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

d shear velocity heterogeneity anisotropy and discontinuity structure beneath the caribbean and central america the d region in the lowermost mantle beneath the caribbean and central america is investigated using shear waves from south american earthquakes recorded by seismic stations in north america we present a large scale composite study of volumetric shear velocity heterogeneity anisotropy and the possible presence of a d discontinuity in the region our data set includes 328 s sdiff sks differential travel times 300 scs s differential travel times 125 s sdiff and 120 scs shear wave splitting measurements and 297 seismograms inspected for scd the seismic phase refracted from a high velocity d layer broadband digital data are augmented by high quality digitized analog wwssn data providing extensive path coverage in our study area in all data from 61 events are utilized in some cases a given seismogram can be used for velocity heterogeneity anisotropy and discontinuity analyses significant mid mantle structure possibly associated with the ancient subducted farallon slab affects shear wave travel times and must be corrected for to prevent erroneous mapping of

shear wave splitting and subcontinental mantle deformation splitting observations are interpreted in terms of the strain induced lattice preferred orientation of mantle minerals especially olivine we consider three hypotheses concerning the origin of the continental anlsotropy 1 strain associated with absolute plate motion as in the oceanic upper mantle 2 crustal stress and 3 the past and present internal deformation of the subcontinental upper mantle by tectonic episodes it is found that the last hypothesis is the most successful namely that the most recent significant episode of internal deformation appears to be the best predictor of q for stable continental regions this is interpreted as fossil anisotropy whereas for presently active regions such as alaska the anisotropy reflects present day tectonic activity in the stable portion of north america there is a good correlation between delay time and lithospheric thickness this is consistent with the anisotropy being localized in the subcontinental lithosphere and suggests that intrinsic anisotropy is approximately constant the acceptance of this hypothesis has several implications for subcontinental mantle deformation first it argues for coherent deformation of the continental lithosphere crust and mantle during orogenies this implies that the anisotropic portion of the lithosphere was present since the deformational episode and rules out the addition of undeformed material to this layer by subsequent underplating or conductive growth of the thermal boundary layer one of the most important issues in the study of orogenies is the need to reconcile the formation of thickened lithosphere with the paradoxically high mantle temperatures often associated with orogenic episodes most efforts to date have focussed on modes of deformation whereby the cold lithospheric mantle is removed by convective instability or delamination and replaced by warm asthenosphere these models however are incompatible with the evidence for preserved coherent lithospheric deformation rather the deformed mantle appears to have been heated in place we suggest that the elevated mantle temperatures may be due to the strain heating accompanying the deformation

the procedure used to develop a coal char classification commission iii combustion working group of the international committee for coal and organic petrology abstract this paper describes an assessment of char classification system by the combustion working group in commission iii of the international committee for coal and organic petrology iccp the work of the group culminated in the production of a char atlas after a final round robin exercise this round robin involved 21 analysts and was an electronic exercise using digitally captured images of individual char particles rather than actual char blocks a software program featuring 170 char images was specifically designed to allow operators to identify each char based on a classification system with 9 individual char types tenuisphere crassisphere tenuinetwork crassinetwork mixed porous mixed dense fusinoid solid and mineroid the program electronically recorded all decisions as well as the time taken for each decision to be made from 170 chars 128 chars were identified by a majority 70 and these chars were then compiled in a char atlas that is now available for download www nottingham ac uk eczehl charatlas as would be expected all analysts appeared to become more confident in identifying chars during the exercise taking less time per image but with no clear evidence of improvement without exception analysts took longer to make an incorrect decision

the shear wave velocity gradient at the base of the mantle the relative amplitudes and travel have been directed toward obtaining global times of scs and s phases are utilized to place averages and the degree of lateral variation in constraints on the shear wave velocity gradient d properties remains an open question above the core mantle boundary a previously a conflicting result was found by mitchell and reported long period scsh sh amplitude ratio helmberger 1973 who utilized the relative minimum in the distance range 65 o to 70 o is shown amplitudes and timing of long period scs and s to be a localized feature apparently produced by phases to constrain the s wave velocity gradient an amplitude anomaly in the direct s phase and in d they found a minimum in the scsh sh therefore need not reflect the velocity gradient amplitude ratio near 68 o which was attributed to at the base of the mantle the amplitude ratios low amplitudes of the scs arrivals unable to that are free of this anomaly are consistent with explain this feature by models with negative or calculations for the jb model or models with mild near zero shear velocity gradients in d they positive or negative velocity gradients in the proposed models with positive s wave velocity lowermost 200 km of the mantle scsv arrivals gradients above the cmb these positive are particularly sensitive to the shear velocity gradients extended over 40 to 70 km above the structure just above the core mantle boundary core reaching velocities at the cmb as high as the apparent arrival time of the peak of scsv is 7 6 to 7 8 km s these models can explain the as much as 4 sreater than that of scsh in the observed amplitude ratio behavior as well as an distance range 75 v to 80 o for sea of okhotsk apparent difference observed in the arrival times events recorded in north america this can be of transversely and radially polarized scs explained by interference effects produced by a mitchell and helmberger also proposed a low q localized high velocity layer or strong positive zone in d or finite outer core rigidity to s wave velocity gradient in the lowermost 20 km explain the baseline of the scsh sh amplitude of the mantle a velocity increase of about 5 ratios while the majority of their data was for is required to explain the observed shift between deep south american events recorded in north scsv and scsh this thin high velocity layer america they did analyze one deep sea of okhotsk varies laterally as it is not observed in event for which the radial and transverse scs similar data from argentine events refined arrival times were not different which suggested estimates of the outermost core p velocity lateral variations in the d velocity structure structure are obtained by modeling sks signals in in this paper we extend the analysis of scs the distance range 75 o to 85 o s

small scale lateral variations in azimuthally anisotropic d structure beneath the cocos plate abstract shear waves from intermediate and deep focus south american events recorded by california broadband seismometers reveal complex anisotropy in the lowermost mantle scs waves densely sample the d region beneath the cocos plate just west of central america 1 16 n 267 277 e our data show evidence for significant near source anisotropy which we constrain for each event by performing polarization analyses on an expanded dataset of s waveforms scs waveforms are corrected for upper mantle and near source anisotropy and estimates of d anisotropy are made using the covariance method we find splits between fast and slow components of scs ranging from 0 4 to 2 5 s with an average of 1 6 s fast polarization directions in the southern portion of our study area are approximately orthogonal to the raypaths north of 7 latitude there is a rapid change in fast polarization direction to nearly raypath parallel beyond 10 latitude fast directions are more highly scattered than in southern regions past work in the region has inferred strong lateral variations in shear wave velocity but fairly uniform transverse isotropy in contrast our results indicate that the lowermost mantle beneath the cocos plate has azimuthal anisotropy that varies laterally over scales of 100 200 km in addition our data suggest connections between previously imaged topography on the d discontinuity and the character of anisotropy

s wave velocity images of the dead sea basin provided by ambient seismic noise abstract based on passive seismic interferometry applied to ambient seismic noise recordings between station pairs belonging to a small scale array we have obtained shear wave velocity images of the uppermost materials that make up the dead sea basin we extracted empirical green s functions from cross correlations of long term recordings of continuous data and measured inter station rayleigh wave group velocities from the daily correlation functions for positive and negative correlation time lags in the 0 1 0 5 hz bandwidth a tomographic inversion of the travel times estimated for each frequency is performed allowing the laterally varying 3 d surface wave velocity structure below the array to be retrieved subsequently the velocity frequency curves are inverted to obtain s wave velocity images of the study area as horizontal depth sections and longitude and latitude depth sections the results which are consistent with other previous ones provide clear images of the local seismic velocity structure of the basin low shear velocities are dominant at shallow depths above 3 5 km but even so a spit of land with a depth that does not exceed 4 km is identified as a salt diapir separating the low velocities associated with sedimentary infill on both sides of the lisan peninsula the lack of low speeds at the sampling depth of 11 5 km implies that there are no sediments and therefore that the basement is near 10 11 km depth but gradually decreasing from south to north the results also highlight the bowl shaped basin with poorly consolidated sedimentary materials accumulated in the central part of the basin the structure of the western margin of the basin evidences a certain asymmetry both whether it is compared to the eastern margin and it is observed in north south direction infill materials down to 8 km depth are observed in the hollow of the basin unlike what happens in the north and south where they are spread beyond the western dead sea shore

