Reconstructing the Exhumation and Paleo‐Earthquake History of a Submarine Normal Fault From Preserved Markers at the Seafloor (Roseau Fault, Lesser Antilles, France)

Assessing seismic and tsunami hazards along coastlines requires understanding past earthquakes and their recurrence along active submarine faults. Subaqueous paleoseismology commonly relies on sediment cores and seismic reflection data, but these methods may be limited by local site conditions or data quality. To overcome these limitations, a new approach using submersible‐based optical imagery can provide valuable insights into the paleoseismic history of submarine faults. In this study, we conducted a near‐bottom geological survey using submersibles along the Roseau normal fault (Lesser Antilles, France). This fault can host a M7 event if broken entirely. In 2004, it generated the Mw6.3 Les Saintes earthquake that produced a prominent coseismic ribbon at its base. High‐resolution submersible observations of the fault free face allowed mapping and characterizing detailed fault scarp morphologies, including new deformation markers such as abrasion bands, notches, roughness variations, dark bands, and uplifted sediments. These geomorphic markers form on the seafloor and are interpreted as records of fault scarp exhumation linked to changes in base level driven by sedimentation and tectonic activity. At one site, the observed morphology can be explained by three distinct earthquakes combined with episodes of rapid sedimentation. The penultimate earthquake produced a minimum vertical offset of 3 m, exceeding the 1.4 m slip associated with the 2004 event, indicating that it was at least as energetic. Sedimentation rates from nearby cores indicate that this penultimate event occurred much more recently than 2.8 kyr. These results demonstrate the value of submersible‐based offshore fault studies for reconstructing seismic histories.