investigation of the relationships between basin morphology tectonic uplift and denudation from the study of an active fold belt in the siwalik hills central nepal the present study investigates correlations between an extensive range of geomorphic properties that can be estimated from a digital elevation model and the uplift rate on geological timescales the analysis focuses on an area in the siwalik hills central nepal where lithology and climate can be considered as uniform this area undergoes rapid tectonic uplift at rates of up to 15 mm yr 1 which are derived from the geometric pattern of a fault bend model of fold growth the selected geomorphic properties can be divided in two categories depending on whether or not the vertical dimension is taken into account none of the planar properties are significantly correlated to uplift rate unlike those that include the vertical dimension such as the mean elevation of basins hypsometric curve and hypsometric integral and relief defined by the amplitude factor of length scaling analysis correlation between relief and uplift rate is observed for all length scales of topography shorter than 600 m which suggests that all orders of the streams are able to adjust to the tectonic signal simple mass balance considerations imply that the average elevation is only 10 of surface uplift suggesting that a dynamic equilibrium has been reached quite rapidly using a simple two process model for erosion we find that fairly high diffusion coefficients order of 10 m 2 yr 1 and efficient transport of the material by rivers are required this unusually high value for mass diffusivity at small length scales may be obtained by either a very efficient linear diffusion or by landsliding actually both processes may be active which appears likely given the nature of the unconsolidated substratum and the favorable climatic conditions local relief in the study area may therefore be used to predict either uplift or denudation but the prediction is calibrated only for that specific climatic and lithologic conditions and cannot be systematically applied to other contexts

upper mantle stratification by p and s receiver functions summary seismic stratification of the upper mantle is investigated by applying two complementary techniques to the records of the graefenberg array in southern germany the anisotropic p receiver function technique kosarev et al 1984 vinnik montagner 1996 is modified by using summary seismic events instead of individual events and different weighting functions instead of the same function for the harmonic angular analysis of the sv and t components of the pds phases the summary events provide better separation of the second azimuthal harmonic than the individual events the parameters of the second harmonics of sv and t thus evaluated should be similar if they reflect the effects of azimuthal anisotropy this can be used as a criterion to identify the anisotropy to detect the sdp phases and their azimuthal variations caused by azimuthal anisotropy we have developed a stacking technique which can be termed the s receiver function technique it includes axis rotation to separate interfering p and s arrivals determination of the principal m component of the s wave motion deconvolution of the p components of many recordings by their respective m components and stacking of the deconvolved p components with weights depending on the level of noise and the angle between the m direction and the backazimuth of the event both techniques yield consistent results for the graefenberg array as indicated by the p receiver functions the upper layer of the mantle between the moho and 80 km depth is anisotropic with dvs vs around 0 03 and the fast direction close to 20 clockwise from north the fast direction of anisotropy below this layer is around 110 the boundary between the upper and the lower anisotropic layers is manifested by the detectable pds and sdp converted phases shear wave splitting in sks is strongly dominated by azimuthal anisotropy in the lower layer asthenosphere

seismic anisotropy of south african upper mantle xenoliths abstract seismic properties of six upper mantle xenoliths from south africa were determined both by laboratory measurements at elevated pressure and numerical calculations from petrofabric analyses in order to provide constraints on the structural interpretation of the field seismic data obtained in recent years the samples studied include harzburgite garnet harzburgite mica harzburgite lherzolite and garnet lherzolite average anisotropies calculated from petrofabrics are 5 4 for v p and 4 4 for v s ultrasonic measured anisotropies from xenolith rock cores are approximately 1 lower than calculated values this difference is likely due to simplifications in modal mineralogy used in the calculations and small amounts of alteration in the samples used in the velocity measurements comparison of laboratory data with the sks and p n data yields possible structural orientations in the upper mantle beneath the south africa continent our results suggest that foliation in the upper mantle is likely horizontal and the stretching lineation olivine a axis is oriented n30 e which coincides with the absolute plate motion apm of the south african continent it is apparent from our data that the fast s wave polarization depends on the propagation direction with respect to petrofabric orientations and does not always indicate the stretching lineation

why fast polarization directions of sks seismic waves are parallel to mountain belts abstract the splitting of sks waves shows that the fast velocity is commonly parallel to the trend of mountain belts this has been related to the anisotropy induced by frozen mantle flow at lithospheric depth when the flow direction is parallel to mountain belts this flow reflects a transcurrent motion parallel to the boundaries of the plates whose collision is responsible for mountain building considering the width of major shear zones transcurrent flow should not reorient the mantle fabric on a transverse width larger than 20 40 km unless the flow is partitioned between several major transcurrent shear zones therefore such a scale seems to be too small to explain the sks results another contribution to the observed mantle anisotropy is suggested to be the fabric induced by mantle flow during a prior event of rifting at the colliding plate boundaries which are derived from passive margins

desert pavement coated surfaces in extreme deserts present the longest lived landforms on earth all exposed rocks on earth s surface experience erosion the fastest rates are documented in rapidly uplifted monsoonal mountain ranges and the slowest occur in extreme cold or warm deserts millennial submeterscale erosion may be approached only in the latter the oldest previously reported exposure ages are from boulders and clasts of resistant lithologies lying at the surface and the slowest reported erosion rates are derived from bedrock outcrops or boulders that erode more slowly than their surroundings thus these oldest reported ages and slowest erosion rates relate to outstanding features in the landscape while the surrounding landscape may erode faster and be younger we present erosion rate and exposure age data from the paran plains a typical environment in the near east where vast abandoned alluvial surfaces 10 2 10 4 km 2 are covered by well developed desert pavements these surfaces may experience erosion rates that are slower than those documented elsewhere on our planet and can retain their original geometry for more than 2 m y major factors that reduce erosion converge in these regions extreme hyperaridity tectonic stability fl at and horizontal surfaces i e no relief and effective surface armoring by a clast mosaic of highly resistant lithology the 10 be concentrations in amalgamated desert pavement chert clasts collected from abandoned alluvial surfaces in the southern negev israel representing the sahara arabia deserts indicate simple exposure ages of 1 5 1 8 ma or correspond to maximum erosion rates of 0 25 0 3 m m y 1 the 36

assessment of erosion and deposition in steep mountain basins by differencing sequential digital terrain models abstract digital elevation models dems built from repeated topographic surveys permit producing dem of difference dod that enables assessment of elevation variations and estimation of volumetric changes through time in the framework of sediment transport studies dem differencing enables quantitative and spatially distributed representation of erosion and deposition within the analyzed time window at both the channel reach and the catchment scale in this study two high resolution digital terrain models dtms derived from airborne lidar data 2 m resolution acquired in 2005 and 2011 were used to characterize the topographic variations caused by sediment erosion transport and deposition in two adjacent mountain basins gadria and strimm vinschgau venosta valley eastern alps italy these catchments were chosen for their contrasting morphology and because they feature different types and intensity of sediment transfer processes a method based on fuzzy logic which takes into account spatially variable dtms uncertainty was used to derive the dod of the study area volumes of erosion and deposition calculated from the dod were then compared with post event field surveys to test the consistency of two independent estimates results show an overall agreement between the estimates with differences due to the intrinsic approximations of the two approaches the consistency of dod with post event estimates encourages the integration of these two methods whose combined application may permit to overcome the intrinsic limitations of the two estimations the comparison between 2005 and 2011 dtms allowed to investigate the relationships between topographic changes and geomorphometric parameters expressing the role of topography on sediment erosion and deposition i e slope and contributing area and describing the morphology influenced by debris flows and fluvial processes i e curvature erosion and deposition relations in the slope area space display substantial differences between the gadria and the strimm basins while in the former erosion and deposition clusters are reasonably well discriminated in the latter characterized by a complex stepped structure we observe substantial overlapping erosion mostly occurred in areas that show persistency of concavity or transformation from convex and flat to concave surfaces whereas deposition prevailingly took place on convex morphologies less expected correspondences between curvature and topographic changes can be explained by the variable sediment transport processes which are often characterized by alternation of erosion and deposition between different events and even during the same event

