the grain size gap and abrupt gravel sand transitions in rivers due to suspension fallout median grain sizes on riverbeds range from boulders in uplands to silt in lowlands however rivers with 1 5 mm diameter bed sediment are rare this grain size gap also marks an abrupt transition between gravel and sand bedded reaches that is unlike any other part of the fluvial network abrupt gravel sand transitions have been attributed to rapid breakdown or rapid transport of fine gravel or a bimodal sediment supply but supporting evidence is lacking here we demonstrate that rivers dramatically lose the ability to transport sand as wash load where bed shear velocity drops below 0 1 m s forcing an abrupt transition in bed material grain size using thresholds for wash load and initial motion we show that the gap emerges only for median bed material grain sizes of 1 5 mm due to reynolds number dependencies in suspension transport the grain size gap therefore is sensitive to material properties and gravity with coarser gaps predicted on mars and titan

using hydroacoustic stations as water column seismometers 1 getting seismic data from the deep oceans usually involves ocean bottom seismometers but hydrophone arrays may provide a practical alternative means of obtaining vector data we here explore this possibility using hydrophone stations of the international monitoring system which have been used to study icebergs and t wave propagation among others these stations consist of three hydrophones at about the depth of the deep sound channel in a horizontal triangle array with 2 km sides we use data from these stations in the very low frequency regime 0 01 0 05 hz band to demonstrate that these stations can also be used as water column seismometers by differencing the acoustic pressure we obtain vector quantities analogous to what a seismometer would record comparing processed hydrophone station records of the 2004 great sumatra andaman earthquake with broadband seismograms from a nearby island station we find that the differenced hydrophones are indeed a practical surrogate for seismometers

dynamics of intertidal gravel dunes 1 this paper examines the dynamics of intertidal gravel dunes subjected to high energy unsteady and reversing tidal currents in the severn estuary uk the dunes were composed of shale particles with median grain size d50 around 4 mm and had mean heights and wavelengths of 60 cm and 7 m respectively acoustic instruments were deployed above a dune to measure the streamwise profile and flow turbulence radar was used to map a section of the dune field on two occasions measurements during the peak spring ebb tides showed that when the measured bed shear stress exceeded the threshold for entrainment of the coarse surface armor sediments were eroded from the upper surface of the dune the dune prograded in the direction of the ebb flow a distance o 1 m and some eroded sediments were deposited on the stoss slope downstream the dune was then reworked during the following flood tide to reestablish approximately the same pre ebb profile shape and location radar data showed also that the exposed dunes at low water occupied approximately the same location over a period of 4 days during peak spring tides the relationship between the depth mean current and the net volume of dune sediments moved was found to conform to a power law the predicted critical bed shear stress crit for d50 4 mm was approximately 1 n m2 however owing to a coarse armor layer on the surface of the dune a measured crit value o 4 n m2 was required to initiate dune erosion although the van rijn formula was found to overestimate both the height and wavelength of dunes at this site the dunes appear to be equilibrium bed forms controlled by local hydraulics and sediment supply sediment transport predicted by bed load formula were within a factor of two of the observed mass transport of dune sediments for ebb tides

use of s wave attenuation from perforation shots to map the growth of the stimulated reservoir volume in the marcellus gas shale abstract water filled fractures stimulated by hydraulic fracturing will severely attenuate s waves by comparing the p and s wave amplitudes generated from perforation shots in the marcellus gas shale one can infer the existence and constrain the location of stimulated hydraulic fractures the waveforms of the perforation shots in unstimulated gas shale are first analyzed to define the prestimulation radiation pattern then the change of perforation shot s wave waveform is examined for information about the development of hydraulic fractures s wave attenuation validates the existence of offstage hydraulic fractures and the invasion of treatment fluid from another neighbor stage this method might have potential use in designing an active seismic survey to more effectively monitor hydraulic fracture stimulation beyond the current microseismic mapping techniques

