upper mantle anisotropy beneath the geoscope stations seismic anisotropy has been widely studied this last decade particularly by measuring splitting of vertically propagating core shear waves the main interest in this technique is to characterize upper mantle flow beneath seismic stations on the other hand the major restriction in this method is that a single station gives a single anisotropy measurement alternative methods have been developed in order to avoid this restriction an accurate determination of upper mantle seismic anisotropy beneath a seismic station may allow one by doing anisotropy correction to characterize remote or deeper anisotropy the geoscope network is ideal for this purpose because it is composed of a large set about 26 of high quality broadband seismometers globally distributed and because some of these stations have run for more than 10 years and most of them for more than 5 years we selected about 100 events at each site generally of magnitude mb 6 0 and we performed systematic measurements of the splitting parameters fast polarization direction and delay time t on sks skks and pks phases splitting on oceanic islands has been difficult to observe owing to the low quality of the signal but also perhaps owing to complex upper mantle structures beneath the stations station kip kipapa hawaii in the pacific is the only oceanic geoscope station with a clear anisotropy we determined well constrained splitting parameters for 10 of the 17 continental stations that may be explained by a single anisotropic layer the poor correlation between fast polarization directions and the absolute plate motion together with the apparent incoherence between the plate velocities and the observed delay times suggest that a simple drag induced asthenospheric flow alone fails to explain most of the observations for some stations located on or near major lithospheric structures tam tamanrasset algeria for instance we observe a good correlation between fast polarization directions and regional structures at station scz santa cruz california we found clear variations of the splitting parameters as a function of the event backazimuth compatible with two layers of anisotropy three stations can canberra hyb hyderabad india and ssb saint sauveur badole france seem to be devoid of detectable anisotropy

mantle flow in regions of complex tectonics insights from indonesia 1 indonesia is arguably one of the tectonically most complex regions on earth today due to its location at the junction of several major tectonic plates and its long history of collision and accretion it is thus an ideal location to study the interaction between subducting plates and mantle convection seismic anisotropy can serve as a diagnostic tool for identifying various subsurface deformational processes such as mantle flow for example here we present novel shear wave splitting results across the indonesian region using three different shear phases local s sks and downgoing s to improve spatial resolution of anisotropic fabrics allows us to distinguish several deformational features for example the block rotation history of borneo is reflected in coast parallel fast directions which we attribute to fossil anisotropy furthermore we are able to unravel the mantle flow pattern in the sulawesi and banda region we detect toroidal flow around the celebes sea slab oblique corner flow in the banda wedge and sub slab mantle flow around the arcuate banda slab we present evidence for deep sub 520 km anisotropy at the java subduction zone in the sumatran backarc we measure trench perpendicular fast orientations which we assume to be due to mantle flow beneath the overriding eurasian plate these observations will allow to test ideas of for example slab mantle coupling in subduction regions

magnetic susceptibility of soil an evaluation of conflicting theories using a national data set magnetic susceptibility values for topsoils across england arc combined with data for soil type geochemistry and concentrations of magnetotactic bacteria in order to evaluate different theories for explaining soil magnetism strongly magnetic soils in unpolluted areas are found over weakly magnetic substrates and are dominated by ultrafine superparamagnetic grains magnetotactic bacteria are present in insufficient concentrations to account for strongly magnetic soils and crop burning is discounted as a major factor a small number of samples show high values associated with either airborne magnetic particulates from pollution or residual primary ferrimagnetic minerals from igneous substrates the results are used to construct a new mechanism for the formation of secondary ferrimagnetic minerals that links abiological weathering and biological fermentation processes the fundamental driving force in the mechanism is fe supply which may be linked to climate observed causative associations between climate and the magnetic susceptibility of loess palaeosol sequences are supported by the findings

mineral magnetic characteristics of podzolic soils developed on sand dunes in the lake gosciaz catchment central poland a number of samples from the a0 a2 b and c horizons have been collected from podzolic soils in the lake gosciaz catchment in central poland the catchment is very uniform consisting of 2 6 m high sand dunes with sparse stands of pine and a grass undervegetation radiocarbon dates of fossil soils covered by dune sand within the same type of environment as the lake gosciaz catchment indicate that the main dune forming phase is of older dryas age magnetic measurements have been carried out on bulk samples and on particle size fractions from the different soil horizons with respect to our mineral magnetic study it can be concluded that the soils are very uniform over the entire catchment relatively high concentrations of magnetic grains are found in the humus layer particularly in the 4 m size fraction as indicated by the highest x xfd sirm and hirm values the most likely mechanism for the magnetic enhancement in these podzolic top soils is continued burning processes low magnetic concentrations in the a2 horizon are due to eluviation and chelation local conditions can lead to a range of magnetic minerals precipitating in the b horizon

stages in the life of a magnetic grain sediment source discrimination particle size effects and spatial variability in the south african karoo mineral magnetic properties are commonly used to trace the sources of river and lake sediments with the aim of identifying areas of a catchment experiencing the high rates of soil loss in some areas however there is poor understanding of how magnetic properties are able to discriminate between potential sediment sources the basis for mineral magnetic source discrimination between topsoils and subsurface material over different rock parent materials was investigated in the south african karoo the effects of particle size soil development alteration and diagenesis processes on the source discrimination were investigated good discrimination up to 100 correct discrimination was found between the sedimentary sources soils and subsurface and dolerite soils due to much higher concentrations of magnetic minerals in the dolerite there was little evidence of alterations to magnetic properties in subsurface sediments resulting in only a small ability of properties to differentiate between surface and subsurface sources it was found that during the development of topsoils there was a loss of high coercivity weakly magnetic grains and an enrichment in small superparamagnetic and stable single domain grains particle size was strongly related to magnetic properties with almost all of the secondary superparamagnetic and stable single domain grains created during soil formation being concentrated in the 125 m fractions the small ability of sediment to discriminate between surface and subsurface sources was based upon the dissolution of primarily fd and arm carrying grains in the 32 m fractions and to a lesser extent the 63 32 m fraction as a result it was recommended that source tracing with the 32 m fraction of soils and sediment should be treated separately from the 63 32 m and larger particle size fractions the relationships between particle size and magnetic properties were fairly consistent in all soil samples in each source group raising the possibility that reliable correction factors could be developed for each source group

paleoclimatic forcing of magnetic susceptibility variations in alaskan loess during the late quaternary visual matches and statistical tests suggest correlations between marine isotope curves retrodictive solar insolation at lat 65 n and magnetic susceptibility profiles through late quaternary age alaskan loess sections the susceptibility changes largely appear to reflect variability in magnetite content due to climatically controlled changes in wind intensity and competence magnetic susceptibility profiles through massive loess can provide stratigraphic context for intercalated paleosols and tephras a prominent paleosol correlated with marine isotope stage 5 occurs several metres above the old crow ash in loess sections indicating that this important tephra is older than suggested by thermoluminescence dates and may have been deposited ca 215 25 ka

