a multilayer model of time dependent deformation following an earthquake on a strike slip fault a multilayer half space model of the earth is used in finite element calculations of time dependent deformation and stress following an earthquake on an infinitely long strike slip fault the model involves shear properties of an elastic upper lithosphere a standard viscoelastic linear solid lower lithosphere a maxwell viscoelastic asthenosphere and an elastic mesosphere time dependent displacements strains and stresses are computed both at the surface of the earth and at depth the analysis includes both systematic variations of fault and layer depths and comparisons with simpler elastic lithosphere over viscoelastic asthenosphere calculations for conditions which may be appropriate for the earth the creep of both the lower lithosphere and the asthenosphere can contribute to the postseismic deformation the magnitude of the deformation is enhanced by a short distance between the bottom of the fault slip zone and the top of the creep layer but is less sensitive to the thickness of the creeping layer furthermore postseismic restressing is increased as the lower lithosphere becomes more viscoelastic but the tendency for the width of the restressed zone to grow with time is retarded

a viscoelastic coupling model for the cyclic deformation due to periodically repeated earthquakes at subduction zones vertical displacements due to periodic reverse faulting events in an elastic plate overlying a viscoelastic maxwell half space are obtained and compared with the observed deformation cycle coseismic strain release postseismic transients interseismic strain accumulation from japan the viscoelastic effects including the influence of buoyant restoring forces are obtained using the method developed by rundle and plate convergence and strain accumulation are incorporated following the procedure suggested by savage the resulting deformation cycle is compared with that of an analogous elastic half space dislocation model in which postearthquake effects are due to transient aseismic slip below the coseismic fault cyclic deformation is similar but not identical for the two models and observations from southwest japan suggest the superiority of the viscoelastic coupling model in particular inclusion of the effects of steady state flow in the asthenosphere overcomes a defect of the elastic half space model and results in agreement with the observed interseismic movement pattern several aspects of the postseismic deformation its landward migration and its transition to the interseismic phase of the cycle are explained as well but the short duration of near trench transients relative to those observed farther inland is not matched the success of a buried slip model in explaining early postseismic near trench movements and asthenospheric flow in accounting for cumulative postearthquake transient motions suggests the existence of a transition zone between lithosphere and asthenosphere whose behavior is brittle elastic in the short term and ductile for longer term deformation and such a modification may reconcile remaining discordant observations however reasonable variations in coupling model parameters cannot account for observed differences in the deformation cycle in other parts of japan and these regional differences remain unexplained

tests of ocean tide models by analysis of satellite to satellite range measurements an update seven years of grace intersatellite range rate measurements are used to test the new ocean tide model fes2014 and to compare against similar results obtained with earlier models these qualitative assessments show that fes2014 represents a marked improvement in accuracy over its earlier incarnation fes2012 with especially notable improvements in the arctic ocean for constituents k1 and s2 degradation appears to have occurred in two anomalous regions the ross sea for the o1 constituent and the weddell sea for m2

recent glacier mass changes in the gulf of alaska region from grace mascon solutions the mass changes of the gulf of alaska goa glaciers are computed from the gravity recovery and climate experiment grace inter satellite range rate data for the period april 2003 september 2007 through the application of unique processing techniques and a surface mass concentration mascon parameterization the mass variations in the goa glacier regions have been estimated at high temporal 10 day and spatial 2 2 arc degrees resolution the mascon solutions are directly estimated from a reduction of the grace k band inter satellite range rate data and unlike previous grace solutions for the goa glaciers do not exhibit contamination by leakage from mass change occurring outside the region of interest the mascon solutions reveal considerable temporal and spatial variation within the goa glacier region with the largest negative mass balances observed in the st elias mountains including the yakutat and glacier bay regions the most rapid losses occurred during the 2004 melt season due to record temperatures in alaska during that year the total mass balance of the goa glacier region was 84 5 gt a 1 contributing 0 23 0 01 mm a 1 to global sea level rise from april 2003 through march 2007 highlighting the large seasonal and interannual variability of the goa glaciers the rate determined over the period april 2003 march 2006 is 102 5 gt a 1 which includes the anomalously high temperatures of 2004 and does not include the large 2007 winter balance year snowfall the mascon solutions agree well with regional patterns of glacier mass loss determined from aircraft altimetry and in situ measurements

