shear wave polarization anisotropy in the mantle wedge above the subducting pacific plate abstract research of azimuthal anisotropy in the mantle wedge above subduction zones opens up a new source of information about rising magma in the region because the physical property estimated from shear wave anisotropy is related to dynamic processes inside the earth regional variation in shear wave polarization is investigated from a teleseismic event and some local deep earthquakes using a spatially dense seismic array of the nied located in the central part of japan a characteristic pattern is found on the spatial distribution of shear wave polarization data obtained from scs waves large and small values of shear wave polarization anisotropy are observed at seismic stations located to the west and east of the volcanic front respectively the anisotropic zone with maximum velocity in n s direction is localized in the wedge portion between the surface and subducting slab using the data of the local deep events the location of the anisotropic zone corresponds with a low q zone obtained from seismic tomography data we conclude that the azimuthal anisotropic zone in the mantle wedge is caused by melt filled cracks which is consistent with models obtained by petrological studies

isotropy or weak vertical transverse isotropy in d beneath the atlantic ocean 1 shear velocity properties of d beneath the central atlantic ocean are explored using predominantly european seismic recordings of intermediate and deep focus 100 km south american earthquakes broadband data are analyzed and when possible corrected for upper mantle models of receiver side anisotropic structure regional shear velocity heterogeneity in d is mapped by analysis of 306 s sks differential times that have been corrected for three dimensional seismic velocity structure above d using a whole mantle tomographic model this correction yields modest less than 2 estimates of seismic velocity heterogeneity in d with a transition from high to low seismic velocities traversing from west to east beneath the central atlantic in agreement with global tomographic models additionally shear wave splitting of s and sdiff for the same recordings was analyzed to assess seismic anisotropy in d the highest quality data provide 105 splitting times between sh and sv onsets that are mostly within the 1 s uncertainty level the few larger values generally exhibit sv delayed relative to sh assuming an anisotropy geometry involving vertical transverse isotropy vti as preferred in most regions of d that have been studied to date 0 5 anisotropy strength within a 100 km thick layer or 0 25 anisotropy within a 300 km thick layer are compatible with the data these values are low in comparison to those found in high velocity regions beneath the circum pacific ocean or in the low velocity region beneath the central pacific and many observations are in fact consistent with isotropic structure the lack of strong vti relative to other regions may be due to 1 the absence of stress from overlying midmantle downwelling 2 relatively weaker shear flow in the d boundary layer and or 3 lack of chemical heterogeneity that could develop either lattice preferred orientation or shape preferred orientation the azimuthal sampling of this region of d is quite limited thus the precise geometry and mechanism of any anisotropy are difficult to constrain it remains possible that this region may contain subtle azimuthal anisotropy that could couple the sv and sh signals however amplitude observations suggest that any such coupling is minor

metastable olivine wedge and deep dry cold slab beneath southwest japan abstract oceanic plates subducted at trenches penetrate into the deep mantle and encounter a structural boundary at a depth of 410 km where olivine the dominant element of mantle rocks transforms into a higher density form wadsleyite this transformation may be delayed within the coldest core of subducting plates slabs due to kinetic effects and it has been suggested that metastable olivine may persist deeper than 410 km using high density seismic array data in japan we show the direct image of the structure corresponding to this metastable olivine wedge mow beneath southwest japan numerical simulation of a subducting slab including the kinetic effect of water h 2 o on the olivine wadsleyite transformation indicates that the presence of the imaged mow requires an insignificant amount of water less than 100 wt ppm be present in the slab mantle thus a deep dry cold slab we infer that the transportation of water into the deep mantle occurs along the top surface of the subducting slab but no significant amount within the slab itself we also demonstrate that a numerical simulation including the kinetics of 660 km phase transformation can reconcile the observed deep depression of the 660 km discontinuity with a gentle clapeyron slope

laboratory and seismological observations of lower mantle isotropy we have carried out seismological and mineral physics investigations to identify the extent and origin of elastic anisotropy in the lower mantle based on observations of shear wave splitting we conclude that the lower mantle is effectively isotropic this result is surprising since the lower mantle is composed of elastically anisotropic minerals silicate perovskite mgo sio 2 that have been extensively strained by geologic processes to reconcile the seismic observations we have measured texture development during deformation and high temperature recrystallization of mantle silicates we show that these experiments provide a direct explanation for the shear wave splitting measurements the lower mantle appears isotropic because silicate perovskite maintains an isotropic texture during deformation and recrystallization

detrital sediment supply in the southern okinawa trough and its relation to sea level and kuroshio dynamics during the late quaternary abstract during leg 195 of the ocean drilling program site 1202 was drilled in the subtropical northwestern pacific ocean beneath the kuroshio black current between northern taiwan and the ryukyu island arc on the northern flank of the i lan ridge at 1274 m water depth the upper 110 m of the site 1202 section composed of dark grey calcareous silty clay provide an expanded record of environmental changes during the last 28 kyr the sediments were deposited at high sedimentation rates between 3 0 and 5 0 m kyr and peak values of 9 0 m kyr between 15 1 and 11 2 ka bp variations in the modes and sources of detrital sediment input as inferred from sediment granulometry mineralogy and elemental xrf scanner data reflect changes in environmental boundary conditions related to sea level changes kuroshio variability and the climate driven modes of fluvial runoff the provenance data point to increased sediment supply from northwestern taiwan between 28 and 19 5 ka bp and from east china sources between 19 5 and 11 2 ka bp the change in provenance at 19 5 ka bp reflects increased fluvial runoff from the yangtze river and strong sediment reworking from the east china sea shelf in the course of increased humidity and postglacial sea level rise particularly after 15 1 ka bp the holocene was dominated by sediments that originated from rivers in northeastern taiwan for the pre holocene period prior to 11 2 ka bp low portions of sortable silt 63 10 m show that the kuroshio did not enter the okinawa trough because of low sea level in turn high proportions of sortable silt and sediment provenance from northeastern taiwan point to strong ocean circulation under the direct and persistent influence of the kuroshio during the holocene the reentrance of the kuroshio to the okinawa trough was heralded by two pulses in relative current strengthening at 11 2 and 9 5 ka bp as documented by stepwise increases in sortable silt in the lower holocene section from a global perspective environmental changes in the southern okinawa trough show affinities to climate change in the western pacific warm pool with little influence of climate teleconnections from the north atlantic realm otherwise seen in many other marine and terrestrial palaeoclimate records from southeastern asia

b type olivine fabric in the mantle wedge insights from high resolution non newtonian subduction zone models several hypotheses have been proposed to explain trench parallel shear wave splitting in the mantle wedge of subduction zones these include 3 d flow effects parallel melt filled cracks and b type olivine fabric we predict the distribution of btype and other fabrics with high resolution thermal and stress models of subduction zones a composite viscous rheology is used that incorporates wet diffusion creep wet dislocation creep and a stress limiting approximated peierls creep law rheological parameters for dislocation and diffusion creep are based on deformation experiments the effects of variable viscous coupling between the slab and mantle are explored using kinematic boundary conditions that change along the top of the slab two end member models are observed which depend on the depth of partial viscous coupling between the slab and mantle 1 deep partial coupling which gives rise to cold high stress conditions in the forearc mantle and high temperature low stress conditions in the arc and back arc mantle 2 full viscous coupling at the base of a 40 km conducting lid which is characterized by high temperature and low stress the case with deep partial coupling which produces a better match with attenuation tomography and heat flow shows a large region with suitable conditions for b type fabric in the forearc mantle and a rapid transition toward the back arc to conditions that are more suitable for a c or e type fabrics full viscous coupling gives rise to high temperature low stress conditions unsuitable for b type fabric our modeling predicts that the best candidates for regions with b type fabric are the forearc mantle and a cold 10 15 km layer above the slab d 2005 elsevier b v all rights reserved

shear wave polarization anisotropy and subduction induced flow in the mantle wedge of northeastern japan abstract shear wave polarization anisotropy in the central part of northeastern ne japan was investigated we analyzed s phases of 293 intermediate depth earthquakes recorded at 77 stations and obtained 1286 splitting parameters the obtained results show the systematic variation in splitting parameters across the arc the leading shear wave polarization directions fast direction obtained at stations in the western side of the study area are oriented nearly e w which is sub parallel to the direction of relative plate motion between the pacific plate and the north american okhotsk plate in contrast fast directions obtained at stations in the eastern side of the study area are oriented approximately n s stations in the western side have a larger average delay time compared to those in the eastern side these variations suggest that the nature of anisotropy is quite different between the eastern and the western sides both experimental studies on the deformation of olivine and numerical simulations of plate driven flow predict that the lattice preferred orientation of olivine causes the fast direction sub parallel to the flow direction for the conditions in the mantle wedge of ne japan we thus infer that the lattice preferred orientation of olivine generated by flow induced strain is the most likely candidate for anisotropy that produces splitting with e w fast direction three possible causes of anisotropy in the eastern side are considered deformation of water rich olivine in the mantle wedge trench parallel flow in the mantle wedge due to along strike dip variations in the slab and anisotropy in the crust and the slab we could not however determine which causes are dominant further systematic study is required to reveal the cause of anisotropy in the eastern side

