timing and origin of recent regional ice mass loss in greenland within the last decade the greenland ice sheet gris and its surroundings have experienced record high surface temperatures mote 2007 box et al 2010 ice sheet melt extent fettweis et al 2011 and record low summer sea ice extent nghiem et al 2007 using three independent data sets we derive for the first time consistent ice mass trends and temporal variations within seven major drainage basins from gravity fields from the gravity recovery and climate experiment grace tapley et al 2004 surface ice velocities from inteferometric synthetic aperture radar insar rignot and kanagaratnam 2006 together with output of the regional atmospheric climate modelling racmo2 gr ettema et al 2009 and surface elevation changes from the ice cloud and land elevation satellite icesat sorensen et al 2011 we show that changing ice discharge d surface melting and subsequent run off m r and precipitation p all contribute in a complex and regionally variable interplay to the increasingly negative mass balance of the gris observed within the last decade interannual variability in p along the northwest and west coasts of the gris largely explains the apparent regional mass loss increase during 2002 2010 and obscures increasing m r and d since the 1990s in winter 2002 2003 and 2008 2009 accumulation anomalies in the east and southeast temporarily outweighed the losses by m r and d that prevailed during 2003 2008 and after summer 2010 overall for all basins of the gris the decadal variability of anomalies in p m r and d between 1958 and 2010 w r t 1961 1990 was significantly exceeded by the regional trends observed during the grace period 2002 2011 2012 elsevier b v

precise p and s wave velocity structures in the kitakami massif northern honshu japan from a seismic refraction experiment the kitakami massif which is located in the eastern part of northern honshu japan is composed of two geological units the northern kitakami terrane is characterized as a jurassic accretionary complex while the southern kitakami terrane consists of pre silurian basement and silurian lower cretaceous marine sediments the boundary region of these two units called the hayachine tectonic belt htb is composed of mafic to ultramafic rocks the kitakami massif experienced intense granitic intrusions in the cretaceous we present a detailed crustal structure model for the eastern part of the massif derived from an extensive seismic refraction experiment conducted on a 194 km n s line the uppermost crust is covered with a very thin 0 5 1 km surface layer with a velocity of 3 1 5 4 km s the velocity structure below this layer shows remarkable lateral variation in the northern kitakami terrane the p wave velocity and vp vs at the top of the basement are 5 85 5 95 km s and 1 68 1 70 respectively the seismic attenuation in this region is high qp 150 200 and qs 70 100 in contrast the uppermost crust in the southern kitakami terrane is characterized by a high p wave velocity 6 05 6 15 km s and vp vs 1 74 1 77 the qp and qs also show high values of 300 400 and 150 200 respectively such a structural difference persists to 14 to 16 km depth at which the p wave velocity increases to 6 45 km s the low velocity and high attenuation in the northern kitakami terrane represent a highly deformed structure of the accretionary complex the high p wave velocity and vp vs in the southern kitakami terrane indicate the relatively mafic crustal composition which may result from the fragment of the oceanic crust incorporated by the accretion process or the uplifting in the latest jurassic early cretaceous a midcrustal interface determined from wide angle reflections shows an abrupt southward depth decrease from 25 to 20 km under the htb the p wave velocity and vp vs between 14 and 16 km depth and the midcrustal interface are 6 45 6 55 km s and 1 74 1 78 respectively the moho depth under the northern kitakami terrane decreases southward from 34 to 32 km in the southern kitakami terrane the moho dips slightly southward the p wave velocity and the vp vs ratio in the lower crust are 6 9 7 0 km s and 1 75 1 76 respectively the p wave velocity in the uppermost mantle is not well resolved but is probably less than 7 7 km s the s wave velocity derived from relatively clear sn is 4 35 4 40 km s our results show that the htb is a prominent structural boundary extending to the moho the crust of kitakami massif was not homogenized by the cretaceous granitic intrusions and the original structural difference remains in the upper crust

secular gravity variation at svalbard norway from ground observations and grace satellite data the svalbard archipelago norway is affected by both the present day ice melting pdim and glacial isostatic adjustment gia subsequent to the last pleistocene deglaciation the induced deformation of the earth is observed by using different techniques at the geodetic observatory in ny alesund precise positioning measurements have been collected since 1991 a superconducting gravimeter sg has been installed in 1999 and six campaigns of absolute gravity ag measurements were performed between 1998 and 2007 moreover the gravity recovery and climate experiment grace satellite mission provides the time variation of the earth gravity field since 2002 the goal of this paper is to estimate the present rate of ice melting by combining geodetic observations of the gravity variation and uplift rate with geophysical modelling of both the gia and earth s response to the pdim we estimate the secular gravity variation by superimposing the sg series with the six ag measurements we collect published estimates of the vertical velocity based on gps and vlbi data we analyse the grace solutions provided by three groups csr gfz grgs the crux of the problem lies in the separation of the contributions from the gia and pdim to the earth s deformation to account for the gia we compute the response of viscoelastic earth models having different radial structures of mantle viscosity to the deglaciation histories included in the models ice 3g or ice 5g to account for the effect of pdim we compute the deformation of an elastic earth model for six models of ice melting extension and rates errors in the gravity variation and vertical velocity are estimated by taking into account the measurement uncertainties and the variability of the grace solutions and gia and pdim models the ground observations agree with models that involve a current ice loss of 25 km3 water equivalent yr 1 over svalbard whereas the space observations give a value in the interval 5 18 km3 water equivalent yr 1 a better modelling of the pdim which would include the precise topography of the glaciers and altitude dependency of ice melting is necessary to decrease the discrepancy between the two estimates

constraints on the moho in japan and kamchatka abstract this review collects and systematizes in one place a variety of results which offer constraints on the depth and the nature of the moho beneath the kamchatka peninsula and the islands of japan we also include studies of the izu bonin volcanic arc all results have already been published separately in a variety of venues and the primary goal of the present review is to describe them in the same language and in comparable terms for both regions we include studies using artificial and natural seismic sources such as refraction and reflection profiling detection and interpretation of converted mode body waves receiver functions surface wave dispersion studies in kamchatka and tomographic imaging in japan the amount of work done in japan is significantly larger than in kamchatka and resulting constraints on the properties of the crust and the uppermost mantle are more detailed japan and kamchatka display a number of similarities in their crustal structure most notably the average crustal thickness in excess of 30 km typical of continental regions and the generally gradational nature of the crust mantle transition where volcanic arcs are presently active

post processing removal of correlated errors in grace data 1 gravity fields produced by the gravity recovery and climate experiment grace satellite mission require smoothing to reduce the effects of errors present in short wavelength components as the smoothing radius decreases these errors manifest themselves in maps of surface mass variability as long linear features generally oriented north to south i e stripes the presence of stripes implies correlations in the gravity field coefficients here we examine the spectral signature of these correlated errors and present a method to remove them finally we apply the filter to a model of surface mass variability to show that the filter has relatively little degradation of the underlying geophysical signals we seek to recover

on secular geocenter motion the impact of climate changes abstract we investigate the impact of recent climate changes on the long term displacement of the center of figure cf of the earth also defined as the geocenter in our convention with respect to the center of mass of the whole earth cm the two realizations of the international terrestrial reference system itrs entitled itrf2000 and itrf2005 present a difference of 1 8 mm yr between the velocities of their respective frame origins suggesting an acceleration of the geocenter towards the north pole we investigate if such a displacement could be explained by geophysical phenomena such as the present ice melting and the sea level rise using published observations on ice caps and glaciers we calculated the range of geocenter motion that may occur today we found that the global ice melting induces long term displacements of the geocenter mainly along the z axis toward the north pole the geocenter velocity is today between 0 3 and 0 7 0 8 mm yr and has doubled during last decade with the recent acceleration of ice melting combining with greff lefftz 2000 results on post glacial rebound we conclude that a present secular geocenter velocity of 1 mm yr is possible however the recent increase of the geocenter velocity cannot explain the difference observed between the two last realizations of the itrs our results comfort the previous conclusions about itrf2000 and itrf2005 and the pre analysis of itrf2008 data suggesting that the large z translation rate between the itrs realizations is probably due to an imprecise itrf2000 origin finally we show that determining precisely the geocenter velocity would give a new type of information that may be useful to more precisely constrain mass exchanges associated with climate changes

seismological features of island arc crust as inferred from recent seismic expeditions in japan abstract crustal studies within the japanese islands have provided important constraints on the physical properties and deformation styles of the island arc crust the upper crust in the japanese islands has a significant heterogeneity characterized by large velocity variation 5 5 6 1 km s and high seismic attenuation qp 100 400 for 5 15 hz the lateral velocity change sometimes occurs at major tectonic lines in many cases of recent refraction wide angle reflection profiles a middle crust with a velocity of 6 2 6 5 km s is found in a depth range of 5 15 km most shallow microearthquakes are concentrated in the upper middle crust the velocity in the lower crust is estimated to be 6 6 7 0 km s the lower crust often involves a highly reflective zone with less seismicity indicating its ductile rheology the uppermost mantle is characterized by a low pn velocity of 7 5 7 9 km s several observations on pmp phase indicate that the moho is not a sharp boundary with a distinct velocity contrast but forms a transition zone from the upper mantle to the lower crust recent seismic reflection experiments revealed ongoing crustal deformations within the japanese islands a clear image of crustal delamination obtained for an arc arc collision zone in central hokkaido provides an important key for the evolution process from island arc to more felsic continental crust in northern honshu a major fault system with listric geometry which was formed by miocene back arc spreading was successfully mapped down to 12 15 km

antarctic mass rates from grace 1 we estimate mass trends over antarctica using gravity variations observed by the gravity recovery and climate experiment grace satellite mission during its first 3 5 years april 2002 november 2005 an image of surface mass trends is constructed from 1 1 pixels over the entire continent and shows two prominent features a region of mass loss along the coast of west antarctica and one of accumulation in east antarctica after adjusting for bias due to smoothing and to grace s limited spatial resolution and removing post glacial rebound pgr effects the rate in west antarctica is 77 14 km3 year similar to a recent estimate of ice mass loss from satellite altimetry and remote sensing data the prominent east antarctic feature in the enderby land region has a rate of 80 16 km3 year published snow ice mass rates from remote sensing measurements indicate approximate ice mass balance in this region suggesting that this feature is either from unquantified snow accumulation in this region or more likely due to unmodeled pgr

methods for inferring regional surface mass anomalies from gravity recovery and climate experiment grace measurements of time variable gravity 1 the gravity recovery and climate experiment grace will deliver monthly averages of the spherical harmonic coefficients describing the earth s gravity field from which we expect to infer time variable changes in mass averaged over arbitrary regions having length scales of a few hundred kilometers and larger to accuracies of better than 1 cm of equivalent water thickness these data will be useful for examining changes in the distribution of water in the ocean in snow and ice on polar ice sheets and in continental water and snow storage we describe methods of extracting regional mass anomalies from grace gravity coefficients spatial averaging kernels were created to isolate the gravity signal of individual regions while simultaneously minimizing the effects of grace observational errors and contamination from surrounding glacial hydrological and oceanic gravity signals we then estimated the probable accuracy of averaging kernels for regions of arbitrary shape and size

