The El Asnam earthquake of 10 October 1980 was originated by a thrust across a SW-NE-oriented fault 36 km long and 15 km wide. It is a complex event with a rupture propagating from the SW to the NE. Fault mapping, hypocenter distribution, and b factor studies indicate fault branching to the NE.
A dislocation model is used to explain the branch with normal faulting at Beni-Rached as a consequence of the thrust across a main fault that changes orientation. The mechanism of the 1954 earthquake must be similar even though only normal faulting was observed at the surface.