Geology Reference
In-Depth Information
(a)
0
1
2
3
km
(b)
0
1
2
3
km
0
0
1
1
2
2
3
3
Fig. 4.27
(a) A structural model of the subsurface and (b) the resultant reflection events that would be observed in a non-migrated seismic
section, containing numerous diffraction events. (After Sheriff 1978.)
(a)
A
B
Distance
W
X
Z
Depth
Y
(b)
A
B
Distance
t
AW
t
BX
t
BZ
t
BY
Fig. 4.28
(a) A sharp synclinal feature in a
reflecting interface, and (b) the resultant
'bow-tie'shape of the reflection event on
the non-migrated seismic section.
Time
eral, if
a
s
is the dip of the record surface and
a
t
is the true
dip of the reflector, sin
a
t
= tan
a
s
. Hence the maximum
dip of a record surface is 45° and represents the case of
horizontal reflection paths from a vertical reflector.This
wavefront common-envelope
method of migration can be
extended to deal with reflectors of irregular geometry. If
there is a variable velocity above the reflecting surface to
be migrated, the reflected ray paths are not straight and
the associated wavefronts are not circular. In such a
case, a
wavefront chart
is constructed for the prevailing
