Institute of Geophysics

The idea that Earth’s Moon may host substantial reserves of water ice buried beneath layers of regolith in the polar permanently shadowed regions (PSR) has excited much interest over the past decade. Here, we present numerical modeling in support of a new instrument concept for exploration of the Moon’s PSR: the Cosmic Ray Lunar Sounder, or CoRaLS, under development via a NASA DALI (Development and Advancement of Lunar Instrumentation) grant. CoRaLS is a passive radio-frequency (RF) receiver, tuned to receive direct and reflected radio signals from the subsurface of the Moon. These signals are created via the Askaryan effect, in which high-energy cosmic rays incident on the lunar regolith collide with atomic nuclei and initiate relativistic cascades of charged particles. These particle showers in turn create coherent, linearly-polarized, wideband radio pulses that propagate along the shower path, faster than the phase velocity of light in the regolith, in a Cherenkov cone. These signals can reflect from subsurface interfaces, or scatter from buried objects, thus providing an opportunity to probe the subsurface from orbit. Because this radiation originates from within the regolith, using a passive sensor to detect reflected signals mitigates the effect of strong spurious off-nadir reflections that plague traditional active-source RF systems. We posit that if deposits of relatively pure water ice reside within the upper ~10 m of the lunar surface in PSR, a CoRaLS-style instrument would be uniquely equipped to find it.Radio pulses generated by the Askaryan effect have been observed in Earth’s atmosphere, in terrestrial glaciers, and in salt deposits in the laboratory. They have also been predicted, and should be expected, to develop in the lunar regolith. Our work to date represents the first systematic investigation of the use of this well-established phenomenon in exploration of the lunar regolith, and in particular, prospecting for deeply buried ice in the lunar polar regions.In this presentation, we show the results of a series of 3D finite-difference time domain (FDTD) numerical simulations of the electric field generated by Askaryan-induced radiation from cosmic ray showers in the lunar regolith. Our simulation volumes consist of layered regolith with an embedded pure ice layer at 6 m depth. We vary the thickness of the ice layer and explore the strength and nature of the electric field from direct and reflected Askaryan pulses as observed at a range of positions both on the surface and at a range of angles and elevations above the surface. We find that in these simulations, we can detect reflections from pure ice layers as thin as 10 cm. For thicker layers, we observe distinct reflections, with opposite polarity, from the upper and lower surfaces of the ice layer, that are stronger than and distinguishable from the direct signals. These simulations inform our ongoing work to calculate likely event detection rates for a variety of mission architecture scenarios, as we continue to develop the CoRaLS concept.

Abstract The southern margin of the Eastern Black Sea is commonly regarded as a region of low seismicity, largely because onshore and offshore fault mapping remains limited. However, focal mechanism solutions from the last century indicate active normal and strike-slip faulting in addition to thrust earthquakes, with the reveal pronounced seismic clustering offshore of the Sinop Basin near Samsun. To investigate the origin of this seismotectonic complexity, approximately 1,300 km of high-resolution multichannel seismic reflection profiles were acquired, processed, and interpreted together with multibeam bathymetric data. This analysis addresses the long-standing debate on whether the basin represents a young foreland basin or a graben-type structure, and evaluates the present-day activity of basin-bounding faults. Fault geometries and their seafloor morphological expressions, particularly negative flower structures-provide key constraints on the regional seismotectonic framework. Four seismic units were identified and correlated with Upper Cretaceous–Paleocene, Eocene, Oligo–Miocene, and Plio–Quaternary successions. Faults that terminate above the Upper Cretaceous–Paleocene units are interpreted as inactive, whereas faults that cut all seismic units and reach the seafloor are considered active. Faults confined to the Plio–Quaternary unit are interpreted as syn-sedimentary. These results indicate that the Sinop Basin is not a passive depression but an actively deforming basin controlled by oblique to strike-slip faulting. The mapped active faults are capable of generating earthquakes with magnitudes of Mw ≈ 6.2–6.9, implying a significant seismic hazard for the central Black Sea region.