modern sangamon and yarmouth soil development in loess of unglaciated southwestern illinois abstract the thebes section in unglaciated southwestern illinois contains a well preserved 500 kyr loess paleosol sequence with four loesses and three interglacial soils various magnetic mineralogical and elemental properties were analyzed and compared over the thickness of soil sola these proxies for soil development intensity have the following trend yarmouth geosol sangamon geosol modern soil quartz plagioclase zr sr and tio 2 na 2 o ratios were most sensitive to weathering frequency dependent magnetic susceptibility and anhysteretic remanent magnetization greatest in a horizons also correspond well with soil development intensity neoformed mixed layered kaolinite expandables suggestive of a warm humid climate were detected in the sangamon and yarmouth soil sola clay illuviation in soils was among the least sensitive indicators of soil development differences in properties among interglacial soils are interpreted to primarily reflect soil development duration with climatic effects being secondary assuming logarithmic decreases in weathering rates the observed weathering in the sangamon geosol is consistent with 50 kyr of interglacial weathering oxygen isotope stage 5 compared to 10 kyr for the modern soil oxygen isotope stage 1 we propose that the yarmouth geosol in the central midwest formed over 180 kyr of interglacial weathering including oxygen isotope stages 7 9 and 11

glacial and nonglacial sediment contributions to wisconsin episode loess in the central united states the relative contributions of various glacial and nonglacial sediments to wisconsin episode loess units along the lower illinois and central mississippi valleys are estimated on the basis of a comparison of magnetic susceptibility and silt and clay mineralogy a mathematical method of source area calculation using four compositional parameters was guided by current knowledge of the regional glacial history on the basis of this technique the roxana silt along the illinois and mississippi river valleys is composed of significant superior lobe sediment 35 40 as well as wadena or des moines lobe sediment about 35 this can account for its high magnetic susceptibility feldspar content kaolinite content and pink hue lower peoria silt contains about 25 35 lake michigan lobe sediment with reduced contributions of the other sources after the mississippi river s diversion 20 4 ka the supply of superior des moines and wadena lobe sediment was cut off from the illinois valley in favor of lake michigan lobe sediment 75 80 contribution this major source area shift accounts for higher dolomite and illite contents and a more yellow hue in approximately the upper two thirds of peoria silt in the study area in loess south of st louis less pronounced compositional shifts occur because superior lobe sediment was not cut off and because des moines lobe wadena lobe and missouri river sediments having more intermediate composition compose 40 50 of the loess thereby diluting other source area changes nonglacial sediment from fluvial and periglacial sources is estimated to compose 10 40 of loess in both regions

pre columbian agriculture in the bolivian lowlands construction history and management of raised fields in bermeo abstract recent archaeological research suggests that some parts of the amazon basin were significantly modified by pre columbian populations one of the most impressive examples of such transformations is the raised fields of south western amazonia in the llanos de moxos in the bolivian lowlands despite a growing interest in raised field agriculture due to the important role it seems to have played in the development of pre columbian complex societies very few field based investigations have been performed in the amazon basin as a result there is limited knowledge of how these fields were constructed managed and within which time frame they were in use this study provides a new interpretation of how pre columbian raised fields were managed and a chronological sequence of their utilisation and eventual abandonment fieldwork was carried out in the indigenous community of bermeo in the vicinity of san ignacio de moxos where some of the best preserved fields in the llanos moxos are found magnetic susceptibility and the geochemistry of the sediments combined with radiocarbon and optically stimulated luminescence dating show that the raised fields were in intermittent use since as early as ad 570 770 the original surface on which the fields were built and distinct periods of construction and use have been identified the data suggests that raised fields were built during a few separate construction events probably linked to periods of more frequent and severe floods the study challenges the most widely accepted theory that suggests that pre columbians were able to cultivate these fields on a continuous basis by transferring nutrient rich sediments from the canals to the fields we conclude that pre columbians built raised fields to overcome periods of increased flooding with the main objective of improving drainage

upper and mid mantle anisotropy beneath the tonga slab measurements of source side splitting in s waves fromevents within the tonga slab reveal anisotropy in the upperand mid mantle beneath the slab we observed splitting forevents originating at both upper mantle and transition zonedepths anisotropic fast directions are trench parallel orsub parallel for both upper mantle and transition zoneevents delaytimes dt decreasewithdepthforuppermantleevents the source of anisotropy for the upper mantle eventsis likely in the sub slab mantle and is likely indicative oftrench parallel flow due to slab rollback the source ofanisotropy for the deeper earthquakes is more difficult toconstrain but the pattern of splitting measurements arguesfor an uppermost lower mantle anisotropic source and slabinduced deformation may be responsible for this anisotropyas well additional constraints from mineral physics studiesare necessary to interpret the mid mantle anisotropy signalin terms of geodynamical processes

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

magnetic indicator of global paleoclimate cycles in siberian loess paleosol sequences abstract the loess paleosol sequences of china siberia alaska and many other regions along with lake sediments and glaciers provide the only accurate paleoclimatic terrestrial records for intervals of thousands to hundreds of thousand years the frequency dependence fd of magnetic susceptibility ms in such sequences has become the leading parameter for analyzing climatic change and milankovitch astronomical periodicity in siberian sequences it is always higher in soil horizons than in loess the enhanced fd parameter in soils is associated with ferromagnetic minerals mostly magnetite produced during pedogenesis the ms and fd parameters of 670 samples from five sections in siberia are reported here inter section correlation is used to produce a combined fd time series for the studied sections chronological control is established by absolute dating and stratigraphic correlation spectral analysis of the fd time series reveals the presence of milankovitch signals at 100 kyr eccentricity 40 kyr obliquity and 23 kyr precession and demonstrates that siberian loess paleosol sequences are excellent continental recorders of long term paleoclimatic changes this suggests that the fd parameter can potentially be used more widely for evaluation of climate periodicity in loess paleosol sequences in other parts of the world

vertical mantle flow associated with a lithospheric drip beneath the great basin rapid surface uplift or subsidence and voluminous magmatic activity have often been ascribed to regional scale downwelling of lithospheric mantle however because lithospheric drips sinking plumes of cold and dense lithosphere are relatively small and transient features direct evidence of their existence has been difficult to obtain moreover the significant vertical mantle flow that should be associated with such structures has not been detected here we integrate seismic anisotropy data with tomographic images to identify and describe a lithospheric drip beneath the great basin region of the western united states the feature is characterized by a localized cylindrical core of cooler material with fast seismic velocities and mantle flow that rapidly shifts from horizontal to vertical our numerical experiments suggest that the drip can be generated by gravitational instability resulting from a density anomaly of as little as 1 and a localized temperature increase of 10 the drip tilts to the northeast opposite to the motion of the north american plate in the hotspot reference frame and thereby indicates northeast directed regional mantle flow seismic anisotropy data for the great basin region of the western united states coupled with tomographic images help delineate a northeast dipping lithospheric drip numerical experiments suggest that the drip could have formed owing to gravitational instability triggered by a density increase of about 1 and a temperature increase of about 10

