litho1 0 an updated crust and lithospheric model of the earth we present the litho1 0 model which is a 1 tessellated model of the crust and uppermost mantle of the earth extending into the upper mantle to include the lithospheric lid and underlying asthenosphere the model is parameterized laterally by tessellated nodes and vertically as a series of geophysically identified layers such as water ice sediments crystalline crust lithospheric lid and asthenosphere litho1 0 is created by constructing an appropriate starting model and perturbing it to fit high resolution surface wave dispersion maps love and rayleigh group and phase over a wide frequency band 5 40 mhz we examine and discuss the model with respect to key lithospheric parameters such as average crustal velocity crustal thickness upper mantle velocity and lithospheric thickness we then compare the constructed model to those from a number of select studies at regional and global scales and find general consistency it appears that litho1 0 represents a reasonable starting model of the earth s shallow structure crust and uppermost mantle for the purposes in which these models are used such as traveltime tomography or in efforts to create a 3 d reference earth model the model matches surface wave dispersion over a frequency band wider than the band used in the inversion there are several avenues for improving the model in the future by including attenuation and anisotropy as well as making use of surface waves at higher frequency

curie point depths in northeast china and their geothermal implications for the songliao basin abstract this work integrates processing and interpretation of the combined geomagnetic anomaly model of ngdc 720 v3 1 to better constrain thermal structures of the northeast china lithosphere which shows intensive extension and active volcanism during the mesozoic and cenozoic numerical tests demonstrate that magnetic anomalies calculated at 20 km altitude can be used for accurate curie depth estimation averaged curie depths using a 3d fractal exponent of 3 0 vary from 13 2 0 to 33 4 1 km with a mean of 22 2 4 km in northeast china with temperature dependent thermal conductivity models constrained by incorporated surface heat flow and curie depths in different geological blocks the thermal lithospheric thicknesses are estimated mostly between 45 and 90 km based on 1d steady state thermal conduction equation beneath the songliao basin the moho temperatures are abnormally high ranging from ca 700 to 1000 c and the mantle contributes about 65 of the total surface heat flow the shallow curie points and thermal lithosphere asthenosphere boundary together with high moho temperatures and mantle heat flow support abnormally high geotherms in the songliao basin originated from hot upper mantle upwelling triggered likely by lithospheric delamination

transition from arc to intraplate magmatism associated with backarc rifting evolution of the sikhote alin volcanism k ar dates and chemical compositions of lavas in sikhote alin far east russia demonstrate marked secular variation in lava chemistry and suggest a linkage between magmatism and the major tectonic opening of the japan sea backarc basin lavas having typical arc magma chemistry were produced at 40 25 ma in the eastern part of sikhote alin a conspicuous volcanic hiatus is revealed in the region at 25 20 ma which is contemporaneous with the period of the major rifting of the backarc basin subduction related magmatism may have been switched off by an oceanward retreat of the arc trench system in contrast intraplate type lavas with typical hotspot magma compositions have dominated magmatism in both the eastern and western sikhote alin since 20 ma and occupy the eastern margin of the cenozoic intraplate magmatism in the ne asian continent

mechanism of backarc opening in the japan sea role of asthenospheric injection abstract the process of backarc extension in the japan sea includes two modes of spreading the parallel and rotational or fan shape opening data from paleomagnetism for rocks on the northeast japan arc radiometric age determination for dredged volcanic rocks and heat flow in the basin have suggested that the parallel opening of the japan sea took place earlier than the rotational opening at 21 14 ma the mechanism of opening of the japan sea has been examined based on the secular change in the geometry of the subducted slab and in the volcanic activity on the northeast japan arc mechanisms of backarc rifting including mantle diapirism mantle flow induced by the slab subduction or interaction of the over and the underriding plates cannot reasonably explain the process of opening of the japan sea the most plausible mechanism operating in the spreading process of the japan sea is injection of the asthenosphere into the mantle wedge that forcefully pushed the subducted slab to cause both steepening of the slab and the backarc extension the asthenospheric current towards the northeast japan arc trench system may have been associated with the large scale upwelling of the asthenosphere beneath the northeastern china region that caused intra plate volcanism and produced continental rift systems in the region the present mechanism can also explain the active backarc rifting in the okinawa trough in the western pacific and the taupo depression in north island new zealand

