Geophysical wave measurements have been used as a remote and non-destructive method to monitor the changes in the state of contact, stress, and deformation in rock joints. In recent studies, geophysical precursors were identified as distinct maxima and minima in the amplitude of transmitted and reflected ultrasonic waves propagating through synthetic rock joints prior to the shear failure. However, the ability to detect seismic precursors and to identify their underlying causes under experimental conditions particularly in natural rock joints with rough contact surfaces has been limited. Here in this study, we conducted single direct shear experiments on sandstone rock joints with rough contact surfaces while employing digital image correlation technique and monitoring ultrasonic compressional (P) and shear (S) waves propagating through the rock joint. Our experimental observations show that depending on the surface roughness and the localized physical mechanisms occurring along the rock joint, the transmitted amplitude may either reach a peak prior to the peak shear stress or follow a continuous decreasing trend with shear displacement. An extensive geophysical analysis including wave conversion analysis was conducted to resolve the complexities in the ultrasonic measurements and improve the possibility of detecting ultrasonic precursors to the shear failure. We observed that the changes in the amplitude of converted S–P wave as well as P–S wave show systematic variations and exhibit a clear precursory signature prior to the peak shear stress. Our results indicate that the precursors identified based on the changes in the amplitude of converted waves are consistent with the evolution of failure mechanisms at the joint during inter-seismic and pre-seismic phases. The findings in this study present novel and additional potentials in ultrasonic waves to evaluate deformation and detect slip initiation in fractured rock materials found in rock slopes as well as tectonic faults.

地球物理波测量已被用作一种远程和非破坏性方法来监测岩石节理中的接触、应力和变形状态的变化。在最近的研究中，地球物理前兆被确定为在剪切破坏之前通过合成岩石节理传播的透射和反射超声波振幅的明显最大值和最小值。然而，在实验条件下，特别是在具有粗糙接触表面的天然岩石节理中，检测地震前兆和确定其潜在原因的能力受到限制。在这项研究中，我们在具有粗糙接触表面的砂岩岩石节理上进行了单次直接剪切实验，同时采用了数字图像相关技术并监测了通过岩石节理传播的超声波压缩 (P) 和剪切 (S) 波。我们的实验观察表明，根据表面粗糙度和沿岩石节理发生的局部物理机制，传输振幅可能在峰值剪切应力之前达到峰值，或者随着剪切位移呈连续下降趋势。进行了包括波转换分析在内的广泛的地球物理分析，以解决超声测量中的复杂性，并提高检测剪切破坏的超声前体的可能性。我们观察到转换的 S-P 波和 P-S 波振幅的变化显示系统变化，并在峰值剪切应力之前表现出清晰的前兆特征。我们的结果表明，基于转换波振幅变化识别的前兆与地震间期和地震前阶段接头处失效机制的演变一致。本研究的发现展示了超声波的新潜力和附加潜力，以评估变形和检测岩石斜坡和构造断层中发现的裂隙岩石材料中的滑移起始。我们的结果表明，基于转换波振幅变化识别的前兆与地震间期和地震前阶段接头处失效机制的演变一致。本研究的发现展示了超声波的新潜力和附加潜力，以评估变形和检测岩石斜坡和构造断层中发现的裂隙岩石材料中的滑移起始。我们的结果表明，基于转换波振幅变化识别的前兆与地震间期和地震前阶段接头处失效机制的演变一致。本研究的发现展示了超声波的新潜力和附加潜力，以评估变形和检测岩石斜坡和构造断层中发现的裂隙岩石材料中的滑移起始。