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GCShaded
Relief in Display of Seismic
Data
*
By
Arthur Barnes1
Search and Discovery Article #40097 (2003)
*Adapted for online presentation from the Geophysical Corner column in AAPG Explorer August, 2002, entitled “What a Relief Shade Can Be,” prepared by the author. Appreciation is expressed to the author, to R. Randy Ray, Chairman of the AAPG Geophysical Integration Committee, and to Larry Nation, AAPG Communications Director, for their support of this online version.
1Landmark Graphics, Englewood, Colorado ([email protected].)
In the shaded relief image of Figure 1 you see a
rugged mountain with craters on its flanks. Lunar topography? A stretch of
remote desert on Earth? Hardly – it is a time slice through a seismic
volume.
Compare this image with Figure 2, a conventional display of the same
data
, and
you will agree that shaded relief wonderfully complements standard
displays by revealing details and presenting them in a form that geologists
readily appreciate. Yet, already knew that, for shaded relief has been employed
for over a century in displays of topography, and today it is ubiquitous in the
display of any geological or geophysical data
that is presented as a map,
including digital elevations, gravity and magnetic
data
, interpreted
seismic
horizons and geologic models. Whatever the application, the motivation for
shaded relief displays is always the same – to transform
data
into
realistic-looking apparent topography and thereby aid
interpretation
by
revealing or suggesting true geology.
uShaded
relief and
uShaded
relief and
uShaded
relief and
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Shaded Relief and
Why was shaded relief not applied to the
display of
Two reasons stand out:
To apply shaded relief to a 3-D
Shaded relief actually contains the same information as the common dip-azimuth attribute (Figure 4). This common information is the reflection dip and azimuth. Shaded relief combines them into apparent topography, whereas dip-azimuth shows them together with dip determining the shading of the display and azimuth determining its color. The difference is only in how it presents this information. Of course, as any marketer can attest, presentation is significant – and in this case, geoscientists are likely to find that dip-azimuth confuses as much as shaded relief enlightens.
While shaded relief replaces dip-azimuth, it
complements other attributes, such as continuity (Figure 5). Both shaded
relief and continuity reveal details hidden in the There is also a difference of directionality, for most attributes reveal structures in all directions, whereas shaded relief is directional, enhancing features perpendicular to the illumination direction while suppressing those that are parallel. As a result, shaded relief displays should be created in pairs with orthogonal illumination directions so as to capture all features. This directionality is useful, as it makes a powerful directional filter of shaded relief, enabling a user to selectively highlight certain trends while hiding others.
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