M. Amalvict a,b,, J. Hinderer a,s.rózsa c. 1. Introduction and tectonic settings

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1 Journal of Geodynamics 41 (2006) Crustal vertical motion along a profile crossing the Rhine graben from the Vosges to the Black Forest Mountains: Results from absolute gravity, GPS and levelling observations M. Amalvict a,b,, J. Hinderer a,s.rózsa c a EOST-IPGS (UMR 7516 CNRS-ULP), 5 rue René Descartes, Strasbourg, France b National Institute of Polar Research, Kaga, Itabashi-ku, Tokyo, Japan c Department of Geodesy and Surveying, P.O. Box 91, 1521 Budapest, Hungary Accepted 30 August 2005 Abstract The Rhine plain is oriented north south and limited by the Vosges Mountains (France) to the West and the Black Forest Mountains (Germany) to the East. The present-day tectonic evolution of this system is not well known and many questions are still pending: is the graben subsiding? Are the mountains uplifting? What is the relative behaviour of the three different geological components? In attempting to answer these questions, we compare for the first time in this region time series of absolute gravity (AG) measurements to the available GPS observations at three sites along a profile crossing the Rhine graben. Our reference station is the gravimetric observatory near Strasbourg (J9), located in the Rhine plain where AG measurements are performed regularly since 1997 and where superconducting gravimeter (SG) observations are available almost continuously for 17 years. The secondary sites are the Welschbruch station in the Vosges Mountains where six AG measurements have been conducted since 1997 and the Black Forest Observatory (BFO) where three AG measurements are available. GPS permanent receivers are collocated at the Strasbourg-J9 site since 1999, at the Welschbruch station since 2000, and at BFO since Levelling data are only available in the BFO region. We compare the long term content of two types of geodetic measurements with special emphasis on the trend despite the limited duration of our data sets. Assuming that the gravity changes are linear in time, we obtain ġ = 1.9 ± 0.2 Gal/yr at Strasbourg-J9, ġ = 0.96 ± 0.2 Gal/yr at Welschbruch site and ġ = 2.5 ± 0.5 Gal/yr at BFO. The trends according to GPS observations are, respectively: 1.51 ± 0.07 and 0.74 ± 0.10 mm/yr at Strasbourg-J9 and Welschbruch site, respectively; there is no GPS result available at BFO. The AG results for BFO are very questionable, as well as the GPS observations at the Welschbruch station. Nonetheless, Strasbourg-J9 and Welschbruch AG measurements lead to subsidence and uplift, respectively, which are expected results in agreement with GPS at Strasbourg-J Elsevier Ltd. All rights reserved. Keywords: Absolute gravity; Gravity variations; Vertical displacement; GPS; Levelling; Rhine graben 1. Introduction and tectonic settings The ultimate goal of this study is the determination of the absolute vertical displacement of the three components of the Rhine graben system (France and Germany) and their relative behaviour. The comparison of observations of (i) Corresponding author. Fax: addresses: mamalvict@eost.u-strasbg.fr, martine.amalvict@eost.u-strasbg.fr (M. Amalvict) /$ see front matter 2005 Elsevier Ltd. All rights reserved. doi: /j.jog

2 M. Amalvict et al. / Journal of Geodynamics 41 (2006) Fig. 1. The Rhine graben with the location of the three stations under study. geometric data (GPS or levelling observations) and (ii) measurements of absolute gravity (AG) helps to separate the two effects, which may be involved: vertical displacement and mass variations. Different types of vertical movements have been analysed so far according to this methodology. Evidence has been given of post-glacial rebound (PGR) which is observed for many years, especially in the northern hemisphere: Canada (Lambert et al., 2001; Larson and van Dam, 2000), Greenland (Wahr et al., 2001), Spitzbergen (Sato et al., 2004), but also of rapid vertical displacement due to ice thawing (Larsen et al., 2004). Thanks to increasingly accurate and precise instruments, the survey of the vertical displacement of the crust in regions of low-level tectonic activity becomes possible. Low-level vertical displacements of lower amplitude have been monitored in Italy and Germany (Richter et al., 2004), Iran (Hinderer et al., 2003), and in the Ardennes (Camelbeeck et al., 2002; Francis et al., 2004a). The