Deep seismic studies in the western part of the Baltic shield

Abstract: The Caledonides form an ancient orogenic belt at the western margin of the Balticshield and in Scotland. They are the result of a three-part continent collision thattook place c. 430-390 million years ago. Later extension events have heavily over-printed, and in some areas completely removed, a mountain chain that probablyhad dimensions similar to the Himalayas today.In order to understand the tectonic processes involved in the collision and tomap what is still visible today, deep seismic data were acquired along profile lines that cross the border zone between the undeformed Baltic Shield and the accreted continents.The seismic method is one of the most important geophysical tools used toimage the structure of the deep crust and lithosphere. The combined use of wide angle seismics and reflection seismics provides reliable information on the velocity distribution and the smaller scale reflectivity pattern in the crystalline crust.This dissertation focusses on the wide-angle seismic data which are used to create two-dimensional velocity models along profiles in the southeastern North Sea and in the central Scandinavian Caledonides. The North Sea models are used to depth migrate the reflection seismic data. Thanks to the profile geometry, new insights contribute to the knowledge on the collision process. In the Scandinavian Caledonides, features in the upper part of the velocity model correlate well with other geophysical results and reveal the crustal thickness, which could not be resolved by other methods. This work contributes substantial new insights to the understanding of the processes involved in the Caledonian orogeny.