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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

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. Source

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

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. Source

Hayakawa M.,University of Electro - Communications | Hayakawa M.,Advanced Wireless Communications research Center | Hayakawa M.,Earthquake Analysis Laboratory

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. Source

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

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). Source

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)

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. Source

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