Wednesday, 01 March 2017 20:37

Geophysical Tasks

High-resolution marine seismic in an offshore area

 

The high-resolution seismoacoustic survey has been carried out in the offshore area near the Sevastopol city using continuous seismic profiling technology. According this technology the seismic source and the receiver have been situated on the fixed distance from each other (1 m) and installed under special catamaran, which has been towed on some distance from the ship.

For geophysical survey, we have used the equipment, designed in Geological Faculty of Lomonosov Moscow State University. We used the sparker with many electrodes as a transducer. High Voltage Unit generated short 5 kV electrical impulse for sparker. When a high voltage energy applied to electrodes, it generates micro explosion and the high-pressure cavity radiates high frequency acoustic waves in water.

After each shot, the generated elastic wave is reflected from geological borders in sediment layers and is received by receiver, then it is registered by computer. The most distinguishable borders are the border between water and sediments, then between soft sediments (sand or clay) and hard rocks (bedrock).

   
Fig. 1. Geophysical equipment and moment of survey.

 

The position of observation points is presented on the fig. 2.

Fig. 2. The lines layout.

 

Line 1 has been made especially for marine seismic with low vessel speed. Line 2 has been made at full throttle of vessel. This fact increased noise level in registered data. The results are shown in fig. 3 and 4. Depth section presented by sands on the top (Qm), 15-30 m of alternated brecciform limestones (N1s, yellow lines), then follow volcanics J2b (green line). The character of reflections geometry can be used for sequence stratigraphy.

Fig. 3. Line 1. Depth section.

 

Unfortunately, the noise level in line 2 was too high for detail analysis of geological section. But the volcanics J2b border is presented in biggest part of section.

Fig. 4. Line 2. Depth Section.
Last modified on Wednesday, 01 March 2017 21:05