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.

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, USADavid Lavallée

University of Newcastle upon Tyne, U.K.

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

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

Comparison of Post-Glacial Rebound Model Predictions

Comparison of Post-Glacial Rebound Model Predictions

Comparison of Post-Glacial Rebound Model Predictions

3-D displacements

ALT JXM

VM2 REF

Comparison of Post-Glacial Rebound Model Predictions

ALT JXM

REF VM4

3-D displacements

Comparison of Post-Glacial Rebound Model Predictions

Standard deviation with respect to global mean

Comparison of Post-Glacial Rebound Model Predictions

Cross correlations

Comparison of Post-Glacial Rebound Model Predictions

REF

JXM ALT

VM2

Normalized Scalar Product of 3-D displacements for VM4 and the other models

Comparison of Post-Glacial Rebound Model Predictions

REF

JXM ALT

VM2

Normalized Scalar Product of 3-D displacements for VM4 and the other models

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

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

Initial Step for Validation

Total of 376 pointsCombination of weekly global and regional solutions1999 - 2005

Initial Step for Validation

For comparison, observed velocities need to be in same frame as predictionsFor 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.

Initial Step for Validation

What is Next?

5 X 5 degreesTotal of 222 grids elements78 elements with multiple values

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