193 research outputs found
Geoelectric field and seismicity changes preceding the 2018 Mw6.8 earthquake and the subsequent activity in Greece
Full text linkA 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
On the motivation and foundation of Natural Time Analysis: Useful remarks
Get PDFSince 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 Sch\"ones 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.Comment: 17 pages including 1 figure. Accepted for publication in Acta
Geophysica on May 1, 201
The fluctuations, under time reversal, of the natural time and the entropy distinguish similar looking electric signals of different dynamics
Full text linkWe show that the scale dependence of the fluctuations of the natural time
itself under time reversal provides a useful tool for the discrimination of
seismic electric signals (critical dynamics) from noises emitted from man made
sources as well as for the determination of the scaling exponent. We present
recent data of electric signals detected at the Earth's surface, which confirm
that the value of the entropy in natural time as well as its value under time
reversal are smaller than that of the entropy of a "uniform" distribution.Comment: 29 pages including 24 figure and 1 Tabl
GROUNDWATER QUALITY OF THE HYDROLOGICAL BASIN OF AMYROS RIVER, AGIA AREA THESSALY, GREECE
Get PDFThe area of Agia (Thessaly, Central Greece) is a highly cultivated region, whose hydrogeochemical status is influenced both by natural and manmade factors. Chemical analyses of 40 groundwater samples from the examined area, revealed that geology has a significant impact to aquifers chemistry, mainly expressed through the presence of carbonate rocks and evaporitic minerals of the Neogene formations of the area., as well as the ultrabasic rocks of the substrate. The manmade influence is assessed through the elevated values of nitrates (values up to 168,7 mg/L). Furthermore, the analytical results of the groundwaters revealed that NO3-, Fe and Se, in several samples, exceeded the EC and SMCL (USEPA) limits. More specifically, the 20% of NO3- samples exceeded the EC limits as well as the 2,5% of Se in samples. The 2,5% of Fe in samples exceeded both the EC and SMCL (USEPA) limits
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