A possible effect of ionospheric perturbations associated with the Sumatra earthquake, as revealed from subionospheric very‐low‐frequency (VLF) propagation (NWC‐Japan)

Abstract

The observation of subionospheric very‐low‐frequency (VLF) propagation between the transmitter NWC (Australia) (frequency 19.8 kHz) and our three receiving sites in Japan (Chofu, Chiba, and Kochi) are used to find a possible precursor of ionospheric perturbations to the Sumatra earthquake in late December 2004. Night‐time fluctuations in VLF propagation data at all three sites have exhibited significant enhancements from 4 days before the earthquake, which is likely to be a precursor to the earthquake.

Acknowledgements

We are grateful to the Mitsubishi Foundation, Japan Society of Promotion of Sciences (#15403012) and ‘R and D promotion scheme funding international joint research’ by NICT for their support. Also, we would like to thank the colleagues of Chiba and Kochi Universities for their help at VLF stations.