Abstract Laboratory experiments are a vital tool for assessing elastic properties of rock and determining the underlying geomechanical processes that inform large scale, predictive models. In some cases, relative values of elastic properties are sufficient, but absolute values are necessary when comparing between locations and to address upscaling from lab to field settings. However, determining absolute values of ultrasonic velocity and elastic parameters in laboratory experiments is often complex and hampered by apparatus design. Moreover, measuring the evolution of elastic properties with shear deformation has proven especially difficult. Here, we describe a method that allows measurements of P- and S-wave velocity as a function of shear deformation under stresses of 10's of MPa. The approach includes rigorous calibration experiments and accounts for the evolution of impedance contrasts at sample interfaces as a function of strain. We describe our method by applying it to sheared layers that represent simulated fault zones composed of clay-quartz mixtures and fault rocks recovered from drilling. P-wave arrival times range from 10 to 20 μs and wave speeds are 2–4 km/s during shear of layers a few mm in thickness subject to normal stress of 25 MPa and shear strains >30. Travel time data for apparatus calibration are fit with rational functions and root mean square error is used to assess uncertainty. Wave speed varies systematically with shear stress and increases with shear strain due to comminution, compaction, internal strain localization and shear fabric development.

中文翻译：

---

一种确定实验剪切带绝对超声速度和弹性特性的方法

摘要 实验室实验是评估岩石弹性特性和确定为大规模预测模型提供信息的潜在地质力学过程的重要工具。在某些情况下，弹性属性的相对值就足够了，但在比较位置和解决从实验室到现场设置的升级时，绝对值是必需的。然而，在实验室实验中确定超声速度和弹性参数的绝对值通常很复杂，并且受到设备设计的阻碍。此外，测量弹性特性随剪切变形的演变已被证明特别困难。在这里，我们描述了一种方法，该方法允许测量 P 波和 S 波速度作为 10 兆帕应力下剪切变形的函数。该方法包括严格的校准实验，并解释了作为应变函数的样品界面阻抗对比的演变。我们通过将其应用于代表模拟断层带的剪切层来描述我们的方法，这些断层带由粘土-石英混合物和从钻井中回收的断层岩组成。P 波到达时间范围为 10 到 20 微秒，波速在几毫米厚的层剪切期间为 2 到 4 公里/秒，受到 25 兆帕的法向应力和剪切应变 > 30。仪器校准的行程时间数据与有理函数拟合，均方根误差用于评估不确定性。由于粉碎、压实、内部应变局部化和剪切织物发展，波速随剪切应力系统地变化并随剪切应变而增加。