Publications

Since GIM was just founded recently, this page lists previous publications by GIM researchers.

  • Integrative analysis of the Aachen geothermal system (Germany) with an interdisciplinary conceptual model

    2025 | Gómez-Díaz, E., Balza Morales, A., Kukla, P. A., Brehme, M.

    Geothermal Energy, doi:10.1186/s40517-024-00327-0

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    Abstract

    The comprehension of geothermal systems involves the efficient integration of geo‑logical, geophysical and geochemical tools that are crucial in unraveling the distinct features inherent in geothermal reservoirs. We provide a first approach to compre‑hending the geologically complex geothermal system in the Aachen area, which has been known for its natural thermal spring occurrences since Roman times. Through a comprehensive analysis involving geochemical interpretation of water samples, a review of 2D seismic profiles, stress analysis, and surface geology, a dynamic model has been built, which serves as a conceptual framework providing a clearer under‑standing of the system. The model characterizes a non-magmatic, detachment faultcontrolled convective thermal system, wherein the reservoir exhibits mixed properties of the mainly Devonian carbonate rocks. NW–SE directed fault lines play a pivotal role in fluid transport, enabling the ascent of thermal waters without the need for addi‑tional energy. We additionally conducted magnetotelluric (MT) surveys and analyzed apparent resistivity and impedance values obtained through forward modeling, along with an assessment of noise levels. These findings contribute to evaluating the potential use of MT methods in further evaluating the study area and for geother‑mal energy exploration in general.

    Cite as

    Gómez-Díaz, E. and Balza Morales, A. and Kukla, P. A. and Brehme, M. (2025): Integrative analysis of the Aachen geothermal system (Germany) with an interdisciplinary conceptual model. Geothermal Energy. https://doi.org/10.1186/s40517-024-00327-0

  • Prospection of faults on the Southern Erftscholle (Germany) with individually and jointly inverted refraction seismics and electrical resistivity tomography

    2024 | Menzel, N., Klitzsch, N., Altenbockum, M., Müller, L., Wagner, F.M.

    Journal of Applied Geophysics, doi:10.1016/j.jappgeo.2024.105549

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    Note: This publication resulted from Nino Menzel's master thesis.

    Abstract

    As part of the Lower Rhein Embayment (LRE), the Southern Erft block is characterized by a complex tectonic setting that influences hydrological and geological conditions on a local as well as regional level. The study area is located in the south of North Rhine-Westphalia and traversed by several NW-SE-oriented fault structures. Since the tectonic structures were located by past studies based on a sparse foundation of geological data, the positions include considerable uncertainties. Therefore, it was decided to re-evaluate and refine the assumed fault locations by conducting geophysical measurements. Seismic Refraction Tomography (SRT) as well as Electrical Resistivity Tomography (ERT) was performed along seven measurement profiles with a length of up to 1.1 km. In addition to compiling individual resistivity and velocity models for all deduced measurements, ERT and SRT datasets were cooperatively inverted using the Structurally Coupled Cooperative Inversion (SCCI). This algorithm strengthens structural similarities between velocity and resistivity by adapting the individual regularizations after each model iteration. Previously assumed locations of the tectonic structures diverge from the new evidence based on ERT and SRT surveys. Especially in the western and eastern parts of the research area, differences between the survey results and formerly assumed locations are in the order of 100 m. Seismic and geoelectric measurements further indicate a fault structure in the southern part of the area, which remained undetected by past studies. The cooperative inversions do not improve the geophysical models qualitatively, since the individually inverted datasets already provide results of good quality and resolution.

    Cite as

    Menzel, N. and Klitzsch, N. and Altenbockum, M. and Müller, L. and Wagner, F.M. (2024): Prospection of faults on the Southern Erftscholle (Germany) with individually and jointly inverted refraction seismics and electrical resistivity tomography. Journal of Applied Geophysics. https://doi.org/10.1016/j.jappgeo.2024.105549

  • Probabilistic geophysical inversion of complex resistivity measurements using the Hamiltonian Monte Carlo method

    2024 | Hase, J., Wagner, F.M., Weigand, M., Kemna, A.

