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

anisotropy gradients from ql surface waves evidence for vertically coherent deformation in the tibet region abstract the india eurasia continental collision has not only caused the high uplift of the tibetan plateau but also created a broad diffuse deformation zone in central asia we relate the well constrained extent of crustal deformation in the tibet region with underlying mantle deformation by interpreting the quasi love ql surface wave scattering in the legacy data of tibet ql waves are waveform anomalies generated from cross mode coupling of earth s free oscillations mainly through azimuthal anisotropy over 50 events with ql observations are identified using recordings in tibet the predominant frequency content of the ql waves is near 10 mhz and reflects peak sensitivity of anisotropy at 150 km depth in the mantle assuming horizontally oriented symmetry axes by calculating the delay times between the ql waves and the main love waves we back project the scatterers to cluster in areas like se tibet sayan mountain and iran noticeably the spatial distribution of these scatterers borders the crustal deformation pattern quite well especially at the deformation limits of central asia this linkage suggests a vertically coherent boundary condition through the crust and the upper mantle for the india eurasia continental collision in central asia

on the estimation of radar polarization orientation shifts induced by terrain slopes in recent studies d l schuler et al 2000 applied polarimetric imaging radar derived orientation angles to measure topography and j s lee et al 2000 used orientation angles for polarimetric sar data compensation to ensure accurate estimation of geophysical parameters in rugged terrain areas to support these applications it is important to accurately estimate shifts in orientation angles induced by the azimuth slope variations however in many cases inconsistency in the estimation of orientation angle shifts was encountered in several areas introducing noisy and erroneous results the present authors develop a unified analysis of estimation algorithms based on the circular polarization covariance matrix the concept of reflection symmetry is used to explain the soundness of the circular polarization method and to show problems associated with other algorithms l band polarimetric synthetic aperture radar sar images of camp roberts ca are used to substantiate this theory

stable carbon isotope variations in northwest europe during the last glacial interglacial transition stable carbon isotope data that span part of the last glacial interglacial transition ca 14 9 ka 14c bp ca 15 11 ka cal bp and which derive from organ specific plant macrofossils recovered from two lake sediment profiles in the uk and one in norway are compared the recorded temporal variations show similar trends which over a millennial time scale appear to parallel the main drift in 18o as determined for the grip ice core it is postulated that some smaller scale variations in the 13c profiles may reflect the shorter term oscillations in 18o values evident in the grip record although this is less certain overall however the results suggest that stable carbon isotope measurements based on organ specific terrestrial plant macrofossils may provide i a means for establishing correlations between terrestrial successions and ii additional paleoenvironmental information as the apparent shadowing of the grip record indicates a common forcing mechanism for both greenland 18o and northwest european 13c variations from the evidence available we suggest that the recorded 13c variations reflect fluctuations in air temperature and or changes in water vapour pressure in the atmosphere 1997 john wiley sons ltd

evidence for small scale mantle convection in the upper mantle beneath the baikal rift zone 1 inversion of teleseismic p wave travel time residuals collected along a 1280 km long profile traversing the baikal rift zone brz reveals the existence of an upwarped lithosphere asthenosphere interface which causes a travel time delay of about 1 s at the rift axis central high an area with early arrivals relative to the stable siberian platform of up to 0 5 s is observed on each side of the rift about 200 km from the rift axis flank lows while the location of the central high is approximately fixed in the vicinity of the rift axis those of the flank lows vary as much as 200 km with the azimuth of the arriving rays we use three techniques to invert the travel time residuals for velocity anomalies beneath the profile two of the techniques assume an isotropic velocity structure and one of them considers a transversely isotropic velocity model with a vertical axis of symmetry we use independent geophysical observations such as gravity active source seismic exploration and crustal thickness measurements to compare the applicability of the models other types of geophysical measurements suggest that the model involving transverse isotropy is a plausible one which suggests that the central high and flank lows are caused by the combined effects of an upwarped asthenosphere with a 2 5 lateral velocity reduction and a velocity increase due to transverse isotropy with a vertical axis of symmetry we consider the anisotropy to be the result of the vertical component of a lithosphere asthenosphere small scale mantle convection system that is associated with the rifting

wide band polarimetric radar inversion studies for vegetation layers the authors show how the entropy alpha target decomposition scheme may be used for parametric inversion studies on random particle cloud models for vegetation layers the decomposition is detailed first and then applied to a two parameter model for backscatter from a random cloud of small anisotropic particles the two main parameters used are the mean particle shape and the mean orientation angle of the cloud an inversion algorithm is presented and applied to broad band polarimetric radar data from the european microwave signature laboratory emsl joint research center ispra italy the results have been obtained from measurements of a fir tree and a ficus tree they show a wavelength scale dependence of the shape and distribution of scatterers which reflects the complex volume scattering nature of such problems moreover the values and trends from these two trees as a function of the frequency are different as expected from their physical structures consequently this algorithm has the potential to be useful in the construction of classification schemes for vegetation

velocity structure around the baikal rift zone from teleseismic and local earthquake traveltimes and geodynamic implications abstract we present new results on the velocity structure of the baikal rift zone asia deduced from a comparative teleseismic and local tomography analysis the aim of this paper is to better identify the role of deep mantle processes versus that of far field tectonic effects on the occurrence of extensional tectonics within a continental plate we use 36000 traveltimes of p refracted waves from the isc catalogues and pg and pn traveltimes of 578 earthquakes recorded by the russian regional network to determine a velocity model by the use of local and teleseismic inversion procedures the models show that some velocity patterns are continuous from the surface down to at least 400 km among them a narrow negative anomaly goes through mongolia and follows the southern and eastern margins of the siberian craton this structure is interpreted as a thin mantle plume rising beneath the rift axis however our results do not evidence any wide asthenospheric upwarp at this place other velocity anomalies observed near the surface are not deeply rooted in particular a negative anomaly is observed at shallow levels 48 km beneath the northern third of lake baikal which is disconnected from deeper structures it may be explained by the existence of underplated magmatic material at the bottom of the crust by comparing the geometry of deep rooted anomalies to the present day stress field patterns we conclude that the sub lithospheric mantle dynamics is not the main factor controlling extensional processes in the baikal rift however it does contribute to a thermal weakening of the lithosphere along a mechanical discontinuity bounding the siberian shield we finally conclude that three favourable conditions are gathered in the baikal area to generate extension far field extensional stress field mechanical inherited lithospheric weakness and heat supply further studies should help to precise the genetic link between these three factors

complicated seismic anisotropy beneath south central mongolia and its geodynamic implications abstract two years of high quality broadband seismic data from 69 temporary stations deployed in south central mongolia provide an opportunity to study the anisotropy forming mechanisms in this area the majority of shear wave splitting observations determined from the analysis of teleseismic sks phase are characterized by nw se trending fast directions with large splitting delay times greater than 2 0 s at six stations which is inferred to be generated by active asthenospheric flow the variation of the fast direction may be associated with deflection of asthenosphere around the deep siberian cratonic keel at the base of the lithosphere several of the ne sw trending fast directions with relatively small delay times observed in the gobi desert are parallel to the strike of the main faults and sutures which may represent lithospheric deformation in addition it is inferred that small scale hot mantle upwelling is responsible for generating a cluster of null measurements observed on the south of the hentiy mountain

the use of stable oxygen and carbon isotope stratigraphy as a dating tool abstract oxygen isotope stratigraphy in foraminifera from deep sea sediments provides a time series record of globally synchronous events with a resolution of a few thousand years for the quaternary despite deficiencies from problems of discerning local from global effects and from isotopic disequilibria and ecological effects oxygen isotope stratigraphy remains a highly powerful tool for dating and correlating deep sea sediments as well as for paleoclimatology in general oxygen isotope records per se do not provide absolute age control although carbon isotope records in some respects are more difficult to interpret than oxygen isotopes and are influenced by local factors such as biological productivity ocean ventilation rates and foraminiferal ecological factors carbon isotope records also reflect global phenomena they can therefore be utilized for correlation and dating purposes in a manner similar to oxygen isotope records and provide additional age control especially in areas where the oxygen isotope records may be influenced by temperature and low salinity overprints

