application of numerical wave propagation techniques to study local soil effects the case of benevento italy many of the numerical techniques used for seismic zonation studies treat one dimensional structural models and or the incidence of plane polarized body waves these techniques are often not adequate for laterally heterogeneous structures and for sources that are not located beneath the site of interest in such cases a more rigorous treatment of the combined effects of the source the path and the site response is needed this can be accomplished with a hybrid approach combining modal summation and the finite difference technique to demonstrate the differences between these techniques the ground motion in the city of benevento italy is modelled we first compare the results obtained with one and two dimensional structural models for vertical incidence of plane polarized body waves these results are then compared with those obtained with the hybrid approach for two dimensional structural models

elastic finite difference modeling of the 1971 san fernando california earthquake finite difference seismograms calculated for the 1971 san fernando earthquake show strong effects due to lateral variation in sediment thickness in the san fernando valley and the los angeles basin using basin structure derived mostly from well logs and teleseismically determined source parameters two dimensional sh and p sv finite difference calculations reproduce the amplitude and duration of the strong motion velocities recorded across the los angeles and san fernando basins for the period range of 2 to 10 sec the edges of basins nearest the seismic source show ground motion amplification up to a factor of 3 over the case without the basin and tend to convert direct shear waves into love and rayleigh waves that travel within the basins

site amplifications observed in the gubbio basin central italy hints for lateral propagation effects abstract in this study we investigate the site amplification effects observed in the gubbio plain central italy the recordings of 140 local earthquakes 1 2 ml 4 7 observed by two linear arrays installed along the longitudinal and perpendicular basin axis are analyzed both in the time and frequency domains to determine the spatial variation of the local site effects in the basin the time series recorded in the gubbio plain are characterized by locally generated surface waves which cause a significant increase in both ground motion duration and amplitude with respect to a nearby reference station on a rock site in the middle of the basin where the sedimentary cover is thickest ca 600 m the peak ground velocity is amplified on average by a factor of 5 with respect to the reference station installed on rock and the duration is increased by a factor of about 2 the analyses in the frequency domain show that the spectral energy of the basin generated waves is mainly distributed over the range 0 4 2 hz and affects both horizontal and vertical components the site responses estimated by applying two reference site methods show that the overall shape of the amplification functions is similar for the sites located inside the basin with a difference in the amplification levels which can reach values as high as 30 in the middle of the valley amplifications up to a factor of 10 affect the vertical component of ground motion over a broad frequency range for nearly all basin sites with the maximum amplifications occurring at around 1 hz finally although the horizontal to vertical spectral ratios were found to provide a reliable estimation of the fundamental resonance frequency of the site they fail to estimate the shape of the site transfer function

influence of different extraction methods on prehistoric phytolith radiocarbon dating abstract the use of carbon in phytoliths for radiocarbon dating is recognized as a non traditional radiocarbon dating method its reliability in constructing the chronological sequence of archaeological sites has been questioned in recent studies the influence of different phytolith extraction methods on dating results has been considered as the potential cause of distortion in phytolith dating however few studies have focused on comparing different phytolith extraction methods for measuring radiocarbon in this study we applied two methods a conventional method utilizing pre treatment with h2o2 and hcl and an improved method to extract phytoliths from the cultural layers of several archaeological sites in china the results showed that phytolith dates acquired using the conventional method were approximately 3000 10 000 years older than those found using the improved method this large distortion in phytolith dates was likely caused by clays within the phytoliths and organic materials on the surfaces of phytoliths which were not completely removed the phytolith dates acquired using the improved method were consistent with the ages estimated from the typological sequence indicating that our soil phytolith dates were not markedly biased by the older carbon absorbed from the soil

ambient vibration analysis of an unstable mountain slope summary a field experiment with small aperture seismic arrays was performed on the unstable rock slope above the village of randa in the southern swiss alps the aim of this experiment was to constrain the seismic response of a potential future rockslide using ambient vibration recordings weak seismic events were identified on the recordings and site to reference spectral ratios were calculated using a reference site located on the stable part of the slope spectral ratios of up to 30 were observed at sites located within the unstable portion of the slope a strong variation of spectral ratios with azimuth indicates a directional site effect neither amplification nor directionality were observed at sites located in the stable part of the slope furthermore time frequency polarization analysis of the ambient noise was performed to provide robust estimates of frequency dependent directions of the maximum polarization it was found that the unstable part of the slope vibrates within a narrow range of directions 130 10 for the frequency range centred around 5 hz the polarization directions estimated from ambient seismic vibrations are in good agreement with the deformation directions obtained by geodetic and in situ measurements no directionality of ambient vibrations was observed at sites within the stable part of the slope

effects of geometry on the seismic wavefield of alpine glaciers passive seismology allows measurement of the structure of glaciers and ice sheets however most techniques used so far in this context are based on horizontally homogeneous media where parameters vary only with depth 1 d approximations which are appropriate only for a subset of glaciers here we analyze seismic noise records from three different types of glaciers plateau valley and avalanching glacier to characterize the influence of the glacier geometry on the seismic wavefield using horizontal to vertical spectral ratios polarization analysis and modal analysis we show that the plateau glacier and the valley glacier can be seen as 1 d whereas the relatively small avalanching glacier shows 3 d effects due to its bed topography and the deep crevasses in principle the techniques proposed here might allow monitoring such crevasses and their depth and thus to constrain a key parameter of avalanching and calving glacier fronts

depth averaged drag coefficient for modeling flow through suspended canopies aquatic suspended canopies are porous obstacles that extend down from the free surface but have a gap between the canopy and bed examples of suspended canopies include those formed by aquaculture structures or floating vegetation the major difference between suspended canopies and the more common submerged canopies which are located on the bottom boundary is the influence of the bottom boundary layer beneath the suspended canopy data from laboratory experiments are presented which explore aspects of the flow through and beneath suspended canopies constructed from rigid cylinders the experiments using both acoustic doppler and two dimensional 2d particle tracking velocimetry give details of the flow structure that may be divided vertically into a bottom boundary layer a canopy shear layer and an internal canopy layer the experimental data show that the penetration of the shear layer into the canopy is limited by the distance between the canopy and bottom boundary layer peaks in velocity spectra indicate an interaction between the bottom boundary and canopy shear layer an analytical model is also developed that can be used to calculate a drag coefficient that includes the effect of both canopy drag and bed friction this drag coefficient is suitable for use in 2d depth averaged hydrodynamic modeling the model also allows the average velocity within and beneath the canopy to be calculated and is used to investigate the effect of canopy density and thickness on both total drag and bottom friction

a new method for extracting the insoluble occluded carbon in archaeological and modern phytoliths detection of 14c depleted carbon fraction and implications for radiocarbon dating phytolith rich layers in archaeological sites constitute well defined stratigraphic horizons that would be invaluable if absolutely dated previous attempts to radiocarbon date phytoliths produced inconsistent results using plants with known ages in this study a new approach to extract and analyze the silica occluded carbon was tested on well dated archaeological contexts in beth shemesh and tell es safi gath and on modern wheat plants that grew in a controlled environment results show that by dissolving the silica using mild conditions phytolith insoluble fractions can be extracted and their radiocarbon contents analyzed reproducibly after phytolith dissolution the remaining insoluble fractions with 10 30 c have radiocarbon concentrations that are statistically similar to associated charred seeds within 2 and insoluble fractions with 40 c show concentrations that are identical to the seeds these results show that the insoluble fraction of phytoliths is a suitable material for answering chronological questions

