SCEC Award Number 19130 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Implementation of Inter-frequency-spatial Ground Motion Correlation in the SDSU BBP Module
Investigator(s)
Name Organization
Kim Olsen San Diego State University
Other Participants Rumi Takedatsu (Research Assistant)
Nan Wang (PhD student)
SCEC Priorities 4c, 4b, 5b SCEC Groups GM, EEII, CS
Report Due Date 03/15/2020 Date Report Submitted 03/27/2020
Project Abstract
 Ground motion time series recorded at stations separated by up to about 50 kilometers show a frequency-dependent spatial coherency structure, and the corresponding ground motion intensity measures are found to be correlated. As omitting this correlation can result in underestimation of seismic losses in risk analysis, it is critical to quantify the spatial correlation structure for ground motion Fourier spectra estimated at different sites during a single event within a region. Toward this goal, we have developed an empirical frequency-dependent spatial correlation model for the within-event residuals of effective Fourier amplitude spectra from the Pacific Earthquake Engineering Research Center (PEER) Next Generation Attenuation (NGA) West2 database. The correlation model shows slower decrease of the spatial correlation with distance at lower frequencies as compared to higher frequencies, in agreement with the underlying ground motion data, and no significant dependence on the magnitude of the earthquakes is observed. We use this empirical model to incorporate frequency-dependent spatial correlation into a hybrid deterministic-stochastic broadband ground motion generation module, which successfully generates synthetic time series for 7 western U.S. earthquakes with frequency-dependent spatial correlation that closely mimics that of the empirical model. Furthermore, the method also significantly improves the correlation for spectral accelerations, Cumulative Absolute Velocities (CAVs), and Arias Intensities (AIs) compared with that derived from the original broadband module.
Intellectual Merit We find that the correlation model shows no significant dependence on the magnitude of the earthquakes is observed. Furthermore, the method can also be used to significantly improve the correlation for spectral accelerations, Cumulative Absolute Velocities (CAVs), and Arias Intensities (AIs) compared with that derived from the original broadband module.
Broader Impacts Our empirical frequency-dependent spatial correlation model for the within-event residuals of effective Fourier amplitude spectra can be used to improve the accuracy of risk analysis based on broadband ground motion synthetics. We use this empirical model to incorporate frequency-dependent spatial correlation into the hybrid deterministic-stochastic broadband ground motion generation module (SDSU Module) on the SCEC Broadband Platform. The method is developed as a post processing tool, which can easily be incorporated in other broadband synthetic ground motion calculation techniques.
Exemplary Figure Figure 1. Comparison of the spatial correlation coefficients of epsilon for EAS at the reference frequency pairs f1=f2=0.2 Hz (left), f1=f2=1 Hz (middle) and f1=f2=5 Hz (right) from the proposed model (red lines) and the SDSU Module before (top) and after (bottom) applying our method (dots) for the Loma Prieta earthquake with 50 source realizations. Credit: Nan Wang.