Shear wave structure of a transect of the Los Angeles basin from multimode surface waves and H/V spectral ratio analysis

Mathieu Perton, Zack J Spica, Robert W Clayton, & Gregory C Beroza

Published October 10, 2019, SCEC Contribution #9091

We use broadband stations of the 'Los Angeles Syncline Seismic Interferometry Experiment' (LASSIE) to perform a joint inversion of the Horizontal to Vertical spectral ratios (H/V) and multimode dispersion curves (phase and group velocity) for both Rayleigh and Love waves at each station of a dense line of sensors. The H/V of the auto-correlated signal at a seismic station is proportional to the ratio of the imaginary parts of the Green's function. The presence of low frequency peaks (~0.2 Hz) in H/V allows us to constrain the structure of the basin with high confidence to a depth of 6 km. The velocity models we obtain are broadly consistent with the SCEC CVM-H community model. Because our approach differs substantially from previous modeling of crustal velocities in southern California, this research validates both the utility of the diffuse field H/V measurements for deep structural characterization and the predictive value of the CVM-H community velocity model in the Los Angeles region. A lower frequency peak (~0.03 Hz) in H/V is the signature of the Moho. Finally, we show that the independent comparison of the H and V components with their corresponding theoretical counterparts gives information about the degree of diffusivity of the ambient seismic field.

Citation
Perton, M., Spica, Z., Clayton, R., & Beroza, G. (2019). Shear wave structure of a transect of the Los Angeles basin from multimode surface waves and H/V spectral ratio analysis. Geophysical Journal International, 220(1), 415-427. doi: 10.1093/gji/ggz458.