seismic anisotropy in the top 400 km of the inner core beneath the eastern hemisphere 1 depth variation in seismic anisotropy at the top 400 km of the inner core beneath the eastern hemisphere is investigated by comparing the differential travel times of pkp phases recorded at distances from 127to 160 at distances less than about 150 there isnonoticeable differencein differential traveltimesforpkpphases samplingboththepolarandtheequatorialpaths atgreaterdistances however pkikp phases arrive systematically earlier about 0 0 5 second in the polar path than in the equatorial path these observations suggest that in the eastern hemisphere seismic anisotropy existsonlyin depthsgreaterthanabout200km belowthe inner core boundary icb with seismic velocities along the polar paths an average of 27 6 from the earth s spin axis being 0 4 faster than those along the equatorial paths index terms 7207 seismology core and mantle 7203 seismology body wave propagation 8115 tectonophysics core processes 1507

growyouric a step toward a coherent model of the earth s inner core seismic structure a complex inner core structure has been well established from seismic studies showing radial and lateral heterogeneities at various length scales yet no geodynamic model is able to explain all the features observed one of the main limits for this is the lack of tools to compare seismic observations and numerical models successfully we use here a new python tool called growyouric to compare models of inner core structure we calculate properties of geodynamic models of the inner core along seismic ray paths for random or user specified datasets we test kinematic models which simulate fast lateral translation super rotation and differential growth we explore first the influence on a real inner core data set which has a sparse coverage of the inner core boundary such a data set is however able to successfully constrain the hemispherical boundaries due to a good sampling of latitudes combining translation and rotation could explain some of the features of the boundaries separating the inner core hemispheres the depth shift of the boundaries observed by some authors seems unlikely to be modelled by a fast translation but could be produced by slow translation associated to super rotation

imaging the inner core under africa and europe abstract the inner core under africa is thought to be a region where the nature of inner core texture changes from the strongly anisotropic western part of the inner core to the weakly anisotropic or isotropic eastern part of the inner core additionally observations of a difference in isotropic velocity between the two hemispheres have been made a very large new dataset of simultaneous pkpdf and pkpbc observations on which differential travel times have been measured is used to examine the upper 360 km of the inner core under europe africa and the surrounding oceans inversion of the differential travel time data for laterally varying inner core anisotropy reveals that inner core anisotropy is stronger under central africa and the atlantic ocean than under the western indian ocean no hemispherical pattern is present in voigt isotropic velocities indicating that the variation in anisotropy is due to differing degrees of crystal alignment in the inner core not material differences when anisotropy is permitted to change with depth the upper east most part of the study region shows weaker anisotropy than the central and western regions when depth dependence in the inner core is neglected the hemisphere boundary is better represented as a line at 40 e than one at 10 e however it is apparent that the variation of anisotropy as a function of depth means that one line of longitude cannot truly separate the more and less anisotropic regions of the inner core the anisotropy observed in the part of the inner core under africa which lies in the western hemisphere is much weaker than that under central america showing that the western hemisphere is not uniformly anisotropic as the region of low anisotropy spans a significant depth extent it is likely that heterogeneous heat fluxes in the core which may cause variations in inner core anisotropy have persisted for several hundred million years

hillslope storage boussinesq model for subsurface flow and variable source areas along complex hillslopes 2 intercomparison with a three dimensional richards equation model 1 the boussinesq equation for subsurface flow in an idealized sloping aquifer of unit width has recently been extended to hillslopes of arbitrary geometry by incorporating the hillslope width function w x into the governing equation where x is the flow distance along the length of the hillslope troch et al 2003 introduction of a source sink term n allows simulation of storm interstorm sequences in addition to drainage processes while a function sc x representing the maximum subsurface water storage can be used to account for surface saturation response in variable source areas activated by the saturation excess mechanism of runoff generation the model can thus simulate subsurface flow and storage dynamics for nonidealized more realistic hillslope configurations in this paper we assess the behavior of this relatively simple one dimensional model in a series of intercomparison tests with a fully three dimensional richards equation model special attention is given to the discretization and setup of the boundary and initial conditions for seven representative hillslopes of uniform convergent and divergent plan shape drainage and recharge experiments are conducted on these hillslopes for both gentle 5 and steep 30 bedrock slope angles the treatment and influence of the drainable porosity parameter are also considered and for the uniform idealized hillslope case the impact of the unsaturated zone is examined by running simulations for different capillary fringe heights in general terms the intercomparison results show that the hillslope storage boussinesq model is able to capture the broad shapes of the storage and outflow profiles for all of the hillslope configurations in specific terms agreement with the richards equation results varies according to the scenario being simulated the best matches in outflow hydrographs were obtained for the drainage experiments suggesting a greater influence of the unsaturated zone under recharge conditions due to transmission of water throughout the hillslope in the spatiotemporal water table response a better match was observed for convergent than divergent hillslopes and the bedrock slope angle was not found to greatly influence the quality of the agreement between the two models on the basis of the intercomparison experiments we make some suggestions for further development and testing of the hillslope storage model

distinct layering in the hemispherical seismic velocity structure of earth s upper inner core the existence of hemispherical variation in the earth s inner core is well documented but consensus has not yet been reached on its detailed structure the uppermost layers are a region of particular importance as they are directly linked to the growth processes and post solidification mechanisms of the inner core here we use a large pkikp pkikp differential travel time residual data set to derive a model for the upper inner core providing new constraints on its isotropic and anisotropic velocity and the amount of scattering we find that the eastern and western hemisphere are separated by sharp boundaries this is incompatible with the recently proposed inner core translation model but might be explained by differences in outer core convection and inner core solidification rates the eastern hemisphere displays weak anisotropy of 0 5 1 0 the western hemisphere on the other hand is characterized by the presence of an isotropic upper layer with a thickness of 57 5 km with anisotropy of 2 8 appearing at deeper depths the boundary between the isotropic layer and the deeper anisotropy appears sharp we also detect for the first time a high velocity layer at the top of the eastern hemisphere with a thickness of 30 km which we interpret as being due to an increased amount of light elements there appears to be no relationship between the layered structure in the two hemispheres with abrupt changes in velocity with depth in one hemisphere without any significant change at the same depth in the other hemisphere our results indicate that there is a difference in composition and mineral structure between the hemispheres resulting in differing responses to external processes

seismic tomography of the uppermost inner core abstract seismic body wave and normal mode analyses have revealed that the inner core is solid strongly anisotropic and characterized by dramatic quasi hemispherical differences in elastic structure and attenuation yet despite these discoveries the highly heterogeneous and incomplete data coverage of the inner core has impeded the development of tomographic models even at the longest wavelengths here we use a probabilistic and transdimensional tomographic approach tbi on a newly expanded dataset of p wave travel times sensitive to the upper 120 km of the inner core the tbi approach yields a ensemble of parsimonious models that simultaneously capture both the dominant hemispheric dichotomy and laterally abrupt velocity variations analysis of the model ensemble allows us to determine the locations of the hemisphere boundaries and rule out the presence of hemispheric dichotomy in anisotropy instead we robustly map regional variations in anisotropy beneath africa and the eastern pacific and detect variations at high latitudes suggesting that cylindrical anisotropy may not be adequate for describing the uppermost inner core

localized temporal change of the earth s inner core boundary compressional waves of an earthquake doublet two events occurring in the south sandwich islands on 1 december 1993 and 6 september 2003 recorded at three seismic stations in russia and kyrgyzstan and reflected off earth s inner core boundary arrived at least from 39 to 70 milliseconds earlier in the 2003 event than in the 1993 event such changes indicate that earth s inner core radius enlarged locally beneath middle africa by 0 98 to 1 75 kilometers between the times of these two events changes of the inner core radius may be explained by either a differential motion of the inner core assuming that irregularities are present at the inner core boundary and fixed to the inner core or a rapid growth of the inner core by this amount

