Field Observations and Modeling of the 1957 Earthquake and Tsunami on the Islands of the Four Mountains, Aleutian Islands, Alaska

• Main Author: Griswold, Frances R.
• Format: Text
• Language: English
• Published: ScholarWorks@CWU 2015
• Subjects: Tsunami; 1957; Aleutians; Alaska; Earth Sciences; Geology; Sedimentology; Pacific; Aleutian Islands
• Online Access: https://digitalcommons.cwu.edu/etd/201; https://digitalcommons.cwu.edu/cgi/viewcontent.cgi?article=1194&context=etd

Due to a lack of research in the Aleutian Islands, a comprehensive history of the Aleutian subduction zone is not developed; however, this study indicates that the Aleutian subduction zone is capable of generating magnitude ~9 earthquakes or larger in addition to trans-Pacific tsunamis. Comparison of simulated runup and observed runup will help to determine the characteristics of rupture in the eastern Aleutians. A recent survey of the tsunami wrackline produced by the 1957 Great Aleutian earthquake (Mw 8.6) indicates runup up to 17.5 m in the Islands of the Four Mountains (presented here). Combined with other nearfield observations of 22 m on Umnak and 18.5 m on Unalaska (USGS), our measurements establish the 1957 tsunami as a significant tsunami in the 20th century. Through modeling this earthquake and tsunami and comparing simulations to nearfield observations, we conclude that the earthquake’s magnitude and amount of eastern slip are both higher than previously estimated. I propose several slip distributions that approximately recreate the observed runup; all of these distributions include high slip in the eastern portion of the aftershock zone, though the location of slip and intensity differ between models. No source model with a Mw = 8.6 was capable of generating the observed 1957 runup; the event was likely at least Mw > 8.9. Because nearfield observations are limited to those listed above, and seismic records are inadequate, a more precise solution to the rupture pattern cannot be determined.