2,630 research outputs found
Order parameter fluctuations of seismicity and Tsallis entropic index q variation before large earthquakes in Japan
No full textΤhe seismicity of Japan from January 1, 1984 to March 11, 2011 (the occurrence time of the M9 Tohoku earthquake) is analyzed in a new time domain[1] called natural time χ. In this domain, an order parameter of seismicity can be defined[2]. We find that the fluctuations of this order parameter exhibit 15 characteristic minima that are followed[3] by the occurrence of large earthquakes 1 to 3 months later. Six (out of 15) of these earthquakes have magnitude 7.6 or larger. By employing event coincidence analysis[4], we show that the probability to achieve such a result is far beyond chance. In addition, we investigate the change of the Tsallis entropic index q [5,6] before these six earthquakes which are all shallow earthquakes of magnitude 7.6 or larger that occurred during the study period.[1] Varotsos, P.A.; Sarlis, N.V.; Skordas, E.S. Natural Time Analysis: The new view of time. Precursory Seismic Electric Signals, Earthquakes and other Complex Time-Series; Springer-Verlag: Berlin Heidelberg, 2011. doi:10.1007/978-3-642-16449-1.[2] Varotsos, P.A.; Sarlis, N.V.; Tanaka, H.K.; Skordas, E.S. Similarity of fluctuations in correlated systems: The case of seismicity. Physical Review E 2005, 72, 041103. doi:10.1103/physreve.72.041103.[3] Sarlis, N.V.; Skordas, E.S.; Varotsos, P.A.; Nagao, T.; Kamogawa, M.; Tanaka, H.; Uyeda, S. Minimum of the order parameter fluctuations of seismicity before major earthquakes in Japan. Proc. Natl. Acad. Sci. USA 2013, 110, 13734–13738. doi: 10.1073/pnas.1312740110[4] Donges, J.; Schleussner, C.F.; Siegmund, J.; Donner, R. Event coincidence analysis for quantifying statistical interrelationships between event time series. Eur. Phys. J. Spec. Top. 2016, 225, 471–487. doi: 10.1140/epjst/e2015-50233-y[5] Tsallis, C. Possible generalization of Boltzmann-Gibbs statistics. J. Stat. Phys. 1988, 52, 479–487. doi: 10.1007/BF01016429[6] Tsallis, C. Introduction to Nonextensive Statistical Mechanics; Springer: Berlin/Heidelberg, Germany, 2009. doi: 10.1007/978-0-387-85359-
M W9 Tohoku earthquake in 2011 in Japan: precursors uncovered by natural time analysis
No full textThis paper reviews the precursory phenomena of the 2011 MW9 Tohoku earthquake in Japan that emerge solely when we analyze the seismicity data in a new time domain termed natural time. If we do not consider this analysis, important precursory changes cannot be identified and hence are missed. Natural time analysis has the privilege that enables the introduction of an order parameter of seismicity. In this frame, we find that the fluctuations of this parameter exhibit an unprecedented characteristic change, i.e., an evident minimum, approximately two months before Tohoku earthquake, which strikingly is almost simultaneous with unique anomalous geomagnetic field variations recorded mainly on the z component. This is consistent with our finding that such a characteristic change in seismicity appears when a seismic electric signal (SES) activity of the VAN method (from the initials of Varotsos, Alexopoulos, Nomicos) initiates, and provides a direct confirmation of the physical interconnection between SES and seismicity. © 2017, The Author(s)
On the recent advances in the study of seismic electric signals (VAN method)
No full textSeismic electric signals (SES) are low frequency (≤1 Hz) changes of the electric field of the earth that have been first observed in Greece [Varotsos, P., Alexopoulos, K., Nomicos, K., 1981a. Seismic electric currents. Pract. Athens Acad. 56, 277-286; Varotsos, P., Alexopoulos, K., Nomicos, K., 1981b. Seven-hour precursors to earthquakes determined from telluric currents. Pract. Athens Acad. 56, 417-433; Varotsos, P., Alexopoulos, K., 1984a. Physical properties of the variations of the electric field of the earth preceding earthquakes, I. Tectonophysics 110, 73-98; Varotsos, P., Alexopoulos, K., 1984b. Physical properties of the variations of the electric field of the earth preceding earthquakes, II. Tectonophysics 110, 99-125] to precede earthquakes, with a lead time from several hours to a couple of months. Here, we review the recent advances on the SES observation and analysis, main points of which are the following: First, at epicentral distances of the order of 100 km, the SES electric field precedes markedly the time-derivative of the magnetic field; this finds applications in the determination of the epicenter of the impending earthquake and in the distinction between true SES and noise emitted from artificial sources. Second, a detectable difference in the time evolutions of the electric field components of SES exists, which can also be used for the determination of the epicenter