Stress state at faults: the influence of rock stiffness contrast, stress orientation, and ratio

IF 3.2 2区 地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS
Moritz O. Ziegler, Robin Seithel, Thomas Niederhuber, Oliver Heidbach, Thomas Kohl, Birgit Müller, Mojtaba Rajabi, Karsten Reiter, Luisa Röckel
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Abstract

Abstract. The contemporary crustal stress state is primarily driven by gravitational volume forces and plate tectonics. However, there are various smaller-scale sources such as geological structures and stiffness contrast that perturb stresses and deviate them from the regional pattern. For example, borehole stress analysis in numerous cases has revealed abrupt rotations of horizontal stress orientation of up to 90° when faults are crossed. Herein, we investigate the rotation of principal stress axes at a fault by means of a 2D generic numerical model. We focus on the near field of the fault and the damage zone with a fault parameterized as a rock stiffness contrast. A substantial influence of the far-field stress field in terms of the differential stress and in terms of the stress ratio RS=S1/S_3 is shown. Furthermore, the contrast in material properties is the basis for any stress rotation, and in particular the stiffness is demonstrated to have a significant influence. Eventually, the impact of the angle between the fault strike and the orientation of SHmax is demonstrated. Our results show that the stress rotation is negatively correlated with the ratio of principal far-field stresses. A small angle between the far-field stress orientation and the fault facilitates stress rotation. A high contrast in rock stiffness further increases the stress rotation angle. Faults striking perpendicular to the maximum principal stress orientation experience no rotation at all. However, faults oriented parallel to the maximum principal stress orientation experience either no rotation or a 90° rotation, dependent on the ratio of principal stresses and the rock stiffness contrast. A comparison with observations from various boreholes worldwide shows that in general the findings are in agreement, even though the dip angle proves to have an influence on the stress rotation, in particular for shallow-dipping faults.
断层处的应力状态:岩石刚度对比、应力方向和比率的影响
摘要当代地壳应力状态主要由重力体积力和板块构造驱动。然而,地质构造和刚度对比等各种较小尺度的应力源也会扰动应力,使其偏离区域模式。例如,在许多情况下,钻孔应力分析表明,当断层穿过时,水平应力方向会突然旋转达 90°。在此,我们通过二维通用数值模型研究断层处主应力轴的旋转。我们重点研究了断层的近场和破坏区,并将断层参数化为岩石刚度对比。结果表明,远场应力场对差应力和应力比 RS=S1/S_3 有很大影响。此外,材料特性的对比是任何应力旋转的基础,特别是刚度被证明具有重大影响。最后,还证明了断层走向与 SHmax 方向之间夹角的影响。结果表明,应力旋转与主远场应力比呈负相关。远场应力方向与断层之间的小角度有利于应力旋转。岩石刚度的高反差会进一步增大应力旋转角度。垂直于最大主应力方向的断层不会发生任何旋转。然而,与最大主应力方向平行的断层要么不旋转,要么旋转 90°,这取决于主应力比率和岩石刚度对比。与世界各地不同钻孔的观测结果进行比较后发现,尽管倾角对应力旋转有影响,特别是对浅倾角断层而言,但总的来说,研究结果是一致的。
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来源期刊
Solid Earth
Solid Earth GEOCHEMISTRY & GEOPHYSICS-
CiteScore
6.90
自引率
8.80%
发文量
78
审稿时长
4.5 months
期刊介绍: Solid Earth (SE) is a not-for-profit journal that publishes multidisciplinary research on the composition, structure, dynamics of the Earth from the surface to the deep interior at all spatial and temporal scales. The journal invites contributions encompassing observational, experimental, and theoretical investigations in the form of short communications, research articles, method articles, review articles, and discussion and commentaries on all aspects of the solid Earth (for details see manuscript types). Being interdisciplinary in scope, SE covers the following disciplines: geochemistry, mineralogy, petrology, volcanology; geodesy and gravity; geodynamics: numerical and analogue modeling of geoprocesses; geoelectrics and electromagnetics; geomagnetism; geomorphology, morphotectonics, and paleoseismology; rock physics; seismics and seismology; critical zone science (Earth''s permeable near-surface layer); stratigraphy, sedimentology, and palaeontology; rock deformation, structural geology, and tectonics.
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