Interpretation of Geophysical Data at EL Fayoum—Dahshour Area, Egypt Using Three Dimensional Models

Abstract

EL Fayoum–Cairo district lies in the north western part of Cairo city. It is affected by several earthquakes. According to the Egyptian Network Seismology of National Research Institute of Astronomy and Geophysics (NRIAG), the last one occurred in July 2005 with a magnitude of 4.2 in Richter scale. The Bouguer and the aeromagnetic anomaly data as well as the detailed land-magnetic survey have been subjected to different techniques of processing and interpretation to better understand the tectonic setting of the study area. For example, different kinds of filters such as 2D spectral analysis, 3D analytical signal, and Euler deconvolution techniques have been applied. Finally, the 2D modeling has been used to simulate the subsurface configuration along some selected profiles at the area. It can be noticed from the obtained results that, the seismic events (Dahshour earthquakes) are closely related to a major NNW normal fault which has a deep extension and slightly lateral displacement, in addition to its NE-conjugate faults. The recent seismic activities in the study area are directly related and/or associated with the rejuvenation of the lateral movements. Three-dimensional interpretations of the magnetic anomaly and Bouguer anomaly maps of Fayoum, Cairo province area, Northern Western Desert of Egypt have been presented. In addition, a high-resolution 3D magnetic and gravity model constrained with the seismic results reveals a possible crustal thickness and density distribution of the northern part of Egypt between the sedimentary cover and the mantel. The results reveal that the basement has an irregular surface with depths ranging from 3,600 to 5,500 m. Faults of the NNW, as well as ENE and NE directions have predominated and affected both the basement and the overlying sedimentary cover. Furthermore, the 2D modeling technique across long gravity and magnetic anomaly profiles have emphasized the basement topography and its overlying sedimentary section. The agreement between the results of gravity and magnetic surveys and geology on the other hand, confirm the reliability of the chosen constraints of interpretation.