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  • Author or Editor: Abdel-Monem Mohamed x
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Many countries are using GPS for monitoring large engineering structures such as dams. Monitoring deformation pattern is often one of the most effective ways to be informed the safety status of such structures. Thus, the safety control of dams lies on the analysis of its structural behaviour, based on monitoring a large set of variables, which contains information about earthquakes, crustal movement, temperature variations etc. and about corresponding stresses. For the purpose of monitoring the deformations of the High and old Aswan dams, a number of methods have been developed. For monitoring the height changes along the High Dam body, eight levelling lines were established at different levels during its construction. The levelling measurements were carried out each month since 1970 and continue till present. Mohamed et al. (2003) have presented and analysed the levelling measurements from 1970 to 2000.  The results reveal different trends for different levels of the High Dam body. The rates of setting of the High Dam body tend to be stable.  During the last five years the rates of the subsidence range 1-2 mm/a at most benchmarks of the levelling lines along the High Dam body.  During the last decade no significant correlation has been found between the rates of setting and the water level changes at the up- and down-stream sides. For monitoring crustal deformations at the High and old Aswan dams region, a local GPS network consisting of 9 geodetic points was established. Three campaigns from December 2001 to April 2003 were performed. The study results indicate a definite correlation between the amount of water in the lake and the deformation in the area. The reservoir pushes the land towards the north where the two dams are. The paper throws light upon the present state of the crustal deformations in the study area.

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Shallow earthquake swarms of focal depths <10 km and magnitude <4 occurred beneath Aswan Lake in 1987 and 1993. The 1987 events are located along the E-W Kalabsha fault and their focal mechanism solution is strike-slip. Events of the 1993 sequence are distributed along a fault segment trending in the N-S direction and show a strike slip fault plane solution, too. Source parameters of 29 earthquakes from these two sequences are determined using a software developed by the Institute of Geophysics, Polish Academy of Science. The seismic moment and corner frequency data indicate weakness of the focal region of these swarms. The weakness may be produced by the presence of a fractured zone. Horizontal movements, which were collected by Kalabsha local geodetic network, are analyzed for epochs 1984-February 1987, February 1987-September 1987 and September 1987-November 1988. The results show different spatial patterns and magnitudes of the horizontal displacement. The large magnitude of the horizontal displacements suggests that the crustal deformation measurements are mixture of seismic and aseismic components. Moreover, correlation between the geodetic data and the stress pattern deduced from seismicity exists.

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Suddenly, Aswan Seismic Network detected and observed a number of events beside Aswan city. The magnitude of these events ranged from 0.9 to 2.6. These events were considered very important events because they were located not far from the Aswan High Dam. The main purpose of this work is to investigate and identification of these events using different seismic methods. Small earthquakes and explosions have the same flat and displacement spectrum for short-period P waves and discrimination of small events rests on detection and location. The final result appears that the source of these events is not an artificial type.

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