Seismic investigation of subsurface structure at the Herrenknecht test site - VS and Q

Deep geothermal energy is considered a crucial renewable resource for future electricity and heat generation, particularly in urban environments. To reduce the risk associated with costly drilling for urban geothermal reservoirs, vibroseis measurement campaigns must be undertaken. This requirement is addressed by the Urban Vibroseis Truck (UVT), which enables high-resolution surveys in spatially constrained settings.
This work presents the first geophysical characterization of the subsurface at the Herrenknecht UVT test site. The objective was to provide an initial model for future full-wave inversion processes and for subsequent validation of the ground force signal generated by the urban vibration truck. To achieve this, a one-dimensional shear-wave velocity (VS) profile was created using the multichannel analysis of surface waves (MASW), along with an estimate of the Rayleigh wave quality factor (Q) using the spectral ratio method. The resulting 1D VS models revealed significant near-surface heterogeneity—up to 2 m in one of the measured profiles, attributed to variable fill material. In contrast, the deeper layers exhibited consistent stratigraphy and velocity structures. ... mehrForward modeling was conducted using SOFI2D software to validate the shear-wave profiles. This was achieved by comparing synthetic and observed seismograms and dispersion images, which highlighted discrepancies in certain shots and convergence in others taken at different locations. The attenuation properties were estimated using the spectral ratio method, which had first been validated through analytical and synthetic viscoelastic models prior to application to the field data. The resulting Q values provided a global measure of site attenuation and demonstrated robustness under well-controlled conditions.