Review of Seismicity and Neogene Tectonics in Northeastern Brazil

Abstract

Brazil comprises most of the continental intraplate part of South America, where seismicity is low but cannot be ignored. Both historical and instrumental seismological data indicate that northeastern Brazil has been one of the most seismically active parts of Brazil. This study presents an extensive review of both historical and instrumental seismicity and Neogene tectonics in this region. Systematic seismological monitoring started in 1986 with the João Câmara earthquake swarm. Seismicity concentrates around and to the west of the Potiguar basin, around the Recôncavo area, and along the Pernambuco shear zone. It occurs as swarms of events that may last for several years. Paleoseismological data from several sources point to paleoseismicity higher than that observed in the short present-day record. Raised marine terraces of late Pleistocene age indicate uplift and subsidence along the coast by as much as 12 m. Paleoliquefaction in late Neogene alluvial terraces indicates that it may have reached as much as magnitude M 7.0. The geological record presents evidence of faults that offset Neogene sedimentary deposits by as much as 260 m. Most of these faults correspond to reactivated Precambrian shear zones and Cretaceous faults. Geodetic monitoring is under way around the Potiguar basin. Most models that correlate intraplate seismicity with Neogene faults suggest that coseismic faulting occurs along preexisting zones of weakness. In a few places, the correlation among seismicity and known geological features has been demonstrated. But the correlation between surface faults and seismicity is still pending in many areas.