The Alaska-Aleutian subduction zone has produced only a handful of major earthquakes in the last century, but coastal sediments hold a 2,000-year record of far more. This project will drill into those sediments along the western edge of the 1964 rupture—the second-largest earthquake ever recorded—to reconstruct the true frequency and size of past quakes and tsunamis. Current seismic hazard maps rely on a short observational window that may underestimate the region’s full potential. By combining a new diatom-based technique to measure vertical coastal deformation with tsunami simulations, the researchers will map where past ruptures stopped and how far they extended. This fills a critical gap: most existing studies at subduction zones worldwide cannot resolve the down-dip and lateral boundaries of prehistoric earthquakes. If successful, the work will directly feed into USGS National Seismic Hazard Maps, which guide building codes and emergency planning for coastal communities in Alaska, the west coast of the United States, and Hawaii. Better maps mean more accurate risk assessments for infrastructure such as ports, fuel storage, and tsunami evacuation routes—systems that quietly determine whether a community can survive the next great quake.
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This is a project jointly funded by the National Science Foundation?s Directorate for Geosciences (NSF/GEO) and the National Environment Research Council (NERC) of the United Kingdom (UK) via the NSF/GEO-NERC Lead Agency Agreement. This Agreement allows a single joint US/UK proposal to be submitted and peer-reviewed by the Agency whose investigator has the largest proportion of the budget. Upon successful joint determination of an award recommendation, each Agency funds the proportion of the budget that supports scientists at institutions in their respective countries. Understanding the long-term history and coastal impacts of earthquakes and tsunamis along the Alaska-Aleutian subduction zone (AASZ) is critical for preparing communities for future natural disasters. Despite the AASZ experiencing a series of significant earthquakes in the 20th century, this is only a brief observational window, and the documented events may not represent the full potential of the subduction zone in the future. This research aims to fill the knowledge gap between observed events and prehistoric events by using innovative methods to build thousands of year-long records of past earthquakes and tsunamis. By examining coastal sediments and microfossils, and simulating tsunamis, the researchers will reconstruct the patterns, timing, and size of earthquakes and tsunamis over the last 2,000 years. This work not only advances scientific knowledge but also provides critical data for improving seismic hazard maps used to protect coastal communities in Alaska, the west coast of the United States, and Hawaii. Furthermore, the researchers are committed to sharing their findings with the scientific community, educating students, and increasing public awareness through outreach programs in collaboration with local educators and the NSF-funded Alaska Native Geoscience Learning Experience (ANGLE). The goal is to enhance resilience to future geohazards by fostering a deeper understanding of earthquake and tsunami science. This project will employ innovative microfossil-based paleogeodetic methods and tsunami simulations to reconstruct the patterns, timing, and magnitude of strain accumulation and release during past AASZ earthquakes on the western edge of the 1964 CE rupture. Trench-parallel and trench-perpendicular site transects will establish the lateral and down-dip extent of past ruptures, addressing a significant limitation of most existing studies at global subduction zones. At new and existing sites, the researchers will (1) quantify vertical deformation over the past ~2,000 years using a new diatom-based Bayesian transfer function technique never applied along the AASZ; and (2) map the spatial distribution of tsunami deposition and conduct a systematic exploration of which kinds of slip distributions and subsequent tsunamis best match the spatial pattern of coastal deformation and tsunami deposit extent. This work will be the first to combine geologic evidence of vertical deformation and tsunami deposit extent with a suite of forward models of possible tsunamigenic earthquake locations to evaluate the down-dip and lateral variability of past ruptures along the AASZ, providing important inputs for the advancement of USGS National Seismic Hazard Maps.
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