Seismoionospheric Variations during the Earthquake in Pakistan (September 2005) as a Precursor of Seismic Events

The results of the monitoring of the state of the ionosphere in the area of a strong earthquake in Pakistan (magnitude of 7,6), which occurred on 2005 8th October at 3:50:35.9 UTC are presented. The monitoring was conducted on the base of the satellite navigation system GPS data using GPS receivers for registration dual-frequency signals by several ground stations. The results of the monitoring performed 3-6 days prior to the coming earthquake revealed tendency to increase of maximum in electronic concentration and 1-3 days prior to the coming earthquake revealed significant (more than twice as much) decrease of the maximum value in electronic concentration at F2 layer of the ionosphere. The analysis of heliogeophysical situation, which carried out in the period of study showed that it was quiet. That is why observed changes in electronic concentration can be provoked by the impact of seismic activities in this region and they may be used as an earthquake precursor during the online monitoring of seismic hazard territories