# Seismic and Geodetic Crustal Moment-Rates Comparison: New Insights on the Seismic Hazard of Egypt
## 9 Seismic-Geodetic Moment-Rates Ratio
\begin{table}
\begin{tabular}{l c c c c c} \hline \hline \multirow{2}{*}{**Source**} & **Area** & **D90** & **Maximum** & **Geodetic Moment-Rate** & \multirow{2}{*}{**SCC (\%)**} \\  & **(10\({}^{10}\) km\({}^{2}\))** & **(km)** & **Strain (ns/yr)** & **(10\({}^{16}\) N-m/yr)** & **SCC (\%)** \\ \hline EG-01 & 1.65 & 18.0 & 19.8 \(\pm\) 1.1 & 35.3 \(\pm\) 1.96 & 29.8 \\ EG-02 & 3.89 & 23.0 & 14.4 \(\pm\) 1.2 & 77.4 \(\pm\) 6.45 & 275.3 \\ EG-03 & 4.20 & 22.5 & 8.6 \(\pm\) 1.7 & 48.8 \(\pm\) 9.65 & 141.8 \\ EG-04 & 5.24 & 20.3 & 12.8 \(\pm\) 1.3 & 81.7 \(\pm\) 8.30 & 49.0 \\ EG-05 & 9.16 & 23.0 & 39.0 \(\pm\) 0.9 & 493.0 \(\pm\) 11.4 & 1.2 \\ EG-06 & 2.37 & 23.8 & 26.2 \(\pm\) 0.7 & 88.7 \(\pm\) 2.37 & 3.5 \\ EG-07 & 3.13 & 25.0 & 17.2 \(\pm\) 1.1 & 80.8 \(\pm\) 5.17 & 24.1 \\ EG-08 & 6.97 & 27.0 & 7.0 \(\pm\) 0.7 & 79.1 \(\pm\) 7.91 & 2.6 \\ EG-09 & 4.10 & 25.0 & 4.3 \(\pm\) 0.9 & 26.4 \(\pm\) 5.53 & 27.8 \\ EG-10 & 8.45 & 25.0 & 9.7 \(\pm\) 0.6 & 123.0 \(\pm\) 7.60 & 1.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Area of the proposed sources, seismogenic thickness (D90) with 10% variation for both lower and upper ranges, maximum strain (nanostrain/year), and their corresponding geodetic moment-rates. Seismic coupling coefficients (SCC %) estimated from the geodetic-seismic moment-rates ratio are also included. The completeness period of the used seismic catalog, as well as its temporal span, may affect seismic moment-rate estimations for a studied region [1]. In other words, to estimate reliable seismic moment-rates, the average earthquake recurrence interval should be shorter than the duration of the catalog [9; 12]. Available historical datasets for Egypt highlight the occurrence of large earthquakes (M \(\geq\) 6.0) since 590 B.C. that could be considered to be complete for the same magnitude since the year 700 (0.0273 events/year; see Figure 2 and Table 1). Taking into consideration that the earthquake occurrences and their statistics are not steady-state over the entire time of the studied catalog, and being familiar that the truncated Gutenberg-Richter law allows the consideration of possible incompleteness of the used catalog [1], our seismic moment-rates for most of the defined source could be considered as reliable estimations. Regarding the geodetic moment-rate estimations, the GNSS measurements sample a relatively large spatial region, so that the data are not significantly affected by the local strain accumulation on any individual fault. Also, they cover a long enough temporal period, so that the uncertainties have a minimal effect on the velocity estimations, and hence they sample seismic, seismic, and long-term deformation transients [6]. Recently, [PERSON] et al. [112] observed an increase of the subsidence rate in the forearc region during the late period of the Mw 9.0 2021 Tohoku earthquake, therefore evidencing possible temporal variation of crustal deformation rates during the interseismic period of very large earthquakes. Moreover, [PERSON] et al. [112], pointed out that strain-rates derived from geodetic measurements around major transform faults are constant during the interseismic period, except for the \(\sim\)10 years period following an earthquake. These observations suggest that significant temporal variations of crustal deformation rates would occur in fast convergent tectonic settings where very large earthquakes are expected, while in other tectonic settings, such as the one considered in this study, short-term geodetic observations can provide realistic contributions to long-term seismic hazard assessment. In the following paragraphs we are going to discuss, compare and frame our results carefully with available geological and geophysical data. The obtained seismic-geodetic moment-rates ratios (SCC%) are depicted in Figure 8 and tabulated in Table 3. Based on the estimated SCC results, we could consider three  
Figure 7: Comparison between the estimated values of the geodetic and seismic moment-rates. principal ratio ranges in the current study.