on the joint distribution of surface elevation and slopes for a nonlinear random sea with an application to radar altimetry the work of longuet higgins 1963 on the effects of wave nonlinearity on the statistics of the sea surface is extended here to obtain the joint distribution of surface elevation and slopes for a nonlinear random sea the results are used to examine the effect of wave nonlinearity on the form of a radar altimeter pulse which is reflected from the sea surface it is shown how wave information may be derived from the return pulse and how this can be used to correct errors in the altimeter mean sea level estimate a problem known as sea state bias

reconstruction of subduction and back arc spreading in the nw pacific and aleutian basin clues to causes of cretaceous and eocene plate reorganizations the eocene 50 45 ma major absolute plate motion change of the pacific plate forming the hawaii emperor bend is thought to result from inception of pacific plate subduction along one of its modern western trenches subduction is suggested to have started either spontaneously or result from subduction of the izanagi pacific mid ocean ridge or from subduction polarity reversal after collision of the olyutorsky arc that was built on the pacific plate with ne asia here we provide a detailed plate kinematic reconstruction of back arc basins and accreted terranes in the northwest pacific region from japan to the bering sea since the late cretaceous we present a new tectonic reconstruction of the intraoceanic olyutorsky and kronotsky arcs which formed above two adjacent oppositely dipping subduction zones at 85 ma within the north pacific region during another pacific wide plate reorganization we use our reconstruction to explain the formation of the submarine shirshov and bowers ridges and show that if marine magnetic anomalies reported from the aleutian basin represent magnetic polarity reversals its crust most likely formed in an 85 to 60 ma back arc basin behind the olyutorsky arc the olyutorsky arc was then separated from the pacific plate by a spreading ridge so that the 55 to 50 ma subduction polarity reversal that followed upon olyutorsky ne asia collision initiated subduction of a plate that was not the pacific hence this polarity reversal may not be a straightforward driver of the eocene pacific plate motion change whose causes remain enigmatic

crustal structure and tectonics of the hidaka collision zone hokkaido japan revealed by vibroseis seismic reflection and gravity surveys abstract this study is the first integrated geological and geophysical investigation of the hidaka collision zone in southern central hokkaido japan which shows complex collision tectonics with a westward vergence the hidaka collision zone consists of the idon nappu belt ib the poroshiri ophiolite belt pob and the hidaka metamorphic belt hmb with the hidaka belt from west to east the pob metamorphosed ophiolites is overthrust by the hmb steeply eastward dipping palaeo arc crust along the hidaka main thrust hmt and in turn thrusts over the idon nappu belt melanges along the hidaka western thrust hwt seismic reflection and gravity surveys along a 20 km long traverse across the southern hidaka mountains revealed hitherto unknown crustal structures of the collision zone such as listric thrusts back thrusts frontal thrust and fold structures and duplex structures the main findings are as follows 1 the hmt which dips steeply at the surface is a listric fault dipping gently at a depth of 7 km beneath the eastern end of the hmb and cutting across the lithological boundaries and schistosity of the hidaka metamorphic rocks 2 a second reflector is detected 1 km below the hmt reflector the intervening part between these two reflectors is inferred to be the pob which is only little exposed at the surface this inference is supported by the high positive bouguer anomalies along the hidaka mountains 3 the shallow portion of the ib at the front of the collision zone has a number of nne dipping reflectors indicative of imbricated fold and thrust structures 4 subhorizontal reflectors at a depth of 14 km are recognized intermittently at both sides of the seismic profile these reflectors may correspond to the velocity boundary 5 9 6 6 km s previously obtained from seismic refraction profiling in the northern hidaka mountains 5 these crustal structures as well as the back thrust found in the eastern end of the traverse represent characteristics of collisional tectonics resulting from the two collisional events since the early tertiary

anomalous pre seismic transmission of vhf band radio waves resulting from large earthquakes and its statistical relationship to magnitude of impending earthquakes summary to confirm the relationship between anomalous transmission of vhf band radio waves and impending earthquakes we designed a new data collection system and have documented the anomalous vhf band radio wave propagation beyond the line of sight prior to earthquakes since 2002 december in hokkaido northern japan anomalous vhf band radio waves were recorded before two large earthquakes the tokachi oki earthquake mj 8 0 mj magnitude defined by the japan meteorological agency on 2003 september 26 and the southern rumoi sub prefecture earthquake mj 6 1 on 2004 december 14 radio waves transmitted from a given fm radio station are considered to be scattered such that they could be received by an observation station beyond the line of sight a linear relationship was established between the logarithm of the total duration time of anomalous transmissions te and the magnitude m or maximum seismic intensity i of the impending earthquake for m4 m5 class earthquakes that occurred at depths of 48 54 km beneath the hidaka mountains in hokkaido in 2004 june and 2005 august similar linear relationships are also valid for earthquakes that occurred at different depths the relationship was shifted to longer te for shallower earthquakes and to shorter te for deeper ones numerous parameters seem to affect te including hypocenter depths and surface conditions of epicentral area i e sea or land this relationship is important because it means that pre seismic anomalous transmission of vhf band waves may be useful in predicting the size of an impending earthquake

on the statistics of the phase of microwave backscatter from the ocean surface in this paper we describe what we believe is the first study of the distribution of the phase of microwave fields backscattered from the ocean surface scatterometry data from the synthetic aperture radar and x band ocean nonlinearities experiment conducted on the german north sea research platform forschungsplatform nordsee in november 1990 have been analyzed to reveal the distribution of phase differences as a function of time lag a theoretical model for these statistics is presented based on modulated gaussian fields this theoretical model is shown to be in good agreement with the measured statistics from this agreement we conclude that the backscattered fields have a gaussian distribution on short time scales but are modulated in amplitude and frequency by the long surface waves these results are of more than purely academic interest with direct applications to the design and analysis of interferometric synthetic aperture radars a relatively new class of instruments that may be capable of providing high resolution maps of ocean surface currents from aircraft or satellites

newly imaged shape of the deep seismic zone within the subducting pacific plate beneath the hokkaido corner japan kurile arc arc junction 1 the geometry of the deep seismic zone associated with the subducting pacific plate beneath the north american plate in the hokkaido corner japan kurile arc arc junction has been investigated based on the hypocenters accurately relocated by a dense local seismographic network with three dimensional p and s wave velocity structures the model suggests that the lateral changes in the dip of the subduction zone are more rapid than previously believed we found that the deep seismic zone in the pacific plate dips at 20 to 30 on the side of the japan arc the dip angle increased in a narrow region around 143 144 e by 10 to 20 and the dip was 40 to 50 on the side of the kurile arc in the transitional zone around 143 144 e an unusual distribution of microearthquakes has been discovered within the pacific plate which was located on a near vertical plane with an area of 50 100 km2 with strike that was perpendicular to the kurile trench axis this feature was named the tokachi oki slab cracking zone we suggest that this is a slab cracking zone torn by the extensional stress due to the rapid lateral changes in the dip of the subduction zone the slab cracking zone may possibly grow into the large disruption or tear of the slab in the future

ocean wave slope observations using radar backscatter and laser altimeters abstract combination of laser and radar aboard an aircraft is used to directly measure long gravity wave surface tilting simultaneously with nadir viewing microwave backscatter from the sea surface the presented dataset is extensive encompassing varied wind conditions over coastal and open ocean wave regimes laser derived slope statistics and ka band 36 ghz radar backscatter are detailed separately to document their respective variations versus near surface wind speed the slope statistics measured for 1 2 m show good agreement with cox and munk s oil slickened sea measurements a notable exception is elevated distribution peakedness and an observed wind dependence in this likely proxy for nonlinear wave wave interactions aircraft ka band radar data nearly mimic ku band satellite altimeter observations in their mean wind dependence the present calibrated radar data along with relevant observational and theoretical studies suggest a large 5 db bias in previous ka band results next wave

evolution of the sea of japan back arc and some unsolved issues abstract the sea of japan back arc system provides an exceptional opportunity to study a virtually intact continent ocean back arc system in which recent tectonic inversion has exposed entire sequences of back arc structure on land moreover japan s dense seismic geodetic monitoring networks deployed country wide as well as moveable pools of ocean bottom seismometers provide a rich data set through which to investigate deep back arc structure earlier investigations have produced an initial understanding of back arc opening timing structural evolution temporal spatial patterns of magmatic activity many questions remain among them the mechanism of back arc opening pull apart or trench rollback the dynamics of interacting plates location of the philippine sea plate with time the origin of the anomalously thick japan sea ocean crust and possible influences of far field forces india asia collision given existing high resolution geophysical data sets and extensive on land exposures of back arc sequences and structures the sea of japan back arc is a promising context in which to address both local and more universal questions of how back arc systems evolve here we review the tectonic setting and geological evolution of the sea of japan based our own and others work and briefly discuss outstanding questions that invite further investigation

collision structure in the upper crust beneath the southwestern foot of the hidaka mountains hokkaido japan as derived from explosion seismic observations the p wave velocity structure of the upper crust beneath a profile ranging from niikappu to samani in the southwestern foot of the hidaka mountains hokkaido japan was obtained through analysis of refraction and wide angle reflection data the mountains are characterized by high seismicity and a large gravity anomaly the present profile crosses the source region of the 1982 urakawa oki earthquake ms 6 8 the length of the profile is 66 km striking northwest and southeast along the profile 64 vertical geophones were set up and 5 shot points were chosen for each shot a 400 600 kg charge of dynamite was detonated the studied area is composed of four major geological belts neogene sedimentary rocks the kamuikotan belt the yezo group and the hidaka belt the measurement line crosses these geological trend at an oblique angle the structure obtained is characterized by remarkable velocity variations in the lateral direction and reflects the surface geological characteristics a thin high velocity layer hvl was found between low velocity materials in the central part of the profile beneath the kamuikotan metamorphic belt at a depth ranging from 0 5 to 6 km overthrusting toward the west on the low velocity materials consisting of neogene sedimentary rocks and forming gentle folds outlines of the velocity structure of the hidaka mountains yielded by other studies have shown a large scale overthrust structure associated with the collision of the outer kurile and the outer northern honshu arcs the shallow velocity structure inferred by the present study showed a similar although small scale overthrust structure the obtained structure shows that the composite tectonic force comprising westward movement of the outer kurile arc and northward movement of the outer northern honshu arc plays an important role in the evolution of the tectonic features of the crust and upper mantle in a wide depth range beneath the hidaka mountains