high resolution investigation of shear wave anisotropy in d beneath the cocos plate 1 broadband shear wave signals from 16 deep south american earthquakes are used in a high resolution analysis of lowermost mantle structure beneath the cocos plate shear wave splitting of 162 scs phases is generally compatible with vertical transverse isotropy vti in the d region with little path length or spatial dependence across the 200 800 km2 area sampled assuming a 250 km thick d layer the vti has an average value of 0 63 scs s differential travel time anomalies for the same data indicate a lateral gradient in positive d transverse component velocity perturbations increasing northward s wave triplication arrivals from a shear velocity discontinuity at the top of d show splitting similar to the scs phases but with smaller magnitude vertical resolution remains limited but the data are consistent with vti material being concentrated in just the upper portion or at the top and bottom of d

evidence for shear velocity anisotropy in the lowermost mantle beneath the indian ocean teleseismic recordings 87 of a deep earthquake beneath the banda sea at stations in tanzania show a difference in the arrival time of the radial ssv and transverse component ssh s wave ranging from 1 3 s shear velocity anisotropy in the lowermost mantle beneath the indian ocean is the likely cause of this signal because recordings at the same stations of closer in events 80 in the same source region do not present a comparable differential travel time for the banda sea event the ssh signals are broader than ssv signals suggesting that a discontinuity or strong vertical gradient in primarily vsh marks the sudden onset of transverse isotropy in d with a magnitude of 1 4 2 7 about 350 km above the core mantle boundary skks coda s to p converted phases at the moho and upper mantle heterogeneity beneath the stations obscure the onset of ssv and complicate wave shapes it is therefore difficult to evaluate whether general anisotropy needs to be invoked into a model of shear velocity anisotropy

analysis of seismic sv waves in the core s penumbra vertically polarized s waves sv attenuate rapidly as they diffract around the earth s core whereas horizontally polarized s waves sh propagate to large distances in the core shadow zone the amplitude decay of diffracted sv signals is so strong that few studies have been made of these phases despite their acute sensitivity to velocity structure just above the core mantle boundary we analyze sv signals in the penumbra of the core s shadow finding systematic waveform complexities indicative of local stratification and apparent anisotropy at the base of the mantle with implications for the dynamic processes in this internal boundary layer

geographic correlation between hot spots and deep mantle lateral shear wave velocity gradients abstract hot spot volcanism may originate from the deep mantle in regions exhibiting the earth s most pronounced lateral s wave velocity gradients these strong gradient regions display an improved geographic correlation over s wave velocities to surface hot spot locations for the lowest velocities or strongest gradients occupying 10 of the surface area of the core mantle boundary cmb hot spots are nearly twice as likely to overlie the anomalous gradients if plumes arise in an isochemical lower mantle plume initiation should occur in the hottest thus lowest velocity regions or in the regions of strongest temperature gradients however if plume initiation occurs in the lowest velocity regions of the cmb lateral deflection of plumes or plume roots are required the average lateral deflections of hot spot root locations from the vertical of the presumed current hot spot location ranges from 300 to 900 km at the cmb for the 10 30 of the cmb covered by the most anomalous low s wave velocities the deep mantle may however contain strong temperature gradients or be compositionally heterogeneous with plume initiation in regions of strong lateral s wave velocity gradients as well as low s wave velocity regions if mantle plumes arise from strong gradient regions only half of the lateral deflection from plume root to hot spot surface location is required for the 10 30 of the cmb covered by the most anomalous strong lateral s wave velocities we find that strong gradient regions typically surround the large lower velocity regions in the base of the mantle which may indicate a possible chemical in addition to thermal component to these regions

the stably stratified outermost core revisited the p wave velocity structure of the outermost 200 km of the outer core the e region is analyzed using a suite of differential travel times for sks skks and s waves bottoming below within and above this depth range core penetrating phases with paths beneath alaska exhibit similar sks skks differential travel time patterns to phases sampling the core beneath the central pacific but very different sks s differential travel times these patterns can be explained by a core velocity model in which the outermost 50 to 100 km has 1 2 slower p wave velocities than standard earth models perhaps due to a stably stratified chemical boundary layer combined with 3 lateral variations in s wave velocity in the lowermost mantle

investigating d structure beneath the north atlantic abstract data from the grsn and spiced array are used to investigate lower mantle structure beneath the north atlantic ocean just south of nova scotia we study s waves in an attempt to determine whether a d discontinuity can be observed in this region the reflected phase sds cannot be observed unambiguously so we cross correlate the traces with synthetic seismograms generated using a number of different 1d earth models that incorporate positive and negative velocity discontinuities and gradients as well as thin high velocity lamellae the cross correlation shows that a discontinuity with an s wave velocity increase of magnitude 1 3 exists which exhibits significant topography between 86 and 286 km above the cmb the study area is located on the edge of a region of anomalously high seismic velocity identified by tomographic modelling which fits with our observation of a high velocity discontinuity

trench parallel flow beneath the nazca plate from seismic anisotropy shear wave splitting of s and sks phases reveals the anisotropy and strain field of the mantle beneath the subducting nazca plate cocos plate and the caribbean region these observations can be used to test models of mantle flow two dimensional entrained mantle flow beneath the subducting nazca slab is not consistent with the data rather there is evidence for horizontal trench parallel flow in the mantle beneath the nazca plate along much of the andean subduction zone trench parallel flow is attributale utable to retrograde motion of the slab the decoupling of the slab and underlying mantle and a partial barrier to flow at depth resulting in lateral mantle flow beneath the slab such flow facilitates the transfer of material from the shrinking mantle reservoir beneath the pacific basin to the growing mantle reservoir beneath the atlantic basin trenchparallel flow may explain the eastward motions of the caribbean and scotia sea plates the anomalously shallow bathymetry of the eastern nazca plate the long wavelength geoid high over western south america and it may contribute to the high elevation and intense deformation of the central andes

shear wave anisotropy in the upper mantle beneath the nazca plate in northern chile data from the projecto de investigacion sismologica de la cordillera occidental pisco seismic network and from six broadband seismographs that were operating in northern chile were used to investigate the mantle in the convergent boundary zone between nazca plate and the south american continent for the presence of anisotropy broadband data as well as long period filtered data of teleseismic sks and pks phases were analyzed for the presence of shear wave splitting as a possible indicator for seismic anisotropy in the mantle beneath the pisco network measurable shear wave splitting was observed with maximum delay times between the slow and fast split wave of the order of 1 s splitting of s waves from intermediate depth events located directly beneath the pisco network in the descending nazca plate is generally associated with small delay times of the order of 0 1 s a value typical for the continental crust near vertical scs reflections from two deep earthquakes in argentina and one nearby intermediate depth earthquake have similar splitting parameters as the sks phases this means that the anisotropic zone causing the splitting of the core phases can be constrained to the pacific mantle underlying the subducting nazca plate it probably does not extend deeper than about 260 km the majority of the anisotropy directions inferred from the core phases are parallel to the absolute plate motion apm direction of the nazca plate which is about n80 e at some stations however the fast polarization direction is pointing n160 e nearly parallel to the strike of the trench and the andes which would be compatible with the trench parallel flow model for south america proposed by russo and silver 1994 this direction is observed over an approximately 100 km wide band to the west of the active volcanic zone it may represent either a second anisotropy regime in the mantle a small scale diversion of slab entrained mantle flow or a relatively small area where slab entrainment of mantle flow is reduced or ceases to exist the large number of observed apm parallel fast directions suggests however that the mantle beneath the descending nazca plate in northern chile deforms mainly as the result of slab entrained mantle flow the large variations of anisotropy directions in the andean subduction zone indicate that asthenospheric flow in the pacific mantle has a complex pattern which may vary over scale lengths of a few hundred kilometers and which may be governed by slab morphology

