RUI: Lithospheric Velocity Structure and Anisotropy of the Alaskan Subduction Margin

Colgate University, Hamilton NY

Investigators

Abstract

The southern coast of Alaska is the most seismically and volcanically active portion of the United States, and was home to the second largest earthquake recorded anywhere on Earth. The behavior of earthquakes and volcanos, however, changes dramatically between regions along the coast. Some areas produce extremely large earthquakes, while other regions have only small to moderate-sized earthquakes. Similarly, the chemistry and eruption styles of volcanos change along the coast. Understanding the origins of these differences could lead to important insights into global earthquake and volcano hazards. Scientists believe that the key to understanding this system may lie in the structure and fluid-content of rocks 100-200 km beneath the surface, where the Pacific tectonic plate dives beneath the North America tectonic plate. This study will use earthquake waves to image these rocks buried under Alaska’s coast. These waves, called surface waves, travel across the earth near the surface and change speeds based on the characteristics of the rocks that they travel through. By measuring differences in wave speed based on location and the direction the waves travel, we will examine whether differences in earthquake and volcano behavior are connected to (a) changes in magma-production regions, (b) changes in the fluid content of rocks, or (c) changes in the direction that rocks slowly flow deep beneath the surface. The work will be completed at a Primarily Undergaduate Institution and provides research experience for undergraduate students. The project also supports the training of an early career Postdoctoral Investigator. The subduction zone along the southern margin of Alaska is home to numerous active volcanos, and is the most seismically active portion of the United States. It has hosted several megathrust earthquakes, including the 1964 Great Alaskan Earthquake, the second largest earthquake in recorded history. The seismic and volcanic behavior of the subduction zone, however, undergoes dramatic changes along strike, with some areas slipping in great (M>8) events while other regions deform primarily through creep. Understanding the origins of this variability could lead to important insights into subduction zone processes and global geophysical hazards. Recent studies have highlighted the role that hydration of the subducting slab and the mantle wedge may play in governing these behaviors. In this study, recently collected data from the Alaska Amphibious Community Seismic Experiment and the Alaska Transportable Array will be leveraged to build Rayleigh and Love wave velocity models and to solve for radial and azimuthal anisotropy of shear waves in the upper mantle beneath the Alaskan subduction zone. These velocity models will be used to determine how forearc mantle structure, hydration of the incoming plate and the mantle wedge, and mantle flow combine to influence volcanic and seismic behavior along the subduction zone. 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.