Geoscience Reference
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It is worth mentioning that the similar effect has been observed in the ionic crystal
samples during the shock loading (Mineev and Ivanov
1976
). In Chap.
9
we have
discussed that the increase in the shock amplitude can result in the sharp changes
in the sign of potential difference between sides of the sample. This effect can be
due to the sharp changes in the character of the sample conductivity, that is, due
to the transition from ionic conductivity to electron/hole conductivity. However,
the above effect was not observed at constant pressure so that the validity of the
above mechanism for the rock at higher depth where the static loading prevails is
questionable.
In conclusion, we note that many other models have been developed to explain
the electromagnetic phenomena in seismo-active regions. Among them are the
piezoelectric (Cutolo
1988
; Yoshino and Tomizawa
1988
; Kingsley
1989
; Sornette
and Sornette
1990
) and tectonomagnetic (Stacey
1964
; Stacey and Johnston
1972
;
Sasai
1991
; Gershenzon and Bambakidis
2001
) effects caused by the influence of
tectonic stress on piezoelectric and piezomagnetic minerals in the rocks. In the
model by Draganov et al. (
1991
) the underground water motion along a water-
bearing stratum is treated as a possible source mechanism for ULF noise preceding
an EQ. However, Surkov and Pilipenko (
1999
) noted that the rock permeability
which has been used by Draganov et al. (
1991
) for their numerical calculations
was overestimated at least by four orders of magnitude. In a very exotic model by
Lockner et al. (
1983
) and by Lockner and Byerlee (
1985
), a number of electrical
and optical effects are assumed to be due to the water vaporation inside underground
cavities and cracks situated near the fault.
10.1.6
Ionospheric Effects Observed Around the Time of EQs
Considerable recent attention has been focussed on experimental evidences for
ionospheric perturbations associated with seismic activity (Leonard and Barnes
1965
; Davies and Baker
1965
; Wolcott et al.
1984
; Tanaka et al.
1984
; Kelley et al.
1985a
; Le Pichon et al.
2002
; Komjathy et al.
2012
). The energy transfer from
an EQ to the atmosphere and ionosphere is essentially due to acoustic waves and
internal/atmospheric gravity waves (IGW) generated in the atmosphere after strong
earthquakes. Four to five minutes after the main shock the atmospheric air waves
arrive at the ionosphere thereby exciting the ionospheric plasma motion that, in
turn, results in the generation of GMPs. The electromagnetic channel of the energy
transfer from the EQ to the ionosphere seems to be improbable because of the low
level of electromagnetic perturbations on the ground surface.
The ground surface vibrations bring about atmospheric air waves not only in
the epicentral region but also at far distances from the EQ. After strong EQs such
as a great Alaska EQ on March 28, 1964 the atmospheric waves with horizontal
phase velocities about 3 km/s and periods about tens seconds have been detected
(e.g., Bolt (
1964
)). The source of atmospheric air waves is believed to be the
EQ-produced Rayleigh surface wave (the detail about Rayleigh wave is found in
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