Crustal Strain and Stress Fields in Egypt from Geodetic and Seismological Data

Abstract

The comparison between crustal stress and surface strain azimuthal patterns has provided new insights into several complex tectonic settings worldwide. Here, we performed such a comparison for Egypt taking into account updated datasets of seismological and geodetic observations. In north-eastern Egypt, the stress field shows a fan-shaped azimuthal pattern with a WNW–ESE orientation on the Cairo region, which progressively rotated to NW–SE along the Gulf of Aqaba. The stress field shows a prevailing normal faulting regime, however, along the Sinai/Arabia plate boundary it coexists with a strike–slip faulting one (σ1 ≅ σ2 > σ3), while on the Gulf of Suez, it is characterized by crustal extension occurring on near-orthogonal directions (σ1 > σ2 ≅ σ3). On the Nile Delta, the maximum horizontal stress (SHmax) pattern shows scattered orientations, while on the Aswan region, it has a WNW–ESE strike with pure strike–slip features. The strain-rate field shows the largest values along the Red Sea and the Sinai/Arabia plate boundary. Crustal stretching (up to 40 nanostrain/yr) occurs on these areas with WSW–ENE and NE–SW orientations, while crustal contraction occurs on northern Nile Delta (10 nanostrain/yr) and offshore (~35 nanostrain/yr) with E–W and N–S orientations, respectively. The comparison between stress and strain orientations over the investigated area reveals that both patterns are near-parallel and driven by the same large-scale tectonic processes.

Updating the seismotectonic setting for the Gulf of Aqaba

“…A difficulty arises when comparing our results to those obtained from previous studies because our inversion is performed separately for three subsets of focal solutions that were categorized based on the tectonic regionalization of the Gulf of Aqaba, whereas previous studies inverted the solutions for the whole Gulf without any categorization 11 , 13 , 15 , 16 , or with a different categorization scheme 12 .…”

“…Stress tensor inversion of 35 focal mechanisms in the Gulf of Aqaba indicated a predominantly strike-slip stress field represented by SHmin of 90.5° and SHmax of 357° 15 . The stress inversion evaluation retrieved from 96 focal mechanism solutions in the Gulf of Aqaba revealed that the area is dominated by a normal stress field with a SHmax of 159° 16 .…”

“…The maximum σ1, intermediate σ2, and minimum σ3 principal stress axes orientations, as well as the scalar that specifies the relative magnitude of the principal stresses, are obtained using this technique. Different stress inversion schemes are developed and implemented in various tectonic environments and scales 9,10 .Stress tensor in the Gulf of Aqaba was studied and introduced by several authors such as [11][12][13][14][15][16] . These studies produced a variety of findings.…”

“…Stress tensor in the Gulf of Aqaba was studied and introduced by several authors such as [11][12][13][14][15][16] . These studies produced a variety of findings.…”

The Current State of Deformation Parameters in the Nile Delta, Egypt, Using GNSS and Seismological Data

“…The Delta has minor seismicity based on instrumental seismicity, although it is substantially impacted by the above mentioned nearby seismic active zones (Marzouk et al, 2011). Egypt (1927Egypt ( -2020 taken from catalogue of the international seismological center, (Rashwan et al, 2021(Rashwan et al, ) 2022, 19-28…”