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.
References
Abe, K. (1979). Size of great earthquakes of 1837–1974 inferred from tsunami data. Journal of Geophysical Research, 84, 1561–1568. doi:10.1029/JB084iB04p01561.
Boston, B., Moore, G. F., Jose Jurado, M., & Sone, H. (2016). Deformation of the Nankai Trough inner accretionary prism: the role of inherited structures. Geochemistry, Geophysics, Geosystems,. doi:10.1002/2015GC006185.
Briggs, R. W., Engelhart, S. E., Nelson, A. R., Dura, T., Kemp, A. C., Haeussler, P. J., et al. (2014). Uplift and subsidence reveal a nonpersistent megathrust rupture boundary (Sitkinak Island, Alaska). Geophysical Reseach Letters, 41, 2289–2296. doi:10.1002/2014GL059380.
Bruns, T. R., von Huene, R., & Culotta, R. C. (1987). Geology and petroleum potential of the Shumagin margin, Alaska. In D. W., Scholl, A., Grantz, & J. G., Vedder, eds., Geology and resource potential of the continental margin of western North America and adjacent ocean basins—Beaufort Sea to Baja California: Houston, Texas, Circum-Pacific Councilfor Energy and Mineral Resources, Earth Science Series, v. 6, pp. 157–190.
Calvert Andrew, J., & Susan, E., McGeary. (2013). Seismic reflection imaging of ultradeep roots beneath the eastern Aleutian island arc. Geology, February 2013. 41(2), 203–206. doi:10.1130/G33683.1g.
Collot, J. -Y., Agudelo, W., Ribodetti, A., & Marcaillou, B. (2008). Origin of a crustal splay fault and its relation to the seismogenic zone and underplating at the erosional north Ecuador-south Colombia oceanic margin. Journal of Geophysical Research, 113, B12102. doi:10.1029/2008JB005691.
Flueh, E. R. & von Huene, R. (1994). FS Sonne Fahrtbericht SO 96, (Cruise Report SO 96) Hong Kong-Kodiak-Kodiak, GEOMAR Research Center for Marine Geosciences, info@geomar.de
Freymueller, J. T., Woodard, H., Cohen, S. C., Cross, R., Elliott, J., Larsen, C. F., Hreinsdóttir, S., & Zweck, C. (2008). Active deformation in Alaska based on 15 years of GPS measurements, In Freymueller, J. T., Haeussler, P. J., & others (eds.), Active Tectonics and Seismic Potential of Alaska. Am. Geophys. Union, Gephys Monograph, 179, 1–42.
Fryer, G. J., Tryon, M. D. (2005). Great earthquakes, gigantic landslides, and the continuing enigma of the April Fool’s tsunami of 1946. EOS transactions AGU86 (52). T11A-0355.
Holbrook, W. S., Lizarralde, D., McGeary, S., Bangs, N., & Diebold, J. (1999). Structure and composition of the Aleutian island arc and implications for continental crustal growth. Geology, 27, 31–34. doi:10.1130/0091-7613(1999)027<0031:SACOTA>2.3.CO;2.
Ide, S., Baltay, A., & Beroza, G. C. (2011). Shallow dynamic overshoot and energetic deep rupture in the 2011 Mw 9.0 Tohoku-Oki earthquake: Science. 332, 1426–1429. doi:10.1126/science.1207020.
Johnson, Jean M., & Satake, Kenji. (1997). Estimation of seismic moment and slip distribution of the April 1, 1946. Aleutian tsunami earthquake: J. Geophys. Res., 102(B6), 11765–11774.
Kathrin, L., Grevemeyer, I., Lange, D., Flueh, E., Tilmann, F., & Contreras-Reyes, E. (2014). Splay fault activity revealed by aftershocks of the 2010 Mw 8.8 Maule earthquake, central Chile. Geology, 42, 823–826. doi:10.1130/G35848.1.
Lander, J. F., & Lockridge, P. A. (1989). United States Tsunamis (Including United States Possessions) 1690–1988, National Oceanic and Atmospheric Administration, National Geophysical Data Center, Boulder, Colorado, USA, Publication 41-2. (URL: http://www.ngdc.noaa.gov/hazard/data/publications/pub41-2.pdf)
Lay, T., Kanamori, H., Ammon, C. J., Koper, K. D., Hutko, A. R., Ye, L., et al. (2012). Depth-varying rupture properties of subduction zone megathrust faults. Journal Geophysical Research, 117, B04311. doi:10.1029/2011JB009133.
Lewis, K. B., Ladd, J. W., & Bruns, T. R. (1988). Structural development of an accretionary prism by thrust and strike-slip faulting: shumagin region. Aleutian Trench: Geological Society of America Bulletin, 100, 767–782.
Lieser, K., Grevemeyer, I., Lange, D., Flueh, E., Tilmann, F., & Contreras-Reyes, E. (2014). Splay fault activity revealed by aftershocks of the 2010 Mw 8.8 Maule earthquake, central Chile. Geology, 42, 823–826. doi:10.1130/G35848.1.
Lim, E., Eakins, B. W., & Wigley, R. (2009). Southern Alaska coastal relief model: procedures,data sources and analysis: available at http://www.ngdc.noaa.gov/mgg/coastal/s_alaska.html.
Lizarralde, D., Holbrook, W. S., McGeary, S., Bangs, N. L., & Diebold, J. B. (2002). Crustal construction of a volcanic arc; wide-angle seismic results from the western Alaska Peninsula. Journal of Geophysical Research, 107(B8), 2164. doi:10.1029/2001JB000230.
