## 4 Discussion
At this point, it is worthwhile to add that, in the case of Japan, where better quality seismological data exist, we could obtain a better estimation of a future EQ epicenter location by means of an NTA [31; 32]. The two cases of the local minima during September 1999, which corresponded to the last row of Table 1 and the last row of Table 2, concerning Duzce and Athens EQs, respectively, were of particular regional interest. These two minima were not reported before, as they corresponded to values \(\beta_{80}\) and \(\beta_{120}\), which were both well above 0.253. Their existence as local minima could be verified in Figure 2, while the corresponding \(\langle\)EPS\(\rangle\) maps shown in Figures 4 and 6 correlate well with the epicenters of the deadly EQs of Duzce and Athens in 1999. Interestingly, the minimum of \(\beta_{80}\) on 3 September 1999 roughly coincided with the observation of an SES activity near Lamia, Greece, which was related to the deadly Athens EQ; see Chapter 17 of Lazaridou-Varotsos [142] (see also p. 105 of Reference [90]). Moreover, a close inspection of Figure 2 revealed that local minima of \(\beta_{80}\) in area \(A_{6}\) coincided with the SES activities recorded on 17 March 2001 [143], 7 November 2007 [144], and 2 October 2018 [136]. These results were remarkable, as they provided additional evidence to support the conclusion [83] that SES activities were accompanied by clear variations of seismicity, giving rise to simultaneous precursory phenomena in independent geophysical observables. This behavior was, of course, more obvious in the case of mega-EQs such as the 2011 M9.0 Tohoku EQ in Japan. In particular, it was found that the deepest minimum \(\beta_{min}\) of the order parameter \(\kappa_{1}\) of seismicity during the 27-year period from 1 January 1984 to the occurrence of the 2011 Tohoku EQ occurrence on 11 March 2011 was observed on 5 January 2011 [29], which agreed with the experimental finding that \(\beta_{min}\) was observed [83] when an SES activity was initiated. This was so because the date of 5 January 2011 overlapped with the \begin{table}
\begin{tabular}{c c c c c} \hline \(\beta_{W,min}\) **Date** & **EQ Date** & **M** & **Epicenter Location** & \(\langle\)EPS\(\rangle\) (\%) \\ \hline
22 June 1982 & 17 January 1983 & 7.0 & Kefalonia, Greece & 64 \\
21 June 1983 & 6 August 1983 & 6.8 & Lemnos, Greece & 32 \\
3 April 1990 & 30 May 1990 & 7.0 & Vrancea, Romania & 20 \\
11 November 1990 & 29 April 1991 & 7.0 & Racha, Georgia & 21 \\
9 April 2001 & 26 July 2001 & 6.5 & Skyros, Greece & 36 \\
21 January 2002 & 3 February 2002 & 6.5 & Afyon, Turkey & 10 \\
15 April 2015 & 17 November 2015 & 6.5 & Lefkada, Greece & 55 \\
12 June 2017 & 12 November 2017 & 7.3 & Halabja, Iraq & 31 \\
24 April 2018 & 25 October 2018 & 6.8 & Zakynthos, Greece & 71 \\
3 September 1999 & 7 September 1999 & 6.0 & Athens, Greece & 53 \\ \hline \end{tabular} \({}^{\pi}\) These data came from a compilation of Tables 2 and 3 of [115].  
\end{table} 
Table 2: The dates of minima observed in the limiting geographical areas of either the 5-core or the 6-core of the area N\({}^{50}_{22}\)E\({}^{64}_{5}\) that preceded the EQs with \(M\geq 6.5\), but were not simultaneous in both areas. \({}^{4}\) On the last row, a local minimum that was also observed before the deadly Athens EQ was also added, see Figure 2. In the last column, we also inserted the \(\langle\)EPS\(\rangle\) value at the grid point nearest to the epicenter when a \(0.25^{\circ}\times 0.25^{\circ}\) grid was used as in Figure 6.  
observation [145; 146; 147] of the abnormal magnetic field variations on the z-component from 4 to 10 January 2011 at two measuring sites--see Figure 1 of [148]--laying at epicentral distances of around 130 km, a fact which was characteristic of the existence of an SES activity [4].