Consequences of experimental transient rheology

Recent analyses of transient creep data for lower crustal and upper mantle substances are used to constrain the viscosity contrast across the 670 km discontinuity, and a 4-layer earth model in which both upper and lower mantles are described by a Burgers body rheology is assumed. Results indicate that the previously inferred viscosity variations would be reduced by a factor of ten using the new transient models. This result is in agreement with a revised viscosity estimate based on long-wavelength geoid anomalies and seismic tomography. Time-dependent perturbations to the gravity field from recent ice movements are shown to be significant.