Structural anisotropy of normal fault surfaces
Structural anisotropy of normal fault surfaces
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DOI：
10.1016/0191-8141(96)00022-3
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发表时间：
1996-08
影响因子：
3.1
通讯作者：
Joong-Jeek Lee;R. Bruhn
中科院分区：
文献类型：
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作者：
Joong-Jeek Lee;R. Bruhn
天然断层面的精确描述对于理解断层的几何学、力学和流体输运性质是必不可少的。在Wasatch断层带和犹他州的Oqualeh山脉的断层面上，以30°的增量测量断层面的剖面，以确定在10 - 3 m和30 m之间波长处表面粗糙度的方向各向异性，然后与更大尺度的断层面的剖面进行比较。表面各向异性和表面振幅与波长之比的增加与自仿射断层地形在1 mm和约5 km之间的波长是一致的。表面轮廓的分形维数一般随着与滑移方向夹角的增大而系统地减小。方向各向异性由方位角标度函数γφ= K sin（φ）+ γ 0或AFφ=（AFmax−1）sin（φ）+ 1描述，其中γφ和AFφ分别是方位角φ处的振幅波长比和各向异性因子，相对于断层面内的滑动方向顺时针测量，γ 0是平行于滑动方向的振幅波长比。K =（γ90−γ0）是一个各向异性系数，在断层面上随空间波长系统性地增加。自然断层表面的表征提供了诸如分形维数（D）、功率谱的截距（log（C））、剖面方差和各向异性因子（AF）的变化等参数，这些参数是使用谱合成生成自然断层表面的分形模型所需的。我们生成的样本模型，说明断层面之间的差异，其特征在于恒定与方位角变化的分形维数。后者的模型表面包含低振幅波纹叠加在细长的脊平行滑动方向。这种表面结构类似于自然断层面，这些断层面穿过岩性层或被次级断层（如R和R′剪切）切割。
Precise description of natural fault surfaces is indispensable to understanding the geometry, mechanics and fluid transport properties of faults. Profiles of fault surfaces in the Wasatch fault zone and Oquirrh Mountains, Utah, are measured at 30° increments within the fault plane to determine the directional anisotropy of surface roughness at wavelengths between 10−3m and 30 m, and then compared with profiles of larger-scale fault surfaces. Surface anisotropy and an increasing ratio of surface amplitude to wavelength are consistent with self-affine fault topography at wavelengths between 1 mm and approximately 5 km. Fractal dimension of surface profiles generally decreases systematically as the angle to the slip direction increases. Directional anisotropy is described by an azimuthal scaling function γφ= K sin(φ) + γ0or AFφ= (AFmax−1) sin(φ) + 1, where γφand AFφare the amplitude to wavelength ratio and anisotropy factor respectively at azimuth φ, measured clockwise relative to slip direction within the fault surface, and γ0is the amplitude to wavelength ratio parallel to slip direction. K = (γ90−γ0) is an anisotropy coefficient and increases systematically with spatial wavelength on the fault surface. Characterization of natural fault surfaces provides parameters such as fractal dimension (D), intercept (log(C)) of power spectra, profile variance, and variation in anisotropy factor (AF), which are needed to generate fractal models of natural fault surfaces using spectral synthesis. We generate sample models which illustrate the differences between fault surfaces characterized by constant versus azimuthally varying fractal dimension. The latter model surfaces contain low amplitude corrugations superimposed on elongate ridges which parallel slip direction. This surface texture resembles that of natural fault surfaces that refract across lithologic layering or are cut by secondary faults such as R and R′ shears.