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Schekotov A.,Russian Academy of Sciences | Fedorov E.,Russian Academy of Sciences | Hobara Y.,University of Electro - Communications | Hobara Y.,Research Station on Seismo Electromagnetics | And 4 more authors.
Telecommunications and Radio Engineering (English translation of Elektrosvyaz and Radiotekhnika) | Year: 2012

The depression (reduction in amplitude) of ULF magnetic field variations of magnetospheric origin is studied at various distances from the epicenter of the strongest earthquake (EQ) which occurred in Japan on March 11, 2011. For this purpose, we have used the ULF data in Japan observed by fluxgate magnetometers at three places located at distances of ~ 300 km to ~ 1300 km from the epicenter of the main shock. The period of data analysis is from December 1, 2010 to May 31, 2011. We have found a sharp increase in depression of the horizontal ULF magnetic field component at the frequency of 0.03 - 0.05 Hz (30-50 mHz) at all of three Japanese observatories (Kakioka, Memambetsu and Kanoya) three days before the first strong foreshock (Mw = 7.5) and five days before the main shock (Mw = 9). This peak in depression is found to be several times greater than all previous values, but the depression seems to be most enhanced at Kakioka, the station nearest to the EQ epicenter. So that it is likely that this phenomenon could be a possible precursor to the huge 3.11 EQ. © 2012 by Begell House, Inc.


Fedorov E.,Russian Academy of Sciences | Schekotov A.,Russian Academy of Sciences | Hobara Y.,University of Electro - Communications | Hobara Y.,Research Station on Seismo Electromagnetics | And 6 more authors.
Journal of Geophysical Research: Space Physics | Year: 2014

A common view is that spectral maxima in observed spectral resonance structures (SRS) of ionospheric Alfvén resonator (IAR) at frequencies f<5 Hz are the signature of resonance frequencies of the IAR. We have studied not only spectra but also waveforms of magnetic fluctuations at IAR frequencies registered at Moshiri station (Japan) and have found that there exist two kinds of signals. The dominant type of signal is a pair of pulses which is caused by an initial exciting impulse and accompanied by a single reflection from the top boundary of the IAR. In the absence of reflection from the lower ionosphere, such signals are not resonant and hence are not caused by IAR excitation. The minority of cases are trains of three or more pulses separated by a nearly constant time interval reflected from both IAR boundaries. We have found that different kinds of signals in time domain may correspond to similar comb-shaped Fourier spectra. So different kinds of signals in time domain practically cannot be distinguished on the basis of their Fourier spectra. We have calculated waveforms and SRS structures of the magnetic field oscillations generated by a model lightning discharge and IAR resonant frequencies. Calculated IAR resonance frequencies can be in disagreement with those of spectral maxima of pulse trains. Then, an analysis of signal waveforms in time domain is highly required to estimate IAR resonance frequencies. Key Points Observed spectra at f < 5 Hz are usually the comb-shaped spectra of 2-3 pulses Comb-shaped spectra are not always the signature of IAR resonance frequencies Calculated IAR response to a lightning coincides with the observed pulse trains ©2014. American Geophysical Union. All Rights Reserved.


Hayakawa M.,University of Electro - Communications | Hayakawa M.,Advanced Wireless Communications Research Center | Hayakawa M.,Earthquake Analysis Laboratory
Animals | Year: 2013

The former statistical properties summarized by Rikitake (1998) on unusual animal behavior before an earthquake (EQ) have first been presented by using two parameters (epicentral distance (D) of an anomaly and its precursor (or lead) time (T)). Three plots are utilized to characterize the unusual animal behavior; (i) EQ magnitude (M) versus D, (ii) log T versus M, and (iii) occurrence histogram of log T. These plots are compared with the corresponding plots for different seismo-electromagnetic effects (radio emissions in different frequency ranges, seismo-atmospheric and -ionospheric perturbations) extensively obtained during the last 15-20 years. From the results of comparisons in terms of three plots, it is likely that lower frequency (ULF (ultra-low-frequency, f ≤ 1 Hz) and ELF (extremely-low-frequency, f ≤ a few hundreds Hz)) electromagnetic emissions exhibit a very similar temporal evolution with that of abnormal animal behavior. It is also suggested that a quantity of field intensity multiplied by the persistent time (or duration) of noise would play the primary role in abnormal animal behavior before an EQ. © 2012 by the authors; licensee MDPI, Basel, Switzerland.


Schekotov A.,Russian Academy of Sciences | Hayakawa M.,University of Electro - Communications | Hayakawa M.,Advanced Wireless Communications Research Center
Physics and Chemistry of the Earth | Year: 2015

The purpose of the paper is to try to find ULF electromagnetic precursors to the 2011 Tohoku earthquake (EQ), on the basis of extensive investigation of radiations in vertical component of the magnetic field or with a large ratio of the vertical to full horizontal component. Nighttime records have been analyzed of three Japanese fluxgate magnetometers located in a distance from 300 to 1300 km from the epicenter of the main shock, and the frequency range from 10 to 150 mHz was used for the analysis. We have applied wavelet analyses to improve the detection of pulsed signals. All obtained scalograms have been averaged over the nighttime interval from 01 h to 05 h JST and flattened by means of multiplication by square of frequency. The sequence of spectra thus obtained has been compared with the evolution of seismicity, which has resulted in that the radiation in the vertical component has been detected. It exhibits seasonal variations with winter maxima, but it increases further by approaching the moment of the EQ and decreases after that. This radiation seems to be correlated with atmospheric parameters - air humidity, temperature, vapor pressure and rainfall. So, we consider that this radiation cannot be caused by subsurface sources, but its possible sources can be atmospheric discharges. The evolution of this phenomenon can be explained by a seasonal variation of atmospheric parameters and also its variations under the influence of injection of gas from the focal zone of a forthcoming EQ. © 2015 Elsevier Ltd.


