The worldwide seismic activity is concentrated on the limits of the tectonic plates. About 90% of the global seismic activity is concentrated on the borders of the lithospheric plates (Sykes & Sbar, 1973), whose occurrence served as guidance for the plates' delimitation and, therefore, as the foundation for the Tectonic Plates' theory. As this seismicity affects important economic regions, Japan and California, for instance, in the past few decades, a major part of the efforts and resources in Seismology has gone into seeking a better understanding of the seismic activity at the edges of a plate, also called interplate.
In the map, it can be observed that there are narrow and prolongated belts of seismicity, keeping great oceanic and continental regions apart from one another, but leaving broad central areas free of earthquakes. This fact can be explained by the Theory of the Plate Tectonics: the seismicity occurs more intensely with the contact between the plates (Inter-Plate seismicity) and becomes low towards the plates' middle (intra-plate seismicity), as in Brazil. The intraplate seisms, which occur due to the tensions generated at the plates' edge being transferred inwards. Generally, they are less frequent, shallower and of lower magnitudes than the edge-occurring ones, but even though they rare, catastrophic earthquakes might take place in such areas.