Seismic evidence for a low-viscosity lower crust beneath the continental deep drilling location, Oberpfalz, Germany

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Abstract

A network of six deep seismic reflection profiles was recorded in the Oberpfalz as part of the pre-site investigations for the German deep drilling programme. In addition, this network is crossed by a longer regional profile. A striking observation is the highly variable reflectivity of the lower crystalline crust. Based on the relationship between (temperature-dependent) viscosity and crustal reflectivity it seems possible to relate the changes encountered here to the tectono-thermal regime. We propose that processes forming the Eger Graben also thermally influence the crust beneath the Oberpfalz. These mechanisms should have a considerable impact on the maximum depth of the deep borehole. The results of the pilot hole give strong support to our interpretation: the temperatures are higher than the maximum estimates from near-surface heat flow determinations and the maximum depth for the borehole has been reduced from 14 to 10 km.

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    1

    Present address: Forschungsanstalt der Bw. für Wasserschall- und Geophysik, Klausdorfer Weg 2-24, 2300 Kiel 14, Germany.

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