Inversion of refraction data from the Fram and Nansen Basins of the Arctic Ocean

Abstract

As a part of the Fram 2 experiment (March–May 1980) six refraction lines were shot in the Pole Abyssal Plain or Fram Basin of the eastern Arctic Ocean. During the Fram 4 experiment (March–May 1982), four refraction lines were also shot in the Nansen basin just northeast of the Yermak Plateau. The Fram 2 lines at 86°N, 24°W cover both the abyssal plain region and the northern flank of the Morris Jessup Rise near magnetic anomalies 22 and 23. The Fram 4 lines near 83°N, 15°–20°E are on slightly younger crust at anomaly 12. In this paper we introduce new methods for processing and inversion of Arctic refraction data and contrast the results from these tectonically similar regions on opposite sides of the spreading center at the Arctic Mid-Ocean (Nansen) Ridge. In both experiments the data were recorded digitally on a two-dimensional array of 24 hydrophones located 93 m below the floe camps. These multi-channel data are processed by high-resolution array processing techniques to yield velocity spectra over the short 1 km apertures of the arrays. These velocity spectra are transformed to tau-slowness and offset-slowness parameterizations and are inverted by 1. (1) velocity-depth migration 2. (2) tau-sum 3. (3) extremal inversion techniques to obtain crustal velocity models down to the Moho. Without the ability of the array processing to discern late breaking primaries, multiples, and shear arrivals, the sparsely shot lines with 5–15 offsets over the 30–100 km line lengths would not be invertible by these methods. These results demonstrate the effectiveness of arrays in determining crustal structure under the constraints of Arctic ice pack environment.