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

avulsions and the spatio temporal evolution of debris flow fans debris flows are water laden masses of sediment that move rapidly through channel networks and over alluvial fans where they can devastate people and property episodic shifts in the position of a debris flow channel termed avulsions are critical for debris flow fan evolution and for understanding flow hazards because avulsions distribute debris flow deposits through space and time however both the mechanisms of flow avulsion and their effects on the long term evolution of debris flow fans are poorly understood here we document and analyze the spatial and temporal patterns of debris flow activity obtained by repeat topographic analyses dendrogeomorphic and lichenometric reconstructions and cosmogenic radionuclide dating on 16 fans from japan usa switzerland france and kyrgyzstan where possible we analyze the observed spatio temporal patterns of debris flow activity in conjunction with high resolution topographic data to identify the main controls on avulsion we identify two main processes that control avulsions on debris flow fans operating over distinct time scales first during individual flows or flow surges deposition of sediment plugs locally blocks channels and forces subsequent flows to avulse into alternative flow paths plug deposition is a stochastic process but appears to depend in part on the sequence of flow volumes the geometry of the channel and the composition of the flows second over time scales of tens of events the average locus of debris flow deposition gradually shifts toward the topographically lower parts of a fan highlighting the importance of topographic compensation for fan evolution our documented debris flow avulsions often but not always follow a pattern of channel plugging backstepping of deposition toward the fan apex over one or more flows avulsion and establishment of a new active channel large flows can have contrasting impacts depending on whether or not they follow smaller flows that have deposited channel plugs these results suggest that avulsions and spatio temporal patterns of debris flow fan formation strongly depend on both the magnitude frequency distribution and the sequence of the flows feeding a fan while individual avulsions are generally abrupt and difficult to predict the presence of debris flow plugs and patterns of backstepping may be useful as indicators of impending avulsions over longer time scales the compensational tendency of flows to avulse into topographic depressions on the fan may also be used to identify sectors of the fan that are at risk of future inundation

review of erosion dynamics along the major n s climatic gradient in chile and perspectives abstract chile is an elongated country running in a north south direction for more than 30 along a subduction zone its climate is progressively wetter and colder from north to south this particular geography has been used positively by a growing number of studies to better understand the relationships between erosion processes and climate land use slope tectonics volcanism etc here we review the erosion rates factors and dynamics over millennial to daily periods reported in the literature in addition 21 new catchment mean erosion rates suspended sediment and 10be are provided and previous suspended sediment derived erosion rates are updated a total of 485 local and catchment mean erosion rates are reported erosion rates vary between some of the smallest values on earth 10 5 mm a to moderate values 0 5 mm a compared to other active ranges this review highlights strong limitations concerning the quantification of local erosion factors because of uncertainties in sampling point location slope and rainfall data for the mean erosion rates e for the millennial and decennial catchments a model of the form e s 1 s 0 6 2 r with 0 3 0 8 accounts for 40 to 70 of the erosion variance confirming a primary role of slope s compared to precipitation rate r over this time scale over the long term this review points to the long 5 to 10 ma response time of rivers to surface uplift in north central arid chile over millennia data provide evidence for the progressive contribution of extreme erosion events to millennial averages for drier climates as well as the link between glacier erosion and glacier sliding velocity in this period of time a discrepancy exists between the long term offshore sedimentological record and continental decennial or millennial erosion data for which no single explanation appears still little information is available concerning the magnitude of variation of millennial erosion rates over centuries data show the variable role of groundwater in the dynamics of suspended load and document a decrease in erosion over hundreds of years probably associated with historical harvesting

fabric related seismic anisotropy in upper mantle xenoliths evidence from measurements and calculations the seismic properties and their directional dependence have been measured in four mantle peridotites from picritic tuffs vitim baikal region russia geothermobarometric data suggest a source depth for the xenoliths corresponding to the spinel garnet transition zone 40 90km the experimental data include the measurement of p and s wave velocities and densities at confining pressures to 600 mpa and temperatures to 600 c and the determination of velocity anisotropy and shear wave splitting the measured velocities are compared with velocity calculations based on lattice preferred orientation lpo of olivine orthopyroxene the modal composition of the rocks and the single crystal stiffness coefficients macroscopic velocity anisotropy is strongly controlled by the lpo of olivine measured 600 mpa room temperature and calculated p wave anisotropies compare fairly well although the experimentally determined velocities are markedly lower than the calculated velocities the correspondence between measured and calculated shear wave splitting data is less pronounced this is attributed to grain boundary effects retrogressive reactions interstitial glass incomplete crack closure and to the fact that the lpo of the cpx fraction has not been included in the calculation the magnitude of p wave anisotropy corresponds to that observed in mantle peridotites exposed at the surface ivrea zone northern italy ronda southern spain

frozen and active seismic anisotropy beneath southern africa 1 p receiver functions from 23 stations of the sase experiment in southern africa are inverted simultaneously with sks waveforms for azimuthal anisotropy in the upper mantle our analysis resolves the long standing issue of depth dependence and origins of anisotropy beneath southern africa in the uppermost mantle we observe anisotropy with a nearly e w fast direction parallel to the trend of the limpopo belt this anisotropy may be frozen since the archean at a depth of 160 km the fast direction of anisotropy changes to 40 and becomes close to the recent plate motion direction this transition is nearly coincident in depth with activation of dominant glide systems in olivine and with a pronounced change in other properties of the upper mantle another large change in the fast direction of anisotropy corresponds to the previously found low s velocity layer atop the 410 km discontinuity

geomorphologic evidence for the late pliocene onset of hyperaridity in the atacama desert the atacama desert has experienced a long and protracted period of hyperaridity that has resulted in what may be the most unusual biome on earth but the duration of this aridity is poorly constrained we reconstructed aspects of the fluvial and geochemical history of this region using integrated landscape features alluvial fans hillslope soils soil chemistry river profiles in the southern portion of the present desert topographic reconstructions of a large watershed 11 000 km 2 show deep incision and sediment removal between the late miocene and the end of the pliocene and modest to negligible incision in post pliocene times these changes in incision suggest an 50 280 reduction in river discharge which should reflect corresponding changes in precipitation changes in the nature of hillslope soils in the atacama desert indicate that in the pliocene or earlier hillslopes were mantled with silicate derived soil this mantle was stripped off and locally deposited as alluvial fans late pliocene to early pleistocene that now block or otherwise cause a rearrangement of pliocene and earlier river channels finally the hillslopes have largely accreted a soil mantle of dust and salt since the apparent late pliocene stripping suggesting a decline in annual precipitation of at least 125 mm yr 1 or more mean annual precipitation map is now 1 embedded in the long post pliocene era of salt accumulation there are a variety of features suggesting overland flow on hillslopes rills striped gravel deposits piping and water spouts and large infrequent storms that infiltrated gentle alluvial fans due to the depth of salt rich horizons despite evidence for episodes that punctuate the hyperaridity the magnitude and duration of these pluvial events have been insufficient to remove the regional accumulations of sulfate chloride and nitrate the late pliocene cessation of many fluvial features is coincident with recent research on the tropical pacific which shows that the pacific was in a permanent el nino state until ca 2 2 ma at which time sea surface temperatures offshore of south america declined greatly relative to those of the western pacific in turn setting up the present el nino southern oscillation enso climate system these observations indicate that the latest period of aridity has been prolonged and largely continuous and it appears to have occurred in step with the onset of the enso climate system beginning 2 m y ago

changes in lead concentration in antarctic penguin droppings during the past 3 000 years anthropogenic lead pb has been found in antarctic seawater surface snow and ice cores here we analyzed a 3 000 year record of lead concentration in lake sediments affected by penguin droppings we found that lead concentration in penguin droppings has significantly increased during the last 200 years especially in the last 50 years as compared to low and stable lead levels prior to the industrial revolution this clearly indicates that global environmental pollution has influenced the antarctic ecological system heavy metal pb may find its way into the food web bioaccumulate and be passed along the chain to penguins

eco environmental implications of elemental and carbon isotope distributions in ornithogenic sediments from the ross sea region antarctica abstract seabirds have substantial influence on geochemical circulation of elements serving as a link for substance exchange between their foraging area and colonies in this study we investigated the elemental and carbon isotopic composition of five penguin affected sediment profiles excavated from ross island and beaufort island in the ross sea region antarctica among the three main constituents of the sediments including weathered bedrock guano and algae guano was the main source of organic matter and nutrients causing selective enrichment of several elements in each of the sediment profiles in the 22 measured elements as cd cu p s se and zn were identified as penguin bio elements in the ross sea region through statistical analysis and comparison with local end member environmental media such as weathered bedrock fresh guano and fresh algae carbon isotopic composition in the ornithogenic sediments showed a mixing feature of guano and algae using a two member isotope mixing equation we were able to reconstruct the historical change of guano input and algal bio mass compared with research in other parts of antarctic arctic and south china sea we found apparent overlap of avian bio elements including as cd cu p se and zn information on the composition and behavior of bio elements in seabird guano on a global scale and the role that bio vectors play in the geochemical circulation between land and sea will facilitate future research on avian ecology and paleoclimatic reconstruction

