anisotropy and the splitting of ps waves the ps wave is radially polarized in an isotropic spherically symmetric earth owing to the p to sv conversion at the free surface if we choose stations with weak sks splitting to minimize the effect of the receiver we can measure the anisotropy beneath the bounce point of the ps wave we find that with a deep source and epicentral range of 90 125 the ps phase can be distinguished from other phases owing to the limitation of recent large deep events with epicentral range between 90 and 125 we analyze data from stations in north america and events beneath the bonin islands and the fiji islands for events in these two regions the bounce points of the ps wave are roughly located northwest of the kuril islands and near the nova canton trough in the central pacific respectively because the first fresnel zone for the ps wave at this distance range is roughly 700 km across each ps splitting observation must be interpreted as a local average of anisotropic properties the average direction of the fast axis of anisotropy below the nova canton trough region is n104 2 e with a standard deviation 12 7 and a typical delay time of 1 8 s landward of the kuril islands the average direction of the fast axis is n127 6 e clockwise from north and the standard deviation is 11 3 with a typical delay time of 1 2 s we have compared the fast axis with the direction of fossil seafloor spreading and with the present day absolute plate motion the fast axis of anisotropy at the nova canton trough agrees well with the direction of absolute plate motion and poorly with the complex fossil spreading pattern this suggests that significant upper mantle shear anisotropy exists in this part of the central pacific and is consistent with mineral alignment owing to strain associated with present day plate motion similarly the fast axis beneath the kuril islands parallels the convergent motion of the slab coupled mode synthetics constructed with the strong born approximation can be used to model the interaction of the ps waves with anisotropic structure that has a horizontal axis of symmetry we use all free oscillations up to 35 mhz in the calculation the coupled mode synthetics show shear wave splitting with delay time and fast axis consistent with the ray theory prediction

mantle deformation and tectonics constraints from seismic anisotropy in the western united states abstract we have examined shear wave splitting in teleseismic shear waves sks skks s from 15 stations in the western united states based on analysis of 123 records from 67 events the varied past and present tectonic styles in this region subduction transform faulting extension and stable domains are expected to cause a wide variety of anisotropic behavior and therefore make it an excellent natural laboratory fast polarization azimuths vary from e w to nearly n s and time delays t range from being barely detectable less than 0 6 s to 1 6 s most stations yielded consistent measurements independent of station event geometry the exceptions were stations situated very close to the san andreas fault which yielded well constrained but inconsistent splitting parameters these have been successfully modeled by two anisotropic layers with different horizontal symmetry axes the upper layer has a fast direction parallel to the fault and t of about 1 s the lower layer with t from 0 6 to 0 9 s is oriented e w near the san francisco bay area and ne sw in the mojave desert other measurements of e w fast are observed as far east as western nevada with large delay times of 1 3 1 5 s but disappear to the north stations in the northwestern basin and range have values of oriented at about 70 with delay times ranging from 0 7 to 1 2 s varies in other regions of the basin and range from 70 in eastern nevada to 20 in the transition zone between the colorado plateau and the basin and range with t of 1 0 s measurements are geographically coherent and in many cases changes correspond to geologic or tectonic boundaries the e w fast feature extends across several tectonic provinces but disappears near the southern boundary of the gorda plate and may therefore be related to the dynamics of plate interactions regional variations in the fast directions of anisotropy within the basin and range suggest that the present extension has not been strong enough to align the fast directions over a great depth extent fast polarization directions within the transition zone between the basin and range and colorado plateau are nearly parallel to the geologic and geophysical boundaries between the two regions and to other geophysical boundaries the size of the delay times suggests that in many of the areas studied either the mantle is almost twice as anisotropic as we estimate or the anisotropy and therefore mantle deformation extends into the sublithospheric mantle we used the two layer method to examine the effect of a postulated lower layer with fast direction parallel to the absolute motion of the north american plate and found the best estimate of contribution from a uniform layer is 0 1 s of t although a contribution of up to 0 7 s cannot be ruled out a value as low as 0 1 s suggests either that olivine is not strongly aligned in a horizontal direction in this layer or that the layer thickness is of the order of 10 km