of the impending earthquake. Third, the analysis of SES is significantly advanced in a recently introduced [Varotsos, P., Sarlis, N., Skordas, E., 2001. Spatio-temporal complexity aspects on the interrelation between seismic electric signals and seismicity. Pract. Athens Acad. 76, 294-321; Varotsos, P., Sarlis, N., Skordas, E., 2002a. Long-range correlations in the electric signals that precede rupture. Phys. Rev. E 66, 011902] new time-domain, termed as natural time domain. This has been inspired from the theory of critical phenomena, which has been suggested long ago by our group. The natural time-domain, beyond other applications in diverse fields, enables the distinction of similar looking electric signals that are emitted from systems of different dynamics as well as provides a better estimation for the time window of an impending mainshock. The spectral content of the seismic activity in natural time, evolves consecutively in time upon the occurrence of every new event, and finally coincides to that of the SES a few hours to a few days before the mainshock, thus allowing the estimation of the occurrence time of the impending mainshock with an accuracy that was not hitherto available. © 2006 Elsevier Ltd. All rights reserved
On the Motivation and Foundation of Natural Time Analysis: Useful Remarks
No full textSince its introduction in 2001, natural time analysis has been applied to diverse fields with remarkable results. Its validity has not been doubted by any publication to date. Here, we indicate that frequently asked questions on the motivation and the foundation of natural time analysis are directly answered if one takes into account the following two key points that we have considered as widely accepted when natural time analysis was proposed: first, the aspects on the energy of a system forwarded by Max Planck in his Treatise on Thermodynamics; second, the theorem on the characteristic functions of probability distributions which Gauss called Ein Schönes Theorem der Wahrscheinlichkeitsrechnung (beautiful theorem of probability calculus). The case of the time series of earthquakes and of the precursory Seismic Electric Signals are discussed as typical examples. © 2016 Varotsos et al
On the difference in the rise times of the two SES electric field components
No full textThe study of low frequency signal transmission in conductive media, reveals that the electric and magnetic fields follow diffusion type equations, in a previous paper (Varotsos et al. 1)) experimental evidence was forwarded that for epicentral distances of the order of 100 km, the SES electric field variations precede those of the magnetic ones by a time of the order of 1 sec. In the present paper, we present evidence that this peculiarity still pertains (but to a smaller extent), when studying the differences in the components of the electric field. This cannot be probably observed in the scale of laboratory measurements, lying usually within the error bars of the current experimental facilities. A tentative theoretical justification, termed as τ-approximation, is presented which accounts for the measurements of electric field components. The present findings can provide a unique tool for the discrimination between remote and nearby sources by using data from electric measurements alone
Identifying the occurrence time of an impending major earthquake: a review
No full textThe procedure through which the occurrence time of an impending major earthquake can be determined is reviewed in the light of the recent advances. This can be achieved by analyzing in natural time the seismicity in the candidate area. To apply this general procedure, we need two important elements: first, to know when we should start the analysis, i.e., set the natural time equal to zero. This is the time at which the system enters the critical stage. Second a reliable estimation of the candidate epicentral area. If geoelectrical measurements are taken and the VAN method (after the initials of the three researchers Varotsos, Alexopoulos and Nomicos) is applied, both these elements become available upon the recording of a precursory Seismic Electric Signals (SES) activity, because its initiation marks the time when the system enters the critical stage, and in addition the SES data enable the determination of the epicentral area of the impending mainshock. On the other hand, if geoelectrical data are lacking, we make use of the following two recent findings by means of natural time analysis: First, the fluctuations of the order parameter of seismicity in a large area exhibit a minimum a few months before a major earthquake almost simultaneously with the initiation of an SES activity. Second, a spatiotemporal study of this minimum unveils an estimate of the epicentral area of the impending major earthquake. Two examples are given that refer to the strongest earthquakes that occurred in Greece and Japan during the last 3 decades, i.e., the MW6.9 earthquake in southwestern Greece on 14 February 2008 and the MW9.0 Tohoku earthquake in Japan on 11 March 2011. © 2017, The Author(s)
