κ0 and Broadband Site Spectra in Southern California from Source Model‐Constrained Inversionκ0 and Broadband Site Spectra in Southern California from Source Model‐Constrained Inversion

Ground-motion modeling requires accurate representation of the earthquake source, path, and site. Site amplification is often modeled by V-S30, the time-averaged shear-wave velocity of the top 30 m of the Earth's surface, though recent studies find that its ability to accurately predict site effects varies. Another measure of the site is kappa(0), the attenuation of high-frequency energy near the site (Anderson and Hough, 1984). We develop a novel application of the Andrews (1986) method to simultaneously invert the spectra of 3357 earthquakes in Southern California into source and site components. These earthquakes have magnitudes 2.5-5.72 and were recorded on 16 stations for a total of 52,297 records. We constrain the inversion with an individual earthquake, demonstrating the most Brune-like shape to preserve the site spectra. We then solve for kappa(0) site amplification at each station in three frequency bands: 1-6 Hz, 6-14 Hz, and 14-35 Hz. The resulting values of kappa(0) range from 0.017 s at ANZA station PFO to 0.059 s at ANZA station SND. We compare our results to values of site kappa(0) from other studies, as well as site residuals from ground-motion prediction equations. We find good agreement between our site kappa(0) and previous studies in the region. We find that kappa(0) and high-frequency site amplification (14-35 Hz band) correlates well with independent site residuals, making it a good first-order approximation for the effects of site attenuation or amplification on ground motion.