cenozoic global ice volume and temperature simulations with 1 d ice sheet models forced by benthic δ18o records variations in global ice volume and temperature over the cenozoic era have been investigated with a set of one dimensional 1 d ice sheet models simulations include three ice sheets representing glaciation in the northern hemisphere i e in eurasia north america and greenland and two separate ice sheets for antarctic glaciation the continental mean northern hemisphere surface air temperature has been derived through an inverse procedure from observed benthic 18o records these data have yielded a mutually consistent and continuous record of temperature global ice volume and benthic 18o over the past 35ma the simple 1 d model shows good agreement with a comprehensive 3 d ice sheet model for the past 3 ma on average differences are only 1 0 c for temperature and 6 2m for sea level most notably over the 35ma period the reconstructed ice volume temperature sensitivity shows a transition from a climate controlled by southern hemisphere ice sheets to one controlled by northern hemisphere ice sheets although the transient behaviour is important equilibrium experiments show that the relationship between temperature and sea level is linear and symmetric providing limited evidence for hysteresis furthermore the results show a good comparison with other simulations of antarctic ice volume and observed sea level

the proportionality between relative plate velocity and seismicity in subduction zones the magnitude and rate of seismicity differ between subduction zones calculations of background seismicity rates based on a global model of subduction zone seismicity reveal a positive correlation between relative plate velocity and background seismicity yet only the seismically quieter zones seem capable of generating magnitude 9 earthquakes

spatiotemporal distribution of interplate coupling in southwest japan from inversion of geodetic data 1 we determine the spatiotemporal distribution of slip or slip deficit on the subduction interface of the nankai trough over an entire earthquake cycle using geodetic data including leveling triangulation and trilateration sea level and gps surveys obtained during the past 100 years in southwest japan we develop a new inversion method that accounts for long term crustal deformation coseismic earthquake displacements and stress relaxation of the viscoelastic asthenosphere from this analysis we obtain a model that shows postseismic afterslip on the deeper part of the plate interface following the 1946 nankaido earthquake significant afterslip is found beneath central shikoku that totals about 0 8 m the slip deficit rate during the interseismic period is 5 6 cm year in the n50 w n60 w direction which is consistent with the relative plate motion between the philippine and amurian plates a fully locked region is found in the shallower portion 30 km and the slip deficit rate has a maximum at a depth of about 20 km the plate interface deeper than 30 km is slowly slipping the amount of slip deficit reaches about 3 3 m off shikoku and about 2 m off the kii peninsula 50 years after the 1946 earthquake this suggests that fault healing and full interplate coupling has occurred by this time along the nankai trough

the miocene astronomical time scale 9 12 ma new constraints on tidal dissipation and their implications for paleoclimatic investigations orbital tuning and understanding climate response to astronomical forcing in the miocene require detailed knowledge of the effect of tidal dissipation td and dynamical ellipticity de on astronomical solutions used to compute insolation and orbital target curves for paleoclimatic studies these earth parameters affect precession and obliquity the determination of their effect is of fundamental importance as phase relations between astronomical forcing and climate response can only be accurately calculated when the relative phasing between precession and obliquity is known this determination can be achieved through comparison of solutions having different values for td and or de with well understood paleoclimate data in this paper we use quantitative color records of precession obliquity interference recorded in two successive 2 4 myr eccentricity minima 9 9 6 and 11 5 12 1 ma in the monte dei corvi section in northern italy to constrain the effect of td using the assumption of a direct response of sapropels to insolation this quantitative approach results in a minimum uncertainty of astronomically tuned age models of 0 8 kyr and td values 0 95 and 1 05 for the 9 9 6 ma interval and of 4 1 kyr td values between 0 95 and 1 15 for the 11 5 12 1 ma interval this un certainty not only limits the precision of determining phase relations but also improves our understanding of the limitations of tuned time scales and determining phase relations in the miocene

geology and tectonics of japanese islands a review the key to understanding the geology of asia abstract the age of the major geological units in japan ranges from cambrian to quaternary precambrian basement is however expected as the provenance of by detrital clasts of conglomerate detrital zircons of metamorphic and sedimentary rocks and as metamorphic rocks intruded by 500 ma granites although rocks of paleozoic age are not widely distributed rocks and formations of late mesozoic to cenozoic can be found easily throughout japan rocks of jurassic age occur mainly in the jurassic accretionary complexes which comprise the backbone of the japanese archipelago the western part of japan is composed mainly of cretaceous to paleogene felsic volcanic and plutonic rocks and accretionary complexes the eastern part of the country is covered extensively by neogene sedimentary and volcanic rocks during the quaternary volcanoes erupted in various parts of japan and alluvial plains were formed along the coastlines of the japanese islands these geological units are divided by age and origin i e paleozoic continental margin paleozoic island arc paleozoic accretionary complexes mesozoic to paleogene accretionary complexes and cenozoic island arcs these are further subdivided into the following tectonic units e g hida oki unazuki hida gaien higo hitachi kurosegawa south kitakami nagato renge nedamo akiyoshi ultra tamba suo maizuru mino tamba chichibu chizu ryoke sanbagawa and shimanto belts the geological history of japan commenced with the breakup of the rodinia super continent at about 750 ma at about 500 ma the paleo pacific oceanic plate began to be subducted beneath the continental margin of the south china block since then proto japan has been located on the convergent margin of east asia for about 500 ma in this tectonic setting the most significant tectonic events recorded in the geology of japan are subduction accretion paired metamorphism arc volcanism back arc spreading and arc arc collision the major accretionary complexes in the japanese islands are of permian jurassic and cretaceous paleogene age these accretionary complexes became altered locally to low temperature and high pressure metamorphic or high temperature and low pressure metamorphic rocks medium pressure metamorphic rocks are limited to the unazuki and higo belts major plutonism occurred in paleozoic mesozoic and cenozoic time early paleozoic cambrian igneous activity is recorded as granites in the south kitakami belt late paleozoic igneous activity is recognized in the hida belt during cretaceous to paleogene time extensive igneous activity occurred in japan the youngest granite in japan is the takidani granite intruded at about 1 2 ma during cenozoic time the most important geologic events are back arc opening and arc arc collision the major back arc basins are the sea of japan and the shikoku and chishima basins arc arc collision occurred between the honshu and izu bonin arcs and the honshu and chishima arcs

