abstract

Two quartz-bar strainmeters were entrenched north of Beatty, Nevada to observe the Benham underground nuclear test of December 19, 1968 (M = 6.3). These instruments, oriented approximately radially to the source, were located at distances of 28 kilometers and 71 kilometers from ground zero. Construction began on December 4, was completed by December 16, and good records were obtained during the test.

Step-like residual strains of 1.8 × 10−7 and 0.35 × 10−7, respectively, were recorded. These results agree with those reported for earthquakes of M = 6.2. They also tend to substantiate the decay with distance law of R−3/2 observed for earthquakes as opposed to the theoretical R−13.

A most significant observation was that, whereas earthquake steps do not decay within several days if at all, the strain step from Benham apparently decayed to near zero within half an hour. This decay with time appears to be a reflection of the pressure history of the cavity.

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