Fractures usually spread over various scales and strongly influence velocity and anisotropy. We investigate elastic velocity and anisotropy in rocks with fractures of different sizes. Based on synthetic rocks with controlled fracture geometries, we create a set of rocks with fracture diameter of 2, 3 and 4 mm and the fracture thickness is 0.06 mm. P- and S-wave velocities are measured at 0.1 MHz, while the rocks are saturated with water and air. For a fixed measurement frequency (0.1 MHz), velocities are higher in rocks with larger fractures, while anisotropy is higher in rocks with smaller fractures, even for the same fracture density. These phenomena are associated with the wave-induced fluid flow process. Some novel effective medium theories are adopted to calibrate with the laboratory data and analyse the anisotropy affected by the fluid flow mechanism and fracture size. The results of our study demonstrate the significant effects of fracture scale on wave responses by effective medium theories in different ways. We suggest that these scale effects should be of considerable concern in some disciplines (e.g. shear wave splitting in earth's crust and hydraulic fracture monitoring with microseismic data). Considering the scale effects of fractures, the accuracy during these investigations would be improved.

中文翻译：

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不同尺寸裂缝人工多孔岩流体流动机理观测与理论标定

裂缝通常分布在各种尺度上，并强烈影响速度和各向异性。我们研究了具有不同尺寸裂缝的岩石的弹性速度和各向异性。基于具有受控裂缝几何形状的合成岩石，我们创建了一组裂缝直径为 2、3 和 4 毫米且裂缝厚度为 0.06 毫米的岩石。P 波和 S 波速度在 0.1 MHz 下测量，而岩石中充满了水和空气。对于固定的测量频率 (0.1 MHz)，裂缝较大的岩石的速度较高，而裂缝较小的岩石的各向异性较高，即使对于相同的裂缝密度。这些现象与波浪引起的流体流动过程有关。采用一些新的有效介质理论，用实验室数据进行标定，分析流体流动机理和裂缝尺寸对各向异性的影响。我们的研究结果通过有效介质理论以不同方式证明了裂缝尺度对波浪响应的显着影响。我们建议在某些学科（例如地壳中的剪切波分裂和使用微地震数据的水力裂缝监测）中，这些尺度效应应该引起相当大的关注。考虑到裂缝的尺度效应，这些调查的准确性将得到提高。我们建议在某些学科（例如地壳中的剪切波分裂和使用微地震数据的水力裂缝监测）中，这些尺度效应应该引起相当大的关注。考虑到裂缝的尺度效应，这些调查的准确性将得到提高。我们建议在某些学科（例如地壳中的剪切波分裂和使用微地震数据的水力裂缝监测）中，这些尺度效应应该引起相当大的关注。考虑到裂缝的尺度效应，这些调查的准确性将得到提高。