SCEC Award Number 16248 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Simple Crack Models for Insight into Earthquake Simulations With Rate-State Friction and Thermal Pressurization
Investigator(s)
Name Organization
Paul Segall Stanford University
Other Participants Lucile Bruhat, Ph.D. student
SCEC Priorities 3d, 2e, 5e SCEC Groups SDOT, Simulators, FARM
Report Due Date 03/15/2017 Date Report Submitted 07/04/2017
Project Abstract
 This project aims to develop basic understanding of factors that control the recurrence interval for through going ruptures on 1D faults with rate and state dependent friction and thermal pressurization, loaded by steady down-dip creep. Requiring that the stress intensity factor equal the fracture toughness predicts that the recurrence interval for full ruptures scale with the dimension of the velocity weakening region to the 3/4 power, consistent with numerical simulations. Recurrence time also depends on thermal, frictional, and transport properties. Only full ruptures occur on faults of modest height relative to a critical nucleation dimension. However, with increasing length partial ruptures occur early in the seismic cycle.

Intellectual Merit This work extends fracture mechanics concepts, introduced by Werner and Rubin (2013) to predict the recurrence interval for faults driven by steady down-dip displacement to more general cases including strong dynamic weakening due to thermal pressurization. The derived analytical expressions reveal how recurrence interval scales with physical parameters, fault dimension, and background stress state. These results should give guidance for understanding behavior of complex numerical simulations.
Broader Impacts This project supported the intellectual development of an international Postdoctoral student.
Exemplary Figure Figure 2.
Simulations of earthquake cycles without (top left) and with (bottom left) thermal pressurization. Distance vs solver time; color is log slip speed in m/s; dotted line is VW-VS transition. Right: Scaling between recurrence interval and normalized fault dimension. Open circles are full ruptures, dots are partial ruptures, stars first partial ruptures. Solid line: eq~\ref{eqTvsDgara} for fracture energy due to thermal pressurization, with grey area indicating the range of values due to the dependence on {co}$; dashed line eq:~\ref{eq:TvsD} for fracture energy with rate-state friction.

Figure Credit: Camilla Cattania