@article{WilkeSchettlerViethHillebrandetal.2018, author = {Wilke, Franziska Daniela Helena and Schettler, Georg and Vieth-Hillebrand, Andrea and K{\"u}hn, Michael and Rothe, Heike}, title = {Activity concentrations of U-238 and Ra-226 in two European black shales and their experimentally-derived leachates}, series = {Journal of Environmental Radioactivity}, volume = {190}, journal = {Journal of Environmental Radioactivity}, publisher = {Elsevier}, address = {Oxford}, issn = {0265-931X}, doi = {10.1016/j.jenvrad.2018.05.005}, pages = {122 -- 129}, year = {2018}, abstract = {We performed leaching tests at elevated temperatures and pressures with an Alum black shale from Bomholm, Denmark and a Posidonia black shale from Lower Saxony, Germany. The Alum shale is a carbonate free black shale with pyrite and barite, containing 74.4 mu g/g U. The Posidonia shales is a calcareous shale with pyrite but without detectable amounts of barite containing 3.6 mu g/g U. Pyrite oxidized during the tests forming sulfuric acid which lowered the pH on values between 2 and 3 of the extraction fluid from the Alum shale favoring a release of U from the Alum shale to the fluid during the short-term and in the beginning of the long-term experiments. The activity concentration of U-238 is as high as 23.9 mBq/ml in the fluid for those experiments. The release of U and Th into the fluid is almost independent of pressure. The amount of uranium in the European shales is similar to that of the Marcellus Shale in the United States but the daughter product of U-238, the Ra-226 activity concentrations in the experimentally derived leachates from the European shales are quite low in comparison to that found in industrially derived flowback fluids from the Marcellus shale. This difference could mainly be due to missing Cl in the reaction fluid used in our experiments and a lower fluid to solid ratio in the industrial plays than in the experiments due to subsequent fracking and minute cracks from which Ra can easily be released.}, language = {en} } @article{ZhaoKuhnOyeetal.2014, author = {Zhao, Peng and Kuhn, Daniela and Oye, Volker and Cesca, Simone}, title = {Evidence for tensile faulting deduced from full waveform moment tensor inversion during the stimulation of the Basel enhanced geothermal system}, series = {Geothermics : an international journal of geothermal research and its applications}, volume = {52}, journal = {Geothermics : an international journal of geothermal research and its applications}, publisher = {Elsevier}, address = {Oxford}, issn = {0375-6505}, doi = {10.1016/j.geothermics.2014.01.003}, pages = {74 -- 83}, year = {2014}, abstract = {Our study presents the results of a moment tensor inversion of 19 microseismic events with M-L between 2.0 and 3.4, associated with the stimulation operation of an enhanced geothermal reservoir in Basel, Switzerland, in 2006. We adopt a three-step procedure to retrieve point source solution parameters based on full waveform inversion. The inversion is performed by fitting displacement amplitude spectra and displacement seismograms in the first and second step, respectively, assuming a double couple source model and thus obtaining focal solutions for all 19 events. Our results are in agreement with focal mechanisms from a previous study, which employed P wave first-motion polarities from more than 40 stations, whereas our solutions are achieved using full waveform data recorded by less than 10 surface stations. In the last step, a full moment tensor inversion is performed. The results from the moment tensor inversion show an improvement on the waveform fitting compared to the double couple models, which is verified by an F-test. We investigate the stability of the moment tensor solutions by employing different velocity models. The isotropic components of the moment tensor solutions of some events are not negligible, suggesting source volume changes due to fluid injection. Events with significant isotropic components occurred mainly during the stimulation phase and close to the injection well. On the other hand, events that occurred in the post-stimulation phase are predominantly pure shear failure and located further away from the well bore. These spatio-temporal patterns can be explained by the influence of pore pressure variations during and after the hydraulic stimulation at the geothermal site. (C) 2014 Elsevier Ltd. All rights reserved.