Produção Nacional
Seismicity patterns and focal mechanisms in southeastern Brazil
1997; Brazilian Society of Geophysics; Volume: 15; Issue: 2 Linguagem: Inglês
10.1590/s0102-261x1997000200002
ISSN1809-4511
AutoresMarcelo Assumpção, José Roberto Barbosa, Jesús Berrocal, Ailton Bassini, J.A.V. Veloso, Vasile Mârza, Mônica G. Von Huelsen, L. C. Ribotta,
Tópico(s)Geological formations and processes
ResumoThe seismicity of SE Brazil is studied with a recent deployment of additional temporary digital and analog seismographic stations. Regional and local stations have allowed the determination of three new composite focal mechanisms for the earthquake series of Betim in 1992/93, Formiga in 1993, and the reservoir-induced events of Nova Ponte in 1995, all in Minas Gerais state. The focal mechanism data in the southern part of the São Francisco craton and adjacent Brasília fold belt indicate both normal and reverse faulting with a common E-W to NE-SW orientation of the maximum horizontal stress. Far from the continental margin, the focal mechanisms are consistent with theoretical estimates of stress directions from finite-element modelings of the forces driving the South American plate. Near the Serra do Mar coastal range, the stress pattern seems more complex. A selection of the earthquake catalog, using threshold magnitudes varying in time to yield a data set with spatially uniform coverage, indicates two main seismic areas: 1) the offshore continental shelf , and 2) the southern part of the Brasília fold belt and the São Francisco craton. The high topography areas of the Serra do Mar and Serra da Mantiqueira (in the Ribeira fold belt) and the Paraná basin are much less seismically active.
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