ALBERT

Description: The dataset contains source parameters of acoustic emission (AE) events recorded during triaxial friction (stick-slip) experiments performed on the Westerly Granite sample WgN05. In addition we provide raw waveform data of AE events recorded in triggered mode with a network of 16 AE sensors. Basic seismic catalog associated with the stick-slip experiment contains origin time, hypocentral location in local Cartesian coordinate system of the sample (with associated uncertainties), and AE-derived magnitude. In addition, for a subset of AEs we provide full moment tensors. This catalog include information on fault parameters (strike, dip and rake of the two nodal planes), percentage of isotropic, compensated linear vector dipole and double-couple components of the full moment tensor, P, T, B axes orientations in the coordinate system of the sample, uncertainty assessment, as well as the six independent moment tensor components. Finally, we provide a time series of axial stress values as presented in the Kwiatek et al. (2023) as well as the coordinates of the AE sensors. The catalog and parametric data is supplemented with the raw waveform recordings stored in HDF5 format from 16 acoustic emission sensors placed on the surface of the sample.

Description: Highly fragmented rocks (i.e., pulverized rocks) in the fault damage zone presumably develop during co-seismic deformation processes. These pulverized rocks close to the fault core are generally thought to originate from high strain rates, whereas the genesis of pulverized rocks that can be found several hundred meters away from the fault core – where quasi-static conditions prevail – remains unclear. We thus conducted uniaxial cyclic loading experiments with axial strain rate of ∼10−3 s−1 on Leiyang marble in a stress-controlled manner in order to produce crushed rocks for analysis. We found that cyclic loading between 0.8 σc and 1.3 σc can simultaneously compact pre-existing cracks and generated new cracks in marble, which strengthened and stiffened the rock. The stiffened marble developed a higher crack density and energy density before rupture, thereby facilitating rock fragmentation compared with the reference sample, which was fractured monotonically in one cycle. Our results provide a plausible explanation for the genesis of pulverized marble at quasi-static strain rate in the field.

Description: Microbes residing in cryoconite holes (debris, water, and nutrient-rich ecosystems) on the glacier surface actively participate in carbon and nutrient cycling. Not much is known about how these communities and their functions change during the summer melt-season when intense ablation and runoff alter the influx and outflux of nutrients and microbes. Here, we use high-throughput-amplicon sequencing, predictive metabolic tools and Phenotype MicroArray techniques to track changes in bacterial communities and functions in cryoconite holes in a coastal Antarctic site and the surrounding fjord, during the summer season. The bacterial diversity in cryoconite hole meltwater was predominantly composed of heterotrophs (Proteobacteria) throughout the season. The associated functional potentials were related to heterotrophic-assimilatory and -dissimilatory pathways. Autotrophic Cyanobacterial lineages dominated the debris community at the beginning and end of summer, while heterotrophic Bacteroidota- and Proteobacteria-related phyla increased during the peak melt period. Predictive functional analyses based on taxonomy show a shift from predominantly phototrophy-related functions to heterotrophic assimilatory pathways as the melt-season progressed. This shift from autotrophic to heterotrophic communities within cryoconite holes can affect carbon drawdown and nutrient liberation from the glacier surface during the summer. In addition, the flushing out and export of cryoconite hole communities to the fjord could influence the biogeochemical dynamics of the fjord ecosystem.

Description: This study investigates the optimization of Semi-Airborne Electromagnetic (SAEM) surveys for enhanced subsurface imaging in mineral exploration. It highlights the utility of multi-transmitter systems and explores real data utilization and the challenges of large-scale surveys. With emphasis on Data obtained from DESMEX project surveys. The use of multiple transmitters is crucial. Single transmitters can distort results and mask subsequent bodies. Employing two transmitters on both sides of the target enhances resolution and depth accuracy. results are based on finite element forward operator custEM and pyGIMLi’s inverse solver [1]. substantial advantages of combining single and multi-patch inversion data. This integration results in improved resolution, reduced artifacts, enhanced continuity of geological structures, superior anomaly detection, minimized edge effects, and improved depth penetration [2]. These findings open promising avenues for further exploration and research in geosciences, offering valuable insights into the Earth's subsurface and its intricate geological features. The next logical step involves expanding our methodology to large-scale inversion using more than three transmitters.

