# Seismic and Geodetic Crustal Moment-Rates Comparison: New Insights on the Seismic Hazard of Egypt
## 6 Delimitation of Seismic Sources
### Seismic Sources along the Nile Valley and the Nile Delta (EG-08 to EG-10)  
The Nile Valley (Figure 1) is a N-S elongated Oligo-Micene rift. Its origin is still a subject of controversy. Some researchers [94] deduced an erosional origin, while others [45; 95] believe in its tectonic origin. Some of the supporting indicators for the latter origin are the fault scarps bounding the valley and the focal mechanisms of recent earthquakes [96; 97]. From the structural point of view, both faults and joints are the dominant features that can be observed along the cliffs bordering the main stream of the Nile River [95; 98]. The main trends of these structural features strike NW-SE and NNW-SSE, however, WNW-ESE, ENE-WSW, and NE-SW directions are also present. On the other hand, the Nile Delta (Figure 1a) can be subdivided by the E-W trending hinge zone (Nile Delta Hinge in Figure 1a) into two major structural sub-basins, the north and the south Nile Delta basins/blocks [98] (see Figure 1a). Three main fault trends comprise the structural pattern of the Nile Delta. They are the NW-SE Misfaq-Bardawil \"Temsah\" Fault (from the northeast side), the NE-SW Qantara-Eratosthenes \"Rosetta\" Fault (from the northwest side), and the E-W fault defining the Messinian salt basin [99] (see Figure 1a). In the current study, the central part of the Nile Valley (to the north of latitude 25\({}^{\circ}\) N) and the Nile Delta was divided into three major seismic sources (EG-08, EG-09, and EG-10; see Figures 3-5). EG-08 covers the shallow crustal seismicity of the surroundings of the northern Nile Delta block (Figures 3-5). This zone is located adjacent to the west of the previous EG-04 seismic source. The southern boundary of this source is approximately coincident with the E-W trending hinge zone (Figure 1a). EG-08 is characterized by moderate seismic activity, located to the south of the active Eastern Mediterranean seismic belts (Hellenic and Cyprian arcs). Such seismicity could be attributed to the continental shelf and its associated deep faults, parallel to the Mediterranean coast [24; 100]. Twenty-five historical earthquakes (between 24 B.C. and 1886) were located within the boundaries of this zone (Figure 3). The largest reported historical events correspond to the 15 September 951, and 31 August 1111 earthquakes, both with an estimated equivalent magnitude of Mw 6.2. However, the maximum observed magnitude within this zone belongs to the 12 September 1955 (mb 6.5, Mw 6.4) Alexandria earthquake (Figure 4). Only two focal-mechanism solutions are reported inside this source, belonging to 17 January 2013 (Mw 4.5) and 29 October 2016 (Mw 3.3) earthquakes (Figure 5), both exhibiting strike-slip faulting with a minor normal component. EG-09 covers the seismic activity of the northern tip of the Gulf of Suez, the southern Nile Delta block, the Cairo-Suez region, as well as the west Cairo region (the epicentral area of 1992 Dahshour, Cairo destructive earthquake) (Figures 3-5). This zone contains 68 historical earthquakes (Figure 3) within the time between 2200 B.C. and 1895. Additionally, some significant instrumental events are located within this source, e.g., 29 April 1974 (mb 4.8, Mw 4.7) Abu Hammad, 29 March 1984 (mb 4.9, Mw 5.2) Wadi Hagul, 2 January 1987 (mb 5.0, Mw 5.0) Ismailia, and 12 October 1992 (Ms 5.9, Mw 5.8) Dahshour earthquakes (Figure 4). Focal mechanism solutions for this seismic source show mostly normal-faulting features with minor solutions with strike-slip faulting style (Figure 5). [PERSON] [93]concluded that an NW-SE to WNW-ESE trending normal-faulting mechanism is dominant for the tip of the Gulf of Suez, which is, in general, in agreement with emergent faults crossing the Eastern Desert towards the Nile Valley (Figures 3-5). [PERSON] and [PERSON] [101] deduced that the Cairo-Suez region is affected by three main normal fault trends: E-W, ENE-WSW, and NW-SE. [PERSON] [102] computed the focal mechanism solution of the 1992 Dahshour earthquake.