recent progress in snow and ice research a review of snow and ice research in 1987 1990 is presented focusing on the effects of layers in seasonal snow covers ice mechanics on fresh water and sea ice and remote sensig of polar ice sheets these topics provide useful examples of general needs in snow and ice research applicable to most areas such as better representation in models of detailed processes controlled laboratory experiments to quantify processes and field studies to provide the appropriate context for interpretation of processes from remote sensing

long term change in tidal dynamics and its cause in the pearl river delta china abstract this paper focuses on identifying changes in the tidal range and the duration of the flood tide in the pearl river delta region china mann kendall test and regression methods are employed to verify the existence of trends in the annual tidal range and duration series from the 1950s to 2005 at 17 stations in the 3 major tributaries of the delta the research results indicate that generally there is an increasing trend in the tidal range and flood tide duration at most of the stations in the channel network moreover the more upstream the location of the station the more obvious the change in trend is and these increasing trends are all significant at the stations in the upper part of the delta specifically the tidal range at shilong station in the east river has increased abruptly since the middle of the 1980s such that the mean level of post 1990 data is approximately three times that for pre 1985 most stations near the mouth of the estuary show significant downward trends in the tidal range and flood tide duration results of the intersection point of the mann kendall test curves for these pearl river delta stations appear mostly in 1980s 1990s indicating that a noticeable change point occurs during this period human activities in the pearl river delta reached their peak during the 1980s among these large scale and long term sand excavation modified the hydrodynamic regime dramatically in a way that increased the water depth and lowered the level of the riverbed leading to an increased tidal prism and upstream movement of the tidal limit land reclamation is also likely to have had a relatively large effect on the tidal range and flood tide duration at stations near to the estuary mouth changes in other factors such as freshwater flow and sea level rise seem to be of relatively minor importance it is noteworthy that in a dry season the tidal dynamics are greatly enhanced and has resulted in strong saltwater intrusion into the estuary in recent years

spatially averaged open channel flow over rough bed in this paper it is suggested that the double averaged in temporal and in spatial domains momentum equations should be used as a natural basis for the hydraulics of rough bed open channel flows especially with small relative submergence the relationships for the vertical distribution of the total stress for the simplest case of 2d steady uniform spatially averaged flow over a rough bed with flat free surface are derived these relationships explicitly include the form induced stresses and form drag as components of the total stress using this approach we define three types of rough bed flows 1 flow with high relative submergence 2 flow with small relative submergence and 3 flow over a partially inundated rough bed the relationships for the double averaged velocity distribution and hydraulic resistance for all three flow types are derived and compared with measurements where possible the double averaged turbulent and form induced intensities and stresses for the case of regular spherical segment type roughness show the dominant role of the double averaged turbulence stresses and form drag in momentum transfer in the near bed region

spatial and temporal patterns in channel change on the snake river downstream from jackson lake dam wyoming abstract operations of jackson lake dam jld have altered the hydrology and sediment transport capacity of the snake river in grand teton national park prior research has provided conflicting assessments of whether the downstream river was perturbed into sediment surplus or sediment deficit in this paper we present the results of an aerial photo analysis designed to evaluate whether the history of channel change indicates either significant deficit or surplus of sediment that could be expressed as narrowing or expansion of the channel over time we analyze changes in braid index channel width channel activity and net channel change of the snake river based on four series of aerial photographs between 1945 and 1969 a period of relatively small main stem floods widespread deposition and up to 31 reduction in channel width occurred throughout the snake river between 1969 and 2002 a period of large main stem floods the style of channel change reversed with a decrease in braid index and an increase in channel width of up to 31 these substantial changes in the channel downstream from the dam primarily occurred in multithread reaches regardless of proximity to tributaries and no temporal progression of channel narrowing or widening was observed we demonstrate that channel change downstream from jld is more temporally and longitudinally complex than previously described