    Geophysical Journal International, doi:10.1093/gji/ggae389

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    Abstract

    In this work, we introduce the probabilistic inversion of tomographic complex resistivity (CR) measurements using the Hamiltonian Monte Carlo (HMC) method. The posterior model distribution on which our approach operates accounts for the underlying complex-valued nature of the CR imaging problem accurately by including the individual errors of the measured impedance magnitude and phase, allowing for the application of independent regularization on the inferred subsurface conductivity magnitude and phase, and incorporating the effects of cross-sensitivities. As the tomographic CR inverse problem is non-linear, of high dimension and features strong correlations between model parameters, efficiently sampling from the posterior model distribution is challenging. To meet this challenge we use HMC, a Markov-chain Monte Carlo method that incorporates gradient information to achieve efficient model updates. To maximize the benefit of a given number of forward calculations, we use the No-U-Turn sampler (NUTS) as a variant of HMC. We demonstrate the probabilistic inversion approach on a synthetic CR tomography measurement. The NUTS succeeds in creating a sample of the posterior model distribution that provides us with the ability to analyze correlations between model parameters and to calculate statistical estimators of interest, such as the mean model and the covariance matrix. Our results provide a strong basis for the characterization of the posterior model distribution and uncertainty quantification in the context of the tomographic CR inverse problem.

    Cite as

    Hase, J. and Wagner, F.M. and Weigand, M. and Kemna, A. (2024): Probabilistic geophysical inversion of complex resistivity measurements using the Hamiltonian Monte Carlo method. Geophysical Journal International. https://doi.org/10.1093/gji/ggae389

  • Uncertainties and robustness with regard to the safety of a repository for high-level radioactive waste: introduction of a research initiative

    2024 | Kurgyis, K., Achtziger-Zupancic, P., Bjorge, M., Boxberg, M. S., Broggi, M., Buchwald, J., Ernst, O. G., Flügge, J., Ganopolski, A., Graf, T., Kortenbruck, P., Kowalski, J., Kreye, P., Kukla, P., Mayr, S., Miro, S., Nagel, T., Nowak, W., Oladyshkin, S., Renz, A., Rienäcker-Burschil, J., Röhlig, K.-J., Sträter, O., Thiedau, J., Wagner, F. M., Wellmann, F., Wengler, M., Wolf, J., Rühaak, W.

    Environmental Earth Sciences, doi:10.1007/s12665-023-11346-8

    RWTH Publications PDF
    Note: This publication introduces the broader research vision behind our SmartMonitoring subproject.

    Abstract

    The Federal Company for Radioactive Waste Disposal (BGE mbH) is tasked with the selection of a site for a high-level radioactive waste repository in Germany in accordance with the Repository Site Selection Act. In September 2020, 90 areas with favorable geological conditions were identified as part of step 1 in phase 1 of the Site Selection Act. Representative preliminary safety analyses are to be carried out next to support decisions on the question, which siting regions should undergo surface-based exploration. These safety analyses are supported by numerical simulations building on geoscientific and technical data. The models that are taken into account are associated with various sources of uncertainties. Addressing these uncertainties and the robustness of the decisions pertaining to sites and design choices is a central component of the site selection process. In that context, important research objectives are associated with the question of how uncertainty should be treated through the various data collection, modeling and decision-making processes of the site selection procedure, and how the robustness of the repository system should be improved. BGE, therefore, established an interdisciplinary research cluster to identify open questions and to address the gaps in knowledge in six complementary research projects. In this paper, we introduce the overall purpose and the five thematic groups that constitute this research cluster. We discuss the specific questions addressed as well as the proposed methodologies in the context of the challenges of the site selection process in Germany. Finally, some conclusions are drawn on the potential benefits of a large method-centered research cluster in terms of simulation data management.

    Cite as

    Kurgyis, K. and Achtziger-Zupancic, P. and Bjorge, M. and Boxberg, M. S. and Broggi, M. and Buchwald, J. and Ernst, O. G. and Flügge, J. and Ganopolski, A. and Graf, T. and Kortenbruck, P. and Kowalski, J. and Kreye, P. and Kukla, P. and Mayr, S. and Miro, S. and Nagel, T. and Nowak, W. and Oladyshkin, S. and Renz, A. and Rienäcker-Burschil, J. and Röhlig, K.-J. and Sträter, O. and Thiedau, J. and Wagner, F. M. and Wellmann, F. and Wengler, M. and Wolf, J. and Rühaak, W. (2024): Uncertainties and robustness with regard to the safety of a repository for high-level radioactive waste: introduction of a research initiative. Environmental Earth Sciences. https://doi.org/10.1007/s12665-023-11346-8

  • Minimum entropy constrained cooperative inversion of electrical resistivity, seismic and magnetic data

    2024 | Ziegon, A.H., Boxberg, M.S., Wagner, F.M.

