Low stress drop and strike-slip detachment faulting: insights from a new earthquake sequence in the El-Nuqra Region, Southeastern Desert, Egypt

The March 22, 2023 earthquake (local magnitude 4.0) and its aftershocks represent a new earthquake sequence in the region Northeast of Aswan, Southern Egypt. A base seismicity map from 1900 to 2023 of Southern part of the eastern desert of Egypt revealed a very low and scattered earthquakes activity regarding the number and with magnitude less than 4.0. The map view of the main earthquake and its aftershocks are distributed and concentrated along the NNW-SSE direction of the main faults' segments in the study area. The movement on the fault inferred from full waveform moment tensor inversion, revealed strike-slip faulting with minor reverse component with nodal planes trending NNW-SSE and NE-SW directions. Different decomposition scheme of the full moment tensor indicates crustal and natural earthquakes type represented by focal mechanisms with double couple component (DC) of 91% and 9% non-double couple one. The observed seismograms of the main event and its aftershocks are inverted to isolate the displacement source spectra from the attenuation and site effects using spectral inversion method (SIM). The obtained displacement spectra are modulated using Brune omega-square analysis to extract the dynamic source parameters of the studied events. The analysed waveforms of the selected earthquakes have corner frequencies fC\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${f}_{C}$$\end{document} range from 3.1-6.8 Hz, source radius r\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$r$$\end{document} vary from 160.5 to 348.6 m, seismic moments MO\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${M}_{O}$$\end{document} range from 5.23E + 18 to 7.78E + 20 dyne.cm, moment magnitudes range from 2.2 to 3.7, and corresponding to stress drop values range from 0.2 to 55.0 bar. The obtained low stress drops value of the studied events interpreted and explained by the partial stress drop model due to aseismic creeping, detachments nature, and brittle shear failure of the associated fault segments. Our findings are valuable for understanding the seismogenesis and valuable inputs for seismic hazard evaluation of the study region.