| Summary: | This dissertation deals with the resolution of P- and S-velocity variations in the upper mantle (down to 600 km) using teleseismic P- and S-wave arrival times. The natural laboratory is the land areas bordering the North Atlantic; the Scandinavian and East Greenland Caledonides and the Northern segment of the Tornquist Zone which includes the Danish and adjacent areas. The seismological methods required were improved. In a methodological inversion study, I investigated the use of irregular cells (trapezoids) in teleseismic tomography. The resulting Ray-Adapted-Trapezoidal-Modeling provides improved resolution when stations follow profiles. The method was tested on the SCANLIPS array across the Scandinavian Peninsula (Paper I). On the data side, I performed a complete reorganization of the in-house MATLAB-based system (Medhus et al., 2012a,b) for handling event extraction, filtering, cross-correlation and arrival-time picking, involving about 50% rewriting and 50% code extension, now also interfacing with the SAC-system and GMT. Ellipticity correction was built in, following the Kennett and Gudmundsson (1996). With these improved methods, I studied the upper-mantle velocity structure in three regions. First study focused on the northern segment of the Tornquist Zone, covering the tectonic transition from the southern part of the Baltic Shield to the Danish and North German Basins. A previously identified main Upper-Mantle Velocity Boundary (UMVB) follows closely along the Sorgenfrei-Tornquist Zone and the Oslo Graben (e.g. Medhus et al. 2012a). Using the above mentioned improved methods, as well as data from the new JULS project, this boundary was confirmed in both P- and S- velocity as well as in the structure of the VP/VS ratio, and additional significant anomalies were identified. The contrasts in VP/VS put important constraints on the required compositional differences in mantle lithosphere and asthenosphere in the region. Second study focused on the Scandinavian Caledonides, using a dense network south of Trondheim (including SCANLIPS profile) and more sparse station coverage to the north. The UMVB was resolved in P-and S-velocity as well as the VP/VS anomaly. From the Oslo Graben the UMVB follows the western edge of the Trans-scandinavian Igneous Belt to the Atlantic coast, from where where it continues northward sub-parallel to the coast. Third study compiled all data in the first two studies with permanent station data from the North Atlantic and Greenland, and a dense temporary profile, the East Greenland Caledonian Central Fjord Array (EGCFA). EGCFA resolves low upper-mantle velocities close to the east coast of Greenland and high mantle velocities below the high topography inland. High and low mantle velocities are separated by a seaward dipping boundary. A final correlation study of topography versus upper-mantle velocity revealed positive correlation in Southern Norway but negative or absent correlation on three other regions bordering the North Atlantic. This result challenges the hypothesis of widespread Late Cenozoic uplift.
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