Breaking the surface of the seafloor: Studying the traces of earthquakes underwater
Earthquakes are ruptures in the Earth’s brittle upper layer, and represent one of the major geological hazards on Earth. Both the ground movement (displacement, shaking). Associated processes that they trigger (e.g., landslides, floodings), can cause significant damage and casualties when they strike. As more than two-thirds of the Earth’s surface is underwater, submarine earthquakes represent approximately ~75% of the Earth’s seismicity; these can cause tsunamis, potentially devastating over widespread and faraway areas. Earthquakes often breach the Earth’s surface, their the ruptures record the geometry of earthquake displacement. The mapping and study of these ruptures (e.g. their geometry, length magnitude of displacement), conducted exclusively onland to date, allow us to understand earthquake dynamics, seismic history, and evaluate risks (e.g., predicting recurrence time and magnitude of earthquakes). The lack of submarine observations is thus a major gap on our understanding of the Earth’s seismicity and associated risks This talk will present the SUBSAINTES’2017 (France) cruise project (April 2017), identifying and mapping an earthquake rupture associated with the 2004 Mw6.3 Les Saintes Earthquake in the French Antilles, at a water depth of ~1 km. This cruise deployed the deep-sea ROV VICTOR6000 and AUV AsterX (IFREMER). Our fieldwork demonstrates that the combination of acoustic and optical mapping techniques, and the use of operational vehicles, now allow us to efficiently conduct geological fieldwork at scales and resolutions that are similar to those onland. We can thus now gather submarine systematycally data to better understand the Earth’s seismicity and associated risks.