TSUNAMI TRAPPING NEAR-CIRCULAR ISLANDS

Trapping of long water waves that are induced by submarine earthquakes and that attack circular islands is studied by applying a theoretical model (TINTI and VANNINI, 1994) that is based on the linear shallow water approximation. The solution is computed as the superposition of the eigenmodes of the water basin. The tsunami trapping is seen in terms of the capability of the source to excite the ''trapped'' eigenmodes of the basin. The bottom depth dependence around the island is shown to be quite important in determining the trapping capability of the island: a depth profile that is downwardly concave as the distance from the island coasts increases is substantially more efficient in amplifying the incoming waves and in trapping their energy than a profile exhibiting an upward concavity.