P- and S-wave reflection profiling for near-surface investigation of glacial sediments

Abstract

Listen

Translate article

In glacial sediments, interpolation between boreholes is often difficult due to non-uniform layering. On the other side, the knowledge on groundwater covering layers and the architecture of groundwater relevant structures is inevitable for sustainable water management. Experience with P-waves shows that information in the upper 20 m is generally not resolvable. To close the gap of near-surface resolution of structures we tested the application of shear waves. The study area belongs to the metropolitan area of Hamburg, Germany. The depth of main interest are the upper 100 m. Both, P- and S-wave seismic reflection data were acquired along a coincident profile line with comparable acquisition parameters (1 m receiver spacing and 2 m shot spacing) using vibrator sources and a 72 m long landstreamer. Additionally, results from airborne electromagnetic survey, ground-penetrating radar and borehole logging are included in the interpretation.The seismic image derived from the P-wave reflection data revealed Pleistocene till and Neogene clay as well as sandy aquifers down to 200 m. The S-wave reflection data provided a clearer picture of the Pleistocene sediments and a reflection at shallow depth. The compilation of the result with resistivity gives a good image of the near-subsurface layering and lateral variability of properties.The results demonstrate exemplarily the potential of S-wave reflection profiling for shallow structures. The combination of S-wave velocity with resistivity from airborne electromagnetics can be regarded as a key for area-covering regional hydrogeophysical characterization. For hydrogeological applications its benefit lies in enabling a classification of subsurface layers as aquifers and aquicludes at meter-scale resolution through a non-invasive remote sensing approach.