Scaling behaviour of vertical magnetic susceptibility and its fractal characterization: an example from the German continental deep drilling project (KTB)

The variations of rock magnetism reflect the geological inhomogeneities of the earth's crust, i.e. its petrological-mineralogical and structural organization. The present state of the crust bears meaningful information of its past dynamic processes and evolution. We analysed magnetic susceptibility data series from the boreholes of the German Continental Deep Drilling Project (KTB). By means of spectral and rescaled-range (R/S) analyses we could detect a scaling behaviour of magnetic data series and quantify it in fractal terms. In particular, the R/S method yields more precise results than the Fourier analysis and leads to Hurst coefficients H > 0.5, which means that the magnetic variations exhibit some persistence with depth. Because of the relation between rock magnetism and crustal features, we suggest that the magnetic vertical inhomogeneities in the KTB area can be described by a self-affine model with H 0.8, corresponding to a fractal dimension D 1.2.