Topofacies analysis of the seafloor offshore Western Nile Delta: implications for geohazard assessment.

Understanding the topography and stability of the seafloor and its associated geohazards is a critical first step to planning offshore infrastructure projects. This is particularly true on the continental slope where gravity and tectonic deformation processes and mass transport of sediment are important factors in shaping the seabed. Here we demonstrate how these factors lead to seabed topography with characteristically different morphological properties. A seafloor map of the West Nile delta slope was created using a 3D seismic data volume from which areas of distinctive topography were identified. Investigation of the shallow facies, structure and stratigraphy shows these zones are formed from a specific depositional bodies or structural features. We define these areas as topofacies and show each is characterised statistically by significantly different distributions of dip, roughness and curvature. The topofacies result from mass transport complexes (MTC1, MTC2) a headwall failure scarp (the Rosetta failure scarp), a prograding wedge of sediment, and channel systems with differing degrees of activity. We show how codifying areas of the seafloor in this way, using metrics more conventionally used in terrestrial geomorphic studies, provides a focus to constrain different submarine geohazards and could guide further data acquisition and analysis for the development and design of seabed infrastructure.