Electromagnetic Precursors to the 2016 Kumamoto Earthquakes

Schekotov, A.; Izutsu, Jun; Asano, Tomokazu; Potirakis, Stelios M.; Hayakawa, Masashi

doi:10.4236/ojer.2017.64010

Cited by 10 publications

(10 citation statements)

References 25 publications

(23 reference statements)

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“…In the area of Kumamoto where the medium-term EQ prediction indicates that the probability of having M7 class EQs in the coming 30 years is about 1%, there are available only few observations as related to the above lithosphere-atmosphere-ionosphere coupling. Schekotov et al (2017) [48] have summarized different electromagnetic effects for this Kumamoto EQ, but no information on radon and crustal changes has been reported up to now. Our future work will be the coordination of different (electromagnetic, mechanical and chemical) data in order to go into details of generation mechanism of the ionospheric perturbation for the 2016 Kumamoto EQ event.…”

Section: Discussionmentioning

confidence: 97%

On the Tempo-Spatial Evolution of the Lower Ionospheric Perturbation for the 2016 Kumamoto Earthquakes from Comparisons of VLF Propagation Data Observed at Multiple Stations with Wave-Hop Theoretical Computations

Asano¹,

Hayakawa²

2018

OJER

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There have been published many papers on VLF (very low frequency) characteristics to study seismo-ionospheric perturbations. Usually VLF records (amplitude and/or phase) are used to investigate mainly the temporal evolution of VLF propagation anomalies with special attention to one particular propagation path. The most important advantage of this paper is the simultaneous use of several propagation paths. A succession of earthquakes (EQs) happened in the Kumamoto area in Kyusyu Island; two strong foreshocks with magnitude of 6.5 and 6.4 on 14 April (UT) and the main shock with magnitude 7.3 on 15 April (UT). Because the EQ epicenters are not far from the VLF transmitter (with the call sign of JJI in Miyazaki prefecture), we can utilize simultaneously 8 observing stations of our network all over Japan. Together with the use of theoretical computations based on wave-hop theory, we try to trace both the temporal and spatial evolutions of the ionospheric perturbation associated with this succession of EQs. It is found that the ionospheric perturbation begins to appear about two weeks before the EQs, and this perturbation becomes most developed 5-3 days before the main shock. When the perturbation is most disturbed, the maximum change in vertical direction is depletion in the VLF effective ionospheric height of the order of 10 km, and its horizontal scale (or its radius) is about 1000 km. These spatio-temporal changes of the seismo-ionospheric perturbation will be investigated in details in the discus-How to cite this paper: Asano, T. and Hayakawa, M.

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Section: Discussionmentioning

confidence: 97%

On the Tempo-Spatial Evolution of the Lower Ionospheric Perturbation for the 2016 Kumamoto Earthquakes from Comparisons of VLF Propagation Data Observed at Multiple Stations with Wave-Hop Theoretical Computations

Asano¹,

Hayakawa²

2018

OJER

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“…All of those are caused by strike-slip faults (Japan Meteorological Agency (JMA), 2016a). Some precursors of this EQ series have been reported, including the anomalies of foreshock activity (Kato et al, 2016), groundwater (Sano et al, 2016), ultralow frequency/extremely low frequency magnetic field (Potirakis, Schekotov, et al, 2018;Schekotov et al, 2017), VLF/LF propagation (Potirakis, Asano, et al, 2018), and total electron contents (Iwata & Umeno, 2017).…”

Section: Eq Treated In This Papermentioning

confidence: 99%

Abnormal Gravity Wave Activity in the Stratosphere Prior to the 2016 Kumamoto Earthquakes

