Seismic Structure of a Deep Alpine Valley from Full Waveform Inversion

Acoustic waveform inversion was applied to a seismic survey from a deep Alpine Valley in Austria. Sparse explosive sources with 1 – 3 kg charges provide frequencies in the 5 – 80 Hz range. Compared to the small size of the survey (3 km) those frequencies are very low. We use a steepest-gradient multi-scale frequency-domain inversion strategy to sequentially invert frequencies up to 16 Hz. The resulting resolution is of the order of 50 m, corresponding to half a wavelength at the wavespeeds that are typical for saturated loose sediments. In the uppermost part of the model, we are able to confirm the waveform model through a coincident resistivity survey. It shows a layer of pressured aquifer sand underlain by large unsaturated zones. In the centre of the valley, the thickness of the sediments reaches a maximum of ~ 460 m.