morphology and controls on the position of a gravel sand transition fraser river british columbia alluvial river channels often exhibit a relatively abrupt transition from gravel to sand bedded conditions the phenomenon is well documented but few prior studies have analyzed the spatial variability through reaches where transitions occur the downstream fining pattern observed in the fraser river is cited as a classic example of an abrupt gravel sand transition in a large alluvial channel however important questions regarding the exact location of the transition its sedimentology and morphology and what controls its location remain unanswered here we present observations of the downstream change in bed material grain size river bed topography and channel hydraulics through the reach within which the transition occurs these observations indicate that the gravel sand transition is characterized by a terminating gravel wedge but there are patches of gravel downstream of the wedge forming a diffuse extension we show that there is a dramatic decrease in shear stress at the downstream end of the wedge and a consequent cessation of general gravel mobility we argue that the patches of gravel observed beyond the wedge are the result of enhanced mobility of fine gravel over a sand bed we also find that sand in suspension declines rapidly at the downstream end of the wedge suggesting that sand is delivered to the bed completing the sedimentary conditions for a gravel sand transition we propose that the break in river slope associated with the transition is a consequential feature of the transition

sediment supply limited bedforms in sand gravel bed rivers the stability of bedforms in mixtures of gravel and sand is not well understood two bedform types are characteristic flow parallel sand ribbons and flow transverse barchans flume experi ments and field data presented here show that gradual transitions exist from sand ribbons to barchans and from barchans to fully de veloped dunes barchans and sand ribbons occur when not enough transportable sediment is available for the formation of fully devel oped ripples or dunes the reason is that a part of the bed sediment is immobile e g with an armor layer which limits the sediment sup ply and thus the volume of sediment available for the formation of bedforms bedform stability diagrams are shown to be extendable to sedi ment supply limited bedforms in sand gravel sediment if the par ticle parameters of the diagrams are derived from the transported sediment instead of the bed sediment barchans and forms transi tional to fully developed dunes plot in the dune stability fields sand ribbons on the other hand plot in the ripple lower plane bed and dune fields in the case of sediment supply limitation bedforms are partly or completely related to the characteristics of the sediment supply from upstream the sediment underlying the bedforms may be a stable armor and the exchange of sediment between this armor and the bedforms may be small or non existent consequently bedform char acteristics in sand gravel mixtures in supply limited conditions often are not predictable from the local hydraulics and sediment charac teristics

sediment transport along lower fraser river 1 measurements and hydraulic computations a comprehensive program of sediment transport measurements was conducted along lower fraser river british columbia between 1966 and 1986 the data yield a detailed sediment budget annual total suspended loads at three stations are virtually identical averaging 17 106 tonnes year t yr 1 the suspended sand load is about 5 5 106 t yr 1 about one third of the total in the gravel bed reach of the river the sand behaves as wash load significant transport of gravel begins at agassiz at a discharge of about 5000 m3 s 1 the annual gravel transport was estimated to be about 0 23 106 t yr 1 only 1 of the total load all of this material is deposited in the reach upstream of mission at mission sands finer than 0 177 mm make up more than 50 of the suspended sand load but are virtually absent from the sand bed therefore a portion of the sand load at mission is wash load the total bed material load here was estimated to be 3 0 106 t yr 1 about 18 of the total sediment load virtually all of the bed material load was transported in intermittent suspension near the bed less than 5 occurring as bed load in the long term the suspended sand load upstream is approximately equal to the total sand load at mission however within individual years some of the sand is stored within the reach temporarily and then reentrained later

initiation and displacement of landslide induced by earthquake a study of shaking table model slope test landslide researches often focus on factor of safety critical acceleration and displacement for an earthquake induced landslide the initiation and displacement of the landslide were important factors for definition of failure in this research the shaking table model slope test is adopted for study of slope failure initiation based on analyses of limit equilibrium particle image velocimetry piv analysis and acceleration time history recorded within the model slope based on the analyses landslide initiation could be defined as surface and local movement of the slope slope failure could be defined based on the massive movement of the slope the piv analysis provides good information for identifying both surface movement and massive movement the landslide displacement determined from the slope movement provides consistent results compared to observed displacements