late miocene high and rapid surface uplift and its erosional response in the andes of central chile 33 35 s 1 we address the question of the late cenozoic geomorphological evolution of the central chile andes 33 35 s using uplift markers river incision previous and new ages of volcanic bodies and new fission track ages the uplift markers consist of relicts of high elevated peneplains that evidence 2 km of regional surface uplift lasting 2 ma with variable amount along an e w transect the eastern coastal cordillera was uplifted 1 5 2 1 km at 33 34 s and 2 5 at 33 45 s and 1 5 km at 34 30 s erosional response to uplift was characterized by the retreat of a sharp knickpoint with celerities between 10 and 40 mm a 1 extrapolation using a stream power law shows that uplift began shortly before 4 ma or at 10 5 4 6 ma 7 6 ma central age depending on the morphostructural units involved the first alternative implies simultaneous uplift of the continental margin the second model the most reliable one implies that the uplift affected together the eastern coastal cordillera and the principal cordillera while the rest of the western fore arc subsided this regional uplift can be mostly balanced by crustal thickening resulting from coeval shortening related to the out of sequence thrusting event in the principal cordillera and the uplift of the frontal cordillera simultaneously emplacement of the southern edge of the flat slab subduction zone might have partially contributed to this uplift event

coarse sediment connectivity in river channel systems a conceptual framework and methodology identification of coarse sediment connectivity down river channel systems is important for understanding the linkages between river reaches the influence of sediment sources on channel morphology and the mechanisms and liability to propagation of morphological change a conceptual framework is developed in which several types and degrees of connectivity are proposed it is hypothesised that sediment connectivity varies with sediment sources and with stream competence to transport the coarse fractions a method of identifying the status of reaches is developed based on field mapping of morphology and sedimentology the analysis is exemplified by two channels one an ephemeral channel in se spain the other a perennial channel in nw england questions arise over whether reaches that lack channel stores transfer coarse sediment three scenarios are suggested 1 lack of flux due to lack of competence of the reach 2 flushing through of sediment due to high competence and 3 potential transport of coarse sediment but exhaustion or lack of availability changes in connectivity will take place over different time scales depending on the nature of exchange and time scales of storage short term variations in connectivity can be identified by repeated mapping

uplift of the western altiplano plateau evidence from the precordillera between 20 and 21 s northern chile 1 we present a quantitative reconstruction of uplift of the western flank of the altiplano plateau central andes one of the largest monoclines on the earth on the basis of an analysis of tectonic structures syntectonic deposits and geophysical data uplift occurred on a west vergent slowly propagating system of high angle reverse faults merging into a joint detachment that ramps down to midcrustal levels below the plateau edge the upper ramps determine local fold geometries while the lower ramp controls large scale surface tilting and uplift at 20 s this fault system was active between 30 ma and 5 10 ma with maximum shortening rates of 0 22 mm yr between 17 and 10 ma it generated some 2600 m of surface uplift with only minor shortening of 3000 m its activity was largely synchronous to eruption of large volume ignimbrites from a midcrustal source geophysical data indicate that the fault system localized deformation at the boundary between a cool strong forearc crust and a presumably fluid rich and or partially molten zone underneath the plateau area the systematic relation between crustal melting and shortening with uplift at the western plateau margin can be traced along most of the plateau flank with a stepwise decrease in age of deformation and magmatism toward the south indicating discontinuous addition of plateau segments crustal thickening to as much as 70 km from westward underthrusting in the back arc parts of the plateau isostatically compensated the tectonic surface uplift and monocline formation with respect to a stable forearc which only reacted with minor tilting

geomorphic evidence for post 10 ma uplift of the western flank of the central andes 18 30 22 s 1 the western andean mountain front forms the western edge of the central andean plateau between 18 5 and 22 s latitude the mountain front has 3000 m of relief over 50 km horizontal distance that has developed in the absence of major local neogene deformation models of the evolution of the plateau as well as paleoaltimetry estimates all call for continued large magnitude uplift of the plateau surface into the late miocene i e younger than 10 ma longitudinal river profiles from 20 catchments that drain the western andean mountain front contain several streams with knickpoint bounded segments that we use to reconstruct the history of post 10 ma surface uplift of the western flank of the central andean plateau the generation of knickpoints is attributed to tectonic processes and is not a consequence of base level change related to pacific ocean capture eustatic change or climate change as causes for creating the knickpoint bounded stream segments observed minor valley filling alluvial gravels intercalated with the 5 4 ma carcote ignimbrite suggest uplift related river incision was well under way by 5 4 ma the maximum age of river incision is provided by the regionally extensive approximately 10 ma el diablo altos de pica paleosurface the river profiles reveal that relative surface uplift of at least1 km occurred after 10 ma

quantification of l band insar coherence over volcanic areas using lidar and in situ measurements abstract interferometric synthetic aperture radar insar is a powerful tool to monitor large scale ground deformation at active volcanoes however vegetation and pyroclastic deposits degrade the radar coherence and therefore the measurement of 3 d surface displacements in this article we explore the complementarity between alos palsar coherence images airborne lidar data and in situ measurements acquired over the piton de la fournaise volcano reunion island france to determine the sources of errors that may affect repeat pass insar measurements we investigate three types of surfaces terrains covered with vegetation lava flows a a pahoehoe or slabby pahoehoe lava flows and pyroclastic deposits lapilli to explain the loss of coherence observed over the dolomieu crater between 2008 and 2009 we first use laser altimetry data to map topographic variations the lidar intensity which depends on surface reflectance also provides ancillary information about the potential sources of coherence loss in addition surface roughness and rock dielectric properties of each terrain have been determined in situ to better understand how electromagnetic waves interact with such media rough and porous surfaces such as the a a lava flows produce a higher coherence loss than smoother surfaces such as the pahoehoe lava flows variations in dielectric properties suggest a higher penetration depth in pyroclasts than in lava flows at l band frequency decorrelation over the lapilli is hence mainly caused by volumetric effects finally a map of lai leaf area index produced using spot 5 imagery allows us to quantify the effect of vegetation density radar coherence is negatively correlated with lai and is unreliable for values higher than 7 5

seismic anisotropy under extended crust evidence from upper mantle xenoliths cima volcanic field california abstract a model of p wave velocity anisotropy and shear wave splitting for upper mantle under extended crust is derived from comparisons of seismic field measurements and observed xenolith anisotropies seismic velocity measurements and anisotropies calculated from petrofabric measurements of 15 upper mantle xenoliths from the cima volcanic field eastern mojave desert california show average maximum anisotropies of 6 9 for v p and 4 5 for v s xenolith compressional wave velocities corrected for upper mantle temperature and pressure agree well with field observations in the vicinity of the cima volcanic field the velocities calculated from the olivine fabrics suggest that upper mantle foliations beneath the region are horizontal and lineations trend ene the fabrics are believed to originate from early cenozoic extension in the area which had the same trend as the lineations the unusually high upper mantle temperatures in this region apparently have not significantly affected upper mantle fabrics

moho depth and crustal composition in southern africa abstract we present new results on structure thickness and composition of the crust in southern africa based on 6300 seismic receiver functions at 85 stations application of hk stacking to the entire sase dataset and use of multi frequency bands improve resolution substantially we observe a highly heterogeneous crustal structure with short wavelength variations in thickness h vp vs ratio composition and moho sharpness which defines 20 blocks that do not everywhere coincide with surface tectonic features in the zimbabwe craton the tokwe block has h 35 38 km and vp vs 1 74 1 79 whereas the thicker crust in the tati block h 47 51 km may be related to deformation of the archean crust along the cratonic margin two distinct crustal blocks with similar crustal thickness 42 46 km but significantly different vp vs ratios are recognized in the limpopo belt extreme values of 1 90 1 94 at the dyke swarms in eastern limpopo and 1 84 at the olifants river dyke swarm and easternmost bushveld intrusion complex bic indicate voluminous magmatic intrusions in the whole crust we find no evidence for magmatic intrusions in the central inferred part of bic where the crust is thick 45 50 km and vp vs is low 1 68 1 70 this thick crustal root may have deflected rising magmas to form the two bic lobes most of central kaapvaal has thin 35 40 km crust and vp vs 1 74 these characteristics are similar to the tokwe block in zimbabwe craton and may indicate delamination of pre existing lower crust which is further supported by a very sharp moho transition the exposed cross section in the vredefort impact crater is non representative of cratonic crust due to shallow moho 34 km and high vp vs 1 80 attributed to shock metamorphism high vp vs 1 76 is typical of the witwatersrand basin and anomalously low vp vs 1 66 1 67 marks the kaapvaal kheis namaqua transition highly heterogeneous crust both in thickness and vp vs ratio is typical of the namaqua natal and cape fold belts

