Exciting news! We're transitioning to the Statewide California Earthquake Center. Our new website is under construction, but we'll continue using this website for SCEC business in the meantime. We're also archiving the Southern Center site to preserve its rich history. A new and improved platform is coming soon!

Model for Small-Scale Crustal Heterogeneity in Los Angeles Basin Based on Inversion of Sonic Log Data

William H. Savran, & Kim B. Olsen

Published January 27, 2016, SCEC Contribution #6178

High-frequency seismic ground motion (10+ Hz), as needed for earthquake engineering design purposes, is largely controlled by the meter-scale structure of the earth’s crust. However, state-of-the-art velocity models poorly resolve small-scale features of the subsurface velocity and density variation. We invert 35 sonic logs (up to 3000 m in depth) in and near Los Angeles basin, CA, to obtain a statistical description of the small-scale heterogeneities of the basin. Assuming a von Karman autocorrelation function, our analysis finds Hurst numbers, nu, between 0.0-0.2, vertical correlation lengths, az, of 15-150 m, and standard deviations of about 5% characterize the variability in the borehole data. We report average parameters for Los Angeles basin of  = 0:064 (0:058; 0:069)  0:01 (0:006; 0:012) and az = 54 (51:1; 57:6)m  5:9 (1:79; 9:53)m with 95% confidence intervals listed in the parentheses. Despite the large depth range of the logs, there is no significant variation of the statistical parameters with depth. Our analysis of 371 depth-averaged shear wave velocities in the upper 30m, Vs30, provides only an upper bound of basin scale-length estimates due to the coarse sampling distance, with a Hurst number of about 0.3 and lateral correlation lengths, ax, of 5-10 km.

Savran, W. H., & Olsen, K. B. (2016). Model for Small-Scale Crustal Heterogeneity in Los Angeles Basin Based on Inversion of Sonic Log Data. Geophysical Journal International, 205, 856-863.

Related Projects & Working Groups
Development and Validation of Stochastic Representation of Small-Scale Velocity and Attenuation Structure in SCEC CVMs, Ground Motion Prediction (GMP), Unified Structural Representation (USR), Community Modeling Environment (CME)