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1 Acta Geophysica Polonica

1 2003

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Kinematics engine of the ongoing deformation field around Cairo, Egypt

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

Acta Geophysica Polonica

2003

Vol. 51, nr 4

447-458

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.