stable isotope ratios of carbon in phytoliths as a quantitative method of monitoring vegetation and climate change the 13c 12c ratios of occluded carbon within opal phytoliths from the northern great plains show potential as a basis for paleoclimatic reconstruction a significant correlation exists between the carbon isotopic composition of a host plant and that of the organic matter in its phytoliths the 13c 12c ratios for phytoliths from surface layers of soils along climatic gradients reflect the current proportions of c3 and c4 plants variations in the 13c values of phytoliths with soil depth are caused by a variety of processes burial of soil surface by dust bioturbation and possible illuviation by percolating water also contributions of phytoliths by dust and roots have unknown isotopic effects the 13c values of phytoliths from soils increase with decreasing 14c age suggesting that the proportion of c4 plants in this region has increased during the holocene phytoliths of apparent mid holocene age suggest exclusive dominance by c4 plants which agrees with paleoclimatic interpretations of an arid middle holocene climate

a combined inversion of rayleigh wave dispersion and 2 d resonance frequencies summary shear wave velocities of the sediment fill of a deep alpine valley are estimated from ambient noise recorded on linear and circular arrays we propose a combined inversion of 2 d reso nance frequencies identified from site to reference spectral ratios and rayleigh wave dispersion curves obtained from frequency wavenumber analysis the method is tested on synthetic noise data and on noise recorded at three sites in the rhone valley in southern switzerland previous studies have shown that 2 d resonance dominates the ambient vibration wavefield at low fre quencies at the investigated sites inversion techniques which assume that the noise wavefield consists mainly of horizontally propagating surface waves will therefore fail to resolve shear wave velocities at depths below around 500 m we show that standard techniques lead to an overestimation of shear wave velocities at depth when applied to synthetic and observed am bient noise the combined inversion is able to resolve the shear wave velocities in the initial velocity model when applied to synthetic noise records application of the method to observed ambient noise improves resolution at depth and yields realistic shear wave velocities for the lower part of the sediment fill

phytolith rich layers from the late bronze and iron ages at tel dor israel mode of formation and archaeological significance the presence of many phytolith rich layers in late bronze and iron age deposits at tel dor israel are indicative of specific locations where plants were concentrated detailed studies of six of these phytolith rich layers and associated sediments from tel dor show that the phytoliths were derived mainly from wild and domestic grasses the most common domestic grass was the cereal triticum aestivum bread wheat three of these layers have a microlaminated microstructure associated dung spherulites and phosphate nodules characteristics that all point to the phytolith rich layers having formed from dung in animal enclosures in two of the layers the microlaminated structure is absent while dung spherulites and phosphate nodules are present suggesting that these too originate from dung that was not deposited in an enclosure the sixth layer is microlaminated but does not contain spherulites we thus cannot suggest a parsimonious explanation of its observed properties concentrations of burnt phytoliths are present in three locations implying that dung was either burnt in situ or the ashes from burnt dung were redeposited the transformation of dung accumulations into phytolith rich layers involves a loss of organic material and hence a significant reduction in sediment volume which is clearly apparent in the stratigraphy of some of the locations examined the volume reduction can be observed in the macrostratigraphy and has important implications with regard to macrostratigraphic interpretation the presence of abundant phytolith rich layers on the tell has significant implications for the concept of urbanism during these periods 2007 elsevier ltd all rights reserved

the seismic response of two dimensional sedimentary deposits with large vertical velocity gradients an extension of the aki larner technique to vertically inhomogeneous media is presented so that vertical velocity gradients may be taken into account in two dimensional models only sh waves are considered here but the theory is valid for p and sv waves as well this method is applied to investigate the seismic response of two dimensional sedimentary deposits with large velocity gradients three different cases are considered a shallow high contrast valley a deep high contrast valley and a deep low contrast valley in each case a comparison is performed with the results of a two dimensional model taking into account only homogeneous sediments and a one dimensional model taking into account the vertical inhomogeneity of sediments the presence of a large velocity gradient does not change a lot the qualitative behavior of a two dimensional deposit local surface waves and or two dimensional resonance patterns are observed as in the case of homogeneous sediments nevertheless the surface waves are much more dispersive with lower phase and group velocities and larger amplitudes only very deep valleys give rise to the development of two dimensional resonance on the other hand the amplifications obtained in such deposits may reach much larger values than those predicted with either two dimensional homogeneous models or one dimensional inhomogeneous models since these results have been obtained for realistic values of valley geometrical and mechanical considerations they should find some application in earthquake engineering or seismic microzonation studies

dispersion model for tidal wetlands tidal wetlands in california are mostly estuarine salt marshes characterized by tidal channels and mudflats that are flooded and drained on a semidiurnal basis depths are rarely greater than 2 or 3 m except where dredging occurs for harbor operations and lengths from head to mouth are usually in the range of 1 10 km this paper presents a coupled set of models for prediction of flow solute transport and particle transport in these systems the flow and solute transport models are based upon depth integrated conservation equations while the particle transport model is quasi three dimensional common to these models is an assumption that a turbulent boundary layer extends vertically from the bed and can be described by the law of the wall this feature of the model accounts for 1 momentum transfer to the bed 2 longitudinal dispersion of dissolved material based on the work of elder 1959 and 3 advection and turbulent diffusion of particles in three dimensions a total variation diminishing finite volume scheme is used to solve the depth integrated equations using this model we show that dispersion can be accurately modeled using physically meaningful mixing coefficients calibration is therefore directed at modifying bed roughness which scales both the rate of advection and dispersion

a natural seismic isolating system the buried mangrove effects the belleplaine test site located in the island of guadeloupe french lesser antilles includes a three accelerometer vertical array designed for liquefac tion studies the seismic response of the soil column at the test site is computed using three methods the spectral ratio method using the vertical array data a numerical method using the geotechnical properties of the soil column and an operative fre quency domain decomposition fdd modal analysis method the belleplaine test site is characterized by a mangrove layer overlaid by a stiff sandy deposit this con figuration is widely found at the border coast of the caribbean region which is exposed to high seismic hazard we show that the buried mangrove layer plays the role of an isolation system equivalent to those usually employed in earthquake engineering aimed at reducing the seismic shear forces by reducing the internal stress within the structure in our case the flexibility of the mangrove layer reduces the distortion and the stress in the sandy upper layer and consequently reduces the potential of liquefaction of the site

array estimators and the use of microseisms for reconnaissance of sedimentary basins a natural field seismic technique is possible to attain by observing microseisms with a suitably designed array and by digitally processing the data to obtain estimates of the phase velocities of rayleigh waves wavelengths of interest in detecting depth to the basement of sedimentary basins are in the range 2 to 20 km and correspond to wave periods from 1 to 7 s an array of five or seven seismometers deployed as an expanding cross configuration simplifies field procedures and is adequate for phase velocity measurements of rayleigh waves in the required wavelength range provided high resolution frequency wavenumber spectral analysis is used this analysis can be implemented on a minicomputer in the field results obtained from observation in a sedimentary basin of known structure show predominantly fundamental mode rayleigh wave propagation the scatter of velocity estimates is small enough to allow inversion by curve matching and depth to the basement can be computed to an accuracy of 30 percent w

