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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy<br />

(S) - <strong>IASPEI</strong> - International Association of Seismology and Physics of the Earth's<br />

Interior<br />

JSS010 Poster presentation 2091<br />

Possible physical mechanisms of the TEC enhancements observed before<br />

earthquakes<br />

Mrs. Irina Zakharenkova<br />

Alexander Namgaladze, Irk Shagimuratov, Oleg Zolotov, Oleg Martynenko<br />

The GPS derived TEC enhancements before earthquakes were discovered using global and regional TEC<br />

maps, TEC measurements over individual stations as well as measurements along individual GPS<br />

satellite passes. This pre-seismic behavior of TEC was detected within several days before the main<br />

event. Anomaly appeared as the local TEC enhancement located in the vicinity of the forthcoming<br />

earthquake epicenter. Such structures were generated in the ionosphere for several days prior to the<br />

main shock. The amplitude of plasma modification reached the value of 30-90% relative to the nondisturbed<br />

level. The ionosphere region of strong positive disturbance extended larger than 1500 km in<br />

latitudes and 3500-4000 km in longitudes. The possible physical mechanisms which can cause this<br />

positive effect associated with seismic activity are discussed. Among them the thermosphere-ionosphere<br />

interaction and electrodynamic mechanisms of the ionospheric earthquake precursors’ formation are<br />

contemplated. The vertical plasma drift caused by the eastward electric field is considered as the most<br />

probable cause of the observed TEC enhancements. The electric potential distribution at the nearepicenter<br />

region boundary required for such electric field maintenance is proposed. The results of the<br />

corresponding numerical model calculations of the electric field and its effects in the ionospheric F2-<br />

layer and plasmasphere are presented.<br />

Keywords: gps tec, precursors, earthquake

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