SCEC Award Number 14089 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Laboratory Experiments on Fault Shear Resistance Relevant to Coseismic Earthquake Slip
Investigator(s)
Name Organization
Terry Tullis Brown University
Other Participants
SCEC Priorities 3a, 3c, 3e SCEC Groups CS, FARM, SDOT
Report Due Date 03/15/2015 Date Report Submitted N/A
Project Abstract
 We have conducted experiments that show that the theoretically predicted and widely discussed dynamic weakening mechanism termed thermal pore-fluid pressurization does in fact occur. The experiments require use of very low permeability rock. We have developed a successful protocol for thermally cracking our initially extremely low permeability Frederick diabase (<10-23 m2) and measuring the resulting permeabilities, which are altered to the 10-23 m2 to 10-18 m2 range. We have conducted finite element model (FEM) calculations of the temperatures achieved in our experiments. To verify the FEM calculations and calibrate the values of thermal conductivities used in them, we have made direct measurements of temperature by placing a thermocouple in a hole drilled to within approximately one mm of the sliding surface. Comparisons of our mechanical and thermal results with theoretical predictions demonstrate that we have been successful in activating thermal pressurization in our experiments. In this report we focus on experimental data collected during the past year in which we have verified our FEM modeling with direct temperature measurements.
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 coseismic shear resistance of faults.
Broader Impacts Results of our experiments are incorporated in coursework at Brown. The experiments have provided new sample fixtures and other enhancements to existing equipment that 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 1. Overall view of the high velocity portion of experiment on diabase with a permeability of ~2×10^-18 m^2, and a thermocouple embedded just below the sliding surface. A number of interrelated variables are plotted. The colors of the titles on the axes correspond to the color of the line being plotted. Temperatures measured are in red and calculated via FEM are in cyan – note their good agreement for each velocity step. See text for discussion of the several interesting features that can be seen.