coherence of seismic body waves from local events as measured by a small aperture array eight local earthquakes were recorded during the operation of a small aperture seismic array at pinyon flat california the site was chosen for its homogeneous granitic geology and its planar topography amplitude spectral ratios for the same signal measured at different stations had average values of less than 2 and maximum values of 7 magnitude squared coherences were estimated for all station pairs these estimates were highest for the p wave arrivals on the vertical component and lowest for the p wave recorded on the transverse component at 500 m station separation the p and s waves were incoherent above 15 hz and 10 hz respectively coherence for both the p and s waves decrease as frequency increases and as distance increases the coherence of signals from borehole sensors located at 300 and 150 m depth displays higher average coherence than equally spaced sites located on the surface the results here suggest that even for sites that appear to be very similar that is those which are located on a planar surface within a few meters of granite bedrock the measured seismic wavefield can be distorted substantially over scale lengths of 500 m coherence properties were calculated from synthetic seismograms which were computed for velocity models with exponential and self similar distribution perturbations standard deviations of 10 are not sufficient for the random velocity distributions to approximate the results from the small aperture array

experimental model for a seismic landmine detection system a laboratory scale experimental model has been developed and tested for a system that uses artificially generated high frequency seismic waves in conjunction with a radar based noncontact displacement sensor to detect buried landmines the principle of operation of the system is to measure the transient displacement field very close to a mine location in this way the absorption and the geometrical spreading of the seismic waves have not reduced the effects of the mine by using a seismic excitation the system exploits the large difference between the elastic properties of a mine and the surrounding soil this difference causes seismic wave interactions in the vicinity of a mine to be quite distinctive and provides a method for imaging mines and distinguishing them from typical buried clutter images of a variety of simulated and inert anti tank and anti personnel mines have been formed using this system burial scenarios involving natural clutter rocks and sticks light surface vegetation localized burial effects and multiple mines in close proximity have been studied none of these scenarios appears to pose serious problems for detection performance

an evaluation of seismic decoupling and underground nuclear test monitoring using high frequency seismic data an effective solution to the problem of the detection and identification of low yield coupled and fully decoupled underground nuclear explosions appears available via use of high frequency seismic data ranging up to 30 or 40 hz in order to evaluate detection identification capabilities when using such data it is necessary to estimate 1 spectral characteristics and relative amplitudes of both p and s waves from explosions and earthquakes over the frequency band from 5 to 40 hz 2 signal transmission characteristics over this band through pertinent types of earth structure and 3 recording system and ground noise characteristics over this frequency band in this study each of these topics is considered in turn as they relate to detection and discrimination of the signals from low yield coupled and decoupled explosions in the regional and teleseismic distance ranges estimates of the capabilities of specific hypothetical networks to detect and identify insofar as signal to noise ratio is an important factor in identification explosions within the ussr are then considered these estimates of signal detection capability provide the central focus for the study as they serve to translate diverse and rather complex sets of observational data and theory into concrete predictions of monitoring capability following the assessment of detection capabilities the problem of identification of small events is considered with particular emphasis on discrimination at regional distances where the network is calculated to provide signals of high signal to noise ratio the principal results and conclusions of this study are as follows 1 seismic system noise can be suppressed to levels well below ground noise at quiet sites up to frequencies at least as high as 30 40 hz when using presently available hardware 2 average amplitudes of high frequency noise in a variety of geological environments are very low and change little with time or season 3 transmission of high frequency p and s wave signals in the regional distance range in stable continental areas and shields is nearly as efficient as at 1 hz with effective q factors in shield areas being about 9000 and 4000 for high frequency pn and sn respectively while the effective q for pn waves in tectonic areas is about 1000 4 a properly designed and deployed network of 25 simple three component nonarray stations internal to the ussr and 15 similar stations surrounding the ussr is predicted to be capable of multistation detection at high signal to noise ratio of fully decoupled 1 kt explosions located at all potential decoupling sites within the ussr 5 by inference from the quantitative agreement of empirical observations and theoretical predictions when using lower frequency data over a great range of explosion yields we conclude that procedures based on the use of both detectable p and s waves will serve to identify explosion generated seismic signals at least as small as those expected from a fully decoupled 1 kt explosion

