Styles of Soft-Sediment Deformation of the Lower Headwall of the Cape Fear Landslide, Offshore North Carolina

Abstract

The lower headwall of the submarine Cape Fear Landslide consists of geological features that may indicate ongoing or future episodes of slope failure. In 2014 new 2-D multi-channel seismic data were gathered in this area for the Eastern North American Margin (ENAM) Community Seismic Experiment. Interpretation of these new seismic data may provide important insight into whether or not the Cape Fear Landslide is experiencing ongoing deformation and/or may fail again in the future. Observed features include: potential listric faults, sediment waves, creep deformation and deformation caused by possible fluid flow (e.g., free gas). Other structures such as an unconformity in the lower portion of the lower headwall are also observed. The deformations that appear as faults (or sediment waves) are possibly a cause of lateral stress reductions associated with the release of slope sediments immediately adjacent to the headwall and potentially the added stress of diapirism in the area. Methane gas hydrates are thought to be located near the Cape Fear Landslide. Potential free gas is shown in and near the detachment zone. Potential creep deformation is also identified as being caused by dissociation of methane hydrates and stress related to the upslope region of the Cape Fear Landslide. The tectonic setting and surrounding features of the Cape Fear Landslide are consistent with a retrogressive submarine landslide. Like many other of the large submarine landslides observed on the modern day ocean floors, it is not clear to what extent the Cape Fear slide is currently deforming or if a future failure at this site is possible. Future work is required to answer that question.