Geoscience Reference
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shock magnetization are different in symmetry that enables us to distinguish these
phenomena.
The irreversible deformation and fracture of rocks may greatly affect natural
terrestrial currents which in turn result in the similar effects. There are a few
causes for the terrestrial current generation such as variations of magnetospheric and
ionospheric fields, electrochemical processes in the ground, groundwater flow, local
hydrological factors, precipitations and etc. The shock impact on the rock leads to
the changes in permeability of capillaries, channels, and fluid-filled cracks followed
by the changes in rock conductivity.
The heated gaseous products of detonation contained in the underground cavity
can produce thermoelectric and thermo-galvanomagnetic phenomena in the sur-
rounding space. The heating of the medium and temperature gradient can save
for the long times if the decay of radioactive elements contained in the detonation
products goes on. These processes could also provide for stable changes of the local
electromagnetic Earth's field in the vicinity of the detonation point.
11.2.3
Electric Field of Gas-Dust Clouds
Surface and shallow buried detonations are accompanied by dustfall and the ejection
of broken ground. The explosion products and air heated by an explosion are mixed
with fragments of the broken ground, thereby producing the gas-dust cloud which
can emerge in the atmosphere by the action of buoyancy force. There are a few
stages of the cratering explosion. At first the ground dome is developed under the
influence of the explosion for subseconds to be followed by the gas break through
the dome and by the gas output in the atmosphere. Then the air-SW is created in the
atmosphere. The coarse fragments of the flying rocks follow ballistic trajectories,
while fine particles are pulled into the gas motion behind the shock front. The gas-
dust cloud rises upward during several seconds or minutes depending on the scale
of explosion. The conventional time scale is several minutes or hours for the dust
deposition and for the dispersal of gas-dust clouds.
The generation of the gas-dust cloud caused by an explosion is accompanied
by the appearance of low-frequency (up to 100 Hz) electromagnetic field in the
atmospheric surface layer (Holzer 1972 ). Adushkin and Soloviev ( 1988 )have
observed the variations of vertical electric field during the surface detonation of
HE with mass 1 t. The amplitude of electric field reached several tens kV/m at the
distance 1 km from the explosion site. As the cratering explosion is performed in the
medium-moisture rock, the electric signals, as a rule, have a bipolar shape and the
polarization of the first phase is negative if z axis is downward directed (Adushkin
and Soloviev 1996 ). This negative phase is usually observed during the course of
ground dome development and over the period of ballistic flying of fractured rock
fragments. The next more durable phase of the electric field evolution is due to the
relaxation of electric charges and the motion of the gas-dust cloud. The duration of
this phase is on the order of precipitation time of charged particles and aerosols.
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