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We determine the deep structure of the eastern Algerian basin and its southern margin in the Annaba region (easternmost Algeria), to better constrain the plate kinematic reconstruction in this region. This study is based on new geophysical data collected during the SPIRAL cruise in 2009, which included a wide-angle, 240-km-long, onshore-offshore seismic profile, multichannel seismic reflection lines and gravity and magnetic data, complemented by the available geophysical data for the study area. The analysis and modelling of the wide-angle seismic data including refracted and reflected arrival travel times, and integrated with the multichannel seismic reflection lines, reveal the detailed structure of an ocean-to-continent transition. In the deep basin, there is an ∼5.5-km-thick oceanic crust that is composed of two layers. The upper layer of the crust is defined by a high velocity gradient and P-wave velocities between 4.8 and 6.0 km s −1 , from the top to the bottom. The lower crust is defined by a lower velocity gradient and P-wave velocity between 6.0 and 7.1 km s −1 . The Poisson ratio in the lower crust deduced from S-wave modelling is 0.28, which indicates that the lower crust is composed mainly of gabbros. Below the continental edge, a typical continental crust with P-wave velocities between 5.2 and 7.0 km s −1 , from the top to the bottom, shows a gradual seaward thinning of ∼15 km over an ∼35-km distance. This thinning is regularly distributed between the upper and lower crusts, and it characterizes a rifted margin, which has resulted from backarc extension at the rear of the Kabylian block, here represented by the Edough Massif at the shoreline. Above the continental basement, an ∼2-km-thick, pre-Messinian sediment layer with a complex internal structure is interpreted as allochthonous nappes of flysch backthrusted on the margin during the collision of Kabylia with the African margin. The crustal structure, moreover, provides evidence for Miocene emplacement of magmatic intrusions in both the deep basin and the continental margin. Based on the crustal structure, we propose that the eastern Algerian basin opened during the southeastward migration of the European forearc before the collision, along a NW-SE elongated spreading centre that ran perpendicular to the subduction trend. Such an atypical geometry is explained by the diverging directions of the subduction rollback during the backarc opening: eastward for the Corsica-Sardinia block, and southward for the Kabylian blocks. This geometry of the forearc can be interpreted as the surface expression of a slab tear at depth, which is responsible for atypical magmatism in the overlying backarc oceanic basin.

Quaternary and Pliocene travertines, deposited from hot springs, can reveal much about neotectonic and hydrothermal activity. The aim of this work is the understanding of the actual tectonic activity in the Guelma Basin and in one of its spa structures. Gravity data were collected during a field study in the Hammam Debagh (HD) area and then analyzed to better highlight the architecture of its subsurface underlying structures. This analysis was performed by means of a Bouguer anomaly, upward continuations, and residual and derivative maps. Comparison of gravity maps, field geology, geomorphic observations, and structural maps allowed us to identify the major structural features in the Hammam Debagh. As a result, we confirm the position of the Hammam Debagh active fault which is superimposed to the hydrothermal active source in the NW-SE direction characterized by a negative gravity anomaly.

International audienceThe Cheliff basin (ex El Asnam) is known as one of the most seismic active zone in Algeria and the West Mediterranean region. We can cite the El Asnam earthquake which occurred in 10.10.01980 with magnitude of 7.3. It was generated by a thrust fault with NE–SW sinistral component. Until now, there is a little information about existence of deep active faults, which generate this strong activity. The gravity field is an important resource of information on crustal structure. The aim of this work is giving a reliable geometry of the major faults relative to the kinematics of this region.The results obtained from various filtered maps (derivatives, upward continuation) of the gravity data, were used to generate a structural map of the studied area. Whilst the continuous wavelet transform method can help in automatic detection of elongated structures in 3-D, to estimate their strike direction, shape and depth. It gives a 3-D image or a model of the region and confirms the existence of several faults, localized or inferred, from former geological studies

Identification of deep magnetized structures in the tectonically active Chlef area (Algeria) from aeromagnetic data analyzed with 2-D and 3-D imaging derived from the wavelet and ridgelet transforms. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Appgeo(2017),