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Close-up view of Fig. 2; variations are made two orders of magnitude larger. The origin of the abscissa corresponds to 00h01m40s (UTC), August 17, 1999. The scale of this figure is nearly the same as that of Fig. 3, as understood by the noise levels before the signals appear. The arrival of electromagnetic signals corresponding to the first arrival of seismic wave is indicated by a vertical dotted line. We can recognize slow rises in some components before the dotted lines, but the arrival times, as indicated by arrows, of these slow signals are earlier only by a fraction of second at all the sites. Nonetheless, these signals exceed the noise levels and hence they are significant.
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Electric and magnetic data were obtained above the focal area in association with the 1999 Izmit, Turkey earthquake. The acquired data are extremely important for studies of electromagnetic phenomena associated with earthquakes, which have attracted much attention even without clear physical understanding of their characteristics. We have already r...
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Context 1
... case of a small aftershock as shown in Fig. 3, the electromagnetic signals are slightly larger than the noise level, but the signals for the main shock shown in Fig. 2 are much larger and we can examine the signals in more detail. Here we focus our attention on the portions near the arrival of electromagnetic signals. Surprisingly, as shown in Fig. 4, gradual changes in some components (E x, H y, H z at site 118; H x, H y, H z at site 120; H x, H y at site 121; H x, H y at site 122) can be seen before the expected arrival of seis- mic waves. Duration of such changes is only a fraction of one second and their arrival is well after the origin time of the Izmit ...
Context 2
... sig- nals could not be detected in the case of the small aftershock shown in Fig. 3 is simply because the signals themselves are much smaller, as explained in more detail below. In Figs. 2 and 4, the ordinate scales are adjusted, respectively, so that the signals under consideration are well recognized. In fact, the scale of the ordinate of Fig. 4 is magnified by two orders of magnitude, compared with Fig. 2, and it is now compara- ble with that of Fig. 3, in which the amplitude of electric field variation is the order of 10 −6 −10 −7 V/m. For the magnetic field, we must make corrections of the frequency-dependent sensor response to the output data and in the case of Fig. 3, the ...
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Earthquake phenomena can be observed and monitored using the presence of vibration. In order to monitor the vibration, fluxgate sensor can be applied based on magnetic flux change. In this research, a vibration measurement instrument based on the fluxgate sensor for an earthquake monitoring application has been made. It is supported by a personal c...
Citations
... Therefore, by refining the frequency band of geomagnetic vertical intensity polarization, we can not only obtain anomalous changes in shallow media but also filter out some of the short-period interference effects and improve the utilization rate of data to enhance the effectiveness of this method in earthquake prediction. Numerous case studies have shown that high polarization anomalies in the 0.01 Hz (100 s) band were observed from several days to three months before earthquakes [21][22][23][24][25][26][27][28][29]. However, from the skin effect, it is known that the frequency range of seismomagnetic disturbances varies for earthquakes with different source depths and different seismic tectonics, and not all preseismic anomalies are concentrated in the 0.01 Hz (100 s) frequency band. ...
Geomagnetic vertical intensity polarization is a method with a clear mechanism, mature processing methods, and a strong ability to extract anomalous information in the quantitative analysis of seismogenic geomagnetic disturbances. The existing analyses of geomagnetic vertical intensity polarization are all based on the 5~100 s frequency band without refinement of the partitioning process. Although many successful results have been obtained, there are still two problems in the process of extracting anomalies: the geomagnetic anomalies that satisfy the determination criteria are still high in occurrence frequency; and the anomalies are distributed over too large an area in space, which leads to difficulties in determining the location of the epicenter. In this study, based on observations from western China, where fluxgate observation points are positioned in areas with frequent, densely distributed medium-strength earthquakes, we refined the frequency bands of geomagnetic vertical intensity polarization, recalculated the spatial and temporal evolution characteristics of geomagnetic disturbances before earthquakes, and improved the crossover frequency anomaly prediction index while promoting the application of the method in earthquake forecasting.
