Elastic wave velocity evolution of shales deformed under uppermost crustal conditions. Issue 1 (7th January 2017)

• Record Type: Journal Article
• Authors: Bonnelye, Audrey; Schubnel, Alexandre; David, Christian; Henry, Pierre; Guglielmi, Yves; Gout, Claude; Fauchille, Anne‐Laure; Dick, Pierre
• Is Part Of: Journal of geophysical research. Volume 122:Issue 1(2017)
• Page Start: 130
• Page End: 141
• Publication Date: 2017-01-07
• Subjects: shales -- elastic properties -- velocities -- anisotropy; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1002/2016JB013540
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: Conventional triaxial tests were performed on a series of samples of Tournemire shale along different orientations relative to bedding (0°, 90°). Experiments were carried out up to failure at increasing confining pressures ranging from 2.5 to 80 MPa, and at strain rates ranging between 3 × 10 −7 s −1 and 3 × 10 −5 s −1 . During each experiment, P and S wave elastic velocities were continuously measured along many raypaths with different orientations with respect to bedding and maximum compressive stress. This extensive velocity measurement setup allowed us to highlight the presence of plastic mechanisms such as mineral reorientation during deformation. The evolution of elastic anisotropy was quantified using Thomsen's parameters which were directly inverted from measurement of elastic wave velocity. Brittle failure was preceded by a change in P wave anisotropy, due to both crack growth and mineral reorientation. Anisotropy variations were largest for samples deformed perpendicular to bedding, at the onset of rupture. Anisotropy reversal was observed at the highest confining pressures. For samples deformed parallel to bedding, the P wave anisotropy change is weaker. Key Points: Triaxial tests performed on Tournemire shale Evidences of plasticity mechanisms with P wave velocities Evidences of anisotropy reversal