Evolving towards a critical point: A possible electromagnetic way in which the critical regime is reached as the rupture approaches

International audienceIn analogy to the study of critical phase transitions in statistical physics, it has been argued recently that the fracture of heterogeneous materials could be viewed as a critical phenomenon, either at laboratory or at geophysical scales. If the picture of the development of the fracture is correct one may guess that the precursors may reveal the critical approach of the main-shock. When a heterogeneous material is stretched, its evolution towards breaking is characterized by the appearance of microcracks before the final break-up. Microcracks produce both acoustic and electromagnetic(EM) emission in the frequency range from VLF to VHF. The microcracks and the associated acoustic and EM activities constitute the so-called precursors of general fracture. These precursors are detectable not only at laboratory but also at geophysical scales. VLF and VHF acoustic and EM emissions have been reported resulting from volcanic and seismic activities in various geologically distinct regions of the world. In the present work we attempt to establish the hypothesis that the evolution of the Earth's crust towards the critical point takes place not only in a mechanical but also in an electromagnetic sense. In other words, we focus on the possible electromagnetic criticality, which is reached while the catastrophic rupture in the Earth's crust approaches. Our main tool is the monitoring of micro-fractures that occur before the final breakup, by recording their radio-electromagnetic emissions. We show that the spectral power law analysis of the electromagnetic precursors reveals distinguishing signatures of underlying critical dynamics, such as: (i) the emergence of memory effects; (ii) the decrease with time of the anti-persistence behaviour; (iii) the presence of persistence properties in the tail of the sequence of the precursors; and (iv) the acceleration of the precursory electro-magnetic energy release. Moreover, the statistical analysis of the amplitudes of the electromagnetic fluctuations reveals the breaking of the symmetry as the theory predicts. Finally, we try to answer the question: how universal the observed electromagnetic critical behaviour of the failing system is

First-order transition features of the 3D bimodal random-field Ising model

Two numerical strategies based on the Wang-Landau and Lee entropic sampling schemes are implemented to investigate the first-order transition features of the 3D bimodal ($\pm h$) random-field Ising model at the strong disorder regime. We consider simple cubic lattices with linear sizes in the range $L=4-32$ and simulate the system for two values of the disorder strength: $h=2$ and $h=2.25$. The nature of the transition is elucidated by applying the Lee-Kosterlitz free-energy barrier method. Our results indicate that, despite the strong first-order-like characteristics, the transition remains continuous, in disagreement with the early mean-field theory prediction of a tricritical point at high values of the random-field.Comment: 19 pages, 6 figures, slightly extended version as accepted for publicatio

Enhanced magnetic properties in antiferromagnetic-core/ferrimagnetic-shell nanoparticles

Bi-magnetic core/shell nanoparticles are gaining increasing interest due to their foreseen applications. Inverse antiferromagnetic(AFM)/ferrimagnetic(FiM) core/shell nanoparticles are particularly appealing since they may overcome some of the limitations of conventional FiM/AFM systems. However, virtually no simulations exist on this type of morphology. Here we present systematic Metropolis Monte Carlo simulations of the exchange bias properties of such nanoparticles. The coercivity, H C, and loop shift, H ex, present a non-monotonic dependence with the core diameter and the shell thickness, in excellent agreement with the available experimental data. Additionally, we demonstrate novel unconventional behavior in FiM/AFM particles. Namely, while H C and H ex decrease upon increasing FiM thickness for small AFM cores (as expected), they show the opposite trend for large cores. This presents a counterintuitive FiM size dependence for large AFM cores that is attributed to the competition between core and shell contributions, which expands over a wider range of core diameters leading to non-vanishing H ex even for very large cores. Moreover, the results also hint different possible ways to enhance the experimental performance of inverse core/shell nanoparticles for diverse applications

VAN, Candidacy and validation with the latest laws of the game and Precursor candidacy and validation, The VAN case so far - Reply to rebuttal to replies I and II

Mulargia et al. [1996] claim that earthquakes (EQs) can be ‘’predicted” (in retrospective) ‘’much more efficiently than VAN” using a ‘’rule”, they obtained from PDE catalogue. We show that this claim is undoubtedly wrong. Their ‘’rule” issues a great number of false alarms, which exceeds that of the ‘’predicted” EQs (mainly aftershocks) by a factor larger than 10. The errors diagram recommended by Keilis-Borok [1996], reveals that Mulargia et al.’s [1996] ‘’rule” corresponds to a non-meaningful algorithm; on the other hand, this diagram reflects that VAN is meaningful

Probability of chance correlations of earthquakes with predictions in areas of heterogeneous seismicity rate: The VAN case - Reply