simultaneous inversion for the earth s mantle viscosity and ice mass imbalance in antarctica and greenland redistribution of mass in the earth due to pleistocene deglaciation and to present day glacial melting induces secular changes in the earth s gravitational field the earth is affected today by the former mechanism because of the viscous memory of the mantle and by the latter because of ongoing surface mass redistribution and related elastic response a self consistent procedure allows us to invert simultaneously for the lower and upper mantle viscosity and for the present day mass imbalance in antarctica and greenland using the observed time variations of the long wavelength gravity field from satellite laser ranging slr analyses the procedure is based on our normal mode relaxation theory for the forward modeling and a newly developed inversion scheme based on the levenberg marquardt method we obtain a large viscosity increase across the 670 km depth transition zone separating the upper and the lower mantle with the lower mantle viscosity varying over the range 5 1021 to 1022 pa s and the less resolved upper mantle viscosity of the order of 1020 pa s when antarctica is the only present day source its rate of melting is 240 gt yr 1 corresponding to a sea level rise of 0 7 mm yr 1 when greenland is added as a source of ice loss the rates of melting are 280 gt yr 1 for antarctica and 60 gt yr 1 for greenland corresponding to sea level rises of 0 8 and 0 2 mm yr 1 slr data indicate that ice melting in the polar regions of the earth is ongoing

evaluation of new grace time variable gravity data over the ocean 1 monthly grace gravity field models from the three science processing centers csr gfz and jpl are analyzed for the period from february 2003 to april 2005 over the ocean the data are used to estimate maps of the mass component of sea level at smoothing radii of 500 km and 750 km in addition to using new gravity field models a filter has been applied to estimate and remove systematic errors in the coefficients that cause erroneous patterns in the maps of equivalent water level the filter is described and its effects are discussed the grace maps have been evaluated using a residual analysis with maps of altimeter sea level from jason 1 corrected for steric variations using the world ocean atlas 2001 monthly climatology the mean uncertainty of grace maps determined from an average of data from all 3 processing centers is estimated to be less than 1 8 cm rms at 750 km smoothing and 2 4 cm at 500 km smoothing which is better than was found previously using the first generation grace gravity fields

geology of the idonnappu belt central hokkaido japan evolution of a cretaceous accretionary complex the cretaceous idonnappu belt located along the western hidaka mountains of central hokkaido island in japan records evidence of west to northwest directed underthrusting of oceanic crust the idonnappu fault divides the idonnappu belt into two subbelts the western oku niikappu on subbelt and the eastern koiboku ko subbelt the on subbelt is dominated by a melange facies it includes various thicknesses of pillow basalts bedded radiolarian cherts limestones and greenish siliceous shales all of which are intermixed with a highly sheared shaley matrix that displays a scaly cleavage the ko subbelt is dominated by a thick flysch sequence and alternations of sandstone and shale with thin tectonic melange the stratigraphic sequences within these belts usually young toward the west and display westward vergent structures outcrop to microscopic scale structures in the melange zone of the idonnappu belt however suggest eastward vergence detailed biostratigraphic studies show that structural packages young toward the east ranging in age from lower to upper cretaceous these observations are consistent with an accretionary prism model in which oceanic crust is underthrust toward the west or north west in the middle miocene a change to westward vergence was caused by uplift of the hidaka mountains

time variability of the earth s gravity field hydrological and oceanic effects and their possible detection using grace the grace satellite mission scheduled for launch in 2001 is designed to map out the earth s gravity field to high accuracy every 2 4 weeks over a nominal lifetime of 5 years changes in the gravity field are caused by the redistribution of mass within the earth and on or above its surface grace will thus be able to constrain processes that involve mass redistribution in this paper we use output from hydrological oceanographic and atmospheric models to estimate the variability in the gravity field i e in the geoid due to those sources we develop a method for constructing surface mass estimates from the grace gravity coefficients we show the results of simulations where we use synthetic grace gravity data constructed by combining estimated geophysical signals and simulated grace measurement errors to attempt to recover hydrological and oceanographic signals we show that grace may be able to recover changes in continental water storage and in seafloor pressure at scales of a few hundred kilometers and larger and at timescales of a few weeks and longer with accuracies approaching 2 mm in water thickness over land and 0 1 mbar or better in seafloor pressure

deep seismic probing of the continents and their margins abstract application of deep seismic methods to studies of the crust and lithospheric mantle receives considerable interest and the methods are constantly refined and new methods are developed which allows the extension of studies to new subjects and regions deep seismic methods are applied to a long range of geoscientific subjects in research on the formation and development of crust and lithosphere in continental and oceanic environments from being an experimental discipline some 30 40 years ago a series of methods can now be applied almost routinely to research on the lithosphere however in many applications the methods are used up to their limits at the present technological state therefore development of methods has high priority in the seismic community this volume provides an overview of recent development of deep seismic techniques and their application to the imaging and probing of the continents and their margins

time variable gravity from grace first results eleven monthly grace gravity field solutions are now available for analyses we show those fields can be used to recover monthly changes in water storage both on land and in the ocean to accuracies of 1 5 cm of water thickness when smoothed over 1000 km the amplitude of the annually varying signal can be determined to 1 0 cm results are 30 better for a 1500 km smoothing radius and 40 worse for a 750 km radius we estimate the annually varying component of water storage for three large drainage basins the mississippi the amazon and a region draining into the bay of bengal to accuracies of 1 0 1 5 cm

a reconciled estimate of ice sheet mass balance we combined an ensemble of satellite altimetry interferometry and gravimetry data sets using common geographical regions time intervals and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of earth s polar ice sheets we find that there is good agreement between different satellite methods especially in greenland and west antarctica and that combining satellite data sets leads to greater certainty between 1992 and 2011 the ice sheets of greenland east antarctica west antarctica and the antarctic peninsula changed in mass by 142 49 14 43 65 26 and 20 14 gigatonnes year 1 respectively since 1992 the polar ice sheets have contributed on average 0 59 0 20 millimeter year 1 to the rate of global sea level rise

separation of the geodetic consequences of past and present ice mass change influence of topography with application to svalbard norway polar regions such as greenland svalbard and antarctica are deforming today because of both the present day ice mass pdim change of glaciers and the glacial isostatic adjustment gia following the pleistocene deglaciation observations handled in these areas contain both the contributions from the pdim change and gia this study aims at separating them by considering two specific gravity variation to vertical displacement ratios we first review the case of the viscoelastic rebound gia subsequent to the pleistocene deglaciation leading to a ratio c v the outcome of previous studies is that c v is approximately equal to 0 15 gal mm and almost independent of the deglaciation history ice geometry and viscosity profile of the mantle similarly we consider the elastic deformation resulting from pdim change which leads to a second ratio c e n several studies have shown that c e n approx 0 26 mu gal mm if one assumes that the changing glaciers are thin layers over the surface of a spherical earth model in this case we show that the separation between the contributions from pdim change and gia is unique if both gravity and height changes observations are available at the same station next we focus on c e n and show that according to the deglaciation glaciation context and from colocated gravity variation and ground vertical velocity measurements one can deduce a range of possible values for c e n studying the influence of the topography on c e n we first show that it tends to positive values if most of surrounding ice mass changes above the altitude of the observation site and to values lower than 0 26 gal mm if changes are below we next apply our general formalism to the case of the past and pdim changes in svalbard norway we compute the ratio c e n at the geodetic observatory at ny alesund and show the influence of the topography of the surrounding glaciers on the measured gravity and uplift rates we show that if the ice mass change is spatially uniform c e n does not depend on the speed of ice mass change and hence the separation of the contributions from pdim changes and gia can still be done univocally however if the ice mass change is not spatially uniform c e n depends on both the speed of ice mass change and the volume of ice change rate

anisotropic tomography of hokkaido reveals delamination induced flow above a subducting slab we present a new 3 d anisotropic seismic model for the crust and upper mantle beneath hokkaido japan based on tomographic inversion of p and s arrival times from a regional seismic database the p model is parameterized with three parameters at each point that describe the azimuthal anisotropy the s model is represented isotropically the isotropic p and s velocity anomalies match nearly perfectly in the crust they show a prominent linear anomaly in central hokkaido along the kamuikotan and hidaka belts which represents the area of eastward underthrusting of the japan block underneath the kuril fore arc we interpret the high velocity anomaly beneath the hidaka zone as being delaminated mafic crust and entrained mantle lithosphere which developed due to crustal shortening in the collision zone one of our vertical sections shows a very unusual configuration for a subduction zone a low velocity slab is overlain by a high velocity body in the mantle wedge we propose that the high velocity delaminated material sinking along the slab surface prevents the escape of fluids and melts from the upper part of the slab where they are generated due to phase transitions as a result a large portion of the fluids is entrained downward and lowers the seismic velocities in the slab the azimuthal anisotropy in the crust clearly corresponds to the major tectonic units and delineates the major suture zones in the mantle the anisotropy has a fan shaped configuration and most likely represents the deviating of flows starting in southern hokkaido and splitting into three directions the western and eastern flows proceed toward the two volcanic groups on hokkaido and they may carry with them additional material to trigger the characteristic caldera forming eruptions in these groups

configuration of the moho discontinuity beneath the japanese islands derived from three dimensional seismic tomography abstract the mohorovicic discontinuity moho is defined on the basis of an abrupt increase in seismic velocity in the lithosphere which has been observed using seismic refraction and receiver function analysis methods worldwide moho depth varies regionally and remains a fundamental parameter of crustal structure we present a new method of mapping the moho using a 3d seismic tomography model since the tomographic method cannot locate discontinuities we treat the moho as a zone of high velocity gradient maximum lower crust minimum upper mantle p wave velocities in japan are known to be 7 0 km s and 7 5 km s respectively we map the residual between isovelocity surfaces of 7 0 km s and 7 5 km s to find areas where the residual is small the separation between the surfaces is narrow and the velocity gradient is high the moho is best constrained where the isovelocity surfaces are close together and under much of japan they are 10 km apart we chose an isovelocity surface of 7 2 km s as a representative moho proxy in these areas our resulting moho map under japan compares favorably with existing regional moho models that were obtained from controlled source seismic investigations the moho varies from shallow 25 30 km to deep 30 km and this variability relates to the structural evolution of the japanese islands the opening of the sea of japan back arc ongoing arc arc collisions at the hidaka and izu collision zones ongoing back arc extension in kyushu and a possible failed back arc extensional event of mesozoic age it is apparent that the moho is less well constrained in areas where the crustal structure has been modified by magmatic activity or thickened due to arc arc collision

