@article {2775, title = {Evidence for frequent, large tsunamis spanning locked and creeping parts of the Aleutian megathrust}, journal = {GSA Bulletin}, volume = {131}, year = {2019}, month = {Jan-05-2019}, pages = {707 - 729}, abstract = {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{\textquoteright}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 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{\textendash}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}, doi = {10.1130/B32031.110.1130/2018296}, url = {https://pubs.geoscienceworld.org/gsa/gsabulletin/article/131/5-6/707/566656/Evidence-for-frequent-large-tsunamis-spanning}, author = {Witter, Rob and Briggs, Rich and Engelhart, Simon E. and Gelfenbaum, Guy and Koehler, Rich D. and Nelson, Alan and Selle, SeanPaul La and Corbett, Reide and Wallace, Kristi} } @article {25, title = {Beach ridges as paleoseismic indicators of abrupt coastal subsidence during subduction zone earthquakes, and implications for Alaska-Aleutian subduction zone paleoseismology, southeast coast of the Kenai Peninsula, Alaska}, journal = {Megathrust Earthquakes and Sea-level Change: a Tribute to George Plafker}, volume = {113}, year = {2015}, pages = {147-158}, abstract = {The Kenai section of the eastern Alaska-Aleutian subduction zone straddles two areas of high slip in the 1964 great Alaska earthquake and is the least studied of the three megathrust segments (Kodiak, Kenai, Prince William Sound) that ruptured in 1964. Investigation of two coastal sites in the eastern part of the Kenai segment, on the southeast coast of the Kenai Peninsula, identified evidence for two subduction zone earthquakes that predate the 1964 earthquake. Both coastal sites provide paleoseismic data through inferred coseismic subsidence of wetlands and associated subsidence-induced erosion of beach ridges. At Verdant Cove, paleo-beach ridges record the paleoseismic history; whereas at Quicksand Cove, buried soils in drowned coastal wetlands are the primary indicators of paleoearthquake occurrence and age. The timing of submergence and death of trees mark the oldest earthquake at Verdant Cove that is consistent with the age of a well documented \~{}900-year-ago subduction zone earthquake that ruptured the Prince William Sound segment of the megathrust to the east and the Kodiak segment to the west. Soils buried within the last 400{\textendash}450 years mark the penultimate earthquake on the southeast coast of the Kenai Peninsula. The penultimate earthquake probably occurred before AD 1840 from its absence in Russian historical accounts. The penultimate subduction zone earthquake on the Kenai segment did not rupture in conjunction with the Prince William Sound to the northeast. Therefore the Kenai segment, which is presently creeping, can rupture independently of the adjacent Prince William Sound segment that is presently locked.}, issn = {0277-3791}, doi = {10.1016/j.quascirev.2015.01.006}, url = {http://www.sciencedirect.com/science/article/pii/S0277379115000220}, author = {Kelsey, Harvey M. and Witter, Robert C. and Engelhart, Simon E. and Briggs, Richard and Nelson, Alan and Haeussler, Peter and Corbett, D. Reide} }