accuracy assessment of global barotropic ocean tide models the accuracy of state of the art global barotropic tide models is assessed using bottom pressure data coastal tide gauges satellite altimetry various geodetic data on antarctic ice shelves and independent tracked satellite orbit perturbations tide models under review include empirical purely hydrodynamic forward and assimilative dynamical i e constrained by observations ten dominant tidal constituents in the diurnal semidiurnal and quarter diurnal bands are considered since the last major model comparison project in 1997 models have improved markedly especially in shallow water regions and also in the deep ocean the root sum square differences between tide observations and the best models for eight major constituents are approximately 0 9 5 0 and 6 5 cm for pelagic shelf and coastal conditions respectively large intermodel discrepancies occur in high latitudes but testing in those regions is impeded by the paucity of high quality in situ tide records long wavelength components of models tested by analyzing satellite laser ranging measurements suggest that several models are comparably accurate for use in precise orbit determination but analyses of grace intersatellite ranging data show that all models are still imperfect on basin and subbasin scales especially near antarctica for the m2 constituent errors in purely hydrodynamic models are now almost comparable to the 1980 era schwiderski empirical solution indicating marked advancement in dynamical modeling assessing model accuracy using tidal currents remains problematic owing to uncertainties in in situ current meter estimates and the inability to isolate the barotropic mode velocity tests against both acoustic tomography and current meters do confirm that assimilative models perform better than purely hydrodynamic models

tide model errors and grace gravimetry towards a more realistic assessment summary the manner in which errors in tide models affect monthly gravity solutions from grace satellite data is re examined we perform a complete simulation of grace gravity estimation including allowance for accelerometer calibrations and satellite state vector adjustment errors in monthly geoid estimates are for most regions of a order of 0 5 mm or roughly 1 cm of equivalent water height when smoothed over radii of 600 km in polar regions where ocean tide models are suspect errors can grow significantly larger over 2 mm in geoid height although over very localized regions errors from diurnal tides tend to cancel but they are not completely eliminated inducing geoid errors of the order of 0 3 mm the currently accepted grace total error budget is roughly an order of magnitude larger than the component arising from tide modelling errors

seawater density variations in the north atlantic and the atlantic meridional overturning circulation seawater property changes in the north atlantic ocean affect the atlantic meridional overturning circulation amoc which transports warm water northward from the upper ocean and contributes to the temperate climate of europe as well as influences climate globally previous observational studies have focused on salinity and freshwater variability in the sinking region of the north atlantic since it is believed that a freshening north atlantic basin can slow down or halt the flow of the amoc here we use available data to show the importance of how density patterns over the upper ocean of the north atlantic affect the strength of the amoc for the long term trend the upper ocean of the subpolar north atlantic is becoming cooler and fresher whereas the subtropical north atlantic is becoming warmer and saltier on a multidecadal timescale the upper ocean of the north atlantic has generally been warmer and saltier since 1995 the heat and salt content in the subpolar north atlantic lags that in the subtropical north atlantic by about 8 9 years suggesting a lower latitude origin for the temperature and salinity anomalies because of the opposite effects of temperature and salinity on density for both long term trend and multidecadal timescales these variations do not result in a density reduction in the subpolar north atlantic for slowing down the amoc indeed the variations in the meridional density gradient between the subpolar and subtropical north atlantic ocean suggest that the amoc has become stronger over the past five decades these observed results are supported by and consistent with some oceanic reanalysis products

