Introduction

The use of shallow seismic refraction in periglacial studies in the Alps dates back to the early 1970s (Barsch 1973). At that time one-channel seismographs with a limited number of source–receiver combinations were generally used and interpretations were limited to simple subsurface models assuming layers of a more or less homogeneous and horizontal structure. The physical properties of frozen ground or ice and their contrast with the unfrozen sediment (up to an order of magnitude) stimulated many researchers to apply seismic refraction. In the 1980s, permafrost investigations – especially the determination of active layer thicknesses – were based on simple one-channel seismic refraction using a sledgehammer as an impact source (e.g. Haeberli 1985, Barsch and King 1989, Van Tantenhoven and Dikau 1990, King et al. 1992). These geophysical surveys provided useful information regarding permafrost occurrence, and in particular about the active layer thickness. With respect to seismic refraction, the interpretation was still usually restricted to the intercept method (see below). In many cases, complex or more heterogeneous subsurface structures were not adequately modelled, because of less powerful computer facilities and time-consuming calculations.

In the 1990s, the use of multi-channel seismographs and new interpretation software led to the application of sophisticated interpretation tools including the Hagedoorn plus-minus method, the generalised reciprocal method (GRM), the wavefront inversion method (WFI), network-raytracing and refraction tomography (Palmer 1981, Vonder Mühll 1993, Knödel et al. 1997, Reynolds 1997). These methods allow the interpretation of structured refractors and layers with varying P-wave velocities.