Tsunami-based evidence for large eastern Aleutian slip during the 1957 earthquake

Abstract

AbstractThe Aleutian subduction zone is capable of generating magnitude ~9 earthquakes that have local impact and broadcast their destructive power across the Pacific through tsunamis. Field surveys of the tsunami from the 1957 Great Aleutian earthquake (reportedMw8.6) indicate a tsunami amongst the largest of the twentieth century. In the eastern half of the rupture zone, stranded logs record up to 18 m run-up in the Islands of Four Mountains (IFM) and 32±2 m on Unalaska Island. In conjunction with archaeological studies in the region, these observations show the potential impact of tsunamis on the ancient peoples in the IFM. Simulation of the near-field tsunami produced from the published slip distribution of 1957 is almost an order of magnitude smaller than all field observations. Increasing the earthquake magnitude and amount of eastern slip used in forward models of the tsunami demonstrate that run-up observations can be achieved throughout the eastern Aleutians if the earthquake was more than twice as large—at leastMw8.8 earthquake with 10–20 m of eastern slip. Additionally, up to five possible IFM paleotsunami deposits agree with the regional picture of regular large events, illustrating the circum-Pacific tsunami hazard from the east-central Aleutians.