Brittle Faulting of Ductile Rock Induced by Pore Fluid Pressure Build‐Up

Under upper crustal conditions, deformations are primarily brittle (i.e., localized) and accommodated by frictional mechanisms. At greater depth, ductile distributed) crystal plasticity, diffusion mass transfer or cataclastic flow. The transition from the to domain is not associated with a critical but rather varies in time space. One main parameter controlling variation of this pore fluid pressure. On one hand, pressure increase reduces effective stresses possibly increases strain rate, bringing system closer conditions. other can favor mechanisms, mostly via chemical effects, facilitating intra-crystalline enhancing fluid-solid fracture healing/sealing. We report triaxial laboratory experiments that investigated effect during deformation Tavel limestone. Three injection rates were tested: 1, 5, 10 MPa/min. demonstrate that: (1) initially conditions immediately turns compaction dilation. (2) Dilation due development localized shear fractures. However, macroscopic localization instantaneous when surpassed; transient creeping phase first needed. (3) To reach failure samples, dilatancy required. (4) Injection rate controls final distribution. build-up rock undergoing induce fracturing system.