A detailed 3-D S wave velocity model is proposed for the region.
A simple procedure to generate a three-dimensional image of Mohorovicic； discontinuity was applied in northeastern Brazil and the Moho 3-D image was in agreement with several isolated crustal thicknesses obtained with different geophysical methods. Furthermore, flexural stresses are playing an important role in the reactivation of the PESZ, possibly controlling the stress field.Ī large number of Rayleigh wave dispersion curves recorded at twenty three seismic stations was used to investigate the 3-D shear wave velocity structure of the northeastern Brazilian lithosphere. We conclude that the superposition of principally flexural and plate-wide stresses explains reasonably the observed stress regimes and SHmax orientations in a great part of NE Brazil. Another possible explanation found was that the spreading stresses might counterbalance the regional stresses. The prediction of stress regime and stress axes orientation in PESZ using low to zero regional compression suggest that a decoupling of the shallow stresses from the plate-wide stresses might occur in this region. However, we highlight the importance of spreading stresses, not considered here, in rotating the maximum horizontal compression (SHmax) predictions. We predict the stress axes orientations and stress regimes for the equatorial margin and the Pernambuco Shear Zone (PESZ) region. Scenarios for the total stress field were calculated by superposing different values for an E-W-oriented regional compression. Our results showed local flexural stresses with magnitudes comparable to those of the plate-wide stresses, and mainly controlled by the long-wavelength Bouguer anomalies. The deviatoric flexural stresses are calculated in the Fourier domain. Our model consists of a horizontally layered elastic slab (the lithosphere) that floats above an inviscid fluid (the asthenosphere), where the surface load is generated by the topography and bathymetry, and the internal loads are calculated from the Bouguer anomalies.
We model the contribution of the stresses generated by the topography and density heterogeneities in the stress field of NE Brazil and the interplay between these and regional stresses.
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