    Journal of Applied Geophysics, doi:10.1016/j.jappgeo.2024.105490

    RWTH Publications PDF
    Note: This publication resulted from the first M.Sc. graduate of GIM – Anton Ziegon.

    Abstract

    Geophysical methods are widely used to gather information about the subsurface as they are non-intrusive and comparably cheap. However, the solution to the geophysical inverse problem is inherently non-unique, which introduces considerable uncertainties. As a partial remedy to this problem, independently acquired geophysical data sets can be jointly inverted to reduce ambiguities in the resulting multi-physical subsurface images. A novel cooperative inversion approach with joint minimum entropy constraints is used to create more consistent multi-physical images with sharper boundaries with respect to the single-method inversions. Here, this approach is implemented in an open-source software and its applicability on electrical resistivity tomography (ERT), seismic refraction tomography (SRT), and magnetic data is investigated. A synthetic 2D ERT and SRT data study is used to demonstrate the approach and to investigate the influence of the governing parameters. The findings showcase the advantage of the joint minimum entropy (JME) stabilizer over separate, conventional smoothness-constrained inversions. The method is then used to analyze field data from Rockeskyller Kopf, Germany. 3D ERT and magnetic data are combined and the results confirm the expected volcanic diatreme structure with improved details. The multi-physical images of both methods are consistent in some regions, as similar boundaries are produced in the resulting models. Because of its sensitivity to hydrologic conditions in the subsurface, observations suggest that the ERT method senses different structures than the magnetic method. These structures in the ERT result do not seem to be enforced on the magnetic susceptibility distribution, showcasing the flexibility of the approach. Both investigations outline the importance of a suitable parameter and reference model selection for the performance of the approach and suggest careful parameter tests prior to the joint inversion. With proper settings, the JME inversion is a promising tool for geophysical imaging, however, this work also identifies some objectives for future studies and additional research to explore and optimize the method.

    Cite as

    Ziegon, A.H. and Boxberg, M.S. and Wagner, F.M. (2024): Minimum entropy constrained cooperative inversion of electrical resistivity, seismic and magnetic data. Journal of Applied Geophysics. https://doi.org/10.1016/j.jappgeo.2024.105490

  • Icy Ocean Worlds - Astrobiology research in Germany

    2024 | Klenner, F., Baqué, M., Beblo-Vranesevic, K., Bönigk, J., Boxberg M.S., Dachwald, B., Digel, I., Elsaesser, A., Espe, C., Funke, O., Hauber, E., Heinen, D., Hofmann, F., Hortal Sánchez, L., Khawaja, N., Napoleoni, M., Plesa, A.C., Postberg, F., Purser, A., Rückriemen-Bez, T., Schröder, S., Schulze-Makuch, D., Ulamec, S., Paul de Vera, J.P.

    Frontiers in Astronomy and Space Sciences, doi:10.3389/fspas.2024.1422898

    RWTH Publications PDF

    Abstract

    Icy bodies with subsurface oceans are a prime target for astrobiology investigations, with an increasing number of scientists participating in the planning, development, and realization of space missions to these worlds. Within Germany, the Ocean Worlds and Icy Moons working group of the German Astrobiology Society provides an invaluable platform for scientists and engineers from universities and other organizations with a passion for icy ocean worlds to share knowledge and start collaborations. We here present an overview about astrobiology research activities related to icy ocean worlds conducted either in Germany or in strong collaboration with scientists in Germany. With recent developments, Germany offers itself as a partner to contribute to icy ocean world missions.

