Superconducting gravimeters in seismology

in Newsletter of the European-Mediterranean Seismological Centre (2004), 21

Indication of the uplift of the Ardenne in long-term gravity variations in Membach (Belgium)

in Geophysical Journal International (2004), 158(1), 346-352

We report on the results of 7 yr of collocated gravity observations made with an FG5 abso- lute (AG) gravimeter and a GWR C-Series superconducting gravimeter (SG) located at the Membach Geophysical ... [more ▼]

We report on the results of 7 yr of collocated gravity observations made with an FG5 abso- lute (AG) gravimeter and a GWR C-Series superconducting gravimeter (SG) located at the Membach Geophysical Station in eastern Belgium. The SG gravity residuals track changes in gravity periodically observed by the AG, at the microgal level. Further, in the SG resid- ual signal we distinguish a quasi-seasonal term that can be mostly explained by variations in local water storage effects. In the AG time-series we observe a small trend in the gravity of −0.6 ± 0.1 μGal yr−1 perhaps indicating that the Membach Station is being displaced up- wards by about 3.0 mm yr−1. An uplift of the region is confirmed by Global Positioning System (GPS) measurements performed 3 km away. We are able to explain the features in the gravity time-series in terms of water storage variability, post-glacial rebound and tectonic activity. [less ▲]

RESEAU DE GRAVIMETRIE ABSOLUE ALGERIEN

in Bulletin des Sciences Géographiques (2003), 09(Avril), 3-9

Sixth International Comparison of Absolute Gravimeters, ICAG-2001

in Francis, Olivier; van Dam, Tonie (Eds.) Proceedings of the Workshop: IMG-2002 Instrumentation and Metrology in Gravimetry (2003)

Genèse et Futur d'un laboratoire de Gravimétrie à Walferdange (Luxembourg)

in Helmut Moritz's Fetschrift zum 70. Geburtstag (2003)

Analysis of the Results of the Sixth International Comparison of Absolute Gravimeters ICAG-2001

in Tziavos, Ilias N. (Ed.) Gravity and Geoid 2002 (2003)

Processing of the Absolute data of the ICAG01

in Francis, Olivier; van Dam, Tonie (Eds.) Proceedings of the Workshop: IMG-2002 Instrumentation and Metrology in Gravimetry (2003)

Results of the Sixth International Comparison of Absolute Gravimeters, ICAG-2001

in Metrologia (2002), 39(5), 407-427

The Sixth International Comparison of Absolute Gravimeters was held from 5 June to 28 August 2001 at the Bureau International des Poids et Mesures (BIPM), Sevres. Seventeen absolute gravimeters were used ... [more ▼]

The Sixth International Comparison of Absolute Gravimeters was held from 5 June to 28 August 2001 at the Bureau International des Poids et Mesures (BIPM), Sevres. Seventeen absolute gravimeters were used to make measurements at five sites of the BIPM gravity network. The vertical gravity gradients at the sites and the ties between them were also measured using seventeen relative gravimeters. For the first time the ties were also measured using absolute gravimeters. Various methods of processing the absolute and relative data were tested to calculate the results. The final results of ICAG-2001 are presented. The acceleration due to gravity at a height of 0.90 m is given as (980925701.2 ± 5.5) Gal and (980928018.8 ± 5.5) Gal for sites A and B, respectively, calculated using a combined adjustment of the absolute and relative data. [less ▲]

Experiment to evaluate crustal motions across the Ardenne and the Roer Graben (north-western Europe) using absolute gravity measurements

in Metrologia (2002), 39(5), 503-508

Absolute gravity measurements using the FG5-202 gravimeter have been conducted twice a year since September 1999 along a 120 km long profile across the Belgian Ardenne and the Roer Graben. As in this ... [more ▼]

Absolute gravity measurements using the FG5-202 gravimeter have been conducted twice a year since September 1999 along a 120 km long profile across the Belgian Ardenne and the Roer Graben. As in this region there is a difference of an order of magnitude between the inferred vertical crustal movements deduced from the difference of levelling (about 1 mm/year) and geological information (0.1 mm/year), our goal is to better constrain the present-day deformation. The absolute gravity measurements are performed at Rochefort, Humain, Werpin, Manhay, Sprimont, Membach (Belgium) and Monschau, Julich and Bensberg (Germany). A complete description of the network is given, and specific difficulties at some stations are presented. The precision achieved, generally less than 2.0 Gal integrated over more than 24 h of observation, is quite satisfactory at all stations but Julich. The mining activities around Julich cause an increase in the noise up to 7 Gal integrated over more than 72 h. We also discuss possible causes of gravity variations in this region. At present, it is still not possible to detect any trend in the available data. However, after five years of observations, we should be able to detect or constrain any possible long-term trend with a limit of 2.5 mm/year, assuming that a height change of 1 mm causes a change in gravity of 0.2 Gal. To ensure that the absolute gravimeter is giving accurate results, it has been regularly compared with the superconducting gravimeter installed at the Membach reference station. [less ▲]

Absolute gravity measurements in Belgium: a tool for geodynamic interpretation

in Degryse, Patrick; Sintubin, Manuel (Eds.) Contributions to the Geology of Belgium and Northwest Europe (2002)