Geophysical Evidence for the occurrence of gas hydrate in the Ulleung Basin, East Sea

Analysis of multi-channel seismic reflection data collected from the Ulleung Basin, East Sea reveals five types of seismic indicators that imply the existence of gas hydrate including the bottom simulating reflector (BSR), seismic chimney/column, acoustic blanking, enhanced reflections, and gas seepage. The BSR, the most common seismic indicator in the Ulleung Basin, is of high amplitude and good continuity in the southern slope, whereas it is of low amplitude and poor continuity in the northern basin. Seismic chimney/column of reduced reflectivity and velocity pull-up is commonly seen in the central basin and northeastern part of the study area suggesting the existence of gas hydrate or gas fluids. Acoustic blanking of reduced reflectivity partly occurs on the central basin consisting of turbidite/pelagic sediment. Acoustic blanking related to column structures is common in the southeastern slope of the study area. Enhanced reflection with strong negative amplitude below the BSR occurs in the western slope of the area and suggests the existence of free gas. Gas seepages combined with dome structures and pockmarks are widely distributed on the southern slope consisting dominantly of debris flow deposits.