2024-08-26 16:01:06
In the middle of the Gulf of Gonâve, west of Haiti, a buoy coming from thousands of meters deep reemerges in the dead of night. In the silence of the bridge of the Why not?, where all lights are off to enhance night vision, Lieutenant Mathis Terret spots the buoy’s flasher among the waves: “OBS at surface.” He starts maneuvering the 107-meter ship to recuperate the object, an orange sphere the size of a large yoga ball. The OBS is not just a buoy, but a €25,000 ocean bottom seismometer (OBS) that scientists use to record earthquakes and seismic waves on the seafloor. Lieutenant Terret is “fishing” one of the 65 OBS that the French Research Institute for Exploitation of the Sea (Ifremer) used this summer to image the structure of the Earth up to 40 kilometers below the seafloor near Haiti.
The OBSs were deployed by Ifremer’s flagship between Haiti, Jamaica and Cuba. They are part of a campaign that is trying to understand the origin, behavior and dangerousness of the two twin faults that cross Haiti from west to east, the Septentrional-Orient fault to the north and the Enriquillo-Plantain Garden fault to the south. Dubbed Haiti Twist, the campaign, which ran from May 31 to July 22, also included sediment coring.
“Other campaigns in the past studied these faults and the tectonic blocks that slide along them,” said Walter Roest, a senior geophysicist at Ifremer and the chief scientist of Haiti Twist. “What we don’t know is their deep structure, or their current activity offshore Haiti. Once you know more about that, you could calculate the potential for earthquakes of certain magnitudes, based on the length of segments where the rupture could happen and their depth. Nobody can predict earthquakes, but we can try to calculate the seismic hazard in a specific area.”
On January 12, 2010, the Enriquillo fault ruptured in southern Haiti, provoking a 7.0-magnitude earthquake that killed between 200,000 and 316,000 people. It is one of the deadliest natural disasters ever recorded. Eleven years later, the same fault slipped again, this time with a magnitude of 7.2. The epicenter of the 2021 earthquake was in a much less populated area, but 2,248 people died.
Santiana Vissière, a Phd student at Université de Bretagne Occidentale, was 15 years old in 2010, and she was at her school in Port-au-Prince when the earthquake unleashed. “We didn’t know it could be so catastrophic. Instinctively, we all went outside and luckily there were no victims at the school,” she recalled on board the Pourquoi Pas?, where she contributes to processing the sediments extracted with coring. “In a way, the 2010 earthquake left a trauma. Here on the ship sometimes I wake up when it starts vibrating. After the one of 2021, I took part in the installation of seismometers in the south of the island, as well as in the survey of landslides in the region.” Now she is writing her thesis on the geology of Haiti.
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