... There have been many reports of temporal variations in the electromagnetic (EM) field accompanying (and thus assumed to be related to) seismic ground motion or earthquake fault rupture (e.g. Eleman 1966 ;Honkura et al. 2000Honkura et al. , 2002Honkura et al. , 2004Skordas et al. 2000 ;Ujihara et al. 2004 ;Abdul Azeez et al. 2009 ;Okubo et al . 2011 ;Sun et al. 2019 ;Gao et al. 2020 ). ...
Temporal variations in the electromagnetic field generated by seismic waves are accounted for mainly by electrokinetic (EK) and motional induction (MI) effects. Currently, these effects are considered in terms of different sets of equations, even though both mechanisms are assumed in data interpretation. In principle, however, they should be described by a single set of equations, possibly including a new type of coupling effect. This inconsistency suggests that the deviation of conventional equations was somewhat incorrect, with some coupling mechanisms having been overlooked. Here, the derivation of the conventional equations was reconsidered, and necessary revisions were applied. The revised equations describe both EK and MI effects and include a previously unrecognized coupling effect (although its effect is negligible). The solution of the new equations is well approximated by a simple sum of EK and MI effects determined by conventional equations. In conclusion, it was confirmed that the conventional procedure for estimation of seismically induced EM variations in terms of the EK and MI effects is sufficiently accurate, in spite of the conventional governing equations missing some of coupling terms related to the EK and MI effects.
... The microfracture electrification mechanism generates both pre-and co-seismic electromagnetic signatures Hayakawa 1995, 1998). The seismic dynamo effect is genered from vibration of the ground with the passage of seismic waves, which may be one of the possible mechanisms of preseismic electromagnetic signatures Honkura et al. 2002). The electrokinetic effect occurred in a porous medium, due to the flow of fluid. ...
The Earth's natural pulse electromagnetic field (ENPEMF) signal, is generally considered to be a nonlinear or nonstationary signal received from our instrument, placed on the surface near the source area. To obtain latent information on the ENPEMF signal, this paper employs the time–frequency analysis (TFA) method to get the instantaneous frequency (IF) of the signal. The traditional Data-driven time–frequency analysis (DDTFA) requires to know the initial phase function (IPF) set of the signal, to accomplish the signal decomposition and its IFA. However, it's difficult to observe directly the IPF set of the ENPEMF signal. To acquire accurate time–frequency distribution, an improved DDTFA method was proposed, which adopts differential evolution (DE) to calculate multiple IPF of multi-component non-stationary signals. In this paper, the ENPEMF signal received from the Lushan \({M}_{w}\) 6.6 earthquake on April 20, 2013, was taken as an example, and the improved method, DE-DDTFA, was used to decompose the signal into multiple intrinsic mode function (IMF) components, and obtained the IF of each IMF. It is demonstrated by the experimental that the number of IMF is 200% more than usual time, and the energy of the signal had grown by approximately 10–20 times, or even more compared with usual in just one week before the earthquake. The experimental result illustrates that the amount of IMF and the energy of the ENPEMF signal show an overall upward trend, which is a distinct trait before the earthquake, and DDTFA is a good reference for studying the time–frequency distribution and energy spectrum variation characteristics of electromagnetic signals before earthquakes.
... There have been many investigations across the world which reported electromagnetic signals associated with earthquakes (Ujihara et al. 2004;Johnston et al. 2005;Zlotnicki et al. 2006;Abdul Azeez et al. 2009;Kappler et al. 2010;Balasco et al. 2014Balasco et al. , 2015Rodriguez-Perez et al. 2020). There are physical mechanisms proposed for pre-and co-seismic electromagnetic signatures generated by earthquakes, such as piezoelectric effect, piezomagnetic effect, microfracture electrification, seismic dynamo effect and electrokinetic effect Hayakawa 1995, 1998;Ogawa and Utada 2000;Matsushima et al. 2002;Honkura et al. 2002;Huang, 2002;Petraki et al. 2015;Ren et al. 2015;Rodriguez-Perez et al. 2020). The piezoelectric effect occurs in the subsurface due to crystal anisotropy. ...
