[1] A 180 km long seismic wide-angle profile was acquired across the Vøring Plateau, NE Atlantic, using a tuned air gun array and three-component ocean bottom seismometers deployed with $5 km spacing. The seismic P wave data have been modeled by ray tracing/inversion, and the model has been constrained by S wave and gravity modeling. The data and modeling have allowed us to depict the crustal structure and nature of the continent-ocean transition (COT) in a classical volcanic margin case. The P wave velocity near the top of the main crustal layer is estimated to $6.0 km/s landward of the $25 km wide COT. The seaward increase to $6.5 km/s in the COT is conformable with heavily intruded continental crust within this zone. Farther seaward, the velocity increase to $6.9 km/s in the same layer suggests the presence of oceanic crust. The abundant magmatism landward of, and within, the COT is primarily observed as extrusives forming wedges of seaward dipping reflectors and mafic lower crustal intrusions/underplating. The maximum thickness of the oceanic crust is measured to $23.5 km at the seaward termination of the COT.Citation: Mjelde, R., T. Raum, B. Myhren, H. Shimamura, Y. Murai, T. Takanami, R. Karpuz, and U. Naess (2005), Continent-ocean transition on the Vøring Plateau, NE Atlantic, derived from densely sampled ocean bottom seismometer data,

Five regional Ocean Bottom Seismic profiles from the northwestern part of the Møre Margin, NE Atlantic, have been modeled with regard to crustal structure, and the interpretations have been supported by the use of multi-channel seismic and potential field data. The chi-squared values (uncertainty) for the studied profiles are generally in the range 1-3, and the uncertainty in the Moho depth is estimated to +/-1 km. The Continent-Ocean-Transition is found to be relatively sharp (10-40 km wide) expressing a change in physical properties corresponding to felsic continental crust along the landward part of the marginal high (V p =6.2-6.5 km/s), and thick, mafic oceanic crust further northwestwards. The Early Eocene breakup was associated with excessive magmatism, and the models document direct continuity between this magmatism and a lower crustal high-velocity layer in the Møre Basin (V p =7.1-7.3 km/s), suggesting a genetic link. The Jan Mayen Lineament is observed across the entire study area as northeastward termination of the lower crustal body, as well as structuring in the top of the crystalline basement and the Moho. We present a 2 speculative model involving lower crustal bodies of eclogites (Vp > 8 km/s) inferred in the easternmost part of the Møre Basin linking the Jan Mayen Lineament to the post-Caledonian Nordfjord-Sogn Detachment.

A computationally efficient procedure was developed for the fitting of a locally stationary autoregressive model. The amount of computations is bounded by a function of the data length and the model order only and does not depend on the number of possible arrival times. This facilitates automatic determination of arrival time by an on-line system. The on-line system FUNIMAR (fast univariate case of minimum AIC method of AR model fitting) was developed to implement the procedure.The method was checked by applying it to weak seismic signals from earthquakes which were superimposed with background noises such as traffic noise, electronic hum noise, and heavy microtremor. Experimental results confirm the effectiveness of the method for determining the onset time of P-wave and suggest that an AR model of the fifth order is sufficient to determine the onset time of the wave even if it is buried in considerably heavy noises. It is also shown that the onset time of S-wave can also be successfully determined by the method.

Modelling of extensive seismic datasets recorded on Ocean Bottom Seismographs (OBS) on the outer Vøring Margin, NE Atlantic, has provided significant new insights into deeper sedimentary structures, distribution of sill-intrusions in the sedimentary section, top of the crystalline crust, the lower crust and Moho. Primarily based on the modelling of S-waves, it is concluded that the high-velocity lower crust most likely consists of a mixture of plume-related Late Cretaceous/Early Tertiary mafic intrusions mixed with older continental blocks. Northeastwards in the Vøring Basin, the landward limit of the lower crustal high-velocity layer steps gradually seawards, closely related to five crustal scale lineaments. Evidence for an interplay between active and passive rifting components is found on regional and local scales on the margin. The active component is evident through the decrease in magmatism with increased distance from the Iceland plume, and the passive component is illustrated by the fact that all resolved crustal lineaments to a certain degree acted as barriers to magma emplacement. A lithospheric delamination model is invoked to explain the observed variations in crustal velocities and thickness. The location of six Tertiary domal structures in the Vøring Basin is between, or in the vicinity of, pre-breakup high-velocity structures, which may act as rigid blocks during compression. It is proposed that the existence and trend of these high-velocity structures, subject to mild NW–SE compression, is the most important factor controlling the formation, spatial distribution and trend of the domes. Structures in the high-velocity lower crust may be the single most important element in controlling the formation of the domes; all modelled highs in the lower crustal Early Tertiary intrusive layer seem to be related to the formation of domes.