Investigation of correlation between the lower ionospheric perturbations with seismic anomaly as detected by subionospheric VLF signals

English Abstract:

The seismogenic lower ionosphereic perturbations in association with the earthquakes are being investigated here, using subionospheric VLF propagation. As the target to find correlation between the VLF propagation anomaly (average nighttime amplitude, nighttime fluctuation) and earthquakes we have analyzed a long period of data over 5 years from 2010 to 2014. VLF data analysis is done for the propagation path from NWC (in North West Cape, Australia) to Agra, India. As the latest advancements in the VLF method analysis we have used the fluctuation power spectra in the frequency range of atmospheric gravity waves (period = 10 min to 100 min) to confirm the presence of seimo-ionospheric perturbations. Further superimposed epoch analysis has been undertaken, in order to find the correlation of the ionospheric perturbations with seismic activity. Analysis results show that there occur significant anomalies in VLF propagation few days (3 and 5 days) before the earthquake, indicating significant correlation with the earthquakes. Finally we have discovered an important correlation between number of pre/after shocks and anomalous signal i.e. ionospheric anomalies.