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

Asano, Tomokazu; Hayakawa, Masashi

doi:10.4236/ojer.2018.73010

Cited by 16 publications

(40 citation statements)

References 34 publications

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“…In this paper, we have compared the stratospheric oscillations with the corresponding lower ionospheric perturbation for the 2016 Kumamoto EQs (Asano & Hayakawa, ). First of all, the temporal evolution indicates that the stratospheric gravity wave activity over the EQ epicenter is clearly seen on the days from 8 April to 14 April, which is found to be in complete consistence with the lower ionospheric perturbation as detected by the VLF network.…”

Section: Discussionmentioning

confidence: 99%

“…In their paper, they have assumed that the shape of the ionospheric perturbation is quasi-circular, even though nobody knows its exact shape. Another important conclusion of Asano and Hayakawa (2018) is that the radius of perturbation is about 100 km on 2 April and it expands to 550 km on 10 April. The expansion speed is about 50-60 km/day during the development, and we can expect that even above Tokyo the ionosphere is…”

Section: Ionospheric Perturbationmentioning

confidence: 99%

“…A comparison of VLF amplitude data of the JJI transmitter signal at multiple stations with the corresponding wave-hop field predicted at each station by changing the reflection heights of one-hop and two-hop waves enabled Asano and Hayakawa (2018) to estimate the temporal and spatial evolutions of the seismoionospheric perturbation for the Kumamoto EQs. Figure 6 illustrates the summary from the paper by Asano and Hayakawa (2018), which is the temporal evolution of the ionospheric perturbation over the EQ epicenter, together with the degree of perturbation (in the form of decrease in the effective reflection height). This figure shows that the first precursory ionospheric perturbation appears on 28-30 March, and the main perturbation seems to appear on 2 April, begins to develop on subsequent days, exhibits the most perturbed condition (with the maximum depletion in the reflection height of about 10 km) on 10-12 April, and followed by a sharp decay.…”

Section: Ionospheric Perturbationmentioning

confidence: 99%

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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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Section: Discussionmentioning

confidence: 99%

Section: Ionospheric Perturbationmentioning

confidence: 99%

Section: Ionospheric Perturbationmentioning

confidence: 99%

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

2019

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“…Asano and Hayakawa (2017) [34] have made further detailed analysis on the basis of VLF data observed at all 8 stations in Japan on the assumption that the ionospheric perturbation appears first above the EQ epicenter and it is assumed to develop temporally and spatially (horizontally and vertically), we compute the temporal evolutions of amplitude changes at all stations by changing independently the reflection height of one-hop sky wave and that of the second-hop wave close to the transmitter side of the relevant path, and we compare those theoretical values based on the wave-hop method with the observational results in order to infer extensively the spatio-temporal evolution of the ionospheric perturbation. Details on the results will be published elsewhere, but we indicate the following conclusion that the ionospheric perturbations appears about two weeks before the EQ, then it seems to develop by expanding horizontally and vertically (its reflection height becomes lower), and the most perturbed perturbation happens on 10 -12 April (in UT), followed by a decay.…”

Section: ) Vlf Monitoringmentioning

confidence: 99%

Electromagnetic Precursors to the 2016 Kumamoto Earthquakes

Schekotov¹,

Izutsu²,

Asano³

et al. 2017

OJER

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The Kumamoto area of Kyusyu Island was attacked by a series of large earthquakes (EQs) in April, 2016. The first two foreshocks had the magnitudes of 6.5 and 6.4, and about 1 day later there was the main shock on 15 April (UT) with magnitude 7.3. These are fault-type EQs, and so we would expect a variety of electromagnetic precursors to these EQs because we had detected different phenomena for the 1995 Kobe EQ, same fault-type EQ. As for the lithospheric effect, the ULF data at Kanoya observatory (about 150 km from the EQ epicenters) are used, but the simple statistical analysis could not provide us with any clear evidence of ULF radiation from the lithosphere. However, our conventional analyses indicated clear signatures in the atmosphere as ULF/ELF impulsive emissions and also in the ionosphere as observed by means of VLF propagation anomalies and ULF depression. ULF/ELF radiation appeared on 8-11 April (in UT) (maximum on 10 and 11 April (UT)), while ULF depression took place on 8 and 10 April (in UT), so that both atmospheric radiation and ionospheric perturbation took place nearly during the same time period.

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“…Asano and Hayakawa (2017) [28] have tried to compare the observational VLF amplitude with the wave-hop theoretical amplitude estimation by changing the reflection heights of 1 hop and 2 hop sky waves for the relevant propagation path, in order to investigate the detailed spatio-temporal evolution of the properties of ionospheric perturbation for the recent 2016 Kumamoto EQ. By using the similar wave-hop computations (details will be published elsewhere), Figure 6 illustrates the area of perturbation (with the VLF reflection height being lowered Figure 6.…”

Section: Discussionmentioning

confidence: 99%

Characteristic Variations of VLF/LF Signals during a High Seismic Activity in Japan in November 2016

Asano¹,

Рожной²,

Solovieva³

et al. 2017

OJER

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The measurements of very low frequency/low frequency (VLF/LF) signals at the Petropavlovsk-Kamchatsky (PTK) and Yuzhno-Sakhalinsk (YSH) stations in Russia and several observing stations in Japan were used for the analysis of lower ionospheric perturbations in possible association with two earthquakes (EQs) which occurred offshore the Pacific Ocean of Japan in November 2016. The first EQ with M (magnitude) = 6.1 (depth 42 km) happened close to the coast line on 11 November (UT). The second EQ was recorded in the sea on 21 November (UT) with M = 6.9 (depth 11 km) and they had a series of aftershocks with M up to 5.6. As for the long-range monitoring, the significant negative nighttime amplitude decreases as propagation anomalies were found for two subionospheric paths: NWC (Australia)-PTK and JJY (Fukushima, Japan)-YSH during about a week, mainly before the first EQ. The anomalies of signal in the path JJY-PTK were observed 4 -5 days before the second EQ and 3 days after it. Extensive analyses have been performed as well for these two EQs by using the short-range monitoring of VLF data observed at all of the seven VLF/LF stations in Japan in relation to the JJY signal. As related with the 1st EQ, there were observed anomalies on the two paths of JJY-STU (Suttsu) and JJY-NSB (Nakashibetsu) (both stations in Hokkaido) on 2 and 3 November. While, for the 2nd EQ clear anomalies have been observed on 14 and 15, and on 21 November at Ito station in Izu peninsula, Kamakura, Togane and Katsuura in Chiba. Taking into account the possible influence of other factors which can produce perturbations in VLF/LF signals and also using control paths, we may conclude that observed anomalies were very likely to be signatures of lower ionospheric perturbations caused by impending EQs. Finally, we try to estimate the possible perturbation scale for both EQs.

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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

Cited by 16 publications

References 34 publications

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

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

Electromagnetic Precursors to the 2016 Kumamoto Earthquakes

Characteristic Variations of VLF/LF Signals during a High Seismic Activity in Japan in November 2016

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