title: Minimum of the order parameter fluctuations of seismicity before major earthquakes in Japan.
abstract: It has been shown that some dynamic features hidden in the time series of complex systems can be uncovered if we analyze them in a time domain called natural time χ. The order parameter of seismicity introduced in this time domain is the variance of χ weighted for normalized energy of each earthquake. Here, we analyze the Japan seismic catalog in natural time from January 1, 1984 to March 11, 2011, the day of the M9 Tohoku earthquake, by considering a sliding natural time window of fixed length comprised of the number of events that would occur in a few months. We find that the fluctuations of the order parameter of seismicity exhibit distinct minima a few months before all of the shallow earthquakes of magnitude 7.6 or larger that occurred during this 27-y period in the Japanese area. Among the minima, the minimum before the M9 Tohoku earthquake was the deepest. It appears that there are two kinds of minima, namely precursory and nonprecursory, to large earthquakes.
authors.affiliation: Physics Department, Solid State Section and Solid Earth Physics Institute, University of Athens, 157 84 Athens, Greece.
authors.forename: Nicholas V
authors.initials: NV
authors.lastname: Sarlis
authors.forename: Efthimios S
authors.initials: ES
authors.lastname: Skordas
authors.forename: Panayiotis A
authors.initials: PA
authors.lastname: Varotsos
authors.forename: Toshiyasu
authors.initials: T
authors.lastname: Nagao
authors.forename: Masashi
authors.initials: M
authors.lastname: Kamogawa
authors.forename: Haruo
authors.initials: H
authors.lastname: Tanaka
authors.forename: Seiya
authors.initials: S
authors.lastname: Uyeda
mesh_terms: D055866:Earthquakes / Q000266:history* / Q000706:statistics & numerical data*; D049673:History, 20th Century; D049674:History, 21st Century; D007564:Japan; D008962:Models, Theoretical; D013997:Time Factors
keywords: criticality; seismic electric signals
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