Interpretation of new gravity survey in the seismogenic Upper Chelif Basin (North of Algeria): deep structure and modeling

The Chelif Basin (North Algeria) is one of the most seismically active zones of the western Mediterranean Sea. It constitutes a key area to study neotectonic structures and their geodynamical context. However, its eastern part of this basin, called Upper Chelif Basin, is an unknown region from geophysical, structural and neotectonic evidences. The aim of this work is to perform a new gravity survey to determine the structural architecture and lithological information of the Upper Chelif Basin. This goal can be achieved by applying to the gravity data different processing methods such as gradients, upward continuation, Euler deconvolution, wavelet and ridgelet transforms and modeling. These processing methods are used to examine the relationship between identified gravity anomalies and the causative structures, included tectonic features. The Bouguer anomaly map processed with different methods, shows for the first time a 2-D and 3-D images of the studied area. The strong gravimetric anomalies noticed, attests the presence of dense geological bodies, maybe deeply rooted. The identified structures and gravimetric lineaments are well correlated with local and regional geological structures. Among these structures, the Oued El Fodda reverse fault stands out, related to the 1980 earthquake with magnitude Ms = 7.2 identified by an NE-SW lineament. In addition, many new structures and contacts both at surface and depth are sketched out, such as those limiting the basin. The identified structures at depth show that the thickness is not constant along the whole basin.