magma reflection imaging in krafla iceland using microearthquake sources the details of magma plumbing beneath active volcanoes remain a major challenge in geochemistry geophysics and volcanic hazard evaluation here we apply a relatively novel variation of seismic interferometry which we call virtual reflection seismic profiling vrsp to produce a high resolution image of a known crustal magma body the technique takes advantage of recent advances in both seismic instrumentation dense arrays and seismic analysis seismic interferometry we have applied this technique to data recently acquired at an iconic volcanic system krafla which lies on the mid atlantic ridge as exposed in northern iceland what make this particular site exceptional are encounters with rhyolitic magma in two drillholes k 39 and iceland deep drilling project 1 iddp 1 these known magma bodies represent a unique calibration opportunity for surface geophysical measurements of magma distribution at depth in this study we produced a stacked seismic reflection section by applying common depth point processing techniques to virtual shot gathers derived from interferometry of p waves from microearthquakes generated by tectonic magmatic and or geothermal activity we observe a strong coherent reflection on the seismic section at a travel time corresponding to the depth at which magma was encountered in the iddp 1 wellbore we interpret this reflection to be from magma or magma related fluids additional coherent reflections may correspond to other components of the magma plumbing beneath krafla these results represent a promising new technique for structural imaging with natural sources that can be applied to a wide array of geologic and energy problems that involve natural or induced seismic clusters

rapid consolidation characteristics of yellow river derived sediment geotechnical characterization and its implications for the deltaic geomorphic evolution abstract the yellow river which presently discharges into the western bohai sea has been widely recognized as having one of the highest sediment loads on earth understanding the consolidation characteristics of yellow river derived sediments is critical for improving our knowledge of the riverine sediment transport depositional processes and evolution of the yellow river delta morphology in this study we conducted in situ experiments from 2004 to 2008 at an abandoned subaqueous delta lobe diaokou lobe in order to investigate the consolidation process of the sediments our results show that the initial consolidation of yellow river derived sediment is a rapid process when the excess pore water pressure caused by sediment aggradation can completely dissipate in 1500 min the change in the physical and geotechnical properties during the consolidation endows the sediments with a certain shear strength however due to the hydrodynamic conditions the distribution of the sediment strength is both temporally and spatially inhomogeneous furthermore a hard layer can develop at the depths of 10 30 cm and the adjacent layer can become a potential sliding surface this study offers some insight into the formation and evolution processes of the yellow river delta s sedimentary and geomorphic forms

disturbances of temperature depth profiles due to surface climate change and subsurface water flow 2 an effect of step increase in surface temperature caused by forest clearing in southwest western australia a series of type curves is presented for estimating vertical groundwater fluxes under the condition of a step increase in surface temperature the depths of minimum groundwater temperature in temperature depth profiles are used as an indicator of the magnitude of the downward groundwater fluxes the type curve method has been applied to the subsurface thermal regime observed in experimental catchments in the collie river basin in southwest western australia to estimate the vertical groundwater fluxes under the condition of surface warming caused by land cover change from forest to agriculture the groundwater fluxes obtained from the type curves and the depths of minimum groundwater temperature in temperature depth profiles agree well with the values obtained from the other studies

lithospheric discontinuities in central australia abstract lithospheric discontinuities are elusive with properties that are strongly frequency dependent results from a temporary deployment of broadband stations along a north south transect through central australia and the permanent arrays asar and wra are used to evaluate the spatial coherence of lithospheric features particularly mid lithospheric discontinuities we exploit stacked station autocorrelograms that provide an estimate of p wave reflectivity beneath stations with imaging methods exploiting teleseismic arrivals we use both common conversion point ccp stacking from ps receiver functions and reflection point imaging using the autocorrelation of the p wavetrain the results tie well for the moho and have a good general correspondence for deeper levels although indications of mid lithospheric discontinuities from changes in the frequency of reflectivity occur at similar depths the spatial continuity of specific features at high frequency around 2 hz is of the order of 10 15 km broader trends can be tracked across the profile but no strong lithospheric interfaces can be mapped except for a south dipping feature traversing the lithosphere on the southern part of the profile that is likely to be a former mantle detachment zone

relationship between the morphological evolution of the river mouth bar and fluvial input in the modaomen estuary river mouth bars commonly exist in estuaries and are important for flood control estuarine ecology and the navigation of estuarine areas the modaomen estuary is a river dominated estuary in the pearl river delta and has a typical river mouth bar here hydrologic and bathymetric datasets that span 2000 2011 are used to analyze the relationship between the fluvial input of river discharge and sediment load and the evolution of the river mouth bar the results show that the eastern and western channels have notably extended seaward since 2000 the evolution rates exhibit distinct asymmetry with the seaward extension rate of the eastern channel being approximately 1 6 times greater than that of the western channel the upstream bar face and bar back of the center mouth bar have been eroded and intensive human activities have significantly affected the evolution of the center mouth bar the center mouth bar s apex has consistently moved seaward from 2000 to 2011 river discharge especially during extreme river floods rather than sediment load has played a more vital role in the development of the bifurcation channels and the center mouth bar an empirical relationship between the bar apex displacement rates and dominant discharge is obtained based on the observations indicating that greater river discharge and longer duration will move the bar apex further seaward the bar apex s displacement during the extreme river floods of 2005 6 and 2008 6 was 133 6 m and 99 4 m respectively

the moho in australia and new zealand abstract australia and new zealand share in part a history in the gondwana supercontinent australia has a long and complex tectonic history with the last major accretion in the early paleozoic whereas new zealand is still undergoing major plate boundary processes the australian continent is relatively well covered with both active and passive seismic techniques multiple sources of information are therefore available for building a model of moho depth results from on shore and off shore refraction experiments are supplemented by receiver functions from a large number of portable stations and the recently augmented set of permanent stations moho picks from more than 10 500 km of full crustal reflection profiles provide valuable additional constraints the composite data set provides good sampling of much of australia though coverage remains low in some remote desert areas the various datasets provide multiple estimates of the depth to moho in many regions and the consistency between the different techniques is high some of the thinnest crust lies beneath the archean craton in the pilbara and in the neighbourhood of the simpson desert thick crust is encountered beneath parts of the proterozoic in central australia and beneath the paleozoic lachlan fold belt in southeastern australia there are a number of zones of sharp contrast in depth to moho notably in the southern part of central australia despite most of the continental material around new zealand being submerged moho data for this region is mainly onshore concentrating on the australia pacific plate boundary two major wide angle reflection transects provide the bulk of the active source data with just a few traditional reflection profiles offshore the plate boundary provides an abundance of local earthquakes for tomographic imaging and this data is supplemented with receiver functions from both portable and permanent networks onshore the combined coverage is as dense as that of australia although it could be argued that a higher spatial resolution is required to capture the nature of the moho of tectonically active new zealand three regions of thickened crust can be identified one beneath the southern alps another beneath fiordland and below the wanganui basin between the north and south island thin crust is identified west of the volcanic arc with extensive underplating below the back arc region

mid lithosphere discontinuities beneath the western and central north china craton by analyzing p reflectivity extracted from stacked autocorrelograms for teleseismic events on a dense seismic profile we obtain a detailed image of the mid lithosphere discontinuity mld beneath western and central north china craton ncc this seismic daylight imaging exploits a broad high frequency band 0 5 4 hz to reveal the fine scale component of multi scale lithospheric heterogeneity the depth of the mld beneath the western and central parts of the ncc ranges 80 120 km with a good match to the transition to negative s velocity gradient with depth from rayleigh wave tomography the mld inferred from seismic daylight imaging also has good correspondence with the transition from conductive to convective regimes estimated from heat flow data indicating likely thermal control within the seismological lithosphere

