of EgyptSeismicity

1
of EgyptSeismicity BadawyAhmed National
Research Institute of Astronomy and Geophysics ,
Cairo, EGYPTHelwan11421-
National Research Institute Of Astronomy and
Geophysics (NRIAG)
Abstract. Spatial distribution of earthquake
epicenters indicates that Egypt has been suffered
from both interplate and intraplate earthquakes.
Most earthquakes activity has been concentrated
in northern Egypt along the geologically
documented borders of Sinai subplate (northern
Red Sea and its two branches Suez rift and Aqaba
Dead Sea transform). Away from this relatively
high seismic zone, inland seismic active
dislocations (e.g. Dahshour, Aswan, Abo-Dabbab
and Abo-Simple dislocations) are also reported.
As a matter of fact the installation of new
Egyptian National seismic Network (ENSN) since
the end of 1997has significantly enhanced the old
picture of seismic activity across Egypt and Red
Sea. New seismically active zones have been
discovered for the first time (e.g. southeast
Beni-Suef and west Sohag). Moreover, old aseismic
areas are now appearing as seismically active
regions. For example, what used to be determined
a seismic gap in seismicity between the southern
Red Sea and northernmost Red Sea there is a
significant observed seismicity off-axis in the
central and northern Red Sea along and outside of
the rift axis. The extensive ENSN seismicity
database will help to constrain hypotheses for
the role of plate boundaries across the Middle
East region (Sea floor spreading in southern Red
Sea, Zagros collision and subduction in the
Hellenic trench).. Focal mechanism
solutions and neotectonic studies including
recent GPS observations indicate that the
Egyptian territory is characterized extensional
deformation. The present-day stress field in
Egypt, as inferred from earthquake focal
mechanisms and borehole breakouts, is dominated
by transtensional stress regime, the trajectory
of which changes with depth, at least in the Gulf
of Suez. This means that Red Sea rift is an
important tectonic zone in the region and
represents to some degree the reactivation of old
Precambrian sutures
Seismic stations in Egypt before 1997
Egyptian National Seismological Network (1997)
Historical seismicity of Egypt from 2200BC to
1899AD
Micro-earthquake activity in Egypt pre-and post
ENSN installation, A,B respectively.
Seismicity of Egypt and Eastern Mediterranean
region from 1964-2003 (ISC data file)

• Conclusions
• Historical and instrumental earthquake catalogs
  have been used to re-evaluate the seismicity of
  Egypt. Focal mechanism solutions of 76
  earthquakes have been used for better
  understanding of Seismotectonics of Egypt as
  well. The following conclusions can be drowning
• A general concentration of the historical
  activity is quite clear around the Nile Valley
  and Nile Delta. These areas are densely
  inhabited, but the presence of thick sediments is
  likely the main cause of the widespread felt
  areas.
• The historical and instrumental earthquakes are,
  concentrated in northern Egypt, distributed in
  relatively similar ways indicating the same areas
  have been active since many centuries.
• Egypt has suffered from both interplate and
  intraplate earthquakes. Indeed, the intraplate
  earthquakes are less frequent, however, they are
  greatly expand the region of seismic hazard in
  Egypt (e.g. 12th October, 1992).
• Earthquake focal mechanisms reveal normal
  faulting with strike-slip component reflecting
  that the present-day stress filed in Egypt has
  dominated by transtensional stress regime with
  maximum horizontal extensional NNE stress axis.
• Earthquake catalogs of Egypt may having all
  information for earthquakes of M?3.5 from 1900 up
  to present, however, for smaller events (Mlt3.0)
  only the last two decades should be considered.
• Finally the deployment of local networks (Aswan,
  ENSN) are highly enhanced the old seismicity
  picture, particularly for micoearthquakes. New
  seismic active areas are discovered in Egypt for
  the first time (e.g. west Sohag, southeast
  Beni-Suef).

Small and Moderate earthquake distribution in
Egypt before 1997 (A) and after 1997 (B)
Focal mechanisms of selected earthquakes in Egypt
from 1900-2003