Effect of Undrained Gouge Plasticity on Rupture Dynamics of Rough Faults

Evan T. Hirakawa, & Shuo Ma

Submitted August 14, 2017, SCEC Contribution #7583, 2017 SCEC Annual Meeting Poster #170

Recent rough fault models show that geometrical irregularities can have a significant effect on rupture propagation, leading to observations of rupture arrest, supershear rupture, fluctuations in rupture velocity, and high frequency ground motions. However, these models ignored the presence of fault gouge, which deforms differently from damage zone rocks. Here, we model dynamic rupture on a rough fault embedded in a layer of fault gouge that has the constitutive behavior as formulated in Hirakawa and Ma [2016], which consists of a combined Mohr-Coulomb (MC) and end-cap surface and allows compaction and dilatancy with undrained pore pressure changes. A heterogeneous initial stress state is used and can cause the off-fault material to be close to MC failure, close to end-cap failure, or relatively far from both. Gouge compaction at restraining bends causes large pore pressure increase and allows rupture to propagate through segments that arrest rupture in the case with purely MC failure. Gouge strengthening by undrained dilatancy at releasing bends limits supershear rupture from the MC case. Slip distributions become much more uniform than in the MC case due to the stabilizing tendency of the pore fluids. The tendency for ruptures to accelerate and decelerate at releasing and restraining bends respectively is diminished or in some cases reversed.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-736776

Hirakawa, E. T., & Ma, S. (2017, 08). Effect of Undrained Gouge Plasticity on Rupture Dynamics of Rough Faults. Poster Presentation at 2017 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)