FY 1985

Azimuthal variations in tsunami interactions with multiple-island systems

Hebenstreit, G.T., and E.N. Bernard

J. Geophys. Res., 90(C2), 3353–3360, doi: 10.1029/JC090iC02p03353 (1985)

The purpose of this study is to examine variations in the response of an island system (the Hawaiian Islands, in this case) to an incoming tsunamilike wave pulse approaching the system along various azimuths. Simulations were carried out numerically by using an explicit finite-difference analog for the linearized equations of motion and continuity for long waves in a variable depth ocean. The model topography is based on the submarine topography of the Hawaiian Island region. Island coastlines are fully reflecting, so no attempt to simulate runup was made. Qualitative comparisons between model results and historical data from tsunamis approaching along similar azimuths show that the model produces realistic simulations. Azimuths were chosen for waves approaching from four general geographic areas: South America, Alaska, Aleutians-Kuriles-Japan-Philippines, and Southwest Pacific. Nearly all distant tsunamis striking Hawaii have come from one of these areas. Our conclusions are: (1) Tsunami response in the overall system does not vary greatly over small (10°–15°) changes in azimuth but does vary significantly over large changes (>60°). (2) Local response may vary greatly with azimuth, but certain areas seem to respond strongly to tsunamis approaching from almost any direction. (3) Topographic focusing seems to play the dominant role in determining localized response.