global anisotropy in the upper mantle inferred from the regionalization of phase velocities a data set of 2600 paths for rayleigh waves and 2170 paths for love waves was selected in order to resolve azimuthal anisotropy of surface waves in the period range 70 250 s the epicenters were chosen so that the paths provide uniform spatial and azimuthal coverage of earth a synthetic seismogram is computed for each path and compared to the observed seismogram in order to infer the phase velocity along each path to process such a large data set a new tomographic technique is designed a good correlation is found with surface tectonics in the whole period range for love waves and at shorter periods for rayleigh waves the directions of maximum velocities are also well correlated with plate tectonics motions for the 2 azimuthal term of rayleigh waves when the power spectrum of heterogeneities is computed it is found that for love waves the even orders are usually larger than the odd orders for rayleigh waves the degrees 2 and 6 dominate only at long periods suggesting a deep origin for these components

lateral heterogeneity and azimuthal anisotropy of the upper mantle love and rayleigh waves 100 250 s the lateral heterogeneity and apparent anisotropy of the upper mantle are studied by measuring rayleigh and love wave phase velocities in the period range 100 250 s spherical harmonic descriptions of the lateral heterogeneity are obtained for order and degree up to 1 m 10 slow regions are evident at the east pacific rise northeast africa tibet tasman sea southwestern north america and triple junctions in the northern atlantic and indian oceans fast regions occur in australia western pacific and the southern atlantic these features are also found by a completely different analysis based on the backus gilbert method the backus gilbert method also shows that the obtained phase velocities are averaged values within an area of about 2000 km radius and the errors are about 1 of the phase velocity in the zeroth order spherically symmetric earth inversion for azimuthal dependence shows that for low angular order the fast phase velocity directions seem to correlate well with the plate motion vectors however resolution analysis by the backus gilbert method shows that the current data do not have enough resolution for everywhere on the globe only a few regions currently have adequate azimuthal coverage thus confirmation of the above correlation requires a more complete data set

a detrital heavy mineral viewpoint on sediment provenance and tropical weathering in se asia abstract understanding heavy mineral preservation is important for interpreting generation pathways provenance and geochemistry of sediments despite this many assumptions about heavy mineral stability are based on ancient strata and few studies consider modern sediments particularly those in tectonically active tropical areas such as se asia we report new heavy mineral data on 69 river sand samples from the malay peninsula and sumatra in which one aim was to find provenance indicators specific to these areas identifications were performed using optical microscopy and confirmed with sem eds in the malay peninsula heavy minerals record granitic and contact metamorphic provenance variable amounts of zircon tourmaline hornblende andalusite epidote monazite rutile and titanite and minor amounts of pyroxene apatite anatase garnet diaspore colourless spinel cassiterite and allanite are typical of this source area the composition of assemblages from sumatra indicates contributions from two major sources the modern volcanic arc i and the basement ii abundant pyroxene particularly hypersthene up to 70 is diagnostic of the volcanic arc source vesuvianite garnet andalusite tourmaline chrome spinel rutile anatase and corundum are present only in small amounts

an experimental approach to the sequence of the stability of rock forming minerals towards chemical weathering abstract the dissolution rates of milligrams per square metre per day for some main rock forming minerals were measured in experiments over prolonged periods of time rectangularly cut pieces of single crystals or monomineralic polycrystalline specimens were used the experimental set up provided for the rapid removal of all dissolved cations from the solution in order to maintain conditions far from chemical equilibrium experiments were performed at ph 5 5 and 4 0 at 20 c the stability towards chemical weathering decreases in the order muscovite alkali feldspar biotite amphibole pyroxene plagioclase nepheline olivine calcite a decrease of the ph from 5 5 to 4 0 accelerates the weathering process considerably

