A list of 300 tsunamis and similar phenomena known in the Mediterranean is given. Data reliability and wave intensity are estimated; mechanisms of tsunami generation are indicated and data from literature sources on the coordinates and magnitudes of tsunamigenic earthquakes are cited. Eighteen zones of excitation and manifestation of tsunamis are identified which can be integrated into four groups with respect to the recurrence period and maximum intensity of the tsunamis. The strongest tsunamis are excited in the Aegean Sea, and the Hellenic and Calabrian island arcs. The focal depth of the earthquake-generating tsunamis in the Mediterranean is, on average, less than that in the Pacific. Correspondingly, the magnitude of tsunamigenic earthquakes is lower. According to preliminary estimates, the Mediterranean tsunamis attenuate with distance more rapidly than do those in the Pacific Ocean.

The spectrum of long waves, which are a background to tsunamis, is analyzed on the basis of records of near--bottom pressure sensors obtained in the Northwest Pacific during the first and second USA-USSR expeditions on the investigation of tsunamis in the open ocean (1975 and 1978). Instrumental trends, tidal oscillations, and quasistationary longwave noise were contained in the records. Special filters were used to pick out small waves generated by the seismicity of the ocean bottom. A decrease of noise level from 10 2 cm (including tides) to 10°1 cm could be reached. The level of long-wave noise is found to depend on the instrument's location. Minimal dis-

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In 1988, short-term (duration 18 hr each) ocean-bottom seismic noise recordings were made in the frequency range of 0.01-10 Hz at the depth of 900-1400 m in the Atlantic ocean. There were two study areas: in the Canary upwelling and on the Reikjanes ridge. T h e spectral curves obtained for these two areas show the existence of a minimum in the frequency range of 0.05-0.10Hz (i.e. in the period range of 10-20 s) together with a maximum reflecting the domain of storm microseisms (0.1-1 Hz). We recommend the use of this minimum for regular recording of strong remote earthquakes and, especially, for surface wave dispersion studies t o obtain velocity sections of the oceanic crust and upper mantle.