modeling of hydroecological feedbacks predicts distinct classes of landscape pattern process and restoration potential in shallow aquatic ecosystems article i nfo it is widely recognized that interactions between vegetation and flow cause the emergence of channel patterns that are distinct from the standard schumm classification of river channels although landscape pattern is known to be linked to ecosystem services such as habitat provision pollutant removal and sustaining biodiversity the mechanisms responsible for the development and stability of different landscape patterns in shallow vegetated flows have remained poorly understood fortunately recent advances have made possible large scale models of flow through vegetated environments that can be run over a range of environmental variables and over timescales of millennia we describe a new quasi 3d cellular automata model that couples simulations of shallow water flow bed shear stresses sediment transport and vegetation dynamics in an efficient manner that efficiency allowed us to apply the model widely in order to determine how different hydroecological feedbacks control landscape pattern and process in various types of wetlands and floodplains distinct classes of landscape pattern were uniquely associated with specific types of allogenic and autogenic drivers in wetland flows regular anisotropically patterned wetlands were dominated by allogenic processes i e processes driven by periodic high water levels and flow velocities that redistribute sediment relative to autogenic processes e g vegetation production peat accretion and gravitational erosion these anistropically patterned wetlands are therefore particularly prone to hydrologic disturbance other classes of wetlands that emerged from simulated interactions included maze patterned amorphous and topographically noisy marshes open marsh with islands banded string pool sequences perpendicular to flow parallel deep and narrow channels flanked by marsh and ridge and slough patterned marsh oriented parallel to flow because vegetation both affects and responds to the balance between the transport capacity of the flow and sediment supply these vegetated systems exhibit a feedback that is not dominant in most rivers consequently unlike in most rivers it is not possible to predict the channel pattern of a vegetated landscape based only on discharge characteristics and sediment supply the antecedent vegetation pattern and vegetation dynamics must also be known in general the stability of different wetland pattern types is most strongly related to factors controlling the erosion and deposition of sediment at vegetation patch edges the magnitude of sediment redistribution by flow patch elevation relative to water level and the variability of erosion rates in vegetation patches with low flow resistance as we exemplify in our case study of the everglades ridge and slough landscape feedback between flow and vegetation also causes hysteresis in landscape evolution trajectories that will affect the potential for landscape restoration namely even if the hydrologic conditions that historically produced higher flows are restored degraded portions of the ridge and slough landscape are unlikely to revert to their former patterning as wetlands and floodplains worldwide become increasingly threatened by climate change and urbanization the greater mechanistic understanding of landscape pattern and process that our analysis provides will improve our ability to forecast and manage the behavior of these ecosystems published by elsevier b v

channel hydrodynamics of submerged flexible vegetation with seepage abstractthe presence of aquatic vegetation changes the flow characteristics in a channel the impact of the presence of submerged flexible vegetation in a channel with an additional parameter such as downward seepage is analyzed in the present work two patterns staggered and uniform and two different vegetation spacing 15 and 10 cm center center were adopted experiments were conducted for the case of no seepage 10 seepage and 15 seepage velocity profiles show the presence of an inflection point near the top of the vegetation where maximum reynolds stress is achieved the velocity profiles measured in the unobstructed region of uniform pattern are higher compared to the velocity measured in line with the vegetation stems downward seepage increases the velocity reynolds stress and turbulent intensities in the average range of 10 15 as compared to the no seepage case higher order turbulent statistics such as moment analysis quadrant analysis and turbulent kinetic budget are derived through

strong ground motion from the michoacan mexico earthquake the network of strong motion accelerographs in mexico includes instruments that were installed under an international cooperative research program in sites selected for the high potenial of a large earthquake the 19 september 1985 earthquake magnitude 8 1 occurred in a seismic gap where an earthquake was expected as a result there is an excellent descripton of the ground motions that caused the disaster

vortex structure and sediment deposition in the wake behind a finite patch of model submerged vegetation abstracta submerged patch of finite width vegetation may produce vortex structures in its wake in both the vertical and horizontal planes this experimental study used velocity and deposition measu

overland flow velocity and roughness properties in peatlands overland flow is an important component of peatland hydrology hydrological models of peatlands are being developed that require estimates of flow velocity and its controls however surprisingly little is known about overland flow velocities in peatlands some peatlands have also been drained using open ditches and these need to be incorporated into flow models this paper presents field data on the velocity of overland flow and drain flow in upland peatlands the relationships between flow velocity vegetation cover slope and water depth are explored sphagnum provided a significantly greater effective hydraulic roughness to overland flow than peatland grasses in all cases a significant break in process occurred for flows with water depths of around 1 cm so that there were two components of the roughness curve this is consistent with partial submergence theory for very shallow flows where resistance increases with depth as the soil surface first becomes fully submerged while each surface cover type should be considered separately the results also suggest that a first order estimate of darcy weisbach roughness and mean velocity can be based on a single parameter for each surface cover this paper presents an empirical overland flow velocity forecasting model that can be applied to peatlands the model combines the partially submerged component for flows with water depths below 1 cm with the fully submerged component for flows with depths up to 5 cm which are representative of the depths of flows that occur across peatlands

identifying 2d resonance in microtremor wave fields to predict local site effects during earthquakes we must know the geometrical and mechanical properties of local sedimentary structures and their resonance behavior we present a concept to identify resonance modes for 2d structures this is done for synthetic as well as measured microtremor wave fields the microtremor data were investigated by using the reference station and horizontal to vertical h v methods analyzing the synthetic microtremor data in profiles across 2d structures the reference station method rsm turned out to be much more suitable for the detection of 2d resonances than the h v method we therefore focused on rsm when analyzing the measurement data from two test sites in switzerland the st jakob tullingen trough near basel in the north and a site in the rhone valley near the village vetroz in the south the results of these two test sites led to different conclusions whereas the spectral peaks in data of the st jakob tullingen trough were not well developed and could only tentatively be interpreted those from the rhone valley clearly exhibited 2d resonance effects the sh 00 and the sv fundamental mode could be successfully identified at 0 32 0 03 and 0 35 0 03 hz respectively

complex polarization analysis of particle motion knowledge of particle motion polarization aids in identifying phases on three component seismograms the scheme of montalbetti and kanasewich 1970 is extended to analytic three component seismograms where the imaginary part of the signal is the hilbert transform of the real part this scheme has only one free parameter the length of the time window over which the polarization parameters are estimated so it can be applied in a routine way to three component data the azimuth and dip of the direction of maximum polarization and the degree of elliptical polarization as a function of time for the seismograms are obtained polarization analysis of strong motion data from the 1971 san fernando earthquake aids in the discrimination between wave types which is important for the understanding of the complicated earthquake induced shaking observed in basins most arrivals are incident on the receivers in the direction of the back azimuth to the epicenter which suggests that despite the complicated motions two dimensional finite difference methods are sufficient to understand the effect on seismic waves of the los angeles and san fernando basins vidale and helmberger 1986b

the importance of accurately representing submerged vegetation morphology in the numerical prediction of complex river flow this paper reports a novel method for the incorporation of complex plant morphologies into a computational fluid dynamics cfd model allowing the numerical prediction of flows around individual plants the morphological complexity which comprises the vertical and lateral distribution of individual branches and leaves is captured through terrestrial laser scanning tls and is maintained in the numerical prediction of flow fields this is achieved where the post processed voxelised plant representation is incorporated into a cfd scheme through a mass flux scaling algorithm mfsa flow around prunus laurocerasus has been modelled under foliated and defoliated states following the removal of leaves the complex plant morphologies are shown to produce spatially heterogeneous downstream velocity fields with velocity profiles that deviate significantly from the idealised inflected shape rapid transition between the high velocity free stream zone and the zone of reduced velocity in the plant wake indicate shearing of flow with the point of reattachment extending up to seven plant lengths downstream the presence of leaves significantly modifies the flow field response with development of a second more pronounced wake structure around the dense foliage this approach provides a full flow numerical description of the pressure field enabling the vegetative drag force to be quantified for the example given here drag force is an order of magnitude greater for the foliated state the methodology outlined here demonstrates the importance of accurately representing complex plant morphology in hydraulic models and allows drag forces and coefficients to be calculated for specific plant species this article is protected by copyright all rights reserved

seismic soil effect in an embanked deep alpine valley a numerical investigation of two dimensional resonance this paper presents a 2d numerical study of the seismic response of a deep embanked sediment filled valley rhone valley switzerland to incident sh and sv waves the 2d modeling is performed with a program developed by pedersen et al 1995 based on the ibem technique this valley exhibits variation in subsurface geometry therefore three representative cross sections are considered in order to investigate the influence of symmetric and asymmetric morphology on the seismic response comparison between 1d and 2d modeling shows that both resonant frequencies and amplification values differ to a large extent looking in the central part of the valley the 2d predicted amplification value is about twice higher than in the 1d case whereas the fundamental resonant frequency value is higher by a factor of 1 7 moreover 2d modeling results show that this valley presents a twodimensional resonance due to its shape ratio and shear wave velocity contrast the main characteristic is the unchanged position of the fundamental resonance frequency regardless of the surface site along the cross section under consideration and the incidence angle however the asymmetric cross section induces a specific spectral amplification pattern at the surface site and along the cross section which is also a function of the direction of incidence of the seismic wave such results show the importance of considering the morphology of a deep and narrow valley when investigating the local seismic response

