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Quantitative anisotropies of palaeopermeability in a strike-slip fault damage zone: Insights from micro-CT analysis and numerical simulations
Tectonophysics ( IF 2.9 ) Pub Date : 2021-04-18 , DOI: 10.1016/j.tecto.2021.228873
R. Gomila , G. Arancibia , M. Nehler , R. Bracke , D. Morata , J. Cembrano

Fracturing and damage around faults related to seismogenesis can enhance hydrothermal fluid percolation, causing mineral precipitation. This study uses hydrothermally sealed microfractures across an ancient exhumed fault to unravel the 3D-spatial distribution of fault damage and related anisotropy in permeability. We studied the fault damage zone of the Jorgillo Fault, a left-lateral strike-slip fault, exposed by ca. 20 km in the Atacama Fault System, northern Chile. The study was conducted by addressing the 3D-spatial distribution of the microfracture network through X-ray micro-computed tomography and palaeopermeability modeling using a computational fluid dynamic approach, thus assessing mm-scale fault-related permeability tensors. 3D modeled fault-directed permeability ellipsoids on both sides of the fault core are transverse anisotropic, where palaeopermeability (matrix permeability) in the fault-parallel plane is higher than across-strike of the Jorgillo Fault (2.4 and 1.9 times in the eastern and western block of the fault, respectively). Modeled 3D permeability values (ca. 10−11 to 10−15 m2) show a mean overestimation factor of 8.4 of the estimated 2D permeability (ca. 10−9 to 10−12 m2). Permeability anisotropy distribution in the damage zone is related to off-fault damage generation, and could be explained by tip propagation fault growth and dynamic rupture due to earthquakes under the fault-valve mechanism. Whereas the fault would act as an impermeable seal except for post-failure, when it became highly permeable for fluids.



中文翻译:

走滑断层破坏带古渗透性的定量各向异性:微观CT分析和数值模拟的见解

与地震发生有关的断层周围的压裂和破坏会加剧热液渗流,引起矿物沉淀。这项研究使用了一个古老的已发掘断层的热密封微裂缝来揭示断层破坏的3D空间分布以及渗透率的相关各向异性。我们研究了Jorgillo断层的断层破坏带,这是一条左旋走滑断层,由ca暴露。智利北部阿塔卡马断层系统20公里。这项研究是通过使用计算流体动力学方法通过X射线微计算机断层扫描和古可渗透性模型解决微裂缝网络的3D空间分布来进行的,从而评估了毫米级断层相关渗透率张量。断层芯两侧的3D建模的断层定向渗透率椭球是横向各向异性的,断层平行面上的古通透性(基质渗透率)高于乔尔吉洛断层的横贯走向(断层东部和西部区块分别为2.4倍和1.9倍)。建模的3D渗透率值(约10-11至10 -15  m 2)显示的平均2D渗透率(约10 -9至10 -12  m 2)的平均高估系数为8.4 。破坏带的渗透率各向异性分布与断层破坏的产生有关,可以用断层阀机制下的尖端传播断层增长和地震引起的动态破裂来解释。当断层对流体具有高渗透性时,除断层后,断层将作为不可渗透的密封。

更新日期:2021-04-22
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