425 research outputs found
Similarity of fluctuations in correlated systems: The case of seismicity
We report a similarity of fluctuations in equilibrium critical phenomena and
non-equilibrium systems, which is based on the concept of natural time. The
world-wide seismicity as well as that of San Andreas fault system and Japan are
analyzed. An order parameter is chosen and its fluctuations relative to the
standard deviation of the distribution are studied. We find that the scaled
distributions fall on the same curve, which interestingly exhibits, over four
orders of magnitude, features similar to those in several equilibrium critical
phenomena (e.g., 2D Ising model) as well as in non-equilibrium systems (e.g.,
3D turbulent flow).Comment: 5 pages, 9 figure
Natural entropy fluctuations discriminate similar looking electric signals emitted from systems of different dynamics
Complexity measures are introduced, that quantify the change of the natural
entropy fluctuations at different length scales in time-series emitted from
systems operating far from equilibrium. They identify impending sudden cardiac
death (SD) by analyzing fifteen minutes electrocardiograms, and comparing to
those of truly healthy humans (H). These measures seem to be complementary to
the ones suggested recently [Phys. Rev. E {\bf 70}, 011106 (2004)] and
altogether enable the classification of individuals into three categories: H,
heart disease patients and SD. All the SD individuals, who exhibit critical
dynamics, result in a common behavior.Comment: Published in Physical Review
Effect of significant data loss on identifying electric signals that precede rupture by detrended fluctuation analysis in natural time
Electric field variations that appear before rupture have been recently
studied by employing the detrended fluctuation analysis (DFA) as a scaling
method to quantify long-range temporal correlations. These studies revealed
that seismic electric signals (SES) activities exhibit a scale invariant
feature with an exponent over all scales investigated
(around five orders of magnitude). Here, we study what happens upon significant
data loss, which is a question of primary practical importance, and show that
the DFA applied to the natural time representation of the remaining data still
reveals for SES activities an exponent close to 1.0, which markedly exceeds the
exponent found in artificial (man-made) noises. This, in combination with
natural time analysis, enables the identification of a SES activity with
probability 75% even after a significant (70%) data loss. The probability
increases to 90% or larger for 50% data loss.Comment: 12 Pages, 11 Figure
Entropy of seismic electric signals: Analysis in natural time under time-reversal
Electric signals have been recently recorded at the Earth's surface with
amplitudes appreciably larger than those hitherto reported. Their entropy in
natural time is smaller than that, , of a ``uniform'' distribution. The
same holds for their entropy upon time-reversal. This behavior, as supported by
numerical simulations in fBm time series and in an on-off intermittency model,
stems from infinitely ranged long range temporal correlations and hence these
signals are probably Seismic Electric Signals (critical dynamics). The entropy
fluctuations are found to increase upon approaching bursting, which reminds the
behavior identifying sudden cardiac death individuals when analysing their
electrocardiograms.Comment: 7 pages, 4 figures, copy of the revised version submitted to Physical
Review Letters on June 29,200
Geoelectric field and seismicity changes preceding the 2018 Mw6.8 earthquake and the subsequent activity in Greece
A strong earthquake of magnitude Mw6.8 struck Western Greece on 25 October
2018 with epicenter at 37.515N 20.564E. It was preceded by an anomalous
geolectric signal that was recorded on 2 October 2018 at a measuring station
70km away from the epicenter. Upon analyzing this signal in natural time, we
find that it conforms to the conditions suggested (e.g., Entropy 19 (2017) 177)
for its identification as precursory Seismic Electric Signal (SES) activity.
Notably, the observed lead time of 23 days lies within the range of values that
has been very recently identified (Entropy 20 (2018) 561) as being
statistically significant for the precursory variations of the electric field
of the Earth. Moreover, the analysis in natural time of the seismicity
subsequent to the SES activity in the area candidate to suffer this strong
earthquake reveals that the criticality conditions were obeyed early in the
morning of 18 October 2018, i.e., almost a week before the strong earthquake
occurrence, in agreement with earlier findings. Furthermore, upon employing the
recent method of nowcasting earthquakes, which is based on natural time, we
find an earthquake potential score around 80% just before the occurrence of
this Mw6.8 earthquake. In the present version of this manuscript, we also
report the recording of additional SES activities after the occurrence of the
latter earthquake and update the results until 16 April 2019.Comment: 10 pages including 12 figures. The major part of this paper appeared
in Entropy 20 (2018) 882 by the first two author
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