convective interactions between oceanic lithosphere and asthenosphere influence of a transform fault abstract current estimates of the asthenospheric viscosity favor the occurrence of small scale convection ssc beneath oceanic lithosphere of sufficient age since transform faults tfs juxtapose lithospheres of distinct ages and thicknesses they are likely to influence their dynamics in this paper we describe 3d numerical models of oceanic spreading for two ridge segments offset by a tf in domains that are sufficiently large for ssc to fully develop a framework based on thermal convection with temperature dependent viscosity and both internal and basal heating is adopted and parameters such as surface velocity age offset at the tf activation energy mantle viscosity and internal heating rate are explored in our numerical experiments the onset time for ssc is identical on each side of the fracture zone fz it is not modified by the presence of a tf moreover scaling relationships for the onset time obtained in 2d experiments remain valid earlier studies focused on the influence of a tf based on 2d experiments corresponding to slices parallel to the ridge axis they noted the rapid development of a sinking thermal instability located at the step in the lithospheric relief our results indicate that the wake of the tf is characterized by the development of a lateral edge driven buoyant flow from the younger thinner side to the older thicker side of the fz however due to the global shearing context this instability does not sink before the onset of ssc characterized by small scale instabilities on each side of the fz as observed in earlier studies the essentially 3d velocity field combining this lateral flow and the prescribed surface spreading velocity results in an angle formed by the tf trail with the spreading direction we describe the parameters controlling this angle in our experiments and propose a scaling relationship in oceanic settings the specific geometry of the ridge axis segment length orientation of the tfs may affect this angle in addition a large scale mantle flow of other geodynamical origin could interact with the spreading flow and also modify the tf trail angle this departure at depth of the boundary between the thick and thin lithospheres from the surface fz may explain the presence of oceanic volcanoes on the older side of the fz usually considered as thicker

mantle flow in subduction systems the subslab flow field and implications for mantle dynamics 1 the character of the mantle flow field in subduction zones remains poorly understood despite its importance for our understanding of subduction dynamics in particular little attention has been paid to mantle flow beneath subducting slabs in order to identify processes that make first order contributions to the global pattern of subslab mantle flow we have compiled shear wave splitting measurements from subduction zones worldwide from previously published studies and estimated average splitting parameters for the subslab region globally the subslab region is overwhelmingly dominated by trench parallel fast splitting directions we tested for relationships between splitting delay time a measure of the strength of anisotropy and parameters that are indicators of tectonic processes such as trench migration velocity convergence velocity and obliquity age of subducting lithosphere and slab dip curvature seismicity and thickness we used several different plate motion models to describe plate and trench motions and evaluated the differences among the models we find that only one parameter namely the trench migration velocity in a pacific hot spot reference frame appears to correlate well with the strength of the subslab splitting signal this finding supports a model in which the mantle beneath subducting slabs is dominated by three dimensional flow induced by trench migration we explore several implications of our model for various aspects of mantle dynamics including the choice of a suitable reference frame s for mantle flow the existence of a thin decoupling zone between slabs and the subslab mantle and consequences for mass transfer between the upper and lower mantle

postglacial uplift neotectonics and seismicity in fennoscandia abstract fennoscandia has experienced major uplift in postglacial time which is assumed to reflect a glacial isostatic process connected to the melting of the last ice sheets extensive modelling of the isostatic movements show that the applied deglaciation and uplift model fit the observations well there are however areas with significant deviations between uplift measurements and regional model predictions the misfit between observations and the isostatic uplift modelling is interpreted here to reflect a tectonic component of the uplift the objective of the present investigation is to isolate this tectonic uplift component interestingly enough the areas found partly correspond to areas with pronounced seismic activity and the assumption that the postglacial rebound is responsible for much of the observed onshore seismicity is substantiated we conclude that there seems to be present day deformation along the shoreline of mid norway southern norway shoreline and mountain areas and along the swedish east coast with the centre northeast of the gulf of bothnia that cannot be explained by glacial isostasy not all of the deformations in these areas are necessarily co seismic the study suggests that such vertical deformations are small in magnitude and overprint the glacial rebound the deformations may be a consequence of the plio pleistocene erosional pattern which is of glacial origin

the present rate of uplift of fennoscandia implies a low viscosity asthenosphere the rate of displacement in fennoscandia has been intensively discussed for many years it is now widely accepted to be an isostatic response of the glacial history of the area the earth s present response to deglaciation in fennoscandia is simulated using a three dimensional 3d viscoelastic model in which the asthenosphere and mantle viscosity are allowed to vary so that the maximum rate of present uplift matches its observed value the deglaciation history is considered to be known and the c14 datings are converted to sidereal years the pattern of the present uplift gives a firm match with the observed data when a low viscosity asthenosphere is introduced assuming a 15 000 years load cycle i e the glacier was applied to the surface for 15 000 years before the melting started the best fitting earth viscosity model is a 1024 nm lithosphere overlying a 75 km thick 2 0 1019 pas asthenosphere and a 1 2 1021 pas mantle the simulations suggest a remaining maximum uplift of 40 m

haskell 1935 revisited the haskell 1935 value of 1021 pa s for mantle viscosity is a classic and enduring constraint on the rheology of the earth s interior we revisit this inference using spherically symmetric self gravitating maxwell viscoelastic earth models our inference is based on both forward and inverse analyses of decay times associated with uplift at two sites considered by haskell angerman river sweden and oslo norway rather than the raw relative sea level rsl data at these sites we demonstrate that predictions of the decay time associated with the angerman river data are insensitive to variations in both the late pleistocene ice load history and the lithospheric thickness of the earth model the predictions at oslo are sensitive to both these inputs and hence decay times at this site provide a remarkably robust constraint on mantle viscosity we derive a constraint on the average viscosity of the mantle of 0 65 1 10 1021 pa s where the average resolved by the data encompasses a region which extends from the base of the lithosphere to a depth of near 1400 km this indicates that many previous analyses which have invoked the haskell value of 1021 pa s as a constraint on the average upper mantle i e above 670 km depth viscosity alone have misinterpreted the resolving power of the inference furthermore our analysis indicates that a number of apparently contradictory inferences of viscosity based on fennoscandian data satisfy the new rigorous interpretation of the haskell constraint finally we demonstrate how the ambiguity in the upper mantle lower mantle viscosity contrast associated with the haskell average may be reduced by invoking decay time constraints estimated from rsl curves in hudson bay a preliminary inversion of decay times at angerman river and richmond gulf in hudson bay suggests a contrast of approximately an order of magnitude between the average viscosities of the upper mantle and the top 1000 km of the lower mantle however a conclusive analysis in this regard must await the determination of consistent decay time estimates for the hudson bay region

deglacial land emergence and lateral upper mantle heterogeneity in the svalbard archipelago i first results for simple load models summary the glacial isostatic adjustment following the removal of the pleistocene ice sheets furnishes basic information on the thickness of the earth s lithosphere and the viscosity of the subjacent mantle paper i is concerned with an elementary interpretation of the post glacial land emergence observed at a restricted set of six locations in the svalbard archipelago the interpretation is based on a three layer incompressible maxwell viscoelastic earth model which is forced by a time dependent load distribution simulating the deglaciation history of the svalbard archipelago and the barents sea in view of inconclusive geomorphological evidence suggesting either total or partial glaciation of the area at glacial maximum two simple load models barents t1 and barents p1 are considered in the first instance a comparison between the calculated and observed values of land emergence suggests increases in lithosphere thickness and asthenosphere viscosity with increasing distance of the location from the continental margin the trends are qualitatively insensitive to the load model load thickness or load cross section used for load model barents t1 with parabolic cross section an initial load thickness of 1 50 km and a relaxed fitting criterion the lateral variations are only weak if a more restrictive fitting criterion is employed the variations become more prominent and suggest increasing values of lithosphere thickness from below 80 km to above 140 km and of asthenosphere viscosity from below 3 1018 pa s to above 2 1019 pa s over a distance of about 300 km in paper ii kaufmann wolf 1995 a high resolution load model and an extended set of land emergence observations are used to study further the possibility of resolving lateral heterogeneity in the upper mantle below the svalbard archipelago

comment on the inference of mantle viscosity from an inversion of the fennoscandian relaxation spectrum by j x mitrovica and w r peltier mitrovica peltier 1993 hereafter mp have recently analysed the fennoscandian uplift data using inversion techniques they concluded that although observations support the presence of a weak asthenosphere under fennoscandia the decay spectrum for the best fit model 1 3 x lo1 pa s asthenosphere overlying a 10zlpas mantle found by previous workers fjeldskaar cathles 1991a b cathles 1975 1980 hereafter fc lies outside the decay spectrum observed in fennoscandia and is thus excluded by the observed data we believe this conclusion results from the authors inadvertantly using a different asthenosphere thickness in their calculations than the one that they report the purpose of this communication is to argue this case and to show that when proper asthenosphere thicknesses are used the models of mp and fc are both compatible with the observed uplift data and that each in fact defines one edge of the observed uplift spectrum the essential difference in the two end member models is the elected tradeoff between lithosphere thickness and asthenosphere viscosity mp choose a stiff lithosphere and a minor asthenosphere whereas fc choose the opposite we believe lithosphere rigidity data not discussed in mp argue for a weak lithosphere in fennoscandia and suggest that the fc model is to be preferred the relaxation spectrum for the best fit model of fc as presented in m p s fig 11 is shown by the dashed curve labelled lvz in fig 1 it clearly lies below and outside the observed fennoscandian relaxation data shaded area the decay spectrum for the lvz model is according to mp based on loading of a 70 km lithosphere on a 90 km asthenosphere of viscosity 2 x lo pa s overlying a 10 p a s mantle the maximum relaxation time for the lvz model exceeds 6000 years however the maximum relaxation time for fc s bestfit asthenosphere model that the lvz curve is supposed to

sediment transport in the new york bight north american atlantic shelf vincent c e swift d j p and hillard b 1981 sediment transport in the new york bight north american atlantic shelf mar geol 42 369 398 aanderaa current meter data collected during the course of noaa s new york bight project are sufficiently extensive in time 135000 observation hours and space 41 stations to permit an estimate of the sediment transport in this area the analysis is based on mean flow observations the role of wave oscillatory currents in resuspending sediment is considered but not explicitly included in the sediment transport calculations an estimate of the potential sediment transport rate qb at each station for three different threshold velocities uth 12 16 and 20 cm s 1 were made using a bagnoldtype transport equation qb const uc uth 3 for uc uth qb 0 for uc uth where uc is the mean current speed comparison was made between the results from this simple equation and other bedload and suspended load transport rates which include wave data for a limited subset of the bight data this comparison indicates that the bagnold results are reasonable for the along isobath transport estimates but are not reliable for the cross isobath transport in the cross isobath direction waves appear to play a dominant role in determining the transport rate the comparison also indicates that the bagnold approach tends to overestimate transport in deep water in shallow water resuspension of sand and rotor pumping of current meters both may become important and sediment transport calculations may not be accurate fine sediment suspended transport is approximately double the potential bedload transport for fine sand 0 02 cm but does not dominate the total transport as is believed to occur on the washington shelf smith and hopkins 1972 the data show that the new york bight is a storm dominated shelf with the general southwestward drift of water 6 cm s 1 modulated by more intense storm induced flows the transport calculations indicate that the bulk of sediment transport occurs during the winter months when wind stress is at a maximum and the water column is well mixed two major transport provinces are present a the hudson shelf valley and b the rest of the shelf the shelf valley acts as a sink and a barrier to the continuity of the mainly southwestward transport of sediment 104 g cm 1 yr 1 along the shelf within the valley the potential transport of material is of the order of l05 g cm 1 yr 1 along the valley axis progressive vector transport paths for fine sediment indicate that removal of sediment out of the ends of the valley can occur rapidly however consider ation of the finesediment budget for the whole hudson shelf valley and of the attenua tion of wave activity with depth show that these results are not inconsistent with the presence of high mud concentrations in the valley up valley sediment rates predominate during the period for which data are available