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

inferring the viscosity and the 3 d density structure of the mantle from geoid topography and plate velocities summary in a dynamic earth mantle mass heterogeneities induce gravity anomalies surface velocities and surface topography these lateral density heterogeneities can be estimated on the basis of seismic tomographic models recent papers have described a realistic circulation model that takes into account the observed plate geometry and is able to predict the rotation vectors of the present plates the relationship between the surface observables and the heterogeneities is sensitive to the viscosity stratification of the mantle here we use this model combined with a generalized least squares method in order to infer the viscosity profile of the earth from the surface observations and to get some new insight into the 3 d density structure of the mantle the computed radial viscosity profile presents a continuous increase of more than two orders of magnitude the asthenosphere has a viscosity close to 2 x lo2 pa s no sharp discontinuity is requested at the upper lower mantle interface the largest viscosity 7 x 10 pas is reached in the middle of the lower mantle at greater depth approaching the core mantle boundary the viscosity decreases by one order of magnitude the model suggests that the well known degree 2 and order 2 anomaly in the transition zone of the upper mantle is merely the signature of the slabs it also slightly increases the degree 2 and order 0 in the lower mantle and decreases it in the upper mantle in other words the inversion requests a hotter lower mantle beneath the equator and a colder upper mantle at the same latitudes

crustal deformation and interplate coupling in the shikoku district japan as seen from continuous gps observation abstract data from the nationwide gps continuous tracking network which has been operated by the geographical survey institute gsi of japan since april 1996 were used to study crustal deformation in the shikoku district japan the crustal deformation data are inverted to estimate interplate coupling between the subducting philippine sea phs plate and the overriding continental plate for this purpose we first extracted site coordinates from daily sinex files for the period from 1 april 1996 to 31 march 1998 and estimated average site velocities by linear regression estimated velocities under itrf96 are converted into a kinematic reference frame k heki j geophys res 101 1996 3187 3198 to discuss the crustal deformation relative to the stable interior of the eurasian eur plate to segregate the signal and noise in the thus obtained velocity vectors we employed the least squares prediction technique estimated signals displacement vectors were used to reconstruct the strains dilatations maximum shear strains principal axes of strains and to estimate the interplate coupling in the area results of crustal strains clearly portray tectonic straining of the shikoku island 1 dilatational strains show that the shikoku island is under a compressive strain regime induced by the subducting phs plate 2 maximum shear is high in the island which may be due to the oblique subduction 3 the principal axes of the strains indicate that the shikoku island is under the influence of the converging oceanic plate beneath the island in contrast the results of the inversion analysis show 1 there is a high coupled region extending from 10 to 30 km deep 2 the average back slip rate in this region reaches 43 5 mm yr and 3 the direction of the plate convergence at the nankai trough is n42 6 w

fine structure of the lowermost crust beneath the kaapvaal craton and its implications for crustal formation and evolution high quality data from a dense seismic array covering an area of approximately 60 40 km2 are used to obtain tight quantitative estimates of the fine scale velocity and density structure of the lowermost crust and the crust mantle boundary moho beneath the kaapvaal craton in the vicinity of kimberley south africa results based on a modified receiver function waveform analysis of moho conversions and crustal reverberation phases show that the crust beneath the array is thin 35 4 km with an average poisson s ratio of 0 254 the minimum s wave velocity contrast across the moho is 17 3 while the contrast in density is 15 4 the density contrast across the moho is particularly diagnostic for an assumed uppermost mantle density beneath kimberley of 3 3 gm cc as determined from mantle xenoliths the density of the lowermost crust is 2 86 gm cc indicating rocks of felsic to intermediate composition analysis of waveform broadening of the crustal reverberation phases relative to that of the direct p wave shows the thickness of the moho transition zone to be less than 0 5 km and the maximum variation in crustal thickness over the region of the array to be less than 1 km the flat and almost perfectly sharp moho together with the absence of a mafic lower crust suggests large scale crustal reworking in the period between crustal formation and the time of cratonic stabilization

ten million year histories of obliquity and precession the influence of the ice age cycle abstract redistribution of mass both on and within the earth due to the direct and indirect effects of the late pleistocene glaciation deglaciation process changes the principal moments of inertia of the planet and consequently causes variations in its dynamical ellipticity h as demonstrated in laskar et al 1993 the numerical calculation of obliquity and precessional parameters of the earth over a long time scale is extremely sensitive to changes in h it is therefore of considerable interest to investigate the influence of such changes when these are determined by a realistic model of the ice age cycle of the late pleistocene epoch of earth history our analyses show that the effect due to physically realistic changes in h t upon the obliquity fluctuations is less than 0 1 over a time scale of 10 myr assuming that the dynamical ellipticity h t were equal to the present day value prior to 780 000 yr ago this impact upon the obliquity is only one third of that due to tidal dissipation if we assume that h t prior to 780 000 yr ago were equal to the average of h t over the time interval from 780 000 yr ago to the present the impact upon the obliquity fluctuations is about 0 2 during the most recent 2 myr which constitute the entire pleistocene epoch the impact upon the minimum average and maximum values of the obliquity oscillation is less than 0 03 for all of the models of h t h 0 considered the induced changes in the precession rate of the spin axis are found to be less than 0 1 s yr these results appear to settle what has become an extremely important issue in paleoclimatology since it has been suggested that the influence of the glaciation cycle upon h could be such as to modify significantly the precession period from its present day value and thus significantly compromise the integrity of the calculations of orbital variations in effective solar insolation that have previously been performed only if the glaciation deglaciation history could be shown to differ significantly from the ice 4g model of peltier 1994 would it be possible to continue to seriously entertain this idea

