Critical features in electromagnetic anomalies detected prior to the L'Aquila earthquake

Electromagnetic (EM) emissions in a wide frequency spectrum ranging from kHz to MHz are produced by opening cracks, which can be considered as the so-called precursors of general fracture. We emphasize that the MHz radiation appears earlier than the kHz in both laboratory and geophysical scale. An important challenge in this field of research is to distinguish characteristic epochs in the evolution of precursory EM activity and identify them with the equivalent last stages in the earthquake (EQ) preparation process. Recently, we proposed the following two epochs/stages model: (i) The second epoch, which includes the finally emerged strong impulsive kHz EM emission is due to the fracture of the high strength large asperities that are distributed along the activated fault sustaining the system. (ii) The first epoch, which includes the initially emerged MHz EM radiation is thought to be due to the fracture of a highly heterogeneous system that surrounds the family of asperities. A catastrophic EQ of magnitude Mw = 6.3 occurred on 06/04/2009 in central Italy. The majority of the damage occurred in the city of L'Aquila. Clear kHz - MHz EM anomalies have been detected prior to the L'Aquila EQ. Herein, we investigate the seismogenic origin of the detected MHz anomaly. The analysis in terms of intermittent dynamics of critical fluctuations reveals that the candidate EM precursor: (i) can be described in analogy with a thermal continuous phase transition; (ii) has anti-persistent behaviour. These features suggest that the emerged candidate precursor could be triggered by microfractures in the highly disordered system that surrounded the backbone of asperities of the activated fault. We introduce a criterion for an underlying strong critical behavior.Comment: 8 pages, 6 figure

Pion production from a critical QCD phase

A theoretical scheme which relates multiparticle states generated in ultrarelativistic nuclear collisions to a QCD phase transition is considered in the framework of the universality class provided by the 3-D Ising model. Two different evolution scenarios for the QGP system are examined. The statistical mechanics of the critical state is accounted for in terms of (critical) cluster formation consistent with suitably cast effective action functionals, one for each considered type of expansion. Fractal properties associated with these clusters, characterizing the density fluctuations near the QCD critical point, are determined. Monte-Carlo simulations are employed to generate events, pertaining to the total system, which correspond to signals associated with unconventional sources of pion production

Abrupt transition in a sandpile model

We present a fixed energy sandpile model which, by increasing the initial energy, undergoes, at the level of individual configurations, a discontinuous transition. The model is obtained by modifying the toppling procedure in the Bak-Tang-Wiesenfeld (BTW) [Phys. Rev. Lett. 59, 381 (1987); Phys. Rev. A 38, 364 (1988)] rules: the energy transfer from a toppling site takes place only to neighboring sites with less energy (negative gradient constraint) and with a time ordering (asynchronous). The model is minimal in the sense that removing either of the two above-mentioned constraints (negative gradient or time ordering) the abrupt transition goes over to a continuous transition as in the usual BTW case. Therefore, the proposed model offers a unique possibility to explore at the microscopic level the basic mechanisms underlying discontinuous transitions. © 2006 The American Physical Society

Unimodal maps and order parameter fluctuations in the critical region

Recently it has been argued that the fluctuations of the order parameter of a system undergoing a second order transition, when considered as a time series, possess characteristic nonstochastic patterns at the critical point. These patterns can be described by a unimodal intermittent map (critical map) and are clearly distinguished from colored noise. In the present work we extend the method introduced in, in order to reveal universal properties in the deformation of the dynamics of the order parameter fluctuations when departing from the critical point. We show that the obtained systematic change in the order parameter fluctuation pattern can be observed in the critical region of thermal critical systems such as the mean field and the 3D Ising model. In addition, we consider the case of order parameter fluctuations near a tricritical point and we derive an associated characteristic deterministic behavior. A corresponding analysis in the Z (3) model confirms our results. Thus, the method of critical fluctuations introduced previously and generalized here, provides us with a classification scheme allowing for the characterization of temporal fluctuations in an observed time series in terms of critical phenomena. © 2007 The American Physical Society

Tsallis and Levy statistics in the preparation of an earthquake

Precursory fracture induced electromagnetic (EM) emissions, rooted in opening cracks and ranging from MHz to kHz, with the MHz appearing earlier, are produced and detected both at laboratory and geophysical scale. Recently, we have proposed the following two epochs/stages model of EQ generation: (i) The final kHz part is triggered by the fracture of high strength and large asperities that are distributed along the activated fault and sustain the system. (ii) The initial MHz part is thought to be due to the fracture of highly heterogeneous system that surrounds the family of asperities. Interestingly, the MHz EM time-series can be described in analogy with a thermal second order phase transition. Herein we focus on the MHz pre-seismic activity, and especially on the naturally arising question: what is the physical mechanism that organizes the heterogeneous system in its critical state? Combining ideas of Levy and Tsallis statistics and criticality with features hidden in the precursory MHz time-series we argue that a Levy walk type mechanism can organize the heterogeneous system to criticality. Based on a numerically produced truncated Levy walk, we propose a way to estimate in the stage of critical fluctuations: (i) the associated Levy index-a, which describes quantitatively the underlying Levy dynamics, and (ii) the range of values where the nonextesitive Tsallis index q is restricted. We also show that the kHz EM activity could not be described by a truncated Levy mechanism. This result further indicates an abrupt sweep of the population of asperities that sustain the system

Wavelet-based detection of scaling behavior in noisy experimental data

The detection of power laws in real data is a demanding task for several reasons. The two most frequently met are that (i) real data possess noise, which affects the power-law tails significantly, and (ii) there is no solid tool for discrimination between a power law, valid in a specific range of scales, and other functional forms like log-normal or stretched exponential distributions. In the present report we demonstrate, employing simulated and real data, that using wavelets it is possible to overcome both of the above-mentioned difficulties and achieve secure detection of a power law and an accurate estimation of the associated exponent. © 2020 American Physical Society

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

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 Earth's crust and the healthy heart's 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 heart's 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. © 2013 Author(s)

Magnetic field fluctuations in an array of randomly directed circular currents

We study the magnetic field fluctuations generated by an array of circular currents with axial symmetry. The fluctuations are induced via the random orientation of the current in each ring. By increasing the number of rings per unit length, we observe a transition from a continuous to a stratified spectrum of possible magnetic field values at a fixed location on the symmetry axis. A semi-analytical description of the properties characterising this transition is obtained revealing the competition between long range and short range contributions in this device. Our work provides a possibility to manipulate magnetic fields in a controllable and experimentally easily accessible manner, a task which can be of interest for accelerator and mesoscopic physics

Monitoring of a preseismic phase from its electromagnetic precursors

Fracture in disordered media is a complex problem for which a definitive physical and theoretical treatment is still lacking. We view earthquakes (EQâs) as large-scale fracture phenomena in the Earthâs heterogeneous crust. Our main observational tool is the monitoring of the microfractures, which occur in the prefocal area before the final breakup, by recording their kHz-MHz electromagnetic (EM) emissions, with the MHz radiation appearing earlier than the kHz. Two fundamental questions (unanswered yet) that scientists in this field ought to address are as follows. (i) Is there a way of estimating the time to global failure? (ii) Is the evolution towards global failure irreversible after the appearance of distinguishing features in the preseismic EM time series? We attempt to put forward physically powerful arguments with regard to answering these two basic questions. 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 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 [1] 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 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. © 2005 The American Physical Society