flow characteristics in different densities of submerged flexible vegetation from an open channel flume study of artificial plants abstract the effect of submerged flexible vegetation on flow structure e g flow velocity reynolds shear stress turbulence intensity and manning coefficient was experimentally studied with a 3d acoustic doppler velocimeter adv in an open channel flume the results from flow observations over artificial plants designed to simulate natural vegetation showed that flow structure was affected markedly by the presence of submerged flexible vegetation the study provides understanding of flow patterns variation in velocity profile and turbulence structures that are affected by plant stem density the study also reveals how the flow patterns return to stability at the downstream end of the vegetated area which is critical in determining the length of the vegetated areas for restoration cases also new mathematical expressions equations have been formulated to clearly express variations in velocity profile manning coefficient and flow discharge ratio with vegetation density vertically the velocity profile could be roughly divided into three layers including the upper non vegetated layer the middle canopy layer and the lower sheath layer in the upper non vegetated layer velocity profiles followed the logarithmic law and a corresponding empirical equation was developed based on the observed data the flow is from left to right in this study and the velocity profile followed a left round bracket with the minimum point located at the canopy area 0 7hv where hv denotes vegetation height within the middle canopy layer however the velocity profile followed a right round bracket in the lower sheath section layer with the maximum point located at the sheath section 0 2hv with increasing vegetation density the velocity and corresponding flow rate increased in the upper non vegetated layer and decreased within the middle canopy layer and the lower sheath layer the ratio of average flow discharge in the non vegetated and vegetated layers followed the exponential function law with increasing vegetation density this analysis revealed the effect of vegetation on flood potential and flow bottom scour reynolds stresses peaked above the canopy top z hv 1 0 1 2 here z denotes vertical coordinate and the turbulence intensities reached their maximum peak at two locations including the sheath section z hv 0 1 0 4 and the canopy top z hv 1 0 1 6 for all vegetation densities manning coefficient was highly correlated to vegetation density and inflow rate with new empirical equations being proposed

source parameters for small events associated with the 1986 north palm springs california earthquake determined using empirical green functions using small events as empirical green functions which include path site and instrument effects on the p waveforms source parameters were estimated for 25 ml 3 4 to 4 4 events associated with the 1986 north palm springs earthquake the static stress drops ranged from 3 to 80 bars for moments of 0 7 to 11 1021 dyne cm there was a spatial pattern to the stress drops of the aftershocks which showed increasing values along the fault plane toward the northwest compared to relatively low values near the hypocenter of the mainshock the highest values were outside the main area of slip and are believed to reflect a loaded area of the fault that still has an higher level of stress which was not released during the main shock the relatively high stress drop of a preshock in 1983 located close to the hypocenter of the main shock is also interpreted as evidence that stress drops of magnitude 3 and 4 events can be used as indicators of the stress level in a particular area

seismic directional random noise suppression by radial trace time frequency peak filtering using the hurst exponent statistic radial trace time frequency peak filtering filters a seismic record along the radialtrace direction rather than the conventional channel direction it takes the spatial correlation of the reflected events between adjacent channels into account thus radial trace time frequency peak filtering performs well in denoising and enhancing the continuity of reflected events however in the seismic record there is often random noise whose energy is concentrated in certain directions the noise in these directions is correlative we refer to this kind of random noise that is distributed randomly in time but correlative in the space as directional random noise under radial trace time frequency peak filtering the directional random noise will be treated as signal and enhanced when this noise has same direction as the signal therefore we need to identify the directional random noise before the filtering in this paper we test the linearity of signal and directional random noise in time using the hurst exponent the time series of signals with high linearity lead to large hurst exponent value however directional random noise is a random series in time without a fixed waveform and thus its linearity is low therefore we can differentiate the signal and directional random noise by the hurst exponent values the directional random noise can then be suppressed by using a long filtering window length during the radial trace time frequency peak filtering synthetic and real data examples show that the proposed method can remove most directional random noise and can effectively recover the reflected events

