An Improved 1-D Velocity Model for Routine Seismic Location in Central Brazil

The Brazilian seismicity is not uniform and in general it is characterized by low magnitude (M<3.5). In the last century occurred only two dozen events of magnitudes above 5, two of which with magnitudes larger than M6.0. The Brazilian Seismic Catalog was initially compiled by Berrocal et al. (1984) and it is continuously upgraded by the seismological centers of the University of Brasilia (UnB), University of São Paulo (USP), University of Rio Grande do Norte (UFRN), Technological Research Institute of São Paulo state (IPT), National Observatory (ON) and Brazilian Geological Survey (CPRM). The catalog is very heterogeneous and the locations quality for some events is very pour. A better and more uniform monitoring phase started only after 2014 with the establishment of the Brazilian Seismograph Network (RSBR), when the Amazon region detection threshold dropped from M4.5 to M3.5. In this study, we propose a new 1-D velocity model for the central Brazil obtained with coupled hypocenter-velocity-model non-linear inversions performed with the code VELEST. From the catalog, we have selected a set of high quality events, with a total of about 1000 - P wave observations from 78 stations, located up to 1200 km. The stations used in this work are from the RSBR and UnB seismic projects. In this study, we started with four velocity models and obtained an optimum and better 1-D velocity model with 7 layers and the respective stations residuals. The used set of events and their respective rays covered most of the working area and as a result, the relocation improved the events positions.