stress strain rate and anisotropy in kyushu japan abstract seismic anisotropy the directional dependence of wave speeds may be caused by stress oriented cracks or by strain oriented minerals yet few studies have quantitatively compared anisotropy to stress and strain over large regions here we compare crustal stress and strain rates on the island of kyushu japan as measured from inversions of focal mechanisms gps and shear wave splitting over 85 000 shear wave splitting measurements from local and regional earthquakes are obtained from the nied network between 2004 and 2012 and on aso sakurajima kirishima and unzen volcano networks strain rate measurements are made from the japanese geonet stations jma determined s arrival times processed with the mfast shear wave splitting code measure fast polarisations related to the orientation of the anisotropic medium and time delays dt related to the path length and the percent anisotropy we apply the tessa 2 d delay time tomography and spatial averaging code to the highest quality events which have nearly vertical incidence angles separating the 3455 shallow depth 40 km earthquakes using square grids with 30 km sides for all the inversions the best correlations are observed between splitting from shallow earthquakes and stress axes of maximum horizontal stress shmax and correlate with a coefficient c of 0 56 significant at the 99 confidence level their mean difference is 31 9 axes of maximum compressional strain rate and shmax are also well aligned with an average difference of 28 but they do not correlate with each other meaning that where they differ the difference is not systematic anisotropy strength is negatively correlated with the stress ratio parameter determined from focal mechanism inversion c 0 64 significant at the 99 confidence level the anisotropy and stress results are consistent with stress aligned microcracks in the crust in a dominantly strike slip regime eigenvalues of maximum horizontal strain rate correlate positively with stress ratio c 0 43 significant at 99 confidence all three orientations are e w in central kyushu where the compressional strain rate is highest both splitting and stress suggest plate boundary parallel maximum principal stress just off the coast of kyushu where strain rate measurements are sparse south western kyushu has the largest difference between directions of strain rate and stress from shallow and deep earthquakes are not well aligned suggesting that the deep earthquake waveforms are not simply split in the crust causes for the anisotropy may be olivine crystals aligned by drag of the subducting philippine sea plate in the mantle and stress aligned microcracks in the crust

stratification of anisotropy in the pacific upper mantle 1 on the basis of the use of broadband 25 150 s rayleigh wave group speeds to estimate the 2 component of azimuthal anisotropy we present evidence for a stratification of anisotropy in the uppermost mantle at large scales across the pacific basin we confirm previous surface wave studies that established that the fast axis directions of azimuthal anisotropy for intermediate and long period rayleigh waves approximately align with present day plate motions at shorter periods 25 50 s however fast axes align nearer to the paleospreading or fossil spreading direction which differs from present day plate motion in the old pacific these observations as well as observations of the age dependence of the amplitude of azimuthal anisotropy imply that azimuthal anisotropy in the pacific upper lithosphere 100 km depth is fixed or fossilized on average reflecting the strain conditions extant during the early evolution of the lithosphere rather than the current ambient flow direction in the deeper lithosphere and asthenosphere anisotropic fast axis directions align nearer to present day plate motions apparently having reoriented to conform to the current conditions of mantle flow the mechanism of anisotropy stratification remains unclear but observations are consistent with the anisotropy of the shallow lithosphere being fixed because the shear flows that can produce dislocation creep and a change in anisotropy will occur at increasing depths as the plate ages

p and s wave tomography and anisotropy in northwest pacific and east asia constraints on stagnant slab and intraplate volcanism we determined three dimensional p and s wave velocities and p wave azimuthal anisotropic tomography of the northwest pacific subduction zones by inverting 1 225 086 p wave and 335 117 s wave arrival times from 13 413 earthquakes our results show some differences between p and s wave images for the stagnant pacific slab in the mantle transition zone mtz beneath northeast china the stagnant slab looks thicker in the p wave image than that in the s wave image which may reflects the effects of both hydration and lower temperature in the mtz though differences in the resolution of p and s wave tomography may also have some effects the changbai intraplate volcanism is caused by hot and wet upwelling in the big mantle wedge above the stagnant pacific slab our p wave anisotropy tomography shows that the fast velocity direction fvd in the subducting philippine sea plate beneath the ryukyu arc is ne sw trench parallel which is consistent with the spreading direction of the west philippine basin during its initial opening stage suggesting that it may reflect the fossil anisotropy a striking variation of the fvd with depth is revealed in the subducting pacific slab beneath the northeast japan arc which may be caused by slab dehydration that changed elastic properties of the slab with depth the fvd in the mantle wedge beneath the northeast japan and ryukyu arcs is trench normal which reflects subduction induced convection beneath the kuril and izu bonin arcs where oblique subduction occurs the fvd in the mantle wedge is nearly normal to the moving direction of the downgoing pacific plate suggesting that the oblique subduction together with the complex slab morphology have disturbed the mantle flow

constraints on subduction geodynamics from seismic anisotropy 1 much progress has been made over the past several decades in delineating the structure of subducting slabs but several key aspects of their dynamics remain poorly constrained major unsolved problems in subduction geodynamics include those related to mantle wedge viscosity and rheology slab hydration and dehydration mechanical coupling between slabs and the ambient mantle the geometry of mantle flow above and beneath slabs and the interactions between slabs and deep discontinuities such as the core mantle boundary observations of seismic anisotropy can provide relatively direct constraints on mantle dynamics because of the link between deformation and the resulting anisotropy when mantle rocks are deformed a preferred orientation of individual mineral crystals or materials such as partial melt often develops resulting in the directional dependence of seismic wave speeds measurements of seismic anisotropy thus represent a powerful tool for probing mantle dynamics in subduction systems here i review the observational constraints on seismic anisotropy in subduction zones and discuss how seismic data can place constraints on wedge slab and sub slab anisotropy i also discuss constraints from mineral physics investigations and geodynamical modeling studies and how they inform our interpretation of observations i evaluate different models in light of constraints from seismology geodynamics and mineral physics finally i discuss some of the major unsolved problems related to the dynamics of subduction systems and how ongoing and future work on the characterization and interpretation of seismic anisotropy can lead to progress particularly in frontier areas such as understanding slab dynamics in the deep mantle

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

evidence for a metastable olivine wedge inside the subducted mariana slab abstract an anomalous seismic velocity structure is revealed inside the subducted pacific plate at northern mariana near the deepest earthquake foci we observe anomalous later phases in the p wave coda for a small cluster of deep earthquakes and an anomalous differential p wave slowness between a few pairs of the earthquakes belonging to the cluster we interpret these observations with a 5 low velocity wedge which is nearly 25 km wide at the depth of 590 km and is truncated at 630 km the wedge is bounded by two steeply dipping 60 70 transition layers with the thickness of about 4 km the highly localized seismic anomaly inside the slab represents a wedge of metastable olivine embedded in dry ringwoodite deep earthquakes occur across only one of the boundaries of the metastable wedge with some of them outside the wedge the mechanism of deep earthquakes is discussed based on the spatial pattern of seismicity relative to the wedge

seismic anisotropy near source region in subduction zones around japan abstract broad band seismographs have been distributed widely over the japanese islands and have provided us with high quality digital waveform data in recent years we have investigated splitting of scs waves from deep earthquakes in the kuril and izu bonin subduction zones recorded on the sts seismograms we used scs waves from 13 events observed in japan and recognized shear wave splitting which is mainly caused by anisotropy in the lithospheric slab the anisotropy was confirmed around the source region by comparing scs wave splitting from deep earthquakes in different regions and at different depths with s wave splitting from deep events just beneath central japan we have found that the anisotropic regions exist within the subducting slab although they are distributed locally in and around the source possibly as patches with a diameter of 100 km or less discrepancy in the direction of the fast polarized shear waves between two nearby events is observed in the izu bonin subduction zone the splitting of the shallower event 289 km shows its fast polarization direction to be parallel to the fossil motion of the pacific plate but that of the deeper event 361 km immediately beneath is parallel to the current motion these observations suggest that the change in shear wave splitting with depth comes from the modification of preferred orientation of minerals depending on depth we propose in this study that the reorientation of minerals olivine occurs owing to the change in physical conditions associated with the phase transformation of olivine phase to modified spinel phase

anisotropic shear wave velocity structure of the earth s mantle a global model 1 we combine a new large data set of surface wave phase anomalies long period waveforms and body wave travel times to construct a three dimensional model of the anisotropic shear wave velocity in the earth s mantle our modeling approach is improved and more comprehensive compared to our earlier studies and involves the development and implementation of a new spherically symmetric reference model simultaneous inversion for velocity and anisotropy as well as discontinuity topographies and implementation of nonlinear crustal corrections for waveforms a comparison of our new three dimensional model s362ani with two other models derived from comparable data sets but using different techniques reveals persistent features 1 strong 200 km thick high velocity anomalies beneath cratons likely representing the continental lithosphere underlain by weaker fast anomalies extending below 250 km which may represent continental roots 2 weak velocity heterogeneity between 250 and 400 km depths 3 fast anomalies extending horizontally up to 2000 3000 km in the mantle transition zone beneath subduction zones 4 lack of strong long wavelength heterogeneity below 650 km suggesting inhibiting character of the upper mantle lower mantle boundary and 5 slow velocity superplumes beneath the pacific and africa the shear wave radial anisotropy is strongest at 120 km depth in particular beneath the central pacific lateral anisotropic variations appreciably improve the fit to data that are predominantly sensitive to the uppermost and lowermost mantle but not to the waveforms that control the transition zone and midmantle depths tradeoffs between lateral variations in velocity and anisotropy are negligible in the uppermost mantle but noticeable at the bottom of the mantle

