Analysis of the 1969 and 1975 Tsunamis
at the Atlantic Coast of Portugal and Spain

A. B. Rabinovich*, P. Miranda**, and M. A. Baptista**

* Tsunami Center, Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia

** Centro de Geophisica da Universidade de Lisboa, Lisboa, Portugal

Received February 5, 1997

Abstract—Tide gauge records from two tsunamis generated by strong submarine earthquakes on February 28,
1969, and May 26, 1975, which occurred in the Atlantic Ocean west of the Iberian Peninsula are analyzed.
Anew approach based on spectral analysis of tsunami and background records at individual stations and on the
estimation of the spectral ratio tsunami/background was used. This approach allowed us to separate the influ-
ence of the topography and the background and reconstruct the initial spectrum in the source area. The recon-
structed source spectra had significant spectral peaks at periods of 12.8 and 9.6 min (in 1969) and of 12.8 and
7.0 min (in 1975), which were in good agreement with the existing seismological data on the foci areas of the
corresponding earthquakes. It is shown that the prominent peak in the initial tsunami spectra with a period of
38 min is associated with the resonant features of the Atlantic shelf of the Iberian Peninsula. It is also shown
that data averaging over multiple stations allows one to suppress the influence of local topographic peculiarities
on the tsunami spectrum.

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