George Antonopoulos

Signature of pending earthquake from electromagnetic anomalies

Two electromagnetic (EM) anomalies have been detected in the VLF frequency band before the Athens earthquake (EQ) (Mw=5.9, Sept. 7, 1999) with the following characteristics: (i) The first and second anomaly lasted for 12 and 17 hours respectively with a cessation of 12 hours; (ii) The second anomaly ceased at about 9 hours before the EQ; (iii) The larger anomaly, the second one, contains approximately 80% of the total EM energy received; (iv) No EM disturbance has been recorded in the VHF frequency band unlike with other cases, e.g., the Kozani Grevena and Egion-Eratini earthquakes. The fault modeling of the Athens EQ, based on information obtained by radar interferometry, predicts two faults. The main fault segment is responsible for 80% of the total energy released, while the secondary fault segment for the remaining 20%. Moreover, a recent seismic data analysis supports the hypothesis that a two-event solution for the Athens EQ, is more likely than a single event solution. In addition, the absence of surface rupture explains the absence of EM detection in the VHF frequency band. The present analysis reveals that the properties of the preseismic electromagnetic anomalies might be considered as signatures of a pending earthquake.

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

Earthquakes (EQs) are large-scale fracture phenomena in the Earth’s heterogeneous crust. Fracture-induced physical fields allow a real-time monitoring of damage evolution in materials during mechanical loading. Electromagnetic (EM) emissions in a wide frequency spectrum ranging from kHz to MHz are produced by opening cracks, this can be considered as the so-called precursors of general fracture. We emphasize that the MHz radiation appears earlier than the kHz on both laboratory and geophysical scales. An important challenge in this field of research is to distinguish characteristic epochs in the evolution of precursory EM activity and identify them with the equivalent last stages in the EQ preparation process. Recently, we proposed the following two-stage model. (i) The first epoch, which includes the initial emergent MHz EM emission, is thought to be due to the fracture of a highly heterogeneous system that surrounds a family of large high-strength asperities distributed along the activated fault sustaining the system. (ii) The second epoch, which includes the emergent strong impulsive kHz EM radiation, is due to the fracture of the asperities themselves. A catastrophic EQ of magnitude Mw=6.3 occurred on 6 April, 2009 (06/04/09) in central Italy. The majority of the damage occurred in the city of L’Aquila. Clear kHz–MHz EM anomalies had been detected prior to the L’Aquila EQ. Here, we investigate the seismogenic origin of the MHz part of the anomalies. The analysis, which is in terms of intermittent dynamics of critical fluctuations, reveals that the candidate EM precursor (i) can be described as analogous to a thermal continuous phase transition and (ii) has anti-persistent behavior. These features suggest that this candidate precursor was triggered by microfractures in the highly disordered system that surrounded the backbone of asperities of the activated fault. A criterion for underlying strong critical behavior is introduced. In this field of research, reproducibility of results is desirable; and is best done by analyzing a number of precursory MHz EM emissions. We refer to previous studies of precursory MHz EM activities associated with nine significant EQs that have occurred in Greece in recent years. We conclude that all the MHz EM precursors studied, including the present one, can be described as analogous to a continuous second-order phase transition having strong criticality and anti-persistent behavior.

Distinguished seismological and electromagnetic features of the impending global failure: Did the 7/9/1999 M5.9 Athens earthquake come with a warning?

Clear VLF electromagnetic (EM) anomalies were detected prior to the Athens earthquake (EQ). We attempt to establish the hypothesis that these emissions were launched from the pre-focal area during micro-fracturing process. The spectral analysis in terms of fractal dynamics reveals that distinquished alterations in the associated scaling parameters emerge as the EQ is approached. These alterations suggests that the evolution of the Earth’s crust towards the “critical point” takes place not only in the seismological sense but also in the pre-fracture EM sense. VAN-signals and space-time TIR-signals were also detected prior to the Athens EQ. These anomalies, as well as the fault modeling of the Athens EQ obtained by interferometric combinations of ERS2 SAR images bring further support for the confidence in the reliability of our conclusions.