Current challenges for pre-earthquake electromagnetic emissions: shedding light from micro-scale plastic flow, granular packings, phase transitions and self-affinity notion of fracture process

Abstract

Abstract. Are there credible electromagnetic (EM) potential earthquake (EQ) precursors? This a question debated in the scientific community and there may be legitimate reasons for the critical views. The negative view concerning the existence of EM potential precursors is enhanced by features that accompany their observation which are considered as paradox ones, namely, these signals: (i) are not observed at the time of EQs occurrence and during the aftershock period, (ii) are not accompanied by large precursory strain changes, (iii) are not accompanied by simultaneous geodetic or seismological precursors and (iv) their traceability is considered problematic. In this work, the detected candidate EM potential precursors are studied through a shift in thinking towards the basic science findings relative to granular packings, micron-scale plastic flow, interface depinning, fracture size effects, concepts drawn from phase transitions, self-affine notion of fracture and faulting process, universal features of fracture surfaces, recent high quality laboratory studies, theoretical models and numerical simulations. We try to contribute to the establishment of strict criteria for the definition of an emerged EM anomaly as a possibly EQ-related one, and to the explanation of potential precursory EM features which have been considered as paradoxes. A three-stage model for EQ generation by means of pre-EQ fracture-induced EM emissions is proposed. The claim that the observed EM potential precursors may permit a real-time and step-by-step monitoring of the EQ generation is tested.

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.…”

“…Detailed investigation on activity in terms of spatiotemporal distribution and focal mechanism of microcracks revealed physical process of rock fracture. The investigation extends to the seismoelectromagnetic phenomena (e.g., Hayakawa and Fujinawa [15], Hayakawa [16], and Eftaxias and Potirakis [17]).…”

“…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].…”

Power law statistics of force and acoustic emission from a slowly penetrated granular bed

“…To characterize the mode of fracturing more precisely, electromagnetic emission (EME) should also be measured simultaneously. According to the previous works (Eftaxias and Potirakis, 2013;Mori et al, 2004Mori et al, , 2009Baddari and Frolov, 2011), there are two kinds of AE signals: (i) AE signals with simultaneous EME that correspond to the creation of new surfaces, and (ii) AE events without EME corresponding to frictional noise of existing surfaces. While the former is closer to real earthquake events, the current experimental condition probably corresponds to the latter.…”

Use of electromagnetic radiation for potential forecast of earthquakes

“…No method of forecasting earthquakes by the commonly used seismic measurements (SM) has yet been found (Bormann, 2011). The development of an earthquake usually takes place in three stages (Eftaxias & Potirakis, 2013): nucleation, stick-slip and a final drastic slip movement. At the nucleation stage, under the increasing stress amplitude, there appear many tiny fractures in the area around the existing fault (known as the ‘heterogeneous environment’).…”