<strong class="journal-contentHeaderColor">Abstract.</strong> Accurately and efficiently modelling topographic evolution is a key challenge in geodynamic modelling, which requires the solution of the Stokes equations with free surface boundary conditions. While finite difference methods on staggered grids, as used in geodynamic modelling codes such as StagYY, I3ELVIS and LaMEM, offer strong computational performance and compatibility with multigrid solvers, the use of fixed Eulerian grids complicates the implementation of realistic, deformable free surfaces. Two existing methods are available to model free surface boundary conditions in StagYY: the commonly used sticky-air method, which suffers from limitations relating to high viscosity contrasts, and the "staircase" method, which improves upon the sticky air method by imposing free surface boundary conditions at cell boundaries. To address the limitations of existing methods of implementing free surface boundary conditions, this study investigates an alternative variational discretisation of the Stokes equations that uses volume fractions to represent a smooth surface within a fixed Eulerian grid, allowing the imposition of accurate free surface boundary conditions while allowing it to bypass the limitations of existing free surface discretisation methods. The variational Stokes method is demonstrated to be an accurate and computationally efficient alternative to existing methods. It reproduces results comparable to existing methods while reducing computational cost and enabling broader applications, including non-zero surface tractions, complex surface loading, and compatibility with 3D spherical geometries.

Abstract. Accurately and efficiently modelling topographic evolution is a key challenge in geodynamic modelling, which requires the solution of the Stokes equations with free surface boundary conditions. While finite difference methods on staggered grids, as used in geodynamic modelling codes such as StagYY, I3ELVIS and LaMEM, offer strong computational performance and compatibility with multigrid solvers, the use of fixed Eulerian grids complicates the implementation of realistic, deformable free surfaces. Two existing methods are available to model free surface boundary conditions in StagYY: the commonly used sticky-air method, which suffers from limitations relating to high viscosity contrasts, and the "staircase" method, which improves upon the sticky air method by imposing free surface boundary conditions at cell boundaries. To address the limitations of existing methods of implementing free surface boundary conditions, this study investigates an alternative variational discretisation of the Stokes equations that uses volume fractions to represent a smooth surface within a fixed Eulerian grid, allowing the imposition of accurate free surface boundary conditions while allowing it to bypass the limitations of existing free surface discretisation methods. The variational Stokes method is demonstrated to be an accurate and computationally efficient alternative to existing methods. It reproduces results comparable to existing methods while reducing computational cost and enabling broader applications, including non-zero surface tractions, complex surface loading, and compatibility with 3D spherical geometries.

В рамках континуальной модели изучены основные факторы, влияющие на характер пространственно-временных изменений температуры по мере развития процесса разрушения твердого тела и, в частности, горных пород. Исследование проведено с использованием осредненного уравнения для внутренней энергии разрушающегося твердого тела. Проанализирована связь между вариациями значений температуры и особенностями временных изменений структурных характеристик материала в процессе разрушения. Within the framework of the continuum model, the main factors infl uencing the nature of spatiotemporal temperature changes as the process of destruction of a solid and, in particular, rocks develops, are studied. The study was carried out using the averaged equation for the internal energy of a collapsing solid. The relationship between variations in temperature values and the characteristics of temporary changes in the structural characteristics of the material during the destruction process is analyzed.

Представлены математические выражения электрических и магнитных составляющих поля линейных проводящих геологических тел, выведенные с использованием параметров, применяемых для расчета токов и потенциалов тяговой сети железной дороги. Полученные формулы могут быть полезными при интерпретации электроразведочных материалов метода сопротивления. Mathematical expressions of electric and magnetic components of the fi eld of linear conductive geological bodies are presented, derived using parameters used in calculating currents and potentials of a railway traction mudfl ow. The obtained formulas can be useful in interpreting electrical exploration materials of the resistance method.

