Planning for simulations of a scenario large aftershock in the Los Angeles Basin - ShakeOut2.0

Ruth A. Harris, Michael J. Barall, Katherine M. Scharer, Ahmed E. Elbanna, Kristen Chiama, Andreas Plesch, Alice-Agnes Gabriel, Chunhui Zhao, James F. Dolan, Craig Nicholson, Kim B. Olsen, Robert W. Graves, Jeanne L. Hardebeck, Karen Luttrell, Scott Callaghan, Mei-Hui Su, Kevin R. Milner, Morgan T. Page, Akash Bhatthal, & Lucile M. Jones

Submitted August 30, 2026, SCEC Contribution #15436, 2026 SCEC Annual Meeting Poster #TBD

Observations of earthquakes over the centuries have taught us that large earthquakes are always followed by aftershocks. The ShakeOut Scenario 2.0 mainshock simulates a dynamically propagating large earthquake rupturing the southern San Andreas fault in California. The Statewide California Earthquake Center - U.S. Geological Survey (SCEC-USGS) dynamic rupture group, as part of SCEC's ShakeOut Scenario Technical Activity Group, is simulating a scenario of a large aftershock occurring in the weeks following the mainshock, in a region of increased static stress due to the mainshock. The scenario aftershock will occur on the Hollywood-Raymond faults in the densely populated Los Angeles Basin, and will be used by members of the engineering and earthquake effects teams to investigate its impact on the built and human environment in the Los Angeles Basin and beyond. Dynamic rupture simulations of the scenario aftershock will incorporate 3D fault geometry adapted from the SCEC Community Fault Model (CFM), 3D velocity and density structure from the SCEC Community Velocity Model (UCVM) truncated at the lowest velocities, slip-weakening friction, and initial stress conditions informed by the SCEC Community Stress Model (CSM). The result will be a physically self-consistent simulation providing coseismic fault slip-rate information and near-field ground motions. More-distant and higher frequency ground motions will be produced by implementing the dynamic rupture results in a kinematic rupture and wave-propagation framework. An overall goal of the aftershock scenario is to communicate how seismic retrofits mandated by some cities in the Los Angeles Basin help reduce earthquake risk.

Key Words
ShakeOut2.0, Los Angeles Basin, scenario earthquake, aftershock, Hollywood fault, Raymond fault, seismic retrofit, ground motions, dynamic rupture

Citation
Harris, R. A., Barall, M. J., Scharer, K. M., Elbanna, A. E., Chiama, K., Plesch, A., Gabriel, A., Zhao, C., Dolan, J. F., Nicholson, C., Olsen, K. B., Graves, R. W., Hardebeck, J. L., Luttrell, K., Callaghan, S., Su, M., Milner, K. R., Page, M. T., Bhatthal, A., & Jones, L. M. (2026, 08). Planning for simulations of a scenario large aftershock in the Los Angeles Basin - ShakeOut2.0. Poster Presentation at 2026 SCEC Annual Meeting.

Related Projects & Working Groups
Ground Motions (GM)