a comparison of eastern north american seismic strain rates to glacial rebound strain rates glacial rebound strain rates computed using a simple laurentide glacial loading model are of the order of 10 9 per year within the region of glaciation and extending several hundred kilometers beyond the horizontal strain rates receive approximately equal contributions from horizontal and vertical velocities a consequence of the spherical geometry adopted for the earth model in the eastern united states and southeastern canada the computed strain rates are 1 3 orders of magnitude greater than an estimate of the average seismic strain rate anderson 1986 and 1 order of magnitude greater than predicted erosional strain rates the predicted glacial rebound strain rates are not in general oriented in such a way as to augment the observed state of deviatoric stress possibly explaining why the seismic strain rates are much smaller than the glacial rebound strain rates an exception to this may be seismically active regions in the st lawrence valley

history and isostatic effects of the last ice sheet in southern british columbia abstract the late wisconsinan cordilleran ice sheet covered british columbia southern yukon territory and parts of alaska washington idaho and montana its major source areas were the high mountain ranges of the canadian cordillera and flow was strongly controlled by topography the last ice sheet began to develop about 30 000 25 000 14c yr ago but it did not achieve its maximum extent until 15 000 14 000 14c yr bp ice sheet growth was interrupted locally by stillstands and retreat ice sheet decay was rapid and was characterized by complex frontal retreat at the periphery accompanied locally by brief readvances and by downwasting and stagnation by 10 000 14c yr bp

brittle deformation during alpine basal accretion and the origin of seismicity nests above the subduction interface geophysical observations on active subduction zones have evidenced high seismicity clusters at 20 40 km depth in the fore arc region whose origin remains controversial we report here field observations of pervasive pseudotachylyte networks interpreted as evidence for paleo seismicity in the now exhumed valpelline continental unit dent blanche complex nw alps italy a tectonic sliver accreted to the upper plate at c 30 km depth during the paleocene alpine subduction pre alpine granulite facies paragneiss from the core of the valpelline unit are crosscut by widespread mm to cm thick pseudotachylyte veins co seismic heating and subsequent cooling led to the formation of ti rich garnet rims ilmenite needles ca rich plagioclase biotite microliths and hercynite micro crystals 39ar 40ar dating yields a 51 54 ma age range for these veins thus suggesting that frictional melting events occurred near peak burial conditions while the valpelline unit was already inserted inside the duplex structure in contrast the base of the valpelline unit underwent synchronous ductile and brittle seismic deformation under water bearing conditions followed by a re equilibration at c 40 ma 39ar 40ar on retrograded pseudotachylyte veins during exhumation related deformation calculated rheological profiles suggest that pseudotachylyte veins from the dry core of the granulite unit record upper plate micro seismicity mw 2 3 formed under very high differential stresses 500 mpa while the sheared base of the unit underwent repeated brittle ductile deformation at much lower differential stresses 40 mpa in a fluid saturated environment these results demonstrate that some of the seismicity clusters nested along and above the plate interface may reflect the presence of stiff tectonic slivers rheologically analogous to the valpelline unit acting as repeatedly breaking asperities in the basal accretion region of active subduction zones

present day tilting of the great lakes region based on water level gauges by using monthly mean water levels at 55 sites around the great lakes a regional model of vertical crustal motion was computed for the region in comparison with previous similar studies over the great lakes 15 additional gauge sites data from all seasons instead of the 4 summer months and 8 additional years of data were used all monthly water levels available between 1860 and 2000 as published by the u s national ocean survey and the canadian hydrographic service were used for each lake basin the vertical velocities of the gauge sites relative to each other were simultaneously computed using the least squares adjustment technique our algorithm solves for and removes a monthly bias common to all sites as well as site specific biases it also properly weighs the input water levels resulting in a realistic estimation of the uncertainties in tilting parameters the relative velocities obtained for each lake were then combined to obtain relative velocities over the entire great lakes region finally the gradient of the relative rates for the regional model was found to agree best with the ice 3g global isostatic model of tushingham and peltier whereas the ice 4g gradients were too small around the great lakes

