The Benham. underground nuclear explosion, with a yield of 1.1 megaton equivalent TNT, caused apparent release of natural tectonic strain at the Earth's surface in decreasing amounts out from the explosion point. Strain changes were measured on quadrilaterals about 1 km (kilometer) on a side at six different localities. Maximum extension of 521 × 10−6 was measured 1 km from the explosion and 33 × 10−6 was measured at 11 km. Maximum strain at each measured location, plotted against distance from the explosion, gave the equation logε = −3.2823−0.1087 d, where ε is strain and d is distance in kilometers. Strain changes measured at distances greater than 5 km appear to be fault controlled and are believed to result from release of tectonic strain. A level line across the area of the explosion showed fault-controlled subsidence of an area, more than 3 km wide in an east-west direction, and probable slight uplift of the area to the east of the fault that is the eastern boundary of the subsidence.

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