autocorrelation of the seismic wavefield at newberry volcano reflections from the magmatic and geothermal systems we show that seismic autocorrelations provide new depth constraints on upper crustal magmatic systems autocorrelations of both ambient noise recorded on seismometers and geophones and teleseismic earthquake coda recorded on seismometers elucidate the structure of newberry volcano these autocorrelations result in the two way body wave green s function beneath a station within the caldera a reproducible coherent p wave reflection is inferred to come from the top of a magma body at 2 5 km depth and maps with the lateral extent of an anomalously low velocity body imaged tomographically on the west flank of the volcano a reflection that deepens with distance from the caldera is inferred to result from a temperature dependent change in metamorphic facies and may map the thermal structure of the edifice our results show that the autocorrelation of diffuse seismic energy reconstructs reflections from seismically sharp boundaries associated with the upper crustal magmatic structure

seismic interferometry reconstructing the earth s reflection response in1968 jonclaerboutshowedthatthereflectionresponseofa 1dacousticmediumcanbereconstructedbyautocorrelatingthe transmission response since then several authors have derived relationships for reconstructing green s functions at the surface using crosscorrelations of noise recordings that were taken at thesurfaceandthatderivedfromsubsurfacesources foracousticmedia wereviewrelationsbetweenthereflection response and the transmission response in 3d inhomogeneous lossless media these relations are derived from a one way wavefield reciprocity theorem we use modeling results to show howtoreconstructthereflectionresponseinthepresenceoftransientsubsurfacesourceswithdistinctexcitationtimes aswellas inthepresenceofsimultaneouslyactingnoisesourcesinthesubsurface weshowthatthequalityofreconstructedreflectionsdepends on the distribution of the subsurface sources for a situation with enough subsurface sources that is for a distribution that illuminates the subsurface area of interest from nearly all directions the reconstructed reflection responses and the migrated depth image exhibit all the reflection events and the subsurface structures of interest respectively with only a few subsurface sources that is with insufficient illumination the reconstructed reflection responses are noisy and can even become kinematically incorrect at the same time however the depth image which was obtained from their migration still shows clearly all the illuminated subsurface structures at their correct positions for the elastic case we review a relationship between the reflection green s functions and the transmission green s functionsderivedfromatwo waywavefieldreciprocitytheorem usingmodelingexamples weshowhowtoreconstructthedifferent components of the particle velocity observed at the surface and resulting from a surface traction source this reconstruciton is achievedusingcrosscorrelationsofparticlevelocitycomponents measured at the surface and resulting from separate p and s wavesourcesinthesubsurface

crustal imaging across the north anatolian fault zone from the autocorrelation of ambient seismic noise seismic images of active fault zones can be used to examine the structure of faults throughout the crust and upper mantle and give clues as to whether the associated deformation occurs within a narrow shear zone or is broadly distributed through the lower crust limitations on seismic resolution within the crust and difficulties imaging shallow structures such as the crust mantle boundary moho place constraints on the interpretation of seismic images in this study we retrieve body wave reflections from autocorrelations of ambient seismic noise the instantaneous phase coherence autocorrelations allow unprecedented ambient noise images of the north anatolian fault zone nafz our reflection profiles show a moho reflected p wave and additional structure within the crust and upper mantle we image a distinct vertical offset of the moho associated with the northern branch of the nafz indicating that deformation related to the fault remains narrow in the upper mantle

receiver structure from teleseisms autocorrelation and cross correlation we present a way of characterizing the structure beneath a seismic station by exploiting stacked correlograms of three component records from teleseismic events this seismic daylight imaging approach exploits the extraction of reflection and conversion information from teleseismic coda via tensor autocorrelation the approach is illustrated for a number of australian stations in a variety of tectonic environments using hundreds of teleseismic events to extract p and s reflectivity and converted ps and sp information the results show a very good agreement with prior knowledge across australia compared with the classical receiver function the broader frequency band of 0 5 4 0 hz provides additional information on finer scale structure

temperature trends over the past five centuries reconstructed from borehole temperatures for an accurate assessment of the relative roles of natural variability and anthropogenic influence in the earth s climate reconstructions of past temperatures from the pre industrial as well as the industrial period are essential but instrumental records are typically available for no more than the past 150 years therefore reconstructions of pre industrial climate rely principally on traditional climate proxy records each with particular strengths and limitations in representing climatic variability subsurface temperatures comprise an independent archive of past surface temperature changes that is complementary to both the instrumental record and the climate proxies here we use present day temperatures in 616 boreholes from all continents except antarctica to reconstruct century long trends in temperatures over the past 500 years at global hemispheric and continental scales the results confirm the unusual warming of the twentieth century revealed by the instrumental record but suggest that the cumulative change over the past five centuries amounts to about 1 k exceeding recent estimates from conventional climate proxies the strength of temperature reconstructions from boreholes lies in the detection of long term trends complementary to conventional climate proxies but to obtain a complete picture of past warming the differences between the approaches need to be investigated in detail

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

distribution and transport of suspended sediments off the yellow river huanghe mouth and the nearby bohai sea abstract hydrological and sedimentological investigations were carried out off the yellow river huanghe mouth and the nearby bohai sea during august september 2007 to examine the distribution and transport of suspended sediments our data witnessed that suspended sediments from the yellow river mouth primarily extend southerly and southeasterly during the flood season high suspended sediment concentration ssc occurs as turbid plume on both sides of the river mouth where it can reach 20 mg l 1 in the surface water and 40 mg l 1 in the bottom water accordingly salinity varies from 25 to 29 psu mean grain size dmz is 200 m and volume concentration vc is 100 l l 1 high ssc was concentrated in the river mouth area as two muddy patches i e the north mud and south mud consisting mostly of fine grained silt and clayey silt sediments our results have verified the larger extent of the south mud than that of the north one implicating south and southeastward sediment dispersal paths that prevail near the river mouth area the existing anti clockwise and clockwise flows in the river mouth area were synthesized as the major hydrodynamics responsible for forming the two muddy patches tidal and residual currents are considered as the key hydrodynamic factors controlling the sediment distribution and transport in the region

recent morphological changes of the yellow river huanghe submerged delta causes and environmental implications abstract the yellow river huanghe submerged delta yrsd has been under the threat of erosion and retreat during the anthropocene due to dramatic climatic and anthropogenic changes in the yellow river basin the analysis of field data shows that over the period of 1977 2005 the changes in climate decrease in precipitation and increase in air temperature and human interventions increase in water diversion projects throughout the watershed have resulted in the sharp reductions of river flow and sediment discharges into the bohai sea consequently over the decadal timescale morphological evolution of the yrsd has gone through three stages i e rapid accumulation 5 77 10 8 m 3 year in 1977 1985 moderate accumulation 3 80 10 8 m 3 year in 1986 1995 and slow accumulation 0 91 10 8 m 3 year in 1996 2005 climatic change within the catchment characterized by the rapid increase of air temperature contributed significantly to the transitions from the rapid accumulation to the moderate accumulation and to the subsequent slow accumulation the decadal morphological changes of the yrsd also show peculiar deposition erosion characteristics over the medium timescale under river input reduction within the three decades the patterns of the main sedimentary body exhibit irregular ellipses with the long axis parallel to the 5 or 10 m isobaths and short axis perpendicular to the isobaths the depocentres of the yrsd are located between the 10 and 15 m isobaths close to the respective river mouths with a high vertical accretion rate of 1 20 m year the time series data of annual volumetric change of the yrsd and river sediment load from 1977 to 2005 further demonstrate significant linear positive relationships between deltaic geomorphic change and fluvial input over shorter timescales annual and 3 year the critical sediment discharges for maintaining the deposition erosion equilibrium state of the yrsd over the annual and 3 year timescales are found to be 1 79 10 8 t year and 1 29 10 8 t year respectively the analysis from the latest hydrological data 2006 2015 suggests that over the decadal timescale the evolution state of the yrsd currently has transitioned from constructive to destructive due to the weakened fluvial input moreover there exists a close quantitative link between the progradation of the yellow river subaerial delta yrad and the yrsd over the five year timescale indicating that every 1 10 8 m 3 year increase of the yrsd s yearly volumetric change will result in a 3 28 km 2 year increase of the yrad s yearly land accretion area and the yrad will reach the extension retreat balance state when yearly morphological change of the yrsd is at 0 73 10 8 m 3 year