geomorphology within the interdisciplinary science of environmental flows article i nfo the field tradition in geomorphology informs beyond studying landforms by also providing a stage for understand ing how geomorphic elements influence the ecology of biota the intersection between fluvial geomorphology and riverine ecology represents an ideal confluence to examine the contribution of the geomorphic field tradition to en vironmental flows and show this area of riverine management as a research frontier for applied geomorphology environmental flows have consisted of a set of ecological based stream flow guidelines designed to inform sustain able water resource management that supports healthy riverine habitats and provides sufficient water supply for society geomorphological understanding is central to environmental flows because it is the interaction between flow form and substrate that influences habitat type condition availability and biotic use across space and time this relationship varies longitudinally laterally vertically overtime and across macro to mesoscale morphologies withintheriverine environment thegeomorphictemplateis therefore asintegralasthe flow wereviewedstudies where field evidence indicated that geomorphology impacts the effectiveness of environmental flow strategies and wemakethecasefortheneedtoincreasegeomorphic considerationsinenvironmental flows although flow iscom monly referred toas themaster variablein environmental flows geomorphologymediatestheeffectsof flow regime on ecological processes concepts and applications from this perspective on the role of geomorphology in riverine ecosystem research will inform the practice policy and implementation of environmental flows

thermally induced icequakes detected on blue ice areas of the east antarctic ice sheet over a year of seismic observations 5000 short duration icequakes were detected by a permanent broadband station installed at the princess elisabeth base located 180 km inland in eastern dronning maud land east antarctica icequake detection via seismic waveform pattern recognition indicates the presence of two dominating clusters of events totalizing 1500 icequakes the corresponding icequake locations point towards two distinct zones of outcropping blue ice areas bias located respectively at 4 and 1 km from the seismic station both on the leeward side of a nunatak protruding through the ice sheet the temporal occurrence of these icequakes suggests a close genetic link with thermal contraction of ice caused by significant surface cooling controlled in summer by variations in diurnal solar radiation and in winter by strong cooling during cold katabatic regimes further analysis demonstrates the dependence of these icequakes on the absolute surface temperature and on its temporal change besides providing information on the ice fracture mechanics and rheology investigations of thermal icequakes may be regarded as a ground based proxy for the monitoring of the thermal state of bias and characterization of ice sheet ablation zones

assessment of vegetation effects on hydraulics and of feedbacks on plant survival and zonation in ephemeral channels the interaction of vegetation and flow in channels is important for understanding the influences of forces in channels and effects on erosion sediment flux and deposition it has implications for channel habitats channel instability and restoration schemes methods are needed for calculating forces on plants and data are required on thresholds for plant destruction and survival a simple method of calculating the effect of hydraulics on vegetation and its zonation within ephemeral channels is described detailed cross section surveys of channel morphology vegetation and estimates of manning s n are input into the software program winxspro to calculate the hydraulics of flows across the channel for a given event or flow level incorporating subdivision into zones of differing morphology and vegetation across the section this was applied to a number of cross sections on ephemeral channels in se spain and typical roughness values for mediterranean vegetation types in channels were assessed the method is demonstrated with reference to two well documented floods in se spain in september 1997 on the torrealvilla and in october 2003 along the salada these flows led to the mortality of herbs reed and smaller shrub species some damage to larger shrubs and trees occurred but trees such as tamarisk tamarix canariensis were shown to withstand high forces some grasses were highly resistant to removal and induced sedimentation significant erosion was limited to areas with little vegetation covering the channel floor further quantification of resistance of vegetation to flows and upper threshold values for removal is continuing by relating calculated hydraulic conditions using the methods outlined to measurements of vegetation responses in events at monitoring sites copyright 2009 john wiley sons ltd

measurements of two types of dilatational waves in an air filled unconsolidated sand this study consists of laboratory measurements of dilatational waves propagating through an air filled unconsolidated sand one excitation technique consists of a loudspeaker suspended in the air above the packing of sand a second excitation technique uses a mechanical shaker in contact with the sand the transmitted signals are received using microphones and geophones located at various depths within the sand an interpretation based on measured phase speeds indicates that the transmitted energy from the suspended loudspeaker source is partitioned primarily but not exclusively into the type ii dilatational wave this wave attenuates rapidly and is only detected at depths of less than about 15 cm for this particular sample at the deeper depths the detected signal is associated with the type i dilatational wave the mechanical shaker produces only a type i dilatational wave both the geophone and microphone sensors can detect both types of dilatational waves

