HR: 0800h
AN: T51B-1340    [Abstracts]
TI: Extracting preseismic VLF-VHF electromagnetic signatures: A possible way in which the critical regime is reached as the earthquake approaches
AU: Eftaxias, K
EM: ceftax@phys.uoa.gr
AF: Physics Department, University of Athens, Panepistimiopolis, Zografos, Athens, 15784 Greece
AU: Kapiris, P
EM: pkapiris@cc.uoa.gr
AF: Physics Department, University of Athens, Panepistimiopolis, Zografos, Athens, 15784 Greece
AU: Karamanos, K
EM: kkaraman@ulb.ac.be
AF: Center for Nonlinear Phenomena and Complex Systems, Universite Libre de Bruxelles, CP231 Campus Plaine, Bruxelles, 1050 Belgium
AU: * Balasis, G
EM: gbalasis@gfz-potsdam.de
AF: GeoForschungsZentrum Potsdam, Telegrafenberg, Potsdam, D-14473 Germany
AU: Peratzakis, A
EM: thperatz@phys.uoa.gr
AF: Physics Department, University of Athens, Panepistimiopolis, Zografos, Athens, 15784 Greece
AB: We view earthquakes EQ's as large-scale fracture phenomena in the Earth's heterogeneous crust. Our main observational tool is the monitoring of the microfractures, which occur in the prefocal area before the final break-up, by recording their kHz-MHz electromagnetic (EM) emissions, with the MHz radiation appearing earlier than the kHz. Our model of the focal area consists of a backbone of strong and almost homogeneous large asperities that sustains the system and a strongly heterogeneous medium that surrounds the family of strong asperities. We distinguish two characteristic epochs in the evolution of precursory EM activity and identify them with the equivalent critical stages in the EQ preparation process. Our approach will be in terms of critical phase transitions in statistical physics, drawing on recently published results. We obtain two major results. First, the initial MHz part of the preseismic EM emission, which has antipersistent behavior, is triggered by microfractures in the highly disordered system that surrounds the essentially homogeneous "backbone asperities" within the prefocal area and could be described in analogy with a thermal continuous phase transition. However, the analysis reveals that the system is gradually driven out of equilibrium. Considerations of the symmetry-breaking and ``intermittent dynamics of critical fluctuations" method estimate the time beyond which the process generating the preseismic EM emission could continue only as a nonequilibrium instability. Second, the abrupt emergence of strong kHz EM emission in the tail of the precursory radiation, showing strong persistent behavior, is thought to be due to the fracture of the high strength ``backbones". The associated phase of the EQ nucleation is a nonequilibrium process without any footprint of an equilibrium thermal phase transition. The family of asperities sustains the system. Physically, the appearance of persistent properties may indicate that the process acquires a self-regulating character and to a great degree the property of irreversibility, one of the important components of predictive capability. We address the role of the order of material heterogeneity on the transition from antipersistent to persistent behavior. We gratefully acknowledge financial support by the European Union Program EPEAEK/PYTHAGORAS 70/3/7357 P. Kapiris, K. Eftaxias and T. Chelidze, Electromagnetic Signature of Prefracture Criticality in Heterogeneous Media, Physical Review Letters, 92(6), 065702, 2004. P. Kapiris, J. Polygiannakis, X. Li, X. Yao and K. Eftaxias, Similarities in precursory features in seismic shocks and epileptic seizures, Europhysics Letters 69, 657-663, 2005. P. Kapiris, K. Nomicos, G. Antonopoulos, J. Polygiannakis, K. Karamanos, J. Kopanas, A. Zissos, A. Peratzakis and K. Eftaxias, Distinguished seismological and electromagnetic features of the impending global failure: did the 7/9/1999 M5.9 Athens earthquake come with a warning?, Earth Planets and Space, 57, 215-230, 2005 Y. Contoyiannis, P. Kapiris and K. Eftaxias, A Monitoring of a Pre-Seismic Phase from its Electromagnetic Precursors, Physical Review E, 71, 066123, 2005. K. Karamanos, A. Peratzakis, P. Kapiris, S. Nikolopoulos, J. Kopanas, and K. Eftaxias, Extracting preseismic electromagnetic signatures in terms of symbolic dynamics, Nonlinear Processes in Geophysics, (in press), 2005.
DE: 1640 Remote sensing (1855)
DE: 3902 Creep and deformation
DE: 7209 Earthquake dynamics (1242)
DE: 8164 Stresses: crust and lithosphere
SC: Tectonophysics [T]
MN: Fall Meeting 2005