The inverse tsunami problem of an island

Abstract

To date there exists no deep water record of a major tsunami from a benthic pressure gauge. Such deep water records and their spectra are desirable as a means of characterizing the tsunami source. The closest thing to such a record is that of the March 1957 event recorded by Van Dorn at Wake Island, a small volcanic atoll in the West Pacific nearly surrounded by a complex chain of sea mounts. While not of the same trapping capacity as the Hawaiian Island or continents, Wake Island and its neighboring sea mounts can produce quasi-resonant responses for periods near 3, 5, 6, 9 and 14 minutes. This effect sufficiently distorts the signals near shore, at the Van Dorn wave gauge and at a tide well within the lagoon, that they are quite different from that in the deep water. An inverse method is discussed by which the deep water signal can be estimated by one gauge and checked by the other. This inverse method is employed to determine an estimate of the deep sea tsunami signal from the Van Dorn gauge. Unfortunately the independent check using the tide gauge was not possible because of the lack of reliable information on its dynamic response characteristics at periods in the spectral band for the tsunami event.