}, language = {en} } @article{SauerSteinGlatzeletal.2015, author = {Sauer, Daniela and Stein, Christine and Glatzel, Stephan and K{\"u}hn, J{\"u}rgen and Zarei, Mehdi and Stahr, Karl}, title = {Duricrusts in soils of the Alentejo (southern Portugal)-types, distribution, genesis and time of their formation}, series = {Journal of soils and sediments : protection, risk assessment and remediation}, volume = {15}, journal = {Journal of soils and sediments : protection, risk assessment and remediation}, number = {6}, publisher = {Springer}, address = {Heidelberg}, issn = {1439-0108}, doi = {10.1007/s11368-015-1066-x}, pages = {1437 -- 1453}, year = {2015}, abstract = {This paper reports on extremely thick and massive duricrusts in soils of two basins in the Alentejo (southern Portugal). Since different types of duricrusts (calcretes, silcretes and palycretes) have been reported from other regions in the Mediterranean, the purpose of this study was to identify the cementing agents in the duricrusts and to compare their composition in the two basins. Moreover, the study aimed at identifying the processes involved in duricrust formation, and especially the role of topography and lateral water and element transport in the landscape, and drawing conclusions about environmental conditions and time of duricrust formation. After studying an extensive number of road cuts in the field and mapping soil patterns in parts of the two basins by manual augering, ten pedons were selected for detailed description and sampling. Thin sections were analysed under a petrographic microscope, focusing on the micromorphology and optical properties of the cementing materials. Selected samples were studied by scanning electron microscopy and energy-dispersive X-ray spectroscopy to reconfirm the optical identification. The laboratory analyses included pH, carbonate contents, and X-ray diffraction analysis. The duricrusts in the eastern Sado basin are indurated by silica. Combination of XRD and thin section analysis allowed to identify opal-CT as a major component, while opal-A is present to a lesser extent, and chalcedony is very rare. The cementing materials of the duricrusts in the Oriola basin are palygorskite and calcite, which may occur alone or in combination within a soil profile. The thick duricrusts formed in the basins through precipitation of calcite, palygorskite and silica from lateral water flows, which ran from the Serra de Portel into the basins, during short moist seasons in a generally warm, semi-arid climate with strong evapotranspiration. Lithology of the upper catchment areas (element sources) and topography control the spatial distribution of the different duricrusts. Their formation took place mainly during the Pliocene. Palygorskite transformation to smectite in the upper parts of the palycretes indicates that palygorskite is unstable in the present (more humid, typical Mediterranean) climate. This study demonstrates the potential role of lateral water and element transport in landscapes that need to be considered in pedological studies and concepts, and the use of mineral indicators of past climates such as palygorskite and the ageing stage of silica precipitations as tools for reconstructing environmental conditions and possible time of duricrust formation.}, language = {en} } @article{KaramzadehKuehnKriegerowskietal.2019, author = {Karamzadeh, Nasim Toularoud and K{\"u}hn, Daniela and Kriegerowski, Marius and L{\´o}pez-Comino, Jos{\´e} {\´A}ngel and Cesca, Simone and Dahm, Torsten}, title = {Small-aperture array as a tool to monitor fluid injection- and extraction-induced microseismicity}, series = {Acta Geophysica}, volume = {67}, journal = {Acta Geophysica}, number = {1}, publisher = {Springer}, address = {Cham}, issn = {1895-6572}, doi = {10.1007/s11600-018-0231-1}, pages = {311 -- 326}, year = {2019}, abstract = {The monitoring of microseismicity during temporary human activities such as fluid injections for hydrofracturing, hydrothermal stimulations or wastewater disposal is a difficult task. The seismic stations often cannot be installed on hard rock, and at quiet places, noise is strongly increased during the operation itself and the installation of sensors in deep wells is costly and often not feasible. The combination of small-aperture seismic arrays with shallow borehole sensors offers a solution. We tested this monitoring approach at two different sites: (1) accompanying a fracking experiment in sedimentary shale at 4km depth and (2) above a gas field under depletion. The small-aperture arrays were planned according to theoretical wavenumber studies combined with simulations considering the local noise conditions. We compared array recordings with recordings available from shallow borehole sensors and give examples of detection and location performance. Although the high-frequency noise on the 50-m-deep borehole sensors was smaller compared to the surface noise before the injection experiment, the signals were highly contaminated during injection by the pumping activities. Therefore, a set of three small-aperture arrays at different azimuths was more suited to detect small events, since noise recorded on these arrays is uncorrelated with each other. Further, we developed recommendations for the adaptation of the monitoring concept to other sites experiencing induced seismicity.