seismic anisotropy indicators in western tibet shear wave splitting and receiver function analysis abstract using recently collected data from western tibet we find significant variation in the strength vertical distribution and attributes of seismic wave speed anisotropy constrained through a joint application of teleseismic shear wave splitting techniques and a study of p s mode converted waves receiver functions we find that the crust of tibet is characterized by anisotropy on the order of 5 15 concentrated in layers 10 20 km in thickness and with relatively steep 30 45 from the vertical slow symmetry axes of anisotropy these layers contribute no more than 0 3 s to the birefringence in teleseismic shear waves significantly smaller than splitting in many of the observations and much smaller than birefringence predicted by models developed through group inversions of shear wave recordings consequently we interpret models constrained with shear wave observations in terms of structures in the upper mantle near the altyn tagh fault our data favor a two layer model with the upper layer fast polarization approximately aligned with the strike of the fault near the karakorum fault our data are well fit with a single layer of relatively modest 0 5 s delay anisotropy fast polarization in this layer is 60 ne similar to that of the lower layer in the model for the altyn tagh fault site assuming that layers of similar anisotropic properties at these two sites reflect a common cause our finding favors a scenario where indian lithosphere under thrusts a significant fraction of the plateau data from a site at the southern edge of the tarim basin appear to be inconsistent with a common model of seismic anisotropy distribution we suspect that thick sediments underlying the site significantly distort observed waveforms our ability to resolve features of anisotropic structure in the crust and the upper mantle of western tibet is limited by the small amount of data collected in a 6 month observing period we stress the importance of future teleseismic data collection in tibet over extended periods to insure better directional distribution of observed seismic sources

iron isotope geochemistry of biogenic magnetite bearing sediments from the bay of vidy lake geneva article dissimilatory microbial iron oxide reduction dir has been hypothesized to be an important respiratory pathway on early earth potentially generating significant quantities of fe ii that have been preserved in proterozoic and archean sedimentary rocks in particular dir has been implicated in the formation of magnetite inprecambrian marine sediments todate however onlyone modern sedimentary environmentexists wherein situ magnetite formation has been linked to dir the bay of vidy in lake geneva switzerland previous work at this locality has characterized a magnetic susceptibility anomaly that reflects the presence of fine grained magnetite produced viamicrobial reduction of amorphous fe iii oxidesthat enterthebayof vidy from a nearby sewage treatment plant in this study we report on the fe isotope composition of aqueous and solid phase fe in the bay of vidy sediments extensive fe iii reduction has occurred resulting in the conversion of nearly all reactive non silicate fe iii to a variety of fe ii bearing phases with mixed fe valence magnetite being a minor but easily detectable component 0 5 8 wt very little fe isotope variation was observed in any solid phase fe components including magnetite although significant fractionation was observed between aqueous and solid phase fe ii because fe mass balance was dominated by the solid phase little net change in 56 fe

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

alluvial landform and the occurrence of paleosols in a humid subtropical climate have an effect on long term soil organic carbon storage abstract soil organic carbon soc storage in alluvial depositional zones is important as it serves as a centennial to millennial timescale sink of c this study examines soc variability in alluvial bars floodplains and terraces in a forested humid subtropical setting along the clarks river in the mississippi river basin mrb using replicated soil sampling characterization and modeling soil and depositional profiles range in age from a minimum of 8000 years ago to modern normalized by depth mean soc stocks kg m 2 of the surface soil and buried layers i e buried soils and layers underlying lithologic discontinuities are highest in the terraces normalized mean surface soc stocks decrease from terraces to floodplains and then to bars whereas normalized mean buried layer soc stocks decrease from terraces to bars and then floodplains the depth distribution of stocks showed that buried layers accounted for 50 of the total soc pool regardless of landform type a regression tree analysis shows that soil horizon ph landform and magnetic susceptibility were significant predictors of mean soc content notably the regression tree shows that alkaline ph 7 9 observed only in buried layers in the terrace is an important predictor in higher mean soc these alkaline soil ph values were associated with paleosol calcite where the 13c and 14c from the calcite suggests it formed under c3 vegetation during the drier than modern mid holocene hypsithermal 8000 years ago buried soil and sediment contain the majority of the soc in this humid subtropical valley bottom while landform position and past buried soil forming environments paleosols played an important role in the storage of that soc this work reconfirms that there is a long record of a passive buried soc pool found deep in our river valley bottoms that holds clues to the past biogeochemical cycling of c on land prior to intensive agriculture and industrialization the legacy of past holocene climates and paleosols are directly linked to our current understanding of long term storage of soc

a uniformly processed data set of sks shear wave splitting measurements a global investigation of upper mantle anisotropy beneath seismic stations anisotropy in the earth s upper mantle is a signature of past and present deformation here we present a new data set of 50 000 uniformly processed sks shear wave splitting measurements that probe upper mantle anisotropy beneath seismic stations in the frequency band 0 02 0 1 hz the data set consists of measurements obtained at 2000 seismic stations from 2000 events we identify several stations characterized by an apparent absence of shear wave splitting so called null stations station averaged measurements are obtained by stacking shear wave splitting error surfaces the stacked data set shows excellent agreement with a compilation of previous sks measurements the average amount of splitting beneath seismic stations after error surface stacking is 0 8 s slightly lower than that found previously by vectorial averaging of non null measurement splitting parameters the data set disagrees however with an azimuthally anisotropic surface wave tomography model dkp2005 suggesting that caution should be exercised when using such models for geodynamic interpretation especially in continental regions studying our data set in detail we find evidence that flow in the asthenosphere exerts partial control over sks splitting in orogenic regions globally in the active orogenic environment of the western usa where we have the densest coverage our data suggest that shallow asthenospheric flow is guided by a wall of thick lithosphere to the east

fingerprinting upland sediment sources particle size specific magnetic linkages between soils lake sediments and suspended sediments accelerated erosion of fine grained sediment is an environmental problem of international dimensions erosion control strategies and targeting of mitigation measures require robust and quantitative identification of sediment sources here we use magnetic fingerprinting to characterize soils and examine their affinity with and contribution to suspended sediments transported within two subcatchments feeding bassenthwaite lake northwest england a high resolution soil magnetic susceptibility survey was made using a field susceptometer zh instruments sm400 probe combining the spatial and vertical down profile soil magnetic data a subset of soil profiles was selected for detailed laboratory based magnetic remanence analyses the magnetic properties of the catchment soils are highly particle size dependent magnetic analyses were performed on the 31 63 m fraction for particle size specific comparison both with the suspended sediments and lake sediments fuzzy cluster analysis groups the soil magnetic data into six clusters apparently reflecting variations in parent material and horizon type with three magnetically hard soils as unclassified outliers examination of the cluster affinity of the soils suspended sediments and lake sediments indicates that topsoils of the upper newlands valley and subsoils around keskadale beck are a major source of the newlands beck suspended load and the recent post nineteenth century sediments in the deep lake basin older lake sediments show strong affinity with a small number of the derwent suspended sediments and one of the glenderamackin soils a large number of derwent suspended sediments show no affinity with any of the soils or lake sediments instead forming a coherent discrete and statistically unclassified group possibly resulting from mixing between the magnetically hard subsoils of the medium to high altitude glenderamackin and troutbeck areas and softer lower altitude glenderamackin soils the lack of any affinity of these suspended sediments with the lake sediments may indicate deposition along the derwent flood plain and or in the shallow delta of lake bassenthwaite particle size specific magnetic fingerprinting is thus shown to be both highly discriminatory and quantitatively robust even within the homogeneous geological units of this catchment area such a methodological approach has important implications for small large scale catchment management where sources of sediment arising from areas with uniform geology have been difficult to determine using other approaches such as geochemical or radionuclide analyses

