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1,2-power of the energy released.
This scaling law is obtained on the
basis of explosions of conventional explosives underground (quarry
blasts). The law is somewhat surprising; theoretically one would
expect that the seismic amplitude would go as the square root of
the energy release, The empirical law has been used in Appendix
A to predict the frequency of earthquakes in the USSR which might
be confused with subsurface shots of various yields,
law clearly gives more
larger
The empirical
results for the seismic signal
to be expected from shots of larger yield than Rainier than the
"theoretical expectation'' would give.
The empirical law indicates that a larger fraction of the
enerpy release goes into seismic waves at higher yield. This
effect certainly must stop at some point; at about 100 kilotons
the entire energy would be converted into seismic energy if the 1.2power law held up to that yield. Experiments are urgently needed
to establish the actual relation between yield and seismic signal.
These should be carried out with nuclear explosions since conventional explosives may not give the same effect due to the evolution
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of large amounts of gas.
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The seismic signal will depend strongly on the medium in
which the test is conducted, The volcanic tuff in which the Rainier
hee. +
test was conducted probably gives a relatively small seismic signal;
a
-
it is only equivalent to an air shot of about 20 times greater yield.
Hard rock would almost certainly give a stronger seismic signal
while on the other hand it may contain the radioactive products in
an even smaller volume. On the other hand, unconsolidated material
which is found in many places near the surface of the earth may well
reduce the seismic effects below those observed in the tuff because
the signal should decrease with decreasing yield stress, and un-
consolidated material may have a yield stress as low as one-tenth
of that of tuff (which has about 10,000 psi).
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It may also be possible, by excavating a large chamber to
begin with, to reduce the energy found at large distances by a
factor of 10. One possibility which may reduce the seismic energy
is the excavation of large cavities in salt domes. Such cavities may
be tens or even kKundreds of millions of cubic feet in volume. and ne ed
not be spherical. For example, a cavity 150 feet in diameter and 30 00
feet long may have nearly the same effect as a spherical one of the