shear wave polarization anisotropy in the upper mantle from a deep earthquake abstract shear wave polarization anisotropy in the upper mantle is investigated at the spatially dense seismic stations of the national research institute for earth science and disaster prevention located in central japan by the use of the scs wave of a deep earthquake which occurred beneath sakhalin island on 12 may 1990 a characteristic pattern is found small and large shear wave anisotropy values are observed at seismic stations located on the east and west sides of the volcanic front respectively

mineralogical and geochemical investigations of sediment source region changes in the okinawa trough during the past 100 ka images core md012404 abstract we present a mineralogical and geochemical study of core md012404 retrieved from the central okinawa trough ot of the east china sea our studies reveal that the sediment sources of the core have been changed through time during the past 100 ka our mineralogical proxies indicate that the sediments source from the yangtze river correlates well sea level changes before 24 ka our ti al ratios otherwise indicate an increase of sediment supply from eastern taiwan after 26 ka the cooler climate of the last glacial maximum lgm 23 19 ka led to a reduction in fluvial sediments from the yangtze river however subsequent climate warming after 19 ka resulted in an abrupt increase in fluvial sediments after the lgm the kuroshio intrusion flow into the ot may have increased we also infer anomalous changes in eolian sources transported by winter monsoons during the lgm and at 80 ka based on an eolian mineralogical indicator feldspar we conclude that the sediment source of core md012404 is primarily of terrestrial origins but influenced by sea level changes and variations in the east asian monsoon

monsoon forcing hydrodynamics of the kuroshio current and tectonic effects on sedimentary carbon and sulfur cycling in the okinawa trough since 90 ka 1 monsoon forcing and hydrodynamic effects controlled carbon and sulfur biogeochemistry over the last 90 ka in a 43 m core from the okinawa trough ot total organic carbon toc contents co vary with summer insolation at 30 n suggesting monsoon forcing of primary productivity and organic carbon burial before the last glacial maximum lgm total sulfur ts contents varied concomitantly with toc however sea level rise and intensified kuroshio inflow during the holocene enhanced deepwater ventilation which resulted in ts depleted sediments with low degree of pyritization dop by contrast dop values were high during the previous highstand at 80 ka bp when sea level was similar to that in the holocene as well as during the lgm when deepwater circulation was relatively weak a topographic barrier is proposed to have sufficiently blocked the kuroshio current out of the ot during the previous sea level highstand which weakened deepwater ventilation and led to reducing diagenetic conditions tectonic rifting in the southern ot at 60 30 ka bp enabled the major change in hydrodynamics and sediment biogeochemistry

longshot experiments to study velocity anisotropy in the oceanic lithosphere of the northwestern pacific abstract several long range explosion seismology experiments have been conducted in the northwestern pacific basin where one of the oldest oceanic lithospheres is postulated to exist the experiments were conducted from 1974 to 1980 highly sensitive ocean bottom seismographs which had been developed for longshot experiments were used the lengths of the profiles ranged from 1000 to 1800 km and the directions were chosen to provide wide azimuthal coverage one of the aims of this series of experiments was to test the existence of velocity anisotropy on a large regional scale the results show that the oceanic lithosphere has anisotropy wherein the velocity changes by 4 7 the anisotropy extends from a depth of at least 40 to 140 km beneath the sea bottom however the magnitude of the anisotropy may vary with depth the azimuth of the maximum velocity is 150 160 clockwise from north and coincides with the fossil direction of spreading of the pacific plate whereas it differs from the present direction of plate motion by 30 the azimuth does not seem to depend on depth in the direction of maximum velocity the lithosphere is basically two layered 8 0 8 2 and 8 6 km s 1 the depth of the interface is 50 60 km beneath the sea floor

deep countercurrent beneath the kuroshio in the okinawa trough 1 the okinawa trough is geographically separated into the northern and southern parts by the kerama gap and the northern part is composed of the northern central and southern subbasins formed by bights of the continental slope previous observations have indicated that a deep countercurrent is present beneath the kuroshio on the continental slope in the northern okinawa trough however its persistence over time and its spatial structure over the entire basin have not been clarified to date the present study examines moored current meter data on the continental slope in the southern and central subbasins of the northern okinawa trough for november 2004 to november 2006 deep flows on the continental slope have a clear seasonality in the southern subbasin eddy motions due to kuroshio meanders are organized into a persistent countercurrent below the kuroshio in the winter spring period during this time high frequency kuroshio meanders with periods near 10 d are likely to diminish in the southern subbasin while low frequency kuroshio meanders with periods of 1 3 months tend to dominate in the northern subbasin in addition a high resolution ocean general circulation model is used to explore the deep flow field over the entire okinawa trough the model indicates that the deep flow field is stable in the southern okinawa trough over the year whereas it is unstable in the northern okinawa trough particularly in the winter spring period this results in a persistent countercurrent driven by cyclonic eddies on the continental slope in the northern okinawa trough

upper mantle anisotropy beneath japan from shear wave splitting in this study we utilize data from 64 broadband seismic stations of the japanese f net network to investigate the threedimensional pattern of anisotropy in the subduction system beneath japan we have compiled a database of approximately 1900 high quality splitting measurements selected by visual inspection of over 25 000 records of s sks and skks phases at f net stations covering a wide range of incidence angles incoming polarization angles and backazimuths analysis of the variations of measured splitting parameters with these parameters allows us to consider complexities in structure such as multiple anisotropic layers dipping symmetry axes and small scale lateral variations in anisotropic properties here we focus on the presentation of the splitting measurements themselves a detailed interpretation in terms of tectonics and mantle flow is beyond the scope of this paper in the southern part of the f net array along the ryukyu arc we find that fast directions are consistently trench parallel with splitting times of 1 s or more moving northward along the array the measured splitting patterns become more complicated with significant variations in apparent splitting parameters that indicate complex anisotropic structure additionally measured fast directions vary significantly over short length scales and stations separated by less than 100 km often exhibit very different splitting behavior this increase in complexity of anisotropic structure coincides geographically with the complicated slab morphology of the subducting pacific plate at stations on hokkaido to the north and kyushu to the south we see some evidence that the fast direction of anisotropy may rotate from trench parallel close to the trench to subduction parallel further away from the trench which may correspond either to a change in stress conditions and or volatile content or to a change in flow regime 2005 elsevier b v all rights reserved

elasticity of single crystal olivine at high pressures and temperatures abstract elasticity of single crystal san carlos olivine has been derived from sound velocity and density measurements at simultaneous high pressure temperature conditions up to 20 gpa and 900 k using in situ brillouin spectroscopy and single crystal x ray diffraction in externally heated diamond anvil cells these experimental results are used to evaluate the combined effect of pressure and temperature on full elastic constants of single crystal olivine to better understand its velocity profiles and anisotropies in the deep mantle analysis of the results shows that the shear moduli display strong concave behaviors as a function of pressure at a given high temperature while the longitudinal modulus c 11 and the off diagonal moduli c 12 and c 13 exhibit greater temperature dependence at higher pressures than at relatively lower pressures using a finite strain theory and thermal equation of state modeling for a pyrolitic mantle composition along an expected mantle geotherm our results show that the magnitude of the v p and v s jumps at the 410 km depth are 6 and 6 4 respectively which are greater than that found in seismic observations suggesting a mantle olivine content of 40 50 vol which is less than what is expected for the pyrolite model our modeled velocity profiles for a metastable olivine wedge in the subduction slabs along a representative cold slab geotherm are 6 and 10 lower than those of wadsleyite and ringwoodite respectively at corresponding depths of the normal mantle our modeled results also show that metastable olivine in the cold slabs could have strong v p and v s anisotropies the maximum v p anisotropy is estimated to be 19 22 at transition zone depth whereas the maximum v s splitting is 13 23 and increases with depth as a result the presence of a metastable olivine wedge at the transition zone depth would exhibit a seismic signature of low velocity and strong seismic anisotropy which are consistent with recent seismic observations for various locations of the slabs and can be used as mineral physics constraints for future seismic detections of the metastable olivine wedges in the deep mantle