rapid phytolith extraction for analysis of phytolith concentrations and assemblages during an excavation an application at tell es safi gath israel abstract a rapid phytolith extraction procedure is described that allows phytolith concentrations and morphotype assemblages to be analyzed within hours this procedure enables the results of these analyses to be used during an archaeological excavation in order to better understand how plants were used the new procedure was tested using a standard phytolith extract and two experimental phytolith sediment blends and found to be both accurate and precise the reliability of partial slide counting was evaluated and found to be as accurate and precise as existing phytolith quantification methods the new extraction and counting procedures were applied to an archaeological site tell es safi gath israel the results demonstrate how information on phytolith concentrations in sediments that are available from one day to the next can be used during an excavation to more effectively document the local features of interest and obtain better information

is the critical shields stress for incipient sediment motion dependent on channel bed slope data from laboratory flumes and natural streams show that the critical shields stress for initial sediment motion increases with channel slope which indicates that particles of the same size are more stable on steeper slopes this observation is contrary to standard models that predict reduced stability with increasing slope due to the added downstream gravitational force processes that might explain this discrepancy are explored using a simple force balance model including increased drag from channel walls and bed morphology variable friction angles grain emergence flow aeration and changes to the local flow velocity and turbulent fluctuations surprisingly increased drag due to changes in bed morphology does not appear to be the cause of the slope dependency because both the magnitude and trend of the critical shields stress are similar for flume experiments and natural streams and significant variations in bed morphology in flumes is unlikely instead grain emergence and changes in local flow velocity and turbulent fluctuations seem to be responsible for the slope dependency due to the coincident increase in the ratio of bed roughness scale to flow depth i e relative roughness a model for the local velocity within the grain roughness layer is proposed based on a 1 d eddy viscosity with wake mixing in addition the magnitude of near bed turbulent fluctuations is shown to depend on the depth averaged flow velocity and the relative roughness extension of the model to mixed grain sizes indicates that the coarser fraction becomes increasingly difficult to transport on steeper slopes

the trouble with shear stress abstract predicted bedload fluxes often have large errors partly because calculations usually do not include spatial and temporal flow variability sediment motion is driven by a temporal distribution of applied fluid forces which are often simplified into time averaged flow velocities or shear stresses in sediment transport equations spatial variations in these flow parameters are also often neglected given the nonlinearities in the relation between flow and sediment flux the reach averaged sediment flux calculated with an average velocity or shear stress will not necessarily equal the measured spatially averaged bedload flux such spatial and temporal flow variations are ignored with the commonly used reach averaged shear stress ds that is a function of the flow depth and channel slope to demonstrate the uncertainties with using reach averaged shear stresses and even local shear stresses to predict bedload transport rates we have three goals first we outline the derivations and assumptions involved with commonly used estimates of shear stress second we summarize the literature on the uncertainties involved with using shear stress and other space and time averaged flow parameters to predict sediment flux third we use a new data set from experiments to add further support to a growing body of literature that suggests ds may not be linked to the mechanics of bedload transport we show considerable uncertainties exist in estimating a reach averaged shear stress by comparing ds and near bed shear stresses calculated from velocity profiles reynolds stresses and local turbulence for example ds was systematically greater than these near bed stresses even for experiments without large bed roughness we also find that correlations between local time averaged sediment fluxes and local reynolds stresses or turbulence intensities are relatively poor the near bed time averaged local flow velocity has the strongest relation with the time averaged local bedload flux because it is closely related to the forces that actually drive sediment transport however sediment transport rates in individual experiments could still vary by orders of magnitude for a given value of this flow velocity suggesting that additional work is needed to identity a parameter or distributions of parameters that will best predict sediment fluxes

assessment of site effects in alpine regions through systematic site characterization of seismic stations abstract in the framework of the renewal project of the swiss strong motion network ssmnet a procedure for site characterization has been established the aim of the procedure was to systematically derive realistic 1d velocity profiles at each station it is mainly based on the analysis of surface waves particularly from passive experiments and includes cross checks of the derived amplification functions with those obtained through spectral modeling of recorded earthquakes the systematic use of three component surface wave analysis allowing the derivation of both rayleigh and love dispersion curves also contributes to the improvement of the quality of the retrieved profiles the procedure is applied to the 30 ssmnet stations installed on various site types within the project covering different aspects of seismic risk the characterization of these 30 sites gives an overview of the variety of possible effects of surface geology on ground motion in the alpine area such effects ranged from deamplification at hard rock sites to amplification up to a factor of 15 in lacustrine sediments with respect to the swiss reference rock velocity model the derived velocity profiles are shown to reproduce observed amplification functions from empirical spectral modeling although many sites are found to exhibit 1d behavior the procedure allows the detection and qualification of 2d and 3d effects the sites are therefore classified with respect to the occurrence of 2d 3d resonance and edge generated surface waves in addition to the large and deeply incised alpine valleys of the rhone the rhine and the aar smaller structures such as local alpine valleys and alluvial fans are shown to exhibit 2d 3d behavior

anthropogenic sources stimulate resonance of a natural rock bridge the natural modes of vibration of bedrock landforms as well as the sources and effects of stimulated resonance remain poorly understood here we show that seismic energy created by an induced earthquake and an artificial reservoir has spectral content coincident with the natural modes of vibration of a prominent rock bridge we measured the resonant frequencies of rainbow bridge utah using data from two broadband seismometers placed on the span and identified eight distinct vibrational modes between 1 and 6 hz a distant induced earthquake produced local ground motion rich in 1 hz energy stimulating a 20 db increase in measured power at the bridge s fundamental mode moreover we establish that wave action on lake powell an artificial reservoir generates microseismic energy with peak power 1 hz also exciting resonance of rainbow bridge these anthropogenic sources represent relatively new energy input for the bridge with unknown consequences for structural fatigue

plant stiffness and biomass as drivers for drag forces under extreme wave loading a flume study on mimics abstract moving water exerts drag forces on vegetation the susceptibility of vegetation to bending and breakage determines its flow resistance and chances of survival under hydrodynamic loading to evaluate the role of individual vegetation parameters in this water vegetation interaction we conducted drag force measurements under a wide range of wave loadings in a large wave flume artificial vegetation elements were used to manipulate stiffness frontal area in still water and material volume as a proxy for biomass the aim was to compare i identical volume but different still frontal area ii identical stiffness but different still frontal area and iii identical still frontal area but different volume comparison of mimic arrangements showed that stiffness and the dynamic frontal area i e frontal area resulting from bending which depends on stiffness and hydrodynamic forcing determine drag forces only at low orbital flow velocities did the still frontal area dominate the force velocity relationship and it is hypothesised that no mimic bending took place under these conditions mimic arrangements with identical stiffness but different overall material volume and still frontal area showed that forces do not increase linearly with increasing material volume and it is proposed that short distances between mimics cause their interaction and result in additional drag forces a model based on effective leaf length and characteristic plant width developed for unidirectional flow performed well for the force time series under both regular and irregular waves however its uncertainty increased with increasing interaction of neighbouring mimics

