Ambient seismic noise tomography in west-central and Southern Brazil, characterizing the crustal structure of the Chaco-Parana, Pantanal and Parana basins

Author(s)

Shirzad, Taghi ^[1] ; Assumpcao, Marcelo ^[1] ; Bianchi, Marcelo ^[1]

Affiliation

^[1] Univ Sao Paulo, Inst Astron Geophys & Atmospher Sci, BR-05508090 Sao Paulo - Brazil

• Document type: Journal article
• Source: Geophysical Journal International; v. 220, n. 3, p. 2074-2085, MAR 2020.
• Web of Science Citations: 0

Abstract

Surface wave analysis provides important information on crustal structure, but it is challenging to obtain accurate/robust models in aseismic regions because of the lack of local earthquake records. In this paper, interstation empirical Green's functions retrieved by ambient seismic noise in 75 broad-band stations from 2016 January to 2018 September were used to study crustal structure in west-central Brazil. Fast marching method was applied to calculate the 2-D surface wave tomographic maps, and local dispersion curves were estimated in the period range of 4 80 s for each geographic cell. 1-D damped least squares inversion method was then conducted to obtained shear wave velocity model. Finally, the average ((V) over tilde (S)) of the calculated V-SV and V-SH quasi 3-D models were used to characterize the crustal structure. Besides the checkerboard test resolution, a stochastic test with the effect of errors in the dispersion curves and choice of inversion parameters were carried out to better evaluate model uncertainties. Our results show a clear relation between the sedimentary thickness and geological units with the shorter period tomographic maps. Agreement has also been observed in longer periods such as the clear N-S anomaly along the Asuncion and Rio Grande Arches representing the boundary between the Chaco-Parana and the Parana basins. A 3-D composite velocity model shows a crustal structure consisting of three main layers. Some differences in lower crustal properties were found between the Parana and Chaco-Parana basins, consistent with a recently postulated, gravity-derived Western Parana suture zone. However, no high velocities along the SW-NE axis of the Parana basin were found to confirm proposed underplating. At the eastern edge of the Pantanal basin, the thin crust seems to be associated with a very thin (or lack of) lower crustal layer, consistent with a recently proposed crustal delamination hypothesis for the formation of the Pantanal basin. (AU)

• FAPESP's process: 13/24215-6 - Pantanal-Chaco-Paraná basins (PCPB): crust and upper mantle seismic structure and evolution
• Grantee: Marcelo Sousa de Assumpção
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 16/20952-4 - Environmental noise tomography in the Pantanal and Paraná basins
• Grantee: Taghi Shirzad Iraj
• Support Opportunities: Scholarships in Brazil - Post-Doctoral