## 5 Statistical Characterization of Seismic Activity
### Progression of Earthquake Activity
#### 5.3.5 Local Variations and Concentrated Areas in Seismic Activity
Non-significant clusters, though less conclusive, may still hold interest as they could represent areas of more random seismic activity or locations with inadequate data to confirm spatial patterns. Overall, the analysis reveals both concentrated and isolated seismic events in the Red Sea region, with varying degrees of statistical significance suggesting a complex seismic structure; some areas, especially along the central axis, have consistently exhibited high seismicity over the examined periods. The persistence of HH clusters could imply ongoing tectonic activities, such as rifting, that continuously produce earthquakes. Additionally, the presence of significant HL outliers highlights potential unforeseen seismic hazards in typically quiescent areas, necessitating further research for comprehensive risk assessment. The Getis-Ord \(Gi^{\star}\) statistic, on the other hand, is used to identify 'hot spots' and 'cold spots' of seismic activity in the mapped area. It is more about the intensity or concentration of earthquake magnitudes in a geographical space of the area. Figures 9 and 10 show the results from the Getis-Ord \(Gi^{\star}\) analysis, which investigates seismic activities in the Red Sea area across four separate time periods: from 1997 to 2002 (illustrated in Figure 9a), 2002 to 2008 (Figure 9b), 2008 to 2014 (Figure 10a), and 2014 to 2020 (Figure 10b). The Getis-Ord \(Gi^{\star}\) method computes a \(Z\)-score for each earthquake's magnitude, signifying the extent of spatial clustering of either high or low magnitude values. This approach evaluates the magnitude of an individual earthquake and its neighboring events, contrasting this localized aggregate with the total sum of magnitudes across the region. This comparison yields an understanding of the concentration levels of either high or low magnitude values in specific areas. Consequently, regions with elevated \(Z\)-scores are classified as hotspots, indicating that the observed earthquake magnitude is significantly above the average. Conversely, areas with diminished \(Z\)-scores are identified as coldspots, signifying that the magnitude is below average. Figure 9a illustrates the Getis-Ord \(Gi^{\star}\) clustering analysis for Red Sea earthquakes between 1997 and 2002, pinpointing areas with diverse intensities of seismic activity. The spatial distribution map categorizes regions into high \(Gi^{\star}\) to signify prominent earthquake clustering and then into zones of progressively decreasing activity. Additionally, the \(Gi^{\star}\) significance map portrays the statistical significance of these concentrated or dissipated seismic activity areas. This analysis accentuates areas with heightened seismic activity, especially along the rift axis where the African and Arabian plates diverge, indicating a robust link with tectonic movements. Expanding on this, Figure 9b continues the analysis for the period from 2002 to 2008. Both the concentrated areas map and the significance map in this figure delineate the spatial intensity or clustering and statistical significance of seismic activities. Notably, high \(Gi^{\star}\) values or clustered seismicity are primarily located along the central axis of the Red Sea, marking the divergent boundary and underscoring areas of intense seismic activity. In contrast, the peripheral areas, designated as low \(Gi^{\star}\) and very low \(Gi^{\star}\), correspond to more stable parts of the oceanic crust. The significance map's corroboration of these clusters underlines their non-random distribution, with a strong association to the tectonic dynamics at the Red Sea's spreading center. This concurrence underscores the efficacy of the Getis-Ord \(Gi^{\star}\) method in discerning seismic patterns in direct relation to tectonic processes. Figure 9: Spatial distribution of Getis-Ord \(G^{\star}\) clustering analysis and associated significance maps for the intervals 1997–2002 and 2002–2008.