Comparison between a Regional and Semi-regional Crustal OBS Model in the Vøring Basin, Mid-Norway Margin

Semi-regional Ocean Bottom Seismograph (OBS) data acquired in the central and northern part of the Vo*ring Basin, mid-Norway margin, have been modeled by use of 2-D ray-tracing. The semi-regional model, derived from the study of twenty-five OBSs deployed along a 120-km long profile, is compared with a regional model consisting of five OBSs from the same profile. The semi-regional model is somewhat more detailed than the regional model, due to the considerably closer receiver spacing. The overall geometry and velocity distribution of the two models are remarkably similar, however, proving that the regional procedure with large OBS spacing provides a reliable regional model. Intrusions of sills, related to early Tertiary continental rifting and break up, are important at intermediate and deep sedimentary levels (2–10 km below sea floor) in most parts of the area. The semi-regional modeling suggests that one of the deepest sills extends much further east and is substantially thicker (locally more than 500 m) than indicated in the regional model. Another important difference is a high-velocity body within the upper crystalline crust at 11–12 km depth in the NW part of the area, indicating that the closer OBS spacing in the semi-regional modeling allows detection of local intra-crustal intrusions. Local differences are also inferred in the lower crust; at about 20 km depth a structure is inferred within the lower crust from wide-angle reflections. This might suggest that the high-velocity lower crustal layer, interpreted as magmatic underplating, consists of a mixture of underplated:intruded magmatic material and blocks of continental lower crust.