UC Santa Barbara

Hydrocarbons, such as methane or oil, flow to the seafloor from subsurface reservoirs and can induce elevated or depressed bathymetric terrains. They can harbor poorly understood life and induce mass wasting or slumping. Identification of hydrocarbon source and seepage activity is a nested process, involving a combination of multibeam surveys, seismic surveys, and direct observations. Classification of terrains induced by different hydrocarbon source based on bathymetric signatures has not yet been attempted in the literature. In this study, geomorphic analysis is conducted on high-resolution bathymetric data, collected by the autonomous underwater vehicle (AUV) Sentry, of hydrocarbon induced terrains formed by various sources offshore Southern California and in the Gulf of Mexico. Analyses of elevated hydrocarbon induced terrains sourced from gas hydrate, mud, and oil suggest that different phases of hydrocarbons may produce detectable scale-dependent geomorphic and hypsometric signatures. Actively seeping depressed hydrocarbon induced terrains, or pockmarks, may be characterized by a higher number of large coalesced and small unit pockmarks when compared to dormant terrains. The quantitative classification of hydrocarbon induced terrains by source or activity shown here suggest that bathymetric signatures may be representative of hydrocarbon seepage properties. These analyses can be easily implemented into existing automated feature detection techniques.