three dimensional laboratory modelling of rifting application to the baikal rift russia abstract continental rifting is treated as a mechanical instability developing under horizontal tectonic tension the instability results in strain localization and the formation of a neck which is interpreted as a rift zone at the scale of the whole lithospheric plate this process occurs in plane stress conditions and can therefore be modelled to a first approximation by a one layer plate whose properties represent integral over thickness properties of the real lithosphere we have designed a scaled experimental single layer lithosphere model having elasto plastic rheology and lying upon a liquid substratum to study its behaviour under axial horizontal tension in a homogeneous plate the instability develops along a linear zone oriented at an angle of 60 to the tension axis this orientation is preserved even when the divergent displacement of the plate boundaries is not plain parallel but rotational in the latter case the strain localization zone is rapidly propagating when the plate length to width ratio is less than 2 5 the necking develops along two branches conjugated at an angle of about 120 which is frequently observed in actual rift systems if the model contains a local weak zone hot spot or fault zone the rift junction is located at this zone in the lithospheric models comprising strong cratonic and weak segments strain localization depends on the configuration of the boundary between different lithospheres the necking starts to form within the weak segment in the vicinity of the cratonic promontories and propagates in opposite directions again at an angle of ca 60 to the tension axis in the models containing both a strong lithosphere and local weak zones the rift configuration depends on their shape and relative positions with necking always going through the weak zones in a set of models we have reproduced the geometry of the boundary between the siberian craton and the thermally much younger 100 ma sayan baikal lithosphere in the baikal rift area in these models we were able to obtain the well known three branch configuration of the baikal rift system only by introducing a weak zone in the area of lake baikal such a zone simulates the paleozoic suture existing in this area as in nature two wide outer branches eastern and western are oblique to the regional tension axis whereas the central one is narrow and orthogonal to the tension direction in nature and in the model rifting starts in the central branch corresponding to lake baikal the modelling also predicts the formation of a fourth oblique ns trending branch to the south of baikal although poorly expressed in the field this branch has some seismotectonic and magmatic manifestations the orientations of all four branches with respect to each other and with respect to the regional tension direction are remarkably similar in nature and in the model

mantle structure and rifting processes in the baikal mongolia region geophysical data and evidence from xenoliths in volcanic rocks abstract the origin of the baikal rift zone brz has been debated between the advocates of passive and active rifting since the 1970s a re assessment of the relevant geological and geophysical data from russian and international literature questions the concept of broad asthenospheric upwelling beneath the rift zone that has been the cornerstone of many active rifting models results of a large number of early and recent studies favour the role of far field forces in the opening and development of the brz this study emphasises the data obtained through studies of peridotite and pyroxenite xenoliths brought to the surface by alkali basaltic magmas in southern siberia and central mongolia these xenoliths are direct samples of the upper mantle in the vicinity of the brz of particular importance are suites of garnet bearing xenoliths that have been used to construct p t composition lithospheric cross sections in the region for the depth range of 35 80 km xenolith studies have shown fundamental differences in the composition and thermal regime between the lithospheric mantle beneath the ancient siberian platform sampled by kimberlites and beneath younger mobile belts south of the platform the uppermost mantle in southern siberia and central mongolia is much hotter at similar levels than the mantle in the siberian craton and also has significantly higher contents of basaltic major elements ca al na and iron higher fe si and fe mg the combination of the moderately high geothermal gradient and the fertile compositions in the off cratonic mantle appears to be a determining factor controlling differences in sub moho seismic velocities relative to the siberian craton chemical and isotopic compositions of the off cratonic xenoliths indicate small scale and regional mantle heterogeneities attributed to various partial melting and enrichment events consistent with long term evolution in the lithospheric mantle age estimates of mantle events based on os sr nd isotopic data can be correlated with major regional stages of crustal formation and may indicate long term crust mantle coupling the ratios of 143 144nd in many lree depleted xenoliths are higher than those in morb or oib source regions and are not consistent with a recent origin from asthenospheric mantle mantle xenoliths nearest to the rift basins 30 50 km south of southern lake baikal show no unequivocal evidence for strong heating unusual stress and deformation solid state flow magmatic activity or partial melting that could be indicative of an asthenospheric intrusion right below the moho comparisons between xenoliths from older and younger volcanic rocks east of lake baikal together with observations on phase transformations and mineral zoning in individual xenoliths have indicated recent heating in portions of the lithospheric mantle that may be related to localised magmatic activity or small scale ascent of deep mantle material overall the petrographic p t chemical and isotopic constraints from mantle xenoliths appear to be consistent with recent geophysical studies which found no evidence for a large scale asthenospheric upwarp beneath the rift and lend support to passive rifting mechanism for the brz

azimuthal anisotropy beneath the bohemian massif from broad band seismograms of sks waves abstract shear wave splitting in sks phases recorded by the two broad band stations khc south bohemia and ksp lower silesia is used to determine the anisotropic properties of the lithosphere beneath the marginal regions of the bohemian massif directions of fast velocity of 80 and 120 clockwise from north were obtained for khc and ksp respectively these directions are consistent with the predominantly e w direction of fast velocity found by different authors using similar techniques in some regions of western europe they disagree however with the directions found for the investigated region by other authors on the basis of teleseismic p wave traveltime residuals the value of the time delay between the two splitted shear waves is close to 1 s for both stations implying that the thickness of the anisotropic zone in the upper mantle essentially exceeds 80 km

terrain and surface modeling using polarimetric sar data features topography and surface slope variations affect perceived scattering polarization state of imaged targets in polarimetric synthetic aperture radar polsar applications accurate modeling of such effects can be used for both polarimetric data correction e g better target classification and topographic feature extraction a framework is established in this paper to model target topography based on analytic relation between surface slopes and polsar data and imagery products polarization orientation angle rotation in particular the developed formalism provides both forward i e polarization rotation from topography and inverse i e terrain slopes from polsar data solutions the synthetic aperture radar sar imaging scenario or mode is assumed to be general with arbitrary parameters e g squint angle and includes multi sar sensors for target terrain modeling

modeling and observation of the radar polarization signature of forested areas to understand radar measurements of forested areas the authors have developed a model of l band 25 cm microwave scattering from a forest the forest floor is layer of nearly vertical dielectric cylinders representing tree trunks above this layer is a second layer consisting of randomly oriented cylinders which represent branches the authors identify several scattering mechanisms and calculate the corresponding stokes matrices which combine to give the total stokes matrix and resulting polarization signature it is found that this simple model permits accurate prediction of the polarization of the scattered waves and that additional mechanisms including the effects of leaves and twigs are not required for the 25 cm observation of the forests studied the authors present measurements of the polarization signature acquired over a forested area and show comparisons with model calculations

analysis and evaluation of the nasa jpl topsar across track interferometric sar system we have evaluated the accuracy of digital elevation models dem s generated by the jpwnasa topsar synthetic aperture radar interferometer instrument by acquiring topographic radar data in the summer of 1992 over the national training center near ft irwin california and comparing the measurements to a very accurate digital elevation model derived for this area by the us army topographic engineering center tec fiducial corner reflectors were deployed in the area and their locations were determined to cm accuracy by the defense mapping agency dma dem s generated from the acquired radar data were rotated and translated to precisely overlay the reference dem allowing an analysis of the achieved height accuracy we present here a detailed description of horizontal and vertical errors and their characteristics the standard deviation measured over a 5 6 x 7 km area was approximately 2 m the corresponding figures for relatively flat areas were in the 1 2 meter range and for mountainous areas in the 2 3 meter range consistent with theoretical expectations we also discuss key factors that presently limit the system performance

the effect of topography on radar scattering from vegetated areas the ways in which radar scattering from vegetated areas is affected by the topography of the surface underneath the vegetation are discussed it is shown using a discrete scatterer model that the dominant scattering mechanism may change drastically when the ground surface is tilted relative to the horizontal for a horizontal ground surface for example the total scattering may be dominated by scattering off the tree trunks followed by a reflection off the ground surface for a relatively small tilt in the ground surface the ground trunk interaction term may be replaced by scattering from the branches alone as the dominant scattering mechanism the effect of the topography is more pronounced for scattering by longer wavelengths and the implications on algorithms designed to infer forest woody biomass and soil and vegetation moisture using polarimetric sar data are discussed the effect of the topography on the scattering behavior from forested areas is illustrated with images acquired by the nasa jpl three frequency polarimetric sar over the black forest in germany

observations of teleseismic shear wave splitting in the basin and range from portable and permanent stations observations of shear wave splitting were obtained from temporary and permanent stations in western nevada and southern california measurements of fast polarization azimuth and delay time t were made on both sks and direct s phases for stations in the northern basin and range the results were consistent yielding an average of t 75 8 0 9 0 3 s one station in the southern basin and range gave 40 11 0 4 0 1 s and one in the mojave desert gave 54 3 1 2 0 1 s t 0 9s is consistent with a 100km thick mantle layer characterized by 4 anisotropy for the northern stations the anisotropy appears unrelated to the present day extension or absolute plate motion rather we suggest that it is fossil anisotropy associated with pre miocene extension whose direction is about 68 for the california station is nearly parallel to the strike of the san andreas fault system and is attributed to shear strain associated with relative plate motion

