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The 21 May 2003 Zemmouri earthquake ( Mw=6.8), which killed 2,278 people, injured 11,450, made 250,000 homeless, and destroyed or seriously damaged 6,000 buildings and 20,800 housing units, is the most significant earthquake to affect Algeria since the 1980 El Asnam earthquake ( Ms=7.3). This paper presents the report of the macroseismic survey conducted by the Centre of Research in Astronomy, Astrophysics, and Geophysics (CRAAG, Algeria) immediately after the earthquake. The collected data set has led to a comprehensive evaluation of damage and estimation of intensity at about 600 sites, a number never reached in previous earthquake damage surveys. The produced isoseismal map portrays the spatial distribution of intensities from III to X EMS. A map highlighting the damage distribution, where various geological and hydrological phenomena are reported, is also presented. The extent of the socioeconomic impact of this event confirmed that Algerian buildings are highly vulnerable to the recurrence of destructive earthquakes.

The Cheliff region has experienced some significant earthquakes in the last century (1937, 1954, and 1980). The most destructive one is that of El Asnam on October 10, 1980, Ms = 7.3 (Io = IX), which destroyed the Chlef city (formerly El Asnam) and its surrounding villages. On December 16, 2006 a moderate earthquake (Mw = 5.0) hit the Cheliff region. The maximum observed intensity (Io = V: MSK-scale) was observed at Abou El Hassen, Benaria, Bouzghaïa and Tadjena. No damages or human losses were recorded. Nevertheless, minor cracks on walls of the old school at Tadjena were observed. The point source focal mechanism of the event was determined by inverting the waveforms of three regional broadband stations of the ADSN (Algerian Digital Seismic Network). It corresponds to thrust-reverse faulting with a strike-slip component. The stress tensor obtained by the inversion of the 15 focal mechanisms available in the Cheliff region exhibits a well constrained compression axis r1 horizontal and trending N145°. The NW dipping nodal plane indicating a NE-SW thrust fault with a right-lateral component (strike, dip, rake = 249, 38, 137) is more compatible with the regional stress tensor than the steep dipping NNE-SSW nodal plane showing reverse faulting with a left-lateral component (strike, dip, rake = 15, 65, 60). Accordingly, the Tadjena moderate size earthquake can be related to the Boukadir active fault bordering the lower Cheliff basin to the north, a situation similar to that of the El Asnam fault bordering the middle Cheliff basin to the north.

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this study describes the deformation in zones affected by regional shearing, and its relation with local factors, in particular rock compositions. the tihaliouine and teg Orak plutons were emplaced close to a major shear zone of the tuareg shield. their magmatic to sub-magmatic fabrics were determined by using measurements of anisotropy of magnetic susceptibility; they are similar to those of some other late Panafrican plutons of the tuareg shield. the eastern part of the teg Orak pluton displays a coherent fabric with a subhorizontal lineation oblique to the 4°50 major shear zone located just to the east. this fabric is clearly related to shearing by a dextral strain-slip movement along the shear zone during magma crystallization. the fabric in the western part of the teg Orak pluton and in the tihaliouine massif presents much more scattered principal axes. It was much less affected by shearing along the shear zone. this difference strongly depends on the nature of the host-rocks: Granitic host-rocks around the tihaliouine and the western part of the teg Orak acted as a rigid block, protecting the intrusions from regional deformation, while basic plutonic and metamorphic host-rocks around the eastern part of the teg Orak pluton had a more plastic behavior and transmitted the regional strain to the intrusion.