an olivine fabric database an overview of upper mantle fabrics and seismic anisotropy we present a unique database of 110 olivine petrofabrics and their calculated seismic properties the samples come from a variety of the upper mantle geodynamic environments ophiolites subduction zones and kimberlites with a wide range of micro structures a phenomenological relationship is established between p and s wave seismic anisotropy and the degree of crystal alignment fabric strength seismic anisotropy increases rapidly at low fabric strength before reaching a near saturation level of 15 to 20 for p waves and 10 to 15 for s waves despite a large variation in the symmetry of fabric patterns the average seismic properties of the different fabric micro structural and geodynamic settings have similar anisotropies in both magnitude and symmetry hence it would seem possible to determine some measure of fabric strength from seismic anisotropy if the dimensions of the anisotropic region are known but not geodynamic environment or details of the petrofabric pattern a simple pattern of seismic anisotropy characterises the average sample of the database which has the following features the polarisation plane of the fastest s wave is parallel or sub parallel to the foliation plane the maximum shear wave splitting is parallel to the y structural direction in foliation plane and normal to the lineation the maximum of the p wave velocity is parallel to the high concentration of 100 axes which is sub parallel to the lineation the 100 orientation distribution has the greatest influence on the p wave seismic anisotropy the 100 and 001 orientation distributions have the greatest influence on the symmetry of s wave anisotropy although the magnitude of anisotropy is influenced by the distribution of all three principal axes although the database only contains olivine petrofabrics this statistical study clearly shows that seismic anisotropy can be used to deduce the orientation of the structural frame in the upper mantle 1998 elsevier science b v all rights reserved

shear wave splitting continental keels and patterns of mantle flow in this study we investigated the origin of seismic anisotropy in the mantle beneath north america in particular we evaluated whether shear wave splitting patterns in eastern north america are better explained by anisotropy caused by lithospheric deformation anisotropy due to mantle flow beneath the lithosphere or a combination of both we examined new measurements of shear wave splitting from the missouri to massachusetts broadband seismometer array moma the north american mantle anisotropy and discontinuity experiment nomad as well as splitting parameters from several previous studies we developed a simple finite difference model that approximates mantle flow around a complex three dimensional continental lithospheric keel to evaluate potential anisotropy from mantle flow beneath the lithosphere in eastern north america we compared shear wave splitting observations to predicted splitting parameters calculated using this mantle flow model our results indicate that a significant portion of observed shear wave splitting in eastern north america can be explained by mantle flow around the continental keel however shear wave splitting patterns in a few regions of eastern north america indicate that a component of lithospheric anisotropy must exist particularly in regions containing the largest keel thicknesses for eastern north america as well as for splitting observations in australia europe and south america we favor a model in which anisotropy is controlled by a combination of both lithospheric deformation and subcontinental mantle flow

stages and rate of the gravel shattering process by salts in desert reg soils abstract gravel shattering by salts is a common process in gravelly young to mature desert reg soils the shattered gravel is found on the surface and in the b and c horizons down to a maximum depth of 50 cm field studies on the process of salt weathering in deserts are scarce therefore the objectives of this study are to present the stages of development of the gravel shattering process by salts in desert reg soils and to discuss factors influencing the rate of development under natural conditions prevailing in the negev desert the studied reg soils were developed on two alluvial fan chronosequences in the negev desert the fan of nahal ze elim and the fan of nahal shehoret the development of the shattering process can be divided into five stages a e based on chemical physical and micromorphological features of the reg soils stages a d very young yo young reg soils represent the early holocene to the present some 14 000 years salinity values are between 0 27 16 mmho cm and the percentage of the shattered gravel is between 20 and 70 the shattered gravel however still maintains its original shape stage e mature reg soil represents the middle pleistocene to early holocene or 500 000 years salinity values at this stage reach 62 mmho cm although part of the gravel does not keep its original shape and starts to disperse in the profile the percentage of shattered gravel is only 75 80 it was found that the process of salt shattering in reg soils does not depend on concentrations or mineralogy of the salts but on the micro environmental conditions of the soil profile the process requires extreme and rapid variations of temperatures and moisture conditions such as found close to the soil surface to cause salt crystallization in a confined system with time the sealing of the soil surface through the development of desert pavement and a gravel free b horizon results in a change in the soil micro environment this change impedes the process irrespective of the amounts concentrations and types of salt minerals which exist in the profile the fact that in extreme arid regions the gravel shattering process develops primarily close to the reg soil surface suggests that it can be used to identify buried reg soils and to reconstruct climatic and micro environmental conditions of paleosols

radar interferometry and its application to changes in the earth s surface geophysical applications of radar interferometry to measure changes in the earth s surface have exploded in the early 1990s this new geodetic technique calculates the interference pattern caused by the difference in phase between two images acquired by a spaceborne synthetic aperture radar at two distinct times the resulting interferogram is a contour map of the change in distance between the ground and the radar instrument these maps provide an unsurpassed spatial sampling density 100 pixels km 2 a competitive precision 1 cm and a useful observation cadence 1 pass month 1 they record movements in the crust perturbations in the atmosphere dielectric modifications in the soil and relief in the topography they are also sensitive to technical effects such as relative variations in the radar s trajectory or variations in its frequency standard we describe how all these phenomena contribute to an interferogram then a practical summary explains the techniques for calculating and manipulating interferograms from various radar instruments including the four satellites currently in orbit ers 1 ers 2 jers 1 and radarsat the next chapter suggests some guidelines for interpreting an interferogram as a geophysical measurement respecting the limits of the technique assessing its uncertainty recognizing artifacts and discriminating different types of signal we then review the geophysical applications published to date most of which study deformation related to earthquakes volcanoes and glaciers using ers 1 data we also show examples of monitoring natural hazards and environmental alterations related to landslides subsidence and agriculture in addition we consider subtler geophysical signals such as postseismic relaxation tidal loading of coastal areas and interseismic strain accumulation we conclude with our perspectives on the future of radar interferometry the objective of the review is for the reader to develop the physical understanding necessary to calculate an interferogram and the geophysical intuition necessary to interpret it

upper mantle anisotropy a preliminary model seismic anisotropy in the upper mantle can be explained by crystallographic mineral alignment achieved through dislocation motion the physical mechanism of mineral alignment requires upper mantle shear flow which reorients and aligns minerals by dislocation glide and climb governed by the dominant glide system of each mineral the dominant glide systems are assumed to be 100 0l0 for olivine and 001 100 for the pyroxenes these yield a predominantly orthorhombic fabric with the olivine 100 and the pyroxene 001 axes aligned in the upper mantle flow direction and the olivine 010 and the pyroxene 100 axes aligned normal to the upper mantle flow plane these glide systems have a threshold temperature of enhanced mobility of 1100 1200 k which yields a solid state thermally defined lithosphere asthenosphere boundary in an olivine pyroxene mantle consistent with recent seismic determinations of the thickness of the lithosphere mantle anisotropy due to mineral alignment is then actively maintained below this boundary asthenosphere and mesosphere and is a fossil state above this boundary lithosphere we use the dominant glide systems to establish the crystallographic orientation of olivine and pyroxene in calculating the maximum seismic anisotropy of two petrologic models pyrolite and piclogite for the upper mantle by an extrapolation of single crystal anisotropic mineral elastic properties to a depth of 400 km the real earth seismic anisotropy will be bound by the limits of maximum anisotropy from perfect mineral alignment and minimum anisotropy isotropy from random mineral alignment the seismic anisotropy of the upper 220 km is best represented by the pyrolite model which reduces to quasi hexagonal symmetry with the unique axis in the direction of mantle flow the lehmann discontinuity is conjectured to be due to a change in composition from pyrolite to piclogite and therefore may represent a change in anisotropy the piclogite model has orthorhombic symmetry distinctly different from that of the pyrolite the piclogite anisotropy model can appear quasi isotropic when measured by transverse isotropy parameterization if the mantle flow is mainly horizontal with a horizontal shear plane that is the shear flow gradient duh dr dominates