estimation of the acoustic to seismic coupling ratio using a moving vehicle source we present a simple passive technique for estimating the acoustic to seismic signal coupling ratio sar in the ground using noise produced by moving vehicles the seismic signal received on a geophone contains some energy that has propagated as seismic waves and some energy that couples from acoustic waves to seismic waves in the vicinity of the geophone we use the frequency domain coherence between the microphone and geophone signals to determine when the seismic signal is predominantly due to acoustic to seismic wave coupling in frequency bands where the microphone and geophone coherence is above 0 8 the ratio of the seismic ground particle velocity to sound pressure sar can be determined with less than 2 db of error the method is applied to data from a summer experiment with grass ground cover and at two winter experiments with snow covered ground at 100 hz the summer analysis yields a sar value of 1 0 times 10 5 m s pa in addition at 100 hz the two winter tests yield sar between 0 1 times 10 5 and 1 0 times 10 5 m s pa in the later winter result our vehicle derived sar estimate is shown to be in excellent agreement with sar estimates obtained from blank pistol shots through the opportunistic exploitation background noise sources our approach opens the possibility for automatic adaptation of unattended acoustic area monitoring sensors to changing ground conditions

relationships between mesoscale morphological units stream hydraulics and chinook salmon oncorhynchus tshawytscha spawning habitat on the lower yuba river california an expert based approach was used to identify 10 morphological unit types within a reach of the gravel bed regulated yuba river california that is heavily utilized by spawning chinook salmon oncorhynchus tshawytscha analysis of these units was carried out using two dimensional hydrodynamic modeling field based geomorphic assessment and detailed spawning surveying differently classified morphological units tended to exhibit discrete hydraulic signatures in most cases the froude number adequately differentiated morphological units but joint depth velocity distributions proved the most effective hydraulic classification approach spawning activity was statistically differentiated at the mesoscale of the morphological unit salmon preferred lateral bar riffle and riffle entrance units these units had moderately high velocity unit median 0 45 m s 1 and low depth unit median 0 6 m but each exhibited a unique joint depth velocity distribution a large proportion of redds 79 were associated with conditions of convective flow acceleration at riffle and riffle entrance locations in addition to reflecting microhabitat requirements of fish it was proposed that the hydraulic segregation of preferred from avoided or tolerated morphological units was linked to the mutual association of specific hydraulic conditions with suitable caliber sediment that promotes the provision and maintenance of spawning habitat

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

the source of infrasound associated with long period events at mount st helens 1 during the early stages of the 2004 2008 mount st helens eruption the source process that produced a sustained sequence of repetitive long period lp seismic events also produced impulsive broadband infrasonic signals in the atmosphere to assess whether the signals could be generated simply by seismic acoustic coupling from the shallow lp events we perform finite difference simulation of the seismo acoustic wavefield using a single numerical scheme for the elastic ground and atmosphere the effects of topography velocity structure wind and source configuration are considered the simulations show that a shallow source buried in a homogeneous elastic solid produces a complex wave train in the atmosphere consisting of p sv and rayleigh wave energy converted locally along the propagation path and acoustic energy originating from the source epicenter although the horizontal acoustic velocity of the latter is consistent with our data the modeled amplitude ratios of pressure to vertical seismic velocity are too low in comparison with observations and the characteristic differences in seismic and acoustic waveforms and spectra cannot be reproduced from a common point source the observations therefore require a more complex source process in which the infrasonic signals are a record of only the broadband pressure excitation mechanism of the seismic lp events the observations and numerical results can be explained by a model involving the repeated rapid pressure loss from a hydrothermal crack by venting into a shallow layer of loosely consolidated highly permeable material heating by magmatic activity causes pressure to rise periodically reaching the pressure threshold for rupture of the valve sealing the crack sudden opening of the valve generates the broadband infrasonic signal and simultaneously triggers the collapse of the crack initiating resonance of the remaining fluid subtle waveform and amplitude variability of the infrasonic signals as recorded at an array 13 4 km to the nw of the volcano are attributed primarily to atmospheric boundary layer propagation effects superimposed upon amplitude changes at the source

