distribution and composition of suspended biogenic particles in surface waters across subarctic and arctic seas 1 suspended biogenic particles were examined across subarctic and arctic seas during the canada three oceans c3o program in the summers of 2007 and 2008 particulate organic carbon poc and nitrogen pon biogenic silica bsio2 and size fractionated chlorophyll a chl a concentrations were measured within the euphotic zone throughout five domains eastern subarctic north pacific esnp bering and chukchi seas be ch southern beaufort sea and canada basin bs cb canadian arctic archipelago caa and baffin bay and labrador sea bb ls despite large variability along the sampling transect and vertically throughout the euphotic zone domain averages of depth integrated poc and pon were relatively invariant across the esnp be ch caa and bb ls ranging from 546 to 670 mmol m 2 poc and 101 to 154 mmol m 2 pon but were much lower in bs cb 199 and 78 mmol m 2 respectively in contrast depth integrated bsio2 averages were highest in be ch and caa 100 mmol m 2 intermediate in esnp and bb ls 34 48 mmol m 2 and low in bs cb 6 mmol m 2 similarly to the bsio2 distribution the biomass of the 5 m chl a size fraction averaged 68 69 of total chl a in be ch and caa 56 in bb ls and 22 23 in esnp and bs cb ratios of bsio2 pon averaged 1 10 1 30 in be ch and caa 0 30 0 34 in esnp and bb ls and 0 08 in bs cb this study highlights the relative importance of siliceous phytoplankton such as diatoms in be ch and caa smaller nonsiliceous cells in bs cb and esnp and a mixed assemblage of variably sized phytoplankton with a less siliceous component in bb ls

silicic acid dynamics in the glacial sub antarctic implications for the silicic acid leakage hypothesis 1 the silicic acid leakage hypothesis salh purports that changes in silicon and nitrogen depletion ratios in the glacial antarctic created a large pool of unused silicic acid that was transported to lower latitudes in subantarctic mode water samw where it enhanced diatom productivity lowering atmospheric pco2 however increased opal accumulation beneath the sub antarctic during glacial times implies significant consumption of silicic acid in subantarctic surface waters that may have significantly diminished or eliminated si leakage to test how nutrient dynamics in the sub antarctic affected the si oh 4 content of samw during the last glacial period we produced 30si opal records for cores from the subantarctic and subtropical zones of the indian ocean spanning the last 50 000 years comparison with diatom bound 15n records shows that subantarctic surface waters were enriched in si relative to n during the last glaciation consistent with the salh the record from the subtropics does not show this enrichment in si during the last glacial period suggesting that subantarctic surface waters were mainly incorporated into samw rather than being transported across the subtropical front isotope mass balance calculations were used to test for si leakage from the sub antarctic the results show that silicic acid concentration in samw would more than double during the last glaciation if upwelling and northward ekman drift in the antarctic were similar to the present day circulation calculations that assume increased stratification in the glacial antarctic eliminate si leakage but they do not produce the known increase in opal burial in the glacial sub antarctic reconciling the isotope data and opal burial records with a highly stratified antarctic requires the addition of a large local source of silicic acid in the glacial sub antarctic that is inconsistent with present day circulation and nutrient distributions including such a source in our calculations results in significant opal burial in the sub antarctic but it does not enhance si leakage over that occurring in the holocene resolving past changes in the circulation of the southern ocean is clearly vital to future tests of the salh

test of source parameter inversion of the intensities of a 54 000 death shock of the seventeenth century in southeast sicily we inverted the macroseismic intensity data set felt reports of the m 5 4 earthquake of 1990 in se sicily and retrieved source parameters that were compatible with those obtained independently by other authors who treated instrumental observations our technique uses voronoi polygons and our kinematic function kf after this validation we attempted the inversion of the macroseismic intensity data set of one of the strongest earthquakes that has ever struck the mediterranean basin in 1693 in southeast sicily 54 000 casualties it was possible to invert the regional intensity patterns of these two earthquakes because their data sets are sufficiently uncontaminated by local site responses and retain regional traces of source effects the 1693 source constrained by our inversion is a nne oriented fault approximately 60 km long dipping from 90 to 54 80 with positive error of 10 and negative error of 26 toward ese 50 strike slip and 50 dip slip which crosses se sicily from the hyblean plateau to the coast of the ionian sea south of the city of catania the nucleation is 37 08 n 14 93 e this source best fits the regional distribution of damage observed in the field at the limit of the negative error of the dip angle a value of 54 makes our line source at depth compatible with the trace of the scicli active transcurrent fault which is 12 14 km to the west the retrieved source is also compatible with the orientation of the maximum horizontal geodynamical compressive stress confidently measured in the area as well as with an authoritative tectonic interpretation independent from this study the combined use of tessellation and of our kf model is promising for inverting intensity data sets of preinstrumental earthquakes

seismic source modeling seismic source modeling is taken to mean the modeling of seismograms to investigate kinematic properties of the earthquake source current trends such as the use of other data types e g geodetic measurements of coseismic deformation and the explicit consideration of source dynamics when modeling seismograms are beginning to blur this definition but i will adhere to it in this review i have divided seismic source modeling into teleseismic regional and near source modeling teleseismic modeling has the advantage of global coverage for earthquakes of magnitude 5 5 and larger but does not provide much more than point source parameters regional distance modeling has the advantage of a more rapid assessment of earthquake source properties but is complicated by relatively complex wave propagation the coverage is also limited to areas of broadband regional networks typically continental areas of developed countries near source modeling has the potential for detailed imaging of source properties but very few earthquakes occur in regions with sufficient instrumentation to allow this i have also included a section on historical earthquakes because of the additional issues that seismologists face in working with pre wwssn data and because of the important issues such as earthquake recurrence that require historical data in addition to reviewing the progress in seismic source modeling during the last four years i have also briefly reviewed some of the progress in understanding earthquake physics and hazards that has come about because of basic research in earthquake source modeling

seagrass wrack induced dune formation on a tropical coast banc d arguin mauritania abstract the banc d arguin mauritania is a shallow water area with mudflats bordering on the sahara desert mass depositions of seagrass litter were observed on some parts of the shore soil profiles of the low dune formations separating the flood debris zone from the desert showed that layers of seagrass detritus in various stages of decay extended under the dune formations the tentative mechanism of dune formation involving the interacting processes of beaching of seagrass litter and wind blown transport of desert sediment in a seaward direction is described this role in dune formation adds a new element to the significance of seagrass vegetation for the coastal environment

long period regional wave moment tensor inversion for earthquakes in the western united states source parameters of moderate to large size mw 4 5 earthquakes in the western united states from 1992 to 1994 are determined by point source moment tensor inversion of complete long period t 35 50 s ground motions recorded at regional distances 1 12 stable long period signals are obtained by low pass filtering records from the very broadband seismometers recently deployed in several networks in the western united states these signals are dominated by fundamental mode rayleigh and love waves which have very simple waveforms due to the limited dispersion on the short paths to regional stations since long period motions are relatively insensitive to the attenuation model and crustal structure used in the inversion they provide robust constraints on the seismic moment and faulting geometry as long as adequate azimuthal coverage is available comparisons of solutions for 21 events with results of other regional and teleseismic wave inversions are made to assess the model dependence and uncertainties of our regional centroid moment tensor rcmt solutions rcmt inversion has limited source depth resolution for shallow crustal events but the focal mechanism and seismic moment determinations prove quite stable over a range of source depths in the crust as well as over a range of crustal propagation models simultaneous waveform inversion of shorter period body wave signals can improve the source depth resolution by applying path corrections for heterogeneous crustal structure shorter period surface wave energy can also be inverted allowing the methodology to be extended to lower magnitude regional events as well the rcmt procedure requires minimal signal processing only a sparse broadband network and a simple laterally homogeneous propagation model thus it can readily be automated and applied in near real time to events in the magnitude range from 4 5 to 7 5 distributed over an area as large as the western united states

relevance of silicon isotopes to si nutrient utilization and si source assessment in antarctic waters 1 we analyzed 29si of dissolved silicate for eight water column profiles across the southern ocean south of australia in spring 2001 from the seasonal ice zone siz north to the subantarctic zone saz including the first isotopic compositions measured for si depleted seawaters all profiles display mixed layer enrichments in heavy si isotopes relative to deep water in accordance with preferential uptake of the light isotope by diatoms as silicate levels decrease from the siz northward across the polar front zone pfz to the saz surface and mesopelagic 29si signatures generally become progressively heavier but the most si depleted saz waters do not exhibit 29si values heavier than in the pfz this intricacy appears to derive from variations in the vertical and horizontal supply of silicate to surface waters and by applying a steady state open system model we estimate a fractionation factor 29 between diatoms and seawater of 0 45 0 17 independently of zones and phytoplankton community though encouraging these results are related to latitudinal changes in mesopelagic 29si values complexity in surface silicate 29si correlations and differences from previous studies which underline the need for caution in the use of silicon isotopes in paleoceanographic studies until systematic efforts have been undertaken to better understand modern variations

