Seismic waves from high-altitude nuclear explosions

Abstract

Seismic waves of long period were well recorded at epicentral distances as great as 9300 km from two highaltitude nuclear explosions, Teak and Orange, which were fired in the Johnston Island area on August 1 and 11, 1958, respectively. Seismic waves recorded at Honolulu, at a distance of approximately 1300 km, may be divided into three types: (1) a normally dispersed, oceanic Rayleigh wave train in which the wave periods decrease from about 35 to l4 sec as the corresponding velocities decrease from about 4.l to l.6 km/sec; (2) an inversely dispersed, oceanic Rayleigh wave train in which the wave periods increase from ahout 6 to 10 sec as the corresponding velocities decrease from about 1.3 to 1.0 km/sec; (3) a T-phase consisting of waves with periods less than about 0.5 sec and corresponding to a velocity of 1.47 km/sec. From the normally dispersed train, group velocities of waves in the 35- to 14-sec period range were computed for the two paths, hoth of which traverse primarily a typical deep oceanic basin. These group-velocity data plus possible corresponding phase- velocity data are compared with theoretical values for oceanic structures. The inversely dispersed train, although predicted by classical theory, has notmore » been observed in seismograms from (natural) earthquakes. Surface waves of long period were recorded at Palisades, New York, from both of the highaltitude nuclear explosions, and these waves have amplitudes comparable to those generated by the larger of the near-surface explosions in the Marshall Islands. Special instruments at Palisades, not operated for Teak, indicate that amplitudes for the long-period body waves from Orange are comparable to those from the Marshall Islands ahots. In contrast, seismic body waves of short period are apparently generated much more efficiently by near-surface explosions than by high-altitude explosions. (auth)« less