Multiscale Modeling of Damage Mechanics in Fault Zones

Ahmed E. Elbanna, Alice-Agnes Gabriel, & Yehuda Ben-Zion

Published September 11, 2022, SCEC Contribution #12514, 2022 SCEC Annual Meeting Poster #170

Natural faults are surrounded by regions of damaged rocks. Damaged fault zones evolve both co-seismically and inter-seismically. It is thus important to include inelastic strain processes on- and off-fault in modeling of individual rupture dynamics and sequences of earthquakes. However, several challenges exist including: (1) development of numerical schemes that enable tracking consistently the nucleation, growth, and propagation of frictional fault surfaces, and (2) Resolving the multiscale dynamics of localization and delocalization of inelastic strains to gain insights into factors controlling the evolution and persistence of shear bands and their impact on fault zone strength.
Here we report on our ongoing progress in addressing these challenges. We have recently co- developed a new phase field formulation for frictional cracks which is consistent with rate and state friction in the limit of vanishing phase field length scale. We have verified the implementation by comparing the evolution of slip rate and shear stress during quasi-dynamic rupture propagation against the solution obtained using our already verified finite element-with-sharp-interface-platform in both the plane strain and the antiplane formulations. Our preliminary results suggest that the method is capable of evolving multiple fault cores and slip planes that emulate the complexity observed in natural fault zone structures. The influence of energy partitioning, rupture characteristics, and effective stress slip response will be discussed.
We are developing a discrete shear transformation zone (STZ) theory for modeling plasticity in pressure-sensitive granular systems. In this new formulation, each localized inelastic strain increment is represented by an Eshelby inclusion with a specified transformation strain history and orientation. When an Eshelby transformation is triggered, it redistributes the stresses locally leading to potential activation of additional STZs. The collective dynamics of these STZs determine the localization and delocalization of the inelastic strains within the continuum. We plan to enrich the phase field parameter evolution equation by incorporating an effective representation of the individual STZs dynamics. This integrated approach will help advance modeling capabilities for the complex evolution of fault zones and enable better connection with observations.

Key Words
Fault zones, damage, friction

Citation
Elbanna, A. E., Gabriel, A., & Ben-Zion, Y. (2022, 09). Multiscale Modeling of Damage Mechanics in Fault Zones. Poster Presentation at 2022 SCEC Annual Meeting.

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