EAR-PF: A Multiscale Seismic Velocity Model for the Gulf of Alaska

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Evans Onyango has been awarded an NSF EAR Postdoctoral Fellowship to conduct research and education activities related to developing a multiscale seismic velocity model for the Gulf of Alaska. This work will take place at the University of Alaska Fairbanks under the mentorship of Dr. Carl Tape. The surface of the Earth is divided into plates that are in constant motion and collide, slide past, or pull away from each other along the boundaries between plates. Plate interactions build mountains, cause volcanic activity, and produce large earthquakes. Alaska hosts one of the world’s most seismically active plate boundaries, which produced the 1964 magnitude 9.2 earthquake, the largest ever recorded in the United States. Scientists rely on three-dimensional models of Earth’s subsurface material to understand plate tectonic processes and to assess geologic hazards. In order to better understand large earthquakes, scientists must understand how seismic waves interact with Earth’s subsurface materials. A primary limitation to modeling the seismic wavefield in southern Alaska is the lack of a three-dimensional offshore model. Permanent seismic stations are on land, far from offshore earthquakes, which makes it difficult to model ground motion at coastal cities. This project seeks to build and test a three-dimensional subsurface model for the Gulf of Alaska to better understand the complex earthquake ground motion in coastal regions. The goal is to create a comprehensive three-dimensional model by combining existing two-dimensional models from previous studies. Computer simulations of seismic wave propagation within this model will be performed to generate predicted seismograms that will be compared with recorded seismograms from moderate earthquakes in the region. The final model will be publicly accessible via the IRIS Earth Model Collaboration, a public repository for Earth models. The project will involve outreach to local coastal communities prone to seismic and tsunami hazards.Offshore regions at tectonically active margins, such as southern Alaska or southern California, often exhibit extreme structural complexity and produce a wide range of earthquakes in terms of magnitudes and mechanisms. In southern Alaska, the active collision and accretion of the Yakutat microplate beneath the North America plate and the structure of the accretionary wedge at this active subduction zone are examples of factors contributing to the complex structure of the region. Small-scale and large-scale deployments of seismic instruments on land such as the EarthScope Transportable Array have yielded numerous tomographic models of the mainland Alaska, most of which include inherent smoothing that cannot capture the sharp interfaces of the offshore setting. By comparison, the offshore region of the Gulf of Alaska has only been studied with a sparse assortment of high-resolution 2D velocity models derived from marine studies between the 1980s and 2000s. This project proposes leveraging these existing images from the Gulf of Alaska to create a comprehensive 3D velocity model that will have many uses such as modeling the seismic wavefield, understanding active tectonics, and modeling geodynamics of the subduction system. Synthetic waveforms calculated from the resultant 3D model will be compared with seismograms recorded from moderate and large earthquakes in the study area to validate the model. Seismogram misfit values will also be compared with the performance of other available tomographic models. This project will develop a 3D velocity model for the Gulf of Alaska that will be publicly accessible via the IRIS Earth Model Collaboration, a public repository for Earth models.This project is jointly funded by the Earth Sciences Postdoctoral Fellowship program and the Established Program to Stimulate Competitive Research (EPSCoR).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.