Fluid Flow and BSR Distribution off Oregon
Abstract: A marine seismic survey was conducted off Oregon as part of the National Science Foundation (NSF) sponsored University-National Oceanographic Laboratory System (UNOLS) chief scientist training cruise from September 26th-October 2nd, 2017. The data collected show indications of gas hydrates based on the observation of prominent bottom simulating reflectors (BSRs) at depths ranging from 95-316 m below the seafloor (mbsf). The shallowest BSR is noted ~103 km north of Hydrate Ridge at ~95-100 mbsf beneath a frontal ridge crest that deepens to ~200-210 mbsf below the ridge flanks. In this area, extensional cracks or perpendicular normal faults, are also observed. Within some of the seismic lines, the presence and accumulation of free gas in the sediment are indicated by strong reflections with opposite polarity beneath the BSR. Additional observations made include disrupted BSR, potential double BSR, methane bubbles in the water column, and high amplitude signatures in the spectral decomposed sections. Several seepage sites through the entirety of the sediment column were observed in the vicinity of Deep Sea Drilling Project Leg 18-site 176, which show strong amplitudes at the seafloor on spectral decomposed sections. These are likely sites of past gas columns that currently have carbonate caps at the seafloor.
Lenora Perkins*, Subbarao Yelisetti, and Dibakar Ghosal
Judging Forms – Official judges only