a mascon approach to assess ice sheet and glacier mass balances and their uncertainties from grace data the purpose of this paper is to assess the mass changes of the greenland ice sheet gris ice sheets over antarctica and land glaciers and ice caps with a global mascon method that yields monthly mass variations at 10 242 mascons input for this method are level 2 data from the gravity recovery and climate experiment grace system collected between february 2003 and june 2013 to which a number of corrections are made with glacial isostatic adjustment gia corrections from an ensemble of models based on different ice histories and rheologic earth model parameters we find for greenland a mass loss of 278 19 gt yr whereas the mass balances for the gris appear to be less sensitive to gia modeling uncertainties this is not the case with the mass balance of antarctica ice history models for antarctica were recently improved and updated historic ice height data sets and gps time series have been used to generate new gia models we investigated the effect of two new gia models for antarctica and found 92 26 gt yr which is half of what is obtained with ice 5g based gia models where the largest gia model differences occur on east antarctica the mass balance of land glaciers and ice caps currently stands at 162 10 gt yr with the help of new gia models for antarctica we assess the mass contribution to the mean sea level at 1 47 0 09 mm yr or 532 34gt yr which is roughly half of the global sea level rise signal obtained from tide gauges and satellite altimetry

determination and localized analysis of intersatellite line of sight gravity difference results from the grail primary mission 1 the line of sight los gravity difference between two coorbiting spacecrafts is determined in terms of intersatellite range acceleration measurements available from the gravity recovery and interior laboratory grail the precise orbit data are crucial for retrieving gravity difference from range acceleration and aligning the los data particularly in altitude a relative orbit error of a few centimeters in position and a few tens m s in velocity is commensurate with the grail ranging instrument noise at a few gal in los gravity difference the power spectrum as well as the topography correlation and admittance is quantified by upward continuing the topographic potential forward modeling the los gravity along the spacecraft trajectory i e bouguer correction and comparing with the grail los observations based on the data analysis from the primary grail mission i found that the los gravity difference observation produced near unity correlation with topography potential out to degree 550 higher than the global estimate over the areas covered by the low altitude orbit 20 km the crustal density was estimated to be 2500 2600 kg m3 with regional variations of about 10 by minimizing the bouguer coherence of the grail data at the degree band 150 300 systematic decrease in the density estimates by 3 4 or 100 kg m3 was observed at shorter wavelengths degree band 300 500 it implies the inadequacy of a uniform density model across the entire lithosphere and suggests radial stratification of the bulk density or porosity due to spatially localized characteristic the los gravity difference data are well suited to regional analysis at the highest possible resolution

taiwan orogeny thin skinned or lithospheric collision abstract the taiwan orogeny is young and presently very active it provides an excellent environment for studying ongoing orogenic processes especially since the region is monitored intensively with dense seismological and geodetic networks and new studies aiming at deciphering shallow and deep structures in and around taiwan have been recently conducted or are being planned the available data can be used continually to test critically hypotheses of the taiwan orogeny hypotheses dealing with the mechanics of mountain building are basic to the understanding of taiwan orogeny and are particularly amenable to testing the widely cited thin skinned tectonics hypothesis was formulated to explain mainly the geologic and relatively shallow

rapid afterslip following the 1999 chi chi taiwan earthquake 1 postseismic displacements of as much as 14 cm were recorded by gps measurements in the 3 months following the mw 7 6 1999 chi chi taiwan earthquake data from 35 continuous and 90 campaign surveyed stations which show continued east over west thrusting are analyzed to estimate the postseismic slip distribution and fault geometry assuming the shallow fault dips 24 e as determined by numerous studies of the mainshock we invert for the deeper fault structure our results show that the fault dip shallows with depth below the hypocenter merging into a nearly horizontal decollement at a depth of 8 12 km the afterslip distribution shows a maximum slip of 25 cm in the hypocentral region at 7 12 km depth as well as significant slip on the lower decollement afterslip is notably absent in the region of maximum coseismic slip consistent with the afterslip being driven by the mainshock stress change