rainfall runoff and sediment transport relations in a mesoscale mountainous catchment the river isabena ebro basin this paper examines the relations between rainfall runoff and suspended sediment transport in the isabena basin during a quasi average hydrological year the isabena is a mesoscale river basin that drains a mountainous area comprising patches of highly erodible materials badlands the paper includes an analysis of the different hydrological and sedimentary responses of the catchment to a similar rainfall thirty four floods were studied with a very variable response observed runoff coefficients ranged from 0 32 to 33 the sedimentary response was also highly variable with maximum suspended sediment concentrations ssc oscillating between 0 1 and 90 g l 1 and flood sediment loads varying from 27 to 54 000 t per hydrological event most sediment load was concentrated in spring when competent floods occur frequently pearson correlation matrix and backward stepwise multiple regression indicate that the hydrological response of the catchment is strongly correlated with total precipitation event duration and rainfall of the previous days very low correlation was observed with rainfall intensity the relation between rainfall and sediment transport followed the same trend sediment variables e g total load and ssc were significantly correlated with variables such as total rainfall and rainfall over the previous days although the significance level was lower in comparison with the runoff related variables there was again no correlation between sediment variables and rainfall intensity on going research in the area suggests that apart from rainfall factors such as sediment availability in the badlands and accumulation of sediment in the channels influences the river s sedimentary response the non linear hydrosedimentary response is reflected in the wide range of runoff coefficients and sediment loads that have been observed in response to similar amounts of precipitation

inner core anisotropy and heterogeneity level an analysis of core phase travel times is performed in order to estimate the relative contributions of heterogeneities and anisotropy and their distribution inside the inner core a stochastic analysis performed on the equatorial paths which are poorly sensitive to anisotropy indicates that the inner core exhibits a heterogeneity level smaller than 0 3 at all depths on scale lengths larger than 200 km this result extended to all path orientations suggests a predominant effect of the anisotropy on travel times anomalies a simultaneous inversion of absolute and differential core phase travel times for any path orientation favours a simple inner core model in which a large homogeneous structure with 3 uniform anisotropy is asymmetrically surrounded by a homogeneous isotropic layer with a thickness of 100 200 km on the western hemisphere increasing to 400 km over a large part of the eastern hemisphere

seismic velocity and attenuation structures in the top 400 km of the earth s inner core along equatorial paths 1 we study seismic velocity and attenuation structures in the top 400 km of the earth s inner core based on modeling of differential traveltimes amplitude ratios and waveforms of the pkikp pkikp phases observed at the epicentral distance range of 120 141 and the pkpbc pkikp phases observed at the distance range of 146 160 along equatorial paths our data are selected from the seismograms recorded in the global seismographic network from 1990 to 2001 and many regional seismic networks the observed pkikp pkikp and pkpbc pkikp phases exhibit distinctive east west hemispheric patterns 1 at the distance ranges of 131 141 and 146 151 pkikp phases arrive about 0 3 s earlier than the theoretical arrivals based on the preliminary reference earth model prem for the pkikp phases sampling the eastern hemisphere 40 e 180 e of the inner core and about 0 4 s later for those sampling the western hemisphere 180 w 40 e at the distance range of 151 160 pkikp phases arrive about 0 7 s earlier than the predicted arrivals based on prem for those sampling the eastern hemisphere and about 0 1 s later for those sampling the western hemisphere 2 amplitude ratios of the pkikp pkikp phases at the distance range of 131 141 and of the pkikp pkpbc phases at the distance range of 146 151 are in general smaller for the pkikp phases sampling the eastern hemisphere than for those sampling the western hemisphere at distances greater than 151 the pkikp pkpbc amplitude ratios become indistinguishable for the two hemispheres these observations can be best explained by two different types of seismic velocity and attenuation models along equatorial paths one for each hemisphere in the top 400 km of the inner core for the eastern hemisphere the velocity structure has a velocity increase of 0 748 km s across the inner core boundary icb a small velocity gradient of 0 0042 km s 100 km in the top 235 km followed by a steeper velocity gradient of 0 1 km s 100 km extending from 235 km to 375 km and a velocity gradient of 0 01 km s 100 km in the deeper portion of the inner core the attenuation structure has an average q value of 300 in the top 300 km and an average q value of 600 in the deeper portion of the inner core for the western hemisphere the velocity structure has a velocity increase of 0 645 km s across the icb and a velocity gradient of 0 049 km s 100 km in the top 375 km the attenuation structure has an average q value of 600 in the top 375 km of the inner core our results suggest that the inner core hemispheric variations in velocity extend deeper than 375 km below the icb and the top 235 km of the inner core in the eastern hemisphere is anomalous compared to the rest of the inner core in having a small velocity gradient high velocity and high attenuation

turbidity and suspended sediment dynamics in small catchments in the nepal middle hills the himalayan environment has until recently been perceived to be in a critical state of environmental decline resulting from rapid population growth and associated land use change recent research however has emphasized the di culty of developing an objective appraisal of the state of the environment in a region where empirical data are scarce and unstructured and where an understanding of the spatial and temporal dynamics of natural environmental processes remains highly uncertain this paper presents results from an intensive three year project designed to help address the regional empirical de cit establish detailed baseline environmental data and to gain an insight into storm period and seasonal suspended sediment dynamics the instrumentation calibration and analysis of high frequency infrared turbidimetric records from a number of small subcatchments in the nepal middle hills are reported storm period and seasonal variation in turbidity and suspended sediment are examined and hysteresis patterns explored and explained a variety of methods to estimate seasonal suspended sediment yield in a mixed land use catchment are examined and found to vary by up to a factor of ve despite the inherent uncertainty all estimates of catchment sediment yield are found to be high with respect to erosion plot studies from the local area and this suggests the importance of riparian and channel erosion as major sediment sources a nding consistent with other regional studies copyright 1999 john wiley sons ltd

the inner core hemispheric boundary near 180 w abstract the inner core ic east west hemispheric dichotomy is widely recognized but the reported position of the hemispheric boundary varies among studies due to uneven sampling coverage and the data analyzed this study investigates the sharpness of the western hemispheric boundary whb near 180 w by analyzing differential time residuals of pkikp pkpdf and pkp bc df for pkpdf phases that sample 155 e 130 w in various azimuthal directions using pkikp pkpdf observations the whb is located at 175 e 180 w in the southern hemisphere based mainly on the lateral isotropy anisotropy transition however based on the lateral isotropic velocity contrast and this isotropy anisotropy transition between the two hemispheres its location is 170 160 w in the northern hemisphere these findings indicate that the whb is sharp and exhibits a latitudinal dependence with a 10 20 kink as well as 1 75 anisotropy in the uppermost ic across the 180 155 w range of the western hemisphere as suggested by pkp bc df the whb could remain at 160 w at depth the isotropic velocity contrast near the whb 160 w between the eastern and western hemispheres is lower than previous estimates using pkpdf phases sampling the bulk part of each hemisphere

regional variations in the uppermost 100 km of the earth s inner core 1 the structure of the uppermost 100 km of the inner core was examined from pkikp and pkikp waveforms in the distance range of 118 140 we found evidence of a low velocity layer in the uppermost inner core in the equatorial region predominantly located between longitude 20 w to 140 e in the latitudinal direction the anomaly is detectable from 35 s beneath the indian ocean to 60 n underneath asia the maximum thickness of the low velocity layer inferred from waveform modeling is 40 km with velocity jump of about 3 we speculate that this layer may represent newly solidified core in the area where vigorous compositional convection in the outer core coincides with new crystal growth in the inner core

