130 E. E. ROSAIRE AND JOSEPH L. ADLER 
STRUCTURAL SIGNIFICANCE OF LARGE MISCLOSURES 
The most significant source of misclosure will, of course, be sought 
in structural conditions. We have seen, however, that only in cases of 
extreme misclosure, namely misclosures in excess of 250 feet, is it 
necessary to seek such a source. One structural condition which would 
readily give misclosure is a short sharp divergence from the normal 
dip, producing in effect a small structural terrace. Such a dip might 
yield a reflection on one side of a closed traverse and, due to the ac- 
cident of dip spacing, fail to be detected where crossed by the other 
side of the traverse. Or the terrace might die out laterally and there- 
fore intersect the traverse at one place only. In the latter case a large 
misclosure would result if no reflection were observed upon the ter- 
race. 
Another structural source of large misclosure may be the inter- 
section of the traverse by a fault at one point only, the fault terminat- 
ing somewhere within the traverse. Likewise a fault that continues 
across both sides of a traverse will produce misclosure if its throw 
differs markedly at the two points of intersection. In either case the 
fault must necessarily be of the hinge type. A fault having approx- 
imately equal displacement at its two points of intersection with the 
traverse cannot produce a misclosure large enough to be safely at- 
tributed to structural conditions. 
In postulating faulting as the explanation of a large misclosure, 
due consideration must be given to the limitations set by common 
geological knowledge of the behavior of hinge faults. While there is, 
of course, some change in the rate of decrease of displacement in pass- 
ing from the point of maximum displacement toward either end of the 
fault, this change in rate is very gradual. Consequently, large mis- 
closures caused by hinge faulting should be observed on several ad- 
joining traverse blocks, should differ more or less uniformly in value, 
and except where passing over the point of maximum displacement, 
should be of like arithmetical magnitude. In passing over the point 
of maximum displacement, however, the sign of the misclosure will 
change. 
If the observer places himself on the upthrown side, faces the 
fault, sums up the changes in elevation around the traverses in a clock- 
wise direction, giving a positive sign to increases in elevation and a 
negative sign to decreases, the following rule will apply: positive mis- 
closures will lie on the right of the point of maximum displacement; 
negative misclosures will lie on the left. By means of this rule the 
upthrown and downthrown sides of the fault may be distinguished. 
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