抄録
Subsurface VLF electric field changes have been monitored at Chaumuhan, Mathura (Geographic Lat. 27.5°N, Geographic Long. 77.68°E), India at the frequency of 3.012 kHz employing borehole and vertical antennas since 24 March 2011. Initial data for the period of 15 days are analysed statistically and it has been found that anomalous enhancements occurred in the VLF amplitudes observed by both the antennas. These anomalous enhancements are examined in the light of magnetic storms, local lightning, and earthquakes and are positively correlated with the devastating India-Nepal border earthquake (M=5.3) occurred on 4 April 2011. The precursory period for borehole data ranges between 3-7 days while for vertical antenna data it is 3 days. The generation and propagation mechanism of ELF/VLF emissions in the crustal region have also been discussed.
