a three dimensional surface velocity field for the mississippi delta implications for coastal restoration and flood potential accurate estimates of the current rate of subsidence in the mississippi delta southern united states provide a context for planning of wetland restoration and predictions of storm surge flooding we present a comprehensive three dimensional surface velocity field for the mississippi delta based on a network of 36 high precision continuous gps stations we show that while the majority of the delta is relatively stable the southern portion continues to experience high rates of subsidence 5 6 mm yr 1 our data are consistent with long term tide gauge records at grand isle louisiana and several stations in florida the current rate of relative sea level rise combined effect of land subsidence and sea level rise along parts of the coastal delta is 8 9 mm yr 1 most tide gauge stations have recorded sea level rise acceleration after a d 1970 these data have implications for land reclamation and wetland restoration in the region parts of the delta may not be viable in the long term

stress field constraints on intraplate seismicity in eastern north america focal mechanisms of 32 north american midplate earthquakes mo 3 8 6 5 were evaluated to determine if slip is compatible with a broad scale regional stress field derived from plate driving forces and if so under what conditions stress regime pore pressure and frictional coefficient using independent information on in situ stress orientations from well bore breakout and hydraulic fracturing data and assuming that the regional principal stresses are in approximately horizontal and vertical planes 10o the constraint that the slip vector represents the direction of maximum resolved shear stress on the fault plane was used to calculate relative stress magnitudes defined by the parameterb s2 s3 s s3 from the fault stress geometry as long as the focal mechanism has a component of oblique slip i e the b axis does not coincide with the intermediate principal stress direction this calculation identifies which of the two nodal planes is a geometrically possible slip plane gephart 1985 slip in a majority of the earthquakes 25 of 32 was found to be geometrically compatible with reactivation of favorably oriented preexisting fault planes in response to the broad scale uniform regional stress field slip in five events was clearly inconsistent with the regional stress field and appears to require a localized stress anomaly to explain the seismicity significantly all five of these events occurred prior to 1970 when many regional networks were installed and their focal mechanisms are inconsistent with more recent solutions of nearby smaller events the frictional likelihood of the geometrically possible slip on the selected fault planes was evaluated in the context of conventional frictional faulting theory the ratio of shear to normal stress on the fault planes at hypocentral depth was calculated relative to an assumed regional stress field regional stress magnitudes were determined from 1 s s3 ratios based on the frictional strength of optimally oriented faults the basis for the linear brittle portion of lithospheric strength profiles 2 the computed relative stress magnitude b values and 3 a vertical principal stress assumed equal to the lithostat two end member possibilities were examined to explain the observed slip in these less than optimally oriented fault planes first the frictional coefficient was held constant on all faults hydrostatic pore pressure was assumed regionally and the fault zone pore pressure was determined since pore pressure is a measurable quantity with real limits in the crust p0 s3 this end member case was used to determine which of the geometrically possible slip planes were frictionally likely slip planes alternately pore pressure was fixed at hydrostatic everywhere and the required relative lowered frictional coefficient of the fault zone was computed slip in 23 of the 25 geometrically compatible earthquakes was determined to also be frictionally likely in response to an approximately horizontal and vertical regional stress field derived from plate driving forces whose magnitudes are constrained by the frictional strength of optimally oriented faults assuming hydrostatic pore pressure regionally the conditions for slip on these 23 relatively well oriented earthquake faults were determined relative to this regional crustal strength model and require only moderate increases in pore pressure between about 0 4 0 8 of lithostatic hydrostatic is about 0 37 of lithostatic or alternately moderate lowering 50 of the frictional coefficient on the faults which slipped superlithostatic pore pressures are not required focal mechanisms for the two other earthquakes with slip vectors geometrically consistent with the regional stress field however did require pore pressures far exceeding the least principal stress or extremely low coefficients of friction these events may reflect either local stress rotations undetected with current sampling or poorly constrained focal mechanisms the analysis also confirmed a roughly north to south contrast in stress regime between the central eastern united states and southeastern canada previously inferred from a contrast in focal mecha nisms between the two areas most central eastern united states earthquakes occur in response to a strike slip stress regime whereas the southeastern canadian events require a thrust faulting stress regime this contrast in stress regime with a constant maximum horizontal stress orientation determined by far field plate driving forces requires a systematic lateral variation in relative stress magnitudes superposition of stresses due to simple flexural models of glacial rebound stresses are of the correct sense to explain the observed lateral variation but maximum computed rebound related stress magnitude changes are quite small about 10 mpa and do not appear large enough to account for the stress regime change if commonly assumed stress magnitudes determined from frictional strength apply to the crust at seismogenic depths

