Delineating active faults by using integrated geophysical data at northeastern part of Cairo, Egypt

Geophysical techniques such as gravity, magnetic and seismology are perfect tools for detecting subsurface structures of local, regional as well as of global scales. The study of the earthquake records can be used for differentiating the active and non active fault elements. In the current study more than 2200 land magnetic stations have been measured by using two proton magnetometers. The data is corrected for diurnal variations and then reduced by IGRF. The corrected data have been interpreted by different techniques after filtering the data to separate shallow sources (basaltic sheet) from the deep sources (basement complex). Both Euler deconvolution and 3-D magnetic modeling have been carried out. The results of our interpretation have indicated that the depth to the upper surface of basaltic sheet ranges from less than 10-600 m, depth to the lower surface ranges from 60 to 750 m while the thickness of the basaltic sheet varies from less than 10-450 m. Moreover, gravity measurements have been conducted at the 2200 stations using a CG-3 gravimeter. The measured values are corrected to construct a Bouguer anomaly map. The least squares technique is then applied for regional residual separation. The third order of least squares is found to be the most suitable to separate the residual anomalies from the regional one. The resultant third order residual gravity map is used to delineate the structural fault systems of different characteristic trends. The trends are a NW-SE trend parallel to that of Gulf of Suez, a NE-SW trend parallel to the Gulf of Aqaba and an E-W trend parallel to the trend of Mediterranean Sea. Taking seismological records into consideration, it is found that most of 24 earthquake events recorded in the study area are located on fault elements. This gives an indication that the delineated fault elements are active.