Constraints on the Slip Distribution of the 1938 MW 8.3 Alaska Peninsula Earthquake From Tsunami Modeling

• Published in: Geophysical research letters 2021-05, Vol.48 (9), p.n/a
• Main Authors: Freymueller, Jeffrey T., Suleimani, Elena N., Nicolsky, Dmitry J.
• Format: Article
• Language: eng ; jpn
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2021GL092812

We simulated tsunami propagation for several scenario slip distributions for the 1938 MW 8.3 earthquake along the Alaska Peninsula and compared these to the observed records at Unalaska/Dutch Harbor and Sitka. The Sitka record is sensitive to the depth of slip but not the along‐strike location and is fit best by slip at shallow depth. The Unalaska record is sensitive mainly to the along‐strike location of slip and is fit best by slip that is concentrated in the eastern part of the presumed 1938 rupture zone. The tsunami data show that the actual 1938 earthquake rupture zone was likely ∼200 km in length or shorter and had no slip near the Shumagin Islands or in the 2020 Simeonof earthquake's rupture zone. The rupture models that best predict the 1938 tsunami lie within the region of high present day slip deficit inferred from GPS. Plain Language Summary Earthquakes are a result of slip (a permanent shift) along a fault or a break within the Earth. Determining the spatial extent of slip in old earthquakes is important, but difficult to do. We used records of the tsunami caused by a 1938 earthquake offshore of the Alaska Peninsula to determine that the earthquake slip was confined to shallow depth and that the slip on the fault mostly happened at the eastern edge of what had been traditionally drawn as the rupture zone. We found that the earthquake involved a smaller area than previously thought and that the rupture zone for the 1938 earthquake did not overlap at all with that of the recent 2020 Simeonof earthquake. Key Points The 1938 MW 8.3 Alaska Peninsula earthquake ruptured at shallow depth, within the region of high interseismic slip deficit Slip was confined to the eastern part of the previously inferred rupture zone and did not overlap with the 2020 Simeonof rupture The 1938 rupture zone was smaller than previously thought, likely no more than ∼200 km long, and the high slip area was likely much smaller than that