viscoelastic afterslip concurrence a possible mechanism in the early post seismic deformation of the mw 7 6 1999 chi chi taiwan earthquake summary observed coseismic data as well as 97 days of post seismic gps data for the chi chi earthquake are used as constraints in the modelling of crustal evolution using the 3 d finite element method first the coseismic gps data are used to justify the use of the elastic earth model and the source rupture model subsequently the most likely rheological model is determined by analysing several modelled time dependent displacements for various viscosity structures the range of viscosities of the lower crust in central taiwan is determined in advance from laboratory measurements and the long term strain rate the estimated viscosity of 5 0 10 17 p as seems to be very low and a relaxation time of 116 days seems very short but the latter approximates the gps measurement of 86 days since earlier studies have indicated that both the viscoelastic response model and the afterslip model may affect post seismic deformation we compare theoretical surface displacements for each of the two models that we evaluate the results reveal that there is little doubt that while neither of these models alone is able to predict the gps measurements well in a 97 day period the combination of the two models improves the predictions considerably we conclude that the afterslip mainly dominated chi chi post seismic deformation in the rupture area while the viscoelastic model did so elsewhere

crustal earthquake instability in relation to the depth variation of frictional slip properties recent stability studies using constitutive relations of the type found by dieterich ruina and others to describe frictional slip of rocks in the laboratory have provided a new explanation of the depth cutoff of shallow crustal earthquakes the class of friction laws discussed has the property that the sliding stress depends on normal stress temperature slip rate and slip history for sliding at a fixed slip rate v and fixed environment e g normal stress temperature etc the shear strength evolves toward a steady state value ss v stability analysis show that for d ss v dv 0 velocity strengthening implies stable steady state sliding at least for a broad class of constitutive laws more fully described in the paper experiments by dieterich and by tullis and weeks on westerly granite with mature sliding surfaces indicate that d ss v dv is negative at room temperature whereas higher temperature experiments by stesky show that d ss v dv becomes positive above approximately 300 c therefore in the case of the earth where temperature increases with depth the above observations seem to suggest that the depth cutoff of crustal earthquake activity can be understood in terms of the variation of the frictional response with depth from a regime with d ss v dv 0 this is not inconsistent with but rather refines the suggestion by sibson and others that the depth cutoff is due to a transition from brittle friction to ductile flow further our results show definitively that the shallow depth confinement of seismicity is compatible with a model in which deformation is localized to a fault zone extending well below the seismogenic depth the depth confinement does not require a model showing transition to a zone of broadly distributed creep flow beneath the seismogenic zone following mavko a two dimensional quasi static strike slip fault model is analyzed but using different numerical procedures and a depth variation of frictional properties based on the laboratory data mentioned above and the lachenbruch sass depth variation of temperature for the san andreas fault the resulting predictions of such features as the confinement of crustal earthquakes to shallow depths the development of locked patches the recurrence time for the seismic cycle the seismic stress drop and displacement etc are generally in agreement with the observed characteristics of large scale strike slip earthquakes along the san andreas fault calculations based on the laboratory data predict for example that stick slip nucleates around 5 7 km that large seismic motion occurs around the nucleation depth and above but diminishes gradually to zero at 13 15 km depths that rapid postseismic creep occurs over another 3 4 km depth and that at greater depths steady slip consistent with the average plate velocity is only modestly perturbed by the earthquakes occurring above the most uncertain parameter is the slip weakening distance l for evolution of fault surface state we illustrate how features of the predicted earthquake cycles vary with l over the range for which calculations are feasible

steric sea level change in the northern seas abstract ocean temperature and salinity data over the period 1950 2000 in the northern seas defined here as the north atlantic ocean north of 50 n north pacific ocean north of 40 n and arctic oceans are combined to diagnose the steric i e density contribution to sea level variation the individual contributions to steric height from temperature thermosteric height and salinity halosteric height are also analyzed it is found that during 1950 2000 steric height rose over the study s domain mostly as a result of halosteric increases i e freshening over a shorter time period late 1960s to early 1990s during which climate indices changed dramatically steric height gradients near the nordic seas minimum were reduced by 18 32 it is speculated that this may be associated with a local slowing of both the meridional overturning circulation and the southward flow through fram strait however steric height increases in the north pacific ocean during this time imply a possible accelerati

assimilation of grace tide solutions into a numerical hydrodynamic inverse model 1 we assimilate localized mass anomalies inferred from grace ranging measurements into a hydrodynamic model to improve tidal solutions around antarctica for the m2 s2 and o1 constituents the variational approach used accounts for the spatial averaging of tidal elevations implicit in the mass anomaly parametrization used for the grace tidal analysis as well as spatial correlation of errors in the resulting estimates the inverse solution shows better agreement with independent station tide measurements around antarctica and it reduces cross over residuals for icesat laser altimeter data over the filchner ronne and ross ice shelves demonstrating that grace data can provide useful constraints for improving hydrodynamic tidal models at high latitudes

