Inclusion of Frequency-Dependent Spatial Correlation into the SDSU Broadband Ground-Motion Generation Method

Nan Wang, Rumi Takedatsu, Kim B. Olsen, & Steven M. Day

Submitted August 14, 2019, SCEC Contribution #9643, 2019 SCEC Annual Meeting Poster #014

Seismic losses (such as disruption of distributed infrastructure and losses to portfolios of structures) are typically dependent upon the regional distribution of ground-motion intensities, rather than the intensity at only a single site. Ground motion time series recorded at stations separated by up to a few tens of kilometers show a frequency-dependent spatial coherency structure, and measures such as PGVs, PGAs and peak spectral accelerations are found to be correlated. Quantifying ground motion over a spatially-distributed region is therefore important and requires information on the correlation between the ground motion intensities at different sites during a single event, where the spatial correlation can be significant within 50 km. Exclusion of spatial correlation in ground motion simulations can result in an under-estimation of the seismic risk. The San Diego State University (SDSU) module on the Southern California Earthquake Center (SCEC) Broadband Platform (BBP) is a hybrid method that merges low-frequency deterministic synthetics and high-frequency stochastic scattering functions. We have implemented frequency-dependent spatial correlation into the SDSU method on the SCEC BBP using a post-processing method. This method makes use of a two-dimensional Gaussian random variable that has covariance corresponding to the spatial cross-correlation model developed from the Pacific Earthquake Engineering Research Center (PEER) Next Generation Attenuation (NGA) West2 database. Our results for the Loma Prieta, CA, event show that the frequency-dependent spatial correlation in our broadband synthetics compares well to that estimated from seismic observations.

Wang, N., Takedatsu, R., Olsen, K. B., & Day, S. M. (2019, 08). Inclusion of Frequency-Dependent Spatial Correlation into the SDSU Broadband Ground-Motion Generation Method. Poster Presentation at 2019 SCEC Annual Meeting.

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