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Abstract: With the help of aerial photographs, satellite photographs and imageries, contour maps, geological and geomorphological information (personal correspondence and unpublished works), geophysical regional data, and field work, it has been possible to map a network of fractures, alignments, and faults in 26 areas (distinguishing them quantitatively and hierarchically). Links with known regional structures were also studied. Interpretation of the linear relief elements confirms the very different density, dimensions, strikes, and function of the fracturation and also, from a microtectonic perspective, explains the activity of some active faults better. It has confirmed some previous results and improved on others; for example, the Oriente fault which is the most active in Cuba with two segments (Western: Cabo Cruz—Santiago de Cuba; Eastern: Santiago de Cuba—Punta de Maisí, the Western fault being the most active); the Nortecubana fault, forming the northern limit of the Cuban megablock, and divided into three segments; and the Cauto—Nipe fault, forming the limit of the neotectonic units, presenting two segments with three seismoactive knots.

Abstract: To Jamaica, macroblock in differential ascent in the plate boundary zone of the Caribbean—North America, a set of morphostructural and geological methods and procedures was applied that permitted its neostructure to be explained. It is composed of two mesoblocks, 11 blocks, 29 microblocks, and 65 nanoblocks. This group configures a heterogeneous network of morphoalignments and knots; knot N1 (Montego) and N11 (Kingston) being the most active. The main watershed was delimited, with an E-W strike, that reflects in its inflections the influence of a shear tectonic, mainly ancient, and that watershed divides the insular territory into two sectors (of rectangular figures) to the north and to the south. The river network is conditioned, in sectors and fundamentally, by tectonic factors. From a morphometric point of view the greater levels of uplifting (>1000 m) are located in the eastern part, in the Blue Mountains, though the estimated raising sectors denote that on its edges the recent intensity reaches values of ∼500 m. The contemporary faulting is more important in the marine parts of the north and of the south zones where the strongest earthquakes are located; however, this element is linked differently with the disruptive structures inherited, modified and active of the emerged part, those which determined that they are neither vast nor homogeneous. The seismic activity is justified by its space—time location in a transpression area of the plate boundary zone and where six relevant seismogenetic zones exist. In these elements the larger geological hazard is framed.

Abstract: Geomorphological analysis; aerial photographs; and geomorphologic, geological, geophysical, topographical, and field studies show that the morphology of Hispaniola can be linked to lateral variations in the geometry and tectonism of the Caribbean-North American Plate Boundary Zone. Three main categories of the relief were established: territorial units (1 megablock, 2 macroblocks, 14 mesoblocks, 209 blocks, 401 microblocks, and 527 nanoblocks), morphostructural alignments (4 first-, 1 second-, 12 third-, and 30 fourth-rank), and 16 knots between morphostructural alignments (second-to fourth-rank). The main seismic activity is concentrated on the first-and second-rank lineaments, and some important epicenters are located in the vicinity of the lineament intersections. The origin of the earthquakes in the vicinity of such knots can be explained by the forcing/pushing of macroblocks northeastward. The existence of earthquakes along the main lineaments may be explained by tension or compression in a restraining bend zone. From the current study, it appears that earthquake occurrence in Hispaniola is related with the stress concentrations in the vicinity of morphotectonic zones. A seismotectonic interpretation of Hispaniola is shown where three zones exist, each of them with a different active level and dimensions.

The sedimentary structure in the Gulf of Cadiz has been extensively studied by oil exploration companies. However, up to now little is known about its deep crustal structure. Moreover, the total thickness of the sedimentary layers remains unknown in large areas. The purpose of this paper is the crustal-scale interpretation of deep seismic near-vertical reflection and refraction/wide-angle reflection data obtained during the IAM (Iberian Atlantic Margins) project, carried out in 1993. Our results indicate that a continental type crust is underlying the entire Gulf of Cadiz, with progressive thinning from east to west. The sedimentary cover shows a great thickness, reaching 8 km in the center of the Gulf. Three main sedimentary units can be recognized: Jurassic-Cretaceous calcareous rocks, continuation of Algarve outcrops; the Allochthonous Units of Guadalquivir/Gulf of Cadiz, the offshore continuation of the inland Carmona nappe; and sub-horizontal post-Miocene marine sediments. The crystalline crust is divided into three main layers: the upper crust is characterized by P-wave velocity values of 5.7–6.1 km/s; the middle crust shows values of 6.3–6.4 km/s; the lower crust has a mean vertical velocity gradient of 0.02 km/s/km, with velocities between 6.9 to 7.1 km/s. The total crustal thickness varies from 27 km for the eastern part of the studied area, to 20 km for the westernmost part. The crustal thinning is more pronounced in a N-S direction than in an E-W direction. No major structures related with a defined Iberia-Africa plate boundary could be found.