antarctic ice mass balance estimates from grace tidal aliasing effects 1 geophysical interpretation of grace gravity fields has provided estimates of antarctic ice mass change such analyses rely on proper consideration of ocean tidal effects through the models csr4 and fes2004 in general mis modeling of tidal constituents with aliasing period less than 30 day will not have significant impact on ice mass change however for constituents such as k1 k2 and s2 the aliasing period is sufficiently large to potentially compromise long term variability studies here we quantify tidal aliasing over antarctica by simulating grace signatures due to differences between csr4 and fes2004 and the best available circum antarctic model tpxo6 2 the s2 simulations are in close agreement with the observed s2 signal from grace simulations of ice mass change show that over 2002 2006 long term k1 and k2 aliasing is equivalent to a rate error of 4 5 1 3 km3 a of ice with csr4 but only 0 2 0 2 km3 a with fes2004 after spatial averaging and destriping k1 plus k2 mis modeling in csr4 fes2004 introduce point wise errors up to 5 2 mm a in equivalent water height over a 3 5 year period with observed mass change equivalent to less than 30 mm a of water height over much of antarctica the simulations show tidal aliasing uncertainty at the 2 3 mm a level for august 2002 january 2006 or 10 of the signal with grace release 04 the revised estimate april 2002 january 2006 of published ice volume decrease is 164 80 km3 a of ice although this value depends very much on the gia model and grace analysis approach

ocean tidal solutions in antarctica from grace inter satellite tracking data 1 long wavelength components of the oceanic tides surrounding antarctica are estimated directly from three years of grace satellite to satellite ranging measurements an inversion is performed for the major constituents m2 o1 and s2 with k1 excluded because of inadequate phase sampling the tides are parameterized as localized average mass anomalies over areas approximately 3002 km2 other parameters including satellite state adjustments are estimated simultaneously with the tides qualitative comparison of our solutions with in situ tide measurements shows agreement in spatial pattern clearly indicating regions where our adopted prior model is inadequate to exploit these solutions follow on work must assimilate these long wavelength components into a high resolution numerical tidal model

chemical characterization of ambient aerosol collected during the southwest monsoon and intermonsoon seasons over the arabian sea labile fe ii and other trace metals atmospheric deposition of iron fe to certain regions of the oceans is an important nutrient source of fe to the biota and the ability of the biota to uptake fe is dependent on the speciation of the fe therefore understanding the speciation of fe in the atmosphere is critical to understanding the role of fe as a nutrient source in surface ocean waters labile ferrous iron fe ii concentrations as well as total concentrations for fe and other important trace metals cations and anions were determined over the arabian sea for two nonconsecutive months during 1995 ambient aerosol samples were collected during the indian ocean intermonsoon and southwest monsoon seasons over the arabian sea sampling took place aboard the german research vessel meteor in the months of may leg m32 3 intermonsoon and july august leg m32 5 southwest monsoon both cruise tracks followed the 65th east meridian traveling for 30 days each from north to south during leg m32 3 and from south to north during leg m32 5 a high volume dichotomous virtual impactor with an aerodynamic cutoff size of 3 m was used to collect the fine and coarse aerosol fractions for metal analysis a low volume collector was used to collect aerosol samples for anion and cation analysis the analysis for labile fe ii was done immediately after sample collection to minimize any possible fe redox reactions which might occur during sample storage the analytical procedure involved filter extraction in a formate formic acid buffered solution at ph 4 2 followed by colorimetric quantification of soluble fe ii metals anions and cations were analyzed after the cruise total atmospheric aqueous labile fe ii concentrations during the intermonsoon were between 4 75 and 80 was present in the fine fraction 3 0 m during the southwest monsoon atmospheric aqueous labile fe ii concentrations were consistently below the detection limit 0 34 to 0 089 ng m 3 depending on the volume of air sampled air mass back trajectories 5 day three dimensional showed that air masses sampled during the southwest monsoon had advected over the open indian ocean while air masses sampled during the intermonsoon had advected over northeast africa the saudi arabian peninsula and southern asia these calculations were consistent with the results of the statistical analysis performed on the data set which showed that the variance due to crustal species during the intermonsoon samples was greater than the variance due to crustal species during the southwest monsoon the factor scores for the crustal components were also greater when the back trajectories had advected over the nearby continental masses principal component analysis was also performed with the intermonsoon samples where aqueous labile fe ii was above the detection limit aqueous labile fe ii did not correlate well with other species indicating possible atmospheric processing of the iron during advection

