<p>An order parameter for seismicity was introduced in the frame of natural time analysis [1]. &#160;Recent studies of the fluctuations of this order parameter revealed the existence of minima preceding major earthquakes [2-7]. Here, we review the statistical significance of these minima by using recent methods of Statistical Physics, such as receiver operating characteristics [8] and event coincidence analysis [9,10]. These methods are also applied to the investigation [11] of the statistical significance of Seismic Electric Signals [12].</p><p>References</p><ol><li>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.</li>
<li>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 110 (2013) 13734&#8211;13738, dx.doi.org/10.1073/pnas.1312740110.</li>
<li>Varotsos, P.A.; Sarlis, N.V.; Skordas, E.S. Study of the temporal correlations in the magnitude time series before major earthquakes in Japan. J. Geophys. Res.: Space Physics 119 (2014) 9192&#8211;9206, dx.doi.org/10.1002/2014JA020580.</li>
<li>Sarlis, N.V.; Christopoulos, S.R.G.; Skordas, E.S. Minima of the fluctuations of the order parameter of global seismicity. Chaos 25 (2015) 063110, dx.doi.org/10.1063/1.4922300.</li>
<li>Sarlis, N.V.; Skordas, E.S.; Christopoulos, S.-R.G.; Varotsos, P.A. Statistical significance of minimum of the order parameter fluctuations of seismicity before major earthquakes in Japan, Pure Appl. Geophys. 173 (2016) 165&#8211;172, dx.doi.org/10.1007/s00024-014-0930-8.</li>
<li>Sarlis, N.V.; Skordas, E.S.; Mintzelas, A.; Papadopoulou, K.A. Micro-scale, mid-scale, and macro-scale in global seismicity identified by empirical mode decomposition and their multifractal characteristics. Scientific Reports 8 (2018) 9206, dx.doi.org/10.1038/s41598-018-27567-y.</li>
<li>Mintzelas, A.; Sarlis, N. Minima of the fluctuations of the order parameter of seismicity and earthquake networks based on similar activity patterns. Physica A 527 (2019) 121293, dx.doi.org/10.1016/j.physa.2019.121293.</li>
<li>Fawcett, T., An introduction to ROC analysis, Pattern Recognit. Lett. 27 (2006) 861&#8211;874, dx.doi.org/10.1016/j.patrec.2005.10.010.</li>
<li>Donges, J.; Schleussner, C.F.; Siegmund, J.; Donner, R. Event coincidence analysis for quantifying statistical interrelationships between event time series. The European Physical Journal Special Topics 225 (2016) 471&#8211;487, dx.doi.org/10.1140/epjst/e2015-50233-y.</li>
<li>Siegmund, J.F.; Siegmund, N.; Donner, R.V. CoinCalc - A new R package for quantifying simultaneities of event series. Computers & Geosciences 98 (2017) 64-72, dx.doi.org/10.1016/j.cageo.2016.10.004.</li>
<li>Sarlis, N.V. Statistical Significance of Earth&#8217;s Electric and Magnetic Field Variations Preceding Earthquakes in Greece and Japan Revisited. Entropy 20 (2018) 561, dx.doi.org/10.3390/e20080561.</li>
<li>Varotsos, P.; Lazaridou, M. Latest aspects of earthquake prediction in Greece based on seismic electric signals, Tectonophysics 188 (1991) 321&#8211;347, dx.doi.org/10.1016/0040-1951(91)90462-2.</li>
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Natural Time Analysis: The Area under the Receiver Operating Characteristic Curve of the Order Parameter Fluctuations Minima Preceding Major Earthquakes
