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Subsaintes 2017 campaign – Underwater earthquake traces

From April 2nd to 24th, 2017, around 20 international scientists embarked from Pointe-à-Pitre aboard IFREMER's oceanographic vessel, Atalante, to study the network of faults that carve up the ocean floor and the many undersea volcanoes, between Guadeloupe's Les Saintes archipelago and the island of Dominica.

Subsaintes 2017 campaign – Underwater earthquake traces

Seafloor Bathymetric Map - Subsaintes

Publication date: 14/03/2017

Observatories, Press, Research

Related teams :
Marine Geosciences

Related themes : Natural Hazards

The SUBSAINTES campaign, led by Javier Escartin (IPGP, CNRS, USaPC) and supported by IFREMER and CNRS, will use the autonomous AsterX robot to produce very high-resolution maps. The remotely operated robot VICTOR 6000 will carry out detailed geological observations and sampling. The scientific team is made up of researchers and engineers from several national institutes (IPGP, U. Nice Sophia Antipolis/Géoazur, U. Lyon, U. Paris Sud, IFREMER) and international institutes (U. Columbia in the USA, U. Girona in Spain, U. Bergen in Norway).

On November 21st 2004, the Les Saintes earthquake (Mw 6.3) ruptured the Roseau submarine fault located to the south-south-west of the Les Saintes archipelago (Guadeloupe). This was the largest earthquake to affect Guadeloupe and this area of the Lesser Antilles since 1897. It was widely felt on land, causing extensive damage in Les Saintes and generating a tsunami of around 1m in amplitude. The main earthquake was followed by a series of aftershocks, which were incessant for the first two hours, adding to the anxiety of the people of Les Saintes.

Victor 6000 Submarine

Numerical models showed that the fault had ruptured over a length of approximately 10 km and that the earthquake had caused a vertical displacement of around 1 m along the fault. In 2013, a preliminary study carried out using the remotely operated robot VICTOR 6000 (IFREMER) and the autonomous robot Abyss (Geomar, Germany) during the ODEMAR campaign, enabled the central part of the Roseau fault to be mapped in detail and the slip plane to be identified at a depth of 1,000 m, thus verifying the modelling.

Preliminary geological observations also identified deformation structures linked to the earthquake of November 21st 2004. The images and 3D reconstructions produced from video sequences acquired by the remotely-operated robot have made it possible to measure, for the first time in the underwater environment, a vertical co-seismic displacement of around 0.9 m. These preliminary results demonstrate that the use of underwater vehicles and advanced 3D imaging and reconstruction technologies can be used to study in detail recent seismic ruptures of underwater faults.

The SUBSAINTES oceanographic campaign was proposed as a result of this first campaign and the limited scope of the 2013 preliminary study. Lasting 21 days over the study area, this campaign will enable a complete and detailed mapping of the Roseau fault, in order to measure the co-seismic displacements along this fault. This data will provide a better understanding of the mechanisms behind tsunamis, and will be a first in the study of subsea co-seismic deformations.

Underwater fault plane (top) along the Roseau fault: 3D reconstruction from video footage taken by the ROV Victor (ODEMAR 2013 campaign) of a slip plane at the foot of the Roseau escarpment. And videomosaic (below) also showing a strip of slip plane recently exposed at the foot of this outcrop (indicated by the white line).

Previous bathymetric surveys (IFREMER BATHYSAINTES, Gwadaseis and Aguadomar campaigns) have identified a complex network of faults, numerous submarine volcanic structures and interactions between faults and volcanoes in this seismically active area (2004 earthquake and several seismic crises since, including one in 2017). Since 2004, more than 35,000 aftershocks have been recorded by the seismological network of the Observatoire Volcanologique et Sismologique de Guadeloupe (OVSG-IPGP) and the West Indies network (OVSG, OVSM, IPGP, SRC). The second objective of this campaign is to map these structures, observe the geology and take samples of volcanic rocks, faults and sediments. The study of these samples and their dating will provide a better understanding of the links with the evolution of the volcanoes of the surrounding islands (Guadeloupe, Les Saintes, Dominica) and, above all, the volcanic and underwater tectonic history of this area, which is little known to date but very active.

The results obtained during this campaign will therefore contribute to improving knowledge of the geological processes involved in volcanic, seismic and tsunami-related hazards in the Lesser Antilles, at the heart of the observation and monitoring networks of the volcanological and seismological observatories in Guadeloupe and Martinique (OVSG and OVSM, IPGP). The result will be to take better account of these hazards in risk prevention strategies in the Lesser Antilles, with implications for other regions of the world exposed to similar telluric risks.

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