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Electromagnetic (EM) emissions in a wide frequency spectrum ranging from kHzto MHz are produced by opening cracks, which can be considered as the so-calledprecursors of general fracture. We emphasize that the MHz radiation appearsearlier than the kHz in both laboratory and geophysical scale. An importantchallenge in this field of research is to distinguish characteristic epochs inthe evolution of precursory EM activity and identify them with the equivalentlast stages in the earthquake (EQ) preparation process. Recently, we proposedthe following two epochs/stages model: (i) The second epoch, which includes thefinally emerged strong impulsive kHz EM emission is due to the fracture of thehigh strength large asperities that are distributed along the activated faultsustaining the system. (ii) The first epoch, which includes the initiallyemerged MHz EM radiation is thought to be due to the fracture of a highlyheterogeneous system that surrounds the family of asperities. A catastrophic EQof magnitude Mw = 6.3 occurred on 06/04/2009 in central Italy. The majority ofthe damage occurred in the city of L'Aquila. Clear kHz - MHz EM anomalies havebeen detected prior to the L'Aquila EQ. Herein, we investigate the seismogenicorigin of the detected MHz anomaly. The analysis in terms of intermittentdynamics of critical fluctuations reveals that the candidate EM precursor: (i)can be described in analogy with a thermal continuous phase transition; (ii)has anti-persistent behaviour. These features suggest that the emergedcandidate precursor could be triggered by microfractures in the highlydisordered system that surrounded the backbone of asperities of the activatedfault. We introduce a criterion for an underlying strong critical behavior.

Critical features in electromagnetic anomalies detected prior to the L'Aquila earthquake