Triggered slip events following the 2010 and 2021 Haiti earthquakes and their implications to seismic hazard in Hispaniola

Hispaniola is the most populous island in the Caribbean and is split into two countries, Haiti and the Dominican Republic. It is also where the North American and Caribbean plates push toward and slide past past each other, making use of two major fault systems: the Enriquillo Plantain Garden Fault (EPGF) in the south part of the island and the Septentrional Fault (SF) in the north. Both faults are active and hazardous; the EPGF ruptured in the devasting 2010 and 2021 Haiti earthquakes, together causing over 250,000 deaths and US$ 9 billion in damage. After the 2010 earthquake, sections of the EPGF that were expected to rupture next did not; the 2021 earthquake occurred elsewhere on the fault. After each earthquake, satellite-based radar data showed that parts of the EPGF were continuing to slip without producing any small earthquakes at all, hinting that these segments might not generate large earthquakes. Following up on this finding by investigating all SF and EPGF segments is crucial for assessing seismic risks throughout Hispaniola and for understanding why the 2021 earthquake happened where it did. This project will primarily use satellite-based radar and GPS data, along with seismometer data from local agencies, to determine the motion and earthquake potential of the EPGF and the SF. The project will foster collaboration between the Florida International University (FIU) and stakeholders in Haiti and the Dominican Republic, as well as scientists in France and South Korea. The island of Hispaniola hosts the Enriquillo Plantain Garden Fault Zone (EPGFZ) and Septentrional Fault Zone (SFZ) fault systems that accommodate most of the strain at this part of the North America-Caribbean (NA-CA) transform plate boundary. NA-CA strike-slip rate of ~17 mm/yr is partitioned on the EPFGZ and SFZ while a shortening component of the relative motion (~5 mm/yr) is accommodated via thrust faulting. Studies of the Mw 7.0 2010 and Mw 7.2 2021 Haiti earthquakes that ruptured the EPGFZ suggested that most of the seismic moment occurred on thrust faults that take up transpressional motion. Also, following both large earthquakes, satellite-based radar revealed an induced triggered slip on the EPGFZ, suggesting that segments of the EPGFZ may creep. Furthermore, the segments of the fault with the maximum Coulomb Failure Stress following the 2010 earthquake did not rupture during the 2021 earthquake. The dynamics of two earthquakes indicate that the EPGFZ is seismogenically segmented. The SFZ hosted historical large earthquakes and is capable of rupturing in a Mw ~7.6 earthquake. This research project will characterize strain partitioning and accumulation along the EPGFZ and SFZ by synthesizing satellite-based radar data from the c-band Sentinel-1 and L-band ALOS-2 missions, Global Navigation Satellite Systems (GNSS) observations, and earthquake data from the relevant local agencies in Haiti and the Dominican Republic. The main research activities include (1) detecting transient aseismic slip events, (2) calculating interseismic surface velocity fields of the EPGFZ and SFZ, and (3) constraining mechanical models that will characterize fault segment depth of lock, creeping, or transition from lock to creeping. The research project products will greatly aid in the seismic hazard assessment of the island. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.