Russian Journal of Earth Sciences

The Vema Fracture Zone is located in the North Atlantic Ridge and extends along 11°N from 38 to 46°W. It is the main pathway for the spreading of Antarctic Bottom Water to the Northeast Atlantic. Due to its location and structure, the Vema Fracture Zone is an excellent object for studying the properties of the bottom gravity flow. An oceanographic section along the entire Vema Fracture Zone was carried out during cruise 52 of the R/V “Akademik Boris Petrov” in November–December 2022. In our work, we analyzed 25 oceanographic stations; at 15 stations, dissolved oxygen and nutrients were also determined. Such studies of the structure of the bottom gravity flow of Antarctic Bottom Water in the central channel of the Vema Fracture Zone based on high spatial resolution in situ data were made for the first time. A supercritical flow accompanied by a hydraulic jump was detected behind the main sill of the fracture zone. Simultaneous measurements of dissolved oxygen, silicate, and phosphate allowed us to examine the hydrochemical structure along the entire Vema Fracture Zone. Its analysis revealed high correlation between the distribution of hydrochemical and oceanographic parameters in both the stable flow and turbulent regimes of the current.

In this paper numerical simulation of tsunami waves is carried out using data from the earthquake off the coast of Mindanao Island in the Philippine Sea on 23 December 2023 in the western part of the Pacific Ocean. The paper considers two scenarios of seismic source localization with different dynamics of the Earth's crust displacement in the seismic source region during the earthquake process. Consideration of two scenarios with different location of keyboard blocks, into which the earthquake source is segmented, allows one to study the influence of source geometry on the characteristics of generated tsunami waves. In the course of simulation, during dynamic displacement of keyboard blocks in the earthquake source, tsunami source formation, tsunami waves and their propagation in the Pacific Ocean water area take place. The wave characteristics of the process along the mainland and island zones in the considered water area were obtained. The results of simulation for the two scenarios are compared with observational data, which makes it possible to identify which type of block arrangement provides better similarity with the recorded tsunami characteristics and, therefore, better describes the real dynamics of the earthquake source.

The paper presents an algorithm for reconstruction of stress state parameters of rock massif based on data on natural fractures. For one well developing an oil field, the directions of the principal in-situ stresses, their relative magnitudes, and the strength of the rocks in the near-wellbore space were reconstructed. Stress inversion results are in agreement with other methods of stress estimation, in particular, with the results of the mini-hydraulic fracture test. The inverse problem of stress state estimation is solved using the Monte Carlo method. An algorithm of applying the apparatus of mathematical statistics – the method of moments for determining distribution parameters from the Pearson distribution family – to quantify the ambiguity of the estimation of the directions of the principal stresses and their relative magnitudes is presented. The proposed algorithm can be used for independent reconstruction of stresses for carbonate rocks, provided that there is information about the conductivity of fractures in the rocks of the near-wellbore space to further improve the quality of one-dimensional and three-dimensional geomechanical modelling.

Here we present the results of observations of short-period internal waves (SIWs) in Fram Strait and near Svalbard based on analysis of Sentinel-1 A/B synthetic aperture radar (SAR) data in June-September 2018. Analysis of 1500 spaceborne SAR images allowed to identify 750 surface signatures of SIWs. Maximal number of SIW identifications is observed in August, when both stratification and ice conditions are favorable for SIW generation and identification in satellite data. Background meteorological conditions in summer 2018 favored the northward movement of the ice boundary up to 82,5 ∘ N that allowed to observe SIWs over the Yermak Plateau. Four main regions of SIW observations were identified – deep Fram Strait region (depths over 2000 m), southwestern Yermak Plateau with depth range of 500–1500 m, and two shelf break/upper continental slope regions northwest from Svalbard with depths below 500 m. Analysis of spatial properties of SIWs has shown that the study region is dominated by SIW trains with a mean crest length of 15 km and mean packet length of about 5 km. The largest SIW trains with area of nearly 400 km2 were observed over the Yermak Plateau where tidal currents are maximal.

The remote sensing analysis within the Hu'u District area is known to face a challenge with dense vegetation. The problem affects the accurate reading of spectral reflectance from satellites, influencing the differentiation between potential mineral zones and vegetation. Therefore, this study aims to carry out a remote sensing analysis of densely vegetated areas to differentiate minerals from vegetation and obtain potential mineral zones. The combination band ratios and principal component analysis (PCA) methods are used to acquire potential mineral zones. Furthermore, Landsat 8 images freely available on Google Earth Engine are adopted and the validation is carried out using a drill hole from previous study. The results show that band ratios method cannot distinguish mineral zones from vegetation. However, PCA method can recognize potential mineral zones. This is the result from PCA method with band combination of bands 1, 2, 3, 4, 5, and 6 as the first group and band 2, 4, 5, and 6 as the second group.

The paper presents the results of pore space studies of highly porous reservoir rocks of underground gas storage (UGS) facilities using the digital analysis of computed microtomography images. The methodology of complex nondestructive analysis of structural and filtration-capacitance properties has been developed. Structural heterogeneities and rock fracturing were evaluated. 3D models of specimen inner space were created on the basis of multi-scale images. The values of open and closed porosity, geodesic tortuosity were calculated, the characteristics of percolation paths in the studied rocks were analyzed for different directions of intrusion. Conclusions were made about the homogeneity of percolation path distribution over the rock volume. The spatial distribution of porosity in the rocks was studied, and porometry analysis of the rocks was carried out. Numerical modeling of filtration processes on the obtained structures in the framework of Stokes approximation for three selected directions in the rock by means of GeoDict software was carried out. It is shown that there is no pronounced dependence of changes in filtration properties in the selected directions on the quantitative characteristics of the pore space. The conclusion is made about the degree of anisotropy of filtration-capacitance properties of rocks. The good correspondence of the characteristics measured in the course of digital analysis with in-situ data and experimentally obtained laboratory values is shown. The described technique allows to simplify data acquisition on the characteristics of fine-grained reservoir rocks, and is designed to extend the approaches to nondestructive analysis of core material. The obtained reservoir properties data is necessary for the operational models development of UGS, clarifying integral reservoir properties and filling hydrodynamic models of hydrocarbon storage and production facilities.