S U M M A R YFast frequency-wavenumber migration is used to migrate synthetic seismograms, calculated by a hybrid method for crustal models with complex 2-D scattering structures in the lower crust. Scatterers with predominantly horizontal or vertical orientation and scatterers without preferred orientation (isotropic scatterers) are investigated; horizontal scatterers or lamellae have frequently been suggested for the lower crust on the basis of modern reflection seismological experiments. In none of the cases studied here are the scattering structures imaged correctly. The reason is mainly multiple scattering which can produce coherent arrivals in the seismogram sections, and hence coherent signatures in the migrated sections, which have no relation to structure. Imaging is generally acceptable for horizontal scatterers, but for isotropic or vertical scatterers the migrated signatures are also horizontal and thus do not represent reality. It is concluded that the highly detailed line drawings, which are popular in crustal reflection seismology, are less reliable than believed, as far as the internal structure of scattering zones and the scatterer orientations are concerned. Horizontal or subhorizontal structures in the lower crust may be less common than assumed.The paper also briefly addresses a few methodical aspects of fast frequencywavenumber migration for depth-dependent background structure, in particular the concept of sounding beams, their width and the construction of a migrated section from several sounding beams.

Oceanic and fluid core effects inherent in polar motion and 1.o.d. -data were analyzed and related results are discussed in detail.A new exact analytic solution to the hydrodynamic equations is obtained, which describes tidal motions at low frequencies in a homogeneous, incompressible, inviscid liquid core with arbitrary core-mantle topography. Some geophysical and astrometrical consequences of this solution are considered.The numerical estimation of the deviations of the pole tide from the static one is obtained. A new hypothesis is proposed that the known interrelation between long-term amplitude and frequency variations in Chandler wobble may be attributed to the influence of turbulent friction of non-equilibrium pole tide.