## 3 Results
### FCAZ Recognition of the Strongest Earthquake-Prone Areas
In Figure 9, the totality of green and red colors shows the recognized FCAZ zones prone to strong earthquakes in California (\(M\geq 6.5\)) and significant earthquakes in the Altai-Sayan region (\(M\geq 5.5\)), in the Caucasus (\(M\geq 5.0\)), and in the Crimean Peninsula and northwestern Caucas (\(M\geq 4.5\)). Figure 9: FCAZ zones prone to earthquakes: (**a**) California, \(M\geq 6.5\) (black stars—epicenters of earthquakes with \(M\geq 6.5\) from 1836 through 2010; blue and white stars—\(M\geq 6.5\), since 2014); (**b**) the Caucas, \(M\geq 5.0\) (black stars–\(M\geq 5.0\) for the period of 650–2008; blue stars—\(M\geq 5.0\), since 2009); (**c**) the Altai–Sayan region, \(M\geq 5.5\) (blue stars—\(M\geq 5.5\) for the period of 1902–2008; yellow stars—\(M\geq 5.5\), since 2011); (**d**) Crimea and the northwestern Caucas, \(M\geq 4.5\) (black stars—\(M\geq 4.5\) for the period of 1900–2008; blue stars—\(M\geq 4.5\), since 2009). At first sight, out of 33 strong earthquakes with \(M\geq 6.5\) (1836-2010) in California, the epicenters of 5 (15%) do not fall within the FCAZ zones (Figure 9a). It should be noted that three of them are located offshore in the Pacific Ocean at a great distance from the coast and are thus not caused by the tectonics of the studied region. Two other earthquakes occurred in 1857 and 1906 a long time before the commencement of systematized instrumental observations in the region. If thus these special cases are excluded from consideration, we will see that, in fact, the result contains no missed target errors [54]. It should be noted that in California, FCAZ zones contain 83% events with \(M\geq 4.5\) among those present in the instrumental catalog. After the end of the catalog used to select recognition objects, two strong earthquakes occurred (Figure 9a). The epicenters of both lie strictly within the FCAZ zones. Accordingly, we have grounds to believe that recognition resulted in building sought areas prone to strong earthquakes with \(M\geq 6.5\) in California. In the Altai-Sayan region, out of 48 (1902-2008) significant earthquakes with \(M\geq 5.5\), only 7 epicenters (15%) are located outside of the recognized FCAZ zones (Figure 9c). It should be noted that 6 of them occurred before the commencement of active seismological observations. That said, 3 epicenters are situated in Mongolia, 2 are located in the south of the Krasnoyarsk region, where a small number of seismic stations now function. FCAZ zones contain 67% of the earthquake epicenters with \(M\geq 4.0\) from among those present in the catalog. After the end of the used instrumental catalog, five significant earthquakes occurred in the region (Figure 9c). Of them, four epicenters are located strictly inside FCAZ zones. Summing it up, the totality of provided arguments allows stating that the results of FCAZ recognition in the Altai-Sayan region shown in Figure 9c have a high degree of reliability [57]. In FCAZ research in the Altai-Sayan region, an attempt was also made to recognize zones with the lowest possible number of missed target errors. For this purpose, localization radius \(r_{q}(W)\) was varied in DPS clustering through changes in a preset interval of values of parameter \(q\). Of all obtained recognition variants, an optimal one was selected, i.e., having the lowest number of omissions of significant earthquake epicenters. This variant had two missed targets less than the main variant of FCAZ zones (Figure 9c). The epicenters of these two significant earthquakes, which make up the difference in the number of missed target errors, are located within and at the border of Mongolia. That said, the resulting area of optimal zones was 1.5 times higher than in the main recognition variant (Figure 9c). Accordingly, in the case of optimal FCAZ zones, the number of false alarms grows inevitably, adversely affecting the reliability of recognition. In this regard, the final choice was made in favor of the main recognition variant (Figure 9c) [57].