Group , Poster #036, Ground Motions

A Nonergodic Ground Motion Model in Southern California with Spatially Varying Coefficients Using a SCEC CyberShake Dataset

Xiaofeng Meng, Christine A. Goulet, Kevin R. Milner, & Scott Callaghan
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Poster Presentation

2021 SCEC Annual Meeting, Poster #036, SCEC Contribution #11358 VIEW PDF
A key input to probabilistic seismic hazard analyses (PSHA) is the total standard deviation of the misfits between ground motion observations and the median ground motion models (GMMs, a.k.a GMPEs). The most promising way to reduce hazard is to reduce the standard deviation through the removal of the ergodic assumption, and instead estimate the variability for site-specific ground motions. Although strong motion networks have been rapidly growing in recent decades, in most cases the empirical data are still too sparse to establish a fully nonergodic (i.e., site specific) model. In comparison, numerical simulations can generate large ground motion datasets for controlled earthquake sources an...d sites, which are optimal to investigate the reduction of total standard deviation by identifying and removing repeatable effects in a fully nonergodic model.
In this study, we evaluate the ability of the physics-based CyberShake platform to capture the repeatable site and path effects from the empirical data, by applying the spatially varying coefficient model (SVCM) as part of the regression analyses. We use ground motion simulation results at 5s spectral period from CyberShake Study 15.4 at 336 sites in southern California. We compute the total residuals from the CyberShake dataset using linear regression with a simple GMM functional form. We then assign spatially varying source effects, site effects, and cell-specific anelastic attenuation by applying the SVCM technique. Preliminary results show systematically large site effects within the Los Angeles and Ventura basins, which are expected from basin effects. However, the cell-specific anelastic attenuation results are not consistent with the input 3D velocity model. We conduct a checkerboard test and find that the cell-specific cell attenuation is highly sensitive to the assumption of the wave propagation path, which is very complicated for the large earthquakes in CyberShake simulation. The results are contrasted with those from sparser empirical datasets, using a similar technique, and a discussion of discrepancy is presented.

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