## 3 Results
### FCAZ Recognition of the Strongest Earthquake-Prone Areas
In the Caucasus, out of 106 (650-2008) significant earthquakes with \(M\geq 5.0\), the epicenters of 8 (7.5%) are located outside of FCAZ zones (Figure 9b). Explaining these missed targets, note that three earthquakes occurred in 957, 1250, and 1667 long before the commencement of systematized instrumental observations in the region. Three more unrecognized epicenters are situated at a great distance from seismic networks based on which the catalogs used for recognition were created. This casts doubt on the fact that these earthquakes are real missed targets. Accordingly, certain missed targets are two epicenters of significant earthquakes. It should be noted that FCAZ zones contain 68% of the epicenters of earthquakes with \(M\geq 4.0\) among those present in the instrumental catalog. The epicenters of all three significant earthquakes which occurred after the end of the used instrumental catalog are located strictly inside of FCAZ zones (Figure 9b). This is an argument in favor of the reliability of the FCAZ recognition results [22]. It should be noted that the subregion in the northwestern part of the Caucasus (white triangle in Figure 9b) was excluded from consideration due to the lack of earthquake epicenters representing recognition objects in this region. FCAZ recognition in this subregion turns out to be impossible. This area forms part of the united region Crime--northwestern Caucasus, in which FCAZ recognition was performed for \(M_{0}=4.5\)[21]. The number of earthquakes with \(M\geq M_{0}\) must be sufficient to assess the level of their alignment with the recognized FCAZ zones. In the instrumental catalog of earthquakes of the Crimea and northwestern Caucas region, there are just 5 events with \(M\geq 5.0\) and 17, since 1900. That said, the magnitudes of earthquakes of the early 20 th century can be overstated. For that reason, two different magnitude thresholds of the earthquake locations being recognized \(M_{0}=4.5\) and \(M_{0}=5.0\) were considered in the region. As can be seen from Figure 9d, FCAZ zones are well aligned with the location of the epicenters of significant earthquakes (1900-2008) with \(M\geq 4.5\). Only 5 (11.4%) out of 44 epicenters are situated outside of recognized zones. It should be noted that all missed earthquakes occurred before the commencement of the used instrumental catalog. That said, 3 earthquakes have magnitudes \(M=4.5\)-4.7 identified to a precision of \(\pm 0.5\). For the threshold \(M_{0}=4.5\), it is fairly safe to say that there are only two missed targets. FCAZ zones contain 67% of the earthquake epicenters, with \(M\geq 3.5\) among those present in the catalog. The recognized FCAZ zones (Figure 9d) turn out to be connected with the events of higher magnitude threshold \(M_{0}=5.0\). At the moment of recognition, there are 17 known earthquakes with \(M\geq 5.0\) in the region. The epicenters of 15 (88.2%) of them are located within or at the boundaries of FCAZ zones. Accordingly, if we consider earthquakes with \(M\geq 5.0\), then FCAZ zones can be interpreted as areas prone to the same events. That said, two missed targets are the same two Black Sea earthquakes as in the previous reasoning about the threshold \(M_{0}=4.5\). Nine earthquakes with \(M\geq 4.5\) occurred in the considered region after the end of the used instrumental catalog. The epicenters of eight of them lie strictly within FCAZ zones. The only missed target error is the epicenter of the earthquake, with \(M=4.6\) located offshore in the Black Sea. The considered Crimea-Caucasus region is the first one for which FCAZ zones were interpreted for two different magnitude thresholds. In other words, in the recognition problem of the areas prone to earthquakes, there was variation in the magnitude threshold \(M_{0}\)[60].