Crustal and upper mantle structure beneath the Gulf of Mexico and the Caribbean Sea from Rayleigh-wave analysis

The elastic structure beneath the Gulf of Mexico and the Caribbean Sea is presented in this paper by means of S-velocity maps, for depths ranging from 0 to 350km, determined from Rayleigh-wave analysis. The S-velocity mapping, for the depth range from 0 to 5km, shows clearly the distribution of sedimentary basins of the study area. For the depth range from 5 to 35km, the higher S-velocity values are associated to the areas in which the crust is thinner (oceanic crust). For the Caribbean Plate, which consists of the Venezuelan and Colombian basins separated by the Beata Ridge, a differentiation between both basins is possible in terms of S-velocity. The thickening of the Caribbean crust (observed in the southern part of the study area), due to the Caribbean-South America plate interactions, is confirmed by the S-velocity mapping; thickened crust is characterized by S-velocities lower than those for the upper mantle. For depths greater than 35km, the S-velocity presents its higher values at the older regions of the study area, while the younger or active regions are imaged with low S-velocity. Finally, a new and very interesting feature presented in this study is the location and thickness of the lithosphere-asthenosphere system. On the other hand, this study provides the mapping necessary to locate the deep geologic structures, present in the study area, which tectonic and geologic evolution is wished to determine, allowing also to know the nature and type of the crust and upper-mantle structure beneath this area. Once this knowledge is reached, an evolutionary model can be developed. This study is especially interesting for areas in the Gulf of Mexico that are hidden beneath near-opaque, complex, and extensive allochthonous salt bodies, which make it difficult to use other seismic exploration techniques such as seismic refraction or reflection techniques.