on the structure of the lowermost mantle beneath the southwest pacific southeast asia and australasia abstract the region of the lowermost mantle beneath the southwest pacific australasia and southeast asia 50 s 50 n and 80 190 e has been studied using a wide variety of seismic techniques we complement these studies with results obtained from long period global digital seismograph network gdsn data using a recently developed phase stripping technique that permits the isolation of d reflections from the stronger neighbouring s and scs signals we identify patches with d reflections and areas where we cannot confidently determine the presence or absence of a d reflection a synthesis of our results with other studies suggests that d varies dramatically through the region generally thickening from 100 150 km in a central zone to about 300 km at the eastern and western margins however there are irregularities in this overall pattern including areas where there seems to be little evidence for a d discontinuity inspection of waveform amplitudes shows considerable scatter in not only the d reflected phases but also core mantle boundary reflected phases experiments with synthetic seismograms for a variety of d models and the observed lateral variability through the region suggest that this is to be expected furthermore ray theory calculations for large scale 3d earth models predict significant variations 30 in s wave amplitudes of lowermost mantle turning rays finally we investigate possible correlations between lower mantle velocity flow and d thickness we find some correlation between d thickness and lower mantle velocities obtained from tomographic inversions with a thin d layer in high velocity regions and a thickening of the layer toward slower regions the relationship between predicted lower mantle flow and d thickness is less clear these results are qualitatively consistent with thermal boundary layer predictions for d but do not preclude the possibility of compositionally distinct material in the layer

distribution and origin of minerals in high rank coals of the south walker creek area bowen basin australia the coals of the south walker creek area in the northern bowen basin with a vitrinite reflectance rvmax of 1 7 to 1 95 are among the highest rank coals currently mined in australia x ray diffraction studies have identified an unusual mineral variation through the vertical sequence with kaolinite rich assemblages typical of other australian coals at the top and bottom of the seam section and an illite chlorite assemblage resembling a metamorphic association in the middle calcite and ankerite are also abundant in parts of the vertical sequence diaspore is abundant in the middle section of the seam in some areas and paragonite dickite or nacrite occurs in some locations as well the distribution of the non carbonate mineral assemblages cross cuts the seam stratigraphy and appears to be primarily controlled by faults and other structural features integration of the mineral distribution with optical and electron microscope data on the coal and non coal bands chemical data from coal ash analysis and information from x ray micro tomography suggests that the illite chlorite and diaspore bearing assemblages resulted from hydrothermal effects associated with fluid migration through the middle part of the coal seam this is further confirmed by the development of metamorphic textures in a tonstein band also altered to illite and chlorite in the illite rich part of the seam section in contrast to a tonstein with more normal sedimentary textures and a kaolinite composition in the kaolinite rich upper part of the seam detailed studies of cleat mineralisation suggest that fluids rich in ca mg and al were introduced relatively early in the seam s post depositional history associated with heat flow sufficient to alter the minerals in the coal and tonstein in the affected part of the seam section the relatively uniform vitrinite reflectance profile observed through the seam section may indicate that the coal was already of high rank before the fluids were introduced or that any localised heat effects on the organic matter associated with the changes in clay mineralogy were overprinted by subsequent wider ranging rank advance processes

anisotropy in the deep earth abstract seismic anisotropy has been found in many regions of the earth s interior its presence in the earth s crust has been known since the 19th century and is due in part to the alignment of anisotropic crystals in rocks and in part to patterns in the distribution of fractures and pores in the upper mantle seismic anisotropy was discovered 50 years ago and can be attributed for the most part to the alignment of intrinsically anisotropic olivine crystals during large scale deformation associated with convection there is some indication for anisotropy in the transition zone particularly in the vicinity of subducted slabs here we focus on the deep earth the lower mantle and core where anisotropy is not yet mapped in detail nor is there consensus on its origin most of the lower mantle appears largely isotropic except in the last 200 300 km in the d region where evidence for seismic anisotropy has been accumulating since the late 1980s mostly from shear wave splitting measurements recently a picture has been emerging where strong anisotropy is associated with high shear velocities at the edges of the large low shear velocity provinces llsvps in the central pacific and under africa these observations are consistent with being due to the presence of highly anisotropic mgsio 3 post perovskite crystals aligned during the deformation of slabs impinging on the core mantle boundary and upwelling flow within the llsvps we also discuss mineral physics aspects such as ultrahigh pressure deformation experiments first principles calculations to obtain information about elastic properties and derivation of dislocation activity based on bonding characteristics polycrystal plasticity simulations can predict anisotropy but models are still highly idealized and neglect the complex microstructure of polyphase aggregates with strong and weak components a promising direction for future progress in understanding the origin of seismic anisotropy in the deep mantle and its relation to global mantle circulation is to link macroscopic information from seismology and microscopic information mineral physics through geodynamics modeling anisotropy in the inner core was proposed 30 years ago to explain faster p wave propagation along the direction of the earth s axis of rotation as well as anomalous splitting of core sensitive free oscillations there is still uncertainty about the origin of this anisotropy in particular it is difficult to explain its strength based on known elastic properties of iron as it would require almost perfect alignment of iron crystals indeed the strongly anomalous p travel times observed on paths from the south sandwich islands to alaska may or may not be due to inner core anisotropy and will need to be explained before consensus can be reached on the strength of anisotropy in the inner core and its origin

occurrence and origin of minerals in a chamosite bearing coal of late permian age zhaotong yunnan china the minerals found in the no 5 coal late permian from the zhaotong coalfield yunnan province southwestern china have been examined and found to consist mainly of kaolinite pyrite chamosite quartz and calcite with trace amounts of illite and mixed layer illite smectite the proportion of chamosite in clay minerals ranges from 32 to 56 wt with an average of 46 wt chamosite is distributed not only in collodetrinite but also occurs as cell fillings in fusinite semifusinite and telinite the high content and mode of occurrence of chamosite in this mine indicate its formation by interaction of kaolinite with fe mg rich fluids during early diagenesis except for a minor amount of terrigenous quartz most quartz is of authigenic origin and formed from kaolinite desilication the calcite content of the no 5 coal is 1 4 6 3 with an average of 3 and is distributed in collodetrinite and as cell fillings of coal forming plants calcite originated from seawater invasion during peat accumulation pyrite occurs in several ways as massive framboidal isolated enhedral anhedral and euhedral forms in addition the presence of a large amount of pyritized red algae provides strong evidence of seawater invasion during peat accumulation the red algae may have played an important role in the enrichment of sulfur in the coal the characteristic assemblage of minerals in this mine resulted from a unique basinal environment in which the mineral matter was derived from a basaltic source region volcanic activity and seawater transgression during coal formation

complex seismic anisotropy at the border of a very low velocity province at the base of the earth s mantle 1 we constrain the anisotropy associated with a very low velocity province vlvp at the base of the earth s mantle using the sks and skks waves sampling the region our selected high quality data sets consist of 415 sks and 111 skks waveforms for 127 deep earthquakes recorded at distances between 90 and 150 by the seismic stations in three temporary broadband passcal seismic arrays the kaapvaal seismic array 1997 1999 the tanzania seismic array 1994 1995 and the ethiopia kenya seismic array 1999 2001 as well as the permanent stations in the global seismographic network these seismic data provide good sampling coverage for some portion of the vlvp and its surrounding areas our results show when the sks or skks phases sample the regions away from the border of the vlvp inside or outside the vlvp the apparent splitting parameters inferred from the sks phases are consistent with those inferred from the skks phases and their variations strongly correlate with seismic stations but not with the exit points at the core mantle boundary of these seismic phases however when the sks or skks phases sample near the border of the vlvp the apparent splitting parameters inferred from the sks phases and skks phases are different and their variations no longer correlate with seismic stations these features indicate that part of the shear wave splitting for the seismic data sampling the border of the vlvp has to originate from deep mantle most likely near the border of the vlvp we assume that the anisotropy in the shallow mantle beneath seismic stations has a horizontal hexagonal symmetry axis and infer the splitting parameters associated with the shallow anisotropy beneath the seismic stations using the sks and skks waveforms for the seismic data sampling the regions away from the border of the vlvp we then obtain the splitting parameters associated with the lowermost mantle anisotropy using the sks and skks waveforms corrected for the inferred shallow anisotropy beneath seismic stations assuming that the medium in the lowermost mantle also has a horizontal hexagonal symmetry axis our results reveal a complex anisotropy pattern near the border of the vlvp such a complex anisotropy pattern may be explained by lattice preferred orientation of anisotropic mantle aggregates aligned by a complex mantle flow near the vlvp margins the complex flow pattern near the vlvp margins may indicate strong interactions between the vlvp a compositional anomaly and the surrounding normal mantle and may provide an explanation to the concentration of some hot spots geographically near the borders of the vlvps in the lowermost mantle