critical role of wave seabed interactions in the extensive erosion of yellow river estuarine sediments abstract integrating field observations in the high erosion rate region of the chinese coastal zone northern estuary of the yellow river were used to investigate the role of wave seabed interactions in seabed erosion combined with laboratory erosion experiments on the variations in sediment erodibility due to cyclic wave loading the field results highlight a strong erosive event that occurred in the presence of high waves during which the seawater turbidity increased sharply from 50 ftu to 600 800 ftu and the bed elevation decreased by 7 7 mm h over 27 h the laboratory results attribute this type of erosion to the contribution of wave actions on seabed sediments where the waves probably acted as a plough and reduced the threshold velocity and critical shear stress values thus enhancing sediment transport that also occurs due to the shear effect of near bed currents during fair weather conditions wave induced liquefaction characterised by the uneven build up of excess pore pressures at different buried depths may also enhance sediment erosion by generating vertical pore water seepage within the sediment and inducing internal sediment re suspension the field observations allowed us to construct a regional mathematical model of seabed erosion that parameterises the wave seabed interactions as well as to explore the implications of this model for extensive erosion of yellow river estuarine sediments this research represents a major step towards validating the critical role of wave induced interactions in extensive sediment erosion events within a shallow estuarine system

dynamic characteristics of the yellow river mouth the yellow river delta is dynamic because the river carries a heavy sediment load and serious siltation occurs in the area massive sediment transport brings fertile soil to the river mouth leading to its expansion by 20 25 km2 per year the dramatic reduction in runoff and sediment in the delta due to increasing water demand has extended the period of flow cut off the river changes its delta channel about once every ten years the channel shifts affect the upstream flood stages since the river shifted to the present delta channel in 1976 the shape of the delta has changed remarkably sediment laden flow has been building channels by depositing sediment in low velocity areas and has extended the river mouth into the sea for more than 40 km the velocity of sea currents is enhanced by the growth of the river mouth spit at a rate of 1 m s 1 per 10 km extension which results in high capacity of sea currents carrying sediment away from the mouth the new river mouth area was silted up by 14 m and the old river mouth area was eroded by 5 m siltation takes place in the low flow season and scouring occurs in the flood season scouring occurs during the rising limb of a flood and siltation occurs during the receding limb of a flood the roughness of the river changes largely following the increase in discharge the minimum manning roughness occurs at non siltation and non erosion discharge tidal influence in the river is restricted to a section extending over only a few kilometres unlike in many other coastal areas the river water with its high sediment concentration develops into density current and flows underneath the seawater during flood this mechanism contributes to sediment transportation in the delta copyright 2000 john wiley sons ltd

retrieval of moho reflected shear wave arrivals from ambient seismic noise theoretical studies on ambient seismic noise asn predict that complete green s function between seismic stations can be retrieved from cross correlation however only fundamental mode surface waves emerge in most studies involving real data here we show that moho reflected body wave sms and its multiples can be identified with asn for station pairs near their critical distances in the short period band 1 5 s we also show that an uneven distribution of noise sources such as mining activity and wind topography interaction can cause surface wave precursors which mask weaker body wave phases

from gullies to mountain belts a review of sediment budgets at various scales this paper reviews the state of the art in the concept as well as in the application of sediment budgets in sedimentary research sediments are a product of mass dispersal at the earth surface and take part in global cycles sediment budgets aim at quantifying this mass transfer based on the principle of mass conservation and are the key to determine ancient fluxes of solid matter at the earth surface this involves fundamental questions about the interplay of uplift climate and denudation in mountain belts and transfer of sediments from the continents to the oceans as well as applied issues such as soil and gully erosion reservoir siltation and coastal protection first after introducing basic concepts relevant scales and methodologies the different components of quaternary routing systems from erosion in headwaters river systems glacial and paraglacial systems lakes deltas estuaries coasts shelves epicontinental seas and deep sea fans are discussed in terms of their sediment budget most suitable are sedimentologically closed or semi closed depositional environments e g alluvial fans lakes deltas and deep sea fans in a second step the dynamics of passive active and collisional tectonic settings and sediment budgets in related sedimentary basins are explored and new concepts of sediment portioning at large geodynamic scales are introduced ancient routing systems are more or less incomplete and may be intensively fragmented or destroyed in active tectonic settings in terms of sedimentary basin types rifts intracontinental and epicontinental settings are preferred objects of sediment budgets because of their persistence and relatively simple overall sedimentary architecture however closing basins such as foreland forearc retroarc piggy back and wedge top basins may provide excellent snapshots of orogenic sediment fluxes in a third step the large long lived routing systems of the amazon the ganges brahmaputra and the rhine are reviewed for each system estimates of either sediment volumes mass or sediment fluxes of continental and marine subsystems have been compiled in order to receive a complete routing in terms of mass conservation for specific time periods since the late glacial maximum as well as the cenozoic following lessons can be taken from these case studies i depositional centers and fluxes show strong shifts in space and time and call for caution when simply looking at subsystems ii the response times of these large systems are within the milankovich time interval thus lower than predicted from diffusion models iii cyclic routing of sediments in continental basins is much more dominated by climate human control than by eustacy and iv at long time scales ultimate sinks win over intermittent storage it is concluded from this review that the quantitative understanding of global sediment cycling over historic and geologic time and its response to allogenic forcing is still in its infancy and further research is needed towards a holistic view of sediment routing systems at various temporal and spatial scales and their coupling with global biogeochemical cycles this includes i to better determine response times of large routing systems by linking quaternary with cenozoic sediment budgets and continental with marine sub systems ii to combine advanced provenance techniques with sediment budgets in order to reconstruct ancient systems iii to study sediment partitioning at the basin scale iv to reconcile continental supply dominated sequence stratigraphy with the eustatic dominated marine concept and iv to account for non actualism of ancient systems with respect to their erosion and transport mode in particular during glaciations and pronounced arid intervals glacial and eolian sediment routing may cross over hydrologic boundaries of drainage basins thus challenging the principle of mass conservation

