GPS based total electron content (TEC) anomalies and their association with large magnitude earthquakes occurred around Indian region

In this paper, the effect of earthquakes on total electron content (TEC) data at Agra (geographic latitude 27.2°N, longitude 78°E), India has been examined. This study has been carried out for a period of 30 months from 01 January 2009 to 30 June 2011 and a dual frequency GPS receiver system is used for recording TEC data. To investigate the seismic effects on TEC, an epicentral distance of 2000 km from the observing station has been selected. This region includes 22 cases of earthquakes during the period of study with large magnitudes (M � 5.5). Different statistical procedures are used to observe the anomalies in TEC data. The results show that TEC fluctuated in the form of enhancements and depletion and maximum precursors are found 5-10 days prior to these earthquakes. The solar and geomagnetic activities during the cases of earthquakes have also been studied and data on disturbed days are omitted to separate out the seismic effects. Hence, the observed TEC anomalies may be due to the occurrences of large magnitude earthquakes around Indian region. The E×B drift due to the electric field generation during earthquake preparation process and ground wave oscillations may possibly be the significant contributors of these anomalies in TEC data.