Differences in the lithosphere seismic structure along the Brazilian continental margin from travel time seismic tomography

Results of the P-wave travel-time seismic tomography method allowed observing differences in the seismic behavior of the lithosphere along the Brazilian continental margin. High velocity anomalies have predominance in the northern portion, which extends from the state of Rio de Janeiro to Alagoas States (between latitudes -22.5 and -8.5), and low velocity anomalies in the southern portion, which extends from Rio de Janeiro to Rio Grande do Sul States (between latitudes -22.5 and -30). Low velocities coincide spatially with the offshore high seismicity areas, as indicated by Assumpção (1998), and the north (high velocities) with low seismicity regions. The high velocity anomalies at northern portion are related to the cratonic and low-stretched lithosphere of San Francisco block that was connected to the Congo block before the opening of the Atlantic Ocean. Low velocities can be assigned to more stretched and weakened lithosphere, where it started the South Atlantic Ocean opening process. The oldest lithosphere in the South Atlantic, indicated by the magnetic anomalies of the oceanic floor, is higher in the southern part than in the northern part, suggesting that the continents in this region were separating, while the northern region was still connected to Africa, which could explain the lithospheric stretching process.