sks splitting measurements with horizontal component misalignment summary the measurement of sks splitting parameters is widely used for the study of deformation in the upper mantle but the misalignment of the station horizontal components for example misorientation of the sensors may result in false measurements in this paper we suggest that the splitting analysis should be repeated with different assumed angles of misalignment two criteria can be applied to correct the measurement of the sks splitting parameters 1 the horizontal rotating angle should produce the global minimum transverse energy as determined using the least transverse energy method 2 there should be consistent results between the least transverse energy method and the minimum eigenvalue method model tests show that the method is suitable for complex anisotropy models such as two layer anisotropy

interpreting paleoclimate from l8o and 2h in plant cellulose comparison with evidence from fossil insects and relict permafrost in southwestern ontario the oxygen isotope content of terrestrial plant cellulose is related to that of the source waters by a two step process involving evapotranspirative leaf water enrichment and equilibrium isotopic exchange between leaf water and atmospheric carbon dioxide a combination of two models that describe these steps yields consistent agreement between measured and predicted climatic and isotopic data humidity is the dominant influence on variations in the cellulose 18o enrichment relative to the source water a good first order approximation of the average daytime relative humidity during the growth season at a site can be based on the linear correlation that exists between humidity and cellulose enrichment without explicit consideration of factors such as temperature 18o of atmospheric vapour and leaf boundary layer dynamics the value of the combined model for paleoclimatic reconstruction has been tested using fossil wood from a late glacial site at brampton ontario estimates of the past relative humidity

paleoclimate reconstruction of the prince creek formation arctic alaska during maastrichtian global warming abstract the upper cretaceous maastrichtian prince creek formation of arctic alaska 82 85 n paleolatitude preserves successions of alluvial paleosols that are used to estimate mean annual precipitation map mean annual temperature mat and meteoric water oxygen isotope composition for the prince creek formation the highest map estimates range between 1000 and 3900 mm yr and the lowest range between 350 and 1200 mm yr the precipitation variability derived from stable carbon isotope analysis occurs on a time scale of 104 years map values agree with previous interpretations from fossil pollen pedological features soil types vegetation composition sedimentological indicators and clamp estimates that suggest high precipitation amounts and high humidity despite the considerable uncertainty with mat proxies our values are consistent with warm month mean temperatures obtained previously from paleobotanical data the 18o of smectite from bentonite beds clusters around 5 0 vsmow the 18o of meteoric water calculated from bentonitic smectite is 23 vsmow assuming a mean annual temperature of 6 3 c which is slightly more 18o depleted than meteoric water calculated from pedogenic siderite in stratigraphically younger beds closer to the brooks range chronostratigraphic correlation with the lower cantwell formation denali national park alaska 64 n paleolatitude suggests higher precipitation rates and highly 18o depleted precipitation in the late cretaceous paleo arctic compared to central alaska these data are consistent with previous studies that suggest a warmer and moister greenhouse earth and an intensified hydrological cycle that enhanced latent heat transport resulting in increased rainout effects

late cenozoic transpression in southwestern mongolia and the gobi altai tien shan connection the gobi altai region of southwestern mongolia is a natural laboratory for studying processes of active transpressional intracontinental mountain building at different stages of development the region is structurally dominated by several major e w left lateral strike slip fault systems the north gobi altai fault system is a seismically active right stepping left lateral strike slip fault system that can be traced along the surface for over 350 km the eastern two thirds of the fault system ruptured during a major earthquake m 8 3 in 1957 whereas degraded fault scarps cutting alluvial deposits along the western third of the system indicate that this segment did not rupture during the 1957 event but has been active during the quaternary the highest mountains in the gobi altai are restraining bend uplifts along the length of the fault system detailed transects across two of the restraining bends indicate that they have asymmetric flower structure cross sectional geometries with thrust faults rooting into oblique slip and strike slip master faults continued ne directed convergence across the fault system coupled with left lateral strike slip displacements will lead to growth and coalescence of the restraining bends into a continuous sublinear range possibly obscuring the original strike slip fault system this may be a common mountain building process the largely unknown gobi tien shan fault system is a major left lateral strike slip fault system 1200 km long that links the southern ranges of the gobi altai with the barkol tagh and bogda shan of the easternmost tien shan in china active scarps cutting alluvial deposits are visible on satellite imagery along much of its central section indicating quaternary activity the total displacement is unknown but small parallel splays have apparent offsets of 20 km suggesting that the main fault zone has experienced significantly more displacement field investigations conducted at two locations in southwestern mongolia indicate that late cenozoic transpressional uplift is still active along the fault system the spatial relationship between topography and active faults in the barkol tagh and bogda shan strongly suggests that these ranges are large coalescing restraining bends that have accommodated the fault s left lateral motion by thrusting oblique slip displacement and uplift thus from a mongolian perspective the easternmost tien shan formed where it is because it lies at the western termination zone of the gobi tien shan fault system the gobi tien shan fault system is one of the longest fault systems in central asia and together with the north gobi altai and other smaller subparallel fault systems is accommodating the eastward translation of south mongolia relative to the hangay dome and siberia these displacements are interpreted to be due to eastward viscous flow of uppermost mantle material in the topographically low e w trending corridor between the northern edge of the tibetan plateau and the hangay dome presumably in response to the indo eurasian collision 2500 km to the south

observations of laterally inhomogeneous anisotropy in the continental lithosphere elastic anisotropy may be an important factor when seismic data are used to determine the structure composition and dynamics of the earth s interior1 2 azimuthal anisotropy has been found in the oceanic and although less definitely in the continental lithosphere from field experiments where the pn wave velocity was observed to vary with direction3 5 these studies suggest a 180 periodicity in travel time variations as the only criterion of the presence of azimuthal anisotropy this criterion however may fail to distinguish between anisotropy and lateral inhomogeneity of the isotropic medium a new method for measuring azimuthal anisotropy has been described recently6 based on the phenomenon of shear wave splitting in anisotropic media which suggests three criteria instead of one to identify azimuthal anisotropy we have now applied this method to the records of permanent seismograph stations in southern germany our results provide strong evidence for the presence of azimuthal anisotropy in the lithosphere of the region and reveal pronounced lateral variations in the parameters of anisotropy on a scale of about 200 km

asymmetric upwarp of the asthenosphere beneath the baikal rift zone siberia in the summer of 1991 we installed 27 seismic stations about lake baikal siberia aimed at obtaining accurately timed digital seismic data to investigate the deep structure and geodynamics of the baikal rift zone and adjacent regions sixty six teleseismic events with high signal to noise ratio were recorded travel time and q analysis of teleseisms characterize an upwarp of the lithosphere asthenosphere boundary under baikal theoretical arrival times were calculated by using the international association of seismology and physics of the earth s interior 1991 earth model and travel time residuals were found by subtracting computed arrival times from observed ones a three dimensional downward projection inversion method is used to invert the p wave velocity structure with constraints from deep seismic sounding data our results suggest that 1 the lithosphere asthenosphere transition upwarps beneath the rift zone 2 the upwarp has an asymmetric shape 3 the velocity contrast is 4 9 in the asthenosphere 4 the density contrast is 0 6 and 5 the p wave attenuation contrast t is 0 1 s

the little ice age as recorded in the stratigraphy of the tropical quelccaya ice cap the analyses of two ice cores from a southern tropical ice cap provide a record of climatic conditions over 1000 years for a region where other proxy records are nearly absent annual variations in visible dust layers oxygen isotopes microparticle concentrations conductivity and identification of the historical a d 1600 huaynaputina ash permit accurate dating and time scale verification the fact that the little ice age about a d 1500 to 1900 stands out as a significant climatic event in the oxygen isotope and electrical conductivity records confirms the worldwide character of this event

