Shear Rupture Along a Fault with an Experimentally-determined Frictional Strength.

Zonghu Liao, & Ze’ev Reches

Published April 2013, SCEC Contribution #1832

We simulated the dynamic shear rupture along a 2D vertical fault in an elastic half-space. The fault has the frictional strength properties which were determined experimentally on granite samples at velocities approaching 1 m/s (Reches and Lockner, 2010). For the simulation, we used the spectral element code of Ampuero (http://web.gps.caltech.edu/~ampuero/software.html). Recent experimental observations indicated that the steady-state frictional strength of silica-rich igneous rocks (granite, syenite, diorite) alternate between dynamic-weakening under low velocity (V < 0.03 m/s) and dynamic-strengthening under higher velocities (V > 0.03 m/s). This strength alternation was attributed to powder-lubrication (weakening), and powder dehydration (strengthening) (Sammis et al., 2011). We converted the observed friction-distance-velocity relations of the experimental results for Sierra White granite into an empirical friction model referred to as WEST (WEakening - STrengthening). The spectral element scheme calculates the rupture along an anti-plane shear (mode III) fracture, and allows for simulation of spontaneous propagation of faults. In the present analysis, the WEST model is used as the fault properties while keeping all other parameters (crust properties and stresses) the same as 2-D model of Version 3 of the Southern California Earthquke Center (SCEC) benchmark problem (Harris et al., 2004). This approach allows the direct comparison between the WEST results and the benchmark results with fault slip-weakening model of Rojas et al (2008).
We found the following differences between the models: (1) WEST-based rupture occurs earlier at all observation points away from the nucleation zone; (2) WEST-based model has lower (~ 35%) peak velocity and shorter rise-time outside the nucleation zone; and (3) WEST-based rupture shows rich, frequent alteration of slip velocity, and consequently, a more complex rupture is simulated including stress drop, displacements, and friction recovery. We discuss the significant contribution of experimentally-based friction model to the understanding of rupture models.

Citation
Liao, Z., & Reches, Z. (2013, 4). Shear Rupture Along a Fault with an Experimentally-determined Frictional Strength. . Presentation at 2013 SSA Annual Meeting.