III. RESULTS AND DISCUSSION:Fig. 1 shows the map of a part of Asia where the stars indicate the location of earthquakes and the solid circle indicates the location of the Agra observation station (27.2o N, 78o E). The details of these earthquakes are mentioned in Table 1 which shows the days they occurred, magnitude, depth (km), locations (latitude and longitude in degrees), radius of the zone of influence (km) and the distances from Agra station (km). The radius of the zone of influence is calculated using the expression R = 100.43 M, where M is the magnitude of the earthquake [21]. Although these earthquakes occurred far from the Agra observation station, at least two of them are well covered (>1000 km) by the radius of the influence zone. The details of the earthquake data were taken from the United States Geological Survey (USGS) website www.earthquake.usgs.gov.in. We also saw the variations of geomagnetic parameters such as Dst index and ∑ Kp index for each case separately and the data was taken from the National Aeronautics and Space Administration (NASA) website http://omniweb.gsfc.nasa. gov/form/dx1.html. We can see from Table 1 that all earthquakes had a shallow depth except one (46 km), but we cannot ignore this earthquake due to its relatively large magnitude (M = 7.8). Furthermore, it can be seen from Table 1 that two of the earthquakes occurred in April, one in July, and the other two in September 2013. The top two panels of Fig. 2 show the daily variation of GPS -TEC for the month of April 2013 observed at Agra station. Here, the vertical TEC is shown by a dashed line and the corresponding sum (m + σ) and difference (m – σ) are shown by solid and dashed lines, respectively. On days when ... middle of paper ... earthquakes occur, the anomalous variations in the TEC cannot be attributed to these factors. The only reason for the anomalies is earthquakes, which is also supported by statistical analysis.IV. CONCLUSIONS In this paper, we analyze three-month GPS-TEC data corresponding to five large earthquakes in the Indian subcontinent and statistical analysis is used for better interpretation of the results. The results of our study are as follows; we found improvements in TEC as precursors to large earthquakes in the Indian subcontinent, but these results are in contrast to the results of other researchers [4]-[6] who also found decreases. This contrast in results may be caused by the latitude dependence and improvements in the TEC data caused by the ascending electric field penetrating the ionosphere eastward according to the mechanism mentioned above.