Dynamic Rupture Simulations and 0-1 Hz Ground Motions of Two Leading Candidate Models for ShakeOut Scenario 2.0

Chunhui Zhao, Ahmed E. Elbanna, & Kristen Chiama

Submitted August 30, 2026, SCEC Contribution #15632, 2026 SCEC Annual Meeting Poster #TBD

The southern San Andreas Fault has not hosted a major rupture in over 300 years and is widely regarded as capable of a magnitude ~7.8 earthquake. Anticipating how such an event would nucleate, propagate, and shake the Los Angeles region is central to hazard assessment for millions of people.

Here we present results from dynamic rupture simulations, using Seisol, of two leading candidate models for ShakeOut Scenario 2.0. We extend the work of SCEC SURE interns, who identified four possible rupture candidates based on the analysis of numerous 3D elastic models, in three important ways: (1) we use off-fault plasticity with spatially varying cohesion and friction angle that depend on rock type, (2) we incorporate viscoelastic attenuation with a seismic-velocity-dependent Q factor, and (3) we spatially perturb fw, the minimum friction coefficient in the rate-and-state formulation with strong dynamic weakening, to ensure a plausible dynamic stress-drop distribution. This investigation narrowed the options to two plausible scenarios, one corresponding to CFM7.0 ALT and the other to CFM7.0 PREF; both include a shallow low-VS layer that can weaken significantly at seismic slip rates.

Our results show that both ruptures propagate at sub-Rayleigh speeds with 6–8 m surface slip, 4–5 m average slip, and 8–10 MPa average stress drop. Rupture directivity focuses strong shaking toward the basin: low-frequency PGV reaches ~4–5 m/s near the fault and ~1.2 m/s within the basin. Comparing the two scenarios reveals how geometric complexity, and the initial tractions it produces, interacts with heterogeneous velocity structure to control on-fault slip-rate signatures, strike- versus dip-slip partitioning, and localized amplification of vertical ground velocity. We also report on ongoing efforts to generate broadband 0–20 Hz ground motion time series for downstream engineering and cascading hazard applications. This effort establishes a baseline for physics-based hazard assessment in Southern California and highlights the need for better characterization of fault geometry, frictional properties of shallow earth materials, and inelastic rock properties at depth.

Acknowledgements: We are grateful to Kate Scharer, Andreas Plesch, Rob Graves, Laura Grenot Jones, Clare IP, Tomoka Ohmori, Ashley Seeman, Ruth Harris, Kim Olsen, Michael Barral, Scott Callaghan, Fabio Silva, Fabian Kutschera, and Alice Gabriel.

Key Words
ShakeOut Scenario 2.0, Dynamic Rupture Simulation, Southern San Andreas Fault, Ground Motion Simulation, Seismic Hazard

Citation
Zhao, C., Elbanna, A. E., & Chiama, K. (2026, 08). Dynamic Rupture Simulations and 0-1 Hz Ground Motions of Two Leading Candidate Models for ShakeOut Scenario 2.0. Poster Presentation at 2026 SCEC Annual Meeting.

Related Projects & Working Groups
Ground Motions (GM)