K. Eftaxias

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.

Summary of the five principles suggested by Varotsos et al. [1996] and the additional questions raised in this debate

The present paper cannot be considered, either as a rebuttal to any participant, or our overview of the debate. Its publication became necessary due to the fact that various participants raised additional questions, i.e., beyond the points suggested by Varotsos et al. [1996]. We clarify these questions that concern the noise discrimination from our electrical recordings, the recent laboratory experiments which support the emission of electrical precursors, and the question on whether, or not, a retroactive adjustment of the VAN prediction parameters was made, after the period 1987–1989 discussed in this debate. We draw attention to the fact that a continuous 9 year (i.e., 1987–1995) sample of VAN predictions is now available. For the benefit of the reader, the present paper also summarizes the essence of the five Principles suggested by Varotsos et al. [1996] (as a consequence, attention is drawn to a correct definition of the success rate). This essence remains exactly the same as it was initially suggested, because we do not feel, after the debate, that the various contributions cast a sound doubt on the correctness of any of these Principles. The calculations which claim that VAN predictions can be ascribed to chance strongly violate these Principles; the incorrectness of these calculations is beyond any doubt, because they “reject” even an ideal earthquake prediction method. On the other hand, several well founded calculations convince that the VANs success (and alarm) rate is very far beyond chance. The study of this paper is highly recommended to the reader before going through the details of each of our individual Replies.

Current challenges for pre-earthquake electromagnetic emissions: shedding light from micro-scale plastic flow, granular packings, phase transitions and self-affinity notion of fracture process

Abstract. Are there credible electromagnetic (EM) potential earthquake (EQ) precursors? This a question debated in the scientific community and there may be legitimate reasons for the critical views. The negative view concerning the existence of EM potential precursors is enhanced by features that accompany their observation which are considered as paradox ones, namely, these signals: (i) are not observed at the time of EQs occurrence and during the aftershock period, (ii) are not accompanied by large precursory strain changes, (iii) are not accompanied by simultaneous geodetic or seismological precursors and (iv) their traceability is considered problematic. In this work, the detected candidate EM potential precursors are studied through a shift in thinking towards the basic science findings relative to granular packings, micron-scale plastic flow, interface depinning, fracture size effects, concepts drawn from phase transitions, self-affine notion of fracture and faulting process, universal features of fracture surfaces, recent high quality laboratory studies, theoretical models and numerical simulations. We try to contribute to the establishment of strict criteria for the definition of an emerged EM anomaly as a possibly EQ-related one, and to the explanation of potential precursory EM features which have been considered as paradoxes. A three-stage model for EQ generation by means of pre-EQ fracture-induced EM emissions is proposed. The claim that the observed EM potential precursors may permit a real-time and step-by-step monitoring of the EQ generation is tested.

Natural time analysis of critical phenomena: The case of pre-fracture electromagnetic emissions

Criticality of complex systems reveals itself in various ways. One way to monitor a system at critical state is to analyze its observable manifestations using the recently introduced method of natural time. Pre-fracture electromagnetic (EM) emissions, in agreement to laboratory experiments, have been consistently detected in the MHz band prior to significant earthquakes. It has been proposed that these emissions stem from the fracture of the heterogeneous materials surrounding the strong entities (asperities) distributed along the fault, preventing the relative slipping. It has also been proposed that the fracture of heterogeneous material could be described in analogy to the critical phase transitions in statistical physics. In this work, the natural time analysis is for the first time applied to the pre-fracture MHz EM signals revealing their critical nature. Seismicity and pre-fracture EM emissions should be two sides of the same coin concerning the earthquake generation process. Therefore, we also examine the corresponding foreshock seismic activity, as another manifestation of the same complex system at critical state. We conclude that the foreshock seismicity data present criticality features as well.

Criticality features in ULF magnetic fields prior to the 2011 Tohoku earthquake

The criticality of ULF (Ultra-low-frequency) magnetic variations is investigated for the 2011 March 11 Tohoku earthquake (EQ) by natural time analysis. For this attempt, some ULF parameters were considered: (1) Fh (horizontal magnetic field), (2) Fz (vertical magnetic field), and (3) Dh (inverse of horizontal magnetic field). The first two parameters refer to the ULF radiation, while the last parameter refers to another ULF effect of ionospheric signature. Nighttime (L.T. = 3 am ± 2 hours) data at Kakioka (KAK) were used, and the power of each quantity at a particular frequency band of 0.03–0.05 Hz was averaged for nighttime hours. The analysis results indicate that Fh fulfilled all criticality conditions on March 3–5, 2011, and that the additional parameter, Dh reached also a criticality on March 6 or 7. In conclusion, criticality has reached in the pre-EQ fracture region a few days to one week before the main shock of the Tohoku EQ.

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

Abstract. 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.

Subtraction of the telluric inductive component from van measurements

Abstract In order to understand the role of electrical properties in the vicinity of VAN stations, that have already been found to be appropriate for the collection of seismic electric signals (SES), a magnetotelluric (MT) investigation was carried out over of the entire VAN network. We present preliminary MT results for two stations of the VAN telemetric network in continental Greece. A procedure was developed by which a “real time” subtraction of the telluric inductive component from the electric measurements can be made. The resulting real time recording of the residual electric field allows a better identification of the SES. Such an example is presented for an SES that preceded a 5.5 magnitude earthquake in western Greece.

A new approach in the determination of characteristic directions of the geoelectric structure using Mohr circles

The use of Mohr circles into magnetotelluric (MT) intepretation was introduced by Lilley (Lilley, 1976). By plotting Zxx-rotated versus Zxy-rotated (real and imaginary parts) important information on the conductivity structure is obtained. In this paper Mohr circles are employed to reveal the directions of polarisation of the electric field. Furthermore, the following procedure for Mohr circle analysis is suggested: plotting Zxx -rotated versus Zyx-rotated (instead of Zxy-rotated) the principal axes system i.e., the strike angle, of the regional 2D structure can be resolved in some cases. The latter analysis is implemented to MT data from Ioannina area, in NW Greece. Results from other intepretation techniques applied to the same dataset, such as decomposition methods, tipper and induction arrows analysis, provide support for the validity of the conclusions reached.

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.

The Earth as a living planet: human-type diseases in the earthquake preparation process

Abstract. The new field of complex systems supports the view that a number of systems arising from disciplines as diverse as physics, biology, engineering, and economics may have certain quantitative features that are intriguingly similar. The Earth is a living planet where many complex systems run perfectly without stopping at all. The earthquake generation is a fundamental sign that the Earth is a living planet. Recently, analyses have shown that human-brain-type disease appears during the earthquake generation process. Herein, we show that human-heart-type disease appears during the earthquake preparation of the earthquake process. The investigation is mainly attempted by means of critical phenomena, which have been proposed as the likely paradigm to explain the origins of both heart electric fluctuations and fracture-induced electromagnetic fluctuations. We show that a time window of the damage evolution within the heterogeneous Earths crust and the healthy hearts electrical action present the characteristic features of the critical point of a thermal second-order phase transition. A dramatic breakdown of critical characteristics appears in the tail of the fracture process of heterogeneous system and the injured hearts electrical action. Analyses by means of Hurst exponent and wavelet decomposition further support the hypothesis that a dynamical analogy exists between the geological and biological systems under study.