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Seismic hazard models for Alaska require estimates of the size and frequency of prehistoric megathrust earthquakes. However, geologic observations that place limits on the size of prehistoric earthquakes along the Alaska-Aleutian subduction zone are scarce so current hazard maps for the region must rely on short instrumental records of seismicity. To help place bounds on the along-strike extent of prehistoric Alaska-Aleutian subduction ruptures, we employ coastal stratigraphic and microfossil methods at a series of coastal sites (Old Harbor, Sitkalidak, and Sitkinak) spanning the western portion of the AD 1964 Mw9.2 rupture patch. We find evidence at all three sites for earthquakes AD 1964, AD 1788, and ~400 cal yr B.P. Our geologic evidence shows that past ruptures in the region extended beyond the western limit of the 1964 rupture and show that permissible maximum magnitudes of future Alaska-Aleutian subduction zone ruptures should consider the possibility for earthquakes larger than those that have occurred in the historical and instrumental period.
Dr. Tina Dura leads the Coastal Hazards Lab at Virginia Tech (2019-present). Dura’s research program in coastal hazards employs subduction zone paleogeodesy, which combines the methods of coastal stratigraphy, sedimentology, micropaleontology, paleoseismology, geophysical and sediment transport modeling, and sea-level research to reconstruct long-term histories of coseismic vertical deformation and tsunami inundation along subduction zone coastlines. Dura has authored 27 peer-reviewed journal articles that have reconstructed >5,000 yearlong earthquake and tsunami records, redefined the spatial and temporal variability of past subduction zone earthquakes, and helped better assess future subduction zone hazards along coastlines around the world.
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