1. A method of analysing seismic data from a geological volume divided into a plurality of voxels, for each voxel a respective neighbourhood being defined that includes that voxel and a predetermined arrangement of neighbouring voxels, the method including the steps of: calculating, for each voxel, the respective normal vectors of a seismic attribute vector field derived from the seismic data; calculating, for each voxel, a respective local structure tensor based on the normal vectors of the voxels of the respective neighbourhood; and calculating, for each voxel, the value of an expression that includes one or more of the eigenvalues (λ 1 , λ 2 , λ 3 ) of the respective local structure tensor.