PREEVENTS Track 2: Cascadia Scenario Earthquakes: Source, Path, and implications for Earthquake Early Warning

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The Cascadia Subduction Zone is a 1200 km-long plate boundary that is capable of hosting a magnitude 9 megathrust earthquake and is the greatest source of seismic and tsunami hazard in the Pacific Northwest. One very pressing issue is accurate estimation of potential ground motions because they are a predictor of damage resulting from an earthquake and can guide emergency response. In Cascadia, current ground motion predictions do not incorporate the physical processes governing earthquake rupture on the plate interface or account for realistic 3D wave propagation in the Earth's crust. The project aims to predict strong ground motions resulting from a magnitude 9 earthquake in the Pacific Northwest by combining physics-based earthquake models and realistic estimates of wave propagation. The predicted ground motions will be used to test the currently operating version of ShakeAlert, the West Coast Earthquake Early Warning system. This project will provide state-of-the-art scientific information about possible Cascadia scenario earthquakes to local residents and help stakeholders make informed decisions to improve earthquake resilience in the Pacific Northwest. The research will facilitate substantial collaboration among three early career female professors, four students (graduate and undergraduate students), and two postdoctoral researchers. Additionally, it builds an effective communication framework between earthquake source, ground motion, and early warning communities to promote a comprehensive methodology for seismic hazard mitigation.The prediction of earthquake ground motions requires fundamental understanding of earthquake source dynamics and accurate estimation of wave propagation path effects. Previous ground motion predictions for megathrust earthquakes either rely on empirical relations that are not well constrained by data in this region or simulate wave propagation assuming a certain kinematic rupture history that does not necessarily satisfy the physics of dynamic ruptures. Moreover, previous calculations strongly rely on the accuracy of a velocity model, in which realistic wave propagation through fore-arc and sedimentary basins is not well represented. Finally, both realistic source processes and accurate wave propagation are necessary to establish reliable information in the seismic waveform for earthquake early warning. The project will construct a suite of realistic scenario earthquakes that could occur in the Cascadia Subduction Zone using an innovative three-stage approach. First, the most up-to-date knowledge of properties of the Cascadia Subduction Zone (e.g. geometry, coupling and stress conditions) will be incorporated in fully dynamic rupture simulations to determine the influence of each of these factors on rupture history and to construct a suite of potential rupture histories for a magnitude 9 earthquake. The earthquake source models will then be combined with Green?s functions derived from the ambient seismic field to estimate ground motions in major population centers in the Pacific Northwest. Finally, the project will explore the implications of these ground motions for earthquake early warning algorithms that are currently under development.