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S51E-1053: Surface wave tomography of the European Arctic

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Abstract

Existing global and regional tomographic models have limited resolution in the European Arctic due to the small number of seismic stations, relatively low regional seismicity, and poor knowledge of the crustal structure. During the last decades, new seismic stations were permanently or temporarily installed in and around this region. However, many of the data from these stations are not easily accessible via the international data centers but only by direct request to various data operators. Recently, a new crustal model of the Barents Sea and surrounding areas had been derived in a joint project between the University of Oslo, NORSAR and the USGS (Bungum et al., 2005). This model with its detailed information on crustal thickness and sedimentary basins in the area helps to constrain the tomographic inversion of the upper mantle velocity structure based on surface wave data. To improve the surface wave data set in the region, we extensively searched for broadband data from stations in the area from the beginning of the 1970s until 2005 and were able to retrieve surface wave observations from the data archives at NORSAR, University of Bergen, University of Helsinki, the Kola Science Center in Apatity, and the Geological Service of Denmark in addition to data from the data centers of IRIS and GEOFON. Rayleigh and Love wave group velocity measurements from 10 sec to 150 sec period obtained on these seismograms were combined with the existing data set provided by the University of Colorado (e.g. Levshin et al., 2001). Using these data, we constructed a new 3-D shear velocity model of the crust and upper mantle beneath the European Arctic which provides higher resolution and accuracy than previous models. The new model reveals substantial variations in shear wave speeds in the upper mantle across the region. Of particular note are clarified images of the mantle expression of the continental-ocean transition in the Norwegian Sea and a deep high wave speed lithospheric root beneath Novaya Zemlya.
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... A programmed grid search algorithm helped to obtain a better fit to the observed gravity field. The 3D model of Levshin et al. (2005) was used to extend our model into the upper mantle. The S-wave structure for the crustal section was estimated using crustal P/S-wave ratios from same model. ...
... Our model was already used as primary input for a new surface-wave inversion and improved, along with an extended set of recordings (Levshin et al., 2005) the mantle model comprehensively. In addition, the model provides assistance for studies of various geodynamic problems concerning the plate tectonic setting of the Barents Sea region, basin formation processes or the distribution of magmatism. ...
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We here present BARENTS50, a new 3D geophysical model of the crust in the Barents Sea region. The target region of interest comprises northern Norway and Finland, parts of the Kola Peninsula and the East European lowlands. Novaya Zemlya, the Kara Sea and Franz-Josef Land terminate the region to the east, while the Norwegian-Greenland Sea marks the western boundary. In total, 680 one-dimensional seismic velocity profiles were compiled, mostly by sampling 2D seismic velocity transects, from seismic refraction profiles, every 25 km. Seismic reflection data in the western Barents Sea were further used for density modeling and subsequent density-to-velocity conversion. Velocities from these profiles were binned into two sedimentary and three crystalline crustal layers. The first step of the compilation comprised the layer-wise interpolation of the velocities and thicknesses. Within the different geological provinces of the study region, linear relationships between the thickness of the sedimentary rocks and the thickness of the remaining crystalline crust are observed. We therefore used the separately compiled (area-wide) sediment thickness data to adjust the crystalline crustal thickness according to the sedimentary thickness where no constraints from 1D velocity profiles existed. The BARENTS50 model is based on an equidistant hexagonal grid with a node spacing of 50 km. The P-wave velocity model was used for gravity modeling in order to obtain 3D density structure in the study region. A better fit to the observed gravity was achieved using a grid search algorithm which focused on the density contrast of the sediment-basement interface. The high resolution of 50 km is an improvement compared to older geophysical models.
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BARENTS50, a new 3-D geophysical model of the crust in the Barents Sea Region has been developed by the University of Oslo, NORSAR and the U.S. Geological Survey. The target region comprises northern Norway and Finland, parts of the Kola Peninsula and the East European lowlands. Novaya Zemlya, the Kara Sea and Franz-Josef Land terminate the region to the east, while the Norwegian-Greenland Sea marks the western boundary. In total, 680 1-D seismic velocity profiles were compiled, mostly by sampling 2-D seismic velocity transects, from seismic refraction profiles. Seismic reflection data in thewestern Barents Sea were further used for density modelling and subsequent density-to-velocity conversion. Velocities from these profiles were binned into two sedimentary and three crystalline crustal layers. The first step of the compilation comprised the layer-wise interpolation of the velocities and thicknesses. Within the different geological provinces of the study region, linear relationships between the thickness of the sedimentary rocks and the thickness of the remaining crystalline crust are observed. We therefore used the separately compiled (area-wide) sediment thickness data to adjust the total crystalline crustal thickness according to the total sedimentary thickness where no constraints from 1-D velocity profiles existed. The BARENTS50 model is based on an equidistant hexagonal grid with a node spacing of 50 km. The P-wave velocity model was used for gravity modelling to obtain 3-D density structure. A better fit to the observed gravity was achieved using a grid search algorithm which focussed on the density contrast of the sediment-basement interface. An improvement compared to older geophysical models is the high resolution of 50 km. Velocity transects through the 3-D model illustrate geological features of the European Arctic. The possible petrology of the crystalline basement in western and eastern Barents Sea is discussed on the basis of the observed seismic velocity structure.
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