calibration of mb pn mb lg scales and transportability of the m0 mb discriminant to new tectonic regions we have developed mo mb relationships for earthquakes and explosions in central asia using regional waveform data from the chinese broadband digital station wmq regional magnitude scales mb pn and mb lg were established by 1 determining the attenuation rates of pn and lg waves 2 calibrating the mb pn against the teleseismic rob and 3 applying nuttli s method to determine m b from the lg waves seismic moments for earthquakes and explosions were obtained by applying the bolt and herraiz 1983 method calibrated using cmt moments for earthquakes and regional moment estimates of the soviet joint verification experi ment jve explosion the results show that mo mb pn relationships for central asian earthquakes and explosions are in excellent agreement with the relationships for the western united states this demonstrates that the mo r discriminant is transportable to other regions and supports theoretical claims patton and walter 1993 that mo m b are directly comparable for explosions detonated in different emplacement media successful application depends upon correcting the mb pn for the magnitude bias known to exist between the shagan river test site and the nevada test site nts in general region specific mb bias must be accounted for whenever regional mag nitude scales are calibrated against teleseismic rob as pointed out by douglas and marshall 1996 transporting mo mb lg can be problematic because attenuation rates based on coda waves or lg waves from earthquakes may not necessarily apply to lg waves from explosions and vice versa this is demonstrated for the western united states where the coda q measured from explosion data is much lower than the coda q from earthquake data we show that mb lg for earthquakes located close to nts is greatly overestimated using the q values determined from the coda of nts explosions this is apparently not a problem for lg calibration in central asia perhaps because of differences in velocity and or q structures for the two regions other important considerations are the character of lg propagation on short paths 400 km for nts explosions versus long paths 1000 kin for east kazakh explosions and the properties of coda wave spreading as a function of distance and velocity structures for different tectonic regions

aeolian sediment transport on a beach surface moisture wind fetch and mean transport abstract temporal and spatial changes in wind speed wind direction and moisture content are ubiquitous across sandy coastal beaches often these factors interact in unknown ways to create complexity that confounds our ability to model sediment transport at any point across the beach as well as our capacity to predict sediment delivery into the adjacent foredunes this study was designed to measure wind flow and sediment transport over a beach and foredune at greenwich dunes prince edward island national park with the express purpose of addressing these complex interactions detailed measurements are reported for one stormy day october 11 2004 during which meteorological conditions were highly variable wind speed ranged from 4 ms 1 to over 20 ms 1 wind direction was highly oblique varying between 60 and 85 from shore perpendicular and moisture content of the sand surface ranged from a minimum of about 3 by mass to complete saturation depending on precipitation tidal excursion and storm surge that progressively inundated the beach the data indicate that short term variations i e minutes to hours in sediment transport across this beach arise predominantly because of short term changes in wind speed as is expected but also because of variations in wind direction precipitation intensity and tide level even slight increases in wind speed are capable of driving more intense saltation events but this relationship is mediated by other factors on this characteristically narrow beach as the angle of wind approach becomes more oblique the fetch distance increases and allows greater opportunity for the saltation system to evolve toward an equilibrium transport state before reaching the foredunes whether the theoretically predicted maximum rate of transport is ever achieved depends on the character of the sand surface e g grain size slope roughness vegetation moisture content and on various attributes of the wind field e g average wind speed unsteadiness approach angle flow compression boundary layer development moisture content is widely acknowledged as an important factor in controlling release of sediment from the beach surface all other things being equal the rate of sediment transport over a wet surface is lesser than over a dry surface on this beach the moisture effect has two important influences a in a temporal sense the rate of sediment transport typically decreases in association with rainfall and increases when surface drying takes place and b in a spatio temporal sense shoreline excursions associated with nearshore processes such as wave run up storm surge and tidal excursions have the effect of constraining the fetch geometry of the beach i e narrowing the width of the beach because saturated sand surfaces such as found in the swash zone will only reluctantly yield sediments to aeolian entrainment the available beach surface across which aeolian transport can occur becomes narrower as the sea progressively inundates the beach under these constrained conditions the transport system begins to shut down unless wind angle becomes highly oblique thereby increasing fetch distance in this study maximum sediment transport was usually measured on the mid beach rather than the upper beach i e closer to the foredunes this unusual finding is likely because of internal boundary layer development across the beach which yields a decrease in near surface wind speed and hence transport capacity in the landward direction although widely recognized in the fluid mechanics literature this decrease in near surface shear stress as a by product of a developing boundary layer in the downwind direction has not been adequately investigated in the context of coastal aeolian geomorphology

coastal foredune topography as a control on secondary airflow regimes under offshore winds aeolian sediment transport under offshore winds is usually discounted from sediment budget considerations of coastal dunes results presented here indicate however that depending on wind orientation and foredune morphology positive contributions to the sediment budget can arise from offshore winds lee side airflow patterns seaward of the foredune crest under offshore winds were studied at three sites of varying foredune geometry along magilligan strand northern ireland ultrasonic anemometers recorded 1 hz wind velocity data at 1 intervals descriptive statistics and wind rose diagrams were used in the analysis of these data under perpendicularly offshore winds each site exhibited a different type of lee side airflow pattern a tall 11 4 m sharp crested foredune produced flow separation with a recirculation cell a lower 6 6 m more rounded foredune crest exhibited lee side flow that remained attached but was deflected parallel to the crest while flow over a low incipient foredune crest resulted in attached flow with no deflection in the lee the morphology of the lee slopes best explained these airflow adjustments more obliquely offshore winds were also found to affect the secondary airflow patterns with a smooth transition from flow separation to flow attachment as the incident angle decreased at higher wind velocities this smooth transition was replaced with a more abrupt switch between the secondary airflow types this threshold was located at similar approach angles to those recorded for desert dunes 90 20 these findings have significant implications for the post storm recovery and long term evolution of beach dune systems where the predominant winds are offshore and offer an explanation for the presence of many beach dune systems in lee coast locations copyright 2010 john wiley sons ltd

influence of vegetation on aeolian sand transport rate from a backshore to a foredune at hasaki japan the influence of vegetation on aeolian sediment transport rate in the region from a backshore to a foredune was investigated at the hasaki coast in japan where an onshore wind was predominant and the creeping beach grasses carex kobomugi and calystegia soldanella were major species the comparison of cross shore distributions of the cross shore component of aeolian sand transport rate with and without vegetation which were estimated on the basis of the beach profile changes and a mass conservation equation showed that the creeping grasses influenced the aeolian sand transport rate the landward aeolian sand transport rate rapidly decreased landward from the seaward limit of vegetation when the grasses grew the aeolian sand transport rate reduced by 95 with a vegetation cover of 28 on the other hand when the grasses were absent the landward aeolian sand transport rate did not decrease near the seaward vegetation limit but near the foot of the foredune

southern ocean control of silicon stable isotope distribution in the deep atlantic ocean the fractionation of silicon si stable isotopes by biological activity in the surface ocean makes the stable isotope composition of silicon delta si 30 dissolved in seawater a sensitive tracer of the oceanic biogeochemical si cycle we present a high precision dataset that characterizes the delta si 30 distribution in the deep atlantic ocean from denmark strait to drake passage documenting strong meridional and smaller but resolvable vertical delta si 30 gradients we show that these gradients are related to the two sources of deep and bottom waters in the atlantic ocean waters of north atlantic and nordic origin carry a high delta 30 sisignature of 1 7 parts per thousand into the deep atlantic while antarctic bottom water transports si with a low delta si 30 value of around 1 2 parts per thousand the deep atlantic delta si 30 distribution is thus governed by the quasi conservative mixing of si from these two isotopically distinct sources this disparity in si isotope composition between the north atlantic and southern ocean is in marked contrast to the homogeneity of the stable nitrogen isotope composition of deep ocean nitrate delta n 15 no3 we infer that the meridional delta si 30 gradient derives from the transport of the high delta si 30 signature of southern ocean intermediate mode waters into the north atlantic by the upper return path of the meridional overturning circulation moc the basin scale deep atlantic delta si 30 gradient thus owes its existence to the interaction of the physical circulation with biological nutrient uptake at high southern latitudes which fractionates si isotopes between the abyssal and intermediate mode waters formed in the southern ocean

estimates of stress directions by inversion of earthquake fault plane solutions in sicily summary the tectonic stress orientation is estimated in the lithosphere of northern sicily the southern tyrrhenian sea and southern calabria and in the wadati benioff zone below the tyrrhenian by inversion of fault plane solutions of earthquakes covering a magnitude range from 2 5 to 7 1 focal mechanisms of 97 earthquakes are taken from the literature after a critical evaluation of their data quality an average misfit of f 13 indicates that the set of all shallow 50 km earthquakes is generated by a heterogeneous stress field for three subsets based on regional and magnitude separation f was small enough 2 8 lfs5 9 to support the assumption of a homogeneous stress direction for an additional subset with f 7 4 such a condition is close to being fulfilled even though some heterogeneity appears to be present the number of earthquakes in these subsets ranged from nine to 22 and the uncertainties of the principal stress directions were generally of the order of 20 at the 90 per cent confidence level the earthquakes with a425 define a regional stress field with the greatest principal stress ul dipping at a shallow angle to the south in north eastern sicily and south western calabria the stress field estimated by earthquakes is extensional with o3 in a direction of wnw and a near vertical ol in agreement with the graben tectonics mapped geologically in this area in western sicily the c1 direction is oriented wnw but this result is judged less reliable than the others based on the broader confidence limits of the solution and the average misfit of 7 4 the earthquakes in the wadati benioff zone define ol dipping at about 70 to the nw subparallel to the zone with o2 horizontal and striking parallel to the zone

rapid source mechanism determination of large mw 5 earthquakes in the western united states inversion of complete long period ground motions is used for rapid determination of source mechanisms of mw 5 earthquakes in the western united states the first few minutes of ground motions on local and regional distance waveforms are inverted for point source centroid moment tensors waveforms recorded at regional distances 300 1500 km can be adequately modeled at periods longer than 50 s using the laterally homogeneous prem model dziewonski and anderson 1981 at closer distances 300 km waves with periods as short as 35 s can be analyzed using prem best double couple focal mechanisms for 18 recent large western u s earthquakes compare very well with those obtained by other methods our procedure interfaced with automated data retrieval and source location methods is a viable tool for reliable determination of seismic moment and fault mechanism within 30 minutes after an earthquake

