Geoscience Reference
In-Depth Information
level correctly, it is possible to make best use of the screen display to show amplitude
variation in the events that the interpreter is working with. Sometimes, however, instead
of clipping being left to the interpreter's choice on final display, the decision is made
for him or her during data loading from SEGY traces; the data are already clipped and
scaled to the 8-bit range at the stage where they are made into a workstation seismic
volume. This has advantages in reducing the volume of seismic data on the workstation
disk and in decreasing the time taken to retrieve data from disk for display, because
amplitudes are stored as 8-bit numbers rather than 16- or 32-bit. It will, however, cause
problems if the interpreter wants to work with amplitudes of very strong events which
have been clipped during data loading. It is therefore a good idea to establish the extent
of clipping in the workstation dataset at an early stage; this is easily done by creating a
display in which the extreme ends of the colour bar are set to a contrasting colour. An
example is shown in
fig. 3.10
, where yellow has been substituted for red and black at
the two ends of the colour bar. If this were a display of the data as loaded, without any
additional clipping at the display stage, there would clearly be a problem in making
amplitude measurements on the strong event in the centre of the picture. However, the
data would still be quite satisfactory for general structural mapping.
an instant map view, which may for instance make it simple to see the fault pattern.
However, they are usually more difficult to understand than vertical sections, partly
Fig. 3.10
Seismic section, red/white/black colour scale with yellow added at both positive and
negative extreme ends of scale; yellow events have clipped amplitudes.
