Coda-Wave Monitoring of Continuously Evolving Material Properties and the Precursory Detection of Yielding.

The nominally incoherent coda of a scattered wavefield has been shown to be a remarkably sensitive quantitive monitoring tool. Its success is however often underpinned by the assumption of a moderate velocity perturbation, and in the absence of notable changes in material scattering properties. The deformation of a rock matrix, represents for a monitoring wavefield pronounced changes in scattering power. In this work we introduce a rolling reference wavefield when applying Coda-Wave Interferometry (CWI) and Coda-Wave-Decorrelation (CWD) in order to monitor relative velocity and material scattering power changes. We demonstrate how this modification enables the qualitative monitoring of stages in material deformation common to Unconfined Compressive Strength (UCS) tests. In addition to the general stages of deformation, the precursory/subtle onset of material yielding is identifiable in both the CWI and CWD method. It is therefore expected that this approach will enable these coda based methods to robustly monitor continuous, destructive processes over a variety of scales. Possible applications include fault, induced seismicity, landslide and critical infrastructure monitoring.