ИСТИНА

Until very recently, understanding of the current thermal state and stability of the subsea permafrost-hydrate system in the East Siberian Arctic Shelf was based on modelling results. Then we thought about application of electromagnetic sounding which was widely used for decades to solve basic geological problems on land. Finally, our group elaborated applications of the Time Domain Electromagnetic method (TDEM) to be used not only on land (in circuits with loop sources and receivers), but also in the polar seas in winter -from the fast ice, and in summer -onboard research vessels. First time TDEM technology was verified for marine surveys in 2012 from the fast ice on the shallow shelf of the Laptev Sea. First, electromagnetic sounding was performed and the subsea permafrost table (PFT) was identified as roof of a layer with high resistivity at a depth of 25m from the bottom surface. After that, scientific drilling was performed at this point and PFT as a roof of submarine perennially frozen rocks which was recorded at depth of 24.3 m. Thus, good agreement has been found between the “drilling”- actual depth, of PFT and TDEM examination. Several detail geoelectrical surveys were conducted from the fast ice in the Laptev Sea (2013-2015). We used the pulled array transient electromagnetic method (PATEM). The PATEM system provides high-lateral resolution and high-data density to ensure data quality. The modelled domain represented a few-layer horizontally bedded medium. Inversion performance was measured by calculating the root mean square error between the measured and modelled apparent resistivity. Inverse model of sub-bottom electrical resistivity for one transect performed in the study area gives active faults in permafrost and indicate on existence of a tectono-genetic talik characterized with ground water (identified by Ra stable and radioactive daughters) from beneath the permafrost body. After that successful use from the fast ice, different modifications of TDEM technology has been used to proof existence of through taliks in methane release spot areas such mega-seeps in all complex marine expeditions accomplished by Semiletov’s team in the Russian Arctic seas at annual base showing representatives results to be considered in “sister” of TDEM team reports (led by Alexeev, Balikhin, Gunar). During (2013-2024), we have developed and created new hardware base, which allows to improve the quality and resolution of recorded signals and reliability of measurements at the sea. As a result, our developments allow us to conduct high-quality geophysical surveys on the continental shelf in the depth range from 5 to 100 meters at ship speed of 3-4 knots, and at some points the probing depth reached 500 meters depth. In (2015-2017) TDEM technique was widely used to map the permafrost table and deep or through taliks for oil giants such as Gasprom at vicinity of the Yamal Peninsula where numerous Holocene-buried “hydrate explosive craters” were discovered and mapped. In present, TDEM is only one technique used successfully the subsea permafrost structure with focus on the position of subsea permafrost table and deep gas pathways for massive bubbling methane release.