rapid weathering processes of a 120 year old chronosequence in the hailuogou glacier foreland mt gongga sw china increasing numbers of young soil chronosequences have become exposed in global alpine areas as glaciers have retreated due to climate warming since the industrial revolution however knowledge on the initial stages of weathering at the decadal time scale is limited our aim is to reveal the weathering processes and influential factors in a 120 year old chronosequence on mt gongga in southwest china sixty nine soil samples and 17 water samples were collected from 6 sites with different exposure ages 0 30 40 52 80 and 120 years mineral compositions were determined using x ray diffractometry and four mineral pools i e 1 exchangeable cations 2 carbonates and apatite 3 biotite and hornblende and 4 refractory minerals were separated using a sequential extraction method the results reveal that the soil particle sizes of 2 mu m clay in the a horizons increased and the particle sizes of 20 2000 mu m sand decreased significantly with time the soil organic carbon accumulation rate was up to 14 g m 2 yr which is relatively high compared with other chronosequences of similar age the weathering can be generally divided into two stages the first stage was dominated by the weathering of carbonates and was present at sites with an exposure age of 52 years the second stage was characterized by the intense weathering of biotite hornblende and apatite and was present at the 80 and 120 year old sites where coniferous trees were the dominant plants the rapid weathering was a result of the interactions of the lithology rapid vegetation succession and climate in the hailuogou chronosequence fine silt was produced in large quantities by the strong glacial abrasion and freeze thaw cycles providing rich materials for the subsequent chemical and biogeochemical weathering the decarbonation and the rapid establishment of the conifer forest due to relatively high temperatures and precipitation promote mineral weathering by decreasing soil ph from 8 5 0 years to 4 8 120 years the high permeability of the soil horizons due to the high content of rock fragments and abundant precipitation allows water and organic acids to infiltrate and dissolve mineral soils above the impervious bedrock this study highlights the importance of carbonate weathering in alpine biogeochemical cycling during the initial stage of weathering in granitoid rock areas furthermore our results indicate that the weathering intensity increases with exposure age due to vegetation succession in the early stages of weathering c 2015 elsevier b v all rights reserved

strontium isotope composition as a tracer of calcium sources in two forest ecosystems in belgium the two main sources of ca in forest ecosystems are mineral weathering release and atmospheric inputs we use the 87 sr 86 sr isotopic ratio sr is used as a proxy for ca to determine the ca contribution from atmospheric deposition input in two forest ecosystems beech stands growing on soils formed from parent materials with contrasting total ca contents and isotopic ratios pleistocene loess in central belgium acid leached soil and lower devonian shales in the ardenne massif of high belgium ochreous brown earth the 87 sr 86 sr ratio and the ca and sr contents were measured in bulk precipitation in vegetation beechwood growth rings and leaves and in main soil horizons total acid extractable and labile pools the relative contributions of atmospheric input and soil mineral weathering to vegetation were calculated using mixing equations calculations based on sr isotope ratios of bulk precipitation end member 1 87 sr 86 sr close to ocean water 0 7090 0 1 m hcl extractable soil fraction end member 2 and beech wood mixing compartment indicate that about 43 central belgium and 39 ardennes of sr uptake originates from atmospheric inputs for ca the contributions of atmospheric input are 75 and 78 respectively these estimations are however very sensitive to the choice of the appropriate 87 sr 86 sr and sr ca ratios for the weathering end member the isotopic composition of the mineral source is estimated from the soil mineralogical composition and the relative weatherability of the sr bearing minerals due to soil processes mineral weathering element recycling and geomorphological events addition of allochtonous minerals to the autochtonous pool inherited from the local bedrock the distribution of minerals in both soil profiles is heterogeneous and varies from horizon to horizon which horizons are relevant and which soil pool total soil acidextractable fraction or labile pool should be selected for isotopic measurement of the weathering end member is therefore open to uncertainty the choice of the appropriate 87 sr 86 sr and sr ca ratios for the weathering end member is discussed our results emphasize the importance of the atmospheric contribution of ca for tree mineral nutrition in the studied forest stands suggesting that these ecosystems on acid soils are sensitive to chemical changes in the atmospheric environment e g acid depositions associated with decreasing input of atmospheric cations our results support therefore

anisotropy in kuril kamchatka subduction zone structure to constrain the orientation and extent of seismic velocity anisotropy in the kuril kamchatka subduction zone we have developed a technique that isolates anisotropy at shallow depths by differencing splitting observed in teleseismic shear wave phases olivine a axis orientations inferred from 29 ss s phase pairs and two local s phases vary between the major tectonic components of the trench back arc system although the ss paths do not uniquely constrain a single model of anisotropy a axes are consistent with finite strain patterns predicted by plate convergence and back arc spreading and shearing