subsurface thermal environment and groundwater flow around tokyo bay japan previous studies and borehole temperature measurements suggest that subsurface temperature distribution on the west side of tokyo bay from tokyo to yokohama is higher than that of the east side chiba side to understand the groundwater flow and other factors which may contribute to the subsurface temperature discrepancy such as geological setting in the study area groundwater temperature profiles were measured in 119 boreholes around the tokyo bay from 2002 to 2007 the data were analyzed and compared with previous studies horizontal distribution of subsurface temperature at the depths of 50 and 100 m was made to show the distribution of thermal regime a cross section across the bay of tokyo was made to see the isothermal lines and distribution of hydraulic heads in a vertical perspective these results show that the highest subsurface temperature zone is in the tokyo area along the river valley subsurface temperature at the depth of 50 and 100 m below sea level in the western part of the bay is comparatively higher than its eastern side at the same elevation and distance from the bay this fact suggests that there is a regional groundwater flow system in the area and it is strongly affected by the geological structure particularly buried valley systems of the bay during the paleo tokyo river and the topographical driving force which is the result of the different elevation of recharge areas groundwater discharge is concentrated along the buried valley of paleo tokyo river

analyzing and modeling sub diffusive transport of bedload along a heterogeneous gravel bed using stochastic and statistical methods abstract bedload transport is one of the main mechanisms for sediment transport in rivers bedload transport may exhibit anomalous dispersion behavior during the formation of clusters on the surface of a heterogeneous river bed which cannot be quantified by the classical fick s law of diffusion this study simplifies the complex bedload transport process to a mass spring damper system which can describe the cluster formation process based on the observed cluster geometry the simulation results are consistent with the morphology of clusters extracted from the experimental gravel bed in our flume the level of spatial heterogeneity of individual clusters is characterized to distinguish the planform morphology of each cluster based on estimation of the hausdorff besicovitch dimension of the cluster area trapping of sediment particles during bedload transport on a heterogeneous gravel bed is quantified using a random walk approach and the birth death emigration immigration markov process sub diffusive dynamics of bedload transport is also modeled simultaneously using the langevin equation that defines statistical properties of bedload sediments further analysis indicates that the microscopic stochastic langevin equation relates to a macroscopic deterministic equation according to the continuous time random walk ctrw theory

crustal properties from seismic station autocorrelograms s u m m a r y stations on the australian continent receive a rich mixture of continuous ground motion with ambient seismic noise from the surrounding oceans and numerous small earthquakes in the earthquake belts to the north in indonesia and east in tonga kermadec as well as more distant source zones the ground motion at a seismic station contains information about the structure in the vicinity of the site and this can be exploited by applying an autocorrelation procedure to the continuous records by creating stacked autocorrelograms of the ground motion at a single station information on crust properties can be extracted in the form of a signal that includes the crustal reflection response convolved with the autocorrelation of the combined effect of source excitation and the instrument response after applying suitable high pass filtering the reflection component can be extracted to reveal the most prominent reflectors in the lower crust which often correspond to the reflection at the moho because the reflection signal is stacked from arrivals from a wide range of slownesses the reflection response is somewhat diffuse but still sufficient to provide useful constraints on the local crust beneath a seismic station continuous vertical component records from 223 stations permanent and temporary across the continent have been processed using autocorrelograms of running windows 6 hr long with subsequent stacking a distinctive pulsewith a time offset between 8 and 30 s fromzero is found in the autocorrelation results with frequency content between 1 5 and 4 hz suggestingp wave multiples trapped in the crust synthetic modelling with control of multiple phases shows that a local pmp phase can be recovered with the autocorrelation approach this identification enables us to make out the depth to the most prominent crustal reflector across the continent we obtain results that largely conform to those from previous studies using a combination of data from refraction reflection profiles and receiver functions this approach can be used for crustal property extraction using just vertical component records and effective results can be obtained with temporary deployments of just a few months

river sedimentation and channel adjustment of the lower yellow river as influenced by low discharges and seasonal channel dry ups fluvial sedimentation can be classified as one of the three types in terms of different morphological units i e vertical overbank deposition vertical deposition on the riverbed and lateral deposition on the riverbank with the example of the lower yellow river the three types of sedimentation have been studied in relation to channel adjustment since 1986 the lower yellow river has entered a new period that is characterized by small discharges with seasonal desiccations dry ups and strong sedimentation has occurred based on the measurement of 36 cross sections along the lower yellow river the rates of the three types of deposition have been calculated and are reported in this study multiple regression has been used to express the relationship between the three rates of deposition and the channel shape adjustment index influenced by the difference in channel sediment and by downstream variations in water discharge and sediment load the indices of channel deposition rate show a clear trend of downstream variation controlled by this the manner of channel adjustment also shows clear trends downstream under the hydrological regime dominated by small discharges the tendencies of adjustment of riverbed slope and bankfull slope are inverse i e the channel slope tends to decrease but the slope at bankfull stage to increase at present the former tendency is dominant thus the sediment carrying capacity of the lower yellow river tends to decrease which intensifies channel sedimentation

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

passive seismic imaging of a craton edge central australia abstract passive seismic recordings of teleseismic p wave arrivals and their immediate coda along a dense profile of stations can be used to image the reflection structure beneath the profile the process exploits the autocorrelation of the seismic signals that extracts the reflection response from the transmitted signals recorded at the surface which can be migrated to provide a depth image this common reflection point crp imaging exploits the same portion of the seismic record used in receiver function studies but is much less influenced by multiple problems in the presence of sediments this style of passive seismic imaging is applied to a dense line of 68 stations at 3 5 km spacing at the northern edge of the gawler craton in south australia in the mal experiment with nine months of passive seismic monitoring it has been possible to image fine scale structural variations throughout the lithosphere there is a strong variation in crustal thickness as the mal profile crosses the inferred location of the craton edge under sedimentary cover a transitional zone between crust and mantle can be identified that extends beneath the receiver function moho pinching out gently at the craton edge the crp imaging reveals distinct reflectivity in the lithospheric mantle with horizontal scales of 10 30 km and vertical scales of no more than a few kilometres the character of this reflectivity appears to change across the craton edge there are indications of a semi continuous mid lithosphere discontinuity at around 90 km depth

river mouth bar formation riverbed aggradation and channel migration in the modern huanghe yellow river delta china this paper addresses the recent 1970s 1990s processes of river mouth bar formation riverbed aggradation and distributary migration in the huanghe river mouth area in the light of station based monitoring field measurements and remote sensing interpretation the results show that the morphological changes of the river mouth bar have been closely associated with the largely reduced fluvial discharge and sediment load landforrn development such as bar progradation occurred in two phases i e before and after 1989 which correspond to faster and lower bar growth rates respectively fast riverbed aggradation in the mouth channel was strongly related to river mouth bar progradation during 1976 1996 about 2 8 of the total sediment loads were deposited in the river channel on the upper to middle delta therefore the river water level rose by a few meters from 1984 to 1996 the frequent distributary channel migration which switched the radial channel pattern into the se directed pattern in the mid 1980s was linked with mouth bar formation marine conditions also constrain seaward bar progradation furthermore the history of river mouth bar formation reflects human impacts such as dredging and dyking in order to stabilize the coastal area c 2005 elsevier b v all rights reserved

cheniers on the east coastal plain of china abstract three to four cheniers are found in the coastal areas of the bohai sea and west yellow sea they are formed in the sheltered low tidal flat coast with low to medium wave energy large quantity of fine sediment supply and shells and a coastal slope of 0 9 3 0 the huanghe river played a major role in controlling the chenier development by either providing sediment supply or cutting off the supply through shifting of its course cheniers may be used to determine the coastal development and dynamic processes

