Emergent Wave Conversion as a Precursor to Shear Crack Initiation

Abstract

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.