using dual well seismic measurements to infer the mechanical properties of a hot dry rock geothermal system high frequency 8 15 khz seismic waves that travel between two boreholes are used to probe the detailed structure of rock in the los alamos national laboratory fenton hill hot dry rock geothermal energy reservoir we study travel times of direct p waves and spectral characteristics of waveforms in an effort to determine whether or not large fluid filled fractures are present in the rock between the two boreholes data from two experiments separated in time by 1 year are studied we find dramatic differences between the two experiments in p wave velocity and in spectral characteristics of waveforms that traversed the same region we also find variations in p wave velocity and spectra as a function of location during one experiment loss of high frequency content of direct arriving p waves during the second dual well seismic experiment is compared with q found by using the coda wave technique aki and chouet 1975 and also with theoretical results on frequency dependence of transmission through a water filled fracture to determine the minimum number of large fractures in the system two to four fractures with thickness about 4 mm and vertical extent of as much as 200 m are required to explain observations during the second experiment efficient transmission of high frequencies observed during the first experiment is interpreted as meaning that fracture thickness was less than 1 mm at that time increased fracture thickness during the second experiment is probably due to a 75 day period of heat extraction during which in situ temperature dropped by as much as 100 below the virgin temperature since the coefficient of linear thermal expansion of granite is approximately 10 5 c a decrease in temperature of 100 c in a region on the order of 1 m around the fracture is required to explain the increased fracture thickness

interaction of seismic waves with a viscous liquid layer abstract the interaction of seismic waves with a layer filled with a viscous fluid is studied this study is intended to provide the basis for designing active seismic experiments to detect the existence of hydraulically induced fractures in a hot dry rock geothermal energy system we compute transmission and reflection coefficients for p sv and sh waves incident at arbitrary angles onto a fluid layer embedded between two homogeneous half spaces we find that coefficients for sh waves at normal incidence can be written in terms of two dimensionless parameters one of these parameters i is the ratio of acoustic impedance of the fluid to the acoustic impedance of the solid the other dimensionless parameter d is a measure of the amount of energy the sh wave loses during one pass through the fluid layer we find that the amplitude of the sh wave transmitted through the fluid layer is equal to the amplitude of the incident sh wave if i is nearly 1 and d is small as d increases energy is lost due to viscous dissipation in the fluid and transmitted wave amplitude diminishes if i is not nearly 1 some energy is reflected by the fluid layer three dimensionless parameters are required for solution for the case of p waves normally incident on the fluid layer one parameter r is the ratio of the bulk modulus to effective shear modulus of the fluid the second parameter is the ratio of elastic impedance of the solid to the shear impedance of the fluid and the third is d we find that the value of r is a good measure of the importance of fluid viscosity on the propagation of p waves through the fluid detailed studies of the effects of fluid and solid physical properties on the amplitudes of transmitted and reflected waves when waves are normally incident provide valuable insight into the importance of physical properties in the calculations for non normal incidence finally reflection and transmission coefficients are computed for p and sv waves incident at arbitrary angle on a viscous fluid layer physical properties of fluid and rock are chosen to be those thought appropriate for the los alamos national laboratory hot dry rock geothermal test site located at fenton hill new mexico

giant dune morphologies and dynamics in a deep continental shelf environment example of the banc du four western brittany france the aim of this paper is to improve the knowledge of spatio temporal variability of very large to giant dunes in deep tide dominated environment their growth mechanisms and dynamic evolution still remain in debate and constitute a significant scientific challenge in regard to difficulties to achieve accurate measures of migrations this motivated the realization of three recent swath bathymetry surveys across the wide dune field of the banc du four located offshore the western brittany the banc du four field is composed of more than 500 large dunes exhibiting a great diversity of morphologies ranging from 2d to 3d shapes and reaching the largest sizes of such sedimentary structure ever described wavelength over 1000 m and height over 30 m the analysis of the entire ensemble of dune parameters offers the opportunity to discuss the relative influence of forcings and the validity of the equations predicting the bedform geometry in shallow waters our results show a good height spacing power law correlation but do not strike the usual statistical regression observed in previous studies the steeper positive slope of the equation and the outstanding values of the height parameter reveal the complexity of local hydrodynamic regime interacting with bed load transport and sediment supply no clear relationship has been observed between asymmetry and size parameters water depth can not be considered as a major factor controlling the size of dunes otherwise the vertical sedimentary variation suggests the action of storm waves on dune crests and the horizontal migration rates of dunes in the eastern field of the banc du four were found to range from 3 to 20 m yr 1 such velocities were only mentioned before by van landeghem et al 2012 on deep continental shelves 70 m deep and attest of the still present morphodynamical equilibrium of the large dunes furthermore as was previously found for similar dunes in the irish sea no power law relationship between dune migration rates and dune size can be deduced similarly no strong correlation is established between migration rates and the degree of asymmetry nevertheless the dune asymmetry can be used to predict the migration direction as for dimension parameters the evolution asymmetry depends on the study area and migration rates more precisely when the crest lines of dunes form straight lines and their migration rates remain below 8 10 m yr 1 the degree of dune asymmetry increases with the migration rate this trend is reversed for the dunes with higher migration velocities and crests which are sinuous these results relativize the migratory predictions based on punctual geometrical observations