geophysical constraints on the dynamics and retreat of the barents sea ice sheet as a paleobenchmark for models of marine ice sheet deglaciation our understanding of processes relating to the retreat of marine based ice sheets such as the west antarctic ice sheet and tidewater terminating glaciers in greenland today is still limited in particular the role of ice stream instabilities and oceanographic dynamics in driving their collapse are poorly constrained beyond observational timescales over numerous glaciations during the quaternary a marine based ice sheet has waxed and waned over the barents sea continental shelf characterized by a number of ice streams that extended to the shelf edge and subsequently collapsed during periods of climate and ocean warming increasing availability of offshore and onshore geophysical data over the last decade has significantly enhanced our knowledge of the pattern and timing of retreat of this barents sea ice sheet bsis particularly so from its late weichselian maximum extent we present a review of existing geophysical constraints that detail the dynamic evolution of the bsis through the last glacial cycle providing numerical modelers and geophysical workers with a benchmark data set with which to tune ice sheet reconstructions and explore ice sheet sensitivities and drivers of dynamic behavior although constraining data are generally spatially sporadic across the barents and kara seas behaviors such as ice sheet thinning major ice divide migration asynchronous and rapid flow switching and ice stream collapses are all evident further investigation into the drivers and mechanisms of such dynamics within this unique paleo analogue is seen as a key priority for advancing our understanding of marine based ice sheet deglaciations both in the deep past and in the short term future

mantle flow and determining position of lab assuming isostasy the assumption of isostatic equilibrium is often used in geophysics e g the depth of the lithosphere asthenosphere boundary lab is determined using data regarding the gravity field and topography together with the assumption of isostasy however isostasy implies a hydrostatic state which is contrary to the mantle convection hypothesis which states that most of the mantle matter is in motion we therefore discuss herein the question of when the assumption of isostasy can be used it is suggested that isostasy may be used for parts of oceanic plates except for subduction zones hotspots and oceanic ridges and for many continental regions except for postglacial regions and regions of intensive volcanic or tectonic activity moreover using the results of a numerical model of convection and calculations of dynamic topography it is shown that some generalization of isostasy is possible in the form of deep dynamic isostasy ddi it is also indicated that for some regions without isostatic equilibrium e g postglacial regions it is possible to use the isostatic method with some corrections to the results

high latitude e and f region coupling signature a case study results from rapid run ionosonde rapid run ionosonde installed in the high latitude sodankyla geophysical observatory enables us to observe for the first time extraordinary details of e f region coupling process in high latitude ionosphere during geomagnetically quiet period we present an example on 15 august 2009 when a dense patchy sporadic e layer was detected associated with this unstable sporadic e layer exhibiting in addition an unusual enhancement with a vertical extent of about 10 km the highly structured f layer plasma was observed with apparent plasma depletions we examine this event taking into account the presence of mesoscale traveling ionospheric disturbances which can initiate coupling between these two regions and compare the data with current theories

the world stress map database release 2016 crustal stress pattern across scales abstract knowledge of the present day crustal in situ stress field is a key for the understanding of geodynamic processes such as global plate tectonics and earthquakes it is also essential for the management of geo reservoirs and underground storage sites for energy and waste since 1986 the world stress map wsm project has systematically compiled the orientation of maximum horizontal stress shmax for the 30th anniversary of the project the wsm database has been updated significantly with 42 870 data records which is double the amount of data in comparison to the database release in 2008 the update focuses on areas with previously sparse data coverage to resolve the stress pattern on different spatial scales in this paper we present details of the new wsm database release 2016 and an analysis of global and regional stress pattern with the higher data density we can now resolve stress pattern heterogeneities from plate wide to local scales in particular we show two examples of 40 60 shmax rotations within 70 km these rotations can be used as proxies to better understand the relative importance of plate boundary forces that control the long wave length pattern in comparison to regional and local controls of the crustal stress state in the new wsm project phase iv that started in 2017 we will continue to further refine the information on the shmax orientation and the stress regime however we will also focus on the compilation of stress magnitude data as this information is essential for the calibration of geomechanical numerical models this enables us to derive a 3 d continuous description of the stress tensor from point wise and incomplete stress tensor information provided with the wsm database such forward models are required for safety aspects of anthropogenic activities in the underground and for a better understanding of tectonic processes such as the earthquake cycle

flexural rigidity of fennoscandia inferred from the postglacial uplift the earth s response to glacial loading unloading offers exceptional promise for the study of the physical properties of the lithosphere in particular tilting of paleoshorelines is very sensitive to the lithosphere rigidity to determine the flexural rigidity the isostatic response to deglaciation in fennoscandia is modeled using an earth model with a layered mantle viscosity overlain by an elastic lithosphere the flexural rigidity and asthenosphere viscosity is allowed to vary to get a match between theoretical and observed present rate of uplift and tilting of paleoshorelines five different ice thickness models are used for a relatively thin ice 2500 m in central areas the resulting flexural rigidity is more or less uniform over fennoscandia with a value of 1023 n m elastic thickness te 20 km this is regarded as minimum for the flexural rigidity of central fennoscandia the pattern of the present rate of uplift and the tilts of the paleoshorelines of the area also sets an upper bound of the flexural rigidity 2 5 1025 n m te 110 km in more central areas of fennoscandia the flexural rigidity at the western coast of norway does not seem to exceed 1023 n m te 50 km the most likely glacier model gives a flexural rigidity of 1023 n m te 20 km at the norwegian coast increasing to above 1024 n m te 50 km in central parts of fennoscandia

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

modelling of stresses in the fennoscandian lithosphere induced by pleistocene glaciations the seismicity observed in fennoscandia is usually explained by tectonic stresses the question of the contribution of stresses induced by glacial isostatic adjustment to the seismicity has not finally been settled yet in order to quantify the isostatic stress field generated by the fennoscandian glacial load we consider layered maxwell viscoelastic half spaces loaded by axisymmetric discs in particular we calculate the maximum shear stress distribution induced by the load model and the associated stress regimes in the lithosphere emphasis is placed on a discussion of the sensitivity of the calculated isostatic stresses to variations in load cross section lithosphere thickness and asthenosphere viscosity we also examine the effects produced by the viscous relaxation of the lithosphere whose viscosity is parameterized according to the stratification expected for temperature activated diffusion creep our results show that the isostatic shear stresses typically reach 2 mpa near the surface at the present time but that their distribution may be modified strongly by the details of the earth and load models investigated the viscous relaxation of the lithosphere becomes particularly important if more than one glaciation is considered since the last ice age in fennoscandia consisted of several glaciations the model of a perfectly elastic lithosphere conventionally employed in models of glacial isostatic adjustment therefore may not be justified when calculating the isostatic stresses

uplift deduced from remanent magnetization of a proterozoic basic dyke and the baked country rock in the hoting area central sweden a palaeomagnetic and 40ar 39ar study remanent magnetization in dyke contact zones in the hoting area of the fennoscandian shield in the central part of sweden has been studied in order to establish the ambient temperature of the host

seismic activity inferred crustal stresses and seismotectonics in the rana region northern norway abstract the seismotectonic significance of the rana region is known both from the fact that this was the location of the largest known earthquake in fennoscandia in recent times the m s 5 8 6 2 earthquake of august 31 1819 and from its relatively high constant seismic activity also in the 20th century in order to study this region in more detail a local seismic network has been in operation there since july 1997 as part of the neonor neotectonics in norway project the network was primarily designed to detect possible activity on the basmoen fault which runs 50 km subparallel to the rana fjord and which shows signs of likely post glacial activity the results have revealed a quite complex spatio temporal distribution of seismic activity and has also shown no activity on the basmoen fault itself during the first 18 months of operation july 1997 january 1999 the network has detected 373 locatable seismic events of which 267 were local earthquakes most of these earthquakes occurred in five groups in the western parts of the network all five groups had similar nnw esw trends in epicenter locations and all have shallow foci 2 12 km similar to what has also been found earlier for other concentrated earthquake zones in northern norway and the magnitude range is between m l 0 1 and 2 8 earthquake focal mechanism solutions within the network reveal a predominance for normal faulting with the tensional stress axis perpendicular do the coastline implying an unusual coast parallel orientation of the principal horizontal compressive stress the earthquakes occur in a region of maximum post glacial uplift gradients which supports deglaciation flexure as a viable explanation for these earthquakes a certain influence from more local factors however tied in general to crustal in homogeneities cannot be ruled out

triggering of the hinlopen yermak megaslide in relation to paleoceanography and climate history of the continental margin north of spitsbergen 1 on the basis of the detailed sedimentological record of the key core ps66 309 1 and a review of open literature we present an assessment of the paleoenvironmental conditions as well as trigger mechanism of the hinlopen yermak megaslide north of spitsbergen the svalbard archipelago is characterized by strong inflow of atlantic water accompanied by rapidly falling sea level rapidly growing svalbard barents sea ice sheet and associated increasing glaciotectonic activity during the time window around 30 calendar kyr b p of this catastrophic failure event thus the potential trigger mechanisms include sediment buoyancy and excess pore pressure hydrate stability and tectonic glaciotectonic processes while the common scenarios seem to fail to explain this unique submarine megaslide we focus on glacial processes and their consequences for the regional tectonic framework we conclude that the hinlopen yermak megaslide has been the consequence of the rapid onset of late weichselian glaciation resulting in a drastic sea level drop asymmetrical ice loading and a forebulge development leading to enhanced tectonic movements along the hinlopen fault zone as the final trigger we assume a strong earthquake positioned below or close to the se sophia basin

