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Fully Nonergodic Ground Motion Models in Central California Using NGA-West2 and SCEC CyberShake Datasets

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

Published August 14, 2019, SCEC Contribution #9597, 2019 SCEC Annual Meeting Poster #023

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), commonly known as σtot. The most promising way to reduce hazard is to reduce σtot through the removal of the ergodic assumption. Although the 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 model. In comparison, numerical simulations can generate large ground motion datasets at any desired site, which are optimal to reduce σtot by identifying and removing repeatable effects in a fully nonergodic model. However, before such PSHA products based on simulations are accepted for engineering applications, it is crucial to validate the simulated ground motions against empirical data and models.

In this study, we evaluate the ability of the physics-based CyberShake platform to capture the repeatable source, site and path effects from the empirical data, by applying the Mixed Effects Regression (MER). We use CyberShake Study 17.3, which was computed for central California and generated over 285 million ground motion seismograms at 438 sites. We firstly conduct a checkerboard test to investigate how to prevent correlation leakage among source, site and path terms in the MER. Next, we apply the MER to the CyberShake dataset at 3s period and compare its results from MER estimates based on subsets of NGA-West2 dataset in the same area. Preliminary results suggest that the correlation of source and site effects between CyberShake and NGA-West2 is relatively stable, while the path effects show a wide range of correlation coefficients, indicating a potential mismatch between the simulations and the recordings. We then examine in detail how slip distribution variations and interface reflections within the velocity model may contribute to the disparity.

Meng, X., Goulet, C. A., Milner, K. R., & Callaghan, S. (2019, 08). Fully Nonergodic Ground Motion Models in Central California Using NGA-West2 and SCEC CyberShake Datasets. Poster Presentation at 2019 SCEC Annual Meeting.

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