Geofísica

The causes of intraplate seismicity are still a matter of debate and many hypotheses have been proposed to explain earthquake zones in stable continental interiors, such as different mechanisms of stress concentration and different definitions of weak zones. In central and western Brazil earthquakes generally occur above regions with low P- and S-wave velocities in the upper mantle. This has been used to explain the seismicity as due to stress concentration in areas of thin lithosphere. Alternatively, flexural stresses have also been proposed to explain the same seismic zones.

The sedimentation in the Paraná Basin started during the Ordovician and ended with the Early Cretaceous magmatic event. Thick lava pilescovered the entire basin, and voluminous dikes and sills occur in the sedimentary sequences, mainly in the northeastern border of the basin. Despite the thermal effect, some Paleozoic sedimentary formations preserved their primary magnetization.