Amplitudes of seismic body waves from underground nuclear explosions

Seismic waves from underground nuclear explosions in Nevada were observed at a number of temporary stations along a line extending eastward to Maine. A study of the seismograms from these stations and from a large number of permanent stations has shown that the amplitude of Pn varies inversely as the cube of the distance between 200 and 1100 km. Pn then disappears and a late-arriving higher velocity wave appears with relatively large amplitude. This later P wave has a slight amplitude maximum at about 2000 km, after which it decreases irregularly with distance. Between 200 and 2000 km the amplitude of S (or Lg) varies inversely as the cube of the distance. The vertical, radial, and transverse components are of approximately equal size, and are about three times the amplitude of Pn between 200 and 1000 km. At distances of 100 km or more the amplitudes of the body waves are proportional to the first power of the explosive yield. The explosions produced seismic waves equivalent in size to those from natural earthquakes of magnitude: M = 3.65 + log Y, where Y is the energy of the explosion expressed in kilotons of TNT equivalent.