spatial patterns of suspended sediment yields in a humid tropical watershed in costa rica humid tropical regions are often characterized by extreme variability of fluvial processes the rio terraba drains the largest river basin covering 4767 km 2 in costa rica mean annual rainfall is 3139 s 419sd mm and mean annual discharge is 2168 s 492sd mm 1971 88 loss of forest cover high rainfall erosivity and geomorphologic instability all have led to considerable degradation of soil and water resources at local to basin scales parametric and nonparametric statistical methods were used to estimate sediment yields in the terraba basin sediment yields per unit area increase from the headwaters to the basin mouth and the trend is generally robust towards choice of methods parametric and loess used this is in contrast to a general view that deposition typically exceeds sediment delivery with increase in basin size the specific sediment yield increases from 112 s 11 4sd tk m 2 year 1 at 317 9k m 2 on a major headwater tributary to 404 s 141 7sd tk m 2 year 1 at 4766 7k m 2 at the basin mouth 1971 92 the analyses of relationships between sediment yields and basin parameters for the terraba sub basins and for a total of 29 basins all over costa rica indicate a strong land use effect related to intensive agriculture besides hydro climatology the best explanation for the observed pattern in the terraba basin is a combined spatial pattern of land use and rainfall erosivity these were integrated in a soil erosion index that is related to the observed patterns of sediment yield estimated sediment delivery ratios increase with basin area intensive agriculture in lower lying alluvial fans exposed to highly erosive rainfall contributes a large part of the sediment load the higher elevation regions although steep in slope largely remain under forest pasture or tree crops high rainfall erosivity 7400 mj mm ha 1 h 1 year 1 is associated with land uses that provide inadequate soil protection it is also associated with steep unstable slopes near the basin mouth improvements in land use and soil management in the lower lying regions exposed to highly erosive rainfall are recommended and are especially important to basins in which sediment delivery ratio increases downstream with increasing basin area copyright 2001 john wiley sons ltd

seismic velocity and attenuation structures in the top of the earth s inner core 1 we collect a global data set of pkikp and pkikp phases recorded by the global seismic network and many regional seismic arrays to study seismic structure in the top of the earth s inner core the pkikp and pkikp observations show different characteristics between those sampling the eastern hemisphere 40 e 180 e of the inner core and those sampling the western hemisphere 180 w 40 e pkikp phases 1 arrive about 0 4 s earlier than the theoretical arrivals based on preliminary reference earth model prem for those sampling the eastern hemisphere of the inner core and about 0 3 s later for those sampling the western hemisphere 131 141 2 bifurcate at smaller epicentral distances for those sampling the eastern hemisphere compared to those sampling the western hemisphere and 3 have smaller amplitudes for those sampling the eastern hemisphere waveform modeling of these observations suggests two different types of models for the two hemispheres of the top of the inner core with a model in the eastern hemisphere having a p velocity increase of 0 765 km s across the inner core boundary a small radial velocity gradient of 0 000055 km s km and an average q value of 250 and a model in the western hemisphere with a p velocity increase of 0 633 km s across the inner core boundary a radial velocity gradient of 0 000533 km s km and an average q value of 600 the hemispherical difference of seismic structures may be explained by different geometric inclusions of melt and or different alignments of iron crystals with anisotropic properties in both velocity and attenuation we speculate that this large scale pattern of seismic heterogeneities may be caused by a large scale heat flow anomaly at the bottom of the outer core and or different vigorousness of convection in the top of the inner core between the two hemispheres

long term patterns and short term dynamics of stream solutes and suspended sediment in a rapidly weathering tropical watershed 1 the 326 ha rio icacos watershed in the tropical wet forest of the luquillo mountains northeastern puerto rico is underlain by granodiorite bedrock with weathering rates among the highest in the world we pooled stream chemistry and total suspended sediment tss data sets from three discrete periods 1983 1987 1991 1997 and 2000 2008 during this period three major hurricanes crossed the site hugo in 1989 hortense in 1996 and georges in 1998 stream chemistry reflects sea salt inputs na cl and so4 and high weathering rates of the granodiorite ca mg si and alkalinity during rainfall stream composition shifts toward that of precipitation diluting 90 or more in the largest storms but maintains a biogeochemical watershed signal marked by elevated k and dissolved organic carbon doc concentration doc exhibits an unusual boomerang pattern initially increasing with flow but then decreasing at the highest flows as it becomes depleted and or vigorous overland flow minimizes contact with watershed surfaces tss increased markedly with discharge power function slope 1 54 reflecting the erosive power of large storms in a landslide prone landscape the relations of tss and most solute concentrations with stream discharge were stable through time suggesting minimal long term effects from repeated hurricane disturbance nitrate concentration however increased about threefold in response to hurricanes then returned to baseline over several years following a pseudo first order decay pattern the combined data sets provide insight about important hydrologic pathways a long term perspective to assess response to hurricanes and a framework to evaluate future climate change in tropical ecosystems

discharge and suspended sediment patterns in a small mountainous watershed with widely distributed rock fragments summary understanding and quantifying sediment loads is important in watersheds with highly erodible materials which will eventually cause environmental and ecological problems within this context suspended sediment ss transport and its temporal dynamics were studied in a small mountainous watershed with sloping lands containing rock fragments in subtropical china soils containing rock fragments with many macro pores have a high permeability rate over a 7 year period the mean runoff coefficient of this watershed was 0 65 overall 30 flood events were monitored and accounted for 95 5 27 3 17 1 of the total ss load precipitation and total discharge respectively over a 5 year period the presence of rock fragments in soils can affect soil loss when comparing the soil loss in the studied watershed with that of other watersheds under similar climatic conditions rock fragments negatively affect soil loss however an extreme event occurred on 14 august 1990 and the sediment load exhibited a phenomenon called small deposits towards lump withdrawal which resulted in a soil loss of 20 499 t 4 6 times the mean yearly soil loss this event exhausted most of the ss s stored by the rock fragments on the slope and channel following this event the mean ss concentration ssc of the 11 events was 1 05 kg m 3 and the mean ssc of the 18 previous events was 1 75 kg m 3 twelve variables were separated using the classical hydrograph separation method partial least squares regression plsr was used to determine the highly co related variables of the discharge the results indicated that plsr could explain runoff well the relationship between discharge and ssc was highly scattered during 24 flood events three types of hysteresis loops were observed clockwise 17 events figure eight 3 events and complex 4 events

regional variation of inner core anisotropy from seismic normal mode observations earth s solid inner core is surrounded by a convecting liquid outer core creating the geodynamo driving the planet s magnetic field seismic studies using compressional body waves suggest hemispherical variation in the anisotropic structure of the inner core but are poorly constrained because of limited earthquake and receiver distribution here using normal mode splitting function measurements from large earthquakes based on extended cross coupling theory we observe both regional variations and eastern versus western hemispherical anisotropy in the inner core the similarity of this pattern with earth s magnetic field suggests freezing in of crystal alignment during solidification or texturing by maxwell stress as origins of the anisotropy these observations limit the amount of inner core super rotation but would be consistent with oscillation

seismic anisotropy of the earth s inner core resulting from flow induced by maxwell stresses seismological observations indicate that the inner core of the earth is elastically anisotropic1 anisotropic structures are likely to be formed by dynamic processes and therefore such observations have the potential to provide constraints on flow in the inner core and on the geodynamo itself but in addition to the difficulties in estimating the relevant physical properties of iron under inner core conditions2 3 4 even the macroscopic processes responsible for generating seismic anisotropy in this region have yet to be determined5 6 7 8 9 as a result the geodynamic significance of seismic anisotropy in the inner core has remained unknown here i propose based on geodynamic and mineral physics considerations that flow induced by the stress due to the magnetic field the maxwell stress near the inner core boundary produces an axisymmetric fabric responsible for the observed seismic anisotropy the resultant seismic anisotropy reflects the geometry of the magnetic field near the inner core boundary and therefore seismological observations might provide constraints on the geodynamo this flow also causes non uniform release of energy at the inner core boundary associated with solidification and melting which may affect the pattern of convection in the outer core