influence of lithospheric thickness variations on 3 d crustal velocities due to glacial isostatic adjustment 1 predictions of 3 d crustal velocities driven by glacial isostatic adjustment gia have generally been based on spherically symmetric earth models we adopt a finite volume formulation to explore the impact of lateral variations in elastic plate strength including lithospheric thickness changes across the continent ocean interface and plate boundary weak zones on these predictions weak zones introduce horizontal rate perturbations with a plate scale coherency and amplitudes reaching 1 2 mm yr radial velocity perturbations can be as large but are geographically isolated to the weak zones specifically the north atlantic ridge a discontinuity in ocean continent lithospheric thickness significantly impacts rates along continental margins order 1 mm yr for radial rates and generally about half this for tangential rates we conclude that lateral variations in lithospheric strength should be included in future gia analyzes of space geodetic survey results and in assessing the impact of gia on the stability of geodetic reference frames

observation of glacial isostatic adjustment in stable north america with gps 1 motions of three hundred and sixty global positioning system gps sites in canada and the united states yield a detailed image of the vertical and horizontal velocity fields within the nominally stable interior of the north american plate by far the strongest signal is the effect of glacial isostatic adjustment gia due to ice mass unloading during deglaciation vertical velocities show present day uplift 10 mm yr near hudson bay the site of thickest ice at the last glacial maximum the uplift rates generally decrease with distance from hudson bay and change to subsidence 1 2 mm yr south of the great lakes the hinge line separating uplift from subsidence is consistent with data from water level gauges along the great lakes showing uplift along the northern shores and subsidence along the southern ones horizontal motions show outward motion from hudson bay with complex local variations especially in the far field although the vertical motions are generally consistent with the predictions of gia models the horizontal data illustrate the need and opportunity to improve the models via more accurate descriptions of the ice load and laterally variable mantle viscosity

glacial isostatic adjustment observed using very long baseline interferometry and satellite laser ranging geodesy in global space geodetic solutions radial site motions are usually estimated relative to the geocenter the center of figure of the solid earth most geodesists estimate the motion of the geocenter assuming both that sites do not move radially and that sites move laterally as predicted by plate motion model nuvel 1a demets et al 1990 1994 here we estimate the motion of the geocenter assuming that the plate interiors deform radially and laterally as predicted by the postglacial rebound model of peltier 1994 or that of peltier 1996 without assuming a priori knowledge about relative plate motion radial site motions estimated relative to this rebound adjusted geocenter are in the same reference frame as the rebound model predictions whereas site motions estimated without adjusting for rebound are not we further constrain the motion of the rebound adjusted geocenter using satellite laser ranging s sensitivity to the center of mass of the solid earth the oceans and the atmosphere by assuming that the mean velocity between the rebound adjusted geocenter and the center of mass is negligible over the time period of geodetic measurement twenty years of observation with satellite laser ranging and very long baseline interferometry record the isostatic response of the solid earth to the unloading of the late pleistocene ice sheets the misfits of the postglacial rebound model of peltier 1994 and that of peltier 1996 are 34 and 16 less respectively than the misfit of the rigid plate model sites at onsala sweden and algonquin park ontario are observed to be rising at 3 mm yr and 2 mm yr respectively reflecting unloading of the fennoscandian and laurentide ice sheets sites along the east coast of the united states are subsiding at 2 mm yr indicating that the forebulge produced by the laurentide ice sheet is currently collapsing very slowly sites beneath the margins of the ice sheets during the last glacial maximum are currently moving laterally away from the ice sheet centers at 1 5 mm yr in disagreement with the moderately fast outward motion predicted by the model of peltier 1996

ice age paleotopography a gravitationally self consistent theory of postglacial relative sea level change is used to infer the variation of surface ice and water cover since the last glacial maximum lgm the results show that lgm ice volume was approximately 35 percent lower than suggested by the climap reconstruction and the maximum heights of the main laurentian and fennoscandian ice complexes are inferred to have been commensurately lower with respect to sea level use of these ice age boundary conditions in atmospheric general circulation models will yield climates that differ significantly from those previously inferred on the basis of the climap data set