All conclusions of Wyss and Allmann [1996] (hereafter cited as WA) are wrong, because their methodology is false. For example, WA’s main conclusion reads: ‘’the probability [P] that the observed correlations of [VAN] predictions with earthquakes (...11 out of 23 attempts) was due to chance is estimated as... 96%...” However, when following WA’s procedure exactly, and assuming that all 23 predictions (out of 23 attempts) are correct, we find a paradox, i.e., values of the probability P larger than unity. In view of this example, any further discussion on WA’s claims becomes unnecessary. However, we proceed to detailed replies, point by point, in order to show that WA have also made several mistakes and major misinterpretations of the true content of VAN’s statements. Characteristic examples of the various misinterpretations (and mistakes) made by WA include: (i) a direct comparison of predicted magnitude values with M(s);(PDE), while VAN had clearly stated that the magnitude values mentioned in the predictions correspond to M(s)(ATH), i.e., to M(L)+0.5. Such a comparison is not allowed because M(L)+0.5 significantly differs (i.e., on the average by 1.0 unit) from M(s)(PDE), (ii) an addition (or deletion) of critical wording to the VAN statements (and predictions) so that they distort VAN’s true meaning, (iii) the use of 22 day prediction time window in the large majority of predictions which, however, correspond to single SES (and hence to an 11 days prediction time window), (iv) an incorrect statement that Varotsos et al. [1993a,b] define the acceptable uncertainty as Delta M less than or equal to 1.0, while VAN repeatedly published that a prediction is accepted as successful only when Delta M less than or equal to 0.7, (v) an erroneous claim that when using SI-NOA ‘’12 out of 22 VAN predictions fail to conform to the error limits,” while the reader can easily check that only 6 (or 7) out of 23 cases deviate from the error limits. Furthermore, WA grossly overestimated the number of the earthquakes (EQs) that should have been predicted, i.e., while VAN clearly stated that predictions are issued only when the expected magnitude is larger than (or equal to) 5.0 units, WA erroneously demand that VAN should predict all EQs with M(s) greater than or equal to 4.3 or M(s) greater than or equal to 4.0. Hence they characterize as a ‘’missed earthquake” any event with M(s) greater than or equal to 4.3 (or M(s) greater than or equal to 4.0 respectively)for which prediction was not issued. Last but not least, we recall that Wyss and Baer [1981] published long term predictions in Greece (for the same time period discussed in this debate) -referring to expected EQs with magnitude 7.75- which turned out to be completely unsuccessful

Understanding the fracture phenomena in inhomogeneous rock samples and ionic crystals, by monitoring the electromagnetic emission during their deformation

The electromagnetic (EM) activity observed before earthquakes has received a lot of attention of the scientific community. Various aspects have been proposed in order to interpret these observed EM phenomena, and the most plausible interpretation is based on the microfracturing electrification. The scope of this paper is the laboratory investigation of this aspect by carrying out laboratory experiments for the detection of EM emission from rock samples and other crystalline materials under uniaxial compression. This paper reveals physical processes that occur in the compressed material, in the microscopic scale, resulting in the observed macroscopic EM phenomena. It was experimentally verified that (a) an abrupt microcracking event generates temporally varying EM field, not only in piezoelectric materials but in non-piezoelectric ionic crystals as well. This implies that the EM generation mechanism is not necessarily of piezoelectric origin. (b) In the presence of a large number of microfractures, each one of them essentially acts as an elementary emission source and thus the resulting spectrum is correlated to the spectral content of each individual pulse and (c) the microcracking process might display criticality. © 2004 Elsevier Ltd. All rights reserved

Inaccuracies in seismicity and magnitude data used by Varotsos and co-workers - Reply

A direct comparison of the predicted magnitude values (M(pred)) to the actual magnitude values (M(EQ)) of the earthquakes (EQs) is allowed only when both values, i.e., M(pred) and MEQ, refer to the same scale. In view of the fact that the Seismological Institute of the National Observatory of Athens (SI-NOA) publicly announces as MEQ the M(L)+0.5 value (Where ML the local magnitude), VAN made it clear long ago, that the predicted values M(pred) (after a proper calibration) referred to M(L)+0.5. Therefore, a self-consistent evaluation of VAN-predictions should consist of a direct comparison of M,red with the actual M(L)+0.5. Unfortunately, Wyss [1996] confuses the discussion by proceeding to a direct comparison of M(pred) With M(s)(PDE); this is not allowed because the values of M(L)+0.5 exceed, on the average, M(s)(PDE) by 1.0 unit. An additional confusion arises from the fact that the relation suggested by Hamada [1993], i.e., M(L)+0.5=m(b)+0.3, is misinterpreted by Wyss as saying M(s)(PDE)=m(b)+0.3. These two alterations by Wyss reveal that his Figures 1 and 2 are erroneous. Wyss [1996] also criticizes VAN, because (in an early publication) Varotsos et al. [1981b] used the Preliminary Bulletin of SI-NOA, instead of the final one. First of all, the final bulletin could not be used by VAN at that time, because it appeared (more than one year) after the publication of the paper by Varotsos et al. [1981b]. Secondly, the correlation between SESs and EQs is evident,when we use consistently, either the preliminary, or the final bulletin of SI-NOA. On the other hand, Wyss [1996] claims that he could not find any correlation between EQs and SESs; we show that this is due to the fact that Wyss included, in his study, small EQs that occurred several hundreds km away from the measuring VAN station (i.e., in Albania, western Turkey, etc.), but he simultaneously deleted the small magnitude EQs that occurred very close to that station. Wyss’s procedure is, of course, not acceptable and hence his Appendix B is wrong. Furthermore, Wyss’s claim that VAN added 25% of events to the list, is shown to be untrue. Beyond the unusual fact that Wyss quotes ‘’VAN’s statements” that have never been published by VAN, the following is also noted: although Wyss [1996] uses quotation marks (in order to indicate that he reproduced exactly what VAN said), he adds critical wording to VAN statements and hence their true meaning is drastically changed. For example, Wyss states: ‘’Varotros et al. [l981a] had first formulated that SESs ‘’occurred a few minutes before each earthquake [related to that SES]” (Varotsos et al. [1981a]).” Thus, Wyss leads the reader to the wrong conclusion that VAN initially claimed that SES have a lead time of a few minutes, and that VAN changed it later. However, we show that this lead time (published by VAN) referred to another the of precursor, and not to SES, but the words in brackets (which are added by Wyss) alter the true meaning of our statement