p wave anisotropy tomography of central japan insight into subduction dynamics abstract a p wave anisotropic tomography under central japan was determined using a large number of arrival time data from 22 244 earthquakes recorded by 770 seismic stations on the japan islands the results show that the anisotropy exists widely beneath the study area except for the central portion of the mantle wedge the fast velocity directions fvds of the mantle wedge are generally trench parallel under the fore arc area and trench normal under the back arc area which may be attributed to the lattice preferred orientation lpo of olivine changing from b type under the fore arc area to a type under the back arc area with the variation of water content and the occurrence of mantle flow the subducting philippine sea plate phs beneath tokai is revealed as a high velocity anomaly dipping northward with nee to ne sw fvds which are consistent with the spreading direction of the phs during its formation and are inferred as the fossil anisotropy of the phs the anisotropy of the upper portion of the pacific slab under central japan is also revealed in this study the fvds of the upper portion of the pacific slab are sub parallel to the japan trench and izu bonin trench at 60 120 km depths and become almost perpendicular to the trenches below 100 120 km depth after comparisons with the mesozoic magnetic anomaly lineations and the principle stresses in the pacific slab we propose that the fossil fvds of the pacific slab beneath central japan were already rebuilt by the principle stresses in the slab

shear wave splitting from local events beneath the ryukyu arc trench parallel anisotropy in the mantle wedge we present shear wave splitting measurements from local slab earthquakes at eight seismic stations of the japanese f net array located in the ryukyu arc we obtained high quality splitting measurements for 70 event station pairs and found that the majority of the measured fast directions were parallel to the strike of the trench and perpendicular to the convergence direction splitting times for individual measurements ranged from 0 25 to 2 s most values were between 0 75 and 1 25 s both the fast directions and the split times were similar to results for teleseismic s k ks and s wave splitting at the same stations which suggests that the anisotropy is located in the mantle wedge above the slab we considered several mantle deformation scenarios that would result in predominantly trench parallel fast directions and concluded that for the ryukyu subduction system the most likely explanation for the observations is corner flow in the mantle wedge combined with b type olivine fabric in this model the flow direction in the wedge is perpendicular to the trench but the fast axes of olivine crystals tend to align perpendicular to the flow direction resulting in trench parallel shear wave splitting

provenance of pliocene clay deposits from the iberian atlantic margin and compositional changes during recycling abstract the xrd mineralogy and geochemistry of recycled fine grained deposits from the west iberia atlantic margin are used to establish sediment provenance and evaluate the features that most closely reflect the nature of the source areas and the transformations during the last depositional cycle a set of pliocene sediment samples is organized according to grain size distribution geochemistry and mineralogy and their chemical composition is compared with the composition of possible source rocks most deposits located to the north of the mondego river were derived from the uplifted precambrian metapelites of the basin edge while to the south of the mondego river they result mainly from recycling of cretaceous and cenozoic clastic units which in turn were derived from precambrian paleozoic granitoids and metasedimentary rocks this differentiation is supported by several element ratios and biplots involving la sm gd sc th u y yb and zr for the specific grain size range of the deposits studied which are mainly made up of silt and clay particles composition is not substantially affected by the grain size distribution of the sediment multi element diagrams designed to discriminate the tectonic setting and the nature of source rocks are of little use in the interpretation of provenance but help to trace geochemical and mineralogical transformations during the last depositional cycles despite the evidence of element leaching during the pliocene depositional cycle the geochemical and mineralogical indicators of weathering intensities are largely determined by the nature of the previous cycle units

surface water evolution of the eastern east china sea during the last 36 000 years abstract planktic foraminifera have been studied in two high resolution cores raised from the continental slope of the eastern east china sea ecs to reconstruct the surface water history ams 14c dating on fifteen horizons revealed that the two cores kh82 4 14 and rn80 pc3 contain continuous records of the last 36 and 17 thousand cal years respectively thirty one planktic foraminiferal species which are commonly found in the present western north pacific and the ecs are recognized in down core samples three faunal phases iii ii and i distinguished by characteristic planktic foraminiferal assemblages suggest three major paleoenvironmental stages of the surface water of the eastern ecs since 36 000 yr b p 1 a stage influenced by coastal water from 36 000 to 19 500 yr b p 2 a stage also influenced by coastal water and extremely low salinity from 19 500 to 10 500 yr b p and 3 a stage controlled by the modern open sea water related to the kuroshio with both higher temperature and higher salinity since 10 5 8 5 thousand years b p oxygen isotope records of the planktic foraminiferal species g bulloides show that the three planktic foraminiferal faunal phases correspond to the last glacial deglacial and postglacial stages respectively the planktic foraminiferal assemblage during the deglacial stage which is represented by high percentages of g quinqueloba is quite different from those during the glacial and postglacial stages linked to a large amount of river discharge from the chinese continent a negative oxygen isotope excursion in g bulloides during the same period is highly correlated to the g quinqueloba anomaly also indicating a decrease in surface water salinity furthermore the sedimentation rate of core kh82 4 14 during 19 15 thousand years b p is much higher than the rates during the glacial and postglacial stages suggesting a great increase in the supply of terrigenous material related to an increased river and sediment discharge during the early deglaciation the coastal water influenced stage of the eastern ecs terminated gradually at 10 5 8 5 thousand years b p since the warm kuroshio current and its branches flowed in the eastern ecs as today the formation of the postglacial surface water circulation pattern in the eastern ecs was closely related to the flow patterns of the kuroshio current

evidence from shear wave splitting for the restriction of seismic anisotropy to the upper crust the existence of anistropy in the propagation speed of seismic waves through the earth s crust has been attributed to the non random alignment of microcracks in the crust1 for sparsely distributed parallel vertical cracks perturbation theory predicts the splitting of a shear wave into two orthogonally polarized waves2 4 here we present extremely clear evidence for shear wave splitting in three component seismograms from crustal and sub crustal microearthquakes recorded in the shikoku district of japan quantitative analysis of travel time differences between split shear waves leads to the conclusion that the observed anisotropy is limited to the upper crust shallower than 10 15 km this model is consistent with recent results from reflection seismology5 and implies that microcrack density or orientation changes from the upper to the lower crust

late quarternary paleoceanographic record from the middle ryukyu trench slope northwest pacific abstract a piston core kt84 14 p1 from the middle ryukyu trench slope contains many paleoceanographic indicators of the past ca 150 000 years the age assignment is based on such criteria as the abundance change between gephyrocapsa ericsoni and emiliania huxleyi the datum of which is here substantiated by tephrochronology of an ash bed and the planktonic foraminiferal 18 o measurements the abundance change of florisphaera profunda which prefers the deepest habitat among calcareous nannoplankton species coincides with fluctuation of the planktonic foraminiferal 18 o the benthic foraminiferal fauna also changes in response to the latest quaternary climatic change particularly during the deglaciation period from the emiliani stages 6 to 5 as well as from 2 to 1 the presence of a counter current of the kuroshio current is inferred during the last interglacial period based upon the distributional pattern of the ata tuff in this and two other cores all recovered east of the southern ryukyu island arc the ash originating from the southern tip of kyushu should have been transported eastwards not southwards by the westerly winds therefore we infer that the ash was transported southwards by the counter current

layered anisotropy within the crust and lithospheric mantle beneath the sea of japan abstract continental rifting during the oligocene to mid miocene caused the opening of the sea of japan and the separation between the japanese islands and the eurasian plate the tectonic evolution in the sea of japan is important for understanding the evolution of back arc regions in active convergent margins here we use data from the seismic stations surrounding the sea of japan to map the rayleigh wave azimuthal anisotropy in the crust and lithospheric mantle beneath the sea of japan we explore the variations of rayleigh wave phase velocity beneath the sea of japan in a broad period range 30 80 s rayleigh wave dispersion curves are measured by the two station technique for a total of 231 interstation paths using vertical component broad band waveforms at 22 seismic stations around the sea of japan from 1411 global earthquakes the resulting maps of rayleigh wave phase velocity and azimuthal anisotropy allow the examination of azimuthal anisotropy at specific periods they exhibit several regions with different isotropic and anisotropic patterns the japan basin displays fast velocities at shorter periods 30 and 40 s with nne ssw anisotropy whereas at 60 s and longer the velocities become slow even if the anisotropy remains ne sw the east china sea shows fast velocities at all periods 30 80 s with constant nw se anisotropy trench normal anisotropy beneath the japanese islands is found at short periods 30 40 s and become trench parallel at periods of 60 s and longer overall our model resolves two layers of anisotropy the shallowest and deepest layers being potentially related to frozen deformation due to recent geodynamic events and asthenospheric flow respectively

anisotropic loci in the mantle beneath central peru abstract seismic anisotropy of the upper mantle beneath the central part of peru is examined by analyzing shear waves observed at broad band stations and a temporary array of short period stations shear wave splitting is seen on various shear phases such as direct s waves from local intermediate to deep earthquakes scs waves from regional deep earthquakes and sks waves from teleseismic earthquakes it is inferred that the shear wave anisotropy in the uppermost 100 km of the subcontinental mantle overlying the subducted nazca plate is 0 5 at most while the anisotropy in the subslab asthenosphere depth range of about 150 350 km is 2 or greater the fast shear wave polarization direction in this depth range as observed at two broad band stations is 30 40 different from the absolute motion of the nazca plate this does not fit simple two dimensional 2 d models of olivine alignment caused by slab induced mantle flow and implies either the existence of a complex flow pattern in the asthenosphere underneath the nazca plate or the presence of an unknown mechanism for the anisotropy formation the lower mantle beneath central peru is found to be effectively isotropic for nearly vertically propagated shear waves