global glacial isostatic adjustment palaeogeodetic and space geodetic tests of the ice 4g vm2 model analyses of the global process of glacial isostatic adjustment and post glacial relative sea level change continue to deliver important insights into earth system form and process one successful model of the related phenomenology is based upon a spherically symmetric internal viscoelastic structure for the solid earth which has been denoted vm2 and a model of the most recent deglaciation event of the current ice age denoted ice 4g the primary purpose of this paper is to describe several new a posteriori tests that have recently been performed to further investigate the quality of this global solution to the inverse problem for both mantle viscosity and deglaciation history that is posed by the observables associated with this large scale geodynamic phenomenon i focus especially upon the misfits of observations to the theoretical predictions of this model which i am currently using to further refine its properties and upon predictions made using it of geophysical signals that should soon become visible in the context of the gravity recovery and climate experiment grace satellite mission among the required refinements to ice 4g one that is necessary to eliminate a recently revealed misfit to space geodetic constraints on the present day rate of radial motion at the yellowknife location well to the west of hudson bay and a similar misfit to absolute gravity measurements to the southwest of the bay is the insertion of a keewatin dome of thick ice centred over yellowknife with a ridge of ice extending to the south east in the geomorphological literature the existence of such a keewatin dome previously has been hypothesised but chronological control was lacking on the surface features that suggested its former existence an important additional constraint that requires the late glacial existence of this important feature consists of new inferences of the last glacial maximum lowstand of the sea from sites in the far field of the main concentrations of land ice copyright 2002 john wiley sons ltd

space geodetic constraints on glacial isostatic adjustment in fennoscandia analysis of global positioning system gps data demonstrates that ongoing three dimensional crustal deformation in fennoscandia is dominated by glacial isostatic adjustment our comparison of these gps observations with numerical predictions yields an earth model that satis es independent geologic constraints and bounds both the average viscosity in the upper mantle 5 x 10 20 to 1 x 10 21 pascal seconds and the elastic thickness of the lithosphere 90 to 170 kilometers we combined gps derived radial motions with fennoscandian tide gauge records to estimate a regional sea surface rise of 2 1 0 3 mm year furthermore ongoing horizontal tectonic motions greater than 1 mm year are ruled out on the basis of the gps derived three dimensional crustal velocity field

investigation of glacial isostatic adjustment in the northeast u s using gps measurements 1 we have been observing three dimensional site velocities at over 60 permanent gps stations in the northeastern u s for the purpose of inferring mantle viscosity and thus improving current models of glacial isostatic adjustment gia we estimate the upper and lower mantle viscosity by comparing radial site velocities from a subset of continuous gps measurements with numerical gia predictions our inferences are consistent with previous esti mates obtained using different methods and data sets

new constraints on laurentide postglacial rebound from absolute gravity measurements repeated absolute gravity measurements have been made over a period of several years at six sites along a 3000 km long mid continental north american profile from the coast of hudson bay southward to iowa with the exception of the southern most site the observed rates of change of gravity are significantly higher than rates predicted by current models such as ice 3g and a laterally homogeneous standard earth the observed gravity change rates suggest significant modifications such as a 2 to 3 fold increase in lower mantle viscosity or a 50 increase in laurentide ice sheet thickness west of lake superior

measuring postglacial rebound with gps and absolute gravity we compare vertical rates of deformation derived from continuous global positioning system gps observations and episodic measurements of absolute gravity we concentrate on 4 sites in a region of north america experiencing postglacial rebound the rates of uplift from gravity and gps agree within one standard deviation for all sites the gps vertical deformation rates are significantly more precise than the gravity rates primarily because of the denser temporal spacing provided by continuous gps tracking we conclude that continuous gps observations are more cost efficient and provide more precise estimates of vertical deformation rates than campaign style gravity observations where systematic errors are difficult to quantify

brine mineral reactions in evaporite basins implications for the composition of ancient oceans the chemical evolution of several european mesozoic and tertiary evaporite basins was reconstructed by using mineral associations primary fluid inclusion analyses and numerical simulations of evaporation scenarios the solute proportion recorded in the fluid inclusions can be explained by the evaporation of present day seawater as a major recharge the sulfate depletion in the brines is responsible for the type of potash deposit formed potassium magnessium sulfates or sylvite this sulfate depletion can be due either to dolomitization or to the addition of a cacl 2 rich solution to the basin the sulfate depletion occurred in varying intensity in basins of the same age as well as throughout the evolution of the same basin therefore changes in potash mineralogy and sulfate depletion in fluid inclusions are not conclusive arguments in favor of secular variations in the composition of the ocean as recently proposed by several authors

