Earthquakes and Stresses in the Brazilian Continental Margin

The seismicity and stress field of the Brazilian continental margin are studied and compared with those of the continental interior. Two different patterns are observed in the eastern and northern margins. In the eastern margin, the earthquakes are concentrated in the continental shelf and are due to reverse faulting in a weak, extended crust. Very little seismicity is observed onshore in eastern Brazil. In contrast, in the northern margin, earthquakes tend to occur onshore as a result of strike-slip stress regime, and almost no activity is observed offshore. Combination of regional stresses (such as ridge-push) with local flexural stresses due to sediment load in the continental shelf can explain most of the observed seismicity patterns.