Proceedings Article

# Sub-ionospheric vlf propagation anomalies associated with the earthquake ON 25 March 2013

20 Oct 2014-pp 1-4
Abstract: Ionospheric perturbations in possible association with the earthquake occurred on 25 March 2013 in India-Oceania region (magnitudes ≈ 6.0) is investigated on the basis of subionospheric propagation data from the NWC transmitter(19.8 kHz) on the North West Cape, Australia to a VLF receiving station at Agra, India. The local nighttime VLF amplitude data are extensively investigated during the period, ±15 days of the earthquake, in which the trend (nighttime average amplitude), dispersion and nighttime fluctuation are analyzed. It is found that a clear precursory ionosphere perturbation is detected, about 12 days before the main shock, which is characterised by the simultaneous decrease in the trend and increase in nighttime fluctuation. Possible seismo-ionospheric mechanisms to demonstrate the physics that how ionosphere starts to feel these earthquakes are discussed.

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Journal Article
Abstract: During the earthquake preparation a zone of cracked rocks is formed in the region of a future earthquake focal zone under the influence of tectonic stresses. In the study of the surrounding medium this region may be considered as a solid inclusion with altered moduli. The inclusion appearance causes a redistribution of the stresses accompanied by corresponding deformations. This paper deals with the study of deformations at the Earth's surface, resulting from the appearance of a soft inclusion. The Appendix contains an approximate solution of the problem for a soft elastic inclusion in an elastic half-space. It is assumed that the moduli of the inclusion differ slightly from those of the surrounding medium (by no more than 30%). The solution permits us to calculate the deformations at the Earth's surface for the inclusion with an arbitrary heterogeneity and anisotropy. The problem is solved by the small perturbation method. The calculation is made for a special case of a homogeneous isotropic inclusion where only the shear modulus decreases. The shear stresses act at infinity. The equations are deduced for the estimation of deformations and tilts at the Earth's surface as a function of the magnitude of the preparing earthquake and the distance from the epicentre. Comparison has shown a satisfactory agreement between the theoretical and field results. Let us assume that the zone of effective manifestation of the precursor deformations is a circle with the centre in the epicentre of the preparing earthquake. The radius of this circle called ‘strain radius’ may be calculated from the equation $$\rho = 10^{0.43M} km,$$ where M is the magnitude. It was shown that the precursors of other physical nature fall into this circle.

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770 Citations

Open accessBook
01 Jan 2004-
Abstract: The Basic Components of Seismo-Ionospheric Coupling.- Ionospheric Precursors of Earthquakes as they are seen from the Ground and from Space.- Near Ground and Troposphere Plasmachemistry and Electric Field.- Physics of Seismo-Ionospheric Coupling.- Main Phenomenological Features of Ionospheric Precursors of Earthquakes.- Are we Ready for Prediction? The Practical Applications.- Ultimate Results, Unexplained Phenomena, Future Tasks.

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709 Citations

Journal Article
Abstract: [1] Empirical evidence of the preearthquake ionospheric anomalies (PEIAs) is reported by statistically investigating the relationship between variations of the plasma frequency at the ionospheric F2 peak foF2 and 184 earthquakes with magnitude M ≥ 5.0 during 1994–1999 in the Taiwan area. The PEIA, defined as the abnormal decrease more than about 25% in the ionospheric foF2 during the afternoon period, 1200–1800 LT, significantly occurs within 5 days before the earthquakes. Moreover, the odds of earthquakes with PEIA increase with the earthquake magnitude but decrease with the distance from the epicenter to the ionosonde station. These results indicate that the PEIA is energy related.

284 Citations

Journal Article
Abstract: Electromagnetic perturbations caused by natural geophysical activity, such as earthquakes and volcanic eruptions, have been studied since the great Alaskan earthquake in 1964. In recent years, interest has been increasing because, when a precursor event occurs, it normally does so less than a few hours before the shock. This paper presents a review of the high-frequency seismo-electromagnetic phenomena already observed, and occurring before, as well as after the shock. The term ‘high frequency’ is to be taken in the seismic sense, i.e. larger than a few Hertz. Mechanisms that might produce these seismo-electromagnetic emissions will be described. It is shown that, at the moment, a causal relationship between electromagnetic signals and seismic activity still remains to be demonstrated. Theoretical as well as intensive experimental studies are necessary to understand the physical processes responsible for seismo or volcano-electric variations, electrical resistivity variations, electromagnetic effects associated with dilatance, as well as electromagnetic fields generated during laboratory experiments, or ionospheric disturbances.