meteor induced transient sporadic e as inferred from rapid run ionosonde observations at midlatitudes 1 observations were made with a rapid run ionosonde during a 1 month period from the end of july to the end of august 2002 that included the perseid meteor shower ionograms were obtained at 1 minute intervals all the echo traces below a virtual height of 200 km were hand scaled for detecting weak and broken traces as well as well determined sporadic e among the scaled e region traces a distinct meteor echo persisting for 40 min was observed this long duration meteor event was similar to that observed during the leonid meteor shower in 2001 however the apparent height of the echo traces in the current event first decreased and then increased after equaling the height of a persistent sporadic e layer while the apparent height of the long duration meteor echo trace observed in leonids 2001 remained nearly constant the descending rate of the meteor echo was approximately 22 m s which was considerably greater than that of the tidal ion layer trapped in a downward moving wind shear node we ascribe the long duration meteor echo to a transient and horizontally drifting sporadic e patch generated from meteor trail plasma

ionospheric effects of the missile destruction on 9 december 2009 we report on ionosonde and meteor radar observations made in sodankyla geophysical observatory sgo 67 22 n 26 38 e finland on 9 december 2009 during a test launch of the russian solid propellant military missile due to a technical problem the missile was self destroyed around 07 ut at an ionospheric height near 200 km altitude over the kola peninsula russia at a distance about 500 km to east from the observatory products of the explosion were spread into a large area and reached the region of sgo meteor radar observations in about 2 h around 09 ut after about 3 h around 10 ut a sporadic e layer presumably composed of the remains including long lived metallic aluminum and its oxides ions was observed near the zenith of the sgo ionosonde we discuss possible mechanisms accounting for transport of the remains 1 since the event occurred during a long lasting period of extremely low solar and magnetic activity the ionospheric electric field was unlikely to play a substantial role in the transport of the remains and sporadic e layer formation 2 the horizontal transport of the remains cannot be explained by the neutral winds based on empirical models 3 theoretical estimations suggest that the observed transport could be due to thermospheric turbulence

evolution of a classic sand ridge field maryland sector north american inner shelf the ridge and swale topography of the middle atlantic bight is best developed on the delaware maryland inner shelf here sand ridges can be seen in all stages of formation several aspects of the ridge field are pertinent to the problem of ridge genesis the first is ridge morphology there is a systematic morphologic change from shoreface ridges through nearshore ridges to offshore ridges which reflects the changing hydraulic regime as successively more seaward ridges are examined maximum side slope decreases the ratio of maximum seaward slope to maximum landward slope decreases and the cross sectional area increases these changes in ridge morphology with depth and distance from shore appear to be equivalent to the morphologic changes experienced by a single ridge during the course of the holocene transgression a second aspect is the change in bottom sediment characteristics that accompanies these large scale morphologic changes megaripples sand waves and mud lenses appear in the troughs between nearshore and offshore ridges these changes indicate that the storm flows which maintain ridges are less frequently experienced in the deeper sector and that the role of high frequency wave surge becomes less important relative to the role of the mean flow component in shaping the sea floor a third aspect is the systematic relationship of grain size to topography grain size is 90 out of phase with topography so that the coarsest sand lies between the axis of the landward trough and the ridge crest while the finest sand lies between the ridge crest and the axis of the seaward trough this relationship is characteristic of large scale bedforms finally flow was measured and transport calculated on the same ridge during a one month period november 1976 threshold was exceeded only during storm events mean transport was southerly and a little seaward with respect to both the ridge crest and the shoreline these flow measurements are in conformity with the pattern of smaller bedforms a 43 year time series of bathymetric change for this ridge reveals a systematic pattern of landward flank erosion seaward flank deposition and seaward crest migration sand ridges are considered the consequence of constructive feedback between an initial topography and the resulting distribution of bottom shear stress the relationship between grain size and topography supports this model but does not account directly for the oblique angle of the ridge with respect to the coastline this feature may be due to a more rapid alongshore migration rate of the inshore edge of the ridge than the offshore edge and the relationship between this migration rate and the rate of shoreface retreat

the inference of mantle viscosity from an inversion of the fennoscandian relaxation spectrum summary a formal inverse theory for mantle viscosity is here applied to a relaxation spectrum derived from the post glacial uplift of fennoscandia the spectrum represents the set of eigenfrequencies or inverse decay times for the fundamental mode of viscous gravitational relaxation between the spherical harmonic degrees 14 to 45 and 65 to 80 theoretical predictions of the eigenfrequencies are based upon the determination of the zeroes of the secular determinant function derived for a spherically symmetric self gravitating visco elastic planet differential kernels relating shifts in the eigenfrequencies to arbitrary perturbations in the radial viscosity profile i e frechet kernels are computed using the variational principle derived by peltier 1976 the inversions are performed within the framework of non linear bayesian inference and the problem has been parameterized in terms of the logarithm of viscosity the inversions have yielded a set of robust constraints which all models for the radial viscosity profile below fennoscandia must satisfy the a posteriori estimates and variance reduction are found to be insensitive to the a priori variance ascribed to the model layers the constraints have furthermore been summarized into a set of a posteriori estimates of the average model viscosity value in radial regions consistent with the resolving power of the data which decreases from a radial length scale of approximately 120km at the base of the lithosphere to 1200km at 1000km depth the data provide essentially no information regarding the mantle rheology below 1200km depth for example for earth models with a lithospheric thickness lt of 100 km the volumetric average logarithm of viscosity in regions in the depth ranges 1040 400 km 670 210 km and 235 100 km is constrained to be respectively 21 03 0 09 20 70 0 08 and 20 37 0 19 we have repeated the inversions for a number of assumed lithospheric thicknesses and have found that a relatively low viscosity layer in the sublithospheric region with respect to the underlying upper mantle is required for lt 120km in this respect we have quantified the previously described trade off between a decrease in the viscosity of this region and a decrease in lt cathles 1975 in forward analyses of the glacial isostatic adjustment data set it is common to use earth models with isoviscous upper and lower mantle regions to investigate this two layer case we have also performed inversions which assume perfect correlation amongst the model layers in the upper and separately the lower mantle under this strict model space limitation the inversions yield models with upper and lower mantle viscosities in the range 3 7 1020 4 5 1020 pa s and 2 2 1021 1 9 1021 pa s respectively the ranges are obtained from a suite of inversions using lithospheric thickness from 70 km to 145 km the a posteriori constraints generated from the bayesian inversions are used together with a statistic based on the computed misfit to the fennoscandian relaxation spectrum to rule out a number of previously published viscosity models

viscosity and thickness of the asthenosphere detected from the fennoscandian uplift the earth s response to the deglaciation in fennoscandia is modelled using a layered viscous model with an elastic lithosphere the modelled tilting of palaeoshorelines at particular locations peripheral to the former ice load and the pattern of the present rate of uplift consistent with the observations strongly suggest a low viscosity asthenosphere earth models without a low viscosity asthenosphere give significant mismatch to the present rate of uplift and are unable to mimic the observed tilting of palaeoshorelines models with a viscosity of the lower mantle of 1 0 2 0 1021 pa s and a viscosity of the upper mantle of 0 7 1 0 1021 pa s overlain by low viscosity asthenosphere with a thickness ranging from 25 to 100 km fit equally well with the observations it is suggested strongly that the asthenosphere has a thickness of less than 150 km and a viscosity of less than 7 0 1019 pa s

recent postglacial rebound gravity change and mantle flow in fennoscandia summary the recent postglacial rebound of fennoscandia is investigated using sea level data levelling data and gravity data in particular an analysis is made of the repeated data obtained hitherto on the fennoscandian land uplift gravity line along latitude 63 methods for this analysis include an iterative procedure for computing the relation between gravity change and absolute land uplift the mass flow parameter and the geoid rise the remaining land uplift is also estimated the mass flow parameter c is used to characterize the relation between additional mass and additional volume due to rebound it is a number between 0 and 1 1 corresponding to full inflow of mantle below the rising crust and 0 to no inflow but some kind of decompression the main result is that c is significantly different from 0 at the 99 per cent level we find c 0 8 this means that models proposed of the present uplift based on pure decompression must be ruled out and that a viscous inflow of mantle is a necessary part of the ongoing uplift process on the other hand this process might be more complicated than a pure viscous flow

estimating past continental ice volume from sea level data we predict sea level change since the last glacial maximum lgm at four far field sites barbados bonaparte gulf huon peninsula and tahiti using a revised theoretical formalism this formalism includes a time varying shoreline geometry an accurate treatment of sea level variations near regions of ice retreat and the influence of glacial cycle perturbations in earth rotation we elucidate the physics of far field sea level change by de constructing the predicted signal into spatially uniform versus spatially varying components as well as isolating contributions due to the ice load the ocean load and the rotational potential we demonstrate that the sum of these three contributions plus the spatially uniform sea level fall associated the with retreat of grounded marine ice sheets can produce a significant difference between predictions of sea level change at far field sites and the eustatic or meltwater curve associated with the adopted ice model this difference is site and time dependent for example the total sea level rise since the lgm predicted using our ice earth model can be either smaller e g barbados or larger e g tahiti than the eustatic sea level change finally we review procedures that have been applied to estimate continental ice volume from far field sea level observations and apply these procedures to data from barbados and bonaparte gulf applying an ice earth model that is tuned to fit the barbados data we estimate a change in grounded ice volume from the lgm to the present of 43 5 51 106 km3 based on barbados data and an lgm ice volume estimate of 51 106 km3 based on bonaparte gulf data our results for the bonaparte gulf data are consistent with the recent study by yokoyama et al nature 406 2000 713 these lgm ice volume estimates map into a eustatic or meltwater sea level rise of 115 135 m taking into account plausible variations in the adopted radial earth model introduces uncertainties in the range of 1 5 106 km3 for ice volume estimates based on the barbados data

fast and partitioned postglacial rebound of southwestern iceland located both on the mid atlantic ridge and above a mantle plume iceland is subject to horizontal and vertical motions many studies described these deformations in terms of rifting episodes that have combined both extensional tectonics and magmatism however few studies have described the glacio isostatic response induced by the retreat of the weichselian ice cap the melting of this ice cap induced a postglacial rebound for the whole of iceland that may be controlled by the geodynamic setting and the rheological layering of the lithosphere this study is devoted to 1 understanding the holocene rebound on the southwestern coast and 2 estimating the asthenosphere viscosity and depth beneath iceland two stages of holocene evolution were determined by means of gps profiles morphological observations and data compilation the first stage corresponds to a vertical uplift of 67 5 to 157 5 m it started at 10 000 years bp and ended at 8500 years bp implying uplift rates between 4 5 and 10 5 cm a it was a quick isostatic response to the fast ice retreat the second stage had vertical motion of tens of meters with a probable tectonic origin and started at 8500 years bp the uplift rate is 1 to 2 orders of magnitude slower than the one during the first stage uplift partitioning during the first stage was controlled by the thermal state of the lithosphere the highest geothermal flux inducing the maximum uplift rates the relaxation time for uplift provides a viscosity estimate of 5 4 5 8 1019 pa s for the asthenosphere this value is similar to those determined for glacial areas in different continental contexts however the flexural wavelength indicates a shallower asthenosphere than that occurring in continental domains therefore this study highlights a coupling between the thermal structure of the icelandic asthenosphere and the glacial rebound

