Transient discharges from marine hydrocarbon seeps: spatial and temporal variability

Marine hydrocarbon gas emissions at an intense, 20-m-deep seep in the Santa Barbara Channel, California were studied with a network of three turbine seep-tents and repeated seabed mapping. The tents observed two gas ejection events that are interpreted as due to blockage of constrictions in fractures and subsequent blow-through. Seabed mapping suggests that very large transient emission events occur, are related to tar, and are temporally and spatially variable. Transient emissions have the potential to more efficiently transport methane to the atmosphere than steady-state emissions. We present an electrical model analog of subsurface seepage useful for seepage flux interpretation. The model predicts that variations in resistance at one vent shifts some of its flux to other connected vents, and that the shift is not zero-sum, i.e., a resistance change at one vent causes a flow change for the overall fracture system.