rates and uncertainties on seismic moment and deformation in eastern canada 1 on the basis of earthquake statistics from the canadian earthquake hazard model we estimate the rates of seismic moment and deformation in seismic zones of eastern canada we use a logic tree approach to derive median values and 66 confidence intervals for models based on earthquake cluster distributions and geological and tectonic structures typical moment rates are low 0 1 1 1017 n m yr 1 equivalent to a magnitude mw 7 earthquake every 350 3500 years in each seismic zone in a few zones such as baffin bay moment rates reach 2 10 1017 n m yr 1 expressed in terms of relative velocity between zone boundaries seismic deformation rates are typically 0 2 0 5 mm yr 1 for a few regions of high seismicity such as baffin bay charlevoix or grand banks the relative velocities reach 1 2 mm yr 1 strain rates are typical of the intraplate environment 10 13 10 10 yr 1 with values locally as high as 10 8 yr 1 these rates give some insight into geodynamic aspects of the northeastern north america plate assuming that the seismic deformation rates represent long term deformation of the lithosphere they provide some constraint to the amplitude and variability of intraplate strain on a shorter timescale seismic strain rates can be compared with postglacial rebound predictions and might help constrain some aspects of these models because they reflect the seismic energy released over the last few hundred years our estimates in combination with geodetic measurements can also help constrain models of earthquake dynamics in eastern north america

gps crustal strain postglacial rebound and seismic hazard in eastern north america the saint lawrence valley example 1 we present global positioning system gps measurements that constrain the amplitude pattern and origin of crustal deformation in the saint lawrence valley quebec one of the most seismically active regions of eastern north america the gps network shows coherent southeastward motion of 0 6 0 2 mm yr 1 relative to north america and uplift of 2 6 0 4 mm yr 1 network average horizontal strain rates are mostly ese wnw shortening at 1 7 1 0 10 9 yr 1 the shortening rate across the charlevoix seismic zone is about twice as big as the regional average these measurements are consistent with both postglacial rebound pgr models and the deformation style indicated by earthquake focal mechanisms although the gps data do not discriminate between various models of crustal deformation they provide important constraints on large earthquake recurrence assuming that the gps strain estimates are representative of seismic moment release they constrain the maximum magnitude of truncated gutenberg richter recurrence statistics in the charlevoix seismic zone to mx 7 8 0 6 one m 7 earthquake per 400 1300 years the remarkable agreement between the gps strain rates seismic catalogue statistics and pgr predictions suggests that in charlevoix most of the pgr driven crustal strain may be released by large m 7 earthquakes in the rest of the saint lawrence valley pgr strain rates are significantly larger than seismic strain rates suggesting either that pgr deformation remains mostly elastic or that large events are more frequent than indicated by small earthquake statistics i e characteristic earthquakes

historical relative gravity observations and the time rate of change of gravity due to postglacial rebound and other tectonic movements in canada 1 a major re adjustment of the primary canadian gravity standardization network cgsn is carried out based on relative gravity measurements spanning over 40 years anticipating that secular variations of gravity dominated primarily by the continuing process of glacial isostatic adjustment could be detected we parameterize the time rate of change of gravity into the observation equation and estimate it directly from a generalised least squares solution time rates of change of gravity from repeated absolute gravity observations as well as absolute gravity values at selected sites are used as weighted constraints the results are presented in form of a map and demonstrate that the primary cgsn with its over 40 year long history can provide us with useful constraints for the evaluation verification and refinement of post glacial rebound models

can deglaciation trigger earthquakes in n america a spherical self gravitating viscoelastic earth model is used to calculate the spatial and temporal evolution of the glacially induced lithospheric stress and fault stability in north america the predicted onset time of a pulse of earthquake activities the mode of failure and the magnitude of instability are investigated for three sites with different distance from the former ice margin it is found that glacial unloading is able to trigger paleo earthquakes within the ice margin near charlevoix 47 5 n 70 1 w and in wabash valley 38 5 n 87 w outside the ice margin however rebound stress decays away from the former ice margin thus glacial unloading is unlikely to have triggered the large m8 earthquakes in new madrid 36 6 n 89 5 w

constraining proposed combinations of ice history and earth rheology using vlbi determined baseline length rates in north america we predict the present day rates of change of the lengths of 19 north american baselines due to the glacial isostatic adjustment process contrary to previously published research we find that the three dimensional motion of each of the sites defining a baseline rather than only the radial motions of these sites needs to be considered to obtain an accurate estimate of the rate of change of the baseline length predictions are generated using a suite of earth models and late pleistocene ice histories these include specific combinations of the two which have been proposed in the literature as satisfying a variety of rebound related geophysical observations from the north american region a number of these published models are shown to predict rates which differ significantly from the vlbi observations

