title: Faulting of rocks in a three-dimensional stress field by micro-anticracks.
abstract: Nucleation and propagation of a shear fault is known to be the result of interaction and coalescence of many microcracks. Yet the character and rate of the microcracks' interactions, and their dependence on the three-dimensional stress state are poorly understood. Here we investigate formation of microcracks during sandstone faulting under 3D-polyaxial stress fields by analyzing multi-stationary acoustic waveforms. We show that in a true three-dimensional stress state (a) faulting forms in a orthorhombic pattern, and (b) the emitted acoustic waveforms from microcracking carry a shorter rapid slip phase. The later is associated with microcracking that dominantly develops parallel to the minimum stress direction. Our results imply that due to inducing the micro-anticracks, the three-dimensional (3D) stress state can quicken dynamic weakening and rupture propagation by a factor of two relatively to simpler stress states. The results suggest a new nucleation mechanism of 3D-faulting with implications for earthquakes' instabilities, as well as the understanding of avalanches associated with dislocations.
authors.affiliation: Department of Civil Engineering and Lassonde Institute, University of Toronto, Toronto, 170 College Street, M5S3E3, ON, Canada.
authors.forename: H O
authors.initials: HO
authors.lastname: Ghaffari
authors.affiliation: Department of Civil Engineering and Lassonde Institute, University of Toronto, Toronto, 170 College Street, M5S3E3, ON, Canada.
authors.forename: M H B
authors.initials: MH
authors.lastname: Nasseri
authors.affiliation: Department of Civil Engineering and Lassonde Institute, University of Toronto, Toronto, 170 College Street, M5S3E3, ON, Canada.
authors.forename: R Paul
authors.initials: RP
authors.lastname: Young