CRUSTAL DEFORMATION MEASUREMENTS AND SEISMICITY OF THE MIDDLE PART OF THE NILE VALLEY IN EGYPT

Abstract

Monitoring of the crustal deformation in the middle part of the Nile Valley in Egypt is being carryied out using a GPS network of 8 geodetic points. In this area, the 1778 strong historical earthquake and few recent events of magnitude (M <5) were located. The focal mechanism solution is made for the December 14, 1998 (M = 4.8) and June 4, 2003 (M = 5), which occurred in the study area using the direction of the first P-wave motion. The result indicates that the December 1998 event was a normal fault and the June 2003 event was a strike-slip fault.Three campaigns of GPS measurements during 2000-2003 were collected for this area and used to derive the velocity vectors and strain components. The horizontal velocity vector is estimated in the range of 1-5 mm/yr. The dilatational, maximum shear strains and the principal strain rates were also estimated. These analyses illustrate that the area can be separated into two zones, namely, the southern zone where the compression strains and high maximum shear strain rates are predominant, and while extension strain and low maximum shear strain rates prevail at the northern zone, where the recent earthquakes took place. This study provides valuable information about the present state of the crustal deformation and its relationship to seismicity and tectonics in the middle part of the Nile Valley.