Speaker
Description
The Einstein Telescope (ET) is a next-generation underground gravitational wave observatory planned to operate at depths of up to 200–300 m, where seismic, thermal and Newtonian noise are significantly reduced compared to surface detectors. ET requires a geologically stable, well-characterised host rock over an exceptionally large volume 100-225 km². The Lusatia (Lausitz) region in eastern Germany is one of the three main candidate sites currently under evaluation, alongside the Sardegna Region and Euregio Meuse-Rhine. A rigorous, multi-disciplinary site characterisation programme is therefore essential to support the site selection decision.
This contribution presents results from the ongoing geological, petrophysical, geotechnical, hydromechanical and hydrogeological assessment of the Lusatian Granodiorite as a potential host rock for the ET. The subsurface rocks in the investigation area comprises Quaternary and Tertiary cover sediments, kaolin horizons and weathered zones, overlying a crystalline basement consisting primarily of granodiorite. A key challenge is the characterisation of the spatial distribution of weathering, hydrothermal alteration and kaolinisation, which critically affect rock mass quality and hydraulic behaviour.
The core drilling campaign consist of 6-7 completed boreholes with 250 m depth, each, which provide direct subsurface information and allow the identification of five principal geotechnical units resembling the variety of the granodiorite and it structural inventory. Laboratory and in-situ measurements yield mechanical, hydraulic and destruction properties. A 3D bedrock surface model is derived by interpolating borehole data of several thousand legacy drill holes and correlating these with the newly drilled cores. Regional characterisation is further supported by geophysical methods including seismics, gravimetry and geomagnetics, as well as geochemical analyses, enabling spatial extrapolation of subsurface structures.
Groundwater modelling integrates the observed hydrogeological conditions on an full area model and detailed site scale models with particular focus on the role of inner alteration zones as potential hydraulic pathways. The inflow to caverns in the granodiorite and the influence on the groundwater body in the sedimentary layers where studied in scenario models. The comprehensive dataset being compiled provides a critical basis for assessing the suitability of the Lusatian Granodiorite as a host rock for the Einstein Telescope and for guiding further site investigation activities.