GJI Seismology Multiscale, finite-frequency P and S tomography of the upper mantle in the southwestern Fennoscandian Shield

We image the P- and S-wave structure of the upper mantle in southwestern Scandinavia using a wavelet-based, multiscale parametrization and finite-frequency theory to model wave propagation. Relative traveltime residuals of direct P and S waves are measured in a high- and low-frequency band and are corrected for crustal structure using a detailed model for the study area. A range of resolution tests are used to find optimal damping values not only for variations in VP and VS separately, but also for perturbations in their ratio VP/VS. The tests show that features down to a size of 100 (150) km can be well resolved in the P (S) tomography. To ease comparison with previous studies we also perform ray-theoretical multiscale tomographies, and to test the degree of vertical smearing we evaluate different parametrizations in the vertical direction (wavelet-based multiscale and convolutional quelling). Our finite-frequency, multiscale images of variations in VP and VS confirm the existence of low velocities below southernNorway andDenmark and high velocities beneath the shield proper in Sweden, as seen in previous studies, but add more details to this simplified picture. The low velocities below southern Norway and Denmark are confined to a channel-like structure at about 100–200 km depth, and the lateral transition from low to high velocities follows zones of Carboniferous