... The microfracture electrification mechanism generates both pre-and co-seismic electromagnetic signatures (Molchanov and Hayakawa 1995). The seismic dynamo effect or resonance of ions is one of the essential physical phenomena that give rise to electromagnetic signals in the Earth due to vibration of the ground with the passage of seismic waves Honkura et al. 2002). It is suggested that the seismic dynamo effect is one of the possible mechanisms for pre-and co-seismic electromagnetic signatures. ...
... Along with electrokinetic phenomena, seismic dynamo effect also plays a crucial role in generating co-seismic electromagnetic signals. The electromagnetic phenomena in the Earth are caused due to vibration of the ground with the passage of seismic waves Honkura et al. 2002 ...
Continuously monitored magnetotelluric (MT) time series data were used to identify the short-term earthquake co-seismic
and pre-seismic electromagnetic phenomenon. The co-seismic behavior of the MT time series data recorded at 15 Hz sampling
frequency is analyzed for the earthquake that occurred on November 24, 2007, of Mw = 4.6. The wavelet analysis of
the MT time series data shows significant enhancement at 3–6 Hz frequency band in the scalogram during the earthquake
in comparison with pre- and post-time. The significant enhancement in the scalogram is related to the onset of the main
shock of the earthquake. In this paper, we have also shown the precursory signatures of several earthquake magnitudes (Mw)
ranging from 3.9 to 4.9 and the focal depth extending from 5 to 10 km mainly dominated by normal and strike-slip faulting.
The spectral polarization ratio technique was implemented on these events to identify the precursory signatures. A few days
before the earthquake, a significant anomaly was identified for most of the earthquakes using this technique. This prominent
anomaly is correlated with Dst index, which provides information about the ionosphere and magnetosphere responses in the
presence of the solar wind and interplanetary magnetic field. We inferred the unusual behavior prior to the earthquake is
related to the precursory signature, but not related to the solar-terrestrial effect. The complex tectonic settings in the study
region suggest that both electrokinetic and seismic dynamo mechanisms are the probable mechanisms playing an important
role in generation of co- and pre-seismic electromagnetic signals.
... There have been many investigations across the world which reported electromagnetic signals associated with earthquakes (Ujihara et al. 2004;Johnston et al. 2005;Zlotnicki et al. 2006;Abdul Azeez et al. 2009;Kappler et al. 2010;Balasco et al. 2014Balasco et al. , 2015Rodriguez-Perez et al. 2020). There are physical mechanisms proposed for pre-and co-seismic electromagnetic signatures generated by earthquakes, such as piezoelectric effect, piezomagnetic effect, microfracture electrification, seismic dynamo effect and electrokinetic effect Hayakawa 1995, 1998;Ogawa and Utada 2000;Matsushima et al. 2002;Honkura et al. 2002;Huang, 2002;Petraki et al. 2015;Ren et al. 2015;Rodriguez-Perez et al. 2020). ...
... The microfracture electrification mechanism generates both pre-and co-seismic electromagnetic signatures (Molchanov and Hayakawa 1995). The seismic dynamo effect or resonance of ions is one of the essential physical phenomena that give rise to electromagnetic signals in the Earth due to vibration of the ground with the passage of seismic waves Honkura et al. 2002). It is suggested that the seismic dynamo effect is one of the possible mechanisms for pre-and co-seismic electromagnetic signatures. ...
... Along with electrokinetic phenomena, seismic dynamo effect also plays a crucial role in generating co-seismic electromagnetic signals. The electromagnetic phenomena in the Earth are caused due to vibration of the ground with the passage of seismic waves Honkura et al. 2002; Abdul Azeez et al. 2009). The complex tectonic settings in the Koyna-Warna region suggest that both electrokinetic and seismic dynamo mechanisms play an important role in generation of co-seismic electromagnetic signals. ...
