Spectral analysis of tsunami waves: Separation of source and topography effects

TLDR

A new approach is proposed to separate the influence of source and topography in observed tsunami spectra and to reconstruct the initial source spectrum. The method assumes a linear tide gauge response, compares tsunami and background spectra, and uses the invariant ratio of their spectra—dependent only on source parameters—to reconstruct source spectra, demonstrated on three historical tsunamis. Reconstructed source spectra from multiple tide gauges agree well with each other and with independent seismological, geodetic, and field survey data.

Abstract

A new approach is proposed to separate the influence of source and topography in observed tsunami spectra and to reconstruct the initial source spectrum. The method assumes a linear tide gauge response to external forcing and is based on comparative analysis of tsunami and background spectra. Evaluation of the ratio of tsunami to background spectra gives functional characteristics that are invariant of station location and dependent only on the source parameters. Three events, the Urup tsunami of December 22, 1991 (northwest Pacific), the Hokkaido Southwest (Okushiri) tsunami of July 12, 1993 (Sea of Japan), and the Shikotan tsunami of October 4, 1994 (northwest Pacific), are used as examples of the proposed approach. The source spectra reconstructed from the analysis of different tide gauges were found to be in good agreement with each other and with the seismological, geodetic, and field survey data.