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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

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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.

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Acknowledgments

We are grateful to our reviewers, especially our colleague David W. Scholl whose comments guided the revision of an early draft manuscript and for discussions within the USGS tsunami source working group in Menlo Park. The suggestions of two anonymous reviewers were insightful and helped us improve this paper.

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Authors and Affiliations

  1. U.S. Geological Survey, Emeritus. 4300 Carlson Way, Diamond Springs, CA, 95619, USA

    Roland von Huene

  2. US Geological Survey, Emeritus, Denver Federal Center, Denver, CO, 80225, USA

    John J. Miller

  3. Geomar Helmholtz-Zentrum für Ozeanforschung, Wishhofstrasse. 1-3, D24148, Kiel, Germany

    Dirk Klaeschen

  4. U.S. Geological Survey, Santa Cruz, CA, 95060, USA

    Peter Dartnell

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  1. Roland von Huene
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  2. John J. Miller
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Correspondence to Roland von Huene.

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von Huene, R., Miller, J.J., Klaeschen, D. et al. A Possible Source Mechanism of the 1946 Unimak Alaska Far-Field Tsunami: Uplift of the Mid-Slope Terrace Above a Splay Fault Zone. Pure Appl. Geophys. 173, 4189–4201 (2016). https://doi.org/10.1007/s00024-016-1393-x

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