rheology of the upper mantle a synthesis rheological properties of the upper mantle of the earth play an important role in the dynamics of the lithosphere and asthenosphere however such fundamental issues as the dominant mechanisms of flow have not been well resolved a synthesis of laboratory studies and geophysical and geological observations shows that transitions between diffusion and dislocation creep likely occur in the earth s upper mantle the hot and shallow upper mantle flows by dislocation creep whereas cold and shallow or deep upper mantle may flow by diffusion creep when the stress increases grain size is reduced and the upper mantle near the transition between these two regimes is weakened consequently deformation is localized and the upper mantle is decoupled mechanically near these depths

transmission electron microscopy of subsolidus oxidation and weathering of olivine olivine crystals in basaltic andesites which crop out in the abert rim south central oregon have been studied by high resolution and analytical transmission electron microscopy the observations reveal three distinct assemblages of alteration products that seem to correspond to three episodes of olivine oxidation the olivine crystals contain rare dense arrays of coherently intergrown ti free magnetite and inclusions of a phase inferred to be amorphous silica we interpret this first assemblage to be the product of an early subsolidus oxidation event in the lava the second olivine alteration assemblage contains complex ordered intergrowths on 001 of forsterite rich olivine and laihunite distorted olivine structure with fe3 charge balanced by vacancies based on experimental results for laihunite synthesis kondoh et al 1985 these intergrowths probably formed by olivine oxidation between 400 and 800 c the third episode of alteration involves the destruction of olivine by low temperature hydrothermal alteration and weathering elongate etch pits and channels in the margins of fresh olivine crystals contain semi oriented bands of smectite olivine weathers to smectite and hematite and subsequently to arrays of oriented hematite crystals the textures resemble those reported by eggleton 1984 and smith et al 1987 we find no evidence for a metastable phase intermediate between olivine and smectite m eggleton 1984 the presence of laihunite exerts a strong control on the geometry of olivine weathering single laihunite layers and laihunite forsteritic olivine intergrowths increase the resistance of crystals to weathering preferential development of channels between laihunite layers occurs where growth of laihunite produced compositional variations in olivine rather than where coherency strain is associated with laihunite olivine interfaces

constraints from seismic anisotropy on the nature of the lowermost mantle the d layer lies at the bottom of the earth s rocky mantle and separates it from the liquid metal alloy core this region extending from the core mantle boundary to a few hundred kilometres above fig 1 is geodynamically analogous to the more easily studied lithosphere at the top of the mantle the structure of d may reflect the style of lower mantle convection the nature of core mantle interaction and perhaps even the fate of subducting lithosphere1 observations of lithospheric seismic anisotropy have provided valuable insight into the nature of the upper mantle boundary layer but discussion of lower mantle seismic anisotropy has been somewhat contentious2 5 here we present evidence from seismic waves that have traversed the lowermost mantle beneath the caribbean region for a zone of seismic anisotropy below the d discontinuity which in this region lies 250 km above the core mantle boundary the anisotropy is most probably due to horizontal layering or aligned inclusions of a material with differing shear wave velocity if d is a graveyard for subducted lithosphere a plausible explanation of the anisotropy may be the contrast between cold lithospheric mantle and material that formerly constituted the oceanic crust which may have lower shear wave velocity owing to the presence of melt

shear wave splitting and waveform complexity for lowermost mantle structures with low velocity lamellae and transverse isotropy 1 shear waves that traverse the lowermost mantle exhibit polarization anomalies and waveform complexities that indicate the presence of complex velocity structure above the core mantle boundary synthetic seismograms for horizontally and vertically polarized shear waves sh and sv respectively are computed using the reflectivity method for structures with low velocity sheets lamellae and for comb like models approximating long wavelength vertical transverse isotropy vti motivated by evidence for partial melt in the deep mantle lamella parameter ranges include 1 vp from 5 to 10 vs 3 vp 2 100 to 300 km thickness of vertical stacks of lamella 3 lamella spacing and thickness varying from 0 5 to 20 km and 4 lamellae concentrated near the top bottom or throughout the d region at the base of the mantle such lamellae represent in effect horizontally emplaced dikes within d excessively complex waveforms are produced when more than 20 of d volume is comprised of low velocity lamellae many lamellae models can match observed sdiff splitting 1 10 s delays of svdiff but typically underpredict scs splitting 1 4 s delays of scsv vti model parameters are selected to address d observations and include 1 0 5 to 3 anisotropy 2 discontinuous d shear velocity increases up to 3 3 d thicknesses from 100 to 300 km and 4 vti concentrated at the top bottom or throughout d vti models readily match observed splits of scs and sdiff we discuss lamellae and vti model attributes in relationship to waveform complexities splitting magnitude triplications from a high velocity d discontinuity and apparently reversed polarity svdiff onsets the possible presence of melt filled lamellae indicates that local chemical or thermal perturbations can produce regions that exceed the solidus within d such melt could occur in the bulk of d because the melt is either close to neutral buoyancy advective velocities exceed percolative velocities or both

effects of d anisotropy on seismic velocity models of the outermost core we explore effects of shear wave anisotropy in d on seismic waves utilized in constructing models of the outermost core reflectivity synthetic seismograms approximating transverse isotropy ti in d yield absolute and differential time perturbations of s sks and skks of up to several seconds especially if laterally varying anisotropy is considered several studies have used anomalies of this magnitude to infer a 0 5 2 5 p velocity reduction in the outermost 50 150 km of the core suggesting a stably stratified layer just beneath the core mantle boundary our data samples the mantle and core beneath alaska and northern pacific a region with strong lateral variations in d anisotropy ti models that predict the magnitude of shear wave splitting seen in the data can account for much but not all of the anomalies that isotropic models attribute to outermost core velocity reductions future outermost core seismic studies should address such d anisotropy effects

some comments on the effects of lower mantle anisotropy on sks and skks phases anisotropy in the lowermost few 100 km of mantle or d region is indicative of deformation induced alignment of crystals and or inclusions of material and as such offers insights into the dynamic nature of this region observations of shear wave splitting in phases that transit this region provide constraints on such anisotropy we investigate the effects of lower mantle seismic anisotropy on sks and skks phases through linked effective medium modelling and ray based waveform modelling a mantle with vertical transverse isotropy vti will not produce any splitting in such core phases instead we consider the effects of azimuthal anisotropy due to aligned disk shaped and tubular inclusions and aligned perovskite periclase and columbite models are constructed subject to constraints imposed by observed anisotropy 3 and plausible variations in aggregate isotropic velocities 2 5 melt filled inclusions are much more effective in generating anisotropy than solid filled inclusions and disk shaped inclusions produce more anisotropy than tubular inclusions in general the degree of splitting produced by most of the models is small similar to that produced by the crust 0 5 s the exceptions are melt filled vertically aligned disk shaped inclusions and horizontally aligned periclase the former most likely in low velocity regions the latter in high velocity regions both models produce splitting significant enough to mask the effects of upper mantle anisotropy strong azimuthal variations in splitting and discrepancies in sks and skks splitting are diagnostic of these anisotropic models 2004 published by elsevier b v

