Previous compilation of crustal structure in South America had large unsampled areas including the thin crust in the Sub‐Andean lowlands, largely estimated by gravity data, and the sparsely sampled Amazon Craton. A deployment of 35 seismic stations in Brazil, Bolivia, Paraguay, Argentina, and Uruguay improved the coverage of the Pantanal Basin in Western Brazil, the intracratonic Paraná and the Chaco Basins. Crustal thicknesses and Vp/Vs ratios were estimated with a modified H‐k method by producing three stacked traces to enhance the three Moho conversions (the direct Ps and the two multiples Ppps and Ppss). This modified method gives lower uncertainties than previous studies and shows more regional consistency between nearby stations. The temporary stations and the Brazilian Network (RSBR) have characterized the crustal structure as follows. The Paraná Basin has a thick crust 40–45 km and average Vp/Vs ratio (1.71–1.77), while the Chaco Basin has a slightly thinner crust (35–40 km) and higher Vp/Vs ratio (1.75–1.79). This confirms the lack of widespread magmatic underplating in the Paraná Basin that could be related to the origin of the flood basalts during the South Atlantic opening. A belt of thin crust (30–35 km) with low Vp/Vs (<1.74) is confined to the eastern edge of the Pantanal Basin. Normal crust (38–43 km) is observed along the western edge of the Pantanal, from the southern part of the Amazon craton to the Rio Apa cratonic block. This study, combined with other published data, provides an updated crustal thickness map of South America.

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ABSTRACT. With the installation and growth of the Brazilian Seismographic Network (RSBR) since 2011, it is now possible to detect and locate events with magnitudes lower than 3.5 mb for Brazil, and better study the local and regional seismicity. Nevertheless, most of these events are located using 1D velocity models that lead to larger uncertainties precluding any correlation with the known geological structures. The use of heterogeneous 3D velocity models better predicts the travel times and guarantees the accuracy of hypocenter location; however, there is not yet a calibrated 3D velocity model for the South American Platform (SAP). In this study, integrating multiple local and regional geological and geophysical knowledge and average velocities of the crust and mantle, we have elaborated 3D P- and S-wave velocity models for the SAP, including the Central Andes area (down to 900 km). We tested the model locating the well-known 1998 Andean Aiquile earthquake (Bolivia), 6.6 Mw, obtaining successful results when compared with its ground truth location. We also satisfactorily located two other recent important events of the SAP, using local and regional body wave arrivals recorded by the RSBR. Finally, S-wave arrivals of near stations helped to constrain the event depths to expected values.Keywords: heterogeneous velocity model, Brazilian seismicity; hypocenter location; NonLinLoc. P- and S-wave 3D velocity models for the South American platformRESUMO. Em decorrência da implantação da Rede Sismográfica Brasileira (RSBR) em 2011, tornou-se possível detectar e localizar eventos com magnitudes menores de 3,5 mb no Brasil e aprofundar o estudo da sismicidade local e regional. Porém, a maioria desses eventos são localizados utilizando-se modelos de velocidade 1D, resultando em incertezas que não permitem correlacionar os hipocentros com as estruturas geológicas conhecidas. Em contrapartida, o uso de modelos 3D de velocidade prediz melhor os tempos de percurso das ondas e garante precisão na localização de hipocentros; porém, ainda não haviam sido desenvolvidos modelos 3D calibrados para a plataforma Sul-Americana. No presente estudo, integrando-se informações geológica e geofísica, local e regional, e velocidades médias da crosta e manto foram elaborados modelos 3D de velocidade das ondas P e S para a Plataforma Sul-americana e para os Andes Centrais (até 900 km de profundidade). Para testar a confiabilidade dos modelos, foi localizado o evento andino de Aiquile 1998, 6,6 Mw (Bolívia) usando-se chegadas regionais da onda P, com resultados compatíveis com o melhor epicentro conhecido. Também foram localizados satisfatoriamente dois outros eventos importantes. Finalmente, o uso de leituras da onda S de estações próximas restringe a profundidade hipocentral para valores esperados em cada caso.Palavras-chave: modelo de velocidade heterogêneo; sismicidade brasileira; localização de hipocentros, NonLinLoc.

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