Geology Reference
In-Depth Information
The abrupt termination of a reflecting horizon at a fault provides a point source of
diffractions, arcuate reflectors that emanate from the fault and cross other reflectors. Time
migration of the seismic profile is designed to restore the reflectors to their correct rela-
tive locations and dips and to remove the diffractions. Nevertheless, some diffractions
may remain in time-migrated profiles, as seen in the region between B and C in Fig. 7.4a.
Fig. 7.5.
Velocity discontinuities create features that look like faults on seismic profiles.
a
Segment of a
seismic line across Wyoming thrust belt (dynamite source, eight-fold common-depth-point stack, migrated
time section, approximate vertical exaggeration 1.3 at 2.7 s; Williams and Dixon 1985).
b
Discontinuities
in seismic reflectors that might be normal faults.
c
Interpretation by Williams and Dixon (1985).
d
Geological
cross section using well control and the seismic line; no vertical exaggeration (Williams and Dixon 1985).
The
box
outlines the area of the seismic line. No normal faults are present.
TWY:
two-way traveltime (s);
C:
Cambrian;
MD:
Mississippian-Devonian;
IPPM:
Pennsylvanian, Permian, Mississippian undifferenti-
ated;
P:
Permian;
Tr, TR:
Triassic;
J:
Jurassic undifferentiated;
Jn:
Jurassic Nugget sandstone;
T:
Tertiary