azimuthal anisotropy in the d layer beneath the caribbean 1 the lowermost mantle beneath central america has anisotropic seismic velocity structure manifested in shear wave splitting of signals from south american earthquakes recorded at north american broadband recording stations prior studies of deep mantle anisotropy in this region have characterized the structure as having vertical transverse isotropy vti which is sufficient to explain a general trend of early tangential sh component arrivals however vti models cannot quantitatively match systematic waveform complexities in the onset of many of the shear waves that graze this region after accounting for splitting effects of upper mantle anisotropy beneath the recording stations we model the corrected waveform data using full wave theory for mantle velocity models with an anisotropic d layer this is the first attempt to quantitatively model a large data set including azimuthal anisotropy in d the models include transverse isotropy with either a vertical or tilted symmetry axis the latter resulting in azimuthal anisotropy for some initial shear wave polarizations tilted transverse isotropy tti produces small reversed polarity arrivals on the sv components at the arrival time of sh consistent with the data geographical variations in the azimuth of the tti symmetry axis are indicated by the data the lack of azimuthal coverage prevents unique resolution of the tti orientation and also precludes distinguishing between tti and other azimuthal anisotropy structures such as that predicted for lattice preferred orientation of minerals nonetheless our modeling demonstrates the need for laterally varying anisotropic structure of more complex form than vti for this region

large strain shearing of halite experimental and theoretical evidence for dynamic texture changes abstract we report results from torsion experiments on polycrystalline halite nacl to shear strains 8 and observe a very complex texture evolution the same behavior was reproduced with polycrystal plasticity simulations suggesting that we capture the underlying mechanisms while crystal shapes gradually rotate into the shear plane crystal orientations change continuously and dynamic texture patterns evolve with increasing shear this is highly significant for ultra large deformation as for example implied from geodynamic modeling for the deep earth where seismic anisotropy patterns may develop and locally disappear again as material is deformed during convection the study also suggests that caution is required when interpreting deformation mechanisms from simple shear preferred orientation patterns

seismic anisotropy in the core mantle transition zone split s waves observed at hockley texas from events in the tonga fiji region of the southwest pacific show predominantly vertically polarized shear wave sv energy arriving earlier than horizontally polarized sh energy for rays propagating horizontally through d after corrections are made for the effects of upper mantle anisotropy beneath hockley a time lag of 1 5 to 2 0 s remains for the furthest events 93 9 100 6 while the time lags of the nearer observations 90 5 92 9 nearly disappear at closer distances the s waves from these same events do not penetrate as deeply into the lower mantle and are not split these observations suggest that a patch of d beneath the central pacific is anisotropic while the mantle immediately above the patch is isotropic the thickness of the anisotropic zone appears to be of the order of 100 200 km observations of shear wave splitting have previously been made for paths that traverse d under the caribbean and under alaska sh leads sv the reverse of the hockley observations but in these areas the fact that sv leads sh in the hkt data shown here suggests a different sort of anisotropy under the central pacific from that under alaska and the caribbean the case of sh travelling faster than sv is consistent with transverse isotropy with a vertical axis of symmetry vti and does not require variations with azimuth the case of sv leading sh is consistent with transverse isotropy with a horizontal axis of symmetry hti an azimuthally anisotropic medium and with a vti medium formed by a hexagonal crystal given that mg fe sio3 perovskite appears unlikely to form anisotropic fabrics on a large scale the presence of anisotropy may point to chemical heterogeneity in the lowermost mantle possibly due to mantle core interactions

evidence of seismic anisotropy and a lower temperature condition in the d layer beneath pacific antarctic ridge in the antarctic ocean abstract we examine shear waves of 23 deep earthquakes in south pacific subduction zones recorded at the syowa station in antarctica to study the anisotropy and velocity structure of shear waves in the d layer beneath pacific antarctic ridge par in the antarctic ocean we observe earlier arrivals of transverse components sh than those of longitudinal components sv for s waves passing through the d layer and scd phases due to the d discontinuity that has been reported beneath circum pacific regions we find that the optimum shear wave velocity structure in the d layer is transversely isotropic from waveform modeling and the differential travel time analysis among s scs and sks phases the sh velocity structure has a 2 0 velocity discontinuity at about 350 km above the core mantle boundary the sv structure is similar to prem the anisotropic d layer v sv v sh beneath the antarctic ocean is significantly thicker than those beneath alaska and the caribbean sea we interpret that the amount of deposited paleo slab material controls the variation in the thickness of the d layer the difference of the thickness of the d layer together with recent experimental and theoretical results of the phase transition from perovskite to post perovskite means that the d layer beneath par is 630 1000 k colder than that beneath alaska the cold mantle beneath par corresponds to the location of stationary patches of intense geomagnetic field in the southern hemisphere this coincidence suggests the existence of the core mantle interactions

small scale lateral shear velocity and anisotropy heterogeneity near the core mantle boundary beneath the central pacific imaged using broadband scs waves core reflected scs waves from 49 large m 5 1 deep tonga fiji events recorded in western north america are used to study a localized region of the core mantle boundary cmb under the central pacific ocean a total of 248 observations from the berkeley digital seismic network bdsn caltech united states geological survey usgs terrascope and the incorporated research institutions for seismology iris broadband arrays span epicentral distances of 73 85 scs reflection points sample a cmb patch southeast of the hawaiian islands at latitude 4 to 16 n and longitude 156 to 144 w near the proposed source location of the hawaiian plume highly variable scs travel times amplitudes waveforms and shearwave splitting indicate that the lowermost mantle in this region is heterogeneous both laterally and radially scsh sh differential travel times are on average 4 s larger than predicted by the preliminary reference earth model prem this is due to delayed scs arrivals and is largely accounted for by a model with a strong velocity decrease in d the scsh sh residuals also show a spatial trend not accounted for by a radial model indicating a lateral decrease in lower mantle shear velocity to the northeast this lateral velocity gradient appears to cause focusing of scs energy scsh sh amplitude ratios are larger than predicted by prem or by a model with a strong negative gradient with depth in d which enhances scs scs splitting corrected for lithospheric anisotropy beneath the receivers indicates spatial variations in d anisotropy with a systematic change in the orientation of the fast polarization direction from transverse to the ray path fast scsh to parallel to the ray path fast scsv along a northeast traverse these spatial trends suggest lateral gradients in the boundary layer shear flow on scale lengths of a few hundred kilometers which may be related to dynamical flow near the near the root of the large hawaiian plume

vermicular kaolinite relics in fly ash derived from bokaro and jharia coals jharkhand india abstract during a study of fly ash from two pulverized fuel power plants bokaro and chandrapura burning coal from the bokaro coalfield in jharkand state india glassy and vermicular mineral forms were found associated with the char a combination of optical microscopy xrd sem eds and xrf analysis has shown that this morphotype reported here for the first time originated from kaolinite that expanded during heating inside the furnace chamber under relatively low combustion temperatures the morphotype has an internal structure that resembles the fanning out structure formed during vermicular kaolinite development

seismic anisotropy in the d layer we present observations of diffracted sv svd for a path between the fiji tonga islands and the eastern coast of north america at distances greater than 110 observed features of s diffracted suggest that coupling between svd and shd can be ruled out as a first order effect for this path arrivals of shd are late relative to iasp91 travel times by about 10 s and those of svd are late relative to shd by 3 s for most records the slope of the log svd shd spectral ratio is around 3hz 1 in the range 0 06 0 15 hz a transversely isotropic low velocity layer in the lowermost mantle with a thickness of 200 300 km may account for most of the observed properties of svd