seismic anisotropy of subducting oceanic uppermost mantle from fossil spreading 1 identifying the sources of seismic anisotropy in subduction zone forearcs is key to understanding mantle deformation processes current models based on the interpretation of shear wave splitting measurements favor the flow induced alignment of olivine crystals around down going slabs or the presence of foliated serpentine minerals due to subduction related processes thereby neglecting fossil slab fabric as a significant source of anisotropy we use seismic receiver functions to show evidence for strong anisotropy within anhydrous uppermost mantle of subducting oceanic plates in the forearcs of nankai cascadia mexico and costa rica subduction zones seismic anisotropy models from the inversion of receiver function waveforms are consistent with fossil fabric generated at spreading ridges

a multiproxy lake record from inner mongolia displays a late holocene teleconnection between central asian and north atlantic climates in order to study how the holocene central asian climate is coupled to the global climate system a 4 24 m long lake core from western inner mongolia in china was studied using a multiproxy approach sedimentology and geochemical parameters such as gypsum and dolomite content presence of lakeshore sand changing to aeolian sand and changes in paleomagnetic properties bear witness to a trend toward a generally drier climate over the late holocene aridification is linked to the southward retreat of the northern boundary of the asian summer monsoon leaving central asia under the influence of the westerly belt the weakening of the asian summer monsoon in turn was caused by an orbitally driven decrease in summer insolation the weakening summer insolation also likely increased the intensity of the siberian high pressure system further promoting aridification of central asia on a shorter time scale the multiproxy record shows the climate to have been relatively dry during the medieval warm period ad 800 1100 with the ensuing humid environment at the end of this period gradually turning to become extremely dry ad 1100 1550 at the little ice age maximum switches in the north atlantic oscillation caused these changes through a teleconnection in the form of westerlies these westerlies provided most of central asia s moisture after the retreat of the asian summer monsoon the central asian climate therefore corresponds closely with late holocene european climate changes

transgressive and highstand systems tracts and post glacial transgression the east china sea abstract the late pleistocene holocene depositional sequence on the shelf in the east china sea ecs is interpreted on the basis of the analyses of four sediment cores and high resolution seismic reflection sub bottom profiler records along a ne sw across shelf transect sedimentary strata deposited above a lowermost planar erosional surface that was formed during sea level fall of the last glacial are divided into two units along a ne sw across shelf transect changjiang okinawa the lower unit is characterized by seaward dipping tangential clinoforms with a thickness of 30 40 m at mid shelf depths and less than 30 m beneath the outer shelf prograding clinoforms are more obvious in mid shelf environments the upper unit is characterized by an upper transparent layer that is formed into ridge and swale topography the boundary between the upper and lower units is sharp and erosional surficial sediments taken by cores from the central ecs shelf are also divided into two facies a sandy facies consisting of sand or sandy gravel with moderately abundant molluscan shell fragments and a muddy facies comprising mud intercalated with thin sand layers the sandy facies is widely distributed on the middle to outer shelf seafloor and has a measured thickness of 30 cm up to several metres radiocarbon ages of molluscan shells in this sediment are less than approximately 10 ka bp except for ages from basal shell lag deposits which are 10 40 ka bp the muddy facies underlies the sandy facies and has radiocarbon ages of 2 7 2 9 ka bp previous work and 20 38 ka bp this study and tl ages of 27 50 ka bp previous work the boundary between these lithologic units is an erosional sharp contact the sandy and muddy facies are correlated with the upper and lower seismic units respectively the lower unit is characterized by prograding clinoforms and is interpreted to represent deltaic or nearshore tidal ridge sediments of the paleo changjiang river that were deposited during the last glacial lowstand of sea level as a lowstand systems tract the underlying erosional surface is interpreted to be a sequence boundary formed as a regressive marine erosional surface during the fall of sea level the erosional boundary between the lower and upper units is interpreted as a transgressive surface of erosion formed during the subsequent rise of sea level the upper unit has a modern sand ridge topography and is interpreted to represent offshore shelf sand ridges of the transgressive to highstand systems tract

shear wave polarization anisotropy in the upper mantle beneath honshu japan shear wave polarization anisotropy in the wedge portion of the upper mantle between a subducting plate and the earth s surface is investigated using three component seismograms of intermediate depth and deep earthquakes recorded at 14 local stations in honshu japan eighty nine high quality seismograms were selected from a period of 3 years the data used in this study are restricted such that incidence angles are smaller than the critical angle of 30 to the earth s surface in order to avoid phase shifts in the shear wave train to find directions of the maximum and minimum velocities in split shear waves where shear waves are resolved into two phases with the maximum time separation each set of the two horizontal component seismograms is rotated in the horizontal plane the split shear waves thus obtained are again recombined after the correction of anisotropy and the anisotropy corrected particle motion is compared with the focal mechanism for a cross check of the observed anisotropy directions of the maximum axes are plotted on azimuthincidence angle stereograms at each station the stereograms and the cross sections of seismic ray paths show that 1 the anisotropic material is distributed at intermediate location between earthquake sources and receiving stations and 2 the anisotropic region is separated into two parts one in the north of the present study area with the polarization of the maximum velocity shear wave trending 0 to 30 from the north north anisotropy and the other in the south with it trending 90 to 120 south anisotropy the maximum time delays between the two shear waves along a vertical seismic ray is about l s for both the anisotropic regions the horizontal extent of the anisotropic area in the north is 50 km at depths of 50 to 150 km perhaps prevalent in west honshu however the depth of anisotropic material is not well constrained because of insufficient coverage of seismic ray paths and angles if we assume the vertical extent of the anisotropic material to be 100 km the maximum velocity contrast would be 4 if we adopt a crack alignment model for the observed anisotropy cracks are inferred to be distributed vertically trending 0 to 30 in the north and 90 to 120 in the south if we assume an olivine alignment model olivine crystals are inferred to be aligned in the north with the a axis of the slip direction trending 0 to 30 and the slip plane normal to the b axis being vertical and in the south anisotropy with the axis trending 90 to 120 and the slip plane being horizontal

mantle flow in subduction systems the mantle wedge flow field and implications for wedge processes 1 the mantle wedge above subducting slabs is associated with many important processes including the transport of melt and volatiles our understanding of mantle wedge dynamics is incomplete as the mantle flow field above subducting slabs remains poorly understood because seismic anisotropy is a consequence of deformation measurements of shear wave splitting can constrain the geometry of mantle flow in order to identify processes that make first order contributions to the pattern of wedge flow we have compiled a data set of local s splitting measurements from mantle wedges worldwide there is a large amount of variability in splitting parameters with average delay times ranging from 0 1 to 0 3 s up to 1 0 1 5 s and large variations in fast directions we tested for relationships between splitting parameters and a variety of parameters related to subduction processes we also explicitly tested the predictions made by 10 different models that have been proposed to explain splitting patterns in the mantle wedge we find that no simple model can explain all of the trends observed in the global data set mantle wedge flow is likely controlled by a combination of downdip motion of the slab trench migration ambient mantle flow small scale convection proximity to slab edges and slab morphology with the relative contributions of these in any given subduction system controlled by the subduction kinematics and mantle rheology there is also a likely contribution from b type olivine and or serpentinite fabric in many subduction zones governed by the local thermal structure and volatile distribution

yangtze river of china historical analysis of discharge variability and sediment flux hydrological records covering a 100 year period from the upper middle and lower yangtze river were collected to examine the temporal and spatial distribution of discharge and sediment load in the drainage basin the yangtze discharge as expected increases from the upper drainage basin downstream only an estimated 50 of the discharge is derived from the upper yangtze with the rest being derived from the numerous tributaries of the middle and lower course however the distribution of sediment load along the yangtze is the reverse of that observed for discharge with most of the sediment being derived from the upper basin a dramatic reduction in sediment load by 0 8 108 tons year occurs in the middle yangtze because of a marked decrease in slope and the change to a meandering pattern from the upper yangtze rock sections considerable siltation also occurs in the middle yangtze drainage basin as the river cuts through a large interior dongting lake system sediment load in the lower yangtze while significantly less than that of the upper river is somewhat higher than the middle yangtze because of additional load contributed by adjacent tributaries a strong correlation exists between the discharge and sediment load along the yangtze drainage basin during the dry season as lower flows carry lower sediment concentration during the wet season a strong correlation is also present in the upper yangtze owing to the high flow velocity that suspends sand on the bed however a negative to poor correlation occurs in the middle and lower yangtze because the flow velocity in these reaches is unable to keep sand in suspension transporting only fine grained particles downstream hydrological data are treated for 30 years 1950 1980 when numerous dams were constructed in the upper yangtze drainage basin at yichang and hankou hydrological stations records revealed a decreasing trend in annual sediment load along with slightly reduced annual discharge at the same stations this can be interpreted as the result of water diversion primarily for agriculture sediment load at datong further downstream is quite stable and not influenced by slightly reduced discharge furthermore sediment concentration at the three hydrological stations increased which can be attributed to sediment loss in association with intensifying human activity especially in the upper drainage basin such as deforestation and construction of numerous dams mean monthly sediment load of these 30 years pulses about 2 months behind discharge implying dam released sediment transport along the entire river basin during the high water stage

