Seismic tomography on the castle hill in Quedlinburg

The collegiate church of Saint Servatius (part of the UNESCO world heritage list) and other buildings on the castle hill in Quedlinburg show evidence of frequent damage caused by foundation subsidence. The geological structure consists of sandstone of differing hardness from the Cretaceous period. Geotechnical investigations to date have provided information about the underground structure at various points, but no comprehensive 3D spatial model of the entire area was heretofore available. Therefore, the non‐destructive seismic tomography method was used. On different locations around and on top of the castle hill, elastic waves were generated with a weight drop. On the other hillside the arrivals of the seismic waves were recorded by geophones. The result was a tomographic model of the 3D distribution of P‐wave velocities. The results showed a zonally differentiated seismic velocity scheme. Considerable differences in the rock strength were shown. Areas with slower seismic velocities indicate lower rock quality and therefore geotechnically weak zones. The areas of our investigations, which were identified as deconsolidated rock, correspond to damage to the buildings above.