Anisotropic imaging of the Alaska-Aleutian subduction zone from shear wave splitting analyses

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The Alaska-Aleutians subduction zone is the most tectonically active convergent margin in North America and represents an area of both scientific and societal relevance. The region has hosted several large mega-thrust earthquakes, has a lot of volcanic activity, and has the potential of generating a tsunami. The region is also an ideal natural laboratory to study subduction systems due to the long-term subduction of the Pacific Plate, volcanism associated with subduction that builds the Aleutian Islands, and high earthquake activity. This project will examine the mantle processes that drive subduction using both onshore and offshore earthquake data. Mantle deformation will be examined within the different portions of the subduction system. The techniques to be used are complementary and when combined will provide a full picture of the subduction zone region. This integrated view will allow an investigation of the operation and interactions of the different subduction regions to create the Alaska-Aleutians subduction zone that is seen today. This project will bring an undergraduate student to the University of Delaware for a summer research experience internship and will provide training for a doctoral student. This project also will include collaborative outreach activities with the University of Delaware Disaster Research Center. This project is a multi-faceted examination of seismic anisotropy throughout the Alaska-Aleutians subduction zone (AASZ). Multiple datasets and techniques will be used in sequence to gain insights into the interactions of the different parts of the subduction system. Shear wave splitting analyses will be performed on a variety of seismic phases that are each tailored to best assess a portion of the AASZ: 1) local-S splitting at island arc stations that target the mantle wedge, 2) source-side splitting in geometries that isolate deformation within the downgoing slab, 3) source-side splitting that targets dynamics in the sub-slab mantle, and 4) traditional splitting at the ocean-bottom and onland stations. Each set of splitting observations targets a specific subduction zone region, with associated targeted questions, in such a way as to be easily integrated together. Combining the suite of complementary techniques will create a complete view of the deformation and active dynamics leading to the modern day AASZ. These results will refine the understanding of slab deformation in the mantle, the association of mantle wedge dynamics and along strike variations in arc magmatism, and the overall evolution of mantle flow beneath the Pacific as it morphs from a surface plate into a subducting slab.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.