low frequency earthquakes and tomography in western japan insight into fluid and magmatic activity abstract low frequency lf microearthquakes are detected in the lower crust and uppermost mantle beneath western japan which may reflect fluid and magmatic activity in the subduction zone in this work we combine seismic tomography and the lf earthquakes to study the crustal and upper mantle structure and fluid and magmatic activity in western japan high resolution tomographic images under this region are determined using high quality arrival time data in kyushu the subducting philippine sea slab is detected clearly as a high velocity zone and the arc magma related low velocity low v anomalies under the active arc and back arc volcanoes are imaged clearly prominent low v zones are visible in the crust and uppermost mantle beneath the quaternary volcanoes along the japan sea coast and lf events occur actively under some of those volcanoes lf events are also detected in the source areas of the 1995 kobe earthquake m 7 2 and the 2000 tottori earthquake m 7 3 supporting the hypothesis that the large crustal earthquakes were triggered by the crustal fluids these results indicate that fluid and magmatic activities exist widely in western japan which are caused by dehydration of the subducting philippine sea slab and corner flow in the mantle wedge

numerical modeling of the global semidiurnal tide in the present day and in the last glacial maximum 1 a hydrodynamic model incorporating a self consistent treatment of ocean self attraction and loading sal and a physically based parameterization of internal tide it drag is used to assess how accurately barotropic tides can be modeled without benefit of data and to explore tidal energetics in the last glacial maximum lgm m2 solutions computed at high resolution with present day bathymetry agree with estimates of elevations from satellite altimetry within 5 cm rms in the open ocean this accuracy and agreement with atlimetric estimates of energy dissipation are achieved only when sal and it drag are included in the model solutions are sensitive to perturbations to bathymetry and inaccuracies in available global databases probably account for much of the remaining error in modeled elevations the 100 m drop in sea level during the lgm results in significant changes in modeled m2 tides with some amplitudes in the north atlantic increasing by factors of 2 or more dissipation is also significantly changed by the drop in sea level if it drag estimated for the modern ocean is assumed dissipation increases by about 50 globally and almost triples in the deep ocean however it drag depends on ocean stratification which is poorly known for the lgm tests with modified it drag suggest that the tendency to a global increase in dissipation is a robust result but details are sensitive to stratification significant uncertainties about paleotides thus remain even in this comparatively simple case where bathymetry is well constrained

extending the astronomical polarity time scale into the miocene an astronomical time scale is presented for the late miocene based on the correlation of characteristic sedimentary cycle patterns in marine sections in the mediterranean to the 65 n summer insolation curve of la90 1 2 with present day values for the dynamical ellipticity of the earth and tidd dissipation by the moon this correlation yields ages for all sedimentary cycles and hence also for the recorded polarity reversals and planktonic foraminiferal and dinoflagellate events the tortonian messinian t m boundary placed at the first regular occurrence of the globorofuliu conomiozea group in the mediterranean is dated at 7 24 ma the duration of the messinian is estimated at 1 91 myr because the miocene pliocene boundary has been dated previously at 5 33 ma 3 the new time scale is confirmed by oar 3gar ages of volcanic beds and by the number of sedimentary cycles in the younger part of the mediterranean messinian

joint seismic geodynamic mineral physical modelling of african geodynamics a reconciliation of deep mantle convection with surface geophysical constraints recent progress in seismic tomography provides the first complete 3 d images of the combined thermal and chemical anomalies that characterise the unique deep mantle structure below the african continent we present a tomography based model of mantle convection that provides an excellent match to fundamental surface geodynamic constraints on internal density heterogeneity that includes both compositional and thermal contributions where the latter are constrained by mineral physics the application of this thermochemical convection model to the problem of african mantle dynamics yields a reconciliation of both surface gravity and topography anomalies to deep seated mantle flow under the african plate over a wider range of wavelengths than has been possible to date on the basis of these results we predict flow in the african asthenosphere characterised by a clear pattern of focussed upwellings below the major centres of late cenozoic volcanism including the kenya domes hoggar massif cameroon volcanicline cape verde and canary islands the flow predictions also reveal a deep seated large scale active hot upwelling below the western margin of africa under the cape verde islands that extends down to the core mantle boundary the scale and dynamical intensity of this west african superplume is comparable to the south african superplume that has long been assumed to dominate the large scale flow dynamics in the deep mantle under africa we evaluate the plausibility of the predicted asthenospheric flow patterns through a comparison with seismic azimuthal anisotropy derived from independent analyses of african shear wave splitting data

seismic imaging of southwest japan using p and pmp data implications for arc magmatism and seismotectonics abstract to better understand the relationship between crustal heterogeneity and seismotectonics and arc magmatism we determined a detailed p wave velocity structure of the crust under a north south belt area in southwest japan by using the first arriving p waves and the reflected p waves from the moho discontinuity pmp from 60 crustal earthquakes recorded by 29 seismic stations our results revealed significant low velocity anomalies beneath the fault zone of the median tectonic line and the daisen volcano which suggest that daisen is potentially an active volcano in the lower crust we detected low velocity anomalies overlying the subducting philippine sea plate which may indicate the existence of fluids released by the slab dehydration the 1955 southern tokusima earthquake m 6 4 occurred between low and high high velocity zones the 2000 western tottori earthquake m 7 3 and other nearby strong earthquakes occurred around the daisen volcano which may be related to the upwelling magma and fluids