    Cite as

    Klenner, F. and Baqué, M. and Beblo-Vranesevic, K. and Bönigk, J. and Boxberg M.S. and Dachwald, B. and Digel, I. and Elsaesser, A. and Espe, C. and Funke, O. and Hauber, E. and Heinen, D. and Hofmann, F. and Hortal Sánchez, L. and Khawaja, N. and Napoleoni, M. and Plesa, A.C. and Postberg, F. and Purser, A. and Rückriemen-Bez, T. and Schröder, S. and Schulze-Makuch, D. and Ulamec, S. and Paul de Vera, J.P. (2024): Icy Ocean Worlds - Astrobiology research in Germany. Frontiers in Astronomy and Space Sciences. https://doi.org/10.3389/fspas.2024.1422898

  • Electrical Conductivity of Hydrate-Bearing Rocks Studied by Pore-Scale Modeling

    2024 | Zhang, Q., Tao, H., Wagner, F. M., Klitzsch, N., Zibulski, E., Lu, H., Zi, M., Chen, D.

    Energy & Fuels, doi:10.1021/acs.energyfuels.4c01295

    Abstract

    Gas hydrates have the potential to significantly disturb global climate change and alter subsurface stability, particularly in the context of production due to their extensive presence and widespread distribution in marine deposits. The electrical conductivity of hydrate-bearing sediments (HBS) serves as a crucial parameter for hydrate reservoir prospection. However, the electrical conductivity of HBS is influenced not only by hydrate saturation but also by the hydrate distribution within the pore space. This study presents a numerical approach for quantifying the relationship between the hydrate volume, distribution, and conductivity of HBS using pore network modeling (PNM). We use two distinct hydrate distributions in pores, ideal grain-contacting and pore-filling. Their electrical conductivities, in relation to hydrate saturation, were simulated on the pore scale using the finite element method. Regardless of the hydrate distribution, the electrical conductivity of the pore network models decreases with increasing hydrate saturation. At the same saturation, the electrical conductivity of PNM with grain-contacting hydrates is higher than that of pore-filling hydrates. While the resistivity index of the hydrate-bearing PNM exhibits a variation pattern consistent with Archie’s formula, the saturation exponent is not a fixed value. The experimental samples represent a closed system where significant local fluid salinity changes would occur due to hydrate formation, strongly influencing the bulk conductivity. The numerical simulation results considering the salinity effect confirm the plausibility of grain-contacting hydrate while challenging the existence of an ideal pore-filling hydrate when compared to the measured data as the conductivity associated with such a uniformly distributed pore-filling hydrate contradicts the experimental measurements. Our research indicates that the variability of the saturation exponent, highlighting the complex nature of hydrate distributions within sediments, calls for refined electrical saturation models to enhance the evaluation of marine hydrate reservoirs.

    Cite as

    Zhang, Q. and Tao, H. and Wagner, F. M. and Klitzsch, N. and Zibulski, E. and Lu, H. and Zi, M. and Chen, D. (2024): Electrical Conductivity of Hydrate-Bearing Rocks Studied by Pore-Scale Modeling. Energy & Fuels. https://doi.org/10.1021/acs.energyfuels.4c01295

  • Field-test performance of an ice-melting probe in a terrestrial analogue environment

    2024 | Baader, F., Boxberg, M. S., Chen, Q., Förstner, R., Kowalski, J., Dachwald, B.

    Icarus, doi:10.1016/j.icarus.2023.115852

    RWTH Publications PDF
    Note: This publication resulted from Marc's time at MBD at RWTH Aachen, i.e. was prepared before GIM was founded.

    Abstract

    Melting probes are a proven tool for the exploration of thick ice layers and clean sampling of subglacial water on Earth. Their compact size and ease of operation also make them a key technology for the future exploration of icy moons in our Solar System, most prominently Europa and Enceladus. For both mission planning and hardware engineering, metrics such as efficiency and expected performance in terms of achievable speed, power requirements, and necessary heating power have to be known. Theoretical studies aim at describing thermal losses on the one hand, while laboratory experiments and field tests allow an empirical investigation of the true performance on the other hand. To investigate the practical value of a performance model for the operational performance in extraterrestrial environments, we first contrast measured data from terrestrial field tests on temperate and polythermal glaciers with results from basic heat loss models and a melt trajectory model. For this purpose, we propose conventions for the determination of two different efficiencies that can be applied to both measured data and models. One definition of efficiency is related to the melting head only, while the other definition considers the melting probe as a whole. We also present methods to combine several sources of heat loss for probes with a circular cross-section, and to translate the geometry of probes with a non-circular cross-section to analyse them in the same way. The models were selected in a way that minimises the need to make assumptions about unknown parameters of the probe or the ice environment. The results indicate that currently used models do not yet reliably reproduce the performance of a probe under realistic conditions. Melting velocities and efficiencies are constantly overestimated by 15 to 50 % in the models, but qualitatively agree with the field test data. Hence, losses are observed, that are not yet covered and quantified by the available loss models. We find that the deviation increases with decreasing ice temperature. We suspect that this mismatch is mainly due to the too restrictive idealization of the probe model and the fact that the probe was not operated in an efficiency-optimized manner during the field tests. With respect to space mission engineering, we find that performance and efficiency models must be used with caution in unknown ice environments, as various ice parameters have a significant effect on the melting process. Some of these are difficult to estimate from afar.

