[1] For the first time in the history of the International Terrestrial Reference Frame, the ITRF2000 combines unconstrained space geodesy solutions that are free from any tectonic plate motion model. Minimum constraints are applied to these solutions solely in order to define the underlying terrestrial reference frame (TRF). The ITRF2000 origin is defined by the Earth center of mass sensed by satellite laser ranging (SLR) and its scale by SLR and very long baseline interferometry. Its orientation is aligned to the ITRF97 at epoch 1997.0, and its orientation time evolution follows, conventionally, that of the no-net-rotation NNR-NUVEL-1A model. The ITRF2000 orientation and its rate are implemented using a consistent geodetic method, anchored over a selection of ITRF sites of high geodetic quality, ensuring a datum definition at the 1 mm level. This new frame is the most extensive and accurate one ever developed, containing about 800 stations located at about 500 sites, with better distribution over the globe compared to past ITRF versions but still with more site concentration in western Europe and North America. About 50% of station positions are determined to better than 1 cm, and about 100 sites have their velocity estimated to at (or better than) 1 mm/yr level. The ITRF2000 velocity field was used to estimate relative rotation poles for six major tectonic plates that are independent of the TRF orientation rate. A comparison to relative rotation poles of the NUVEL-1A plate motion model shows vector differences ranging between 0.03°and 0.08°/m.y. (equivalent to approximately 1-7 mm/yr over the Earth's surface). ITRF2000 angular velocities for four plates, relative to the Pacific plate, appear to be faster than those predicted by the NUVEL-1A model. The two most populated plates in terms of space geodetic sites, North America and Eurasia, exhibit a relative Euler rotation pole of about 0.056 (±0.005)°/m.y. faster than the pole predicted by NUVEL-1A and located about (10°N, 7°E) more to the northwest, compared to that model.

Les documents de travail ne reflètent pas la position du CREST et n'engagent que leurs auteurs. Working papers do not reflect the position of CREST but only the views of the authors.

Abstract. Although tectonic deformation in western Europe is essentially concentrated in the Appenines and Alpine (Alps, Pyrenees) mountain ranges, several large historical and instrumentally recorded earthquakes (M>6) are known in the supposedly "stable" part of Europe. Because of its accuracy and internal consistency at a global scale, the International Terrestrial Reference Frame 1997 (ITRF97) velocity field allows testing of intraplate rigidity in western Europe at a millimeter per year level. Using the full statistical information available on the ITRF97 velocities, we identify a subset of sites located in central Europe that satisfies a rigid cap rotation with residual velocities <1 mm/yr and therefore provide a stable europe reference fYame (SERF). In this reference frame we find residual velocities at European ITRF sites that are consistent with known active tectonic features. We identify a northward motion at sites located in Italy, with internal deformation of the Adriatic block rather than rigid plate motion and a westward motion of the westernmost part of Europe of the order of 1-2 mm/yr relative to central Europe. The relative motion of the Adriatic block and western Europe agrees with the current extension known in the Tyrrhenian sea and the Apennines. In central Europe, we find active deformation < 1 mm/yr in the eastern Alps and western Carpathians. In the Alpine range our results indicate E-W extension across the western Alps and N-S compression across the central and eastern Alps, in agreement with the strain regime deduced from seismotectonic observations. In Belgium and the Netherlands we find residual velocities of 1-1.5 mm/yr to the northwest at all the sites, most likely accommodated along the Upper and Lower Rhine Graben structures. An important outcome of this study is the identification of internal deformation of the order of 1-2 mm/yr in an area usually interpreted as "stable" Europe. This result should be further checked as new, denser, and more accurate space geodetic data sets with longer observation time spans, become available for Europe.

We show that the bulk of Earth’s water was delivered before the high-energy collision that led to the formation of the Moon.

No abstract