Collaborative Research: Cross-Validation of Empirical and Physics-based ground motion predictions

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Many densely populated areas such as Tokyo, Seattle, and Los Angeles are located near active plate boundaries capable of producing large earthquakes. These cities are often built on top of sedimentary basins which trap, focus and amplify earthquake seismic energy. Prediction of strong ground motions is critical in these areas to prevent the loss of life and property in future large events. Here, the principal investigators pioneered a new empirical approach which uses seismic ambient noise, for example generated by ocean waves, to predict large earthquake ground motions. They are also expert in 3D numerical simulations of ground-notion dynamics. The team join effort to cross-validate these approaches in the greater Los Angeles. They use ambient noise and small past-earthquake data to create a suite of large scenario earthquakes (magnitude 6.5 to 7.8) on the southern San Andreas fault. The simulations allow evaluating whether the underlying geological structure may channel earthquake waves and thereby strongly amplify the ground motions. This 2-year project will help mitigating seismic hazards in southern California. The developped methodology can be applied to other urban areas located in similar geological context. The project also supports an early career female scientist and provides training to three graduate students.The goal of the project is to characterize the coupling effect between the amplification due to seismic waveguides and that due to source directivity. This effect may enhance shaking intensity in sedimentary basins. The project uses southern California as a natural laboratory. Other large metropolitan areas, such as Tokyo, Mexico City, Seattle, Salt Lake City and Jakarta, are subjected to similar hazards. Here, the team innovates in using cross-validation between two state-of-the-art ground-motion prediction approaches: the ambient-noise Virtual Earthquake Approach and 3D dynamic simulations. This cross-validation allows i) establishing bounds of confidence in the two methods, ii) examining the coupling between path and source effects in enhancing ground motion, and iii) evaluating the extent of nonlinear effects on future ground motions. The novelty of the project is the unique combination of theoretical and observational seismology. In this effort, newly collected data from dense arrays including both broadband and nodal-seismic instruments will be exploited.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.