mantle transition zone discontinuities beneath the baikal rift and adjacent areas like most other major continental rifts the baikal rift zone brz in siberia ispresumably underlain by a hot and partially molten mantle which has a reduced seismicvelocity relative to surrounding areas recent seismic tomography studies however gaveconflicting results about the depth extent and even the existence of the low velocityanomaly beneath the brz suggesting that additional constraints are needed here wepresent results from stacking of about 1700 radial p to s receiver functions from asingle long running seismic station tly located at the sw tip of lake baikal a clearuplift of the 410 km discontinuity d410 with a magnitude of about 47 km relative tothe south margin of the siberian platform is observed beneath the rift currently availableseismic results suggest that the uplift is unlikely to be caused by addition of water tomantle transition zone mtz silicates but is the result of a 550 c reduction in temperaturein the vicinity of the d410 in addition the 660 km discontinuity d660 shows adownward trend toward the rift from the south suggesting that the entire mtz might havea low temperature beneath the rift the thickening of the mtz suggests a high velocityanomaly of about 2 in the mtz and rules out the possibility that the rifting is caused bya mantle plume originated in or beneath the mantle transition zone

unsupervised classification of scattering behavior using radar polarimetry data the use of an imaging radar polarimeter data for unsupervised classification of scattering behavior is described by comparing the polarization properties of each pixel in an image to that of simple classes of scattering such as even number of reflections odd number of reflections and diffuse scattering for example when this algorithm is applied to data acquired over the san francisco bay area in california it classifies scattering by the ocean as being similar to that predicted by the class of odd number of reflections scattering by the urban area as being similar to that predicted by the class of even number of reflections and scattering by the golden gate park as being similar to that predicted by the diffuse scattering class it also classifies the scattering by a lighthouse in the ocean and boats on the ocean surface as being similar to that predicted by the even number of reflections class making it easy to identify these objects against the background of the surrounding ocean

polarimetric sar data compensation for terrain azimuth slope variation this paper addresses the problem of polarimetric sar polsar data correction for changes in radar cross sections which are caused by azimuth slopes most radiometric slope corrections remove slope effects to account for the effective scattering pixel area however few studies address the slope effect on the radar cross section as a function of polarization states the authors propose two approaches to compensate for this azimuth slope effect for polsar data in the first approach the digital elevation model dem obtained from interferometric sar or from other means is used to estimate orientation angles and in the second approach orientation angles are derived directly from the polsar data they have developed three new methods to implement this second approach one is based on the right right and left left circular polarizations and the other two are based on cloude s and huynelt s decompositions the results are compared with the original polarization signature method using the dem generated orientation angles as the reference polsar data is then compensated using the derived orientation angles significant changes were observed in many elements of the coherency matrix the compensated polsar data should improve the accuracy of geophysical parameter estimation techniques nasa jpl airsar data for an area in central california is used for illustration

azimuthal shear wave velocity anisotropy in the basin and range province using moho ps converted phases an eight station large aperture seismometer array was deployed in the basin and range province of west central nevada for the 1988 1989 program for array seismic studies of the continental lithosphere passcal passive source seismic experiment during the 10 months of data collection a total of 100 teleseismic events were recorded 30 source equalized p wave receiver functions show waveform variations in timing amplitude and polarity in the moho ps phase that is diagnostic of shear wave velocity anisotropy information regarding the crustal anisotropic component can be recovered through the ps phase since it is generated at the moho and is sensitive to shear wave splitting in the crust only we utilize single event stacked and array beam formed receiver functions to minimize the influence of structural variations and scattering on the observed converted phases analysis of shear wave splitting of the ps conversion from the crust mantle boundary indicates a fast azimuth of anisotropy oriented approximately nw se with observed time delays of 0 20 s this strongly suggests coherent crustal anisotropy with a fast direction perpendicular to the strike of fault block mountain ranges this fabric is most likely due to the preferred crystallographic orientation of seismically anisotropic minerals in the middle to lower crust rather than the distribution of basin and range upper crustal fracture systems

preparation of pollen for stable carbon isotope analyses abstract differential diagenesis of the chemical components of pollen in sub fossil records necessitates the isolation of a single resistant chemical component of pollen prior to its isotopic analysis as sporopollenin is particularly resistant to diagenesis and comprises typically 65 80 of the pollen grain it is a suitable component for this purpose conventional acetylation methods of pollen preparation for palynological studies are reliant on the use of carbon bearing compounds which introduce large errors to the pollen carbon isotopic composition 13 c we present results from a novel non carbon containing acid extraction technique to isolate sporopollenin using this technique we demonstrate that the 13 c signals in raw and processed pollen are highly correlated but display an offset associated with the non sporopollenin components

seismic anisotropy and mantle flow beneath the baikal rift zone seismic studies have shown that continental rifts such as lake baikal and the great rift valley of east africa are like mid ocean rifts in that they lie above broad regions of asthenospheric upvvarp of much greater extent than the surface expression of rifting1 4 the direction of mantle flow in such regions can be investigated using the seismic anisotropy created by flow induced orientation of mantle olivine crystals5 8 seismic studies of the mid atlantic ridge have revealed upwelling mantle flow beneath the ridge and flow normal to the ridge axis on either side8 10 here we present results from an array of seismic stations across the baikal rift zone in southern siberia the splitting in arrival times of sks seismic waves indicates that the upper mantle beneath the rift zone is anisotropic with the fast direction which reflects the direction of mantle flow being horizontal and normal to the rift axis this suggests that the broad upwarp associated with this continental rift is caused by similar mantle flow to that at mid ocean rifts this may help to elucidate the processes involved in continental rifting

complex seismic anisotropic structure beneath the central tien shan revealed by shear wave splitting analyses summary shear wave splitting parameters fast polarization directions and splitting times obtained at the permanent broad band station wushi wus which is situated in central tien shan china demonstrate systematic azimuthal variations the fast polarization directions range from 26 to 85 and the delay times range from 0 4 to 1 6 s suggesting a complex anisotropic structure that cannot be adequately explained by a single anisotropic layer with horizontal axis of symmetry the azimuthal variations have an apparent 90 periodicity and thus can be best explained by a two layer anisotropic model with horizontal symmetry axes the optimal fast direction for the upper layer is in the 60 80 range that is subparallel to the strike of the tien shan orogenic belt and can consequently be attributed to the ongoing n s directed shortening the fast direction for the lower layer ranges from 85 to 105 and can be explained by lattice preferred orientation of olivine crystals in the asthenosphere associated with present day absolute plate motion of the eurasian plate

anisotropic convection with implications for the upper mantle on the basis of polycrystalline theory describing the plasticity in olivine and enstatite the flow in a convection cell has been simulated using a finite element formulation the spatial variations in anisotropic properties are computed from the textures that evolve with the flow a kinematically constrained equilibrium based assumption is used to partition the macroscopic deformation among crystals within an aggregate we model the convection for one specific cell geometry and two sets of boundary conditions a complete map of textures throughout the cell is obtained the textured convection cell is structurally very heterogeneous and textures along streamlines do not correlate with the finite strain the results of the simulations indicate that during up welling a strong texture develops rapidly it convects during spreading and is attenuated during subduction results are compared with features of the upper mantle in our predictions the pattern of preferred orientation during spreading is inclined to the flow coordinates due to deformation by simple shear this is contrary to hess 1964 intuition that 001 slip planes of olivine orient themselves parallel to the flow planes yet the pattern is consistent with natural fabric data significant differences are observed as a function of depth within the cell the variations in the p wave velocities in this textured model mantle are analyzed and correspond well with observed seismic data

upper mantle flow beneath and around the hangay dome central mongolia mongolia represents the northernmost area affected by the india asia collision and it is actively deformed along transpressive belts closely associated with large scale strike slip faults the active and past mantle flow beneath this region is however poorly known in order to investigate deep mantle deformation beneath central mongolia and its relation with the surrounding major structures such as the siberian craton the gobi altay belt and the baikal rift a ns trending profile of broadband seismic stations has been deployed in the summer 2003 from the southern siberian craton to the gobi altay range crossing the entire hangay dome mantle flow is deduced from the splitting of teleseismic shear waves such as sks phases in eastern mongolia the permanent station uln in ulaanbaatar reveals the presence of two anisotropic layers the upper one being oriented ne sw close to the trend of lithospheric structures and the lower one nw se close to the trend of eurasia absolute plate motion along the ns profile in central mongolia seismic anisotropy deduced from sks splitting reveals a homogeneous nw se trending structure fully consistent with the observations made in the altay sayan in western mongolia the observed delay times of 1 5 to more than 2 0 s favor consistent mantle flow over large mantle thicknesses since the lithosphere is less than 100 km thick beneath central mongolia and since the observed fast directions are parallel to the trend of the lithospheric structures but also close to the trend of the absolute plate motion we propose that both the lithosphere and the asthenosphere may join their anisotropic effects beneath central mongolia to explain the large delay times although gps vectors represent the instantaneous displacement of the earth s surface and sks splitting the time and vertical integration of finite strain at depth we use the opportunity of the dense geodetic measurements available in this region to discuss the anisotropy pattern in term of present day deformation in the eurasia fixed reference frame gps and sks both depict a similar trend beneath central mongolia suggesting a lithospheric block escaping toward the east that could orient olivine a axes in the upper mantle within a transpressive tectonic regime a different behaviour is observed in western mongolia the gps vectors trend ns close to the regional compression direction whereas the fast sks directions trend ew suggesting a tectonic regime close to a mode of axial shortening generating the development of an ew trending foliation at depth we therefore propose that mongolia is a place where active and frozen lithospheric deformation may add their effects together with the sublithospheric flow in the three sources of anisotropy inferred a fundamental role is played by the siberian craton that acted as an undeformable core of the continent through time the frozen paleozoic and mesozoic structures wrap around the craton building up the fast anisotropic direction pattern the present day sublithospheric flow induced by the plate motion is likely deflecting around its deep roots finally the present day tectonic regime appears to be controlled by the presence of the craton to the north