Continuously monitored magnetotelluric (MT) time series data were used to identify the short-term earthquake co-seismic
and pre-seismic electromagnetic phenomenon. The co-seismic behavior of the MT time series data recorded at 15 Hz sampling
frequency is analyzed for the earthquake that occurred on November 24, 2007, of Mw = 4.6. The wavelet analysis of
the MT time series data shows significant enhancement at 3–6 Hz frequency band in the scalogram during the earthquake
in comparison with pre- and post-time. The significant enhancement in the scalogram is related to the onset of the main
shock of the earthquake. In this paper, we have also shown the precursory signatures of several earthquake magnitudes (Mw)
ranging from 3.9 to 4.9 and the focal depth extending from 5 to 10 km mainly dominated by normal and strike-slip faulting.
The spectral polarization ratio technique was implemented on these events to identify the precursory signatures. A few days
before the earthquake, a significant anomaly was identified for most of the earthquakes using this technique. This prominent
anomaly is correlated with Dst index, which provides information about the ionosphere and magnetosphere responses in the
presence of the solar wind and interplanetary magnetic field. We inferred the unusual behavior prior to the earthquake is
related to the precursory signature, but not related to the solar-terrestrial effect. The complex tectonic settings in the study
region suggest that both electrokinetic and seismic dynamo mechanisms are the probable mechanisms playing an important
role in generation of co- and pre-seismic electromagnetic signals.
... There have been some possible examples of such 'early EM waves' (e.g. Honkura et al. 2002;Okubo et al. 2011). ...
Very clear coseismic electric and magnetic signals accompanying seismic waves were observed during the 2017 Mw 6.5 Jiuzhaigou earthquake, which took place in western China. In order to understand the generation mechanism of these observed signals, we simulate electric and magnetic responses to this specific earthquake based on three mechanisms, namely, the electrokinetic effect, the motional induction effect and the rotation effect of the coil-type magnetometer. We conduct the simulations using a point source model and a realistic layered earth model and compare to the observed data in the frequency band 0.05–0.3 Hz. Our results show that the electrokinetic effect can explain the observed electric fields in both waveform and amplitude, but it cannot explain the magnetic signals accompanying the Rayleigh wave. The motional induction effect cannot explain either the coseismic electric or magnetic data because it predicts much weaker coseismic electric and magnetic fields than the observed data. The magnetic fields resulting from the rotation of the magnetometer agree with the observed data in the waveforms though their amplitudes are two to four times smaller than the observed data. Our simulations suggest that the electrokinetic effect is responsible for the generation of coseismic electric fields and that rotation of the coil magnetometer is likely the main cause of coseismic magnetic fields. The results improve our interpretation of the coseismic electromagnetic (EM) phenomenon and are useful for understanding other kinds of earthquake-associated EM phenomena.
... This attenuation effect has been assumed to be due to the changes in hydrologic status of the ground surface layer . Electric and magnetic perturbations have been observed after the Izmit earthquake ( = 7.6) in Turkey on August 1999 immediately upon arrival of the seismic P-wave at the magnetotelluric stations [Honkura et al, 2002]. ...
... Substituting equation (41) for ( ) into equation (35) From Figure 3, the typical frequency of the electric field vibrations is close to though the electric signal is phase shifted with respect to the seismic variations of the pressure or mass velocity, which are described by the function ( ). Such co-seismic geoelectric field changes after earthquakes occurrence have been observed by many researchers [e.g., Eleman, 1965;Nagao et al., 2000;Honkura et al., 2002;Balasco et al., 2014;Romano et al., 2018]. ...
... Depending on the ground conductivity the velocity of the GMI diffusion can even supersede the seismic wave velocity, thereby producing an "electromagnetic precursor" of a seismic wave front [Surkov 1997]. Such a kind of electromagnetic changes in both magnetic [Honkura et al., 2002] and electric components [Balasco et al., 2014;Romano, 2018] before the arrival of seismic waves has been occasionally observed. However, in practice, it is difficult to conclude unambiguously which of those mechanisms prevails because of a large variability of the realistic crust parameters, such as porosity, permeability, conductivity and etc. [Surkov et al. 2018]. ...