main features of the so-called Rhine graben system (Fig. 1) are presented in Amalvict et al. (2004). They can be summarised as: (i) the graben itself with the Rhine river flowing from south to north (150 km long), (ii) the Vosges Mountains in France on the west side and (iii) the Black Forest in Germany on the east side. The total width of the graben is not more than 150 km. The geodynamic context presents the Upper Rhine Graben as part of the complex Cenozoic rift system of Western and Central Europe that extends from the shores of the North Sea over a distance of some 1100 km into the western Mediterranean. It corresponds to a zone of elevated seismic activity and hazard, as evidenced by historical earthquakes, such as the 1356 event that destroyed the city of Basel located in the southern part of Rhine graben. The present-day tectonic evolution of this region is a challenging question on which authors do not agree. Is the graben subsiding and are the mountains uplifting? This question is still controversial and there are extremely few geodetic papers on the subject (Malzer and Schlemmer, 1975; Villemin et al., 1986). Research institutes from France, Switzerland, Germany and Holland have agreed to initiate in January 1999 a 5-year joint multi-disciplinary research project that aims to provide a better understanding of the seismic hazard, neotectonics and evolution of the Upper Rhine Graben. This project, called EUCOR-URGENT (Upper Rhine Graben evolution and tectonics), integrates all kinds of information provided by geological, magmatic, geophysical, geomorphologic, geodetic and seismological data. In particular, recent crustal movements, which are to a large extent unknown, will be tracked by geodetic and geomorphologic data. A network of about 25 GPS stations has been installed recently in the Upper Rhine Graben in order to determine present-day displacement rates. In addition, it is also planned to determine any subsidence/uplift in this tectonically active region from repeated precision levelling (see, e.g. Lenôtre et al., 1999; Demoulin and Collignon, 2000 in another tectonic settings). This integrated GPS system is in operation and to our knowledge, no final conclusion could yet be inferred which is not surprising in view of the small observational period available and the small vertical rates which are expected. Nevertheless one can find interesting conclusions on the Freiburg region in Rózsa et al. (in press) (especially on vertical displacements).

3 360 M. Amalvict et al. / Journal of Geodynamics 41 (2006) Data 2.1. Global positioning system (GPS) The GPS observations are conducted with permanent receivers installed according to strict standards concerning the pillars, the antenna, and the quality of the site. Moreover, differential mobile receivers are used during temporary campaigns. The time series of positioning data is a direct monitoring of the station coordinates and of their changes (if any). In this study, we focus on the vertical component of motion (if any). Three GPS permanent stations are installed in our region of interest in: one at the Strasbourg-J9 station belongs to the RGP (French GPS National Network), Strasbourg-J9 and the Welschbruch station in the Vosges Mountains belongs to REGAL (GPS network in the French Alps) and RENAG. The permanent GPS receiver at the BFO station is operated by BFO and Karlsruhe University. The map, in Fig. 2, shows the GPS networks during the 1999, 2000 and 2002 campaigns operated by Swisstopo, RGP, RENAG and SAPOS Levelling Levelling campaigns started over a century ago and their repetition enables us to directly quantify the geometrical vertical displacements (if any). This technique was used to monitor vertical displacements before the development of GPS and other satellite positioning techniques. It is still of interest because of the duration of the time series and because it provides more accurate results than GPS in some cases (large separation of GPS receivers; time series are too short). Lenôtre et al. (1999) presented some case studies and analysed more specifically the region of Brittany (north-western part of France) showing a generalized uplift of the region during the first half of the 20th century. In the German side of the graben repeated levelling observations have been analysed with various approaches. Network-based analyses Fig. 2. GPS networks and campaigns (after Rózsa et al. (in press)).