flow and sediment suspension events over low angle dunes fraser estuary canada 1 the morphodynamics of large sand bedded rivers and estuaries are ultimately controlled by the way bed material is moved and the development of large subaqueous sand dunes that control hydraulic flow resistance it is widely thought that the primary mechanism for moving sandy bed material in these channels is large scale coherent flow structures that cause suspension events whose properties vary with flow especially in tidally influenced environments here we examine mean flow and sediment suspension events over low angle dunes lee face angle 30 in the unsteady flow of the fraser estuary canada at high tide flow nearly ceased and a salt wedge entered the channel forcing salt water under the downstream moving fresh water the salt wedge persisted in the channel until late in the falling tide causing stratification in the water column and instabilities along the saline fresh water interface at low tide mean velocities peaked and forced the saline water out of the channel flow over the low angle dunes displayed topographically induced patterns previously observed over high angle dunes but permanent flow separation was not observed large scale sediment suspension events dominated sediment flux during low tide and became larger scale yet less frequent as the tide began to rise the suspension events appeared to form over the lower stoss of the dunes and grew up over the bed forms and less commonly emerged downstream of the crest suspension events move 69 of the total sediment in the flow above low angle dunes when they are present

effects of filling fluid type and composition and joint orientation on acoustic wave propagation across individual fluid filled rock joints abstract wave propagation and attenuation in subsurface rock masses could be highly affected by rock joints filled with fluids however the understanding of acoustic behaviours across fluid filled rock joints is still at its infancy to determine the effects of the type and composition of filling fluids as well as joint orientation on compressional wave propagation and attenuation across individual fluid filled rock joints extensive laboratory acoustic tests were conducted in this paper results showed that the existence of water in fluid filled rock joints results in higher wave velocity more wave transmission and less wave attenuation compared to light oils in most circumstances increasing liquid content in a single liquid filled joint enhances wave velocity and wave transmission for dual liquid filled joints both wave velocity and wave transmission increase with increasing water content joint orientation significantly affects wave characteristics of rock joints partially filled with liquids while it has slight influences on wave attributes of rock joints fully filled with liquids in addition wave velocity and attenuation across fluid filled rock joints increases with increasing central frequency of incident compressional waves

the gravel sand transition sediment dynamics in a diffuse extension as gravel bedded rivers fine in the downstream direction they characteristically exhibit an abrupt transition from gravel to sand bedded conditions the prevailing theory for why abrupt gravel sand transitions emerge is based on bed load sorting of a bimodal sediment the abruptness is thought to be a consequence of sand overwhelming the gravel sand mixture once it reaches a critical coverage on the bed the role suspension plays in the development of gravel sand transitions has not been fully appreciated the fraser river british columbia is an archetypical abrupt gravel sand transition with a diffuse extension composed of a sand bed with some patches of gravel we examine flow shear stress and suspended sediment flux in the diffuse extension to better understand sediment dynamics where the sand bed emerges sand is carried in suspension upstream of the primary abrupt gravel sand transition but in the diffuse extension sand is moved as both bed load and suspended load we do not observe downstream gradients in shear stress or suspended sand flux through the diffuse extension that would suggest a gradual rain out of sand moving downstream which raises the question how is the sand bed formed sediment advection length scales indicate that with the exception of very fine sand that moves as wash load in the diffuse extension fractions coarser than the median sand size cannot be carried in suspension for more than one channel width this suggests that sand is deposited en masse at the beginning of the diffuse extension forming a sediment slug at low flood flows that is smeared downstream at high flood flows to form the sand reach

