Steven Dutch, Professor Emeritus, Natural and Applied Sciences,University
of Wisconsin - Green Bay
Sometimes a fault will not be readily apparent on the ground orfrom outcrop mapping, but will show up when structure contoursare plotted. The clue that a fault may be present is a mismatchbetween structure contours in different parts of the map.
If the mismatch is abrupt, the explanation is probably a fault.If the mismatch is small or occurs over a wide area, there may bea fault or a flexure. If the mismatch is comparable to theuncertainties in the data, there may be no significance to it.If the contours change orientation gradually, the structure isprobably not planar.
The sill above is known from the outcrops shown. Is it faulted?
Try to construct structure contours. As long as the contours areconsistent with the outcrops, the layer is probably continuous.A mismatch or discontinuity may indicate a fault.
You may have to try several techniques. If you have enough data,try drawing structure contours using three-point constructions.Small differences in spacing and strike between adjacenttriangles are probably not significant.
If you extrapolate from a single strike and dip measurement, youmust be sure your measurement is representative of the structureas a whole, and the mismatch between the structure contours mustbe absolutely unmistakeable before you are justified in drawing afault.
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Created
17 March 1999, Last Update 17 March 1999