Seismic Observations from the 1956 Atomic Explosions in Australia

A discussion is given of seismic observations from the four 1956 British atomic explosions, at Maralinga, in South Australia. Both P and S phases were observed at field stations set up along the Trans-Australian railway for 0.4° < A < 11°, and on a Benioff seismograph located near Adelaide at 8°. The travel-times indicate a Pn velocity of 8.21±0.005 km/s and an Sn velocity of 4.75 ± 0.01 km/s. There is also evidence for P and S phases travelling near the surface with velocities of 6.03 ± 0.09 km/s and 3.55 ± 0.04 km/s respectively. No onsets corresponding to paths through intermediate layers were observed. The observations can be explained by a single crustal layer having constant seismic velocities. This hypothesis gives a crustal thickness of 32 km from P and 39 km from S. The paper contains a more detailed treatment of the Maralinga data previously discussed by Doyle. These data have provided the first published studies of Australian crustal structure based on refraction methods.