Regionalization of Global Subduction Ground Motion Model for Application in Central America and Mexico

For engineering design and seismic risk assessments, earthquake ground motions are characterized using intensity measures such as peak acceleration or spectral accelerations. Ground motion models (GMMs) estimate statistical distribution of intensity measures given information about the source, source-site path (distance), and site condition. This research extends data resources originally developed for Central America and Mexico for the NGA-Subduction (NGA-Sub) project database and uses the data to provide regional customization of global GMMs for application in Mexico.
This research is the result of U.S.-Mexico collaboration that led to significant enhancements of the data resources for that region (relative to NGA-Sub). The database for Mexico is extended by considering small magnitude (M < 6) events and three large events (M 7.2-8.3) in 2017 and 2018. The latter are particularly important, because they are well recorded over a broad distance range and apply for hazard-critical conditions. These changes increase the size of the database from 593 recordings from 66 events (NGA-Sub) to 1882 recordings from 121 events.
The expanded data are examined relative to global NGA-Sub models, which reveals a number of interesting features including faster anelastic attenuation in backarc than forearc regions and generally similar levels of site response as in the global GMM. A novel model for site response in Mexico City is proposed that is properly centered with respect to GMMs and that accounts for the unique Lake Texcoco geology. The model predicts significantly stronger site response than prior models that utilized a reference site approach using a medium-stiff soil site as the reference site. The site amplification model is conditioned on VS30 and is nonlinear (dependent on input motion amplitude). The provided models significantly improve upon current ground motion modeling approaches for Mexico because a common framework is used within and outside of the Valley of Mexico (unlike current practice) and the model combines the applicable features of global models while providing appropriate regional and subregional customization.