Modeling the effect of local fault kinematics on shallow fault deformation along the M7.1 2019 Ridgecrest earthquake surface rupture with discrete element analysis

Curtis W. Baden, Josie M. Nevitt, Fernando E. Garcia, Benjamin A. Brooks, Todd L. Ericksen, & Simone Yeager

Published September 8, 2024, SCEC Contribution #14017, 2024 SCEC Annual Meeting Poster #159

Surface deformation associated with shallow strike-slip faulting produces complex fracture networks and shear zones whose geometries can significantly vary along-strike despite having formed along the same fault during the same earthquake and even in the same surface materials. Along the 2019 Ridgecrest earthquake surface rupture, detailed fracture mapping and analysis of near-fault displacement gradients within a ~2-km-long section of the maximum slip zone reveal that increases in vertical shear strain, likely accommodated by relative increases in dip-slip to strike-slip displacement, correlate with longer continuous fractures. We hypothesize that mode II-dominated fracture propagation may produce longer surface fractures because the propagating fracture tipline remains more intact than under mode III fracture propagation conditions, which often produces discontinuous echelon fracture sets.

We test this hypothesis with a series of 3D discrete element method (DEM) models designed to simulate shallow faulting in the upper tens of meters in Earth’s crust. We impose the observed variations in kinematic loading conditions and assign material properties consistent with the playa sediments along the Ridgecrest rupture in the study area. We find that the simulated deformation is consistent with observed fracture patterns. Strike-slip dominated motion produces echelon fractures that coalesce as slip accrues. In contrast, oblique and dip-slip motion produces long, linear fractures that appear more continuous, even in areas where the total amount of slip is less than in pure strike-slip settings. These models resolve and provide insight into the initiation and coalescence of fractures that ultimately produce the final “surface rupture” observed following earthquakes. Our results suggest that fracture continuity is not necessarily a reflection of total slip accrual, but instead is more reflective of the local fault loading conditions and resulting fracture propagation mode.

Key Words
Ridgecrest, surface rupture, rheology, deformation

Citation
Baden, C. W., Nevitt, J. M., Garcia, F. E., Brooks, B. A., Ericksen, T. L., & Yeager, S. (2024, 09). Modeling the effect of local fault kinematics on shallow fault deformation along the M7.1 2019 Ridgecrest earthquake surface rupture with discrete element analysis. Poster Presentation at 2024 SCEC Annual Meeting.

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