Distribution of gas-charged sediment in Norton sound and Chirikov basin, northeastern Bering Sea

Abstract

Numerous zones of anomalous acoustic responses caused by gas in the subsurface sediment layers have been detected on seismic reflection records from Norton Sound and Chirikov Basin. Sound sources used range in size and power from 3.5 kHz transducers to 1326 in3 (21.71) air gun arrays. The frequency and distribution of these zones suggest that as much as 7000 km2 of the northeastern Bering Sea may be underlain by gas-charged sediment. Much of the gas is of shallow biogenic origin, having been generated in buried peat deposits. Compressional velocity is about 1.5 km/s in these Iayers. 7 percent below the velocity in gas free areas as determined from seismic refraction studies. Seismic velocity beneath a large gas seep south of Nome decreases to about 1.2 km/s in the interval from 250 to 440 m below the seafloor. where thermogenic gases of deeper origin are migrating upward along a system of basin margin faults.