Modelling of relation between large earthquakes and ionosphere electron density using GPS data

The ionosphere is a part of the earth's atmosphere, laying at the heights between 50 km and 2000 km above the earth's surface, and consisting of several layers identified by differences in the level of ionization. In the customary two dimensional modeling techniques, ionosphere is approximated by a thin spherical shell of free electrons, located; 250 to 450 Km from the surface of the earth. The existing two dimensional methods of modeling the electron density can be classified to non-grid based and grid based techniques. The former modeling techniques are based on the least squares estimation of a functional model for certain types of observables derived from the GPS carrier phase and code measurements. The network consists of two parts: a) base network that covers the entire country of Iran, consisting of 41 GPS stations and b) three local networks in the most populated and active zones. The local networks are established in Tehran, Azerbaijan, and Khorasan with critical tectonic activities. GPS measurements of 12 successive days in August 2012 (DOY#219, 220, 221, 222, 223, 224, 225, 226, 227, 228, 229 and 230) have been used for modeling and processing. VTEC values at a temporal resolution of 15 min were derived from the dual frequency GPS receivers. According to results, it can be easily deduced that there are temporal variations in the electron content of the ionosphere. The characteristics which are the constituents of the ionosphere morphology are also reported elsewhere and confirmed by the analysis of the direct measurement techniques. The diurnal pattern of TEC exhibited a steady decrease from DOY#220. This decline has occurred at all hours. Also using these results can be clearly seen that the maximum value of TEC observed in daytime (8 UT), while the lowest occurred at nighttime (4 UT).