The Russian sector of the arctic shelf is the longest in the world. Quite a lot of places of massive discharge of bubble methane from the seabed into the water column and further into the atmosphere were found there. This natural phenomenon requires an extensive complex of geological, biological, geophysical, and chemical studies. This article is devoted to aspects of the use of a complex of marine geophysical equipment applied in the Russian sector of the arctic shelf for the detection and study of areas of the water and sedimentary strata with increased saturation with natural gases, as well as a description of some of the results obtained. This complex contains a single-beam scientific high-frequency echo sounder and multibeam system, a sub-bottom profiler, ocean-bottom seismographs, and equipment for continuous seismoacoustic profiling and electrical exploration. The experience of using the above equipment and the examples of the results obtained in the Laptev Sea have shown that these marine geophysical methods are effective and of particular importance for solving most problems related to the detection, mapping, quantification, and monitoring of underwater gas release from the bottom sediments of the shelf zone of the arctic seas, as well as the study of upper and deeper geological roots of gas emission and their relationship with tectonic processes. Geophysical surveys have a significant performance advantage compared to any contact methods. The large-scale application of a wide range of marine geophysical methods is essential for a comprehensive study of the geohazards of vast shelf zones, which have significant potential for economic use.

The Arctic seas are now of particular interest due to their prospects in terms of hydrocarbon extraction, development of marine transport routes, etc. Thus, various geohazards, including those related to seismicity, require detailed studies, especially by instrumental methods. This paper is devoted to the ocean-bottom seismographs (OBS) based on broadband molecular–electronic transfer (MET) sensors and a deployment case study in the Laptev Sea. The purpose of the study is to introduce the architecture of several modifications of OBS and to demonstrate their applicability in solving different tasks in the framework of seismic hazard assessment for the Arctic seas. To do this, we used the first results of several pilot deployments of the OBS developed by Shirshov Institute of Oceanology of the Russian Academy of Sciences (IO RAS) and IP Ilyinskiy A.D. in the Laptev Sea that took place in 2018–2020. We highlighted various seismological applications of OBS based on broadband MET sensors CME-4311 (60 s) and CME-4111 (120 s), including the analysis of ambient seismic noise, registering the signals of large remote earthquakes and weak local microearthquakes, and the instrumental approach of the site response assessment. The main characteristics of the broadband MET sensors and OBS architectures turned out to be suitable for obtaining high-quality OBS records under the Arctic conditions to solve seismological problems. In addition, the obtained case study results showed the prospects in a broader context, such as the possible influence of the seismotectonic factor on the bottom-up thawing of subsea permafrost and massive methane release, probably from decaying hydrates and deep geological sources. The described OBS will be actively used in further Arctic expeditions.

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The paper presents the comparative characteristics of self-pop-up digital seabed seismometers that have been developed since the early 2000s. The requirements for the main technical characteristics that should be considered for developing the new-generation of self-pop-up seabed seismometers have been proposed. The microcontroller and reference frequency generator are the key parts for a seabed seismometer design. The paper provides the development results of these key components, which are essential for the seismometer performance (power consumption and functionality). A draft proposal for seabed seismic exploration project in the Russian sector of the Black Sea solving the current actual geological problems is presented. Implementation of the project will contribute to determination of the crystalline basement depth within the Shatsky ridge and the Tuapse depression; detection of P and S wave velocities in the lower part of sedimentary cover and in the basement, and to the refinement of the Earth’s crust thickness. The extension of regional seabed seismic lines from the Turkish to the Russian sector of the Black Sea will give the scientists a clearer picture of the Earth’s crust structure over the whole east Black Sea basin. The results of seabed studies will verify and improve the results of the Black Sea 2011 towed-streamer survey (with 10 km streamer) on the sedimentary cover structure and the Earth’s crust.

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It is emphasized that the Russian complex of "KRAB-400" seismic bottom stations was developed for hydrocarbon survey on the continental shelf of the Russian Federation within the framework of import substitution program. The tests carried out on a limited sample of 10% of the complex bottom stations in the first stage have revealed unavailability of the complex for further tests. This fact has dictated the necessity to develop procedures for hardware integrated check to identify engineering faults. The second stage of full-scale tests performed on the basis of the developed integrated check procedures is described in the paper. The test procedures to validate the key parameters of bottom stations are explained. They include the adjustment of seismic signal source, accuracy assessment for seismic station timer, identity evaluation for bottom station seismic channels, assessment of station displacement on the seabed with respect to the shipboard launch point, analysis of station compass and tiltmeter indications on the seabed, definition of hydrophone channel optimum gain. The technology of seismic profile mapping using MultiChannel Seismic (CDP method) at test range is offered. The performed tests have revealed that the overall reject rate of stations by the various parameters (failed hydrophones, reversed polarity of connection, channels nonidentity, failure to meet timer specifications) is 9.18% of total number of stations. This reject rate is unacceptable for the field trials. Regardless of hardware engineering deficiencies the second stage of tests has validated the general system availability to gain high-quality seismic data. Hardware performance is rated at the level of the best world-class products. The processed seismic data has enabled evaluating the accuracy of the obtained results, developing recommendations for designer to enhance reliability and efficiency of the stations ready for pilot testing at one of the licensed areas of the continental shelf of the Russian Federation.

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