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A review of the S‐velocity structure beneath South America, for the crust and upper mantle, is performed using a recent methodology based on Rayleigh wave analysis, and a new 3D S‐velocity model (from 0 to 400 km depth) is achieved for this study area. The precise location and structure of the asthenosphere have been both determined from this new model, which have not been obtained in other previous studies, allowing to know how the different geological units that compose South America are delimited in terms of S‐velocity and lithosphere thickness. For example, the highest S‐velocities and the thickest lithosphere of the cratonic areas, are determined at the east of the Amazonian Craton and the São Francisco Craton. The lithosphere beneath the Guyana Shield is thinner than beneath the Central Brazil Shield, and the lithospheric root of the Amazonian Craton is determined deeper than the São Francisco Craton. The lithosphere at the east of the Central Brazil Shield is the thickest (~200‐km thick). Another interesting feature depicted in terms of S‐velocity and lithosphere thickness is the Transbrasiliano Lineament, which is determined in the crust and the upper mantle, confirming that it is not just a surface feature but a deep feature. [ABSTRACT FROM AUTHOR]

A new 3D S-velocity model for the crust and upper mantle beneath the Yellow Sea, the East China Sea, the Japan Sea, and the Philippine Sea is determined by means of Rayleigh-wave analysis for depths ranging from 0 to 400 km, and the most conspicuous features of the earth structure in this region are revealed from this model. In the depth range from 5 to 30 km, the S-velocity is principally affected by the thickness of the crust. In the areas with thin crust (oceanic crust), the highest S-velocity values are determined, while the lower S-velocity values are shown for the areas with a transitional crust. For the Japan Sea, the decrease observed in crustal thickness towards the north can be the result of the back-arc spreading that formed this sea from 32 to 10 Ma. Thus, from the four models proposed to explain the oceanic structure of this sea, the model supported by the results determined in the present study is the back-arc spreading model. For the Philippine Sea, the difference in the type of crust determined for the western part and the eastern-northeastern part is consistent with the two different theories, proposed to explain the origins of both parts of this sea. In the depth range from 30 to 60 km, the western part of the Philippine Sea shows higher S-velocity values than the eastern part, because the age of western part of this sea is greater than that of eastern part. The S-velocity difference of 0.2 km/s determined between both parts of this sea implies that the temperature difference within the lithosphere may reach ~370°C. For the western part of this sea, the controversy between the previous different lithospheric-thickness determinations is solved in the present study determining a lithosphere thickness of 90 km. The Japan Sea, the East China Sea, and Okinawa Trough are characterized by thin lithosphere, thick asthenosphere, and low S-velocities. These results and other evidence suggest that from the two models proposed to explain the formation of East Asian rifting system, the model of the back-arc spreading is the most realistic model. The asthenosphere beneath all study area has been precisely located and mapped in S-velocity, for the first time. The Pacific and Philippine Sea slabs and their corresponding mantle wedges above the slabs are also mapped with S-velocities. [ABSTRACT FROM AUTHOR]

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 350 km, determined from Rayleigh‐wave analysis. The S‐velocity mapping, for the depth range from 0 to 5 km, shows clearly the distribution of sedimentary basins of the study area. For the depth range from 5 to 35 km, 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 35 km, 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. [ABSTRACT FROM AUTHOR]