the lowermost mantle beneath northern asia ii evidence for lower mantle anisotropy summary we have analysed prediffracted s waves with turning points beneath northern siberia in a study of anisotropy in the lowermost mantle deep focus earthquakes beneath the marianas izu bonin and the sea of japan recorded at stations in western europe are used a correction for upper mantle anisotropy is applied to the data comparisons of the data with synthetic data for models with and without a high velocity d layer suggest that there is a velocity discontinuity at the top of the d region and that the style of anisotropy is transversely isotropic in this region time separations between s waves on the radial and transverse component show a weak trend where the separation increases with epicentral distance a normalization of this separation with the travel distance within d 300 km thick in this region suggests that the anisotropy is uniformly distributed within this layer and has an average value of 0 5 per cent a combination of different studies which investigate the structure of the lowermost mantle beneath europe and northern siberia reveals a complicated picture tomographic models from this area and evidence of d anisotropy lower mantle scatterers reflections from a d discontinuity and ultralow velocity zones suggest two distinct regions one exhibits high velocities d anisotropy a d discontinuity and no evidence of scatterers or ultra low velocity zones these features are likely associated with the palaeosubduction of the izanagi plate well into the lowermost mantle the other region has a lower overall velocity and shows evidence of scatterers and ultra lowvelocity zones perhaps suggesting the presence of partial melt these results suggest dramatic lateral variations in the nature of the lowermost mantle beneath northern asia over a length scale of roughly 30 degrees

deformation crystal preferred orientations and seismic anisotropy in the earth s d layer abstract we use a forward multiscale model that couples atomistic modeling of intracrystalline plasticity mechanisms dislocation glide twinning in mgsio3 post perovskite ppv and periclase mgo at lower mantle pressures and temperatures to polycrystal plasticity simulations to predict crystal preferred orientations cpo development and seismic anisotropy in d we model the cpo evolution in aggregates of 70 ppv and 30 mgo submitted to simple shear axial shortening and along corner flow streamlines which simulate changes in flow orientation similar to those expected at the transition between a downwelling and flow parallel to the core mantle boundary cmb within d or between cmb parallel flow and upwelling at the borders of the large low shear wave velocity provinces llsvp in the lowermost mantle axial shortening results in alignment of ppv 010 axes with the shortening direction simple shear produces ppv cpo with a monoclinic symmetry that rapidly rotates towards parallelism between the dominant 100 010 slip system and the macroscopic shear these predictions differ from mgsio3 post perovskite textures formed in diamond anvil cell experiments but agree with those obtained in simple shear and compression experiments using cairo3 post perovskite development of cpo in ppv and mgo results in seismic anisotropy in d for shear parallel to the cmb at low strain the inclination of scs sdiff and skks fast polarizations and delay times vary depending on the propagation direction at moderate and high shear strains all s waves are polarized nearly horizontally downwelling flow produces sdiff scs and skks fast polarization directions and birefringence that vary gradually as a function of the back azimuth from nearly parallel to inclined by up to 70 to cmb and from null to 5 change in the flow to shear parallel to the cmb results in dispersion of the cpo weakening of the anisotropy and strong azimuthal variation of the s wave splitting up to 250 km from the corner transition from horizontal shear to upwelling also produces weakening of the cpo and complex seismic anisotropy patterns with dominantly inclined fast scs and skks polarizations over most of the upwelling path models that take into account twinning in ppv explain most observations of seismic anisotropy in d but heterogeneity of the flow at scales

modeling lower mantle anisotropy development in a subducting slab a model is presented that simulates anisotropy development in a subducting slab from the upper lower mantle boundary 661 km to the core mantle boundary 2891 km two phases are considered orthorhombic mgsio3 perovskite and cubic magnesiowuestite mg fe o single crystal elastic properties at mantle conditions are obtained from existing density functional theory calculations and quasiharmonic approximation it is assumed that deformation is accommodated by slip a polycrystal plasticity model predicts strong texture development for perovskite and weaker texture for magnesiowuestite when averaging single crystal elastic properties with the orientation distribution this results for both phases in weak p wave anisotropy and shear wave splitting in the upper part of the lower mantle but pronounced anisotropy near the core mantle boundary up to 4 for vp and 7 for vs the anisotropy pattern is complex and asymmetric and local heterogeneity is expected these predictions are consistent with seismic observations

apparent splitting of s waves propagating through an isotropic lowermost mantle observations of shear wave anisotropy are key for understanding the mineralogical structure and flow in the mantle several researchers have reported the presence of seismic anisotropy in the lowermost 150 250 km of the mantle i e d urn x wiley jgrb media jgrb52636 jgrb52636 math 0002 layer based on differences in the arrival times of vertically sv and horizontally sh polarized shear waves by computing waveforms at a period 6 s for a wide range of 1 d and 3 d earth structures we illustrate that a time shift i e apparent splitting between sv and sh may appear in purely isotropic simulations this may be misinterpreted as shear wave anisotropy for near surface earthquakes apparent shear wave splitting can result from the interference of s with the surface reflection ss for deep earthquakes apparent splitting can be due to the s wave triplication in d urn x wiley jgrb media jgrb52636 jgrb52636 math 0003 reflections off discontinuities in the upper mantle and 3 d heterogeneity the wave effects due to anomalous isotropic structure may not be easily distinguished from purely anisotropic effects if the analysis does not involve full waveform simulations

seismic anisotropy in the lowermost mantle beneath the pacific onset time differences of up to 3 s are observed between transverse ssh and longitudinal ssv components of broadband s waves at distances of 85 to 120 for paths traversing the lowermost mantle d beneath the pacific after correction for upper mantle anisotropy ssh usually arrives earlier than ssv with the splitting increasing with distance from 100 to 120 the data yield two possible models of anisotropy 1 anisotropy may vary laterally with transverse isotropy existing in higher than average shear velocity regions beneath the northeastern pacific or 2 anisotropy may vary with depth with transverse isotropy concentrated in a thin 100 km thermal boundary layer at the base of d a few recordings at distances less than 105 show that ssv arrives earlier than ssh indicating that general anisotropy likely exists in shallower regions of d

elasticity and strength of hydrous ringwoodite at high pressure oh bearing hydrous ringwoodite compressed non hydrostatically in a diamond anvil cell supports a differential stress that increases from 2 9 to 4 5 gpa over the pressure range of 6 7 13 2 gpa at room temperature this result suggests a significant water weakening effect when compared with results from similar experiments on the anhydrous counterpart kaver and duffy geophys res lett 28 2001 2691 2694 the elastic anisotropy 2c44 c11 c12 of hydrous ringwoodite is measured to be 0 87 7 throughout this pressure range similar to measured values for anhydrous ringwoodite kaver and duffy geophys res lett 28 2001 2691 2694 this lattice anisotropy cannot be explained by anelastic effects such as faulting and twinning within the structure these results suggest that hydrous minerals in the upper mantle and transition zone may have higher ductile strain rates for a fixed shear stress at high temperature resulting in stronger preferred lattice orientation this in turn may be seismically detectable which opens the possibility of using seismic anisotropy as a marker for local volatile containing areas within the upper mantle and transition zone

where can seismic anisotropy be detected in the earth s mantle in boundary layers during the last 30 years considerable evidence of seismic anisotropy has accumulated demonstrating that it is present at all scales but not in all depth ranges we detail which conditions are necessary to detect large scale seismic anisotropy firstly minerals must display a strong anisotropy at the microscopic scale and or the medium must be finely layered secondly the relative orientations of symmetry axes in the different crystals must not counteract in destroying the intrinsic anisotropy of each mineral and there must be efficient mechanisms of orientation of minerals and aggregates finally the strain field must be coherent at large scale in order to preserve long wavelength anisotropy part of shallow anisotropy can be related to the past strain field frozen in anisotropy however the deep anisotropy is due to the present strain field all these conditions are fulfilled only in boundary layers of convective mantle we review in this paper the seismic data sets which provide insight into the location at depth of large scale anisotropy from the d layer up to the lithosphere in addition to the well documented seismic anisotropy in the lithosphere and asthenosphere there is new evidence of seismic anisotropy in the upper 400 660 km and lower 660 900 km transition zones and in the d layer nonetheless the bulk of the lower mantle seems close to isotropy if we assume the hypothesis that seismic anisotropy is associated with boundary layers in convective systems these observations strongly suggest that the transition zone is a boundary layer which makes the pasage of matter between the upper and the lower mantle difficult however this general statement does not rule out flow circulation between the upper and lower mantles finally the geophysical mineral physics and geological applications are briefly reviewed an intercomparison between surface wave anisotropy and body wave anisotropy data sets is presented we discuss the scientific potential of seismic anisotropy and how it makes it possible to gain more insight into continental root deformation and geodynamics processes