Description: The Atacama Desert along the Chilean Coastal Cordillera is a unique landscape to understand the Earth's evolution in hyper-arid and arid environments. The Paranal clay pan has studied by the CRC 1211 project to recover a continuous climate record for paleoclimate research. The goal is to provide the sedimentary architecture and bedrock topography of the Paranal site by interpreting multidimensional inversion of loop source transient electromagnetic (TEM) data. A total of 133 TEM soundings were carried out using a central loop configuration, with a transmitter loop size of 40×40 m2 and a receiver of about 10×10 m2. The TEM data was processed and analyzed, exhibiting high-quality data, with an average of noise level of about ηnoi = 3·10−10V/Am2. The 1D Occam inversion results exhibits a clear three-layered resistivitydepth structure with a second conductive layer of roughly 20 Ωm. The clay pan's resistivity distribution is well-resolved with a global misfit of around 1.1. However, the study site showed 2D effects that were stronlgy visible at the edges of the clay pan, leading to misinterpretations of the TEM data. This was confirmed based on 2D forward modelling. In this manner, to better deal with the observed 2D distortions in the TEM data and to derive a more accurate geometry of the clay pan, the recently developed Julia Package (3DTEMinv) for time-domain 3D inversion and modeling data was performed. The resulting 3D inversion presents a high convergence rate, and acceptable solutions are obtained after ten iterations with a good misfit of about 1.6. The 3D model exhibits a well-resolved geometry of the clay pan, with a high resolution of the derived conductive body. The drill core results confirm the 1D and 3D TEM models at the center of the clay pan, which is in good agreement with the resulting lithology with a maximum thickness of about 171 m depth and a weathered granodioritic bedrock below. These results agree with the local and regional geological context, improving the understanding of sediment deposition and transportation in this hilly and arid environment.

Description: Multi-dimensional inversion of Transient electromagnetic data is a computationally expensive task. Only few developments and practical interpretation tools exist. Here, we present a multidimensional inversion framework for loop source time-domain electromagnetic data. The developed algorithm is a robust, efficient, and user-oriented tool for the multi-dimensional inversion of typical loop source time-domain electromagnetic configurations. A time-domain finite volume discretization and the direct solver MUMPS are utilized to solve the 3D TEM forward problem. An iterative Gauss-Newton optimization method is implemented for the inversion kernel. The code is parallelized for calculating multiple sources simultaneously to accelerate the inversion. Based on exploration tasks, different configurations exist for commonly used loop source TEM configurations and typical field scales. Synthetic examples are used to verify the effectiveness and benchmark the developed 3D algorithm. Considering that TEM data is often gathered along profiles, adjusting the model roughness along the different modeling domain directions, sufficiently constrains to allow for 2D imaging. In addition to the vertical signal components, we also included horizontal components for large scale fixed loop applications. Subsequent to synthetic validation, the inversion algorithm is further verified using ~120 dense TEM soundings collected over a clay pan site in the Atacama Desert, Chile, to provide bedrock geometry information and suitable coring sites. The 3D inversion result provided an excellent depth estimate of sedimentary infill as well as the bedrock topography and was later confirmed by deep coring. Another interesting site is the Roter Kamm impact crater in Namibia. Our preliminary results obtained from largescale multicomponent fixed loop TEM data reveal a sedimentary infill down to ~300 m depth. In conclusion, our presented 3D inversion code is capable to handle data from various exploration scenarios and provides a robust tool for advanced EM interpretation.

Description: Carrying out laboratory experiments is usually a time-consuming process. In addition, the options for varying parameter studies are limited and adjustments to the design of the measuring equipment are often not possible at all. In order to circumvent these limitations, we supplement our laboratory experiments with virtual experiments as best as possible. For this purpose, we have expanded our finite element library FEMALY [1] to include the so-called complete electrode model [2], which allows us to simulate electrodes of any shape for DC and IP applications and also provides us with explicit mathematical expressions for calculating sensitivities [3]. As a first case study, we consider an IP measurement on a measuring cylinder with embedded ring electrodes to virtually reproduce the time-varying change of the apparent resistivity for laboratory tracer experiments (Figure 1). We present the real and imaginary part of the sensitivity distribution of the underlying measurement configuration that confirms our initial assumption that the actual electrode surface shape has a relatively small influence on the observed measurement quantities.

Description: The transition towards renewable energies demands secure supply with critical raw material and requires efficient non-invasive methods for deep earth resources exploration. The novel DESMEX (Deep electromagnetic sounding for mineral exploration) semi-airborne electromagnetic (semi-AEM) exploration concept aims at efficient exploration of resources down to 1 km depth. Here we present a large-scale semi-AEM exploration study in a graphite mining district in eastern Bavaria, Germany. At the ground, several horizontal electrical dipole transmitters were deployed and helicopter-towed magnetic field sensors measure the EM fields along flight lines within several overlapping flight areas, providing a fast data acquisition and a high spatial coverage. Imaged shallow high conductivity structures can be correlated with graphite-rich zones and match well with existing helicopter-borne EM results. The presence of graphite leads to significant induced polarization (IP) effects with considerably high chargeabilities superposing electromagnetic induction. We include these effects in a realistic 3D inversion using a synthetic data study to analyse, if the IP effect alters the overall conductivity structure and demonstrate that the obtained 3D model is reliable.