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Preliminary kinematic model for the Gulf of Suez, Egypt, using geodetic and seismic observations

Saleh S., Hamdy A.M., Tealeb A.

Acta Geophysica Polonica

2005

Vol. 53, nr 1

87-102

The Suez Rift has been re-evaluated from recent three GPS measurements and earthquake data analysis. The GPS analysis reveals local principal strains along the southern part taking a NE-SW contraction. However, it takes a NNE-SSW direction in the northern part with tensile principal strains. Throughout the central part of the gulf, the principal strains tend to be in the ENE-WSW direction due to right lateral movement. The Gulf of Suez can be divided into three seismic provinces. Generally, earthquake activity markedly increases from north to south. Slip vector analyses were carried out for 23 available earthquake focal mechanisms along the Gulf of Suez. In the southern part, the slip vector is generally trending ENE-WSW and NE-SW. However, in the northern part the direction of the slip vector varies from NNE-SSW to NE-SW. The central region represents a seismic gap between the northern and southern provinces with slip vectors of a NE-SW trend. Contrary to the previous tectonic studies, compressional field has been detected from GPS analysis and focal mechanism solutions of a few earthquakes. This raises from the highly complicated motion of Sinai subplate relative to African plate to the postseismic viscoelastic relaxation of the ductile shallow layers after the occurrence of November 1995 earthquake.

Source characteristics and tectonic implications of moderate earthquake, northeastern Cairo Prefecture

Abdel-Fattah A.K., Badawy A.

Acta Geophysica Polonica

2004

Vol. 52, nr 1

29-43

Using local seismograms of the Egyptian National Seismological Network (ENSN), source characteristics of a moderate earthquake Mw = 4.5 (28 December 1999) are analyzed. In this analysis, the Empirical Green's Function (EGF) deconvolution technique is applied. The records of an appropriate aftershock are taken as the EGF and are used to deconvolve the mainshock seismograms, thus obtaining a Relative Source Time Function (RSTF) at each station. The deconvolution is performed using P waves in frequency domain. From the time-domain analysis of the RSTF, the resulting source time functions indicate a simple rupture process. The azimuthal dependencies of the RSTF pulse amplitudes and widths are used to estimate rupture velocity and rupture direction for the mainshock. The azimuth of rup-ture direction is obtained using a global optimization method. We found that the rupture direction of the main event propagated toward S175 E with an averaged rupture velocity around 0.75 Vs. The result obtained for rupture direction is in agreement with one of the nodal planes of focal mechanism. From the rupture directivity analysis, focal mechanism and geological evidence it follows that the investi-gated event reflects a reactivation of a NW-SE Oligocene deep-seated normal faulting with sinistral movement. Source parameters were estimated using RSTFs of the mainshock, including seismic moment of 2.85×1015 Nm, fault radius of 344 m, fault length 1460 m, and static stress drop of 3.071 MPa.