VLF/LF Amplitude Perturbations before Tuscany Earthquakes, 2013
2017
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
5.2 and 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
and 10.2082°E) at 10:33 UT, and also analyzed the effects of this
earthquake on the sub-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
month of June, from few days to few weeks prior to the earthquakes. Moreover, we
filtered the possible effects due to geomagnetic storms, auroras, and solar
activities using parameters like Dst 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.
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