shear wave anisotropy beneath the andes from the banjo seda and pisco experiments we present the results of a detailed shear wave splitting analysis of data collected by three temporary broadband deployments located in central western south america the broadband andean joint experiment banjo a 1000 km long east west line at 20 s and the projecto de investigacion sismologica de la cordillera occidental pisco and seismic exploration of the deep altiplano seda deployed several hunderd kilometers north and south of this line we determined the splitting parameters fast polarization direction and t splitting delay time for waves that sample the above and below slab regions teleseismic ks and s scs waves from local deep focus events as well as s waves from intermediate focus events that sample only the above slab region all but one of the ks stacks for the banjo stations show e w fast directions with t varying between 0 4 and 1 5 s however for ks recorded at most of the seda and pisco stations and for local deep focus s events north and south of banjo there is a rotation of to a more nearly trench parallel direction the splitting parameters for above slab paths determined from events around 200 km deep to western stations yield small delay times 0 3 s and n s fast polarization directions assuming the anisotropy is limited to the top 400 km of the mantle olivine stability field these data suggest the following spatial distribution of anisotropy for the above slab component as one goes from east where ks reflects the above slab component to west changes from e w to n s and delay times are substantially reduced this change may mark the transition from the brazilian craton to actively deforming e w shortening andean mantle we see no evidence for the strain field expected for either corner flow or shear in the mantle wedge associated with relative plate motion the small delay times for above slab paths in the west require the existence of significant spatially varying below slab anisotropy to explain the ks results the implied anisotropic pattern below the slab is not easily explained by a simple model of slab entrained shear flow beneath the plate instead flow induced by the retrograde motion of the slab in combination with local structural variations may provide a better explanation

a strong lateral shear velocity gradient and anisotropy heterogeneity in the lowermost mantle beneath the southern pacific 1 velocity heterogeneity and seismic anisotropy in the d region beneath the southern pacific ocean is investigated using broadband shear waves from southwest pacific and south american earthquakes recorded by permanent and temporary stations in antarctica australia south america and on islands in the south pacific shear velocity perturbations vs are inferred from the differential travel times between hand picked horizontally polarized sh direct or diffracted s arrivals and vertically polarized sv sks arrivals derived patterns in vs roughly agree with global shear velocity models but reveal a stronger shear velocity lateral gradient north of approximately 52 s where vs transitions from approximately 0 5 to 1 0 relative to radially averaged reference models over less than 600 km along the base of d waveform analyses provide an even stronger constraint on the transitional region where there is a change in waveform behavior occurring over length scales less than 300 km differential travel times between skks and sks calculated by cross correlating sks with hilbert transformed skks support large vs amplitudes and help to constrain the location of the transitional region anisotropy in d ks is inferred from handpicked differential travel times between the sv and sh components of direct or diffracted s and display a slight spatial trend where the sh component precedes the sv in the north and east of the study area but arrives after sv in the center and southwest of it however there is high ks variability in the center of the study region there is no apparent correlation between vs and ks abrupt changes in the character of velocity and anisotropy in this region of d may be related to chemical heterogeneity at the boundary of the pacific superswell as well as small scale convection in the deep mantle

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

the lowermost mantle beneath northern asia i multi azimuth studies of a d heterogeneity summary in most areas of the globe it is only possible to sample the lowermost mantle or d region with a limited range of azimuths this is due to limitations in source receiver geometries an exception is the region beneath northern siberia where we are able to sample d along orthogonal great circle paths using northern pacific earthquakes recorded in europe and hindu kush earthquakes recorded in canada receiver vespagrams slant stacks of one source recorded at many receivers for a kurile event recorded at the german regional seismic network grsn and the grafenberg array and source vespagrams many sources one receiver of hindu kush events recorded at stations of the canadian national seismograph network cnsn show reflections from a discontinuity at the top of d vespagrams for real data are compared to vespagrams for synthetic data in order to guide their interpretation additional support for our interpretation comes from frequency wavenumber f k analysis which provides a measure of the slowness and azimuth of a given phase the traveltimes of the d reflected phases are then used to provide estimates of d thickness in regions where the roughly orthogonal paths overlap we estimate the thickness to be 310 15 km which is in agreement with existing models for this region we also estimate a thickness of 210 15 km in a previously unsampled region east of this area using the slowness backazimuth and traveltime values for a third source receiver combination we find a reflection point at a depth of 2800 km thickness of d of 91 km in a region several degrees to the west these results and those of previous studies suggest considerable topographic relief 100 km over distances of less than 5 approximately 300 km at the cmb comparing the results from this study with results from other seismic studies of d structure in this area we find this to be a complicated region which exhibits heterogeneity on many scales this region may be the lower mantle graveyard of the subducted izanagi plate and one interpretation of this complexity is that it is due to subduction related deformation at the base of the mantle

multi technique study of fly ash from the bokaro and jharia coalfields jharkhand state india a contribution to its use as a geoliner abstract the chemical mineralogical petrographic and textural characteristics of fly ashes from one fluidized bed and two pulverized fuel power stations in india have been evaluated by a range of complementary methods including optical and electron microscopies laser granulometry quantitative x ray diffraction x ray fluorescence spectrometry and inductively coupled plasma techniques mineralogical and geochemical analyses have also been carried out on the feed coals from the respective power stations and the results were used to evaluate the changes produced during different combustion processes differences in particle size and shape for the ashes and also differences in ash petrology and mineralogy have been related to differences in the mineral matter of the feed coals and to the milling characteristics and combustion temperatures in the different power plants there is a potential of using these fly ashes as geoliner because of their fine texture and low permeability leaching tests have also been carried out on the fly ashes as a basis for assessing the potential for adverse impacts on groundwater systems the materials were blended with bentonite to decrease the permeability further the major and trace element compositions of these ashes were determined most of the elements studied were leached in lower concentrations than averages for the same elements from european fly ashes it is thus expected that these ashes will not provide significant source of additional contamination to permeating water if they are used with bentonite as geoliner material

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

transformation textures in post perovskite understanding mantle flow in the d layer of the earth 1 deformation and texture formation in mg fe sio3 post perovskite ppv is a potential explanation for the strong seismic anisotropy that is found in the d layer of the earth however different experimental approaches have resulted in different lattice preferred orientations lpo in deformed ppv that have led to ambiguity in the interpretation of deformation in the lowermost mantle here we show that deformation of the analogue substance cairo3 during a phase transformation from perovskite to ppv leads to a transformation texture that differs from the cairo3 ppv deformation texture but resembles the results from ppv deformation experiments in diamond anvil cells assuming material spreading parallel to the core mantle boundary our results predict a widespread shear wave splitting with fast horizontal s waves which is compatible with seismic studies downwelling material that undergoes a phase transformation may develop a transformation texture that would locally result in vertically polarized fast s waves

partial melting in a thermo chemical boundary layer at the base of the mantle abstract seismological detections of complex structures in the lowermost mantle boundary layer the d region motivate a conceptual model of a compositionally stratified thermo chemical boundary layer tcbl within which lateral temperature variations sustained by large scale mid mantle flow cause variations of partial melt fraction partial melt fractions of from 0 to 30 in the tcbl occur due to the eutectic of the boundary layer material lying below the high temperature at the core mantle boundary cmb coupled with the presence of steep thermal gradients across the boundary layer regions of the tcbl with the highest temperatures have extensive partial melting producing lateral chemical variations and strong effects on seismic velocities and boundary layer dynamics this tcbl concept provides a relatively simple framework that can plausibly account for diverse seismological observations such as predominance of large scale volumetric elastic wave velocity heterogeneity in the boundary layer laterally extensive but intermittent abrupt shear and compressional velocity increases and decreases at the top of the d region small scale topography of d velocity discontinuities thin ultra low velocity zones at the cmb widespread shear wave anisotropy in d bulk sound velocity anomalies detected in low shear velocity regions of d and large scale upwellings from the most extensively melted regions of the boundary layer neutral or negative buoyancy of the partial melt in the tcbl is required along with an increase in bulk modulus and some density increase of the boundary layer material relative to the overlying mantle more complex models in which the partially melted chemical boundary layer is laterally displaced by mid mantle downwellings are also viable but these appear to require additional special circumstances such as a phase change efficient segregation of slab crustal material or abrupt onset of anisotropy in order to account for rapid velocity increases at the top of d the precise nature of the compositional anomaly or anomalies in d and the eutectic composition of this zone are yet to be determined but it appears likely that partial melting within the lowermost mantle plays a paramount role in the observed seismic velocity heterogeneity increased resolution geodynamic calculations of dense boundary layer structures with partial melting and attendant viscosity reductions and chemical heterogeneity are needed to quantify this tcbl concept

