Geoscience Reference
In-Depth Information
Chapter 7
Seaquakes: Analysis of Phenomena
and Modelling
Abstract The main manifestations of seaquakes and possible consequences of
this phenomenon are described. The seaquake intensity scale is given. Historical
evidence of seaquakes, originating in the Pacific Ocean and in the Mediterranean
Sea, has been collected and analysed. Information is presented on instrumental
observations of variations in the temperature fields in the ocean after submarine
earthquakes. The possibility is estimated for a submarine earthquake to result in
destruction of the temperature stratification in the ocean. Theoretical ideas of the
parametric generation of surface waves, due to an underwater earthquake, are ex-
pounded. The results are described of laboratory experiments, devoted to the inves-
tigation of wave structures on the surface of a liquid and of the transformation of
stable stratification in its column, in the case of bottom oscillations.
Keywords Underwater earthquake
seaquake
Faraday ripples
stratification
ver-
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tical exchange
SST anomaly
internal waves
biogenes
upwelling
sea colour
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historical testimony
turbulence
mixing
parametric resonance
non-linear cur-
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rents
weather phenomena
turbulence energy
earthquake energy
Mathieu equa-
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tion
instability
increment
experimental set-up
bottom oscillations
dynamic
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modes
dissipative structures
temperature profile
turbulent exchange coefficient
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shadow method
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Every year over 100 strong (
M
>
6) earthquakes, most of which are under water,
take place on the Earth. The enormous energy released during an earthquake, even
if an insignificant part is transferred to the ocean near the source, can lead to strong
and even catastrophic dynamic perturbations of the water mass, which is known as
a seaquake.
A seaquake usually represents a strong perturbation of a large area (of diame-
ter of the order of 10-100 km) of the surface layer of water, which continues sev-
eral minutes, and is manifested in the generation of a system of very steep stand-
ing waves of large amplitudes (up to 10 m), the sudden ejection of vertical water
jets, the development of a foaming cavitation zone over the entire area, generation
of local eddies and splashes of water, strong blows of compression waves against
the boat's bottom and the appearance of powerful low-frequency acoustic effects in
the atmosphere [Levin (1996)].
