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Elastic wave velocity evolution of shales deformed under uppermost crustal conditions
Author(s) -
Bonnelye Audrey,
Schubnel Alexandre,
David Christian,
Henry Pierre,
Guglielmi Yves,
Gout Claude,
Fauchille AnneLaure,
Dick Pierre
Publication year - 2017
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1002/2016jb013540
Subject(s) - anisotropy , bedding , geology , overburden pressure , brittleness , bed , perpendicular , deformation (meteorology) , mineralogy , geotechnical engineering , materials science , composite material , geometry , optics , physics , mathematics , horticulture , biology , oceanography
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.