characterisation of soils by mineral magnetic measurements processes of iron mineral authigenesis diagenesis and dissolution in interaction with primary inputs of iron minerals act to produce vertical differentiation of soil magnetic properties thus magnetic iron oxides in common with other iron forms may both respond to and reflect soil forming processes investigation of the degree of detectable and persistent magnetic differentiation within different soil materials can provide insights into the nature and direction of distinct sets of soil processes evidence of clear association between magnetic variation and discrete types of soil environment also has applied significance in several areas of environmental study for example the observed magnetic variation can be used to discriminate between individual soils and soil horizons for the purposes of soil surveying sediment tagging and tracing and empirical modelling of source sediment linkages this paper reports the use of mineral magnetic techniques to characterise the iron oxide assemblages within soils of varying type and provenance the effect of different pedogenic regimes have been investigated through measurement of a range of magnetic parameters including magnetic susceptibility frequency dependent susceptibility and anhysteretic and saturation remanences contrary to current pedological thought but in accord with other magnetically based studies e g mullins the presence of magnetite maghemite typically of superparamagnetic single domain grain size within soils has been found to be an extremely widespread phenomenon its contemporary neoformation within the soil environment is inferred however the input of artificially generated ferrimagnetic material is indicated for one of the magnetically enhanced soils examined here and the possibility of extraneous sources of magnetite in topsoils should be considered before pedogenic processes of magnetic enhancement are inferred from the data presented discrimination of industrially derived magnetic particles appears possible on the basis of their very low levels of frequency dependent susceptibility fd low anhysteretic remanence arm and dissociation from the finer clay sized not the formation but the active dissolution of ferrimagnetic minerals is indicated for soils affected by the processes of gleying and podsolisation eluvial horizons of podsolised profiles demonstrate almost total loss of detectable magnetic content variations in the form of the iron reprecipitated in the underlying illuvial layers may reflect differences in the pedological characteristics of these horizons within gleyed waterlogged soils processes of magnetite dissolution appear to be grain size specific preferential reduction of those grains of ultrafine superparamagnetic and fine single domain magnetic grain size is indicated where soil forms a major contributor to catchment sediment loads this has significance in the area of source sediment modelling soil derived from permanently wet or highly leached catchment areas is unlikely to contribute to peaks in the magnetic content of deposited sediments further only those erosional processes that operate at a faster rate than those of magnetic depletion will have the capacity to produce peaks in sediment ferrimagnetic concentrations such as have been observed within the historical magnetic record

shear wave splitting and implications for mantle flow beneath the melt region of the east pacific rise shear wave splitting across the fast spreading east pacific rise has been measured from records of sks and skks phases on the ocean bottom seismometers of the mantle electromagnetic and tomography melt experiment the direction of fast shear wave polarization is aligned parallel to the spreading direction delay times between fast and slow shear waves are asymmetric across the rise and off axis values on the pacific plate are twice those on the nazca plate splitting on the pacific plate may reflect anisotropy associated with spreading induced flow above a depth of about 100 km as well as a deeper contribution from warm asthenospheric return flow from the pacific superswell region

rock magnetism and pedogenetic processes in luvisol profiles examples from central russia and central mexico abstract despite a vast literature concerning magnetic properties of loess sequences we still do not fully understand how magnetic components and properties are related to particular soil forming processes that can vary with each type of genetic horizon in order to establish the role of lithogenic factors in the link between magnetic properties and soil forming processes we carried out a study of two complete profiles of buried interglacial luvisols one formed in loess in russia alexandrovsky quarry and the other in volcaniclastics in mexico barranca tlalpan in both profiles soil genetic horizons have contrasting differences of their magnetic properties in the alexandrovsky profile the magnetic susceptibility is enhanced in the paleosol compared to parent material in the barranca tlalpan sequence enhancement is absent in the soil profile increase of fine grained magnetic components in the soil is attributed to neoformed minerals however this process cannot compensate for the loss of lithogenic magnetic minerals in any of the genetic horizons and the resulting trend is depletion in the whole soil profile the pedogenic environment of eluvial horizons in both luvisols is destructive to all magnetic components both primary and secondary higher concentrations of antiferromagnetic components hematite and goethite found in e horizons are related to redoximorphic processes

a quantitative model of magnetic enhancement in loessic soils we present a quantitative model for the climatic dependence of magnetic enhancement in loessic soils the model is based on the widely accepted hypothesis that ultrafine magnetite precipitates during alternating wetting and drying cycles in the soil micropores the rate at which this occurs depends on the frequency of drying wetting cycles and on the average moisture of the soil both parameters are estimated using a statistical model for the soil water balance that depends on frequency and intensity of rainfall events and on water loss by evapotranspiration monthly climatic tables are used to calculate the average soil moisture and the rate of pedogenic magnetite production which is proportional to a new parameter called magnetite enhancement proxy mep our model is tested by comparing mep calculated for known present day climates with the magnetic enhancement of modern soils the magnetic enhancement factor defined as the ratio between a given magnetic enhancement parameter and mep is expected to be a site independent constant we show that magnetic enhancement differences between soils from the chinese loess plateau and from midwestern u s are explained by our model which yields similar magnetic enhancement factors for the two regions our model is also successful in predicting the mean annual rainfall threshold above which magnetic enhancement declines in a given type of climate

mineral magnetic properties of chinese paddy soils and its pedogenic implications abstract magnetic susceptibility ms of paddy soils hydragric anthrosols and their corresponding dryland soils formed on the same parent materials in zhejiang province of eastern china were measured in order to understand better magnetic profile discrimination and pedogenic magnetic minerals in paddy soils magnetic measurements showed that the ms values of paddy soils were much lower than those of dryland soils formed on the same parent materials the higher the ms value of the original dryland soil is the more remarkable the decrease in the ms value is when the soil is put under rice cultivation gleyed paddy soils exhibited very low ms value