2019

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Earthquake (EQ) prediction is an essential topic in recent geophysics and disaster management. In order to explain EQ precursory phenomena, especially the ionospheric perturbations, a few hypotheses have been proposed as the mechanism of lithosphere‐atmosphere‐ionosphere coupling. The most reliable seems to be the atmospheric gravity wave (AGW) hypothesis, because a lot of subionospheric very low frequency (VLF) observations and also ground surface measurements support this hypothesis. However, no direct signature of AGW activity in the middle atmosphere has been yet obtained. So in this study, we have used the ERA5 reanalysis data to investigate the tempo‐spatial evolution of stratospheric AGW activity before a recent huge seismic event of the 2016 Kumamoto EQ on 15 April (Mw7.2). It was found that the AGW potential energy is enhanced significantly during about 1 week before the EQ. The enhancement was mainly distributed around the EQ epicenter and expanded toward eastern Japan. The AGW activity was highest around 11 April, then it calmed down and returned to the background level right before the EQ. These results were compared with the subionospheric VLF observations during the same period, and then the tempo‐spatial evolutions of the lower ionospheric perturbation are found to be very consistent with the stratospheric behavior. The present paper reports on the first finding that the abnormal AGW activity in the stratosphere is detected before a major EQ, and the coincidence of stratospheric AGW activity with VLF subionospheric perturbations provides further support to the AGW hypothesis of the lithosphere‐atmosphere‐ionosphere coupling process.

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“…In this sense, it is worthwhile to investigate the EM phenomena for these Kumamoto events. A variety of different ionosphere-related precursory signatures possibly related to the Kumamoto EQs have already been reported, such as ionospheric anomalies as detected by total electron content (TEC) calculated by GNSS receivers [ 23 ], or GIM-TEC [ 24 ], or GPS-TEC [ 25 ], transient variations on atmospheric and ionospheric parameters [ 26 , 27 ], subionospheric very low frequency (VLF) propagation anomalies [ 28 , 29 ], atmospheric ULF/ELF radiation and ULF depression [ 30 ], criticality in the ground-observed ULF magnetic fields [ 31 ], and intermittency-induced criticality in the VLF subionospheric propagation data [ 32 ].…”

Section: Introductionmentioning

confidence: 99%

Criticality Analysis of the Lower Ionosphere Perturbations Prior to the 2016 Kumamoto (Japan) Earthquakes as Based on VLF Electromagnetic Wave Propagation Data Observed at Multiple Stations

Potirakis

Asano

Hayakawa

2018

Entropy

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Abstract:The perturbations of the ionosphere which are observed prior to significant earthquakes (EQs) have long been investigated and could be considered promising for short-term EQ prediction. One way to monitor ionospheric perturbations is by studying VLF/LF electromagnetic wave propagation through the lower ionosphere between specific transmitters and receivers. For this purpose, a network of eight receivers has been deployed throughout Japan which receive subionospheric signals from different transmitters located both in the same and other countries. In this study we analyze, in terms of the recently proposed natural time analysis, the data recorded by the above-mentioned network prior to the catastrophic 2016 Kumamoto fault-type EQs, which were as huge as the former 1995 Kobe EQ. These EQs occurred within a two-day period (14 April: M W = 6.2 and M W = 6.0, 15 April: M W = 7.0) at shallow depths (~10 km), while their epicenters were adjacent. Our results show that lower ionospheric perturbations present critical dynamics from two weeks up to two days before the main shock occurrence. The results are compared to those by the conventional nighttime fluctuation method obtained for the same dataset and exhibit consistency. Finally, the temporal evolutions of criticality in ionospheric parameters and those in the lithosphere as seen from the ULF electromagnetic emissions are discussed in the context of the lithosphere-atmosphere-ionosphere coupling.

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Electromagnetic Precursors to the 2016 Kumamoto Earthquakes

Cited by 10 publications

References 25 publications

On the Tempo-Spatial Evolution of the Lower Ionospheric Perturbation for the 2016 Kumamoto Earthquakes from Comparisons of VLF Propagation Data Observed at Multiple Stations with Wave-Hop Theoretical Computations

On the Tempo-Spatial Evolution of the Lower Ionospheric Perturbation for the 2016 Kumamoto Earthquakes from Comparisons of VLF Propagation Data Observed at Multiple Stations with Wave-Hop Theoretical Computations

Abnormal Gravity Wave Activity in the Stratosphere Prior to the 2016 Kumamoto Earthquakes

Criticality Analysis of the Lower Ionosphere Perturbations Prior to the 2016 Kumamoto (Japan) Earthquakes as Based on VLF Electromagnetic Wave Propagation Data Observed at Multiple Stations

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