back arc extension in the okinawa trough the okinawa trough lying to the east of china is a back arc basin formed by extension within continental lithosphere behind the ryukyu trench arc system middle to late miocene uplift associated with normal faulting of the initially adjacent ryukyu nonvolcanic arc and the taiwan sinzi folded belt corresponds to the first rifting phase the timing of rifting is supported by the presence of marine sediments of corresponding age drilled in the northern okinawa trough the rifting occurred after a major early miocene change in the motion of the philippine plate with respect to eurasia and ceased during the pliocene a second rifting phase started about 2 m y ago at the plio pleistocene boundary and has continued until the present time it has proceeded to a more advanced stage in the middle and southern okinawa trough than it has farther north detailed bathymetric sea beam seismic reflection and magnetics data collected during the pop 1 cruise of the r v jean charcot reveal the principal features of the extensional processes the back arc spreading phase started very recently in the southern and middle okinawa trough as exemplified by several en echelon and in some cases overlapping active central graben oriented n70 e n80 e some of these depressions are intruded by volcanic ridges of fresh back arc basalt with associated large magnetic anomalies transform faults between these en echelon active rifts are not obvious we suggest that the major part of the southern okinawa trough is underlain by a thinned continental crust and that except for the system of en echelon rifts of the southern okinawa trough the back arc basin oceanic domain is limited to a width of a few tens of kilometers or less in the axial portion of the trough the system of axial back arc volcanic ridges that occur in the rifts ends at the latitude of okinawa island whereas active volcanoes in the ryukyu arc occur only north of okinawa island we refer to this transition between active arc and back arc volcanism as the volcanic arc rift migration phenomenon vamp globally back arc volcanism propagated from the southern okinawa trough to the okinawa vamp area rifting continues to occur in the northern okinawa trough but is not yet accompanied by associated volcanism the okinawa vamp area is characterized by a series of parallel basaltic ridges oriented n75 e with associated linear magnetic anomalies characteristic of dyke intrusions we suggest that the formation of the back arc oceanic domain took place along the axial back arc extensional zone trending n75 e and that this zone presently ends at the southern extremity of the active volcanic chain the initial phase of formation of back arc basin oceanic crust is non steady state and is characterized by the lack of a developed fracture zone pattern the termination of the vamp area in the direction of the volcanic zone of the arc is consistent with the suggestion of molnar and atwater that the volcanic arc is a fundamental line of weakness which determines where initial back arc spreading occurs apparently back arc extension initially occurred within the continental lithosphere located westward of the ryukyu arc along its whole length but the subsequent back arc volcanism was initiated in the southernmost portion of the region and then moved northward this migration was accompanied by the shutting down of volcanic activity along the abandoned portions of the arc it is this transfer of volcanism that we call the vamp process thus arc and back arc basin volcanism seem to be associated in such a manner that spreading tends to migrate simultaneously with a cessation in volcanic activity along the arc this interplay of arc and back arc activity is probably linked to changes in the parameters of plate convergence since the plate motion in the phillippine sea is oblique to the trench at least in the southern part of the okinawa trough we suggest that the oblique resisting force applied to the edge of the overriding plate engenders the development of en echelon extensional features within and behind the arc the motion of the ryukyu platelet with respect to eurasia is consequently an extensional strike slip motion trending roughly parallel to the okinawa trough

rayleigh wave group velocity distributions for east asia using ambient seismic noise vertical component data from 206 broadband seismometer stations from korean networks korean institute of geoscience and mineral resources and korea meteorological administration the japanese f net network and the chinese new china digital seismograph network and northeast china extended seismic array network are collected for the year 2011 and the ambient seismic noise is analyzed rayleigh wave group velocity distribution maps are created in the period range 10 to 70 s our results are largely consistent with previous studies of the area but provide greater detail in the korean peninsula and the sea of japan low group velocities are observed in the ulleung basin and the chubu kanto and kyushu regions in japan at 10 s period sediment basins in the sea of japan appear as low group velocity regions relative to higher group velocity continental regions at periods longer than 40 s a low group velocity region emerges in the ulleung basin region and is bounded by the korean peninsula

