Geoscience Reference
In-Depth Information
Fig. 2.32 Total energy of
waves generated by piston-
like (1) and running (2) dis-
placements versus duration
of the process in the active
area. In the case of a running
displacement
= 2
av
−
1
τ
(a)
(b)
Fig. 2.33 Directional diagrams for emission energy of waves caused by piston-like (a) and
membrane-like (b) displacements of ocean bottom. Curves 1-7 correspond to
τ
= 0
.
5, 1, 2, 4,
8, 16, 32
the main part of energy starts to be emitted in the direction of propagation of the dis-
placement. When the duration of the process at the source is small (
= 2), the direc-
tional diagrams for both cases investigated are practically identical. But in the case
of large values of
τ
, the character of motion of the ocean bottom already exerts
significant influence on the parameters of the excited wave.
Figure 2.32 presents the dependence of the total wave energy (integrated over all
directions) upon the duration of the process at the source. In the case of a piston-like
displacement (curve 1) the dependence is monotonous—the energy falls as the dura-
tion of the process increases. In the case of a running displacement (curve 2) the de-
pendence reveals a maximum, which corresponds to coincidence of the propagation
velocity of the displacement and the velocity of long waves. The running displace-
ment is also seen to be noticeably more effective than the piston-like displacement
within a wide range of
τ
values. When durations of the process at the source are
small or large, the efficiencies of both mechanisms of wave generation are approxi-
mately identical.
Figure 2.33 presents energy directional diagrams for waves due to piston-like
and membrane-like displacements. The dotted line shows the shape and orientation
τ
