This contribution proposes a numerical microstructural modeling approach to investigate stress-induced seismic velocity changes on anisotropic rocks. By introducing pre-existing cracks with preferential orientations in bonded-particle assemblies, the transverse isotropic structure of the Whitby Mudstone is simulated. Using power-law distributed aperture and calibrated micro-properties, we successfully reproduce stress-dependent velocity changes on Whitby Mudstones with different anisotropic angles in relation to the applied loads. The proposed model also duplicates the directional dependence of wave speed with respect to the bedding plane as expected theoretically. The numerical models show that velocity increase results from the closure of pre-existing cracks due to load increase. Direct relations are established between velocity changes and opened crack density (or crack closure), which displays a similar tendency compared with theoretical predictions. This relation can be used to quantify the micromechanisms behind the velocity changes. The proposed model provides the ability to directly examine the micro-processes underlying velocity changes.

中文翻译：

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一种模拟各向异性岩石应力引起的速度变化的创新方法

该贡献提出了一种数值微结构建模方法，以研究应力引起的各向异性岩石上的地震速度变化。通过在粘结颗粒组件中引入具有优先取向的预先存在的裂缝，模拟了惠特比泥岩的横向各向同性结构。使用幂律分布孔径和校准的微特性，我们成功地再现了 Whitby 泥岩上与施加载荷相关的具有不同各向异性角度的应力相关速度变化。正如理论上预期的那样，所提出的模型还复制了波速相对于层理平面的方向依赖性。数值模型表明，由于载荷增加，预先存在的裂缝闭合导致速度增加。速度变化与打开的裂纹密度（或裂纹闭合）之间建立了直接关系，与理论预测相比，显示出类似的趋势。这种关系可用于量化速度变化背后的微观机制。所提出的模型提供了直接检查速度变化背后的微观过程的能力。