Geology Reference
In-Depth Information
Fig. 1.47.
Seismic model of a faulted fold.
a
Geometry of the model, no vertical exaggeration.
b
Model
time section based on normal velocity variations with lithology and depth. Vertical scale is two-way
travel time in milliseconds. (After Morse et al. 1991)
Fig. 1.48.
Mislocation of seismic reflection points caused by dip of the reflector.
a
Ray path end points
in vertical cross section.
b
Structure contours on a seismic reflector, depths subsea in kilofeet, showing
actual and interpreted locations of the reflecting points on a seismic line. (After Oliveros 1989)
to the surface beyond the outer limit of the recording array and so are not represented
on the seismic profile. The structural interpretation of seismic reflection data requires
the conversion of the travel times to depth. This requires an accurate model for the
velocity distribution, something not necessarily well known for a complex structure.
The most accurate depth conversion is controlled by velocities measured in nearby
wells (Harmon 1991).
If the trend of a seismic line is oblique to the dip of the reflector surface, two-dimen-
sional reflection data have location problems similar to those of unknowingly deviated
wells. This is in addition to the location problems associated with the conversion of