shear wave splitting around the northern atlantic frozen pangaean lithospheric anisotropy abstract although the number of teleseismic shear wave splitting measurements has considerably increased world wide during the last decade there is no consensus on a unique and universal interpretation of these data splitting might primarily originate in the lithospheric and or asthenospheric mantle but the technique has no vertical resolution and therefore leaves this question of anisotropy location unresolved generally the consequences of the two possibilities are used to infer which is more likely if splitting occurs in the lithosphere the splitting parameters the orientation of the fast split shear wave o and the delay time t should be related to frozen or active deformation on the other hand if the splitting occurs in the asthenosphere the observed splitting parameters should be related to the present day flow induced by the differential motion between the tectonic plates and the underlying mantle the aim of this paper is to test these hypotheses against shear wave splitting observations from western europe and the eastern u s indeed except in a few places splitting on either side of the atlantic on hercynian caledonian or grenvillian structures do not appear to have been deeply and pervasively affected by the opening of this ocean this provides us the opportunity to place these results in the pangaean reference frame of the hercynian caledonian belt before the opening of the atlantic in many places the close parallelism between lithospheric structure and the absolute plate motion apm impedes a reliable identification of the origin of the anisotropy especially an asthenospheric flow channelled around the deeply rooted north american craton may be compatible with the large scale anisotropy pattern in the eastern u s despite this ambiguity fast polarization directions o observed on or near some major lithospheric structures correlate better with the trend of the local tectonic structures than with the expected asthenospheric flow therefore we suggest that these lithospheric structures developed before the opening of the atlantic remain frozen since hercynian caledonian or grenvillian times and are responsible for the observed splitting at these places

measurement of topography using polarimetric sar images a processing technique for polarimetric synthetic aperture radar sar data has been developed which produces profiles of terrain slopes and elevations in the azimuthal or along track direction this technique estimates the average shift in orientation angle of copolarization backscatter caused by azimuthal tilts of the scattering plane using p band data tests of this technique have been made for an area in the black forest near villingen schwenningen in baden wurttemberg germany the radar measured slope and derived elevation profiles have low rms errors and high correlation values when compared with a stereo photograph digital elevation map dem for the area this algorithm is capable of adaptively making transitions from the forested areas to nearby regions with open terrain subsequent tests of the algorithm have been conducted using polarimetric sar l band data for a mountainous nonforested region in the mojave desert ft irwin ca where an accurate dem also was available complete elevation and slope mapping of the terrain in two dimensions using this technique is possible when azimuthal elevation profiles are produced throughout the range extent of the sar image

anisotropy beneath 9 stations of the geoscope broadband network as deduced from shear wave splitting polarization of sks scs and s waves has been analyzed on digital 3 components seismograms recorded at 9 stations of the recently installed geoscope broadband network splitting was observed for about 15 records and is interpreted as being due to seismic anisotropy beneath the stations from every record it is possible to retrieve the fast direction at the station and the time difference between the fast and slow polarization directions some 30 observations of quasi linear s pulses also help constrain the direction of fast velocity synthetic seismograms were built to test the validity of the method used to retrieve the parameters of anisotropy typical time differences are about 1 sec corresponding for example to a 80 km thick zone of perfectly oriented pyrolite the fast directions obtained at 3 continental stations in america westford santa cruz heredia could be related to plate tectonic processes on the other hand the fast directions found in 3 oceanic islands kipapa papete la reunion differ strongly from the oceanic plate velocity direction there

shear wave anisotropy beneath the tibetan plateau eleven broadband digital seismic stations were deployed across the central tibetan plateau in the first extensive passive source experiment attempted within the tibetan plateau one year of recording resulted in 186 event station pairs which we analyze to determine the characteristics of shear wave splitting in the upper mantle beneath the array measurements of the fast polarization direction and delay time t for sks and direct s arrivals reveal systematic variations along the north south oriented array in the north central region of the plateau very large delay times are observed at three stations the largest of which is budo with of t 2 4 s however at tunl which is off the northern edge of the plateau and 110 km from budo and at sites in the south central plateau t decreases by nearly a factor of 3 we also observe systematic rotation of from about 45 ne to 90 e w from south to north along the array a previously identified zone of inefficient sn propagation correlates well with our region of large t observations the large delay times suggest that a relateively high number of anisotropic crystals are preferentially alligned within the mantle lid beneath the north central portion of the tibetan plateau in most cases fast polarization directions appear to be parallel to surface geologic features suggesting as much as 200 km of the upper mantle has been involved in the collisional deformation that has produced the tibetan plateau

seismic anisotropy and mantle dynamics beneath the malawi rift zone east africa sks skks and pks splitting parameters measured at 34 seismic stations that we deployed in the vicinity of the cenozoic malawi rift zone mrz of the east african rift system demonstrate systematic spatial variations with an average splitting time of 1 0 0 3 s the overall ne sw fast orientations are consistent with absolute plate motion apm models of the african plate constructed under the assumption of no net rotation of the global lithosphere and are inconsistent with predicted apm directions from models employing a fixed hotspot reference frame they also depart considerably from the trend of most of the major tectonic features these observations together with the results of anisotropy depth estimation using the spatial coherency of the splitting parameters suggest a mostly asthenospheric origin of the observed azimuthal anisotropy the single layered anisotropy observed at 30 and two layered anisotropy observed at four of the 34 stations can be explained by apm related simple shear within the rheologically transitional layer between the lithosphere and asthenosphere as well as by the horizontal deflection of asthenospheric flow along the southern and western edges of a continental block with relatively thick lithosphere revealed by previous seismic tomography and receiver function investigations this first regional scale shear wave splitting investigation of the mrz suggests the absence of rifting related active mantle upwelling or small scale mantle convection and supports a passive rifting process for the mrz

spatial changes of seismic attenuation and multiscale geological heterogeneity in the baikal rift and surroundings from analysis of coda waves abstract the baikal rift system is undergoing an active tectonic deformation expressed by a high level of seismic activity this deformation leads to physical and mechanical changes of crustal properties which can be investigated by the seismic quality factor and its frequency dependence using a single backscattering model a seismic quality factor qc a frequency parameter n and an attenuation coefficient have been estimated by analyzing coda waves of 274 local earthquakes of the baikal rift system for nineteen lapse time windows w from 10 to 100 s every 5 s and for six central frequencies 0 3 0 75 1 5 3 6 and 12 hz the average qc value increases with the frequency and lapse time window from 46 52 at 0 75 hz to 502 109 at 12 hz for w 10 s and from 114 49 at 0 3 hz to 1865 679 at 12 hz for w 100 s the values of qc f and were estimated for the whole baikal rift system and for separate tectonic blocks the stable siberian platform main rift basins spurs and uplifts along the rift system the q0 value qc factor at the frequency f 1 hz varies within 72 109 and the frequency parameter n ranges from 0 87 to 1 22 whereas q0 is 134 and n is 0 48 for the stable siberian platform vertical variations of attenuation reveal that sharp changes of and n are confined to the velocity discontinuities the comparison of lateral variations of seismic wave attenuation and geological and geophysical characteristics of the baikal rift system shows that attenuation is correlated with both seismic activity and heat flow and in a lesser degree with the surface fault density and the age of the crust seismic wave attenuation found across the main shear zones of the south western baikal rift main sayan strike slip fault zone and tunka obruchev and primorsky normal faults is increased by more than 25 60 compared to the neighboring areas

