George Plafker
C.E. Synolakis
J.C. Borrero
E.A. Okal
2003
<p><span>The </span>1946<span> </span>Aleutian<span> earthquake stands out among tsunamigenic events because it generated both very high run-up </span>near<span> the earthquake source region and a destructive trans-Pacific </span>tsunami<span>. We obtained new data on the distribution of its </span>tsunami<span> in the </span>near<span> </span>field<span> along south-facing coasts between </span>Unimak<span> Pass on the west and </span>Sanak<span> </span>Island<span> on the east by measuring the height of driftwood and beach materials that were deposited by the </span>tsunami<span> above the extreme storm tide level. Our data indicate that (1) the highest measured run-up, which is at the Scotch Cap lighthouse, was 42 m above tide level or about 37 m above present storm tide elevation; (2) run-up along the rugged coast from Scotch Cap for 12 km northwest to Sennett Point is 12-18 m, and for 30 km east of Scotch Cap to Cape Lutke it is 24-42 m; (3) run-up along the broad lowlands bordering </span>Unimak<span> Bight is 10-20 m, and in-undation is locally more than 2 km; (5) run-up diminishes to 8 m or less at the southeast corner of </span>Unimak<span> </span>Island<span>; (6) no evidence was found for run-up above present storm tides (about 4-5 m above MLLW) on the Ikatan Peninsula or areas along the coast to the west; and (7) run-up above storm tide level in the </span>Sanak<span> </span>Island<span> group is restricted to southwest-facing coasts of </span>Sanak<span>, Long, and Clifford </span>Islands<span>, where it is continuous and locally up to 24 m high. Generation of the </span>tsunami<span> by one or more major earthquake-triggered submarine landslides </span>near<span> the shelf edge south of </span>Unimak<span> </span>Island<span> seems to be the only viable mechanism to account for the data on wave arrival time, run-up heights, and distribution, as well as for unconfirmed anecdotal reports of local postquake increases in water depth and diminished bottom-fisheries productivity. A preliminary hydrodynamic simulation of the local </span>tsunami<span> propagation and run-up using a dipolar model of a possible landslide off Davidson Bank provides an acceptable fit to the characteristics of the distribution of local run-up, with a value at 34 m at the Scotch Cap lighthouse.</span></p>
application/pdf
10.1785/0120020198
en
Seismological Society of America
Near-field survey of the 1946 Aleutian tsunami on Unimak and Sanak Islands
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