completing the neogene geological time scale between 8 5 and 12 5 ma a much improved high resolution magnetostratigraphy is presented for the interval between 8 5 and 12 5 ma in the deep marine astronomically tuned monte dei corvi beach section in northern italy this section contains the formally designated boundary between the middle and upper miocene defined by the tortonian gssp the natural remanent magnetization is carried by an unusual low temperature component of primary origin according to interpretations of isothermal remanent magnetization irm acquisition curves the palaeomagnetic signal is most probably carried by iron sulphides such as greigite or pyrrhotite the resultant magnetostratigraphy is reliable and can be straightforwardly calibrated to the astronomically tuned neogene time scale atnts2004 showing that the section ranges from chron c5an 2n up to c4 2r 1 the inferred correlation of the tortonian gssp to the older part of chron c5r 2n is confirmed thereby guaranteeing global correlation potential in addition the monte dei corvi beach section has been re tuned to the new numerical solution la2004 for the interval between 8 5 and 12 9 ma this exercise shows that the characteristic cycle patterns are not consistent with a single solution with fixed values for dynamical ellipticity and tidal dissipation for the younger part of the section sedimentary cycles show an excellent fit with intricate details of precession obliquity interference in the nominal la2004 1 1 solution however this solution produces serious mismatches between the sedimentary cycles and the precession obliquity interference in the interval older than 10 2 ma for this interval changes in tidal dissipation value while keeping dynamical ellipticity constant at its present day value are necessary to maintain a perfect fit a detailed visual comparison reveals a very good to excellent fit with la2004 1 1 2 and to lesser extent with la2004 1 0 5 however la2004 1 1 2 is the preferred tuning target for the moment in the interval older than 10 2 ma the astronomical re tuning on precessional scale to la2004 1 1 yielded slightly different astronomical ages for each basic cycle and hence also for the calcareous plankton events and magnetic reversal boundaries with uncertainties ranging within a few thousand years the age of the tortonian gssp turns into 11 625 ma instead of the previously published 11 608 ma our ages should replace existing ages in the astronomically tuned neogene time scale atnts2004

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

the effects of transient rheology on the interpretation of lower mantle viscosity we have reexamined the role played by transient rheology in the interpretation of mantle viscosity this investigation has been carried out by comparing the amplitude responses with the data of secular variation of the relative sea level histories at sites well within the ice margins and at the ice margin like the city of boston a linear burgers body rheology has been assumed in the lower mantle the data near the edge of the ice load proves most sensitive to the transient viscosity structure the non monotonic behavior of sea level data near boston can be explained both by a steady state lower mantle viscosity of 1022p with a thick lithosphere and also by a transient lower mantle rheology but with a thin lithosphere the long term viscosity of the lower mantle in this second model has a steady state value of around 5 1023p

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

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

a resonance in the earth s obliquity and precession overthe past 20 myr drivenbymantle convection the motion of the solar system is chaotic to the extent that the precise positions of the planets are predictable for a period of only about 20 myr ref 1 the earth s precession obliquity and insolation parameters over this time period1 2 3 4 5 6 can be influenced by secular variations in the dynamic ellipticity of the planet which are driven by long term geophysical processes such as post glacial rebound5 7 8 9 10 here we investigate the influence of mantle convection on these parameters we use viscous flow theory to compute time series of the earth s dynamic ellipticity for the past 20 myr and then apply these perturbations to the nominal many body orbital solution of laskar et al 5 we find that the convection induced change in the earth s flattening perturbs the main frequency of the earth s precession into the resonance associated with a secular term in the orbits of jupiter and saturn5 and thus significantly influences the earth s obliquity we also conclude that updated time series of high latitude summer solar insolation diverge from the nominal solution for periods greater than the past 5 myr our results have implications both for obtaining precise solutions for precession and obliquity and for procedures that adopt astronomical calibrations to date sedimentary cycles and climatic proxy records

late pleistocene and holocene ice mass fluctuations and the earth s precession constant abstract we computed using a set of previously published maxwell visco elastic earth models time dependent variations in the earth s precession constant h associated with glacial cycles of duration 105 yr we found peak perturbations which are approximately an order of magnitude less than previous upper bound estimates which assumed that variations in h arose solely from the redistribution of the ice age surface mass ice plus ocean load that is these studies neglected the visco elastic isostatic adjustment of the solid planet and assumed a rigid earth a number of subsequent studies have cited and or adopted the rigid earth variation in h to argue for a series of potentially important effects on the earth s orbital dynamics rotation and palaeoclimate the results presented herein suggest that these arguments require significant re appraisal we also compute variations in h associated with the documented retreat of small ice sheets and glaciers over the last century and potential recent mass variations in the antarctic and greenland ice complexes we find in the case of a net mass loss from the antarctic and greenland ice sheets that these effects may contribute a perturbation to h which is approximately the same amplitude as but has the opposite sign to the contribution from ongoing glacial isostatic adjustment during the last century

an enigma in estimates of the earth s dynamic ellipticity summary the precession and obliquity frequencies of the earth s rotational motion are functions of the dynamic ellipticity of the earth s gravitational figure and this connection has provided a novel bridge between studies of palaeoclimate and geodynamics in particular analyses of tuned climate proxy records have yielded bounds on the mean relative perturbation in dynamic ellipticity over both the last 3 myr and 25 myr that are less than 3 per cent of the non hydrostatic component of the ellipticity we demonstrate that this apparent consistency actually defines an important geophysical enigma over the last 3 myr changes in the earth s figure are likely dominated by ice age forcings in this case a small perturbation to dynamic ellipticity implies significant isostatic compensation of the ice ocean surface mass loads and hence a relatively low mantle viscosity in contrast over the last 25 myr changes in the earth s long wavelength gravitational form are likely dominated by mantle convective flow and in this case the small perturbation to dynamic ellipticity implies sluggish convection and a relatively high mantle viscosity there are at least four possible routes to resolving this enigma the viscosity in the earth s mantle is transient i e dependent on the timescale of the applied forcing tidal dissipation changed in a manner between the last 3 myr and 25 myr that was sufficient to resolve the issue the observationally inferred bounds are unrealistically restrictive or earth models exist in which the ice age and convection effects approximately cancel leading to no net perturbation in this paper we compute a suite of numerical predictions of ice age and convection induced perturbations to the dynamic ellipticity to illustrate the enigma described above

