Earthquakes focal mechanism and stress field pattern in the northeastern part of Egypt

Abstract

Egypt is characterized by moderate size seismicity where earthquakes are distributed within several active regions. In the present study, we investigated the source mechanism of earthquakes using the digital waveform data recorded by the Egyptian National Seismic Network (ENSN) during the period from 2004 to 2008. The focal mechanisms are constructed with high reliability based on the polarity of the first motion of P-wave.These solutions are used to examine the mode of tectonic deformation and the present-day stress field pattern affecting on different tectonic provinces in the northern part of Egypt. The results demonstrate mainly a normal faulting mechanism with minor strike slip component generally trending parallel to the northern Red Sea, the Suez rift, Aqaba rift with their connection with the great rift system of the Red Sea and the Gulf of Suez and Cairo-Alexandria trend.The inversion technique scheme is used also in the present study for determining the regional stress field parameters for earthquake focal mechanism solutions based on the grid search method of Gephart and Forsyth (1984). The Results of the stress tensor using focal mechanisms of recent earthquakes show a prevailed tension stress field in N52°E, N41°E and N52°E for the northern Red Sea, Gulf of Suez and Gulf of Aqaba zone respectively.

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

“…Southward, the stress field orientation shows a progressive clockwise rotation toward a NW-SE attitude along the Gulf of Aqaba. Overall, along this portion of the Sinai/Arabia plate boundary the stress field shows both normal and strike-slip faulting features with generally low R values (as indicated by the FPSs stress results) and therefore highlighting the coexistence of both faulting stress regimes in agreement with previous stress inversions [5,18,19] and with the extensional pattern of the geodetic strain-rates computed in this study (Figure 5). [25] pointed out that motion along the Dead Sea fault system primarily occurs under a primary left-lateral strike-slip faulting regime while the normal faulting regime reflects the extensional component of the fault system.…”

“…Information on the stress field of the investigated area came from the intensive hydrocarbon exploratory drilling carried out in the last six decades [14,15] and earthquake fault plane solutions (FPSs) [15][16][17][18][19]. Achieved results highlighted a spatial variation of the stress field with (i) pure normal faulting mechanism to normal faulting with a secondary strike-slip component on the region comprised between Dahshour, western Cairo and the Gulf of Suez [15,[17][18][19], (ii) strike-slip faulting with a secondary normal slip component or normal faulting with a strike-slip component for the Gulf of Aqaba region [5,15,18,19] and (iii) strike-slip faulting for the surrounding Aswan region [15,17,19]. All these studies inferred a sub-horizontal extensional stress with roughly WSW-ENE orientations on both the Gulf of Suez and the Gulf of Aqaba and NNE-SSW orientations on Dahshour and Aswan regions.…”

Fracture Electric Field: A Synthetic Model for Seismogenic Process and its Relationship with Preseismic Electric Anomalies and Earthquakes

“…4), as indicated by studies on the focal mechanism (e.g. Gu et al 1976;Sandu and Zaicenco 2009;Zeng et al 2013;Dologlou 2014;Mohamed et al 2015). Yet, the prerequisite of localised stress-accumulation on a fault-plane is the roughness or undulant shape of the plane, which determines the existence of the seismogenic zone.…”

“…2), geological studies on granite formation and distribution (Fig. 3), and seismological studies on the focal mechanism solutions (Gu et al 1976;Ekström and England 1989;Sipkin 1994;Sandu and Zaicenco 2009;Zeng et al 2013;Dologlou 2014;Mohamed et al 2015), we present a synthetic model to explain the seismogenic process of a causative fault and the correlation between the process and the geophysical phenomena observed on the ground surface, i.e., the PSEAs and the EQs.…”

“…4a3, b3). Currently, we can use the information from the seismograms to calculate the stress-eld orientation and the slip direction in the EQ source (Ekström and England 1989;Sipkin 1994;Sandu and Zaicenco 2009;Mohamed et al 2015). The structural model in Fig.…”