FAULTING MECHANISM OF THE EL-ASNAM (ALGERIA) 1954 AND 1980 EARTHQUAKES FROM MODELING OF VERTICAL MOVEMENTS

Since 1980, most of the papers published on the El Asnam earthquake co ncern the geological and seismological aspects of the fault zone. Only one paper, published by Ruegg et al. (1982), constrains the faulting mechanism with geodetic measurements. The purpose of this paper is to reexamine the faulting mechanism of the 1954 and 1980 events by modell ing the associated vertical movements. For this purpose we used all av ailable data, and particularly those of the levelling profiles along t he Algiers-Oran railway that has been remeasured after each event. The comparison between 1905 and 1976 levelling data shows observed vertic al displacement that could have been induced by the 1954 earthquake. O n the basis of the 1954 and 1980 levelling data, we propose a possible model for the 1954 and 1980 fault systems. Our 1954 fault model is pa rallel to the 1980 main thrust fault, with an offset of 6 km towards t he west. The 1980 dislocation model proposed in this study is based on a variable slip dislocation model and explains the observed surface b reak displacements given by Yielding et al. (1981). The Dewey (1991) a nd Avouac et al. (1992) models are compared with our dislocation model and discussed in this paper.