changes in sediment yield of the yellow river basin of china during the holocene this research reconstructs the changes in sediment yield of the yellow river based mainly on a large number of 14 c dates collected from the literature the total volume of sediment yield of the basin during the holocene is estimated to be 8 0 x 10 12 tons the annual sediment yield had an increasing trend over the holocene from 0 68 0 72 0 79 to 1 0 1 x 10 9 tons over each 2500 year period from the early holocene to the present the changes in sediment yield are ascribed to both natural and anthropogenic reasons in which the latter became important in the late holocene the mean rate of increase in natural sediment yield throughout the holocene is estimated to be about 0 027 x 10 6 ton year and the natural annual sediment yield is projected to be 0 95 x 10 9 tons at the present the increasing trend of natural sediment yield is reasoned to be the consequence of evolution of landforms enhanced by tectonic movement and climatic change in the loess plateau the principal sediment source of the river towards a condition favorable to soil erosion comparing the estimated annual natural sediment yield with the current annual sediment load of 1 6 x 10 9 tons of the river it is clear that human activities have augmented natural soil erosion by about 41 in the yellow river basin furthermore an estimate of the overall pattern of anthropogenic sediment yield shows an accelerated increasing trend which is approximately correspondent with that of population in the loess plateau area c 2002 elsevier science b v all rights reserved

do river deltas in east india retreat a case of the krishna delta abstract the construction of multiple dams and barrages in many indian river basins over the last few decades significantly reduced river flow to the sea and affected the sediment regime more reservoir construction is planned through the proposed national river linking project nrlp which will transfer massive amounts of water from the north to the south of india the impacts of these developments on fertile and ecologically sensitive deltaic environments are poorly understood and quantified at present in this paper an attempt is made to identify locate and quantify coastal erosion and deposition processes in one of the major river basins in india the krishna using a time series of landsat images for 1977 1990 and 2001 with a spatial resolution ranging from 57 0 m to 28 5 m the dynamics of these processes are analyzed together with the time series of river flow sediment discharge and sediment storage in the basin comparisons are made with similar processes identified and quantified earlier in the delta of a neighboring similarly large river basin the godavari the results suggest that coastal erosion in the krishna delta progressed over the last 25 years at the average rate of 77 6 ha yr 1 dominating the entire delta coastline and exceeding the deposition rate threefold the retreat of the krishna delta may be explained primarily by the reduced river inflow to the delta which is three times less at present than 50 years ago and the associated reduction of sediment load both are invariably related to upstream reservoir storage development

sediment dispersion pattern off the present huanghe yellow river subdelta and its dynamic mechanism during normal river discharge period hydrological observations were conducted synchronically along three transects in the southeast middle and northeast off the present huanghe yellow river subdelta during normal discharge approximately 200 m 3 s 1 period on august 8 13 2003 suspended sediment fluxes and dispersion patterns off the present huanghe subdelta were studied based on the hydrographic data collected in these surveys along each survey transect tidal shear fronts were identified that in combination with the tidal currents were the dominant factors controlling the pattern of sediment dispersal most of the river laden suspended sediment from the river mouth was transported via hypopycnal flow and was limited within the 5 m isobath off the mouth due to the barrier effect of the tidal shear front and the weak river flow in northern and southern areas off the subdelta the sediment fluxes at stations farther from the coast were much higher than those at the nearshore ones indicating that the river laden sediments were transported to north and south offshore via deeper water areas at both sides of the river mouth the tidal shear fronts revealed in the northern and southern nearshore areas of the subdelta jointly with tidal currents barred the sediment transport from offshore to nearshore this resulted in offshore sediment deposition on the northern and southern parts of the subaqueous subdelta rather than in the nearshore area thus forming nearshore erosion and offshore accumulation areas respectively

flood management on the lower yellow river hydrological and geomorphological perspectives abstract the yellow river known also as china s sorrow has a long history of channel changes and disastrous floods in its lower reaches past channel positions can be identified from historical documentary records and geomorphological and sedimentological evidence since 1947 government policy has been aimed at containing the floods within artificial levees and preventing the river from changing its course flood control is based on flood retarding dams and off stream retention basins as well as artificial levees lining the channel the design flood for the system has a recurrence interval of only around 60 years and floods of this and larger magnitudes can be generated downstream of the main flood control dams at sanmenxia and xiaolangdi rapid sedimentation along the river causes problems for storage and has raised the bed of the river some 10 m above the surrounding floodplain the present management strategy is probably not viable in the long term and to avoid a major disaster a new management approach is required the most viable option would appear to be to breach the levees at predetermined points coupled with advanced warning and evacuation of the population thus put at risk

seismic interferometry applied to regional and teleseismic events recorded at planchon peteroa volcanic complex argentina chile abstract the planchon peteroa volcanic complex ppvc is located in the central andes argentina chile even though this active volcanic system is considered one of the most dangerous volcanoes in the region with more than twenty modest vei seismic interferometry si is a high resolution technique based on analyses of the interference of the propagation seismic energy at one or many stations si can be used to characterize the subsurface properties of a target area in particular previous si studies performed in the area of the ppvc describe specific ranges of depth therefore more information is required for a thorough description of the subsurface features in the area and for a better understanding of the ppvc dynamics we apply si based on autocorrelations of selected regional and teleseismic events to image the subsurface structures below stations located in argentina and chile during 2012 the selection of the events is performed according to their location magnitude angle of incidence of p wave seismic energy and signal to noise ratio in the records for each station we extract time windows and we process them using two ranges of frequency which are sensitive to different depth ranges this work describes depths and zones previously not analyzed in the area using si methods the results not only complement the available geological geochemical and geophysical information but present new information for depths between 10 and 750 km depth increasing the general knowledge of the subsurface features in the ppvc finally we also propose a model for the subsurface down to the moho which indicates the crustal structure and the likely distribution of magma bodies in depth

moho geometry gravity inversion experiment moggie a refined model of the australian moho and its tectonic and isostatic implications abstract at the continent scale models of moho depth based on seismic estimates alone can be inadequate due to irregular or sparse data gravity based moho modelling provides better coverage however the methods used are typically hampered by an inability to explicitly honour seismic constraints and are also limited by over simplistic model conditions e g laterally homogenous layering i present a new method to generate a continent scale moho model based on the constrained inversion of free air gravity data this method explicitly honours seismic moho estimates and accounts for a laterally heterogeneous crust and mantle resolution and sensitivity testing shows that for wavelengths greater than 200 km crustal density and moho depth are recovered with reasonable accuracy 30 kg m 3 and 3 km respectively moggie uses a six layer model incorporating ocean sedimentary basin upper crust lower oceanic crust eclogitised crust and mantle inversion variables were the density of the crustal layers constrained by a standard density model and the depths to intra crustal boundaries and the moho constrained by 230 seismic depth estimates the results demonstrate that a balanced approach to seismically constrained gravity inversion has the capability to generate detailed and well constrained models of the moho and crustal density at the continent scale for australia this is a clear improvement on the sparse and irregular resolution of the moho provided by seismic estimates of crustal thickness which fail to resolve short wavelength features newly defined tectonic features include extensive magmatic underplates crustal scale shear zones and the boundaries between tectonic blocks isostatic analysis reveals that little of the continent is close to isostatic equilibrium with isostatic disequilibria preserved at multiple scales from hundreds of kilometres to the entire continent these disequilibria are interpreted to indicate long wavelength flexure of highly competent continental lithosphere

