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Preliminary kinematic model for the Gulf of Suez, Egypt, using geodetic and seismic observations

Saleh S., Hamdy A.M., Tealeb A.

Acta Geophysica Polonica

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2005

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Vol. 53, nr 1

87-102

EN

The Suez Rift has been re-evaluated from recent three GPS measurements and earthquake data analysis. The GPS analysis reveals local principal strains along the southern part taking a NE-SW contraction. However, it takes a NNE-SSW direction in the northern part with tensile principal strains. Throughout the central part of the gulf, the principal strains tend to be in the ENE-WSW direction due to right lateral movement. The Gulf of Suez can be divided into three seismic provinces. Generally, earthquake activity markedly increases from north to south. Slip vector analyses were carried out for 23 available earthquake focal mechanisms along the Gulf of Suez. In the southern part, the slip vector is generally trending ENE-WSW and NE-SW. However, in the northern part the direction of the slip vector varies from NNE-SSW to NE-SW. The central region represents a seismic gap between the northern and southern provinces with slip vectors of a NE-SW trend. Contrary to the previous tectonic studies, compressional field has been detected from GPS analysis and focal mechanism solutions of a few earthquakes. This raises from the highly complicated motion of Sinai subplate relative to African plate to the postseismic viscoelastic relaxation of the ductile shallow layers after the occurrence of November 1995 earthquake.

2

Kinematics engine of the ongoing deformation field around Cairo, Egypt

Badavy A., Issavy E., Hassan G., Tealeb A.

Acta Geophysica Polonica

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2003

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Vol. 51, nr 4

447-458

EN

Kinematics engine of the ongoing deformation field around Cairo, Egypt, has been investigated from earthquakes, repeated GPS and gravity observations. First results provided from this combined strategy are presented, by focusing on both stress field and surface kinematics. The spatio-temporal distribution of earthquakes reveals that the Cairo region has suffered not only from interplate earthquakes but also from inland seismic dislocations. Earthquake focal mechanisms indicate that the stress field around Cairo is dominated by the transtensional stress regime (normal faulting with strike-slip component). The results of deformation analysis indicate three different deformation zones in the investigated area. The northem part dominates as a compressional area with a magnitude of 0.19 microstrain/year. The compressions in this area are generally in NW-SE direction. Hwever, an extensional area a magnitude of 0.21 microstrain/year in the NE-SW direction has been observed in the southern part. The central part of the investigation area seems to be in a state of no significant deformation. Repeated gravity measurements around Cairo proved an existence of considerable temporal variations of gravity. These non-tidal changes could be explained by dynamics processes within the upper crust related to the development of local stress conditions. The comparison between the observed GPS and gravity shows a remarkable agreement and provides a convincing explanation for the observed fluctuations with seismic activity.

3

Attenuation of intensity in the northern part of Egypt associated with The May 28, 1998 Mediterranean earthquake

Hassoup A., Tealeb A.

Acta Geophysica Polonica

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2000

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Vol. 48, nr 1

79-92

EN

On May 28, 1998, a moderate size earthquake of magnitude 6 occurred at lat, 31.45°N; long. 27.63°E. It was strongly kit in the northern part of Egypt. This study presents its intensity distribution based on the field observations and 280 MMI questionnaires describing the situation in the northern part of Egypt immediately after the mainshock. These reports indicate that this earthquake caused a strong shaking in Cairo and in many localities along the Nile Delta area. Cracks on buildings were observed in several places in Mersa-Matruh province, the western area of the Mediterranean Sea coast in Egypt, but cracks on ground were only observed on the sea beach area of Ras E1-Hekma village. Based on these data, the intensity-distribution map is presented here; its isoseismals are of non uniform distribution. The attenuation of MM intensity (I) with epicentral distance (D in km) of the studied shock is determined using a simple relation of type log I = log Io - mD, where Io is the epicentral intensity and m is constant. According to the variation in m constant, the isoseismal map of the studied area is divided into two zones, (a) and (b) of which zone-a is characterized by a higher m. The interpretation of the remarkable change in the m-value is attributed to the obvious variations in geological structures between zone-a and zone-b.