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VLF radio signal anomaly associated with geomagnetic storm followed by an earthquake at a subtropical low latitude station in northeastern part of India
Indian Journal of Physics ( IF 1.6 ) Pub Date : 2021-01-04 , DOI: 10.1007/s12648-020-01966-2
Bakul Das , Arnab Sen , Prabir K. Haldar , Sujay Pal

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 (dAn), amplitude difference between pre-sunrise signal and sunrise minimum signal (dAm), amplitude difference between sunset minimum signal and post-sunset signal (dAe), time (Tm) and amplitude (Am) during sunrise minimum, time (Te) and amplitude (Ae) 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/cm3 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.



中文翻译:

与地磁风暴有关的VLF无线电信号异常,随后在印度东北部的亚热带低纬度站发生了地震

本文介绍了一个案例研究,该案例研究是在2018年9月10日的中等地磁风暴(Kp = 6,Ap = 80和Dst = − 60 nT)以及随后的中等地震(M  = 5.3 )期间的极低频(VLF)无线电信号异常)发生在2018年9月12日,发生在印度Cooch Behar(CHB)的一个亚热带低纬度站附近(〜80 km)(北纬26.345 °,东经89.448 °)。本研究分析了来自两个发射机VTX(18.2 kHz)和NWC(19.8 kHz)的信号幅度。七个VLF参数,例如夜间振幅波动(dA n),日出前信号与日出最小信号之间的振幅差(dA m),日落最低信号与日落后信号之间的振幅差(dA e),日出最小时间的时间(T m)和振幅(A m),日落最小时间的时间(T e)和振幅(A e)已进行了检查。在2018年9月10日至12日期间观察到了所有参数的异常行为。使用长波传播能力代码估算了D区电子密度,该代码揭示了VTX上85 km的高度最大〜20电子/ cm 3的增量-CHB路径〜地震发生前2天。地震发生前1-2天的VLF信号异常行为被认为是可能的地震前兆,这可能与地震前的各种地震电磁过程有关。

更新日期:2021-01-04
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