We present a two-dimensional, high-resolution full-waveform inversion approach of crosshole seismic data to image fine glacial sediments in an overdeepened Alpine valley, the Tannwald Basin (ICDP site 5068_1) north of Lake Constance. A vertically polarizing shear-wave source is employed to excite elastic waves, which are recorded by an eight-station three-component geophone string at 105–134 m depth. Based on traveltime tomography models derived separately from the P- and S-wave first arrival picks, we reconstruct the vertically polarized shear-wave velocity distributions from the vertical component data using isotropic, elastic full-waveform inversion. In order to mitigate the effects of source and receiver coupling, we use the global correlation norm as an objective function. The resolution is enhanced by applying an anisotropic gradient filter. The final model shows small-scale structures that look similar to a structural image obtained by seismic imaging at frequencies above 200 Hz. It provides a satisfying data fit and resolves layers of at least 1 m thickness that correlate well with the lithology derived from the core information within the errors of the source and receiver positions.