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Chen C.-H.,Academia Sinica, Taiwan | Chen C.-H.,Research Station on Seismo Electromagnetics | Wen S.,National Center for Research on Earthquake Engineering | Yeh T.-K.,National Taipei University | And 5 more authors.
Journal of Asian Earth Sciences | Year: 2013

A blind thrust fault with a unique strike, which is orthogonal to the strike of most tectonic structures in Taiwan, triggered the Jiashian earthquake on March 4, 2010 (M=6.4; 22.96°N, 120.70°E). This study utilizes 100 global positioning system stations to examine changes of surface displacements during the Jiashian earthquake. We mitigate effects of short-term noise and long-term plate movements from surface displacement data using a frequency dependent filter via the Hilbert-Huang transform and compute the horizontal azimuth (i.e. GPS-azimuth) using residual data at the NS component relative to residual data at the EW component. Analytical results show that orientations of horizontal azimuths were aligned and orthogonal to the strike of the blind thrust fault. Meanwhile, inverse orientations are observed before and after the earthquake that agrees well with the seismic rebound theory. As stress disturbed on strata a few days before the earthquake, an impeded region can be clearly identified by disordered orientations of horizontal azimuths for anticipating the mainshock. These results provide an additional view to explore stress disturbance associated with earthquakes and offer more information to examine diverse models of tectonic evolution in this region. © 2012 Elsevier Ltd.


Chen C.-H.,National Chung Cheng University | Wen S.,National Center for Research on Earthquake Engineering | Liu J.-Y.,National Central University | Hattori K.,Chiba University | And 5 more authors.
Journal of Asian Earth Sciences | Year: 2014

Daily resolution data retrieved from the 1243 ground-based Global Positioning System (GPS) stations in Japan are utilized to expose surface displacements before the destructive M9 Tohoku-Oki earthquake (March 11, 2011). Variations in the residual GPS data, in which effects of the long-term plate movements, short-term noise and frequency-dependent variations have been removed through a band-pass filter via the Hilbert-Huang transform, are compared with parameters of the focal mechanism associated with the Tohoku-Oki earthquake for validation. Analytical results show that the southward movements, which were deduced from the residual displacements and agree with the strike of the rupture fault, became evident on the 65th day before the Tohoku-Oki earthquake. This observation suggests that the shear stress played an important role in the seismic incubation period. The westward movements, which are consistent with the angle of the maximum horizontal compressive stress, covered entire Japan and formed an impeded area (142°E, 42°N) about 75. km away from the epicenter on the 47th day prior to the earthquake. The horizontal displacements integrated with the vertical movements from the residual GPS data are very useful to construct comprehensive images in diagnosing the surface deformation from destructive earthquakes along the subduction zone. © 2013 Elsevier Ltd.


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.,Research Station on Seismo Electromagnetics | Hayakawa M.,Analysis Inc. | Raulin J.P.,Mackenzie Presbyterian University | And 6 more authors.
Natural Hazards and Earth System Science | Year: 2011

Ionospheric perturbations in possible association with the 2010 Haiti earthquake occurred on 12 January 2010 (with a magnitude of 7.0 and depth of 10 km) are investigated on the basis of subionospheric propagation data from the NAA transmitter on the east coast of the USA to a VLF receiving station in Peru. The local nighttime VLF amplitude data are extensively investigated during the period from the beginning of October 2009 to the end of March 2010, in which the trend (nighttime average amplitude), dispersion and nighttime fluctuation are analysed. It is found that a clear precursory ionosphere perturbation is detected just around New Years day of 2010, about 12 days before the main shock, which is characterised by the simultaneous decrease in the trend and the increases in dispersion and nighttime fluctuation. An additional finding might be the presence of the effect of the Earth's tide one and two months before the main shock, which can only be seen for a huge EQ. © Author(s) 2011.


Hayakawa M.,University of Electro - Communications | Hayakawa M.,Research Station on Seismo Electromagnetics | Hayakawa M.,Analysis Inc.
Natural Hazards and Earth System Science | Year: 2011

In order to increase the credibility on the presence of electromagnetic phenomena associated with an earthquake, we have suggested the importance of the modulation (or fluctuation) seen in the time-series data of any seismogenic effects. This paper reviews the fluctuation spectra of seismogenic phenomena in order to indicate the modulation mechanisms in the lithosphere, atmosphere and ionosphere/magnetosphere. Especially, the effect of Earth's tides in the lithosphere and the modulation in the atmosphere (acoustic and atmospheric gravity waves) are discussed and this kind of fluctuation spectra would further provide essential information on the generation mechanisms of different seismogenic effects. Furthermore, the important role of the slope of fluctuation spectra is suggested in order to investigate the self-organized criticality before the lithospheric rupture and its associated effects in different regions such as the ionosphere. © Author(s) 2011.


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).