4 M. Amalvict et al. / Journal of Geodynamics 41 (2006) Fig. 3. Vertical displacements from first and second order levellings in the Freiburg area (mm/yr) (after Rózsa et al. (in press)). have been carried out by Zippelt (1988), while Schweizer (1992) has analysed individual levelling lines in the Southern Rhine Graben. The detected vertical displacements can be seen (Fig. 3) Absolute gravimetry (AG) The absolute gravimeters involved in this study are FG5 instruments. The principle of the measurement is the monitoring of the drop of a reflective object free-falling in a vacuum chamber. Accuracy of the instrument is 2 Gal (1 Gal=10 8 ms 2 ) with a precision of 1 Gal that is confirmed by regular international intercomparisons of AGs (Francis et al., 2004b). The repetition of AG measurements at a given station allows monitoring the changes (if any) in gravity. These changes can be due either to a geometrical vertical displacement (uplift or subsidence) of the station, to a variation of the involved masses (above or below the station), or to a combination of the two phenomena. 3. GPS transverse line J9-Welschbruch As stated previously, there is a permanent receiver at the BFO station since 2002, but the observations have not been processed yet. Only GPS campaigns and levelling campaigns are available in this region. Let us examine the Welschbruch and Strasbourg-J9 GPS observations. Data are routinely processed by the RENAG team with a daily sampling ( Welschbruch (name code: WELS), see Fig. 4a A permanent GPS receiver is installed 100 m apart from the magnetic vault since November It belongs to the REGAL network (permanent network of GPS receivers in the Alps Mountains). In this work we use the solutions available on the REGAL website.

5 362 M. Amalvict et al. / Journal of Geodynamics 41 (2006) Fig. 4. Vertical position changes from permanent GPS stations WELS and STJ9 ( (a) Welschbruch station (WELS); (b) Strasbourg station (STJ9); (c) Strasbourg vs. Welschbruch.

6 M. Amalvict et al. / Journal of Geodynamics 41 (2006) From day 275 of 2000 (starting of observations) to mid-2005 (time of last Welschbruch AG measurement) the trend of the vertical displacement is 0.74 ± 0.10 mm/yr, which corresponds to a subsidence of the station. Let us note that from day 275 of 2000 (start of GPS observations) to day 60 of 2004 (time of the last AG measurement at Strasbourg-J9), the trend of the vertical displacement is ± 0.14 mm/yr, corresponding to an uplift of the station. This shows that for this station there is a real challenge to retrieve the small sub-millimetric trend with a limited time span Strasbourg-J9 (name code: STJ9), see Fig. 4b An Astech permanent GPS receiver is installed directly on the top of the gravity bunker since November It also belongs to the REGAL network and we use the solutions available on the REGAL website. From day 275 of 1999 (start of GPS observations) to day 60 of 2004 (time of the last AG measurement at Strasbourg- J9), the trend of the vertical displacement is 1.51 ± 0.07 mm/yr; from day 275 of 1999 (start of GPS observations) to day 130 of 2005 (time of the last AG measurement at the Welschbruch station), the trend of the vertical displacement is 0.97 ± 0.05 mm/yr. In both cases, the station subsides but this shows the high sensitivity of the trend to the period of observation STJ9 to WELS, see Fig. 4c According to the same REGAL processing, the trend of the difference in vertical displacement between the two stations is ± 0.04 mm/yr from fall 2000 to mid-2004, it is ± 0.02 mm/yr from fall 2000 to mid The vertical distance between the two stations is increasing. 