Superposition of Local and Regional Stresses in NE Brazil: Evidence from Mechanisms Around the Potiguar Marginal Basin

The region around Potiguar Basin, NE Brazil, is one of the most important seismic regions of the country. Since 1986 temporary seismographic networks, with smoked paper recording equipment were deployed at many sites of the region. Several composite focal mechanism solutions were determined by FPFIT program. Most focal plane solutions are in good agreement with the fault plane determined from the hypocentral data. P axis direction obtained from focal mechanisms and the SHmax from well bore breakouts show that the direction of the horizontal compression is parallel to the northern coastal line of the region. This pattern may be interpreted as the superposition of local stresses, generated by continentocean structural transition, with regional stresses, due to the plate driving forces.