secondary ferrimagnetic minerals in welsh soils a comparison of mineral magnetic detection methods and implications for mineral formation summary a range of low temperature and isothermal magnetic measurements are used to identify the secondary ferrimagnetic mineral sfm grain sizes in 10 representative soil samples from wales a comparison of percentage frequency dependent susceptibility fd percentage and low temperature remanence measurements shows that they are sensitive to different ranges of superparamagnetic sp grains the relative distributions of sp grains and stable single domain ssd grains are similar in nine of the samples typical distributions for soils dominated by sfms are 20 30 per cent ssd and 70 80 per cent sp multidomain md grains were not detected in the samples studied there is evidence that some soils contain significant numbers of ultrafine sp grains 0 010 m that are not detected by low temperature remanence measurements at 20 k and which will have the effect of depressing values of low field susceptibility lf and fd percentage a mixing model suggests that fd percentage may be used semi quantitatively to estimate the proportion of sp grains in a sample the positively skewed grain size distributions strongly suggest a mechanism of sfm formation that is driven by processes at the 10 8 m scale thus supporting weathering and fermentation as controlling processes rather than the degradation of ssd bacterial magnetosomes and primary minerals

using magnetic susceptibility to facilitate more rapid reproducible and precise delineation of hydric soils in the midwestern usa abstract standard field indicators currently used for hydric soil delineations usda nrcs 1998 field indicators of hydric soils in the united states version 4 0 in g w hurt et al ed united states department of agriculture nrcs fort worth tx are useful but in some cases they can be subjective difficult to recognize or time consuming to assess magnetic susceptibility ms measurements acquired rapidly in the field with a portable meter have great potential to help soil scientists delineate and map areas of hydric soils more precisely and objectively at five sites in illinois from 5 to 15 ha in area with contrasting soil types and glacial histories the ms values of surface soils were measured along transects and afterwards mapped and contoured the ms values were found to be consistently higher in well drained soils and lower in hydric soils reflecting anaerobic deterioration of both detrital magnetite and soil formed ferrimagnetics at each site volumetric ms values were statistically compared to field indicators to determine a critical ms value for hydric soil delineation such critical values range between 22 10 5 and 33 10 5 si in silty loessal or alluvial soils in illinois but are as high as 61 10 5 si at a site with fine sandy soil a higher magnetite content and slower dissolution rate in sandy soils may explain the difference among sites with silty parent material the lowest critical value 22 10 5 si occurs in soil with low ph 4 5 5 5 since acidic conditions are less favorable to ferrimagnetic mineral neoformation and enhance magnetite dissolution because of their sensitivity to parent material properties and soil ph critical ms values must be determined on a site specific basis the ms of studied soil samples 0 5 cm depth is mainly controlled by neoformed ultrafine ferrimagnetics and detrital magnetite concentrations with a minor contribution from anthropogenic fly ash neoformed ferrimagnetics are present in all samples but based on high fd 5 to 10 are most prevalent in high ph mollisols of northeastern illinois scanning electron microscope images display significantly more detrital magnetite alteration in hydric soils substantiating that reductive dissolution of magnetite aided by microorganisms is a primary cause for lower ms fly ash comprises 8 50 of the 5 m strongly magnetic particles and typically accounts for 5 15 of the total ms signal the proportion of fly ash in 5 m strongly magnetic fractions is greater in hydric soils because of lower natural magnetite contents possibly combined with historical topsoil accumulation in lower landscapes magnetic fly ash particles are also more altered in low ms soils implying that significant magnetite dissolution can occur in less than 150 years

lithosphere asthenosphere interaction beneath the western united states from the joint inversion of body wave traveltimes and surface wave phase velocities summary the relation between the complex geological history of the western margin of the north american plate and the processes in the mantle is still not fully documented and understood several pre usarray local seismic studies showed how the characteristics of key geological features such as the colorado plateau and the yellowstone snake river plains are linked to their deep mantle structure recent body wave models based on the deployment of the high density large aperture usarray have provided far more details on the mantle structure while surface wave tomography ballistic waves and noise correlations informs us on the shallow structure here we combine constraints from these two data sets to image and study the link between the geology of the western united states the shallow structure of the earth and the convective processes in mantle our multiphase dna10 s model provides new constraints on the extent of the archean lithosphere imaged as a large deeply rooted fast body that encompasses the stable great plains and a large portion of the northern and central rocky mountains widespread slow anomalies are found in the lower crust and upper mantle suggesting that low density rocks isostatically sustain part of the high topography of the western united states the yellowstone anomaly is imaged as a large slow body rising from the lower mantle intruding the overlying lithosphere and controlling locally the seismicity and the topography the large e w extent of the usarray used in this study allows imaging the slab graveyard a sequence of farallon fragments aligned with the currently subducting juan de fuca slab north of the mendocino triple junction the lithospheric root of the colorado plateau has apparently been weakened and partly removed through dripping the distribution of the slower regions around the colorado plateau and other rigid blocks follows closely the trend of cenozoic volcanic fields and ancient lithospheric sutures suggesting that the later exert a control on the locus of magmato tectonic activity today the dna velocity models are available for download and slicing at http dna berkeley edu

timescales for the evolution of seismic anisotropy in mantle flow 1 we study systematically the relationship between olivine lattice preferred orientation and the mantle flow field that produces it using the plastic flow recrystallization model of kaminski and ribe 2001 in this model a polycrystal responds to an imposed deformation rate tensor by simultaneous intracrystalline slip and dynamic recrystallization by nucleation and grain boundary migration numerical solutions for the mean orientation of the a axes of an initially isotropic aggregate deformed uniformly with a characteristic strain rate show that the lattice preferred orientation evolves in three stages 1 for small times recrystallization is not yet active and the average a axis follows the long axis of the finite strain ellipsoid 2 for intermediate times the fabric is controlled by grain boundary migration and the average a axis rotates toward the orientation corresponding to the maximum resolved shear stress on the softest slip system 3 for the fabric is controlled by plastic deformation and average a axis rotates toward the orientation of the long axis of the finite strain ellipsoid corresponding to an infinite deformation the infinite strain axis in more realistic nonuniform flows lattice preferred orientation evolution depends on a dimensionless grain orientation lag parameter x defined locally as the ratio of the intrinsic lattice preferred orientation adjustment timescale to the timescale for changes of the infinite strain axis along path lines in the flow explicit numerical calculation of the lattice preferred orientation evolution in simple fluid dynamical models for ridges and for plume ridge interaction shows that the average a axis aligns with the flow direction only in those parts of the flow field where 1 calculation of provides a simple way to evaluate the likely distribution of lattice preferred orientation in a candidate flow field at low numerical cost

magnetic investigation of late quaternary loess deposition ili area china abstract a late quaternary loess section in ili river valley xinjiang northwest china has been studied magnetically samples from two sections exhibit variations in magnetic susceptibility which displays a positive relationship with pedogenesis intensity in s 0 and negative in s 1 and l 1 the detailed magnetic properties investigation reveals that concentration of initial magnetite and maghemite fm varies and may be dominated by wind intensity and source mineralogy furthermore this is the most important magnetic component influencing magnetic properties of loess paleosol sequences and controls magnetic properties of loess deposition in contrast concentration of pedogenic fm is low and has little influence on magnetic properties of loess however it is an ideal magnetic parameter to assess paleoclimate the magnetic minerals in s 1 soil units might be linked to reducing environments reflected by the enhancement of the coercive force of remanence

