Mesures topographiques sur le segment SW de Ia zone faillée d'El Asnam et interprétation mécanique des relations entre failles inverses et normales

Abstract

Using topographic measurements, we document the relationship between thrust movement along the SW segment of the El Asnam fault, and normal movements on secondary faults in the hanging wall. Cumulative displacements of calcarenite beds on the normal faults of this segment correspond to an increasing number of seismic events towards the north. This suggests a southwards propagation of the faulted structure. In the zone between the SW and central segments of the El Asnam fault, near Zebabdja, one sees the passage from the reverse fault, activated in 1980 to a normal fault. This observation, and the monoclinal lithology, suggest that normal faults merge with the main reverse faults plane where bedding forces this plane to dip more gently. These normal faults, which strike perpendicular to the regional compressive stress, maintain the kinematic compatibility between over and underthrusted blocks. These observations allow us to propose a kinematic model for the SW segment of El Asnam fault zone.