Seismoelectric effect is studied in the framework of classical Lamb's problem with impulse or time-variable mechanical action on an elastic porous half-space. Radiation of elastic waves gives rise to pressure variation of groundwater fluid contained in pores and cracks. This causes the generation of telluric electric fields and currents due to the seismoelectric effect. A diffusion type equation is applied to describe the variations of the pore pressure and telluric electric field. Particular emphasis has been placed on the properties of seismoelectric signals caused by Rayleigh wave propagation since this wave has maximal amplitude at a considerable distance from the seismic source. For practical purposes and geophysical application, the co-seismic phenomena related to seismoelectric effect are examined in more detail.
... Order estimation of the SES strength [32] suggests that the dominant causes are the seismo-dynamic effect [28] and/or the electro-kinetic effect. The unstable detection of the present phenomena excludes the induction effect. ...
... This system uses the focal parameters determined by P-wave arrival data at a small number of observation sites. The practical use of this information started from October 2007 in Japan with the implementation of counter-measure systems, such as the emergency shutdown of gas fittings and home electrical devices(28). But it generally provides insufficient time (seconds) in cases of shallow depth just under the city. ...
... while changes associated with geomagnetic abnormalities occurred from 06:37:54 to 06:51:40, i.e., 344 s later than the P-wave arrival and 116 s later than the S-wave arrival (Cha N et al., 2016). Changes in electromagnetic signals were recorded 3 s after the Izmit earthquake in 1999 (Honkura et al., 2002). Zhao BQ and Hao YQ (2015) similarly found that the geomagnetic disturbances recorded during the Wenchuan earthquake occurred after the arrival of seismic waves (see Fig. 6 and Fig. 7 of Zhao BQ and Hao YQ, 2015). ...
Twenty-seven FHDZ-M15 combined geomagnetic observation systems (each of which is equipped with a fluxgate magnetometer and a proton magnetometer) had been installed in the China geomagnetic network before the 2008 Wenchuan earthquake, during which coseismic disturbances were recorded by 26 fluxgate magnetometer observatories. The geomagnetic disturbances have similar spatial and temporal patterns to seismic waves, except for various delays. Six proton magnetometer observatories recorded coseismic disturbances with very small amplitudes. In addition, fluxgate magnetometers registered large-amplitude disturbances that are likely to have included responses to seismic waves. However, two problems remain unresolved. First, why do these geomagnetic disturbances always arrive later than P waves? Second, why do the geomagnetic disturbances have spatial and temporal directivity similar to the main rupture direction of the earthquake? Solving these two problems may be crucial to find the mechanism responsible for generating these geomagnetic anomalies. (2019). Characteristics of the coseismic geomagnetic disturbances recorded during the 2008 M w 7.9 Wenchuan Earthquake and two unexplained problems. Earth Planet. Phys., 3(5), 436-444.
... In some cases, STADs could further travel into the ionosphere and interact with the ionized gas resulting in seismo-traveling ionospheric disturbances (STIDs) [see papers listed in Davies (1990)]. Meanwhile, scientists reported that co-seismic geomagnetic pulsations can result from instrument oscillations due to seismic waves (Li et al. 2018) and regional geomagnetic field fluctuations induced by STIDs (Iyemori et al. 1996(Iyemori et al. , 2005Honkura et al. 2002;Azeez et al. 2009;Widarto et al. 2009;Hao et al. 2013;Gao et al. 2014;Yen et al. 2015;Liu et al. 2016a). Due to the low sampling rate, co-seismic fluctuations in the geomagnetic field were hard to distinguish from the effect of magnetometer sensor oscillation (Breiner 1964;Eleman 1965), and therefore, high resolution (e.g., 1 Hz) observation are necessary for such researches (Iyemori et al. 1996). ...