constraints on s wave velocity structures of the lithosphere in mainland china from broadband ambient noise tomography abstract in this study a 3 d s wave velocity model of the lithosphere in mainland china down to 150 km depth was determined from ambient noise data first we collected 2 year continuous waveforms recorded by 1031 broadband stations of the china regional seismic network and necessarray then by applying the procedures of noise cross correlation and time frequency domain phase weighted stacking we obtained the interstation empirical green s functions of rayleigh waves we measured the group and phase velocity dispersions at periods of 5 125 s from the egfs and inverted both group and phase velocities for the s wave velocity model our model revealed that the lithospheric thickness in the northern songliao basin is 70 110 km a weak high velocity anomaly that is discontinuous in the vertical direction was detected beneath the southern songliao basin which may indicate that the lithosphere is delaminated in this area the model also revealed that deep 150 km high velocity lithospheric roots exist beneath the ordos and sichuan basins the lithospheric thicknesses in eastern parts of the northeast china block the north china craton and the south china block are only 60 100 km which may be the result of a series of deep processes caused by the subduction of the pacific plate to the eurasian plate that produced strong lithospheric thinning in eastern china the lithospheric thickness within the tanlu fault belt is generally thinner than that in the adjacent areas of the fault belt and the s wave velocity of the mantle lithosphere beneath the fault belt is also lower than that beneath the adjacent areas indicating that the tanlu fault belt is a deep fault belt cutting through the lithosphere

global p wave tomography of earth s lowermost mantle from partition modeling 1 determining the scale length magnitude and distribution of heterogeneity in the lowermost mantle is crucial to understanding whole mantle dynamics and yet it remains a much debated and ongoing challenge in geophysics common shortcomings of current seismically derived lowermost mantle models are incomplete raypath coverage arbitrary model parameterization inaccurate uncertainty estimates and an ad hoc definition of the misfit function in the optimization framework in response we present a new approach to global tomography apart from improving the existing raypath coverage using only high quality cross correlated waveforms the problem is addressed within a bayesian framework where explicit regularization of model parameters is not required we obtain high resolution images complete with uncertainty estimates of the lowermost mantle p wave velocity structure using a hand picked data set of pkpab df pkpbc df and pcp p differential travel times most importantly our results demonstrate that the root mean square of the p wave velocity variations in the lowermost mantle is approximately 0 87 which is 3 times larger than previous global scale estimates

small scale hot upwelling near the north yellow sea of eastern china 1 in order to image the structure of the upper mantle discontinuity beneath eastern china we have applied a common conversion point ccp stacking method of receiver function rf both the 410 km and the 660 km discontinuities hereafter called the 410 and the 660 clearly show continuous positive phases along the selected profile the 410 shows depression whereas the 660 shows uplift in the eastern section of the study profile the transition zone tz to the west of longitude 122 is thicker than the global average though the tz is thinner to the east of that longitude the thinnest part of the tz with 10 15 km of thinning an increase in temperature of up to 100c is located at the north yellow sea we suggest that either the small scale convection associated with the deep penetration of the sinking slab into the lower mantle or a small plume from lower mantle has generated hot upwelling in this region citation ai y t zheng w xu and q li 2008 small scale hot upwelling near the north yellow sea of eastern china geophys res lett 35 l20305 doi 10 1029 2008gl035269

the murray springs clovis site pleistocene extinction and the question of extraterrestrial impact some of the evidence for the recent hypothesis of an extraterrestrial impact that caused late pleistocene megafaunal extinctions firestone et al 2007 proc natl acad sci usa 104 16016 16021 was based upon samples collected at murray springs a clovis archaeological site in southeastern arizona here we describe sampling and analyses of magnetic separates from within above and below the lower younger dryas boundary lydb black mat at murray springs as well as radiation measurements from the lydb at murray springs and two other well stratified clovis sites the main magnetic fraction at murray springs is maghemite magnetic microspherules have terrestrial origins but also occur as cosmic dust particles we failed to find iridium or radiation anomalies the evidence for massive biomass burning at murray springs is addressed and found to be lacking we could not substantiate some of the claims by firestone and others but our findings do not preclude a terminal pleistocene cosmic event

intraplate volcanism controlled by back arc and continental structures in ne asia inferred from transdimensional bayesian ambient noise tomography intraplate volcanism adjacent to active continental margins is not simply explained by plate tectonics or plume interaction recent volcanoes in northeast ne asia including ne china and the korean peninsula are characterized by heterogeneous tectonic structures and geochemical compositions here we apply a transdimensional bayesian tomography to estimate high resolution images of group and phase velocity variations with periods between 8 and 70 s the method provides robust estimations of velocity maps and the reliability of results is tested through carefully designed synthetic recovery experiments our maps reveal two sublithospheric low velocity anomalies that connect back arc regions in japan and ryukyu trench with current margins of continental lithosphere where the volcanoes are distributed combined with evidences from previous geochemical and geophysical studies we argue that the volcanoes are related to the low velocity structures associated with back arc processes and preexisting continental lithosphere

