Ground-Motion Variance from Modeling of Multiple Rupture-Directivity Scenarios on the Newport-Inglewood/Rose Canyon Fault System

John N. Louie, Mounira Boudjema, Michelle Dunn, & Graham M. Kent

Published August 12, 2017, SCEC Contribution #7537, 2017 SCEC Annual Meeting Poster #257 (PDF)

We use LLNL’s SW4 wave-propagation modeler to produce shaking maps and synthetic seismograms for hypothetical, nonetheless geologically plausible earthquake ruptures of the Newport Inglewood Rose Canyon (NI/RC) fault system along the Southern California coast. We simulate a number of worst-case through-going rupture scenarios with magnitudes up to 7.4, with a focus on estimating shaking uncertainty around NI/RC due to variance in rupture directivity. To date we have modeled the fault strands as vertically dipping rectangular planes and produced a first estimate of average shaking and its potential variance at low frequencies (<1 Hz). We employ a simplified kinematic source model with parameters selected to sensibly fit recorded peak ground velocities (PGVs) of shaking from the 1992 M7.3 Landers earthquake. Overall, the results show that the placement of the hypocenter has a strong influence on the predicted ground-motion maps; PGVs increase in the direction of the rupture propagation, with the greatest amplifications (up to a factor of five) observed in the Los Angeles Basin for the northwestward rupture directivity scenarios. Given more exact locations and geometry information of the NI/RC fault system strands, we are conducting tests to see whether the resulting more complex directivity has similar effects on variance; and testing which scenarios may produce higher ground motions in the Los Angeles region. The results of this study may assist planning for earthquake resilience in Southern California coastal communities.

Key Words
earthquake, ground motion, prediction, variance, rupture directivity, hazard, Newport Inglewood/Rose Canyon

Citation
Louie, J. N., Boudjema, M., Dunn, M., & Kent, G. M. (2017, 08). Ground-Motion Variance from Modeling of Multiple Rupture-Directivity Scenarios on the Newport-Inglewood/Rose Canyon Fault System. Poster Presentation at 2017 SCEC Annual Meeting.

Related Projects & Working Groups
Ground Motions