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Landslides are considered to be the most important and frequent natural events causing considerable damage. Many areas in Algeria and elsewhere in the world are affected by this type of phenomenon. Located in the Tellian Chain of the Northwest of Algeria, Fergoug watershed is largely affected by several landslide events that led to (siltation of dams and roads, bridges, and buildings destruction). The damage cost amounted to hundreds of thousands of dollars and sometimes exceeds the reaction of the authorities concerned. In order to help local authorities in their prevention approach, a landslide sensitivity map has been realized using different models: (i) the frequency ratio (FR), (ii) the linear multiple regressions (MLR), and (iii) the information value model (IVM). The landslide inventory was established and includes 142 landslides and 10 conditioning factors (slope angle, slope aspect, profile curvature, distance to rivers, roads, faults, earthquakes, land use, lithology, and precipitation). These factors were prepared from several multisource data sources. The results were validated using the operating characteristic of the receiver and the areas under the curves obtained using the methods FR, IVM, and MLR are respectively 0.87, 0.83, and 0.81. It is proposed that the landslide susceptibility map produced from the FR model be more useful for the study area. The results demonstrate that for the frequency ratio model, the very high, high, moderate, low, and very low susceptibility classes are 58%, 24%, 5%, 2%, and 9.5%, respectively. Almost 73 landslides events are situated along the Fergoug River. These results could reveal the relative importance of different factors in explaining landslides and help engineers plan land use planning.

In the world, people are increasingly exposed to natural hazards such as earthquakes. To this end, seismic risk mapping remains an essential topic of study in order to minimize their destructive effects. These maps are needed for both seismic risk management and for the design of infrastructure. The challenge is to take into account local information provided by seismic sources (historical seismicity) as well as information related to active tectonic faults. In this article, we calculated the seismic risk in the Mascara Mountains (western Algeria) using the geo-metric characteristic of known faults. This study is based on an important collection of a tectonic database of these faults (Nature, geometry and geological context). This information is relevant for their seismic potential. Indeed, by including these formations we tried to compute the seismic risk this region characte-rized by weak seismicity. Our results show more or less alarming facts. Indeed, the magnitude values calculated are between 4.85 and 7.25, whereas the magnitudes obtained by experimental seismicity do not exceed 6 on the Richter scale. The values of the maximum ground acceleration (PGA) are between 0.03 and 0.28g. These results were compared with assessments made on the basis of historical seismicity; the maximum values obtained do not exceed 0.2 g. The higher values of magnitude calculated from the active faults is due to: (i) the nature of the faults (inverse, normal and strike slip), (ii) the geometry (length and depth) and (ii) that some of these faults may have an aseismic character.

The Ouarsenis area is one of the most developed karstic systems of Algeria. It is a karst reservoir drinking water with a population of more than 50,000 people taking fully benefit from it. To understand the development of this karstic system, the local tectonic history of the four main mountain ranges of this culminating area (Ouarsenis) has been analyzed. Although previously identified primarily Cenozoic tectonic activities have been observed, a set of NW-SE joints intersecting the Jurassic limestone has been associated to a post-nappes tectonic events. Moreover, numerous joint sets oriented NNE/SSW have been identified almost over the entire culminating area. These joints are the direct consequence of the following stress history: (i) a NW/SE shortening responsible for a major overlap and the first fold (P1) phase, (ii) a second NNE/SSW shortening stage responsible for the second folding (P2) phase associated with 70° N sinistral strike-slip trend, (iii) a WNW/ESE extension phase resulting from the change of σ 3 stress vertical axis, and (iv) a shearing stress creating a 120° N sinistral strike-slip fault. Only the late phases are responsible of the development of joints, which have been karstified later on. Indeed, significant families of karstified joints, i.e., 20° and 70° N have been found. These joints are related to the extensional and shearing modes, respectively, and linked to a particular in situ karstogenesis. Moreover, this study suggests an ancient establishment of the karstic systems in the Ouarsenis region in at least two stages: pre-figured and activated behaviors during the Cenozoic.

Les bassins sublitoraux de l'Algérie centro-occidentale s'alignent parallèlement à la côte méditerranéenne formant des zones peu élevées par rapport aux chaînes secondaires plissées qui les encadrent. Ce sont des bassins néogènes dont l'histoire est étroitement liée aux phases ultimes et paroxysmales de l'orogenèse alpine. Le bassin du Cheliff (Fig. 1) qui évolue dans ce milieu est un bassin subsident de type intramontagneux fonctionnant en graben le long de grandes flexures bordières. La plaine d'ech chelifboukadir d'une superficie de 360 km2 occupe le centre du silon du chelif constituée de formations plio-quaternaires atteignant par endroits les 400 m d'épaisseur. Le climat est semi aride avec une pluviométrie moyenne de l'ordre de 390 mm (1922-1990) répartie en averses irrégulières, le déficit est estimé à 360 mm. L'interprétation des analyses hydrogéochimiques des eaux des puits de la plaine ainsi que celles de l'oued chelif pour l'année 1990 a permis de vérifier la relation entre les écoulements souterrains et superficiels.