Intraplate seismicity in Brazil (book chapter)


We describe the development of the Brazilian earthquake catalogue and the distribution of seismicity in Brazil and neighbouring areas in mid-plate South America. This large mid-plate region is one of the least seismically of the least seismically active stable continental region (SCR) in the world: the maximum known earthquake had a magnitude of 6.2 mb and events with magnitudes 5 and above occur with a return period of 4 years. Several seismic zones can be delineated in Brazil, including some along craton edges and in sedimentary basins. Overall, the exposed cratonic regions tend to have half as many earthquakes compared to the average expected rate for all of mid-plate South America. Earthquakes tend to occur in Neoproterozoic foldbelts especially in areas of thin lithosphere, or near craton edges around cratonic keels. Areas with positive isostatic gravity anomalies tend to have more earthquakes, indicating the flexural stresses from uncompensated lithospheric loads are an important factor in explaining the intraplate seismicity. We also found that earthquakes are two to three times more lokely to occur within 20 km of mapped netectonic faults, compared to events at larger distances. On closer examination, however, we observe that most of these events occur near but not directly on the major neotectonic faults. This discrepancy could be explained by the model of stress concentration near intersecting structures. The Brazilian passive margin is also a region of higher than average seismicity. Although clear differences are found between different areas along the passive margin (extended crust in southeast Brazil having especially high seismicity compared to narrow continental shelves elsewhere), overall the Brazilian passive margin has 70% more earthquakes (magnitudes above 3.5) than the average stable continental region.

ASSUMPÇÃO, Marcelo; FERREIRA, Joaquim; BARROS, Lucas; BEZERRA, Hilario; FRANÇA, George San; Barbosa, José Roberto; Menezes, Eduardo; Ribotta, Luís Carlos; PRICHINER, Marlon; NASCIMENTO, Anderson do; DOURADO, João Carlos. Intraplate seismicity in Brazil. In: TALWANI, Preadeep. Intraplate earthquakes. São Paulo: Cambridge University Press, 2014. Cap.3, p. 50-71.

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