Christoph J. Keysers

Dr. rer. nat., Diplom-Physiker

Christoph J. Keysers, H.-J. Kümpel

Two local precise gravity networks in the Lower Rhine Embayment, Germany

 Cahiers du Centre Europeen de Geodynamique et de Seismologie, Vol. 17, Luxembourg, pp. 207-216.

A project is presented in which a combined analysis of height and gravity changes aims at a better understanding of tectonic processes and fluid movements in the Lower Rhine Embayment, Germany. GPS height data since 1993 reveal significant height changes of up to 2.4 cm/year on various sites here. Gravity observations with LaCoste & Romberg gravimeters so far suffered from problems like instrumental drift and calibration, so that the accuracy required to verify possible contributions from mass displacements, e.g. in the hydrologic regime, could not be reached in the past. A new strategy includes the restriction to local networks and a permanent control of the calibration factors. As a first result, the linear feedback factor has been found to increase with a rate of about 2 10^(-3)/year. Early field results indicate fluctuating gravity changes of opposite signs on either side of a steeply dipping tectonic fault in the Lower Rhine Embayment which also acts as a hydraulic barrier. Whether this is due to any hydrogeological cause will be further investigated.