Preseismic Perturbations and their Inhomogeneity as Computed from Ground‐ and Space‐Based Investigation during the 2016 Fukushima Earthquake

Abstract

We present the atmospheric anomalies instigated through seismogenic sources by a multichannel observation using ground- and satellite-based systems. This study emphasizes the seismic event which happened on the east coast of Japan, near the Fukushima Prefecture on November 21, 2016 (in UTC), with a magnitude of 6.9 and a depth of 11.4 km. We mainly focus on the atmospheric and ionospheric irregularities via acoustic and electromagnetic channels originating from earthquakes in the process of the lithosphere, atmosphere, and ionospheric coupling (LAIC) mechanism. In the acoustic channel, we study the seismogenic atmospheric gravity wave (AGW) which perturbs the local lower atmosphere. The observation of nighttime fluctuations in the very low frequency (VLF) signals and total electron content (TEC) is used to investigate the atmospheric perturbation through the electromagnetic channel. For the ground-based observations, a VLF signal network consisting of 5 receivers in Japan is used to study by recording the VLF amplitude transmitted from the Japanese transmitter JJI (22.2 kHz). VLF nighttime fluctuation is used to check the unusualities due to the earthquake. Preseismic wavelike structures having periods of AGW are observed in the nighttime signal. Direct investigation of such AGWs is done by computing the potential energy related to AGW from the sounding of the atmosphere using broadband emission radiometry (SABER) temperature profiles mounted on the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite. Ionospheric TEC inspection is done by using a ground-based global navigation satellite system (GNSS) receiver from the International GNSS Survey (IGS) station MIZU in Japan and observing anomalies in diurnal TEC around 6 and 10 days prior to the earthquake. We also obtain the wavelike structure of AGW from the small-scale fluctuation of TEC using wavelet analysis. All the parameters are found to be preseismic for this earthquake; the acoustics channel gives more consistent outcomes than the electromagnetic channel.

Multi-parametric study of seismogenic anomalies during the 2021 Crete earthquake (M=6.0)

“…Other phenomena like thermal anomalies [Peleli et al, 2022] and sub-ionospheric VLF anomalies [Politis et al, 2023] also show significant seismogenic effects.…”

“…Thus, this particle burst can be treated as significant indirect evidence of the seismogenic anomalies in the upper atmosphere. In the upper atmosphere, ionospheric variabilities during and before EQs can be well estimated through Pre-seismic anomalies in multi-parameters the sub-ionospheric VLF radio-sounding techniques [Chakrabarti et al, 2005;Chakrabarti et al, 2007;Sasmal et al, 2009;Chakrabarti et al, 2010;Chakraborty et al, 2017;Biswas et al, 2022;Biswas et al, 2023;Ghosh et al, 2019;Pal et al, 2017;Maurya et al, 2016;Nina et al, 2021;Politis et al, 2021;Potirakis et al, 2018a;Ray et al, 2010;Ray et al, 2011;Ray et al, 2012;Sasmal et al, 2010;Sasmal et al, 2014;Yoshida et al, 2008;Rozhnoi et al, 2014a;Rozhnoi et al, 2013;Popov et al, 2004]. Another important parameter is the F-layer's critical frequency, which shows significant anomalies before the EQs [Ghosh et al, 2017].…”