Jorum early aftershock measurements

An instrumentation system devised specifically to aid in differentiating the locus of early aftershocks in the vicinity of a large underground nuclear explosion was tested during the Jorum event in September 1969. This system included six stations located on three radii from Jorum surface zero. Records from these stations included 115 aftershocks during the initial three-hour postshot period. Arrival times from the 40 largest events during the first hour indicated that 12 were in the chimney area and 28 were at distances between 100 meters and 6.3 kilometers from the explosion. Six events appear to be directly associated with faults identified prior to the shock, and two groups near surface zero suggest new faults in that vicinity. Four later aftershocks, identified in Seismological Notes (Seismological Society of America) for September and October 1969, were found to be within the chimney area.