estimating tectonic uplift of the cape fear arch south eastern united states using reconstructions of holocene relative sea level we use relative sea level rsl reconstructions and a spatiotemporal statistical model to estimate the rate of uplift of the cape fear arch a mesozoic structural high during the last 4000 years we reconstructed rsl using 12 radiocarbon dated samples of basal salt marsh sediment preserved at elizabeth creek marsh on the cape fear river the new data show that rsl rose by 3m during the past 4 6 ka at an average rate of 0 67 0 12mm a 1 rsl reconstructions from other sites in southern north carolina which have rates of 0 91 0 10 to 0 84 0 24mm a 1 probably show p 0 9 higher rates of regional rsl rise for the same period while sites from northern south carolina which have rates of 0 72 0 17 to 0 80 0 21mm a 1 probably p 0 67 show the same we attribute the differences between elizabeth creek marsh and neighboring regions to uplift of the cape fear arch which we estimate to be 0 24 0 15mm a 1 uplift of the arch may be responsible for lower rates of 20 th century rsl rise recorded by the wilmington tide gauge relative to rates measured elsewhere along the us mid atlantic coast copyright 2014 john wiley sons ltd

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

sedimentation in the northern apennines corsica tectonic knot northern tyrrhenian sea central mediterranean offshore drilling data from the elba pianosa ridge the northern tyrrhenian sea is located on the collisional zone between the alpine corsica and the northern apennines and is a key area for gaining a better understanding of the complex relationships between these two systems the knowledge of the wide offshore part of this zone located between corsica france and mainland italy is based primarily on the analysis of several seismic profiles tied to the outcropping geology and unpublished preliminary reports of few offshore wells the here presented study of two offshore wells provides a revision of the sedimentology biostratigraphy and petrography of the thick mainly siliciclastic tertiary successions about 3 600 m composing the elba pianosa ridge epr a structural morphological high separating the tuscan shelf to the east from the corsica basin to the west a comparison with similar deposits cropping out in the surrounding onshore areas northern apennines corsica tuscan archipelago piedmont tertiary basin provides additional constraints for refinement of the complex geodynamic and regional setting in which the epr evolved

land motion estimates from gps at tide gauges a geophysical evaluation summary space geodesy applications have mainly been limited to horizontal deformations due to a number of restrictions on the vertical component accuracy monitoring vertical land motion is nonetheless of crucial interest in observations of long term sea level change or postglacial rebound measurements here we present a global vertical velocity field obtained with more than 200 permanent gps stations most of them colocated with tide gauges tgs we used a state of the art homogeneous processing strategy to ensure that the reference frame was stable throughout the observation period of almost 10 yr we associate realistic uncertainties to our vertical rates taking into account the time correlation noise in the time series the results are compared with two independent geophysical vertical velocity fields 1 vertical velocity estimates using long term tg records and 2 postglacial model predictions from the ice 5g vm2 adjustment the quantitative agreement of the gps vertical velocities with the internal estimates of vertical displacements using the tg record is very good with a mean difference of 0 13 1 64 mm yr 1 on more than 100 sites for 84 per cent of the gps stations considered the vertical velocity is confirmed by the tg estimate to within 2 mm yr 1 the overall agreement with the glacial isostatic adjustment gia model is good with discrepancy patterns related either to a local misfit of the model or to active tectonics for 72 per cent of the sites considered the predictions of the gia model agree with the gps results to within two standard deviations most of the gps velocities showing discrepancies with respect to the predictions of the gia model are however consistent with previously published space geodesy results we in turn confirm the value of 1 8 0 5 mm yr 1 for the 20th century average global sea level rise and conclude that gps is now a robust tool for vertical land motion monitoring which is accurate at least at 1 mm yr 1

