Geoscience Reference
In-Depth Information
Distributing the earthquake energy
E
uniformly over the area of the tsunami
source and the ocean depth
H
, we estimate the upper limit of the energy of the source
of turbulence,
W
lim
=
[m
2
s
−
2
]:
β
0
τ
E
W
lim
=
.
(7.11)
π
R
2
H
ρ
0
Substituting the empirical dependences (7.9) and (7.10) into expression (7.11)
and taking into account that
m
−
3
ρ
0
= 1
,
000 kg
·
π
≈
0
.
5, we obtain the fol-
and lg
lowing estimation formula:
W
lim
H
−
1
10
0
.
8M
−
1
.
3
.
≈
(7.12)
In Fig. 7.11 the dependence of the quantity
W
lim
upon the earthquake magni-
tude is presented in a logarithmic scale. From the figure it is seen that the quantity
W
lim
can amount to 100 and even 1,000 m
2
s
−
2
. On the basis of data presented in
Figs. 7.8-7.10, the conclusion can be made that strong earthquakes have a suffi-
cient reserve of energy for essential transformation of the ocean stratification struc-
ture. Tenths of a percent of the energy of an earthquake is sufficient for formation
on the ocean surface of a temperature anomaly with a characteristic horizontal di-
mension, measured by hundreds of kilometers and with a temperature deviation
of the order of 1
◦
C. Note, that a comparable amount of energy (less than 1% of
the earthquake energy) is spent on the formation of tsunami waves.
The formation of a temperature anomaly of the ocean surface is most proba-
ble in the case of a shallow thermocline and for seismic events, characterized by
a persistent process at the source or by a large number of aftershocks. The most
striking manifestation of the effect is to be expected in the case of realization of
the turbulence generation mechanism with a scale exceeding 10 m. Local variations
of the vertical temperature distribution should serve as a source of internal waves
even in those cases, when temperature variations are insignificant.
The estimates obtained show that noticeable transformation of the stratification
structure in the ocean, including formation of a temperature anomaly on its surface,
(m
2
s
−2
)
1,000
500 m
5,000 m
Fig. 7.11 Upper energy limit
for a hypothetical turbulence
source
W
lim
versus the earth-
quake magnitude