}, language = {en} } @article{KuehnHainzlDahmetal.2022, author = {K{\"u}hn, Daniela and Hainzl, Sebastian and Dahm, Torsten and Richter, Gudrun and Vera Rodriguez, Ismael}, title = {A review of source models to further the understanding of the seismicity of the Groningen field}, series = {Netherlands journal of geosciences : NJG}, volume = {101}, journal = {Netherlands journal of geosciences : NJG}, publisher = {Cambridge Univ. Press}, address = {Cambridge}, issn = {0016-7746}, doi = {10.1017/njg.2022.7}, pages = {12}, year = {2022}, abstract = {The occurrence of felt earthquakes due to gas production in Groningen has initiated numerous studies and model attempts to understand and quantify induced seismicity in this region. The whole bandwidth of available models spans the range from fully deterministic models to purely empirical and stochastic models. In this article, we summarise the most important model approaches, describing their main achievements and limitations. In addition, we discuss remaining open questions and potential future directions of development.}, language = {en} } @article{KuhnTavaresJacquesTeixeiraetal.2021, author = {Kuhn, Eug{\^e}nia Carla and Tavares Jacques, Maur{\´i}cio and Teixeira, Daniela and Meyer, S{\"o}ren and Gralha, Thiago and Roehrs, Rafael and Camargo, Sandro and Schwerdtle, Tanja and Bornhorst, Julia and {\´A}vila, Daiana Silva}, title = {Ecotoxicological assessment of Uruguay River and affluents pre- and biomonitoring}, series = {Environmental science and pollution research : ESPR}, volume = {28}, journal = {Environmental science and pollution research : ESPR}, number = {17}, publisher = {Springer}, address = {Berlin ; Heidelberg}, issn = {0944-1344}, doi = {10.1007/s11356-020-11986-4}, pages = {21730 -- 21741}, year = {2021}, abstract = {Uruguay River is the most important river in western Rio Grande do Sul, separating Brazil from Argentina and Uruguay. However, its pollution is of great concern due to agricultural activities in the region and the extensive use of pesticides. In a long term, this practice leads to environmental pollution, especially to the aquatic system. The objective of this study was to analyze the physicochemical characteristics, metals and pesticides levels in water samples obtained before and after the planting and pesticides' application season from three sites: Uruguay River and two minor affluents, Mezomo Dam and Salso Stream. For biomonitoring, the free-living nematode Caenorhabditis elegans was used, which were exposed for 24 h. We did not find any significant alteration in physicochemical parameters. In the pre- and post-pesticides' samples we observed a residual presence of three pesticides (tebuconazole, imazethapyr, and clomazone) and metals which levels were above the recommended (As, Hg, Fe, and Mn). Exposure to both pre- and post-pesticides' samples impaired C. elegans reproduction and post-pesticides samples reduced worms' survival rate and lifespan. PCA analysis indicated that the presence of metals and pesticides are important variables that impacted C. elegans biological endpoints. Our data demonstrates that Uruguay River and two affluents are contaminated independent whether before or after pesticides' application season. In addition, it reinforces the usefulness of biological indicators, since simple physicochemical analyses are not sufficient to attest water quality and ecological safety.}, language = {en} } @article{KuhnOhrnbergerDahm2011, author = {Kuhn, Daniela and Ohrnberger, Matthias and Dahm, Torsten}, title = {Imaging a shallow salt diapir using ambient seismic vibrations beneath the densely built-up city area of Hamburg, Northern Germany}, series = {Journal of seismology}, volume = {15}, journal = {Journal of seismology}, number = {3}, publisher = {Springer}, address = {Dordrecht}, issn = {1383-4649}, doi = {10.1007/s10950-011-9234-y}, pages = {507 -- 531}, year = {2011}, abstract = {Salt diapirs are common features of sedimentary basins. If close to the surface, they can bear a significant hazard due to possible dissolution sinkholes, karst formation and collapse dolines or their influence on ground water chemistry. We investigate the potential of ambient vibration techniques to map the 3-D roof morphology of shallow salt diapirs. Horizontal-to-vertical (H/V) spectral peaks are derived at more than 900 positions above a shallow diapir beneath the city area of Hamburg, Germany, and are used to infer the depth of the first strong impedance contrast. In addition, 15 small-scale array measurements are conducted at different positions in order to compute frequency-dependent phase velocities of Rayleigh waves between 0.5 and 25 Hz. The dispersion curves are inverted together with the H/V peak frequency to obtain shear-wave velocity profiles. Additionally, we compare the morphology derived from H/V and array measurements to borehole lithology and a gravity-based 3-D model of the salt diapir. Both methods give consistent results in agreement with major features indicated by the independent data. An important result is that H/V and array measurements are better suited to identify weathered gypsum caprocks or gypsum floaters, while gravity-derived models better sample the interface between sediments and homogeneous salt. We further investigate qualitatively the influence of the 3-D subsurface topography of the salt diapir on the validity of local 1-D inversion results from ambient vibration dispersion curve inversion.}, language = {en} }