An analysis of a moderate earthquake, eastern flank of the Red Sea, Saudi Arabia

Abstract

The present study presents the analysis of a moderate earthquake (Mw 4.0) and its largest aftershocks located along the Red Sea coast, southwestern Saudi Arabia, with the aim to understand the enigma of peculiar seismicity in the Arabian Shield. We analyzed a high-quality waveform dataset collected from ten well-recorded earthquakes of moment magnitude ranging from 2.0 to 4.0 in order to determine the hypocenter locations and focal mechanisms. The focal mechanisms were retrieved from the regional moment-tensor inversion for the mainshock and using the P-wave polarities for the corresponding aftershocks of Mw ≥ 2.0, respectively. The focal mechanism solutions were inverted to retrieve the seismogenic stress using the stress tensor inversion. The combination of the nearby fault trends and the obtained results from hypocentral relocations, focal mechanism solutions, and stress tensor inversion emphasizes that the NE fault trend is likely to be the causative fault resulting in the 2017 Namas earthquake sequence, implying that the local tectonic setting is incompatible with the large-scale regional tectonics of the Red Sea opening. On the contrary, estimates of low-stress drops exhibit typical values compatible with those reported for the shallow plate-boundary earthquakes that occurred in the Red Sea, suggesting that the existing weak zones in the southernmost part of the Arabian Shield may be attributed to the large-scale regional tectonics of the Red Sea opening.

The key role of conjugate fault system in importing earthquakes into the eastern flank of the Red Sea

“…It is worth-knowing that the conjugate fault system, evidenced by the gravity data analysis and inherited in the region, plays a vital role in Arabian Shield. This finding is consistent with the results obtained from recent studies of Abdelfattah et al (2017bAbdelfattah et al ( , 2020 for earthquake sequences in the Jizan and Namas seismogenic zones, located in the Arabian Shied southward of the HL seismogenic zone.…”

“…The current geodynamic process acting in the Red Sea is characterized by the extensional tectonic stress regime as accommodated by the Arabian plate's divergence movement away from the African plate (Stoeser and Camp 1985;Abdelfattah et al 2020). Within the Red Sea's eastern flank, the stress regime is presumably imported by a shallow active asthenosphere (Abdelfattah et al 2017b); forming a complex structure consisting of several fault styles differently orientated, such as the NW-SE dykes and the NNW normal faults.…”

“…Seismological studies and geodetic observations revealed that the Arabian Shield is undergoing an NE-SW extensional stress regime, presumably prompted by the Red Sea rift system , 2012ArRajehi et al 2010). However, recent studies of Abdelfattah et al (2017bAbdelfattah et al ( , 2020 showed incompatibility between the large-scale regional tectonic stress in the Red Sea opening and suggested that the stress is transferring into the Red Sea's eastern flank across the conjugate fault system in the region. The active continental lithosphere of the northernmost part of the Red Sea's flanks is tectonically manifested by inland earthquakes occurring in several seismic dislocation zones (Fig.…”

Unravelling seismogenesis and characterizing the unique features of two significant felt earthquakes (M > 4.0) of 2020 in the southwestern parts of the Delhi region

“…Several researchers have suggested that a low friction coefficient in a weak zone along the fault may be causative for seismic activity (Pınar et al, 2010;Fojtíková and Vavryčuk, 2018;Abdelfattah et al, 2020). Furthermore, a low friction coefficient indicates low stress drops in the source, as high shear stress may not be accumulated in extensional tectonics (Abdelfattah et al, 2020).…”