Model for Small-Scale Crustal Heterogeneity in Los Angeles Basin Based on Inversion of Sonic Log Data
William H. Savran, & Kim B. OlsenPublished 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.
Citation
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)
