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A Possible Source Mechanism of the 1946 Unimak Alaska Far-Field Tsunami: Uplift of the Mid-Slope Terrace Above a Splay Fault Zone

  • Roland von Huene
  • John J. Miller
  • Dirk Klaeschen
  • Peter Dartnell
Chapter
Part of the Pageoph Topical Volumes book series (PTV)

Abstract

In 1946, megathrust seismicity along the Unimak segment of the Alaska subduction zone generated the largest ever recorded Alaska/Aleutian tsunami. The tsunami severely damaged Pacific islands and coastal areas from Alaska to Antarctica. It is the charter member of “tsunami” earthquakes that produce outsized far-field tsunamis for the recorded magnitude. Its source mechanisms were unconstrained by observations because geophysical data for the Unimak segment were sparse and of low resolution. Reprocessing of legacy geophysical data reveals a deep water, high-angle reverse or splay thrust fault zone that leads megathrust slip upward to the mid-slope terrace seafloor rather than along the plate boundary toward the trench axis. Splay fault uplift elevates the outer mid-slope terrace and its inner area subsides. Multibeam bathymetry along the splay fault zone shows recent but undated seafloor disruption. The structural configuration of the nearby Semidi segment is similar to that of the Unimak segment, portending generation of a future large tsunami directed toward the US West coast.

Keywords

Alaska subduction zone 1946 tsunami splay fault zone tsunami source mechanics subducted relief Alaska tsunami hazard 

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Copyright information

© Springer International Publishing (outside the USA) 2016 2016

Authors and Affiliations

  1. 1.U.S. Geological SurveyDiamond SpringsUSA
  2. 2.US Geological Survey, Emeritus, Denver Federal CenterDenverUSA
  3. 3.Geomar Helmholtz-Zentrum für OzeanforschungKielGermany
  4. 4.U.S. Geological SurveySanta CruzUSA

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