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

using global positioning system derived crustal velocities to estimate rates of absolute sea level change from north american tide gauge records 1 we identified 37 tide gauges each located within 40 km of a geodetic station whose international terrestrial reference frame of 2000 itrf2000 crustal velocity had been rigorously derived from continuous global positioning system gps observations spanning from 3 to 11 years the tide gauges are located along the coasts of north america bermuda hawaii and kwajalein in the marshall islands we obtained the itrf2000 crustal velocities by averaging values from six solutions each produced by a team of investigators acting essentially independently of the other teams we then applied crustal velocities to convert rates of relative sea level change to rates of absolute sea level change in a sample containing 30 sites we found that the mean rate of absolute sea level change equals 1 80 0 18 mm yr in the 1900 1999 period the scatter about the mean for individual sites in this sample is characterized by a weighted rms value of 0 85 mm yr this scatter primarily reflects the uncertainty associated with derived crustal velocities the remaining seven sites i e five sites on the pacific coast of alaska one on dauphin island alabama and one on kwajalein an atoll in the pacific ocean experienced relatively low rates of absolute sea level change we hypothesize the low rates in alaska are caused by ongoing melting of mountain glaciers and ice masses near the stations while the low rates found for dauphin island and kwajalein remain unexplained

mid pliocene shorelines of the us atlantic coastal plain an improved elevation database with comparison to earth model predictions abstract for nearly a century the atlantic coastal plain acp of the united states has been the focus of studies investigating pliocene and pleistocene shorelines however the mapping of paleoshorelines was primarily done by using elevation contours on topographic maps here we review published geologic maps and compare them to paleoshoreline locations obtained through geomorphometric classification and satellite data we furthermore present the results of an extensive field campaign that measured the mid pliocene 3 3 2 9 ma shorelines of the atlantic coastal plain using high accuracy gps and digital elevation models we compare our new dataset to positions and elevations extracted from published maps and find that the extracted site information from earlier studies is prone to significant error both in the location and more severely in the elevation of the paleoshoreline we also investigate using geophysical modeling the origin of post depositional displacement of the shoreline from georgia to virginia in particular we correct the elevation of our shoreline for glacial isostatic adjustment gia and then compare the corrected elevation to predictions of mantle flow induced dynamic topography dt while a subset of these models does reconcile the general trends in the observed elevation of the mid pliocene shoreline local discrepancies persist these discrepancies suggests that either i the dt and gia models presented here do not capture the full range of uncertainty in the input parameters and or ii other influences such as sediment loading and unloading or local fault driven tectonics may have contributed to post depositional deformation of the mid pliocene shoreline that are not captured in the above models in this context our field measurements represent an important observational dataset with which to compare future generations of geodynamic models improvements in models for dt gia and other relevant processes together with an expanded geographically distributed set of shoreline records will ultimately be the key to obtaining more accurate estimates of eustatic sea level not only in the mid pliocene but also earlier in the cenozoic

on the origin of late holocene sea level highstands within equatorial ocean basins abstract late holocene sea level highstands of amplitude 3 m are endemic to equatorial ocean basins these highstands imply an ongoing and moderate sub mm yr sea level fall in the far field of the late pleistocene ice cover that has long been linked to the process of glacial isostatic adjustment gia clark et al 1978 mitrovica and peltier 1991 coined the term equatorial ocean syphoning to describe the gia induced sea level fall and they provided the first physical explanation for the process they argued that water migrated away from far field equatorial ocean basins in order to fill space vacated by collapsing forebulges at the periphery of previously glaciated regions we provide a complete physical explanation for the origin of equatorial ocean syphoning and the associated development of sea level highstands using numerical solutions of the equation that governs meltwater redistribution on spherical viscoelastic earth models in particular we separate the total predicted sea level change into contributions associated with ice and meltwater loading effects and by doing so isolate a second mechanism that contributes significantly to the ocean syphoning process ocean loading at continental margins induces a levering of continents and a subsidence of offshore regions that has also long been recognized within the gia literature walcott 1972 we show that the influx of water into the volume created by this subsidence produces a sea level fall at locations distant from these margins indeed over the major ocean basins that is comparable in amplitude to the syphoning mechanism isolated by mitrovica and peltier 1991

a gps velocity field for fennoscandia and a consistent comparison to glacial isostatic adjustment models in fennoscandia the process of glacial isostatic adjustment gia drives ongoing crustal deformation crustal velocities from gps observations have proved to be a useful tool in constraining gia models however reference frame uncertainties plate tectonics intraplate deformations as well as other geophysical processes contaminate the results former studies have shown that different international terrestrial reference frames have large discrepancies especially in the vertical component which hamper geophysical interpretation we present new velocity estimates for the fennoscandian and north european gps network our gps velocity field is directly realized in a gia reference frame using this method named the gia frame approach we are able to constrain gia models with minimal influence of errors in the reference frame or biasing signals from plate tectonics the drawbacks are more degrees of freedom that might mask real but unmodeled signals monte carlo tests suggest that our approach is robust at the 97 level in terms of correctly separating different models of ice history but depending on deformation patterns the identified earth model may be slightly biased in up to 39 of cases we compare our results to different one and three dimensional gia models employing different global ice load histories the gia models generally provide good fit to the data but there are still significant discrepancies in some areas we suggest that these differences are mainly related to inaccuracies in the ice models and or lateral inhomogeneities in the earth structure under fennoscandia thus gia models still need to be improved but the gia frame approach provides a base for further improvements

