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Within the ICDP-funded project COSC (Collisional Orogeny in the Scandinavian Caledonides), mountain building processes are investigated with the help of two ~2.5 km deep fully cored boreholes in Central Sweden. Drilled in 2014, borehole COSC-1 near Åre studied the emplacement of the high-grade metamorphic allochthons and obtained a section through the Lower Seve Nappe as well as the underlying mylonite zone. The second borehole COSC-2, drilled in 2020 near Järpen/Mörsil, focuses on defining the character and age of deformation of the underlying greenschist facies thrust-sheets, the main Caledonian décollement and the Precambrian basement.An extended walkaway VSP survey at the COSC-2 drill site was performed in September-October 2021. This study aims to support the geological interpretation with a high-resolution 3D image of the subsurface in the direct vicinity of the borehole. This allows the determination of the origin of the basement reflections and reveals the nature of the main décollement as well as the degree of basement thrusting. Two 2D surface seismic lines approximately perpendicular to each other (North to South, West to East) and centered around the COSC-2 drill site were acquired using single (1C) and three-component (3C) geophones at 5-30m intervals. Furthermore, the West-East line was extended by 30 geophones at 100m intervals on each line end to allow the registration of wide-angle shots. A 32 t Vibroseis source operated along both lines with source point distances of 100 m within the central part of the line and 500 m at the wide-angle stations, respectively. Ocean bottom seismometers (OBS) were deployed on the bottom of a lake north of the borehole along a ~1.5 km portion of the North-South line. An airgun source was activated on this part of the profile. Along the entire borehole down to a depth of 2.26 km a 3C geophone chain recorded the seismic wavefield from all source points with a geophone spacing of 10 m, complemented by the recording from one single zero-offset source point with a geophone spacing of 2 m.The obtained surface seismic and VSP data set exhibits exceptionally good quality and shows many pronounced and clear reflections in the raw gathers. They are observed even at the largest source-receiver offsets (~11 km) and are visible at two-way-traveltimes up to 3-4 s, corresponding to structures at a depth of approximately 11 km. We present results of the ongoing surface seismic data processing and analysis, including a P-wave velocity model obtained from first arrival traveltime tomography, an analysis of seismic anisotropy related to the geological structures in the area and a first imaging result from the surface seismic data.

Summary The modular seismic acquisition system at the GFZ is basically suitable for underground exploration in crystalline, salt and clay rocks. Special features of the application result from the different properties of the media such as degree of heterogeneity, damping, anisotropy and their interaction with the excavation zone (EDZ) induced by the cavity (drifts, tunnels). This manifests itself in different frequency damping behaviour for compressional, shear and surface waves, which require a specific use of impulse and vibration sources at the joint depending on the task. Seismic borehole measurements can contribute to a significant improvement of the resolution.

The Baltic Sea Underground Innovation Network BSUIN is a European research project funded by Interreg Baltic Sea Region. The BSUIN network consists of six underground laboratories in Finland, Sweden, Russia, Poland and Germany with associated business and research partners. Each of the underground laboratories is unique in its geology, underground space and use. The BSUIN aims to build up a platform for innovative research and business concepts for the use of underground infrastructures and also especially for applications after completion of mining activities.For an innovation management it is important to identify research and application fields in underground labs for the present but also research areas of interest in the future. Also it is significant to define the relevant research fields, which are more likely to result in innovations and business applications.Within BSUIN an innovation platform concept will be established as a guideline for innovation management and support for the innovation processes. For that purpose we questioned aspects of the use of underground labs for users from several kind of customers and users from research and business of small and medium-sized enterprises.Here we present an overview of the evaluation of the questionnaire. What are the main aspects which are important for the use of underground labs for research and innovation and especially for business activities? Within BSUIN a concept of an innovation platform concept will be integrated in the BSUIN web based tool. This will allow to apply innovation keywords to site-specific research activities in each BSUIN mine.

