Abstract
The variance κ1 of the natural time analysis of earthquake catalogs was proposed in 2005 as an order parameter for seismicity, whose fluctuations proved, in 2011, to be minimized a few months before the strongest mainshock when studying the earthquakes in a given area. After the introduction of earthquake networks based on similar activity patterns, in 2012, the study of their higher order cores revealed, in 2019, the selection of appropriate areas in which the precursory minima βmin of the fluctuations β of the seismicity order parameter κ1 could be observed up to six months before all strong earthquakes above a certain threshold. The eastern Mediterranean region was studied in 2019, where all earthquakes of magnitude M≥7.1 were found to be preceded by βmin without any false alarm. Combining these results with the method of nowcasting earthquakes, introduced in 2016, for seismic risk estimation, here, we show that the epicenter of an impending strong earthquake can be estimated. This is achieved by employing—at the time of observing the βmin—nowcasting earthquakes in a square lattice grid in the study area and by averaging, self-consistently, the results obtained for the earthquake potential score. This is understood in the following context: The minimum βmin is ascertained to almost coincide with the onset of Seismic Electric Signals activity, which is accompanied by the development of long range correlations between earthquake magnitudes in the area that is a candidate for a mainshock.
Highlights
The natural time analysis (NTA) was introduced in the early 2000s [1,2,3], and revealed hidden properties in the time series of complex systems that cannot be observed in conventional time; for a review, see, e.g., [4]
It was observed that the inclusion of high-degree nodes in the geographical area in which we applied the NTA of seismicity was important for the clearer observation of βW,min before strong EQs
In order to determine the important highdegree nodes that should have been included in the geographical areas where we studied seismicity in natural time, Mintzelas and Sarlis [115] searched for k-cores in EQ networks based on similar activity patterns (ENBOSAP)
Summary
The natural time analysis (NTA) was introduced in the early 2000s [1,2,3], and revealed hidden properties in the time series of complex systems that cannot be observed in conventional time; for a review, see, e.g., [4] It has found applications in various disciplines ranging from statistical physics [5,6,7,8], solid state physics [9] and, rock physics [10] to environmental physics [11,12,13], cardiology [14,15,16,17,18], and engineering [19,20,21]. Landau and Lifshitz [79] state: “To describe quantitatively the change in the structure of the body when it passes through the phase transition point, we can define a quantity η, called the order parameter, in such a way that it takes non-zero (positive or negative) values in the unsymmetrical phase and is zero in the symmetrical phase”
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