TITLE:
VLF/LF Amplitude Perturbations before Tuscany Earthquakes, 2013
AUTHORS:
Balaram Khadka, Keshav Prasad Kandel, Sudikshya Pant, Karan Bhatta, Basu Dev Ghimire
KEYWORDS:
D-Layer, VLF/LF, Terminator Times, SST, SRT, DLPT, DLDT, Night Time Fluctuation
JOURNAL NAME:
Natural Science,
Vol.9 No.12,
December
29,
2017
ABSTRACT: The US Navy VLF/LF Transmitter’s NSY signal (45.9 kHz) transmitted
from Niscemi, Sicily, Italy, and received at the Kiel Long Wave Monitor,
Germany, was analyzed for the period of two months, May and June (EQ-month) of
2013. There were 12 earthquakes of magnitude greater than 4 that hit Italy in
these two months,of which the earthquake of 21st June having magnitude of
5.2and a shallow focal depth of 5 km was the major one. We studied the
earthquake of 21st of June 2013, which struck Tuscany,Central Italy, (44.1713°N
and10.2082°E) at 10:33 UT, and also analyzed the effects of this
earthquake on thesub-ionos-pheric VLF/LF signals. In addition, we also studied another earthquake, of
magnitude 4.9, which hit the same place at 14:40 UT on 30th of
June and had shallow focal depth of 10 km. We assessed the data using
terminator time (TT) method and night time fluctuation method and found unusual
changes in VLF/LF amplitudes/phases. Analysis of trend, night time dispersion,
and night time fluctuation was also carried and several anomalies were
detected. Most ionospheric perturbations in these parameters were found in the
monthof June, from few days to few weeks prior to the earthquakes. Moreover, we
filtered the possible effects due to geomagnetic storms, auroras, and solar
activitiesusing parameters likeDst index, AE index, and Kp index for analyzing the geomagnetic effects,and Bz (sigma) index, sunspot
numbers, and solar index F10.7 for analyzing the solar activities for the
confirmation of anomalies as precursors.