An experimental investigation of frictional and hydraulic properties of shear zones, with application to earthquake faults and glacial till

Faulting in the brittle crust is controlled by rate and state friction (RSF) and fluid migration. In a series of four manuscripts, this work explores shear zones with a series of laboratory experiments on both natural and synthetic materials. I conduct shear experiments to investigate how localization of shear controls the gouge zone of faults. Experiments show that shear localizes progressively into a central zone. Localized shear can lead to a change in the RSF parameters where micromechanics of the shear zone overrides the expectations of the commonly used laws. I also find that subtle changes in the fabric of the shear zone can enhance the possibility of seismic slip. I find that slow, seismic slip can be produced in laboratory experiments as creep rupture rather than strictly RSF and stick-slip sliding. Acoustic emissions of slow-slip have a similar form to stick-slip; however, the duration is ∼1s rather than ∼1ks observed in laboratory stick-slip. In my experiments it is possible to propagate slow-slip in both velocity-strengthening and weakening materials. Elevated fluid pressure in gouge zones can mitigate the effects of the frictional behavior by increasing pressure and thus decreasing effective stress though thermal pressurization or by decreasing fluid pressure by dilatancy hardening. Tests on fault gouge from the San Andreas shows that the fault core has low permeability. The San Andreas would act as a barrier to fluid flow and could behaved as an undrained zone leading to dilantant hardening or thermal weakening. The results of this dissertation are an important step in understanding fault behavior from stable (aseismic) sliding to slow-slip and finally stick-slip (seismic) sliding.