Intermittent dynamics of critical pre-seismic electromagnetic fluctuations

摘要

It has been proposed that large earthquakes (EQ) are similar to critical phenomena. A new method for the research of the critical fluctuations and for the estimation of corresponding critical exponents is applied to the very high frequency (VHF) electromagnetic (EM) time-series recorder prior to the Kozani-Grevena (K-G) earthquake (EQ) in Greece (M_s = 6.6, on May 13, 1995). Such ruptures involve interactions between structures at many different scales. The system investigated might be considered as possessing two phases. The heterogeneous system first develops isolated cracks, which are nucleated in the weak regions (phase Ⅰ). As the applied strain increases, the cracks join, i.e., long-range correlations are developed between the cracks (phase Ⅱ). A possible phase transition in the fracture process could be elevated by the behavior of the long-range correlations. A basic question in this treatment concerns the critical window in which the transition from the first to the second phase takes place. We argue that the recently proposed intermittent dynamics of critical fluctuations (IDCF)-model indicates the presence of a precursory Critical Window of Stationarity during which the "short-range" correlations evolve to "long-range". The corresponding part of the electromagnetic (EM) time-series reveals: (ⅰ) A remarkable Stationarity, which can be studied in terms of a continuous phase transition at equilibrium. We show that the organization of the precursory EM phenomenon during the phase transition can be described in terms of intermittent dynamics of type Ⅰ. (ⅱ) A power law behavior in the distribution of suitably defined laminar regions and a power spectral density S(f) that can also be approximated by a power-law spectrum S(f) ～ f~(-β). The estimated critical exponents classify the reported critical phase transition to the 3D-Ising-universality class.