the kaapvaal craton seismic anisotropy petrophysical analyses of upper mantle kimberlite nodules a dense network of seismic stations has been deployed on the kaapvaal craton south africa to investigate the upper mantle seismic structures in order to bring independent petrophysical constraints we analyze a direct sampling of the cratonic upper mantle and determine the seismic properties of 48 mantle nodules brought up to the earth s surface by kimberlite eruptions seismic properties of these nodules are calculated from the olivine and pyroxene crystal preferred orientations and the single crystal elastic constants despite variations in the nodules compositions microstructures and crystallographic preferred orientations seismic anisotropy is rather homogeneous throughout the craton mean s wave anisotropy is weak 2 64 which is compatible with the small measured sks wave splitting mean delay time of 0 62 s

constraints on seismic velocity anomalies beneath the siberian craton from xenoliths and petrophysics high seismic vp velocity anomalies 8 7 9 0km s 1 have long been known about in regions of the uppermost mantle of the siberian craton often in association with kimberlite fields laboratory measurement of seismic properties of five xenoliths three peridotites and two eclogites from the udachnaya kimberlite under confining pressures up to 600 mpa were extrapolated to uppermost mantle p t conditions of 1500 mpa and 500 c however none of the velocities are high enough to explain the observations eclogites or peridotites are commonly considered to be the source of anomalous high velocities we prefer a peridotitic source to an eclogitic source due to the unusual chemistry and regional uniformity of eclogitic garnets required maximum velocity limitations on laboratory measurements of seismic properties of natural eclogites and purported abundance of eclogites in the lithosphere alternatively a highly depleted peridotite such as dunite or harzburgite can produce velocities high enough to match observations olivine petrofabrics in most peridotites including the three peridotites used in this study are great enough to produce the observed high velocities provided olivine petrofabrics are continuous enough and correctly oriented to be seismically detectable and the modal proportion of olivine is high there have been suggestions by other authors that the siberian upper mantle is highly depleted and that a lithosphere scale shear zone exists which may have acted to organize fabrics into segments large enough for detection anomalously high vp vs velocity ratios of greater than 1 8 are expected parallel to the olivine 100 maxima required to be present in a high velocity olivine dominated upper mantle vp vs velocity ratios can serve as a means of inferring large scale anisotropy when limited seismic data are available as in siberia 2006 elsevier b v all rights reserved

anisotropic stratification beneath africa from joint inversion of sks and p receiver functions 1 the analysis of rock anisotropy revealed by seismic waves provides fundamental constraints on stress strain field in the lithosphere and asthenosphere nevertheless the anisotropic models resolved for the crust and the upper mantle using seismic waves sometimes show substantial discrepancies depending on the type of data analyzed in particular at several permanent stations located in africa previous studies revealed that the observations of sks splitting are accounted for by models with a single and homogeneous anisotropic layer whereas 3 d tomographic models derived from surface waves exhibit clear anisotropic stratification here we tackle the issue of depth dependent anisotropy by performing joint inversion of receiver functions rf and sks waveforms at four permanent broadband stations along the east african rift system ears and also on the congo craton for three out of the four stations studied stratified models allow for the best fit of the data the vertical variations in the anisotropic pattern show interesting correlations with changes in the thermomechanical state of the mantle associated with the lithosphere asthenosphere transition and with the presence of hot mantle beneath the afar region and beneath the ears branches that surround the tanzanian craton our interpretation is consistent with the conclusion of earlier studies that suggest that beneath individual stations multiple sources of anisotropy chiefly olivine lattice preferred orientation and melt pocket shape preferred orientation in our case exist at different depths our study further emphasizes that multiple layers of anisotropy must often be considered to obtain realistic models of the crust and upper mantle

global scale analysis of the mantle pds phases a global scale analysis of travel times of the mantle pds phases converted from p to s from the discontinuity at a depth d beneath the receiver is presented most of the data are related to p 410 s and p 660 s recorded by the broadband stations of geoscope incorporated research institutions for seismology iris and other networks in order to provide a good global scale coverage published measurements at 37 stations are complemented by our measurements at 45 stations lateral resolution of our data is many times higher than that of ss and its precursors previously used for similar purposes but we have fewer data in the oceans lateral variations of travel times of the major pds phases are strongly correlated with the lateral p and s velocity variations in the uppermost mantle as revealed by tomographic studies the scaling coefficient between the teleseismic s and p residuals as found from the variations of travel times of the major pds phases is around 3 7 for north america and around 3 3 for the rest of the world almost all the differential travel times t p 660 s t p 410 s are in the range of 1 s relative to the average value of 24 0 s if the lateral variations of the velocities within the mantle transition zone mtz can be neglected the corresponding variations of thickness of the mtz are in the range of 10 km relative to the standard depth of 250 km and do not show significant correlation with either velocities in the upper mantle above the mtz or with the variations of thickness of the mtz as found in some recent studies of precursors to ss there is a weak but marginally significant positive correlation between the variations of thickness of the mtz inferred from our data and the s velocity variations in the mtz as given by su et al 1994 this correlation suggests that both variables contain temperature dependent components lateral variability of the mtz is also manifested by extreme weakness of p 410 s at several locations this may indicate either anomalous topography on 410 km discontinuity or strong broadening of the otherwise sharp discontinuity at some stations there are arrivals that can be interpreted as p 520 s this interpretation implies that the strengh and or sharpness of 520 km discontinuity as well as its depth are laterally variable in a broad range

structure of the kaapvaal craton from surface waves phase delays of rayleigh and love waves from teleseismicearthquakesrecordedduringthesouthernafrica seismic experiment have been inverted for upper mantle seismic velocities along the propagation paths and beneath the station array successful models of subarray struc turedisplayedsignicantradialanisotropyintheuppermost mantle but no shear wave low velocity zone supporting the hypothesisthatthelithospherebeneaththekaapvaalcraton isthick theazimuthalvariationsofrayleigh waveslowness are not consistent with simple models based onskssplit tingobservationsandanisotropy measurementsofkaapvaal mantlexenoliths thisdiscrepancymayimplysomeamount of small scale heterogeneity in anisotropy

combined analysis of sks splitting and regional p traveltimes in siberia summary azimuthal anisotropy in the upper mantle of many continental regions is documented by swave splitting measurements with sks techniques here we present observations of splitting of the sks seismic phase at seismograph stations in the siberian platform where few such data were known previously the parameters of splitting are coherent the fast direction everywhere is around 150 and the delay of the slow split wave is close to 1 0 s these observations provide no constraints on the distribution of anisotropy with depth however the siberian platform is remarkable in that it is covered by a network of long range profiles where p waves from nuclear explosions are recorded at epicentral distances of 2000 km and more depending on epicentral distance these waves sample the upper mantle from the moho to the transition zone two profiles run approximately parallel to the fast direction of the azimuthal anisotropy whereas the directions of the two others are intermediate between the fast and slow we examine the observed p traveltimes for their dependence on the azimuth and epicentral distance with the available data on elastic anisotropy in mantle xenoliths the values of p wave anisotropy for horizontal propagation can be used to evaluate s wave splitting for vertical propagation it appears that the upper mantle between the moho and 150 km depth is responsible for not more than about 30 per cent of the large scale effect in the sks phase the major effect is accumulated in a broad low velocity zone the top of which is found at a depth of 150 km anisotropy within this zone can be caused by recent mantle flow a similar distribution with depth might explain discrepancies between the estimates of azimuthal anisotropy from phase velocities of surface waves and sks splitting in north america and south africa

the oxaya anticline northern chile a buckle enhanced by river incision a prominent structure in the western escarpment of the andes of northern chile is the oxaya anticline dissected at the culmination by 1500 m deep valleys the distribution of fault and fold structures indicates that the anticline could represent a simple buckle buckling thus appears to have accommodated crustal shortening in the plate overriding the subducting plate between the trench and the western cordillera cross cutting relationships between structures and dated strata indicated that the time interval of enhanced buckling coincides with the period when rates of valley formation were enhanced we thus propose that the formation of this anticline was enhanced by fluvial incision which is consistent with the results of published theoretical models

