If seismic surveys were conducted in 1987, 1992 & 2015, why do they need repeating?

The survey we will be completing will be a 3D assessment of the seabed and underlying geology. The 1987 and 1992 surveys were sparse 2D surveys that cannot provide the detailed and accurate 3D image required. The 2015 Dong Energy survey focused on the shallow geology for the placement of wind turbines, whereas the Crogga survey will appraise the geology over two kilometres below the seabed. This will provide the most detailed picture the Island has of the seabed to date.