Source and Site Spectral Inversion for κ0 Computation in the Bay Area

Elias King, Alexis Klimasewski, Valerie J. Sahakian, & Annemarie S. Baltay

Published August 15, 2019, SCEC Contribution #9727, 2019 SCEC Annual Meeting Poster #001

Site characterization is an important component of understanding ground motion, and is one of the only parameters that can be constrained prior to an earthquake. κ0, the attenuation of high frequency energy near the site (Anderson & Hough, 1984), is an oft-employed parameter in determining site effects, from stochastic simulations of ground-motion to statistical ground-motion models. There are currently very few constraints on κ0 in the San Francisco Bay Area. This study seeks to determine values of κ0 in this region, as well as other site parameters, to improve constraints on shallow site characteristics and allow more rigorous testing of κ0 versus other site motion predictor variables, such as Vs30 in order to determine which is a better predictor of ground motion.

We apply a novel application of the Andrews (1986) method, developed in Klimasewski et al. (2019) to invert Northern California earthquake spectra and separate into source and site components. We use 3,797 earthquakes of magnitudes 2.5 to 6 recorded on the horizontal channels of 31 broadband and strong-motion stations in the networks BK, NC, and NP, for a total 14,778 records with a signal-to-noise ration above 5. We constrain the inversion with an individual earthquake demonstrating the most Brune-like shape to preserve the site spectra. We then solve for κ0 site amplification at each station following the functional form e-πf κₒ. In addition to this parameter, the full site and source spectra are obtained, and can be used for future region-specific ground-motion studies in the San Francisco Bay Area. The findings of this work will be important for not only characterizing ground-motions in Northern California, but studying the applicability κ0 models for site response to other regions of the United States.

Key Words
Kappa

Citation
King, E., Klimasewski, A., Sahakian, V. J., & Baltay, A. S. (2019, 08). Source and Site Spectral Inversion for κ0 Computation in the Bay Area. Poster Presentation at 2019 SCEC Annual Meeting.

Related Projects & Working Groups
Ground Motions