地球科学最新文献

During periods of increased geomagnetic activity, perturbations within the terrestrial magnetosphere are known to induce currents within conducting materials, at the surface of Earth through rapid changes in the local magnetic field over time (dB/dt). These currents are known as geomagnetically induced currents and have potentially detrimental effects on ground based infrastructure. In this study we undertake case studies of five geomagnetic storms, analyzing a total of 19 days of 1-s SuperMAG data in order to better understand the magnetic local time (MLT) distribution, size, and occurrence of “spikes” in dB/dt, with 131,447 spikes in dB/dt exceeding 5 nT/s identified during these intervals. These spikes were concentrated in clusters over three MLT sectors: two previously identified pre-midnight and dawn region hot-spots, and a third, lower-density population centered around 12 MLT (noon). The noon spike cluster was observed to be associated with pressure pulse impacts, however, due to incomplete magnetometer station coverage, this population is not observed for all investigated storms. The magnitude of spikes in dB/dt are determined to be greatest within these three “hot-spot” locations. These spike occurrences were then compared with field-aligned current (FAC) data, provided by the Active Magnetospheric Planetary Electrodynamic Response Experiment. Spikes are most likely to be co-located with upward FACs (56%) rather than downward FACs (30%) or no FACs (14%).

Submesoscale motions may substantially influence similarity relationships within the Stable Boundary Layer (SBL), leading to considerable uncertainty in these relationships. Therefore, we conducted a comparison of similarity relationships within the SBL in the Taklimakan Desert before and after the removal of submesoscale motions, aiming to gain deeper insights into the impacts of submesoscale motions on the similarity relationships. We introduced a method utilizing Discrete Wavelet Transform with orthogonal wavelets to identify and filter out submesoscale motions. By investigating nocturnal observations from June 29 to July 31, 2021, daily from 22:00 to 07:00 local time, we tested and confirmed that submesoscale motions indeed exert a substantial influence on similarity relationships in different ways. After removing submesoscale motions, dimensionless wind velocity standard deviations become more consistent across different averaging periods, with notably higher Correlation Coefficients and lower Root Mean Square Errors. This highlights the effectiveness of the method in eliminating submesoscale motions. Submesoscale motions themselves do not exert a direct and significant influence on the flux–profile relationship for wind speed. It seems the enhanced turbulence intermittency induced by episodic submesoscale motions results in notable deviations from the Businger-Dyer relationship within the strong stable regime. The influence of submesoscale motions on intermittency appears more pronounced as stability increases. Submesoscale motions significantly influence the relationship between turbulence intensity and wind speed. The episodic submesoscale motions appear to be the direct cause for the presence of moderate turbulence intensity at low wind speeds. Horizontal wind velocity variances are mainly influenced by submesoscale motions, while vertical wind variance is predominantly associated with small-scale turbulence. These findings may contribute to a more accurate understanding of the impacts of submesoscale motions on similarity relationships in the SBL and provide genuine and stable similarity relationships of small-scale turbulence for SBL modeling.

Abstract—It is shown that most marsquakes epicenters are located in the zones of extension and fairly high shear stresses associated with deviation of the planet from hydrostatic equilibrium. In this paper, non-hydrostatic stresses in the interior of Venus are calculated for two types of models: an elastic model and a model with a lithosphere of variable thickness (150–500 km) covering a weakened layer that has partially lost its elastic properties. Numerical modeling of the system of elastic equilibrium equations for a gravitating planet is carried out with a step of 1° × 1° degrees in latitude and longitude down to a depth of 480 km, which is the first phase transition in the mantle. The boundary conditions of the problem are the topography and the gravitational field of the planet. In general, the level of nonhydrostatic stress on Venus is not very high. On the surface and in the crust, the highest shear stresses are observed in the region of the Maxwell Montes on Ishtar Terra. Beneath the Maxwell Montes, shear stresses in the crust reach 80 MPa and compressive stresses, 125–150 MPa, depending on the model. Tensile stresses around this area are about 20 MPa. The highest tensile stresses occur in the regions beneath such structures as Lavinia Planitia, Sedna Planitia, and Aino Planitia.

In India, Rajasthan, the northwestern part of India, possesses geological diversity comparable to its cultural richness. This paper focuses on evaluating a promising geological heritage site in Rajasthan, the Palaeo-Mesoproterozoic Stromatolite Park at Bhojunda (District Chittorgarh). The Bhagwanpura Limestone Formation of the Lower Vindhyan Group hosts well-preserved stromatolites at this geosite. The paper assesses, both qualitatively and quantitatively, the potential of this stromatolite-bearing site and based on the available data and analysis considers it to be a strong candidate for a potential geoheritage site. SWOT analysis also suggests that the site has immense potential but at the same time, is in urgent need of geoconservation. Stromatolites provide valuable insights into the early life on Earth; the Stromatolite Park at Bhojunda holds a significant potential as a Geoheritage site due to its extensive geological exposure. Stromatolites are layered sedimentary structures formed mainly by photosynthetic microorganisms that include cyanobacteria, sulfate-reducing bacteria, and Pseudomonadota. They produce cementing materials that bind sediments (sand and other rocky materials) to form “microbial mats”. In the present study, species from seven genera, namely Conophyton cylindricus, Baicalia baicalica, Collenia columnaris, and Kussiella kussiensis, Tungussia sp., Stratifera rara, and Weedia walcott are recorded suggesting a lower‒middle Riphean age. Petrographically, the Bhagwanpura Limestone is composed of fine grains of calcite and dolomite with dispersed grains of cryptocrystalline silica, iron oxide, chert fragments, and veinlets of quartz and calcite. Present analysis suggests that the Bhojunda Stromatolite Park meets all standards to become a Global Geopark. It is crucial to take the necessary actions to apply for UNESCO confirmation, advocating not just community-driven conservation of the region’s geological heritage but also fostering sustainable development by improving the native tribes’ standard of living.

Abstract

The paleodirection and paleointensity of the geomagnetic field are determined from seven andesibasalt–basalt samples of three lava flows (L1–L3) from the Avachinskii (Avacha) volcano. Based on the sample from the recent lava flow TFE-50 (Tolbachik Fissure Eruption), the reliability of the Thellier–Coe method for geomagnetic field paleointensity determination is demonstrated: the deviation of the calculated H_an from the IGRF12 values is at most 3% with a quality factor q > 13. The age of lava flows L1–L3 is refined using paleomagnetic data. Flows L1, L2 of the Molodoi Cone were formed in 1827 and 300–600 years ago, respectively, and the age of flow L3 at the crest of the somma is determined at 30–32 ka, which agrees with the known age estimate of the debris avalanche associated with the catastrophic destruction of the Avachinskii volcano 29 900 ± 37 900 ¹⁴C years ago.

Abstract—Stability of a heavy inclusion in the Earth’s upper crust is studied by the linear theory method for small perturbations. The presence of such inclusions with an increased density is associated with chemical inhomogeneity or phase transformations. The stability problem of a heavy elastic layer above a less dense elastic layer representing the lower crust and mantle lithosphere is solved. It is shown that such a system is stable: small initial perturbations produce low-amplitude oscillations. The corrections of oscillation frequencies for the density jump at the boundary between the layers are calculated. The changes introduced to the solution by the consideration of creep, which is present even in cold geomaterials, are discussed. Creep causes instability of heavy inclusions in the upper crust. However, due to the very high effective viscosity of the cold upper crust, this instability is of a formal nature, since it develops so slowly that heavy inclusions in the upper crust hardly change their position on timescales comparable to the age of the Earth.