SCEC Award Number 17249 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Experimental Study of Thermal Pressurization and the Role of Fault Roughness
Name Organization
Terry Tullis Brown University
Other Participants Nick Beeler
SCEC Priorities 2d, 3d, 2e SCEC Groups FARM, Seismology, CISM
Report Due Date 06/15/2018 Date Report Submitted 06/15/2018
Project Abstract
We continue to focus our attention on the widely discussed dynamic weakening mechanism termed thermal pore-fluid pressurization. There are many theoretical and numerical studies of thermal pressurization and it is increasingly used in dynamic rupture and earthquake nucleation models. However, experimental data suggesting the operation of this mechanism is limited, a shortcoming we are working to resolve. The only machine in existence capable of doing the required experiments is our unique high-pressure rotary shear friction machine that combines arbitrarily large slip displacement with independent control of both confining pressure and flow-through pore pressure capability. Ours is the first study in which the thermal pressurization mechanism has been isolated and is beginning to be characterized under controlled conditions on confined samples. This year we have focused some of our attention on comparing dry and water-saturated diabase in order to remove any other velocity dependent effects on friction that might be included in the results on the fluid saturated rocks. We have also begun to measure both the permeability and the storage capacity of the samples using the pressure oscillation technique in order to know the fluid diffusivity of the samples. We have often found that following the expected decline in shear resistance that it unexpectedly increases somewhat. Although we do not understand this behavior, we are investigating the possibility that it could result from dependence of some of the critical parameters on the spatially and temporally varying effective stress, something not accounted for in current models.
Intellectual Merit The research contributes to our understanding of the earthquake energy budget, strong ground motions, and accelerations associated with earthquake faulting, by providing fundamental knowledge of the co-seismic shear resistance of faults.
Broader Impacts Results of our experiments are incorporated in coursework at Brown and in public lectures. The experiments have resulted in new methods of sample preparation that allow us and others to conduct experiments on mated fault surfaces and they enhance the infrastructure for research and education. Society benefits from an acquisition of scientific knowledge and in improved understanding of earthquakes and how to mitigate their damage.
Exemplary Figure Figure 4. Observed friction and calculated change in pore fluid pressure with slip, during fast sliding at 2.5 mm/s.