1. National Research Institute of Astronomy and Geophysics (NRIAG), Helwan 11722, Egypt
2. Geology Department, Faculty of Science, Mansoura University, El-Gomhoria st. 1, Mansoura 35516, Egypt
3. Institute of Geophysics and Meteorology, University of Cologne, Pohligstr. 3, 50969 Cologne, Germany