Cataclastic shear bands in sands and sandstones are typically stronger, stiffer, and exhibit lower permeability than the surrounding matrix, and therefore act as barriers to fluid flow. Previous work has quantified the reduction in permeability associated with these features; however, little is known about the role of shear band structure in controlling the way they impact permeability and elastic properties. Here, we report on a suite of laboratory measurements designed to measure the poromechanical properties for host material and natural shear bands, over effective stresses from 1–65 MPa. In order to investigate the role of host material properties in controlling poromechanical evolution with stress, we sampled shear bands from two well‐studied sandstones representing structurally distinct end‐members: a poorly cemented marine terrace sand from the footwall of the McKinleyville thrust fault in Humboldt County, California, and a strongly‐cemented sandstone from the hanging wall of the Moab Fault in Moab, Utah. The permeability‐porosity trends are similar for all samples, with permeability decreasing systematically with increasing effective stress and decreasing porosity. The permeability of the host material is consistently >1 order of magnitude greater than the shear bands for both localities. For the unconsolidated case, shear bands are less permeable and stiffer than the host material, whereas for the consolidated case, shear bands are slightly less permeable, and wave speeds are slower than in the host. We attribute the differences between the McKinleyville and Moab examples to changes in structure of the nearby host material that accompanied formation of the shear band.

中文翻译：

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形变带在疏松砂和砂岩孔隙力学特性中的作用

沙子和砂岩中的碎裂剪切带通常比周围的基质更坚固，更硬，并且渗透率较低，因此成为流体流动的障碍。先前的工作已经量化了与这些特征相关的渗透率的降低。然而，人们对剪切带结构在控制其影响渗透性和弹性的方式中所起的作用知之甚少。在这里，我们报告了一组实验室测量值，这些测量值旨在在1–65 MPa的有效应力下测量宿主材料和自然剪切带的渗透力学性能。为了研究基质材料特性在控制应力作用下的机体力学演化中的作用，我们从两个经过充分研究的砂岩中取样剪切带，这些砂岩代表了结构上不同的末端成员：加利福尼亚洪堡县McKinleyville逆冲断层下盘的胶结较差的海洋阶地砂，以及犹他州摩押Moab断层的悬壁的胶结砂岩。所有样品的渗透率-孔隙率趋势相似，渗透率随着有效应力的增加和孔隙率的降低而系统地降低。主体材料的渗透率始终比两个位置的剪切带都大> 1个数量级。对于未固结的情况，剪切带的渗透性和刚性低于基质材料，而对于固结的情况，剪切带的渗透性略差于基质材料，并且波速比基质材料慢。