determination of the ocean circulation using geosat altimetry a spherical harmonic model of the sea surface topography complete to degree and order 10 and a model of the earth s geopotential field complete to degree and order 50 have been obtained in a simultaneous solution using geosat altimeter data and tracking data from 14 different satellites the sea surface topography model compares well with oceanographic models computed using hydrographic data and ship drift data currently errors in the estimated gravity field model limit the determination of the spherical harmonic coefficients of the general ocean circulation to degrees 10 and lower corresponding to a minimum wavelength of 4 000 km error analysis indicates that the correlation between the geoid and the sea surface topography model is less than 0 2 indicating good separation of the geoid and the sea surface topography at wavelengths of 4 000 km or longer estimates of the scale factor for the significant wave height h sub 1 3 which is used to compute the electromagnetic bias correction and the bias for the geosat altimeter are obtained the estimate of the h sub 1 3 correction is 3 6 plus minus 1 5 and the height bias estimate is zero

a baseline antarctic gia correction for space gravimetry abstract within the past decade newly collected gps data and geochronological constraints have resulted in refinement of glacial isostatic adjustment gia models for antarctica these are critical to estimating and understanding ice mass changes at present day a correction needs to be made when using space gravity for ice mass balance assessments due to the fact that any vertical movements of the solid earth masquerade as changes in ice mass and these must be carefully removed the main upshot of the new antarctic gia models is a downward revision of negative ice mass trends deduced from the gravity recovery and climate experiment grace resulting from a reduced gia correction this revision places grace inferred trend in mass balance within the one sigma uncertainty of mass balance deduced by altimetry because uncertainties in holocene ice history and the low viscosity rheology beneath the west antarctic ice sheet wais continue to vex further improvement in predictions of present day gia gravity rate more emphasis has been given to regional scale gia models here we use a bayesian method to explore the gravimetric gia trend over antarctica both with and without the impact of a late pleistocene antarctic ice loads along with the contribution of oceanic loads we call this model without loads associated with antarctica a baseline for regional gia models to build upon we consider variations of the radial mantle viscosity profile and the volume of continental scale ice sheets during the last glacial cycle the modeled baseline gia is mainly controlled by the lower mantle viscosity and continental levering caused by ocean loading we find that the predicted baseline gia correction weakly depends on the ice history this correction averages to 28 4 16 5 41 9 95 confidence gt yr of which 23 6 5 3 are contributed by east antarctica in contrast with late pleistocene antarctic proximal ice included the total modeled mass trend due to gia is 73 7 30 1 114 7 gt yr a baseline gia correction of 28 4 gt yr is of order 50 of the mean net mass trend measured during the period 1992 2017 the statistical analysis provides tools for properly synthesizing any regional antarctic gia model with a self consistent far field component this may prove important for accounting for both global and regional 3 d variations in mantle viscosity

changes in the velocity structure of the greenland ice sheet using satellite radar interferometry observations of greenland we detected widespread glacier acceleration below 66 north between 1996 and 2000 which rapidly expanded to 70 north in 2005 accelerated ice discharge in the west and particularly in the east doubled the ice sheet mass deficit in the last decade from 90 to 220 cubic kilometers per year as more glaciers accelerate farther north the contribution of greenland to sea level rise will continue to increase

lower satellite gravimetry estimates of antarctic sea level contribution a new model of glacial isostatic adjustment used in conjunction with grace satellite data suggests that ice loss from antarctica is contributing 0 19 millimetres per year to global mean sea level which is substantially less than previous grace based estimates estimates for recent mass loss from antarctica vary widely making it difficult to calculate any subsequent contributions to sea level rise one prominent approach uses the grace gravity recovery and climate experiment satellites to detect changes in gravity but the final estimates are dependent on the modelled response of the continent to changes in ice loading over time and to changes in lithospheric elastic rebound matt king and colleagues apply a new model of this glacial isostatic adjustment to the grace data and estimate antarctic mass loss between 2002 and 2010 to be about 69 gigatonnes per year much lower than previous estimates and equivalent to an annual sea level rise of about 0 2 millimetres recent estimates of antarctica s present day rate of ice mass contribution to changes in sea level range from 31 gigatonnes a year gt yr 1 ref 1 to 246 gt yr 1 ref 2 a range that cannot be reconciled within formal errors3 time varying rates of mass loss2 4 5 6 contribute to this but substantial technique specific systematic errors also exist3 in particular estimates of secular ice mass change derived from gravity recovery and climate experiment grace satellite data are dominated by significant uncertainty in the accuracy of models of mass change due to glacial isostatic adjustment7 8 gia here we adopt a new model of gia developed from geological constraints which produces gia rates systematically lower than those of previous models and an improved fit to independent uplift data9 after applying the model to 99 months from august 2002 to december 2010 of grace data we estimate a continent wide ice mass change of 69 18 gt yr 1 0 19 0 05 mm yr 1 sea level equivalent this is about a third to a half of the most recently published grace estimates2 5 which cover a similar time period but are based on older gia models plausible gia model uncertainties and errors relating to removing longitudinal grace artefacts destriping confine our estimate to the range 126 gt yr 1 to 29 gt yr 1 0 08 0 35 mm yr 1 sea level equivalent we resolve 26 independent drainage basins and find that antarctic mass loss and its acceleration is concentrated in basins along the amundsen sea coast outside this region we find that west antarctica is nearly in balance and that east antarctica is gaining substantial mass

sea state related altitude errors in the seasat radar altimeter a significant waveheight dependent bias is identified in seasat measured surface heights which cannot be neglected when using seasat data at accuracies within 10 cm ten second averages of the data from 63 waveform sampling rates in the seasat radar altimeter were least squares fitted with a six parameter model the time origin parameter of which provides a measure of the position of the actual mean radar waveform relative to the sampling rate and therefore provides altitude measurement corrections attention is given to actual altimeter point target response function waveform sampler noise baseline waveform sampler gain calibration attitude angle and sea surface skewness as effects not accounted for in seasat altimeter measurements and standard data processing

satellite gravity measurements confirm accelerated melting of greenland ice sheet using time variable gravity measurements from the gravity recovery and climate experiment grace satellite mission we estimate ice mass changes over greenland during the period april 2002 to november 2005 after correcting for the effects of spatial filtering and limited resolution of grace data the estimated total ice melting rate over greenland is 239 23 cubic kilometers per year mostly from east greenland this estimate agrees remarkably well with a recent assessment of 224 41 cubic kilometers per year based on satellite radar interferometry data grace estimates in southeast greenland suggest accelerated melting since the summer of 2004 consistent with the latest remote sensing measurements

can the okhotsk plate be discriminated from the north american plate the plate geometry in northeast asia has been a long standing question with a major issue being whether the sea of okhotsk and northern japanese islands are better regarded as part of the north american plate or as a separate okhotsk plate this question has been difficult to resolve because earthquake slip vectors along the kuril and japan trenches are consistent with either pacific north america or pacific okhotsk plate motion to circumvent this difficulty we also use slip vectors of earthquakes along sakhalin island and the eastern margin of the japan sea and compare them to the predicted eurasia okhotsk and eurasia north america motions for a model with a separate okhotsk plate we invert 10 eurasia okhotsk and 255 pacific okhotsk slip vectors with pacific north america and eurasia north america nuvel 1 data alternatively for a model without an okhotsk plate those eurasia okhotsk and pacific okhotsk data are regarded as eurasia north america and pacific north america data respectively the model with an okhotsk plate fits the data better than one in which this region is treated as part of the north american plate because the improved fit exceeds that expected purely from the additional plate the data indicate that the okhotsk plate can be resolved from the north american plate the motions on the okhotsk plate s boundaries predicted by the best fitting euler vectors are generally consistent with the recent tectonics the eurasia okhotsk pole is located at northernmost sakhalin island and predicts right lateral strike slip motion on the nne striking fault plane of the may 27 1995 neftegorsk earthquake consistent with the centroid moment tensor focal mechanism and the surface faulting along the northern boundary of the okhotsk plate the north america okhotsk euler vector predicts left lateral strike slip consistent with the observed focal mechanisms on the nw boundary of the okhotsk plate the eurasia okhotsk euler vector predicts e w extension discordant with the limited focal mechanisms and geological data this misfit may imply that another plate is necessary west of the magadan region in southeast siberia but this possibility is hard to confirm without further data such as might be obtained from space based geodesy

accelerated antarctic ice loss from satellite gravity measurements accurate quantification of antarctic ice sheet mass balance and its contribution to global sea level rise remains challenging gravity recovery and climate experiment data spanning the period april 2002 to january 2009 confirm earlier estimates of ice loss for antarctica and indicate that east antarctica started losing mass in about 2006

the latest cretaceous early paleogene rapid growth of accretionary complex and exhumation of high pressure series metamorphic rocks in northwestern pacific margin episodic growth of accretionary complexes along the northwestern pacific margin is well documented from detailed biostratigraphy and radiometric dating of metamorphic rocks the latest cretaceous to early paleogene rapid growth of the accretionary complexes observed in hokkaido and sakhalin islands was caused by the supply of a large amount of terrigenous sediments from an intracontinent collision zone the mongolia okhotsk zone in the northern asian continent rapid growth of the accretionary prism resulted in episodic tectonic events in the forearc and magmatic arc rapid underplating caused uplift and exhumation of previously accreted complexes along with high pressure series metamorphic rocks now exposed as the kamuikotan complex in hokkaido and the susunai complex in sakhalin the forearc basin shallowed as a result of the uplift the uplift collapsed the old accretionary complex and supplied olistoliths onto the forearc region magmatic activity along the continental margin was also active at the same time subduction of a large amount of terrigenous sediments into the mantle may have contributed to active magmatism at that time a large supply of water trapped in the subducted sediments entered the mantle and increased partial melting of the mantle wedge

acceleration of greenland ice mass loss in spring 2004 in 2001 the intergovernmental panel on climate change projected the contribution to sea level rise from the greenland ice sheet to be between 0 02 and 0 09 m from 1990 to 2100 ref 1 however recent work has suggested that the ice sheet responds more quickly to climate perturbations than previously thought particularly near the coast here we use a satellite gravity survey by the gravity recovery and climate experiment grace conducted from april 2002 to april 2006 to provide an independent estimate of the contribution of greenland ice mass loss to sea level change we detect an ice mass loss of 248 36 km3 yr 1 equivalent to a global sea level rise of 0 5 0 1 mm yr 1 the rate of ice loss increased by 250 per cent between the periods april 2002 to april 2004 and may 2004 to april 2006 almost entirely due to accelerated rates of ice loss in southern greenland the rate of mass loss in north greenland was almost constant continued monitoring will be needed to identify any future changes in the rate of ice loss in greenland

a new inference of mantle viscosity based upon joint inversion of convection and glacial isostatic adjustment data we present new profiles of mantle viscosity derived on the basis of non linear occam style joint inversions of an extensive set of data associated with mantle convection and glacial isostatic adjustment gia the convection related observables include satellite derived free air gravity harmonics the geodetically inferred excess ellipticity of the cmb and tectonic plate motions the gia constraints involve two classes of observables previously shown to be relatively insensitive to errors in the late pleistocene ice history the so called fennoscandian relaxation spectrum frs and a set of site specific decay times determined from the postglacial sea level history in hudson bay and sweden the inverted viscosity profiles show a significant three orders of magnitude increase from the upper mantle mean value of f4 10 20 pa s to a high viscosity 10 23 pa s peak at