Imamura T.,University of Electro - Communications | Imamura T.,Research Station on Seismo Electromagnetics | Ida Y.,University of Electro - Communications | Ida Y.,Research Station on Seismo Electromagnetics | And 8 more authors.
Natural Hazards and Earth System Science | Year: 2010

Fractal analysis has been applied to the local nighttime data of subionospheric LF propagation, and the fractal dimension is estimated every day in the two distinct frequency ranges (AW: acoustic wave and AGW: atmospheric gravity wave). The data during several years are analyzed for the propagation paths from the Japanese transmitter of JJY to Moshiri (Hokkaido) and to Kochi. As the result of analysis, we come to the conclusion that when we pay attention to the period just around the earthquake, we sometimes detect some significant increases in the fractal dimension either in AW or AGW range. This indicates that the self - organization effect prior to an earthquake in the lithosphere, might be seen even in the lower ionosphere, probably in terms of atmospheric oscillation effect. © Author(s) 2010.


Hayakawa M.,University of Electro - Communications | Hayakawa M.,Research Station on Seismo Electromagnetics | Kasahara Y.,University of Electro - Communications | Kasahara Y.,Research Station on Seismo Electromagnetics | And 7 more authors.
Journal of Atmospheric and Solar-Terrestrial Physics | Year: 2010

The long-term data during seven years from January 2001 to December 2007, as observed by the Pacific VLF/LF network consisting of several Japanese stations and one station in Kamchatka, are extensively utilized to perform a statistical correlation study between the lower ionospheric perturbations as detected by subionospheric propagation and earthquakes (EQs). In this paper, we adopt a physical parameter, the maximum seismicity intensity observed (I) to define the strength of an EQ unlike the previously and conventionally used EQ magnitude and depth, which is a combined effect of EQ magnitude and depth, together with the Earth's surface information and geological condition around the EQ epicenter. After considering EQs only take place on the land because of the use of seismicity and by using the superimposed epoch analysis, it is found for the larger EQs with I from 5 to 7 (we feel serious trembling and we expect serious damage) that the most important VLF/LF parameter, trend (nighttime average amplitude), shows a definite decrease about 10 days before the EQ by exceeding 2σ(.σ: standard deviation) criterion; the dispersion shows a maximum about 10 days before the EQ but not exceeding 2σ line and finally the nighttime fluctuation shows an enhancement about 10 days before the EQ (with exceeding the 2σ level). A definite statistical correlation is confirmed between the ionospheric perturbations and I when I is strong enough in a range from 5 to 7. Whereas, there is no significant correlation between the two when I is in a range from 3 to 4. Finally, together with the corresponding results for EQs in the sea, but close to the land, these results are discussed in the light of lithosphere-ionosphere coupling mechanism. © 2010 Elsevier Ltd.


Hayakawa M.,University of Electro - Communications | Hayakawa M.,Research Station on Seismo Electromagnetics | Ohta K.,Chubu University | Sorokin V.M.,RAS Institute of Radio Engineering and Electronics | And 4 more authors.
Journal of Atmospheric and Solar-Terrestrial Physics | Year: 2010

The observation of ULF/ELF electromagnetic waves in the frequency range below 50Hz has been continued at Nakatsugawa (in the Gifu prefecture), Japan since 1998. This paper summarizes anomalous Schumann resonance (SR) phenomena and SR-like line emissions observed at Nakatsugawa in possible association with recent nearby earthquakes (EQs) (the 2004 Mid-Niigata prefecture and the 2007 Noto-Hanto (peninsula) EQs), which have been already described in detail by Ohta et al. (2009). The intensity of particular modes of SR increased before these large EQs and the excitation of other anomalous SR-like line emissions also existed at the frequency shifted by about 2. Hz from the typical SR modes. Since temporal changes of the anomalous SR modes and line emissions are synchronous in time, there might be a possibility that the line emission is a consequence of the anomalous SR. In this paper we propose an interpretation of those anomalous phenomena in terms of excitation of gyrotropic waves due to input wave from below with a band from 15 to 20. Hz as an exciter. The theoretical computational results seem to be generally consistent with the observational finding. © 2010 Elsevier Ltd.


Hayakawa M.,University of Electro - Communications | Hayakawa M.,Research Station on Seismo Electromagnetics | Hobara Y.,UEC | Hobara Y.,Research Station on Seismo Electromagnetics
Geomatics, Natural Hazards and Risk | Year: 2010

Short-term (timescale of hours, days and weeks) earthquake (EQ) prediction is of essential importance to mitigate EQ disasters. Short-term EQ prediction has so far been based on seismic measurements (i.e. mechanical observation of crustal movements), but it was concluded in Japan about 10 years ago that EQ prediction is impossible by means of the mechanical method. Hence, there has been an increased interest and a lot of progress in non-seismic measurement during the last decade. A new approach was developed where electromagnetic measurements provide microscopic information on the lithosphere. The present paper is intended to give a history of short-term EQ prediction, and also we hope that this paper reviews the current status of a new science field, 'seismo-electromagnetics'. We make a general review of different phenomena taking place in the lithosphere, atmosphere and the ionosphere, but we pay more attention to the subjects of our preference including lithospheric ultra low frequency (ULF) electromagnetic emissions, and seismo-ionospheric perturbations. © 2010 Taylor & Francis.

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