Crustal structure of the central part of the Vøring Basin, mid-Norway margin, from ocean bottom seismographs

Abstract

Regional Ocean Bottom Seismograph (OBS) data acquired in the central and northern part of the Vøring Basin, mid-Norway margin, have been modelled by use of two-dimensional (2-D) ray-tracing. The regional dataset comprises thirty OBSs deployed along seven 100–170 km long profiles. The deeper part of the Vøring Basin is difficult to map using multichannel reflection data due to the presence of sills at intermediate sedimentary levels (2–5 km below sea-floor), but the modelling of the OBS-data reveals that this technique provides a reliable estimate of structures and seismic velocities from the sea-floor to the upper mantle. The shallow and intermediate sediments (to 5 km below sea-floor) are characterized by a vertical increase in velocity due to increased confining pressure. There is also considerable lateral variation in the velocities within sedimentary layers at all levels. The OBS-data confirm that intrusions of sills are important at intermediate and deep sedimentary 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 thickness is generally inferred to be about 200 m. The low velocity in the upper crystalline crust (6.2 km/s) confirms that the crust in the Vøring Basin is of continental origin. In most parts of 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 body 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 estimated to 8.2 km/s.