relation between the erosion and sedimentation zones in the yellow river china sedimentation in the lower reaches of the yellow river is a major problem requiring implementation of large scale control measures in the upper and middle drainage basin for maximum benefit major sediment generation areas must be delimited for this purpose the upper and middle drainage basin of the yellow river has been divided into four major sediment and water source areas a series of databases of runoff and sediment yields from these source areas and for the corresponding quantities of sedimentation in the lower yellow river channel have been established on this basis a set of multiple regression equations has been established that define the relationships between sedimentation in the lower yellow river and the yearly or event based runoff and sediment yields from the four source areas or subsystems based on the regression equations obtained the contribution of the four major source areas to the sedimentation in the lower yellow river channel can be estimated the results obtained indicate that given other factors for each ton of sediment reduced from the coarse sediment producing area csa the sediment deposited in the lower yellow river would be reduced by 0 455 ton for each ton of sediment reduced from the fine sediment producing area fsa the sediment deposited in the lower yellow river would be reduced by 0 154 ton only therefore if limited erosion control measures are applied to the coarse sediment producing area the benefits for sedimentation reduction in the lower yellow river will be much larger than if similar resources are applied to the fine sediment producing area c 2002 elsevier science b v all rights reserved

overbank and channelfill deposits of the modern yellow river delta abstract the huanghe is noted for its high transport rate of silt and clay which may reach depth averaged values of 200 kg m 3 during peak discharge the sediment load transported through the river on entering the delta plain amounts to 1012 kg per year in contrast to most other large deltas only one distributary channel is active at any one time the high sediment load causes the rivermouth to prograde at a yearly rate of 1 4 km into the shallow less than 20 m deep bohai gulf the vertical aggradation of the channel belt and mouth bar complex is also rapid decimetres per year on average so that after a normal average of twelve years increasing channel instability and avulsion create the start of a new delta lobe a series of satellite images covering the last fifteen years has provided insight in the evolution of the river pattern as well as the progradation of the delta front a newly developed distributary passes from a multichannel to a single straight channel system and ends with the formation of meanders the protruding mature delta lobe shows a radiating pattern of crevasse channels overbank crevasse deposits are made of vertically stacked dm scale waning flow sequences structurally characterized by from bottom to top small scour and fills even parallel lamination and climbing ripple crosslamination accumulation rates on crevasse splays can be predicted on the basis of estimated river sediment discharge it can be concluded that each sequence has been deposited within a few hours and that tidal waterlevel fluctuations may have played a role in the generation of a single sequence

morphological adjustment of the qingshuigou channel on the yellow river delta and factors controlling its avulsion abstract the avulsion time scale of channels on the yellow river delta yrd is about a decade due to the large sediment load and rapid channel aggradation and progradation nevertheless the qingshuigou channel has been maintained for about four decades since 1976 this channel provides an ideal opportunity to study channel evolution following avulsion and to examine different avulsion criteria in this study we analyzed the geomorphic adjustment of the lower qingshuigou channel during 1976 2015 and calculated normalized gradient advantage and superelevation at the channel to estimate how close the channel was to avulsion results showed that channel evolution processes may be divided into four phases i 1976 1980 rapid aggradation ii 1980 1985 channel widening and enlargement iii 1985 1996 main channel aggradation and shrinkage and iv 1996 2015 main channel incision and deepening evolution phases i ii and iii are similar to the avulsion cycle observed in natural and experimental fluvial systems the calculated values of normalized gradient advantage and superelevation in early 1990s exceeded the critical values suggested by previous studies implying that the channel was prone to avulsion nevertheless avulsion was prevented mainly due to limited overbank flows constriction from artificial dikes and slowed channel extension as a result of reduced sediment load the evolution of the qingshuigou channel confirms previous arguments that superelevation and gradient advantage are not sufficient for avulsion and multiple factors should be considered including flood frequency lateral mobility sediment diameter and human interruptions

yangtze river of china historical analysis of discharge variability and sediment flux hydrological records covering a 100 year period from the upper middle and lower yangtze river were collected to examine the temporal and spatial distribution of discharge and sediment load in the drainage basin the yangtze discharge as expected increases from the upper drainage basin downstream only an estimated 50 of the discharge is derived from the upper yangtze with the rest being derived from the numerous tributaries of the middle and lower course however the distribution of sediment load along the yangtze is the reverse of that observed for discharge with most of the sediment being derived from the upper basin a dramatic reduction in sediment load by 0 8 108 tons year occurs in the middle yangtze because of a marked decrease in slope and the change to a meandering pattern from the upper yangtze rock sections considerable siltation also occurs in the middle yangtze drainage basin as the river cuts through a large interior dongting lake system sediment load in the lower yangtze while significantly less than that of the upper river is somewhat higher than the middle yangtze because of additional load contributed by adjacent tributaries a strong correlation exists between the discharge and sediment load along the yangtze drainage basin during the dry season as lower flows carry lower sediment concentration during the wet season a strong correlation is also present in the upper yangtze owing to the high flow velocity that suspends sand on the bed however a negative to poor correlation occurs in the middle and lower yangtze because the flow velocity in these reaches is unable to keep sand in suspension transporting only fine grained particles downstream hydrological data are treated for 30 years 1950 1980 when numerous dams were constructed in the upper yangtze drainage basin at yichang and hankou hydrological stations records revealed a decreasing trend in annual sediment load along with slightly reduced annual discharge at the same stations this can be interpreted as the result of water diversion primarily for agriculture sediment load at datong further downstream is quite stable and not influenced by slightly reduced discharge furthermore sediment concentration at the three hydrological stations increased which can be attributed to sediment loss in association with intensifying human activity especially in the upper drainage basin such as deforestation and construction of numerous dams mean monthly sediment load of these 30 years pulses about 2 months behind discharge implying dam released sediment transport along the entire river basin during the high water stage

multimode surface wave tomography for the australian region using a three stage approach incorporating finite frequency effects 1 a three stage inversion technique for surface wave tomography is applied to the australian region the inversion procedure consists of three independent processes in the first stage path specific one dimensional 1 d shear velocity profiles are derived from multimode waveform inversion to provide dispersion information the information from all paths is then combined to produce multimode phase speed maps as a function of frequency the first version of these phase speed maps is derived from linearized inversion based on the assumption of surface wave propagation along great circle paths subsequently the 2 d phase speed maps are updated by including ray tracing and finite frequency effects through the influence zone around the surface wave paths over which the phase is coherent finally in the third stage the 3 d shear wave speed distribution is reconstructed from the set of updated multimode phase speed maps this three stage inversion of surface waves has significant benefits because it is possible to incorporate multimode dispersion off great circle propagation and finite frequency effects for surface waves in a common framework the final 3 d model which includes the effects of ray bending and finite frequency shows improvement in the definition of the model in regions with high gradients in shear velocity such as near tectonic boundaries especially in eastern australia despite the natural smoothing imposed by considering the influence zone around the surface wave paths the final models still require rapid change in shear wave properties in the neighborhood of the edge of the craton

mechanics of river mouth bar formation implications for the morphodynamics of delta distributary networks 1 in this paper we use observational data and numerical modeling to present a new explanation for the formation of river dominated delta networks observational data from deltas throughout the world show that distributary channel widths depths and lengths decrease nonlinearly with successive bifurcations trends in width and depth are an outcome of hydraulic geometry scaling the trend in channel length is a consequence of delta growth analyses of serial maps show that the positions of bifurcations are the fossilized locations of river mouth bars also called middle ground and distributary mouth bar in front of old delta channel mouths therefore the trend in channel length can be explained through the mechanics of river mouth bar formation and evolution we use delft3d a coupled hydrodynamic and morphodynamic model to simulate the process of river mouth bar formation within an expanding turbulent jet in front of distributary channel mouths our results describe in detail the formation and evolution of a river mouth bar system and demonstrate that the distance to the river mouth bar is proportional to jet momentum flux and inversely proportional to grain size therefore channel length decreases down delta because with each successive bifurcation the jet momentum flux decreases these results can be used to predict the future evolution of river dominated deltas and can be used to aid in hydrocarbon exploration of these depositional environments

