On the Interplay Between Distributed Bulk Plasticity and Local Fault Slip in Evolving Fault Zone Complexity

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

Published September 8, 2024, SCEC Contribution #13789, 2024 SCEC Annual Meeting Poster #131

Fault zones evolve continuously over sequences of seismic and aseismic slip due to feedback between nonlinear rheology, complex fault surface geometry, and long-range static and dynamic stress transfer. Natural faults are usually embedded in a bed of damaged rocks with variable damage intensity and spatial extent. Damage affects local stress fields, mechanical properties of the fault zone, and energy partitioning.The evolution of fault zone structure and bulk stresses in turn affect creep, rupture characteristics, and slip accumulation on the fault surface.
We numerically investigate the role of plastic strain accumulation on the mechanical response of a planar rate-and-state strike‐slip fault. Our models show that fault‐zone strength significantly impacts the ensuing sequence of earthquakes. By exploring a realistic parameter space of cohesion, we observe that weaker fault zones accumulating more plastic strain promote more complexity in the seismicity pattern through aperiodic earthquake occurrences and intermittent episodes of rupture and arrest. However, if the fault zone strength is high enough, the overall earthquake sequence is characterized by periodic fault‐spanning events. We find that both the fault normal stress and the fault geometric profile evolve throughout the earthquake sequence, suggesting a self‐roughening mechanism. Despite the significant impact of plasticity on the fault response, the width of the plastically deforming region in the fault zone is small compared to the fault length. Furthermore, our results indicate that the extent and distribution of plastic strain depend on both the angle of maximum compressive principal stress and cohesion. Specifically, at lower cohesion values,, we find that plastic strain accumulation may occur in both the extensional and compressional sides of the off‐fault bulk even at higher angles of maximum compression. This produces damage patterns that deviate from the traditional off‐fault fan‐like distribution observed in single dynamic rupture simulations and emphasizes the significance of long‐term deformation in interpreting observations. Our numerical results show agreement with field observation regarding damage extent and distribution. Future extensions of this implementation will explore alternative damage models that account for healing and temporal variations in the elastic wave speeds.

Key Words
SEAS, Plasticity, complexity

Citation
Elbanna, A. E., Abdelmeguid, M., Mia, M., & Zhao, C. (2024, 09). On the Interplay Between Distributed Bulk Plasticity and Local Fault Slip in Evolving Fault Zone Complexity. Poster Presentation at 2024 SCEC Annual Meeting.

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