Upper Plate Structure and Tsunamigenic Faults near the Kodiak Islands

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Marlon Dale Ramos , Lee M Liberty, Peter J Haeussler, Robert Humphreys


The Kodiak Islands lie near the southern terminus of the 1964 Great Alaska earthquake rupture area and within the Kodiak subduction zone segment. Both local and trans-Pacific tsunamis were generated during this devastating megathrust event, but the local tsunami source region and the causative faults are poorly understood. We provide an updated view of the tsunami and earthquake hazard for the Kodiak Islands region through tsunami modelling and geophysical data analysis. Through seismic and bathymetric data, we characterize a regionally extensive sea floor lineament related to the Kodiak shelf fault zone, with focused uplift along a 50-km long portion of the newly named Ugak fault as the most likely source of the local Kodiak Islands tsunami in 1964. We present evidence of Holocene motion along the Albatross Banks fault zone, but suggest that this fault did not produce a tsunami in 1964. We relate major structural boundaries to active forearc splay faults, where tectonic uplift is collocated with gravity lineations. Differences in interseismic locking, seismicity-rates, and potential field signatures argue for different stress conditions at depth near presumed segment boundaries. We find that the Kodiak segment boundaries have a clear geophysical expression and are linked to upper plate structure and splay faulting. The tsunamigenic fault hazard is higher for the Kodiak shelf fault zone when compared to the nearby Albatross Banks fault zone, suggesting short travel paths and little tsunami warning time for nearby communities.




Physical Sciences and Mathematics


Geophysics, marine geophysics, Alaska subduction zone, Splay faults


Published: 2021-09-17 16:59

Last Updated: 2021-09-17 23:59


CC BY Attribution 4.0 International

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Data Availability (Reason not available):
For our tsunami source and fault mapping analysis, we utilize a regional bathymetry dataset to identify Kodiak shelf seafloor scarps (National Geophysical Data Center, 2009. Southern Alaska Coastal Relief Model. National Geophysical Data Center, NOAA. doi:10.7289/V58G8HMQ). Seafloor topographic data is available from NOAA at https://www.ngdc.noaa.gov/mgg/bathymetry/hydro.html. The legacy seismic profiles were obtained as digital scans of stacked travel time images from MMS permit 75-02 (https://www.boem.gov/Geological-and-Geophysical-Data-Acquisition-and-Analysis/; Liberty, 2013). EMAG2: Earth Magnetic Anomaly Grid (Stefan Maus, 2009) was obtained at the National Geophysical Data Center, NOAA. Model. doi:10.7289/V5MW2F2P. Global marine gravity model from CryoSat-2 and Jason-1 was obtained from the National Geophysical Data Center at https://data.noaa.gov (Sandwell et al., 2014).

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