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Sequential inversion of surface wave dispersion curves and geoid anomalies integrated to shear wave splitting analysis: new constraints on the velocity, attenuation, density, and anisotropy structures of the crust and upper mantle beneath South America

Grant number: 22/04357-0
Support type:Regular Research Grants
Duration: August 01, 2022 - July 31, 2024
Field of knowledge:Physical Sciences and Mathematics - Geosciences - Geophysics
Principal researcher:Carlos Alberto Moreno Chaves
Grantee:Carlos Alberto Moreno Chaves
Home Institution: Instituto de Astronomia, Geofísica e Ciências Atmosféricas (IAG). Universidade de São Paulo (USP). São Paulo , SP, Brazil
Assoc. researchers: Cristobal Condori Quispe ; George Sand Leão Araújo de França ; Giuliano Sant'Anna Marotta ; Jeroen Ritsema ; Mônica Giannoccaro Von Huelsen ; Roberto Hirata Junior ; Susanne Tainá Ramalho Maciel ; Victor Sacek

Abstract

Integrating different geophysical datasets is essential to obtain improved models of the Earth's interior heterogeneities, as it helps to restrict the solution space of the properties investigated by each method. Although new models of physical properties in South America have been derived, they still lack resolution, making it difficult to clearly distinguish all geological features and estimate compositional and thermal variations in order to link them with past geodynamic processes responsible for the current tectonic setting of this region. These models are no longer just important for pure research since it has been shown they have, for example, important socioeconomic and environmental applications, such as targeting potential giant metal reserves of base metals, which are essential for the replacement of fossil energy by the so-called clean energy for sustainable development purposes. Thus, in this project, we will use a combination of methodologies to obtain new constraints on the 3D shear wave velocity, attenuation, density, and anisotropic structures of the crust and mantle beneath South America. High-resolution S-wave velocity, attenuation, anisotropy, and density models will be derived from the sequential inversion of phase velocity and amplitude dispersion curves of Rayleigh and Love waves and geoid anomalies. A joint posterior probability density function will be used to express the likelihood of the solution to our problem. We will develop a machine-learning-based algorithm to measure Rayleigh and Love waves amplitude and phase velocity dispersion curves from seismograms recorded by all stations available in South America and model them with Fréchet kernels so that finite-frequency effects are considered. The residual geoid anomalies to be inverted will be obtained by removing the known lithospheric component effects, which mask the signal of density perturbations in the mantle, and modeled using tesseroids to take into account the Earth's sphericity. We will provide additional constraints to our surface-wave anisotropy model by integrating receiver function studies for analysis of P-wave phases converted to S-wave, and analysis of seismograms for determination of anisotropic parameters associated with the shear wave splitting of WKS, with the use of the traversal component minimization method. The isotropic high-resolution S-wave velocity will be used to derive a new lithosphere thickness model for the whole continent. Based on the improved 3D density structure of the lithosphere obtained in this project, we will numerically calculate the stress field in the crust and lithospheric mantle considering variable rheology in accordance with the different lithological layers in the continental lithosphere and adjacent oceanic plates. Geodetic observations using GNSS time series will be performed and combined with azimuthal seismic anisotropy and numerical simulation of the stress field to provide insight into the balance of forces driving deformation across South America. (AU)

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