SCEC Award Number 21116 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title Improving southern California crustal model by jointly inverting Rayleigh wave phase velocity/ellipticity, Love wave phase velocity, and frequency dependent receiver functions
Investigator(s)
Name Organization
Fan-Chi Lin University of Utah Vera Schulte-Pelkum University of Colorado, Boulder
Other Participants Konstantinos Gkogkas
SCEC Priorities 4a, 3a SCEC Groups Seismology, CXM, GM
Report Due Date 03/15/2022 Date Report Submitted 03/26/2022
Project Abstract
 This study was a continuation of PI Lin and Co-PI Schulte-Pelkum’s previous SCEC projects targeting southern California crustal structure using joint surface waves and receiver functions. The goal of this study was to produce a reference 3D crustal model that simultaneously accounts for all ambient noise and earthquake Rayleigh and Love wave measurements and receiver functions made available by the previous projects using the broadband seismic network across southern California. A particular target was the addition of Love wave phase dispersion measurements and frequency dependent receiver functions to continue improvements in the accuracy of the shallow crustal model that is important for accurate ground motion prediction. A main finding of our research was that the high-frequency ambient noise derived Love wave phase velocity measurements from Qiu et al. (2019) was incompatible with other measurements including Rayleigh wave phase velocity and ellipticity and receiver function within major sedimentary areas such as the LA Basin. In order to reconcile all measurements, unrealistic high radial anisotropy would need to be introduced. Using the 2019 Ridgecrest earthquake waveforms recorded across the dense CSMIP strong motion network, we confirm that the noise derived short period phase velocities were overestimated systematically within the basins, likely due to the sharp velocity change and insufficient station coverage.
Intellectual Merit An accurate shallow crustal model is important for precise ground motion prediction. Previous inversion of Rayleigh wave phase velocity and ellipticity and receiver functions has already resolved detailed upper crustal Vs and Vp/Vs structures. Including short period Love wave dispersion measurements in the inversion would further refine the model and resolve radial anisotropy. In this project, we show that the short period Love wave phase velocities extracted from our previous ambient noise study surface wave measurements (Qiu et al., 2019) are incompatible with other measurements. We then show that more accurate but lower resolution Love wave measurements can be extracted using earthquake waveforms recorded across the denser CSMIP strong motion network. This demonstrates the need to densify the seismic network within major basin areas to record passive seismic waveforms continuously, enabling resolution of detailed 3D basin structure.
Broader Impacts The funded SCEC project helped to support a graduate student, Konstantinos Gkogkas, at University of Utah to perform joint surface wave and receiver function inversion across southern California. Improved basin characterization aids in seismic hazard estimates.
Exemplary Figure Figure. (A) The broadband station (red) and CSMIP strong motion stations (blue) available in Southern California. The location of the 2019 Ridgecrest earthquake is marked by the star. (B) The transverse component record section of the Ridgecrest earthquake recorded by the CSMIP strong motion stations. The waveforms are 5-10 second bandpassed. (C) The 5 second Love wave phase velocity map from Qiu et al. (2019). (D) Same as (C) but from the Ridgecrest earthquake using 2D beamforming. (Credit to Gkogkas et al., 2021; Poster Presentation at 2021 SCEC Annual Meeting)