Quantification of gravitational mass wasting and controls on submarine normal fault scarp evolution: An example from the Roseau fault, Lesser Antilles

Abstract:

Due to challenges involved in mapping the seafloor at high-resolution (e.g., < 2 m), data are lacking to understand processes that control the evolution of submarine normal fault scarps, which cover large parts of the global seafloor. In this study, we use data from autonomous deep-sea vehicles to quantify local erosion and deposition associated with a pronounced tectonic surface scarp formed by the 2004 M_w 6.3 Les Saintes earthquake and previous ruptures on the submarine Roseau normal fault (Lesser Antilles). We use high-resolution video imagery, photomosaics, and high-resolution bathymetry data (0.1–10 m/pixel) to identify active erosional features on the scarp including channels, steep gullies, head scarps, and dejection cones (submarine talus cones). We perform mass-balancing calculations and find that dejection cones effectively record the erosion signal of mass wasting from the footwall with a ratio of hanging wall deposition to footwall erosion of 0.80. Eroded volumes are used to estimate earthquake-induced landslide erosion rates for the Roseau fault of 14–46 m Ma^-1, which indicate that earthquake induced mass-wasting can occur at similar rates in submarine environments to various terrestrial lithological and tectonic settings. We present a process-based model of submarine scarp degradation in basement lithologies where scarp have a threshold stability height of 20–40 m and an equilibrium slope value of 30–40°. The data from the Roseau fault demonstrates that gravitationally driven mass-wasting is the key process that controls the morphology of uplifting submarine normal fault scarps in basement lithology. Over the lifespan of the scarp, mass wasting can be viewed as a continuous process that maintains a critical slope on an active scarp. More generally, the results presented here can potentially be applied to develop models of submarine landscape evolution based of degradation of normal fault scarps on the seafloor.