Structural interpretation - 3-D Seismic Interpretation - page 87

Fig. 3.20 Coherency map showing lineations due to faults; solid line is section of fig. 3.21 .

are no obvious displacements of bedding lineaments. An example is shown in fig. 3.20 ,
from the Lower Tertiary of the UK North Sea. A subdued colour-scale, such as the
grey-scale used here, or a sepia scale, is often best for picking out subtle lineations.
There are a number of lineations due to small faults. The bold black line marks the
location of the seismic section shown in fig. 3.21 . The small fault in the centre of the
line is easily followed across the map view in fig. 3.20 . Another example is shown in
fig. 3.22 , where a salt diapir pierces the horizon in the centre of the map and radial
faults can be seen, especially in the south-eastern quadrant. Since the fault planes are
surfaces of low coherence which are distinct from the higher coherence values within
the 3-D volume generally, they can be visualised in 3-D from any perspective using
the techniques discussed in chapter 7 . They can also be autotracked using techniques
similar to those used for horizons, though this has not yet become standard practice in
the same way as horizon autotracking. The coherence cube methodology can also be
used to reveal stratigraphic detail in the 3-D volume, such as channel/fan systems (see
chapter 4 ) .
Care is needed in interpreting all these attributes where there is significant coherent
noise present in the seismic data. Interference of noise events (e.g. multiples) with real
reflectors gives rise to discontinuities in reflectors that can be misinterpreted as faults