High-resolution Imaging of the Mantle Transition Zone using EarthScope USArray

Virginia Polytechnic Institute And State University, Blacksburg VA

Investigators

Abstract

The dominant tectonic process responsible for earthquakes, volcanoes and landform evolution in the continental United States in the past 200 million years has been the subduction of the Farallon plate beneath the North American Plate. Understanding this subduction process has been a challenge as most of the Farallon plate is now several hundred kilometers below the surface. This research takes advantage of a new technique to analyze seismic data and a rich data set collected by EarthScope USArray stations to image the subducted Farallon slab beneath the continental United States, a process similar to the imaging in medical CT Scan. This research aims to advance understanding of the subduction process with focuses on the following questions: (1) How does the older and deeper subducted Farallon plate connect with the younger plate now subducting beneath the Pacific Northwest? (2) What is the relation between the subduction of Farallon plate and the formation of the Yellowstone volcanic track? (3) How does the subducted Farallon plate interact with the deeper mantle across the US continent? High-resolution images of the Farallon slab, seismic measurements as well as computer codes based on the new seismic theory will be made available to the broader Geosciences community. Hands-on course projects and labs based on this research will be developed and implemented in undergraduate teaching. Slab anomalies have been imaged in wavespeed models in a broad region in North America mantle transition zone, extending from the west coast to the eastern US. The resolutions of wavespeed models are limited in the mantle transition zone due to data sensitivity and the subduction process in the mid mantle remains unclear. The second unresolved question is the role of a deep mantle plume in the formation of the Yellowstone hotspot track. In this research, we will compute finite-frequency sensitivities for waves generated at the 410-km and 660-km discontinuities to image high-resolution mantle transition zone structure beneath the continental US using seismic data recorded at USArray TA stations. The high-resolution models will provide new insights into the dynamics of subduction, especially the relation between subducted materials in the western and eastern US and the role of slab fragmentation in the formation of the Yellowstone hot-spot track. This research will provide a solid foundation for future imaging of mantle transition zone discontinuities and allow the community to take full advantage of frequency-dependent seismic data to tackle scientific questions on mantle convection dynamics.