Towards dynamic rupture models with high resolution fault zone physics

Ahmed E. Elbanna, Xiao Ma, & Setare Hajaroalsvadi

Published August 15, 2017, SCEC Contribution #7817, 2017 SCEC Annual Meeting Poster #179

Earthquake processes span a wide range of length and time scales with the fault zone dynamics holding the key to resolving many outstanding seismological observations. The details of strength evolution in fault zones are dictated by the poro-thermo-mechanical deformation processes in the gouge layer as well as the dynamic evolution of damage and permeability in the surrounding host rock. These details, in turn, determine source characteristics and contribute to phenomena like heat flow paradox, variation of fault zone thickness with depth, and energy partitioning. A flexible multiscale approach is thus critical for linking theory and observations over different spatial and temporal scales. In this presentation, I report on recent progress in my group to address several facets of this spatio-temporal complexity from grain scale to fault scale.

First, I will present a gouge-specific viscoplasticity model that incorporate grain scale processes such as grain rearrangement, flash heating and grain fragmentation. We further incorporate pore fluids into the model using Darcy’s flow assumption for the fluid flux and Terzaghi effective stress concept in the limit of undrained flow. We demonstrate an implementation for our model in the nonlinear finite element software package MOOSE using finite deformation kinematics. With this model, we show several instances for the transition between distributed and localized deformation as a function of initial porosity, confining pressure, initial pore pressure and loading rate. We discuss further extensions of the model to incorporate shear heating effects through the feedback between temperature evolution and pore fluid thermal pressurization.

Next, we introduce a new numerical scheme, coupling the finite difference and the spectral boundary integral equation methods, to establish an exact truncation of the near field elasto-dynamic solution. Using this methodology we demonstrate the ability to accurately model long fault zones with near field heterogeneities using a simulation domain that is much smaller than what is required in pure volume discretization approaches. This saving in computational cost may be then directed towards increasing the modeling resolution of fault zone Multiphysics or in exploring larger scale problems. Finally, we discuss plans for extending this method to simulate earthquake cycles on fault zones with nonlinear material or geometric features.

Key Words
Gouge, dynamic rupture, shear bands

Citation
Elbanna, A. E., Ma, X., & Hajaroalsvadi, S. (2017, 08). Towards dynamic rupture models with high resolution fault zone physics. Poster Presentation at 2017 SCEC Annual Meeting.

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