moment tensor inversion of regional phases application to a mine collapse the aim of our study consists of analyzing potentially non double couple seismic events recorded at regional distances in order to define the nature of the seismic source a moment tensor inversion is carried out as this method is general enough not to initially constrain the source mechanism in this paper we present an application to a seismic event induced by a mine collapse which occurred near the town of halle in germany because of its induced nature many parameters such as the location and geometry of this seismic source are known this information allows us to test the influence of inadequate propagation modeling on the moment tensor obtained from the inversion green s functions have been computed with the reflectivity method in a flat layered medium using the european model eurid du et al 1998 dufumier et al 1997 from the inversion of p wave seismograms recorded by the german regional seismic network will we obtained a source time function which can be decomposed into two subevents the first one has a large isotropic part and a deviatoric mechanism with near vertical nodal planes no volume change is observed for the second subevent but a deviatoric component opposite of the first one the addition of s waves does not change the results of the inversion which are stable surface waves were not used because of their poor dispersion curves based on the moment tensor obtained from these inversions the physical process at the source is compatible with a large cavity collapse

aeolian sediment transport and morphologic change on a managed and an unmanaged foredune sediment transport and short term morphologic change were evaluated at a site where sand fences are deployed and the beach is raked managed site and a site where these human adjustments are not practiced unmanaged site data were gathered across the seaward portion of a low foredune when winds blew nearly shore normal at mean speeds 8 9 to 9 3 m s 1 data from traps revealed sediment transport rates at unvegetated portions of the foredune crest 40 2 to 43 5 kg m 1 h 1 were greater than on the backshore 4 9 to 11 2 kg m 1 h 1 due to onshore decreases in surface moisture and speed up of the wind passing over the foredune data from erosion pins indicate sediment input to the dune was 1 48 m3 m 1 alongshore at the managed site and 1 25 m3 m 1 at the unmanaged site the unmanaged site had deposition at the dune toe erosion at mid slope and deposition at the crest deposition occurred at mid slope on the managed site near a partially buried 0 58 m high fence with a porosity of about 65 deposition at partially buried wrack on the upper backshore and dune toe at the unmanaged site was about twice as great as deposition in this zone at the managed site results indicate that 1 the seaward slope of the foredune can be a more important source of sand to the lee of the crest than the beach 2 wrack near the toe can decrease transport into the foredune 3 a scour zone can occur on the foredune slope above the wrack line 4 a fence placed in this location can promote deposition and offset scour but fences can restrict delivery of sediment farther inland evaluation of alternative configurations of fences and strategies for managing wrack is required to better determine the ways that humans modify foredunes copyright 2012 john wiley sons ltd

airflow up the stoss slope of sand dunes limitations of current understanding the windward stoss side of a sand dune acts as a streamlined obstacle in the path of the wind continuity principles necessitate compression of the flow field up the stoss slope of a dune and shear stress must progressively increase as the flow accelerates measurements in transverse flow over thirteen dunes at padre island texas the algodones california and white sands new mexico confirm that velocity profiles on the stoss slope are not log linear and that flow acceleration occurs very close to the surface within an internal boundary layer as a consequence in the overlying flow where measurements have historically been made an overall decrease in shear stress occurs up the slope the actual shape of the velocity profiles and the identification of the appropriate segment of the profile from which to derive the shear stress that drives saltation represent major problems not approachable by traditional means

effects of time dependent moisture content of surface sediments on aeolian transport rates across a beach wildwood new jersey u s a a one day field investigation on an unvegetated backbeach documents the importance of surface sediment drying to aeolian transport surface sediments were well sorted fine sand moisture content of samples taken in the moist areas on the backbeach varied from 2 9 to 9 2 per cent lack of dry sediment inhibited transport prior to 08 50 by 09 10 conspicuous streamers of dry sand moved across the moist surface barchan shaped bedforms 30 to 40 mm high and composed of dry sand moisture content 0 10 per cent formed where sand streamers converged the surface composed of dry sand increased from 5 per cent of the area of the backbeach at 09 50 to 90 per cent by 12 50 mean wind speeds were beetween 5 6 and 8 6 m s 1 at 6 m above the backbeach corresponding shear velocities were always above the entrainment threshold for dry sand and below the threshold for the moist sand on the backbeach measured rates of sand trapped by vertical cylindrical traps increased during the day relative to calculated rates the measured rate of sand trapped on the moist foreshore was higher than the rate trapped on the backbeach during the same interval indicating that the moist foreshore moisture content 18 per cent was an efficient transport surface for sediment delivered from the dry portion of the beach upwind measured rates of sand trapped show no clear relationship to shear velocities unless time dependent surface moisture content is considered results document conditions that describe transport across moist surfaces in terms of four stages including 1 entrainment of moist sediment from a moist surface 2 in situ drying of surface grains from a moist surface followed by transport across the surface 3 entrainment and transport of dry sediment from bedforms that have accumulated on the moist surface and 4 entrainment of sand from a dry upwind source and transport across a moist downwind surface 1997 john wiley sons ltd

automated procedure for point and kinematic source inversion at regional distances 1 the development of fast automatic routines for the retrieval of point source parameters of medium to large earthquakes was convincingly established in the last years and decades providing an increasing number of focal mechanism solutions original applications at teleseismic distances have been successively accompanied by specific routines for regional data sets the majority of these methods are based on the fit of low passed time traces we present here a new technique for the automatic retrieval of point source parameters and highly parameterized kinematic rupture models at regional distances assuming the recently proposed eikonal model to describe the extended source in our approach we use a larger set of information to better constrain the source parameters including the fit of amplitude spectra and displacements at different phases and frequency ranges the time consumption of the inversion process is significantly improved thanks to the implementation of green s functions databases we adopt a multistep inversion approach finally providing the focal mechanism magnitude and centroid location of the point source for events with magnitude higher than a threshold of mw 5 5 source geometry rupture extension and average slip may be additionally retrieved we discuss the methodology and the inversion stability showing applications to significant earthquakes in two case areas we focus on germany and greece and their neighboring areas considering major shallow earthquakes in the last 5 years the proposed method is currently implemented for automatic data processing at the seismological observatory of the federal institute for geosciences and natural resources in germany

broadband modeling of local earthquakes three component broadband waveforms of two small earthquakes near upland california recorded on the pasadena broadband high dynamic range instrument were modeled to obtain useful green s functions for this path and to examine the sensitivity of the synthetic seismograms to perturbations of the crustal model we assumed that the source of each event was both simple and known as determined from the caltech usgs array first motions a trapezoidal time function was chosen to fit the width of the direct s wave generalized rays reflectivity and finite difference techniques were used to compute the synthetic seismograms we found that a simple layer over a half space model is an adequate approximation of the upper crust along this profile in particular the waveforms are controlled by a relatively slow 4 km thick surficial layer 4 5km s 1 2 6 km s 1 over a faster layer 5 9 km s 1 3 5 km s 1 the relative amplitudes of direct and multiple s indicate that the main shock occurred at a depth of 6 km while the aftershock occurred at a depth of 8 to 9 km sensitivity analyses indicate that for distances less than 50 km and for periods longer than 1 sec the synthetic seismograms are not very sensitive to perturbations of the deep crustal structure analysis of upper crustal model perturbations revealed that the surficial layer is between 3 to 5 km thick in addition the contact between this layer and the underlying material can be smoothed with a 2 km wide velocity gradient without adversely affecting the fit to the data two dimensional finite difference calculations show that a ridge structure beneath the recorder acts as a lowpass filter the lower frequency phases are largely unaffected other two dimensional models with ridges between the source and receiver clearly did not fit the data synthetic seismograms computed for the best fitting model were used to estimate a long period moment of 6 2 1022 dyne cm ml 4 6 and 1 1022 dyne cm ml 3 7 with identical triangular source time durations of 0 3 sec assuming the same fault dimension of 0 4 km from standard scaling laws stress drop estimates of 410 and 70 bars are obtained for the two events respectively generally we found that it is possible to reproduce local waveforms at frequencies up to 1 hz without a complete knowledge of fine structural detail resulting green s functions can be useful in studying historic events and in simulations of large events from a given source region

meso scale modelling of aeolian sediment input to coastal dunes the collection of a time series coupling hourly wind data speed and direction with sand transport over months has provided new insights into the dynamics of transport events that input sediment to the foredune at greenwich dunes prince edward island national park canada this paper summarises the key aspects of aeolian sedimentmovement for a period of 9 months and presents amodelling approach for resolving aeolian transport to coastal dunes at the meso scale the main hypothesis of the modelling approach is that a small number of key factors control both the occurrence and the magnitude of transport events thresholds associated with these factors may be used to filter the time series and isolate potential transport periods over the year the impacts of nearshore processes are included in the approach as part of the dynamics of coastal dunes as are supply limiting factors and trade offs between fetch distances angle of wind approach and beach dimensions a simple analytical procedure based on previously published equations is carried out to assess the general viability of the conceptual approach results show that the incorporation of moisture and fetch effects in the calculation of transport for isolated potential transport periods result in improved predictions of sediment input to the dune net changes measured with three different techniques suggest that survey data with coarse temporal resolution underestimates the amount of sand input to the dune because sediment is often removed from the embryo dune and foredune by other processes such as wave scarping predictions obtained by the proposed modelling approach are of the same order of magnitude as measured deposition andmuch less than predicted bymodels based solely onwind speed and direction areas for improvement and alternative modelling approaches such as probabilistic approaches similar to weather forecasting are covered in the discussion

