资源环境科技发展态势分析平台

Geophysical assessments of subsurface instability rely on a link between physical failure mechanisms and a geophysical measurement. Here a laboratory study demonstrates the emergence of a converted phase at the damage onset in limestone prior to failure from shear crack formation. Shear (S) to compressional (P) wave conversions arise from the presence of an array of disconnected microcracks and occur prior to the crack initiation detection from surface displacement measurements. The converted waves increase in amplitude with shear crack propagation until crack coalescence. The inception of the S to P wave converted phase supports the use of elastic wave conversions as an active diagnostic tool to detect the initiation and propagation of shear cracks.

Plain Language Summary Crack initiation, propagation, and coalescence in the Earth's subsurface is caused by natural and engineering processes. Understanding a link between physical failure mechanisms and a geophysical measurement to identify precursors to failure is significantly important. The authors has identified precursors associated with crack formation, distinct changes in the compressional (P) and shear (S) wave amplitudes with stress prior to the initiation of tensile cracks. However, shear crack initiation could not be detected from compressional or shear amplitudes. Here a laboratory study demonstrates that S to P converted waves arise at the onset of shear damage in rock as a precursory signature of shear crack formation. These converted phases, even at normal incidence, are attributed to the formation of an array of oriented microcracks that dilate under shear stress. The results present an intriguing potential geophysical signal for monitoring damage evolution in the subsurface.