Undergraduates Investigate the Underground: Seismic Imaging of the Alaskan Subduction System

The Alaskan Subduction Zone is home to numerous seismic and volcanic events, including the historic 1964 magnitude 9.2 Great Alaskan Earthquake and the recent magnitude 8.2 event in July 2021. The generation of these earthquakes and volcanic eruptions, however, is not uniform across the subduction zone. Most notably, the Semidi Segment of the subduction zone, which regularly generates great earthquakes, abuts the Shumagin Segment, which does not appear to have generated a great earthquake for thousands of years. Here, we present the results of an undergraduate summer research experience in which four undergraduate researchers used surface wave tomography from data collected by several regional seismic networks to image the upper mantle structures associated with the Alaskan Subduction Zone, and how they vary within the system. Students from a range of academic disciplines and class cohorts developed and applied computational skills including command line computing, data retrieval and management, Unix/Linux scripting, Matlab scripting, data preparation (including quality control, seismogram tilt and compliance removal, surface wave isolation at different frequencies) and time series analysis to build an initial model of the subsurface. Primary findings from the preliminary model include the delineation of thicker crust beneath mountainous area and pronounced low velocity zones in the mantle wedge along the system. The model will be further refined, incorporating additional data and model parameters, and will be combined with complementary tomographic models, to determine why this variability occurs within the Alaskan Subduction Zone, lending important insights into hazards and risk management.