Broadband Ground Motion Simulations for an Earthquake “Doublet” on the Newport-Inglewood and Palos Verdes Faults

The occurrence and impact of the February 2023 earthquake doublet in Türkiye, where an Mw 7.8 event was followed roughly 9 hours later by an Mw 7.5 event on an adjacent fault, begs the question: What would be the impact of such a sequence in California? As part of the effort to address this question, this Data Release consists of simulated ground motions for a hypothetical doublet scenario on the Newport-Inglewood and Palos Verdes faults in the Los Angeles region. The fault locations and orientations are based on the 2023 USGS National Seismic Hazard Model. The magnitudes are Mw 7.25 for the 84-km Newport-Inglewood rupture and Mw 7.05 for the 70-km Palos Verdes rupture. Broadband ground motions are computed using a combination of deterministic and stochastic approaches for the lower- and higher-frequency components, respectively. The deterministic calculations use the SCEC 3D Community Velocity Model version CVM-S4.26.M01 extracted using the UCVM software platform with a minimum shear velocity of 400 m/s, and the stochastic simulations use a 1D reference model with Vs30-based site-specific adjustments using period-dependent factors. Three-component waveforms are saved on a 1.2 km by 1.2 km grid of points, and PGA, PGV, and spectral accelerations at periods of 0.3, 1.0, and 3.0 s are extracted to produce scenario ShakeMaps. Comparison of the simulated motions with empirical ground-motion models (GMMs) are generally favorable; however, noticeable differences exist due to rupture directivity and basin response effects.

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