a shaking table model test on a rock slope anchored with adaptive anchor cables abstract to determine the load transfer mechanism and dynamic response characteristics of an adaptive anchor cable aac equipped with a mechanical energy dissipation device a shaking table model test was conducted on rock slope test models anchored with a system consisting of several aacs that were fabricated based on a landslide mass in xiangjiapo during the test the strain of the aac structure and the dynamic response of the slope model were monitored to determine the anchoring mechanism of the aac system and the dynamic characteristics of the aac system anchored slope model the sliding sleeve energy dissipation device of the aac automatically adjusted its tension or deformation to allow its deformation to be consistent with that of the rock and earth mass thereby buffering the impact at the instant of the start of seismic loading the constant sliding resistance of the aac determined its working conditions under a certain seismic loading condition when the constant sliding resistance was set excessively high the energy dissipation device was ineffective under the seismic loading when the constant sliding resistance was set too small the aac slid at the instant of the start of seismic loading however when the constant sliding resistance and the sliding distance were set to proper values the aac slid gradually in a stepwise motion and its peak strain was significantly lower the test results can be used as a reference for designing cut slopes in regions of high seismicity and in selecting anti seismic engineering measures for these slopes

the lowermost mississippi river a mixed bedrock alluvial channel in this study the distribution of channel bed sediment facies in the lowermost mississippi river is analysed using multibeam data complemented by sidescan sonar and compressed high intensity radar pulse seismic data as well as grab and core samples of bed material the channel bed is composed of a discontinuous layer of alluvial sediment and a relict substratum that is exposed on the channel bed and sidewalls the consolidated substratum is made up of latest pleistocene and early holocene fluvio deltaic deposits and is preferentially exposed in the deepest thalweg segments and on channel sidewalls in river bends the exposed substratum commonly displays a suite of erosional features including flutes that are quantitatively similar in form to those produced under known laboratory conditions a total of five bed facies are mapped three of which include modern alluvial deposits and two facies that are associated with the relict substratum a radius of curvature analysis applied to the mississippi river centreline demonstrates that the reach scale distribution of channel bed facies is related to river planform from a broader perspective the distribution of channel bed facies is related to channel sinuosity higher sinuosity promotes greater substratum exposure at the expense of alluvial sediment for example the ratio of alluvial cover to substratum is ca 1 5 1 for a 45 km segment of the river that has a sinuosity of 1 76 and this ratio increases to ca 3 1 for a 120 km segment of the river that has a sinuosity of 1 21 the exposed substratum is interpreted as bedrock and given the relative coverage of alluvial sediment in the channel the lowermost mississippi river can be classified as a mixed bedrock alluvial channel the analyses demonstrate that a mixed bedrock alluvial channel boundary can be associated with low gradient and sand bed rivers near their marine outlet

hydrodynamic significance of variable ripple morphology across deep water barchan dunes in the faroe shetland channel a combination of high resolution 30 khz sidescan sonar and seafloor photography has been used to image barchan dunes and sand ripples in the faroe shetland channel the barchan dunes display body lengths and horn to horn widths of up to 120 m and the horns point downcurrent to the southwest the seafloor surrounding the dunes is variable with gravel patches sand with gravel streaks and uniform rippled sand all observed the pattern of sand ripples across the dune surface is strongly controlled by the dune morphology on the lower stoss slopes of the dunes straight crested transverse ripples gradually merge upslope into sinuous crested transverse ripples most of the upper dune surface is dominated by short crested linguoid ripples this sequence represents an increase in height above seafloor and increasing flow velocity the overall pattern of ripples across the dune surface indicates that the bottom current flow is modified by the dune morphology with flow concentrated over the dune crest and along the inner edge of the horns it is also possible to estimate flow velocity across the dune field using published analogues and short term current meter observations generally published examples of submarine barchans suggest a flow velocity of 40 80 cm s this range of values is in agreement with near bed current meter measurements in the study area which indicate peak flow velocities of 50 60 cm s however in the longer term higher flow speeds may be possible especially considering the presence of erosional furrows adjacent to the dune field

