Submarine slope failures near Seward, Alaska, during the M9.2 1964 earthquake

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Abstract

Following the 1964 M9.2 megathrust earthquake in southern Alaska, Seward was the only town hit by tsunamis generated from both submarine landslides and tectonic sources. Within 45 seconds of the start of the earthquake, a 1.2-km-long section of waterfront began sliding seaward, and soon after, ~6-8-m high waves inundated the town. Studies soon after the earthquake concluded that submarine landslides along the Seward waterfront generated the tsunamis that occurred immediately after the earthquake. We analyze pre- and post-earthquake bathymetry data to assess the location and extent of submarine mass failures and sediment transport. New NOAA multibeam bathymetry shows the morphology of the entire fjord at 15 m resolution. We also assembled all older soundings from smooth sheets for comparison to the multibeam dataset. We gridded the sounding data, applied corrections for coseismic subsidence, post-seismic rebound, unrecovered co-seismic subsidence, sea-level rise (vertical datum shift), and measurement errors. The difference grids show changes resulting from the 1964 earthquake. We estimate the total volume of slide material to be about 211 million m3. Most of this material was transported to a deep, flat area, which we refer to as “the bathtub”, about 6 to 13 km south of Seward. Sub-bottom profiling of the bathtub shows an acoustically transparent unit, which we interpret as a sediment flow deposit resulting from the submarine landslides. The scale of the submarine landslides and the distance over which sediment was transported is much larger than previously appreciated.

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Additional publication details

Publication type Book chapter
Publication Subtype Book Chapter
Title Submarine slope failures near Seward, Alaska, during the M9.2 1964 earthquake
DOI 10.1007/978-1-4020-6512-5_28
Volume 27
Year Published 2007
Language English
Publisher Springer
Contributing office(s) Coastal and Marine Geology Program, Alaska Science Center
Description 10 p.
Larger Work Type Book
Larger Work Subtype Other Government Series
Larger Work Title Submarine mass movements and their consequences
First page 269
Last page 278
Country United States
State Alaska
City Seward
Online Only (Y/N) N
Additional Online Files (Y/N) N