Modeling Inelastic deformations in fault zones: From discrete to distributed damage

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

Published August 16, 2021, SCEC Contribution #11506, 2021 SCEC Annual Meeting Poster #154

The internal structure of fault zones in the upper crust exhibits considerable complexity. There are variations along strike in the form of bends and segmentation, and with depth due to changes in deformation mechanisms. Large faults have several basic structural elements including (i) slip zones of concentrated shear with extremely comminuted gouge; (ii) a damage zone that includes the fault core in addition to a complex network of secondary faults and fractures; and (iii) host country rock with little or no damage. Overall, fault zones exhibit a combination of distributed damage as well as discrete anisotropic secondary fractures of different orientations and density. An outstanding question is how to model such complexity arising from the multiscale inelastic processes in a meaningful way to properly interpret observations and forecast future hazard.

To address this question, our research aims at critically evaluating the appropriateness of different off-fault inelasticity models and the extent to which they are consistent with observations. We plan to do this by running a series of controlled 2D dynamic rupture simulations, along with a number of carefully selected 3D simulations, and compare different rupture and ground motion characteristics in the following three scenarios: (1) dynamic rupture with an off-fault Drucker-Prager plasticity model, (2) dynamic rupture with an off-fault continuum damage model, and (3) dynamic rupture with generation of discrete secondary fractures.

Here we report on initial progress. Focusing primarily on the discrete representation of anisotropic damage features we present results from two models: (1) dynamic rupture on a fault plane with multiple pre-existing secondary small fractures, and (2) a diffuse crack representation that incorporates finite strain nonlinear material behavior and enables spontaneous co-seismic secondary crack nucleation and propagation. We show that explicit representation of discrete damage features significantly affects rupture characteristics including rupture speed, radiation patterns, and stress heterogeneity. Models with diffuse crack representation show additional effects on ground motion and fault zone topology that will be missed if the fault zone structure is assumed a-priori. We discuss these preliminary findings within long-term objectives of understanding the co-evolution of faults and fault zones.

Citation
Elbanna, A. E., Gabriel, A., & Ben-Zion, Y. (2021, 08). Modeling Inelastic deformations in fault zones: From discrete to distributed damage. Poster Presentation at 2021 SCEC Annual Meeting.

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