Site Response Across the San Gabriel, Chino and San Bernardino Sedimentary Basins from Application of the Spectral Ratio Method to Ambient Noise Recorded by Seismic Node Transects

Anisha D. Tyagi, Samuel Gurley, Margaret Grenier, Rachel Kreuziger, & Jascha Polet

Published August 14, 2019, SCEC Contribution #9566, 2019 SCEC Annual Meeting Poster #062

The San Gabriel, Chino and San Bernardino Basins are heavily populated sedimentary basins that are bounded by a series of faults. Sedimentary basins are known to amplify earthquake ground motions; therefore, it is crucially important to understand the subsurface structure of these basins, in an effort to mitigate their seismic hazard. Additionally, if a major rupture on the southern San Andreas Fault occurs, these Basins could potentially channel seismic energy into the Los Angeles Basin (Denolle et al., 2014), operating as a waveguide.

Over the course of the past three years, numerous linear seismic arrays of nodal seismometers were deployed across the San Gabriel, Chino and San Bernardino Basins for approximately one month. Hundreds of temporary nodes, and several temporary as well as permanent broadband seismometers, have collected ambient noise three component waveform data in and around these Basins, which we processed utilizing the Geopsy software. The resulting Horizontal-to-Vertical Spectral Ratio (HVSR) curves provide information about the resonance frequency and ground motion amplification of each site. To evaluate the clarity of the HVSR peaks and the reliability of the curves, the Site Effects Assessment Using Ambient Excitations (SESAME) guidelines were applied.

The resulting HVSR curves for nodes in the Western portion of the San Gabriel Basin show peak frequencies above 1 Hz for nodes located to the North of the Raymond fault, while peak frequencies for nodes South of the Raymond fault range from 0.15-0.30 Hz, corresponding to a basin depth of approximately 1-1.5 km. These frequencies are similar to those predicted from the SCEC CVM-H 15.0 velocity model for simple 1-D velocity models, using a quarter-wavelength approximation to calculate the resonance frequency. However, a lateral shift of the basin edge was necessary to match the pattern of measured frequencies. Results for the Central part of the San Gabriel Basin show two sets of peak frequencies ranging from 0.15-0.45 Hz. We will also show results from a recent short-term broadband seismometer deployment, to verify results for six sites along the southern section of this profile. Results for nodes in the Chino Basin, show peak frequencies ranging from 0.25-0.60 Hz. The peak amplitudes across all three Basins range from 2.0-4.5, suggesting the potential for significant ground motion amplification.

Citation
Tyagi, A. D., Gurley, S., Grenier, M., Kreuziger, R., & Polet, J. (2019, 08). Site Response Across the San Gabriel, Chino and San Bernardino Sedimentary Basins from Application of the Spectral Ratio Method to Ambient Noise Recorded by Seismic Node Transects. Poster Presentation at 2019 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology