Poster #045, Ground Motions

Joint Calibration of NGA-East GMMs and Site Amplification Models Against CENA Ground Motions

Maria E. Ramos-Sepulveda, Grace P. Parker, Meibai Li, Okan Ilhan, Halil Uysal, Youssef Hashash, Ellen Rathje, & Jonathan P. Stewart
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Poster Presentation

2021 SCEC Annual Meeting, Poster #045, SCEC Contribution #11551 VIEW PDF
Ground motion models (GMMs) are used by the engineering community to estimate ground motion intensity measures given the source earthquake and wave propagation path. The Next Generation Attenuation (NGA) projects have developed GMMs for the main areas of interest: NGA-sub for subduction earthquakes, NGA-West and NGA-West2 for active tectonic regions and NGA-East for stable continental regions. During the development of NGA-East, the GMMs were calibrated by correcting central and eastern North America (CENA) data to a reference site condition using a site amplification model appropriate for active tectonic regions since an equivalent model for stable continental regions had not been developed... yet.

Typically, in the development of GMMs, the core GMM (i.e., to predict the dependencies on magnitude and distance) and the site amplification model are developed iteratively and in a coordinated manner, as they are dependent on each other. This was not the case for the NGA-East project due to requirements in the GMM development associated with it having been a SSHAC Level 3 project (Budnitz et al. 1997).

We demonstrate that the combination of the NGA-East GMMs and CENA-specific site amplification factors leads to biased ground motions at short periods, whereas longer periods are relatively unbiased. We are in the process of expanding the NGA-East database using 333 events recorded since 2011. The new and original data will be used in mixed effects analysis, informed by new simulations of 1D ground response, to identify the primary sources of that bias (i.e., GMM or site amplification model) and provide the necessary adjustments to remove it. We expect that any modification to the GMM would be in its constant term, whereas modifications to the site amplification model would be made to a model component that predicts amplification of 760 m/s sites relative to 3000 m/s sites