when do plants modify fluvial processes plant hydraulic interactions under variable flow and sediment supply rates flow and sediment regimes shape alluvial river channels yet the influence of these abiotic drivers can be strongly mediated by biotic factors such as the size and density of riparian vegetation we present results from an experiment designed to identify when plants control fluvial processes and to investigate the sensitivity of fluvial processes to changes in plant characteristics versus changes in flow rate or sediment supply live seedlings of two species with distinct morphologies tamarisk tamarix spp and cottonwood populus fremontii were placed in different configurations in a mobile sand bed flume we measured the hydraulic and sediment flux responses of the channel at different flow rates and sediment supply conditions representing equilibrium sediment supply transport rate and deficit sediment supply transport rate we found that the hydraulic and sediment flux responses during sediment equilibrium represented a balance between abiotic and biotic factors and was sensitive to increasing flow rates and plant species and configuration species specific traits controlled the hydraulic response compared to cottonwood which has a more tree like morphology the shrubby morphology of tamarisk resulted in less pronation and greater reductions in near bed velocities reynolds stress and sediment flux rates under sediment deficit conditions on the other hand abiotic factors dampened the effect of variations in plant characteristics on the hydraulic response we identified scenarios for which the highest stem density patch independent of abiotic factors dominated the fluvial response these results provide insight into how and when plants influence fluvial processes in natural systems

flow resistance law in channels with flexible submerged vegetation in this paper experimental data collected in a straight flume having a bed covered by grasslike vegetation have been used to analyze flow resistance for flexible submerged elements at first the measurements are used to test the applicability of kouwen s method then a calibration of two coefficients appearing in the semilogarithmic flow resistance equation is carried out finally applying the p theorem and the incomplete self similarity condition a flow resistance equation linking the friction factor with the shear reynolds number the depth vegetation height ratio and the inflection degree is deduced

urban flood modeling with porous shallow water equations a case study of model errors in the presence of anisotropic porosity porous shallow water models porosity models simulate urban flood flows orders of magnitude faster than classical shallow water models due to a re lately coarse grid and large time step enabling flood hazard mapping over far greater spatial extents than is possible with classical shallow water models here the errors of both isotropic and anistropic porosity models are exam ined in the presence of anisotropic porosity i e unevenly spaced obstacles in the cross flow and along flow directions which is common in practical applications we show that porosity models are affected by three types of errors a structural model error associated with limitations of the shallow water equations b scale errrors associated with use of a relatively coarse tel

on the limitation of the h v spectral ratio using seismic noise as an exploration tool application to the grenoble valley france a small apex ratio basin the h v spectral ratio method based on seismic noise hvsrn was used in the grenoble basin france an alpine valley characterized by a small apex ratio the resonance frequencies obtained in the experiments were compared to the thickness of the sediments deduced from a microgravimetric survey and to the 1 d theoretical assessment of site responses given the abundance of data on the sediments and depth of the basin the values of the theoretical resonance frequency fo can be determined quite accurately however it has been observed that the effects of basin geometry can disturb fo measurements using the hvsr method in particular for a case like the grenoble basin which has a small apex ratio w h and strong suspected 2 d and or 3 d effects interpretation of fo values in terms of bedrock depth gives rise to estimation errors of about 10 in certain cases with the most significant errors 50 occurring on the edges of the basin where subsurface layers are characterised by larger heterogeneities and where the basin topography is accentuated this study suggests that great care must be taken when using the hvsrn method as an exploration tool at least in valleys with a small apex ratio

a vortex based model of velocity and shear stress in a partially vegetated shallow channel 1 this paper presents a method for predicting the distributions of velocity and shear stress in shallow channels with a boundary of emergent vegetation experiments in a laboratory channel with model vegetation show that the velocity profile exhibits a distinct two layer structure consisting of a rapidly varying shear layer across the vegetation interface and a more gradual boundary layer in the main channel in addition coherent vortices are observed which span both layers and are the dominant contributors to lateral momentum fluxes from these observations we propose a model for the vortex induced exchange and find expressions for the width of momentum penetration into the vegetation the velocity and shear stress at the vegetation edge and the width of the boundary layer in the main channel these variables along with a momentum balance in the main channel comprise a modeling framework which accurately reproduces the observed velocity and shear stress distributions the predictions for the velocity and shear stress can provide a basis for modeling flood conveyance overbank sediment transport and scalar residence time in the vegetated layer

taphonomy of phytoliths and macroplants in different soils from olduvai gorge tanzania and the application to plio pleistocene palaeoanthropological samples the abundance and types of phytoliths in the fossil record are taphonomically biased and do not correspond with the macroplant record to better understand the bias and improve the interpretation of samples from olduvai gorge tanzania we analysed the phytoliths from three sample sets modern grasses sedges palm and dicots in the area modern soils in the area and the fossil soils from the eastern palaeolake margin in lowermost bed ii fourier transform infrared spectrometry analyses were performed in parallel to compare the mineral composition of both modern soils and fossil soils we found that the abundance of phytoliths is greatly reduced in soil samples compared with modern plant material but the morphotypes can be reliably interpreted dicotyledonous wood bark phytoliths appear to be over represented in the soil types grass phytoliths and sedges to a lesser degree are preserved in the soils but in lower abundances resulting in these groups being under represented the macroplant fossils are fragments of grass and sedge aerial culms and dicotyledonous stems that are preserved in fluvial and lacustrine deposits it is suggested that phytoliths represent the continuous flora whereas macroplant fossils represent the more robust tissues of selected plants preserved under more catastrophic conditions a post depositional model is proposed and the palaeovegetation is reinterpreted as being richer and more complex than indicated by other fossil data

prediction of velocity profiles and longitudinal dispersion in salt marsh vegetation to predict the behavior of solutes and suspended particles in wetlands it is necessary to estimate advection and longitudinal dispersion to better understand these processes measurements were taken of stem frontal area velocity vertical diffusion and longitudinal dispersion in a spartina alterniflora salt marsh in the plum island estuary in rowley massachusetts vegetation volumetric frontal area peaked at 0 067 6 0 007 cm 21 near 10 cm from the bed if the velocity profile in a dense emergent marsh canopy depends on the local balance between pressure forcing and vegetation drag the velocity will vary inversely with canopy drag i e velocity is minimum where the frontal area is maximum in fact the minimum velocity was observed at 10 cm from the bed the momentum balance therefore provides a way to predict the velocity profile structure from canopy morphology the vertical diffusion coefficient also depends on canopy characteristics such that the vertical diffusion coefficient normalized by the velocity and stem diameter had a constant value of 0 17 6 0 08 at this study site the canopy morphology also controls the longitudinal dispersion observed in this study to be 4 to 27 cm 2 s 21

geoarchaeology in an urban context the uses of space in a phoenician monumental building at tel dor israel abstract interpretation of past urban societies in the near east whose settlements are known mostly as tell sites is largely based on macro stratigraphy and on the association of architecture with macroscopic artifacts analyses of sediments common in prehistoric sites are rare in tell sites here we show the results of a detailed geoarchaeological study of the micro stratigraphy of a sedimentary sequence associated with early iron age phoenician monumental architecture the study involves mineralogical micromorphological and phytolith analyses and provides new insights into the stratigraphic sequence and the use of architectural spaces the sedimentary sequence examined comprises alternating layers of gray fill deposits and white floors we show that floors made from local calcareous sandstone in the lower part of the sedimentary sequence were heated and are thus in effect plaster floors a concentration of micro laminated trampled fish remains above the most elaborate of these plaster floors indicates activities related to fish processing fine white layers in the upper part of the sedimentary sequence that were considered as plaster based on macroscopic examination are in fact composed almost entirely of opaline grass phytoliths the phytoliths appear in an undulating micro laminated structure and are associated with dung spherulites and phosphate nodules thus probably reflecting livestock penning the formation of phytolith floors involves extensive volume reduction due to the degradation of the organic material and this may result in floor subsidence a phenomenon that is often observed in archaeological sites most fill deposits include macroscopic and microscopic remains of wood ash bones phytoliths charcoal ceramics plaster and mollusk shells reflecting the debris produced from household activities this study shows how a combination of macro stratigraphy with microscopic and mineralogical analyses of the sediments within architectural spaces can provide information on the varying ways in which the space was used through time and also contributes to solving macro stratigraphic problems

