ABSTRACT

Earthquakes are ubiquitous natural hazards that impact vulnerable populations near active fault systems across the globe. Despite longstanding and intensive research by the scientific community, several key aspects of the earthquake rupture process remain poorly understood. This project focuses on understanding the physical origin of the high-frequency seismic energy that is generated during the rupture process as earthquake faults slip past one another. These advances in scientific understanding have broad implications for earthquake hazard mitigation, informing how future building design codes should be constructed in order to prevent earthquake damage to vulnerable structures. The project also supports early career scientists and provides research opportunities to traditionally underrepresented groups in the geosciences. Through targeted outreach efforts, the project will engage high school students from a diverse range of socioeconomic backgrounds, with an aim toward experiential learning that will guide them in their future careers.

The physical origins for high-frequency ground motions have traditionally been explained in terms of a frictional model that postulates that frictional processes during fault slip determine rupture properties like stress drop, which in turn control shaking amplitudes. However, these classical frictional models often struggle to explain many aspects of the high-frequency ground motions observed in nature. This discrepancy has led to the hypothesis that elastic impacts of fault-zone structures that occur to accommodate the geometric complexity of fault systems may play an important role in the generation of high-frequency ground motions. The project will explicitly test this hypothesis using three sets of seismological observations ? corner frequencies, radiation patterns, and the ratio of S-wave to P-wave radiated energy ? for which the frictional and impact models make distinctly different predictions. This work has a number of important implications for our understanding of the physics of earthquake rupture, including determining the degree to which detailed measurements of fault zone structure are needed to make accurate ground motion predictions, revising the physical interpretation of seismological stress drop estimates, and constraining the degree of wave scattering in the Earth?s crust. These advances, taken holistically, will provide crucial observational constraints for future earthquake hazard mitigation efforts.

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.

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