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

摘要

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 Parana and Chaco-Parana 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-Parana basin. Our results obtained from a more complete dataset reveal an average crustal thickness for the Chaco-Parana 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. (C) 2015 Elsevier Ltd. All rights reserved.