Probabilistic Seismic Hazard Analysis for NE Brazil

Performing seismic hazard analysis in Stable Continental Regions presents unique challenges due to the low rates of seismicity, long recurrence intervals of significant earthquakes, and limited historical earthquake records. These factors complicate the identification and characterization of active seismic zones and the accurate modelling of seismic hazard. However, assessing seismic hazard in these regions is crucial, especially when considering the presence of critical infrastructure and urban areas where even low-probability, high-impact events can pose significant risks. The Northeast of Brazil stands out as one of the most active seismic areas in the stable part of South America, with records of events that have caused considerable damage to civil structures in recent decades. We present a Probabilistic Seismic Hazard Analysis for Northeast Brazil, incorporating an updated regional earthquake catalog and newly defined seismic source zones. This study focuses on calculating Peak Ground Acceleration and spectral accelerations for critical locations, including state capitals and key infrastructure sites. The results show that while most of NE Brazil conforms to the current Brazilian seismic design code, certain regions exhibit significantly higher seismic hazards. In some areas, PGA values exceed the design code thresholds of 2.5%g and 5.0%g for 10% probability of exceedance in 50 years. The disaggregation reveals that local, moderate-magnitude events drive the seismic hazard around some sites, whereas others are more affected by larger, distant earthquakes.