EM anomalies before the Kozani earthquake: A study of their behavior through laboratory experiments

Abstract

Strong electromagnetic (EM) anomalies have been detected, from MHz to kHz, prior to the three destructive earthquakes occurred during 1995–1999 in Greece. The observed sequence of EM anomalies before the Kozani‐Grevena earthquake (K‐G) of Ms = 6.6 on May 13, 1995 showed some important characteristics: (i) an increasing electromagnetic emission rate; (ii) an emergence of lower kHz frequencies with large amplitudes at the tail of the MHz electromagnetic anomaly; (iii) an electromagnetic quiescence approximately a few hours before the earthquake and (iv) a total absence of EM anomalies during the aftershock period. All these features are compatible with those reported by other authors. This sequence of the field observed EM signals revealed, in terms of emission pattern, similarities to the laboratory acoustic (AE) emissions during different stages of failure preparation process in rocks.

Unfolding the procedure of characterizing recorded ultra low frequency, kHZ and MHz electromagnetic anomalies prior to the L'Aquila earthquake as pre-seismic ones - Part 2

“…Their lead time is ranged from a few days to a few hours. Importantly, the MHz radiation precedes the kHz one at geophysical scale, as well (Eftaxias et al, 2002;Kapiris et al, 2004a;Contoyiannis et al, 2005). Notice that a complete sequence of SES, MHz and kHz EM anomalies have been observed one after the other in a series of significant EQs that occurred in Greece (Eftaxias et al, 2000(Eftaxias et al, , 2002Karamanos et al, 2006;Papadimitriou et al, 2008).…”

“…Clear MHz-kHz EM anomalies have been detected over periods ranging from a few days to a few hours before shallows land-based (or near coastline) EQs with magnitude 6 or larger since the installation of the station. Recent results indicate that the observed precursors contain characteristic pre-fracture features (Eftaxias et al, 2002(Eftaxias et al, , 2004(Eftaxias et al, , 2007bKapiris et al, 2004a, b;Contoyiannis et al, 2005Contoyiannis et al, , 2008Karamanos et al, 2006;Kalimeri et al, 2008;Papadimitriou et al, 2008).…”

“…Studies on the small (laboratory) scale reveal that the MHz EM radiation appears earlier than the kHz one, while the kHz EM emission is launched from 97% up to 100% of the corresponding failure strength (Eftaxias et al, 2002 and references therein). On the large (geological) scale, intense MHz and kHz EM emissions precede EQs that: (i) occurred in land (or near coast-line), (ii) were strong (magnitude 6 or larger), (iii) were shallow (Eftaxias et al, 2002(Eftaxias et al, , 2004(Eftaxias et al, , 2007bKapiris et al, 2004a, b;Karamanos et al, 2006). Their lead time is ranged from a few days to a few hours.…”

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

“…These precursors are detectable not only at laboratory but also at geophysical scales. VLF and VHF acoustic and EM emissions have been reported resulting from volcanic and seismic activities in various geologically distinct regions of the world (Diodati et al, 1991;Fujinawa and Takahashi, 1994;Fujinawa et al, 1997;Eftaxias et al, 2001aEftaxias et al, , 2002a.…”

“…Our main tool is the monitoring of micro-fractures that occurs before the final breakup, by recording their radio-electromagnetic emissions during the last tens of hours prior to the main shock Vallianatos and Nomikos, 1998;Eftaxias et al, 2000Eftaxias et al, , 2001aEftaxias et al, , 2002a. The observed precursory EM fluctuations might represent EM signatures of the energy rearrangements that occur as the external field drives the heterogeneous system of the pre-focal area from one meta-stable local free-energy minimum to another.…”