cyclostratigraphy and its revolutionizing applications in the earth and planetary sciences over the past 25 yr the science of stratigraphy has evolved to include time correlative data from vastly disparate components of the earth system not least of these is the global signal afforded by cyclostratigraphy which has recorded the evolution of earth s astronomical milankovitch forcing of insolation and the paleoclimate system fossil astronomical signals are collected from cyclic sedimentary sequences by detailed sampling and study of facies geochemistry mineralogy rock magnetism color etc in step with the documentation of astronomically forced paleoclimate from ever older older geologic times innovations in computational science have provided ever longer high accuracy astronomical model targets that can be used for time scale calibration the earth s orbit is affected by motions of other planets notably the orbital perihelia of venus and jupiter which impose a dominant 405 k y eccentricity cycle on earth s orbital evolution the large mass of jupiter stabilizes this cycle over hundreds of millions of years the cyclostratigraphic record of 405 k y cycles is therefore often used to correct chronologies affected by variable sedimentation earth s shape and rotation rate are influenced by tidal dissipation and climate friction these effects affect earth s precession rate through time thus a record of earth moon evolution is also embedded in cyclostratigraphy the geochronologic value of cyclostratigraphy has been affirmed through intercalibration with high precision radioisotope dating which today has the potential to define the ages of stratigraphic horizons with 2 uncertainties at the scale of a precession cycle precession index phasing relative to that of the obliquity elucidates the seasonal nature of astronomical forcing of the paleoclimate system cyclostratigraphy contributes to our knowledge of planetary dynamics for times prior to the current ca 50 ma limit of accurate astronomical solutions and it will guide our future understanding of solar system evolution and the evidence for chaotic diffusion astronomical modeling is undergoing its own revolution with development of new numerical integrators to extend accuracy further back in time finally space exploration has revealed prominent sedimentary bedding and ice stratigraphy on the surface of mars with patterns suggestive of astronomical forcing analogous to earth

secular effects of oceanic tidal dissipation on the moon s orbit and the earth s rotation the earth and moon are considered as a two body system in gravitational isolation from the sun and other planets the lunar orbit is taken as circular and the solid earth is assumed to be a rigid sphere with no tidal deformation so that there are no precessional torques other than those arising from the tidally deformed ocean numerical solutions to laplace s tidal equations with dissipation by linear bottom friction are used to obtain ocean wide distributions of tidal amplitude for two idealized continentalities a single circular continent spherical cap centered at the north pole and a single spherical cap centered on the equator calculations are made for two different values of the frictional resistance coefficient thus giving rise to four sets of solutions the computed tidal amplitudes are used to calculate the oceanic tidal torque which in turn is used to integrate the orbital equations backward in time for solution of the two body problem the coriolis parameter and the tidal frequencies change with time thus requiring that the tidal equations be solved several times during the course of each orbital integration in this manner the earth s rotational and the moon s orbital histories are determined on a geologic time scale for each of the four models the calculated position of the lunar orbit at 4 5 billion years ago is found to range from 38 to 53 earth radii in the four models and corresponds to a sidereal month of 330 to 550 hours the sidereal day would have been 12 to 18 hours with a relative inclination of 3 to 22 between the terrestrial and lunar poles these results are in sharp contrast to those from previous studies of the earth moon system most of which indicated a roche limit approach of the two bodies roughly 1 to 2 billion years ago and presented therefore a time scale difficulty in theories of lunar origin this contrast arises mainly from the fact that previous modelers avoided solution of laplace s tidal equations by prescribing a constant frictional phase lag angle between the angular position of the moon and the major axis of the second degree harmonic of the tidally deformed surface of the earth the amount of phase lag was established from the present astronomically deduced rate of tidal dissipation but this precluded dynamic variations in tidal torque over geologic time which are critical for determination of the orbital time scale the present rate of oceanic tidal dissipation is evidently anomalously high because of the near resonance of the oceanic response in both frequency and shape to the tidal forcing for the earth and moon to have evolved to their present separation from a distance of less than about 35 earth radii solely on the basis of oceanic tidal dissipation would have required the m2 response to have been near resonance for a significant portion of geologic history a rather implausible scenario the calculations reported here show that on the contrary frictional coupling between the earth and moon was much weaker than at present throughout most of the orbital history and consequently the moon s closest approach could not have been as small as 35 earth radii although idealized continentalities were used in these calculations the general conclusion of a weaker frictional coupling in the past is believed to be relatively insensitive to the continental configuration this is because at faster paleorotation the semidiurnal tidal frequencies would be resonant only with smaller scale normal modes of the ocean rather than with global scale modes as at present the time scale difficulty heretofore present in models of orbital evolution is thereby eliminated it should be noted that the orbital history developed here supports the theory of binary planetary accretion for lunar origin as opposed to fission or tidal capture

seismic anisotropy and mantle dynamics beneath china abstract we analyzed the shear wave splitting at 138 permanent seismograph stations to study seismic anisotropy and mantle dynamics under mainland china to obtain reliable results we used three different methods to measure the shear wave splitting parameters using core phases sks skks skiks and pks as well as the direct s waves from regional and distant earthquakes our results show that the fast orientations of the anisotropy wnw ese in eastern china are generally consistent with the absolute plate motion apm direction of the eurasian plate suggesting that the anisotropy is mainly located in the asthenosphere resulting from the lattice preferred orientation of olivine due to the shear deformation there the fast axes in western china generally agree with the strikes of the orogens and active faults while they are perpendicular to the direction of the maximum horizontal stress suggesting that the anisotropy in the lithosphere contributes significantly to the observed shear wave splitting the fast axes in western china are also consistent with the apm direction suggesting that the apm driven anisotropy in the asthenosphere is another source of the shear wave splitting there these results suggest that apm driven anisotropy commonly exists under continents similar to that under oceanic regions even though the continental lithosphere has suffered extensive deformation