new models for satellite altimeter sea state bias correction developed using global wave model data sea level determination via satellite altimetry is subject to numerous error sources one of these is the sea state bias where changing surface wave conditions alter an altimeter s estimate of mean sea level recent work suggests that present day methods for correcting this bias based solely on wave and wind information from the altimeter may be improved if additional surface gravity wave field measurements become available this paper tests this hypothesis by developing several new sea state bias correction models using a year long combination of jason 1 data with wave field statistics generated from an hindcast of the wavewatch3 ocean wave model each candidate model is produced in the same manner through a nonparametric mapping between jason 1 sea surface height anomaly estimates and two correlatives the first is always the significant wave height from jason 1 and the model differences come through choice of the second variable past studies dictate our selection of these second parameters and they include terms related to the local wind speed swell energy wave age wave period and wave slope evaluation of model skill is conducted in term of explained variance several candidate models do indicate promise for wave model use in future empirical developments results show that in the low latitudes the models developed using the swell height and mean period modestly outperform the operational parameterisation of the bias model thus this study indicates that systematic regional error in the present sea level corrections may be improved by inclusion of wave model information

on postglacial geoid subsidence over the equatorial oceans we develop two new spectral formalisms for the gravitationally self consistent solution of the sea level equation which governs the redistribution of glacial meltwater on a visco elastic earth the first is a purely spectral technique based on an extension of theory outlined by dahlen 1976 for determining the equilibrium oceanic tide on an elastic planet using this technique with a feasible spherical harmonic truncation level l 30 we can obtain convergence in the computed sea level variations within the degree range l 10 we also develop a second pseudospectral technique however which permits the construction of gravitationally self consistent solutions to much higher degree and order l 100 the pseudospectral formalism is employed here to develop a comprehensive physical explanation for the global pattern of present day sea level variations due to ongoing glacial isostatic adjustment in particular we focus upon a mechanism which we term equatorial ocean syphoning that acts to draw water toward the oceanic portion of the collapsing peripheral bulge that encircles previously glaciated regions the collapse of the forebulge induces a flow of water which is required to maintain hydrostatic equilibrium the syphoning mechanism dominates the relative sea level rsl variation in oceans in the far field of the ice sheets that is beyond the peripheral bulge during periods such as the interglacial of the past 4000 years during which the volume of the ice sheets has not apparently changed appreciably while at the same time isostatic adjustment persists the rsl change in the near field is in contrast dominated by the local vertical displacement of the solid surface finally comparison of gravitationally self consistent predictions of rsl change in the far field with the observational data at small pacific island sites has provided an upper bound of 1 to 2 m for the eustatic sea level rise produced by any recent last 3000 years melting of the antarctic ice sheet

measurements of electromagnetic bias in radar altimetry the accuracy of satellite altimetric measurements of sea level is limited in part by the influence of ocean waves on the altimeter signal reflected from the sea surface the difference between the mean reflecting surface and mean sea level is the electromagnetic bias the bias is poorly known yet for such altimetric satellite missions as the topography experiment topex poseidon it is the largest source of error exclusive of those resulting from calculation of the satellite s ephemeris previous observations of electromagnetic bias have had a large apparently random scatter in the range of 1 5 of significant wave height these observations are inconsistent with theoretical calculations of the bias to obtain a better understanding of the bias we have measured it directly using a 14 ghz scatterometer on the chesapeake bay light tower we find that the bias is a quadratic function of significant wave height h1 3 the normalized bias defined as the bias divided by the significant wave height is strongly correlated with wind speed at 10 m u10 and much less strongly with significant wave height the mean value for is 0 034 and the standard deviation of the variability about the mean is 0 0097 the standard deviation of the variability after removing the influence of wind and waves is 0 0051 0 51 the results are based on data collected over a 24 day period during the synthetic aperture radar and x band ocean nonlinearities saxon experiment from september 19 to october 12 1988 during the experiment hourly averaged values of wind speed ranged from 0 2 to 15 3 m s significant wave height ranged from 0 3 to 2 9 m and air minus sea temperature ranged from 10 2 to 5 4 c because u10 can be calculated from the scattering cross section per unit area 0 of the sea measured by spaceborne altimeters we investigated the usefulness of 0 for calculating bias we find that is strongly correlated with 0 and much less strongly with h1 3 the standard deviation of the variability after removing the influence of the radio cross section and waves is 0 0065 0 65 the results indicate that electromagnetic bias in radar altimetry may be reduced to the level required by the topex poseidon mission using only altimetric data we find furthermore that the relationship between 0 and wind speed agrees with previously published power law relationships within the accuracy of the measurement the mean value of its variability and the sensitivity of to wind speed all agree well with previous measurements made using a 10 ghz radar carried on a low flying aircraft the mean value of its variability and the sensitivity to wind were all significantly larger than previous measurements made using a 39 ghz radar also carried on a low flying aircraft all experiments included a similar range of wind speeds and wave heights the saxon data were however much more extensive and the statistical relationships correspondingly more significant the mean value of is very close to the mean value determined from global measurements of sea level made by geosat

greenland mass balance from grace 1 we use 22 monthly grace gravity recovery and climate experiment gravity fields to estimate the linear trend in greenland ice mass during 2002 2004 we recover a decrease in total ice mass of 82 28 km3 of ice per year consistent with estimates from other techniques our uncertainty estimate is dominated by the effects of grace measurement errors and errors in our post glacial rebound pg correction the main advantages of grace are that it is sensitive to the entire ice sheet and that it provides mass estimates with only minimal use of supporting physical assumptions or ancillary data

detailed seismic attenuation structure beneath hokkaido northeastern japan arc arc collision process arc magmatism and seismotectonics in this study we imaged a detailed seismic attenuation structure frequency independent q 1 beneath hokkaido japan by merging waveform data from a dense permanent seismic network with those from a very dense temporary network corner frequency of each event used for t estimation was determined by the s coda wave spectral ratio method the seismic attenuation qp 1 structure is clearly imaged at depths down to about 120 km for the fore arc side of hokkaido high qp zones are imaged at depths of 10 to 80 km in the crust and mantle wedge above the pacific slab low qp zones are clearly imaged in the mantle wedge beneath the back arc areas of eastern and southern hokkaido these low qp zones extending from deeper regions extend to the moho beneath volcanoes the locations of which are consistent with those of seismic low velocity regions these results suggest that the mantle wedge upwelling flow occurs beneath hokkaido except in the area where there is a gap in the volcano chain in contrast an inhomogeneous seismic attenuation structure is clearly imaged beneath the hokkaido corner a broad low qp zone is located at depths of 0 60 km to the west of the hidaka main thrust the location almost corresponds to that of the seismic low velocity zone in the collision zone the fault planes of the 1970 m6 7 and 1982 m7 1 earthquakes are located at the edges of this broad low qp zone observations in this study indicate that our findings contribute to understanding the detailed arc arc collision process magmatism and seismotectonics beneath hokkaido

measurements of time variable gravity show mass loss in antarctica using measurements of time variable gravity from the gravity recovery and climate experiment satellites we determined mass variations of the antarctic ice sheet during 2002 2005 we found that the mass of the ice sheet decreased significantly at a rate of 152 80 cubic kilometers of ice per year which is equivalent to 0 4 0 2 millimeters of global sea level rise per year most of this mass loss came from the west antarctic ice sheet

global sea level change from satellite altimetry we examine the feasibility of using satellite altimeter data to measure the long term change of global sea level estimated from tide gauge data to be a rise of approximately 0 2 cm yr 1 two and one half years of collinear geosat altimeter data 1986 1989 are used together with a 17 day set of seasat altimetry july august 1978 having nearly the same ground track a consistent set of precise orbits was used throughout and residual orbit error was removed as a sinusoidal fit to approximately 3 day arcs of sea level collinear differences the globally averaged geosat data show sea level falling at 1 2 0 3 cm yr 1 over the first 2 years even after removal of tide errors and instrument biases not accounted for in the geosat geophysical data records this unrealistic result is found to be due largely to long term error in the ionospheric model for the single frequency geosat altimeter the geosat seasat comparison based on data 10 years apart shows an apparent sea level rise of 1 0 cm yr 1 assuming this result is also unrealistic a possible explanation is a biased scale to the doppler determined geosat orbit which unlike seasat did not have the benefit of laser tracking it is also possible that the geosat altimeter without external in orbit calibration had a bias of the order of 10 cm we conclude that for satellite altimetry to make a fundamental contribution to monitoring global mean sea level change both the altimeter including its media corrections and the orbit model which provides a geocentric reference for the ocean surface will need continuing and careful calibration with absolute standards

the effect of the degree of wave development on the sea state bias in radar altimetry measurement the effect of the degree of wave development on the sea state bias ssb in geosat altimeter height measurement is evaluated theoretical considerations suggest that the altimetric ssb is generally not a linear function of significant wave height but depends also on other factors of wave development of particular interest is its dependence on wave age defined as the ratio of the phase speed of the dominant ocean waves to ocean wind speed we estimate wave age rather crudely on the basis of the significant wave height h and wind speed measured by the altimeter under general conditions when the sea is not in equilibrium with the wind this estimate may not correspond to the wave age in a strict sense and hence is called pseudo wave age in this paper nevertheless the pseudo wave age is a rough indicator for the degree of wave development the general trend in the dependence of the ssb on pseudo wave age as found by analyzing 2 7 years worth of geosat data agrees well with the theoretical prediction for a given h the ssb decreases as the degree of the wave development measured by the pseudo wave age increases this empirical trend is modeled as ssb a m m h where and m are the pseudo wave age and its average value respectively a 0 013 0 005 and m 0 88 0 37 statistically this model performs slightly better than a standard model i e ssb h with being a constant in terms of the global rms error the improvement is by 1 6 cm however because the degree of wave development varies with the season and geographical location this small improvement could become important for more accurate altimetric missions in the future when the centimetric basin scale signals are the focus of the study