faulting process of the 1990 june 20 iran earthquake from broadband records summary we study the rupture process of the iranian earthquake of 1990 june 20 from broad band data we redetermined its moment tensor and source mechanism from long period surface waves then we studied the p and sh broad band recordings from the geoscope and iris seismic networks we inverted the body waves using a full waveform modelling for the inversion we used the gradient method of nab lek mixed with a limited exploration of the parameter space in order to control the resolution of inversion we proceeded by a stepwise procedure increasing the model complexity with every new inversion we used the reduction of cost functional as a criterion for the validity of the inverted model we first inverted the body waves considering a single point source model we found that body waves are dominated by a large energy release about 20 s from the onset of the signals in the next step fixing fault plane solution we inverted for the directivity of the source we found clear evidence of propagation towards the east of the epicentre we determined a rupture velocity of 2 5km s 1 the preceding source inversion reduced the variance of the residuals by about 30 per cent further improvement of the fit of the body wave signals was obtained using an extended line source with constant fault plane solution we obtained a very good fit with an asymmetrical model initially rupture is bilateral but north western propagation stops after 10 s later rupture continues unilaterally in the south eastern direction with a rupture velocity of the order of 2 5 km s 1 finally an inversion was attempted with a line source with varying fault mechanism the final solution obtained by this procedure reduces the variance of the body wave residuals by 60 per cent with respect to the variance of the observed body wave signals variations in fault plane solution along the fault are considered to be well resolved

the dynamic effects of moisture on the entrainment and transport of sand by wind abstract there is an increasing awareness of the influence of surface moisture on aeolian entrainment and transport of sediment existing wind tunnel studies have shown the impact of a limited range of moisture contents on entrainment thresholds but similar investigations are lacking in the field the research reported here investigated the influence of changes in surface moisture content on sand entrainment and transport on a meso tidal beach in anglesey north wales high frequency 1 hz wind velocities measured with hot wire anemometers were combined with grain impact data from a sensit monitor and mass flux measurements from a standard sand trap surface and near surface moisture contents were assessed gravimetrically from surface sand scrapes and also directly by using a thetaprobe critical threshold values for entrainment were specified using a modified form of the time fraction equivalence method stout j e zobeck t m 1996a establishing the threshold condition for soil movement in wind eroding fields proceedings of the international conference on air pollution from agricultural operations mwps c 3 kansas city 7 9 february 1996 pp 65 71 results indicate a time dependent change in dominant control of the sand transport system from moisture to wind speed dependent upon the moisture content of the surface sediment this interchange between controlling parameters on both entrainment and transport was very sensitive to prevailing moisture conditions and took place over a period of minutes to hours under conditions experienced in the experiments presented here the critical moisture threshold for sediment entrainment was determined to be between 4 and 6 higher than the 1 4 specified in previous wind tunnel experiments furthermore a moisture content of nearly 2 where moisture was adhered to transported sediment appeared to have little or no impact on the rate of sand flux

silicon isotope variations in central siberian rivers during basalt weathering in permafrost dominated larch forests abstract this work is devoted to the characterization of natural mechanisms of silicon isotope fractionation within siberian watersheds and predicting the climate warming effect on si fluxes from the land to the arctic ocean to unravel the different sources of silica generated by basalt weathering in central siberia under permafrost and larch deciduous forest conditions we measured the si isotopic composition of large and small rivers surface flow interstitial soil solutions plant litter and soils the average annual discharge weighted 30 si values of the second largest tributary of the yenissei river nyzhnaya tunguska and its main northern tributary kochechum are equal to 1 08 0 10 and 1 67 0 15 respectively while their average annual si concentrations are very similar 3 46 and 3 50 mg l respectively during summer baseflow the dissolved si isotope composition of both large rivers and a small stream ranges between 1 5 and 2 5 this is much heavier compared to the source basaltic rocks but similar to the fresh litter of larix gmelinii the dominating tree species in this region it could be consistent with litter degradation in the uppermost soil horizons being the dominant source of solutes annually exported by central siberian rivers during spring flood accounting for 60 80 of annual si flux the 30 si of the large rivers dissolved load decreases by 1 1 5 thus approaching the value of the bedrock and the silicate suspended matter of the rivers rsm this may reflect the dissolution of the silicate suspended load at high water mineral ratio the winter 30 si values of the large river dissolved load range between 1 0 and 2 5 during this period contributing to 10 of the annual si chemical flux the interaction between bedrock porous tuffs and deep ground waters occurs at a very high solid solution ratio leading to the precipitation of isotopically light secondary minerals and enrichment of 30 si in the fluids that feed the river through the unfrozen flowpaths results of this study imply that more than a half of the silica transported by siberian rivers may transit through the biogenic pool and that like in other stable basaltic regions bedrock water interactions account for a lesser fraction of the silica flux as a result of projected future climate warming and weathering increases in boreal regions the 30 si isotopic composition of large siberian rivers is likely to shift towards less positive values

regional moment tensor determination in the european mediterranean area initial results the broadband seismic network in the european mediterranean area provides high quality data we invert these regional three component data for the source parameters of moderate to strong earthquakes in the entire european mediterranean area regional seismograms have a good signal to noise ratio even for moderate sized events that are too small for teleseismic analysis the magnitude threshold for source parameter determination can thus be significantly lowered the threshold depends on the average event station distances within dense broadband networks we analyze mw 3 0 earthquakes in areas far from broadband seismic stations the lower bound is mw 4 5 4 8 still considerably lower than the teleseismic analysis threshold about mw 5 0 5 3 for larger events we perform rapid moment tensor analysis using near real time data solutions are posted within hours after event occurrence in a second step we merge near real time and later available data to obtain a regional moment tensor catalog of moderate to large earthquakes for the entire european mediterranean area within less than 1 year we have analyzed 67 earthquakes ranging in size from mw 2 9 to 7 5 the solutions cover the seismically active areas of the european mediterranean area particularly important are solutions for slowly deforming regions where large earthquakes that could be analyzed with teleseismic data occur infrequently the solutions are reliable for events with independent source parameter estimates the agreement is generally high the solutions are robust variations in epicentral parameters source depth or exact choice of stations do not affect source parameter estimates strongly the moment magnitudes provide a unified estimate of earthquake size for the european mediterranean area we perform regression analyses to link our moment magnitudes with local body and surface wave magnitudes

influence of reed stem density on foredune development vegetation density on foredunes exerts an important control on aeolian sediment transport and deposition and therefore on profile development in a long term monitoring field experiment three plots were planted with regular grids of reed bundles in three different densities 4 2 and 1 bundles per m2 this study reports on the differences in profile development under the range of vegetation densities topographic profiles were measured between may 1996 and april 1997 results indicate important differences in profile development for the three reed bundle densities in the highest density plot a distinct steep dune developed while in the lowest density a more gradual and smooth sand ramp was deposited when the stems had been completely buried differences in profile evolution vanished after a second planting of reed stems in january 1997 the process was repeated in may 1997 all plots had gained a sand volume ranging from 11 5 to 12 3 m3 m 1 indicating that the sediment budget is relatively constant regardless of the particular profile evolution the field evidence is compared with simulations of profile development generated by the foredune development model safe the model successfully reproduces the overall profile development but in general the equations used for vegetation transport interaction overestimate the effect of vegetation this causes some deviations between field and model results several reasons for this are discussed based on the experiments reported here recommendations are given for further research copyright 2001 john wiley sons ltd

aeolian sediment transport on a human altered foredune changes in wind speed and sediment transport are evaluated at a gap and adjacent crest of a 2 to 3 m high 40 m wide foredune built by sand fences and vegetation plantings on a wide nourished fine sand beach at ocean city new jersey anemometer masts cylindrical sand traps and erosion pins were placed on the beach and dune during two obliquely onshore wind events in february and march 2003 results reveal that 1 changes in the alongshore continuity of the beach and dune system can act as boundaries to aeolian transport when winds blow at an angle to the shoreline 2 oblique winds blowing across poorly vegetated patches in the dune increase the potential for creating an irregular crest elevation 3 transport rates and deflation rates can be greater within the foredune than on the beach if the dune surface is poorly vegetated and the beach has not had time to dry following tidal inundation 4 frozen ground does not prevent surface deflation and 5 remnant sand fences and fresh storm wrack have great local but temporary effect on transport rates temporal and spatial differences due to sand fences and wrack changes in sediment availability due to time dependent differences in surface moisture and frozen ground combined with complex topography and patchy vegetation make it difficult to specify cause effect relationships effects of individual roughness elements on the beach and dune on wind flow and sediment transport can be quantified at specific locations at the event scale but extrapolation of each event to longer temporal and spatial scales remains qualitative copyright 2006 john wiley sons ltd

foredune accretion under offshore winds experiments carried out at magilligan strand on the north coast of ireland suggest that topographic steering of offshore winds is an important facet of the aeolian sediment transport system at this location a five day study 18 22 june 2005 investigated the pattern of airflow over the foredune while simultaneously collecting data on sediment flux a simple instrument setup was used to characterise the airflow a sonic anemometer was placed at the dune crest with another on the mid beach horizontal traps electronic and integrating measured sediment flux on the supra tidal beach results show that offshore wind flow deviated from its original direction in the lee of the dune seaward of foredune the change in direction was not a simple steering of flow to a singular new direction but rather flow separation resulting in turbulent multidirectional flow including reversal traps located at the foot of the dune scarp recorded sediment transport during events forced by offshore winds data from sediment traps wind and observational evidence have been used to argue that sedimentation was occurring in this zone when budgeting for sediment movement within beach dune systems it is important to take into account the effect of secondary airflow patterns during offshore winds and their role in constructive processes of foredune formation particularly in post storm recovery c 2008 elsevier b v all rights reserved