characteristics of the landslide dams induced by the 2008 wenchuan earthquake and dynamic behavior analysis using large scale shaking table tests abstract the ms 8 0 wenchuan earthquake triggered at least 257 landslide dams more than 300 aftershocks with the magnitudes higher than ms 4 0 occurred after the formation of these landslide dams which might largely influence the structure and soil properties of these dams this paper aims to comprehensively investigate the characteristics of the landslide dams induced by the 2008 wenchuan earthquake and study the dynamic behaviors of the landslide dams under aftershocks using large scale shake table tests first the characteristics of the landslide dams including the distribution geometric parameters stability and longevity mitigation measures and the influence of the aftershocks are proposed then two groups of shaking table tests to simulate the dynamic behaviors of two types of landslide dams under aftershocks are illustrated one with quartz sand contained 10 kaolin dam i and the other with quartz sands all dam ii finally the results of the tests including the acceleration distribution dam deformation and dam breaching process are discussed through this study it is found that the landslide dams caused by high magnitude earthquakes have distinctive characteristics which may largely influence the stability breach process and risks of these dams in the model tests the accelerations are generally higher on the surface of the dams either on the crest or on the both upstream and downstream slopes the dam i was prone to settlement and cracking the aftershocks may not directly trigger the failures of landslide dams but accelerate the overtopping failures by lowering the dam crest with settlement and cracking

equivalent medium representation of fractured rock a similarity may be found between various approaches for determining the effects of parallel fractures or aligned cracks on seismic wave propagation at wavelengths that are long compared with the scale length of the cracks fractures can be modeled using an empirical linear slip condition however natural fracture surfaces can also be simulated directly as planar distributions of small isolated areas of slip cracks model 1 or conversely as planar distributions of imperfect interfacial contacts model 2 an alternative is plane surfaces separated by thin continuous layers of viscous fluid or a soft material model 3 we present analytic expressions for the fracture compliances for these three models and using these analytic results compute the effective compliances and stiffnesses of the fractured material as a result it is possible to relate the measured compliances or stiffnesses directly to the statistics of the microstructural details of a fracture given appropriate a priori information on the fracture surfaces the results for model 1 are equivalent to a volume distribution of cracks as studied by hudson 1980 1981 for small crack density the results for model 2 are basically the same as those given by white 1983 for a packing of spheres and finally the results for model 3 are in agreement with those given by backus 1962 for combinations of two constituent layers these results can be extended to the case of nonaligned fractures and to allow for fluid flow between cracks and into a porous matrix rock finally it is shown that the ratio of the normal to shear fracture compliance is a good indicator of the properties of the fracture infill

the relationship between microseismicity and high pore pressures during hydraulic stimulation experiments in low permeability granitic rocks several hundred microearthquakes with local magnitudes ranging between 4 and 2 were recorded during hydraulic stimulation experiments at the hot dry rock demonstration site fenton hill new mexico these events are probably caused by shear failure induced by high pore fluid pressures since the event locations seem to cluster in a narrow band near the hydraulic fracture we were able to use micro seismic techniques to locate the hydraulic fracture and monitor its growth we calculate the minimum pore pressure increase necessary to induce rock failure using a simple model of slippage on preexisting fractures by comparing a pore pressure distribution calculated using a one dimensional diffusion model with the distribution of event foci we demonstrate that high pore pressures are a probable cause for these microearthquakes stress drops for these microearthquakes calculated from spectral parameters increased by a factor of 3 during the course of the experiment the stress drop increase correlates with a migration of seismic activity away from the injection well bore which suggests relatively low in situ shear stresses near the well bore caused by strain release in this region during previous pressurizations

