HR: 1340h
AN: G43B-1196    [Abstracts]
TI: Intraplate Vertical Land Movements Constrained by Absolute Gravity Measurements
AU: * Van Camp, M
EM: mvc@oma.be
AF: Royal Observatory of Belgium, Avenue Circulaire, 3, Bruxelles, Be-1180, Belgium
AU: Williams, S D
EM: sdwil@pol.ac.uk
AF: Proudman Oceanographic Laboratory, Joseph Proudman Building 6 Brownlow Street, Liverpool, L3 5DA, United Kingdom
AU: Hinzen, K G
EM: hinzen@uni-koeln.de
AF: Cologne University Earthquake Geology Division, Vinzenz-Pallotti-Strasse 26, Bergisch Gladbach, DE-51429, Germany
AU: Camelbeeck, T
EM: thierry.camelbeeck@oma.be
AF: Royal Observatory of Belgium, Avenue Circulaire, 3, Bruxelles, Be-1180, Belgium
AB: We have conducted repeated absolute gravity (AG) measurements across the tectonically active intraplate regions in Northwest Europe: the Ardenne and the Roer Graben. At most of the stations measurements were undertaken since 2000 and repeated twice a year. Our analysis of these measurements, performed in Belgium and Germany, show that at all stations except Jülich, there is no detectable gravity variation higher than 10 nm s^-2 at the 95% confidence level. This is equivalent to vertical movements of 5 mm/yr. Although not yet significant, the observed rates do not contradict the subsidence predicted by glacial isostatic adjustment models and provide an upper limit on the possible uplift of the Ardennes. In Jülich, a gravity rate of change of 36.7 nm s^-2/year equivalent to 18.4 mm/yr is due to anthropogenic subsidence. The amplitudes of the seasonal variations range from 18±0.8 nms^-2 to 43±29 nms^-2, depending on the location. These variations should have a negligible effect on the long-term trend, but at the Membach reference station, were a longer time series is available, differences in the rates observed since 1996 and 1999 indicate that long-term environmental effects may influence the inferred trend. The observed seasonal effects also demonstrate the repeatability of AG measurements. In Ostend, the AG time series agrees with tide gauge data, global mean sea level and altimeter measurements but disagrees with the CGPS. This study indicates that, even in difficult conditions, AG measurements repeated once a year can resolve vertical land movements at a few mm level after 5 years. This also confirms the need to measure for decades, using accurate and stable geodetic techniques like AG, in order to constrain slow deformation processes in an intraplate context.
DE: 1200 GEODESY AND GRAVITY
DE: 1209 Tectonic deformation (6924)
DE: 1217 Time variable gravity (7223, 7230)
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 1244 Standards and absolute measurements
SC: Geodesy [G]
MN: 2007 Fall Meeting