Casas, Jordi JuliaNuñez, Hugo Esteban Poveda2018-11-272018-11-272018-08-29NUÑEZ, Hugo Esteban Poveda. Crustal and upper mantle shear wave velocity structure and radial anisotropy beneath the Colombian Andes inferred from ambient noise and surface wave tomography. 2018. 241f. Tese (Doutorado em Geodinâmica e Geofísica) - Centro de Ciências Exatas e da Terra, Universidade Federal do Rio Grande do Norte, Natal, 2018.https://repositorio.ufrn.br/jspui/handle/123456789/26214The objective of this work is to investigate how subduction-related processes in NW South America deform and alter the composition of the overriding plate, as well as the relationship between crustal fluids and active/inactive volcanism. To that end, this study developed: (1) Vertical, radial and transverse ambient seismic noise cross-correlations between all possible pairs of permanent stations deployed by the Colombian Geological Survey between 2012 to 2016, to reconstruct empirical Green’s functions for inter-station Rayleigh and Love waves in the region; (2) New surface-wave group-velocity measurements for Rayleigh and Love waves from regional and teleseismic earthquake sources; (3) Surface-wave dispersion maps of phase and group velocity variation between 7 and 150 s for Love and Rayleigh waves; (4) New maps of VSV and VSH velocity at crustal and upper mantle depths (down to 140 km); and, (5) a 3D model of radial anisotropy for NW South America. S-wave velocity and radial anisotropy for the crust and upper mantle under NW South America have been developed from 1,300 empirical Green’s functions from ambient noise cross-correlations and from 11,000 fundamental-mode, surface-wave trains from earthquake sources. Phase- and group-velocity curves for Rayleigh and Love waves were measured in the 7-150 s period range from the combined dataset, and tomographically inverted to produce maps of phase- and group-velocity variation in a 0.5◦ x 0.5◦ grid for ambient noise and 1.0◦ x 1.0◦ for surface waves. VSV and VSH velocity-depth profiles were constructed from the joint inversion of local group and phase dispersion curves at each node in the tomographic grid down to 140 km depth. The S-velocity models reveal zones of slow velocity at 25-35 km depth under regions of both active and inactive volcanism, suggesting the presence of melts that carry the signature of segmented subduction into the overriding plate. The regions of slow crustal S-velocity display negative radial anisotropy (VSH < VSV ) under active volcanoes, suggesting the presence of sub-vertical magmatic dykes feeding the volcanics, and positive radial anisotropy (VSH > VSV ) under inactive volcanic regions, consistent with magma storage along flat-lying sills. At 40 km depth, slow velocities under the Central and Eastern cordilleras display positive radial anisotropy (up to 15%), which is interpreted as storage of subduction-related magmas in the lower crust. Slow S-velocities with positive radial anisotropy are observed in the Lower Magdalena Basin at all crustal levels, consistent with a combination of alternating fast and slow velocities within the sedimentary package, extensional stresses, sub-horizontal shear, and/or sub-lithospheric melts from a fractured Caribbean flat slab. Negative radial anisotropy is also observed under Lower Magdalena Basin at upper mantle levels, coinciding with the location of the Caribbean flat slab. At upper to mid crustal levels negative radial anisotropy and high velocities coincide with major tectonic terrains (Santa Marta Massif, Antioquia Batholith, Santander Massif, Ibague Batholith), while that positive anisotropy and slow velocities characterizes major coastal basins (e.g., Lower Magdalena Basin, Tumaco Basin). In tectonic terrains, negative anisotropy may be explained through escape tectonics, while positive anisotropy under the coastal basins could be resulting from a combination of flay-lying magmatic sills, extensional tectonics, and/or sub-horizontal shear.Acesso AbertoTomografia de ruído ambienteTomografia de ondas de superfícieAnisotropia radialVulcanismo relacionado à subducçãoAmérica do SuldoctoralThesisCNPQ::CIENCIAS EXATAS E DA TERRA::GEOCIENCIAS::GEOFISICA