4. Levelling 4.1. Alsace, France There are two levelling campaigns available in Alsace: Lallement levelling in the first part of 20th century, and the IGN levelling in the second half of 20th century (Polaud, 1999). But unfortunately, no publication (to our knowledge), analyses and compares the two campaigns in this region Germany In the German side of the graben, altogether three levelling surveys have been done in the 20th century. In Rózsa et al. (in press), first and second order levelling lines have been analysed, which cross some well-known faults in the Freiburg area. The results of this study showed that the vertical displacement along the Main Border Fault averages 0.25 ± 0.02 mm/yr over 55 years. This value has been computed from the analysis of three levelling campaigns in 1925, 1959 and One should note that the vertical displacement varies strongly between the first two and the second two campaigns. From 1925 to 1959, the vertical displacement is 0.15 ± 0.03 mm/yr while between 1959 and 1982 the value is 0.45 ± 0.05 mm/yr. 5. Absolute gravity measurements AG measurements involve three stations: the Strasbourg-J9 station of the Gravimetry Observatory which is the reference station located in the Rhine graben between the two secondary stations located in the surrounding mountainous massifs: Black Forest Observatory in the Black Forest and the Welschbruch station in the Vosges Mountains. The IPGS/EOST FG5#206 meter performed all the measurements but two; the others (one at BFO and one at the Strasbourg station) were performed by FG5#301 from BKG, Federal Agency for Cartography and Geodesy, Frankfurt am Main (Germany). As for the Strasbourg measurement that took place in February 2004, the two instruments were running in parallel and the final values were within 1 Gal. In order to compare the different values of gravity at a given station and given time with value at another station or at another time, it is necessary to reduce the raw data recorded at the time of observation. The applied reductions are: the solid earth tide correction, the oceanic

7 364 M. Amalvict et al. / Journal of Geodynamics 41 (2006) tide loading, the atmospheric pressure effect, the vertical gradient of gravity, the motion of the rotation axis of the Earth BFO The BFO is in operation since 1972, Karlsruhe and Stuttgart Universities jointly operate it. It houses a large range of instruments: gravimeter (Lacoste&Romberg), seismometers (STS0, STS1, STS2), tilt meter and strain meter. It is located in a mine which is known for long to be a quiet site, and which is excavated in the granitic basement covered by sediments. The Strasbourg Gravimetry Observatory team operated the two first AG measurements using FG5#206 instrument: from 14 to 20 March 2001, which lasted 7 days, and from 25 to 27 November 2003 that lasted 3 days. The Bundesamt für Kartographie und Geodäsie (BKG) team operated the FG5#301 on 2 April The meters were set-up in the so-called Heinrich Kluft (outside the pressure gate) in a 2 m tall, heated ( 18 C) styrofoam box. The coordinates of the station are: N, E, its elevation is 589 m. The corrections applied to raw data are the same for the three periods of measurements. The earth tide and oceanic loading corrections are applied according to standard models. The vertical gravity gradient has been measured twice using a Scintrex relative gravimeter; its value is: 2.01 ± 0.01 Gal/cm. The data have been processed by the Strasbourg team according to the same procedure; the results have been confronted to those of BKG. The three (g g r ) values, where g r is a reference value g r = 980,771,000 Gal, are respectively 448.9, and Gal and the respective set standard deviations are: 1.2, 1.2 and 1.4 Gal. A linear adjustment of the data, weightened by the error bars (set standard deviation) leads to a 2.6 ± 0.4 Gal/yr increase in gravity (Fig. 5a). A comment on the intercomparison of the two FG5#206 and #301 is given in the Strasbourg-J9 section. The value of gravity has apparently increased between 2001 and ; nevertheless, we can hardly refer to this in terms of trend since the number of measurements is obviously insufficient. An increase of gravity would correspond to a subsidence of the station (in the hypothesis where there is no associated mass variation) Welschbruch The Welschbruch station is operated by EOST/IPGS, and permanently houses geomagnetic instruments and seismometers. The