Observations and theory of a shoaling tsunami wave

A WERA phased array HF radar was used in Chile to observe the disturbance of the 11 March 2011 tsunami which originated near Japan. In this pilot study, three sites on a transect across the shelf were analysed at water depths of 40, 160 and 880m. The maximum wave orbital velocities increased as the wave-group propagated into shallow water. The increase in maximum wave orbital velocities between 160 m depth and 40 m depth followed linear theory, but between 880 m and 160 m depths, the tsunami wave-group was non-linear and over half the amplitude was lost. The HF radar data indicate that non-linear processes are occurring at this location as the tsunami disturbance propagates from deep water onto the continental shelf.