Studies on the Influence of Two Large Earthquakes (M>6) Upon 9 kHz Sferics Recorded from Kolkata

摘要

The outcome of the analyses of some significant observations in the records of VLF sferics over Kolkata (Lat. 22.56o N, Long. 88.5o E) at 9 kHz during the occurrences of two large earthquakes on July 07, 2013 will be presented here. Discrete spike-type signals are obtained as the precursors of two earthquakes with magnitude M > 6. The number of spikes and their intensities are found to vary irregularly and reached their maximum value on the day of occurrence. It then decreases gradually and finally ceased.