Hayakawa M.,University of Electro - Communications | Hayakawa M.,Advanced Wireless Communications research Center | Hayakawa M.,Analysis Inc. | Schekotov A.,University of Electro - Communications | Schekotov A.,Russian Academy of Sciences
Geomatics, Natural Hazards and Risk | Year: 2016

The presence of seismo-lower ionospheric perturbation for the Kobe earthquake (EQ) has been revisited with a relatively new phenomenon of ULF (ultra-low-frequency) magnetic field depression effect. By using the ULF data in Japan only at Kakioka belonging to Japan Meteorological Agency (because data from Memambetsu and Kanoya were not available), we have found that a very clear ULF depression was observed at Kakioka on 14 January 1995. A comparison with our former result on subionospheric VLF (very low frequency) propagation anomaly indicates that the occurrence of ULF depression exhibits a temporal coincidence (synchronization) with that of subionospheric VLF anomaly. This may be acceptable because the ULF depression can be explained in terms of enhanced absorption of magnetospheric ULF waves through the disturbed lower ionosphere prior to an EQ. The result of ULF magnetic field depression in this paper is likely to provide a further support to the presence of the lower ionospheric perturbation before the Kobe EQ. © 2014 Taylor & Francis.


Kasahara Y.,University of Electro - Communications | Kasahara Y.,Research Station on Seismo Electromagnetics | Muto F.,University of Electro - Communications | Muto F.,Research Station on Seismo Electromagnetics | And 4 more authors.
Natural Hazards and Earth System Science | Year: 2010

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. © 2010 Author(s).


Potirakis S.M.,University of Piraeus | Hayakawa M.,University of Electro - Communications | Hayakawa M.,Advanced Wireless Communications Research Center | Schekotov A.,Advanced Wireless Communications Research Center | Schekotov A.,Russian Academy of Sciences
Natural Hazards | Year: 2016

The fractal characteristics of the ultra-low-frequency (ULF) magnetic field variations recorded prior to the Tohoku earthquake (EQ) with MW = 9 which happened on 11 March 2011 are studied in this article with the use of detrended fluctuation analysis and Higuchi fractal dimension algorithm. In the specific study, we use for our calculations only nighttime (LT = 3 a.m. ± 2 h) data because of their lowest contamination by industrial noise. A key aspect of our analysis is the investigation about any possible correlation of the ULF magnetic field variations or their calculated fractal characteristics with geomagnetic indices. Different preprocessing approaches are examined aiming at the minimization of any possible influences from global phenomena in the fractal analysis results, while in the same time retaining the scale-invariant character of ULF magnetic field variations after preprocessing. The obtained fractal analysis results imply locally driven change in the fractal characteristics of the ULF data prior to the Tohoku EQ, which is compatible with the change that has been reported prior to other large EQs. © 2016 Springer Science+Business Media Dordrecht


Schekotov A.,Russian Academy of Sciences | Schekotov A.,University of Electro - Communications | Izutsu J.,Chubu University | Hayakawa M.,University of Electro - Communications | And 2 more authors.
Journal of Asian Earth Sciences | Year: 2015

After the 2011 Tohoku earthquake (EQ), there have been numerous aftershocks in the eastern and Pacific Ocean of Japan, but EQs are still rare in the western part of Japan. In this situation a relatively large (magnitude (M). ~. 6) EQ happened on April 12 (UT), 2013 at a place close to the 1995 Kobe EQ (M ~. 7), so we have tried to find whether there existed any electromagnetic precursors to this EQ. Two precursory signatures are detected: one is the depression of ULF (ultra-low-frequency, 0.01-0.02. Hz) geomagnetic variations on April 9, and the second is wideband ELF (extremely low frequency) electromagnetic radiation on April 11. These results for the 2013 Kobe EQ are compared with the corresponding results for the former 1995 Kobe EQ. © 2015 Elsevier Ltd.


Yamaguchi H.,Fuji Security Systems Co. | Hayakawa M.,Analysis Inc. | Hayakawa M.,Hayakawa Institute of Seismo Electromagnetics Co. | Hayakawa M.,Advanced Wireless Communications Research Center
Journal of Asian Earth Sciences | Year: 2015

It is so far believed that ionospheric perturbations as detected by subionospheric VLF/LF (very low frequency/low frequency) propagation, are generated above and around the earthquake (EQ) epicenter. This paper presents very rare cases, which are in complete contrast to the above fact. We have found that in extremely rare cases when EQs happened (i) in the Pacific Ocean or (ii) offshore the Soya cape (Hokkaido) both with very large depths (300-400. km), corresponding ionospheric perturbations take place far away from the EQ epicenter and above the regions with considerable seismic intensity at the time of each EQ. Two EQs happened in the Torishima area of Izu islands (magnitude ~7 and depth ~400. km), and corresponding seismic intensity was observed in the Tokyo and Ibaraki districts. Our VLF data have indicated that the ionospheric perturbation takes place over such regions with high seismic intensity. Another group is two EQs (magnitude ~5) offshore the Soya cape of Hokkaido, and the spatial distribution of seismic intensity at the time of each EQ is just around Aomori prefecture. VLF data have indicated the ionospheric perturbations taken place over the same Aomori area, which is in complete coincidence with the spatial distribution of seismic intensity. As a conclusion, these exceptional examples are, in principle, very similar to the concept of 'selectivity' (or sensitive zone) of geoelectric measurement by the Greek group, and we try to interpret these cases in the context of lithosphere-atmosphere-ionosphere coupling. © 2014 Elsevier Ltd.

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