Investigating North Caribbean geohazards: First results from the TWiST sea campaign

The transpressive Northern Caribbean plate boundary contains an active twin strike-slip fault system – the Septentrional-Oriente fault zone (SOFZ) and the Enriquillo-Plantain Garden fault zone (EPGFZ). Within the past 15 years, the EPGFZ has generated two devastating earthquakes along this transpressive front – the 2010 Mw7.0 Léogâne and the 2021 Mw7.2 Nippes events, of which the 2010 event generated a small tsunami. The 2010 and 2021 earthquakes ruptured only short segments of the roughly 1,000-km long active fault system with partial reverse slip. These events are intriguing because the EPGFZ is assumed to be purely vertical / strike-slip, but the partial reverse slip testifies to the significant hazard they pose to densely populated areas. This severe risk level, in one of the least developed countries, warrants further investigation of the complex seismotectonics and geohazards in the region. As such, the Haiti-TWiST oceanographic campaign was developed and carried out in Summer 2024 on the R/V “Pourquoi pas?” to characterize geological hazards posted to Western Hispaniola. During this sea campaign, we conducted several geophysical surveys. In the first leg, we collected seafloor bathymetric data and conducted wide-angle seismic and high-resolution seismics surveys to image the roots and shallow portions of the SOFZ and EPGFZ. In the second leg, we deployed ocean bottom seismometers for earthquake monitoring near the SOFZ and EPGFZ and acquired a multitude of other data, such as seafloor bathymetry, acoustic water column data for imaging seeps, heat flow measurements near faults, and 15 sediment cores ranging from 30 cm to 11 m long. Two of these sediment cores were the first ever to be taken offshore Cuba. In this presentation, we give an overview of our first observations from data collected during the TWiST sea campaign.