World Applied Sciences Journal 21 (12): 1721-1728, 2013 ISSN 1818-4952 © IDOSI Publications, 2013 DOI: 10.5829/idosi.wasj.2013.21.12.721 Corresponding Author: Khaled H. Zahran, National Research Institute of Astronomy and Geophysics, Helwan, Egypt. 1721 Gravity Observation and Crustal Deformation at Cairo Region and its Geodynamical Implications Khaled H. Zahran, Abdel-Monem S. Mohamed, M. Salah, 1 1 1 Mostafa M. Yousef, Awad A. Omran and Ali M. Radwan 2 2 1 National Research Institute of Astronomy and Geophysics, Helwan, Egypt 1 Geology Department, Faculty of Science, Assiut University, Assiut, Egypt 2 Abstract: Seismic activities in and around Cairo region suggest interested geodynamic behavior of this region due to the existence of local seismo-active tectonics from one side. On the other side, its location indicates the effect of the regional tectonic between the African plate and both the Eurasian and Arabian plates on it. Thus, Crustal deformation study was carried out in Cairo region after the October 12, 1992 earthquake that occurred at Dahshour region 35 km southwest the center of Cairo with a magnitude of 5.9. The main objective of this study was to delineate the crustal stress and strain field in Cairo region using GPS measurements. The calculated deformation analysis shows accumulated stress and strain covered the south and southeast of the area under investigation. Thus, it was important to determine subsurface structures attributed to the stress-strain accumulation and its relation to the earthquake occurrence. Therefore, spatial gravity map of the selected region deduced from satellite altimeter data was figured out. The gravity indicated important mass discontinuities zones which were well correlated with the seismological and deformation activities. The complete figure of the gravity map indicated that the tectonic settings of Cairo region obey the regional tectonic between the African plate and both the Eurasian and Arabian plates. The Gravity Recovery and Climates Experiment (GRACE) have been monitoring time-varying changes of the earth's gravitational field on a near global scale since 2002. Thus, data from GRACE has been used to determine the regional trends of the gravity variation along Cairo region. Locations of the anomalous gravity region shown to be comparable with locations of active crustal deformation deduced for GPS observations and seismological studies. This might be due to the restraining and releasing of stress in those areas. The final compiled output from the gravity, geodetic and seismic analysis will focus on the geodynamical regime of the seismo-active region and it is an attempt to delineate the crustal stress and strain fields. Key words: Cairo GPS Satellite Altimeter and Gravity INTRODUCTION affected by both regional and local tectonic settings [1]. In Egypt, earthquake activities have been observed observation suggest the importance of the determination in various regions. The north-eastern part of Egypt with of any spatial or temporal mass variations attributed the capital Cairo plays an important role in both historical with its neo-tectonics. On the Other hand, repeated and recent seismicity. This area has an interesting seismic activity suggests significant mass tectonic features, as it is dominated by the relative redistribution attributed with its neo-tectonics. The main movements of major plates (Africa, Arabia and Eurasia) outcome of the tectonic and seismological studies of and a relatively aseismic small plates from one side. Cairo is that it is affected by both regional and local On the other side, most destructive earthquakes occurred tectonics. Therefore, revealing the tectonic effects of at Cairo are located on the southeastern part and Cairo and its relation to the seismicity is of great attributed with two local active faults. Thus, Cairo is interest [2]. Significant crustal deformation obtained from GPS