Recent Seismic Activity in Northern ALGERIA

In these last twenty years, northern Algeria experienced a number of moderate sized earthquakes. Among these events, the most important were earthquakes of Constantine,October,27th,1985, Ml=6.0; Tipaza, October,29th,1989, Ml=6.0 ; Mascara, August,18th,1994,Ml=5.7; Ain Benian, (Algiers) September,4th,1996,Ml=5.8; Ain Temouchent (Oran region),December,22 th, 1999, Ml=5.8 ; Beni Ouartilane (Bejaïa region), November, 10 th, 2000,Ml=5.4.. They caused large damages to the urban centers located in the epicentral areas and many people were killed.Although less studied than the El Asnam earthquake due to the difficulties to carried out field investigations, the occurrence of these seismic events allowed to precise deformation of the northern region.First of all, we can point out that :- the Tellian region is the most active region. In this later, the recent activity expressed more in the western and central regions of Algeria.- Second, the occurrence of these earthquakes revealed six faults never mapped before. They are reverse faults or thrust faults oriented NE-SW, dipping to the NW, and distributed ‘en echelon’in the intermoutain basins. The existence of some of the coastal faults (Tipaza fault, Ain Benian fault) which extended in the algerian margin, explain now many offshore epicenters located previously.-From the focal mechanism, we notice that from the western to central part of the northern region, compressional movements express, indicating a NW-SE stress regime ; in the eastern region, strike slip movements generated by the faults indicate a reorientation in a NS stress regime.-Occurrence of last moderate eathquakes confirms that the northern region of Algeria is under compression due to the convergence of the two major plates the African and Eurasiatic plates.