VAN, Candidacy and validation with the latest laws of the game and Precursor candidacy and validation, The VAN case so far - Reply to the re-rebuttal to the reply

In our preceding Reply, we indicated that Mulargia et al. [1996] made (beyond their obvious error that they checked their predictive ‘’rule” only for its ‘’learning period”) a number of mistakes; we also showed that their ‘’rule” does not correspond to a meaningful algorithm. Mulargia et al.’s Re-Rebuttal admits that Mulargia er al. [1996] actually made a number of mistakes due to a ‘’bug in the [Mulargia et al.’s, 1996] code”, which not only omitted from their list two (non-”predicted” by their ‘’rule”) ‘’large” earthquakes (EQs), but also scored two missed (”large”) EQs as successfully ‘’predicted”. Furthermore, they now admit that Mulargia et al.’s [1996] rule ‘’is certainly not an efficient predictor”, in contrast to their earlier claims. The main issue of our present Reply is to point out that Mulargia et al., in their Re-Rebuttal, now make a very serious error, when constructing the errors diagram: they confuse predictions of main shocks with those of the aftershocks, and hence incorrectly conclude that one can ‘’build very simple, zero-cost predictive tools superior to VAN”. We show that their erroneous procedure leads to the following paradox: when a ‘’rule” (which fails to predict all main shocks) correctly ‘’predicts” a number of aftershocks, one can (incorrectly) claim that he found a predictive ‘’rule” superior to the ideal prediction method; the latter (i.e., the ideal one), in spite of the fact that it predicts all main shocks, is (incorrectly) obtained to correspond to ‘’random predictions”

EM anomalies before the Kozani earthquake: A study of their behavior through laboratory experiments

Strong electromagnetic (EM) anomalies have been detected, from MHz to kHz, prior to the three destructive earthquakes occurred during 1995-1999 in Greece. The observed sequence of EM anomalies before the Kozani-Grevena earthquake (K-G) of Ms = 6.6 on May 13, 1995 showed some important characteristics: (i) an increasing electromagnetic emission rate; (ii) an emergence of lower kHz frequencies with large amplitudes at the tail of the MHz electromagnetic anomaly; (iii) an electromagnetic quiescence approximately a few hours before the earthquake and (iv) a total absence of EM anomalies during the aftershock period. All these features are compatible with those reported by other authors. This sequence of the field observed EM signals revealed, in terms of emission pattern, similarities to the laboratory acoustic (AE) emissions during different stages of failure preparation process in rocks. Copyright 2002 by the American Geophysical Union

Degradation of emerging contaminants from water under natural sunlight: The effect of season, pH, humic acids and nitrate and identification of photodegradation by-products

Both photodegradation and hydrolysis of non-steroidal anti-inflammatory drugs (NSAIDs) and endocrine disrupting chemicals (EDCs) were investigated in order to evaluate their photochemical fate in aquatic environment and to assess the effect of season and specific characteristics of water (pH, humic acids and nitrate concentration) on the removal of target EDCs and NSAIDs through photodegradation. An additional objective was the identification of the photodegradation by-products of specific NSAIDs and their dependence on irradiation time. Selected compounds' transformation was investigated under natural sunlight radiation while control experiments were conducted in the dark. As expected, most of compounds' degradation rate decreased with decreasing light intensity between two different experimental periods. Most of the tested compounds exhibited different rates of degradation during direct and indirect photolysis. The degradation rate of the selected compounds increased in the presence of NO3- and the photodegradation rate was higher for some compounds in alkaline than in acidic solution. The effect of humic acids' presence in the water depends on the absorbance spectrum of the compound and the produced photosensitizers. More specifically, humic acids act as inner filter toward most of the selected NSAIDs and as photosensitizers toward most of the EDCs. The results of the irradiation experiments in the presence of both humic acids and NO3-, indicate that the direct photolysis is much more efficient than indirect photochemical processes. Finally, several degradation by-products of ketoprofen and diclofenac were identified in the samples, exposed to sunlight. The dependence of these by-products on radiation time is also demonstrated. © 2015 Elsevier Ltd