Crustal structure and velocity anisotropy beneath the Beaufort Sea

Abstract

Crustal-scale seismic refraction data obtained in the Beaufort Sea during 1976 reveal a 4–5 km thick sedimentary layer overlying an oceanic crust that thickens rapidly as it approaches the continental terrace of Alaska. A synthetic seismogram analysis of multiple reflected, water-wave events indicates that the upper sedimentary layer has a compressional velocity of 1.8 km/s and a shear velocity of about 0.2 km/s. An oceanic layer 2A of 4.3 km/s, a layer 3A of 6.6 km/s, and a layer 3B of 7.6 km/s overlying an anisotropic (3%) upper mantle with a median velocity of 8.3 km/s are interpreted. The direction of maximum upper-mantle velocity appears to be approximately north–south in the area surveyed, suggesting that a rotation of the Northwind Ridge–Chukchi Plateau away from the Barrow–Martin Point sector of Alaska may have occurred.