Мурманская МИЛЯ. 2018 г. №4.

EXPLORATIONS 64 below water surface in order to avoid contact with ice. IPD is mounted at the stern and al­ lows fixing the air guns circuit and a streamer along the device. Thus it is used as a de­ vice protecting towed equipment from the ice floating on the water surface. The IPD installed on board the vessel is designed as a streamlined column with an in­ ternal niche for running and fixing of tow and clamp cables as well as for seismic equip­ ment. The niche is formed by side walls of the column and a base in the form of hori­ zontal platform mounted to the ship bottom with horizontal rails. The internal zone is di­ vided longwise for placing tow and air guns clamp cables and the streamer as well as for fixing of reserve tow and/or clamp ca­ bles, which are not in service. The upper part of the device is situated beyond the draught line. The side walls of the column form a ver­ tical niche and go upwards of the fixture point of the IPD to the ship bottom forming cowls. The vertical niche is divided longwise by the internal zone intended for installation and fix­ ing of tow and clamp cables as well as for seismic cables. Internal zone is divided into three long ductings each of which is intended for arrangement of tow and clamp cables for air guns and seismic equipment as well as for tow and clamp cables out of operation. Three rollers are designed for running the streamer and the guns arrays. According to the field trial results there have been determined the best possible parameters of recording in ice bound conditions. The dimensions of the device are as fol­ lows: height - 17.5 m, bottom width - 6.5 m. Total weight: 10 tons. In 2015 the ice protec­ tion device has been patented. The exploration works were performed in July - October 2014. Reasearch vessels AKADEMIK FEDOROV and NIKOLAY TRU- BYATCHINSKY took part in the expedition assisted by the nuclear icebreaker YAMAL [7]. The RV AKADEMIK FEDOROV was reequipped on purpose for sub-ice seismic survey performance. CMP reflection seismic survey was performed in two forms, namely: using a 4,500 m long receiver and using a 600 m solid streamer along with reflec­ tion and refraction sounding. 24-bit Sercel SEAL seismic streamer was used for seis­ mic response recording. The channel num­ ber varied from 48 to 360 depending on the streamer length. Each array contained 16 hy­ drophone receivers GEOPOINT EXPORT. The source point interval was 50 m. The sampling rate was 2 ms and the record length was 12 seconds. The accuracy of horizontal and vertical correlation of shot points was ± 10 m the least, 1% of depth. The towing depth of the receiving device varied depending on the ice conditions within 10 - 15 m, to 20 m sometimes. Airguns Bolt 1500 and Bolt 1900/Bolt 8500APG of 1300 cu. inches were used as sources. In order to determine velocity properties of main boundaries in the sedimentary cover and to create a velocity model integrated with CMP reflection survey, reflection and re­ fraction seismic survey was performed. The exploration was performed using radiote­ lemetry acquisition system BOX along with a floating unit of the telemetric seismic system BOX supplied with MP-24L3 (GeoSpace) hy­ drophone. The sampling rate was 4 ms, the sounding space was 50 km maximum. The length of recording hydrometer was equal to 15 - 25 km with the record time of 8 -1 2 seconds [6]. Besides this the DSS line was shot. The sounding was performed using the upgrad­ ed equipment system consisting of self­ floating autonomous bottom systems with multicomponent digital recording of seis­ mic response (ADGS-2М, ADSS-5000), low frequency air gun SIN-6 and on-board con­ trol devices [7]. The shot at the lines was performed on a regular basis every 150 seconds. The sampling rate - 8 ms, seis­ mic record length - 60 s. On the DSS wave fields at first kicks the refracted waves are detected, associated with the boundaries in the sedimentary cover and inside the crust. There was recorded a refracted wave from the M limit (PmP) which can be traced from 4 0 -6 0 km distance along almost the whole line. Sufficiently consistent tracking interval is 6 0 -8 0 km and sometimes reaches 100­ 110 km. For the regional study of bottom relief along the lines multibeam echo sounder EM122 (1 x 2 degrees) Kongsberg Maritime AS, Norway and backup single beam echo sounder EA 600 12 kHz produced by the same company were used[1, 12]. In order to acquire additional data on the upper part of section and on the bottom re­ lief TOPAS PS 18 profiler was used. Gravity survey was performed using two gravity meters simultaneously: portable gravity meter Chekan-AM and portable gravimeter sys­ tem Shelf-E. All required preliminary works were performed. Both gravimeters were calibrated. In Naantali (Finland) key gravity observations were performed before and after the voyage. MURMANSK MILE • 4-2018