causes for continuous siltation of the lower yellow river previous studies indicate that aggradation of a river channel is caused by upriver and or downriver controls but the evaluation of their relative importance is often difficult a method is proposed to isolate the effect of the downriver control based on the slopes of the existing river profile those of the graded profile estimated from the discharge sediment relationship and slope reduction due to local base level rise the method was applied to the rapidly aggrading lower yellow river the downriver control in this case refers to the local base level rise associated with deltaic extension during the period under discussion the result shows that the main portion of siltation along the river is not caused by downriver control but by the slope difference between the existing and the graded profiles over a period within the last 700 years assuming conditions of discharge and sediment load during the period from 1962 to 1985 are reflective of the long term the marked slope difference between the existing and the graded profiles of the river is a result of changes in the river environment in the past several thousand years including the increase of sediment load local base level rise associated with river lengthening by deltaic growth and relative sea level rise due to tectonic subsidence of the coastal alluvial plain

crust mantle boundary reflectors in nevada from ambient seismic noise autocorrelations summary the depth of reflector layers in the earth s crust is usually estimated using controlled sources or earthquake signals ambient seismic noise however can also be used for this purpose we develop and apply a new method based on continuous waveform analysis to estimate the two way p wave reflection component of the green s function beneath each station the green s functions are retrieved from continuous record autocorrelation stacks at broad band sensor locations within the usarray earthscope transportable array in the western great basin and the sierra nevada in a region with complex crustal and upper mantle structure in this paper we show evidence of a reflector at the crust mantle boundary moho discontinuity derived for the first time from ambient noise autocorrelations using short period 1 s data our results compare well with earthquake and controlled source investigations and with tomography findings in the region moho depth is difficult to resolve seismically because of the lack of favourable spatial distribution of source and receiver geometries in contrast our method can be applied at any desired sensor spacing to estimate earth reflector depth beneath surface located sensors providing unprecedented resolution

progradation of the yellow huanghe river delta in response to the implementation of a basin scale water regulation program the water and sediment supply to the lower reach and estuary of the yellow huanghe river have been altered to a very significant degree by the construction of numerous small to large reservoirs and the progressive implementation of water and soil conservation measures across the entire drainage basin since the late 1950s followed by a basin scale water regulation program since 2002 there is an urgent need to know how progradation of the yellow river delta yrd an area on which people live and farm has continued and will continue to respond to these controls this study examines the changing patterns of water and sediment supply to the yrd over the period of 1950 2013 and using remote sensing it evaluates the morphological changes of the delta during 1976 2013 although both water and sediment input to the delta have been described as declining significantly since the mid 1960s we show that since 2005 the supply of water has remained at around 20 billion m 3 yr 1 and that for sediment at about 0 13 billion t yr 1 water input has been even slightly increasing the dynamics of extension shrinking and avulsion in river mouth channels and accretion erosion of shorelines is an integrated response to the complex variations in both sediment and water supply this study develops a quantitative relationship between water and sediment supply and the area of land accretion and it predicts the critical condition for land accretion in the yrd to ensure that delta land will not be lost care is needed in the future implementation of the basin scale water regulation program c 2015 elsevier b v all rights reserved

estimation of sediment compaction and its relationship with river channel distributions in the yellow river delta china abstract the geomechanical properties of the stratigraphic sequences strongly influence the land surface subsidence as the latter can be caused by the sediment compaction depositional units of transitional environments such as coastal plain and deltas are characterized by a high lithological variability due to the history and complexity of the sedimentary processes therefore detailed modeling of the stratigraphic architecture is necessary to better understand the land surface subsidence process and accurately estimate its rates the frequent avulsion and rearrangement of the channel network in the modern yellow river delta since 1855 has led to the rapid accumulation and deposition of large amounts of sediment in the delta plain the compaction of the substratum sediment due to the new sediment load and the consolidation of younger deposits caused land surface subsidence we used 108 sediment core data covering the delta and obtained detailed stratigraphic structural information a detailed distribution of clay and soft clayey soils which are the primary contributors to land subsidence was identified furthermore the compaction rates and the consolidation at time of the subaerial area and neritic area for the entire modern yellow river delta were estimated we also analyzed the characteristics of present land subsidence by combining a ground movement dataset obtained by high resolution topographic surveys with synthetic aperture radar sar interferometry insar of satellite images the results show that during the early stages of the development of the active deltaic lobe the compaction of neritic sediments was the primary contributor to initial subsidence furthermore combined with the relevant sedimentary age and environment determined by previous studies we found that the spatial variation in compaction induced subsidence in the subaerial deltaic area over time is closely related to the historical distributions of the river channels in the modern yellow river delta our findings providing a better characterization of the spatial and time heterogeneity of the land surface subsidence of both subaerial and submarine areas significantly improved the previous knowledge on land subsidence of the yellow river delta our results also demonstrate that the subaerial delta becomes increasingly stable over time with the gradual decrease in the average subsidence rate of each deltaic lobe

stacking autocorrelograms to map moho depth with high spatial resolution in southeastern australia current estimates of moho depth in southeastern australia are based on sparse sampling the results are augmented with 180 new moho estimates constructed from spatial stacks of crustal p wave reflectivity derived from autocorrelograms at over 750 stations the spatial stacks of reflectivity are constructed using a gaussian with half width 0 5 picks of the base of crustal reflectivity are made with the aid of the previous moho model based on the sparser data and knowledge of the variation in the character of the crust mantle boundary across the region good ties can be made to previous results from deep reflection profiling the new information fills in many holes in coverage and provides a moho map with closer ties to geological provinces the procedure exploits the continuous records at the stations and just the vertical components and so can be applied to older data for which receiver function techniques cannot be used

sedimentation in the yellow river delta part ii suspended sediment dispersal and deposition on the subaqueous delta abstract rapid deposition and suspended sediment dispersal off the modern yellow river mouth has been examined from the data of topographic maps 1 25 000 suspension and bed sediments current and salinity which were measured in the field the results show that the sedimentation rate of the mouth bar is the highest of all the environments of deposition in the modern yellow river delta about 30 40 of the sediment that the river transports into the sea has been deposited within the mouth bar area rapid deposition of the mouth bar results mainly from kinetic energy dissipation of the river under the influence of three ambient mechanisms these three mechanisms occur simultaneously as shear front movement which obstructs the river s jet like flow small scale circulations where large velocity gradients occur and the bulldozer effect of the tide sensitive zone in the estuary at ebb based on the analysis of morphologic changes the mouth bar can be divided into two morphologic types one is the double lobe and single channel type and the other double channel and single lobe type weak hyperpycnal plumes with small density differences between the river flow and ambient water dissipate rapidly and deposit about 20 of the river sediments on the delta front slope while hyperpycnal underflows from the river mouth can go through the steep delta front slope to form a rise apron along the upper part of the prodelta grain size analysis of suspended sediment shows that the flow can be divided into three layers a tide layer in the upper part and a hyperpycnal layer in the lower part these two layers are normally graded and a transition layer with inverse grading in the mid part the fine suspended sediments have been transported in the hypopycnal plume layer into the prodelta and deep sea such as the north huanghai sea north yellow sea this study indicates that the tidal current field has dominated the distribution of deposition of sediment on the subaqueous delta and the movements of the river effluent and hyperpycnal underflows