waveform search for the innermost inner core abstract waveforms of the pkikp seismic phase are inconsistent with the effects of a sharp boundary at 300 km radius of an inner most inner core seismograms synthesized for the distance range 150 to 180 in models having a discontinuity at 300 km radius in the inner core exhibit focused diffractions around the innermost sphere at antipodal range that are inconsistent with observed pkikp waveforms a few examples however can be found of pkikp complexity near 165 consistent with a triplication created by a 475 km radius discontinuity a rapid change in the magnitude and variance of seismic attenuation of pkikp whose rays turn between 400 and 600 km radius is also observed consistent with an innermost sphere of low regionally uniform seismic attenuation models predicting waveforms in agreement with observed waveforms have either a transition in elastic and anelastic properties spread over a depth interval greater than 100 km or an innermost sphere of differing elastic properties that exceeds 450 km radius the weak but suggestive evidence for an innermost inner core may simply represent a transition in fabric spread over 100 km or more centered near 500 km radius this change may signify the end stage of solidification flow and re crystallization resulting in the highest ordering and largest grain sizes of intrinsically anisotropic crystals

oceanic export of relict carbon by small mountainous rivers small mountainous rivers smr export globally significant quantities of particulate organic carbon poc to the oceans the composition of which may be distinct from poc delivered by major world rivers to better constrain the controls on the 14c signatures of poc suspended in smr we examined the temporal variability of 14c and 13c of poc suspended in the santa clara river a smr in california usa our data suggest mixing of bedrock and contemporary soil which can be applied to other smr in contrasting climate zones and with varying land cover the data also suggest that chemical denudation is incomplete but effective to the point that only the most recalcitrant moieties of the parent poc are exported we further propose sediment yield as a potentially useful proxy for the 14c of riverine poc a preliminary analysis of the existing data for a spectrum of rivers supports this hypothesis

inner core attenuation anisotropy abstract we investigate the attenuation structure of the earth s inner core and its relationship to the velocity structure globally and along various sampling directions by studying the amplitude ratios and the differential travel times of the pkikp pkikp and pkpbc pkikp phases our observations reveal that the amplitude ratios of these core phases like the differential travel times vary in both sampling direction and geographic location and the correlation is ubiquitous between small large pkikp pkikp or pkikp pkpbc amplitude ratios and large small differential pkikp pkikp or pkpbc pkikp travel times these observations indicate that the earth s inner core is anisotropic in attenuation and the direction of high low attenuation corresponds to that of high low velocity such anisotropic behaviors can be explained by different alignments of the hexagonal close packed hcp iron crystals under the hypothesis that the hcp iron crystals are anisotropic in attenuation with their axis of high low attenuation corresponding to that of high low velocity

inner core transition zone and anomalous pkp df waveforms from polar paths 1 short period pkp df waves which travel through the inner core from polar paths nearly ns were observed to have small amplitudes and complex waveforms but the cause has been a mystery here we examine both short period and broadband pkp record sections from a single earthquake in south sandwich islands ssi the data from polar paths show clear evidence for an inner core triplication our waveform modeling suggests a 250 km thick isotropic upper inner core uic overlying an anisotropic lower inner core lic with about 8 anisotropy the synthetics match the observed waveforms and amplitudes well with a normal value of inner core attenuation we propose that such a uic lic transition zone structure may be the cause of anomalous df waveforms along polar paths the inferred level of anisotropy in the lic 2 3 times previous estimates has important implications for understanding physical properties of the inner core and sources of inner core anisotropy

anisotropy of earth s inner core intrinsic attenuation from seismic normal mode models the earth s inner core the slowly growing sphere of solid iron alloy at the centre of our planet is known to exhibit seismic anisotropy both normal mode and body wave studies have established that when the global average is taken compressional waves propagate faster in the north south direction than in the equatorial plane recent body wave studies also indicate that this fast direction may be more attenuating and interpret this anisotropic attenuation in terms of anisotropic scattering due to inner core texturing here we use the earth s normal modes to study the attenuation anisotropy of both compressional and shear waves in the inner core as normal modes have wavelengths several orders of magnitude longer than estimates of inner core grain size any attenuation anisotropy quantified using normal modes must reflect the anisotropy of intrinsic viscoelastic attenuation of the crystalline inner core alloy by inverting zonal anelastic and elastic normal mode splitting function coefficients of twenty inner core sensitive modes we construct models of inner core intrinsic attenuation and velocity anisotropy we find that for compressional waves the north south direction is both fast and more strongly attenuating the existence of intrinsic inner core attenuation anisotropy can be interpreted in terms of anisotropic zener relaxation in the metallic alloy comprising the inner core such anisotropic zener relaxation has only been observed in the presence of solute atoms and is thus entirely consistent with the presence of a few atomic per cent of light elements in the earth s inner core

character and origin of deep arenaceous weathering mantles on the bega batholith southeastern australia summary arenaceous weathering mantles on the bega batholith southeastern australia are similar to those described from europe by millot as in europe they have been formed by hydrothermal alteration of the parent rock and later by chemical weathering of biotites and feldspars but comparisons with nearby torfields shows that their distribution is determined largely by mineralogical variations in the parent rock unlike the examples cited by millot in the bega mantles kaolinite is the dominant clay mineral nonetheless these mantles seem to be contemporary not relict features and apparently formed under a temperate climate

depth dependence of anisotropy of earth s inner core both body wave pkp travel times creager 1992 song and helmberger 1993a mcsweeney and creager 1993 shearer 1994 and fits to the splitting of core modes tromp 1993 show general agreement that the top 300 km of inner core is very anisotropic the anisotropy displays axial symmetry around the earth s spin axis with the polar direction 3 faster than the equatorial direction one key problem now is the depth dependence of the inner core anisotropy here we extend our polar path studies to include both long period and short period modeling for the pkp phases at ranges 120 to 173 arrivals from the top of the inner core pkikp and reflections from the inner core boundary pkikp can be observed distinctly in short period records at ranges 130 to 140 and as waveform distortions in the long period records at ranges 130 to 146 these waveforms provide a new set of data for examining the topmost 150 km of the inner core which is not well sampled by the previous body wave travel times record sections of waves traversing the inner core nearly parallel to the earth s spin axis polar paths from three events two beneath the south sandwich islands and one along the macquarie ridge recorded at world wide standardized seismograph network canadian network and long range seismic measurements stations are analyzed our results suggest that the top 150 km of the inner core is only weakly anisotropic less than 1 with strong evidence indicating that the top 60 km is not anisotropic at all

sediment concentration versus water discharge during single hydrologic events in rivers relations between sediment concentration c and water discharge q for a hydrologic event such as a flood are studied qualitatively by analyzing smoothed temporal graphs discharge and concentration vs time in terms of mode spread and skewness comparing cq ratios at a given discharge on the rising and falling limbs of the discharge hydrograph provides a consistent reliable method for categorizing c q relations five common classes of such relations are single valued straight or curved clockwise loop counterclockwise loop single valued plus a loop and figure eight temporal graph mode and skewness influence the type of relation whereas temporal graph spread affects the details of the particular c q relation its graphical breadth shape orientation and plotted location field examples of the various types of relations are given including varieties that heretofore have received little attention such as the figure eight explanations for each type of c q relation are discussed

a similarity framework to assess controls on shallow subsurface flow dynamics in hillslopes 1 an understanding of the dominant controls on water fluxes through landscapes at scales smaller than the resolution of a hydrologic model is useful for choosing appropriate parameterizations and for developing a classification system for landscape hydrology the links between these controls and the parameters in hillslope scale models of subsurface lateral saturated flow have been treated implicitly in both physical e g characteristic response function and empirical formulations such as power law storage discharge relations in particular the controls exerted by the boundary condition at the toe of the hilslope and the temporal variability of the recharge have not been integrated with the understanding of the controls of topography and soil properties in this work we develop a dimensionless similarity framework for assessing these controls on the subsurface flow dynamics based on the boussinesq equation in an idealized hillslope system using this framework we demonstrate the relationship between 1 the exponents of the storage discharge relations 2 the boundary conditions and 3 the characteristic storage thickness used in the characteristic response function parameterization we use the concept of hydrologic regimes to incorporate information about the population of recharge events that drive the system and set up the initial condition of saturated storage for each storm event the analysis demonstrates that for planar hillslopes with uniform soil properties exponents range between 0 when the flow through the hillslope is dominated by the topographic gradients and is in the early stages of draining and 2 when the flow is driven by water table gradients and the thickness of the aquifer at the seepage face is small compared to the average thickness the similarity framework can be used to make first order predictions of these exponents and classify hillslopes using a simple typology of subsurface flows based on two components of the behavior the relative dominance of the topographic and water table gradients and the responsiveness of the hillslope discharge to temporal variability of the recharge inputs

