MS Plan B presentation: Resonance patterns along the US west coast from the 2011 Tohoku tsunami

Ryan Braman

The 2011 Tohoku earthquake devastated northeast Japan and caused damage and loss of life as far away as the Americas coasts. The pattern of the impact along the US west coast closely resembles those in previous tsunamis originated from different locations. This study seeks to understand the mechanism behind the impact through analysis of non-hydrostatic model results for the tsunami’s propagation across the Pacific and wave action over continental shelves . Recorded data from 13 tide gauges were selected from Washington to California and compared against the computed water surface elevation for model validation. A fast Fourier transform of both the computed and observed data was utilized to examine the frequency contents at each site. The amplitude spectrum was inspected for type and quantity of error to determine the extent that local bathymetry plays in resonance and the subsequent impact to infrastructure. The model results show both trapped and progressive edge waves along the coast, coupled through a set of standing waves spanning across the Pacific via island and seamount chains. Basin-wide coupling of large-scale resonance with continental shelves explains the prevalence of specific periods and local excitation responsible for persistent bay and harbor oscillations well after the earthquake.