The International Comparison of Absolute Gravimeters ICAG-2005 was held at the Bureau International des Poids et Mesures (BIPM), Sèvres, France in September 2005. The organization of ICAG2005, measurement strategy, calculation and presentation of the results were described in a technical protocol pre-developed to the comparison. Nineteen absolute gravimeters carried out 96 series of measurements of free-fall acceleration g at the sites of the BIPM gravity network. The vertical gravity gradients were measured by relative gravimeters. For the first time the budgets of uncertainties were presented. The g-values for the sites A and B of the BIPM gravity network at a height of 0.90 m are (980,925,702.2 ± 0.7) μGal and (980,928,018.5 ± 0.7) μGal, respectively. This result is in a good agreement with that obtained in ICAG-2001.

We used GPS method to investigate the preseismic, coseismic and postseismic deformation due to the 27 September 2003, Mw = 7.3 Chuya (Altay) earthquake, which occurred south of Russian Altay mountains in southern Siberia near the Russia-Mongolia-China border. On the basis of GPS data measured during the campaigns of observation covering the period 2000-2007, we determined the magnitude and space distribution of 3D displacement fields for different epochs. Geodynamical GPS network consists of 23 sites and extends over structural elements of Russian Altay and surroundings territory (from 49.5°N to 54.8°N, from 81.2°E to 91.4°E). GPS data have been analyzed by GAMIT-GLOBK. Evidence was available of the existence of preseismic (2000-2003 years), coseismic (2003-2004 years) and postseismic (20042007 years) processes in this region. We used absolute gravity observation to check vertical motion at base points. Map of preseismic contemporary rates showed values from 0.5 to 10 mm/y and features in 3D velocity field. Russian Altay preseismic motion is connected with present-day displacement in West China and Mongolia. By analysis of the GPS data for 20032004 we got the map of coseismic displacements, reflecting the right-lateral strike-slip process in epicentral zone (130N140N orientation for rupture line). Coseismic horizontal displacements depend on distance between rupture line and GPS benchmarks position, for example, we obtained values from 350 mm at 15 km to 25 mm at 90 km. Vertical motion was smaller (10 ÷ 40 mm). GPS data for 6 benchmarks in epicenter zone show correlation with 2-D model with parameters for jump on rupture line – 2 m, for maximal depth – 15 km, for shear strain 4 MPa. 3D modeling of coseismic process allowed us to understand displacement field for vertical motion at the end of earthquake rupture (10  40 mm jump). Coseismic deformation on 10 level extended over the epicentral zone (100 km). Postseismic displacement field (2004-2007 years) showed the right-lateral motion in epicenter zone (3 ÷ 7 mm/y). Postseismic data allowed to develop a postseismic model for Chuya earthquake and to determine lower crust parameters (viscosity 10 Pas). Analyses of 2000-2007 data allowed us to separate ongoing seismic motion from tectonic motion for West part of Russian Altay (2 mm/y to NW).

The International Comparison of Absolute Gravimeters ICAG-2005 was held at the Bureau International des Poids et Mesures (BIPM), Sèvres, France in September 2005. The organization of ICAG-2005, measurement strategy, calculation and presentation of the results were described in a technical protocol pre-developed to the comparison. Nineteen absolute gravimeters carried out 96 series of measurements of free-fall acceleration g at the sites of the BIPM gravity network. The vertical gravity gradients were measured by relative gravimeters. For the first time the budgets of uncertainties were presented.

The fifth in the series of International Comparisons of Absolute Gravimeters (ICAG) was held at the Bureau International des Poids et Measures (BIPM) in November 1997. Fifteen absolute gravimeters participated in the comparison. The mean gravity value obtained at station A (0.9 m) at the BIPM was found to be 980 925 707.8 µGal with a standard uncertainty of 2.8 µGal. This is consistent with the results obtained in previous comparisons at this site. Conclusions based on the analysis of the present results and proposals for future activities are presented.