Thickness Analysis using the Surface Geometry Tool in
Move
Thickness variations within syn-tectonic sedimentary packages provide important information about the
tectonic evolution of a region and can also be used to identify problems with an interpretation. The Surface
Geometry tool in Move™ is a quick and easy way to generate thickness maps between mesh surfaces. In this
Move Feature, we describe two methods for generating thickness maps in Move.
Thickness Maps
In both extensional and compressional terrains, variations in sediment thickness can be used to decipher the
temporal evolution of active structures. The starting point for such analysis is to generate sediment thickness
maps for each sedimentary unit or interval in the area of interest. An example of a sediment thickness map is
shown in Figure 1. We will use this image to highlight some of the key features associated with variations in
the thickness of this unit.
C
A
D
B
1 km
Figure 1. Sediment thickness map of a depositional unit dissected by two extensional faults, faults 1 and 2 (black polygons,
tick on downthrown side). The surface is colour mapped for sediment thickness (key to the colours is shown inset) and
contoured at 25 m intervals. Note the duplicated stratigraphic gap (fault polygon) to the east of Fault 2, which will be
explained at the end of the article. Sediment thicknesses at points A, B, C, and D are as follows: A = 177 m; B = 542 M;
C = 429 m, and; D = 418 m.
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During deposition of the sedimentary unit shown in Figure 1, the variation in thickness across Fault 1 (points A
and B) indicates that sedimentation rates were larger on the downthrown (NE) side of Fault 1. This thickness
variation indicates that the NW-SE orientated fault was active during deposition. The lack of thickness
variations across Fault 2 (Figure 1; points C and D) suggests that sedimentation rates were relatively constant
across this NE-SW orientated fault, which was probably inactive during deposition. The presence of thickness
variations on a surface with no mapped fault may indicate that a fault does exist at this location, or it could
reflect deposition onto an irregular surface. Careful examination of the original seismic and/or well data might
help to resolve the issue.
Sediment thickness maps are produced in Move by defining a source and target surface, between which
thickness is calculated. Two methods are used to measure sedimentary thickness (Figure 2): (a) the parallel
construction method measures the thickness of a sedimentary interval in a perpendicular direction from the
source surface to the target surface, and; (b) the similar construction method measures the thickness of a
sedimentary interval from the source surface to the target surface in a user-defined orientation. Thickness can
be measured from the centres of faces or from the vertices of the source surface.
Figure 2. Two construction methods are available during thickness analysis in Move; the parallel (a) and similar (b)
methods. Construction (measurement) lines are shown as black arrows.
In the Surface Geometry tool, the results of a thickness analysis are visualized on the source surface as a
colour map of sediment thickness. Once thickness attributes have been calculated and visualized, thickness
attributes can be saved onto the source surface for further analysis and visualization.
Generating thickness maps in Move
Thickness maps can be generated in move using the following workflow. The number of the step corresponds
to the numbered labels in Figure 3 below.
1. Open the Surface Geometry tool, located on the Data and Analysis panel.
2. Toggle on Thickness as the property to analyse.
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Figure 3. The Surface Geometry toolbox. Features of the toolbox described in the suggested workflow are highlighted using
the red rectangles.
3. Collect the source and target surfaces into the toolbox.
4. Select the construction method (Parallel or Similar). Define the Plunge and Azimuth of the
construction lines if you are using the similar construction method.
5. Define whether thickness is measured from the Vertices or the Face Centres of the source surface.
6. Construction lines (Figure 4) can be displayed by toggling on Display Construction Lines. The
number of construction lines visualized can be filtered using the sliding bar (Figure 4 inset).
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1 km
Figure 4. Construction lines (green) visualized during a parallel thickness analysis using a 50% display filter (see sliding bar
inset). Thickness is measured perpendicular from the source surface (transparent grey) to a target surface (colour mapped
for elevation). See colour bar at base of figure for key to colours.
7. To visualize the results of the thickness analysis as a colour map on the source surface, click the Apply
button located under the colour bar. The scale of the colour bar can be adjusted by manually defining
Min and Max values, or by using the Expand Colour Map to selection and Expand Colour Map to
model buttons.
8. To save the results onto the source surface as a thickness attribute, toggle on Attribute Creation, give
the attribute an appropriate name, and click Create Vertex Attribute.
The thickness analysis workflow is now complete. The analysis can be updated to incorporate any changes
made to the construction parameters using the Update Thickness Calculation button. If a thickness
attribute was created, the source surface will have thickness as a vertex or face attribute. Thickness attributes
can be visualized and manipulated further in tabular format using the Vertex Attribute Analyser or Face
Attribute Analyser, or as a colour mapped surface using the Colour Map tool.
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Measurement errors and artefacts
When performing thickness analysis of faulted surfaces, measurement errors and artefacts are commonly
spatially associated with faults (e.g. Fault 2 in Figure 1). Invalid thickness measurements or multiple
stratigraphic gaps can occur over large distances into the hanging wall or footwall of a fault (Figure 5).
Stratigraphic gaps associated with extensional faulting of both the source and target surfaces may result in
multiple areas with no thickness measurements (no data; Figure 5). Additionally, overlap of the source surface
in the hanging wall and the target surface in the footwall of an extensional fault, could result in erroneous
thickness measurements (Figure 5). Similar errors and artefacts are associated with compressional faulting. In
Figure 1, there are two stratigraphic gaps associated with Fault 2 that are separated by invalid thickness
measurements, similar to the scenario depicted in Figure 5. Only thickness measurements away from obvious
fault-related artefacts should be compared (e.g. points C and D on Figure 1). In general, great care should be
taken to ensure valid thickness measurements are used when analysing thickness maps that were constructed
using faulted surfaces.
Figure 5. During thickness analysis, measurement errors and artefacts are commonly spatially associated with faults.
If you require any more information about thickness analysis in Move, then please contact us by email:
[email protected] or call: +44 (0)141 332 2681.
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