CAREER: Assimilation of Geodetic Data in Physical Models of Subduction Zones

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Earthquake and tsunami hazards represent significant threats to society. They threaten large population centers, notably around the Ring of Fire in Asia and across the Pacific. As direct observations of past seismic events are limited, mitigation of the associated risks hinges on the understanding of the underlying physics. Here, the researchers develop realistic computer simulations of the largest earthquakes on Earth. Those occur at subduction zones, a type of tectonic-plate boundary where one plate slides under another and sinks into the mantle. The team examines the interactions between shallow and deep deformation processes within the Earth. The goal is to better predict how the surface deforms before, during, and after large earthquakes. The researchers also study how earthquakes at subduction zones generate tsunamis. This type of calculations is challenging because it must account for the shape of the plate-boundary fault and for the variations of rocks' properties in space and time. Furthermore, it must encompass different timescales from the short earthquake duration (a few seconds or minutes) to the thousands of years of Earth's slow deformation in the context of plate tectonics. The simulations give a framework to understand numerous observations worldwide from seismic instruments and the Global Positioning System (GPS). This project provides support to a graduate student and a postdoctoral associate, training for two undergraduate students and outreach to local schools and the public. It also promotes the development of open-source software made freely available to the scientific community, as well as that of teaching material at the undergraduate and graduate level. This work, thus, advances numerical modeling of the solid earth and contribute to a safer, more educated and resilient society. This project aims to understand the seismic cycles at subduction zones and how megathrust slip and mantle flow interact. Subduction zones around the Ring of Fire have produced among the largest historical earthquakes. Expansive ruptures spreading along a low-angle subducting slab that cut through the continental crust generate great (Mw8) and giant (Mw9) earthquakes. Such earthquakes impact the viscoelastic flow at greater depths, which may induce rapid changes in regional sea levels. Here, the researchers build comprehensive numerical models for three chosen subduction zones in Japan, Sumatra and Chile. The models incorporate realistic morphology and material properties. They account for the evolution of friction on the megathrust and the effective viscosity in the surrounding rocks (oceanic asthenosphere and mantle wedge); inputs are based on laboratory results on rocks' friction and plastic flow. Outputs reproduce a wide range of observed slip behaviors, including slow-slip events, low-frequency earthquakes, slow and fast earthquakes, and tsunami earthquakes. The project outcomes include state-of-the-art open-source software to model the seismic cycle and surface deformation. The project results are integrated into teaching materials and activities for local-school and university students, and the public. The team also organizes workshops to train modeling practitioners.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.