A multidisciplinary analysis for traces of the last state of earthquake generation in preseismic electromagnetic emissions

Abstract

Abstract. Many questions about earthquake (EQ) generation remain standing. Fracture induced electromagnetic (EM) fields allow real-time monitoring of damage evolution in materials during mechanical loading. An improved understanding of the EM precursors has direct implications for the study of EQ generation processes. An important challenge in this direction is to identify an observed anomaly in a recorded EM time series as a pre-seismic one and correspond this to a distinct stage of EQ generation. In previous papers Contoyiannis et al., 2005;Papadimitriou et al., 2008), we have shown that the last kHz part of the emerged precursory EM activity is rooted in the fracture of the backbone of asperities distributed along the activated fault, sustaining the system. The crucial character of this suggestion requires further support. In this work we focus on this effort. Tools of information theory (Fisher Information) and concepts of entropy (Shannon and Tsallis entropies) are employed. The analysis indicates that the launch of the EM precursor is combined with the appearance of a significantly higher level of organization, which is an imprint of a corresponding higher level of organization of the local seismicity preceding the EQ occurrence. We argue that the temporal evolution of the detected EM precursor is in harmony with the Intermittent Criticality approach of fracture by means of energy release, correlation length, Hurst exponent and a power-law exponent obtained from frequency-size distributions of seismic/electromagnetic avalanche events. The candidate precursory EM activity is also consistent with other Correspondence to: K. Eftaxias (ceftax@phys.uoa.gr) precursors from other disciplines. Thus, accumulated evidence, including laboratory experiments, strengthen the consideration that the emergence of the kHz EM precursor is sourced in the fracture of asperities indicating that EQ occurrence is expected.

Traces of Long-Memory in Pre-Seismic MHz Electromagnetic Time Series-Part 1: Investigation Through the R/S Analysis and Time-Evolving Spectral Fractals

“…Despite the amount of research and the conflicting related argumentation and analysis e.g. the recent publications [11][12][13][55][56][57][58] and the references therein, the restricted number of detected LF pre-seismic kHz bursts still bounds the analysis and, more or less, confines the predictive power of the kHz radiation. On the other hand, the MHz recordings collected from aboveground antennas, exhibit low EM noise and high predicting ability [6,7,31,54] as proved from more than 15 signals in the MHz range published so far.…”

On the puzzling feature of the silence of precursory electromagnetic emissions

“…First, based on a multidisciplinary statistical analysis, we have shown that the kHz EM time series is characterized by the following crucial symptoms of an extreme phenomenon (Potirakis et al, 2011Eftaxias, 2012, and references therein): (i) high organization or high information content. Tools of information theory, concepts of entropy rooted in the extensive and non-extensive Tsallis statistical mechanics, and measures of complexity have been used in order to identify the aforementioned features (Shannon nblock entropy, Shannon n-block entropy per letter, conditional entropy, entropy of the source, Kolmogorov-Sinai entropy, T entropy, approximate entropy -ApEn, Fisher information, correlation dimension, R/S analysis, detrended fluctuation analysis, fractal dimension, and finally fractal wavelet spectral analysis).…”

Fractal Analysis of Pre-Seismic Electromagnetic and Radon Precursors: A Systematic Approach

“…It is important to note also that some values above 2 can be observed. These are associated with persistency which has been interpreted by some researchers [10][11][12][13]70,71] as the most significant precursory sign of the inevitable phase of the earthquake occurrence. According to other researchers [11,16,17,43,44,[55][56][57][58] the most important sign is the change between anti-persistency and persistency -which can be observed in Figure 3a -whereas the majority of values is well above 1.5 -the case of Figure 4a, as aforementioned.…”

“…In addition, the LF emissions of the kHz range have been employed only in few cases (Kozani-Grevena, Athina and L'Aquila earthquakes) as seismic precursors. Despite the great research and argumentation [6,[10][11][12][13]70,71], the few detected signals still restrict the results and set them under scientific debate. Note that, based on several arguments, the investigators of these papers claim that the detected kHz anomalies refer to the inevitable last phase of the earthquake evolution.…”