Seismicity and seismic hazard in the continental margin of southeastern Brazil

Although seismic activity in Brazil is low to moderate, some earthquakes with damage potential occurred in the past. Engineering structures located along the coast and those installed in deep waters need to comply with safety requirements. In addition, there is a need to address the public interest regarding the effects of seismically-induced landslides. Therefore, a probabilistic seismic hazard assessment was carried out for the offshore south/southeast regions of Brazil, in order to estimate potential levels of ground motion. A historical and recent instrumental seismicity catalog for this region has been compiled. A stochastic attenuation relation with different seismic source models and recurrence parameters was used in a hazard analysis with the CRISIS 2012 software. To capture the epistemic and aleatoric uncertainties in the hazard calculations, a logic tree approach was adopted, considering different seismic zone models, seismic activity parameters, and scaling factors in the Ground Motion Prediction Equation. It was verified that the Peak Ground Accelerations are mostly less than 2.0% g in the continental portion of the region (for 10% exceedance probability in 50 years). At a particular point of interest located offshore in the continental slope of the study area, the seismic hazard is also low, with the maximum acceleration for the probability of exceedance of 10% and 2% in 50 years reaching mean values of 3.2% and 19.1% g, respectively, for very hard rock conditions.