joint seismic geodynamic and mineral physical constraints on three dimensional mantle heterogeneity implications for the relative importance of thermal versus compositional heterogeneity summary the joint interpretation of seismic and geodynamic data requires mineral physical parameters linking seismic velocity to density perturbations in the earth s mantle the most common approach is to link velocity and density through relative scaling or conversion factors r s dln dlnv s however the range of possible r s values remains large even when only considering thermal effects we directly test the validity of several proposed depthdependent conversion profiles developed from mineral physics studies for thermally varying properties of mantle materials the tests are conducted by simultaneously inverting shear wave traveltime data and a diverse suite of convection related constraints interpreted with viscous flow response functions of the mantle these geodynamic constraints are represented by surface spherical harmonic basis functions up to harmonic degree 16 and they consist of the global free air gravity field tectonic plate divergences dynamic surface topography and the excess ellipticity of the core mantle boundary cmb the tests yield an optimum 1 d thermal r s profile that is generally compatible with all considered data with the exception of the dynamic surface topography that is most sensitive to the shallow upper mantle this result is not surprising given that cratonic roots are known to be compositionally distinct from the surrounding ambient mantle moreover it is expected that the temperature dependence of the thermal r s in the upper mantle is significant due to the temperature dependence of seismic attenuation or q therefore a simple 1 d density velocity relationship is insufficient to address this problem we obtained independent estimates of the first order correction factors to the selected r s profile within the cratonic roots and in the ambient thermal upper mantle these correction factors defined as r s lnv s are highly negative within the cratons signifying considerable compositional buoyancy this result confirms that the negative buoyancy associated with the low temperatures in the cratons is significantly counteracted by the composition induced positive buoyancy resulting in near neutral buoyancy of the cratonic roots within the ambient upper mantle the correction factors are found to be positive which is consistent with the expected behaviour of the r s relationship in thermally varying upper mantle material we obtain a significantly greater reconciliation of the global gravity anomalies and dynamic surface topography when applying these laterally varying corrections compared to a simple 1 d r s relationship inversion for a fully 3 d r s relationship reveals secondary effects including additional compositional variation within the cratonic roots and the deep mantle superplume structures we estimate the relative magnitude of the thermal and compositional non thermal contributions to mantle density anomalies and conclude that thermal effects dominate shear wave and density heterogeneity throughout the non cratonic mantle we also demonstrate the potential pitfalls of scaling a purely seismically derived model to obtain density rather than performing a true joint inversion to obtain velocity and density simultaneously

secular crustal deformation and interplate coupling of the japanese islands as deduced from continuous gps array 1996 2001 abstract data from the nation wide gps continuous tracking network that has been operated by the geographical survey institute of japan since april 1996 were used to study crustal deformation in the japanese islands we first extracted site coordinate from daily sinex files for the period from april 1 1996 to february 24 2001 since raw time series of station coordinates include coseismic and postseismic displacements as well as seasonal variation we model each time series as a combination of linear and trigonometric functions and jumps for episodic events estimated velocities were converted into a kinematic reference frame heki k 1996 horizontal and vertical crustal movements from three dimensional very long baseline interferometry kinematic reference frame implication for reversal timescale revision j geophys res 101 3187 3198 to discuss the crustal deformation relative to the stable interior of the eurasian plate a least squares prediction technique has been used to segregate the signal and noise in horizontal as well as vertical velocities estimated horizontal signals horizontal displacement rates were then differentiated in space to calculate principal components of strain dilatations maximum shear strains and principal axes of strain clearly portray tectonic environments of the japanese islands on the other hand the interseismic vertical deformation field of the japanese islands is derived for the same gps data interval the gps vertical velocities are combined with 31 year tide gage records to estimate absolute vertical velocity the results of vertical deformation show that 1 the existence of clear uplift of about 6 mm yr in shikoku and kii peninsula whereas pattern of subsidence is observed in the coast of kyushu district this might reflect strong coupling between the philippine sea plate and overriding plate at the nankai trough and weak coupling off kyushu 2 no clear vertical deformation pattern exists along the pacific coast of northeastern japan this might be due to the long distance between the plate boundary japan trench and overriding plate where gps sites are located 3 significant uplift is observed in the southwestern part of hokkaido and in northeastern tohoku along the japan sea coast this is possibly due to the viscoelastic rebound of the 1983 japan sea mw 7 7 and the 1993 hokkaido nansei oki mw 7 8 earthquakes and or associated with distributed compression of incipient subduction there we then estimate the elastic deformation of the japanese islands caused by interseismic loading of the pacific and philippine sea subduction plates the elastic models account for most of the observed horizontal velocity field if the subduction movement of the philippine sea plate is 100 locked and if that of the pacific plate is 70 locked however the best fit for vertical velocity ranges from 80 to 100 coupling factor in southwestern japan and only 50 in northeastern japan since horizontal data does not permit the separation of rigid plate motion and interplate coupling because horizontal velocities include both contributions we used the vertical velocities to discriminate between them so we can say there is strong interplate coupling 80 100 over the nankaido subduction zone whereas it is about 50 only over the kurile japan trench

late pleistocene and holocene sea level change in the australian region and mantle rheology summary spatial and temporal variations in sea level are produced by the melting of the late pleistocene ice and by the earth s response to the redistribution in surface loads by examining different parts of the sea level curves of the past 20 000 yr from geographically widely distributed regions it becomes possible to constrain models of the melting history of the ice sheets and of the earth s rheology observations from sites away from the former arctic ice sheets such as the australian and south pacific region are particularly important for constraining the total meltwater volumes added into the oceans in the past 20 000 yr and the rates at which this occurred these observations indicate that the antarctic ice sheets provided a significant contribution to the sea level rise at a rate that was approximately synchronous with the melting of the laurentide ice sheet except for the interval 9000 6000 yr ago when it may have lagged behind minor melting of the antarctic ice sheet appears to have continued throughout the late holocene differential observations of the late holocene sea level change recorded at sites in the same region are particularly useful for estimating parameters describing the earth s non elastic response to surface loading the effective parameters used here are a lithospheric thickness an upper mantle viscosity and a lower mantle viscosity describing the response below 670 km depth with the observations used here it is not possible to separate the lithospheric thickness h from the upper mantle viscosity and the viscosity results are based on the assumption that 50 h 100 km neither do these observations provide a resolution of the depth dependence of viscosity in the upper mantle and the resulting estimates are effective parameters only differential sea levels along continental margins and along the shores of large gulfs and bays constrain the effective upper mantle viscosity to be about 1 2 1020 pa s 1 while differential values from islands of different sizes are suggestive of a somewhat lower value the lower mantle taken to be below 670 km depth viscosity is about two orders of magnitude greater than this the estimated ice and rheological models explain many of the holocene sea level observations throughout the australian and southern pacific region the tilting of continental margins as exemplified by observations of variable amplitudes of the holocene high stands and the variable times at which sea levels first reached their present level along the north queensland coast and great barrier reef is well represented by these models differential holocene sea levels observed along the narrow spencers gulf of south australia are also well explained by the models and in neither case is it necessary to invoke tectonic motions predicted late holocene sea levels at small to medium sized islands are characterized by small amplitude high stands that reached their maximum values about 4000 2000 yr ago consistent with observations from the society cook and tuamotu islands

