Análise probabilística da ameaça sísmica para o Nordeste do Brasil

Abstract

Although they exhibit lower seismicity compared to plate boundary regions, Stable Continental Regions (SCR) are not free from adverse seismic impacts. Assessing seismic hazard in these regions is essential, especially considering the presence of critical infrastructure and urban areas, where low-probability but significant-sized events can still pose substantial risks. In this context, Northeast Brazil stands out as one of the most seismically active areas in the SCR of South America, with events in recent decades causing significant damage to civil structures. This study conducted a Probabilistic Seismic Hazard Analysis for Northeast Brazil, focusing on critical locations, using an updated regional earthquake catalog and newly defined seismic source zones. For this, the application of more appropriate models for magnitude distribution was sought, revealing the rejection of the Gutenberg-Richter relation in one of the seismic sources. The results showed PGA values < 0.01 g for most of the study area, typically ranging between 0.01 g and 0.04 g for much of its northeastern portion, considering a 10% probability of exceedance over 50 years. In this region, under the same conditional probability, the highest PGA values were found in the range of 0.10 g to 0.20 g around the four most active seismic sources. The uniform hazard spectrum indicated values between 0.18 g and 0.08 g over a wide range of structural period for a critical location, reaching an average peak of 0.31 g. The findings suggest that, although most of the region complies with the current Brazilian seismic code, certain areas present significantly higher seismic hazard. In these areas, the respective seismic intensities can vary between VI and VIII, potentially causing damage ranging from minor in civil constructions to the collapse of older buildings.