an improved method to extract very broadband empirical green s functions from ambient seismic noise the extraction of green s functions by cross correlation of continuous seismic records at station pairs is best achieved in a diffuse wave field where energies radiated by random sources have equal power to partially satisfy the diffuse wave field condition original seismic records must be normalized as they are highly nonstationary and may have amplitude variations of orders of magnitude within the cross correlation time window we adapt a frequency time normalization method to obtain seismograms with an even spectrum at all times within the data processing unit compared with the commonly used one bit normalization the new method improves the signal to noise ratio of empirical green s functions by a factor of 2 and increases the effective data recording duration by a factor of 4 assuming random local and instrument noise it yields useful rayleigh waves at periods up to 300 s for program for array seismic studies of the continental lithosphere passcal type deployments and 600 s for permanent stations with very broadband sensors thus the new method makes it possible to extend surface wave signals to frequencies beyond those in traditional earthquake based surface wave tomography at both the high and low frequency ends

transdimensional inversion of ambient seismic noise for 3d shear velocity structure of the tasmanian crust abstractambient seismic noise tomography has proven to be a valuable tool for imaging 3d crustal shear velocity using surface waves however conventional two stage inversion schemes are severely limited in their ability to properly quantify solution uncertainty and account for inhomogeneous data coverage in response to these challenges we developed a two stage hierarchical transdimensional bayesian scheme for inverting surface wave dispersion information for a 3d shear velocity structure and apply it to ambient seismic noise data recorded in tasmania southeast australia the key advantages of our bayesian approach are that the number and distribution of model parameters are implicitly controlled by the data and that the standard deviation of the data noise is treated as an unknown in the inversion furthermore the use of bayesian inference which combines prior model information and observed data to quantify the a posteriori probability distribution means that model uncertainty information can b

u th systematics of dispersed young volcanoes in ne china asthenosphere upwelling caused by piling up and upward thickening of stagnant pacific slab abstract young 300 to 5500years old dispersed intraplate volcanism characterized by small volume of melt and large compositional variability occurred over ne china at jingbohu long gang tianchi and wudalianchi these young volcanic rocks provide ideal opportunities for investigating the mechanism of dispersed continental volcanism using short lived uranium series isotopes we present systematic u series nd sr pb isotope and trace element analyses of the young lavas from ne china jingbohu lavas display variable extents of 230th excesses 10 to 28 and moderately depleted nd isotopic compositions end 1 5 to 3 3 long gang lavas have pronounced 33 to 35 230th excesses and slightly depleted nd isotopic compositions end 0 5 to 0 7 the tianchi lavas display moderate 12 230th excesses and slightly enriched nd isotopic compositions end 1 0 to 1 1 230th enrichments in all these volcanic rocks are uncharacteristic of melts generated by subduction the strongest evidence against the involvement of subduction related fluids is derived from the long gang lavas having more than 30 230th excesses low u th sr th and ba th ratios and positive nb and ta anomalies the fluids released from the subduction of the pacific plate under the eurasian plate might have already been completely lost before the slab reached the mantle beneath ne china we postulate that in addition to the convective circulation process the continuous piling up and upward thickening of stagnant pacific slab in the mantle transition zone may help drive a broad asthenosphere upwelling far from the trench leading to mantle partial melting and the formation of the young volcanoes in ne china in addition our u th disequilibrium data provide constraints on magma evolution time the magma evolution time from low sio2 47 5 basalt to higher sio2 50 4 basalt at long gang is within 10 thousand years 10ka the magma evolution time from trachyte to rhyolite at tianchi volcano is also less than 10ka if the tianchi silicic rocks were evolved from long gang basaltic magmas with minor crustal assimilation then the magma evolution time from basaltic magma to silicic magmas is less than 110 thousand years

