Tsunami inundation maps for Akhiok, Chiniak, Old Harbor, Ouzinkie, and Port Lions on Kodiak Island, Alaska

Abstract

Report of Investigation 2021-6, Tsunami inundation maps for Akhiok, Chiniak, Old Harbor, Ouzinkie, and Port Lions on Kodiak Island, Alaska, evaluates potential tsunami hazards for the Kodiak Island communities of Akhiok, Chiniak, Old Harbor, Ouzinkie, and Port Lions, Alaska, by numerically modeling the extent of inundation from tsunami waves generated by hypothetical earthquakes. Worst-case inundation scenarios are defined by analyzing the tsunami dynamics related to various plausible earthquake slip distributions along the Alaska-Aleutian megathrust. Potential worst-case tsunami sources include megathrust earthquakes in the Kodiak Island region. A hypothetical earthquake near Kodiak Island with maximum slip distributed at depths between 10 and 20 km (6.2-12.4 mi) with a splay fault dipping 60 degrees in the Albatross fault zone results in 'worst case' tsunami inundation for Akhiok, and an earthquake with maximum slip distributed at depths between 0 and 10 km (0-6.2 mi) with a splay fault dipping 30 degrees in the backstop splay zone is the 'worst case' scenario for the remaining communities. The maximum predicted overland flow depths in the communities ranges from 10 to 25 m (33 to 82 ft), and the currents in community harbors could be as strong as 8.4 m/sec (16.3 knots). Dangerous wave activity is expected to last for at least 12 hours after the hypothetical worst-case earthquakes. Results presented here are intended to provide guidance to local emergency management agencies for tsunami inundation assessment, evacuation planning, and public education to mitigate future tsunami damage. The complete report and digital data are available from the DGGS website: http://doi.org/10.14509/30760.