the early mid holocene transgression tapes at the norwegian coast comparing observations with numerical modelling abstract the early to mid holocene transgression dated between approximately 10 000 and 7000 cal yr bp inundated a significant part of the coastal areas of norway in this paper we compare observations of the amplitude of the transgression with numerical modelling the observations of the transgression along the coast vary from a couple of meters to more than 20 m and depend on the distance from the margin of the last ice sheet over fennoscandia we reviewed and evaluated the uncertainty of the data and present here the most reliable observations of the transgression data derived from the analysis of isolation basins from 17 locations spread along the norwegian coast the numerical model simulates the response of the earth to the deglaciation and changing sea level and shows that the transgression is mainly a result of the rising sea level and movements of the earth due to postglacial rebound our earth model consists of two viscous layers overlain by an elastic lithosphere we found a good match to the observations in southern norway with a weak effective elastic lithosphere 30 km this is consistent with a previous study of tilt of the raised late glacial shorelines in southwestern norway in northern norway however the same earth model and ice model give significant mismatch to the observations the best fit model for northern norway has a significantly thicker effective elastic lithosphere an alternative explanation for the mismatch could be a later deglaciation of the barents sea than generally assumed or neo tectonism in the area

sea level change glacial rebound and mantle viscosity fornorthern europe northwestern europe remains a key region for testing models of glacial isostasy because of the good geological record of crustal response to the glacial unloading since the time of the last glacial maximum models for this rebound and associated sea level change require a detailed knowledge of the ice sheet geometry including the ice thickness through time existing ice sheet reconstructions are strongly model dependent and inversions of sea level data for the mantle response may be a function of the model assumptions thus inverse solutions for the sea level data are sought that include both ice and earth model parameters as unknowns sea level data from fennoscandia the north sea the british isles and the atlantic and english channel coasts have been evaluated and incorporated into the solutions the starting ice sheet for fennoscandia is based on a reconstruction of a model by denton hughes 1981 that is characterized by quasi parabolic cross sections and symmetry about the load centre both global northwestern europe as a whole and regional subsets of the data solutions have been made for earth model parameters and ice height scaling parameters the key results are as follows 1 the response of the upper mantle to the changing ice and water loads is spatially relatively homogenous across scandinavia the north sea and the british isles 2 this response can be adequately modelled by an effective elastic lithosphere of thickness 65 85 km and by an effective upper mantle viscosity from the base of the lithosphere to the 670 km depth seismic discontinuity of about 3 4 1020 pa s the effective lower mantle viscosity is at least an order of magnitude greater 3 the ice thickness over scandinavia at the time of maximum glaciation was only about 2000 m much less than the 3400 m assumed in the denton hughes model 4 the ice profiles are asymmetric about the centre of the ice sheet with those over the western part being consistent with quasi parabolic functions whereas the ice heights over the eastern and southern regions increase much more slowly with distance inwards from the ice margin

influence of lithosphere asthenosphere interaction on the overriding lithosphere in a subduction zone numerical modeling 1 several factors influence the topography of the overriding plate in a subduction zone mantle wedge flow caused by motion of the descending slab lithosphere elasticity and interaction between the solid lithosphere and the viscous asthenosphere this paper presents the results of new subduction modeling that incorporates both elastic elastoplastic deformation in the overriding plate and viscous deformation in the asthenosphere the effects of fluid solid coupling and interaction were considered using an arbitrary lagrangian eulerian technique that solves for the continuous deformation of fluid flow in contact with the rigid plate modeling results show that thicker lithosphere which is harder to deform contributes to the development of broadly shallower back arc basins as lithospheric strength decreases its ability to withstand outside force fluid load resulting from flow in the mantle wedge also declines leading to the development of deep and narrow basins large scale deformation of the lithosphere modifies both the mantle wedge geometry and the wedge flow pattern which in turn increases the fluid load and thereby enhances topographic variation generally the effect of interaction is enhanced with lithospheric deformation the elastoplastic model also leads to a weaker lithosphere and a correspondingly larger deflection in the lithosphere similarly to previous studies back arc basins are deeper when mantle viscosity is higher for a 50 km thick elastic lithosphere the lithosphere asthenosphere interaction is negligible when the asthenospheric viscosity is less than 4 1019 pa s increasing the rate of subduction or decreasing the dip angle will also lead to the development of deeper basins

response of normal faults to glacial interglacial fluctuations of ice and water masses on earth s surface 1 changes in surface loads during glacial interglacial cycles and the associated flexure and rebound of the lithosphere alter the stress field in actively extending regions and may lead to slip rate variations on normal faults in particular loading may cause a period of seismic quiescence that is followed by temporal clustering of earthquakes during and after unloading here we present a suite of finite element experiments to evaluate how the magnitude distribution and temporal evolution of the load as well as rheological parameters of the lithosphere and asthenosphere influence the response of a normal fault the results show that the duration of the seismically quiet period during loading and the intensity of the slip rate increase during unloading are primarily controlled by the magnitude of the load the time lag between the changes in loading and the reaction of the fault is mainly determined by the viscosity of the asthenosphere parameters that play only a minor role for the fault s response include the rate of load removal fault strength and the thickness of the lithosphere our results imply that earthquake recurrence models derived from holocene slip histories may not be representative for the long term evolution of seismogenic faults

slip rate variations on faults during glacial loading and post glacial unloading implications for the viscosity structure of the lithosphere abstract many active faults in extensional and contractional tectonic settings experienced a slip rate increase after the last glacial period when the volume of nearby glaciers and lakes decreased this post glacial slip rate increase is caused by transient stresses that are generated by the unloading induced rebound and superimposed on the tectonic background stress field as the latter is different for normal and thrust faults the response to loading and unloading should depend on the fault type here we use finite element models including a fault in rheologically layered lithosphere to explore the conditions under which both normal and thrust faults experience a post glacial slip rate increase the results show that a post glacial slip rate increase occurs on normal faults if the lower crust is stronger than the lithospheric mantle whereas thrust faults accelerate if the lower crust is weaker than the lithospheric mantle these findings imply that the response of faults to mass fluctuations on the earth9s surface may provide constraints on the rheological stratification of the lithosphere we use our results to make predictions on the viscosity structure of the basin and range province and northern scandinavia where palaeoseismological data document a pronounced increase in seismicity as a result of post glacial unloading and rebound

continuous gps measurements of postglacial adjustment in fennoscandia 1 geodetic results 1 data collected under the auspices of the bifrost gps project yield a geographically dense suite of estimates of present day three dimensional 3 d crustal deformation rates in fennoscandia johansson et al 2002 a preliminary forward analysis of these estimates milne et al 2001 has indicated that models of ongoing glacial isostatic adjustment gia in response to the final deglaciation event of the current ice age are able to provide an excellent fit to the observed 3 d velocity field in this study we revisit our previous gia analysis by considering a more extensive suite of forward calculations and by performing the first formal joint inversion of the bifrost rate estimates to establish insight into the physics of the gia response in the region we begin by decomposing a forward prediction into the three contributions associated with the ice ocean and rotational forcings from this analysis we demonstrate that recent advances in postglacial sea level theory in particular the inclusion of rotational effects and improvements in the treatment of the ocean load in the vicinity of an evolving continental margin involve peak signals that are larger than the observational uncertainties in the bifrost network the forward analysis is completed by presenting predictions for a pair of fennoscandian ice histories and an extensive suite of viscoelastic earth models the former indicates that the bifrost data set provides a powerful discriminant of such histories the latter yields bounds on the assumed constant upper and lower mantle viscosity nu um nu lm specifically we derive a 95 confidence interval of 5 x 10 20 less than or equal to nu um less than or equal to 10 21 pa s and 5 x 10 21 less than or equal to nu lm less than or equal to 5 x 10 22 pa s with some preference for elastic lithospheric thickness in excess of 100 km the main goal of the bayesian inverse analysis is to estimate the radial resolving power of the bifrost gps data as a function of depth in the mantle assuming a reasonably accurate ice history we demonstrate that this resolving power varies from similar to 200 km near the base of the upper mantle to similar to 700 km in the top portion of the lower mantle we conclude that the bifrost data are able to resolve structure on radial length scale significantly smaller than a single upper mantle layer however these data provide little constraint on viscosity in the bottom half of the mantle finally elements of both the forward and inverse analyses indicate that radial and horizontal velocity estimates provide distinct constraints on mantle viscosity

the formation of sedimentary strata in an allochthonous shelf environment the washington continental shelf nittrouer c a and sternberg r w 1981 the formation of sedimentary strata in an allochthonous shelf environment the washington continental shelf mar geol 42 201 232 models of fine scale 120 m shelf regions the inner shelf sand and mid shelf sandy silt are the predominant accretionary deposits on the shelf important sedimento logical observations obtained by boxcoring the upper 1 2 m of these deposits are a progressive decrease in grain size with distance from the columbia b downward coarsening within the seabed c loss of distinct sedimentary structure homogenization of sediment with distance from the columbia non dimensional parameters based on sediment transport and benthic biological studies can be used to relate rates of sediment mixing re working to rates of accumulation these parameters have the potential for quantitative prediction of strata formation from measurements of active processes physical and biological mixing can be assumed to remain relatively constant in an alongshelf direction on the washington shelf and accumulation rate is known from pb 210 geochronology to decrease away from the columbia together these factors tend to increase the ratio of mixing to accumulation with distance from the columbia and predict the sedimentological observations listed above

global sea level trend in the past century data derived from tide gauge stations throughout the world indicate that the mean sea level rose by about 12 centimeters in the past century the sea level change has a high correlation with the trend of global surface air temperature a large part of the sea level rise can be accounted for in terms of the thermal expansion of the upper layers of the ocean the results also represent weak indirect evidence for a net melting of the continental ice sheets

estimates of twenty first century sea level changes for norway in this work we establish a framework for estimating future regional sea level changes for norway following recently published works we consider how different physical processes drive non uniform sea level changes by accounting for spatial variations in 1 ocean density and circulation 2 ice and ocean mass changes and associated gravitational effects on sea level and 3 vertical land motion arising from past surface loading change and associated gravitational effects on sea level an important component of past and present sea level change in norway is glacial isostatic adjustment central to our study therefore is a reassessment of vertical land motion using a far larger set of new observations from a permanent gnss network our twenty first century sea level estimates are split into two parts firstly we show regional projections largely based on findings from the fourth assessment report of the intergovernmental panel on climate change ipcc ar4 and dependent on the emission scenarios a2 a1b and b1 these indicate that twenty first century relative sea level changes in norway will vary between 0 2 to 0 3 m 1 sigma 0 13 m secondly we explore a high end scenario in which a global atmospheric temperature rise of up to 6 c and emerging collapse for some areas of the antarctic ice sheets are assumed using this approach twenty first century relative sea level changes in norway are found to vary between 0 25 and 0 85 m min max 0 45 m we attach no likelihood to any of our projections owing to the lack of understanding of some of the processes that cause sea level change

