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ship seemed to batter the rocky sea floor, although the depth of the water exceeded
100 m. The impression was that enormous barrels full of water were jumping up and
down in the hold and that the sheathing was on the brink of breaking. The shrouds
trembled, the handrails of the ladder broke down, the windows of the deck cabin
crumbled, the deck superstructures started to move and fall to pieces.
The vessel prepared for its unavoidable death.
Suddenly, the din stopped. The sea continued to vibrate, gradually calming down.
The vessel, that had suffered in 2 mimutes more than from the most monstrous storm,
was rocking quietly on the breezeless sunlit surface of the sea. If the seaquake had
continued for half a minute more, then it would have surely led to the appearance
of still another 'Flying Dutchman', abandoned by its crew, or to the mysterious
disappearance in the ocean of one more vessel together with its crew.
In most parts of the World Ocean there exists a very clearly expressed and stable
temperature stratification. Cold depth waters (a layer
10 3 m thick) are separated
10 1 -10 2 m) warm layer, which contains
a mixed layer and a thermocline. The evidence, reflected in the synthesized descrip-
tion of seaquakes due to witnesses, permits to assume underwater earthquakes to be
capable of causing so intense displacements of water that they are accompanied by
sharp, but short, enhancement of the vertical exchange in the ocean (seismogenic
upwelling). The concrete physical mechanisms of enhancement of the vertical ex-
change may be due to non-linear flows or to turbulence, the development of which
in a layer of water results from strong seismic motions of the ocean bottom.
Seismogenic upwelling may affect many processes in the ocean. Sea water
changing colour or becoming turbid as a result of ocean-floor sediments being car-
ried up toward the surface and suspended represents the most noticeable manifes-
tation of seismogenic upwelling. Moreover, the formation is possible of extensive
anomalies in the sea surface temperature (SST) and, consequently, unusual weather
phenomena may develop. The arrival of biogenes in the surface layer, usually de-
pleted of such substances should be accompanied by explosive development of phy-
toplankton. Evolution of the zone with violated, and therefore unstable, stratification
should create a powerful system of internal waves.
Some results of the research in seismogenic upwelling, under way since 1993
with participation and under the leadership of the authors of this topic will be pre-
sented in Chap. 7.
from the atmosphere by a relatively thin (
1.7 Hydroacoustic Signals in the Case of Underwater
Earthquakes
The capability of underwater earthquakes to excite hydroacoustic signals has been
known long ago [Ewing et al. (1950); Soloviev et al. (1968); Kadykov (1986)].
Hydroacoustic waves propagating in the ocean from the epicentral zone of an earth-
quake are called the T-phase. Investigation of this phenomenon traditionally per-
tains to the scientific activity of seismologists. The term T-phase originated from
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