correcting grace gravity fields for ocean tide effects 1 the grace mission will be launch in early 2002 and will map the earth s gravity fields and its variations with unprecedented accuracy during its 5 year lifetime unless ocean tide signals and their load upon the solid earth are removed from the grace data their long period aliases obscure more subtle climate signals which grace aims at the difference between two existing ocean tide models can be used as an estimate of current tidal model error for the m2 s2 k1 and o1 constituents when compared with the expected accuracy of the grace system both expressed as spherical harmonic degree variances we find that the current ocean tide models are not accurate enough to correct grace data at harmonic degrees lower that 35 the accumulated tidal errors may affect the grace data up to harmonic degree 56 furthermore the atmospheric radiation tides may cause significant errors in the ocean tide model if altimetry corrected for inverted barometer effects was used in its derivation to study the temporal characteristics of the ocean tidal constituents when sampled by grace approximate alias frequencies were derived assuming a sampling of half a sidereal day those results show that the ocean tide errors will not cancel in the grace monthly averaged temporal gravity fields the s2 and the k2 terms have alias frequencies much longer than 30 days so they remain almost unreduced in the monthly averages

time dependent changes in failure stress following thrust earthquakes two dimensional 2 d viscoelastic finite element models were used to calculate the time dependent changes in coulomb failure stresses following thrust earthquakes due to respective effects of relaxation of viscous lower crust or upper mantle and postseismic creep on the main fault or its downdip extension results suggest that thrust earthquakes cause a coseismic increase in coulomb stress along antithetic lobes normal to the slip plane following a quake creep processes that reduce stresses in a ductile lower crust or upper mantle are calculated to cause a transfer of stress to the upper crust under certain conditions transfer of stress may lead to a further buildup of high coulomb stress along the base of the upper crust potentially shortening the time to failure of other faults in the region the conditions under which an antithetic lobe of high coulomb stress are favored to expand at the base of the upper crust postseismically within a few decades include the following the lower crust or upper mantle has an effective viscosity not greater than 1019 pa s the thrust fault has a moderate dip angle 40 50 the brittle ductile transition is deep enough to provide a corridor at the base of the upper crust for expansion and the crust has a low apparent coefficient of friction 0 2 postseismic increases in coulomb stress within the upper crust may also be caused by aseismic creep on the fault stress changes due to this mechanism are maximized with a high apparent coefficient of friction analysis of experimentally determined non newtonian flow laws suggests that wet granitic quartz and feldspar aggregates may have a viscosity of the order of 1019 pa s the calculated rate of stress transfer from a viscous lower crust or upper mantle to the upper crust becomes faster with increasing values of the power law exponent and the presence of a regional compressive strain rate results of this 2 d analysis suggest a potentially important role of viscous flow in controlling time dependent postseismic stress changes that warrant further investigation using 3 d viscoelastic analysis

the gravity recovery and climate experiment mission overview and early results 1 the grace mission is designed to track changes in the earth s gravity field for a period of five years launched in march 2002 the two grace satellites have collected nearly two years of data a span of data available during the commissioning phase was used to obtain initial gravity models the gravity models developed with this data are more than an order of magnitude better at the long and mid wavelengths than previous models the error estimates indicate a 2 cm accuracy uniformly over the land and ocean regions a consequence of the highly accurate global and homogenous nature of the grace data these early results are a strong affirmation of the grace mission concept