complex seismic anisotropy in the top of the earth s inner core beneath africa 1 we report complex seismic anisotropy in the top 80 km of the earth s inner core beneath africa the anisotropy in the top 80 km of the inner core is constrained using differential travel times amplitude ratios and waveforms of the pkikp pkikp phases sampling africa along various directions the differential pkikp pkikp time residuals relative to the preliminary reference earth model prem along the polar paths are larger than those along the equatorial paths by 0 1 4 s indicating the presence of seismic anisotropy in the top 80 km of the inner core furthermore the observations along the polar paths show complex regional variations beneath africa the differential pkikp pkikp travel time residuals vary from 1 2 s beneath eastern africa to 0 1 s beneath central africa and to 0 2 to 0 8 s beneath western africa a correlation between small pkikp pkikp amplitude ratios and large differential pkikp pkikp travel time residuals is observed the waveform data are spatially binned into six groups to constrain the regional dependence of velocity and attenuation anisotropy in the top 80 km of the inner core overall the seismic data can be explained by an isotropic upper inner core uic overlying an anisotropic lower inner core lic in the top 80 km of the inner core across africa the thickness of the isotropic uic varies from 0 to 50 km and the p velocity transition from the isotropic uic to the anisotropic lic is sharp with velocity increases laterally varying from 1 6 to 2 2 the attenuation structure along the polar paths has a q value of 600 for the isotropic uic and q values varying from 150 to 400 for the anisotropic lic the complex seismic anisotropy in the top of the inner core is found in a region where a rapid change of the inner core boundary icb between 1993 and 2003 was discovered wen 2006 and may be explained by complex alignments of iron crystals resulting from a localized anomalous solidification of the inner core

measuring the seismic velocity in the top 15 km of earth s inner core abstract we present seismic observations of the uppermost layer of the inner core this was formed most recently thus its seismic features are related to current solidification processes previous studies have only constrained the east west hemispherical seismic velocity structure in the earth s inner core at depths greater than 15 km below the inner core boundary the properties of shallower structure have not yet been determined because the seismic waves pkikp and pkikp used for differential travel time analysis arrive close together and start to interfere here we present a method to make differential travel time measurements for waves that turn in the top 15 km of the inner core and measure the corresponding seismic velocity anomalies we achieve this by generating synthetic seismograms to model the overlapping signals of the inner core phase pkikp and the inner core boundary phase pkikp we then use a waveform comparison to attribute different parts of the signal to each phase by measuring the same parts of the signal in both observed and synthetic data we are able to calculate differential travel time residuals we apply our method to data with ray paths which traverse the pacific hemisphere boundary we generate a velocity model for this region finding lower velocity for deeper more easterly ray paths forward modelling suggests that this region contains either a high velocity upper layer or variation in the location of the hemisphere boundary with depth and or latitude our study presents the first direct seismic observation of the uppermost 15 km of the inner core opening new possibilities for further investigating the inner core boundary region

the innermost inner core of the earth evidence for a change in anisotropic behavior at the radius of about 300 km since the discovery of the inner core in 1936 no additional spherical subshell of the earth has been observed based on an extensive seismic data set we propose the existence of an innermost inner core with a radius of 300 km that exhibits a distinct transverse isotropy relative to the bulk inner core specifically within the innermost inner core the slowest direction of wave propagation is 45 from the east west direction in contrast the direction of the slowest wave propagation in the overlying inner core is east west the distinct anisotropy at the center of the earth may represent fossil evidence of a unique early history of inner core evolution

organic carbon fluxes to the ocean from high standing islands the transfer of terrestrially derived yet poorly quantified organic carbon to the oceans is an important yet unagreed upon proportion of the world s carbon budget the few data that exist suggest that high standing oceanic islands in the southwest pacific may make important contributions to the overall terrestrial flux of particulate organic carbon poc to the oceans we have determined the poc flux from several streams in new zealand with those data and previous measurements from taiwan and papua new guinea we estimate the poc flux from high standing islands in the southwest pacific to be 48 1012 g c yr 1 a value slightly lower than previous estimates these islands which make up only 3 of earth s landmass contribute 17 35 of the estimated poc entering the world s oceans annually and thus may be important sources of terrestrial carbon to the ocean anthropogenic activities especially deforestation and forest harvesting have probably exacerbated the natural flux few to no data exist for many of these islands and thus a more detailed assessment awaits further measurements

seismic velocity structure in the earth s outer core 1 we constrain seismic velocity structure in the earth s outer core by analyzing differential travel times waveforms and amplitude ratios of several pairs of core phases we use differential travel times and waveforms of pkpbc pkikp at 144 148 pkikp pkikp at 120 141 pkikp pkpbdiff at the pkp caustics distance range 141 145 and differential travel times and amplitude ratios of pkpab pkpbc at 146 159 to avoid the influence of the inner core anisotropy in velocity we only use the pkikp pkikp and the pkpbc pkikp observations whose pkikp phases sample the inner core along the equatorial paths paths with their ray angles being larger than 35 from the earth s rotation axis these observations show the following characteristics 1 both the observed pkpbc pkikp and pkikp pkikp differential travel times show a distinct east west hemispheric pattern pkikp phases arrive about 0 7 s earlier for those sampling the eastern hemisphere 40 e 180 e than those sampling the western hemisphere 180 w 40 e 2 the observed differential pkikp pkpbdiff travel time residuals also exhibit a hemispheric difference pkikp pkpbdiff differential travel times are about 0 9 s larger for those sampling the western hemisphere than those sampling the eastern hemisphere and 3 both the observed pkpab pkpbc differential travel times and pkpbc pkpab amplitude ratios show scatter overall these observations can be best explained by two one dimensional p velocity models one for each hemisphere at the bottom of the outer core the seismic data sampling the eastern hemisphere can be explained by prem at the bottom of the outer core while those sampling the western hemisphere can be explained by a lower velocity gradient at the bottom of the outer core which has reduced velocities relative to prem linearly increasing from 0 at 200 km above the inner core boundary icb to 0 35 at the icb different velocity gradients at the bottom of the outer core indicate that there may exist a compositional difference and or a large scale temperature difference there and that inner core formation processes may be different between the two hemispheres different inner core formation processes may produce different geometric inclusions of melt in the top of the inner core and thus may provide an explanation to the hemispheric variation of seismic velocity and attenuation in the top of the inner core the seismic data also suggest that the variation of seismic velocity in the tangential cylinder of the outer core if it exists is less than 0 1 we use a compressional wave tomographic model to study the travel time delays caused by the seismic heterogeneities in the mantle the tomographic model is unable to explain the scatter of the travel time data suggesting the existence of unknown strong small scale seismic heterogeneities in the mantle

small scale structure of the geodynamo inferred from oersted and magsat satellite data the geodynamo in the earth s liquid outer core produces a magnetic field that dominates the large and medium length scales of the magnetic field observed at the earth s surface1 2 here we use data from the currently operating danish oersted3 satellite and from the us magsat2 satellite that operated in 1979 80 to identify and interpret variations in the magnetic field over the past 20 years down to length scales previously inaccessible projected down to the surface of the earth s core we found these variations to be small below the pacific ocean and large at polar latitudes and in a region centred below southern africa the flow pattern at the surface of the core that we calculate to account for these changes is characterized by a westward flow concentrated in retrograde polar vortices and an asymmetric ring where prograde vortices are correlated with highs and retrograde vortices with lows in the historical 400 year average magnetic field4 5 this pattern is analogous to those seen in a large class of numerical dynamo simulations6 except for its longitudinal asymmetry if this asymmetric state was reached often in the past it might account for several persistent patterns observed in the palaeomagnetic field7 8 9 10 we postulate that it might also be a state in which the geodynamo operates before reversing

