A new swath bathymetry compilation of the Gulf of Cadiz Area and SW Iberia is presented. The new map is the result of a collaborative research performed after year 2000 by teams from 7 European countries and 14 research institutions. This new dataset allow for the first time to present and to discuss the missing link in the plate boundary between Eurasia and Africa in the Central Atlantic. A set of almost linear and sub parallel dextral strike-slip faults, the SWIM Faults (SWIM is the acronym of the ESF EuroMargins project "Earthquake and Tsunami hazards of active faults at the South West Iberian Margin: deep structure, high-resolution imaging and paleoseismic signature") was mapped using a the new swath bathymetry compilation available in the area. The SWIM Faults form a narrow band of deformation over a length of 600 km coincident with a small circle centred on the pole of rotation of Africa with respect to Eurasia, This narrow band of deformation connects the Gloria Fault to the Rif-Tell Fault Zone, two segments of the plate boundary between Africa and Eurasia. In addition, the SWIM faults cuts across the Gulf of Cadiz, in the Atlantic Ocean, where the 1755 Great Lisbon earthquake, M∼8.5-8.7, and tsunami were generated, providing a new insights on its source location.

S U M M A R YDeep penetration multichannel reflection and Ocean Bottom Seismometer wide-angle seismic data from the Congo-Angola margin were collected in 2000 during the ZaïAngo cruise. These data help constrain the deep structure of the continental margin, the geometry of the pre-salt sediment layers and the geometry of the Aptian salt layer. Dating the deposition of the salt relative to the chronology of the margin formation is an issue of fundamental importance for reconstructing the evolution of the margin and for the understanding of the crustal thinning processes. The data show that the crust thins abruptly, from a 30-40 km thickness to less than 10 km, over a lateral distance of less than 50 km. The transitional domain is a 180-km-wide basin. The pre-salt sediment layering within this basin is parallel to the base of the salt and hardly affected by tectonic deformation. In addition, the presence of a continuous salt cover, from the continental platform down to the presumed oceanic boundary, provides indications on the conditions of salt deposition that constrain the geometry of the margin at that time. These crucial observations imply shallow deposition environments during the rifting and suggest that vertical motions prevailed-compared to horizontal motions-during the formation of the basin.

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SUMMARY The deep structure of the West African continental margin between 5°S and 8°S was investigated using vertical reflection and wide‐angle reflection/refraction techniques, during the ZaïAngo project, a joint programme conducted in 2000 April by Ifremer and TotalFinaElf. To penetrate below the salt layer, a non‐conventional, low‐frequency seismic source was used in the ‘single‐bubble’ mode, together with ocean bottom instruments (hydrophones and seismometers) and a 4.5 km long streamer that recorded multichannel seismic reflection (MCS). The data show that the continental crust thins abruptly over a lateral distance of less than 50 km, from 30 km thick below the continental platform (based on gravity data), to less than 4 km thick below the Lower Congo Basin that formed prior to the Aptian salt deposition. This subsalt sedimentary basin (180 km wide, 4 km thick, with velocities varying from 4.7 km s−1 to 5.8 km s−1 at the bottom) is located between the foot of the continental slope and the oceanic domain. It is underlain by crust of an intermediary or transitional type, between continental crust and what can be recognized as oceanic crust. In the transitional zone, a crustal upper layer is present below the pre‐salt sedimentary basin, 3 to 7 km thick, with velocities increasing from 5.8 km s−1 at the top to 6.8 km s−1 at the bottom of the layer. This layer appears to thin regularly, from 6–7 km thick below the depocentre of the pre‐salt sedimentary basin to 3–4 km thick below the western termination of the basin. Below this upper crustal layer, an anomalous velocity layer (7.2 to 7.8 km s−1), is documented, below the eastern side of the basin, where the crustal thinning is at a maximum. The origin of this layer is unknown. Several arguments, like rifting duration (between 15 Ma and 30 Ma) or the absence of seaward‐dipping reflectors, precludes the hypothesis of underplated mantle material, but other hypotheses (such as serpentinized material or high‐grade metamorphic crustal rocks or a mixture of mafic and ultramafic crustal rocks) are plausible. Near the ocean termination of the basin, the transitional zone is bounded to the west by a basement ridge that is clearly documented on two profiles (‘7+11’ and 14) having a dense ocean bottom seismometer/hydrophone (OBS/OBH) spacing. On these profiles, an anomalous velocity layer is present in the westernmost part of the transitional zone (below the basement ridge) and in the oceanic domain. This layer, absent on profile 3, may be related either to oceanization and slow seafloor spreading processes or to a consequence of the rifting process.

International audienceThe Bay of Biscay is bounded to the North by the North Biscay margin, which comprises the Western Approaches and Armorican segments. In the 1970s and 1980s, most researchers considered this margin typical of a non-volcanic passive margin: It is characterized by a striking succession of tilted blocks beneath which occurs the S reflector and the continent/ocean boundary is abrupt. This paper examines the Armorican segment and is based on a study of all early seismic profiles together with new multichannel reflection and refraction seismic data (NORGASIS cruise). An important result is the discovery of a 80-km wide Ocean-Continent Transition zone that coincides with the Armorican Basin (a deep sedimentary basin). It is characterized by a High-Velocity Layer-Crust (7.4-7.5 km/s) overlain by sediments. The other results are: i) the main crustal thinning occurs exclusively under the narrow continental slope. ii) The tilted blocks and the S-reflector are observed only at the base of the continental slope in the narrow domain called "neck area". iii) the North Biscay Ridge is a large oceanic plateau present only off the NW Armorican margin rather than a long ridge elongated off the whole North Biscay Margin