SCEC Award Number 21143 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title Fourier-Based Site Response of Southern California Sedimentary Basins
Name Organization
Jeff Bayless AECOM Scott Condon AECOM Chukwuebuka Nweke University of Southern California Jonathan Stewart University of California, Los Angeles
Other Participants
SCEC Priorities 4a, 4b, 4c SCEC Groups EEII, GM
Report Due Date 03/15/2022 Date Report Submitted 03/22/2023
Project Abstract
We provide a site amplification model for Fourier Amplitude Spectra (FAS) inferred from
earthquake ground motion recordings in southern California. The model is conditioned on the
time-averaged shear wave velocity in the upper 30 m (Vs30) coupled with the depth to 1.0 km/s
shear wave velocity isosurface (Z1.0), with the Z1.0 component further conditioned on type of
geomorphic province: Basin and Basin Edges, Valleys, and Mountains/Hills. The Z1.0-scaling is
centered with respect to the Vs30-scaling and is dependent on the differential depth (𝛿𝑧1),
defined as the difference between a site-specific depth and a Vs30-conditioned average depth.
This work closely follows the procedures set forth by Nweke et al. (2022; Nea22), which
developed a 𝛿𝑧1-scaling model conditioned on geomorphic province in southern California for
response spectral acceleration. The ground motion database and geomorphic province
classifications from Nea22 are also utilized.

This report describes the 𝛿𝑧1-scaling component of the model and complements the Vs30-scaling
model developed for the same region under SCEC Award #19097. The Vs30-scaling and 𝛿𝑧1-
scaling components are combined to form a comprehensive FAS site amplification model
specific to southern California. This site amplification model updates and regionalizes the
Bayless and Abrahamson (2019; BA19) ergodic site amplification model developed for greater
California. The model is applicable over the frequency range 0.1 – 24 hertz (Hz).
Intellectual Merit This research is directly related to the Ground-Motion prediction focus group and to refining site response models. These models have many applications, including their use in physics-based simulations such as SCEC Cybershake and the SCEC Broadband Platform. The results of this research can facilitate future validations of the simulations against recorded ground motions by providing a regionally appropriate Fourier-amplitude based site amplification model.
Broader Impacts This project has supported the already strong collaboration of the group of scientists who work on and for the SCEC broadband platform and CyberShake, by contributing to the research goals and interacting with scientists (and engineers.) Possible benefits of the activity to society involve the improvement of earthquake simulations, which will eventually be used in seismic design, particularly for near fault ground motions.
Exemplary Figure Figure 19