Dynamic Rupture Propagation on Fault Planes with Explicit Representation of Short Branches: Stress Heterogeneity, High Frequency Generation, and Novel Supershear Transition Mechanism

Ahmed E. Elbanna

Submitted August 15, 2019, SCEC Contribution #9784, 2019 SCEC Annual Meeting Poster #151

Active fault zones are homes for a plethora of complex structural and geometric features that are expected to affect earthquake rupture nucleation, propagation, and arrest, as well as interseismic deformation. Simulation of these complexities have been largely done using continuum plasticity or scalar damage theories. In this paper, we use a highly efficient novel hybrid finite element-spectral boundary integral equation scheme to investigate the dynamics of fault zones with small scale pre-existing branches as a first step towards explicit representation of anisotropic damage features in fault zones. The hybrid computational scheme enables exact near-field truncation of the elastodynamic field allowing us to use high resolution finite element discretization in a narrow region surrounding the fault zone that encompasses the small scale branches while remaining computationally efficient. Our results suggest that the small scale branches may influence the rupture in ways that may not be realizable in homogenized continuum models. Specifically, we show that these short secondary branches significantly affect the post event stress state on the main fault leading to strong heterogeneities in both normal and shear stresses and also contribute to the enhanced generation of high frequency radiation. The secondary branches also affect off-fault plastic strain distribution and suggest that co-seismic inelasticity is sensitive to pre-existing damage features. Furthermore, we discover that for a range of branch angles, the rupture mode on the main fault plane may transition to supershear even if the ambient initial stress conditions favor sub-Rayleigh propagation. The transition is also unusual as it appears the main rupture continuously accelerate to supershear and not through the classical Burridge-Andrews mechanism. We discuss our results in the larger context of the need for modeling earthquake ruptures with high resolution fault zone physics and the importance of mapping fine scale anisotropic damage features in fault zones as they may have strong implications for seismic hazard.

Key Words
Dynamic rupture, Fault zone complexity, High frequency generation, Supershear ruptures

Citation
Elbanna, A. E. (2019, 08). Dynamic Rupture Propagation on Fault Planes with Explicit Representation of Short Branches: Stress Heterogeneity, High Frequency Generation, and Novel Supershear Transition Mechanism. Poster Presentation at 2019 SCEC Annual Meeting.


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