Acquisition of seismic data

August 22 – Seismic data is used for many prospects like e.g. gas and oil exploration and to recognize appropriate localities for establishing offshore wind farms, in research, et cetera. To assemble marine seismic data, an airgun, the seismic energy source, is used. Compressed air is released in seismic pulses and converted into soundwaves that propagates spherically through the water column and down into the subsurface. Some of the energy in the seismic soundwaves will be reflected at layer boundaries, and returned to the surface. With hydrophones, located in a receiver cable (aka. a streamer), dragged after the ship, the reflected seismic energy can be converted into a 2D or 3D image of the underground.

By participating in studies like the East Greenland narwhal project, gives us an unique opportunity to identify the impact of seismic surveys on narwhals. Hopefully this will lead to future seismic data is collected in a responsible way, to protect marine wildlife.

This is also a rare opportunity to collect seismic data in an area with previous sparse seismic surveys. The hydrophones in the streamer cable are really sensitive, and in areas like Scoresby Sound, the quality of the data is affected by noise from ice floes. Nevertheless, one of the seismic lines, collected during the expedition, is illustrated below with a limited and quick interpretation. The water column is ranging between 300 and 1200 meters. The seafloor is dominated by topography in the basement, with two sedimentary basins, deposited material from melting glaciers.

Seismic profile from Gåsefjord.
Collision between streamer and ice leads to noise affected data.
Airgun

Written by:
Andreas Skifter Madsen, Master student, Geosciences
Lars Mejlgaard Rasmussen, Technician
Per Lynnerup Trinhammer, Seismic engineer
Department of Geoscience at University of Aarhus