Electromagnetic Effects Resulted from Natural Disasters - Ultra and Extremely Low Frequency Electromagnetic Fields - page 395

Interestingly enough, the size variations of the anomaly areas in seismo-active
regions have been observed occasionally several days before and after strong EQs in
Central Asia (Gorny et al. 1988 ; Tronin et al. 2002 ), China (Qiang et al. 1991 , 1999 ),
European Union (Tramutoli et al. 2001 ), and Japan (Hayakawa et al. 2001 ). Whether
these effects are really associated with seismic activity and what is the origin of
such stable and non-stationary IR anomalies is not well understood. Perhaps, the
abnormal behavior of such an area is due to an output of optically active gases such
as CO 2 ,CH 4 , and water vapor which results in the local green house effect (Tronin
1999 ).
In the theory by Surkov et al. ( 2006 ) the stable ground temperature anomalies
can be due to the geothermal convective heat flow induced by slow filtration of the
underground fluid. This heat flux is much smaller in magnitude than that arising
from the solar radiation and other thermal fluxes of natural origin. Nevertheless this
mechanism can play a substantial role in the presence of groundwater that can filtrate
along the system of interconnected cracks in the upper crust. The tectonic stresses
in the fault zone result in gradual squeezing-out of the groundwater from higher
depth towards the ground surface thereby heating the rocks since the groundwater
temperature is higher than that of the upper layers. The theory predicts a surface
temperature increase of a few K if the mean filtration velocity amounts to 10 6 m/s
and if the mean rock porosity near the fault exceeds the value n D 0:01-0:1.The
estimations have shown that there happen the anomalous regions with enhanced
surface temperature of the order of a few K on the geological time scales. However,
the convection mechanism appears to have no effect during the short time domain
and thus cannot provide any explanation of the nonstationary IR anomalies that
occasionally appear several days before EQs. Perhaps, one can concede that a
sudden enhancement of rock porosity may occur prior to an EQ followed by
rapid groundwater lifting that in turn results in an increase of the ground surface
temperature. In principle, this picture correlates with the known effect of water level
changes occasionally observed prior to seismic events (Wakita 1975 ;Barsukovetal.
1985 ; Roeloffs 1988 ; King et al. 1999 ; Sobolev and Ponomarev 2003 )
This effect can be connected with other phenomena probably associated with
impending EQs, that is, the propagation of over-the-horizon FM signals (Kushida
and Kushida 1998 , 2002 ; Fukumoto et al. 2001 , 2002 ; Fujiwara et al. 2004 ). Though
we have not received any signal from a VHF transmitter out of the light-of-sight, we
sometime receive the signals with small incident angle from the transmitter and
we define this as being abnormal. Kushida and Kushida ( 1998 ) have detected the
signals from an over-the-horizon transmitter in Central Japan several days or weeks
prior to the Kobe EQ. Some correlation was found between the abnormal VHF
wave propagation and the EQs which happened at certain sensitive regions. This
phenomenon has been studied intensively for a number of EQs in Central Japan
(Fukumoto et al. 2001 , 2002 ). In spite of the FM transmitter (77.1 MHz) in Sendai,
that is 312 km far from the receiver in Chofu, the FM signals have been occasionally
received in Chofu although the distance of line-of-sight was 80 km. Fukumoto et al.
( 2001 , 2002 ) have found that the cross-correlation between the abnormal over-the-
horizon FM signals and EQs exhibits a significant peak around 7 days before an
EQ.