Seismic exploration for an underground rock laboratory in crystalline rocks – The GeoLaB site at Tromm (Odenwald)

Seismic imaging projects in mountainous areas, such as the Odenwald around the Tromm site, face various challenges, such as limited accessibility for placing seismic source and receiver locations according to the needed spatial resolution, or receiving a complex reflected/backscattered wave field due to a complex underground structure, violating common assumptions made in classical seismic exploration approaches. The main task of seismic exploration at the Tromm site is to provide high-resolution imaging and characterization of the Tromm Granite and neighbouring formations, in terms of their structural architecture, and the presence of potentially highly permeable fault zones. The target zone of characterization is relatively shallow (< 500 m below ground level), resulting in requirements concerning high-frequency seismic signals and a dense source and receiver spacing. Initial pilot measurements along two perpendicular seismic surface profiles have demonstrated the ability of this method to provide a structural image of the area (see also Grimmer et al., this conference), but a detailed interpretation of this data set for potentially permeable fault zones remains challenging without further additional information. ... mehrTwo exploration boreholes complement, so far, the exploration infrastructure of the Tromm site, and the combination of surface-based seismic acquisition with the use of these borehole allows an enhanced structural imaging, focusing on the rock volume around these boreholes. In this contribution, we present results from the combined surface-borehole acquisition and provide an outlook to future seismic exploration and monitoring at the GeoLaB Tromm site.