mantle flow geometry from ridge to trench beneath the gorda juan de fuca plate system shallow mantle flow could be induced by the motions of overriding tectonic plates or by deeper mantle convection analysis of mantle flow patterns in the pacific northwest shows that flow aligns with the motions of the largest oceanic plates

ionospheric effects of the leonid meteor shower in november 2001 as observed by rapid run ionosondes 1 we operated ionosondes at four stations in a rapid run mode to obtain ionograms every minute for 102 hours during the period of the leonid meteor shower in november 2001 plenty of radio echoes that looked like echo traces produced by sporadic e reflection were seen in the ionograms and this allowed statistical analysis in a single meteor shower event including discrimination of the backscattering by meteor trails from reflection by a horizontally stratified sporadic e layer the radio echoes seen in the ionograms were categorized into three types the first were spontaneous echoes which were distributed across a wide range of virtual heights at times during the period of maximum meteor activity there was a statistically good correlation among the echoes seen at the four stations the echoes of this type appear to be produced by fresnel backscattering from meteor trails the second were also spontaneous echoes observed during the shower period but persisted for several tens of minutes at the same virtual height as the typical sporadic e layer and the top frequency of these echoes decayed with time echoes of this type are thus attributed to the reflection from a meteor induced sporadic e patch echoes of the last type appeared outside the period of maximum activity of the meteor shower in the same range of virtual heights as the conventional sporadic e layer and there was no time correlation between the events observed at the four stations these events are attributed to a periodical increase in foes which is modulated by planetary wave activity and have no relation with the meteor shower

glacial isostatic adjustment of scandinavia and northwestern europe and the radial viscosity structure of the earth s mantle summary during the last glacial maximum lgm large ice sheets covered scandinavia the barents sea and the northern british isles subsequent to the lgm the ice sheets disappeared and the solid earth readjusted towards a new isostatic equilibrium the glacial isostatic adjustment process is documented in numerous observations for example palaeoshorelines covering the last deglaciation phase and ongoing crustal deformations monitored by gps stations for example the bifrost project in this study we use palaeoshoreline data from scandinavia the barents sea and northwestern europe nw as well as radial crustal velocities from the bifrost campaign to infer the radial viscosity structure of the earth s mantle underneath scandinavia and nw europe a global inverse procedure based on the neighbourhood algorithm allows us to explore the hypothesis of a low viscosity zone in the upper mantle which has been proposed in the literature our results indicate a low viscosity zone underneath the barents sea with viscosities between 1019 and 1020 pa s in a depth interval of 160 200 km no such low viscosity zone is found underneath scandinavia and no clear indication for such a zone underneath nw europe the thickness of the rheological lithosphere increases from 60 to 70 km underneath nw europe and the barents sea towards values exceeding 120 km underneath scandinavia

modelling the influence of glacial isostasy on late weichselian ice sheet growth in the barents sea a fully integrated ice sheet and glacio isostatic numerical model was run in order to investigate the crustal response to ice loading during the late weichselian glaciation of the barents sea the model was used to examine the hypothesis that relative reductions in water depth caused by glacio isostatic uplift may have aided ice growth from scandinavia and high arctic island archipelagos into the barents sea during the last glacial two experiments were designed in which the bedrock response to ice loading was examined i complete and rapid glaciation of the barents sea when iceberg calving is curtailed except at the continental margin and ii staged growth of ice in which ice sheets are allowed to ground at different water depths model results predict that glacially generated isostatic uplift caused by an isostatic forebulge from loads on scandinavia svalbard and other island archipelagos affected the central barents sea during the early phase of glaciation isostatic uplift combined with global sea level fall is predicted to have reduced sea level in parts of the central barents sea by up to 200 m this reduction would have been sufficient to raise the sea floor of the central bank into a subaerial position such sea floor emergence is conducive to the initiation of grounded ice growth in the central barents sea the model indicates that prior to its glaciation the depth of the central deep would have been reduced from around 400 m to 200 m such uplift aided the migration of grounded ice from the central barents sea and scandinavia into the central deep we conclude that ice loading over scandinavia and arctic island archipelagos during the first stages of the late weichselian may have caused uplift within the central barents sea and aided the growth of ice across the entire barents shelf copyright 2000 john wiley sons ltd

some effects of lateral heterogeneities in the upper mantle on postglacial land uplift close to continental margins summary we investigate the effects of lateral heterogeneities in the upper mantle on the calculation of postglacial land uplift for the model calculations we use a commercial finiteelement code which enables us to solve the equations governing a layered isotropic incompressible maxwell viscoelastic half space with laterally varying layer thicknesses and physical properties following previous investigations performed by sabadini yuen portney 1986 and gasperini sabadini 1989 we extend their results using a more realistic loading history and different earth models we then focus our attention on the question whether lateral heterogeneities in the upper mantle can be modelled correctly using a set of homogeneous earth models to this end a comparison of model calculations using both laterally homogeneous and heterogeneous earth models is performed we find that lateral heterogeneities in the upper mantle significantly influence the calculated postglacial land uplift the resolving power of relative sea level observations for the prescribed lateral heterogeneities used in this study is mainly focused on observations around the load margin and outside the glaciated areas where differences in predicted land uplift between individual models are large enough to be resolved by observations we can qualitatively determine lateral heterogeneities in the upper mantle using a set of laterally homogeneous earth models if the geological structure for example a continental margin is known however in order to infer the correct values of lithospheric thickness and asthenospheric viscosity we need to use laterally heterogeneous models

radar interferometric imaging studies of long duration meteor echoes observed at jicamarca a large number of long duration 15 s meteor echoes were detected at the jicamarca radio observatory on two nights in early august 1990 during an evening electrojet experiment using an interferometric imaging technique we were able to measure a zonal velocity profile for each meteor trail our analysis procedure differs from conventional meteor wind methods in that it provides instantaneous profiles rather than long term average information significant altitudinal and temporal variabilities of the horizontal velocities were noted zonal speeds of up to 100 m s 1 large vertical shears of up to 20 m s 1 km and rapid temporal variations of up to 50 m s 1 over an hour interval were observed spectral analysis indicates the presence and decay of asymmetrical high frequency signal components possible explanations for the observed high frequency components are discussed as are the angle of arrival of and the scattering mechanism responsible for the meteor echoes

mining induced crustal deformation in northwest germany modelling the rheological structure of the lithosphere abstract large scale coal mining in germany causes deloading of the crust by the removal of weight the crust responds by regional uplift while locally in the mining areas proper the surface subsides by sagging above extracted coal seams and removed groundwater in this study only the regional uplift is addressed the deloading consists of the total annual mass of coal and ground water removal since the 19th century for all significant mines the uplift data are from repeated levellings between about 1950 and 1980 reduced to mean annual rates of elevation change these observations are interpreted as the visco elastic response of the crust and uppermost mantle but alone they cannot discriminate layering from a homogeneous viscous half space or an elastic layer above such a half space if the seismically determined layered structure of upper and lower crust lithosphere mantle and asthenosphere is assumed to constrain the rheological structure a plausible model can be found by inversion only the lower crustal and asthenospheric effective maxwell viscosities are subjected to inversion a model consistent with the observations has the following properties 15 km of elastic upper crust 15 20 km thick lower crust of surprisingly low viscosity of 6 10 17 0 3 pas 30 50 km visco elastic mantle lithosphere with an assumed average viscosity of about 10 22 pas a visco elastic asthenosphere assumed bottomless with 5 10 19 0 6 pas the low viscosity values are consistent with active rifting and above average heat flow in the region the very low effective viscosity of the lower crust in this model it could be even lower if the thickness is smaller may be explained by elevated stresses quartz rheology and water content as suggested by xenoliths from the lower crust below the eifel region as a by product the tectonic subsidence in the lower rhine embayment filled with tertiary and quaternary sediments can be better defined by taking the anthropogenic effect into account

the westward drift of the lithosphere a rotational drag net westward rotation of the lithosphere relative to the underlying mantle is a controversial phenomenon fi rst attributed to tidal effects and later to the dynamics of mantle convection in spite of a number of independent geological and geophysical arguments for westward tectonic drift this phenomenon has received little recent attention we suggest that this differential rotation is a combined effect of three processes 1 tidal torques act on the lithosphere generating a westerly directed torque decelerating earth s spin 2 the downwelling of the denser material toward the bottom of the mantle and in the core slightly decreases the moment of inertia and speeds up earth s rotation only partly counterbalancing the tidal drag 3 thin 3 30 km layers of very low viscosity hydrate channels occur in the asthenosphere it is suggested that shear heating and the mechanical fatigue self perpetuate one or more channels of this kind which provide the necessary decoupling zone of the lithosphere

on the formation of sand banks of finite extent we consider a model where the fluid depth depends on both horizontal coordinates quasi steady depth uniform non divergent fluid flow is governed by inertial pressure and bottom frictional forces sand transport is proportional to the cube of the instantaneous current but augmented by a down slope component and by wind wave action and sand is conserved it is found that low parallel banks grow fastest so that in an extensive spatially uniform sea previous calculations for linear banks are appropriate the inclination of banks to the tidal currents can be interpreted in terms of similarly inclined deposition bands resulting from vorticity generation and advection in flow over a small isolated hump a small bump can evolve to an equilibrium bank typically after an initial rapid extension across the tidal currents provided that sand is sufficiently restricted and particularly if some wind wave action prevents growth up to the sea surface sand banks are likely to be in a late stage of evolution when the main change is a slow lengthening as the net current and transport along the bank side slows and turns around the bank end with net deposition the equilibrium is apparently stable except when there is an overall bed slope in the direction of the tidal currents or when sand is abundant

the effect of spatially non uniform water loads on prediction of sea level change summary numerical modelling of postglacial rebound predics a spatially variable pattern of sea level change yet many previous models predicting late pleistocene sea level change either neglect the load of water added to the oceans or assume a spatially uniform time dependent load over the whole ocean this is a poor approximation of the load near the former ice sheet since sea level change varies geographically in addition the coastline goemetry changes through time a spectral technique has been used to solve the sea level equation on an earth model with axisymmetric distribution of ice and oceans and also for a realistic ice ocean configuration the axisymmetric model is useful for demonstrating the fundamental physics involved in sea level changes caused by changes in surface loads in particular it can be seen that the elastic and gravitational response to the load is spread over a great distance whereas the viscous response is more localized a realistic ice ocean configuration has been used to demonstrate that neglect of the melt water load underestimates the amount of uplift in fennoscandia and other regions where rebound occurs in the ocean as previously noted by wu peltier 1983 in hudson bay and that movement of the coastlines and spatially varying water loads must both be included in calculations for the north sea and other near field regions with shallow seas sea level calculations including these effects and careful analysis of the sea level and ice melting record are required to determine modifications to the viscosity profile and ice model inferred by previous inaccurate models of the ocean load in the near field