anisotropy in inner core attenuation a new type of data to constrain the nature of the solid core during the last decade the presence of velocity anisotropy inside the inner core with a fast axis parallel to the earth s rotation axis has been well established the quantitative analysis of the amplitudes of waves which sample a particular region of the inner core under africa but exhibit various orientations allows us to document and characterize the presence of anisotropy in attenuation the analysis is based on a comparison of both amplitudes and travel times of the pkp df wave which samples the inner core and the pkp bc wave which has nearly the same path but bottoms inside the liquid core the data reveal that the direction of strong attenuation correlates with that of fast velocity when referred to the same epicentral distance and focal depth the pkp df pkp bc amplitude ratio are about five times lower for paths tilted by 25 with respect to the earth rotation axis than for nearly equatorial paths a clear negative correlation is observed between travel time and amplitude residuals when the angle to earth rotation axis varies this first quantitative analysis combined with experimental results on oriented crystals and mushy media may bring important constraints on the mechanism responsible for anisotropy in the inner core

how important and different are tropical rivers an overview abstract tropical river systems wherein much of the drainage basin experiences tropical climate are strongly influenced by the annual and inter annual variations of the inter tropical convergence zone itcz and its derivative monsoonal winds rivers draining rainforests and those subjected to tropical monsoons typically demonstrate high runoff but with notable exceptions high rainfall intensities from burst weather events are common in the tropics the release of rain forming aerosols also appears to uniquely increase regional rainfall but its geomorphic manifestation is hard to detect compared to other more temperate river systems climate driven tropical rivers do not appear to transport a disproportionate amount of particulate load to the world s oceans and their warmer less viscous waters are less competent tropical biogeochemical environments do appear to influence the sedimentary environment multiple year hydrographs reveal that seasonality is a dominant feature of most tropical rivers but the rivers of papua new guinea are somewhat unique being less seasonally modulated modeled riverine suspended sediment flux through global catchments is used in conjunction with observational data for 35 tropical basins to highlight key basin scaling relationships a 50 year daily model simulation illuminates how precipitation relief lithology and drainage basin area affect sediment load yield and concentration local sediment yield within the amazon is highest near the andes but decreases towards the ocean as the river s discharge is diluted by water influxes from sediment deprived rainforest tributaries bedload is strongly affected by the hydraulic gradient and discharge and the interplay of these two parameters predicts foci of net bedload deposition or erosion rivers of the tropics have comparatively low inter annual variation in sediment yield

hemispherical transition of seismic attenuation at the top of the earth s inner core in contrast to the liquid outer core the earth s inner core is mostly solid and its composition is more pure iron based on dynamic arguments related to the freezing process of the inner core and the observation of much lower p wave quality factor in the inner core q 10 000 it has been suggested that a mushy layer with liquid inclusions may exist at the top of the inner core on the other hand seismic measurements indicate that q increases towards the center of the inner core we here present estimates of q in the depth range 32 110 km beneath the inner core boundary icb based on the measurement of pkikp pkikp amplitude ratios after a narrow band pass filtering 0 7 2 0 hz our measurements indicate that there are pronounced hemispherical differences in the values of q 335 and 160 in the western 180 w to 40 e and eastern 40 e to 180 e hemispheres respectively and in the depth of transition from decreasing to increasing q 32 km beneath the icb in the eastern hemisphere and 85 km in the western hemisphere below 85 km the hemispherical pattern disappears we also confirm the existence of a correlated hemispherical pattern in p velocity down to 85 km the p velocity and q variations are compatible with an interpretation in terms of small hemispherical variations of temperature at the top of the inner core and their influence on the morphology of porosity and connectivity of liquid inclusions in the mushy zone the disappearance of the differences in q beneath 85 km provide constraints on the likely depth extent of the mushy zone

constraints on inner core anisotropy from pkp df travel times pkp df travel times reported by the international seismological centre isc are analyzed to study the depth dependence of inner core anisotropy plots of pkp df travel time residuals versus range for different subsets of the data clearly show large anomalies at ranges beyond about 149 for those paths with inner core ray angles within 30 of the rotation axis on average the times are about 3 to 5 s earlier for these paths than for rays at other angles consistent with recent waveform measurements of anomalous pkp df times by creager 1992 and song and helmberger 1993 and indicative of inner core anisotropy in which the p velocity is about 3 faster for n s paths than e w paths the size of these apparent anomalies in the isc data are much larger than those inferred from several previous analyses of isc pkp df data which indicated 0 5 to 2 s anomalies at these ranges the earlier studies applied binning and averaging schemes to the data using windows that were overly tight thus excluding some of the most anomalous data points and biasing the results toward smaller anomalies to avoid this problem i apply a method for computing summary ray residuals that finds the maxima in smoothed histograms of the residuals and does not rely on a fixed interval to window the data points standard errors on each summary ray residual are estimated using a bootstrap technique that randomly resamples the data plots of the summary ray residuals for several range intervals reveal a small number of independent paths nearly parallel to the rotation axis for which the arrivals are 3 to 5 s early although the data are sparse for paths within 30 of the rotation axis anisotropy does not appear to diminish with depth within the inner core and may cause a much larger anomaly near 180 than the 2 s value obtained in several prior studies of isc data the uniform anisotropy models of creager 1992 and song and helmberger 1993 fit the bulk of the data reasonably well however the observed residuals at ranges between 132 and 140 are smaller than those predicted by most anisotropy models suggesting that the anisotropy may diminish within the outermost 50 km of the inner core

interpreting sediment delivery processes using suspended sediment discharge hysteresis patterns from nested upland catchments south eastern australia in this study suspended sediment concentration ssc and discharge q hysteresis patterns recorded at the outlets of two nested upland catchments in south eastern australia were examined detailed monitoring of sediment flux was undertaken in a 1 64 km2 sub catchment located within a 53 5 km2 catchment for which sediment yield was measured and the extent of incised channels mapped the analysis of ssc q hysteresis patterns was supplemented by these additional datasets to contribute to the explanation of observed patterns clockwise ssc q hysteresis loops with the suspended sediment peak leading the discharge peak were recorded most frequently at both sites this was attributed to initial rapid delivery of sediment from channel banks the dominant sediment source in the sub catchment and probably also for the catchment in conjunction with remobilization of in channel fine sediment deposits sediment exhaustion effects were considered to enhance clockwise hysteresis with reduced ssc on the falling limb of event hydrographs pronounced exhaustion effects were observed on some multi rise events with subsequent flow peaks associated with much reduced sediment peaks to compare ssc q hysteresis patterns between the two catchments a dimensionless similarity function sf was derived to differentiate paired event hysteresis patterns according to the extent of pattern similarity this analysis coupled with the other datasets provided insight into the function of erosion and sediment delivery processes across the spatial scales examined and indicated the dependency of between scale suspended sediment transfer on defined flow event scenarios quantitative measures of event ssc q hysteresis pattern similarity may provide a mechanism for linking the timing and magnitude of process response across spatial scales this may offer useful insights into the between scale linkage of dominant processes and the extent of downstream suspended sediment delivery copyright 2009 john wiley sons ltd

