High-Fidelity 0-5 Hz Physics-Based Ground-Motion Simulation for the Los Angeles Basin Using the EQSIM Framework

Rie Nakata

Submitted August 30, 2026, SCEC Contribution #15345, 2026 SCEC Annual Meeting Poster #219

The Los Angeles Basin Area contains dense urban communities, major lifeline infrastructure, and multiple active faults capable of producing damaging earthquakes. Because its three-dimensional sedimentary structure can amplify ground motion, extend shaking duration, and introduce strong path dependent variability during earthquakes, seismic hazard analysis in this region requires models that capture both fault rupture and wave propagation effects. Physics based deterministic simulations provide a direct way to evaluate these effects. Based on refinements to the SCEC CVM S4.26.M01 model, we developed a Los Angeles Basin model with a target application of 0 to 5 Hz deterministic simulations with the Earthquake Simulation (EQSIM) platform. The model includes a near-surface geotechnical layer that is further updated by the modified Ely taper method to ensure consistent Vp, Vs, and density and avoid material property gaps and discontinuities that can create unrealistic wave propagation effects. We validate the updated model using small earthquakes recorded across the region by comparing synthetic and observed waveforms through Fourier amplitude spectra residuals and duration metrics. Compared to the original SCEC CVM S4.26.M01 model, the revised model improves the goodness-of fit between the recorded and simulated waveforms in the simulated frequency range 0-5Hz. In our anelastic material model we adopted a Qs = 150Vs. We then perform simulations of Mw 6.5 scenario earthquakes on the Raymond strike-slip fault. The kinematic rupture models were generated using the Graves-Pitarka method, with an irregular geometry guided by the SCEC CFM. Based on comparisons with NGA-West2 ground-motion empirical models, we found reasonable agreement at distances less than about 10 km. At distances longer than 10 km, where waves travel longer paths across the Los Angeles basin, we observed an increasing discrepancy. This result highlights the pronounced influence of the three-dimensional velocity structure on amplitude, duration, and spatial ground motion variability which are not fully represented by the empirical ground motion models. This study demonstrates the efficiency of new simulation platforms, such as the EQSIM framework, and improved SCEC community models, in high-frequency, physics-based ground-motion predictions for earthquakes in the Los Angeles Basin.

Citation
Nakata, R. (2026, 08). High-Fidelity 0-5 Hz Physics-Based Ground-Motion Simulation for the Los Angeles Basin Using the EQSIM Framework. Poster Presentation at 2026 SCEC Annual Meeting.

Related Projects & Working Groups
Ground Motions (GM)