a comparison of vlbi data with the ice 3g glacial rebound model crustal motion predicted by the ice 3g glacial rebound model exhibits a pattern of tangential horizontal divergence away from the centres of uplift which in north america and europe are located around hudson bay and the gulf of bothnia tangential velocities reach peak magnitudes of 1 2 mm yr and must be included when predicting very long baseline interferometry vlbi baseline length change rates due to post glacial rebound out of 18 observed vlbi baselines examined 3 are situated such that their predicted length rates are around their 2 uncertainties or greater it is encouraging that 2 of these baselines exhibit predicted length rates within 2 of the observed rates

ice 3g a new global model of late pleistocene deglaciation based upon geophysical predictions of post glacial relative sea level change a new high resolution global model of late pleistocene deglaciation is inferred on the basis of geophysical predictions of postglacial relative sea level variations in which the ice ocean solid earth interaction is treated in a gravitationally self consistent fashion for the purpose of these analyses the radial viscoelastic structure of the planet is assumed known on the basis of previously published sensitivity tests on solutions of the forward problem only radiocarbon controlled relative sea level histories from sites that were actually ice covered with one or two additions are employed to constrain the model leaving relative sea level rsl data from sites that were not ice covered to be employed to confirm its consistency results for these confirmatory analyses are reported elsewhere here the new deglaciation model referred to as ice 3g is compared to previous models derived by several independent means and tested against a number of additional observations other than sea level histories including geologically controlled retreat isochrones oxygen isotope data from deep sea sedimentary cores and coral terrace elevations the latter two observations strongly constrain the net sea level rise that has occurred since the onset of deglaciation and therefore the mass of ice that melted during the last glacial interglacial transition

postglacial sealevels on a spherical self gravitating viscoelastic earth effects of lateral viscosity variations in the upper mantle on the inference of viscosity contrasts in the lower mantle abstract previous studies of lateral viscosity variations on postglacial rebound often neglect the spherical shape of the earth and the self gravity of the solid earth and oceans in this paper the consistent sealevel equation is solved by the coupled laplace finite element method for a spherical self gravitating incompressible maxwell earth it confirms the importance of self gravity in the oceans on sealevel computation near the ice margin where the data are most sensitive to the existence of lateral variations in lithospheric thickness and asthenospheric viscosity the effects of lateral variations in lower mantle viscosity asthenospheric viscosity and lithospheric thickness are investigated this paper confirms the finding of earlier investigations the combined effect of lateral viscosity variations in the lower mantle with reverse viscosity contrasts in the upper mantle is also investigated for sealevel data near the center of rebound the effect of lateral viscosity contrast in the lower mantle can be masked by the existence of a reverse lateral viscosity contrasts in the upper mantle however this is not the case for sealevel data just outside the ice margin

deglacial land emergence and lateral upper mantle heterogeneity in the svalbard archipelago ii extended results for high resolution load models summary in paper i breuer wolf 1995 a preliminary interpretation of the postglacial land emergence observed at a restricted set of six locations in the svalbard archipelago was given the study was based on a simple model of the barents sea ice sheet and suggested increases in lithosphere thickness and asthenosphere viscosity with increasing distance from the continental margin in the present paper the newly developed high resolution load model barents 2 and land uplift observations from an extended set of 25 locations are used to study further the possibility of resolving lateral heterogeneity in the upper mantle below the northern barents sea a comparison of the calculated and observed uplift values shows that the lithosphere thickness is not well resolved by the observations although values above 110 km are most common for this parameter in contrast to this there are indications of a lateral variation of asthenosphere viscosity whereas values in the range 10 8 1020 pa s are inferred for locations close to the continental margin 1020 102 pa s are suggested further away from the margin a study of the sensitivity of the values found for lithosphere thickness and asthenosphere viscosity to modifications of load model barents 2 shows that such modifications can be largely accommodated by appropriate changes in lithosphere thickness whereas the suggested lateral variation of asthenosphere viscosity is essentially unaffected an estimate of the influence of the fennoscandian ice sheet leads to the conclusion that its neglect results in an underestimation of the thickness of the barents sea ice sheet by about 10 per cent

