L. Vieira Barros¹ , M. Sousa de Assumpcao² , J.M. De Carvalho¹

¹University of Brasilia, Seismological Observatory
²University of São Paulo, Seismological Center

Abstract:

Seismicity in Brazil is at a low level, with only three continental earthquakes of magnitude five in the last three decades. Until recently there has been a low number of seismic stations in the region. Both factors explain why it is very difficult to detect events at regional distances that can be classed as Ground True 5 (GT5). In the first PTS - CTBTO RSTT meeting (in 2012) seismologists from South America were encouraged to cooperate in identifying GTx events. At that time, Brazil appeared completely empty in the world map of GT events. With the deployment of the Brazilian Seismographic Network (RSBR) and using aftershock sequences well recorded by local and regional stations as reference events, it was possible to relocate mainshocks which would fulfill GT5 event criteria. We studied aftershock activity induced by a 4.6 mb mainshock on January 3, 2017. This event was registered by 25 regional stations of the RSBR. A local seismic network, which consisted of 5 stations, enabled to relocate this earthquake with an accuracy of a GT5 event. For hypocentral location an accurate velocity model was determined using phase conversion, which was clearly identified on the interface sediment-basement. In this work, we present a new GT5 event in order to better define the 3D velocity model for Brazil.