lateral variation in crustal structure along the lesser antilles arc from petrology of crustal xenoliths and seismic receiver functions abstract we reconstruct crustal structure along the lesser antilles island arc using an inversion approach combining constraints from petrology of magmatic crustal xenoliths and seismic receiver functions xenoliths show considerable island to island variation in xenolith petrology from plagioclase free ultramafic lithologies to gabbros and gabbronorites with variable proportions of amphibole indicative of changing magma differentiation depths xenoliths represent predominantly cumulate compositions with equilibration depths in the range 5 to 40 km we use xenolith mineral modes and compositions to calculate seismic velocities v p v s and density at the estimated equilibration depths we create a five layer model of crustal structure for testing against receiver functions rf from island seismic stations along the arc lowermost layer 5 comprises peridotite with physical characteristics of mantle xenoliths from grenada uppermost layer 1 consists of 5 km of volcaniclastics and sediments whose physical properties are determined via a grid inversion routine the three middle layers 2 to 4 comprise igneous arc crust with compositions corresponding to the xenoliths sampled at each island by inversion we obtain a petrological best fit for the rf on each island to establish the nature and thicknesses of layers 2 to 4 along the arc we see variations in the depth and strength of both moho and mid crustal discontinuity mcd on length scales of tens of km moho depths vary from 25 to 37 km mcd from 11 and 32 km the moho is the dominant discontinuity beneath some islands st kitts guadeloupe martinique grenada whereas the mcd dominates beneath others saba st eustatius along arc variability in mcd depth and strength is consistent with variation in estimated magmatic h2o contents and differentiations depths that in turn influence xenolith lithologies a striking feature is steep along arc gradients in v p similar to those observed at other oceanic arcs these gradients reflect abrupt changes in rates and processes of magma generation in the underlying crust and mantle we find no evidence for large interconnected bodies of partial melt beneath the lesser antilles instead the crustal velocity structure is consistent with magma differentiation in vertically extensive crystal mush dominated reservoirs along arc variation in crustal structure may reflect heterogeneous upwelling within the mantle wedge itself driven by variation in slab derived h2o fluxes

extensional structure in northern honshu arc as inferred from seismic refraction wide angle reflection profiling a recent extensive seismic wide angle experiment revealed a new image of crustal and uppermantle structure across northern honshu arc japan the western part of the arc recorded the crustal deformation by the miocene back arc spreading of the sea of japan the crust is composed of highly deformed tertiary sedimentary layers a relatively low velocity 5 75 5 9 km s crystalline basement and a 15 km thick lower crust with a velocity of 6 6 7 0 km s clear westward crustal thinning from 32 to 27 km represents the extensional deformation by the backarc spreading the crust attains the maximum thickness 32 35km east of the backbone range for which the magmatic intrusion underplating since 10 15 ma is a predominant factor the eastern part of the arc has a less deformed upper crust and a reflective middle lower crust probably remaining a stable block since the time of the backarc spreading

delamination wedge structure beneath the hidaka collision zone central hokkaido japan inferred from seismic reflection profiling in the hidaka collision zone of hokkaido northern japan the kuril island arc collides with the northeast japan arc in order to better understand the collision process new high resolution information about lithospheric structure was obtained by means of a series of seismic reflection surveys these seismic profiles reveal distinct zones of seismic lamination in the lower crust of the kuril arc the upper portion of the lower crust is characterized by numerous east dipping reflectors in contrast west dipping reflectors dominate the lower part of the lower crust from this reflector configuration the lower crust of the kuril arc is interpreted to be delaminated by the collision the geometry of delamination is consistent with other geophysical data as well as the peak metamorphic grades exposed in the hidaka mountains as earthquakes indicate that delamination here is ongoing the hidaka collision zone represents an active model for continental growth by arc accretion with delamination of lower arc crust

upper and middle crustal deformation of an arc arc collision across hokkaido japan inferred from seismic refraction wide angle reflection experiments abstract the hidaka collision zone hcz central hokkaido japan is a good target for studies of crustal evolution and deformation processes associated with an arc arc collision the collision of the kuril arc ka with the northeast japan arc nja which started in the middle miocene is considered to be a controlling factor for the formation of the hidaka mountains the westward obduction of middle lower crustal rocks of the ka the hidaka metamorphic belt hmb and the development of the foreland fold and thrust belt on the nja side the hokkaido transect project undertaken from 1998 to 2000 was a multidisciplinary effort intended to reveal structural heterogeneity across this collision zone by integrated geophysical geological research including seismic refraction reflection surveys and earthquake observations an e w trending 227 km long refraction wide angle reflection profile found a complicated structural variation from the ka to the nja across the hcz in the east of the hcz the hinterland region is covered with 4 4 5 km thick highly undulated neogene sedimentary layers beneath which two eastward dipping reflectors were imaged in a depth range of 10 25 km probably representing the layer boundaries of the obducting middle lower crust of the ka the hmb crops out on the westward extension of these reflectors with relatively high vp 6 0 km s and vp vs 1 80 consistent with middle lower crustal rocks beneath these reflectors more flat and westward dipping reflector sequences are situated at the 25 27 km depth forming a wedge like geometry this distribution pattern indicates that the ka crust has been delaminated into more than two segments under our profile in the western part of the transect the structure of the fold and thrust belt is characterized by a very thick 5 8 km sedimentary package with a velocity of 2 5 4 8 km s this package exhibits one or two velocity reversals in paleogene sedimentary layers probably formed by imbrication associated with the collision process from the horizontal distribution of these velocity reversals and other geophysical geological data the rate of crustal shortening in this area is estimated to be greater than 3 4 mm year which corresponds to 40 50 of the total convergence rate between the nja and the eurasian plate this means that the fold and thrust belt west of the hcz is absorbing a large amount of crustal deformation associated with plate interaction across hokkaido island

isolating the pgr signal in the grace data impact on mass balance estimates in antarctica and greenland summary redistribution of mass over the earth and within the mantle changes the gravity field whose variations are monitored at high spatial resolution by the presently flying grace space gravity mission from nasa or at longer wavelengths by the satellite laser ranging slr constellation in principle grace data allow one to study the time evolution of various earth phenomena through their gravitational effects the correct identification of the gravitational spatial and temporal fingerprints of the individual hydrologic atmospheric oceanographic and solid earth phenomena is thus extremely important but also not trivial in particular it has been widely recognized that the gravitational estimates of present day ice mass loss in greenland and antarctica and the related effect on sea level changes depend on an accurate determination of the postglacial rebound pgr after pleistocene deglaciation which in turn depends on the assumed solid earth parameters and deglaciation model here we investigate the effect of the uncertainty of the solid earth parameters viscosity litospheric thickness and of different deglaciation processes on pgr in greenland and antarctica we find that realistic constraints to the trend in ice mass loss derived from grace data determine a range of variation substantially wider than commonly stated ranging from an important ice loss of 209 gt yr 1 to an accumulation of 88 gt yr 1 in antarctica and greenland ablation at a rate between 122 and 50 gt yr 1 however if we adopt the set of most probable earth parameters we infer a substantial mass loss in both regions 171 39 and 101 22 gt yr 1 for antarctica and greenland respectively

high resolution seismic velocity structure beneath the hokkaido corner northern japan arc arc collision and origins of the 1970 m 6 7 hidaka and 1982 m 7 1 urakawa oki earthquakes 1 using travel time data from both a nationwide dense seismic network and a dense temporary seismic network we obtain a high resolution three dimensional seismic velocity structure beneath the hokkaido corner considerable inhomogeneity in the seismic velocity structure is clearly imaged above the subducting pacific slab our results indicate that a broad low velocity zone of p and s waves with velocities consistent for crustal rocks is observed west of the hidaka main thrust at depths of 35 90 km the images also indicate that several smaller scale high velocity zones are located at depths of 0 35 km striking approximately north south and inclined to the east northeastward at 40 60 all of these anomalous high velocity zones are located at the deeper extension of neogene thrust faults the clearest high velocity zone is located beneath the hidaka metamorphic belt and is in contact with the eastern edge of the broad low velocity zone moreover the boundary between the clearest high velocity and the broad low velocity zones corresponds to the fault plane of the 1970 mj magnitude determined by the japan meteorological agency 6 7 hidaka earthquake the western boundary of another small high velocity zone at depths of 20 to 30 km within the broad low velocity zone corresponds to the fault plane of the 1982 mj 7 1 urakawa oki earthquake these observations suggest that these two large and anomalously deep inland earthquakes occurred at sharp material boundaries under a northeast southwest compressional stress field caused by ongoing arc arc collision process

collision rotation and back arc spreading in the region of the okhotsk and japan seas the india eurasia collision caused extensive deformation in the eurasia continent since late eocene time we propose that back arc spreading in the okhotsk and japan seas was related to the movement of microplates relevant to the india eurasia collision the kuril basin of the okhotsk sea and the basins of the japan sea were formed as back arc basins simultaneously their late oligocene to middle miocene age is constrained by sediment stratigraphy basement depth and heat flow data the movements of two microplates the okhotsk and amuria plates are significant for the tectonics of the okhotsk and japan seas simultaneous retreat of both microplates from trench hinge lines caused back arc spreading in the kuril basin and the japan sea the amuria plate moved north northeastward due to the india eurasia collision this caused pull apart opening of the baikal rift along a transform boundary between the siberia and amuria plates and a collision along the stanovoy range at its northern margin this movement triggered a clockwise rotation of the okhotsk plate with a component of dextral collision between the okhotsk and amuria plates which is well observed along the central zone of the sakhalin hokkaido islands between the two back arc plates the clockwise rotation of the okhotsk plate is suggested by the southwestward fan shaped opening of the kuril basin the kuril basin narrows to the northeast and terminates south of the kamchatka peninsula where a relative rotation pole between the okhotsk and kuril forearc plates is located the kamchatka peninsula was a zone of collision on the other side of the clockwise rotating okhotsk plate during the opening of the kuril basin the sredinny range in the kamchatka peninsula is one of the results of the collision between the okhotsk plate and the forearc plate of the kuril arc the bending of the japanese islands occurred in association with the back arc spreading of the yamato basin of the japan sea