predicting the terrestrial flux of sediment to the global ocean a planetary perspective a new model for predicting the long term flux of sediment from river basins to the coastal ocean is applied to a global data set of 340 river basins the model is based on relief basin area or averaged discharge and basin averaged temperature basinaveraged temperature is determined from basin location latitude longitude and the lapse rate across the basin relief hypsometric approximation the sediment flux model incorporates climate through basin temperature and hydrologic runoff solutions are provided for each of the major hemispheric climate regions polar temperate and tropic the model successfully predicts the pre anthropogenic flux of sediment to within the uncertainties associated with the global observations within a factor of two for 75 of rivers that range across five orders of magnitude in basin area and discharge most of the problem rivers are associated with low observational loads often smaller rivers where anthropogenic impacts are often magnified and temporal variability is high model predictions provide a baseline for researchers 1 to question the quality of observational data where available and disagreement is greatest 2 to examine a river basin for unusually large anthropogenic influences i e causes of erosion or causes of hinterland sediment retention and 3 to uncover secondary factors not addressed by our model lithology lakes the model provides a powerful tool to address the impact of paleo climate fluctuations warmer colder wetter drier on the impact of sediment flux to the coastal ocean d 2003 elsevier b v all rights reserved

possible heterogeneity of the earth s core deduced from pkikp travel times the core of the earth is usually described by spherically symmetrical velocity models the core is made of two main spherical layers the fluid outer core with a radius close to 3 480 km and a p velocity increasing with depth from 8 km s 1 to 10 3 km s 1 and the solid inner core with a radius of 1 220 km and a p velocity close to 11 km s 1 refs 1 2 station residuals of the seismic core phase pkikp have been computed for 400 seismological observatories worldwide using 5 yr of the international seismological centre isc bulletins pkikp travel times can be corrected for upper mantle propagation by subtracting p delays thus pkikp p residuals are a measurement of the average vertical travel times in the lower mantle and in the core of the earth beneath seismic stations a spherical harmonic development of pkikp p delays up to degree 4 explains 58 of the variance in the data pkikp p exhibit a latitudinal dependence polar stations tend to be faster than equatorial stations we show here that this pattern may reflect a departure from spherical symmetry in the p velocity distribution in the vicinity of the inner core boundary of the earth

isotropy overlying anisotropy at the top of the inner core we investigate the existence of anisotropy near the top of the inner core under the western hemisphere using differential travel times of pole parallel pkpcd pkpdf phase pairs and comparisons to equatorial data we invert a large dataset of pkp differential travel time residuals in the same region for a layered model of inner core anisotropy our analysis shows that the uppermost 50 150 km of the inner core in this region is isotropic this implies that anisotropy at greater depths is higher than previous estimates perhaps as high as 5 the transition from isotropy to strong anisotropy is modeled as a discontinuity but a broad transition zone is not excluded by the data we offer several possible mechanisms for the existence of a layered structure of anisotropy

the secular variation of earth s magnetic field models of the magnetic field at the core mantle boundary at selected epochs from 1715 0 to 1980 0 reveal novel features in the field at the core these suggest that the flow of core fluid is coupled to the mantle and that magnetic diffusion is significant

factors influencing storm generated suspended sediment concentrations and loads in four basins of contrasting land use humid tropical puerto rico abstract the significant characteristics controlling the variability in storm generated suspended sediment loads and concentrations were analyzed for four basins of differing land use forest pasture cropland and urbanizing in humid tropical puerto rico statistical analysis involved stepwise regression on factor scores the explanatory variables were attributes of flow hydrograph peaks and rainfall categorized into 5 flow periods 1 the current storm hydrograph 2 the flow and rainfall since the previous storm event 3 the previous storm event 4 2nd previous storm event and 5 the 3rd previous storm event the response variables storm generated sediment loads and concentrations were analyzed for three portions of the storm hydrograph 1 the entire storm 2 the rising limb and 3 the recessional limb hysteresis differences in sediment concentration between the rising and falling limb were also analyzed using these explanatory variables sediment availability in the study basins is related to land use and underlying geology the supply of sediment and its location in the watershed have a strong influence on how current and previous storm events and flow and rainfall between storm events affect sediment loads and concentrations in basins with limited sediment availability forest and pasture previous storm events supply sediment to the channel this in channel sediment becomes the source of sediment on the rising limb of the next event and clockwise hysteresis occurs in the cropland basin with high sediment availability sediment delivered to the channel during events becomes the source of sediment on the rising limb of the next event and clockwise hysteresis occurs in the urbanizing basin with high sediment availability counterclockwise hysteresis is prevalent as stormwater runoff dilutes suspended sediment concentrations on the rising limb and upland sediment arrives on the hydrograph recession in the urbanized basin previous storm events flush sediment from the system the statistical approaches presented here can be used to generate hypotheses on the location and delivery of watershed sediment sources which can improve the design of appropriate field studies

a low attenuation layer in the earth s uppermost inner core the attenuation structure of the earth s inner core in combination with the velocity structure provides much insight into its rheological and mineralogical properties here we use a large data set of pkikp pkikp amplitude ratios to derive attenuation models for the upper 100 km of the inner core incorporating the effects of velocity models calculated using the same data set we confirm that the upper inner core is hemispherical in attenuation with stronger attenuation in the east hemisphere we also observe for the first time a low attenuation upper layer of approximately 30 km thickness throughout the top of the inner core attenuation increases beneath this layer and then gradually decreases going deeper into the inner core although the data appear to show attenuation anisotropy below 57 5 km depth in the west we find that this can be explained by the velocity models alone with no requirement for attenuation anisotropy in the upper inner core

sedimentation processes in a coral reef embayment hanalei bay kauai oceanographic measurements and sediment samples were collected during the summer of 2006 as part of a multi year study of coastal circulation and the fate of terrigenous sediment on coral reefs in hanalei bay kauai the goal of this study was to better understand sediment dynamics in a coral reef lined embayment where winds ocean surface waves and river floods are important processes during a summer period that was marked by two wave events and one river flood we documented significant differences in sediment trap collection rates and the composition grain size and magnitude of sediment transported in the bay sediment trap collection rates were well correlated with combined wave current near bed shear stresses during the non flood periods but were not correlated during the flood the flood s delivery of fine grained sediment to the bay initially caused high turbidity and sediment collection rates off the river mouth but the plume dispersed relatively quickly over the next month the flood deposit was reworked by mild waves and currents and the fine grained terrestrial sediment was advected around the bay and collected in sediment traps away from the river mouth long after the turbid surface plume was gone the reworked flood deposits due to their longer duration of influence and proximity to the seabed appear to pose a greater long term impact to benthic coral reef communities than the flood plumes themselves the results presented here display how spatial and temporal differences in hydrodynamic processes which result from variations in reef morphology and orientation cause substantial variations in the deposition residence time resuspension and advection of both reef derived and fluvial sediment over relatively short spatial scales in a coral reef embayment

convection and anisotropy of the inner core estimation of the rayleigh number of the inner core suggests that this region is convecting the flow pattern is likely to produce crystallographic preferred orientation of the elastically anisotropic hexagonal closest packed phase of iron such that compressional wave velocities would be greater in the axial relative to the equatorial direction by roughly 1 percent this result is in agreement with seismological evidence that the inner core is elastically anisotropic

measured and predicted sediment yield from a subtropical heavy rainfall steep sided river basin hanalei kauai hawaiian islands to determine the sediment yield of the 54 4 km hanalei river basin we employ three methods 1 the universal soil