space geodesy constrains ice age terminal deglaciation the global ice 6g_c vm5a model a new model of the last deglaciation event of the late quaternary ice age is here described and denoted as ice 6g c vm5a it differs from previously published models in this sequence in that it has been explicitly refined by applying all of the available global positioning system gps measurements of vertical motion of the crust that may be brought to bear to constrain the thickness of local ice cover as well as the timing of its removal additional space geodetic constraints have also been applied to specify the reference frame within which the gps data are described the focus of the paper is upon the three main regions of last glacial maximum ice cover namely north america northwestern europe eurasia and antarctica although greenland and the british isles will also be included if peripherally in the discussion in each of the three major regions the model predictions of the time rate of change of the gravitational field are also compared to that being measured by the gravity recovery and climate experiment satellites as an independent means of verifying the improvement of the model achieved by applying the gps constraints several aspects of the global characteristics of this new model are also discussed including the nature of relative sea level history predictions at far field locations in particular the caribbean island of barbados from which especially high quality records of postglacial sea level change are available but which records were not employed in the development of the model although ice 6g c vm5a is a significant improvement insofar as the most recently available gps observations are concerned comparison of model predictions with such far field relative sea level histories enables us to identify a series of additional improvements that should follow from a further stage of model iteration

does the mid atlantic united states sea level acceleration hot spot reflect ocean dynamic variability 1 to test a hypothesized faster than global sea level acceleration along the mid atlantic united states i construct a gaussian process model that decomposes tide gauge data into short term variability and longer term trends and into globally coherent regionally coherent and local components while tide gauge records indicate a faster than global increase in the rate of mid atlantic u s sea level rise beginning 1975 this acceleration could reflect either the start of a long term trend or ocean dynamic variability the acceleration will need to continue for 2 decades before the rate of increase of the sea level difference between the mid atlantic and southeastern u s can be judged as very likely unprecedented by 20th century standards however the difference is correlated with the atlantic multidecadal oscillation north atlantic oscillation and gulf stream north wall indices all of which are currently within the range of past variability

influence of tidal range change and sediment compaction on holocene relative sea level change in new jersey usa we investigated the effect of tidal range change and sediment compaction on reconstructions of holocene relative sea level rsl in new jersey usa we updated a published sea level database to generate 50 sea level index points and ten limiting dates that define continuously rising rsl in new jersey during the holocene there is scatter among the index points particularly those older than 7 ka a numerical model estimated that paleotidal range was relatively constant during the mid and late holocene but rapidly increased between 9 and 8 ka leading to an underestimation of rsl by 0 5 m we adjusted the sea level index points using the paleotidal model prior to assessing the influence of compaction on organic samples with clastic deposits above and below an intercalated sea level index point we found a significant relationship p 0 01 with the thickness of the overburden r 0 85 we altered the altitude of intercalated index points using this simple stratigraphic relationship which reduced vertical scatter in sea level reconstructions we conclude that rsl rose at an average rate of 4 mm a 1 from 10 ka to 6 ka 2 mm a 1 from 6 ka to 2 ka and 1 3 mm a 1 from 2 ka to ad 1900

on a tectonic mechanism for regional sealevel variations abstract no satisfactory tectonic explanations have yet been offered for the apparent sealevel fluctuations of about 1 cm 1000 years and a magnitude of up to a few hundred meters that have been proposed by vail et al 1 we propose a mechanism that does appear to be able to explain these changes if horizontal stresses of the order of a few kilobars occur in the lithosphere and if changes in these stress fields occur on geological time scales the proposed model is one of an interaction between these stresses and the deflections of the lithosphere caused by sedimentary loading apparent sealevel changes of up to 100 m can be produced at the flanks of the sedimentary basins by this interaction the mechanism is most effective for young margins that are subject to rapid sediment loading by its nature the tectonic model can explain contemporaneous fluctuations in apparent sealevel in neighbouring depositional environments in principle it implies the possibility of regional correlations in different basinal settings