seismic anisotropy in the mantle beneath an oceanic spreading centre beneath an active mid ocean ridge the mantle upwells in response to the divergence of the newly formed plates leading to high temperatures and pressure release melting below the ridge axis the width of the upwelling region and the amount of melting depend on mantle rheology1 5 but all models predict a maximum decrease in seismic velocity at the ridge axis it has also been suggested however that the alignment of anisotropic minerals by shear in the upwelling mantle will increase seismic velocity for rays travelling subvertically through the upwelling zone6 7 here we report the observation of a consistent pattern of anomalously early p wave arrival times at an array of ocean bottom seismographs deployed across the axis of the southern mid atlantic ridge p waves from distant earthquakes arrive earlier at stations near the axis than at those further away our results are consistent with a model of anisotropy in which the degree of mineral alignment is greatest directly beneath the ridge axis and significant anisotropy extends tens of kilometres from the axis

a review on the lithospheric structures in the tibetan plateau and constraints for dynamics in the last decade several international joint projects were conducted in the tibetan plateau by chinese american and french geophysicists and geologists in the present review the results from vertical reflections wide angle reflections and broadband digital seismic recordings are reviewed and compared constraints for the dynamics of continent continent collision from the lithospheric structures seismicity focal mechanism and anisotropy are discussed

comparison of shear wave splitting and finite strain from the india asia collision zone we investigate whether observations of shear wave splitting in asia may be related to distributed strain of the lithosphere or to strain caused by motion of the asian lithosphere over the deep mantle the hs2 nuvel angular velocity for eurasia and that of minster and jordan 1978 predict absolute plate motions that are a factor of at least 4 slower than the nne relative motion of india with respect to stable eurasia shear of the upper mantle beneath the south asian lithosphere is therefore likely to be dominated by the velocity field caused by the internal deformation of asia rather than by plate motion if that shear causes sks splitting fast polarization directions in tectonic asia should be aligned approximately in the direction of the motion of asian lithosphere relative to the deep mantle which for southern asia is nne in general however fast polarization directions are not aligned with this direction and in some cases are nearly orthogonal to it we calculate finite deformation of the asian lithosphere in response to its indentation by india and from the deformation predict the orientations of fast polarization directions aligned with the principal axes of elongation these predictions agree with the gross features of the anisotropy in tibet and the tien shan orientations of anisotropy in the baikal region of siberia are consistent with the orientations of the local principal axes of active strain orientations of anisotropy in mongolia however are inconsistent both with the azimuth of the velocity of this region with respect to the deeper mantle and with the orientation of the calculated maximum elongation of the region we conclude that sks splitting observations from asia agree better with those predicted by calculations of internal lithospheric deformation due to indentation by india than with strain predicted from motion of the lithosphere over the deeper mantle these results place constraints on the depth range where shear wave splitting occurs which we propose lies predominantly within the lithospheric mantle

tomography based mantle flow beneath mongolia baikal area abstract recent progress in seismic tomography of asia allows us to explore and understand more clearly the mantle flow below the mongolia baikal area we present a tomography based model of mantle convection that provides a good match to the residual topography the model provides predictions on the present day mantle flow and flow induced asthenospheric deformation which give us new insights on the mantle dynamics in the mongolia baikal area the predicted mantle flow takes on a very similar pattern at the depths shallower or deeper than 400 km and almost opposite flow directions between the upper shallower than 400 km and lower deeper than 400 km parts the flow pattern could be divided into the simple eastern region and the complex western region in the mongolia the upwelling originating from about 350 km depth beneath baikal rift zone is an important possible drive force to the rifting the seismic anisotropy cannot be simply related with asthenospheric flow and flow induced deformation in the entire mongolia baikal area but they could be considered as an important contributor to the seismic anisotropy in the eastern region of mongolia and around and in sayan baikal orogenic belt

mantle structure from inter station rayleigh wave dispersion and its tectonic implication in western china and neighboring regions abstract we processed more than 3000 inter station great circle paths to determine the phase velocity for the fundamental mode of rayleigh wave and finally arrived at 110 paths of high quality dispersion data which show good spatial coverage in western china and neighboring regions rayleigh wave phase velocity dispersion model wchina1d was obtained and compared with previous global and regional models phase velocity maps from 15 to 120 s were inverted and the maps of 20 40 80 and 120 s are presented in this paper checkerboard tests show the average lateral resolution in our area of interest is about 7 our tomographic results corroborate a prominent low velocity anomaly lying mainly in the lower crust and uppermost mantle in the chang thang terrane the apparent low velocity anomaly also appears in the wide area of northeastern tibet in the crust and upper mantle the low velocity area around southeastern tibet may be created by the southeastern migration of the low velocity mass of the tibetan plateau the eastern tarim shows structure with higher velocities relative to that of central tarim a large scale low velocity anomaly is clearly seen in central and western mongolia our high quality measurements were also used to evaluate the cub global shear velocity model shapiro n ritzwoller m 2002 monte carlo inversion for a global shear velocity model of the crust and upper mantle geophys j int 151 88 105 of the crust and upper mantle the 40 s rayleigh phase velocity map predicted from cub model shows an apparent discrepancy with our measurements in western china and western mongolia which implies a higher estimated about 1 2 phase velocity model in these regions probably due to the gaussian smoothing condition in their tomography inversion

upwarp of anomalous asthenosphere beneath the rio grande rift continental rifts are possible analogues of mid ocean ridges although major plate tectonic features are less clearly observed1 current thermal models of mid ocean ridges2 4 consist of solid lithospheric plates overlying the hotter less viscous asthenosphere with plate thickness increasing away from the ridge axis the lithospheric lower boundary lies at or near the melting point isotherm so that at greater depths higher temperatures account for lower viscosity lower seismic velocities and possibly partial melting upwarp of this boundary at the ridge axis concentrates heat there thus lowering densities by expansion and raising the sea floor to the level of thermal isostatic equilibrium at slow spreading ridges a major central graben forms owing to the mechanics of magma injection into the crust5 topography heat flow gravity and seismic studies support these models on the continents a low velocity channel has been observed although it is poorly developed beneath ancient cratons6 9 plate tectonic models have been applied to continental basins and margins10 12 but further similarities to the oceanic models remain elusive topographic uplift is often ascribed to airy type isostatic compensation caused by crustal thickening rather than thermal compensation in the asthenosphere here we discuss the rio grande rift in southwestern united states teleseismic p wave residuals show that regional uplift is explained by asthenosphere uplift rather than crustal thickening

topography retrieval from single pass polsar data based on the polarization dependent intensity ratio at present many polarimetric synthetic aperture radar polsar remote sensing applications still perform radio metric terrain correction whereas other types of terrain slope analysis rely on shuttle radar topography mission and advanced spaceborne thermal emission and reflection radiometer digital elevation model dem databases however the terrain relief characteristics present in fully polsar images can also be used for topography retrieval from single flight data based on the analysis of the polarization signature peak shift we propose a new topography retrieval algorithm based on the polarization dependent intensity ratio the intensity term conforms to both the polarimetric orientation angle shift model and the lambertian scattering model which is refined for synthetic aperture radar sar imaging geometry this is useful in avoiding solving an ill conditioned problem and it is more practical than considering the two models independently another key idea of this algorithm is the derivation of a second order residual error equation for revising the ground range slope error with homogeneous media using the full multigrid fmg technique furthermore the fake topographic relief effect induced by geophysical terrain variations is also considered and reduced by including an bar alpha scattering angle based weighting coefficient in the second order residual error equation in addition a first order residual error equation combined with tie points is proposed for calculating the least squares estimation of the height from slope integration by fmg national aeronautics and space administration jet propulsion laboratory airsar and uavsar l band polsar and interferometry sar dem data are used to illustrate and validate this algorithm our results demonstrate the high potential of this method for employing a low resolution dem to match the corresponding high resolution polsar data

compensation of terrain azimuthal slope effects in geophysical parameter studies using polarimetric sar data abstract the existence of significant terrain relief reduces the accuracy of algorithms intended to extract geophysical parameters from polarimetric synthetic aperture radar sar images for this reason most inversion studies attempting to estimate biomass crop type snow cover surface roughness or soil moisture from sar data are best done in areas of flat earth in areas which require compensation for topography limited corrections have been made in the past for range slopes using a coregistered digital elevation model dem no corrections have been made however for terrain slope induced polarimetric effects in the azimuthal or along track direction recent methods using polarimetric sar data of measuring terrain slopes in the azimuthal direction have been developed this article presents an algorithm to use these slope estimates to compensate for the effects of azimuthal terrain slopes the algorithm involves rotation of the polarimetric covariance matrix to achieve maximum azimuthal symmetry evidence is given to substantiate the degree to which azimuthal slope effects have been removed from the data nasa airsar p l and c band data obtained for open terrain in death valley national park california 1994 are used to evaluate the compensation algorithm

