Experimental Investigation of Mechanisms for High Pore Fluid Pressure Associated Slow Faulting

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Slow slip at various subduction zones provides a new opportunity to study the state of megathrust faults in between great earthquakes. Elevated pore fluid pressure in the subduction zone is often detected in regions where slow slip events occur, but it is not well understood how this high pore pressure is actually linked to the slow slip. This project explores this link between fluids and the mechanisms for slow slip through laboratory experiments on how rocks deform. The project will use a new imaging technique, dynamic microtomography, that helps image the interior of a rock sample as it is pressed to the point of failure. These experiments can be conducted at different levels of pore pressure and at different and variable speeds to explore the range of conditions that can lead a fault to move from fast slip to steady slow slip.Recent experimental studies show that high pore fluid pressure can stabilize both fault propagation in intact rocks and decelerates frictional slip in rocks with an existing fault. Dilatant hardening under undrained conditions is thought to be responsible for these observed stabilization effects. Preliminary experimental data show that high pore fluid pressure can also impede fault growth under nominally drained conditions. This project is a systematic set of fracture and friction experiments to understand the role of elevated pore fluid pressure on stabilizing faulting and frictional slip. The goal is to 1) characterize the real-time microstructure evolution using dynamic microtomography. This will result in a quantitative assessment of the spatio-temporal distributions of permeability, porosity, and pore shape, thus better constraints of the drainage conditions during brittle failure; 2) elucidate the role of dilatant hardening in the transition from stick-slip events to slow slip events along a pre-existing fault. The researchers will use different gouge materials to produce different drainage conditions and investigate the mechanical link between high pore fluid pressure and slow slip behaviors; 3) identify diagnostic characteristics of fault geometry and off-fault damage associated with slow faulting. The findings of this study will lead to a better understanding of different instabilities and the mechanical processes responsible for them.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.