AG measurements took place in the so-called magnetic vault, which is installed on the bedrock of the sandstone part of Vosges Mountains. All measurements have been operated by FG5#206. There are five series of measurements: March and June 1997; 30 September 7 October 1998; March 2001 and November In addition, a second station has been established in March 2001 on a pillar built in a shelter 20 m apart from the magnetic vault, and reoccupied on May The two sites have been linked several times using a Scintrex relative gravimeter. In this paper, we use the difference of absolute values (20.66 Gal) measured in 2003 to transport the 2001 and 2005 values to the magnetic vault. The coordinates of the station are: N, E, its elevation is 765 m. The seven (g g r ) values are plotted in Fig. 5b, the reference value is g r = 980,771,000 Gal. The 2003 value is quite smaller than the other ones, but it is, for sure, not due to an instrumental reason. At that time, indeed, FG5#206 has been participated to the international intercomparison at Walferdange (Luxemburg) and was in good agreement with other instruments (Francis et al., 2004b). The earth tide and oceanic loading corrections are applied according to standard models. The vertical gravity gradient has been measured using a Scintrex relative gravimeter; its value is: 2.74 ± 0.02 Gal/cm. The number of measurements is larger than at BFO but is still sparse with seven measurements in 8 years. A linear fit of values of gravity weighted by the error bars (set standard deviation) has been applied, which leads to a 0.96 ± 0.2 Gal/yr trend. Let us note that the adjustment gives the same value for the fit with the five measurements at the magnetic vault and the fit with the seven measurements including the transported value. This negative trend would correspond to an uplift of the station (in the hypothesis where there is no associated mass variation). The seasonal variations (if any) cannot be observed due to the small number of measurements Strasbourg-J9 The Strasbourg-J9 station is housed in a bunker at about 15 km from Strasbourg, in the Alsace Plain. It is located at the top of small hill of sediments. The bunker has been built at the end of the 19th century and became a gravity

8 M. Amalvict et al. / Journal of Geodynamics 41 (2006) Fig. 5. AG measurements at secondary stations (IPGS/EOST operated all measurements except the 2004 measurement at BFO (operated by BKG)): BFO station, g r = 980,771,000 Gal: Welschbruch station, g r = 980,768,000 Gal. station in the mid-20th century. The coordinates of the station are: N, E, its elevation is 180 m. A GWR superconducting relative gravimeter is continuously recording gravity variations at this station since 1987; the present instrument (since July 1996) is a compact one, which has replaced the first one ( ). The FG5 raw data are corrected for the tides (including both solid-earth tide and oceanic tide) using the tidal parameters derived from the analysis of the record of the SG running at the station. The vertical gravity gradient has been measured several times using both Lacoste&Romberg and Scintrex relative gravimeters; its value is: 2.89 ± 0.02 Gal/cm: FG5#206: From 1987 to February 1997, six AG measurements have been performed with Jilag-5 by Jaakko Mäkinen from the Finnish Geodetic Institute (FGI) (Amalvict et al., 2004). When the French Geodetic community purchased the absolute gravimeter FG5#206, it was operated more frequently at the Strasbourg Gravity Observatory, the site of the SG relative gravimeter. The AG measurements show both a trend and seasonal variations. Intercomparison FG5#206/FG5#301: FG5#206 and FG5#301 have been measuring side by side at Stasbourg-J9 site in March The two instruments measured in the same room at two points separated by 1 m, then swapped. After processing of data according to the same scheme (using the same value for vertical gradient of gravity and same tidal analysis for the reduction of tides), at each position the values agreed within 1 Gal.

