CRUSTAL STRUCTURE OF THE CENTRAL PART OF THE VORING BASIN, MID-NORWAYMARGIN, FROM OCEAN-BOTTOM SEISMOGRAPHS

Regional Ocean Bottom Seismograph (OBS) data acquired in the central a nd northern part of the Voring Basin, mid-Norway margin, have been mod elled by use of two-dimensional (2-D) ray-tracing. The regional datase t comprises thirty OBSs deployed along seven 100-170 km long profiles. The deeper Dart of the Voring Basin is difficult to map using multich annel reflection data due to the presence of sills at intermediate sed imentary levels (2-5 km below sea-floor), but the modelling of the OBS -data reveals that this technique provides a reliable estimate of stru ctures and seismic velocities from the sea-floor to the upper mantle, The shallow and intermediate sediments (to 5 km below sea-floor) are c haracterized by a vertical increase in velocity due to increased confi ning pressure, There is also considerable lateral variation in the vel ocities within sedimentary layers at all levels. The OBS-data confirm that intrusions of sills are important at intermediate and deep sedime ntary levels (2-10 km below sea-floor) in most parts of the area. The sills seem to vary in lateral extent from about 20 km to more than 100 km, and their thick?ess is generally inferred to be about 200 m. The low velocity in the upper crystalline crust (6.2 km/s) confirms that t he crust in the Voring Basin is of continental origin, In most parts o f the area the velocity of the lower crust is as high as 7.3-7.6 km/s. This high-velocity layer is interpreted as a magmatic underplated bod y with strong lateral variations in thickness, The base of the 7.3 km/ s layer is interpreted as the Moho, and the upper mantle velocity is e stimated to 8.2 km/s.