Study of ionospheric precursors using GPS and GIM-TEC data related to earthquakes occurred on 16 April and 24 September, 2013 in Pakistan region

In this paper, we have examined the diurnal variations of GPS-TEC observed at two Indian stations of Agra (27.2 degrees N, 78 degrees E) and Surat (21.16 degrees N, 72.78 degrees E) and global ionospheric maps data (GIM-TEC) for the months of April and September 2013 in search of ionospheric precursors of three major earthquakes (M > 6.5) that occurred in these months. The well-established quartile based statistical technique is adopted for the analysis of TEC data. The results show two kinds of anomalies, one in which simultaneous enhancements in TEC occurred in the three sets of data, 1-9 days and 3 days before the main shock in the two months respectively, and another in which anomalies occurred 15 days before in April, and 21 days before in September at Surat respectively. The depletions have also been found in three data sets but they are not significant. These anomalies are unlikely be influenced by geomagnetic parameters due to quiet magnetic conditions. The effect of also solar activity have also been considered and examined very precisely. The results are interpreted in terms of Lithosphere-Atmosphere-Ionosphere coupling (LAIC) mechanisms available in the literature. (C) 2017 Published by Elsevier Ltd on behalf of COSPAR.