# Seismic and Geodetic Crustal Moment-Rates Comparison: New Insights on the Seismic Hazard of Egypt
###### Abstract  
A comparative analysis of geodetic versus seismic moment-rate estimations makes it possible to distinguish between seismic and aseismic deformation, define the style of deformation, and also to reveal potential seismic gaps. This analysis has been performed for Egypt where the present-day tectonics and seismicity result from the long-lasting interaction between the Nubian, Eurasian, and Arabian plates. The data used comprises all available geological and tectonic information, an updated Poissonian earthquake catalog (2200 B.C.-2020 A.D.) including historical and instrumental datasets, a focal-mechanism solutions catalog (1951-2019), and crustal geodetic strains from Global Navigation Satellite System (GNSS) data. The studied region was divided into ten (EG-01 to EG-10) crustal seismic sources based mainly on seismicity, focal mechanisms, and geodetic strain characteristics. The delimited seismic sources cover the Gulf of Aqaba-Dead Sea Transform Fault system, the Gulf of Suez-Red Sea Rift, besides some potential seismic active regions along the Nile River and its delta. For each seismic source, the estimation of seismic and geodetic moment-rates has been performed. Although the obtained results cannot be considered to be definitive, among the delimited sources, four of them (EG-05, EG-06, EG-08, and EG-10) are characterized by low seismic-geodetic moment-rate ratios (\(<\)20%), reflecting a prevailing aseismic behavior. Intermediate moment-rate ratios (from 20% to 60%) have been obtained in four additional zones (EG-01, EG-04, EG-07, and EG-09), evidencing how the seismicity accounts for a minor to a moderate fraction of the total deformational budget. In the other two sources (EG-02 and EG-03), high seismic-geodetic moment-rates ratios (\(>\)60%) have been observed, reflecting a fully seismic deformation. seismicity; GNSS data; seismic and aseismic deformation; seismic hazard; moment-rates; Gulf of Aqaba; Gulf of Suez; Red Sea; Egypt +
Footnote †: journal: Applied Sciences  
of buried faults but only count the seismic component of deformation and largely suffer from both the temporal length and the completeness degree of available catalogs. Because of these different perspectives, the complementarity of the three approaches, along with other independent observations can provide reliable constraints on achieved estimations, therefore providing relevant insights for seismic hazard assessment and geological deformation studies [3; 4; 5; 6; 7]. However, because of the lack of spatially dense estimation of geological slip-rates of active outcropping faults and the poor knowledge of buried faults, earthquake occurrence rates and deformation budget comparisons are generally performed by taking into account only geodetic and seismic observations [4; 6; 7; 8; 9; 10; 11; 12; 13; 14]. Hence geodetic and seismic moment-rates comparison has enabled identification of regions in which the total deformation-rate budget is released completely by crustal earthquakes, or in the case that there is an excess of the budget, it could be released either as aseismic slip across faults or through large future earthquakes [7; 9; 11; 12; 13; 15; 16; 17]. In the present study, an updated and Poissonian earthquake catalog for Egypt (historical and instrumental data within the period between 2200 B.C.-2020 A.D.), focal mechanism solutions coming from previous publications, and novel strain-rate field data were used to study the spatial patterns of seismic and geodetic moment-rates. The seismic moment-rates have been estimated by considering the truncated cumulative Gutenberg-Richter recurrence relationship [18] together with the characteristic earthquake model [19] when it was strictly required. The geodetic moment-rate was estimated by adopting the Savage and Simpson [20] approach.