subduction triggered magmatic pulses a new class of plumes article i nfo a variety of atypical plume like structures and focused upwellings that are not rooted in the lower mantle have recently been discussed and seismological imaging has shown ubiquitous small scale convection in the uppermost mantle in regions such as the mediterranean region the western us and around the western pacific we argue that the three dimensional return flow and slab fragmentation associated with complex oceanic subduction trajectories within the upper mantle can generate focused upwellings and that these may play a significant role in regional tectonics the testable surface expressions of this process are the outside arc alkaline volcanism topographic swell and low velocity seismic anomalies associated with partial melt using three dimensional simplified numerical subduction models we show that focused upwellings can be generated both ahead of the slab in the back arc region though five times further inward from the trench than arc volcanism and around the lateral edges of the slab in the order of 100 km away from slab edges vertical mass transport and by inference the associated decompression melting in these regions appears strongly correlated with the interplay between relative trench motion and subduction velocities the upward flux of material from the depths is expected to be most pronounced during the first phase of slab descent into the upper mantle or during slab fragmentation we discuss representative case histories from the pacific and the mediterranean where we find possible evidence for such slab related volcanism

a persistent localized microseismic source near the kyushu island japan 1 very strong signals with apparent velocity higher than rayleigh wave velocity are observed on noise correlation functions ncfs between seismic stations in east asia these signals are present on one month ncfs in ten years period with stable arrival times indicating their persistent and localized nature the signals are strong in the frequency band of 0 07 0 12hz and their amplitudes show inter annual but not seasonal variation location obtained from two algorithms with gsn and fnet data indicates that the source is situated in kyushu island japan after an earthquake is used to account for heterogeneity effects the location is closer to the ariake bay but still in the island the non seasonal amplitude variation and the peak frequency of 0 1hz suggest the signals are probably not generated by oceanic sources this persistent localized microseismic source needs to be taken into consideration in ambient noise tomography studies in east asia

3d upper mantle structure beneath japan and its surrounding region from inter station dispersion measurements of surface waves abstract three dimensional shear wave speed structure of the upper mantle beneath the japanese islands and the surrounding regions is constructed from the measurements of inter station phase speeds of surface waves we employ the dense broad band seismic network f net deployed throughout japan as well as permanent stations of global seismic network in east asia a temporary broad band seismic network in far east russia which has been constructed as a part of the stagnant slab project since 2004 is also used in combination with the permanent stations using seismic events from 2005 to 2007 with moment magnitude greater than 6 0 and depth shallower than 100 km we measure the phase speeds of the fundamental mode rayleigh and love waves working with the conventional two station technique phase speed maps of the japanese islands and the sea of japan are obtained from the inversions of inter station phase speeds that are measured for a large number of station pairs we have collected over 5300 paths for rayleigh waves and 3800 paths for love waves the phase speed maps of rayleigh waves in the period range from 25 to 140 s are inverted to obtain an isotropic 3d shear wave speed model in the depth range from 40 to 200 km the isotropic s wave model represents prominent fast wave speed anomalies in northeastern japan associated with the subducting pacific plate fast anomalies of the lithosphere beneath the sea of japan are also imaged implying that the average thickness of lithosphere beneath the yamato rise and japan basin is about 60 10 km immediately below this oceanic lithosphere slow anomalies are found in the asthenosphere beneath the entire region of the sea of japan in the depth down to about 200 km in southwestern japan the low angle subduction of the philippine sea plate is mapped clearly indicating that the northern end of the plate extends beyond the northern coast of the chugoku region reaching beneath the oki islands in the sea of japan a strong low velocity anomaly off the west coast of kyushu is found in the depth down to about 130 km which supports the existence of an upwelling flow beneath this area we also invert the phase speed maps of rayleigh and love waves in the period range from 30 to 80 s simultaneously to construct the radially anisotropic shear wave speed model a remarkable anisotropy with sh sv is found in the mantle wedge beneath northeastern japan while only weak anisotropy is seen beneath the sea of japan such anisotropic properties which cannot readily be obtained from body wave studies only will be an important key to understanding the dynamic processes in this tectonically actively region