seismic anisotropy beneath the continents probing the depths of geology seismic anisotropy beneath continents is analyzed from shear wave splitting recorded at more than 300 continental seismic stations anisotropy is found to be a ubiquitous property that is due to mantle deformation from past and present orogenic activity the observed coherence with crustal deformation implies that the mantle plays a major if not dominant role in orogenies no evidence is found for a continental asthenospheric decoupling zone suggesting that continents are coupled to general mantle circulation

lateral variations in lowermost mantle shear wave anisotropy beneath the north pacific and alaska s waves recorded by long period world wide standardized seismograph network and broadband stations in north america for deep northwest pacific subduction zone earthquakes provide evidence for anisotropy in the lowermost mantle shear velocity structure beneath the north pacific and alaska systematic delays of up to 4 s are observed between longitudinal components sv and transverse components sh of motion for core reflected scs waves as well as for core grazing and diffracted s waves the absence of significant splitting for s waves that have turning points more than a few hundred kilometers above the core mantle boundary indicates that anisotropy is localized within the d region the lowermost portion of the mantle sv sh differential arrival times for both scs and sdiff along with path length estimates assuming a 250 km thick d region indicate spatial variations in the strength of shear wave anisotropy the strongest anisotropy 1 1 5 is found in the eastern part of the study area with systematic reduction in magnitude toward the west a transverse isotropy model can explain the data with the velocity structure for horizontally polarized waves vsh having a 2 3 discontinuous shear velocity increase at the top of d as proposed in earlier studies of the region and a similar structure for s wave particle motion in the direction normal to the core mantle boundary vsv but with the velocity jump at the top of d and the velocity within d being reduced from that for vsh by 0 5 1 5 km s large uncertainties exist for velocity gradients above and below the velocity jump but the requirement of a reduced vsv relative to vsh in d is clear synthetic waveforms calculated by using separate isotropic structures for sh and sv match the observations well and constrain the basic anisotropic structure because the shear waves all traverse the region with near grazing geometries the study area exhibits strong lateral variations in lower mantle shear velocity structure and variable thickness of the d layer topography of the d layer is not well resolved because of trade off with volumetric heterogeneity

modelling d structure beneath central america with broadband seismic data deep south american events recorded at distances between 70 and 96 are used to constrain the lower mantle structure beneath central america employing data from the terrascope bdsn iris and cnsn canadian national seismic network broadband arrays we obtain a 1 d shear model with a 200 km thick d layer with a 3 velocity jump at the top and a negative gradient within the layer from broadband waveform modelling of sh polarized s scs and scd the shear structure above d is similar to the preliminary reference earth model prem dziewonski and anderson 1981 preliminary reference earth model physics of earth planetary interiors 25 297 356 in terms of dt d and s sks differential times sv synthetics for this model assuming a prem core produce a satisfactory fit to the data except at the larger ranges to the north where the waveforms display rapid variation this feature is indicative of lateral variation of the type suggested by grand 1994 where the discontinuity becomes less well defined synthetics computed for a simplified 2 d cross section through this structure produce the scd phase and simple s at larger distances while scd is easily observed in the shear wave data there is little evidence of its counterpart in the p data by testing several models with different p velocity jumps at the same depth as the d jump in shear structure we conclude that the velocity jump must be less than 1 in fact prem provides an excellent fit both in timing and waveform shapes and therefore we conclude that lower mantle structure beneath central america shows clear evidence for a discontinuity in s velocity but not in p

lowermost mantle anisotropy beneath the pacific imaging the source of the hawaiian plume we utilized recordings of seismic shear phases provided by several north american broadband seismometer arrays to provide unique constraints on shear wave anisotropy beneath the northern and central pacific ocean using a new analysis method that reduces measurement errors and enables the analysis of a larger number of available waveforms we examined relative travel times of teleseismic s and sdiff that sample a large area of lowermost mantle structure the results of this study provide evidence for small scale lateral and depth variations in shear wave anisotropy for a broad region of the lowermost mantle beneath the pacific ocean in particular we image a localized zone of anomalously strong anisotropy whose strength increases toward the top of dq beneath hawaii our results combined with a previous study of vp vsh ratios indicate that ancient subducted slab material may be responsible for observations beneath the northern pacific while lenses or layers of core mantle boundary reaction products or partial melt oriented by horizontal inflow of mantle material to the hawaiian plume source can explain observations beneath the central pacific fl 2001 elsevier science b v all rights reserved

d discontinuity structure beneath the north atlantic from scd observations we analyzed transverse and radial component recordings from the 2010 m6 3 southern spain earthquake depth 620 km recorded on 370 broadband stations in north america we grouped these seismograms into subarrays and applied fourth root vespa processing vespagram analysis in order to enhance low amplitude arrivals these vespagrams show clear scd arrivals which indicate the existence of the d discontinuity beneath the north atlantic ocean 45 60 n 45 55 w these observations are best fit with a 2 4 velocity increase at the top of the d discontinuity at a height above the core mantle boundary of 304 14 km we do not observe scd arrivals at the eastern end of our study region which is consistent with the presence of the easternmost edge of the ancient farallon plate

evidence for anisotropy in the deep mantle beneath alaska we consider the possibility that the velocity structure of d is anisotropic the data we examined consist of seismograms from 9 deep japanese earthquakes recorded at wwssn receiver stations in north america the source receiver combinations span distances of 70 106 with associated s waves passing through d beneath alaska differential travel times of the s scd scs and sks phases are used to constrain the velocity structure in d shear waves refracted by d are observed beyond 72 2 and provide a sensitive measurement of the velocity structure in d beyond 93 the vertically polarized sv and horizontally polarized sh shear waves often appear distinctly split although at distances less than 89 the components are more nearly synchronous near 94 sh occurs as a double arrival sv in this range however remains a single arrival roughly synchronous with the second sh arrival we have been unable to reproduce these effects in isotropic model synthetics synthetics for transversely isotropic models have been computed that do match these waveforms the anisotropy was constrained to be only within d with a vertical symmetry axis we conclude that these observations may be explained by an anisotropic d layer the d discontinuity may be due to a transition to anisotropic mantle a few hundred kilometers above the core mantle boundary

a strongly negative shear velocity gradient and lateral variability in the lowermost mantle beneath the pacific a new approach for constraining the seismic shear velocity structure above the core mantle boundary is introduced whereby sh sks differential travel times amplitude ratios of sv sks and sdiff waveshapes are simultaneously modeled this procedure is applied to the lower mantle beneath the central pacific using da ta from numerous deep focus southwest pacific earthquakes recorded in north america we analyze 90 broadband and 248 digitized analog recordings for this source receiver geometry sh sks times are highly variable and up to 10 s larger than standard reference model predictions indicating the presence of laterally varying low shear velocities in the study area the travel times however do not constrain the depth extent or velocity gradient of the low velocity region sv sks amplitude ratios and sh waveforms are sensitive to the radial shear velocity profile and when analyzed simultaneously with sh sks times rnveal up to 3 shear velocity reductions restricted to the lowermost 190 50 km of the mantle our preferred model for the central eastern pacific region ml has a strong negative gradient with 0 5 reduction in velocity relative to the preliminary reference earth model prem at 2700 km depth and 3 reduction at 2891 km depth and slight velocity reductions from 2000 to 2700 km depth 0 0 5 lower than prem significant small scale 100 500 km shear velocity heterogeneity 0 5 1 is required to explain scatter in the differential times and amplitude ratios