Deep seismic profiling was carried out in south and central Oaxaca as a multinational (Mexico, Spain and Switzerland) project. Sixteen sea-bottom explosions, ranging from 20 to 1000 kg were recorded by thirty portable instruments along three profiles, two along the coast and one going inland in an approximate N-S direction.

In summer 1982 a network of crustal seismic profiles was established in NW Spain with shotpoints at sea and on land. Some profiles were designed to capture the general features of the crust whereas others were aimed at resolving the detailed structure of specific geological features. The interpretation of three profiles aimed at the most important features of the earth's crust in northwest Spain is discussed here. The crust consists of three layers with compressional velocities of 6.0–6.1 km/s, 6.2–6.3 km/s and 6.7–6.9 km/s. The thicknesses of these layers vary laterally, the average values under the central part of Galicia being 13 km, 8 km and 10 km. The fine structure of the lower crust has still to be determined. So far, lateral variations in the velocity structure of the lower crust from a constant velocity layer to a gradient layer have been detected along the main profile from NE to SW over a distance of 250 km. The Moho discontinuity is reached at 30–32 km in the central part of the surveyed area: this decreases to 23–27 km to the north and to the west. On the basis of P MP amplitudes, the Moho seems to be rather sharp.

The dimensions of the Iberian Peninsula, the facility of firing large charges in the surrounding waters, the well-known and relatively uniform geology, and prior knowledge of the crustal structure, resulted in it being chosen as a study area for the investigation of the seismic structure of the lower lithosphere via refraction-wide-angle reflection seismic profiling. The Iberian lithosphere Heterogeneity and Anisotropy experiment (ILIHA), with a star-shaped arrangement of six long-range DSS profiles, was carried out in October 1989. The models derived from a first interpretation of the recorded data are presented. Three crustal profiles cover the same western and central part of the Hercynian Massif as the mantle profiles. The resulting interpretations all include a middle as well as a lower crustal layer above the mantle. The velocities of the layers in all three models are similar; however, the layer depths vary beneath the profiles.

Two seismic refraction/wide-angle reflection experiments were carried out in 1982 in the northwest of the Iberian Peninsula, one in Galicia (Spain), and the other in the north of Portugal. The joint interpretation of four of these profiles is discussed in this paper. Travel time and amplitude information have been used. The four resulting crustal models show similar characteristics with regard to the number of layers and the thickness of the crust (30 km), and differences in the distribution of P-wave velocities. A low-velocity layer of 5.7 km · s −1has been found in the north of Galicia at a depth between 5 and 10 km, which could establish a lower border to the Ordenes Massif, discarding the possibility of a deep rooting of the Massif and favoring the hypothesis of an alloctonous emplacement. In the central part of the studied area, the middle crust shows a P-wave velocity of 6.2–6.4 km · s −1at a depth between 10 and 23 km. In the southern part, outside the Galicia-Tras-os-Montes zone, the velocity of P-waves varies from 6.0 to 6.2 km · s −1at a depth between 7 and 19 km. In the lower crust, the velocity of P-waves increases from 6.6 to 7.1 km · s −1under the Ordenes Massif and from 6.8 to 7.2 km · s −1in the central part of Galicia; in the north of Portugal a constant velocity value of 6.8 km · s −1has been found. The lower crust in the area of the Ordenes Massif is characterized by a lamellar structure. In the uppermost mantle P-waves propagate with a velocity of 8.1–8.2 km · s −1in the Galicia-Tras-os-Montes zone, while in the southern part P-wave velocity varies from 8.2 to 8.3 km · s −1. The Moho presents itself as a first-order discontinuity. T comparable with those obtained for other Hercynian areas of the Iberian Peninsula.