Evidence for frequent, large tsunamis spanning locked and creeping parts of the Aleutian megathrust
Geological Society of America Bulletin
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- USGS data release - Alaska Tephra Data
- USGS data release - Radiocarbon, Cesium-137, Grain Size, and X-ray Fluorescence Data for Tsunami Geology Investigation, Driftwood Bay, Umnak Island, Alaska (2018)
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Abstract
At the eastern end of the 1957 Andreanof Islands 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 137Cs 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 ~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.
Suggested Citation
Witter, R., Briggs, R.W., Engelhart, S.E., Gelfenbaum, G.R., Koehler, R.D., Nelson, A.R., La Selle, S., Corbett, R., Wallace, K.L., 2019, Evidence for frequent, large tsunamis spanning locked and creeping parts of the Aleutian megathrust: Geological Society of America Bulletin, v. 131, no. 5-6, p. 707-729, https://doi.org/10.1130/B32031.1.
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Evidence for frequent, large tsunamis spanning locked and creeping parts of the Aleutian megathrust |
| Series title | Geological Society of America Bulletin |
| DOI | 10.1130/B32031.1 |
| Volume | 131 |
| Issue | 5-6 |
| Publication Date | November 16, 2019 |
| Year Published | 2019 |
| Language | English |
| Publisher | Geological Society of America |
| Contributing office(s) | Alaska Science Center Geology Minerals |
| Description | 23 p. |
| First page | 707 |
| Last page | 729 |