On the elastic anatomy of heterogeneous fractures in rock

TL;DR

This paper demonstrates a high-resolution ultrasonic method to characterize rock fractures, revealing detailed contact behavior, geometry, and stiffness profiles through full-field wavefield measurements and elastography techniques.

Contribution

It introduces a novel ultrasonic approach combining elastography and wavefield analysis to fully characterize heterogeneous fractures in rock specimens.

Findings

High-resolution elastic modulus maps before and after fracturing

Reconstruction of fracture geometry from ultrasonic data

Identification of fracture contact stiffness profiles

Abstract

This study examines the feasibility of the full-field ultrasonic characterization of fractures in rock. To this end, a slab-like specimen of granite is subjected to in-plane, O(10$^4$Hz) excitation while monitoring the induced 2D wavefield by a Scanning Laser Doppler Vibrometer (SLDV) with sub-centimeter spatial resolution. Upon suitable filtering and interpolation, the observed wavefield is verified to conform with the plane-stress approximation and used to: (i) compute the maps of elastic modulus in the specimen (before and after fracturing) via a rudimentary application of the principle of elastography; (ii) reconstruct the fracture geometry; (iii) expose the fracture's primal (traction-displacement jump) contact behavior, and (iv) identify its profiles of shear and normal specific stiffness. Through the use of full-field ultrasonic data, the approach provides an unobscured, high-resolution insight into the fracture's contact behavior, foreshadowing in-depth laboratory exploration of interdependencies between the fracture geometry, aperture, interphase properties, and its seismic characteristics.