Geoscience Reference
In-Depth Information
(a)
(b)
(c)
(d)
(e)
(f)
Fig. 2.31 Distribution of amplitude of the first crest (a, b), of the 'maximum span' (c, d) and
of the energy (e, f) of a wave over the azimuthal angle. Curves 1-6 correspond to piston-like
displacements (a,c,e)of durations
τ
= 2
,
3
.
3(3)
,
5
,
10
,
12
.
5
,
20 and to running displacements (b,
d, f) with propagation velocities
v
= 5, 3, 2, 1, 0.8, 0.5. The durations and propagation velocities
are chosen so as to have
τ
= 2
av
−
1
. The dotted line shows the shape and orientation of the active
area (
a
= 5
,
b
= 1)
piston-like and running displacements, as the duration of the process at the source
varies. When the duration of a piston-like displacement increases, the amplitude and
energy of waves monotonously decreases, while their distribution over the azimuthal
angle tends to be isotropic. Here, the wave of largest amplitudes and energy are al-
ways emitted in a direction, perpendicular to the largest extension of the source.
In the case of a running displacement, as the duration of the process at the source
increases (the propagation velocity of the displacement decreases), the directional
diagrams gradually transform from two-pronged into single-pronged diagrams, and