studies of multibaseline spaceborne interferometric synthetic aperture radars the authors have utilized a set of seasat synthetic aperture radar sar data that were obtained in nearly repeat ground track orbits to demonstrate the performance of spaceborne interferometric sar insar systems an assessment of the topography measurement capability is presented a phase measurement error model is described and compared with the data obtained at various baseline separations and signal to noise ratios finally the implications of these results on future spaceborne insar design are discussed

shear wave splitting in the rio grande rift fast directions and lag times associated with sks shear wave splitting are determined for six digital stations in the rio grande rift rgr the mean fast direction for three stations in the central rgr is about 45 oblique to the axis of the rgr in contrast fast directions approximately parallel to the axis of the rgr are found for two stations in the southern rgr 10 and one station in the northern rgr 26 the fast directions for southern stations are not aligned with the ne sw extension direction of the oligocene to early miocene stage of extension the significant n s lateral variation in the sks shear wave splitting parameters is difficult to explain by fossil anisotropy because the mantle structure beneath the rgr is underlain by hot material with low seismic wave velocities hence the fast direction of azimuthal anisotropy is probably related to the preferred orientation of olivine created by the present deformation in the upper mantle because none of the fast directions are parallel to the present e w extension direction of the rgr the dominant upper mantle flow direction is not perpendicular to the axis of the rgr the pattern of the fast directions along the rgr provides evidence for a rising asthenosphere beneath the central to southern rgr and suggests that thermally driven small scale convection may be faster for flow parallel to the rift than perpendicular to it

global patterns of azimuthal anisotropy and deformations in the continental mantle summary we present a summary of measurements of azimuthal anisotropy in the continental mantle based on the sks technique and performed mostly with the active participation of the authors the directions of polarization of the fast quasi shear wave and the time delays between the quasi shear waves are obtained at nearly 70 locations in all continents except antarctica these data are interpreted in terms of lattice preferred orientation of olivine which is caused by deformations in the mantle the depth interval responsible for anisotropy is unknown but the data suggest that it may reach at least 300 km the fast directions in sks do not show clear correlation with the fast directions of the teleseismic p at the same seismograph stations in the regions of present day convergence the fast direction of anisotropy usually aligns with the plate boundary this correlation implies that the direction of shortening is the same in the crust and the upper mantle in the regions of rifting the inferred direction of mantle flow usually aligns with the direction of extension in the crust outside the regions of recent tectonic activity we most likely observe a combined effect of frozen anisotropy in the subcrustal lithosphere and of recently formed anisotropy in the asthenosphere on a global scale in these regions there is a positive correlation between the absolute plate velocity directions and the fast directions of anisotropy the correlation is especially strong in central and eastern parts of north america a clear absence of any evidence of large scale azimuthal anisotropy in the data of long range refraction profiling for the upper 100 km of the mantle of that region implies that the effect in sks is generated mainly at greater depths in the asthenosphere orientation of olivine at these depths reflects recent and present day flow in the mantle rather than processes of a distant geologic past

azimuthal anisotropy in the earth from observations of sks at geoscope and nars broadband stations abstract we have analyzed observations of low frequency sks waves recorded on horizontal components at several broadband stations of the geoscope and nars arrays splitting of sks is consistently observed and in good agreement with a hypothesis of azimuthal anisotropy due to transverse anisotropy with a horizontal axis in the upper mantle beneath the receivers we have designed an inversion method which takes advantage of observations made simultaneously at different azimuths and which permits us to obtain estimates of the direction of fast axis of anisotropy as well as the time delay between the orthogonal quasi shear waves in general the directions of fast velocity obtained both for stations around the atlantic and around the pacific appear to be related to directions of past and present plate motions

thickness of the lithosphere beneath the baikal rift zone and adjacent regions abstract methods of separation of gravity anomalies related to mantle density inhomogeneity are developed based on the inversion of these anomalies with regard to some constraints obtained from seismic data the map of lithospheric thickness beneath the baikal rift zone and adjacent regions was made the lithospheric thickness beneath the baikal rift zone is estimated to be 40 50 km i e the lithosphere is thinned here to a crustal thickness beneath the siberian platform the lithospheric thickness increases to 200 km and underneath the trans baikal region of moderate cenozoic tectonic activity it ranges from 75 to 160 175 km therefore a wide asthenospheric upwelling was revealed beneath the rift zone the data available on the configuration of the baikal depression and that of the crust and the lithosphere as a whole made it possible to estimate the magnitudes of extension at different lithospheric levels the significant increase in extension with depth implies that rifting in the baikal zone was caused by asthenospheric diapirism

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

a new approach for reconstruction of the holocene climate in the mongolian altai the high resolution δ13c records of toc and pollen complexes in hoton nur lake sediments abstract 13 c of total organic carbon toc and pollen grain toc c n ratio and 15 n of total organic nitrogen ton in a 2 57 m long core from hoton nur lake in mongolian altai have been measured for reconstruction of the holocene climates the 13 c values of toc and pollen carbon have similar average values but different ranges pollen 13 c has negative correlation with ap arboreal taxa pollen and positive correlation with nap herbaceous pollen and spores that are connected with conditions of humidity in the area taiga biome has lighter 13 c than steppe biome hence pollen 13 c composition is more sensitive to changes of humidity in the analogous spectra than palynotaxonomical structure and 13 c of toc based on our results the holocene climates in mongolian altai are 1 dry conditions prior to 11 5 kyr bp 2 wet conditions between 11 5 and 6 0 kyr bp 3 a relatively dry cool episode during 6 4 kyr bp 4 stable cool and semiarid conditions with moderately effective moisture during the past 4000 years two abrupt climatic changes occurred at 7 45 kyr bp and 11 5 kyr bp might be related to glacial activities the holocene climatic trend in mongolian altai which is controlled by the westerlies is similar to the trend of monsoonal climate shown by the chinese speleothem records as well as the lake sand dune evidence in the deserts of nw china the contact of the two climatic systems and shift of the monsoonal boundary during the past need to be further studied

seismic anisotropy estimated from p wave arrival times in crosshole measurements summary seismic anisotropy is evidenced in the inner core upper mantle and the lower crust in large scale and the evidence is generally provided by shear wave splitting analysis here this paper searches for the evidence of anisotropy in the uppermost crust by using p wave arrival times from crosshole seismic measurement to directly estimate velocity anisotropy associated with the fine layering effect of multiple sedimentary beds conceptually fine layering causes the so called vti vertical transverse isotropy anisotropy with a vertical symmetry and the effect is parametrized by the horizontal and vertical velocity ratio it is found however that the vti anisotropic parameter does not have a simple vertical symmetry but is also azimuth dependent this azimuthal anisotropy may reflect the fracture orientation due to large scale tectonic movements and is very important in the production of oil reservoirs as the seismically fast directions can indicate preferred directions of fluid flow this paper presents innovative methods for anisotropy analysis in both vertical and horizontal plane integrated seismic anisotropy interpretation clearly indicates distinguished strain orientations forming fractures in oligocenic miocenic and pliocenic sediment in the edge of the extensional basin immediately next to tan lu fault an active continental strike slip fault zone

significant seismic anisotropy beneath the southern lhasa terrane tibetan plateau 1 shear wave splitting measurements using teleseismic pks skks and sks phases recorded by station lsa on the southern part of the lhasa terrane of the tibetan plateau reveal significant azimuthal anisotropy with a splitting time of up to 1 5 s a conclusion that is contradictory to previous studies which suggested isotropy or weak anisotropy in addition systematic variations of the splitting parameters fast polarization direction and splitting time with the arriving azimuth of the seismic ray path are observed suggesting a model of anisotropy that is more complicated than a single layer with horizontal axis of symmetry the measurements are consistent with a model with two layers of anisotropy the top layer has a ne sw fast direction which is consistent with gps revealed direction of surface movement and can be associated with lattice preferred orientation of middle lower crustal minerals such as amphibole the lower layer has a nearly e w fast direction and can be the consequence of either the n s directed compressional stress originated from the india eurasia collision or flow in the asthenosphere related to the absolute motion of eurasia this study underlines the importance of a long duration of deployment of seismic stations in resolving complex anisotropy