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

the sea state correction for geos 3 and seasat satellite altimeter data troughs of the ocean surface reflect more electromagnetic radiation to a satellite altimeter than crests causing an apparent lengthening of the altimeter path this effect called the em bias has been estimated to be 2 10 of significant wave height swh by various authors from geos 3 and aircraft experiments or theoretical analyses for the case of the seasat altimeter born et al 1982 at jet propulsion laboratory jpl made an empirical estimate that gave the total correction to the altimeter path length as 7 of the swh a large value was expected for seasat because an instrumental effect in addition to the em bias is known to exist waveform analyses performed at nasa wallops flight center hayne and hancock 1982 give a correction for the instrument effect but according to the authors their results cannot be compared with results obtained elsewhere for several reasons including the large uncertainty 30 of the jpl result in this paper we resolve the situation for both geos and seasat altimeters by reinterpreting the results of hayne and hancock and making empirical studies using very large data sets to estimate the correction required for the effect of sea state empirical estimates of the correction were made by finding a value that minimized in the sense of least squares the differences of many about 300 repeated pairs of altimetric profiles for each satellite the total correction obtained is 1 9 of significant wave height for geos 3 and 6 4 for seasat the latter result consistent with the analysis done at jpl of a smaller data set and our interpretation of the hayne and hancock waveform analysis

ocean mesoscale variability from repeat tracks of geos 3 altimeter data the geos 3 satellite altimeter observed numerous sea surface profiles along nearly repeated tracks in the western north atlantic during its 3 5 year lifetime enabling observation of the variation of sea surface topography along these tracks analysis of 14 north going and 13 south going sets of repeated tracks has yielded the variability of the surface at a resolution of 1 from 25 to 41 n latitude and from 60 to 80 w longitude the observed rms variation of surface topography ranges from about 8 cm in the sargasso sea to a maximum of 48 cm in the gulf stream meander region in agreement with known mesoscale energetics of this region

clearing observed pgr in grace data aimed at global viscosity inversion weighted mass trends technique 1 the time variable gravity field shows the effects of large present day mass variations associated with hydrological phenomena and melting ice sheets resulting in a shaded post glacial rebound pgr signal a meaningful viscosity inversion based on a global scale comparison of grace data and pgr predictions is thus hard to obtain we derive a weighted surface mass distribution in water equivalent starting from an initial guess which portrays the secular effects of present day phenomena the gravity field it generates is then carefully removed from grace data resulting in a gravity pattern where the effects of pgr are clearer and ready to be compared with the predictions on the basis of viscoelastic stratified earth models and different pleistocene deglaciation models we show that the quality of a global preliminary viscosity inversion greatly improves

present rate of uplift in fennoscandia from grace and absolute gravimetry abstract fennoscandia is a key region for studying effects of glacial isostatic adjustment the associated mass variations can be detected by the gravity recovery and climate experiment grace satellite mission which observes the earth s gravity field since april 2002 as well as by absolute gravimetry field campaigns since 2003 annual absolute gravity ag measurements have been performed in fennoscandia by the institut fur erdmessung ife institute of geodesy of the leibniz universitat hannover germany within a multi national cooperation this offers a unique opportunity for validation and evaluation of the grace results in this preliminary study the grace results are compared to secular gravity changes based on the surveys from 2004 to 2007 with the fg5 220 gravimeter of the ife the results from grace monthly solutions provided by different analysis centres show temporal gravity variations in fennoscandia the included secular variations are in good agreement with former studies the uplift centre is located west of the bothnian bay the whole uplift area comprises northern europe nevertheless the differences between the grace solutions are larger than expected and the different centre specific processing techniques have a very strong effect on possible interpretations of grace results the comparison of grace to the ag measurements reveals that the determined trends fit well with results from grace at selected stations especially for the solution provided by the gfz variations of land hydrology clearly influence results from grace and the ag measurements

lateral structural variation across a collision zone in central hokkaido japan as revealed by wide angle seismic experiments the crustal evolution in the central part of hokkaido island japan has been dominated by a series of accretion and collision processes from the late jurassic to the present this region is divided into three main tectonic belts the sorachi yezo hidaka and tokoro belts from west to east formed in different cretaceous subduction systems since the miocene the sorachi yezo belt and the western part of the hidaka belt the hidaka metamorphic belt hmb have suffered severe deformation during two tectonic events the dextral oblique collision between the north american okhotsk and eurasian plates and the arc arc collision of the kuril forearc sliver with the western part of hokkaido the ne japan arc a thrust belt along the western margin of the sorachi yezo belt is considered to represent the miocene to pliocene eastward subduction of the ne japan arc due to the compressional stress regime this subduction jumped to the eastern margin of the japan sea in pleistocene time the reanalysis of wide angle seismic data collected in central hokkaido has provided a new image of crustal scale structural variation and deformation in the tectonic environments mentioned above the western part of the sorachi yezo belt is characterized by a 2 4 5 km thick forearc sedimentary layer with a velocity of 3 0 3 9 km s 1 beneath which a 3 9 5 8 km s 1 body forms an eastward dipping boundary to the upper unit this boundary may be the eastward extension of the thrust belt representing the miocene to pliocene plate boundary a 5 3 5 7 km s 1 body almost crops out beneath the eastern part of the sorachi yezo belt where ophiolite sequences and high p metamorphic rocks are exposed our rather low velocity of 5 3 5 7 km s 1 may suggest that the original oceanic crustal rocks or the metamorphics were fragmented and merged with low velocity accretionary prism rocks plausible tectonic events responsible for this process are fast uplift of a large amount of underplated materials in the cretaceous subduction system of this region and or severe deformation by collision tectonics since the miocene the hmb is characterized by high t metamorphic rocks almost equivalent to those of continental or arc crust the seismic velocity in the upper 5 7 km of crust in this part increases westwards from 5 6 to 5 85 km s 1 showing a good correlation with the change in metamorphic grade of the exposed rocks the velocity structure in the eastern part of the hidaka belt is composed of 15 20 km thick upper crust overlying 6 6 6 7 km s 1 lower crust the crystalline part of the upper crust is divided into a 6 7 km thick 5 6 6 0 km s 1 layer and an 8 5 11 km thick 6 2 6 35 km s 1 layer in the depth range 25 45 km there exist crustal laminations probably forming a ductile and sheared zone good agreement of this velocity structure with physical properties of the metamorphics exposed in the hmb indicates that a 25 26 km thick brittle part of the hidaka crust was obducted towards the west to form the hmb under the collision framework in this region major layer boundaries east of the hmb show a gentle eastward dip which might have acted as a decollement at the time of the obduction the tokoro belt which is composed of accreted jurassic seamounts is marked by a high upper crustal velocity 6 1 km s 1 in our model this velocity represents relatively mafic rock compositions of the seamounts and or oceanic crust trapped in this belt

crustal evolution of the southwestern kuril arc hokkaido japan deduced from seismic velocity and geochemical structure abstract the southwestern kuril arc which is not affected by a series of accretion and collision processes is one of the most important experimental sites among the world arc trench systems for investigating the evolution of arc crust published petrological and seismic studies have shown that in south central hokkaido the upper part of the kuril arc crust is thrusting upward toward the west while the lower part is descending downward in the same direction among several hypotheses for formation of continental crust we discuss the role of delamination of the island arc lower crust based on geochemical and seismic velocity structure models seismic velocity structure is obtained from an onshore offshore seismic survey across the southwestern kuril arc trench system the structure in the back arc area shows a thick accretionary complex formed by paleogene accretion and collision based on published seismic results this accretionary complex is considered to continue on land to the cretaceous accretionary complex observed in the hidaka belt the structure of the kuril arc appears characteristic of upper crustal andesitic rocks 6 0 6 2 km s and thick middle to lower crust 6 5 7 3 km s based on published geochemical study we consider a geochemical model of simple crustal evolution explaining the mechanism of generation of andesitic rocks on the kuril arc each volume of andesitic basaltic and mafic layers estimated from the geochemical model is consistent with those obtained from the seismic velocity model crustal composition estimated from the geochemical model and major element chemistry of the volcanic rocks in the kuril arc indicate that mechanical delamination is insufficient to cause the oceanic island arc crust to evolve into continental crust

electromagnetic bias estimates based on topex buoy and wave model data 1 for quantitative studies of the ocean using altimetric measurements the sea surface height measurements must be corrected for the electromagnetic em bias effect project provided em bias correction algorithms were derived from the altimeter data as a function of wind speed and wave height through variance minimization techniques gaspar et al 1994 in this paper we characterize the impact of those corrections on the altimeter data and compare it with an empirical algorithm based on tower observations of wave slopes and wave age w k melville et al wave slope and wave age effects in measurements of em bias submitted to journal of geophysical research 2002 and with theoretical predictions of em bias srokosz 1986 we find a significant correlation between high frequency ocean signals with the project provided em bias correction this suggests that an em bias algorithm cannot be estimated from altimeter data alone through variance minimization techniques since the em bias depends on parameters that cannot be measured by an altimeter e g wave slope improved theoretical corrections appear to be preferable to altimetry based empirical estimates using wave buoy and wave model wam data we find good agreement between existing theoretical correction and empirical corrections based on wave slope and wave age information over a significant range of parameters although further work is needed to extend our tests of algorithms to larger wave slopes existing wave slope and wave age based algorithms appear comparable in goodness to project provided empirical algorithms and may be used for routine altimetry processing in combination with wam output on a global basis

an empirical determination of the effects of sea state bias on seasat altimetry a simple linear empirical model has been developed to allow the user of seasat altimetry data to correct the altitude measurements for sea state bias effects this bias is the result of two separate effects one relating to instrumental effects and the other relating to a bias in the electromagnetic mean sea level relative to the geometric mean sea level the electromagnetic bias is caused by the fact that the troughs of the ocean waves reflect the altimeter signal more strongly than the crests thus causing the altimeter determined mean sea level to shift toward the wave troughs an additional but independent instrument related bias is introduced because height corrections applied in the ground processor are not sufficient to compensate for simplifying assumptions made for the processor aboard seasat this altitude bias also is predominately wave height dependent and directed toward the wave trough the sum of these two effects is referred to as sea state bias after applying appropriate corrections to the altimetry data an empirical model for the sea state bias is obtained by differencing significant wave height and height measurements from coincident ground tracks ignoring small temporal variations in surface topography the height differences on a given track should be zero consequently any residual height difference is attributed to sea state bias the height differences are minimized by solving for the coefficient of a linear relationship between height differences and wave height differences that minimize the height differences it is concluded that for the altimeter data released by the jet propulsion laboratory 7 of the value of significant wave height should be subtracted from the seasat height measurements to correct for sea state bias this correction reduced biases in the seasat data by more than 50 in the 36 cases examined here

collision and subduction structure of the izu bonin arc central japan revealed by refraction wide angle reflection analysis abstract since the middle miocene the izu bonin arc iba has been colliding from the south with the honshu arc in central japan associated with subduction of the philippine sea plate psp this process is responsible for forming a complex crustal structure called the izu collision zone icz to obtain direct evidence of the deep structure dominated by collision and subduction an intensive seismic experiment using explosive and vibroseis sources was conducted in the eastern part of the icz cmp reflection and refraction wide angle reflection data were acquired on a 130 km long seismic line crossing the kanto mountains km the tonoki aikawa tectonic line tatl and the tanzawa mountains tm from north to south the tatl is considered to be a collision boundary separating the honshu arc km from the iba tm the structural model constructed by refraction tomography and forward ray tracing shows remarkable lateral velocity variation across the tatl and some clear reflectors in the deep crust a north dipping reflector beneath the km was interpreted to be the deeper extension of the tatl from the geometry of reflectors we interpret the tanzawa block is delaminated from the subducting slab due to the collision to form a wedge like body thrusting between the upper and lower crust of honshu the tm itself shows a velocity structure almost consistent with the upper part of the crust of the izu intraoceanic arc south of our study area the relocated hypocenter distribution using our velocity model shows high seismic activity concentrated around the collision boundary which is in a marked contrast of low seismicity within the tanzawa block these features of seismicity are strongly dominated by the collision of the iba with the honshu arc

