress. The fracture orientations relative to the faults reflect small stress drops during slip on the faults. The observations and model together have direct implications for how faults grow and conduct fluids. Secondary fractures are likely to be larger at the ends of small strike-slip faults rather than at their tops and bottoms. As a result, if strike-slip faults grow in an unrestricted manner, they are more likely to be linked end-to-end rather than top-to-bottom, especially where slip is small. Hydraulic conductivity is likely to be enhanced at the linkages between faults, so highly conductive regions along linked strike-slip faults are more likely to be vertical rather than horizontal.