sedimentation in the yellow river delta part i flow and suspended sediment structure in the upper distributary and the estuary abstract a 44 year data record measured by lijin hydraulic station on the yellow river shows that sediment concentration has been increasing while river discharge has been decreasing into the delta since the 1970s these changes are important because flood waters of the yellow river which are heavily laden with sediment must be used to supply dongying city and shengli oil company which are located on the delta based on the analyses of data of velocity sediment concentration salinity and sediment grain size from four cross section measurements at lijin station and one 8 vessel simultaneous measurement cruise in the estuary structural characteristics of the river flow and suspended sediments throughout the upper distributary and the estuary have been studied and discussed results show that when sediment concentrations of the yellow river exceed 100 kg m 3 in the lower layer of the river flow during the flood period the river flow structure does not coincide with the logarithmic law of wall and becomes vertically layered and the vertical distributions of suspended sediment do not coincide with the diffusion law the channel length influenced by the tide wave is less than 15 km and there is no tidal intrusion flow only weak osmosis of salinity occurs inside the river mouth during the flood period of the yellow river simultaneous 8 vessel measurements and simulation using the method of preissman show that there is a tidal sensitive zone inside the river mouth bar with a length of 6 7 km when the discharge is as large as 1100 m 3 s and an area of very active sedimentation the tidal sensitive region near the river mouth becomes a low velocity zone that traps a large amount of river sediment which rapidly forms a plastic bed at flood tide and a high velocity zone with a strong hydrodynamic action to erode the new bed and transport the sediments into the sea at ebb tide

modeling deltaic lobe building cycles and channel avulsions for the yellow river delta china river deltas grow by repeating cycles of lobe development punctuated by channel avulsions so that over time lobes amalgamate to produce a composite landform existing models have shown that backwater hydrodynamics are important in avulsion dynamics but the effect of lobe progradation on avulsion frequency and location has yet to be explored herein a quasi 2 d numerical model incorporating channel avulsion and lobe development cycles is developed the model is validated by the well constrained case of a prograding lobe on the yellow river delta china it is determined that with lobe progradation avulsion frequency decreases and avulsion length increases relative to conditions where a delta lobe does not prograde lobe progradation lowers the channel bed gradient which results in channel aggradation over the delta topset that is focused farther upstream shifting the avulsion location upstream furthermore the frequency and location of channel avulsions are sensitive to the threshold in channel bed superelevation that triggers an avulsion for example avulsions occur less frequently with a larger superelevation threshold resulting in greater lobe progradation and avulsions that occur farther upstream when the delta lobe length prior to avulsion is a moderate fraction of the backwater length 0 3 0 5l b the interplay between variable water discharge and lobe progradation together set the avulsion location and a model capturing both processes is necessary to predict avulsion timing and location while this study is validated by data from the yellow river delta the numerical framework is rooted in physical relationships and can therefore be extended to other deltaic systems

historical changes in the yellow river delta china abstract the lower yellow river delta has experienced numerous avulsions during the last 2000 years and the floodplain can be divided into four provinces alluvial fan western plain middle plain and eastern plain coastal deltas the yellow river delta complex is composed of several delta superlobes resulting from shifts in the lower river channel and each delta superlobe consists of several smaller lobes formed by shifts in the distributary channels these two kinds of channel shifts have resulted in a complicated imbrication pattern in the delta complex two imbricated delta superlobes are divided by a reworked bed and buried shelf deposits shelly ridges form the surface boundaries between the various delta superlobes the delta superlobes passed through an active stage a reworking stage and were then finally overlain by later superlobes

ausmoho the variation of moho depth in australia summary since 2004 more than 7000 km of full crustal reflection profiles have been collected across australia to give a total of more than 11000 km providing valuable new constraints on crustal structure a further set of hitherto unexploited results comes from 150 receiver functions distributed across the continent mostly from portable receiver sites these new data sets provide a dramatic increase in data coverage compared with previous studies and reveal the complex structure of the australian continent in considerable detail a new comprehensive model for moho depth across australia and its immediate environment is developed by utilizing multiple sources of information on shore and off shore refraction experiments are supplemented by receiver functions from a large number of portable stations and the recently augmented set of permanent stations and moho picks from the full suite of reflection transects the composite data set provides a much denser sampler of most of the continent than before though coverage remains low in the remote areas of the simpson and great sandy deserts the various data sets provide multiple estimates of the depth to moho in many regions and the consistency between the different techniques is high in a number of instances differences in estimates of moho depth can be associated with the aspects of the structure highlighted by the particular methods the new results allow considerable refinement of the patterns of moho depth across the continent some of the thinnest crust lies beneath the archean cratons in the pilbara and the southern part of the yilgarn thick crust is encountered beneath parts of the proterozoic in central australia and beneath the palaeozoic lachlan fold belt in southeastern australia the refined data indicate a number of zones of sharp contrast in depth to moho notably in the southern part of central australia

dynamic morphology of small south eastern mediterranean river mouths a conceptual model river mouths along the israeli mediterranean coast are characterized by a dynamic morphology as their channels migrate hundreds of meters along the coast this study examines the dynamic morphology of seven such river mouths it offers a conceptual model aimed at generalizing and describing their spatial and temporal morphological patterns and the environmental factors influencing them the study methodology comprised a detailed monitoring and mapping by gis techniques with quantitative data derived from historic aerial photographs river discharge records wave measurements and a digital elevation model these data were incorporated into a homogenous database and subsequently applied in the investigation of the morphological patterns of these mouths and the analysis of their influencing factors river mouths in this study occur in two distinctive topographic settings in one setting here termed barrier topography the river mouth is deflected alongshore by a sandy barrier in the second setting termed funnel topography the river mouth is confined to a funnel shaped topographic depression perpendicular to the coast the behavior of river mouths in these two settings is quite distinctive barrier mouths usually migrate over larger distances as they tend to deflect along a sand barrier and establish semi permanent channels along the dune toe this enables the wide range migration of semi permanent channels over decades funnel topography mouths deflect over shorter distances and they rapidly migrate within the funnel boundaries this study concludes that the topographic setting of the beach a constant element in the temporal scale of this study is the primary influencing factor on the morphology of the mouths studied the influence of other factors on the morphology of these mouths differs in space and time and depends on the topographic settings

processes and mechanisms of dynamic channel adjustment to delta progradation the case of the mouth channel of the yellow river china this paper analyses the processes and mechanisms of a three stage channel adjustment over a cycle of the yellow river mouth channel extension based on data comprising hydrologic measurements and channel geometric surveys rapid siltation in the mouth channel takes place in the young stage when the channel is being built by deposits and in the old stage when the channel cannot further adjust itself to keep sediment transport in equilibrium it is disclosed that the bankfull width depth ratio bed material size and slope decrease in the young and mature stages but do not change in the old stage the reduction of bankfull width depth ratio and bed material size during the young and mature stages is found to be able to offset the effect of the slope reduction on sediment transport due to continuous mouth progradation they reach their limits in old stage and a constant slope is kept by unceasing sediment accumulation the grain size composition of incoming sediment and the fining mechanism are responsible for the occurrence of lower limit of bed material size the reason for the existence of a limit of bankfull cross sectional shape is that the large flows can fully transport the sediment load they are carrying and siltation in the channel in the old stage takes place mainly in the low flows it is suggested that the bankfull discharge plays an important role in shaping the channel but that the entire channel form is the product of both the large and low flows plus the effects of interaction between them channel pattern change shows a process from a braided pattern in the young stage to a straight pattern in the mature and old stages and the straight channel becomes gradually sinuous the occurrence and transformation of the channel patterns are supported by two planform predictors but are also facilitated by some other conditions copyright c 2003 john wiley sons ltd