spatial and temporal evolution of the subducting pacific plate structure along the western pacific margin 1 tomographic images of the subducting pacific plate beneath the izu bonin mariana arc illustrate a progression of geometries from shallow dipping to vertical from north to south along the arc recent advances in technology and inversion techniques have improved resolution of slab structure beneath the western pacific island arcs but reasons for the variation in geometry and morphology are still poorly understood by comparing high resolution tomographic images of the western pacific and updated paleogeographic reconstructions we are able to link the spatiotemporal evolution of the subducting pacific plate back to the mid miocene we have reconstructed tectonic motions along the kurile japan izu bonin mariana arc system and the ryukyu arc to provide an independent additional interpretation of the subducting pacific plate using the most current plate motion data we then investigate the plausibility of our model and three other proposed models based on the interpreted slab structure from tomographic images the new reconstruction agrees with the basic characteristics of former trench retreat models but illustrates the importance of the collision of the ogasawara plateau with the trench in the mid miocene and its subsequent effect on the slab structure at depth and the impact of other aseismic ridge collisions along the plate boundary the combination of evidence in changed physical properties imaged with tomography and the current interpreted slab morphology can be analyzed with the past plate motions to understand subduction zone processes

changbaishan volcanism in northeast china linked to subduction induced mantle upwelling the changbaishan volcanic complex in china cannot be easily explained as the consequence of a mantle plume seismic images from the region identify buoyant mantle material that may have been entrained and dragged downwards by the subducting pacific plate but is now escaping upwards through a gap in the plate and producing the intraplate volcanism

crust and uppermost mantle beneath the north china craton northeastern china and the sea of japan from ambient noise tomography 1 a 3 d shear velocity model of the crust and uppermost mantle to a depth of 100 km is presented beneath the north china craton ncc northeastern china the korean peninsula and the sea of japan ambient noise rayleigh wave tomography is applied to data from more than 300 broadband seismic stations from chinese provincial networks cearray the japanese f net and the iris global seismic network continuous data from 2007 to 2009 are used to produce group and phase velocity maps from 8 s to 45 s periods the model is motivated to constrain the distributed intraplate volcanism crustal extension cratonic rejuvenation and lithospheric thinning that are hypothesized for the study region numerous robust features are observed that impose new constraints on the geometry of these processes but discussion concentrates only on four 1 the north south gravity lineament follows the 40 km contour in crustal thickness and crustal thickness is anticorrelated with water depth beneath the sea of japan consistent with crustal isostasy for a crust with laterally variable composition 2 the lithosphere is thin 70 km beneath the songliao bohai graben but seismically fast 3 even thinner more attenuated lithosphere bounds three sides of the eastern ncc in a horseshoe shape identifying a region of particularly intense tectonothermal modification where lithospheric rejuvenation may have reached nearly to the base of the crust 4 low velocity anomalies reach upward in a y shape in the mantle beneath the eastern and western borders of the sea of japan extending well into continental east asia in the west and are separated by a 60 km thick lithosphere beneath the central sea of japan this anomaly may reflect relatively shallow slab dehydration in the east and in the west may reflect deeper dehydration and convective circulation in the mantle wedge overlying the stagnant slab

the role of the east asian active margin in widespread extensional and strike slip deformation in east asia east asia is a region of widespread deformation dominated by normal and strike slip faults deformation has been interpreted to result from extrusion tectonics related to the india eurasia collision which started in the early eocene in east and se china however deformation started earlier than the collision latest cretaceous to palaeocene suggesting that extrusion tectonics is not the only driving mechanism for east asia deformation it is suggested that the east asian active margin has influenced deformation in east asia significantly along the margin cenozoic back arc extension took place behind several adjoining arcs implying eastward rollback of the subducting slab and collapse of the overriding plate towards the retreating hinge line we show that extension took place along a c 7400 km long stretch of the east asian margin during most of the cenozoic physical models are presented simulating overriding plate collapse and back arc extension the models reproduce important aspects of the strain field in east asia for geometrical and rheological conditions scaled to represent east asia modelling shows that the active margin can be held responsible for deformation in east asia as far west as the baikal rift zone located c 3300 km from the margin

the shear wave velocity structure in the upper mantle beneath eurasia summary we develop an approach that allows us to invert for the mantle velocity structure within a finely parametrized region as a perturbation with respect to a low resolution global tomographic model we implement this technique to investigate the upper mantle structure beneath eurasia and present a new model of shear wave velocity parametrized laterally using spherical splines with 2 9 spacing in eurasia and 11 5 spacing elsewhere the model is obtained from a combined data set of surface wave phase velocities long period waveforms and body wave traveltimes we identify many features as narrow as few hundred kilometres in diameter such as subducting slabs in eastern eurasia and slow velocity anomalies beneath tectonically active regions in contrast to regional studies in which these features have been identified our model encompasses the structure of the entire eurasian continent furthermore including mantleand body wave waveforms helped us constrain structures at depths larger than 250 km which are poorly resolved in earlier models we find that up to 9 per cent faster than average anomalies within the uppermost 200 km of the mantle beneath cratons and some orogenic regions are separated by a sharp gradient zone from deeper 1t o 2 per cent anomalies we speculate that this gradient zone may represent a boundary separating the lithosphere from the continental root which might be compositionally distinct from the overlying lithosphere and remain stable either due to its compositional buoyancy or due to higher viscosity compared with the suboceanic mantle our regional model of anisotropy is not significantly different from the global one

