A model of the distribution of crustal magnetization in central Europe compatible with the field of magnetic anomalies deduced from Magsat results

Abstract

S U M M A R YMagsat data have been used to design scalar magnetic anomaly maps in an area that covers about half of Europe on both sides of the north-south directed European Geotraverse (EGT). The two maps refer to different altitudes and are intended to place recent compilations of aeromagnetic surveys along the EGT (Wonik er af. 1992) into global perspective.The presentation of the magnetic anomalies and their compatibility with the aeromagnetic data required (i) a suitable reference field for subtraction from the measured total field, which was derived from the field model M102089 by Cain, and (ii) a proper function of time reduction to the epoch 1980.0, which has been obtained from the actual satellite data. Because of the considerable noise in the data only those anomalies have been chosen for mapping, which show up in all Magsat tracks independent of altitude and epoch of measurement. The anomaly maps are based upon the less disturbed dawn track data, but a few dusk tracks have also been used as tie lines.The anomalies are interpreted in terms of a magnetization model, which divides the Earth's lithosphere in Europe into blocks of extension 1"N-S by 2"E-W and attributes to each block the 'Depth Integrated Magnetization' of the magnetized layer, i.e. the magnetization integrated over the vertical extension of the block. Each block is represented by a dipole parallel to the inducing core field, and the calculated model field is adjusted to the anomaly maps by trial and error, starting with an initial coarse distribution that seems plausible from the anomalies and from local geomagnetic surveys. For a realistic model field in the EGT area a rather large portion of the Earth's magnetized lithosphere outside the area under investigation must be included in the calculation.In order to check, whether the features of the magnetization model are necessary for the interpretation of the field anomalies, they are compared with the distribution of magnetization that is obtained by the application of linear inverse theory.Prominent features of the model of crustal magnetization are the contrast between high values over the East European Platform and low values in the younger parts of Europe, maxima at the iron ore districts of Kiruna and Kursk, a broad minimum centred at St Petersburg, and only small differences between the Mediterranean Sea and the adjacent continental areas. There is a fairly good agreement of these anomaly maps with the corresponding maps presented by Cain er af. (1989a).

Crustal geomagnetic field and secular variation by regional and global models for Austria

“…Very long-wavelength magnetic anomalies (>600 km) have been revealed by near-Earth satellite missions, e.g., MagSat. These magnetic anomalies are modeled by the ESI method (Taylor and Ravat, 1995;Nolte and Hahn, 1992). Dipole schemes can be used to fit the MagSat magnetic anomalies over the Austrian region.…”

Magnetic anomaly map for Northern, Western, and Eastern Europe*

“…(1984), De Santis et al . (1989), Wendorff (1990), Nolte and Hahn (1992), Arkani‐Hamed et al . (1994), and Taylor and Ravat (1995).…”

“…The amplitude of this anomaly is 10–20 nT in all of the above‐mentioned maps. As an example the map by Nolte and Hahn (1992) is presented in Fig. 3.…”

“…A number of magnetic anomaly maps for Europe produced from the MAG-SAT satellite data (c. 360±500 km altitude) were published by various investigators: Coles et al (1982), Cain et al (1984), De Santis et al (1989, Wendorff (1990), Nolte and Hahn (1992), Arkani-Hamed et al (1994), and Taylor and Ravat (1995). The maps differ slightly in the shape and amplitude of the main European anomaly caused by the different magnetic properties of the Palaeozoic and Precambrian crust.…”

“…These dierences between the amplitudes of anomalies at an altitude of c. 360 km derived from MAGSAT data and that from upward-continued low-level data in Europe also have an effect on the interpretation of MAG-SAT data. Nolte and Hahn (1992), Taylor and Ravat (1995), and Pucher and Wonik (1998) computed model bodies based solely on MAGSAT anomalies. Therefore, the computed lateral changes of magnetization or the thickness of magnetic layers are much smaller than they would if derived from model calculations based on low-level data.…”