Modeling Sequence of Earthquakes and Aseismic Slip on Fault Step-Overs with Off-Fault Plasticity

Mohamed Abdelmeguid, Md Shumon Mia, & Ahmed E. Elbanna

Published September 11, 2022, SCEC Contribution #12458, 2022 SCEC Annual Meeting Poster #160 (PDF)

Fault step-overs are ubiquitously observed in on long strike-slip fault systems and are very likely to produce slip complexities through the interaction between nearby faults. However, resolving stress interactions among different fault segments throughout the entirety of an earthquake cycle remain challenging numerically. Here, we rely on the numerical efficiency of the hybrid finite element spectral boundary integral scheme (FEBE) to model two parallel faults having a compressional step over in a two-dimensional plane strain model. Full account of inertia is considered during rapid seismic rupture and radiation damping approximation is used for inertia during slow aseismic deformation. The off-fault bulk response is elastoplastic governed by a Drucker-Prager plasticity model with viscous regularization. Our results indicate that stress interactions between the two faults affect the long-term evolution of aseismic and seismic deformation, as well as lead to possible triggering mechanisms within the fault network. We show that fault interaction leads to delays between ruptures in the two faults which were initially synchronous. Furthermore, we demonstrate that the plasticity response within the fault zone can enhance fault interaction resulting in additional seismic events. We show that off-fault plastic strain accumulates primarily near the fault ends and subsequently encompasses the over-lapping gap region between the two faults. Evolution of mean stress shows that over-lapping gap region experiences increasing compression with subsequent seismic events whereas regions near the fault ends tend to experience reduced compression and potentially tensile stresses. The significant increase in the mean stress suggests some limitations of classical Coulomb like plasticity models and points to the necessity of incorporating some more general formulations such as cap-plasticity models or a fully-resolved continuum damage breakage model. Furthermore, we observe significant rotations in the direction of the principal stresses within the overlapping region compared to the stress orientations in the far-field. This emphasize the critical role of resolving geometrical complexity and long-term deformation history in understanding the stress evolution in space and time. Our preliminary results uncover new insights into the mechanics of fault step-overs and contribute to the understanding of interaction dynamics in fault networks and geometrically complex fault zones.

Citation
Abdelmeguid, M., Mia, M., & Elbanna, A. E. (2022, 09). Modeling Sequence of Earthquakes and Aseismic Slip on Fault Step-Overs with Off-Fault Plasticity. Poster Presentation at 2022 SCEC Annual Meeting.

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