geomorphology on geologic timescales evolution of the late cenozoic pacific paleosurface in northern chile and southern peru abstract the atacama desert on the western margin of the central andes is one of the driest and oldest deserts in the world it is defined by a distinct and ancient surface known as the pacific paleosurface pps or atacama paleosurface the age of this surface is determined as the time at which sediment deposition ceased and the surface was effectively abandoned early studies suggested that this abandonment took place between 14 and 10 ma and was related to both the uplift of the andes and the onset of hyperaridity in the region here we provide a regional re examination of the pps compiling existing work on the underlying geology sedimentology surface exposure dating and seismic profiling we also present new multispectral satellite maps of the pps and 45 new cosmogenic 3he and 21ne surface exposure ages in order to constrain the formation age and the preservation and incision history of the paleosurface we conclude that the pps is not a single paleosurface but instead is a mosaic of smaller surfaces that were formed by aggradational and degradational processes over 19 million years or more and should be termed collectively as the pacific paleosurfaces the time at which individual paleosurfaces formed is related to regional climate where the location of each is controlled by regional tectonic activity cosmogenic surface exposure ages suggest that the surfaces are a record of regional scale climate events

variability in erosion rates related to the state of landscape transience in the semi arid chilean andes we quantify erosion rates in the higher sectors of the huasco valley in the main cordillera of the semi arid andes of chile using elevation differences between three successive geomorphic markers pediments and paleo valleys and the present day valley available ar ar ages of neogene pediments are used to estimate mean erosion rates for the three periods 16 to 13 my 13 to 8 my and following 8 my the landscape of the huasco valley is in a transient state as indicated by well preserved pediment surfaces in interfluves valleys deeply incised by fluvial and glacial erosion and scarped head valleys that represent the current knickzones higher erosion rates 45 75 m my are calculated for the more recent period 8 my during which deep incision developed compared to previous periods 6 31 m my quantitative data indicate that glaciers had a much higher erosional capability than fluvial activity in the higher sectors of the main cordillera comparison with erosion rates calculated in other drainage basins of the chilean andes suggests that the variability of erosion rates depends on the landscape s transient erosive state the landscape s geomorphologic response to the uplift of the main cordillera results in the retreat of a knickzone for which retreat velocity depends on precipitation rate pattern and glacial erosion intensity copyright 2011 john wiley sons ltd

erosion rates and mechanisms of knickzone retreat inferred from 10be measured across strong climate gradients on the northern and central andes western escarpment escarpment edge deep gorges and distinct knickzones in river profiles characterize the landscape on the western escarpment of the andes between 5 s and 18 s northern peru to northern chile th

sks splitting beneath continental rift zones we present measurements of sks splitting at 28 digital seismic stations and 35 analog stations in the baikal rift zone siberia and adjacent areas and at 17 stations in the east african rift in kenya and compare them with previous measurements from the rio grande rift of north america fast directions in the inner region of the baikal rift zone are distributed in two orthogonal directions ne and nw approximately parallel and perpendicular to the ne strike of the rift in the adjacent siberian platform and northern mongolian fold belt only the rift orthogonal fast direction is observed in southcentral mongolia the dominant fast direction changes to rift parallel again although a small number of measurements are still rift orthogonal for the axial zones of the east african and rio grande rifts fast directions are oriented on average nne that is rotated clockwise from the n s trending rift all three rifts are underlain by low velocity upper mantle as determined from teleseismic tomography rift related mantle flow provides a plausible interpretation for the rift orthogonal fast directions the rift parallel fast directions near the rift axes can be interpreted by oriented magmatic cracks in the mantle or small scale mantle convection with rift parallel flow the agreement between stress estimates and corresponding crack orientations lends some weight to the suggestion that the rift parallel fast directions are caused by oriented magmatic cracks

depth localized azimuthal anisotropy from sks and p receiver functions the tien shan summary shear wave splitting in the seismic sks phase provides a unique possibility to judge on deformations at depths inaccessible for direct observations fast s wave polarization direction in collisional belts is often parallel to the trend of the belt although deformations of the mantle lithosphere in low angle thrusts would lead to the fast polarization direction normal to the trend of the belt these considerations suggested that the upper mantle in collisional belts is decoupled from the crust however sks technique is notable by a poor depth resolution and usually it assumes that the fast polarization direction is the same at any depth which is hard to justify here to investigate depth dependent azimuthal anisotropy in the mantle we invert jointly p receiver functions and sks particle motions at a number of seismograph stations the technique involves azimuthal filtering of the receiver functions and provides a criterion to discriminate between the effects of azimuthal anisotropy and lateral heterogeneity of isotropic medium a search for the optimum models is conducted with a technique similar to simulated annealing testing with synthetics demonstrates that this approach is robust the results for 10 seismograph stations in the tien shan the world s most active intracontinental collisional belt in central asia reveal a pronounced change in the patterns of azimuthal anisotropy at a depth around 100 km in the mantle lithosphere at depths less than 100 km anisotropy is relatively weak and fast wave polarization direction varies laterally in a broad range this layer is not necessarily decoupled from the crust its anisotropy can be a combined effect of present day thrusting and of deformations of the geologic past in the lower layer asthenosphere the average azimuth of fast wave polarization is close to the trend of the belt whereas magnitude of s wave anisotropy is stable and large between 5 and 6 per cent this anisotropy is a likely result of recent uniaxial shortening at right angle to the trend of the belt at some stations the data require anisotropy in the crust there is no evidence for anisotropy at depths exceeding 150 250 km

timing of the late quaternary glaciation in the andes from 15 to 40 s the central andes play a pivotal role for glacier and climate reconstruction along the american pole equator pole transect nevertheless knowledge about late quaternary palaeoenvir onmental changes in this region is extremely limited with the advent and application of surface exposure dating during the last few years the establishment of more detailed glacial chronologies could provide important insights into forcings and mechanisms of glaciation and climate change this paper reviews previously published exposure ages and compares them with independent age control on glacial chronologies and with information about the palaeohydrological conditions although available data are still very limited and there are remaining systematic uncertainties related to surface exposure dating the following simplified palaeoglacial palaeoclimate model is presented to serve as a testable hypothesis for future studies i glaciers in the humid tropical andes were mainly temperature sensitive and therefore advanced during temperature minima advances are dated to 20 25 ka 15 ka and 11 13 ka i e synchronous to the global last glacial maximum lgm the heinrich event 1 and the younger dryas antarctic cold reversal ii further south and west precipitation decreases and glaciers therefore become more precipitation sensitive maximum or at least prominent glacial advances as far south as 308 s are dated into the lateglacial i e synchronous with lake transgression phases tauca 14 18 ka and coipasa 11 13 ka iii between 30 and 408 s glaciers reached their maximum extent much earlier during the pre lgm 35 40 ka this is attributed to a northward shift and or intensification of the westerlies whereas conditions during the global lgm were too dry to allow for significant glacial advances iv south of 408 glaciers become temperature sensitive again and reached their maximum accordingly synchronous to the global lgm copyright 2008 john wiley sons ltd

recent deformations of the deep continental root beneath southern africa seismic anisotropy manifested by the splitting of shear waves into two orthogonal polarizations provides evidence for deformation in the earth s upper mantle where such deformation has been inferred beneath precambrian cratons it has been interpreted either as related to recent plate motion1 2 or inherited from the precambrian3 4 here we present data from a portable seismograph array in the kaapvaal craton of south africa which indicate that the inferred direction of mantle flow underneath the array is close to the direction of absolute plate motion for southern africa since the end of the jurassic period such an alignment has also been reported for the north american craton2 suggesting that the flow in both regions is related mainly to shearing of the sublithospheric mantle by the plate above the old continental roots that are likely to exist in this depth range5 6 must therefore be deformed by the plate motion but the deformations are not strong enough to be seen in the presently available seismic tomography data