interplate seismogenic zones along the kuril japan trench inferred from gps data inversion stress accumulation between earthquakes results from slip that is insufficient to fully accommodate plate movement an inverse analysis of gps data from the kuril japan trench reveals a trench parallel belt of stress accumulation with six peaks in the depth range of 10 40 km suggesting potential source regions for future earthquakes in the subduction zones around japan where four plates interact with one another large earthquakes have occurred repeatedly1 these interplate earthquakes are part of the process of tectonic stress accumulation and release that is driven by relative plate motion2 3 4 stress accumulation between earthquakes results from slip deficit slip that is insufficient to fully accommodate plate movement for the prediction of large earthquakes it is therefore important to monitor the distribution of slip deficit on plate interfaces here we apply an inversion method based on bayesian modelling using direct and indirect prior information on the magnitude and distribution of fault slip5 to horizontal and vertical velocities from global positioning system data for the seismically calm period between 1996 and 2000 we obtain a precise distribution of slip deficit rates on the interface between the north american and pacific plates around japan which reveals a trench parallel belt of slip deficit with six peaks in the depth range of 10 40 km these peaks agree with the source regions of past large interplate earthquakes along the kuril japan trench we conclude that the slip deficit zones identified with our method are potential source regions of large earthquakes

contemporary deformation and seismicity analysis in southwest japan during 2010 2018 based on gnss measurements a significant amount of work has been conducted in the japanese islands on high precision positioning surveying natural disaster mitigation reference frame and datum definitions however there is substantial scope for exploring the current seismotectonic activity of japan which would provide further awareness of disaster management the short recurrence time of great inter plate earthquakes and well recorded geodetic observations provide one of the best examples to analyze the combination of contemporary deformation and seismic intensity in southwest sw japan in the current study we analyzed three districts of sw japan which include mainly kyushu district and parts of chugoku and shikoku districts we predicted global navigation satellite system gnss measurements based on amurian fixed reference frame aref velocities with the help of singular spectrum analysis ssa method and examined the regional deformation from april 01 2010 to december 31 2018 in addition we analyzed the earthquakes clustered calculated by the nearest neighborhood distance method which showed prominently bimodal seismicity of sw japan and revealed the existence of two statistically distinct earthquake populations the events inside a cluster were normally close to their nearest neighbors whereas events from distinct clusters were comparatively aloof from each other finally the paper provides the spatial strain and rotational rate variation for selected seismotectonic districts that are in relatively good agreement with the seismic deformation inferred from earthquake focal mechanisms we believe that our integrated approaches would provide a better insight into the active deformation of sw japan

geological constraints on tidal dissipation and dynamical ellipticity of the earth over the past three million years the evolution of the solar system has been shown to be chaotic which limits our ability to retrace the orbital and precessional motion of the earth over more than 35 50 myr ref 2 moreover the precession obliquity and insolation parameters can also be influenced by secular variations in the tidal dissipation and dynamical ellipticity of the earth induced by glacial cyclicity and mantle convection here we determine the average values of these dissipative effects over the past three million years we have computed the optimal fit between an exceptional palaeoclimate record from the eastern mediterranean sea and a model of the astronomical and insolation history by testing a number of values for the tidal dissipation and dynamical ellipticity parameters we find that the combined effects of dynamical ellipticity and tidal dissipation were on average significantly lower over the past three million years compared to their present day values determined from artificial satellite data and lunar ranging this secular variation associated with the plio pleistocene ice load history has caused an average acceleration in the earth s rotation over the past 3 myr which needs to be considered in the construction of astronomical timescales and in research into the stationarity of phase relations in the ocean climate system through time

continuous gps array and present day crustal deformation of japan a gps array with about 1 000 permanent stations is under operation in japan the gps array revealed coseismic deformations associated with large earthquakes and ongoing secular deformation in the japanese islands based on daily coordinate data of the gps stations strain rate distribution is estimated most regions with a large strain rate are related to plate boundaries and active volcanoes in addition the niigata kobe tectonic zone nktz is recognized as a region of large strain rate along the japan sea coast and in the northern chubu and kinki districts this newly found tectonic zone may be related to a hypothetical boundary between the eurasian or amurian and the okhotsk or north america plates precise observation of crustal deformation provides important boundary conditions on numerical modeling of earthquakes and other crustal activities appropriate computation methods of continuous deformation field are directly applicable to data assimilation for such numerical simulations

geodynamics of the baikal rift zone and plate tectonics of asia the baikal rift zone stretches from the southern termination of lake baikal as far as 118 e and includes the baikal basin and the barguzin upper angara and muysk grabens that form its easterly continuation coincident with the rift zone is a narrow seismic belt which extends further east along the stanovoy range to the okhotsk sea this belt can be considered as the boundary between the eurasian and amurian lithospheric plates earthquake focal mechanism solutions that show a consistent orientation of extensional axes across the strike of the rift zone indicate the behaviour of the eurasian and amurian plates as rigid bodies from 83 focal mechanism solutions the pole of rotation of the eurasian and amurian plates was computed to lie at the point 56 95n 117 45e the angular rate estimated from the amount of baikal opening is about 1 10 7 deg year the position of the pole at the eastern termination of the rift zone accounts for the dying out of the rift zone and for the appearance east of the pole of compressive structures in the stanovoy range to the southwest the baikal rift zone is replaced by the mosaic of microplates in central asia that occupy the space between the eurasian and indian lithospheric plates prominent are the mongolian dzungarian alashan tarim tibetan and pamir microplates earthquakes in central asia are dispersed although higher concentrations of earthquakes associated with microplate boundaries are prominent the tectonics of central asia are considered to be due to the interaction of rigid microplates assuming that plastic deformations occur within the relatively wide zones along the microplate boundaries by considering the strike slip faults to define the trajectories of microplate motions the parameters of relative movements of the microplates have been computed the microplate mosaic of central asia is moving northeasterly as a result of the collision and continued convergence of india and eurasia the mosaic acts as a wedge splitting off the amurian plate from eurasia causing it to rotate counterclockwise so opening the baikal rift