mantle anisotropy beneath the earth s mid ocean ridges observations of seismic anisotropy at oceanic spreading centres offer insights into mid ocean ridge processes and the formation of new plates here remote observations of seismic anisotropy beneath mid ocean ridges are made using measurements of source side shear wave splitting over 100 high quality measurements are made using earthquakes that occur near mid ocean ridges and transform faults but are observed at teleseismic distances in general for off axis ridge events the polarisation of fast shear waves phi prime prime is approximately parallel to the spreading direction nearer the ridge lesssim 50 km phi prime prime becomes more scattered and is often ridge parallel delay times delta t tend to increase from 1 s near the ridge axis to sim 3 s further away slow spreading regions gakkel and southwest indian ridges show smaller amounts of splitting than faster spreading centres at transform zones the pattern is more complex coverage beneath the east pacific rise is especially good and we observe a systematic increase in delay times in s wave splitting measurements compared to previous sks splitting observations made at ocean bottom seismometers one compatible explanation is the presence of horizontally aligned connected layers of melt at depth with an inclusion density which increases near the top of the layer this is also compatible with other observations of the lab discontinuity and surface wave derived measurements of radial anisotropy

paleosols bones phytoliths and δ13c signatures of humus and teeth in the alluvial sequence of axamilpa puebla inferences for landscape evolution and megafauna paleoecology during mis 3 2 in southern mexico abstract alluvial paleosol sedimentary sequences containing animal fossils and paleobotanical and paleopedological archives have a potential for reconstructing quaternary paleoenvironments in southern mexico and for understanding the paleoecology of pleistocene megafauna in the section of axamilpa river four pedostratigraphic units were recognized the lower gleyic and vertic pedological units are at the end of marine isotopic stage mis 3 while the upper humic and most probably calcic units correspond to mis 2 according to the radiocarbon dates of humus the micromorphological analysis indicates an incipient development and syn sedimentary character of paleopedogenesis in the periodically water saturated environment indicated by redoximorphic features hydrogenic carbonates and low values of magnetic susceptibility in most strata the 13 c values of the paleosol humus range from 22 6 to 24 7 indicating a c3 vegetation whereas in the modern soil it is higher 15 2 pointing to an abundance of the c4 and cam plants the 13 c signature of the vegetation inferred from the teeth enamel of the fossil fauna appeared to be less negative than that of humus from corresponding paleosols the alimentary preferences of the paleofauna which fed on grasses with high proportion of c4 plants explain this difference the phytolith analysis shows dominance in conifer forms followed by c4 and c3 grasses the content of conifer phytoliths is progressively reduced towards the top of the sequence we interpret the late pleistocene landscape of this area as a heterogeneous forest grassland landscape with the forest shrinking through time and the grass areas increasing swampy floodplain meadows inferred from paleopedological results could provide a habitat for grassy vegetation both isotope and phytolith records demonstrate a contrasting difference between pleistocene and recent vegetation dominated by xerophytic shrubs and succulents this vegetation change could play important role in the extinction of pleistocene megafauna

global azimuthal seismic anisotropy and the unique plate motion deformation of australia differences in the thickness of the high velocity lid underlying continents as imaged by seismic tomography have fuelled a long debate on the origin of the roots of continents1 2 3 4 5 some of these differences may be reconciled by observations of radial anisotropy between 250 and 300 km depth with horizontally polarized shear waves travelling faster than vertically polarized ones2 this azimuthally averaged anisotropy could arise from present day deformation at the base of the plate as has been found for shallower depths beneath ocean basins6 such deformation would also produce significant azimuthal variation owing to the preferred alignment of highly anisotropic minerals7 here we report global observations of surface wave azimuthal anisotropy which indicate that only the continental portion of the australian plate displays significant azimuthal anisotropy and strong correlation with present day plate motion in the depth range 175 300 km beneath other continents azimuthal anisotropy is only weakly correlated with plate motion and its depth location is similar to that found beneath oceans we infer that the fast moving australian plate contains the only continental region with a sufficiently large deformation at its base to be transformed into azimuthal anisotropy simple shear leading to anisotropy with a plunging axis of symmetry may explain the smaller azimuthal anisotropy beneath other continents

geochemical normalization of magnetic susceptibility for investigation of floodplain sediments magnetic susceptibility ms is commonly used as a proxy for industrial pollution in natural sediments or as a proxy for the percentage of detrital components in peat or carbonates the ms may also reflect the geology of the sediment source and post depositional processes in sediments such as soil development the aim of our research was to test the usefulness of fe normalized mass specific ms and ti normalized fe in a study of floodplain sediments we sampled 27 floodplain sediment cores from several geologically different catchments throughout the czech republic analysed their fe and ti concentrations using x ray fluorescence spectroscopy and determined their to decipher sediment grain size dependence and possible magnetic enrichment background functions for were constructed using similar approach as that used for geochemical background functions of the risk element concentrations with fe concentrations as an independent variable it provides a mechanism to calculate of sediments as it would be pristine i e without post depositional changes and pollution sediments derived from mafic source rocks had fe larger by two orders of magnitude than sediments derived from felsic rocks sediments derived from mafic source rocks also exhibit lower mean fe ti ratio in pristine sediment strata than the average upper continental crust the magnetic carriers inherited from mafic rocks are stepwise destroyed by pedogenesis in the floodplains and thus slowly approach of sediments derived from felsic rocks gleying processes may change fe fe ti ratio allows identifying a past action of those post depositional processes

deformation and mantle flow beneath the sangihe subduction zone from seismic anisotropy abstract subduction of oceanic lithosphere is the most direct feedback between the earth s surface and deep interior however the detail of its interaction with the broader convecting mantle is still unclear mantle flow around subduction zones can be constrained using seismic anisotropy but despite many such studies a simple global picture is lacking the sangihe subduction zone where the molucca sea microplate is subducting westward beneath the eurasian plate is part of the tectonically complex sulawesi philippine region and an ideal natural laboratory to study complex subduction processes we investigate the anisotropic structure of the sangihe subduction zone with shear wave splitting measurements of local s and sks phases at two stations mni in sulawesi dav in the philippines as well as downgoing s phases at five stations at teleseismic distances combining different phases allows a better vertical resolution of anisotropic fabrics than is possible with a single phase the broad depth distribution of local events 60 630 km allows us to observe a change in splitting behaviour at 380 km depth above fast directions are trench parallel and delay times t are 0 34 0 53 s with no increase with depth we suggest this anisotropy is caused by aligned cracks possibly melt filled beneath the volcanic arc and fossil anisotropy in the overriding plate below 380 km is predominantly trench normal and t are slightly higher 0 53 0 65 s as no correlation is observed with inferred distance travelled inside the slab we attribute this anisotropy to shear layers atop the slab which are coherent from 200 to 400 km depth and perhaps extend into the transition zone sks and source side measurements show larger t 1 53 and 1 33 s respectively and trench parallel since these phases predominantly sample sub slab mantle we consider along strike lateral flow associated with the double sided subduction of the molucca sea microplate to be the most likely explanation we thus infer three dominant regions of anisotropy at the sangihe subduction zone one within the overriding lithosphere one along the slab wedge interface and one below the subducting molucca sea slab the mantle wedge above 200 km depth and the slab itself do not seem to contribute notably to the measured anisotropy this study demonstrates the insight seismic anisotropy can provide into mantle dynamics even in tectonically complex subduction systems