anisotropy and shear velocity heterogeneities in the upper mantle long period surface waves are used to map lateral heterogeneities of velocity and anisotropy in the upper mantle the dispersion curves are expanded in spherical harmonics up to degree 6 and inverted to find the depth structure the data are corrected for the effect of surface layers and both love and rayleigh waves are used shear wave velocity and shear polarization anisotropy can be resolved down to a depth of about 450 km the shear wave velocity distribution to 200 km depth correlates with surface tectonics except in a few anomalous regions below that depth the correlation vanishes cold subducted material shows up weakly at 350 km as fast s wave anomalies in the transition region a large scale pattern appears with fast mantle in the south atlantic s anisotropy at 200 km can resolve uprising or downwelling currents under some ridges and subduction zones the pacific shows a nw se fabric

recharge history and controls on groundwater quality in the yuncheng basin north china environmental isotopes and water quality indicators e g tds and no 3 contents were used to characterize the age recharge history and controls on the quality of groundwater resources in the yuncheng basin north china where extensive extraction occurs for agriculture and domestic supply delta 18 o and delta 2 h values as low as 10 6 and 73 parts per thousand respectively together with low radiocarbon activities 70 pmc indicating a significant component of modern post 1950s recharge the shallow groundwater has higher delta 18 o and delta 2 h values up to 8 1 and 54 parts per thousand that are similar to those in modern summer monsoon rainfall indicating that current recharge is via direct infiltration and or leakage of ephemeral streams during heavy rain events historic recharge rates estimated using radiocarbon ages are between 1 and 10 mm year corresponding to 20 mg l in some deep wells 180 m preferential leakage has occurred near the linyi fault in the northern sushui river basin salinisation nitrate contamination and excessive drawdown of deep groundwater are major concerns for the future of the groundwater resources in this region c 2010 elsevier b v all rights reserved

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

evaluating the role of sulfide weathering in the formation of sulfates or carbonates on mars orbital and landed missions to mars have revealed complex sulfate and fe oxide bearing mineralogical assemblages which have been interpreted as the result of a late planet wide acidic period due to large so2 emissions however this global scenario does not explain the recent discovery of hesperian and noachian aged carbonates in several regions because they should have been dissolved by the acidic conditions nor the restriction of sulfate occurrences in preferential regions here we present the results of a 4 year long experimental study designed to test the impact of fe sulfides pyrrhotite fe0 9s on the weathering of basaltic silicates olivine clino and orthopyroxene under an early martian like co2 rich atmosphere our weathered silicate sulfide mixtures showed complex parageneses containing elemental sulfur hydrated sulfates gypsum hexahydrite jarosite and fe oxy hydroxides olivine only samples produced nesquehonite an mg carbonate precursor of hydromagnesite and magnesite these secondary phases are similar to those observed in the martian sulfate and carbonate bearing deposits therefore we propose a geochemical model in which on the one hand martian sulfates mainly formed from weathering of sulfide enriched basalts producing locally acidic environments and on the other hand carbonates were preserved and could even have formed in regions initially devoid of sulfides thereby resolving the apparent paradox arising from the possible coeval formation of the two types of minerals these results raise doubts on the need for a global acidic event to produce the sulfate bearing assemblages suggest that regional sequestration of sulfate deposits is due to regional differences in sulfide content of the bedrock and pave the way for reevaluating the likelihood that early sediments preserved biosignatures from the earliest times

a theory for plastic deformation and textural evolution of olivine polycrystals seismic anisotropy in the upper mantle is due primarily to preferred orientation of olivine crystals induced by progressive deformation in order to understand better the origin of seismic anisotropy we present a simple theory for plastic deformation and textural evolution of olivine polycrystals each crystal in the aggregate is assumed to deform by intracrystalline slip on three major slip systems whose hardnesses and stress exponents are known from experiments the evolving grain orientation distribution in the aggregate is calculated by minimizing the difference between the local crystal deformation and the global aggregate deformation subject to the constraint of global strain compatibility the axial compression texture predicted by our model agrees well to first order with that determined experimentally by nicolas et al 1973 although there are significant discrepancies in the details our results suggest that the orientation texture developed during progressive plane strain deformation is a nearly unique function of the finite strain such that the crystallographic axes 100 010 and 001 are concentrated around the finite strain axes a c and b respectively a b c this result may allow the state of finite strain at depth to be estimated from observations of seismic anisotropy

