Injection-induced Seismic Moment Release and Laboratory Fault slip: Implications for Fluid-induced Seismicity

Abstract:

Fault slip induced by fluid injection is partitioned in aseismic and seismic moment release. In an effort to investigate the effect of injection rate on slip characteristics and strain partitioning we conducted laboratory fluid injection experiments on permeable sandstone samples in a triaxial deformation apparatus equipped with a 16-channel acoustic emission (AE) recording system. We injected fluid in sawcut samples containing a critically stressed fault at different pressurization rates. Episodic slow stick-slip events are induced at high fluid pressurization rate while the fault creep occurs in response to slow fluid pressurization rate. Fluid-induced fault deformation is dominantly aseismic. The released total seismic moment is found to be related to total injected volume, independent of fault slip behavior. Seismic moment release rate of AE is related to measured fault slip velocity. In our experiments, the fluid pressure migration is faster than rupture propagation by about five orders of magnitude, resulting in induced fault slip fully confined within a homogenous pressurized zone. The relation between moment release and injected volume is affected by fault slip behavior, characterized by a linear relation for slip at constant rate and fault creep while a cubic relation for unstable and dynamic slip. Our experimental results allow separating a stable pressure-controlled injection phase from a run-away phase, when cumulative moment release with injected volume follows a nonlinear trend.