Nikolay A. Palshin

The article presents the results of geomagnetic studies of the southeastern part of the King Trough and central segment of the Azores–Biscay Rise, carried out in the Northeast Atlantic in 2023 on cruise 55 of the R/V Akademik Nikolaj Strakhov. These are the first systematic magnetic field measurements, which made it possible to compile a map of the magnetic anomaly of the study area. Strong magnetic anomalies were identified on the ridges bounding the King Trough, as well as linear anomalies on its flanks and in the southeastern part of the study area in the central segment of the Azores–Biscay Rise. Spectral analysis and transformations of the magnetic anomaly indicate the existence of deep anomalies within the survey site. The strong deep anomalies are volcanic in origin and were formed in a different geomagnetic epoch than the deep parts and flanks of the King Trough. The results confirm the hypothesis of a complex two- or multistage formation of geological structures at the King Trough, with the exception of its southeastern part, which belongs to the Azores–Biscay Rise.

The paper deals with the description of new geomagnetic data collected in the North Atlantic during cruises of research vessels of the Russian Academy of Sciences performed in 2020–2022. Modern technologies of geomagnetic measurements in the ocean and methods of their processing are considered. The obtained geomagnetic data indicate the heterogeneous nature of the sources of magnetic anomalies in the Charlie–Gibbs fracture zone and adjacent areas of the Mid-Atlantic Ridge and allow solving a wide range of geological and tectonic problems. Priority directions for further research aimed at adjusting spreading parameters and constructing models of the magnetic layer typical for transform faults and amagmatic segments of the Mid-Atlantic Ridge are formulated.

The paper deals with the description of new geomagnetic data collected in the North Atlantic during voyages of research vessels of the Russian Academy of Sciences performed in 2020–2022. Modern technologies of geomagnetic measurements in the ocean and methods of their processing are considered. The obtained geomagnetic data indicate the heterogeneous nature of the sources of magnetic anomalies in the Charlie-Gibbs fault zone and adjacent areas of the Mid-Atlantic Ridge and allow solving a wide range of geological and tectonic problems. Priority directions for further research aimed at adjusting spreading parameters and constructing models of the magnetic layer typical for transform faults and amagmatic segments of the Mid-Atlantic Ridge are formulated.

Subsea permafrost stability is the key to whether pre-performed methane sequestered in hydrate deposits escapes to the overlying strata. By making use of the 1D numerical modeling and field data, we analyze the capabilities of the time-domain (transient) electromagnetic method (TDEM) when being applied for subsea permafrost mapping, and study the effect of the background resistivity structure on the inversion models’ accuracy for a series of settings typical for the East Siberian Arctic Shelf—the broadest and shallowest shelf in the world ocean, which represents more than 70% of the subsea permafrost. The synthetic response analysis included the construction of a series of resistivity models corresponding to different settings (presence/absence of ice-bonded permafrost layer, different position of its top and bottom boundaries, different width and thickness of thawed bodies or taliks, variable seawater depth and its resistivity), and calculation of synthetic apparent resistivity responses used to assess their sensitivity to changes in the target parameters of the resistivity structure. This was followed by regularized inversion of synthetic responses and comparing resulting models with original (true) ones, which allowed us to understand the possible uncertainties in the geometry and resistivity of the reconstructed permafrost layer, depending on seawater depth and unfrozen layer thickness, as well as confirm the overall efficacy of TDEM technology for the subsea permafrost imaging. That is crucially important for understanding the current state of the subsea permafrost-hydrate system and possible future dynamics.

A fundamentally new conclusion that zones of high seismic activity are controlled by electroconducting (fluid-saturated) fragments rather than by the entire deep fault is drawn. It is shown that the...

Understanding the processes that occur in the transition from the Pacific Ocean to Eurasia is key to constructing the tectonic models of the Earth’s shells and the convection models of the upper mantle. The electromagnetic methods permit estimating the temperature and fluid content (and/or carbon (graphite) content) in the Earth’s interior. These estimates are independent of the traditionally used estimates based on seismic methods because the dependence of electrical conductivity on the physical properties of the rock is based on different principles than the behavior of the elastic waves. The region is characterized by a complicated geological structure with intense three-dimensional (3D) surface heterogeneities, which significantly aggravate the retrieval of the information about the deep horizons in the structure of the Earth’s mantle from the observed electromagnetic (EM) fields. The detailed analysis of the nature of the deep electrical conductivity and structural features of the transition from the Pacific to Eurasia included numerical modeling of the typical two- and three-dimensional models has been carried out. Based on this analysis, the approaches that increase the reliability of the interpretation of the results of the EM studies are suggested.

The origin of background fluctuations in the natural electric field observed in the measurements on the seafloor of shallow seas and oceans, as well as in the lakes and estuaries of large rivers is considered. It is shown that the presence of these fluctuations, which have a quasi-harmonic behavior, is due to the surface waves and can be accounted for by the action of the (1) magnetohydrodynamic and/or (2) electrokinetic effects, with the predominance of the latter in the freshwater basins. The excitation models of the background fluctuations in the electric field by both the long surface waves and interacting short waves are analyzed. The estimates of the electric field of background fluctuations are obtained.

The transverse current anomalies evident from magnetotelluric sounding (MTS) data in the transition zone from the Asian continent to the Pacific Ocean and a geoelectrical model suitable for explaining these effects are discussed. Using simulation results and new MTS data on Sakhalin and northern Vietnam, ultra-deep fluid–fault system (UDFFS) models are constructed, comprising steeply dipping low-resistivity and high-resistivity linear bodies which penetrate through the whole section of the lithosphere, continuing deep into the asthenosphere. The structure of these systems reflects the development of deep and ultra-deep fault zones, along which mantle-originated fluids may migrate through sediments to reach the surface. This allows the anisotropic–conductive fractured structures adjacent to these faults to be considered as being most favorable for hydrocarbon accumulations.