History of earthquakes and tsunamis along the eastern Aleutian-Alaska megathrust, with implications for tsunami hazards in the California Continental Borderland

Abstract

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Tsunami recurrence in the eastern Alaska-Aleutian arc: A Holocene stratigraphic record from Chirikof Island, Alaska

“…Although it is unclear if reports of severe flooding in the western part of the ruptured zone occurred following the 21 July earthquake or the later 6 August earthquake, 1 or 2 high tsunamis (reported run-up heights range from 3 to >30 m) caused much damage and many deaths from Kodiak Island to Sanak Island ( Fig. 1; Lander, 1996;Ryan et al, 2012b;Witter et al, 2014). The highest tsunami inundation at Southwest Anchorage was probably on 21 July, when the tsunami severely flooded Three Saints Harbor on Kodiak Island, 215 km to the northeast.…”

“…It is unlikely that anyone was living on Chirikof Island at the time; the only reports of the height of the 1938 tsunami are <0.3 m from distances of >650 km from the island (Lander and Lockridge, 1989;Lander, 1996;Ryan et al, 2012b). The tsunami was measurable, however, as far away as Japan, and Johnson and Satake (1994) used the tsunami wave forms to estimate the earthquake magnitude as 8.2, its rupture length as 300 km, and its depth as >20 km.…”

“…The variable source characteristics and tsunami-generating potential of megathrust ruptures in the region (Ryan et al, 2012b;Briggs et al, 2014aBriggs et al, , 2014bShennan et al, 2014aShennan et al, , 2014bWitter et al, 2014) suggest that Southwest Anchorage has been exposed to a large range in inundation heights that may only loosely correlate with tsunami volume, rupture extent, and earthquake magnitude. For this reason, forecasting future great earthquakes in the eastern Aleutian arc accompanied by southwarddirected high tsunamis will require carefully reconstructed histories of rupture lengths and inundation extents for the past 3-5 k.y.…”

“…For this reason, forecasting future great earthquakes in the eastern Aleutian arc accompanied by southwarddirected high tsunamis will require carefully reconstructed histories of rupture lengths and inundation extents for the past 3-5 k.y. at many sites (Ryan et al, 2012b). Until more complete tsunami chronologies are available, we recommend that a high-tsunami recurrence of ~180-270 yr ( Fig.…”

“…1A;Nishenko and Jacob, 1990;Vallier et al, 1994;Carver and Plafker, 2008;Ryan et al, 2012b;Ruppert et al, 2013;Butler et al, 2014;Shennan et al, 2014b). That the Aleutian arc is capable of sending damaging tsunamis across the Pacific basin is illustrated by those produced by the series of mid-twentieth century M 8-9 ruptures in the central and eastern Aleutian arc, in 1946, 1957, 1964, and 1965(Butler, 2012Ross et …”