Мурманская МИЛЯ. 2018 г. №4.

EXPLORATIONS 50 MAGE was responsible for the work organi­ zation and planning, technical support, gen­ eral management of field works and direct seismic studies [4]. The works were performed in July-Oc- tober 2014. The RV AKADEMIK FEDOROV and RV NIKOLAY TRUBYATCHINSKY with the support of the nuclear-powered icebreaker YAMAL were a part of the expedition. The vessel AKADEMIK FEDOROV was special­ ly reequipped to perform under-ice seismic survey. CMP seismic studies were carried out in two versions: with a 4,500 m receiving device and with a 600 m solid streamer in combination with seismic reflection and re­ fraction sounding. To record a seismic sig­ nal, the digital 24-bit Sercel SEAL streamer was used. The number of channels varied from 48 to 360 depending on the streamer length. 16 GEOPOINT EXPORT hydrophones were in each group. Source points spacing was 50 m. The sampling rate equaled to 2 ms, and the record time was 12 s. The ac­ curacy of the horizontal and vertical correla­ tion of the shot points was maintained at least ± 10 m, 1% of the depth. The towing depth of the receiving device varied depending on the ice conditions in the range of 10-15 m, sometimes down to 20 m. Bolt 1500 and Bolt 1900/Bolt 8500APG air gun arrays with a vol­ ume of 1,300 cu.in. were used as sources. [7]. In order to determine velocity characteris­ tics of the main sedimentary boundaries and to build a velocity model, the innovative in­ tegrated CMP reflection and refraction seis­ mic works were performed. The studies were carried out by the BOX radiotelemetry system for seismic data acquisition along with the floating module of the BOX telemetric seis­ mic system with the MP-24L3 (GeoSpace) hydrophone. The sampling rate equaled to 4 ms, and the sounding interval was not more than 50 km. The spread length was 15-25 km with the record time of 8-12 s [1]. Besides, a Deep Seismic Sounding (DSS) line was shot for the first time. To per­ form the DSS works a modernized hardware system consisting of self-floating autono­ mous bottom seismic stations with a multi­ component digital seismic signal registration (ADGS-2M, ADSS-5000), a seismic low-fre­ quency air gun (SIN-6) and on-board control devices was used. Shots on the lines were carried out every 150 s. The sampling rate was equal to 8 ms, and the record time was 60 s. Refracted waves associated with the boundaries in the sedimentary cover and the Earth crust are distinguished in the first arriv­ als on the wave fields of the DSS soundings. A reflected wave from the boundary M (PmP) was recorded; it is traced from the 40-60 km offsets throughout almost the entire line. A sufficiently steady tracking interval is 60-80 km, in some cases reaching 100-110 km [5, 8]. For the regional survey of the seabed fea­ tures along the lines the Kongsberg Maritime AS (Norway) ЕМ122 multi-beam echosound- er and the spare 12 kHz EA 600 single-beam echosounder of the same manufacturer were used. With a view to obtaining additional in­ formation about the upper part of the section and the seabed features, the 18 kHz TOPAS PS 18 profiler was used [1, 12]. Gravimeter survey was carried out si­ multaneously by the use of two gravim- eters: the Chekan-AM portable gravimeter and the Shelf-E portable gravimetric sys­ tem [7]. Before the work commencement all the required preparatory works were carried out, and both gravimeters were calibrated. The backup gravimeter survey was carried out in Naantali (Finland) prior and after the voyage. The total volume of the integrated hydrographic and geophysical survey com­ prised more than 10,000 km: CMP survey with a 600-meter streamer in combination with seismic reflection and seismic refrac­ tion sounding equaled to 3,373.2 km; using a 4,500-meter streamer - 5,596.950 km. In addition, bottom relief survey was performed in the volume of 1,165.9 km in combination with gravimeter survey. The map of the ac­ tual date is shown in Fig. 2. Most of the work was performed with the ice concentration of 9-10 points, with its thickness of up to 160 cm. On some lines there was a two-year-old ice up to 240 cm in thickness and hummocks of up to 4 m. Of­ ten, the icebreaker YAMAL first made its way and then returned and paved the way for the RV AKADEMIK FEDOROV [7]. Data quality control confirmed the validity of the seismic data for solving the geological tasks. The surface of the acoustic basement and the reflecting boundaries in the sedi­ mentary stratum are traced on the majority of the sections confidently and continuously. All the reflectors are steadily traced accord­ ing to their classification adopted for the East Arctic seas. It should be emphasized that for the first time ever on August 10, 2014, integrated geophysical survey was carried out in the North Pole area, including CMP seismic sur­ vey (using a 600-meter streamer in combi­ nation with seismic reflection and seismic refraction sounding), seabed features survey and gravimeter survey. All these works were performed by the forces of exclusively Rus­ sian specialists on the basis of the innovative geophysical system developed by JSC MAGE MURMANSK MILE • 4-2018