when the carbon being dated is not what you think it is insights from phytolith carbon research abstract for proper interpretation of radiocarbon 14c age results the carbon fraction being dated must be identified beforehand ideally as a single homogeneous entity that best represents the event being studied radiocarbon dating of fossil phytoliths biosilica formed in living higher plants has been used in a number of archaeology and paleoenvironmental studies more precisely the carbon occlusion phytc has been 14c dated this method relies on the phytc being photosynthetic in origin so that its 14c signature is similar to that of the host plant however we have recently presented overwhelming evidence that phytc in modern plants is made up of a mixture of carbon photosynthesized by the plant from atmospheric co2 and soil carbon comprised of multiple 14c signatures ages the discussion presented here is based on our assessments of phytc 14c signatures their chemical nature location origin and fate as well as the current state of knowledge on plant cell silica interactions with biomolecules finally regardless of the fact that there are cases where fossil phytc 14c results appear to match expected values the impossibility of establishing a priori either the amount of the soil carbon contribution to phytc or the mean 14c age of its occluded mixed pool precludes the use of phytoliths as a reliable 14c dating tool

what controls the transition from confined to unconfined flow analysis of hydraulics in a river delta abstractrecent field work at the wax lake delta wld in coastal louisiana indicates lateral outflow from channels to islands upstream of the receiving basin in this region of the delta the flow t

spatial distribution of deposition within a patch of vegetation 1 this laboratory study describes the spatial pattern of deposition observed in a patch of vegetation located at the wall of a channel there are two sources of sediment flux to the patch the advection of particles across the upstream leading edge and the lateral dispersion of particles from the adjacent open channel the relative contribution of these two supplies determines the spatial pattern of net deposition in the patch we define the advection length scale within the patch as the longitudinal distance over which advection contributes a significant sediment source at distances from the leading edge that are within the advection length scale net deposition in the patch is laterally uniform reflecting the laterally uniform mean flow delivering the particles at distances farther than the advection length scale from the leading edge the net deposition is highest near the flow parallel edge and decreases into the patch which is the signature of dispersive transport from the patch edge two processes contribute to the lateral dispersion both of which are associated with the shear layer vortices formed at the flow parallel interface between the patch and the channel the vortices generate turbulence and enhance the turbulent diffusion of sediment across the interface in addition the vortices induce a wave oscillation in the flow field within the patch that appears to enhance the lateral transport inside the patch

1 d and 2 d resonances in an alpine valley identified from ambient noise measurements and 3 d modelling summary h v spectral ratios are regularly used for estimating the bedrock depth in 1 d like basins exhibiting smooth lateral variations in the case of 2 d or 3 d pronounced geometries observational and numerical studies have shown that h v curves exhibit peculiar shapes and that the h v frequency generally overestimates 1 d theoretical resonance frequency to investigate the capabilities of the h v method in complex structures a detailed comparison between measured and 3 d simulated ambient vibrations was performed in the small size lower romanche valley french alps which shows significant variations in geometry downstream and upstream the sechilienne basin analysing the h v curve characteristics two different wave propagation modes were identified along the valley relying on previous geophysical investigation a power law relationship was derived between the bedrock depth and the h v peak frequency which was used for building a 3 d model of the valley geometry simulated and experimental h v curves were found to exhibit quite similar features in terms of curve shape and peak frequency values validating the 3 d structure this good agreement also evidenced two different propagation modes in the valley 2 d resonance in the sechilienne basin and 1 d resonance in the external parts this study underlines the interest of h v curves for investigating complex basin structures

spectral amplification in a sediment filled valley exhibiting clear basin edge induced waves various site response estimates are presented for a linear array deployed in the coachella valley california during the 1992 landers big bear aftershock sequence this systematic comparison is unique in that the response of the site is clearly dominated by basin edge induced waves average sediment to bedrock spectral ratios for long s wave windows which include the basin edge induced waves exhibit amplification factors as high as 18 below 7 hz the deep basin structure which gives rise to the obvious multi dimensional effects produces a fundamental resonant peak that shifts between basin sites from 0 23 to 0 48 hz as the depth to bedrock changes above 0 6 hz where the largest amplifications occur the response is remarkably similar between sites and appears to be dominated by a near surface layer that is relatively uniform across the valley the apparent fundamental resonant frequency of this layer is between 0 8 and 1 hz sediment to bedrock spectral ratios computed using shorter windows that exclude the basin edge induced waves imply that the multi dimensional effects are significant only below 4 hz where they increase amplifications by an approximate factor of 2 spectral ratios computed using coda windows taken at twice the s wave travel time exhibit amplifications that are an average factor of 1 7 greater between 1 and 4 hz than those of the s wave estimates this discrepancy does not improve by taking coda windows later at four times the s wave travel time horizontal to vertical component s wave spectral ratios do not agree with the sediment to bedrock ratios however they do exhibit a clear peak at the fundamental resonant frequency of the deep basin structure sediment to bedrock spectral ratios of ambient seismic noise are also inconsistent with the s wave estimates however horizontal to vertical noise ratios exhibit clear peaks near the fundamental resonant frequencies of both the deep basin structure below 0 6 hz and the suspected near surface layer between 0 8 and 1 hz therefore ambient noise data appear to provide valuable constraints on the basin structure ongoing efforts involve multi dimensional modeling of the observed basin edge induced phases and resonant frequencies

hydraulic resistance of flow in channels with cylindrical roughness a laboratory study on the hydraulics of flow in an open channel with circular cylindrical roughness is presented the laboratory study consists of an extensive set of flume experiments for flows with emergent and submerged cylindrical stems of various sizes and concentrations the results show that the flow resistance varies with flow depth stem concentration stem length and stem diameter the stem resistance experienced by the flow through the vegetation is best expressed in terms of the maximum depth averaged velocity between the stems physically based formulas for flow resistance the apparent channel velocity and flow velocities in the roughness and surface layers are developed the formulas are validated with the flume data from the present study as well as those from past studies a method for calculating channel hydraulic conditions using these formulas is presented

observation of 1 to 5 second microtremors and their application to earthquake engineering part ii evaluation of site effect upon seismic wave amplification due to extremely deep soil deposits abstract the usefulness of long period microtremor observation for earthquake engineering problems at extremely deep soil deposit site was examined in this study microtremor observations were made in the niigata plain japan and in los angeles california where depths to the basement rock are several kilometers these two locations were selected because strong motion records obtained during the niigata earthquake of 1964 and the san fernando earthquake of 1971 contain large long period amplitudes understanding why these predominate long period motions were recorded is important for the evaluation of seismic input motions for large scale structures long period microtremor observations were carried out in both areas in order to evaluate the characteristics of deep soil observations were performed simultaneously at a number of stations to distinguish the nature of deep soil deposit the result of fourier analysis showed that amplitude of microtremors in long period range increases systematically from the point of basement rock outcrop to deep deposit site with the increase corresponding to the depth to basement rock this relationship coincides with that observed in the strong motion earthquake records these analyses indicated that simultaneous observation of long period microtremors at a number of stations can provide insight to the characteristic of deep soil amplification and therefore permit estimation of seismic input motions for large scale structures

overland flow in wetlands vegetation resistance emergent wetland vegetation frequently provides most of the resistance to flow of surface water stems are typically spaced many diameters apart therefore fluid friction should be computed from drag on single objects not channel or packed bed equations complication arises from vertical variation of vegetation density and nonoriented spatial variation of soil elevations further flows are often in the transition region between laminar and turbulent and the manning equation is therefore not appropriate a detailed approach requires knowledge of statistical distributions of wetland ground elevation depth and velocity ground slopes are typically in the range of 0 1 100 cm km however the depth range is small so the combined effects recorrelate to a simple power law equation for dense emergent vegetation with spatial uniformity on the scale of 10 m parameters in the model can be estimated with sufficient accuracy from vegetation and soil surveys combined with relatively little hydrologic data dat

