Ground Strains in Southern California from Earthquakes on the San Jacinto Fault

Andrew J. Barbour, & Annemarie S. Baltay

Published July 25, 2016, SCEC Contribution #6369, 2016 SCEC Annual Meeting Poster #278

Strainmeters record high-frequency seismic waves with signal-to-noise ratios that can be comparable to those of traditional seismometers, for average phase dispersion characteristics in Southern California. Yet, to date, the efficacy of using strainmeters for ground motion studies has not been investigated. Here we compare direct and inferred strains from all M ≥ 4.5 earthquakes on the San Jacinto Fault since the Plate Boundary Observatory borehole network was installed (5 events), finding that measured strains are comparable to estimates from PGV (peak ground velocity) scaled by S-wave slowness. We compare the strains and converted PGV values for these events to NGA-West2 ground-motion prediction equations (GMPEs), also scaled by the S-wave slowness. While there is an overall match between the data and GMPEs, we observe a significant departure from expected attenuation behavior: peak inferred strains in the Los Angeles basin resulting from moderate earthquakes in the Anza region are significantly larger than predicted by GMPEs, and cannot be understood in terms of site-to-site variations in Vs30 alone. We thus explore the effects of basin amplification in the GMPEs. Together, the strain and seismic network infrastructure in California are complementary networks that can be used for hazard assessment in critical areas.

Key Words
strainmeters, San Jacinto Fault, ground motion, GMPEs

Citation
Barbour, A. J., & Baltay, A. S. (2016, 07). Ground Strains in Southern California from Earthquakes on the San Jacinto Fault. Poster Presentation at 2016 SCEC Annual Meeting.

Related Projects & Working Groups
Ground Motion Prediction (GMP)