seismic waves from elephant vocalizations a possible communication mode 1 we conducted experiments with trained african elephants that show that low frequency elephant vocalizations produce rayleigh waves we model a potential range for these seismic waves under ideal conditions of c 2 km in appropriate conditions surface waves from an elephant s infrasonic vocalizations might propagate further than airborne sound and provide advantages over acoustic communication however if we use the detection capabilities of the human ear as a benchmark for the signal detection thresholds of elephants our estimates of attenuation and ambient seismic noise suggest that the seismic detection range is unlikely to exceed the acoustic detection range under normal atmospheric conditions we conclude that elephants may benefit from seismic detection in circumstances where the range of acoustic communication is limited or in cases where multimodal communication is advantageous given our current understanding elephants are unlikely to rely on seismic waves as their primary mode for long range communication

engineered channel controls limiting spawning habitat rehabilitation success on regulated gravel bed rivers in efforts to rehabilitate regulated rivers for ecological benefits the flow regime has been one of the primary focal points of management strategies however channel engineering can impact channel geometry such that hydraulic and geomorphic responses to flow reregulation do not yield the sought for benefits to illustrate and assess the impacts of structural channel controls and flow reregulation on channel processes and fish habitat quality in multiple life stages a highly detailed digital elevation model was collected and analyzed for a river reach right below a dam using a suite of hydrologic hydraulic geomorphic and ecological methods results showed that despite flow reregulation to produce a scaled down natural hydrograph anthropogenic boundary controls have severely altered geomorphic processes associated with geomorphic self sustainability and instream habitat availability in the case study given the similarity of this stream to many others we concluded that the potential utility of natural flow regime reinstatement in regulated gravel bed rivers is conditional on concomitant channel rehabilitation

varying seismic acoustic properties of the fluctuating lava lake at villarrica volcano chile villarrica volcano outgasses through an open lava lake with bubbles ranging in size from submillimeter to several meters the largest of which produce strombolian bursting events that are visible from the crater rim thousands of shallow strombolian events identified through seismic waveform cross correlation were found to produce discrete and repetitive long period seismic and infrasonic signals we identified variations of up to 0 7 s in seismic acoustic arrival delay times between april and july 2010 at a station 750 m from the vent which we interpret as due to fluctuations in the level of lava lake during time periods interpreted as having high lava lake levels based on reduced time delays interevent times were also reduced and average seismic amplitude measurements seismic and acoustic event energies and volcano acoustic seismic ratios were all high as compared to times when the lava lake was lower the crater is also a source of nearly continuous monotonic infrasonic tremor we found that the peak frequency of this infrasonic tremor typically around 0 5 1 0 hz was inversely correlated with seismic acoustic delay times and therefore an indicator of lava lake level we use this correlation to propose a new model for infrasonic tremor generation namely using crater geometry to approximate a bessel horn we interpret the two clearest cycles of elevated seismicity and lava lake level as due to an increase in exsolved gas resulting from an injection of volatile rich magma or an overturn in a deeper magma reservoir

high frequency seismic noise as a function of depth abstract evidence is presented supporting the view that high frequency seismic noise decreases with increased depth noise amplitudes are higher near the free surface where surface wave noise cultural noise and natural wind induced noise predominate data were gathered at a hard rock site in the northwestern adirondack lowlands of northern new york between 15 and 40 hz noise levels at this site are more than 10 db less at 945 m depth than they are at the surface and from 40 to 100 hz the difference is more than 20 db in addition time variability of the spectra is shown to be greater at the surface than at either 335 or 945 m depths part of the difference between the surface and subsurface noise variability may be related to wind induced noise coherency measurements between orthogonal components of motion show high frequency seismic noise is more highly organized at the surface than it is at depth coherency measurements between the same component of motion at different vertical offsets show a strong low frequency coherence at least up to 945 m vertical offsets as the vertical offset decreases the frequency band of high coherence increases

