The nature and origin of off-fault damage surrounding strike-slip fault zones with a wide range of displacements: A field study from the Atacama fault system, northern Chile
The nature and origin of off-fault damage surrounding strike-slip fault zones with a wide range of displacements: A field study from the Atacama fault system, northern Chile
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DOI：
10.1016/j.jsg.2009.05.002
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发表时间：
2009-08-01
影响因子：
3.1
通讯作者：
Faulkner, D. R.
中科院分区：
文献类型：
--
作者：
Mitchell, T. M.;Faulkner, D. R.
断层核心周围的损伤表现为从岩石基质的微观破裂到宏观裂缝网络的一系列尺度上的变形。不同尺度下损伤的空间分布和几何特征可以帮助预测断裂带的断层生长过程、后续力学、整体水力学和地震学性质。在智利北方的阿塔卡马断层系统中，分析了微尺度和宏观尺度的断裂密度以及围绕走滑断层的方向，这些断层具有近5个数量级（类似于0.12 m-5000 m）的位移。研究了切割花岗闪长岩的断层，并从6至10公里深处被动地挖出。这允许直接比较不同位移的断层周围的损害。断层由一个断层核和相关的损伤带组成。损伤区的宏观裂缝主要是剪切裂缝，与所研究的断层成高角度。它们有一个合理定义的指数下降与距离的故障核心。微骨折是开放、愈合、部分愈合和流体包裹体平面（FIP）的组合。FIN是最早的一组裂缝，并且随着与断层核的垂直距离，裂缝密度呈指数下降。后期的微裂缝并没有表现出一个明确的关系，微裂缝密度与垂直距离断层核心。由FIPs密度定义的损伤区宽度与断层位移成比例，但似乎在几公里的位移处达到最大值。一个故障，在故障核心的两侧损伤的特点是没有损伤不对称。所有故障似乎有一个临界微裂缝密度在故障核心/损伤区边界，是独立的位移。提出了微裂缝密度分布与位移的经验关系式。优选的FIP取向具有与靠近断层核的断层的高角度，并且随着距离而变得更加分散。预测断层外损伤的模型，如断层形成过程中的迁移过程区，几何不规则性和动态破裂的磨损都与我们的数据一致。我们的结论是，很难区分它们之间的基础上的现场数据，至少在本研究的范围内。(C)2009爱思唯尔有限公司保留所有权利。
Damage surrounding the core of faults is represented by deformation on a range of scales from micro-fracturing of the rock matrix to macroscopic fracture networks. The spatial distribution and geometric characterization of damage at various scales can help to predict fault growth processes, subsequent mechanics, bulk hydraulic and seismological properties of a fault zone. Within the excellently exposed Atacama fault system, northern Chile, micro- and macroscale fracture densities and orientation surrounding strike-slip faults with well-constrained displacements ranging over nearly 5 orders of magnitude (similar to 0.12 m-5000 m) have been analyzed. Faults have been studied that cut granodiorite and have been passively exhumed from 6 to 10 km depth. This allows direct comparison of the damage surrounding faults of different displacements. The faults consist of a fault core and associated damage zone. Macrofractures in the damage zone are predominantly shear fractures orientated at high angles to the faults studied. They have a reasonably well-defined exponential decrease with distance from the fault core. Microfractures are a combination of open, healed, partially healed and fluid inclusion planes (FIPs). FIN are the earliest set of fractures and show an exponential decrease in fracture density with perpendicular distance from the fault core. Later microfractures do not show a clear relationship of microfracture density with perpendicular distance from the fault core. Damage zone widths defined by the density of FIPs scale with fault displacement but appear to reach a maximum at a few km displacement. One fault, where damage was characterized on both sides of the fault core shows no damage asymmetry. All faults appear to have a critical microfracture density at the fault core/damage zone boundary that is independent of displacement. An empirical relationship for microfracture density distribution with displacement is presented. Preferred FIP orientations have a high angle to the fault close to the fault core and become more diffuse with distance. Models that predict off-fault damage such as a migrating process zone during fault formation, wear from geometrical irregularities and dynamic rupture are all consistent with our data. We conclude it is very difficult to distinguish between them on the basis of field data alone, at least within the limits of this study. (C) 2009 Elsevier Ltd. All rights reserved.