Broadband Simulations for Mw 7.8 Southern San Andreas Earthquakes: Ground Motion Sensitivity to Rupture Speed

Robert W. Graves, Brad T. Aagaard, Kenneth W. Hudnut, Lisa M. Star, Jonathan P. Stewart, & Thomas H. Jordan

Published November 20, 2008, SCEC Contribution #1238

Using the high-performance computing resources of the Southern California Earthquake Center, we simulate broadband (0–10 Hz) ground motions for three Mw 7.8 rupture scenarios of the southern San Andreas fault. The scenarios incorporate a kinematic rupture description with the average rupture speed along the large slip portions of the fault set at 0.96, 0.89, and 0.84 times the local shear wave velocity. Consistent with previous simulations, a southern hypocenter efficiently channels energy into the Los Angeles region along the string of basins south of the San Gabriel Mountains. However, we find the basin ground motion levels are quite sensitive to the prescribed rupture speed, with peak ground velocities at some sites varying by over a factor of two for variations in average rupture speed of about 15%. These results have important implications for estimating seismic hazards in Southern California and emphasize the need for improved understanding of earthquake rupture processes.

Key Words
San Andreas fault, rupture speed, basin response

Citation
Graves, R. W., Aagaard, B. T., Hudnut, K. W., Star, L. M., Stewart, J. P., & Jordan, T. H. (2008). Broadband Simulations for Mw 7.8 Southern San Andreas Earthquakes: Ground Motion Sensitivity to Rupture Speed. Geophysical Research Letters, 35(22). doi: 10.1029/2008GL035750.