A History of Research and a Review of Recent Developments

24
sometimes written in psi as
The nature of explosions
Table 1.1 Soil properties and seismic wave
velocity
(1.28)
Note that the value of q is orders of magnitude greater than the external wind
pressure used in the design of conventional surface structures. At 6 km from
the centre of a 1 megaton explosion the peak overpressure would be 42 Kp a
and the windspeed 81 m/sec; the arrival time of the shock front would be 14
seconds and the duration of the positive pressure pulse 3.0 seconds. At the
same distance from the centre of a 10 megaton explosion the figures would be
135, 200, 12.5 and 4.7. At 12 km the respective sets of figures would be: 1
megaton: 15, 31, 31, 3.7; and 10 megaton: 46, 96, 30 and 6.3.
Nuclear explosions also produce earth shocks in the neighbourhood of
surface or underground structures. These shocks can arrive by direct travel
through the earth from the point of detonation when this point is on or below
the surface. Whether the air induced earth shock front outruns or lags behind
the air blast wave front depends on the relationship between the air blast
wave velocity ū, and the seismic velocity for the soil.
Direct earth shock travels at the seismic wave velocity (c s), which varies
with soil properties as shown in Table 1.1.
At depths of 100 feet or less, and for distances (R) for which p 0