coefficients for sea surface wind stress heat flux and wind profiles as a function of wind speed and temperature surface layer coefficients for wind profiles wind stress and heat flux in typical open sea conditions are briefly reviewed businger dyer flux gradient relationships and a charnock wind stress formula fit the empirical data and are dimensionally consistent these have been solved by an iterative method and the results are presented in a tabular form suitable for climatological calculations from marine wind and temperature data

characterization of the deep water surface wave variability in the california current region surface waves are crucial for the dynamics of the upper ocean not only because they mediate exchanges of momentum heat energy and gases between the ocean and the atmosphere but also because they determine the sea state the surface wave field in a given region is set by the combination of local and remote forcing the present work characterizes the seasonal variability of the deep water surface wave field in the california current region as retrieved from over two decades of satellite altimetry data combined with wave buoys and wave model hindcast wavewatch iii in particular the extent to which the local wind modulates the variability of the significant wave height peak period and peak direction is assessed during spring summer regional scale wind events of up to 10 m s are the dominant forcing for waves off the california coast leading to relatively short period waves 8 10 s that come predominantly from the north northwest the wave climatology throughout the california current region shows average significant wave heights exceeding 2 m during most of the year which may have implications for the planning and retrieval methods of the surface water and ocean topography swot satellite mission

the sea level conundrum case studies from palaeo archives uncertainties in sea level projections for the 21st century have focused ice sheet modelling efforts to include the processes that are thought to be contributing to the recently observed rapid changes at ice sheet margins this effort is still in its infancy however leaving us unable to make reliable predictions of ice sheet responses to a warming climate if such glacier accelerations were to increase in size and frequency the geological record however has long identified examples of nonlinear ice sheet response to climate forcing shackleton nj opdyke nd 1973 oxygen isotope and paleomagnetic stratigraphy of equatorial pacific core v28 239 late pliocene to latest pleistocene geological society of america memoirs145 449 464 fairbanks rg 1989 a 17 000 year glacio eustatic sea level record influence of glacial melting rates on the younger dryas event and deep ocean circulation nature342 637 642 bard e hamelin b arnold m montaggioni l cabioch g faure g rougerie f 1996 sea level record from tahiti corals and the timing of deglacial meltwater discharge nature382 241 244 thus suggesting an alternative strategy for constraining the rate and magnitude of sea level change that we might expect by the end of this century copyright 2009 john wiley sons ltd

three dimensional crustal s wave velocity structure in japan using microseismic data recorded by hi net tiltmeters 1 we developed a three step method for three dimensional 3 d s wave velocity tomography by fitting synthetic cross spectra to the observed ones of ambient seismic noise we applied this method to the recording of hi net tiltmeters in japan at 679 stations from june 2004 to december 2004 first we calculated normalized cross spectra between radial components and those between transverse components for every pair of stations the first step is local 1 d s wave velocity inversion for each station assuming small lateral heterogeneity under a 100 km circle of a station we measured the dispersion curves of fundamental rayleigh waves fundamental love waves and first overtone of love waves by fitting the synthetic cross spectra to the observed ones between pairs of stations within the circle we inverted the measured dispersion curves for obtaining a 1 d s wave velocity model the second step is the inversion of the observed cross spectra for obtaining path averaged 1 d s wave velocity structure the third step is the inversion of the resultant path averaged structures for obtaining 3 d s wave velocity structure 0 1 0 1 1 km grid from the surface to a depth of 50 km using ray approximation the resultant s wave velocity structures show clear low velocity anomalies along tectonic lines from the surface to a depth of 20 km in particular along the hidaka mountain range we observed s wave perturbation more extreme than 20 they also show low velocity anomalies under volcanoes in kyusyu and tohoku in the southwestern part of shikoku our results show a clear low velocity anomaly corresponding to an accretional belt shimanto belt below 20 km we observe a low velocity anomaly in the center of japan which suggests a thick crust citation nishida k h kawakatsu and k obara 2008 three dimensional crustal s wave velocity structure in japan using microseismic data recorded by hi net tiltmeters j geophys res 113 b10302 doi 10 1029 2007jb005395

heterogeneous structure around the rupture area of the 2003 tokachi oki earthquake mw 8 0 japan as revealed by aftershock observations using ocean bottom seismometers abstract large earthquakes have repeatedly occurred in the area off southeastern hokkaido island japan as the pacific plate subducts beneath the island which is on the north american plate the most recent large earthquake in this area the 2003 tokachi oki earthquake mw 8 0 occurred on september 26 2003 in order to investigate aftershock activity in the rupture area 47 ocean bottom seismometers obss were quickly deployed after the main shock in the present study we simultaneously estimate the hypocenters and 3 d seismic velocity models from the p and s wave arrivals of the aftershocks recorded by obss the subducting plate is clearly imaged as a northwest dipping zone in which vp is greater than 7 km s and the relocated hypocenters also show the subducting pacific plate the aftershock distribution reveals that the dip angle of the plate boundary increases abruptly around 90 km from the kuril trench the bending of the subducting plate corresponds to the southeastern edge of the rupture area the island arc crust on the overriding plate has p wave velocities of 6 7 km s and a vp vs of 1 73 a region of vp vs greater than 1 88 was found north of the epicenter of the main shock the depth of the high vp vs region extends about 10 km upward from the plate interface the plate boundary just below the high vp vs region has the largest slip at the main rupture a high vp anomaly 7 5 km s is found in the island arc crust in northeast part of the study area which we interpret as a structural boundary related to the arc arc collisional tectonics of the hokkaido region as the rupture of the main shock terminated at this high vp region we suggest that the plate interface geometry and the trench parallel velocity heterogeneity in the landward plate are principal factors in controlling the rupture area of the main shock

constraining hydrological and cryospheric mass flux in southeastern alaska using space based gravity measurements 1 watersheds draining into the gulf of alaska goa experience large seasonal and inter annual variations of water in the form of rain snow and ice but accurate constraints on these variations have been difficult to obtain over larger geographic regions water variations can be inferred directly from the gravity recovery and climate experiment grace data however because goa variations occur over such a small region the inferred average value of water flux increases as the applied smoothing of the grace data decreases we use this observed scaling together with scaling results obtained from forward models to infer a seasonal amplitude of 115 20 km3 of water and an average contribution to sea level rise over the two years of data of 0 31 0 09 mm yr these results suggest that accelerated melting that began in the late 1990s as inferred from altimetry continues unabated

delamination structure imaged in the source area of the 1982 urakawa oki earthquake 1 the kuril arc collides with the northeast japan arc in the southern part of hokkaido japan 3 d tomographic inversion of data from a dense network of sensitive ocean bottom seismographs and land stations has allowed imaging of previously unseen details of the arc arc collision structure a low velocity body dips gently southwestward at depths of 35 to 45 km from east of the hidaka mountains to the source area of the 1982 urakawa oki destructive earthquake ms 6 8 the low velocity body is the lower half of the lower crust of the kuril arc which must have been delaminated by the collision we believe that the continuing collision of the delaminated lower crust with the northeast japan arc resulted as an episode of aseismic slow slip prior to the 1982 urakawa oki earthquake as well being the reason for the high seismic activity in this region

mass changes of the greenland and antarctic ice sheets and shelves and contributions to sea level rise 1992 2002 changes in ice mass are estimated from elevation changes derived from 10 5 years greenland and 9 years antarctica of satellite radar altimetry data from the european remote sensing satellites ers 1 and 2 for the first time the dh dt values are adjusted for changes in surface elevation resulting from temperature driven variations in the rate of firn compaction the greenland ice sheet is thinning at the margins 42 2g t a 1 below the equilibrium line altitude ela and growing inland 53 2g t a 1 above the ela with a small overall mass gain 11 3g t a 1 0 03 mm a 1 sle sea level equivalent the ice sheet in west antarctica wa is losing mass 47 4g t a 1 and the ice sheet in east antarctica ea shows a small mass gain 16 11 gt a 1 for a combined net change of 31 12 gt a 1 0 08 mm a 1 sle the contribution of the three ice sheets to sea level is 0 05 0 03 mm a 1 t he antarctic ice shelves show corresponding mass changes of 95 11 gt a 1 in wa and 142 10 gt a 1 in ea thinning at the margins of the greenland ice sheet and growth at higher elevations is an expected response to increasing temperatures and precipitation in a warming climate the marked thinnings in the pine island and thwaites glacier basins of wa and the totten glacier basin in ea are probably ice dynamic responses to long term climate change and perhaps past removal of their adjacent ice shelves the ice growth in the southern antarctic peninsula and parts of ea may be due to increasing precipitation during the last century

polar wandering and the forced responses of a rotating multilayered viscoelastic planet changes in the earth s rotation produced by the waxing and waning of large mobile ice sheets can be used to infer the viscosity of the mantle from a comparison with the recent secular polar drift as revealed in the international latitude service data and also in the estimates of the nontidal acceleration of the length of the day we have developed by using an analytical approach a physical model of a rotating earth consisting of an elastic lithosphere a viscoelastic mantle and an inviscid core forcings from the two major ice sheets laurentide and fennoscandia have been considered sensitivity analysis of the parameters governing the external forcings such as the length and the time of termination of the deglaciation phase show in general that there exist two families of mean mantle viscosities 0 1022 p and 0 1023 p which can match the data satisfactorily however we find it an improvement to incorporate some amount of shrinkage from the antarctic ice sheet obtaining simultaneously a better fit with the two rotational data sets to the lower viscosity solutions hence forcings from the southern hemisphere may be able to remove the ambiguity associated with the extraction of mantle viscosity from rotational data we have also solved the initial value problem of the components of instantaneous angular velocity by means of the laplace transform for applied loads characterizing the continental ice sheets which since the mid pliocene have periodically expanded and contracted over the northern hemisphere in consequence of this continual forcing polar wander of around 5 10 degrees can take place for a mean mantle viscosity 0 1022 p recent reanalysis of paleomagnetic data in conjunction with hot spot tracks have revealed that several degrees of true polar wander could have occurred in the last 5 m y these calculations thus provide a physical explanation for the observed movement of the rotation axis membrane stresses of 0 10 bars can develop from this secular polar motion

oblique subduction and collision forearc tectonics of the kuril arc the tectonics of the southwestern kuril arc are a result of the oblique subduction of the pacific plate at the kuril trench in association with forearc sliver migration caused by the oblique subduction collision tectonics occur at the leading margin of the sliver and tensional tectonics take place at the tapering margin as a result of the collision a deep crustal section of island arc is observed at the leading margin of the forearc sliver tectonics of the kuril arc related to oblique subduction are different from those of the western sunda arc where backarc spreading occurs at the leading margin this difference is due to margin morphology of the oblique subduction zone