On the puzzling feature of the silence of precursory electromagnetic emissions

Abstract

Abstract. It has been suggested that fracture-induced MHzkHz electromagnetic emissions (EME), which emerge from a few days up to a few hours before the main seismic shock occurrence permit a real-time monitoring of the damage process during the last stages of earthquake preparation, as it happens at the laboratory scale. Despite fairly abundant evidence, electromagnetic (EM) precursors have not been adequately accepted as credible physical phenomena. These negative views are enhanced by the fact that certain "puzzling features" are repetitively observed in candidate fractureinduced pre-seismic EME. More precisely, EM silence in all frequency bands appears before the main seismic shock occurrence, as well as during the aftershock period. Actually, the view that "acceptance of "precursive" EM signals without convincing co-seismic signals should not be expected" seems to be reasonable. In this work we focus on this point. We examine whether the aforementioned features of EM silence are really puzzling ones or, instead, reflect well-documented characteristic features of the fracture process, in terms of universal structural patterns of the fracture process, recent laboratory experiments, numerical and theoretical studies of fracture dynamics, critical phenomena, percolation theory, and micromechanics of granular materials. Our analysis shows that these features should not be considered puzzling.

Field Detection of Microcracks to Define the Nucleation Stage of Earthquake Occurrence

“…It is generally reported that there are considerable correlation between occurrence time of earthquakes and those of emission: the strength of electromagnetic emission increase before and/or after earthquake (e.g., [20,21] Fujinawa et al [46], Parrot et al [47]). Some reports suggest that MHz emission occur several weeks before and the VLF emission occurs only in the nucleation period [8,9,17] in contrary to the appearance of VLF type variation (C type) in this report. We do not have data to discuss the MHz event because of the detection frequency that is less than about 10 kHz.…”

“…Those evidences have been utilized to build the physical and statistical models of nucleation process [1,5]. These models have been further developed: for instance, superimposed undulation of foreshock activity was utilized to infer dynamical critical phenomena to estimate more exact final rupture time (e.g., Sornette and Sammis [7], Kapiris et al [8], Eftaxias et al [9], and many papers referred in the report).…”

“…Electromagnetic approaches have been providing many interesting clues to shed light on preparatory process of earthquakes (e.g., Park et al [22]). As for the nucleation process of natural earthquake, Eftaxias has been investigating in detail by referring laboratory and earthquake generation model by assuming that the VLF emissions are induced by the microcracks [9,17].…”

“…Also shown are the two largest preshocks, which occurred two days before (e, M7.3) and one day before (e, M6.8) the earthquake (revised from Suzuki et al [33]). earthquake and volcanic eruptions by using electromagnetic measurement on the surface (e.g., [8,9,[21][22][23], Nagao et al [35], Revil and Saracco [36], and Han [37]). But there are still no consensus on the characteristics of waveform and the generation mechanism, though there are large extent of similarity in the waveforms and pulse width and uniformity of amplitudes.…”

An Integrated Study of ULF Magnetic Field Variations in Association with the 2008 Sichuan Earthquake, on the Basis of Statistical and Critical Analyses

“…There has been a lot of evidence accumulated during the last few decades on the presence of electromagnetic phenomena associated with or prior to earthquakes (EQs), and such seismo-electromagnetic effects are considered to be promising for short-term EQ prediction (e.g., [1]- [3]). It is found that there are two different kinds of electromagnetic precursors: one is direct radiation in different frequency bands from the EQ hypocenter (or epicenter), and the other is seismo-atmospheric and -ionospheric perturbations (i.e., pre-EQ perturbations of the atmosphere and ionosphere) (e.g., [4]- [7]).…”