Sismotectónica y esfuerzos en Brasil.

Abstract

The main features of the intraplate seismicity in Brasil are presented. The level of seismic activity is lower than several other intraplate areas in the Marcelo Assumpcao Sismoteelónica esfuerzos en Brasil y world: only five events with magnitudes =5,4 ni1, are known. Despite ihe small number of events for detailed statistical analyses, it seems that the activíty is not uniform in Brazil: some areas are more seismically active than others. Sorne seismotectonic zones are suggested taking into account not only the epicentral distribution but also the few focal mechanisms available. The intraplate stress data, derived mainly from focal mechanisms and breakouts, reveal a somewhat uniform regional field with strike-slip stresses in the eastem part of the continent, possibly changing to more compressional towards the west. The maximum horizontal stresses are roughly oriented E-W on average. In the southeastem continental shelf, stresses are compressional. Resides this regional component, due both to the plate driving forces and to the large-scale lateral structural variations, other local sources of stress (such as crustal flexural forces from sediment loading in the continental shelf) are also very important and can overcome the regional component in some cases. 1.