ANALYSIS OF THE 1969 AND 1975 TSUNAMIS ON THE ATLANTIC COAST OF PORTUGAL AND SPAIN

We analyse tide gauge records from two tsunamis generated by strong su bmarine earthquakes of 28 February 1969 and 26 May 1975 occurred in th e Atlantic Ocean, westward from the Iberian coast. A new approach base d on spectral analysis of tsunami and background records and estimatio n of the corresponding spectral ratio was used to separate influence o f source and topography and to reconstruct the initial tsunami spectru m in the source area. The reconstructed source spectra were found to h ave significant spectral maxima at periods 12.8 and 9.6 min (1969), an d 12.8 and 7.0 min (1975), in good agreement with the existing seismol ogical data on the associated source areas. It is shown that the promi nent peak in coastal tsunami spectra with period of 38 min is related to the resonant feature of the Atlantic shelf of Iberian Peninsula. It is also shown that processing the individual coastal tsunami records it is possible to suppress effeciently influence of local topography a nd to amplify influence of the initial source by averaging spectra fro m different stations.