9 366 M. Amalvict et al. / Journal of Geodynamics 41 (2006) Fig. 6. Strasbourg-J9: gravity changes observed by SG and AGs from January 1997 to March; hydrological variations modelled for the and periods, g r = 980,777,000 Gal, the trend of the linear fit of AG measurements is 1.9 ± 0.2 Gal/yr. Fig. 6 presents the residuals of gravity observations (SG and AG) after removing the tidal variation, the effect of atmospheric pressure (constant admittance factor: 0.3 hpa/ Gal), the polar motion; the instrumental drift has been removed from the SG record as well as spikes and jumps. The two instruments show comparable seasonal and longterm variations of gravity (Amalvict et al., 2004) that need to be explained. The linear fit of values weighted by error bars leads to 1.9 ± 0.2 Gal/yr. The effect of hydrology on gravity records is known for long, though it is not easy to model. Several sources of hydrological phenomena can be thought of and are usually summing up at a given station. These effects have to be removed from the gravity residuals, in order to improve the study of gravity variations of tectonic origin. One can consider (i) different scales: local, regional, global; (ii) different sources: rainfall, groundwater, snow, glacier thawing, water storage (dam, etc.), soil moisture; (iii) different means of measuring: rain gauges, water gauges, snow gauges, humidity sensors, worldwide meteorological database, satellite. The nature, the geographical scale and the time scale of hydrological phenomena that we have to consider depend on the location of the study (geographical, geological context) and on the time-span of gravity (or GPS) records under study. The recovery of groundwater variations at a global scale is the present goal of many studies connected to recent satellite missions such as GRACE and CHAMP (Rodell and Famiglietti, 2001; Swenson et al., 2003; Andersen and Hinderer, 2005; Ramillien et al., 2004; Wahr et al., 2004). There is also an attempt to compare the observations of these satellites to the surface gravity data from the GGP network of SG involving a large region, such as Europe for instance, and this is not a straightforward operation (see Crossley and Hinderer, 2002; Crossley et al., 2003, 2004; Llubes et al., 2004). Modelling of hydrological phenomena at continental scale is rapidly developing (Milly and Shmakin, 2002; Rodell et al., 2004). At a smaller scale, the regional or even local effects have also to be taken into account (Boy and Hinderer (2006)). It is of primary importance to consider as many phenomena as possible. For example, Richter et al. (2004) show that the long-term variation of gravity, which is observed at Medicina and Wetzell, is more likely due to mass changes (involving atmosphere, ocean, soil consolidation) than to tectonic displacements. Virtanen (2004) evidences the effect of the Baltic Sea on gravity. As far as seasonal gravity variations at the Strasbourg-J9 are concerned, hydrology is a clear candidate to explain them but there is still a debate on the exact contribution of each component of the hydrological system. The level of the water table beneath the Strasbourg-J9 Observatory is monitored by a water gauge in a well. The seasonal variation is evidenced in Amalvict et al. (2004), but its origin, though quite well correlated with local hydrology seems to be in very good agreement with global models. The hydrological effect of continental soil moisture (snow contribution is negligible) is presented in Fig. 5, according to two different models (the LAD model by Milly and Shmakin, 2002; GLDAS model by Rodell et al., 2004) and is in fair agreement with the observed gravity variations.

