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Evidence for frequent, large tsunamis spanning locked and creeping parts of the Aleutian megathrust

Rob Witter, Richard W. Briggs, Simon E. Engelhart, Guy Gelfenbaum, Rich D. Koehler, Alan Nelson, SeanPaul La Selle, Reide Corbett and Kristi Wallace
Evidence for frequent, large tsunamis spanning locked and creeping parts of the Aleutian megathrust
Geological Society of America Bulletin (November 2018) 131 (5-6): 707-729


At the eastern end of the 1957 Andreanof Islands, Alaska, USA, moment magnitude 8.6 earthquake rupture, Driftwood Bay (Umnak Island) and Stardust Bay (Sedanka Island) lie along presently locked and creeping parts of the Aleutian megathrust, respectively, based on satellite geodesy onshore. Both bays, located 200 km apart, face the Aleutian trench and harbor coastal evidence for tsunami inundation in 1957. Here we describe the evidence at Driftwood Bay, including eight sheets of landward-fining, normally-graded marine sand that extend up to 375 m inland and 23 m above mean tide level. Drift logs that corroborate historical accounts of 1957 tsunami runup on Umnak Island's Pacific coast overlie the youngest sand sheet, which (super 137) Cs activity shows was deposited in the decade before 1963. The older sand sheets probably record tsunamis prior to 1957 because an emergent coastal terrace lacks evidence for storm-wave erosion and overwash since ca. 2 ka. Comparisons of the Driftwood Bay and Stardust Bay tsunami histories suggest that at least twice in the past 1700 years inundation occurred at one site but not the other. In contrast, Bayesian age-depth modeling suggests that the two bays may record five tsunamis like the 1957 tsunami, generated by earthquake ruptures that spanned the presently locked and creeping parts of the Aleutian megathrust. However, serial tsunamis occurring within days to centuries cannot be precluded. Our findings imply 164-257-year recurrence intervals for large eastern Aleutian tsunamis and challenge the notion that creeping parts of the megathrust, inferred from geodesy onshore, pose lower earthquake and tsunami hazards than locked areas.

ISSN: 0016-7606
EISSN: 1943-2674
Serial Title: Geological Society of America Bulletin
Serial Volume: 131
Serial Issue: 5-6
Title: Evidence for frequent, large tsunamis spanning locked and creeping parts of the Aleutian megathrust
Affiliation: U. S. Geological Survey, Alaska Science Center, Anchorage, AK, United States
Pages: 707-729
Published: 20181116
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
Accession Number: 2019-007049
Categories: Quaternary geologyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2018296
N53°13'26" - N53°13'26", W168°25'55" - W168°25'55"
Secondary Affiliation: University of Rhode Island, USA, United StatesUniversity of Nevada at Reno, USA, United StatesEast Carolina University, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201906
Program Name: USGSOPNon-USGS publications with USGS authors
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