Sudden drop of fractal dimension of electromagnetic emissions recorded prior to significant earthquake

The variation of fractal dimension and entropy during a damage evolution process, especially approaching critical failure, has been recently investigated. A sudden drop of fractal dimension has been proposed as a quantitative indicator of damage localization or a likely precursor of an impending catastrophic failure. In this contribution, electromagnetic emissions recorded prior to significant earthquake are analysed to investigate whether they also present such sudden fractal dimension and entropy drops as the main catastrophic event is approaching. The pre-earthquake electromagnetic time series analysis results reveal a good agreement to the theoretically expected ones indicating that the critical fracture is approaching

Relation between seismicity and pre-earthquake electromagnetic emissions in terms of energy, information and entropy content

In this paper we show, in terms of Fisher information and approximate entropy, that the two strong impulsive kHz electromagnetic (EM) bursts recorded prior to the Athens earthquake (EQ) (7 September 1999, magnitude 5.9) present compatibility with the radar interferometry data and the seismic data analysis, which indicates that two fault segments were activated during Athens EQ. The calculated Fisher information and approximate entropy content ratios closely follow the radar interferometry result that the main fault segment was responsible for 80 % of the total energy released, while the secondary fault segment for the remaining 20 %. This experimental finding, which appears for the first time in the literature, further enhances the hypothesis for the seismogenic origin of the analyzed kHz EM bursts. © 2012 Author(s)

Analysis of electromagnetic pre-seismic emissions using Fisher information and Tsallis entropy

In this work, we investigate the dynamics of electromagnetic precursors, recorded prior to significant earthquakes in Greece. The analysis of these signals is performed using Fisher information, which is a powerful tool for investigating complex and non-stationary signals. Our results point to a decrease of the precursor complexity as the main tectonic event is approaching. The results are compatible to those derived using Tsallis entropy. The sensitivity of Fisher information and Tsallis entropy are compared on the basis of the features of the underlying fracture process which they reveal. © 2011 Elsevier B.V. All rights reserved

Sudden drop of fractal dimension of electromagnetic emissions recorded prior to significant earthquake

The variation of fractal dimension and entropy during a damage evolution process, especially approaching critical failure, has been recently investigated. A sudden drop of fractal dimension has been proposed as a quantitative indicator of damage localization or a likely precursor of an impending catastrophic failure. In this contribution, electromagnetic emissions recorded prior to significant earthquake are analysed to investigate whether they also present such sudden fractal dimension and entropy drops as the main catastrophic event is approaching. The pre-earthquake electromagnetic time series analysis results reveal a good agreement to the theoretically expected ones indicating that the critical fracture is approaching. © 2012 Springer Science+Business Media B.V

Dynamical analogy between epileptic seizures and seismogenic electromagnetic emissions by means of nonextensive statistical mechanics

The field of study of complex systems considers that the dynamics of complex systems are founded on universal principles that may be used to describe a great variety of scientific and technological approaches of different types of natural, artificial, and social systems. Several authors have suggested that earthquake dynamics and neurodynamics can be analyzed within similar mathematical frameworks. Recently, authors have shown that a dynamical analogy supported by scale-free statistics exists between seizures and earthquakes, analyzing populations of different seizures and earthquakes, respectively. The purpose of this paper is to suggest a shift in emphasis from the large to the small scale: our analyses focus on a single epileptic seizure generation and the activation of a single fault (earthquake) and not on the statistics of sequences of different seizures and earthquakes. We apply the concepts of the nonextensive statistical physics to support the suggestion that a dynamical analogy exists between the two different extreme events, seizures and earthquakes. We also investigate the existence of such an analogy by means of scale-free statistics (the Gutenberg-Richter distribution of event sizes and the distribution of the waiting time until the next event). The performed analysis confirms the existence of a dynamic analogy between earthquakes and seizures, which moreover follow the dynamics of magnetic storms and solar flares. © 2012 Elsevier B.V. All rights reserved

Linking electromagnetic precursors with earthquake dynamics: An approach based on nonextensive fragment and self-affine asperity models

Understanding the earthquake (EQ) preparation process in terms of precursory electromagnetic (EM) emissions has been an evolving field of multi-disciplinary research. EM emissions in a wide frequency spectrum ranging from kHz to MHz are produced by opening cracks, which can be considered as precursors of general fracture. An important feature, observed on both laboratory and geophysical scale, is that the MHz radiation systematically precedes the kHz one. Yet, the link between an individual EM precursor and a distinctive stage of the EQ preparation comprises a crucial open question. A recently proposed two-stage model on preseismic EM activity suggests that the MHz EM emission is due to the fracture of the highly heterogeneous system that surrounds the fault. The finally emerged kHz EM emission is rooted in the final stage of EQ generation, namely, the fracture of entities sustaining the system. In this work we try to further penetrate and elucidate the link of the precursory kHz EM activity with the last stage of EQ generation building on two theoretical models for EQ dynamics. First, the self-affine model states that an EQ is due to the slipping of two rough and rigid fractional Brownian profiles, one over the other, when there is an intersection between them. Second, the fragmentasperity model, rooted in a nonextensive Tsallis framework starting from first principles, consists of two rough profiles interacting via fragments filling the gap. In the latter approach, the mechanism of triggering EQ is established through the interaction of the irregularities of the fault planes and the fragments between them. This paper shows that these models of EQ dynamics can be linked with the detected kHz EM emission. In this framework of analysis of preseismic EM activity, we identify sufficient criteria that offer the possibility to discriminate whether a seismic shock is sourced in the fracture of fragments filling the gap between the rough profiles or in the fracture of "teeth" distributed across the fractional Brownian profiles that sustain the system. © 2011 Elsevier B.V. All rights reserved

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

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 (Kapiris et al., 2004; 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 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. © 2012 Author(s)

Foreshocks and Short-Term Hazard Assessment to Large Earthquakes using Complex Networks: the Case of the 2009 L’Aquila Earthquake

The monitoring of statistical network properties could be useful for the short-term hazard assessment of the occurrence of mainshocks in the presence of foreshocks. Using successive connections between events acquired from the earthquake catalog of the Istituto Nazionale di Geofisica e Vulcanologia (INGV) for the case of the L'Aquila (Italy) mainshock (<i>M</i>_w = 6.3) of 6 April 2009, we provide evidence that network measures, both global (average clustering coefficient, small-world index) and local (betweenness centrality) ones, could potentially be exploited for forecasting purposes both in time and space. Our results reveal statistically significant increases in the topological measures and a nucleation of the betweenness centrality around the location of the epicenter about 2 months before the mainshock. The results of the analysis are robust even when considering either large or off-centered the main event space windows