Seismotectonics of the Lower Cheliff Basin: Structural background of the El Asnam (Algeria) Earthquake

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Abstract
The 1980 El Asnam earthquake should be understood within its tectonic environment. A seismotectonic map of the lower Cheliff basin (scale: 1/500,000) has been synthesized from known geologic, tectonic and seismological work on the region, and from satellite photos. The data set was integrated by a computer in order to handle different scales and projections. Several important tectonic features divide the region into 5 domains. Active faults and recent folds are consistent with a NNW‐SSE direction of compression. The Cheliff basin is limited to the south by the Relizane fault. The basin is also crossed by three broken folds, the eastern one being the one associated with the El Asnam fault. Historical and instrumental seisinicity seems to be located at both ends of Relizane fault. It is suggested that the sites corresponding to folds and reverse faulting crossing the basin are relevant to seismic risk. A simple tectonic model is proposed.