Structural Analysis and Synthesis. Stephen M. Rowland

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Structural Analysis and Synthesis - Stephen M. Rowland


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that dip upstream also “V” upstream (Figure 2.4).

      5 Planes/contacts that dip downstream at the same dip angle as the stream gradient appear parallel to the stream bed (Figure 2.5).Figure 2.1 Horizontal layer in a stream valley. (a) Block diagram. (b) Map view.Figure 2.2 Vertical layer strikes perpendicular across a ridge and valley. (a) Block diagram. (b) Map view.Figure 2.3 Inclined layer strikes perpendicular across a horizontal ridge. (a) Block diagram. (b) Map view.

      6 Planes/contacts that dip downstream at a gentler angle than the stream gradient “V”/point upstream (Figure 2.6).

      7 Planes/contacts that dip downstream at a steeper angle than the stream gradient (the usual case) “V”/point downstream (Figure 2.7).

Schematic illustrations of inclined layer dipping upstream that flows 90 degrees to strike. (a) Block diagram. (b) Map view. Schematic illustrations of layer dipping parallel to stream gradient (perpendicular strike). (a) Block diagram. (b) Map view. Schematic illustrations of layer dipping downstream more gently than the stream gradient with strike perpendicular to stream. (a) Block diagram. (b) Map view. Schematic illustrations of layer dipping downstream more steeply than the stream gradient; stream perpendicular to strike. (a) Block diagram. (b) Map view.

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      Structure‐contour maps are used for depiction and recognition of features in the subsurface. They are used extensively in petroleum exploration to identify structural traps and in hydrology to characterize the subsurface configurations of water tables and aquifers. Although there are more sophisticated methods to model the hydrogeology of an area, structure contouring of the water table is an invaluable skill for all geologists working on environmental delineation/remediation projects.

Schematic illustration of an example of structure contours on a structural surface.

      There are various techniques for contouring elevations. In the case of structure contours, there are usually not enough data to produce an unequivocal map, so experienced interpretation is valuable. Although there are computer programs that draw contour lines between data points, such programs cannot substitute for the judgment of an experienced geologist.

Schematic illustrations of block diagram (a) and structure-contour map (b) of a subsurface faulted structural dome with contours on the top of shaded layer.

       Step‐by‐Step Solution

      1 Label the three known points A, B, C and their elevations on the map.

      2 Draw lines connecting the three points and making a triangle.

      3 One of the lines connects the highest to the lowest of the three points. Scale this


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