landslides triggered by the 20 april 2013 lushan earthquake sichuan province china abstract the 20 april 2013 lushan earthquake with a magnitude of m s 7 0 induced widespread landsliding along the southern segment of the longmen shan fault zone this paper presents a preliminary analysis of the characteristics of these co seismic landslides triggered in an area of 13 323 km 2 a total of 3810 individual landslide points were identified through an intensive field investigation and from digital aerial photographs taken after the lushan earthquake to facilitate the more detailed analysis on the areal frequency of co seismic landslides as polygons we selected an area of 732 km 2 around the epicenter that had the highest density of co seismic landslides the sizes of the landslides are in general much smaller than those that were triggered by the 2008 wenchuan earthquake the most common types of landslides in the study area were rock falls and shallow disrupted landslides from steep slopes which typically involved the top few meters of weathered bedrock and colluvium in this study the relation between the landslide distribution and five main factors was analyzed fault proximity epicenter proximity peak ground acceleration pga slope angle and lithology our study results show that the landslide concentration tends to decrease with distance from the seismogenic fault and the highest landslide concentration is located within a distance of 5 km regarding the distance to the epicenter the largest landslide density is found at a distance between 5 and 10 km the landslide concentration also increases with increasing slope angle until a maximum for the slope class 45 55 in addition results show that slopes consisting of deeply weathered and fractured sandstones and mudstones were the most susceptible to co seismic landslides in this study we found that the location of the hanging wall and the footwall of the fault did not seem to have an important effect on the landslide distribution this is in contradiction to what has been reported in other earthquake areas such as the wenchuan area

transport of fine sediment over a coarse immobile riverbed sediment transport in cobble boulder rivers consists mostly of fine sediment moving over a coarse immobile bed transport rate depends on several interrelated factors boundary shear stress the grain size and volume of fine sediment and the configuration of fine sediment into interstitial deposits and bed forms existing models do not incorporate all of these factors approaches that partition stress face a daunting challenge because most of the boundary shear is exerted on immobile grains we present an alternative approach that divides the bed into sand patches and interstitial deposits and is well constrained by two clear end member cases full sand cover and absence of sand entrainment from sand patches is a function of their aerial coverage entrainment from interstices among immobile grains is a function of sand elevation relative to the size of the immobile grains the bed sand coverage function is used to predict the ratio of the rate of entrainment from a partially covered bed to the rate of entrainment from a completely sand covered bed which is determined using a standard sand transport model we implement the bed sand coverage function in a morphodynamic routing model and test it against observations of sand bed elevation and suspended sand concentration for conditions of nonuniform fine sediment transport in a large flume with steady uniform flow over immobile hemispheres the results suggest that this approach may provide a simple and robust method for predicting the transport and migration of fine sediment through rivers with coarse immobile beds

evaluation of the three dimensional configuration of a subsurface artificial fracture by the triaxial shear shadow method we have determined the three dimensional configuration of a single fracture in the hot dry rock model field at higashi hachimantai japan by the triaxial shear shadow method the crack was created by hydraulic fracturing in intact welded tuff at a depth of 370 m we have carried out crosshole seismic measurements by using a downhole air gun and a triaxial seismic detector extinction at a special polarization direction and the dependency of transmissivity in shear wave component on incident angle were determined by a triaxial hodogram analysis of detected signals we have evaluated the orientation and distribution of the fracture using the shear wave extinction and the three dimensional configuration of the fracture by a continuation of the evaluated orientations the results are in good agreement with the data obtained by independent experiments in the field

the morphodynamics and internal structure of intertidal fine gravel dunes hills flats severn estuary uk in the macrotidal severn estuary uk the dynamics of intertidal fine gravel dunes were investigated these dunes are migrating across a bedrock platform systematic observations were made of hydraulic climate geometry migration rates and internal sedimentary structures of the dunes during spring tides the ebb flow is dominant dunes grow in height and have ebb orientated geometry with bedrock floors in the troughs during neap tides a weak flood flow may dominate dunes then are flood orientated or symmetrical neap dune heights decrease and the eroded sediment is stored in the dune troughs where the bedrock becomes blanketed by muddy gravel during spring tides instantaneous bed shear stresses reach 8 n m 2 sufficient to disrupt a 9 mm gravel armour layer however a sustained bed shear stress of 4 n m 2 is required to initiate dune migration at which time the critical depth mean velocity is 1 m s 1 ebb and flood inequalities in the bed shear stress explain the changes in dune asymmetry and internal structures during flood tides the crests of the dunes reverse such that very mobile sedimentary caps overlie a more stable dune core because ebb tides dominate internal structures of the caps often are characterised by ebb orientated steep open work foresets developed by strong tidal currents and some lower angle crossbeds deposited as weaker currents degrade foresets the foresets forming the caps may be grouped into cosets tidal bundles and are separated from mud infused cores of crossbeds that lie below by reactivation and erosion surfaces blanketed by discontinuous mud drapes the cores often exhibit distinctive muddy toe sets that define the spacing of tidal cosets