concepts of sediment deposition and accumulation applied to the continental shelf near the mouth of the yangtze river a fundamental understanding of how sedimentary strata form requires distinction between deposition and accumulation of particles deposition refers to the temporary emplacement of particles on the seabed accumulation is the net sum of many episodes of sediment deposition and removal the difference between rates of deposition and accumulation affects the ability of an environment to record sedimentary events radionuclide profiles of 234 th and 210 pb within the seabed can be used to determine 100 day deposition rates and 100 yr accumulation rates respectively on the continental shelf near the mouth of the yangtze river short term deposition rates are about 4 4 cm month whereas accumulation rates integrated over a century are an order of magnitude less about 5 4 cm yr

clay mineralogy of pliocene pleistocene mudstones eastern taiwan combined effects of burial diagenesis and provenance unroofing pliocene pleistocene sedimentary rocks in the coastal range of eastern taiwan were deposited in a synorogenic collisional basin that developed immediately east of the growing taiwan fold and thrust belt during active arc continent collision unmetamorphosed mudstones from this stratigraphic sequence which were buried up to 6 km deep contain abundant detrital illite and chlorite derived from the adjacent metamorphic orogen a surprisingly small down section increase in percent illite layers in mixed layer illite smectite provides evidence for a low paleogeothermal gradient about 14 c km possibly combined with kinetic retardation of the illitization reaction resulting from the short duration of maximum burial illite crystallinity increases from the base to the top of the stratigraphic sequence opposite to the expected trend for burial metamorphism this reverse trend parallels lithic fragment detrital modes of sandstones from the same sequence and records progressive unroofing of the nearby prograde metamorphic terrane during collision related uplift and deformation

monsoon hydrography and productivity changes in the east china sea during the past 100 000 years okinawa trough evidence md012404 1 we analyzed the high resolution foraminifer isotope records total organic carbon toc and opal content from an okinawa trough core md012404 in order to estimate the monsoon hydrography and productivity changes in the east china sea ecs of the tropical western pacific over the past 100 000 years the variability shown in the records on orbital time scales indicates that high toc intervals coincide with the increases of boreal may september insolation driven by precession cycles 21 ka implying a strong connection to the variations in monsoons we also observed possibly nearly synchronous millennial scale changes of the ecs surface hydrography mainly driven by salinity changes but also by temperature effects and productivity coincident with monsoon events in the hulu dongge stalagmite isotope records we found that increased freshening and high productivity correlate with high monsoon intensity in interstadials this study suggests that the millennial scale changes in monsoon hydrography and productivity in the ecs are remarkable and persistent features over the past 100 000 years

lowermost mantle anisotropy beneath the northwestern pacific evidence from pcs scs sks and skks phases 1 in this study we utilize data from broadband seismic stations of the japanese f net network to investigate anisotropic structure in the lowermost mantle beneath the northwestern pacific the comparison of shear wave splitting from phases that have similar paths in the upper mantle but different paths in the lowermost mantle such as pcs scs or sks skks can yield constraints on anisotropy in the d region we measured splitting for sks skks pcs and scs phases at f net stations and compared the measured splitting parameters to previously published estimates of upper mantle anisotropy beneath the region we observed many examples of discrepant sks skks splitting and splitting of scs pcs sks and skks phases that does not agree well with the known upper mantle anisotropy beneath individual stations the most likely explanation for these discrepancies is a contribution to splitting from anisotropy in the lowermost mantle in particular for sks skks phases that sample the lowermost mantle just to the south and east of the kamchatka peninsula we observed generally n s fast directions with delay times between 0 5 and 1 5 s these data suggest the presence of a fairly large coherent region of deformation in the lowermost mantle beneath the northwestern pacific our preferred model for these observations is that solid state flow at the base of the mantle induces a lattice preferred orientation of lowermost mantle minerals generating a seismically anisotropic fabric

evidence from core reflected shear waves for anisotropy in the earth s mantle seismologists have begun to recognize that the upper mantle at depth is anisotropic and that seismological data are not fully explicable if anisotropy is ignored1 5 on entering an anisotropic zone a plane shear wave splits into two orthogonally polarized phases6 an effect observed by several researchers7 notably by ando et al 5 8 9 the near vertical scs wave an s wave reflected once at the core mantle boundary is one of the most suitable phases to study the phenomenon of shear wave birefringence because it is isolated from other phases and because its particle motion is nearly horizontal and thus free from s to p conversion the split scs shear waves travel with different velocities in the anisotropic zone and consequently there is a time delay between their arrival at stations my aim was to determine this time delay and the azimuth of polarization using the scs records of two horizontal components from the japanese islands for a deep shock beneath the sea of okhotsk from the total of 41 stations 34 show a polarization of the maximum velocity phase in the nnw sse direction with an average time advance of 0 8s from the minimum velocity phase the relevant anisotropic zone seems to be deep seated

holocene variability of the kuroshio current in the okinawa trough northwestern pacific ocean abstract cores 255 and b 3gc from the southern and northern okinawa trough respectively were studied for determining the variability of the kuroshio current on centennial scales during the holocene based on detailed ams 14 c dates stable isotope and planktonic foraminiferal distribution the main flow of the kuroshio current was inferred to re enter the okinawa trough at 7 3 calendar cal kyr bp leading to abrupt changes in sedimentation rate remarkably increased abundance of the kuroshio current indicator pulleniatina obliquiloculata increased sea surface temperature sst and depth of thermocline dot during 4 6 2 7 cal kyr bp the abundance of p obliquiloculata sharply decreased corresponding to a decreases in sst and dot implying that the influence of the kuroshio current weakened at that time possibly as a result of the intensified winter monsoon significantly the kuroshio current proxies e g the difference in sst between the southern and northern okinawa trough display periodicities of 1500 yr and 700 800 yr ascribed to the second harmonic of the 1500 yr cycle in oceanic thermohaline circulation during the holocene the holocene events at 0 6 1 7 3 3 4 6 5 9 8 1 9 4 cal kyr bp in the okinawa trough appear to be the most recent manifestation of the millennial scale climate cycle recorded in the north atlantic arabian sea marine sediment cores and greenland ice cores suggesting global climatic tele connections

seismic anisotropy in the sumatra subduction zone an important tool for understanding deformation occurring within a subduction zone is the measurement of seismic anisotropy through observations of shear wave splitting sws in sumatra two temporary seismic networks were deployed between december 2007 and february 2009 covering the fore arc between the fore arc islands to the back arc we use sks and local sws measurements to determine the type amount and location of anisotropy local sws measurements from the fore arc islands exhibit trench parallel fast directions which can be attributed to shape preferred orientation of cracks fractures in the overriding sediments in the sumatran fault region the predominant fast direction is fault trench parallel while in the back arc region it is trench perpendicular the trench perpendicular measurements exhibit a positive correlation between delay time and raypath length in the mantle wedge while the fault parallel measurements are similar to the fault parallel fast directions observed for two crustal events at the sumatran fault this suggests that there are two layers of anisotropy one due to entrained flow within the mantle wedge and a second layer within the overriding crust due to the shear strain caused by the sumatran fault sks splitting results show a nnw sse fast direction with delay times of 0 8 3 0 s the fast directions are approximately parallel to the absolute plate motion of the subducting indo australian plate the small delay times exhibited by the local sws 0 05 0 45 s in combination with the large sks delay times suggest that the anisotropy generating the teleseismic sws is dominated by entrained flow in the asthenosphere below the slab

paleoenvironmental change in the middle okinawa trough since the last deglaciation evidence from the sedimentation rate and planktonic foraminiferal record well dated high resolution records of planktonic foraminifera and oxygen isotopes from two sediment cores a7 and e017 in the middle okinawa trough reveal strong and rapid millennial scale climate changes since similar to 18 to 17 thousand years before present kyr b p sedimentation rate shows a sudden drop at similar to 11 2 cal kyr b p due to a rapid rise of sea level after the younger dryas yd and consequently submergence of the large continental shelf on the east china sea ecs and the retreat of the estuary providing sediment to the basin during the last deglaciation the relative abundance of warm and cold species of planktonic foraminifera fluctuates strongly consistent with the timing of sea surface temperature sst variations determined from mg ca measurements of planktonic foraminifera from one of the two cores these fluctuations are coeval with climate variation recorded in the greenland ice cores and north atlantic sediments namely heinrich event 1 h1 bolling allerod b a and yd events at about 9 4 kyr b p a sudden change in the relative abundance of shallow to deep planktonic species probably indicates a sudden strengthening of the kuroshio current in the okinawa trough which was synchronous with a rapid sea level rise at 9 5 9 2 kyr b p in the ecs yellow sea ys and south china sea scs the abundance of planktonic foraminiferal species together with mg ca based sst exhibits millennial scale oscillations during the holocene with 7 cold events at about 1 7 2 3 4 6 6 2 7 3 8 2 9 6 10 6 cal kyr bp superimposed on a holocene warming trend this holocene trend together with centennial scale sst variations superimposed on the last deglacial trend suggests that both high and low latitude influences affected the climatology of the okinawa trough c 2006 elsevier b v all rights reserved

