Abu-Dabbab area is the most active seismic zone in
the central Eastern Desert of Egypt, where seismic activities are
daily recorded. The reported earthquakes are microearthquakes
of local magnitudes (ML < 2.0). A spatial distribution of these
microearthquakes shows that the earthquakes of the area follow
an ENE–WSW trending pattern, which is nearly perpendicular
to the Red Sea Rift. Focal mechanisms of different fault styles
were recognized with dominant normal faulting (with a strikeslip
component) events characterized by focal depths greater
than 7 km and reverse ones of shallower focal depths. Several
lines of evidence indicating that the brittle-ductile transition
zone underlies the Abu-Dabbab area occurs at a relatively shallow
depth (10–12 km) and it is acting as a low-angle normal
shear zone (LANF). Field-structural, EMR and seismic data
(this study) reveal that the maximum compressive stress (σ1)
in the area is perturbed from the regional NW–SE direction to
ENE–WSWorientation. This stress rotation is evidently akin to
the reactivation of the crustal scale Najd Fault System (NFS),
where such reactivation is attributed to the ongoing activity/
opening of the Red Sea. Our tectonic model proposes that the
continuous activity on the brittle-ductile transition zone including
the LANF led to stress localization, which triggering a
brittle deformation in the upper crustal-levels and associated
shallow dipping thrusts. Such bimodal tectonic model suggests
that the deep earthquakes are owing to the tectonic movement
on the LANF (transtension), whereas the shallow earthquakes
are related to a brittle deformation inside the fault blocks of the
upper crust (transpression). Deformation creep along this zone
didn’t permit continuous accumulation of strain and hence reduce
the possible occurrence of large earthquakes. |