a space geodetic target for mantle viscosity discrimination horizontal motions induced by glacial isostatic adjustment a model of mantle viscosity recently obtained on the basis of the inversion of glacial isostatic adjustment data is herein shown to predict a highly characteristic signature in tangential motion due to this cause

glacial rebound of the british isles iii constraints on mantle viscosity summary observations of sea level change since the time of the last glacial maximum provide important constraints on the response of the earth to changes in surface loading on time scales of 103 104 years this response is conveniently described by an effective elastic lithospheric thickness and effective viscosities for one or more mantle layers considerable trade off between the parameters describing these layers can occur and different combinations can give rise to comparable predictions of sea level change in particular the trade off between lithospheric thickness and upper mantle viscosity can be important and for any reasonable value for the lithospheric thickness a corresponding mantle viscosity structure can be found that gives a plausible comparison of sealevel predictions with observations in particular thin lithosphere models will lead to low estimates for the upper mantle viscosity while thick lithosphere models lead to high viscosity values however either solution may represent only a local minimum in the model parameter space and may not correspond to the optimum solution it becomes important therefore that in the inversion of observational data a comprehensive search is conducted throughout the entire model parameter space to ensure that the solution identified does indeed correspond to the optimum solution the sea level data for the british isles lend themselves well to such an inversion because of the relatively high quality of the data the good geographic distribution of the data relative to the former ice sheet and reasonable observational constraints on the dimensions of the former ice sheet and on its retreat furthermore because of the contribution to the sea level signal from the distant ice sheets as well as from the melt water load the observational data base for the region also has some resolving power for the viscosity of the deeper mantle the parameter space explored is defined by up to five mantle layers the lithosphere of effective elastic thickness d and a series of upper mantle layers i 2 4 extending down to depths of 200 400 and 670 km respectively each of viscosity qi and a lower mantle layer of viscosity qlm extending down to the coremantle boundary the range of parameters explored is 30 d i 120 km 3 x loi9 iqi

near field hydro isostasy the implementation of a revised sea level equation summary we describe how the existing sea level equation incorrectly predicts the change in sea level and thus the ocean load in ice covered subgeoidal geographic regions during periods of deglaciation we go on to present a new sea level equation that overcomes this problem and we describe how this equation can be solved in a gravitationally self consistent manner by employing a well known spectral technique application of the new theory to predict relative sea level rsl histories and present day 3 d solid surface deformation rates in northeastern canada based on a single earth model characterized by a lithospheric thickness of 100 km and upper and lower mantle viscosities of 5 1020 and 5 1021 pa s respectively demonstrates that a significant error is introduced when the original theory is employed to predict the oceanic component of the surface load predictions of rsl curves show a discrepancy of 40 per cent at sites where data have been obtained and employed to constrain models of earth viscosity structure and ice sheet histories this error will significantly bias estimates of mantle viscosity structure and ice thicknesses that are based on the original theory in addition predictions of 3 d deformation rates differ by up to 25 per cent in some regions and so future applications that employ these data to constrain models of the glacial isostatic adjustment process should adopt the improved sea level theory in contrast estimates of inverse decay times from the predicted rsl curves are insensitive to within the observational error to the improvement in the surface load introduced by the new theory thus viscosity structure inferences based on this parametrization and the original sea level equation are unaffected by the error in the ocean load finally the new theory predicts a eustatic i e globally uniform rise in sea level over the postglacial period that is 11 m lower than that determined via the original theory therefore estimates of the global ice budget at the last glacial maximum based on far field rsl data and the original sea level theory will be too small by 10 per cent

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

global glacial isostasy and the surface of the ice age earth the ice 5g vm2 model and grace abstract the 100 kyr quasiperiodic variation of continental ice cover which has been a persistent feature of climate system evolution throughout the most recent 900 kyr of earth history has occurred as a consequence of changes in the seasonal insolation regime forced by the influence of gravitational n body effects in the solar system on the geometry of earth s orbit around the sun the impacts of the changing surface ice load upon both earth s shape and gravitational field as well as upon sea level history have come to be measurable using a variety of geological and geophysical techniques these observations are invertible to obtain useful information on both the internal viscoelastic structure of the solid earth and on the detailed spatiotemporal characteristics of glaciation history this review focuses upon the most recent advances that have been achieved in each of these areas advances that have proven to be central to the construction of the refined model of the global process of glacial isos