    Cite as

    Baader, F. and Boxberg, M. S. and Chen, Q. and Förstner, R. and Kowalski, J. and Dachwald, B. (2024): Field-test performance of an ice-melting probe in a terrestrial analogue environment. Icarus. https://doi.org/10.1016/j.icarus.2023.115852

  • Ice transit and performance analysis for cryorobotic subglacial access missions on Earth and Europa

    2023 | Boxberg, M. S., Chen, Q., Plesa, A.-C., Kowalski, J.

    Astrobiology, doi:10.1089/ast.2021.0071

    RWTH Publications
    Note: This publication resulted from Marc's time at MBD at RWTH Aachen, i.e. was prepared before GIM was founded.

    Abstract

    Ice-covered ocean worlds, such as the Jovian moon Europa, are some of the prime targets for planetary exploration due to their high astrobiological potential. While upcoming space exploration missions, such as the Europa Clipper and JUICE missions, will give us further insight into the local cryoenvironment, any conclusive life detection investigation requires the capability to penetrate and transit the icy shell and access the subglacial ocean directly. Developing robust, autonomous cryorobotic technology for such a mission constitutes an extremely demanding multistakeholder challenge and requires a concentrated interdisciplinary effort between engineers, geoscientists, and astrobiologists. An important tool with which to foster cross-disciplinary work at an early stage of mission preparation is the virtual testbed. In this article, we report on recent progress in the development of an ice transit and performance model for later integration in such a virtual testbed. We introduce a trajectory model that, for the first time, allows for the evaluation of mission-critical parameters, such as transit time and average/overall power supply. Our workflow is applied to selected, existing cryobot designs while taking into consideration different terrestrial, as well as extraterrestrial, deployment scenarios. Specific analyses presented in this study show the tradeoff minimum transit time and maximum efficiency of a cryobot and allow for quantification of different sources of uncertainty to cryobot's trajectory models.

    Cite as

    Boxberg, M. S. and Chen, Q. and Plesa, A.-C. and Kowalski, J. (2023): Ice transit and performance analysis for cryorobotic subglacial access missions on Earth and Europa. Astrobiology. https://doi.org/10.1089/ast.2021.0071

  • Ice Melting Probes

    2023 | Dachwald, B., Ulamec, S., Kowalski, J., Boxberg, M. S., Baader, F., Biele, J., Kömle, N.

    Handbook of Space Resources, doi:10.1007/978-3-030-97913-3_29

    RWTH Publications PDF
    Note: This publication resulted from Marc's time at MBD at RWTH Aachen, i.e. was prepared before GIM was founded.

    Abstract

    The exploration of icy environments in the solar system, such as the poles of Mars and the icy moons (a.k.a. ocean worlds), is a key aspect for understanding their astrobiological potential as well as for extraterrestrial resource inspection. On these worlds, ice melting probes are considered to be well suited for the robotic clean execution of such missions. In this chapter, we describe ice melting probes and their applications, the physics of ice melting and how the melting behavior can be modeled and simulated numerically, the challenges for ice melting, and the required key technologies to deal with those challenges. We also give an overview of existing ice melting probes and report some results and lessons learned from laboratory and field tests.

    Cite as

    Dachwald, B. and Ulamec, S. and Kowalski, J. and Boxberg, M. S. and Baader, F. and Biele, J. and Kömle, N. (2023): Ice Melting Probes. . https://doi.org/10.1007/978-3-030-97913-3_29