space geodesy subsidence and flooding in new orleans a subsidence map of the city offers insight into the failure of the levees during hurricane katrina

studies of worldwide secular trends in the solar daily geomagnetic variation summary secular changes in the solar geomagnetic variation at 11 observatories with a worldwide distribution have been studied the secular changes at uk observatories were found to be large numerical calculations details of which are described in this paper agree in predicting the large changes at uk observatories the numerical calculations also predict a large secular change in sq at hermanus in all elements this would be expected as the main field at this station shows a large secular change the secular change in sq observed at hermanus is however found to be fairly small compared with that observed at the other stations

gulf stream s induced sea level rise and variability along the u s mid atlantic coast 1 recent studies indicate that the rates of sea level rise slr along the u s mid atlantic coast have accelerated in recent decades possibly due to a slowdown of the atlantic meridional overturning circulation amoc and its upper branch the gulf stream gs we analyzed the gs elevation gradient obtained from altimeter data the florida current transport obtained from cable measurements the north atlantic oscillation nao index and coastal sea level obtained from 10 tide gauge stations in the chesapeake bay and the mid atlantic coast an empirical mode decomposition hilbert huang transformation emd hht method was used to separate long term trends from oscillating modes the coastal sea level variations were found to be strongly influenced by variations in the gs on timescales ranging from a few months to decades it appears that the gs has shifted from a 6 8 year oscillation cycle to a continuous weakening trend since about 2004 and that this trend may be responsible for recent acceleration in local slr the correlation between long term changes in the coastal sea level and changes in the gs strength was extremely high r 0 85 with more than 99 99 confidence that the correlation is not zero the impact of the gs on slr rates over the past decade seems to be larger in the southern portion of the mid atlantic bight near cape hatteras and is reduced northward along the coast the study suggests that regional coastal sea level rise projections due to climate change must take into account the impact of spatial changes in ocean dynamics

subsidence along the atlantic coast of north america insights from gps and late holocene relative sea level data the atlantic coast of north america is increasingly affected by flooding associated with tropical and extratropical storms exacerbated by the combined effects of accelerated sea level rise and land subsidence the region includes the collapsing forebulge of the laurentide ice sheet high quality records of late holocene relative sea level rsl rise are now available allowing separation of long term glacial isostatic adjustment induced displacement from modern vertical displacement measured by gps we compare geological records of late holocene rsl to present day vertical rates from gps for many coastal areas there is no significant difference between these independent data exceptions occur in areas of recent excessive groundwater extraction between virginia 38 n and south carolina 32 5 n the present day subsidence rates in these areas are approximately double the long term geologic rates which has important implications for flood mitigation tide gauge records therefore should be used with caution for studying sea level rise in this region

spatial variability of late holocene and 20th century sea level rise along the atlantic coast of the united states accurate estimates of global sea level rise in the pre satellite era provide a context for 21 st century sea level predictions but the use of tide gauge records is complicated by the contributions from changes in land level due to glacial isostatic adjustment gia we have constructed a rigorous quality controlled database of late holocene sea level indices from the u s atlantic coast exhibiting subsidence rates of 0 8 mm a 1 in maine increasing to rates of 1 7 mm a 1 in delaware and a return to rates 0 9 mm a 1 in the carolinas this pattern can be attributed to ongoing gia due to the demise of the laurentide ice sheet our data allow us to defi ne the geometry of the associated collapsing proglacial forebulge with a level of resolution unmatched by any other currently available method the corresponding rates of relative sea level rise serve as background rates on which future sea level rise must be superimposed we further employ the geological data to remove the gia component from tide gauge records to estimate a mean 20 th century sea level rise rate for the u s atlantic coast of 1 8 0 2 mm a 1 similar to the global average however we fia distinct spatial trend in the rate of 20 th century sea level rise increasing from maine to south carolina this is the fi rst evidence of this phenomenon from observational data alone we suggest this may be related to the melting of the greenland ice sheet and or ocean steric effects

sea level change and subsidence in the delaware estuary during the last 2200 years abstract we produced eight new sea level index points that reconstruct a 2 5 m relative sea level rsl rise at sea breeze in the delaware bay from 200 bce to 1800 ce the precision of our reconstruction improved upon existing data by using high resolution surveying methods ams radiocarbon dating of in situ plant macrofossils collected immediately above the basal contact between pre holocene sand and salt marsh sediments foraminifera as sea level indicators and by accounting for tidal range changes through time our new data were combined with a database of 65 sea level index points available for the delaware bay to estimate the rate of rsl rise in the upper 1 26 0 33 mm yr and lower bay 1 30 0 36 mm yr using a spatial temporal model correction for changes in tidal range through time removed the disparity in rate between the upper and lower delaware bay that had previously been postulated after paleotidal correction the rates of rsl rise estimated for the delaware bay 1 25 0 27 mm yr correlate with the 1 3 mm yr rate reported for new jersey maryland and virginia and confirm that the maximal ongoing forebulge collapse along the u s atlantic coast is focused on the mid atlantic

