Seismotectonics of the El Asnam earthquake

The large Algerian earthquakes (267 A.D.-2017)

“…It displayed a reverse focal mechanism indicating the activation of a N45°reverse fault dipping 54° to the NW with a 83°rake angle. In fact, there are three segments of this fault still visible on the land surface ( Figure 6) which ruptured on a about 40 Km displaying mainly a reverse focal mechanism (Ouyed et al, 1981) (Table 1). Many secondary effects as liquefaction, floods, rock falls were associated with this main event (Meghraoui, 1996).…”

“…This earthquake of magnitude Ms: 7.3 (Mw: 7.1) destroyed a great part of the city of El Asnam and also many villages around the city (Ouyed et al, 1981). In the epicentral area of intensity X, about three thousand people died and 50 000 persons were homeless.…”

“…Daily, several minor shocks are recorded by the Algerian seismological network with an average of about a hundred of events per month. However, sometimes moderate to large seismic events could happen as demonstrated by the occurrence of the main El Asnam earthquake (200 Km west of Algiers) in October 1980 (Ms:7.3) (Ouyed et al, 1981) or the recent Boumerdes earthquake of May, 2003 (Mw: 6.8) (Yelles-Chaouche et al, 2003a).…”

Tectonic Evolution of the Active "Chelif" Basin (Northern Algeria) from Paleomagnetic and Magnetic Fabric Investigations

“…Few studies were dedicated to these faults (Aoudia & Meghraoui, 1995;Chiabbara et al, 1996;Meghraoui, 1988;Phillip & Meghraoui, 1983), consequently the timing and amount of displacement of these faults, as well as their relationship with the Neogene basin development, are still a matter of debate (Thomas, 1985;Neurdin-Trescartes, 1992;Belkebir et al, 1996;Bessedik et al, 2002). The seismic activity is mainly characterized by moderate to destructive magnitude events as it was shown by the recent 21 May 2003 Zemmouri earthquake (Mw=6.8) (Meghraoui et al, 2004) and the 10 October 1980 El Asnam (presently Chlef) earthquake (Mw=7.3) (Ouyed et al,1981). These two earthquakes are the strongest recent ones that occurred in this part of Western Mediterranean area.…”

“…The neotectonic studies (Philippe & Meghraoui, 1983, Meghraoui et al, 1986 showed that the present deformation in the Chelif basin is mainly related to a transpression with N-S to NNW-SSE shortening direction, which is expressed by active tectonic responsible of the earthquake activity. Indeed, NE-SW trending folds and NE-SW active sinistral transpressive faults were activated during the 1954 and 1980 destructive earthquakes (Bezzeghoud et al, 1995;Ouyed et al, 1981). These reverse faults and related folding are disposed on right lateral echelon and should be coupled with NW-SE to E-W trending strike-slip deep active faults.…”