magnetic analyses of soils from the wind river range wyoming constrain rates and pathways of magnetic enhancement for soils from semiarid climates in order to constrain the rate of magnetic enhancement in soils we investigated modern soils from five fluvial terraces in the eastern wind river range wyoming profiles up to 1 2 m deep were sampled in 5 cm intervals from hand dug pits or natural riverbank exposures soils formed in fluvial terraces correlated to the sacajawea ridge 730 610 ka bp bull lake 130 100 ka bp and pinedale age 20 ka bp glacial advances one soil profile formed in holocene age sediment abundance mineralogy and grain size of magnetic minerals were estimated through magnetic measurements magnetic enhancement of the a horizon as well as an increase in fine grained magnetic minerals occurred mostly in bull lake profiles but was absent from the older profile such low rates of magnetic enhancement may limit the temporal resolution of paleosol based paleoclimate reconstructions in semiarid regions even where high sedimentation rates result in multiple paleosols a loss of ferrimagnetic and an increase in antiferromagnetic minerals occurred with age our findings suggest either the conversion of ferrimagnetic minerals to weakly magnetic hematite with progressing soil age or the presence of ferrimagnetic minerals as an intermediate product of pedogenesis absolute and relative hematite abundance increase with age making both useful proxies for soil age and the dating of regional glacial deposits all coercivity proxies are consistent with each other which suggests that observed changes in hirm and s ratio are representative of real changes in hematite abundance rather than shifts in coercivity distributions even though the modified l ratio varies widely

magnetic properties of modern soils and quaternary loessic paleosols paleoclimatic implications the magnetic properties of paleosols developed in quaternary sequences of loess have been used for stratigraphic definition correlation with other terrestrial and deep sea sequences and paleoclimatic paleorainfall reconstruction in some loess paleosol sequences including those of the chinese loess plateau tajikistan and the czech republic maxima in magnetic susceptibility values correspond with the paleosol horizons and minima with the least weathered loess layers in other loess soil sequences including those of siberia alaska and argentina the relationship is completely opposite with susceptibility minima associated with the most developed paleosols to account for these opposite relationships the respective roles of 1 magnetic enhancement and 2 magnetic depletion and or dilution in determining soil magnetic properties are investigated for a range of modern soil types most magnetic enhancement is seen in the upper horizons of well drained cambisols absence or loss of magnetic iron oxides is apparent in acid podsol profiles and waterlogged soils for the cambisol profiles significant correlation is found between susceptibility and organic carbon cation exchange capacity and clay content the mineralogy morphology and grain size of soil magnetic carriers extracted from three modern enhanced soils and a paleosol from the chinese loess plateau are also identified by independent petrographic means microscopy and x ray diffraction of magnetic extracts magnetite and maghemite of ultrafine grain size from 0 4 to 0 001 i m are the major contributors to the magnetically enhanced soils weathering can concentrate detrital magnetic grains especially in the fine silt size fractions of soils the magnetic data from the modern soils indicate that interpretation of paleosol magnetic properties must be done on a site specific basis taking into account the possibilities of pedogenic enhancement pedogenic dilution or depletion and allochthonous inputs of magnetic minerals excessively arid wet or acid soils are unable to form significant amounts of pedogenic ferrimagnets well drained intermittently wet dry soils with reasonable buffering capacity and a substrate source of fe show most magnetic enhancement for those soils which favour magnetic enhancement processes correlation has been found between the maximum value of the pedogenic susceptibility and the annual rainfall the almost unique pedogenic system in the chinese loess plateau where variation in soil forming factors other than climate is reduced to a global minimum allows use of the paleo susceptibility values as proxy paleorainfall values to identify the mechanism of any link between magnetic properties for example susceptibility and climate change the mineralogy and grain size of soil magnetic carriers requires detailed investigation given the prospect of 1 quantitative paleorainfall records from continental loess records 2 predictions of present and future climate change and 3 the value of paleoclimate data for testing of numerical climate models such magnetic investigations can contribute significantly to our understanding of past and future environmental change

evidence for the dissolution of magnetite in recent scottish peats abstract magnetic hydrological and geochemical data for 11 scottish peat cores confirm previous reports that anthropogenic pollutants constitute the principal source of ferrimagnets to such environments but indicate that postdepositional fe3o4 persistence may be more limited than formerly envisaged in all cores the lower stratigraphic limit of magnetic enrichment coincides with the water table below which negative mv values and enhanced ratios of fe mn and cu zn depict an abrupt transition to a strongly anoxic regime dissolution of fe3o4 in the reducing inundated zone is also signified by the more rapid down core loss of magnetic properties in cores from topographically depressed sphagnum lawns than in those from more elevated calluna hummocks as a consequence the peak and cumulative sirm values for cores from the former settings appear disproportionately low and the magnetostratigraphic records from adjacent but topographically variant sites are frequently asynchronous in contrast to most marine and lacustrine sediments dissolution of fe3o4 in peat induces a refinement of magnetic mineral assemblages highlighted by declining sirm arm ratios with depth and a hardening of remanence near the base of the magnetically enhanced strata sem micrographs of magnetic extracts from one scottish core indicate that this refinement results from preferential dissolution along crystallographic weaknesses within multidomain phases ultimately causing their disintegration and the adoption of single domain type magnetic behavior rates of dissolution are considerably greater than those reported for marine sediments probably due to the unusually high dissolved sulfide concentrations in mire waters