viscoelastic perturbations of the earth significance of the incremental gravitational force in models of glacial isostasy summary the incremental gravitational force igf arises from perturbations of the earth s gravitational potential in glacial isostasy its sources are the surjicial and internal mass redistributions associated with the growth and decay of the continental ice sheets we examine the errors caused by the neglect of the igf using closed form solutions of the equations governing surface load induced perturbations of two types of incompressible spherical earth models 1 maxwellian viscoelastic mantle enclosed by elastic lithosphere and 2 maxwellian viscoelustic mantle enclosing inviscid core calculations in the legendre domain of the radial surface displacement for these models show that neglecting the igf causes enhancement of the elastic response and acceleration of the viscous relaxation in the space domain these changes entail corresponding modifications of the calculated land adjustment the magnitude of the error caused by the neglect of the igf strongly depends on the deglaciation history and load radius adopted assuming a typical deglaciation history the error reaches a maximum of less than 20 m at the end of the deglaciation phase for loads comparable in size to the canadian or the fennoscandian ice sheets we also compare sphericul earth models with igf and plane earth models without igf calculations of the radial surface displacement show that the errors due to the neglect of sphericity and the igf partially compensate each other taking the uncertainties of the observational data into account we conclude that the majority of the canadian and fennoscandian glacial isostatic adjustment data can be modelled with sufficient accuracy using a plane earth model without igf

palaeoshoreline records of glacial isostatic adjustment in the dry valleys region antarctica we present a new record of crustal deformation for the dry valleys and surrounding region of antarctica values of crustal tilt resulting from the differential uplift of lacustrine strandlines are derived and linked with age data to provide a history of solid earth deformation since deglaciation we present tilt directions and gradients for 13 strandlines formed c 18 100 2100 cal yr bp derived gradient magnitudes increase exponentially with age and indicate an ongoing response to deglaciation since the last glacial maximum azimuths of crustal tilting are consistently down to the se towards west antarctica this tilt pattern is opposite to that predicted by models of glacial isostatic adjustment for antarctica tilt magnitudes are significantly larger than tilted strandlines documented elsewhere in the world suggesting an influence from thin crust and weak mantle underlying the region this study presents the first use of lacustrine strandline tilts to document crustal deformation due to glacial unloading in antarctica and provides an important new datum for constraining glacial isostatic adjustment models for more than a century observations of uplifted and tilted marine and lacustrine strandlines have been used to understand glacial isostatic adjustment gia from retreating ice sheets e g spencer 1891 goldthwait 1908 as the earth s crust rebounds in response to ice mass loss ice proximal shorelines are raised and tilted away from ice load centres these geological shoreline records can be used in different ways depending on whether original elevation and or age of the features are known when both the original elevation and age are known uplift through time can be reconstructed the most common application of this case is analysis of marine raised beaches and shorelines where past elevation is determined through comparison to present day sea level radiocarbon dates from organic material extracted from shoreline deposits are correlated with raised beach elevations to produce a relative sea level curve e g hall denton 1999 lambeck et al 2002b baroni hall 2004 when corrected for eustatic sea level change relative sea level curves reflect the influence of solid earth and geoid variations resulting from deglaciation providing essential constraints for models of glacial isostatic adjustment that solve the sea level equation farrell clark 1976 peltier et al 1978 lambeck chappell 2001 mitrovica milne 2003 peltier 2004 for lake palaeoshorelines the original shoreline elevation is unknown but differential uplift since the time of deposition results in shoreline tilt analysis of strandline tilt through time provides a record of solid earth deformation since deglaciation for the case of glacial isostatic adjustment the total amount of uplift is a function of shoreline position relative to former ice mass centres greatest uplift occurs closer to the centre of ice mass loss and decreases away from the load subsidence occurs in the forebulge region e g clark et al 1978 shorelines located between the ice load and forebulge tilt away from the centre of ice loss whereas shorelines outboard of the forebulge tilt towards the load centre in addition to tilt direction both temporal and spatial variances in tilt magnitude manifest ice history and geometry older deglacial shorelines have a greater magnitude of tilt than younger shorelines from the same location and shorelines closer to the centre of ice mass loss have a greater magnitude of tilt than shorelines of the same age located farther away from the load given these relationships analysis of the direction magnitude and rate of tilting provides valuable information regarding ice history intersections of projected strandline tilt directions have been used to interpret the location of past ice mass centres improving reconstructions of former ice geometry barnett peterson 1964 andrews barnett 1972 tilted palaeoshorelines linked with age data provide a relaxation curve for the earth s crust since deglaciation enabling studies of mantle rheology and lithospheric thickness parameters crucial for understanding the geodynamic processes involved in from hambrey m j barker p f barrett p j bowman v davies b smellie j l tranter m eds antarctic palaeoenvironments and earth surface processes geological society london special publications 381 http dx doi org 10 1144 sp381 26 the geological society of london 2013 publishing disclaimer www geolsoc org uk pub ethics by guest on september 16 2013 http sp lyellcollection org downloaded from

on the vhf radar echoes in the region of midnight aurora signs of ground echoes modulated by the ionosphere we present all sky interferometric meteor radar mr vhf 36 9 mhz observations from sodankyla geophysical observatory and report on the unusual echoes which were detected at low elevation on the northern horizon typically during substorms these echoes have a near zero doppler shift relatively low power but with a sharp rise to the power peak short lifetime less than 2 s and nonexponential decay ned we suggest that such auroral ned echoes are in fact ground backscatter of the mr waves which have been refracted in the ionosphere passing through the ionosphere in the substorm region where pulsating aurora at a frequency higher than 1 7 hz occurs and causes quasiperiodic modulation of the wave propagation conditions which leads to corresponding modulation of the amplitude of return the mr treats such oscillating signal as meteor trails

observations of flexure and the rheology of oceanic lithosphere the principal evidence for the long term i e 1 myr mechanical behaviour of the oceanic lithosphere has come from studies of how it deforms in response to large loads such as volcanoes and sediments a model widely used to explain the deformation is an elastic plate in which flexural rigidity depends on the thermal age of the lithosphere at the time of loading an elastic model however is time invariant and does not take into account temporal changes that may occur in the flexural rigidity as a consequence of loading there is evidence for example that the flexural rigidity of the oceanic lithosphere also depends on load age being large at short times and small at long times thus competing effects may exist between thermal cooling which strengthens the lithosphere and some form of load induced stress relaxation which weakens it in order to investigate the relative roles of these processes we have developed a multilayered viscoelastic model which is based on the results of experimental rock mechanics that creep in the lithosphere is a thermally activated process and on a thermal structure that is given by the plate cooling model by comparing the predictions of the model with a new compilation of flexural rigidity estimates we have found that if the upper mantle viscosity is 1020 pa s the activation energy that best describes the long term mechanical behaviour of the oceanic lithosphere is 120 kj mol 1 this parameter pair explains the dependence of flexural rigidity on both plate and load age it also helps account for the subsidence and uplift history of oceanic islands and the stratigraphic patterns that develop in the flexural moats that flank them at atolls a multilayered viscoelastic model explains the rapid subsidence that follows shield building and does not require that the age of the lithosphere that supports a volcano is thermally re set to a younger value our studies suggest that while the oceanic lithosphere has viscoelastic properties the viscosity of its upper layers is so much higher than that of its lower layers that in effect it behaves as a thin elastic plate on long timescales there will therefore be a certain permanence to the observations of oceanic flexure such that they may be used with some confidence to evaluate the tectonic setting of individual features of the seafloor and in some cases their age

shallow upper mantle rheology and secular ice sheet fluctuations on time scales from decades to centuries continental cryospheric forcing in response to climate change constitutes a major source of isostatic disequilibrium that may influence future regional sea level variations current vertical displacements and gravity field variations are often estimated neglecting rheological effects and thus assuming a fully elastic response of the earth in this study we adopt a more general point of view aiming at describing ongoing surface movements resulting from recent glacial instabilities also taking into account the effects associated with shallow upper mantle and crustal rheologies our computations are based on the post widder laplace inversion formula which permits the straightforward computation of load deformation coefficients for steady state and transient rheologies up to very high harmonic degrees using a surface load with a simple geometry and time history we compare the classical elastic solutions to those obtained considering the rheological response of the shallow upper mantle while at the center of the ice sheet rheology only magnifies the elastic response the pattern and time history of vertical displacement at the ice sheet margins show a greater complexity mainly due to the development of lateral forebulges whose shape and amplitude are particularly sensitive to the rheology of the shallow upper mantle in this region assuming an elastic rheology is generally appropriate on a century time scale but significant deviations from a purely elastic response both sign and amplitude are observed at longer time scales or when a low viscosity zone with maxwell rheology is taken into account

autochthonous block fields in southern norway implications for the geometry thickness and isostatic loading of the late weichselian scandinavian ice sheet the consistent geographical and altitudinal distribution of autochthonous block fields mantle of bedrock weathered in situ and trimlines in southern norway suggests a multi domed and asymmetric late weichselian ice sheet low gradient ice sheet profiles in the southern baltic region in the north sea and along the outer fjord areas of southern norway are best explained by movement of ice on a bed of deforming sediment although water lubricated sliding or a combination of the two may not be excluded the ice thickness distribution of the late weichselian scandinavian ice sheet is not in correspondence with the modern uplift pattern of fennoscandia early holocene crustal rebound was apparently determined by an exponential glacio isostatic rise later however crustal movements appear to have been dominated by large scale tectonic uplift of the fennoscandian shield centred on the gulf of bothnia the region of maximum lithosphere thickness

holocene relative sea level change isostatic subsidence and the radial viscosity structure of the mantle of northwest europe belgium the netherlands germany southern north sea abstract a comprehensive observational database of holocene relative sea level rsl index points from northwest europe belgium the netherlands northwest germany southern north sea has been compiled in order to compare and reassess the data collected from the different countries regions and by different workers on a common time depth scale rsl rise varies in magnitude and form between these regions revealing a complex pattern of differential crustal movement which cannot be solely attributed to tectonic activity it clearly contains a non linear glacio and or hydro isostatic subsidence component which is only small on the belgian coastal plain but increases significantly to a value of ca 7 5 m relative to belgium since 8 cal ka bp along the northwest german coast the subsidence is at least in part related to the post glacial collapse of the so called peripheral forebulge which developed around the fennoscandian centre of ice loading during the last glacial maximum the rsl data have been compared to geodynamic earth models in order to infer the radial viscosity structure of the earth s mantle underneath nw europe lithosphere thickness upper and lower mantle viscosity and conversely to predict rsl in regions where we have only few observational data e g in the southern north sea a very broad range of earth parameters fit the belgian rsl data suggesting that glacial isostatic adjustment gia only had a minor effect on belgian crustal dynamics during and after the last ice age in contrast a narrow range of earth parameters define the southern north sea region reflecting the greater influence of gia on these deeper older samples modelled rsl data suggest that the zone of maximum forebulge subsidence runs in a relatively narrow wnw ese trending band connecting the german federal state of lower saxony with the dogger bank area in the southern north sea identification of the effects of local scale factors such as past changes in tidal range or tectonic activity on the spatial and temporal variations of sea level index points based on model data comparisons is possible but is still complicated by the relatively large range of earth model parameters fitting each rsl curve emphasising the need for more high quality observational data