asthenospheric flow and origin of volcanism in the baikal rift area the origin of low volume hotspot like volcanism often observed in continental rift areas is debated as is the nature of the flow in the mantle beneath in this paper we assemble seismic constraints on the mantle flow below the baikal rift zone we combine new evidence from upper mantle tomography and from a radially anisotropic shear velocity profile measured beneath and se of the rift with published shear wave splitting constraints on azimuthal anisotropy fast directions of azimuthal anisotropy are perpendicular to the rift on both of its sides stable siberian platform lithosphere on the northern side extends down to 200 km on the southern side the lithosphere is only 60 70 km thick this asymmetry with the thick cratonic root forming a barrier to convective flow inhibits a mid ocean ridge like flow pattern the radially anisotropic profile yields evidence for horizontal flow in the upper asthenosphere 60 100 km se of the rift but no evidence for vertical flow these results are consistent with horizontal asthenospheric flow nw to se perpendicular to the rift from beneath the thick siberian towards the thin baikal mongolian lithosphere when asthenosphere ascends from the 200 km depth beneath the craton to shallower depths beneath the rift decompression melting of embedded veins of enriched rock can produce the hotspot like basaltic volcanism observed the occurrence of such veins of enriched mantle in sub cratonic asthenosphere has been predicted by geochemical mantle models we propose that sub horizontal asthenospheric flow from beneath cratons is a common cause for hotspot like volcanism in continental rift zones

topographic mapping using radar interferometry processing techniques a new processing algorithm for the nasa jpl topsar topographic radar mapper is described it incorporates extensive motion compensation features as well as accurate three dimensional target location algorithm the processor applies an algorithm to resolving the absolute phase ambiguity this allows rectified height maps to be generated without any use of ground reference points the processor was tested using data acquired with extreme aircraft motion so that performance could be evaluated under adverse conditions the topographic maps generated by the radar were compared to digital elevation models dems derived using conventional optical stereo techniques in one region the rms elevation deviations measured were less than the specified dem accuracy and in the region covered by the more accurate dem errors varied from 2 2 m rms in relatively flat terrain up to 5 0 m in mountainous area the rms difference between radar and dem elevation over the 6 5 km by 22 km area covered by the more accurate dem was 3 6 m

na sws 1 1 a uniform database of teleseismic shear wave splitting measurements for north america 1 this version of shear wave splitting sws database db for north america na contains 6224 pairs of splitting parameters fast polarization directions and splitting times measured using all the available data recorded by digital broadband seismic stations over the period of 1980 2007 and archived at the incorporated research institutions for seismology data management center the measurements were produced using a set of robust procedures that involve automated batch processing and manual screening and were ranked quantitatively on the basis of a uniform criterion the result is a homogeneous database of individual rather than station averaged splitting parameters that can be used by a variety of geoscientists for the understanding of the structure and dynamics of the earth s deep interior beneath na this data brief describes the seismic data and techniques used to generate the sws results the spatial and azimuthal coverage and the limitations of the db the db will be periodically updated and enhanced by adding newly recorded data and by measuring splitting parameters using the pks and skks phases in addition to sks the database can be accessed at http www mst edu liukh sws

measurement of ocean surface slopes and wave spectra using polarimetric sar image data abstract methods have been investigated which use fully polarimetric synthetic aperture radar sar image data to measure ocean slopes and wave spectra independent techniques have been developed to measure wave slopes in the sar azimuth and range directions the azimuth slope technique in particular is a more direct measurement than conventional intensity based backscatter cross section measurements in the azimuth direction wave induced perturbations of the polarimetric orientation angle are used to sense the wave slopes in the range direction a new technique involving the alpha parameter from the cloude pottier h a entropy anisotropy and averaged alpha polarimetric scattering decomposition theorem is used to measure slopes both measurement types are sensitive to ocean wave slopes and are directional taken together they form a means of using polarimetric sar polsar image data to make complete measurements of either ocean wave slopes or directional wave spectra these measurements must still contend with fundamental nonlinearities in the sar image processing i e azimuth direction velocity bunching that are due to wave velocity and acceleration effects nasa jpl airsar l and p band data from california coastal waters were used in the studies wave parameters measured using the new methods are compared with those developed using both conventional sar intensity based methods and with in situ noaa national data center buoy measurement products

low seismic velocity layers in the earth s crust beneath eastern siberia russia and central mongolia receiver function data and their possible geological implication analysis of teleseismic receiver functions at digital stations along the bratsk irkutsk ulanbaatar undurshil profile suggests that low velocity layers in the earth s crust exist not only beneath the baikal rift zone where such a layer was found earlier by deep seismic sounding dss but also beneath early paleozoic sayan baikal paleozoic mongolian early mesozoic mongolia okhotsk fold areas and beneath the siberian platform the reliability of detection of the low velocity layers by receiver function analysis has been checked by numerical modeling the results of this modeling demonstrate that receiver functions can reveal the low velocity layers in the crust if the initial model starting approximation is close to real velocity distribution and if the model medium is divided into thin layers averaged dss velocity model without low velocity layers was used as starting approximation for the inversion of observed receiver functions the low velocity layers are interpreted to reflect inhomogeneities of the earth s crust formed during its evolution most of these layers are presumed to correspond to thick mylonite zones related to large pre cenozoic thrusts the mylonites possess a great seismic anisotropy caused by the mineral orientation formed by the ductile flow in large thrust zones they can result in low velocity layers only for seismic waves whose rays are oriented perpendicular to the mylonite foliation i e in the direction of the minimum velocity the velocities along the foliation direction can be rather high therefore the low angle mylonite zones can be distinguished by the receiver function method which uses the waves from the teleseismic events with nearly vertically oriented rays the suggestion that the low velocity layers mark low angle thrusts is in agreement with gravity and geological data the amount of overthrusting is estimated to be as large as several hundred kilometers multichannel seismic profiling can be used to verify the existence and the deep geometry of the presumed thrusts d 2002 elsevier science b v all rights reserved

shear wave splitting and small scale convection in the continental upper mantle the deformation of the upper mantle beneath a collisional belt is key to the dynamics of the belt but this deformation is difficult to observe seismic azimuthal anisotropy manifested by shear wave splitting provides the best geophysical evidence of deformation in the upper mantle here we use observations of shear wave splitting to investigate deformation in the upper mantle beneath the tien shan in central asia we find that underneath most of the tien shan the fast direction of azimuthal anisotropy is roughly parallel to the axis of the belt but it deviates by nearly 90 where the upper mantle is anomalously hot the former relationship previously observed in other collisional belts seems to be usual for this environment the anomalous directions however provide evidence of a rising plume beneath the range suggesting more generally that the along strike flow of the mantle beneath collisional belts is a reflection of thermally driven convection

seismicity structure and rheology of the lithosphere in the lake baikal region this paper combines observations of seismicity gravity topography and thermal and velocity structures to investigate the rheological properties of the lithosphere in the lake baikal region we examine the seismogenic thickness ts using 25 earthquakes of mw 5 1 7 1 whose full source parameters have been determined by inversion of teleseismic waveforms 13 of which are presented here for the first time these 25 events plus six others mw 5 0 5 8 whose depths are well constrained show that moderate earthquakes occur at depths up to 30 km in the northeast baikal rift based on the teleseismic waveform modelling results and published relocations of microearthquakes using regional networks we conclude that the mantle is not a significant source of seismicity in the baikal region using the admittance between free air gravity and topography we estimate the effective elastic thickness te in the region to be between 5 and 20 km nowhere do the data require that te ts consistent with the simple interpretation that the long term strength of the lithosphere resides in its seismogenic layer a weak mantle in the baikal region can be explained by its high temperature which we estimate by combining local geotherm estimates with the regional upper mantle velocity structure obtained from fundamental and higher mode surface waves geotherms are fitted to pressure and temperature estimates from mantle nodules at four sites both within and outside the siberian shield in order to constrain the temperatures at the moho we estimated crustal thicknesses using teleseismic receiver functions moho temperatures are estimated to exceed 550 c beneath the siberian shield and are higher in the more recently deformed mountain belts to the south based on a reassessment of oceanic geotherms and seismicity it seems likely therefore that the mantle in the baikal region is too hot to be a source of long term strength this is consistent with the recent suggestion that the distribution of mantle seismicity in both the oceans and the continents is dependent on temperature alone finally we note that results from s wave tomography studies combined with the observed locations of rift related earthquakes lead us to suspect that the frequently published position of the edge to the siberian shield at the surface provides a poor description of that same boundary at depth