seismic structures in the earth s inner core below southeastern asia documenting seismic heterogeneities in the earth s inner core ic is important in terms of getting an insight into its history and dynamics a valuable means for studying properties and spatial structure of such heterogeneities is provided by measurements of body waves refracted in the vicinity of the inner core boundary icb here we investigate eastern hemisphere of the solid core by means of pkpbc pkpdf differential travel times that sample depths from 140 to 360 km below its boundary we study 292 polar and 133 equatorial residuals measured over the traces that probe roughly the same volume of the ic in both planes equatorial residuals show slight spatial variations in the sampled ic volume mostly below the level of 0 5 whereas polar residuals are up to three times as big direction dependent and can exhibit higher local variations the measurements reveal fast changes in seismic velocity within a restricted volume of the ic we interpret the observations in terms of anisotropy and check against several anisotropy models few of which have been found capable of fitting the residuals scatter we particularly quantify the model where a dipping discontinuity separates fully isotropic roof of the ic from its anisotropic body whereas the depth of isotropy anisotropy transition increases in southeast direction from 190 km below southeastern asia off the coast of china to 350 km beneath australia another acceptable model cast in terms of localized anisotropic heterogeneities is valid if 33 largest polar measurements over the rays sampling a small volume below southeastern asia and the rest of polar data are treated separately this model envisages almost isotropic eastern hemisphere of the ic at least down to the depth of 360 km below the icb and constrains the anisotropic volume only to the ranges of north latitudes from 18 to 23 east longitudes from 125 to 135 and depths exceeding 170 km the anisotropy strength in either model is about 2 further effective pursuit of the models presents challenges in terms of resolution and coverage and basically requires a significant dataset extension

hemispherical variations in seismic velocity at the top of the earth s inner core knowledge of the seismic velocity structure at the top of the earth s inner core is important for deciphering the physical processes responsible for inner core growth1 2 3 previous global seismic studies4 5 6 7 8 9 have focused on structures found 100 km or deeper within the inner core with results for the uppermost 100 km available for only isolated regions10 11 12 here we present constraints on seismic velocity variations just beneath the inner core boundary determined from the difference in travel time between waves reflected at the inner core boundary and those transmitted through the inner core we found that these travel time residuals observed on both global seismograph stations and several regional seismic networks are systematically larger by about 0 8 s for waves that sample the eastern hemisphere of the inner core 40 e to 180 e compared to those that sample the western hemisphere 180 w to 40 e these residuals show no correlation with the angle at which the waves traverse the inner core this indicates that seismic anisotropy is not strong in this region and that the isotropic seismic velocity of the eastern hemisphere is about 0 8 higher than that of the western hemisphere

constraints on upper inner core structure from waveform inversion of core phases summary the determination of the inner core boundary structure is key to understanding the mechanisms of inner core growth iron solidification and anisotropy formation in the inner core a waveform inversion of a worldwide data set of pkikp and pkikp core phases is performed to investigate the velocity and the attenuation structure of this region the data set is chosen to sample the top 50 km of the inner core two inversion methods combining time and frequency domain observations are presented synthetic tests are performed in order to evaluate the resolution and the confidence intervals of the model parameters the attenuation of p waves in the uppermost inner core is poorly resolved but appears to be high q 100 the uppermost inner core interface is divided into two regions a region extending from 180 w to 60 e and characterized by negative p wave velocity perturbations dv v 0 per cent and a region extending from 60 e to 180 e and characterized by positive p wave velocity perturbations dv v 1 per cent the results of the inversion do not favour the presence of transverse isotropy aligned along the spin axis of the earth in the uppermost inner core for these two regions however these regions are correlated with those where large scale variations of the inner core anisotropy have been determined previously in the deeper inner core 100 km beneath the inner core boundary

structure of the inner core inferred from observations of its spheroidal shear modes spheroidal modes of elastic gravitational oscillation that have an energy partition dominated by shear energy in the inner core are called core modes recordings from the ida gravimeter network of an earthquake in the tonga region on june 22 1977 have provided the first unambiguous observations of core modes they conclusively show that at low frequencies the inner core has a very high q about 3500 they also tightly constrain the ratio of the inner core radius to the mean shear velocity to be 345s with an uncertainty of 0 5

influence of declining mean annual rainfall on the behavior and yield of sediment and particulate organic carbon from tropical watersheds abstract the capacity to forecast climate and land use driven changes to runoff soil erosion and sediment transport in the tropics is hindered by a lack of long term data sets and model study systems to address these issues we utilized three watersheds characterized by similar shape geology soils vegetation cover and land use arranged across a 900 mm gradient in mean annual rainfall mar using this space for time design we quantified suspended sediment ss and particulate organic carbon poc export over 18 months to examine how large scale climate trends mar affect sediment supply and delivery patterns hysteresis in tropical watersheds average daily ss yield ranged from 0 128 to 0 618 t km 2 while average daily poc ranged from 0 002 to 0 018 t km 2 for the largest storm events we found that sediment delivery exhibited similar clockwise hysteresis patterns among the watersheds with no significant differences in the similarity function between watershed pairs indicating that 1 in stream and near stream sediment sources drive sediment flux and 2 the shape and timing of hysteresis is not affected by mar with declining mar the ratio of runoff to baseflow and inter storm length between pulse events both increased despite increases in daily rainfall and the number of days with large rainfall events increasing with mar there was a decline in daily ss yield possibly due to the exhaustion of sediment supply by frequent runoff events in high mar watersheds by contrast mean daily poc yield increased with increasing mar possibly as a result of increased soil organic matter decomposition greater biomass or increased carbon availability in higher mar watersheds we compared results to modeled values using the load estimator loadest fortran model confirming the negative relationship between mar and sediment yield however because of its dependency on mean daily flow loadest tended to under predict sediment yield a result of its poor ability to capture the high variability in tropical streamflow taken together results indicate that declines in mar can have contrasting effects on hydrological processes in tropical watersheds with consequences for instream ecology downstream water users and nearshore habitat

seismic evidence for an inner core transition zone seismic waves that traverse earth s inner core along north south paths produce unusually broad pulse shapes at long periods compared with waves along east west paths and reflections from below the inner core boundary at short periods the observations provide compelling evidence for a seismic velocity discontinuity along north south paths about 200 kilometers below the inner core boundary separating an isotropic upper inner core from an anisotropic lower inner core the triplication associated with such a structure might be responsible for reported waveform complexity of short period inner core arrivals along north south paths and if the depth of the boundary is laterally variable their large travel time variation

heterogeneity and anisotropy of earth s inner core seismic observations provide strong evidence that earth s inner core is anisotropic with larger velocity in the polar than in the equatorial direction the top 60 80 km of the inner core is isotropic evidence for an innermost inner core is less compelling the anisotropy is most likely due to alignment of hcp hexagonal close packed iron crystals aligned either during solidification or by deformation afterward the existence of hemispherical variations used to be controversial but there is now strong evidence from both seismic body wave and normal mode observations showing stronger anisotropy less attenuation and a lower isotropic velocity in the western hemisphere two mechanisms have been proposed to explain the hemispherical pattern either a inner core translation wherein one hemisphere is melting and the other is solidifying or b thermochemical convection in the outer core leading to different solidification conditions at the inner core boundary neither is yet able to explain all se

a subordinated kinematic wave equation for heavy tailed flow responses from heterogeneous hillslopes 1 analytical expressions of hillslope scale subsurface stormflow discharge are currently restricted to hillslopes with homogeneous or mildly heterogeneous conductivity fields in steep straight hillslopes with uniform recharge these exhibit a classical piston flow response which arises from an assemblage of impulses all moving at a constant velocity but with different starting locations heterogeneity within a hillslope soil creates variations in the downslope velocity of these impulses which may lead to nonpiston flow responses with either exponential or heavy power law tails the presence of heavy tails suggests that heterogeneity imparts a temporal memory on the motion of the impulses using this assumption a subordinated kinematic wave equation is proposed for moderately to highly heterogeneous hillslopes this equation convolves the piston response from a homogenous hillslope with a stable subordinator the stable subordinator randomizes the time that impulses spend in motion and produces nonpiston solutions with heavy tails through comparisons of synthetic data generated from numerical hillslope simulations with physically realistic parameters this equation faithfully reproduces both early and late time characteristics of heavy tailed flow responses from moderate to highly heterogenous hillslopes a systematic evaluation of hillslope responses under different degrees of heterogeneity revealed a quantitative link between the statistical properties of the heterogeneous random fields and the parameters of the subordination framework this suggests that the subordinator can be parameterized with the physical measurement of hillslope properties