Resonance of the 2006 Kuril Islands tsunami on the U.S. western continental shelf

Abstract

Throughout history, tsunamis have been a regular threat on the western coast of the U.S. However, some coastal communities have developed a reputation for tsunami wave activity. These cities have become well known not only for being affected by the most unnoticeable of tsunamis, but also for the amplified destruction they witness during larger tsunami events. This study examines large-scale oscillations on the U.S. western continental shelf to provide an explanation for tsunami wave amplification at some coastal communities. The 2006 Mw 8.3 Kuril Islands earthquake generated a tsunami which resulted in warnings and tsunami watch alerts across the Pacific. Although this tsunami was not particularly destructive on the West Coast, the earthquake source mechanism and the surface elevation of the resulting tsunami have been well-characterized and provide a good dataset with which to model and study wave oscillations on the West Coast. A depth-integrated non-hydrostatic model was used to reproduce the 2006 Kuril Islands tsunami. Comparison with sea surface elevations and amplitude spectra at DART buoys and tide stations shows good agreement between model output and observations. A Fast Fourier Transform of the computed sea surface elevation at each grid point describes the frequency content of the tsunami. Surface plots of the amplitudes and phase angles of the Fourier coefficients identify areas of amplification and abrupt phase changes respectively. Total energy is calculated by integrating the power spectrum over all of the frequencies present in the tsunami. Spectral analysis reveals oscillations on the West Coast with periods up to 129 minutes. Strong coupling between offshore and shelf resonance patterns is observed at long periods with a transition to partial standing waves at lower periods. A pattern of shelf oscillations forcing coastal amplifications begins to develop at periods shorter than 46 minutes. This study provides an explanation of why some coastal communities on the West Coast are historically hit harder than other cities as well as a first look at coastal communities which may experience tsunami wave amplification in the event of a large, locally-generated tsunami with long periods.