Studies of the correlation between ionospheric anomalies and seismic activities in the Indian subcontinent

It is long conjectured that the ionosphere is affected by the seismic activities and these effects can be detected in the VLF wave signal. We present the results of the sunrise and sunset terminators for the VTX 18.2 kHz signal received at Kolkata for a period of four years and draw a standardized calibration curve to study deviation from this curve which may be due to influences by terrestrial (such as earthquakes) and extra-terrestrial(such as solar activities and other high energy phenomena) events. We present examples of deviations of terminator shifts, D-Layer preparation time and disappearance time in several days of sixteen months of data and compute the correlations with seismic events. We found that correlation exists on 1-2 days prior to the events. We also discuss the effects of depths of the earthquakes on the correlation.