Seismic electric signals in seismic prone areas
No full textThe Varotsos-Alexopoulos-Nomicos (VAN) method of short-term earthquake prediction was introduced in the 1980s. The VAN method enables estimation of the epicenter, magnitude and occurrence time of an impending earthquake by observing transient changes of the electric field of the Earth termed seismic electric signals (SES). Here, we present a few examples of SES observed in various earthquake prone areas worldwide. © 2018, Earthquake Science. All rights reserved
Long-range correlations in the electric signals that precede rupture: Further investigations
No full textThe correlations within the time series of the seismic electric signal (SES) activities have been studied in a previous paper [P. Varotsos, N. Sarlis, and E. Skordas, Phys. Rev. E 66, 011902 (2002)]. Here, we analyze the time series of successive high- and low-level states’ durations. The existence of correlation between the states is investigated by means of Hurst and detrended fluctuation analysis (DFA). The multifractal DFA (MF-DFA) is also employed. The results point to a stronger correlation, and hence longer memory, in the series of the high-level states. Furthermore, an analysis in the “natural” time domain reveals that certain power spectrum characteristics seem to distinguish SES activities from “artificial” (man-made) electric noises. More precisely, for natural frequencies [Formula presented] the curves of the SES activities and artificial noises lie above and below, respectively, that of the “uniform” distribution (UD). A classification of these two types of electric signals (SES activities, artificial noises), cannot be achieved on the basis of the values of the power-law exponents alone, if the Hurst analysis, DFA, and MF-DFA are applied to the original time series. The latter two methods, however, seem to allow a distinction between the SES activities and artificial noises when treating them (not in conventional the time frame, but) in the natural time domain. To further test the techniques, a time series produced by another system was examined. We chose a signal of ion current fluctuations in membrane channels (ICFMCs). The following conclusions, among others, have been obtained: First, the power spectrum analysis in the natural time domain shows that the ICFMC curve almost coincides (in the range [Formula presented] with that of the UD, and hence ICFMC lies just in the boundary between the SES activities and artificial noises. Second, MF-DFA indicates monofractality for the ICFMCs with a generalized Hurst exponent [Formula presented] in the range 7–70 ms. © 2003 The American Physical Society
Influence of anharmonicity on some transport properties of AgBr
No full textRecent measurements show that the migration entropy for Na+ diffusion in AgBr is 5.1 kB. This value is appreciably higher than that found in alkali halides for cation vacancy motion. A plausible explanation of this fact is proposed. Furthermore, a calculation is made of the migration volumes for the vacancy and interstitial motion of Ag + in AgBr which leads to values comparable with experiment.Des mesures récentes montrent que l'entropie de migration pour la diffusion de Na+ dans AgBr est de 5,1 kB. Cette valeur est notablement supérieure à celle trouvée dans les halogénures alcalins pour le mouvement des lacunes cationiques. Une explication plausible est, de ce fait, proposée. De plus, on a fait un calcul des volumes de migration pour le mouvement des lacunes et interstitiels de Ag+ dans AgBr qui mène à des valeurs comparables aux expériences
Simple drag prediction strategies for an Autonomous Underwater Vehicle’s hull shape
No full textThe range of an AUV is dictated by its finite energy source and minimising the energy consumption is required to maximise its endurance. One option to extend the endurance is by obtaining the optimum hydrodynamic hull shape with balancing the trade-off between computational cost and fluid dynamic fidelity. An AUV hull form has been optimised to obtain low resistance hull. Hydrodynamic optimisation of hull form has been carried out by employing five parametric geometry models with a streamlined constraint. Three Genetic Algorithm optimisation procedures are applied by three simple drag predictions which are based on the potential flow method. The results highlight the effectiveness of considering the proposed hull shape optimisation procedure for the early stage of AUV hull desig
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