Fig. 1

a Possible layout of the planned geothermal URL (not to scale), GeoLaB, with an access tunnel to a fracture zone, three experimental caverns, and exploration wells (blue) and observation wells (green) from the tunnel into the fracture zone. In addition to the monitoring stations (red cones), the main injection well (black) for controlled high-flow experiments (CHFE) is reached from surface boreholes targeting the fracture zones next to experimental caverns. b Possible CHFE with high flow rate injection from the surface into a fracture zone (blue volume) and related mechanical deformation indicated by red ring segments