A possible effect of ionospheric perturbations associated with the Sumatra earthquake, as revealed from subionospheric very‐low‐frequency (VLF) propagation (NWC‐Japan)

Horie, Takeshi; Maekawa, Shigeru; Yamauchi, Takeshi; Hayakawa, Masashi

doi:10.1080/01431160601094476

Cited by 50 publications

(36 citation statements)

References 6 publications

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“…There have been so many case studies on subionospheric VLF/LF propagation anomalies; e.g., Kobe EQ (Hayakawa et al, 1996), Tokachi-oki EQ (Shvets et al, 2004), Niigata-chuetsu EQ , Indonesia-Sumatra EQ (Horie et al, 2007), etc. In addition to these case studies, statistical studies on the correlation of ionospheric perturbations with EQs are highly required.…”

Section: Introductionmentioning

confidence: 99%

On the statistical correlation between the ionospheric perturbations as detected by subionospheric VLF/LF propagation anomalies and earthquakes

Kasahara

Muto

Horie

et al. 2008

Nat. Hazards Earth Syst. Sci.

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Abstract. Relatively long-period (4 years) data on different propagation paths by means of Japanese-Pacific VLF/LF network observation, are used to obtain further statistical significance on the correlation of ionospheric perturbations as revealed by VLF/LF propagation anomalies with earthquakes. Earthquakes with magnitude greater than 6.0, taken place only within the fifth Fresnel zone of each great-circle path are selected for the correlation study. It is finally found based on the superimposed epoch analysis that the nighttime trend (average amplitude) exhibits a significant decrease exceeding 2σ (σ : standard deviation) several days before the earthquake and the nighttime fluctuation exceeds the corresponding 2σ again several days before the earthquake when the earthquake depth is smaller than 30 km (shallow earthquakes). However, when we treat all earthquakes including deep earthquakes, the trend shows a significant decrease (just approaching 2σ line), and the nighttime fluctuation shows a less significant broad enhancement before the EQ.

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Section: Introductionmentioning

confidence: 99%

On the statistical correlation between the ionospheric perturbations as detected by subionospheric VLF/LF propagation anomalies and earthquakes

Kasahara

Muto

Horie

et al. 2008

Nat. Hazards Earth Syst. Sci.

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“…Two possible methods have been proposed for such a study of subionospheric VLF/LF propagation data. The first is based on the analysis of nighttime amplitude and/or phase anomalies (Gokhberg et al, 1989;Gufeld et al, 1992), and further developed as the "fluctuation method" (Shvets et al, , 2004aHayakawa et al, 2002Hayakawa et al, , 2004aHorie et al, 2006). The second method is called the "terminator time" method, which is based on the determination of the characteristic times of minimums in the amplitude/phase diurnal variations during sunrise and sunset (Hayakawa et al, 1996;Maekawa and Hayakawa, 2006).…”

Section: Introductionmentioning

confidence: 99%

A statistical study on the effect of earthquakes on the ionosphere, based on the subionospheric LF propagation data in Japan

et al. 2006

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Abstract.A superimposed epoch analysis has been undertaken, in order to find the correlation of the ionospheric perturbations with seismic activity. We take the wave path from the Japanese LF transmitter (frequency=40 kHz) and an observing station of Kochi (wave path length of 770 km), and a much longer period (of five years) than before, is considered. This subionospheric LF propagation can be called "an integrated measurement" in the sense that any earthquakes in the LF sensitive area just around the great-circle path can influence the observed LF signals, so that we define the "effective magnitude" (Meff) by integrating the total energy from different earthquakes in the sensitive area on a current day and by converting it back into magnitude. A superimposed epoch analysis for the effective magnitude greater than 6.0 has yielded that the ionosphere is definitely disturbed in terms of both amplitude and dispersion, and that these perturbations tend to take place prior to an earthquake. The statistical z-test has also been performed, which has indicated that the amplitude is definitely depleted 2-6 days before the earthquake day and also that the dispersion is very much enhanced during the same period. This statistical study has given strong support to the existence of seismo-ionospheric perturbations for high seismic activity.

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“…In this paper we pay attention to a medium distance (about 6∼8 Mm) propagation path and we focus on several EQs for this distance propagation path. Unlike the above-mentioned TT method to identify seismo-ionospheric effect, we use an alternative method (we call it "nighttime fluctuation" method) (Rozhnoi et al, 2004;Horie et al, 2007a) for the VLF analysis in this paper, in order to examine whether we will be able to detect any seismoionospheric perturbation for the medium-distance propagation and to study the dependence of seismo-ionospheric disturbances on the distance of an EQ epicenter from the greatcircle path, the effect of EQ depth, etc.…”

Section: Introductionmentioning

confidence: 99%

The ionospheric perturbations associated with Asian earthquakes as seen from the subionospheric propagation from NWC to Japanese stations

Kasahara

Muto

Hobara

et al. 2010

Nat. Hazards Earth Syst. Sci.

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Abstract. Huge five earthquakes with magnitude greater than 6.0 took place in Asia (include Philippines, Indonesia, etc.) during the period from the beginning of August 2008 to the end of Junuary 2009, and the corresponding data of subionospheric VLF propagation between the NWC transmitter (Australia, 19.8 kHz) and a few Japanese stations (distance 6∼8 Mm) are examined. As the result of our analysis by means of (1) trend (average nighttime amplitude), (2) dispersion, (3) nighttime fluctuation, and (4) atmospheric gravity wave enhancement, three earthquakes from the five taking place within the fifth Frenel zone are found to have accompanied a precursory signature in VLF propagation. On the other hand, there were observed no such precursory signatures for the remaing two earthquakes. One is too deep (>400 km) and another is too distant from the great-circle path. These characteristics of seismo-ionospheric perturbations would be of essential importance in studying the spatial/temporal properties of seismo-ionospheric perturbations for medium-distance propagation.

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A possible effect of ionospheric perturbations associated with the Sumatra earthquake, as revealed from subionospheric very‐low‐frequency (VLF) propagation (NWC‐Japan)

Cited by 50 publications

References 6 publications

On the statistical correlation between the ionospheric perturbations as detected by subionospheric VLF/LF propagation anomalies and earthquakes

On the statistical correlation between the ionospheric perturbations as detected by subionospheric VLF/LF propagation anomalies and earthquakes

A statistical study on the effect of earthquakes on the ionosphere, based on the subionospheric LF propagation data in Japan

The ionospheric perturbations associated with Asian earthquakes as seen from the subionospheric propagation from NWC to Japanese stations

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