field observations of wave induced streaming through a submerged seagrass posidonia oceanica meadow 1 this paper reports the findings of a 2 week field campaign designed to study wave induced flows within a meadow of posidonia oceanica at water depth 9 m previous laboratory experiments suggest that waves induce a mean mass drift in the direction of wave propagation streaming through submerged canopies of vegetation this paper provides the first field measurements of this wave induced streaming during periods of high wave activity streaming flows with magnitudes as high as 20 of the near bed oscillatory velocity were measured within the meadow in addition to presenting field measurements of wave induced streaming this paper also considers the damping of wave induced oscillatory flow within the seagrass meadow oscillatory velocities measured within the meadow were reduced by less than 30 relative to those above the meadow over the duration of the study this is in agreement with previous laboratory and field measurements which show that oscillatory flows are damped less within submerged canopies compared to unidirectional flows existing analytical models underpredict the magnitude of the streaming flow and overpredict oscillatory velocity reductions these discrepancies are thought to arise because the drag generated by flexible seagrasses moving with wave induced flow is not well described

efficient three dimensional reconstruction of aquatic vegetation geometry estimating morphological parameters influencing hydrodynamic drag abstract aquatic vegetation can shelter coastlines from energetic waves and tidal currents sometimes enabling accretion of fine sediments simulation of flow and sediment transport within submerged canopies requires quantification of vegetation geometry however field surveys used to determine vegetation geometry can be limited by the time required to obtain conventional caliper and ruler measurements building on recent progress in photogrammetry and computer vision we present a method for reconstructing three dimensional canopy geometry the method was used to survey a dense canopy of aerial mangrove roots called pneumatophores in vietnam s mekong river delta photogrammetric estimation of geometry required 1 taking numerous photographs at low tide from multiple viewpoints around 1 m2 quadrats 2 computing relative camera locations and orientations by triangulation of key features present in multiple images and reconstructing a dense 3d point cloud and 3 extracting pneumatophore locations and diameters from the point cloud data step 3 was accomplished by a new sector slice algorithm yielding geometric parameters every 5 mm along a vertical profile photogrammetric analysis was compared with manual caliper measurements in all 5 quadrats considered agreement was found between manual and photogrammetric estimates of stem number and of number mean diameter which is a key parameter appearing in hydrodynamic models in two quadrats pneumatophores were encrusted with numerous barnacles generating a complex geometry not resolved by hand measurements in remaining cases moderate agreement between manual and photogrammetric estimates of stem diameter and solid volume fraction was found by substantially reducing measurement time in the field while capturing in greater detail the 3d structure photogrammetry has potential to improve input to hydrodynamic models particularly for simulations of flow through large scale heterogenous canopies

the effect of topography on earthquake ground motion a review and new results a brief review of experimental and theoretical results about the effect of topography on seismic motion shows that they are consistent only on a qualitative basis amplification at mountain tops for wavelengths comparable with mountain widths is predicted and observed but the numerical simulations often underestimate the actual observed effects we propose that this disagreement is because current models are not complex enough we therefore computed the response to incident sh waves of a set of different complex configurations that include two dimensional surface topography with or without periodic ridges and subsurface layering the results show that 1 the topographic effect in itself is difficult to isolate from other effects like surface layering and therefore the amplification on top of geomorphologically complex sites cannot be predicted by a priori estimations based solely on topography and 2 the high crest base amplification ratio observed in the field cannot usually be matched even with complex two dimensional structures with incident plane sh waves which suggests that more complex models are needed to incorporate more complex wave fields e g sv surface and three dimensional geologic configurations

the use of rayleigh wave ellipticity for site specific hazard assessment and microzonation application to the city of lucerne switzerland summary the sediments underlying the city of lucerne switzerland consisting of fluvio lacustrine deposits of quaternary age have the potential to produce strong amplification of the seismic wavefield to obtain a reliable estimation of the deep soil structure we combine different methodologies based on ambient noise recordings such as single station horizontal to vertical ratios and three component array analysis two novel techniques to estimate rayleigh wave ellipticity from ambient noise recordings are tested these are based on a single and a multistation approach respectively the first utilizes the continuous wavelet transform to perform a decomposition of the noise wavefield and to isolate and extract the rayleigh wave contribution the second conversely relies on a high resolution f k method to achieve the same result we compare the results from the two techniques to provide an evaluation of their capabilities and limitations a two step inversion scheme is then presented to improve resolution on the bedrock depth in particular the surface wave dispersion information is initially used to constrain the soft sediment part while the rayleigh wave ellipticity peak is subsequently used for constraining the bedrock depth it is shown that such an approach is beneficial to map the bedrock geometry over dense urban areas the output velocity model is then used to compute the local seismic amplification by means of gridded 1 d approximation

are microtremors useful in site response evaluation we have reviewed the applicability of microtremor measurements to evaluate site response of soft soils to this end we evaluated three different techniques commonly used to estimate site effects from microtremor measurements interpretation of fourier amplitude spectra computation of spectral ratios relative to a firm reference station and finally computation of spectral ratios of horizontal components relative to the vertical component of ground motion nakamura s technique these techniques are applied to microtremor records obtained in three cities in mexico mexico city oaxaca and acapulco these cities differ in their local geological conditions and in their seismotectonic environment in order to evaluate the results obtained from microtremor measurements we compare them with standard spectral ratios of the intense s wave part of weak or strong motion records obtained at the same sites our results showed that microtremor measurements can be used to estimate the dominant period of a site with very acceptable reliability in the range 0 3 to 5 hz the best results were obtained with nakamura s technique which also gives a rough estimate of amplification of seismic waves when the local geology is relatively simple simple numerical simulations indicate that the underlying assumptions of nakamura s technique are consistent with the propagation of rayleigh waves these simple numerical simulations also explain why different researchers have been able to successfully characterize 1d site effects using microtremor records regardless of whether they consider microtremors to consist of surface or body waves our results strongly suggest that the technique by nakamura effectively compensates for source effects in microtremor measurements which eliminates a major limitation to their application in earthquake engineering

mean and turbulent velocity fields near rigid and flexible plants and the implications for deposition 1 the transport of fine sediment and organic matter plays an important role in the nutrient dynamics of shallow aquatic systems and the fate of these particles is closely linked to vegetation we describe the mean and turbulent flow near circular patches of synthetic vegetation and examine how the spatial distribution of flow is connected to the spatial distribution of suspended sediment deposition patches of rigid emergent and flexible submerged vegetation were considered with two different stem densities for the rigid emergent vegetation flow adjustment was primarily two dimensional with flow deflected in the horizontal plane horizontal shear layers produced a von karman vortex street flow through the patch shifted the vortex street downstream resulting in a region directly downstream of the patch in which both the mean and turbulent velocities were diminished net deposition was enhanced within this region in contrast for the flexible submerged vegetation flow adjustment was three dimensional with shear layers formed in the vertical and horizontal planes because of strong vertical circulation turbulent kinetic energy was elevated directly downstream of the patch consistent with this deposition was not enhanced at any point in the wake this comparison suggests that morphological feedbacks differ between submerged and emergent vegetation further enhanced deposition occurred only in regions where both turbulent and mean velocities were reduced relative to the open channel reduced deposition indicating enhanced resuspension occurred in regions of high turbulence kinetic energy regardless of local mean velocity these observations highlight the importance of turbulence in controlling deposition

microtremor measurements used to map thickness of soft sediments the observations about the behavior of microtremor spectra presented here show that noise measurements can be used as a powerful tool to determine the thickness of soft cover layers the most suitable method for this determination is nakamura s technique which is the ratio of the horizontal component noise spectrum and that of the vertical component i i v spectrum the frequency of the main peak in these spectral ratios correlates well with the sediment thickness at the site using an extensive database of microtremor measurements carried out in the western lower rhine embayment germany it was possible to show that this correlation is clearly valid for a wide range of thickness namely from tens of meters to more than 1000 m a simple formula was derived that for the sediments to be found in the area investigated directly calculates the cover thickness from the frequency of the main peak in the h v spectrum a comparison with calculated resonant frequencies sug gests the relation derived from the noise measurements depending on the velocity depth function of the shear wave classical spectral ratios are shown to be strongly influenced by the noise level and are therefore less reliable in determining the res onant frequency of the subsoil the practical relevance of the investigation is illus trated by means of cross sections constructed from results of the microtremor anal yses which provide a convincing image of the surficial structure of the areas investigated

