Waveguide or Not? Revised Ground Motion Simulations for Greater Los Angeles From the M7.8 ShakeOut Earthquake Scenario

Te-Yang Yeh, & Kim Olsen

Under Review 2024, SCEC Contribution #13577

The ShakeOut scenario of a M7.8 northwestward rupture on the southern San Andreas fault (SSAF) (Jones et al., 2008) predicted significant long-period ground motion amplification in the greater Los Angeles, CA, area, caused by a waveguide from interconnected sedimentary basins. However, the early ShakeOut ground motion simulations omitted important model features with immature versions of the velocity structure and fault geometry. Here, we present 0-1 Hz 3D numerical wave propagation simulations for the ShakeOut scenario including surface topography, as well as updated high-resolution velocity structure and SSAF fault geometry. Spectral Accelerations at 3s are increased by the local high-resolution basin models (25-45%) but decreased from complexity in velocity and density updates outside the basins (65-100%) and inclusion of surface topography ~30%). The updated model reduces peak ground velocities in the waveguide from 250 cm/s to 100 cm/s, significantly closer to the values predicted by a leading NGA-West2 ground motion model.

Citation
Yeh, T., & Olsen, K. (2024). Waveguide or Not? Revised Ground Motion Simulations for Greater Los Angeles From the M7.8 ShakeOut Earthquake Scenario. Seismological Research Letters, (under review).

Related Projects & Working Groups
GMSV, Ground Motion