Geoscience Reference
In-Depth Information
Most regions of the World Ocean are known to be characterized by a clearly pro-
nounced stable temperature stratification—the cold lower column several kilometers
thick is separated from the atmosphere by a relatively thin (measured by hundreds
of meters) warm 'film', comprising a thermocline and a mixed layer. The possibility
of cold deep-water masses being transferred up to the surface layer of the ocean by
non-linear flows in the seaquake zone was first mentioned in [Levin et al. (1993)]
in relation to the identification of a tsunami source from outer space. Later it was
pointed out in [Nosov, Ivanov (1994)] that a seaquake can cause the development of
such powerful turbulence as to result in the warm film destruction and in formation
on the surface of the ocean of a cold 'spot' with an area exceeding 1,000 km
2
;itwas
noted that such a 'spot' is capable of exerting significant influence on the structure
of the temperature field of near-the-water layer of the atmosphere and to lead to
weather anomalies.
7.1 Manifestations of Seaquakes: Descriptions by Witnesses
and Instrumental Observations
7.1.1 Historical Evidence
In this section we shall mostly deal with data to be found in tsunami catalogues for
the Mediterranean sea and the Pacific Ocean [Soloviev et al. (1997); Soloviev, Go
(1974), (1975)]. About 300 events of tsunamis and of similar phenomena are known
in the case of the Mediterranean sea (2000
BC
-
AD
1991), and for the Pacific Ocean
there are about 1,000 events (years 173-1968). Among all the cases we have singled
out 25 events in the Mediterranean sea and 65 events in the Pacific Ocean, the de-
scriptions of which refer directly or indirectly to an intensification of the vertical
exchange in the ocean resulting from seismic movements of the ocean bottom. It
is important to note, here, that the information we are interested in is not the main
information for tsunami catalogues.
Most cases, recorded in catalogues, are based on evidence presented by wit-
nesses, who once in a while happened to see phenomena proceeding in the open
ocean or at uninhabited coasts. When interpreting testimonies of catastrophic earth-
quakes and tsunamis it is necessary to take into account the extremely strong shock
felt by the witnesses—the people could have not noticed a certain phenomenon, or,
contrariwise, might describe something that actually had not taken place. Thus, it
would not be correct to do any probability estimations on the basis of the number of
singled out events (90) and the total number of cases (
∼
1
,
300), described in tsunami
catalogues.
The technique for singling out an event among the entire amount was based on
the assumption of consequences of short and sharp enhancement of the vertical ex-
change in the ocean, which from our point of view may be the following:
1. Transfer of bottom sediments, sand, and so on up to the surface and, as a conse-
quence, the water becoming turbid or changing colour—similar phenomena take
place in shallow water during a storm.
