A study of small explosions and earthquakes during 1961--1989 near the Semipalatinsk Test Site, Kazakhstan

Several Russian sources have stated that 343 underground nuclear explosions were conducted during 1961--1989 at the Semipalatinsk Test Site. However, only 282 of them appear to have been described, in the openly available technical literature, with well-determined coordinates; and only 272 have both good locations and magnitudes. The authors have used regional data from 52 stations to study 65 seismic sources initially thought to be in or near the Semipalatinsk region, additional to the 272 underground nuclear explosions with known locations and magnitudes. Of these 65 events, the authors believe 8 are not explosions on the test site, namely: two earthquakes close to the test site; three earthquakes or chemical explosions 100--300 km from the test site; and three events at greater distances from Semipalatinsk. Of the remaining 57 events: 10 were known to be underground nuclear explosions with known locations and the authors have supplied magnitudes where none were previously available; one was a chemical explosion at Degelen; they believe 21 were underground nuclear explosions; 13 were chemical explosions at Balapan; 8 were chemical explosions elsewhere on the test site; three were either nuclear or chemical explosions; and one was either a chemical explosion or a cavity collapse. The largest magnitude of their 44 possible underground nuclear explosions is around 5 (February 4, 1965, obscured at many teleseismic stations by a large Aleutian earthquake). Others lie in the magnitude range 3.5--4.5, and clearly most have sub kiloton yields. Their data set of small events is important for purposes of evaluating the detection capability of teleseismic arrays, and the detection and identification capability of regional stations.