الفهرس 
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Abstract
The terms intraplate and interplate are in common use in describing earthquakes. An earthquake that occurs on a well-defined plate boundary is clearly an interplate earthquake, and that one occurs in a mid-plate region far from any known plate boundary is clearly intraplate. Yet there is a large class of earthquakes intermediate in both their frequency of occurrence and their tectonic environment from those simple extreme cases. These are the earthquakes that occur either in a diffuse zone surrounding a plate boundary and which contribute, secondarily, to the deformation associated with the plate boundary, e.g., inland earthquakes, or those which occur within plate boundaries which are altogether diffuse. Therefore, three categories of earthquakes have been suggested, in which a distinction is made between two types of intraplate events, the latter mentioned type, which we call the plate boundary-related type, and what might be considered a ”true” intraplate earthquake, which we call the mid-plate type. (Scholz, et. al., 1986)
Seismic waveform data for the most inland earthquakes that are well recorded by the modern Egyptian National Seismological Network (ENSN) in three dislocation zones (Dahshour, Southeast Beni-Suef and East-Cairo) have been studied. This data set consists of two hundred and fifty nine earthquakes recorded in the period from October 1997 to December 2006 with local magnitudes (ML) among 0.8 – 5.0. These earthquakes have good azimuth coverage of ENSN stations and a homogeneous geographic distribution.
An efficient method (the Double-Difference Hypocenter earthquake relocation (HypoDD)) has been used to determine high-resolution hypocenter locations over large distances. The location method incorporates ordinary absolute travel-time measurements and/or cross-correlation P-wave and S-wave differential travel-time measurements. Residuals between observed and theoretical travel-time differences (or double-differences) are minimized for pairs of earthquakes at each station while linking together all observed event-station pairs. A singular value decomposition solution is found by iteratively adjusting the vector difference between hypocentral pairs.
Data for the three studied dislocation zones are selected and transferred into SEISAN format; the earthquake analysis software (Jens Havskov and Lars Ottemöllerformat 2005). The hypocenter locations resulted from SEISAN software were used as the starting locations for HypoDD relocation software. The HypoDD relocation of 259 earthquakes located in the studied areas and recorded on 52 digital seismographs demonstrated three clusters at Dahshour, four sources at southeast Beni-Suef and one source at East-Cairo dislocations containing 214 clustered events and recorded in 26 seismic stations.
The SEISAN program FOCMEC is used to determine double couple earthquake focal mechanisms. FOCMEC uses a grid search routine, however, it minimizes the misfit between possible nodal planes and broader observed data set. In addition to P-wave first motions, FOCMEC utilizes SH, and SV first-motion observations, and amplitude ratios SV/SH, SH/P and SV/P to constrain the possible focal mechanisms.
Actually, the fault plane solutions of Dahshour earthquakes displayed normal faulting with a strike-slip component to strike-slip faulting with a minor normal dip-slip component. Most of earthquake focal mechanism orientations are varying from NE-SW to NW-SE. The fault plane solutions of Beni-Suef earthquakes represented normal faulting with a strike-slip component. If the NNW-SSE striking plane has been chosen to be the actual fault plane, some solutions would indicated normal faulting with a sinistral strike-slip motion and other reflect normal faulting with a dextral strike-slip component (Badawy et. al., 2008). The fault plane solutions of East-Cairo earthquakes are compatible with the E-W to ENE-WSW striking normal fault with a dextral strike-slip motion.
The characterizations of the rupture process were obtained from studying aftershock distributions and azimuthal variations of Relative Source Time Functions (RSTFs). In this study, the Empirical Green’s Function (EGF) deconvolution technique is applied. The rupture directivities, incorporated with P-wave focal mechanisms, allowed us to select the actual planes as favorable rupture.
At Dahshour dislocation; the rupture directivities, incorporated with P-wave focal mechanisms, allowed us to select the west-dipping planes as favorable rupture. This indicated that the NW-SE faults in northern Egypt are the most seismogenic active faults, and implied a reactivation of Oligocene deep-seated faults in the Gulf of Suez-Red Sea trend. As well, the inland earthquakes are strongly related to plate boundaries that interact around Egypt. Consequently the respective events could be considered as type II intraplate earthquakes (Scholz et al., 1986) that are tectonically related to plate boundaries. Moreover, the source parameters of these events are highly consistence with the regional classifications (Ali, 2004).
At southeast Beni-Suef dislocation; the preferred fault geometry based on rupture directivity combined with generalized iso-seismal lines; focal mechanisms and aftershock distributions suggest that the rupture mainly propagated towards NNW (Abdel-Fattah and Badawy, 2002 and Badawy, et al., 2008). The NNE-SSW trend of extension stress axes agrees with the general figure of stress field in northern Egypt (Bosworth and Steckler, 1997; Badawy, 2001a & b and 2005b).
As a result of the low number of stations surrounding East-Cairo dislocation, the determination of the rupture directivity was not successful and as well as the actual fault plane. For that we recommend increasing number of stations especially in west Gulf of Suez and Eastern-Desert.