glaciers on svalbard survived the holocene thermal optimum abstract about 60 of svalbard is covered by glaciers today but many of these glaciers were much reduced in size or gone in the early holocene high resolution modeling of the glacial isostatic rebound reveals that the largest glaciers in nordaustlandet and eastern spitsbergen survived the early holocene warming while the smaller more peripheral glaciers especially in the northwest started to form about 5 500 years ago and reached 3 4 of their current size about 600 years ago relative sea level has been rising during the last few millennia in the north and western parts of spitsbergen while land still emerges in the remaining part of svalbard here we show that this sea level rise in the northwest is caused by the regrowth of glaciers in the mid to late holocene that slowed down and even reversed the post glacial isostatic uplift and caused the crust to subside over large areas of spitsbergen

re evaluation of coquinoid sandstone depositional model upper jurassic of central wyoming and south central montana the most extensive jurassic marine transgression in north america reached its maximum limits during the oxfordian age at this time siliciclastic sediments were being brought into the north american seaway from an uplifted zone to the west within this setting complexes of sand ridges and coquinoid sands layers were deposited coquinoid sandstones appear to fill erosional scours and were interpreted as channel fills re evaluation of these features in the light of recently discovered attributes of modern shelf sediments and processes has produced a revised model of coquinoid sand deposition in this setting coquinoid sandstones which fill channel like scours in the oxfordian upper jurassic rocks of central wyoming and south central montana appear to have formed through the migration of sand waves across the crests of inner shelf sand ridges during periods of storm and tidal flow erosion in the zone of flow reattachment in the troughs between sand waves resulted in the development of shell lags migration of these scour zones as the sand waves advanced resulted in the deposition of sheet like coquinoid sandstone bodies sand waves crossing the ridge crest tended to migrate more slowly and to be overstepped by later sand waves sand wave troughs thus buried have channel like geometries with apparent epsilon bedding

geographic gradients in the formation of shell concentrations plio pleistocene marine deposits gulf of california abstract shell bed coarse concentrations of invertebrate bioclastic material are rich sources of paleontologic and stratigraphic information studies often emphasize the relationship between shell bed formation and bathymetric gradients because many sedimentologic and ecologic factors that influence shell concentrating processes vary with water depth however shell bed formation is also influenced by factors that are not related to water depth shell beds in plio pleistocene marine sediments of the gulf of california mexico formed in less than 10 15 m water depth but under varying conditions of coastal topographic relief and tidal range sampling of shell beds focused on two regions the northern mainland coast and the southern peninsular coast shell beds in the northern mainland region 13 total formed along a macrotidal low relief coastline whereas shell beds in the southern peninsular region 27 total formed along a microtidal high relief coastline shell beds represent community beds 11 storm beds 3 beach berm beds 6 tidal channel bed 1 or current wave winnowed beds 19 the community beds represent biogenic concentrations the other four types represent sedimentologic concentrations sedimentologic concentrations formed either through short term concentrating events storm beds or long term dynamic bypassing beach berm beds tidal channel beds and current wave winnowed beds concentrations formed through dynamic bypassing are far more common 26 beds than storm concentrations 3 beds of the 26 concentrations formed through dynamic bypassing 10 cap major stratigraphic discontinuities representing temporal breaks ranging from 103 to 108 years the abundance and distribution of the five types of shell beds is significantly different between the two sampling areas the northern mainland coast is dominated by allochthonous beach berm beds capping linear beach ridges the formation of beach ridges in the north is favored by the wide shallow shelf representing a large reservoir for beach shells and sediment starved conditions resulting from the low topographic relief and periodic reductions in sediment supply from the colorado river delta beach berm beds are absent along the southern peninsular coast where coarse terrigenous sediment shed from adjacent highlands overwhelms shell input to the beach and the narrow steep shelf supplies the beach with few shells the southern peninsular coast is dominated by parautochthonous current wave winnowed beds and autochthonous community beds southern shell beds have undergone significantly less reworking winnowing and transportation than northern shell beds this is a function of both the relative weakness of tidal currents in the south and the relatively higher rates of terrigenous sedimentation along the rugged southern coastline which can bury shell concentrations relatively rapidly geographic variation in topographic relief and tidal range results in significant variation in the distribution and abundance of shell beds within these shallow marine sediments these variables have root tectonic cause relief reflects tectonic activity tidal range reflects basin configuration underscoring the potential utility of fossil concentrations for reconstructing earth history

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

tidal inlet sequence sundance formation upper jurassic north central wyoming the sandstones and coquinas of the upper 20 m of the sundance formation are interpreted as a tidal inlet back barrier shoal and sandy tidal flat sequence deposited at the close of marine jurassic sedimentation in north central wyoming the barrier strandline maintained a generally e w trend as it prograded to the north the lateral migration of inter barrier tidal inlets along the regressive shoreline of the late sundance sea caused the coquinas and sandstones of the uppermost sundance formation to be deposited as tabular laterally extensive units tidal bundles sigmoidal reactivation surfaces herringbone cross lamination and abundant mud drapes within the sandstones are evidence of considerable tidal influence during the deposition of the uppermost sundance formation earlier models which attach an offshore environment of deposition to the sequence do not explain the tabular geometries of the sandstone and coquina units and their conformable stratigraphic relationship with the overlying non marine sediments of the morrison formation

seafloor response to flow in a southern hemisphere sand ridge field argentine inner shelf abstract the inner continental shelf adjacent to buenos aires province argentina is characterized by a series of sand ridges averaging 4 7 m in relief and spaced about 2 7 km apart the ridges trend north south forming a 20 to 35 southward opening angle with the northeast southwest trending coast although the adjacent coast is of depositional strand plain origin it is presently undergoing erosional retreat and the formation of the ridges appears to be part of the retreat process seafloor grain size distributions and bedform arrays are responses to the same velocity field that has formed the ridges along transects normal to the ridges grain size variation is 90 out of phase with the topography the coarsest sediment is not at ridge crests or trough axes but instead occurs on the landward slope finest sands are on the seaward slope side scan sonar reveals bedforms aligned obliquely to both ridges and the coast these are inferred to be sand waves the grain size and bedform patterns suggest that the formative flows are northward currents with an offshore flow component near the bottom although flows observed during the study period were dominantly north to south the grain size gradients and bedform orientations are equivalent to those characteristic of the atlantic shelf of north america with a north south inversion the comparison suggests that inner shelf transport directions in response to wind events can be predicted from the regional geometry and climate of the shelf

along strike variations of the slip direction on normal faults insights from three dimensional finite element models normal faults in nature exhibit a systematic variation of the slip direction along strike with pure dip slip at their centres that changes gradually to oblique slip near their tips here we evaluate the variation of the slip direction along normal faults by three dimensional finite element modelling the model results reveal a nearly linear increase of the strike slip component over two thirds of the distance from the fault centre to its tips which results in an increasing obliqueness of the slip vector along strike excluding the fault tips the relationship between lateral slip and fault length can be approximated by a power law function which shows that the strike slip component is proportional to the dip slip and to the fault dip the development of the sinistral and dextral slip components is caused by the orientation of the minimum principal stress which is deflected toward the fault centre in both footwall and hanging wall a comparison with two faults in the central apennines italy shows good agreement between modelled and measured slip vectors the occurrence of converging slip patterns implies that caution is advised when inferring oblique extension regional stress trajectories and palaeostress fields from slip vectors measured away from the fault centre

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

shoreline displacements in southern central sweden and the evolution of the baltic sea since the last maximum glaciation during late and post glacial times the baltic basin has been periodically isolated from the atlantic and freshwater and saline conditions have alternated this is a consequence of the interactions between the spatially variable glacial rebound of the region and the simultaneous eustatic sea level rise in the adjacent atlantic observations of the timing of these isolations and of the location of the barriers therefore provide constraints on the rebound models high resolution numerical models of rebound of southern sweden the danish straits and the baltic have been developed and tested against observations of lake level change as well as against the observed elevations of the last baltic ice lake shoreline which formed before about 10 3 ka bp predictions of sea and lake levels are used to test two alternative hypotheses about the ice thickness over scandinavia and to estimate parameters that describe the earth s response optimum values for the latter are lithospheric thickness of 60 20 km upper mantle viscosity of 3 3 10 20 pa s and lower mantle viscosity of 10 22 pa s the rapid lake level fall at the end of the baltic ice lake stage is estimated to be 30 5 m the optimum ice model for scandinavia is one in which the ice thickness over southeastern and southern scandinavia was relatively thin compared with the ice thickness over sweden and norway the ice thickness in the southeast and south changes slowly with distance inwards of the ice margin whereas over sweden and norway the ice thickness profiles are considerably steeper the earth and ice models have been combined with high resolution digital terrain data to develop a comprehensive model for the evolution of the baltic basin since the time the area last became ice free the reconstructions predict the occurrence of barriers at certain times which impede free flow between the atlantic and baltic and confirm that the baltic lake levels are controlled by rebound at four localities degerfors in the narke region of southern central sweden the vanern outlet through the gota alv oresund and the darss langelands store baelts in denmark

a comparison of different ways of dealing with isostasy examples from modelling the antarctic ice sheet during the last glacial cycle the bedrock isostatic response exerts a strong control on ice sheet dynamics and is therefore always taken into account in ice sheet models this paperreviews the various methods normally used in the ice sheet modeling community to deal with the bedrock response and compares these with a moresophisticated full earth model each of these bedrock treatments five in total are coupled with a three dimensional thermomechanical ice sheet model underthe same forcing conditions to simulate the antarctic ice sheet during the last glacial cycle the outputs of the simulations are compared on the basis of thetime dependent behavior for the total ice volume and the mean bedrock elevation during the cycle and of the present rate of uplift over antarctica thiscomparison confirms the necessity of accounting for the elastic bending of the lithosphere in order to yield realistic bedrock patterns it furthermoredemonstrates the deficiencies inherent to the diffusion equation in modeling the complex deformation within the mantle nevertheless when characteristicparameters are varied within their range of uncertainty differences within one single method are often of the same order as those between the variousmethods this overview finally tries to point out the main advantages and drawbacks of each of these methods and to determine which one is mostappropriate depending on the specific modeling requirements

on deglaciation induced perturbations of the geoid the importance of geoid perturbations in interpreting tilts of glacial lake levels is investigated using a representative theoretical model it is shown that near the ice margin the slope of the earth s perturbed surface is everywhere large compared with the slope of the associated undulation of the geoid perturbations of the geoid may therefore be neglected in interpretations of glacial strandline tilt

