Mathematics – Logic
Scientific paper
Mar 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997e%26psl.147..107k&link_type=abstract
Earth and Planetary Science Letters, Volume 147, Issue 1-4, p. 107-123.
Mathematics
Logic
13
Scientific paper
Large-scale coal mining in Germany causes deloading of the crust by the removal of weight. The crust responds by regional uplift while locally, in the mining areas proper, the surface subsides by sagging above extracted coal seams and removed groundwater. In this study only the regional uplift is addressed. The deloading consists of the total annual mass of coal and ground water removal since the 19th century for all significant mines. The uplift data are from repeated levellings (between about 1950 and 1980), reduced to mean annual rates of elevation change. These observations are interpreted as the visco-elastic response of the crust and uppermost mantle but alone they cannot discriminate layering from a homogeneous viscous half-space or an elastic layer above such a half-space. If the seismically determined layered structure of upper and lower crust, lithosphere mantle and asthenosphere is assumed to constrain the rheological structure, a plausible model can be found by inversion (only the lower crustal and asthenospheric effective Maxwell viscosities are subjected to inversion). A model, consistent with the observations, has the following properties: 15 km of elastic upper crust; 15-20 km thick lower crust of surprisingly low viscosity of 6 . 1017 +/- 0.3 Pas; 30-50 km visco-elastic mantle lithosphere with an assumed average viscosity of about 1022 Pas; a visco-elastic asthenosphere (assumed bottomless) with 5 . 1019 +/- 0.6 Pas. The low viscosity values are consistent with active rifting and above-average heat flow in the region. The very low effective viscosity of the lower crust in this model (it could be even lower if the thickness is smaller) may be explained by elevated stresses, quartz rheology and water content as suggested by xenoliths from the lower crust below the Eifel region. As a by-product, the tectonic subsidence in the Lower Rhine Embayment (filled with Tertiary and Quaternary sediments) can be better defined by taking the anthropogenic effect into account.
Jacoby Wolfgang
Klein Annette
Smilde Peter
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