A study of ionospheric precursors associated with the major earthquakes occurred in Pakistan region

The GPS-TEC measurements have been in progress at Agra station (27.2 degrees N, 78 degrees E), India since 01 April 2006. In the present paper, we analyze the GPS-TEC data for two months of April and September, 2013 in which two major earthquakes (M > 7) occurred in the adjoining region of Pakistan. We use the quartile based statistical technique for the analysis of data and identify the significant precursors associated with the earthquakes. These precursors occurred on different days in the interval of 2-10 days prior to the earthquakes. We also examine the effect of geomagnetic storms on the total electron content (TEC) data and find that the precursors are not influenced by the storms. The cause of the precursors is E x B drift with the electric field generated over seismic regions and penetrated the ionosphere.