postglacial rebound at the northern cascadia subduction zone postglacial rebound is the response of the earth to the decay of ice sheets a postglacial rebound model explains crustal tilting and rapid uplift at the northern cascadia subduction zone that occurred during retreat of the cordilleran ice sheet observations explained by the model include the shoreline tilts of two proglacial lakes that formed at 13 5 14 ka 14c yr ago and rapid sea level fall land uplift at 12 12 5 ka modelled mantle viscosity values range from 5 1018 to 5 1019 pa s and are consistent with previous viscosity inferences from observations of crustal deformation following subduction zone earthquakes 1018 1019 pa s no lower limit to subduction zone mantle viscosity is apparent from our model but viscosity values equal to or larger than 1020 pa s are de nitely ruled out our modelled subduction zone viscosity values are smaller than most upper mantle viscosity estimates derived from postglacial rebound studies of tectonically less active regions 1020 1021 pa s the rapid observed uplift at 12 ka requires in addition to a low mantle viscosity rapid unloading from a sudden collapse of remaining coastal portions of the southern cordilleran ice sheet the sudden collapse provides 0 18 m of global eustatic sea level rise approximately 0 7 of the sea level rise associated with melt water pulse ia predictions of a global postglacial rebound model ice 3g with a 1021 pa s upper mantle viscosity were previously applied to geodetic data from this region to isolate signals associated with the earthquake cycle owing to the low viscosity values and resulting rapid recovery of glacial deformation our model predicts present day postglacial rebound uplift rates at least 10 times smaller than ice 3g less than about 0 1 mm yr as the ice 3g adjustments were substantial this indicates the need for re evaluation of the geodetic data 2000 elsevier science ltd all rights reserved

what about the asthenosphere viscosity comment on sea level change glacial rebound and mantle viscosity for northern europe by k lambeck c smither and p johnston lambeck et al 1998a hereafter lsj present a thorough in my own studies fjeldskaar 1994 1997 i have shown that the best fitting models have a low viscosity asthenosphere study of the sea level change connected to the deglaciation of fennoscandia they establish a comprehensive observational based on fjeldskaar 1994 the thickness and viscosity of the asthenosphere are not precisely determined but are within database on crustal rebound for the whole of northern europe this database is used in a high resolution modelling of the the range shown in fig 1 it is clearly demonstrated that the asthenosphere has a thickness of less than 150 km a thicker rebound based on the observed deglaciation pattern a key result is an estimate of the effective elastic thickness of the asthenosphere shows significant discrepancies from the observed uplift data lithosphere and the viscosity structure of the mantle lsj give a brief overview of previous results on the mantle models similar to the one favoured by lsj were tested in fjeldskaar 1994 model no 14 it was pointed out that models rheology models established by a similar approach lsj s comment to models with a low viscosity asthenosphere and with a lower mantle viscosity of 2 0 1021 pa s or higher without a low viscosity asthenosphere are not viable options the various other previously published viscosity models is that the differences are attributable to a number of factors these reason is that the short wavelength components decay too slowly giving significant deviations in central parts of the uplift dome factors include the fact that the other studies used only a subset of the data and that some of them assumed the ice sheet to be this is clearly demonstrated in the theoretical present uplift pattern calculated with the rheology parameters of lsj given perfectly known a third factor is that none of the studies has examined the entire range of possible earth model parameters in lambeck et al 1998b the predicted present day uplift centre lies further to the west than the observed centre this would this immediately gives the reader the impression that lsj do not have similar shortcomings and that the final resulting not be the case if a low viscosity asthenosphere was used fjeldskaar 1994 fig 6 furthermore the rheology model of earth rheology model is better constrained than the previous studies however this is not the case lsj have ignored models lsj cannot produce the observed shoreline tilts fjeldskaar 1994 this is also demonstrated in lsj figs 28 and 29 with a low viscosity asthenosphere on this basis it is rather peculiar that they 1 criticize others for not having used the in conclusion lsj have not been able to come up with a model for the earth rheology that gives optimum fit to entire range of possible earth models and 2 give the reader the impression that models with a low viscosity asthenosphere the observed rebound because models with a low viscosity asthenosphere have not been considered the lsj rheology is are unrealistic

india asia collision and the cenozoic slowdown of the indian plate implications for the forces driving plate motions the plate motion of india changed dramatically between 50 and 35 ma with the rate of convergence between india and asia dropping from 15 to 4 cm yr this change is coincident with the onset of the india asia collision and with a rearrangement of plate boundaries in the indian ocean on the basis of a simple model for the forces exerted upon the edges of the plate and the tractions on the base of the plate we perform force balance calculations for the precollision and postcollision configurations we show that the observed euler poles for the indian plate are well explained in terms of their locations and magnitudes if 1 the resistive force induced by mountain building in the himalaya tibet area is 5 6 10 12 n m 2 the net force exerted upon the indian plate by subduction zones is similar in magnitude to the ridge push force 2 5 10 12 n m and 3 basal tractions exert a resisting force that is linearly proportional to the plate velocity in the hot spot reference frame the third point implies an asthenospheric viscosity of 2 5 10 19 pa s assuming a thickness of 100 150 km synthetic euler poles show that crustal thickening in the tibetan plateau was the dominant cause of the cenozoic slowdown of the indian plate

subduction initiation and continental crust recycling the roles of rheology and eclogitization abstract a mechanical model with viscous ductile and plastic brittle rheologies is used to investigate the effect of eclogitization on the dynamics of convergence density increases by 300 600 km m3 during eclogitization of crustal rocks and continental lower crust and oceanic crust reach higher density than mantle we explore cases of intracontinental deformation subduction and continental collision we consider a wide range of parameters for friction activation energy and initial thermal state and cases with or without eclogitization the style of deformation appears to be primarily controlled by the presence or absence of weak zones simulations are run with a constant convergence velocity 1 5 or 4 cm year and the evolution of the compressive force through time is thus a critical test of the model viability for intracontinental deformation when the brittle crust is decoupled from the mantle the mantle deforms by symmetrical bending or subduction and a variable amount of lowermost crust is entrained with the sinking mantle in these cases the compressive force remains in the 1012 3 1013 n m acceptable range oceanic subduction only occurs if a low friction shear zone is specified in the brittle realm during the transition from oceanic subduction to collision the oceanic crust in this shear zone remains trapped between colliding crusts eclogitization has no influence on the initial mode of deformation thus it is probably not an important factor in the initiation of subduction in all simulations the influence of eclogitization increases progressively with time in proportion of the amount of lower continental crust and oceanic crust entrained into the mantle the structural evolution of the orogen model depends on eclogitization if initial decoupling occurs at mid crustal level the simulations thus indicate that eclogitization promotes convergence and also in some cases enables the recycling of the whole continental lower crust into the mantle we also suggest that eclogitization could regulate the long term convergence rate in orogens

holocene glacial rebound and sea level change in nw europe summary observations of late pleistocene and holocene sea level change relative to the crust exhibit very considerable variations across nw europe in consequence of the response of the earth s crust to the deglaciation of fennoscandia and of the water added to the oceans from the melting of all late pleistocene ice sheets inversion of sea level observations from a site near the centre of the fennoscandian ice sheet and from three sites located beyond the margin of the ice sheet at the time of maximum glaciation yield a range of plausible models for the earth s response and for the ice models further constraints on this range of models is placed by a comparison of observed sea levels with predicted values at other sites near the former ice sheet margins the resulting mantle parameters are upper mantle viscosity 3 5 x 10 pa s lower mantle viscosity 2 7 x loz1 pa s lithospheric thickness 100150 km these values represent effective parameters that describe the response of the earth to surface loading of short to intermediate wavelengths on a time scale of 104yr the lower mantle viscosity is poorly constrained but the marked increase from upper to lower mantle is a characteristic of all plausible solutions the inversion places a constraint on the total volume of ice in the fennoscandian ice sheet such that the equivalent sea level rise from this contribution is about 13 14 m a less well determined constraint of about 10 m equivalent sea level rise is suggested for the barents kara ice sheet the inversion also indicates that a small amount of melt water from ice sheets far away from europe continued to be added into the oceans during late holocene time so as to raise the equivalent sea level by about 3 m during the past 6000 yr consistent with similar inversions of data from sites in the australian and pacific regions

mid latitude e region field aligned irregularities observed with the mu radar fine structures e region field aligned irregularities were observed on june 24 25 1989 with the mu radar at shigaraki japan 34 9 n 136 1 e geomagnetic latitude 25 0 n the 3 2 m scale irregularities were observed with the mu radar in five main beam directions each of which was nearly perpendicular to the geomagnetic field at 100 km altitude doppler spectra were obtained every 20 s with a range resolution of 600 m field perpendicular echoes appeared from 2130 to 2330 lt and from 0400 to 1100 lt times that correspond to postsunset and postsunrise period in the e region a preliminary examination of the doppler spectra indicates spectral widths of 50 120 m s 1 and the mean doppler velocities are well below the ion acoustic speed these spectral characteristics are consistent with those obtained in the equatorial and auroral electrojets and have been attributed to the gradient drift instability the echoes observed during the postsunset and postsunrise periods showed quite different morphologies in the time height distribution for this reason they are classified into two types continuous and quasi periodic the appearance of the continuous echoes was mainly continuous in time and situated between 90 and 100 km altitude during the postsunrise period the appearance of the quasi periodic echoes was intermittent with periods of 5 10 min and situated above 100 km altitude during the postsunset period the quasi periodic echoes showed phase propagation toward the radar while the averaged mean doppler velocity was away from the radar by measuring the time delays in echo regions from five directions an apparent westward motion approximately 120 m s 1 of the irregularity regions was estimated

effect of ice sheet growth and melting on the slip evolution of thrust faults abstract field investigations suggest that postglacial unloading and rebound led to the formation or re activation of reverse faults even in continental shields like scandinavia here we use finite element models including a thrust fault embedded in a rheologically layered lithosphere to investigate its slip evolution during glacial loading and subsequent postglacial unloading the model results show that the rate of thrusting decreases during the presence of an ice sheet and strongly increases during deglaciation the magnitude of the slip acceleration is primarily controlled by the thickness of the ice sheet the viscosity of the lithospheric layers and the long term shortening rate in contrast the width of the ice sheet the rate of deglaciation or the fault dip have an only minor influence on the slip evolution in all experiments the slip rate variations are caused by changes in the differential stress the modelled deglaciation induced slip acceleration agrees well with the occurrence of large earthquakes soon after the melting of the fennoscandian ice sheet which led to the formation of spectacular fault scarps in particular in the lapland fault province furthermore our model results support the idea that the low level of seismicity in currently glaciated regions like greenland and antarctica is caused by the presence of the ice sheets based on our models we expect that the decay of the greenland and antarctica ice sheets in the course of global warming will ultimately lead to an increase in earthquake frequency in these regions

the seek chemical release experiment observed neutral wind profile in a region of sporadic e wind measurements made with the chemical release technique during a sporadic e layer event are presented the data were obtained as part of the sporadic e experiment over kyushu seek sounding rocket campaign the winds show a strong maximum in the lower e region approaching 150 m s 1 near 105 km altitude and a large shear below the maximum the large shear was within a few kilometers altitude of the peak in the electron densities measured on the downleg of the rocket trajectory calculations of the richardson numbers for the wind profile show that the altitude range near the layer was highly unstable