κ0 and broadband site spectra in Southern California from source model-constrained inversion

Bulletin of the Seismological Society of America
By: , and 

Links

Abstract

Ground-motion modeling requires accurate representation of the earthquake source, path, and site. Site amplification is often modeled by VS30, the time-averaged shear-wave velocity of the top 30 meters of the Earth’s surface, though recent studies find that its ability to accurately predict site effects varies. Another measure of the site is κ0, the attenuation of high frequency energy near the site (Anderson & Hough, 1984). We develop a novel application of the Andrews (1986) method to simultaneously invert the spectra of 3,357 earthquakes in Southern California into source and site components. These earthquakes have magnitudes 2.5 to 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 κ0 site amplification at each station in three frequency bands: 1-6 Hz, 6-14 Hz, and 14-35 Hz. The resulting values of κ0 range from 0.017 seconds at ANZA station PFO to 0.059 seconds at ANZA station SND. We compare our results with values of site κ0 from other studies as well as site residuals from GMPEs. We find good agreement between our site κ0 and previous studies in the region. We find that κ0 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.

Study Area

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title κ0 and broadband site spectra in Southern California from source model-constrained inversion
Series title Bulletin of the Seismological Society of America
DOI 10.1785/0120190037
Volume 109
Issue 5
Year Published 2019
Language English
Publisher GeoScienceWorld
Contributing office(s) Earthquake Science Center
Description 12 p.
First page 1878
Last page 1889
Country United States
State California