Find Strike And Dip Given Structure Contour And One Other Point

Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay
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This is a very simple problem if we recall that structure contours are always parallel and equally spaced. The other structure contours will be parallel to our given contour, so the only real problem is to find the dip.

To determine the dip of the bed, we need to draw a line through the additional point (P) and perpendicular to the structure contour. There are two ways of doing this:

1. Use a right angle like the corner of an index card or a draftsman's triangle to draw the perpendicular.

2. Use a compass:

Using point P as a center, draw an arc that cuts the structure contour in two places (A and A').
Using A and A' as centers, draw two intersecting arcs. A line from point P to this intersection (B) is the perpendicular.

Example

1. Find the strike and dip of the limestone layer from the data at left.

2. Find the dip either by drawing a cross-section or by trigonometry.

3. With the dip known, find the map spacing between contours using either cross-section or trigonometry.

4. Construct other contours parallel to the known contour and with the correct spacing.

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Created 5 January 1999, Last Update 5 January 1999
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