two dimensional crustal structures of taiwan from gravity data to delineate the tectonic character of taiwan an island wide gravity survey of taiwan was conducted between 1980 and 1987 the bouguer anomaly map shows that in general isogals trend nne in consonance with the overall structural trend of the island with seismic and other geophysical data as constraints the subsurface density structures were modeled along three profiles across the major structural trends the gravity data are consistent with average continental moho depths of 26 km in the coastal plain and the western foothills 28 km underneath the coastal range in eastern taiwan and 33 km under the central range a lack of significant correlation of the bouguer anomalies with the topography implies dynamic rather than isostatic support of topography in the taiwan region

mobility of continental mantle evidence from postseismic geodetic observations following the 1992 landers earthquake the crust around the rupture zone of the 1992 landers earthquake has continued to deform in the years following the earthquake at rates 3 times greater than pre earthquake rates we use a combination of global positioning system gps and synthetic aperture radar insar data collected during a 3 year epoch following the earthquake in order to investigate postseismic mechanisms responsible for the high transient velocities in order to maximize the potential signal from viscoelastic relaxation we evaluate and model postseismic relaxation following the first few months of documented accelerated deformation the combination of gps and insar data allows us to establish viscoelastic relaxation of the lower crust and upper mantle as the dominant postseismic process and to discriminate among possible viscoelastic models the data particularly require the presence of a highly ductile uppermost mantle beneath the central mojave domain with temperature between the wet and dry basalt solidus this is consistent with independent seismic and geochemical inferences of a regionally warm uppermost mantle further consideration of seismic velocity variations in conjunction with faulting patterns within the mojave desert suggests that the primary faulting characteristics of the mojave desert namely the pervasive late cenozoic deformation within the eastern california shear zone versus the near absence of faults in the western mojave domain are controlled by the rheology of the uppermost mantle

estimating geocenter variations from a combination of grace and ocean model output 1 in this study we estimate a time series of geocenter anomalies from a combination of data from the gravityrecoveryandclimateexperiment grace satellitemissionandthe outputfromoceanmodels amatrixequationisderivedrelating totalgeocentervariations to the grace coefficients of degrees two and higher and to the oceanic component of the degree one coefficients we estimate the oceanic component from two state of the art ocean models results are compared to independent estimates of geocenter derived from other satellite data such as satellite laser ranging and gps finally we compute degree one coefficients that are consistent with the processing applied to the grace level 2 gravity field coefficients the estimated degree one coefficients can be used to improve estimates of mass variability from grace which alone cannot provide them directly

quality assessment of a satellite altimetry data product in the nordic barents and kara seas 1 satellite altimetry provides high quality sea surface height data that have been successfully used to study the variability of sea level and surface geostrophic circulation at different spatial and temporal scales however the high latitude regions have traditionally been avoided due to the persistent sea ice cover most of the validation studies have focused on the areas below the polar circles in this paper we examine the quality and performance of a gridded satellite altimetry product in the nordic barents and kara seas the altimetric sea level in coastal areas is validated using available tide gauge records we show that at most locations in the nordic seas the altimetry and tide gauge measurements are in a good agreement in terms of the root mean square differences and the amplitudes and phases of the seasonal cycle the agreement deteriorates in the shallow areas of the barents and kara seas subject to the seasonal presence of sea ice and where the altimetry data are contaminated by the residual aliasing of unresolved high frequency signals the comparison of linear trends at the locations of tide gauges reveals discrepancies that need to be taken into account when interpreting long term changes of sea level in the region away from the coast the altimetry data are compared to drifter trajectories corrected for ekman currents the drifter trajectories are found consistent with the mesoscale variability of the altimetric sea level this study provides the first comprehensive validation of a gridded satellite altimetry data product in the high latitude seas

