SCEC Award Number 16266 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Dynamic Rupture Simulations with Spontaneous Shear Localization from Thermal Pressurization
Investigator(s)
Name Organization
Eric Dunham Stanford University
Other Participants Ossian O'Reilly (postdoc)
SCEC Priorities 3c, 3e, 3f SCEC Groups SDOT, CS, FARM
Report Due Date 03/15/2017 Date Report Submitted 05/21/2017
Project Abstract
 This project examines shear localization within rate-strengthening fault gouge susceptible to weakening from thermal pressurization. We utilize the description of the sheared gouge developed by Rice et al. [2014] and Platt et al. [2014]. However, rather than imposing slip rate and solving for fault strength, we couple to an elastic loading system and simultaneously solve for slip rate and strength. This permits us to examine the onset of shear localization during earthquake nucleation, as well as spontaneous delocalization following the stress relaxation that accompanies slip. We are currently studying localization in the context of a spring-slider system, with plans to move on to elastic continua next.
Intellectual Merit A fundamental question in earthquake science is, what determines the evolution of fault strength during seismic shear? While dynamic weakening from thermal pressurization has received considerable attention, almost all previous work assumes, a priori, the width of the shear zone. The model utilized in this work captures spontaneous localization and delocalization for the first time together with the elastic response of the material surrounding the fault.
Broader Impacts This project supported a female PhD student.
Exemplary Figure Figure 2. Shear zone thermal pressurization model for fault strength coupled to spring-slider. Shear, initially uniform, begins to localize around 1 ms, triggering pressurization of pore fluids and weakening of fault strength. Slip velocity explosively increases. The localized region of high strain rate migrates back and forth across the fault core. Ultimately, sufficient slip occurs and the spring relaxes, causing the gradual deceleration of sliding. Around 7 ms, shear spontaneously delocalizes, slip velocity drops to a negligible value, and peaks in pore pressure and temperature diffuse away. This example neglects temperature dependence of frictional properties (increased T implies a higher degree of rate-strengthening), but that can be accounted for in our simulations. Spring constant chosen to represent a 30-m-wide slipping patch.