Evidence of shear and tensile fracturing in the western desert earthquakes, Egypt

Abstract

In this study, a widely used moment tensor decomposition scheme and source-type plot diagrams are applied to determine the source type and mechanism of recent earthquakes in northwestern and southern Egypt. First, the full-waveform moment tensor inversion is conducted to determine the optimal faulting mechanism using an appropriate 1-D structural velocity model. Second, the complete moment tensors are decomposed into deviatoric (DEV) and isotropic (ISO) components. The earthquakes in the northwestern Dahshour region exhibit ISO components ranging from 9.2 to 38.7%, while those in the Aswan region have ISO components ranging from 2.6 to 56.4%, indicating tensile/compressive nature of fracturing. This suggests that in the Dahshour region, cracks may open or close at the source due to fluid extraction and/or injection. Similarly, earthquakes in the Aswan region are likely influenced by the charge/discharge circulation of the High Dam reservoir. Our findings suggest that in addition to natural dynamic and tectonic factors, secondary anthropogenic influences play a role in controlling seismic activity in the investigated regions. Identifying the source type and mechanism of non-double-couple earthquakes is crucial for time-dependent seismic hazard assessment, particularly in areas where large-scale fluid operations are ongoing.