origin of the high plateau in the central andes bolivia south america the bolivian altiplano in the central andes of south america is part of the second largest high plateau on earth it is an elongate region of subdued relief 1 2 105 km2 and 4 km above sea level bounded by the eastern cordillera and volcanic arc western cordillera here the crust is up to 75 km thick we describe the cenozoic geological evolution of this region using a revised chronostratigraphy and an analysis of the crustal and lithospheric structure crustal shortening and magmatic addition and locally sedimentation are the main mechanisms of cenozoic crustal thickening leading to nearly 4 km of surface uplift since the paleocene addition of mafic melts appears to be a first order mechanism of cenozoic crustal growth contributing 40 of the crustal thickening beneath the volcanic arc removal of the basal part of the lithosphere may have caused two episodes of widespread arc and behind arc mafic volcanism at 23 ma and 0 5 ma contributing to the surface uplift the altiplano originated as a sedimentary basin several hundred kilometers wide between the proto western cordillera and a narrow zone of uplift proto eastern cordillera farther east the latter zone formed by inversion of the center of a wide lacustrine or marine cretaceous paleocene basin close to sea level at 45 ma a thickness of 2 4 km of paleogene continental elastics accumulated in the proto altiplano basin subsequently in the oligocene we estimate that this region and the western margin of the eastern cordillera were technically shortened 22 65 km resulting in 9 km of average crustal thickening the altiplano basin was rejuvenated at 25 ma and subsequently flooded with up to 8 km thickness of detritus eroded from the uplifting eastern and western cordilleras between 25 and 5 ma folding and thrusting in the western margin of the eastern cordillera migrated westward into the center of the altiplano basin essentially terminating deposition except in local subbasins and accommodating 13 30 km of shortening and an estimated 7 km of average crustal thickening subsequently there has been strike slip deformation and limited local thrusting 5 km of shortening geomorphological and geochronological evidence for 1 5 2 km of surface uplift of this region since the late miocene suggests 14 km of lower crustal thickening beneath an essentially rigid lid and can be explained by 100 150 km of underthrusting of the brazilian shield and adjacent regions beneath the eastern margin of the central andes the present subdued relief in the altiplano may be a result of ductile flow in the lower crust and sedimentation and erosion in an internal drainage basin

exhumation by debris flows in the 2013 colorado front range storm the relative importance of extreme events in the long term exhumation of landscapes is difficult to determine the degree to which modern records capture long term mean process rates is therefore commonly unknown in september 2013 a massive precipitation event in the front range of colorado usa triggered over 1100 landslides and debris flows in a historically sedate landscape here we employ topographic differencing utilizing repeat aerial lidar to quantify net sediment transport volumes in 120 of these mass movements within an area of 102 km 2 west of boulder colorado comparing our results against published long term erosion rates we find that these mass movements evacuated the equivalent of hundreds to thousands of years of hillslope weathering products we conclude that 1 rare debris flows perform the majority of sediment transport and channel erosion within steep channels along the eastern edge of the front range potentially explaining discrepancies between modern sediment yields and long term erosion rates in such settings and 2 the high spatial density of debris flows along the corridors bounding steep canyons suggests that the landscape switches to debris flow dominance as knickpoints pass headward along the canyons

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

mapping the mantle lithosphere for diamond potential using teleseismic methods abstract recent developments in seismic magnetotelluric and geochemical analytical techniques have significantly increased our capacity to explore the mantle lithosphere to depths of several hundred kilometres to map its structures and through geological interpretations to assess its potential as a diamond reservoir several independent teleseismic techniques provide a synergistic approach in which one technique compensates for inadequacies in another shear wave anisotropy and discontinuity studies using single seismic stations define vertical mantle stratigraphic columns for example beneath the central slave craton seismic discontinuities at depths of 38 110 140 and 190 km appear to bound two distinct anisotropic layers tomographic 3 d inversions of seismic wave travel times and 2 d inversions of surface or scattered waves use arrays of stations and provide lateral coverage in combination and by correlation with electrical conductivity and xenolith petrology studies these techniques provide maps of key physical properties within parts of the cratons known to host diamonds beneath the slave craton the discontinuity at 38 km is the base of the crust the boundaries at 110 and 140 km appear to bound a layer of depleted harzburgite that is interpreted to contain graphite to date only some of these techniques have been applied to the slave and kaapvaal cratons so that the origin and geological history of the currently mapped mantle structures are not as yet generally agreed

rill network development and sediment budgets threshold conditions for rill incision are well known but few studies have examined the effect of network geometry on water and sediment fluxes within an evolving rill system this paper reports the first in a series of studies designed to identify the influence of soil properties on rill network and confluence geometry and on water and sediment fluxes in rill systems the object of this study was to prepare detailed rill network water and sediment budgets identifying important sources and sinks simulated rainfall experiments were carried out on a canadian silt loam soil in a 7 1 m 2 4 m flume on a 5 slope rill networks of varying complexity developed which were ultimately constrained by flume boundaries sediment and water fluxes and hydraulic conditions were measured within networks and at a terminal weir networks evolved by initial knickpoint incision in the lower flume as flow shear velocities reached critical levels of 4 5 5 cm s 1 followed by headward migration and tributary development microtopography determined tributary location but the timing and intensity of development were controlled by the incision and migration rate of the main channel which changed local thalwegs and base levels raising shear velocities on side slopes above critical levels sediment discharge at the weir broadly reflected rill incision intensity and transport limited conditions but as active incision moved headward the linkage became attenuated and identification of discrete erosional incidents e g local bank collapse in the signal of the weir record became very difficult detailed water and sediment budgets showed much more complex patterns of localized incision and deposition within networks strongly influenced by local changes in thalweg and in water discharge due to seepage or return flow and by the effect of confluences on hydraulic conditions results indicate the value of detailed sediment budgets in interpreting weir water and sediment flux records and the necessity of linking such measurements for erosion plots and hillslope segments to rill network characterization experimental results are consistent with a simple model of rill system evolution based on channel incision headward migration and the critical shear velocities for rill initiation copyright 2000 john wiley sons ltd

an integrated analysis of the march 2015 atacama floods in march 2015 unusual ocean and atmospheric conditions produced many years worth of rainfall in a 48 h period over northern chile s atacama desert one of earth s driest regions resulting in catastrophic flooding here we describe the hydrologic and geomorphic drivers of and responses to the 2015 atacama floods in the salado river we estimated a flood peak discharge of approximately 1000 m3 s which caused widespread damage and high sediment loads that were primarily derived from valley fill erosion hillslopes remained surprisingly intact despite their lack of vegetation in the coastal city of chanaral flooding of the salado river produced maximum water depths over 4 5 m meters thick mud deposition in buildings and along city streets and coastal erosion the atacama flooding has broad implications in the context of hazard reduction erosion of contaminated legacy mine tailings and the atacama s status as a terrestrial analog for mars

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

teleseismic travel time residuals in north america and anelasticity of the asthenosphere abstract the slope a of the relation t s a t p b for the teleseismic s and p travel time residuals t s and t p is practically the only robust observational value that is equally sensitive to the lateral s and p velocity variations in the upper mantle published estimates of a for north america are about twice higher than those at ultrasonic frequencies in olivine at comparable pressures and temperatures in our study lateral variations of the s residuals in north america are found not from the s wave readings which can be easily biased but from accurately determined delays relative to p of the ps phases converted from 410 km and 660 km discontinuities nevertheless the estimates of a thus derived are close to the values obtained with the standard technique the discrepancy between the ultrasonic and seismic estimates of a can be explained by physical velocity dispersion on the assumption of a single absorption band our value of a is consistent with the published values of q in the seismic frequency band and velocities in the ultrasonic range if the high frequency cutoff of the absorption band in the upper mantle beneath western north america is on the order of several hundred hertz however in the literature there are indications of a cutoff at around 1 hz then our data imply the presence of another absorption band at high frequencies outside the seismic frequency band this band may correspond to the viscous dissipation in the walsh walsh j b 1969 a new analysis of attenuation in partially melted rock j geophys res 74 4333 4337 model of penny shaped inclusions of melt

a unified continental thickness from seismology and diamonds suggests a melt defined plate thick rigid continents move over the weaker underlying mantle although geophysical and geochemical constraints on the exact thickness and defining mechanism of the continental plates are widely discrepant xenoliths suggest a chemical continental lithosphere 175 kilometers thick whereas seismic tomography supports a much thicker root 250 kilometers and a gradual lithosphere asthenosphere transition consistent with a thermal definition we modeled ss precursor waveforms from continental interiors and found a 7 to 9 velocity drop at depths of 130 to 190 kilometers the discontinuity depth is well correlated with the origin depths of diamond bearing xenoliths and corresponds to the transition from coarse to deformed xenoliths at this depth the xenolith derived geotherm also intersects the carbonate silicate solidus suggesting that partial melt defines the plate boundaries beneath the continental interior

a geomorphological approach to determining the neogene to recent tectonic deformation in the coastal cordillera of northern chile atacama the large 10000 km2 and local scale 300 m sedimentary succession was deposited east of the afs the succession fills previously deep paleovalleys and it consists of gravel so called atacama gravels which passes laterally into fine grained playa related deposits near the afs we interpret the deposition of this succession as a result of a blocking closure of the valley flowing from the precordillera due to the activity on afs a pedimentation episode followed sediment deposition and is locally strongly re incised by the main modern day river valleys draining the precordillera incision may result from either regional uplift of the forearc and or from more localized activity on the afs furthermore recent quaternary tectonic activity on the afs has been observed which is consistent with a localized relative uplift of the crustal block west of the afs

