VLF radio signal anomaly associated with geomagnetic storm followed by an earthquake at a subtropical low latitude station in northeastern part of India

This paper presents a case study of very low frequency (VLF) radio signal anomaly during a moderate geomagnetic storm (Kp = 6, Ap = 80 and Dst = − 60 nT) on September 10, 2018 followed by a moderate earthquake ( M  = 5.3) on September 12, 2018 which occurred near to (~ 80 km) a subtropical low latit...

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Bibliographic Details
Published in:Indian journal of physics 2022, Vol.96 (1), p.13-24
Main Authors: Das, Bakul, Sen, Arnab, Haldar, Prabir K., Pal, Sujay
Format: Article
Language:English
Subjects:
Amplitudes
Astrophysics and Astroparticles
D region
Earthquake prediction
Earthquakes
Electron density
Geomagnetism
Latitude
Magnetic storms
Original Paper
Parameters
Physics
Physics and Astronomy
Radio signals
Sunset
Transmitters
Very Low Frequencies
Wave propagation
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Summary:This paper presents a case study of very low frequency (VLF) radio signal anomaly during a moderate geomagnetic storm (Kp = 6, Ap = 80 and Dst = − 60 nT) on September 10, 2018 followed by a moderate earthquake ( M  = 5.3) on September 12, 2018 which occurred near to (~ 80 km) a subtropical low latitude station Cooch Behar (CHB), India (26.345 ° N, 89.448 ° E). Signal amplitudes from the two transmitters, VTX (18.2 kHz) and NWC (19.8 kHz), are analyzed for this study. Seven VLF parameters, such as nighttime amplitude fluctuation (dA n ), amplitude difference between pre-sunrise signal and sunrise minimum signal (dA m ), amplitude difference between sunset minimum signal and post-sunset signal (dA e ), time ( T m ) and amplitude ( A m ) during sunrise minimum, time ( T e ) and amplitude ( A e ) during sunset minimum have been examined. Anomalous behaviors of all the parameters have been observed during September 10–12, 2018. D-region electron density is estimated using the long wave propagation capability code which revealed a maximum increment of ~ 20 electron/cm 3 at altitude 85 km over the VTX-CHB path ~ 2 days before the earthquake event. The anomalous behaviors of the VLF signals ~ 1–2 days before the earthquake are identified as possible precursor of the earthquake which could be linked with various pre-earthquake seismo-electromagnetic processes.
ISSN:0973-1458
0974-9845
DOI:10.1007/s12648-020-01966-2