Gravimetric Evidences of Active Fault and Underground Structure of Chelif Seismogenic Basin (Algeria)

The gravity data were collected in different surveys carried out in this area. All these data were in first step homogenised. The stations are irregularly distributed. This distribution however, is generally sufficient for our purposes. The data were uniformly reduced to Bouguer anomaly at mean sea level, and topographic reductions were computed. The Bouguer gravity map shows ENE-WSW oriented isoanomalies increasing from SSE to NNW. The positive oriented E_W anomalies near the cost reach to 70 mgals, are mainly due to the effect of the oceanic nature of the Mediterranean crust. In the South we note the positive effect of the Ouarsenis Mountain. The central part of the map is characterized by closed low anomaly correlated with Chellif basin. The results based on various filtered maps (horizontal derivative, upward continuation) and continuous wavelet transform of the gravity data were used to make a structural map of the study area; this map confirms the existence of several faults, localised or inferred, from former geological studies. It complements information on some of them and outlines a great number of deep or near-surface faults that had remained unknown until the present time.