Drainage diversions as evidence of propagating active faults: example of the El Asnam and Thenia faults, Algeria |
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| Authors: | Boudiaf Ritz & Philip |
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| Institution: | Laboratoire de Géophysique et Tectonique-CNRS, ISTEEM, University of Montpellier II, 34095 Montpellier Cedex 05, France, and Centre Algérien de Recherche Appliquée en Génie Parasismique (CGS), BP 252, Hussein Dey 16040, Alger, Algérie; Laboratoire de Géophysique et Tectonique-CNRS, ISTEEM, University of Montpellier II, 34095 Montpellier Cedex 05, France; Laboratoire de Géophysique et Tectonique-CNRS, ISTEEM, University of Montpellier II, 34095 Montpellier Cedex 05, France |
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| Abstract: | Digital elevation models and aerial photographs provide evidence of past drainage diversions associated with known and inferred active faults in Northern Algeria. The El Asnam anticline is a fault-bend fold that is growing in response to displacement on the historically active El Asnam fault. The diversion 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 associated with the 1980 El 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 relations are observed between the Isser River and the Thenia fault. Diversions of the Isser River and evidence for Quaternary uplift indicate that the Thenia fault, which is close to Algiers, is tectonically active and should be considered to be a source of potentially damaging earthquakes. |
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