1. Towards a standard model for present-day signals due to postglacial rebound H.-P. Plag, C. Kreemer Nevada Bureau of Mines and Geology and Seismological Laboratory University of Nevada, Reno, Nevada, USA David Lavallée University of Newcastle upon Tyne, U.K.

2. Background Comparison of PGR model predictions The secular surface velocity fields Separating rigid body motion from PGR Is there consistency between observation and model predictions? Towards a standard model for present-day signals due to postglacial rebound

3. Background Motivation: There is a variety of PGR models with large differences The uncertainties in the prediction of the present-day signal are poorly known Many applications in geosciences need to correct for PGR IERS Conventions are not explicit in how to handle PGR The SBL Project: Goal is to set up, if possible, a standard model for the present-day PGR signal with solid error bars In 2005, Call for Submission of predictions of the present-day PGR signal in sea level, 3-D surface displacements, gravity field, and Earth Rotation Establishment of a web page with the submissions and the results of model inter-comparison (partly finished) Model intercomparison is under way Comparison of model to observations just started

4. Comparison of Post-Glacial Rebound Model Predictions

6. 3-D displacements ALT JXM VM2 REF

7. Comparison of Post-Glacial Rebound Model Predictions ALT JXM REF VM4 3-D displacements

8. Comparison of Post-Glacial Rebound Model Predictions Standard deviation with respect to global mean

9. Comparison of Post-Glacial Rebound Model Predictions Cross correlations

10. Comparison of Post-Glacial Rebound Model Predictions REF JXM ALT VM2 Normalized Scalar Product of 3-D displacements for VM4 and the other models

11. Comparison of Post-Glacial Rebound Model Predictions REF JXM ALT VM2 Normalized Scalar Product of 3-D displacements for VM4 and the other models

12. Intercomparison of all quantities (3-D, LSL, geoid, Earth rotation, free air anomaly Comparison to observations: - 3-D to GPS,... - LSL to tide gauges - Geoid to GRACE - Earth rotation to IERS Plan for Comparison and Validation

13. Separation of PGR and rigid plate motion: Plag et al. (2002): include PGR in the determination of rigid plate motion Kierulf and Plag (2003): significant improvement for Eurasia Kreemer et al. (2006):... Initial Step for Validation

14. Total of 376 points Combination of weekly global and regional solutions 1999 - 2005

15. Initial Step for Validation For comparison, observed velocities need to be in same frame as predictions For each PGR model, we calculating a scale and translation rate from a least square fit of the 220 vertical velocities for sites on 15 tectonic plates. All models suggest a translation of the GPS velocities of ~1.2-2.1 mm/yr towards western Europe, and a scale change of a factor between 1 and 2.

16. Initial Step for Validation

17. What is Next? 5 X 5 degrees Total of 222 grids elements 78 elements with multiple values

18. Regional intermodel differences larger than the uncertainties in the observed velocity field, particularly for North America and Eurasia. Space-geodetic observations provide valuable constraints for these models. ICE-5G history inconsistent with the observed velocity field in North America. Accounting for the PRG signal in the determination of the rigid body rotation improves the estimates for N.A. and Eurasia For plates in the far-field of the former ice loads, the improvement is either small or negligible. There, PGR signal may be below the error of the observed velocity field or erroneous for several reasons (including the effect of lateral heterogeneities in the solid Earth). Conclusions