Geoscience Reference
In-Depth Information
The present statistical study of numerous ionospheric data permits to propose sev-
eral conclusions:
• The study shows possible relations between the amplitude (or trend) of the dis-
turbance zone, the magnitude M, depth D of the seismic event, and the distance
from the satellite to the earthquake epicenter (r km and ∆λ). Disturbances above
10 mV/m are only observed for strong and major earthquakes. No disturbances
are observed for moderate earthquakes at D > 234 km and for light earthquakes
at D > 117 km. Generally the disturbances are observed for ∆λ < 20°.
• During the study two forms of quasi-static electric field disturbance zones in
the upper ionosphere are recognized. The bulge with different amplitudes is
observed in very narrow seismic belts where the earthquake manifestations are
numerous. The wave discordance is established in regions with limited numbers
of seismic events.
• The ionosphere disturbance zones are generated several days before the main
shock. The ionosphere zones of electric field disturbances in cases of earth-
quakes in the Southern Hemisphere are shifted to the north from the earthquake
epicenters. The same ionospheric zones (of electric field disturbances) related
to earthquakes in the Northern Hemisphere take place to the south of the earth-
quake epicenters. This is connected with the electric field projection along mag-
netic field lines into the low ionosphere at satellite altitudes. The effects are
also observed in the magnetic conjugate region as it has been already noted by
Chmirev et al. (1989) and Gousheva et al. (2008b). Finally we suppose the pres-
ence of a source of quasi-static electric field of a seismic origin.
• At the moment of the main shock the disturbance zone is located above the epi-
center and its amplitude increases.
• The disturbance zone changes its position with the time. It migrates back in l
altitude several hours to 2-3 days later.
• The data about the seismic situation 15 days before and after the observations in
regions with high seismic activity and 5 days before and after observations for
regions of moderate and low seismicity gives us a possibility to separate fore-
and after-shocks from the main shocks.
• Pre- and post-cumulative effects of several events are established very often.
In several cases it is difficult to determine the predominant influence of one
seismic phenomena.
• We found similar pre- and post effects during observations at magnetically very
quiet, quiet, and medium quiet days for ionosphere zones of electric field distur-
bances in cases of earthquakes in the Northern and Southern Hemisphere.
• The ionospheric disturbance takes place above seismic active territories, mainly
along the boundaries of the plates because these boundaries represent tectonic
structures of the most considerable energy accumulation and liberation.
• The anomalous disturbance zone persists in a wide latitudinal interval and could
represent one of numerous other indications for the activity of earthquake sources.
