PSHA for the Dominican Republic

The Dominican Republic, situated on eastern Hispaniola Island in the Caribbean, is subject to moderate to high seismic hazard mostly controlled by oblique convergence at the Caribbean/North American plate boundary. Offshore of the island, the North Hispaniola Trench (NHT) and Los Muertos Trough (LMT) subduction-like structures accommodate shortening, while crustal faults both onshore and offshore also take up some deformation. Historically, the Dominican Republic’s large cities, as well as those in Haiti (which shares Hispaniola) have been damaged by earthquakes, the worst of which required the population to relocate (e.g. the 1562 Santiago de los Caballeros earthquake).  Given the elevated hazard, the Dominican Republic was selected to engage in the Global Earthquake Model (GEM) Foundation coordinated USAID-funded “Training and Communication for Earthquake Risk Assessment” project, which aimed to improve earthquake risk assessment capacity in Latin American cities. This project and the collaborations that emerged were the basis for developing a seismic hazard model for the Dominican Republic.

The seismic hazard model is implemented in the OpenQuake Engine, and mostly uses GEM’s model-building tools and state-of-practice. Two main datasets were used for the seismic source characterization: a homogenized earthquake catalogue that benefited from local seismicity records contributed by the Servicio Geológico Nacional (SGN) and Universidad Autónoma de Santo Domingo (UASD), and an active faults database that combines GEM’s global database and one compiled by SGN during recent seismic hazard projects. Together, these datasets were used to constrain seismic source geometries and rates for active shallow crustal earthquakes, subduction interfaces and subduction-like thrusts, and intraslab earthquakes. Active shallow crustal sources were characterized as a combination of fault ruptures and off-fault (distributed) smoothed seismicity. Fault rupture geometries were pre-defined using the Seismic Hazard and Earthquake Rate In Fault Systems (SHERIFS) method, which allows multi-fault ruptures, incorporating epistemic uncertainty in the magnitude scaling relationship (and thus maximum magnitude), portion of earthquakes modelled on and off faults, and slip rates of two major fault systems. Additional uncertainty was considered in the assumptions used to smooth distributed seismicity rates. The NHT and LMT were also modelled using the SHERIFS method, while the other subduction sources were modelled using GEM’s more standard approaches (i.e. a single fault with complex geometry for the interface and pre-defined ruptures constrained to the intraslab volume). Two end-member magnitude frequency distributions were used for the Puerto Rico Trench interface: one assigning more moment to large magnitudes, and one obeying the Gutenberg-Richter relationship. For intraslab sources, epistemic uncertainty was captured in the assumptions for smoothing rupture probabilities according to past earthquakes. The ground motion characterization relied on residual analyses performed in past GEM projects, but replacing outdated GMPEs on subduction sources with more recent counterparts.

Hazard results generally reinforce former perceptions. In Santiago de los Caballeros, PGA reaches ~1g for 2% probability of exceedance in 50 years, controlled by the Septentrional Fault, while in the capital (Santo Domingo) PGA of ~0.5g is impacted by all tectonic region types, and includes contributions from moderate magnitude earthquakes (M_w 5-6).