crustal deformation in kyushu derived from geonet data 1 an investigation was conducted on the horizontal crustal deformation in kyushu using the coordinate data from gps earth observation network geonet for the 4 years from 1998 to 2002 for which the annual variations are corrected we examined the spatial differences in the displacement rate relative to the amurian plate by subtracting the velocity of the amurian plate at each of the global positioning system gps stations models for interplate coupling in hyuganada and the dilatational source beneath sakurajima are obtained the crustal deformation in eastern kyushu is well explained by the model of interplate coupling in hyuganada which is strong in the north and weak in the south when the effects of the interplate coupling and the dilatational source are removed a southward extensional field is recognized in and to the south of the beppu shimabara graben in western kyushu in southern kyushu to the south of around latitude 32 n a southeastward movement is conspicuous it must be noted that the displacement field is extensional indicating that southern kyushu is being dragged at the base by a flow in the mantle not moving like a raft on the flow it is probable that the flow in the mantle is driven by the rising of hot materials in the okinawa trough and a retreat of the trench where the philippine sea plate is subducting a gap in the magnitude of the eastward displacement rate around latitude 32 n implies that the velocity of the flow in the mantle decreases substantially to the north of the line the beppu shimabara graben may be a continuation of the okinawa trough but the significant southwestward displacement rate observed in the eastern part suggests that the deformation in the graben at least to the east of aso volcano is affected by the westward movement of the forearc sliver produced by the oblique subduction of the philippine sea plate on the nankai trough off shikoku island we think that the strong coupling in the bungo channel in our model is probably not real but might be a result of our assumption that all the westward displacements in northeastern kyushu a part of which are actually due to the movement of the forearc sliver are produced by interplate coupling

pleistocene glaciation and the earth s precession constant we predict time dependent variations in the earth s precession constant arising from the ice and ocean mass fluctuations associated with the late pleistocene glacial cycles our predictions incorporate contributions from both the surface mass load redistribution and the adjustment of the solid earth in this regard we adopt spherically symmetrical self gravitating maxwell viscoelastic earth models and obtain results for a large suite of radial viscosity profiles these profiles include a set obtained from published inferences based on post glacial relative sea level and uplift histories as well as a set intended to sample the sensitivity of the results to variations in the viscosity within a number of major subregions of the mantle e g the transition zone the upper mantle and the lower mantle a more detailed measure of this sensitivity is also obtained by computing frechet kernels for the predictions we construct an ice model which incorporates the ice 3g model for the final deglaciation event and which is constrained to yield a eustatic sea level variation which matches observed fluctuations in oxygen isotope records over the last 800 kyr in all cases the ocean mass redistribution is constrained to be gravitationally self consistent the computed frechet kernels indicate that the predictions are most sensitive to variations in viscosity in the deepest regions of the mantle indeed in some cases the sensitivity peaks at the core mantle boundary both positive and negative perturbations to the precession constant are predicted with the maximum peak to peak relative variation being 0 20 per cent for the published viscosity models and 0 32 per cent for all other models furthermore the mean relative perturbation in the precession constant with respect to the present day value is found to reach 0 08 per cent for the published viscosity models and 0 20 per cent for other models recent solutions for the earth s precession obliquity and insolation parameters laskar joutel boudin 1993 indicate a passage through resonance associated with a perturbation of jupiter and saturn in the case when the mean relative perturbation in the precession constant is 0 15 per cent we find that this threshold is not achieved for any of the published viscosity models however it is reached for example for earth models with lower mantle viscosities which exceed 30 50 1021 pa s or models characterized by large two orders of magnitude jumps in viscosity at mid lower mantle depths

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

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

a large intraplate earthquake triggered by latent magmatism 1 a magnitude mj 7 3 intraplate earthquake occurred in the western tottori area southwest japan on 6 october 2000 where there was no apparent prefaulting subsurface indication of the source fault of the 2000 earthquake magnetotelluric soundings were taken in and around where the aftershocks occurred in order to image three dimensional electrical resistivity structure at depths of up to 40 km which could indicate an anomalously conductive body in the middle crust to the upper mantle on the southwestern side of the source fault free gas and dissolved gases collected from groundwater wells around the seismic source region are characterized by 3he 4he ratios several times higher than the atmospheric value the highest value of 5 1ra is similar to those of typical arc related volcanic gases although alkali basalts of early pleistocene age are sparsely distributed in the western tottori area the observed 3he 4he ratios are higher than the calculated 3he 4he ratio derived from the ancient magmatism considering postextrusive radiogenic ingrowth of 4he by decay of u and th included in the magma therefore it is concluded that the geophysical anomaly imaged to the southwest of the source fault is attributed to latent magmatism in the present day subduction system aqueous fluids separated from the cooling crustal magma could cause deep low frequency earthquakes around the moho discontinuity and migrate into the brittle upper crust in addition the presence of aqueous fluid is expected to weaken the crustal materials locally anelastic deformation implying notable compressive deformation in the e w direction was observed in the region where aftershocks were distributed under overpressure conditions the existing fault could serve as a pathway for aqueous fluids expelled from magma with high 3he 4he ratios so the upwelling of overpressurized fluids toward the earth s surface results in the emanation of groundwaters with high 3he 4he ratios along the trace of the source fault segments