Thin crust beneath the Chaco-Paraná Basin by surface-wave tomography

Abstract

We present the results of surface-wave group velocity tomography for South America, using dispersion curves from a) regional earthquakes recorded at permanent and portable stations and b) inter-station cross-correlation of ambient noise for stations in and around the Paraná and Chaco-Paraná basins, achieving better path coverage and a more azimuthally uniform distribution. A 2D group velocity tomographic inversion, using two different smoothing criteria (first- and second-derivative smoothing) was performed in the period 10–150 s for the Rayleigh wave and 10–90 s for the Love wave, displayed improved resolution in northern Argentina and southern Brazil, compared with previous studies. A grid-search method was applied to estimate sediment, crustal thickness and upper mantle Sn velocity maps for the Chaco-Paraná basin. Our results obtained from a more complete dataset reveal an average crustal thickness for the Chaco-Paraná basin of about 35 km, reaching approximately 28–30 km beneath the northern region. S-wave velocities in the uppermost mantle are about 2% lower than IASP91 model, especially for the northern region, suggesting a shallower asthenosphere. These results are consistent with previous estimates, but are more robust because we used a larger dataset and tested different inversion constraints.