orbital and millennial scale variations in asian dust transport path to the japan sea abstract orbital and millennial scale variations in the asian monsoon and its probable association with the dansgaard oeschger d o cycles have been demonstrated by previous studies however the origin and nature of such variations are poorly understood the japan sea is located down wind of the arid areas of the eurasian continent and thus receives significant amounts of aeolian dust consequently the hemipelagic sediments of the japan sea are expected to record a continuous aeolian dust accumulation which may provide information about the past variations in asian monsoon grain size flux and provenance of aeolian dust in the sediments were examined using two sediment cores obtained from the northern and southern parts of the japan sea in order to understand the spatial variability of asian monsoon since the silt fraction of the detrital materials in hemipelagic sediments of the japan sea is composed predominantly of aeolian dust the grain size flux and provenance of the silt fraction were examined the taklimakan desert loess plateau and siberia northeast china areas were identified as possible source areas of aeolian dust in the sediments of the japan sea based on the electron spin resonance esr signal intensity and crystallinity of quartz moreover the relative contribution of aeolian dust from each source area was estimated based on the esr signal intensity and crystallinity of quartz aeolian dust fluxes from the two source areas at the southern site were then estimated grain size and flux of eolian dust at the northern site and fluxes of aeolian dust from two source areas at the southern site show orbital scale variations in harmony with the insolation change at 30 n in june these results indicate orbital scale changes in the extent of the arid area and or frequency of dust storms in the taklimakan desert loess plateau and siberia northeast china areas and suggest that southward northward shifts of the westerly jet axis occurred together with either intensified weakened winter monsoon decreased increased winter precipitation in the siberia northeast china area or southeastward northwestward shifts of summer monsoon limit during periods of smaller larger insolation at 30 n in june in addition to these orbital scale variations millennial scale variations possibly associated with the d o cycles are observed in the grain size record of aeolian dust at the two sites based on analogy with orbital scale variations these millennial scale variations are considered to reflect millennial scale changes in the position of the westerly jet axis together with the changes either in winter monsoon intensity winter precipitation or position of summer monsoon limit our results suggest n s oscillations in the westerly jet and summer monsoon limit and changes in the intensity of the winter monsoon on orbital and millennial timescales

earthquakes and plastic deformation of anhydrous slab mantle in double wadati benioff zones double wadati benioff seismic zones dsz with two parallel planes of seismicity separated by 15 30 km are a global feature of subduction zones in the 50 200 km depth range upper plane seismicity is generally attributed to dehydration of the oceanic crust but the origin of the lower seismicity plane is debated serpentine or hydrous phase dehydration embrittlement is a commonly advocated mechanism that implies significant slab mantle hydration high resolution seismic tomography revealed low seismic velocities in the lower seismicity plane that are better explained by seismic anisotropy of anhydrous deformed peridotites than by serpentinization earthquakes correlate with anisotropic planar shear zones and favor a shear instability mechanism as the cause of lower plane seismicity without requiring the presence of water in the center of subducting slabs the contribution of the subducted lithospheric mantle to the water budget of subduction zones is thus likely limited to the first 2 3 kilometers beneath oceanic crust

mantle anisotropy beneath northwest pacific subduction zones to assess the location strength and orientation of seismic anisotropy in the southern kuril japan and izu bonin subduction zones we analyzed shear wave splitting in local s phases and teleseismic sks phases fast directions from these phases are roughly parallel to the direction of absolute pacific plate motion wnw in izu bonin roughly parallel to the strike of the trench nne in central honshu and roughly n in the southern kuril back arc in the vicinity of sakhalin island assuming that the orientation and strength of anisotropy does not vary with depth modeling of splitting times from local s and teleseismic phases recorded at sakhalin island requires that the maximum depth of anisotropy lies between 480 km and 950 km in contrast splitting times for local s phases from events in izu bonin rule out anisotropy in the transition zone all the data are consistent with a model in which the lower transition zone 520 660 km and lower mantle are largely isotropic and in which anisotropy occurs intermittently in the upper transition zone 410 520 km possibly due to preferred orientation of spinel assuming that splitting in the upper mantle is produced by preferred orientation of olivine the observed fast directions indicate that the geometry of back arc strain varies systematically between subduction zones the relationship of fast directions and plate motions suggests that the subducting slab exerts significant control on back arc flow but that flow correlated with upper plate deformation must also exist

azimuthal anisotropy of the pacific region azimuthal anisotropy is the dependence of local seismic properties on the azimuth of propagation we present the azimuthally anisotropic component of a 3d sv velocity model for the pacific ocean derived from the waveform modeling of over 56 000 multi mode rayleigh waves followed by a simultaneous inversion for isotropic and azimuthally anisotropic vsv structure the isotropic vsv model is discussed in a previous paper a maggi e debayle k priestley g barruol multi mode surface waveform tomography of the pacific ocean a close look at the lithospheric cooling signature geophys j int 166 3 2006 doi 10 1111 j 1365 246x 2006 03037 x the azimuthal anisotropy we find is consistent with the lattice preferred orientation model lpo the hypothesis of anisotropy generation in the earth s mantle by preferential alignment of anisotropic crystals in response to the shear strains induced by mantle flow at lithospheric depths we find good agreement between fast azimuthal anisotropy orientations and ridge spreading directions recorded by sea floor magnetic anomalies at asthenospheric depths we find a strong correlation between fast azimuthal anisotropy orientations and the directions of current plate motions we observe perturbations in the pattern of seismic anisotropy close to pacific hot spots that are consistent with the predictions of numerical models of lpo generation in plume disturbed plate motion driven mantle flow these observations suggest that perturbations in the patterns of azimuthal anisotropy may provide indirect evidence for plume like upwelling in the mantle

upward decrease of organic c n ratios in the okinawa trough cores proxy for tracing the post glacial retreat of the continental shore line abstract six piston cores were collected along the nw se line in the okinawa trough close to the chinese continental shelf edge and dated by 23 ams 14 c measurements along with planktonic 18 o stratigraphy and an ash layer dated as 6 3 ka on a time scale to 19 ka the ratio of total organic carbon to total nitrogen concentration c n ratio displays gradual decreases toward the present and suggests the decrease of vascular plant fragment input to the trough from continental rivers this suggestion is confirmed by similar decreases of lignin phenol content and ratio of c 28 fatty acid to c 16 fatty acid content in core rn93 pc3 the gradual decrease of land plant fragment input is interpreted to be a consequence of the retreat of the continental coastline during the deglacial period

deep structure of the japan subduction zone abstract we determined 3 d p wave velocity structure down to 700 km depth under the japan islands using a large number of arrival time data from local and teleseismic events simultaneously we collected 207 000 arrival times from 7743 shallow and deep earthquakes occurred in and around japan and 34 148 data from 333 teleseismic events which were recorded by over 1000 seismic stations on the japan islands our tomographic model revealed some new features the philippine sea slab is found to subduct down to 500 km depth under southwest japan though the seismicity within the slab ends at 150 200 km depth significant low velocity anomalies are found to exist in the deep portion of the mantle wedge above the pacific slab which may be caused by the deep dehydration process of the slab slow anomalies are detected in the mantle beneath the pacific slab which may be caused by a mantle plume or upwelling of hot mantle materials associated with the deep subduction of the pacific slab and its collapsing down to the lower mantle

scs wave splitting of deep earthquakes around japan summary scs wave splitting of five deep earthquakes in subduction zones near japan is investigated using horizontal seismograms recorded al jma stations for each earthquake we clearly observe uniform scs wave splitting in all stations over japan especially for the events located south of honshu in 1982 1984 and 1993 however the directions of fast polarized waves of these events differed by a maximum of about 50 from one another the orientation of fast polarized waves in the 1982 event was nnw sse those in the two later events wnw ese we also recognize this discrepancy in the results of the analysis of the 1971 sea of okhotsk event reported by fukao 1984 the sakhalin islands event in 1990 reveals a linear particle motion without such a change in direction of the second arrivals implying no anisotropy these observations are interpreted as indicating an anisotropic region within the slab near the earthquake sources but not beneath the receivers since the orientations of fast polarized waves recorded at each station are not common to all the earthquakes furthermore we consider that anisotropy exists non uniformly within the slab the event in 1982 which occurred in almost the same area as those in 1984 and 1993 showed a fast direction different from the events in 1984 and 1993 the 1982 event was 179 km deep but the two later events were at 398 km and 360 km respectively the fast direction observed from the 1982 event is parallel to the fossil plate motion whereas those from the events in 1984 and 1993 are parallel to the compression axis within the subducting slab the depth of 400 km is a phase boundary where olivine changes to spinel we consider that the most likely cause of the change in anisotropy direction is the re orientation of crystals associated with the phase change of olivine to spinel due to subduction of the slab