continuous measurements of microtremors on sediments and basement in los angeles california abstract continuous measurement of microtremors at two sites on basement rock and sediments was carried out in los angeles california in order to understand the fundamental characteristics of microtremors a predominant peak with a period of about 6 5 sec was found in the microtremor spectra in both media the spectral amplitude of the peaks varied gradually with time in a similar manner at the two sites their time variant characteristics are in agreement with change in oceanic swell height observed at an oceanic buoy in the southwest of los angeles this suggests that they originate from an oceanic disturbance on the other hand a clear daily variation of spectral amplitudes at a period of 0 3 sec indicates that short period microtremors are caused by cultural noises it was found that the spectral ratio of long period microtremors between the basement and the sediments was repeatable although the spectral amplitudes at the two sites were time variant the spectral ratio of the long period microtremors was similar to that derived from strong motion records this suggests the applicability of spectral ratios of microtremors to assess the effects of deep sediments on long period earthquake ground motion

analytical solution of the depth averaged flow velocity in case of submerged rigid cylindrical vegetation a new model for the depth averaged velocity for flow in presence of submerged vegetation is developed the model is based on a two layer approach where flow above and through the vegetation layer is described separately vegetation is treated as a homogeneous field of identical cylindrical stems and the flow field is considered stationary and uniform it is demonstrated that scaling considerations of the bulk flow field can be used to avoid complications associated with smaller scale flow processes and that still the behavior of depth averaged flow over vegetation is described accurately the derived scaling expression of the average flow field is simple in form it follows fundamental laws of fluid flow and it shows very good agreement with laboratory flume experiments the new model can be used for quick evaluation of a river s hydraulic response in cases where vegetated floodplains are inundated

bathymetric error estimation for the calibration and validation of estuarine hydrodynamic models abstract this paper investigates the impact of uncertainty in the definition of bathymetry on the performance of estuarine shallow water models a depth averaged hydrodynamic model is used to simulate tidal flows in a meso tidal estuary simulations are performed for a range of bathymetric and bed roughness scenarios which encompass the uncertainties typically encountered in the specification of estuarine and shallow coastal models the relative sensitivity of model output to uncertainty in bathymetry and bed friction is analysed using monte carlo methods and a new generalised error model is presented that allows various sources of error in bathymetry to be treated as a calibration parameter numerical results are compared with observed current speed and water level time series at multiple locations it is shown that calibration that incorporates bathymetric uncertainty can be significantly more efficient than a classic calibration based only on adjustment of a bed friction coefficient these findings have wide ranging implications for the calibration and validation of estuarine and shallow coastal hydrodynamic models importantly our proposed bathymetry calibration framework offers the prospect of significantly improved performance from the current generation of numerical models

the effect of quaternary alluvium on strong ground motion in the coyote lake california earthquake of 1979 abstract the effect of alluvium on strong ground motion can be seen by comparing two strong motion records of the coyote lake california earthquake of 6 august 1979 m l 5 9 one record at a site on franciscan bedrock had a peak horizontal acceleration of 0 13 g and a peak horizontal velocity of 10 cm sec the other at a site 2 km distant on 180 meters of quaternary alluvium overlying franciscan had values of 0 26 g and 32 cm sec amplifications by factors of 2 and 3 horizontal motions computed at the alluvial site for a linear plane layered model based on measured p and s velocities show reasonably good agreement in shape with the observed motions but the observed peak amplitudes are greater by a factor of about 1 25 in acceleration and 1 8 in velocity about 15 per cent of the discrepancy in acceleration and 20 per cent in velocity can be attributed to the difference in source distance the remainder may represent focusing by refraction at a bedrock surface concave upward there is no clear evidence of nonlinear soil response fourier spectral ratios between motions observed on bedrock and alluvium show good agreement with ratios predicted from the linear model in particular the observed frequency of the fundamental peak in the amplification spectrum agrees with the computed value indicating that no significant nonlinearity occurs in the secant shear modulus computations show that nonlinear models are compatible with the data if values of the coefficient of dynamic shear strength in terms of vertical effective stress are in the range of 0 5 to 1 0 or greater the data illustrate that site amplification may be less a matter of resonance involving reinforcing multiple reflections and more the simple effect of the low near surface velocity application of traditional seismological theory leads to the conclusion that the site amplification for peak horizontal velocity is approximately proportional to the reciprocal of the square root of the product of density and shear wave velocity

hydrodynamics of turbid underflows i formulation and numerical analysis a mathematical model is developed for unsteady two dimensional single layer depth averaged turbid underflows driven by nonuniform noncohesive sediment the numerical solution is obtained by a high resolution total variation diminishing finite volume numerical model which is known to capture sharp fronts accurately the monotone upstream scheme for conservation laws is used in conjunction with predictor corrector time stepping to provide a second order accurate solution flux limiting is implemented to prevent the development of spurious oscillations near discontinuities the model also possesses the capability to track the evolution and development of an erodible bed due to sediment entrainment and deposition this is accomplished by solving a bed sediment conservation equation at each time step independent of the hydrodynamic equations with a predictor corrector method the model is verified by comparison to experimental data for currents driven by uniform and nonuniform sediment

experimental investigation of shallow recirculating flows experiments were conducted to study the bed friction influence in the recirculating zone of a shallow open channel flow velocity measurements were made using a hot film anemometer the recirculating flow rate and the length of the recirculating zone were determined from the measurements and they are related to a horizontal length scale and a bed friction length scale for deep flows the results are independent of the bed friction length scale for shallow flows the results are independent of the horizontal length scale turbulence in the recirculating flows is generated on one hand by the bed friction and on the other hand by the transverse shear the bed generated component is proportional to the bed friction velocity the transverse component is confined to a transverse mixing region in the limit of shallow water depth when the flow is under strong bed friction influence both the transverse mixing region and the recirculating zone have the same length of about one friction length scale

finite volume model for shallow water flooding of arbitrary topography a model based on the finite volume method is developed for unsteady two dimensional shallow water flow over arbitrary topography with moving lateral boundaries caused by flooding or recession the model uses roe s approximate riemann solver to compute fluxes while the monotone upstream scheme for conservation laws and predictor corrector time stepping are used to provide a second order accurate solution that is free from spurious oscillations a robust novel procedure is presented to efficiently and accurately simulate the movement of a wet dry boundary without diffusing it in addition a new technique is introduced to prevent numerical truncation errors due to the pressure and bed slope terms from artificially accelerating quiescent water over an arbitrary bed model predictions compare favorably with analytical solutions experimental data and other numerical solutions for one and two dimensional problems

spatially distributed modeling of surface water flow dynamics in the everglades ridge and slough landscape summary a two dimensional spatially distributed flow dynamics model was developed and tested for a 1 5 by 4 km area of the patterned ridge and slough landscape of the florida everglades this model is intended to support a deepened understanding of the system ecohydrological dynamics and provide a useful tool for management decision support the model was constructed with a fine enough mesh structure to ensure proper representation of ridge and slough topographic detail as well as capture local hydrologic influences upstream and downstream stage data collected near the study area in central water conservation area 3a were used to establish the initial and boundary conditions water velocities measured in the ridges and sloughs over a 3 year period were used to calibrate and verify the model hydraulic resistance was computed using a power law relationship with water depth the simulated water levels water depths and flow velocities showed good agreement with the 3 year field monitored data with percent model errors of approximately 4 12 and 10 respectively computed differences in hydraulic resistance between ridge and slough were reduced significantly during the storm season compared to the dry season this suggests that more solute and suspended solid mass can be redistributed from the sloughs to the ridges in particular during wet seasons due to the weakened heterogeneity of hydraulic resistance during high flows