Crust and upper mantle structure in central Brazil derived by receiver functions and SKS splitting analysis

Three broadband stations were installed in central Brazil to survey possible induced seismic activity during the building of a new power plant. From the continuous recordings more than 30 receiver functions were calculated and used to derive MOHO depth values (38–41 km), average vp/vs ratio (1.68–1.71) and the average arrival times for the upper mantle discontinuities in this region. Arrival times, not otherwise sampled by global stations, were delayed by about 1.5 s compared to IASP91. SKS shear-wave splitting results suggest the presence of anisotropy in the mantle. The orientation of the fast splitting axis (E–W) follows major deep tectonic structures. The observed E–W splitting direction also correlates well with the current South America plate motion (i.e. relative to mesosphere). The splitting direction also correlates with observed aeromagnetic trends. This similarity leaves open the possibility of a linkage between the upper mantle fabric imaged by shear wave splitting analysis and the lower crustal structure imaged by aeromagnetometry.In the area of the former foredeep and fold-and-thrust belt of the Tocantins province in central Brazil, as in other Precambrian geologic areas, the measured SKS anisotropy parallels the major geologic features in the shield. The non-uniformity of the measured anisotropy directions in the center of the South American plate and the correlation with aeromagnetic trends suggest that the anisotropy maybe produced by crustal structure rather than by mantle flow.

► We calculated receiver functions to derive MOHO depth in central Brazil.
► We derived SKS shear-wave splitting to study anisotropy in the mantle.
► Measured SKS anisotropy parallels the major geologic features in the shield.
► The splitting direction correlates well with observed aeromagnetic trends.
► Correlation suggests that anisotropy may be produced by crustal structure.