SCEC Award Number 17031 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Assessing the Deep Geometry of the Los Angeles Basin Using Full Horizontal-to-Vertical Spectral Ratio Inversion
Name Organization
Gregory Beroza Stanford University Zack Spica Stanford University Mathieu Perton Universidad Nacional Autónoma de México (Mexico)
Other Participants
SCEC Priorities 4a, 4d, 3g SCEC Groups Seismology, CME, MSW
Report Due Date 06/15/2018 Date Report Submitted 11/14/2018
Project Abstract
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) along with multimode dispersion curves (phase and group) for both Rayleigh and Love waves at each station of the 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 the 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 allows also retrieving the Moho depth. Finally, we show that the independent comparison of the H and V components with their corresponding theoretical counterparts give information about the degree of diffusivity of the ambient seismic field.
Intellectual Merit We confirmed the reliability of the SCEC velocity model (CVM-H) in the LA region by obtaining similar results with independent method. Our method (full-spectrum HVSR inversion) shows some interesting promises to image deep interfaces like the Moho, which pushes forward the capabilities of the technique.
Broader Impacts We confirmed SCEC velocity model in the LA region which is important for future ground motion modeling. We are currently developing a method to image the Moho with only few days of seismic broad-band data. One paper is about to be submitted.
Exemplary Figure Fig.9: Vs sections along the line A-A' realized from the results of our inversion (top) and from CVM-H model bottom.