analysis of anthropogenic and natural noise from multilevel borehole seismometers in an urban environment auckland new zealand abstract two short period seismometers were permanently installed at depths of 26 and 383 m beneath the eden park stadium in central auckland in october 2008 and incorporated into the auckland volcano seismic network in 2011 these borehole seismometers were temporarily augmented by a surface sensor to characterize the site response at this location despite the borehole installations seismic monitoring is challenging in this urban environment due to high anthropogenic noise that superimposes the earth s signal we analyze the power spectral density of continuous noise records over long and short time periods to quantify the reduction in noise with depth and the effect of temporal noise variations on the detection capabilities for earthquakes and volcanic tremor we identify natural and anthropogenic noise sources that temporarily elevate noise levels by 10 15 db using records from the rugby world cup matches held at the eden park stadium and by comparing records of daytime versus nighttime periods and windy versus calm days characterization of these noise sources shows that the frequency ranges of traffic and train noise at this site overlap 1 35 hz and 8 35 hz respectively however they exhibit distinct maxima at peak frequencies of 7 and 26 hz modeling of the structure beneath the stadium shows that the noise spectrum generated by the nearby train excites frequencies within the topmost waitemata sequences that get efficiently trapped in the low velocity waveguide beneath the 20 m thick basalt layer at the surface although the shallow borehole sensor generally shows a noise improvement of 5 db in comparison to the surface sensor it exhibits higher noise levels in the 8 35 hz frequency range due to the trapped noise waves wind causes increased microseismic noise at 0 1 1 hz that is coherent at all depth levels and shows the most pronounced time variation online material figures of earthquake and quarry blast locations spectrogram and coherency

investigation of microphones as near ground sensors for seismic detection of buried landmines commercially available microphones were investigated as near ground sensors to measure the acoustic pressure and the vertical pressure gradient of evanescent air acoustic waves associated with audio frequency seismic waves measurements in close proximity to the surface and the use of waveguides were found to improve the microphone signal s quality the comparison of its seismic sensitivity to its sensitivity to propagating sound ambient acoustic noise and nonseismic reverberation landmine images formed using microphone data collected in a laboratory experimental model clearly locate buried inert landmines but exhibit more clutter than images of the same objects formed with seismic displacement data collected using other techniques

windshield and sound barrier for seismic sensors a system and method for reducing acoustic wind or other background noise that may interfere with sensing of a seismic signal is provided more specifically a shield is provided to enclose a geophone and thereby protect it from harmful noise the shield may comprise a rigid shell a structural damping material an acoustically absorptive material and a compliant seal for coupling the shield to the ground or reference surface

time and the rivers flowing fluvial geomorphology since 1960 fluvial geomorphology has been the largest single subdiscipline within geomorphology for many decades fluvial geomorphic expertise is integral to understanding and managing rivers and to developing strategies for sustainable development this paper provides an overview of some of the significant advances in fluvial geomorphology between 1960 and 2010 with respect to conceptual models fluvial features and environments being studied tools used by fluvial geomorphologists geomorphic specialty groups within professional societies journals in which fluvial geomorphic research is published and textbooks of fluvial geomorphology during this half century fluvial geomorphology broadened considerably in scope from a focus primarily on physical principles underlying process and form in lower gradient channels with limited grain size range to a more integrative view of rivers as ecosystems with nonlinear behavior and great diversity of gradient substrate composition and grain size the array of tools for making basic observations analyzing data and disseminating research results also expanded considerably during this period as did the diversity of the fluvial geomorphic community

studies of high frequency seismic noise in eastern kazakhstan abstract three seismographic stations have been established in the region of the principal underground nuclear weapons test site in the republic of kazakhstan in the soviet union instrumentation includes both surface and borehole seismometers with a bandwidth of 100 hz and a system dynamic range of 180 db power spectra of the regional ambient ground acceleration peak between 4 and 6 hz and are on average frequency independent above 10 hz where levels are approximately equal to 10 15 to 10 16 m sec 2 2 hz 1 kazakh noise levels are roughly equivalent to those observed by the regional seismic test network between 1 and 20 hz and about 10 to 20 db higher than the very low noise model for lajitas texas in the same band noise observed by the borehole sensors is about 10 db less than that observed by the surface instruments above about 20 hz under low wind conditions at two of the three kazakh sites borehole improvement is greater under high winds the third kazakh site karasu is characterized by much higher surface noise levels 15 to 20 db higher than the borehole levels from 4 to 40 hz under both low or high wind conditions which is attributed to amplification by local site conditions and the exposed terrain power spectra of individual runs of ambient vertical ground acceleration measured down the borehole show that high frequency slopes between 10 and 80 hz vary between f 0 60 and f 0 22 depending on wind and site conditions

