National Oceanic and
Atmospheric Administration
United States Department of Commerce


FY 2014

Multiple wave arrivals contribute to damage and tsunami duration on the US West Coast

Barberopoulou, A., M.R. Legg, E. Gica, and G. Legg

In Tsunami Events and Lessons Learned, Environmental and Societal Significance, Y.A. Kontar, V. Santiago-Fandiño, T. Takahashi (ed.), Advances in Natural and Technological Hazards Research, Vol. 35, Springer Netherlands, 359–376, ISBN: 978-94-007-7268-7 (Print) 978-94-007-7269-4 (Online) (2014)

Tsunamis persist long after the triggering geophysical events diminish. The Tohoku, Japan tsunami of March 11, 2011 was an extreme event that continued to disturb the Pacific Ocean for many days following its initiation. Historically Japan was considered a source of low tsunami wave energy for the US West Coast. However, damage in California from the last great Japan tsunami was second to that suffered during the 1964 Alaska earthquake. Computer animations of the catastrophic Japan tsunami and other recent significant tsunamis combined with source wavelet cross-correlations help to identify multiple paths of tsunami wave energy refracted and reflected by complex bathymetry across the Pacific Ocean basin. Using recent large tsunamigenic earthquakes we demonstrate that the long duration and damage suffered in the far field during the great 2011 Tohoku Japan tsunami was a result of several factors. Shallow water waveguides and continental margins act as tsunami lenses and mirrors to direct the wave energy to diverse locations around the ocean basin; directionality affected by islands and seamounts, large reflections off of South America and Oceania (New Guinea region), bathymetric features far and near the area of impact and shelf geometry may delay and further amplify the main tsunami energy. This contribution of Ocean basin scatterers can be estimated a-priori and can help define impact zones vs. shadow zones and duration of events. This has direct implications on the prediction of tsunami impacts because the US West Coast often appears to receive maximum wave heights much later than first wave arrivals from far field tsunamis.

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