reevaluating dune scaling relations abstract in sand bedded rivers dunes dominate sediment transport and flow resistance dunes are also commonly preserved in fluvial deposits as cross stratified units that record their size shape and migration rates prediction of dune dimensions is therefore important for forecasting modern river channel dynamics as well as reconstructing past fluvial environments on earth and other planets predictions are often made by assuming that the formative flow depth h sets dune dimensions with height scaling as 1 6h and length as 5h yet there is a suite of other scaling relations that link dune dimensions to other variables like grain size transport stage and froude number here we present a new compilation of flow and dune dimension data to evaluate scaling relations the data reveal approximately two orders of magnitude variation in dune height and length at any given flow depth dune heights in shallow flows 2 5 m are often more symmetric have lower lee angles are relatively shorter in height than 1 6h and have a wider range of observed heights for a given depth none of the scaling relations predict the observations exceptionally well likely because of natural variability in dune dimensions and because they do not explicitly account for the apparent scaling break that occurs at 2 5 m we propose new simple depth scaling relations with added statistical uncertainty for the prediction of dune height and length from flow depth as well as flow depth from dune height we conclude that shallow and deep flow dunes exhibit different scaling due to a change in the dominant process controls as dunes get larger

development of subaqueous barchanoid shaped dunes due to lateral grain size variability in a tidal inlet channel of the danish wadden sea development of barchanoid shaped dunes

sediment dynamics across gravel sand transitions implications for river stability and floodplain recycling data collection was funded through a nerc gcrf building resilience grant ne p015905 1 to h d s and an epsrc gcrf institutional grant ep p510944 1 to m a sampling equipment was lent by ed tipper and bob hilton the rtk gps was loaned from the nerc geophysical equipment facility

stability analysis of three dimensional seismic landslides using the rigorous limit equilibrium method abstract in this paper a new method combining the rigorous limit equilibrium method and the pseudo dynamic method is proposed to investigate stability of 3d seismic landslides in which the force equilibrium conditions along three coordinate axes and the overall moment equilibrium conditions around three coordinate axes are all strictly satisfied moreover sinusoidal cosinusoidal wave is applied to simulate earthquake displacement and an amplification factor of peak seismic acceleration is referred to as the amplification of seismic wave when it propagates from the bottom to the top of landslides the pseudo dynamic factor of safety of 3d seismic landslides is determined using trust region reflective iterative algorithm the effects of the parameters of the seismic landslides on the stability are analyzed by the bp neural network algorithm in which a database to investigate the stability of 3d seismic landslides is established in addition the stability of donghekou landslide is studied to verify the accuracy and precision of the present method

an experimental study into the geometry of supply limited dunes the relationship between dune geometry and the volume of mobile sediment was studied in flume experiments in these flume experiments the volume of mobile sediment on top of an immobile coarse sediment layer was increased stepwise and the bedform characteristics were observed a strong relationship was found between the volume that is mobile and therefore available for bedform formation and the dune dimensions and regularity if the sediment supply is limited dunes are smaller and more regular series of experiments with a decreasing supply limitation were conducted for different flow velocities and water depths the relationship between the dune dimensions and the available volume is different for each series the observed relationships between dune dimensions and layer thickness collapse to one relationship for height and one for length if scaling parameters are introduced current models for bedform dimensions under alluvial conditions can be extended to partial transport conditions using this relationship

macroturbulence generated by dunes fraser river canada abstract a selectable frequency acoustic profiler and electromagnetic current meter were deployed in the lower fraser river canada to examine large turbulent structures features were generated on the lower stoss sides of dunes and appeared at the surface tens of metres downstream as strong upwellings boils they were identified with acoustic clouds in the acoustic profile event recurrence periods measured from acoustic time series and from ejection events identified in the current meter record had similar two component frequency distributions but the acoustic values lacked the highest frequencies a comparison of measured periods with predictions from the strouhal law indicate that both dune amplitude and the internal boundary layer developed over the dunes are significant length scales associated with the generation of the macroturbulence our data give no support to the notion that boils develop from microturbulent bursts