Power law distribution of susceptibility and density and its relation to seismic properties: An example from the German Continental Deep Drilling Program (KTB)

We examine the nature of continental crust from the power law scaling behaviour of magnetic susceptibility and density variations. We analyze the data from the main hole of the German Continental Deep Drilling Program (KTB) using the Fast Fourier Transform (FFT) and the multitaper method. On the basis of depth-dependent behaviour of the calculated scaling exponents the KTB well can be divided into four zones of depth 0–0.8 km, 0.8–3.5 km, 3.5–7.7 km and 7.7–9.1 km which are also lithologically distinguishable. The scaling exponents for the susceptibility data correlate by 22–32% and 16–25% with the conversion log and the fracture density. In the case of density a correlation between the scaling exponent values and conversion log and the fracture density are found to be 19–45% and 44–66%, respectively. The multitaper method provides more reliable values of scaling exponents and calculated values are having higher correlation with the conversion log and fracture density than the FFT. The defined zones 3 and 4 are having lower values of scaling exponents and higher values of fractal dimension than the shallower sections. This observation indicates an increase of crustal heterogeneity in terms of fault or fracture density.

Research highlights
► Scaling exponents of magnetic susceptibilities and densities from KTB vary with depth.
► Scaling exponents (fractal dimensions) image different lithological units.
► Scaling exponents correlate with seismic conversion log and fracture density.
► Crustal heterogeneity in terms of faults and fracture densities increases with depth.
► The multitaper method provides better results than the Fast Fourier Transform.