The El Asnam Fault, named after the town now called Chlef in northern Algeria, is a northeast-southwest reverse fault within the Tell Atlas mountains. It lies in the slow but active convergence zone where the African plate presses northward against Eurasia across the Maghreb.
The fault is a classic thrust that pushes older rocks up and over younger sediments, building folds and uplifting the Chlef basin margin. Slip rates are modest, yet the reverse geometry concentrates strong shaking and permanent ground deformation when it ruptures.
It produced two of Algeria's deadliest modern earthquakes: the 1954 Orléansville event and the 1980 El Asnam earthquake (magnitude ~7.1), which killed roughly 2,500 people and levelled much of the town. The 1980 rupture became a textbook example of a blind-to-surface thrust and reshaped earthquake engineering across North Africa.