southern ocean nitrogen and silicon dynamics during the last deglaciation abstract the reinvigoration of overturning in the southern ocean is hypothesized to have returned co2 from the deep ocean to the atmosphere at the end of the last ice age large peaks in opal accumulation have been put forward as evidence for an increase in wind driven upwelling between 10 and 15 ka here we use coupled nitrogen and silicon isotope records alongside opal accumulation rates to provide quasi quantitative estimates of southern ocean nutrient supply by upwelling and nutrient utilization across this interval significant changes in the consumption of n and si across the two opal accumulation peaks indicate major changes in both upwelling and nutrient demand we find n and si consumption to be relatively incomplete during peak opal accumulation at the onset of the deglaciation this indicates that nutrient supply was significantly enhanced the second deglacial peak in opal accumulation is associated with more complete si consumption and variable n consumption we suggest that this peak represents strong upwelling and more complete utilization of the available silicic acid pool differences between the si and n responses during opal peaks may stem from decreasing iron availability across the glacial termination the nutrient isotope evidence for excess nutrients during the deglaciation indicates that the high export productivity was insufficient to overcome the evasion of co2 to the atmosphere as a result of physical circulation changes previous work has demonstrated that the reinvigoration of overturning circulation during the deglaciation causes a transient peak in nutrient supply to the low latitudes this is supported by our data which indicate that relatively high macronutrient concentrations were maintained in the southern ocean surface waters that are incorporated into mode waters despite high demand

sediment supply from shoreface to dunes linking sediment transport measurements and long term morphological evolution a significant problem in current coastal research is the understanding of linkages between morphological phenomena occurring on different temporal and spatial scales morphodynamic processes in the nearshore typically exhibit nonlinear behaviour and consequently phenomena which occur on short temporal event scales as e g observed during field experiments have generally been difficult to upscale to provide an understanding of the long term behaviour of the coast on the time scale of seasons or decades this paper documents a persistent onshore migration of nearshore bar features over a period of 3 decades using a set of cross shore profile surveys from a barrier on the danish north sea coast the observed behaviour is consistent with experimental data obtained during weeklong field campaigns when sediment transport and bar migration were found to be landward directed during high energy dissipative conditions hydrodynamic and sediment transport processes leading to onshore bar migration and eventually welding of the bars are documented to provide an explanation for the observed long term evolutionary trends in addition bar welding and the resulting intertidal bar formation represent an onshore sediment storage which is subsequently available for aeolian transport observations on aeolian sediment transport indicate that transport rates and sediment supply to the foredunes critically depend on the presence of dry sand sources as represented by well drained intertidal bars measurements of long term accretion rates in foredunes indicate that volumes deposited on the crest and lee slope of the dunes are in reasonable correspondence with volumes supplied to the subaerial beach through the process of bar welding hence the data suggest that a persistent onshore directed sediment supply occurs from the shoreface across the surf and intertidal zones and into the dunes of the investigated barrier

active fault kinematics and crustal stresses along the ionian margin of southeastern sicily since the late cretaceous onset of plate convergence between africa and europe the malta escarpment has been converted from a mesozoic passive margin into a mega hinge fault system with an additional sinistral strike slip component the modern tectonic stress regime with nw se directed maximum horizontal stresses has been established since late messinian times since the pleistocene sinistral strike slip deformation and contemporaneous normal faulting along the malta escarpment have induced the opening of oblique trending onshore grabens at the eastern margin of the hyblean plateau in this study we focus on the kinematics the controlling state of stress and the temporal variation of the neotectonic to active strike slip and normal fault structures the stress tensor calculations reveals that the widespread map scaled to meso scaled normal fault structures are governed by the long term extensional state of stress during the quaternary this long term stress tensor is predominantly controlled by gravitational induced stresses due to vertical load 1 sv and lateral extension due to the topographic gradient of the malta escarpment 3 sh ne sw in this case the average tectonic stresses 2 sh nw se transmitted by the regional to plate tectonic stress field are significantly smaller than the gravitational induced stresses in contrast the clear localization of conjugate sets of meso scaled strike slip fault structures and shear zones without accompanying normal fault structures give strong indications for episodic seismotectonic strike slip faulting under critical stress conditions in this state tectonically induced maximum horizontal stresses are successively increased by ongoing plate convergence from low level stress magnitudes 1 sv 2 sh nw se up to critical stress magnitudes 1 sh nw se 2 sv which are significantly larger than gravitational stresses at the critical state seismotectonic stress release occurs by active strike slip faulting as recently indicated in mid crustal levels by the moderate 1990 augusta earthquake and re establishes the long term extensional state of stress because the strike slip faults and shear zones in the study area were formed as surface ruptures they additionally give indications of episodic large earthquakes in this region with magnitudes greater than 6 0 as reported by several large earthquakes devastating e and se sicily in historical times

the influence of coarse woody debris on gravel beach geomorphology abstract coarse woody debris cwd is an important component of fluvial systems affecting in channel hydrology and sediment storage which in turn controls channel geometry and evolution the role of coarse woody debris in coastal geomorphology is an emerging research field and this study investigates its role on mixed sand and gravel beach systems a case study approach is used whereby two field areas in wellington new zealand each with two distinct beaches with differing wood accumulations were investigated through field surveying it is found that on gravel beaches cwd is most important during storm events where it causes the berm crests to be 0 5 1 0 m higher than on unwooded beaches as well as making the beachface twice as steep during calm periods the berm appears to be inactive as non storm waves can only rework the lower beachface a review of the literature indicates that on sandy beaches cwd is most important in the post storm recovery of beach systems the same wave event that causes beach erosion also deposits the cwd during calm periods the woody material is a trap for sand being transported along the beachface and therefore aids in re establishing foredune systems the differing sediment composition between sandy and gravelly beaches drives their morphological response to storm events and in turn determines how cwd interacts with the beach profile

a general framework for modeling sediment supply to coastal dunes including wind angle beach geometry and fetch effects a series of spatially explicit equations are derived that form the foundation of a modeling framework that provides insight into how the interaction of the fetch effect and angle of wind approach leads to tradeoffs that govern the magnitude of aeolian sediment transport across beaches of different geometry the spatial distribution of sediment transport rate per unit width at any point on the beach is shown to vary predictably as a function of wind angle critical fetch and beach geometry and this has evident implications for the total volume and distribution of sediment transport into the dunes behind the beach as well as the proportion of sediment lost from the beach dune system at the downwind margin as the wind field shifts from onshore shore perpendicular to oblique shore parallel approach angle total sediment transport rate across a dune line segment will reflect a tradeoff between transport reduction because of the cosine effect and transport enhancement because of potentially longer fetch distances traversed by the wind prior to encountering the dune line this tradeoff is most evident on long narrow beaches when beach width is less than the critical fetch for such beaches and with onshore winds the total sediment transport rate across the dune line will be less than that predicted for a wide beach because of the constraint imposed by the fetch effect however as the angle of wind approach becomes oblique the available fetch becomes progressively longer transport limitations imposed by the fetch effect are negated and transport enhancement across the dune line is to be expected with very large angles of wind approach the cosine effect dominates the interaction and transport reductions across the dune line occur until the wind is shore parallel and sediment supply to the dunes ceases altogether this sequence of adjustments and tradeoffs were only partially understood prior to this study and yet they form the foundation of coastal dune modeling the framework proposed in this paper serves to place future studies of process form interaction in beach dune systems on a robust theoretical foundation it also facilitates the testing of various alternative hypotheses regarding the uneven spatial and temporal distribution of dune height and growth rate in coastal environments

shear stress partitioning in sparsely vegetated desert canopies shear velocity ratios were derived for six neighbouring localities representing rangeland abandoned farmland and a playa in the semi arid region of the sonoran desert near surface and above canopy wind speeds mostly below saltation threshold were used to evaluate the partitioning of shear velocities and shear stresses between the plant canopy and the surface the technique utilized represents an alternative to the threshold shear velocity ratio rt approach of musick and gillette land degradation and rehabilitation 1990 2 87 94 and results demonstrate the need for partitioning over a range of wind speeds shear velocity ratios were variable over the playa and abandoned farmland while variance in near surface wind speeds was highest over shrub dominated sites the relationship between lateral cover lc and shear velocity r is comparable to previous findings utilizing rt although methodological differences result in mean shear velocity ratios less than shear velocity ratios derived for threshold conditions with respect to the model of raupach et al journal of geophysical research 1993 98 d2 3023 3029 this may be attributed to the difference between measured shear stresses and the average shear stress on the exposed surface at high lateral covers shear velocity ratios are lower than threshold shear velocity ratios due to increased wake interactions or decreased drag on the shrub elements at higher wind speeds

patterns of sand transport on vegetated foredunes the aeolian development of coastal foredunes is studied at two sites along the dutch coast amounts of sand transport are measured in cross sections over the foredunes and changes in surface height are monitored sand transport decreases rapidly landward of the vegetation boundary near the dunefoot changes in surface roughness and topography generate turbulence and upward flow causing a small part of the sand to be transported in suspension patterns of transport are found to be closely related to air flow which in turn is related to topography and vegetation density with steeper topography the amounts of sand transported landward from the dunefoot increase if vegetation density is low during oblique onshore winds most of the sand accumulates at the dune front during perpendicular onshore winds a large proportion of the sand is deposited landward of the slope when deflection of flow occurs landward transport of sand is interrupted

very broad band seismology in northern africa under the mednet project abstract the mediterranean and north african regions are characterized by strong seismicity and active complex tectonics which are often poorly monitored and understood owing to a lack of high quality seismic recordings to increase the instrumental coverage in the mediterranean region the istituto nazionale di geofisica began in 1987 the deployment in this area of a network of 12 very broad band seismic stations termed m ed n et motivated both by research interests and by considerations on seismic hazard monitoring m ed n et has been designed following the highest technical standards its geometry will provide a homogeneous coverage of the mediterranean and north african area with installations in most countries and an average spacing between stations of 800 1000 km the network should be completed by 1992 three stations are now installed in north african countries morocco tunisia and egypt and one is in preparation in algeria great care is being taken in choosing isolated underground sites for the installations to ensure optimal signal to noise ratios at all frequencies the noise level at these stations overlaps and at low frequencies is sometimes better than the current low noise model data are recorded locally and forwarded to the m ed n et data centre in rome for collection and distribution