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

holocene sea level database for the atlantic coast of the united states we have constructed a database of holocene relative sea level rsl observations for the atlantic coast of the united states the database contains 492 index points which locate the position of rsl in time and space and 344 limiting dates which constrain the minimum or maximum limit of former sea level the majority of the index points in the database are from 6 ka bp to present with only 7 older than 6 ka bp spatially index points are distributed between maine and south carolina but there is an absence of data from georgia and the atlantic coast of florida the database is sub divided into 16 regions based on the distance from the former laurentide ice sheet and are classified depending upon their susceptibility to compaction the index points and limiting data demonstrate that rsl did not exceed present 0 m during the holocene except potentially in regions 1 and 2 eastern maine and southern maine rates of rsl change were highest during the early holocene and have decreased over time due to the diminishing response of the earth s mantle to glacial isostatic adjustment and reduction of ice equivalent meltwater input along the atlantic coast of the united states the linear rate of rsl rise prior to 4 ka bp ranged from 0 5 to 4 5 mm a 1 compared to 0 6 1 8 mm a 1 from 4 ka bp to ad 1900 the database suggests minimal 0 3 mm yr changes in these rates of rsl rise during the late holocene deglaciation of the laurentide ice sheet caused the spatial variability captured by the database the maximum rate of late holocene and ongoing rsl rise occurred in mid atlantic regions new jersey and inner delaware because of collapse of the peripheral forebulge

rheological stratification of the lithosphere a direct inference based upon the geodetically observed pattern of the glacial isostatic adjustment of the north american continent 1 a sequence of new analyses of the process of glacial isostatic adjustment gia is described the focus is upon the resolution of a recognized flaw in the currently prevalent model of this process that denoted ice 5g vm2 the flaw concerns a previously noted inability of the model to simultaneously reconcile the vlbi and gps measured rates of vertical and horizontal motion in the region of the north american continent that lay outboard and to the south of the laurentide ice sheet lis at last glacial maximum this characteristic misfit of the model to the data has been suggested to be reconcilable only by recourse to models that explicitly incorporate the influence of lateral viscosity heterogeneity it is demonstrated herein that on the contrary this flaw is entirely and unambiguously attributable to the rheological stratification of the lithosphere an influence not previously accounted for in global models of the gia process but which must exist on a priori grounds

late holocene sea level changes and isostatic crustal movements in atlantic canada abstract it has long been recognised that sea levels along the shores of atlantic canada have been rising rapidly during the holocene in response to isostatic crustal movements new sea level data for the bay of fundy coast of southern new brunswick little dipper harbour and the atlantic coast of nova scotia chezzetcook inlet show that late holocene average rates of sea level rise in these areas have been 1 0 and 2 5 m per 1000 yr respectively numerical model calculations suggest that the high rates of sea level rise are due to crustal subsidence produced by the combined effects of laurentide ice loading forebulge collapse and ocean loading of the scotian shelf although ice loading is the dominant contributor to the regional sea level pattern ocean loading is also important contributing up to 40 of the total crustal subsidence in some areas tide gauges record rates of sea level rise during the 20th century that are 0 7 1 9 mm yr higher than late holocene trends with the highest residuals occurring in the bay of fundy

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

impact effects and regional tectonic insights backstripping the chesapeake bay impact structure the chesapeake bay impact structure is a ca 35 4 ma crater located on the eastern sea board of north america deposition returned to normal shortly after impact resulting in a unique record of both impact related and subsequent passive margin sedimentation we use backstripping to show that the impact strongly affected sedimentation for 7 m y through impact derived crustal scale tectonics dominated by the effects of sediment compaction and the introduction and subsequent removal of a negative thermal anomaly instead of the expected positive thermal anomaly after this the area was dominated by passive margin thermal sub sidence overprinted by periods of regional scale vertical tectonic events on the order of tens of meters loading due to prograding sediment bodies may have generated these events