Lopez, A. M. & Okal, E. A. (2006). A seismological reassessment of the source of the 1946 Aleutian ‘tsunami’ earthquake. Geophysical Journal International, 165–3, 835–849.
Miller, J. J., von Huene, R., Ryan, H. F. (2014). The 1946 Unimak Tsunami Earthquake Area-Revised tectonic structure in reprocessed seismic images and a suspect near field tsunami source, U.S. Geol. Surv. Open File Rep., 2014–1024. doi:10.3133/ofr20141024
Moore, G. F., Bangs, N. L., Taira, A., Kuramoto, S., Pangborn, E., Tobin, H. J. (2007). Three-dimensional splay fault geometry and implications for tsunami generation. Science, 318, 1128. doi:10.1126/science.1147195.
Nelson, A. R., Briggs, R. W., Dura, T., Engelhart, S. E., Gelfenbaum, G., Bradley, L.-A., et al. (2015). Tsunami recurrence in the eastern Alaska-Aleutian arc: a Holocene stratigraphic record from Chirikof Island. Alaska, Geosphere, 11(4), 1–32. doi:10.1130/GES01108.1.
Okal, E. A., & Hebert, H. (2007). Far-field simulation of the 1946 Aleutian tsunami. Geophysical Journal International, 169, 1229–1238. doi:10.1111/j.1365246X.2007.03375.
Okal, E. A., Plafker, G., Synolakis, C. E., & Borrero, J. C. (2003). Near-fieldsurvey of the 1946 Aleutian tsunami on Unimak and Sanak Islands, Bull.seism. Soc. Am., 93, 1226–1234.
Okal, E. A., Synolakis, C. E., Fryer, G. J., Heinrich, P., Borrero, J. C., Ruscher, C., et al. (2002). A field survey of the 1946 Aleutian tsunami in the far field. Seismological Research Letters, 73, 490–503.
Park, J.-O., Tsuru, T., Kodaira, S., Cummins, P. R., & Kaneda, Y. (2002). Splay fault branching along the Nankai subduction zone. Science, 297, 1157–1160. doi:10.1126/science.1074111.
Ramirez, S. G., Gulick, S. P. S., & Hayman, N. W. (2015). Early sedimentation and deformation in the Kumano forearc basin linked with Nankai accretionary prism evolution, southwest Japan. Geochemistry, Geophysics, Geosystems, 16, 1616–1633. doi:10.1002/2014GC005643.
Rathburn, A. E., Levin, L. A., Tryon, M., Gieskes, J. M., Martin, J. B., Perez, M. E., et al. (2009). Geological and biological heterogeneity of the Aleutian margin (1965–4822 m). Progress in Oceanography, 80(2009), 22–50.
Shillington, D. J., Becel, A., Nedimovic, M. R., Webb, S. C., Kuehn, H., Abers, G. A., et al. (2015). Link between plate fabric, hydration and subduction zone seismicity in Alaska. Nature Geoscience, 8, 961–964. doi:10.1038/ngeo02586.
Steven, Holbrook W., Lizarralde, D., McGeary, S., Bangs, N., & Diebold, J. (1999). Structure and composition of the Aleutian island arc and implications for continental crustal growth. Geology, 27, 31–34. doi:10.1130/0091-7613(1999)027<0031:SACOTA>2.3.CO;2.
The SAFRR Tsunami Modeling Working Group. (2013). Modeling for the SAFRR Tsunami Scenario—Generation, propagation, inundation, and currents in ports and harbors, chap. D In: Ross, S. L., & Jones, L. M., eds., The SAFRR (Science Application for Risk Reduction) Tsunami Scenario: U.S. Geological Survey Open-File Report 2013–1170. http://pubs.usgs.gov/of/2013/1170/d/.
Turner, R. F., Lynch, M. B., Conner, T. A., Halin, P. J., Hoose, P. I., Martin, G. C., Olson, D. L., Larson, J. A., Fett, T. O., Sherwood, K. W., & Adams, A. J. (1987). Geological and 860 operational summary, Kodiak Shelf stratigraphic test wells, Alaska: U.S. Department of the 861 Interior, U.S. Minerals Management Service (MMS), Alaska, USA OCS Report MMS 87-862 0109.
von Huene, R., Miller, J. J., & Dartnell, P. (2015). A possible transoceanic tsunami directed toward the U.S. west coast from the Semidi segment, Alaska convergent margin. Geochemistry, Geophysics, Geosystems, 17, 645–659. doi:10.1002/2015GC006147.
von Huene, R., Miller, J., & Weinrebe, W. (2012). Subducting plate geology in three great earth-quake ruptures on the western Alaska margin, Kodiak to Unimak [online]. Geosphere, 8(3). doi:10.1130/GES00715.
von Huene, R., Kirby, S. Miller, J., & Dartnell, P. (2014). The Destructive 1946 Unimak near-field tsunami: New evidence for a submarine slide source from reprocessed marine geophysical data; Geophys. Res. Lett. 41, 6811–6818. doi:10.1002/2014GL061759
Wang, Kelin, Yan, Hu, & Jiangheng, He. (2012). Deformation cycles of subduction earthquakes in a viscoelastic earth. Nature,. doi:10.1038/nature11032.
Wendt, J., David, D. O., & Eric L. G. (2009). Tsunamis and splay fault dynamics. Geophysical Research Letters, 36, L1, 15303. doi:1029/2009GL038295.
Winston, J. G. (1983). Kodiak Shelf, Gulf of Alaska: American Association of Petroleum Geology. Studies in Geology #15, 3, 3.4.2–146
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.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
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
Received:
Revised:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00024-016-1393-x