the effect of wind gusts moisture content and fetch length on sand transport on a beach this paper reports on an analysis of instantaneous sediment transport in relation to wind gusts moisture content and fetch length from a field study carried out at skallingen denmark wind speeds were measured with cup anemometers and instantaneous sediment transport with vertical traps coupled to electronic balances moisture content was measured gravimetrically using samples taken along a beach profile at intervals of 1 to 2 h sediment transport and wind speeds were sampled at 1 hz and a 5 s running mean was used to smooth the data from the trap because of limitations of the balance resolution three measures of the threshold of sediment motion the intermittency threshold minimum threshold and maximum threshold were explored using data from five runs carried out on october 26 2000 the intermittency threshold and maximum threshold were largely insensitive to wind speed but varied spatially along the fetch distance the minimum threshold increased significantly with increasing mean wind speed as a result of reduced time for drying of the surface layer examination of time series for instantaneous wind speed and sediment transport for a number of runs on october 26 and november 6 2000 showed close agreement between fluctuations in wind speed and fluctuations in sediment transport cross spectral analysis of instantaneous wind speed and sediment transport for one run on each day where there was continuous transport showed high coherence between the two variables over a range of frequencies from 0 2 hz to 0 01 hz plots of all non zero instantaneous sediment transport values versus wind speed show considerable scatter in general transport rates are highest for traps located further from the upwind non erodible boundary i e along the fetch best fit power relationships show r2 values generally ranging from 0 4 to 0 6 and exponents ranging from 4 5 to 6 94 i e much higher than the traditional value of 3 found in most transport equations traps located close to the upwind boundary had lower r2 values and exponents 2 5

aeolian transport rates across raked and unraked beaches on a developed coast wind characteristics and aeolian transport were measured on a naturally evolving beach and dune and a nearby site where the beach is raked and sand trapping fences are deployed the beaches were composed of moderately well sorted to very well sorted fine to medium sand the backshore at the raked site was wider and the foredune was more densely vegetated and about 1 m higher than at the unraked site wind speeds were monitored using anemometers placed at 1 m elevation and sand transport was monitored using vertical traps during oblique onshore alongshore and offshore winds occurring in march and april 2009 inundation of the low backshore through isolated swash channels prevented formation of a continuously decreasing cross shore moisture gradient the surface of the berm crest was dryer than the backshore making the berm crest the greatest source of offshore losses during offshore winds the lack of storm wrack on the raked beach reduced the potential for sediment accumulation seaward of the dune crest during onshore winds and the higher dune crest reduced wind speeds and sediment transport from the dune to the backshore during offshore winds accretion at wrack seaward of the dune toe on the unraked beach resulted in a wider dune field and higher narrower backshore although fresh wrack is an effective local trap for aeolian transport wrack that becomes buried appears to have little effect as a barrier and can supply dry sand for subsequent transport aeolian transport rates were greater on the narrower but dryer backshore of the unraked site vegetation growth may be necessary to trap sand within zones of buried wrack in order to allow new incipient foredunes to evolve copyright 2010 john wiley sons ltd

moment tensor inversion from mednet data 1 large worldwide earthquakes of 1990 we develop a method for the rapid determination of the moment tensor of large worldwide earthquakes by inversion of long period data recorded by the mednet regional network and we apply it to the most significant events of 1990 march 3 fiji and 25 costa rica may 12 sakhalin 20 sudan and 30 romania june 20 iran july 16 luzon and december 30 new britain the comparison with cmts and moment tensors by usgs shows that an advanced regional seismic network is capable of providing reliable and rapid control of the seismic source for worldwide seismicity

waveform modelling of the may 20 1990 sudan earthquake abstract very broad band seismic waveforms were modelled to derive the moment tensor the source time function and the depth of the may 20 1990 sudan earthquake long period body waves surface waves and broad band displacement recorded by the m ed n et regional network were merged with digital data from global seismic networks to compare fault geometries obtained by different methods and assess associated uncertainties our analysis indicates that the may 20 earthquake had a seismic moment of 5 3 10 26 dyne cm and a depth of about 10 km the focal mechanism shows a mixture of transcurrent geometry with one plane striking nw se and a smaller dip slip component with the t axis oriented in the n s direction the fault geometry agrees with models calling for the recent re activation of the nw se trending aswa transform zone marking the northern termination of the western branch of the rift in contrast the n s tensional component which also dominates the focal mechanisms of the aftershocks dziewonski et al 1991 supports the evidence for the rotation of the regional quaternary stress field to the north in contrast with simple two plate models of rifting in east africa the juba event allowed us to test the capability of the m ed n et regional seismic network to provide an accurate real time description of the seismic source

quantifying sand storage capacity of large woody debris on beaches using lidar abstract the sedimentological role of large woody debris lwd on beaches is understudied and is relevant for the morphodynamics of sandy high energy beach dune systems of the northeast pacific ocean on the west coast of canada this debris consists largely of historical escape logs from the coastal logging industry in areas with competent wind regimes lwd can trap appreciable amounts of windblown sand in the backshore which can alter beach foredune sediment budgets and initiate incipient dune formation as this additional store of sediment must be reworked first during high water events it provides an important buffer that reduces erosion of established foredunes this study examines the morphology and sand storage capacity of three backshore lwd deposits of varying morphologies on northeastern graham island haida gwaii queen charlotte islands british columbia canada a new method was developed using coincident high spatial resolution lidar data and digital orthophotographs to derive dems for distinct ground cover classes sand lwd these dems were then used to quantify relative storage capacities of lwd and sand in the backshore significant amounts of sand are stored within and around lwd on beaches in the study region existing storage quantities above hhwmt range from 9 19 10 4 to 1 39 10 5 kg m 1 beach width or 1 14 to 1 60 m storage depth the same lwd deposits have a further potential storage capacity ranging from 1 04 to 1 70 10 4 kg m 1 beach width or 0 21 to 0 28 m depth the relative storage capacity of these features is reflected in the backshore morphology of each site with sediment transport further into the backshore dependent upon the morphology and relative in filling of the log debris jam with this additional sediment storage log debris could enhance development of large incipient dunes in the backshore thereby buffering against increasing storminess and gradual sea level rise in the region as the use of precise lidar data is increasing in geomorphic research the development of a verifiable methodology for estimating beach dune storage volumes is timely

air flow over foredunes and implications for sand transport more than 4000 hourly wind profiles measured on three topographically different foredunes are analysed and discussed wind flow over the foredunes is studied by means of the relative wind speed the ratio between wind speed at a certain location and the reference wind speed at the same height relative wind speeds appear to be independent of general wind speed but dependent on wind direction for perpendicular onshore winds the flow over the foredune is accelerated due to topographic changes and decelerated due to changes in surface roughness accelerations dominate over decelerations on the seaward slope the pattern of acceleration and deceleration in relation to wind direction is more or less comparable for different foredunes but the magnitudes differ an increase in foredune height from 6 to 10m leads to an increase in speed up near the top of the seaward slope from 110 to 150 per cent during onshore wind but further increase of foredune height from 10 to 23 m appears to have little effect due to increased roughness and deflection of flow topography also influences the direction of the flow between beach and top the flow deflects in the direction of the normal during onshore winds during offshore winds the flow is deflected to the parallel near the dunefoot deflection is always in the direction of the parallel and increases with steeper topography the maximum deflection near the dunefoot was 90 over a 23 m high dune observed during offshore winds patterns of erosion and sedimentation resulting from winds from different directions can be explained by the observed accelerations and decelerations owing to speed up on the seaward front of the foredune sand transport capacity of the wind increases which results in erosion if vegetation is absent during strong onshore wind sand is lifted near the dunefoot and moves over the foredune in suspension during weaker winds vertical wind velocities do not exceed fall velocities of the sand grains and most of the sand is deposited near the dunefoot

formation and behavior of aeolian streamers received 5 december 2004 revised 31 march 2005 accepted 9 june 2005 published 7 september 2005 1 field experiments were conducted to determine the characteristic spatial and temporal dimensions and behavior of aeolian streamers and to identify the processes responsible for their formation an instrument array that included anemometer towers piezo electric transport sensors safires and hot film probes was deployed to measure streamers and airflow dynamics on both a coastal dune and a desert sand mound in california aeolian transport occurs predominantly in the form of families of intertwining and bifurcating streamers while under intense wind forcing more complex patterns of nested streamers and clouds with embedded streamers develop the streamers display a characteristic width of approximately 0 2 m and an average lateral spacing of about 1 m these dimensions appear to be independent of mean airflow characteristics the observations and measurements of streamers under different environmental conditions suggest that bed surface control in the form of differentiation in moisture content grain size or microtopography is not a necessary condition for the formation of streamers the results show little correlation between possible streamwise vortices or burst sweep events and streamers it is proposed that streamers are generated by near surface gusts that originate from large eddies propagating to the ground from higher regions of the boundary layer these elongated and stretched eddies scrape across the surface and initiate saltation along their path this concept accounts for the characteristic size and spacing of streamers their rapid propagation and the fast response of saltation to wind speed fluctuations

