Experience of short term earthquake precursors with VLF–VHF electromagnetic emissions

Abstract

Abstract. Electromagnetic anomalies (EMA) covering a wide range of frequencies from ULF, VLF up to VHF have been observed before recent destructive earthquakes in continental Greece. We show that the features of these signals are possibly correlated with the fault model characteristics of the associated earthquake and with the degree of geotectonic heterogeneity within the focal zone. The time evolution of these electromagnetic sequences reveals striking similarities to that observed in laboratory acoustic and electromagnetic emissions during different stages of failure preparation process in rocks. If we consider that the same dynamics governs the large-scale earthquakes and the microscopic scale sample rheological structure, the results of this analysis suggest that the recorded EMA might reflect the nucleation phase of the associated impending earthquake. We focus on the rise of the statistical view of earthquakes. We find electromagnetic fingerprints of an underlying critical mechanism. Finally, we conclude that it is useful to combine ULF and VLF-VHF field measurements in an attempt to enhance the understanding of the physics behind these observations and thus to improve the quality of earthquake prediction. Further, the identification of an EMA as a seismogenic one supports the characterization of a sequence of shocks as foreshocks at the time they occur, further helping the earthquake prediction effort.

Evolving towards a critical point: A possible electromagnetic way in which the critical regime is reached as the rupture approaches

“…The above mentioned literature indicates the existence of a possible universal behaviour in the temporal evolution of the critical exponents as the failure approaches. For example: (i) a similar increase with the time of the Hurst exponent from H ≈ 0.1 to H ≈ 0.5 was also observed in the VLF preseismic time-series associated with the Athens EQ (Kapiris et al, 2002;Eftaxias et al, 2002b); (ii) an increase of the exponents β and H (approximately from 0.1 to 0.25) has been observed in the tail of the electromagnetic ULF timeseries associated with the Biak Earthquake (M w = 8.2), on 17 February 1996 (see Fig. 4 in Hayakawa et al, 2000a) and the Guam Earthquake (Ms = 8.0) on 8 August 1993 (see Fig.…”

“…Notice that we found that the spectrum of this strong impulsive emission also displays decreasing power law behaviour, with the scaling exponent increasing during the process of the Earthquake preparation. At the tail of the activity the evolution of the VLF precursors also attains persistent behaviour (Kapiris et al, 2002;Eftaxias et al, 2002b).…”

Unified approach to catastrophic events: from the normal state to geological or biological shock in terms of spectral fractal and nonlinear analysis

“…Figure 1a shows the time series of the 10 kHz magnetic field variations associated with the Athens EQ. We concentrate on this kHz EM activity observed before the 7 September 1999 Athens EQ (38.2 • N, 23.6 • E) with a magnitude Ms (AT H )=5.9 at Zante station (Eftaxias et al, 2000(Eftaxias et al, , 2001(Eftaxias et al, , 2003Kapiris et al, 2004). In terms of literature, this precursory emission has a strange, long duration (approximately a few days), thus it provides sufficient data for a statistical analysis.…”

Effects on atmospherics at 6 kHz and 9 kHz recorded at Tripura during the India-Pakistan Border earthquake

“…Both precursory and post-seismic variations in ELF-VLF amplitudes and in ionospheric parameters are well-known from satellite-based observations surrounding the earthquake zones (Pulinets, 1998;Shvets et al, 2002;Molchanov and Hayakawa, 1998;Calais and Minster, 1995;Liu et al, 2004). Electromagnetic anomalies (EA) before the destructive earthquake in Greece covering wide range of frequencies have been analyzed by Eftaxias et al (2003). The paper asserts that EA are correlated with the fault model characteristics of the associated earthquake and with the degree of geotectonic heterogeneity within the focal zone.…”