Since 20 years the GFZ (German Research Centre for Geosciences) operates in an underground lab in the research and education mine Reiche Zeche at Freiberg in eastern Germany. This underground lab is used as testing lab for newly developed geophysical equipment and methods for 3D seismics. Therefore, in the underground space several galleries and boreholes can be used for seismic exploration in 2D and 3D approaches and for testing and validation of seismic acquisition equipment.Now, a Helmholtz Innovation Lab will be established at the GFZ in Potsdam. The Helmholtz Innovation Lab 3D-Underground Seismic Lab (3D-US Lab) is a place where scientific expertise and the needs of industry and its customers will meet together. By involving partners from mining and tunnelling in joint development projects on a long-term basis and transferring approaches from research into commercially successful applications a sustainable 3D-US Lab will be established.The 3D-US Lab bundles the seismic methods developed at the GFZ in a single technology platform, standardizes and modularizes them. It combines the technological and methodological developments in tunnel and borehole seismics for 3D seismic exploration of underground structures. The technology platform and the GFZ underground laboratory in Freiberg are of great interest for various partners from mining and tunnelling. In the long term the Helmholtz Innovation Lab aims to establish 3D underground seismics as a key technology for the effective and safe construction and use of underground buildings.

Geophysical exploration is indispensable for planning deep drilling. Usually 2Dor 3D-seismics investigations are applied and, depending on the resulting geologic model for the underground, the drill site and drilling path are determined. In recent years the focus of exploration has shifted towards small-scale geological structures such as local layers and faults. Depending on the source frequencies and the target depth, 2Dor 3D-seismics from surface cannot always resolve such structures in particular at larger depths. In general, signal frequencies of about 30–70 Hz are typical for surface seismic methods. The deeper and smaller the sought-after structures are, the worse will be the resolution. Therefore, borehole seismic measurements like Vertical Seismic Profile (VSP) or Seismic While Drilling (SWD) have been developed (Fig. 1). For the VSP method geophones are normally integrated in the borehole, while the seismic source generates seismic waves at the surface. The SWD method uses the drill bit as the seismic source. Hence, the quality of the seismic signals is highly dependent on the drilled rock and the type of drill bit, but even well-suited rock conditions and adequate drilling may not provide sufficient data quality. Compared to 2Dand 3D-seismics, the distances between source and receiver to the target are shorter for VSP, and for SWD in particular. Signal frequencies up to about 100 Hz are observed yielding a slightly better resolution compared to surface seismics. However, subtle yet important features (e.g., fault zone) often cannot be identified with certainty. Accordingly, a method or tool that would improve the resolution is of high importance since this would allow adjusting the drilling path to minimize risks and costs of drilling.

The GFZ Underground Laboratory is operated by the Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences. It is located in the research and education mine “Reiche Zeche” in Freiberg, Germany allows testing of geophysical and geotechnical tools and methods in boreholes and galleries. The lab is ideally suited for seismic system components such as receivers and sources for three-dimensional high resolution seismic imaging and tomography surveying. The lab layout of a basement rock block surrounded by galleries around a vertical as well as two horizontal boreholes enables the realization of various underground survey geometries e.g. well-to-well and well-to-gallery. The galleries are equipped with thirty 3-component geophone anchors installed in 1 m and 2 m depths for tomographic measurements or the recording of radiation pattern of seismic borehole sources.

In borehole seismics several methods are in use while drilling. In the case of small layer structures, for instance thin layers or faults, the resolution of surface seismic methods is often not sufficient to determine and locate these structures for exploration. Combining a seismic source and receiver in a common device in the drill string would increase the seismic resolution. In the project SPWD such a prototype of a device has been designed, manufactured and tested. The used source signal frequencies are up to 5000 Hz, which allows a resolution of up to one metre. The resolution is therefore significantly higher than for VSP and SWD. With a penetration depth of about 100 metres an exploration of the borehole surrounding is possible. By applying this method while drilling the risks and costs of drilling can be minimized because of the possibility of adjusting the drill path and locating small sought-after structures.

In this paper, we report first acoustic communications experiments along deep drill strings enabling data rates up to 20 kbit/s. To reduce costs for geothermal energy, search for water-bearing fault zones in the rocks hundreds of meters below the ground will be assisted by seismic prediction while drilling (SPWD) enabling control of the drilling direction. The SPWD tool needs higher data rates to the ground. In contrast to common mud-pulse telemetry offering few bit/s, our approach is based on acoustic wave propagation along the steel wall of the drill string. Based on waveguide theory, we develop a tractable channel model for drill-string communication predicting the pass and stopbands created by regular screw joints between the pipes. For data transmission, we use closed-loop adaptive orthogonal frequency division multiplexing (OFDM) following the 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE). First results indicate that, in this way, much higher data rates can be realized in future deep drilling applications.