single station cmt application to the michoacan mexico earthquake of september 19 1985 observations of three dimensional ground motion at a single point on the surface of the earth following an earthquake can be sufficient to determine the zeroth order moment tensor of the event we adapt the centroid moment tensor cmt method dziewonski et al 1981 of analysis to single station data and apply it to the september 19 1985 michoacan earthquake the obtained mechanism indicates faulting on a shallow plane consistent with the ongoing subduction of the cocos plate the scalar moment is 1 3 1028 dyne cm a direct deconvolution of the observed p wave train indicates that the moment release occurred in two subevents each of 20 seconds duration with a peak to peak separation in time of 25 seconds

the november 13 1990 earthquake off the coast of the primorskij region the eastern russia we study the november 13 1990 off primorskij earthquake which occurred near the northern end of the japan sea off the coast of the primorskij region by using data from short period and broad band seismograph networks in hokkaido japan the main shock and four aftershocks are located from arrival times of p and s waves recorded by these networks the main shock epicenter is located about 50 km off the coast at a depth of about 10 km and the largest aftershock is located about 20 km southwest of the main shock it is difficult to read the polarities of p waves recorded by the short period network the source mechanism of the main shock is determined by moment tensor inversion of long period wave forms recorded by broad band instruments the source mechanism is characterized by a reverse faulting with a vertical t axis and a horizontal p axis trending in the wnw ese direction we have examined earthquake data reported by the isc and by the academy of sciences of the ussr to study previous seismicity in the vicinity of the november 13 earthquake no significant well located earthquake is reported in this region the stress orientation in this region may have significant implications for the tectonics of the northern end of the japan sea where a plate boundary between the eurasian and north american plates has been proposed

automatic regional moment tensor inversion in the european mediterranean region summary we produce fast and automatic moment tensor solutions for all moderate to strong earthquakes in the european mediterranean region the procedure automatically screens near real time earthquake alerts provided by a large number of agencies each event with magnitude m 4 7 triggers an automatic request for near real time data at several national and international data centres moment tensor inversion is performed using complete regional long period 50 100 s waveforms initially the data are inverted for a fixed depth to remove traces with a low signal tonoise ratio the remaining data are then inverted for several trial depths to find the best fitting depth solutions are produced within 90 min of an earthquake we analyse the results for the period 2000 april to 2002 april to evaluate the performance of the procedure for quality assessment we compared the results with the independent swiss regional moment tensor catalogue srmt and divided the 87 moment tensor solutions into three groups 38 a quality solutions with well resolved m w depth and focal mechanism 21 b quality solutions with wellresolved m w and 28 unreliable c quality solutions the non homogeneous station and event distributions varying noise level and inaccurate earthquake locations affected solution quality for larger events m w 5 5 we consistently obtained a quality solutions for m w 4 5 5 5 we obtained a and b quality solutions solutions that pass empirical rules mimicking the a posteriori quality for our data set are automatically disseminated

biological fractionation of silicon isotopes in southern ocean surface waters 1 the fractionation of silicon isotopes by diatoms during silicification i e opaline cell wall formation provides a new tool for paleoceanographic studies of the silicon cycle here we examine the natural variations of the 30si 28si ratio in silicic acid si oh 4 and biogenic silica bsio2 in surface waters of the antarctic circumpolar current acc along 170 w the results provide direct evidence of biologically mediated fractionation of silicon isotopes with an enrichment factor of between 1 1 and 1 9 depending on the model employed comparison of the mass flux of bsio2 captured in sediment traps deployed in the study area with the silicon isotopic composition of that material establishes a direct linkage between diatom dynamics in surface waters and the isotopic signature of exported particles we calculated si oh 4 no3 utilization ratios from variations in silicon and nitrogen isotopic ratios in surface waters and sediment traps that agree well with direct observations of 4 1 in this region this work supports the use of variations in silicon isotopes in sedimentary opal as a proxy for relative si oh 4 utilization in surface waters

heavy silicon isotopic composition of silicic acid and biogenic silica in arctic waters over the beaufort shelf and the canada basin the silicon isotopic composition of silicic acid 30si oh 4 and biogenic silica 30si bsio2 were measured for the first time in marine arctic waters from the mackenzie river delta to the deep canada basin in the late summer of 2009 in the upper 100 m of the water column 30si oh 4 signals 1 82 to 3 08 were negatively correlated with the relative contribution of mackenzie river water the biogenic si isotope fractionation factor estimated using an open system model 30e 0 97 0 17 agrees well with laboratory and global ocean estimates nevertheless the 30si dynamics of this region may be better represented by closed system isotope models that yield lower values of 30e between 0 33 and 0 41 depending on how the contribution of sea ice diatoms is incorporated in the upper 400 m 30si bsio2 values were among the heaviest ever measured in marine suspended bsio2 2 03 to 3 51 a positive correlation between 30si bsio2 and sea ice cover implies that heavy signals can result from isotopically heavy sea ice diatoms introduced to pelagic assemblages below the surface bsio2 production zone the 30si oh 4 distribution followed that of major water masses vertical 30si oh 4 profiles showed a minimum average of 1 84 0 10 in the upper halocline 125 200 m composed of modified pacific water and heavier average values 2 04 0 11 in atlantic water 300 500 m deep in the canada basin deep water below 2000 m 30si oh 4 averaged 1 88 0 12 which represents the most positive value ever measured anywhere in the deep ocean since most si oh 4 enters the arctic from shallow depths in the atlantic ocean heavy deep arctic 30si oh 4 signals likely reflect the influx of relatively heavy intermediate atlantic waters a box model simulation of the global marine 30si oh 4 distribution successfully reproduced the observed patterns with the 30si oh 4 of the simulated deep arctic ocean being the heaviest of all deep ocean basins

offshore aeolian sediment transport across a human modified foredune concepts derived from previous studies of offshore winds on natural dunes are evaluated on a dune maintained for shore protection during three offshore wind events the potential for offshore winds to form a lee side eddy on the backshore or transfer sediment from the dune and berm crest to the water are evaluated as are differences in wind speed and sediment transport on the dune crest berm crest and a pedestrian access gap the dune is 18 20 m wide near the base and has a crest 4 5 m above backshore elevation two sand trapping fences facilitate accretion data were obtained from wind vanes on the crest and lee of the dune and anemometers and sand traps placed across the dune on the beach berm crest and in the access gap mean wind direction above the dune crest varied from 11 to 3 deg from shore normal no persistent recirculation eddy occurred on the 12 deg seaward slope wind speed on the berm crest was 85 89 of speed at the dune crest but rates of sediment transport were 2 27 times greater during the strongest winds indicating that a wide beach overcomes the transport limitation of a dune barrier limited transport on the seaward dune ramp indicates that losses to the water are mostly from the backshore not the dune the seaward slope gains sand from the landward slope and dune crest sand fences causing accretion on the dune ramp during onshore winds lower the seaward slope and reduce the likelihood of detached flows during offshore winds transport rates are higher in access gaps than on the dune crest despite lower wind speeds because of flatter slopes and absence of vegetation transport rates across dunes and through gaps can be reduced using vegetation and raised walkover structures

responses of three dimensional flow to variations in the angle of incident wind and profile form of dunes greenwich dunes prince edward island canada abstract this study reports the responses of three dimensional near surface airflow over a vegetated foredune to variations in the conditions of incident flow during an 8 h experiment two parallel measurement transects were established on morphologically different dune profiles i a taller concave convex west foredune transect with 0 5 m high densely vegetated 45 seaward incipient foredune and ii a shorter concave straight east foredune transect with lower sparsely vegetated 14 seaward incipient foredune five stations on each transect from the incipient dune to the crest were equipped with ultrasonic anemometers at 0 6 and 1 65 m height and logged at 1 hz incident conditions were recorded from a 4 m tower over a flat beach winds increased from 6 m s 1 to 20 m s 1 and were generally obliquely onshore ene 73 three sub events and the population of 10 minute averages of key properties of flow u w s cvu from all sample locations on the east transect n 235 are examined to identify location and profile specific responses over 52 of the incident direction of flow from 11 to 63 onshore topographic steering and forcing cause major deviations in the properties and vectors of near surface flow from the regional wind topographic forcing on the concave straight dune profile increases wind speed and steadiness toward the crest with speed up values to 65 in the backshore wind speed and steadiness of flow are least responsive to changes in incident angle in the backshore because of stagnation of flow and are most responsive at the lower stoss under pronounced streamline compression on the steeper concave convex profile speed and steadiness decrease toward the crest because of stagnation of flow at the toe and flow expansion at the slope inflection point on the lower stoss net downward vertical velocity occurs over both profiles increases toward the crest and reflects enhanced turbulent momentum conveyance toward the surface all of these flow responses are enhanced with faster speeds of incident flow and or more onshore winds significant onshore steering of near surface vectors of flow to 37 occurs and is greatest closer to the surface and during highly oblique winds 15 onshore therefore even subtle effects of streamline compression and amplification of flow under alongshore conditions effectively steer flow and sand transport toward the dune as topographic forcing and steering cause significant three dimensional deviations in near surface properties of flow most regional scale and or two dimensional models of dune process response dynamics are insufficient for characterizing coastal and desert dune sediment budgets and morphodynamics in particular deflection of sand transport vectors with greater fetch distances than those derived from regional winds may occur coincident flow transport and morphological response data are required to better quantitatively model these processes

