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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS008 Oral Presentation 1989
On the physical mechanism of vertical electric field generation over active
tectonic faults
Prof. Sergey Pulinets
Space Physics Depratment Institute of Geophysics
The anomalously high vertical electric field gradients before strong earthquakes were reported by many
authors. At the same time there are a lot of cases when no electric field anomalies were registered
before earthquakes. This contradiction does not permit to consider the electric field as a precursor up to
now. The problem can be resolved if the nature of the observed (or not observed) anomaly will be
clear. It is well established that the main source of the atmospheric boundary layer (BL) ionization
providing its conductivity over the continents is natural ground radioactivity. So the natural radioactivity
is one of the important parts of the Global Electric Circuit (GEC). The major contribution to this
radioactivity is provided by the radon emanation and its progeny. Lithosphere-Atmosphere-Ionosphere
Coupling (LAIC) model developed recently explains the thermal anomalies observed before earthquakes
as a latent heat released by water vapor condensed on ions produced by radon ionization (Pulinets et
al., 2006). It means that the thermal anomalies could serve as indicators of the increased radon release.
The thermal anomalies monitored by the remote sensing satellites clearly show the anomalies along the
active tectonic faults what is consistent with the radon behavior established earlier. The size of the
thermal anomalies for the strong earthquakes of order of hundreds thousand square kilometers implies
the important changes of atmospheric electricity over these areas. The sharp increases of the
atmospheric electric field before earthquakes can be explained by the formation of large ion clusters
(result of water condensation on ions) with very low mobility. Low mobility leads to the drop of BL
conductivity and sharp increase of potential drop (and consequently vertical electric field gradient) near
the ground surface. Large particle formation before earthquakes is confirmed by Aeronet network
measurements at California and Mexico with time scales similar to those of thermal and ionospheric
anomalies. We can say that some kind of haze is formed over earthquake preparation area few days
before earthquakes changing the electric properties of BL. Another possibility (with no strong electric
field on the ground surface) can be realized in the case of the sharp increase of the latent heat release.
In this case the ions will be raised by the convective thermal flux in the upper layers of atmosphere. In
this case the electric field can be amplified (Sorokin et al., 2005) or even generated (Morozov, 2006)
providing high values of electric field in upper atmosphere and ionosphere and consequent ionosphere
modification (ionospheric precursors). This type of electric field anomalies can be checked only by
balloon or rocket measurements of the vertical profiles of electric field. The only experimental support
for this model up to now is formation of so called earthquake clouds what confirms the raise of ions as
centers of condensation up to levels of several kilometers of altitude. Ionospheric anomalies observed
before the earthquakes (especially in equatorial regions) can be explained only by anomalous electric
field effects from the point of view of their morphology. References Morozov V. N., The influence of
convective current generator on the global current, Nonlin. Processes Geophys., 13, 243–246, 2006
Pulinets S. A., Ouzounov D., Karelin A.V., Boyarchuk K. A., Pokhmelnykh L. A., The physical nature of
the thermal anomalies observed before strong earthquakes, Physics and Chemistry of the Earth, 31,
143-153, 2006 Sorokin V. M., A. K. Yaschenko, V. M. Chmyrev, and M. Hayakawa, DC electric field
amplification over seismically active faults, Natural Hazards and Earth System Sciences, 5, 661–666,
2005
Keywords: atmospheric electric field, radon, ionization