effective timescales of coupling within fluvial systems this paper presents a review of the coupling concept in fluvial geomorphology based mainly on previously published work coupling mechanisms link the components of the fluvial system controlling sediment transport down the system and the propagation of the effects of base level change up the system they can be viewed at several scales at the local scale involving within hillslope coupling hillslope to channel coupling and within channels tributary junction and reach to reach coupling at larger scales coupling can be considered as zonal coupling between major zones of the system or as regional coupling relating to complete drainage basins these trends are illustrated particularly by the examples of hillslope to channel coupling in the howgill fells northwest england badland systems in southeast spain alluvial fans in spain usa and uae and base level induced dissection of neogene sedimentary basins in southeast spain as the spatial scales increase so do the timescales involved effective temporal scales relate to magnitude and frequency characteristics recovery time and propagation time the relative importance changing with the spatial scale for downsystem coupling at the local scale the first two are important with propagation time increasing in importance in larger systems especially in those involving upsystem coupling related to base level change the effective timescales range from the individual event with a return period of decades through decadal to century timescales for downsystem coupling to tens to hundreds of thousands of years for the basinwide response to base level change the effective timescales influence the relative importance of factors controlling landform development

oligocene miocene age of aridity in the atacama desert revealed by exposure dating of erosion sensitive landforms the age of onset of hyperaridity in the atacama desert chile which is needed to validate geological and climatological concepts has been heretofore uncertain measurement of cosmogenic 21 ne in clasts from erosion sensitive sediment surfaces in northern chile shows that these surfaces have been barely affected by erosion since 25 ma surface exposure ages of sediment clasts give replicate values at 25 20 and 14 ma and individual values at 37 and 9 ma predominantly hyperarid conditions are required to preserve these oldest continuously exposed surfaces on earth our findings are compatible with the hypothesis that the onset of aridity in the atacama desert could be the reason for rather than the consequence of uplift of the high andes

a 1 800 year record of arsenic concentration in the penguin dropping sediment antarctic heavy toxic metals have been widely investigated in the antarctic however there are rare reports on arsenic up to now here we analyzed a 1 800 year record of arsenic concentration in lake sediments affected by penguin droppings we found that arsenic enriches in the penguin dropping sediments with 12 41 0 45 g g on dry weight which is about two times higher than the one in the background sediments with absence of penguin historical change in arsenic concentration was found to significantly correlate with the fluctuation of penguin number indicating that penguin activity will result in the enrichment of arsenic somewhere in the maritime antarctic

how to relate body wave and surface wave anisotropy seismic anisotropy is one of the most efficient geological and geodynamical tools for understanding the dynamics of the earth upper mantle anisotropy is evident in seismic data sets for the last 30 years primarily from surface wave dispersion curves and body wave sks data we demonstrate in this paper that surface wave and body wave derived anisotropy can be explained by the same anisotropic parameters l gc gs in the simplest case of a horizontal fast symmetry axis one application of this method is to display the sks delay time and the corresponding azimuth which can be derived from surface wave global with a lateral resolution of around 2000 km and regional lateral resolution of 350 km anisotropy tomography a global scale comparison is disappointing since there are only a few areas where both data types are correctly retrieved at the same spatial scale same lateral resolution the anisotropy is well resolved in oceanic basins from surface waves whereas most measurements of sks splitting are available below continents however there is a good agreement between surface wave and body wave anisotropy in regions where large scale processes primarily tectonic are taking place such as the western united states and in central asia in particular we show that at high frequency 1hz the observed sks delay time and azimuth depend on the order in which s waves propagate through the layers a comparison between synthetic and observed sks phases in central asia highlights the varying sensitivity of sks waves at depth we can obtain a good correlation between synthetic and observed sks by considering anisotropy only between 80 and 200 km depth in the tomographic model rather than in the entire upper mantle however it is more difficult to explain the discrepancy between synthetic and observed sks under the eastern united states where a large scale coherent sks anisotropy is present such results call for more sophisticated sks waveform modeling and for enhanced lateral resolution in anisotropic tomographic models

anisotropic lithosphere under the fennoscandian shield from p receiver functions and sks waveforms of the polenet lapnet array abstract seismic azimuthal anisotropy is the key evidence of the past and present strains in the upper mantle the standard analysis of shear wave splitting with the sks techniques is useful in mapping lateral variations but it is insensitive to depth of anisotropy and to variations of anisotropy with depth to retrieve the depth localized anisotropy under the fennoscandian shield we inverted p wave receiver functions of the polenet lapnet array in northern finland jointly with sks recordings shear wave anisotropy of 2 5 with the fast direction of 40 60 in a depth range from the moho to 110 km is a robust result of the inversion the obtained direction is nearly normal to the azimuth of the maximum horizontal compressional stress in the lithosphere but a recent origin of this anisotropy is in doubt this anisotropy may be frozen since the precambrian but it shows no clear relation with the trends of the precambrian tectonics the upper anisotropic layer accounts for 40 of shear wave splitting in sks and to explain the rest another anisotropic layer is required the top of the second layer with a practically similar fast direction is found at a depth of 200 240 km this direction is close to the current apm direction of the lithosphere with implication that the inferred anisotropy may be related with the current plate motion and the anisotropic layer belongs to the asthenosphere the bottom of this layer is uncertain but it is at least 320 km deep in a depth range from 160 km to 200 240 km the fast anisotropy direction is 110 150 origin of this direction is unclear

linking environmental regimes space and time interpretations of structural and functional connectivity connectivity as a concept has been increasingly part of discussions or explanations in hydrology geomorphology and ecology we address recent critiques of this approach by demonstrating how a refinement which distinguishes structural connectivity from functional connectivity can be used to explain patterns observed in very different environmental systems these systems are found in linkages between surface and subsurface flowpaths and the hyporheos in the river don a temperate river channel in yorkshire uk in surface and subsurface fluxes in agricultural land in the uk and in vegetation and surface conditions in a degrading environment at the sevilleta lter site in the semi arid southwest usa first we demonstrate long term geological and structural controls mediated by in channel processes second human organization of landscape elements is a significant control on runoff and erosion so that similar events can produce very different responses and vice versa third linkages between the removal of grass vegetation and runoff and erosion produce non linear and path dependent feedbacks which control the subsequent degradation of the landscape making the process difficult to reverse as a result of these studies we argue that even in cases where connectivity cannot be directly quantified at least at present this limitation does not prevent the concept from being a useful heuristic device for exploring responses of complex systems furthermore this result implies that an increasing need exists for disciplinary connectivity to investigate such systems

late cenozoic deformation and uplift of the western flank of the altiplano evidence from the depositional tectonic and geomorphologic evolution and shallow seismic activity northern chile at 19 30 s 1 we analyze the west vergent thrust system wts along the western flank of the altiplano in northern chile 18 s 21 s in our study area 19 20 s 19 50 s the wts consists of three thrust propagation monocline folds flexures developing growth strata the relative uplift accommodated by the flexures is rapid between 26 and 8 ma 0 1 mm yr diminishing to 0 02 mm yr after 8 ma approximately 2000 m of relative surface uplift was accommodated by the flexures since the late oligocene sedimentological and geomorphological analysis shows that westward tilting of the forearc occurred after 10 ma coeval with the shifting of deformation from the altiplano to the sub andean zone where the underthrusting of the brazilian craton would have resulted in crustal thickening surface uplift in the orogen and westward ductile subcrustal flow forearc tilting is accommodated by east vergent thrusts ets issued from the benioff zone beneath the central depression emerging into the western cordillera contributing 500 1400 m of surface uplift the wts connects the ets in the brittle ductile crustal transition 25 km depth continuing farther east as the altiplano low velocity zone configuring the western altiplano as a crustal scale fault bend fold forearc tilting would be caused by westward ductile flow in the lower crust pushing the rigid forearc in the ets meanwhile between 19 s and 21 s the wts accommodates dextral strike slip and 3 km of n s shortening occurred in the coastal cordillera transcurrence and strain partitioning are probably the result of slight plate convergence obliquity strong coupling within the interplate zone westward continental concavity and high elevation opposing horizontal contraction