the durability of rocks developing a test of rock resistance to chemical weathering dissolution rates of 39 rock forming minerals were determined at 20 c and 100 c and different ph values using experimental set ups which achieve near zero cation concentrations weathering rates in nature for rock above surface were estimated from data in this study and data in the literature extraction in a soxhlet extractor with boiling 2 5 m acetic acid causes an acceleration of such estimated natural weathering rates by a factor of 0 25 103 to 7 104 for nearly all important rock forming minerals including the carbonates the applicability of such a comparative test for rock resistance to chemical weathering was corroborated by testing 32 different rocks and building stones run times of only one to four days were needed for a reliable result

rayleigh wave phase velocities in the pacific with implications for azimuthal anisotropy and lateral heterogeneities summary the lateral distribution of fundamental mode rayleigh wave phase velocities in the pacific has been calculated in order to determine the variation in velocity as a function of the age of the oceanic plate the importance of azimuthal anisotropy and the presence of secondary lateral heterogeneities the data set used in this study consists of phase velocity measurements in the period range 20 125 s for 178 paths traversing the pacific both the pure path and spherical harmonic inversion techniques are used in this investigation with an emphasis placed on determining the effectiveness and resolving power of these methods in calculating the velocity distribution in an oceanic regime the first order velocity age relation which dominantly characterizes surface wave dispersion in an oceanic environment can be adequately modelled by either the pure path or spherical harmonic techniques azimuthal anisotropy is the dominant second order effect and is best developed in regions less than 80 myr in age in this age zone the faster direction of wave propagation is either in the direction of fossil seafloor spreading or in the direction of present day absolute plate motion in the western pacific there is a correlation with paleo relative motion fossil seafloor spreading for periods less than 50 s lateral velocity heterogeneities which are not related to the age of the oceanic plate are found by pure path inversions and are correlated with regions associated with shallow residual depth anomalies this effect slow velocities with respect to the velocity age model monotonically decreases as a function of period and is indicative of a shallow origin age independent anomalies were also modelled by the application of the pure path and spherical harmonic methods in a sequential inversion

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

seismic anisotropy and mantle flow seismic anisotropy in the mantle is primarily due to deformation induced lattice preferred orientation lpo of olivine crystals the aim of this paper is to better understand how such lpo is produced by flow and to learn whether observations of seismic anisotropy can be used to infer the local direction of flow within the mantle the basis of the work is a two dimensional theory which describes how lpo evolves during an arbitrary time dependent deformation ribe 1989 i investigate the evolution of lpo beneath ocean ridges above subducted slabs and in thermal convective flows the ocean ridge model predicts that the seismic anisotropy produced at a fast spreading ridge should be greater in magnitude than that produced at a slow spreading ridge and that the fast axis should be more nearly horizontal the subduction zone model predicts that strong seismic anisotropy should be produced above subducted slabs with the fast axis aligned with the slab regardless of the subduction angle the evolution of lpo in typical convective flows is extremely complex and depends strongly on such factors as the mode of heating and the surface boundary conditions in general there is no simple relation between the lpo and the local flow direction in any of the models considered the attempt to use seismic anisotropy to map flow patterns on a global scale is therefore probably unwarranted however the lpo does become aligned with the flow direction when the flow is a progressive simple shear such a flow occurs in limited portions of the mantle beneath the lithosphere at a fast spreading ridge above subducted slabs and in boundary layers beneath rigid surfaces such as continents observations of seismic anisotropy may therefore indicate the sense of shear at shallow depths in the mantle

seismic determination of elastic anisotropy and mantle flow when deformed many rocks develop anisotropic elastic properties on many seismic records a long period 100 to 250 seconds quasi love wave with elliptical polarization arrives slightly after the love wave but before the rayleigh wave mantle anisotropy is sufficient to explain these observations qualitatively as long as the fast axis of symmetry is approximately horizontal quasi love observations for several propagation paths near pacific ocean subduction zones are consistent with either flow variations in the mantle within or beneath subducting plates or variations in the direction of fossil spreading in older parts of the pacific plate

hunting for azimuthal anisotropy beneath the pacific ocean region lateral variations in azimuthal anisotropy cause significant waveform anomalies in long period surface waves 8 mhz suggesting lateral variations with wavelength twice the spacing of fracture zones in the north central pacific