qualitative comparisons of global ocean tide models by analysis of intersatellite ranging data 1 four global ocean tide models are compared in terms of their contribution to gravity recovery and climate experiment grace satellite to satellite tracking residuals the residuals are computed relative to a comprehensive model of earth s time varying gravity including allowance for mass motions in the atmosphere ocean terrestrial hydrology and mantle in addition to tides for each analyzed tide model 4 years of grace range rate data are processed range and range acceleration residuals are tidally analyzed by geographic location all four global tide models are shown to be error prone in various ways leaving tidally coherent residuals especially in polar regions but also in some lower latitude regions considerable power in the solar semidiurnal s2 tide in low latitudes suggests errors in our adopted model of atmospheric tides which is based on 3 hourly european centre for medium range weather forecasts operational analyses anomalies in the 2 tidal constituent over some shallow seas suggest the presence of unmodeled nonlinear compound tides in this case 2ms2 similarly anomalies in the nonlinear m4 tide are seen if this constituent is omitted from the models errors in assumed seawater density may be contributing to some residuals

arctic ocean tides from grace satellite accelerations 1 models are routinely used to remove the effects of global ocean tides from grace data during processing to reduce temporal aliasing into monthly grace solutions these models have typically been derived using data from satellite altimeters such as topex poseidon therefore the arctic ocean components of tide models are not constrained by altimetry data potentially resulting in errors that are likely to alias into monthly grace gravity fields at all latitudes seven years of grace inter satellite accelerations are inverted to solve for corrections to the amplitude and phase of major solar and lunar ocean tides at latitudes north of 50 n using a mascon approach the tide model originally applied to our data was fes2004 truncated to maximum degree lmax 90 simulations are performed to verify that our inversion algorithm works as designed uncertainty estimates are derived from tidal solutions on land and by subtracting two independent solutions that each use 3 5 years of data features above the noise floor in the m2 k1 s2 and o1 solutions likely represent errors in fes2004 errors due to truncating the spherical harmonic expansion of fes2004 are too small and errors in the land mask model needed to transform sea surface heights into mass only affect coastal areas and do not produce similar relative amplitudes for any examined tides in the oceans north of 50 n these residuals tend to reduce the fes2004 amplitudes for m2 k1 s2 and o1 reductions in the variance of accelerations not used in our inversion suggest that our results can be used to improve grace processing

grace observations of m2 and s2 ocean tides underneath the filchner ronne and larsen ice shelves antarctica 1 by processing the grace satellite to satellite tracking data and estimating the temporal gravity fields regionally over the southern polar region with a 5 day interval we observed m2 and s2 ocean tides underneath the filchner ronne and larsen ice shelves antarctica based on the predicted aliased periods we extracted the m2 and s2 signals from the time series of 5 daily mean grace regional gravity estimates the grace observations agreed well with the predicted tides from the fes2004 and cats02 01 models after smoothing the models to the commensurate spatial resolution as grace overall the grace and the models agreed within 10 20 difference in the tidal amplitude and 20 in phase for both m2 and s2 our results suggest that grace provides valuable observations of ocean tides with a spatial resolution as short as 300 km over the remote area lacking of quality observations such as the antarctica ice shelves

ocean tides in the weddell sea new observations on the filchner ronne and larsen c ice shelves and model validation 1 ocean tides under the large weddell sea ice shelves are among the least well observed on earth here we present new spatially extensive observations of the vertical tidal motion of the filchner ronne and larsen c ice shelves using global positioning system gps data spanning a few weeks to years we pay particular attention to the major tidal constituents m2 s2 o1 k1 as well as important grace aliasing periods k2 and s1 we compare the estimated constituents with recent global and regional tide models and find that no single model is the most accurate across all constituents or ice shelves the root sum square errors are 7 8 cm cats2008a and tpxo7 2 and 11 12 cm got4 7 and fes2004 with the energetic m2 rmse 4 8 cm and s2 4 5 cm generally dominating these statistics the fes2004 k1 is particularly inaccurate near the larsen c ice shelf with errors approaching 20 cm meaning that grace release 4 estimates of mass change in the northern antarctic peninsula will be biased we find tidal energy at 3 4 5 6 and weakly at 7 cycles per day at all of our sites the largest amplitudes within these bands are at m4 mo3 and sp3 and approach 30 mm although significant spatial variations exist we show that they generally do not appear to originate in areas of reduced water column in ice shelf grounding zones comparing model estimates with our m4 ms4 and mn4 values shows that models do not accurately represent these terms