A regional shear-wave velocity model in the central Voring basin, N. Norway, using three-component ocean bottom seismographs

摘要

A regional Ocean Bottom Seismometer (OBS) dataset was acquired in the central and northern part of the Voring Basin, N. Norway, in 1992. Thirty three-component OBSs were deployed along seven regional profiles, and the shear waves recorded on the horizontal components have been modelled by use of 2-D ray-tracing utilizing an established P-wave model. In the shallow sediments (1-4 km depth) mean V-p/V-s ratios of 2.1-2.2 and 2.3-2.5 are inferred along the NW-SE- and NE-SW-trending profiles, respectively. The relatively high mean V-p/V-s ratios in this interval are probably related to unconsolidated sediments in the uppermost layers. The azimuthal variation in the V-p/V-s ratios with the fast direction NW-SE, indicates a shear-wave anisotropy of 5-10% in this interval, consistent with observations further north in the Lofoten area. In the 5-10 km depth interval high-velocity sill intrusions in the sediments are mapped by the P-wave modelling. These high-velocity intrusions act as efficient conversion interfaces, confirmed by the shear-wave modelling. A regional decrease in the V-p/V-s ratios to 1.7-1.8 are observed at 4-6 km depth, possibly related to sand-rich sediments in the middle Cretaceous. The upper crust is clearly mapped by the shear waves, and the inferred V-p/V-s ratio of 1.75 confirms that the crust in the Voring Basin is of continental origin. An increase of the V-p/V-s ratio (1.8-1.85) in the lower crust indicates a change in its composition, possibly explained by a 'mixing' of continental crust and magmatic underplating. (C) 1998 Elsevier Science B.V. All rights reserved. [References: 34]