Natural gas hydrates on the southeast U.S. margin: Constraints from full waveform and travel time inversions of wide-angle seismic data

Strong bottom-simulating reflectors (BSR) have been mapped over a region of approximately 50,000 km2 on the southeastern U.S. margin and have been associated with possible abundance of natural gas hydrates. In June 1992, coincident single-channel seismic and wide-angle ocean bottom seismic data were acquired in the region, focusing on the Blake Ridge and the Carolina Rise. Wide-angle reflections from the BSRs were clearly observed at offsets up to ∼6 km. Joint travel time inversion was conducted with wide-angle and vertical-incidence data in order to explore possible regional variation, and the resultant two-dimensional average velocity models imply higher background velocities on the Carolina Rise. Full waveform inversion was then performed to determine the seismic origin of the BSRs. The best fit model shows a similar low velocity (∼1.4 km/s) beneath the BSR at both sites, indicating trapped free gas with low saturation (