Wrapround Multiple Reflectors over the Seafloor in the Gas Hydrate Area: A Possible Indicator of Methane Plume

Abstract

Seismic wraparound multiples which are produced by the previous shot and trapped between the sea surface and flat seabed in the two-dimensional marine seismic reflection data have the potential to provide information about oceanographic phenomena because their repetition in the water column could enhance the detectability of the disturbance of seismic wave propagation. By focusing on the disturbance of wraparound multiples, we inferred the possible presence of methane gas bubbles emitting from the seafloor over several kilometers within a submarine canyon with a flat seabed. We observed the significant disturbance of wraparound multiples in both pre-stacked gathers and common mid-point stacked sections, which may be caused by methane bubbles. The existence of a bottom simulating reflection, a fault, and Calyptogena colonies provides indirect evidence of methane gas bubble seeps, while the existence of a cold seep is direct evidence of them in the study area. Finally, we conducted preliminary numerical simulations of acoustic wave propagation to investigate the cause of disturbances of wraparound multiples. Our preliminary numerical simulations imply that the disturbance of wraparound multiples might be associated with the internal scattering caused by an aggregation of gas bubble seeps in the water column.