PRELIMINARY MODELING OF PALEOTSUNAMIS AND HISTORICAL TSUNAMIS NEAR THE ISLANDS OF THE FOUR MOUNTAINS, ALEUTIAN ISLANDS

Adequate geophysical and historical information for assessing the potential danger of earthquakes and predicting patterns of rupture are beginning to be collected for the Aleutian subduction zone. However, to accurately assess the tsunami hazard facing countries throughout the Pacific Ocean because of the Aleutian subduction zone, the past and prehistoric seismicity of the arc needs to be better documented and quantified. As part of the NSF-funded project on Prehistoric Resilience in the Islands of the Four Mountains (IFM), we modeled paleotsunamis, the 1946 tsunami, and the 1957 tsunami deposits to estimate the magnitude of tsunamis in the east-central Aleutian field area of the IFM. We simulated these events using GeoClaw, a two-dimensional, shallow wave, open-source software package. Preliminary modeling results indicate that the largest waves are located in South Cove of Chuginadak Island, the largest island of IFM and the primary field area of this project. Additionally, the current source model of the 1957 earthquake from Johnson et al, 1994, does not produce a large enough tsunami by almost an order of magnitude, suggesting slip off of IFM was likely greater than previously estimated. Finally, largest paleotsunami events likely require high slip immediately adjacent to IFM during rupture.