10 M. Amalvict et al. / Journal of Geodynamics 41 (2006) Table 1 Secular tendencies derived from AG measurements and GPS observations at the three stations AG GPS BFO Subsidence Not available Strasbourg-J9 Subsidence Subsidence Welschbruch Uplift Subsidence 6. Conclusions Let us summarise in Table 1, the conclusions concerning the vertical displacements that we can draw from the above sections: The subsidence of BFO implied by the increase in gravity is not realistic, according to the geological knowledge. The subsidence of the Strasbourg-J9 station is implied by the AG trend and is observed from GPS data. This is what tectonicians would expect. The uplift of the Welschbruch station is implied by the AG trend and is not observed from GPS data. Some tectonicians would expect an uplift. Nevertheless, the orders of magnitude of subsidence and uplift observed by GPS and AG measurements at the other stations are not compatible. The displacement derived from the AG trend (whatever the converting factor is) is by far too large, according to the tectonics of the region. We have to remind that the processing of GPS data leads to a smaller precision in vertical component than in horizontal components. Moreover, the length of period of observation is also very sensitive and should not be shorter than 2 3 years (Blewitt and Lavallée, 2002). Moreover, the magnitude of the displacements involved is very small: 1 mm/yr or smaller which makes their observation very tricky. Acknowledgments This paper was written during the stay of MA as Visiting Professor at the National Institute of Polar Research, at Tokyo (Japan). Authors thank Jean-Paul Boy for his hydrological gravity loading computation for Strasbourg-J9 station, BKG and ORB for providing their data at Strasbourg-J9 and BFO stations, the BFO staff for its helpful kindness during the measurements, as well as Bernard Luck who operates FG5#206. The authors also thank Alan Goodacre and an anonymous referee for their critical comments to improve the manuscript. References Amalvict, M., Hinderer, J., Mäkinen, J., Rosat, S., Rogister, Y., Long-term and seasonal gravity changes at the Strasbourg station and their relation to crustal deformation and hydrology. J. Geodyn. 38, Andersen, O.B., Hinderer, J., Global interannual gravity changes from GRACE: early results, Geophys. Res. Lett., 32, L01402, doi: /2004gl Blewitt, G., Lavallée, D., Effect of annual signals on geodetic velocity. JGR B 107 (B7), doi: /2001jb Boy, J.-P., Hinderer, J., Study of the seasonal gravity signal in superconducting gravimeter data. J. Geodyn. 41 (1 3), Camelbeeck, T., van Camp, M., Jongmans, D., Francis, O., van Dam, T., Comment on Nature of the recent vertical ground movements inferred from high-precision levelling data in an intraplate setting: NE Ardenne, Belgium by A. Demoulin and A. Collignon. JGR B 107 (11), 2281, doi: /2001jb Crossley, D., Hinderer, J., GGP ground truth for satellite gravity missions. Bull. Inf. Marées Terrestres 136, Crossley, D., Hinderer, J., Llubes, M., Florsch, N., The potential of ground gravity measurements to validate GRACE data. Adv. Geosci. 1, 1 7. Crossley, D., Hinderer, J., Boy, J.-P., Regional gravity variations in Europe from superconducting gravimeters. J. Geodyn. 38, Demoulin, A., Collignon, A., Nature of the recent vertical ground movements inferred from high-precision leveling data in an intraplate setting: NE Ardenne, Belgium. JGR B 105, Francis, O., van Camp, M., van Dam, T., Warmant, R., Hendrickx, M., 2004a. Indication of the uplift of the Ardenne in long-term gravity variations in Membach (Belgium). Geophys. J. Int. 158,

