About

Purposes of  the working group

The purposes of this working group are twofold:

• First there are pure scientific interests in improving the knowledge of surface deformations in Eurasia and adjacent areas,
• Second, a velocity model will potentially be a valuable tool in the management and use of the national realisations of the ETRS89. Applications of geodetic reference frames in the presence of crustal deformations will be studied in detail.

Background

Given the amount of interplate and intraplate deformations present within the EUREF area of interest, the development of a roadmap towards a European velocity model is proposed. This includes crustal deformations such as plate boundary zones, Fennoscandian GIA (Glacial Isostatic Adjustment), episodic events such as earthquakes, as well as other surface deformations of known (e.g. volcanic swelling, long-term hydrological changes, compaction in sedimentary basins, anthropogenic influence due to oil or gas extraction, CO2 sequestration) or not yet known causes.

The goal is European velocity models

The goal of this working group (WG) is – relying on the known 3D crustal velocities of GNSS reference stations with sufficient detail and accuracy – to obtain velocity models and to significantly improve the prediction of the time evolution of coordinates and overcome the limitations in the use of the ETRS89 (new window). A general understanding of the physics behind such a velocity field (GIA, interplate and intraplate deformation, atmospheric effects, etc.) is also part of this WG.

When this initiative proves to be successful, interplate and intraplate deformations could be modelled and corrected for while using the reference frame, which will extend the useful lifetime of a realisation of the ETRS89. Therefore this work is important for applied geodesy. It is also relevant for scientific activities. Sometimes, ITRF (new window) may be utilised in scientific work. However, for scientific studies of geodynamics in Europe, it is handy to remove the plate tectonic motion and use the ETRS89 in order to present velocities relative to "stable Eurasia" in a standardised way.

With the need of increasing precision for national reference frames over time, the European velocity model should fill a gap between the global look on a stable Eurasian Plate defined by ITRF and the more or less stable (or unstable) parts of this plate. It should be noted that national boundaries are not identical to boundary zones and therefore EUREF (new window) should offer cross-boundary models for mapping agencies for consideration to be applied for national realisations of ETRS89. It should be kept in mind that some countries need such models to maintain a consistent national reference frame at all.

The first re-processing of EPN (new window) has recently been completed successfully (EPN-Repro1) and has significantly improved the quality of the velocities of the EPN stations. Further re-processing initiatives are foreseen. Relying on EPN-Repro1 and the routine EPN analysis, a regularly updated EPN multiyear solution is created and maintained by the EPN Reference Frame Coordinator. In addition a densification (based on weekly SINEX solutions from national densification networks) of this solution is under preparation by the Reference Frame Coordinator. This EPN product can be considered as the backbone for crustal deformation studies in Europe.

Related work

On the global scale, the IAG (new window) WG on the "Integration of dense velocity fields into the ITRF" is a key initiative towards the elaboration of strategies, procedures on the improved realisation and delivery of velocity products from global to regional level. EUREF and the EPN are also part of this WG and essential work has already been done to realise the European part of the global velocity field.

On a regional scale, the MoU between CEGRN (new window) and EUREF also aims to densify the velocities of permanent GNSS stations in Central Europe, with the intent to improve the predictability of future positions of reference stations and, at the same time, to gain a better understanding of Central European geokinematics.
Other initiatives like the European Plate Observing System (EPOS, new window) are currently being designed. Such initiatives will probably contribute to the improved understanding of geodynamic processes relevant for Europe.

Availability of station velocity solutions

Key information for improved knowledge of crustal deformations is observed motions at stations. This includes station velocities, and possible station position shifts for the case of episodic events, where the EPN is considered as the core infrastructure. However, a denser network of GNSS stations than the EPN will be needed to sample the crustal deformations sufficiently. The availability of velocity solutions including additional stations compared to the EPN stations is therefore of high interest for this working group, provided the processing standards used for these solutions comply with the EPN/IGS specifications. The work related to the realisation of improved station velocity solutions are covered by other initiatives and operational procedures of EUREF and will therefore not be done within this WG. Rather, this WG will build on the results from these initiatives.

In this sense the key input to this WG will be expected from the EPN Densification initiated and operated by the EPN Reference Frame Coordinator. The target of that work – in agreement with the IAG WG on the "Integration of dense velocity fields into the ITRF" and the EUPOS Combination Centre – is to integrate the national permanent GNSS sites/networks from possibly all European countries on the weekly (for the future possibly daily) SINEX level, where the EPN serves as the backbone of the combination. The main product of this work will be a combined position/velocity solution.