В статье рассматривается первый опыт применения аудиомагнитотеллурических и маг- нитовариационных исследований на грунтовых плотинах. Проведено сопоставление полученных ау- диомагнитотеллурических разрезов электрофизических параметров с результатами дистанционных индукционных зондирований. Отмечается общая сходимость выделяемых структурных горизонтов и локальных аномалий электропроводности, что позволяет проводить литологическое расчленение грун- тов и выявлять потенциально опасные участки нарушения целостности строения гидротехнических сооружений. Результаты работ показывают, что методы аудиомагнитотеллурики способствуют получе- нию более подробной информации о коренных породах в основании плотин за счет большей глубины исследований, по сравнению с традиционными геофизическими технологиями. The article discusses the fi rst experience of the use of audio-magnetotelluric and magnetization studies on ground dams. The obtained audiomagnetotelluric sections of electrophysical parameters with the results of remote induction sounding was compared. There is a general convergence of the distinguished structural horizons and local abnormalities of electrical conductivity, which allows for lithological dismemberment of soils and identify potentially dangerous areas of violation of the integrity of the structure of hydraulic structures. The results of the work show that the methods of audiomagnetotelluriks contribute to more detailed information about indigenous rocks at the base of dams due to a greater depth of research, compared with traditional geophysical technologies.

Soil erosion is a significant land degradation process in Hungary, especially in agricultural regions. This study assesses soil erosion susceptibility in a loess-covered, intensively cultivated area near Úri and Mende (central Hungary) using Random Forest and Light Gradient Boosting Machine (LightGBM) models. A balanced erosion inventory (500 erosion-affected and 500 non-erosion points) and thirteen geo-environmental factors were used to generate erosion susceptibility maps. Permutation importance and Shapley Additive Explanations (SHAP) identified slope, land use/land cover (LULC), and NDVI as the most influential predictors. The susceptibility maps indicate that 43% (Random Forest) and 46% (LightGBM) of the study area fall within the High and Very High susceptibility classes, with croplands being the most vulnerable. Random Forest achieved AUROC = 0.90, Overall Accuracy = 0.81, RMSE = 0.38, MAE = 0.14, and Kappa = 0.70 for the test dataset; LightGBM achieved AUROC = 0.91, Overall Accuracy = 0.82, RMSE = 0.39, MAE = 0.16, and Kappa = 0.67 for the test dataset. The results identified erosion-prone areas and confirm the reliability of the models. They also highlight the key driving factors as critical determinants of erosion susceptibility. The findings provide a solid foundation for designing targeted soil conservation measures and supporting sustainable land management strategies in central Hungary.

Abstract Soft-sediment deformation structures (SSDS) in water-saturated, unconsolidated sediments are the product of various causes and provide a valuable record of environmental and geological perturbations. We report a record of SSDS preserved in a ∼166 m-long drill core (DX-2) extracted from the Late Pleistocene Diexi Palaeolake, eastern Tibetan Plateau. Two factors make this an outstanding site for studying SSDS: (1) it is among the most seismically active regions on Earth, and (2) it has experienced extremely fast sedimentation rates (∼15 mm/yr) thanks to the prodigious sediment supply from seismically perturbed hillslopes and rivers upstream. We describe and interpret 13 SSDS types within the DX-2 based on detailed sedimentological, morphological, and lithological analysis. We consider the genesis of the abundant SSDS observed in the DX-2 core with several possibilities: mass movement, rock avalanche-driven tsunamis, rapid sedimentation, and seismic shaking as the most probable triggering mechanisms. We suggest high-intensity earthquakes of VI (Modified Mercalli Intensity) or greater as drivers of SSDS in the DX-2. Based on our observations, we propose a conceptual model that attempts to explain the transition from ductile to brittle SSDS behaviour with progressive accumulation and consolidation of the sediment pile. This paper highlights the value of SSDS analysis in palaeo-earthquake identification, aiming to improve the applicability of SSDS as a palaeo-earthquake marker in alpine and canyon areas.