Precursor of earthquake using night time VLF amplitude

The results of the analysis of the year-long (2007) monitoring of the night time data of the VLF signal amplitude from the Indian Navy station VTX at 18.2kHz, received at the Indian Centre for Space Physics, Kolkata, are presented. We analyzed this data to find out the correlation, if any, between the night time fluctuation and the seismic events. We found, using individual cases (with magnitudes >; 5) as well as statistical analysis (of all the events with effective magnitudes greater then 3.5) that the night time fluctuation of the signal amplitude has the highest probability to be beyond 2<;r level about three days prior to the events. Thus the night time fluctuation could be considered as a precursor to the enhanced seismic activities.