The Interaction of Tsunamis With Ocean Swell: An Experimental Study

Our objective is to investigate the effect of combined swell–tsunami interaction on the nature of the tsunami — in particular the surface elevation, the runup speed and the near-bottom velocities. Laboratory testing in the Tsunami Wave Basin at Oregon State University has been performed to simulate this interaction, with free surface elevations and near-bottom velocities measured at various locations over a plane sloping beach. Random wavetrains with varying initial mean steepness were generated in concert with the tsunami. Preliminary analysis of the data reveals that high steepness ocean swell changes the spectral signature of the tsunami, particularly at high frequencies. There is also a significant difference in location of the breakpoint of the tsunami with overriding swell.