11 368 M. Amalvict et al. / Journal of Geodynamics 41 (2006) Francis, O., van Dam, T., Amalvict, M., Andrade da Sousa, M., Bilker, M., Billson, R., d Agostino, G., Desogus, Falk, R., Gremak, A., Gitlein, O., Jonhson, D., Klopping, F., Kostelecky, J., Luck, B., Mäkinen, J., McLaughlin, D., Nunez, E., Origlia, C., Palinkas, V., Richard, P., Rodriguez, E., Ruess, D., Schmerge, D., Thies, S., Timmen, L., van Camp, M., van Westrum, D., Wilmes, H., 2004b. Results of the International Comparison of Absolute Gravimeters in Walferdange (Luxembourg) of November 2003, GGSM, submitted for publication. Hinderer, J., Sedighi, M., Bayer, R., Ghazavi, K., Luck, B., Amalvict, M., Nilforoushan, F., Masson, F., The absolute gravity network in Iran: an opportunity to analyse gravity changes caused by present-day tectonic deformation. Cahiers du Centre Européen de Géodynamique et de Séismologie 22, Lambert, A., Courtier, N., Sasagawa, G.S., Klopping, F., Winester, D., New constraints on Laurentide postglacial rebound from absolute gravity measurements. Geophys. Res. Lett. 28 (10), Larsen, C.F., Motyka, R.J., Freymueller, J.T., Echelmeyer, K.A., Ivins, E.R., Rapid uplift of southern Alaska caused by recent ice loss. Geophys. J. Int. 158, Larson, K.M., van Dam, T., Measuring postglacial rebound with GPS and absolute gravity. Geophys. Res. Lett. 27 (23), Lenôtre, N., Thierry, P., Blanchin, R., Brochard, G., Current vertical movement demonstrated by comparative levelling in Brittany (northwestern France). Tectonophysics 301, Llubes, M., Florsch, N., Hinderer, J., Longuevergne, L., Amalvict, M., Local hydrology, the Global Geodynamics Project and CHAMP/GRACE perspective: some case studies. J. Geodyn. 38, Malzer, H., Schlemmer, H., Geodetic measurements and recent crustal movements in the Southern Upper Rhine Graben. Tectonophysics 29, Milly, P.C.D., Shmakin, A.B., Global modelling of land water and energy balances. Part I. The land dynamics (LaD) model. J. Hydrometeorol. 3 (3), Polaud, E., Comparaison de nivellements en Alsace. Stage d été, BRGM. Ramillien, G., Cazenave, A., Brunau, O., Global time variations of hydrological signals from GRACE satellite gravimetry. Geophys. J. Int. 158, Richter, B., Zerbini, S., Matonti, F., Simon, D., Long-term crustal deformation monitored by gravity and space techniques at Medicina, Italy and Wettzell, Germany. J. Geodyn. 38, Rodell, M., Famiglietti, J.S., An analysis of terrestrial water storage variations in Illinois with implications for the Gravity Recovery and Climate Experiment (GRACE). Water Resour. Res. 37, Rodell, M., Houser, P.R., Jambor, U., Gottschalck, J., Mitchell, K., Meng, C.-J., Arsenault, K., Cosgrove, B., Radakovich, J., Bosilovich, M., Entin, J.K., Walker, J.P., Lohmann, D., Toll, D., The Global Land Data Assimilation System. Bull. Am. Meteor. Soc. 85 (3), Rózsa, Sz., Heck, B., Mayer, M., Seitz, K., Westerhaus, M., Zippelt, K., in press. Determination of displacements in the upper Rhine graben from GPS and levelling data, Int. J. Sci. Sato, T., Okuno, J., Hinderer, J., van Dam, T., MacMillan, D.S., Francis, O., Falk, R., Fukuda, Y., Plag, H.-P., A geophysical interpretation of the secular displacement and gravity rates observed at Ny-Alesund, Svalbard in the Arctic effects of the post-glacial rebound and present-day ice melting, Geophys. J. Int., submitted for publication. Schweizer, R., Höhenänderungen von Nivellementpunkten im südlichen Oberrheingraben. Dissertation. Universität Karlsruhe, Schriftenreihe Angewandte Geologie, No. 16. Swenson, S., Wahr, J., Milly, C., Estimated accuracies of regional water storage variations inferred from the Gravity Recovery and Climate Experiment (GRACE). Water Resour. Res. 39 (8), 1223, doi: /2002wr Villemin, T., Alvarez, F., Angelier, J., The Rhine graben: extension, subsidence and shoulder uplift. Tectonophysics 128, Virtanen, H., Loading effects in Metsähovi from the atmosphere and the Baltic Sea. J. Geodyn. 38, Wahr, J., van Dam, T., Larson, K., Francis, O., Geodetic measurements in Greenland and their implications. JGR B 106 (8), Wahr, J., Swenson, S., Zlotnicki, V., Velicogna, I., Time-variable gravity from GRACE: first results. Geophys. Res. Lett. 31 (11), L11501, doi: /2004gl Zippelt, K., Modellbildung, Berechnungsstrategie und Beurteilung von Vertikalbewegungen unter Verwendung von Präzisionsnivellements. Dissertation. DGK Reihe C, Heft No. 343, p. 153.