Drainage diversions as evidence of propagating active faults: example of the El Asnam and Thenia faults, Algeria

Digital elevation models and aerial photographs provide evidence of past dr ainage diversions associated with known and inferred active faults in North ern Algeria, The El Asnam anticline is a fault-bend fold that is growing in response to displacement an the historically active El Asnam fault. The di version of the Fodda River and a sequence of uplifted palaeovalleys across the anticline formed in response to the active southwestward propagation of the Sidi Ada-El Ardja segment of the El Asnam anticline, Deformation assoc iated wits the 1980 EI Asnam earthquake (Ms 7.3) and its effect on drainage demonstrate the occurrence of coseismic: uplift of the El Asnam anticline associated with slip on the underlying thrust fault. Similar geomorphic rel ations are observed between the Isser River and the Thenia fault. Diversion s of the Isser River and evidence for Quaternary uplift indicate that the T henia fault, which is close to Algiers, is tectonically active and should b e considered to be a source of potentially damaging earthquakes.