Geoscience Reference
In-Depth Information
events (Cervone et al.
2004
,
2006
; Dey et al.
2004
; Singh et al.
2006
; Alvan et al.
2012
,
2013
). SLHF data with resolution of 1.9 by 1.9 are available from the
National Center for Environmental Prediction (NCEP-NCAR), reanalysis data of
the IRI/LDEO Climate Data Library (
http://iridl.ldeo.columbia.edu
) which are
generated by taken into consideration the measured values at various worldwide
stations and also those retrieved from satellite data.
Among all gases emitted from rocks during the earthquake preparation stages,
radon is the only gas which has radioactive isotopes under normal conditions. Its
most stable isotope,
222
Rn, has a half-life of 3.8 days. Once the isotope Radon222
seeps out of rocks and its decay begins. This causes emission of a-particles from
active tectonic faults. Emission of this positive ions results in ionization of the near-
ground layer (Igarashi et al.
1995
; Toutain and Baubron
1998
; Omori et al.
2007
;
Inan et al.
2008
; Ondoh
2009
; Choubey et al.
2009
; Kuo et al.
2010
; Sac et al.
2011
).
The air ionization and emanation of some other gases like CO
2
leads to the changes
in air temperature and humidity (Pulinets and Ouzounov
2011
). But in fact, the
origins and mechanisms leading to an expected higher air temperature in the
seismic area is still a matter of debate among scientific theoreticians. In
2009
,
Freund et al. attributed this phenomenon to the local earthquake related electronic
fields. They suggested that the ever increasing level of stress on rocks during the
preparation stage of an earthquake causes the activation of highly mobile electronic
charges in rocks and consequently air ionization. Then, a large number of atomic
(ionic or covalent) bonds break increasing the crystal structure of the rocks. Finally,
a chain of reactions result in an unbalanced charge distribution in underground
material and the onset of strong local electric fields (Zoran
2010
).
3.3 Seismography
The process of earthquake preparation does not end up with a single release of
energy. In fact, much of the underground stress is released during small shakes
before earthquakes. This low magnitude quakes which usually are not felt are
called foreshocks (Console et al.
1993
). Aftershocks are the signs of minor frac-
turing in compressed rocks which take place before main break in the earth's
surface. They can start up to a year before a main event (Enescu et al.
2007
).
However, foreshocks do not necessarily occur before every earthquake. On the
other hand, sometimes there is a chain of similar size earthquakes which occur one
after the other without being followed by a strong main shake. These may limit the
usefulness of foreshock monitoring in earthquake prediction.
On the whole, the appearance of seismic activities in seismic records is a
subject of further analysis. Nowadays, with advances in seismograph technology
we can get enough information about the origin and size of shakes in an earth-
quake prone area. Broadband, digital seismographs record the earth's movement in
different directions which will allow for the identification of various stages of a
quake, distance and direction, the extent and direction of effect, etc. In addition,
