Recent Seismic Activity in the S-W Edge of the Mato Grosso-Goiás- Tocantins (MGT) Belt (Central Brazil)

In Central Brazil lies one physiographic province with outstanding geological, geophysical and seismotectonical features, it is known as Goias- Tocantins seismic belt (Assumpcao et al. 1986; Veloso 1988; Fernandez et al. 1991), but for reasons to be explained bellow, we advance the more appropriate denomination Mato Grosso-Golas- Tocantins seismic belt. This physiographic province (Fig. 1) is a Proterozoic orogen formed by an inversion of an oceanic basin, provided by the convergence between the Amazon and the San Francisco-Congo cratons during formation of the eastern part of the Gondwana super-continent (Fuck et al. 1993, 1994; Fuck 1994). The present dynamics of this province is represented, among other factors, by the conspicuous seismicity ranging the microearthquake to small earthquake levels (Fig. lA) , that present a NE to SW trend, extending from Tocantins state (in north) to Mato Grosso state (in south)[hence, we consider more suitable to call it Mato Grosso-Goias-Tocantins seismic belt (MGT belt)]. During the beginning of 1996 a salient seismic sequence originated some 10 to 15 km north of the small town of Araguaiana (Mato Grosso). This paper is intended to introduce a brief presentation of the main features and findings related to this earthquake sequence.