Geoscience Reference
In-Depth Information
A reduction of the oscillation frequency down to 0.1 Hz leads to an increase
in the quantity
η
0
= 0
.
1m),
which makes it doubtless larger, than the earthquake duration. In the case of small
frequencies, parametric resonance will have time to develop only if the oscillation
amplitude is very large,
τ
by three orders of magnitude (up to 3,000 s for
10 m. Such amplitudes can, apparently, be achieved,
when the frequency of seismic movements of the bottom happens to be close to one
of the normal frequencies of elastic oscillations of the water column.
Another mechanism restricting the exponential growth of amplitudes may be
the collapse of waves exceeding the critical steepness. In this case, the wave en-
ergy starts to be effectively transferred to the turbulent motion, which contributes to
intensification of vertical exchange in the water column [Ermakova et al. (2007)].
η
0
∼
7.4 Experimental Study of Wave Structures and of Stable
Stratification Transformation in a Liquid in the Case
of Bottom Oscillations
Processes arising in the ocean in the case of underwater earthquakes have been
studied experimentally with the aid of a simple physical model [Levin, Trubnikov
(1986); Alexandrov et al. (1986); Levin (1996); Nosov et al. (1996); Nosov, Ivanov
(1997); Nosov, Skachko (2000, 2004)].
The experimental set-up represented a round basin of diameter 0.45 and height
0.25 m, fixed on a massive foundation. Its layout is shown in Fig. 7.13. In the central
part of the basin there was a circular opening with a piston of diameter 0.15 m. The
piston underwent vertical oscillations with controlled amplitude and frequency. The
basin was filled with fresh water. In some of the experiments a stable temperature
stratification was created in the basin. To avoid intense cooling of the water, due to
evaporation, the basin was tightly covered with a specially adjusted lid of plexiglas.
Piston
Measurement
circuit
Fig. 7.13 Layout of experimental set-up. Distributed temperature sensor
