SCEC Award Number 14104 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Supershear Ruptures on Rough Faults in Heterogeneous Media
Investigator(s)
Name Organization
Eric Dunham Stanford University
Other Participants Samuel Bydlon, graduate student, Stanford University
SCEC Priorities 6b, 3e, 4b SCEC Groups FARM, GMP, CS
Report Due Date 03/15/2015 Date Report Submitted N/A
Project Abstract
 Natural faults are geometrically complex, as evidenced by bends, branches,
and fractal surface roughness. During SCEC3, we initiated an effort to understand rupture dynamics on nonplanar faults. Complex fault geometry leads to fluctuations in slip and rupture velocity, and can even trigger bursts of propagation at supershear speeds. In this project we quantified the prevalence of supershear ruptures in an ensemble of over a thousand 2D dynamic rupture simulations on rough faults. In contrast to the prevailing view that supershear is most likely on smooth faults, we found that supershear is most common on rough faults. To complement these efforts in 2D, we have developed a 3D code for rupture dynamics on nonplanar faults. Results from our code, WaveQLab3D, compare favorably to those of other SCEC groups on the SCEC benchmark TPV30, featuring a fractal fault and off-fault plasticity.
Intellectual Merit The geometric complexity of faults has emerged as a key component of realistic earthquake models. Complex geometry generates incoherent high frequency ground motion, increases resistance to slip, and can trigger bursts of supershear rupture propagation. Our simulations call into question the prevailing view that supershear is most likely on smooth faults, instead suggesting that rough faults are most likely to host supershear events. That has important consequences for seismic hazard assessment from different faults.
Broader Impacts Our 3D dynamic rupture code was developed by postdoctoral fellow Kenneth Duru, an African from Nigeria. Kenneth's participation in the SCEC Annual Meeting and Dynamic Rupture Code Verification TAG has enhanced diversity. Kenneth has also been promoting our research within the applied math and numerics community, thereby broadening the impact of SCEC's work and getting other numerical mathematicians excited about earthquake science.

The project also contributes toward our understanding of ground motion and seismic hazard from an important class of ruptures, those that propagate at supershear speeds. Supershear ruptures create Mach fronts that carry strong shaking to large distances from the fault. Our work helps identify which properties of the fault might lead to supershear propagation.
Exemplary Figure Figure 1: Probability density function of rupture velocity from our ensemble dynamic rupture simulations. (top) On a smooth fault, rupture velocities remain sub-Rayleigh, even when the background stress is raised to levels where the rupture mode transitions from slip pulse to crack (at which point, slip and stress drop become unrealistically large). (bottom) On a rougher fault, supershear ruptures begin to appear, particularly at higher background stress levels. [Fang and Dunham, 2013; Bruhat, Fang, and Dunham, work in progress, 2014]