pervasive seismic low velocity zones within stagnant plates in the mantle transition zone thermal or compositional origin abstract we exploit conversions between p and s waves for large scale high resolution imaging of the mantle transition zone beneath northwest pacific and the margin of eastern asia we find pervasive reflectivity concentrated in two bands with apparent wave speed reduction of 2 to 4 about 50 km thick at the top of the transition zone and 100 km thick at the bottom this negative reflectivity associated with the scattered waves at depth is interpreted jointly with larger scale mantle tomographic images and is shown to delineate the stagnant portions of the subducted pacific plate in the transition zone with largely positive shear wave velocity contrasts the upper reflectivity zone connects to broad low velocity regions below major intra plate volcanoes whereas the lower zone coincides locally with the occurrence of deep focus earthquakes along the east asia margin similar reflectivity is found in pacific northwest of the usa we demonstrate that the thermal signature of plates alone is not sufficient to explain such features alternative explanations for these reflective zones include kinetic effects on olivine phase transitions meta stability compositional heterogeneities within and above stagnant plates complex wave propagation effects in the heterogeneous slab structure or a combination of such factors we speculate that part of the negative reflectivity is the signature of compositional heterogeneities as revealed by numerous other studies of seismic scattering throughout the mantle and that such features could be widespread across the globe

intensive hydration of the mantle transition zone beneath china caused by ancient slab stagnation the mantle transition zone beneath china is anomalously hydrated geochemical analyses of basalts erupted above the mantle transition zone in northeast china indicate that water may have been added to this zone during the dehydration of subducted slabs on two separate occasions over the past one billion years

deciphering oblique shortening of central alborz in iran using geodetic data the alborz is a narrow 100 km and elevated 3000 m mountain belt which accommodates the differential motion between the sanandaj sirjan zone in central iran and the south caspian basin gps measurements of 12 geodetic sites in central alborz between 2000 and 2002 allow to constrain the motion of the belt with respect to western eurasia one site velocity on the caspian shoreline suggests that the south caspian basin moves northwest at a rate of 6 2 mm year with respect to western eurasia north south shortening across the alborz occurs at 5 2 mm year to the south deformation seems to extend beyond the piedmont area probably due to active thrusting on the pishva fault we also observe a left lateral shear of the overall belt at a rate of 4 2 mm year consistent with the geological motion observed along e w active strike slip faults inside the belt e g the mosha fault

deep slab subduction and dehydration and their geodynamic consequences evidence from seismology and mineral physics abstract we present new pieces of evidence from seismology and mineral physics for the existence of low velocity zones in the deep part of the upper mantle wedge and the mantle transition zone that are caused by fluids from the deep subduction and deep dehydration of the pacific and philippine sea slabs under western pacific and east asia the pacific slab is subducting beneath the japan islands and japan sea with intermediate depth and deep earthquakes down to 600 km depth under the east asia margin and the slab becomes stagnant in the mantle transition zone under east china the western edge of the stagnant pacific slab is roughly coincident with the ne sw daxing anling taihangshan gravity lineament located west of beijing approximately 2000 km away from the japan trench the upper mantle above the stagnant slab under east asia forms a big mantle wedge bmw corner flow in the bmw and deep slab dehydration may have caused asthenospheric upwelling lithospheric thinning continental rift systems and intraplate volcanism in northeast asia the philippine sea slab has subducted down to the mantle transition zone depth under western japan and ryukyu back arc though the seismicity within the slab occurs only down to 200 300 km depths combining with the corner flow in the mantle wedge deep dehydration of the subducting pacific slab has affected the morphology of the subducting philippine sea slab and its seismicity under southwest japan slow anomalies are also found in the mantle under the subducting pacific slab which may represent small mantle plumes or hot upwelling associated with the deep slab subduction slab dehydration may also take place after a continental plate subducts into the mantle