Poster #220, Ground Motions

A frequency-dependent spatial correlation model of within-event residuals for Fourier amplitude spectra

Nan Wang, Kim B. Olsen, & Steven M. Day
Poster Image: 

Poster Presentation

2020 SCEC Annual Meeting, Poster #220, SCEC Contribution #10545 VIEW PDF
We have developed an empirical spatial correlation model of normalized within-event residuals for the Fourier Amplitude Spectra (FAS), as FAS is a more straightforward representation of the ground motion frequency content than the traditionally-used pseudo-spectral acceleration. The spatial correlation model is developed using the orientation-independent Effective Amplitude Spectra from the Pacific Earthquake Engineering Research Center Next Generation Attenuation West2 database. The database includes shallow crustal earthquakes (M>3) in active tectonic regions. A linear coregionalization model (with three functions representing short-range, long-range and nugget effects) is used to fit t...he semivariogram from data using the Goulard-Voltz algorithm (Goulard and Voltz, 1992) for frequencies from 0.1 Hz to 20 Hz and separation distances up to 120 km. No significant magnitude dependence is found for the spatial correlation coefficients.

Since exclusion of spatial correlation in ground motion simulations can result in an under-estimation of the seismic risk, the developed frequency-dependent spatial correlation has been implemented into the San Diego State University ground motion generation module on the Southern California Earthquake Center Broadband Platform using a post-processing method. This method makes use of three independent two-dimensional Gaussian random variables with covariance corresponding to the three functions of the spatial correlation model. We present results from applying the method to several historical earthquakes in the western USA. The results indicate that the spatial correlation model for FAS is consist with the model for spectral acceleration (Loth and Baker, 2013), providing an additional improvement of the spatial correlation in spectral accelerations.