empirical green function deconvolution of broadband surface waves rupture directivity of the 1992 landers california mw 7 3 earthquake we present a simple method to determine gross temporal and spatial characteristics of faulting that can uniquely define the fault plane for a relatively large earthquake the technique involves deconvolution of teleseismic and regional broadband surface waves and or body waves of a small event an empirical green function from the corresponding signals at the same stations for a large mainshock this deconvolution corrects each mainshock seismic record for propagation and instrument response and if the focal mechanisms and centroid depths are identical deconvolution provides relative source time functions for the mainshock azimuthal variations of source time function width or subevent interference reveal the mainshock rupture directivity changes in the source mechanism during rupture can be evaluated for some classes of events our empirical green function procedure is novel in its application to surface waves and its use for large m 7 earthquakes we perform synthetic tests to establish intrinsic limitations of the method the procedure requires very little data processing and can be applied in near real time with the current distribution of seismic stations that have dial up data retrieval capability it also provides a straightforward procedure for reducing bias in source duration estimates resulting from aspherical heterogeneity and for detecting anomalous long period radiation we apply the procedure to the 28 june 1992 landers california mw 7 3 earthquake the landers earthquake source duration lasted about 25 sec and was dominated by two subevents with predominantly north northwestward rupture extending 60 to 70 km the subevents show counter clockwise rotations of at least 12 in strike that correlate well with mapped surface rupture

moment tensor inversion from mednet data 2 regional earthquakes of the mediterranean we present a method for the rapid determination of the moment tensor suitable for application to regional earthquakes up to 3000 km distance the algorithm is based on the inversion of long period waveforms in the time domain and is routinely applied to significant events of the mediterranean from iran to the azores using digital data recorded by the mednet regional network we show results for 20 significant earthquakes of 1990 1992 including the large shocks in romania may 30 1990 iran june 20 1990 caucasus april 29 1991 turkey march 13 1992 and egypt october 12 1992 the damaging italian earthquakes of potenza may 5 1990 and siracusa december 13 1990 unusual events in the southern mediterranean november 11 1990 and holland april 13 1992 and the recent shocks of october 23 1992 in morocco and caucasus the comparison with published focal mechanisms and centroid moment tensors show our results to be consistent with those retrieved using global data and local networks proving that an advanced regional seismic network is capable of providing accurate rapid control of regional seismicity

seismic source and structure estimation in the western mediterranean using a sparse broadband network we present a study of regional earthquakes in the western mediterranean geared toward the development of methodologies and path calibrations for source characterization using regional broadband stations the results of this study are useful for the monitoring and discrimination of seismic events under a comprehensive test ban treaty as well as the routine analysis of seismicity and seismic hazard using a sparse array of stations the area consists of several contrasting geological provinces with distinct seismic properties which complicates the modeling of seismic wave propagation we started by analyzing surface wave group velocities throughout the region and developed a preliminary model for each of the major geological provinces we found variations of crustal thickness ranging from 45 km under the atlas and betic mountains and 37 km under the saharan shield to 20 km for the oceanic crust of the western mediterranean sea which is consistent with earlier works throughout most of the region the upper mantle velocities are low which is typical for tectonically active regions the most complex areas in terms of wave propagation are the betic cordillera in southern spain and its north african counterparts the rif and tell atlas mountains as well as the alboran sea between spain and morocco the complexity of the wave propagation in these regions is probably due to the sharp velocity contrasts between the oceanic and continental regions as well as the the existence of deep sedimentary basins that have a very strong influence on the surface wave dispersion we used this preliminary regionalized velocity model to correct the surface wave source spectra for propagation effects which we then inverted for source mechanism we found that this method which is in use in many parts of the world works very well provided that data from several stations are available in order to study the events in the region using very few broadband stations or even a single station we developed a hybrid inversion method which combines p nl waveforms synthesized with the traditional body wave methods with surface waves that are computed using normal modes this procedure facilitates the inclusion of laterally varying structure in the green s functions for the surface waves and allows us to determine source mechanisms for many of the larger earthquakes m 4 throughout the region with just one station we compared our results with those available from other methods and found that they agree quite well the epicentral depths that we have obtained from regional waveforms are consistent with observed teleseismic depth phases as far as they are available we also show that the particular upper mantle structure under the region causes the various p n and s n phases to be impulsive which makes them a useful tool for depth determination as well thus we conclude that with proper calibration of the seismic structure in the region and high quality broadband data it is now possible to characterize and study events in this region both with respect to mechanism and depth with a limited distribution of regional broadband stations

catchment scale cumulative impact of human activities on river channels in the late anthropocene implications limitations prospect abstract evidence for the proposed anthropocene epoch in fluvial geomorphology hinges on the influence of human activities relative to natural forcing however research on cause effect understanding in river channel evolution has rarely focused on the cumulative impact of multiple drivers for change limiting insights systematic review of 25 recent studies professing to explain reach scale channel responses to cumulative impacts of human activities and natural forcing over the recent past ca 1880 2005 reveals some consistencies in spatio temporal response across various catchment sizes median 3000 km2 in mostly industrialized nations common drivers for change include changing flood and flow regimes dam construction changing land uses and forest cover bank protection and instream aggregate mining recent channel evolution has predominantly involved narrowing incision and terrace development reduced bed sediment storage lower activity rates and simplified channel geometries rates of channel change frequently peaked 1955 1990 providing some support for the anthropocene great acceleration evidence here suggests that many river systems are now in morphologically novel configurations coinciding temporally with dramatic recent declines in global freshwater aquatic biodiversity sustainable approaches to freshwater management must acknowledge these configurations placing emphasis on process based approaches to river ecosystem health in which sediment cascades are reconceived to reflect altered longitudinal and lateral connectivity however the reviewed studies are driven largely by expert judgment depicting cause effect associations through summary conceptual models based on spatial proximity and temporal synchronicity providing insufficient scientific proof for the anthropocene based on the overwhelming impact of human factors more conclusive cause effect statements will require hypothetic deductive approaches explicit functional criteria and best practice environmental model building geomorphologists should now move beyond the phase of discovery and develop rigorous proofs for cause effect relationships of cumulative impact this may be enhanced by developing an avowedly anthropocene perspective in which rivers are viewed critically as socio biophysical systems co evolving with human activity

waveform inversion of small to moderate earthquakes located offshore southwest iberia summary in this paper we apply the kinematic waveform inversion kiwi tools to the study of smallto moderate earthquakes in southwest sw iberia the earthquakes have magnitudes in the range ml 3 5 4 9 with the exception of one earthquake with magnitude ml 6 0 most events are located offshore are recorded with a large azimuthal gap and generate waves that travel throughastronglyheterogeneous crustalstructure weobtainnewestimatesofcentroid depth seismic moment strike dip and rake for 12 of the 29 studied events the earthquakes whose waveforms we cannot successfully model are 1 located too far from the stations 2 have small magnitude hence low signal to noise ratio or 3 are located within the cadiz basin which is a major sedimentary basin that affects wave propagation notably our results indicate that onshore earthquakes occur at shallow depths 15 km whereas offshore earthquakes occur deeper down to 46 km focal mechanisms indicate transpressive faulting

modeling the modern marine δ30si distribution 1 the silicon isotopic composition of opal sediments can be used as a proxy for past si utilization and hence paleoproductivity for a fixed ocean circulation interpretation of this si utilization proxy is limited by our understanding of the present marine si isotope distribution observations show significant isotopic variations is silicic acid between deep water masses that are not captured by a previous global climate model gcm here simple box models of the global oceans for the si cycle are presented which can account for the observed 0 3 o difference between atlantic and pacific deep water 30 si values using typical opal export fluxes the 30 si gradient results from both a high 30 si of dissolved si overturning in the north atlantic and the dissolution of low 30 si of opal in the deep waters around the southern ocean that feed into the pacific

flow dynamics over a foredune at prince edward island canada time averaged windspeed profiles at eight locations over a relatively high 8 m vegetated topographically simple foredune were measured using cup and ultrasonic anemometry during an onshore wind event in may 2002 the experiment was part of a largerstudyonthesedimentarydynamicsofabeach dunecomplexinthegreenwichdunes princeedwardisland pei canada the foredune is vegetated with ammophila breviligulata and vegetation density ranged from 0 on the foredune ramp to upward of 70 at the dune crest topographic forcing and resulting flow acceleration was observed distinctly in windspeed profiles and linear speedup occurred for all elevations above the vegetation canopy a distinct inflection point is evident in normalized windspeed profiles over the dune indicating a net momentum sink below the vegetation canopy top and systematic speed down within the vegetation was observed up the foredune stoss slope wind speed profile structure was consistent for the range of incident wind speeds measured a comparison of normal and slightly oblique incident winds indicated that for similar approach winds wind speeds are consistently higher during oblique flow conditions the implications for foredune morphodynamics and sedimentation are discussed d 2004 elsevier b v all rights reserved

the effects of surface moisture on aeolian sediment transport threshold and mass flux on a beach this paper presents results from a study designed to explore the effects of beach surface moisture and fetch effects on the threshold of movement intensity of sand transport by wind and mass flux the experiment was carried out over a period of five weeks at greenwich dunes prince edward island canada in may and june 2002 moisture content was measured with a delta t moisture probe over a 50 m by 25 m grid established on the beach measurements of wind speed and direction were made with arrays of cup anemometers and a two dimensional sonic anemometer transport intensity was measured at a height of 2 4 cm above the bed using omnidirectional saltation probes which count the impact of saltating grains on a piezoelectric crystal anemometers and saltation probes were sampled at 1 hz sand transport was measured with vertical integrating sand traps over periods of 10 20 minutes results show that where there is a considerable supply of dry sand the saltation system responds very rapidly 1 2 s to fluctuations in wind speed i e to wind gusts where sand supply from the surface is limited by moisture mean transport rates are much lower and this reflects in both a reduction in the instantaneous transport rate and in a transport system that becomes increasingly intermittent threshold wind speed is significantly correlated with an increase in surface moisture content near the upwind end of the beach fetch but the relationship is not significant at the downwind end where sediment transport is initiated primarily by saltation impact from upwind mass flux increases with increasing fetch length and the relationship is described best by a power function further work is necessary to develop a theoretical function to predict the increase in transport with fetch distance as well as the critical fetch distance copyright 2007 john wiley sons ltd