multiple scs technique for measuring anisotropy in the mantle we describe a technique for measuring shear wave splitting in the mantle of the oceans and poorly instrumented continental regions the idea of the method is to analyse evolution of the form of the particle motion in the long period multiple scs and sscs phases as a function of the order of reflection the differential motion is inverted into the parameters of azimuthal anisotropy the technique is applied to the digital recordings of events from the tonga kermadek seismic zone at station afi it is found that the fast direction of anisotropy in the mantle beneath the pacific plate is close to the present day absolute velocity direction of the plate

influence of intermediate water in the western okinawa trough by the outflow from the south china sea although the kuroshio and the south china sea scs waters flow in and out of the luzon strait near surface the scs water mainly flows out of the scs at mid depth between 350 and 1350 m in all seasons and years that we studied the eastward flowing scs intermediate water is blocked by and joins the northward flowing kuroshio at about 122 e thus the kuroshio intermediate water kiw is composed of the west philippine sea wps proper water on the east centered at 600 m depth because the ridge east of taiwan separating the okinawa trough from the wps is mostly shallower than 600 m the eastern portion of the kiw is largely blocked by the ridge and is forced to turn eastward this water does not enter the okinawa trough freely until it reaches a deep gap in the ryukyu ridge farther north subsequently forming the eastern portion of the intermediate water in the trough the western portion of the kiw is the mixed water of scs and wps the nutrient rich scs intermediate water centered at 500 m is less influenced by the ridge and is able to flow into the okinawa trough the scs intermediate water thus retains its signature in the southern and western okinawa trough upwells onto the east china sea shelf and becomes a major source of nutrients to the shelf water

paleoenvironmental changes in the northern area of the east china sea during the past 42 000 years a 33 65 m long images md982195 core with very high sedimentation rate ca 80 cm kyr retrieved from the northern part of the east china sea was analyzed at 10 cm intervals about 125 years for oxygen carbon isotope of globigerinoides ruber sensu stricto sea surface temperature sst from alkenones u37 k and principal component analysis of planktonic foraminiferal assemblage the general pattern of the 18o curve resembling the alkenone sst curve is similar to the standard open ocean oxygen isotope curve it reveals many light 18o peaks apparently corresponding to dansgaard oeschger d o cycles as observed in greenland ice cores for the last 42 ka the alkenone sst at the core top is 24 c which is close to the modern annual mean sst around the core site on the other hand sst during the last glacial maximum lgm was about 5 c lower than that in the present day alkenone derived sst does not correlate with the light negative 18o peaks corresponding to the d o cycles the oxygen isotope ratios for the surface waters based on oxygen isotopes of g ruber and alkenone ssts indicate approximately 1 0 increase on average during the lgm and many light peaks at the warm d o events this suggests that fresh water was supplied to the core site during these events the meandering of the westerlies during the cold and warm d o cycles would have caused an atmospheric tele connection between east asia and greenland the core was divided into four periods based on q mode factor analysis of the planktonic foraminiferal assemblage i e 1 a strong upwelling period from 42 to 24 ka indicated by abundant occurrence of globigerina bulloides 2 a cold and low salinity water mass period from 24 to 14 ka suggested by increase of neogloboquadrina pachyderma neogloboquadrina incompta and globigerina quinqueloba 3 a transitional period from cold to warm water masses from 14 to 8 ka as indicated by the increase of warm water species such as pulleniatina obliquiloculata and globigerinoides ruber and 4 the present day warm kuroshio current condition after 8 ka the kuroshio current flowed into the ecs since the last 42 ka and weakened during the last glacial maximum lgm due to the expansion of the coastal water in the northern part of the ecs

seismic anisotropy of the pacific slab and mantle wedge beneath the japanese islands 1 the mantle beneath the japanese islands is complex because of subduction of the pacific and philippine sea plates and the deformation associated with it detection of seismic anisotropy should be useful for understanding the processes occurring in such mantle here we resolve seismic anisotropy of the mantle wedge from that of the underlying subducted pacific slab using a large number of measurements of shear wave splitting for a family of core reflected shear phases scs sscs scs2 and sscs2 the anisotropy of the mantle wedge changes sharply across the volcanic front on the pacific side of the volcanic front a vertically propagating shear wave is polarized with the fast direction approximately parallel to the trench whereas on the back arc side it is polarized with the fast direction approximately parallel to the plate convergence direction the pacific slab is uniformly anisotropic with the nnw fast direction consistent with the paleospreading direction of the northwestern pacific seafloor the preferential alignment of anisotropic crystals frozen in the plate at the time of its formation appears to be preserved down to depths beyond 400 km within the slab

crustal origin of trench parallel shear wave fast polarizations in the central andes abstract in this study sks and local s phases are analyzed to investigate variations of shear wave splitting parameters along two dense seismic profiles across the central andean altiplano and puna plateaus in contrast to previous observations the vast majority of the measurements reveal fast polarizations sub parallel to the subduction direction of the nazca plate with delay times between 0 3 and 1 2 s local phases show larger variations of fast polarizations and exhibit delay times ranging between 0 1 and 1 1 s two 70 km and 100 km wide sections along the altiplano profile exhibit larger delay times and are characterized by fast polarizations oriented sub parallel to major fault zones based on finite difference wavefield calculations for anisotropic subduction zone models we demonstrate that the observations are best explained by fossil slab anisotropy with fast symmetry axes oriented sub parallel to the slab movement in combination with a significant component of crustal anisotropy of nearly trench parallel fast axis orientation from the modeling we exclude a sub lithospheric origin of the observed strong anomalies due to the short scale variations of the fast polarizations instead our results indicate that anisotropy in the central andes generally reflects the direction of plate motion while the observed trench parallel fast polarizations likely originate in the continental crust above the subducting slab

spatial and temporal variability of surface water in the kuroshio source region pacific ocean over the past 21 000 years evidence from planktonic foraminifera abstract the kuroshio current is the major western boundary current of the north pacific ocean and has had a large impact on surface water character and climate change in the northwestern pacific region the kuroshio current becomes a distinctive surface flow in the ryukyu arc region after diverging from the north equatorial current and passing through the okinawa trough therefore the ryukyu arc area can be called the kuroshio source region we reconstructed post 21 ka time space changes in surface water masses in the ryukyu arc region using 15 piston cores which were dated by planktonic 18 o stratigraphy and ams 14 c ages our analysis utilized spatial and temporal changes in planktonic foraminiferal assemblages which were classified into the kuroshio subtropical coastal and cold water groups on the basis of modern faunal distributions in the study region these results indicate that the kuroshio current and adjacent surface water masses experienced major changes during 1 the last glacial maximum lgm and 2 the so called pulleniatina minimum event pme from 4 500 to 3 000 yr bp the kuroshio lgm event corresponds to severe global cooling and is marked by decreases in planktonic 18 o values and estimated sea surface temperature sst with the dominance of the cold water group of planktonic foraminifera cooling within the kuroshio source region was enhanced during the lgm event because the kuroshio current was forced eastward due to the formation of a land bridge between taiwan and the southern ryukyu arc which prohibited its flow into the okinawa trough except for the severe reduction and disappearance of the pulleniatina group no clear cooling signal was identified during the pme based on 18 o values estimated sst values and variations in the composition of planktonic foraminiferal faunas the pme assemblages are marked by high abundances of neogloboquadrina dutertrei a distinctive kuroshio type species along with other species assigned to the coastal and central water groups subtle ecological differences exist between pulleniatina obliquiloculata and n dutertrei i e p obliquiloculata exhibits lower rates of reproduction under conditions of lower primary productivity in the central equatorial pacific ocean el nino like conditions in the equatorial pacific ocean result in lower rates of surface transport in the kuroshio current in turn this response triggers lower rates of primary productivity in central equatorial surface waters as well as in the upstream kuroshio source region ultimately resulting in a lower abundance of p obliquiloculata thus we interpret the pme as a possible proxy signal of el nino like conditions and enhancement of the el nino southern oscillation climate system after the pme in the tropical and sub tropical pacific ocean

latest pleistocene climate variation of the east asian monsoon from pollen records of two east china regions abstract pollen analyses performed on borehole cores from the present delta plains of the paleo changjiang incised valley and the paleo huanghe fluvial china lead to reconstruction of the latest pleistocene variation of the east asian monsoon and permit direct correlation with the vegetation history of eastern china from 13 000 to 11 670 cal yr bp the short term climatic deterioration stcd possibly corresponding to the younger dryas characterized by cold dry conditions caused by a strengthened winter monsoon and a weakened summer monsoon is reflected in the predominance of xerophytic herbaceous pollen e g artemisia input indicative of open grasslands during the subsequent early post glacial pg interval 11 670 11 270 cal yr bp pollen of conifer forest grassland taxa with thermophilous hardwood tree pollen indicate climatic warming cool humid conditions artemisia chenopodiaceae a c ratios reveal that climatic changes led to increased precipitation at the transition between the stcd and the early pg intervals moreover both the phytogeographic differences and the a c ratios indicate that during the stcd episode the humidity levels between the paleo changjiang incised valley and the paleo huanghe fluvial were different because they were located in different monsoonal zones finally the possible correspondence of the stcd episode to the yd cold event is believed to indicate that the yd is not confined to the circum north atlantic region but at minimum is a hemispheric climatic event