interrelation of magnetic susceptibility soil color and elemental mobility in the pliocene pleistocene siwalik paleosol sequences of the nw himalaya india abstract apart from imparting color characteristics the precipitation and dissolution of fe oxides and hydroxides during pedogenesis is coeval with transformation and translocation of major and trace elements based on rock magnetic and geochemical parameters for 27 paleosol profiles from three stratigraphic columns of pliocene pleistocene siwalik sequence in the nw himalaya we describe here the relationship amongst elemental mobility munsell color and low field mass normalized magnetic susceptibility lf the study shows a consistent positive correlation of the rock magnetic parameters principally magnetic susceptibility with munsell hue and redness rating rr index torrent et al 1980 blavet et al 2000 of the soil profiles the late miocene profiles show an increase of 29 of al 2 o 3 concentration and that for the pliocene and pleistocene profiles show 33 to 60 increase as a result of pedogenesis similarly the other immobile elemental oxide fe 2 o 3 is increased by 54 in the late miocene profiles and 50 to 63 in the pliocene pleistocene profiles geochemical trends correlate with the lf showing r 2 0 39 to 0 68 with al 2 o 3 and fe 2 o 3 and r 2 0 40 to 0 73 for sio 2 similarly the munsell color parameters especially the rr index display significant positive correlation where the magnetic mineralogy is dominated by hematite and goethite these first order relationships amongst lf rr index and elemental mobility demonstrate the potential use of magnetic susceptibility for rapid characterization of the widespread and heterogeneous pedogenic episodes within the dynamic sedimentary environments of the himalayan foreland basin

shear wave splitting beneath western united states in relation to plate tectonics we have examined shear wave splitting in teleseismic shear waves from 26 broadband stations in the western united states fast polarization directions and delay times t show spatial variations that are coherent within geologic provinces stations located near the san andreas fault show clear evidence for fault parallel anisotropy in the crust and upper mantle 115 125 km thickness this can be explained by the finite strain associated with the relative plate motion between the north american and pacific plates the lateral extent of this strain field is probably narrow to the west because stations 55 km west of the san andreas fault do not show fault parallel anisotropy in southern california station lac located 80 km east of the san andreas fault shows large fault parallel anisotropy this suggests that the pacific north american plate boundary in the mantle might be displaced to the east in southern california a deeper e w oriented fast direction of anisotropy underlies the fault parallel anisotropic layer in the vicinity of the san andreas fault an e w fast feature is also present beneath the western basin and range and the foothills of the sierra nevada although local variations are present the magnitude of delay times suggests that this feature resides in the asthenosphere we interpret this feature as the asthenospheric flow in the slabless window left behind the farallon plate the flow induced anisotropy may partially be frozen in at shallow depths station orv is located near the southern edge of the gorda slab where no anisotropy is detected the absence of anisotropy at this location could therefore mark a boundary between farallon associated flow and regions where e w oriented asthenospheric flow did not occur the lack of evidence for ne sw fast orientation within the walker lane shear belt of western nevada suggests that this crustal feature does not extend into the mantle or that is not as well developed as that beneath the san andreas fault stations located over the young subducting gorda plate mark a change in the fast direction to nearly ne sw this direction aligns well with the maximum compressive stress direction in the overlying north american plate and the ne sw directed internal shearing of the gorda plate the anisotropic thicknesses calculated from delay times suggest roughly double that expected for purely lithospheric contributions this implies that the anisotropic thickness may include some of the asthenosphere alternatively using a higher anisotropy of 8 can bring thicknesses in line with other measures of lithospheric thicknesses the correspondence between the fast directions and the present plate tectonic deformations suggest that mapping upper mantle deformation through seismic anisotropy is a viable method and that asthenospheric flow may be a significant contributor to seismic anisotropy

soil magnetic susceptibility and its relationship with naturally occurring processes and soil attributes in pedosphere in a tropical environment abstract soil magnetic susceptibility has potential to be used as a pedoenvironmental indicator from which mineralogy pedogeochemical pedogeomorphological and pedogenic processes can be inferred it can be used in pedosphere studies as an auxiliary information for appropriate and sustainable soil use and management this research aimed to analyze how pedogenesis and geochemical processes affect the and some of its attributes as well as its potential use in discriminating soil great groups following the digital soil mapping approach the study area is located in sao paulo state brazil soil samples were collected for physical chemical analysis from 79 locations 0 20 cm depth at these sites magnetic susceptibility was measured with a portable field instrument and analyzed in terms of geology relief and soil class the results showed that geology strongly affects mainly in diabase derived soils followed by metamorphosed siltstone and siltstone in fluvial sediments the exhibits different behaviors due to different sediments deposited by the capivari river in less evolved soils such as cambisols lithology is a more important contributor to than pedogenesis in more evolved soils pedogenesis increases whereas argilluviation ferralitization reduces it the values did not decrease significantly or even increase downslope due to the presence of diabase on the lower parts differences in where observed between diabase bedrock located in different parts of the study area indicating more of an influence by geomorphic processes rather than lithology with respect to soil attributes positive correlations between and base saturation cation exchange capacity organic matter and iron and clay content were found whereas a negative correlation was found between and sand content the correlates with changes in lithology and soil class demonstrating its application as a potential tool for the discrimination of soil great groups and digital soil mapping

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

complex anisotropy beneath the peruvian flat slab from frequency dependent multiple phase shear wave splitting analysis flat or shallow subduction is a relatively widespread global occurrence but the dynamics remain poorly understood in particular the interaction between flat slabs and the surrounding mantle flow has yet to be studied in detail here we present measurements of seismic anisotropy to investigate mantle flow beneath the peruvian flat slab segment the largest present day region of flat subduction we conduct a detailed shear wave splitting analysis at a long running seismic station nna located near lima peru we present measurements of apparent splitting parameters fast direction and delay time t for sks scs and local s phases from 80 events we observe well defined frequency dependence and backazimuthal variability indicating the likely presence of complex anisotropy forward modeling the observations with two or three layers of anisotropy reveals a likely layer with a trench normal fast direction underlying a layer with a more trench oblique to trench subparallel fast direction in order to further constrain the anisotropic geometry we analyzed the source side splitting from events originating within the slab measured at distant stations beneath the flat slab segment we found trench normal fast splitting directions in the subslab mantle while within the dipping portion of the slab further to the east likely trench subparallel anisotropy within the slab itself this subslab pattern contradicts observations from elsewhere in south america for normal i e more steeply dipping slab conditions it is similar however to inferences from other shallowly dipping subduction zones around the world while there is an apparent link between slab dip and the surrounding mantle flow at least beneath peru the precise nature of the relationship remains to be clarified

magnetic susceptibility of soils in different slope positions in saskatchewan canada abstract the magnetic susceptibility of soils varies with the slope position due to some factors such as texture and drainage class this study attempts to link to soil profile characteristics soil horizon type organic and inorganic c sand and oxalate feo and dithionite fed extractable iron measured on soil cores collected from the three uncultivated soil catenas in saskatchewan the parent material at all sites consisted of medium textured hummocky glacial till the waitville catena gray luvisol was developed under trees the weyburn catena dark brown chernozem under grass and the oxbow catena black chernozem had trees on the lower slope and grass in the center of the depression and on the upper and middle slopes in all the three catenas a downslope decrease in was correlated with increasing feo fed ratios and decreasing sand content lower slope gleyed profiles in the two chernozemic catenas had high feo fed ratios and low the impact of gleying was most evident in the solum and tended to increase in the c horizons of these profiles the of the sand and silt fractions was positively correlated with that of the bulk soil whereas the of the clay fraction did not vary with the of the bulk soil stable sand sized magnetite grains are believed to be rare in these soils