First direct observation of coseismic slip and seafloor rupture along a submarine normal fault and implications for fault slip history

Authors Javier Escartín | Frederique Leclerc | Jean-Arthur Olive | Catherine Mevel | Mathilde Cannat | Sven Petersen | Nico Augustin | Nathalie Feuillet | Christine Deplus | Antoine Bezos | Diane Bonnemains | Valérie Chavagnac | Yujin Choi | Marguerite Godard | Kristian Haaga | Cedric Hamelin | Benoit Ildefonse | John Jamieson | Barbara John | Thomas Leleu | Christopher MacLeod | Miquel Massot Campos | Paraskevi Nomikou | Marine Paquet | Celine Rommevaux | Marcel Rothenbeck | Anja Steinführer | Masako Tominaga | Lars Triebe | Ricard Campos | Nuno Gracias | Rafael Garcia | Muriel Andreani
In Earth and Planetary Science Letters, Elsevier, vol. 450, pp. 96-107, September, 2016.


Properly assessing the extent and magnitude of fault ruptures associated with large earthquakes is critical for understanding fault behavior and associated hazard. Submarine faults can trigger tsunamis, whose characteristics are defined by the geometry of seafloor displacement, studied primarily through indirect observations (e.g., seismic event parameters, seismic profiles, shipboard bathymetry, coring) rather than direct ones. Using deep-sea vehicles, we identify for the first time a marker of coseismic slip on a submarine fault plane along the Roseau Fault (Lesser Antilles), and measure its vertical displacement of ∼0.9 m in situ. We also map recent fissuring and faulting of sediments on the hangingwall, along ∼3 km of rupture in close proximity to the fault’s base, and document the reactivation of erosion and sedimentation within and downslope of the scarp. These deformation structures were caused by the 2004 Mw 6.3 Les Saintes earthquake, which triggered a subsequent tsunami. Their characterization informs estimates of earthquake recurrence on this fault and provides new constraints on the geometry of fault rupture, which is both shorter and displays locally larger coseismic displacements than available model predictions that lack field constraints. This methodology of detailed field observations coupled with near-bottom geophysical surveying can be readily applied to numerous submarine fault systems, and should prove useful in evaluating seismic and tsunamigenic hazard in all geodynamic contexts.

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