Results of subionospheric radio LF monitoring prior to the Tokachi (M=8, Hokkaido, 25 September 2003) earthquake

Швец, А. В.; Hayakawa, Masashi; Maekawa, Shigeru

doi:10.5194/nhess-4-647-2004

Cited by 37 publications

(34 citation statements)

References 15 publications

(21 reference statements)

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“…Our former case studies include the (1) Kobe EQ (17 January 1995) (Hayakawa et al 1996), (2) Tokachi-oki EQ (25 September 2003) (Shvets et al 2004;Cervone et al 2006), (3) Niigata-chuetsu EQ (23 October 2004) Yamauchi et al 2007), (4) the 1999 Chi-chi EQ in Taiwan (Hayakawa et al 2005) and, (5) the 2004 Sumatra EQ (Horie et al 2007a, b). The details of seismogenic effects for these EQs are summarized in our review by Hayakawa (2009c).…”

Section: Introductionmentioning

confidence: 99%

The Ionospheric Precursor to the 2011 March 11 Earthquake Based upon Observations Obtained from the Japan-Pacific Subionospheric VLF/LF Network

Hayakawa¹,

Hobara²,

Рожной³

et al. 2013

Terr. Atmos. Ocean. Sci.

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By using network observation of subionospheric VLF (very low frequency)/LF (low frequency) signals in Japan and in Russia, we have found a significant ionospheric perturbation prior to the recent 2011 March 11 Japan earthquake (EQ) which occurred at sea proximate to the Tohoku area on the main island (Honshu) of Japan was an exceptionally huge plate-type EQ. A remarkable anomaly (with a decrease in the nighttime amplitude and also with enhancement in dispersion) was detected on March 5 and 6 along the propagation path from the NLK (Seattle, USA) transmitter to Chofu (together with Kochi and Kasugai). We also have observed the corresponding VLF anomaly during a prolonged period of March 1 -6, with minima in the nighttime amplitude on March 3 and 4 along the path from JJI (Miyazaki, Kyushu) to Kamchatka, Russia. This ionospheric perturbation has been discussed extensively with respect to its reliability. (1) How abnormal is this VLF/LF propagation anomaly? (2) What was the temporal evolution of terminator times? (3) Were there any solar-terrestrial effects (especially the effect from geomagnetic storms) on the VLF/LF propagation anomaly? (4) The effect of any other EQs and foreshock activities on the VLF/LF anomaly? (5) Were there any correlations with other related phenomena? Finally, (6) are there any other examples of a VLF/LF propagation anomaly for oceanic EQs? We then compared the temporal properties of ionospheric perturbations for this EQ with those of a huge number of inland EQs and compared the corresponding spatial scale with the former result of the same oceanic 2004 Sumatra EQ with nearly the same magnitude. Finally, the generation mechanism of those seismo-ionospheric perturbations is briefly discussed.

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Section: Introductionmentioning

confidence: 99%

The Ionospheric Precursor to the 2011 March 11 Earthquake Based upon Observations Obtained from the Japan-Pacific Subionospheric VLF/LF Network

Hayakawa¹,

Hobara²,

Рожной³

et al. 2013

Terr. Atmos. Ocean. Sci.

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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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“…Some of these signals can propagate into the ionosphere and generate variations of the ionosphere parameters such as critical plasma frequency f 0 F2, virtual height h m F2 and of the ionospheric total electron content (TEC). The mechanism of appearance of the ionospheric anomalies includes direct coupling between the Earth's surface and the lower ionosphere through electric current (e.g., Pulinets et al, 2000), and triggering of atmospheric gravity waves by gas releases or thermal anomalies (Shalimov, 1992a(Shalimov, , 1992bGokhberg et al, 1994Gokhberg et al, , 1996Pertsev and Shalimov, 1996;Molchanov and Hayakawa, 2001; Shvets et al, 2004). Thereby, at present, pre-seismic ionosphere anomalies seem to be well analyzed, and discussed in numerous papers (e.g., Pulinets, 1998 Wenchuan Earthquake (M7.9) by using global ionosphere maps (GIM), and have found that TEC above the forthcoming epicenter anomalously decreased in the afternoon period four to six days before the earthquake, and in the late evening period three days before the earthquake.…”

Section: Introductionmentioning

confidence: 99%

Vertical TEC over seismically active region during low solar activity

Astafyeva

Heki

2011

Journal of Atmospheric and Solar-Terrestrial Physics

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Using data of Japanese dense array of GPS receivers (GEONET) we analyzed variations of total electron content (TEC) over Japan during a period of lowest solar and geomagnetic activity in AprilSeptember 2008. During that time, five large earthquakes with magnitude M>6.8 occurred around the Japanese Islands. We calculated vertical TEC with time resolution 1 hour and we compared the TEC over Japan with TEC over southwestern USA. In order to detect abnormal signals, we processed daily TEC based on median and quartile of preceding 15 days. Knowing that the decisive role in the ionosphere state is performed by space weather effects, we compared the estimated TEC values with time series of the B z component of the interplanetary magnetic field (IMF), UV solar radiation, index of geomagnetic activity Dst and planetary index Kp. We have found that though the analyzed time period falls on the minimum of solar activity, the observed positive anomalies in the regional TEC correspond to fluctuations of IMF B z and to the following increase in Kp and Dst indices. Other case of ~25% TEC increase of duration of four days (DOY: 140-143) is, most likely, caused by increase in the solar UV radiation and coincides with growth of the global TEC. Other positive or negative abnormal TEC variations coincide with fluctuations of the global mean TEC or are of large spatial scale, i.e. much larger than the earthquake preparation zone. Therefore, it is rather difficult to find correlation between the observed anomalies and the five large earthquakes. Our results do not disprove the possibility of precursory phenomena but show the difficulties in identifying earthquake precursors in the ionosphere TEC on the background of TEC changes produced by space weather effects, even during solar minimum.

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Results of subionospheric radio LF monitoring prior to the Tokachi (M=8, Hokkaido, 25 September 2003) earthquake

Cited by 37 publications

References 15 publications

The Ionospheric Precursor to the 2011 March 11 Earthquake Based upon Observations Obtained from the Japan-Pacific Subionospheric VLF/LF Network

The Ionospheric Precursor to the 2011 March 11 Earthquake Based upon Observations Obtained from the Japan-Pacific Subionospheric VLF/LF Network

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

Vertical TEC over seismically active region during low solar activity

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