a comparison of the high frequency 1 hz surface and subsurface noise environment at three sites in the united states abstract surface and subsurface high frequency 1 hz noise data were recorded using nearly identical instrumentation at three widely separated sites in the united states amarillo texas datil new mexico and pinedale wyoming for extended periods of time under varying wind conditions while the sites are geologically distinct the near surface noise environments have many common features that we believe may be due in large part to the presence of a surficial layer of highly attenuative unconsolidated material at each site noise levels seen at or near the surface 5 m or less are much higher up to 30 db and much more variable power range up to 44 db than those seen at depth the smallest range was 9 db for 1951 m at amarillo the greatest gains in noise level reduction are realized within the first 100 m and probably much shallower

riffle pool maintenance and flow convergence routing observed on a large gravel bed river abstract geomorphologists have studied and debated over the processes responsible for natural riffle pool maintenance for decades most studies have focused on small wadable rivers but they lack much description of overbank flood conditions or a spatially explicit characterization of morphodynamics in this study 1 m horizontal resolution digital elevation models were collected from a riffle pool run sequence before and after an overbank flood with a 7 7 year recurrence interval on the relatively large gravel bed lower yuba river california digital elevation model differencing was used to quantify the magnitude and pattern of flood induced morphodynamic change cross section based analysis and two dimensional hydrodynamic modeling of flows ranging from 0 147 to 7 63 times bankful discharge were completed to evaluate the hydraulic mechanisms responsible for the observed topographic changes one key finding was that riffle pool relief increased by 0 42 m confirming the occurrence of natural hydrogeomorphic maintenance spatially complex patterns of scour and deposition exceeding 0 15 m at the scale of subwidth morphological units were reasonably predicted by the two dimensional mechanistic model that accounts for convective acceleration the one dimensional cross section based method underperformed the two dimensional model significantly consequently multiple scales of channel non uniformity and a dynamic flow regime caused the observed maintenance of the pool riffle morphology through the mechanism of flow convergence routing proposed by macwilliams et al macwilliams m l wheaton j m pasternack g b kitanidis p k street r l 2006 the flow convergence routing hypothesis for riffle pool maintenance in alluvial rivers water resources research 42 w10427 doi 10 1029 2005wr004391

infrasonic component of volcano seismic eruption tremor air ground and ground air elastic wave coupling are key processes in the rapidly developing field of seismoacoustics and are particularly relevant for volcanoes during a sustained explosive volcanic eruption it is typical to record a sustained broadband signal on seismometers termed eruption tremor eruption tremor is usually attributed to a subsurface seismic source process such as the upward migration of magma and gases through the shallow conduit and vent however it is now known that sustained explosive volcanic eruptions also generate powerful tremor signals in the atmosphere termed infrasonic tremor we investigate infrasonic tremor coupling down into the ground and its contribution to the observed seismic tremor our methodology builds on that proposed by ichihara et al 2012 and involves cross correlation coherence and cross phase spectra between waveforms from nearly collocated seismic and infrasonic sensors we apply it to datasets from mount st helens tungurahua and redoubt volcanoes

hydrodynamics of flow through double layer rigid vegetation vegetation in riparian environment varies in size from grass to shrubs to trees a double layer approach with an array of short and tall acrylic dowels is employed here to simulate such an environment the focus of the present work is to study the response of the flow as it travels through a double layer arrangement for a variety of conditions for this purpose instantaneous measurements of velocity were collected using a one dimensional laser doppler velocimeter at multiple locations to create velocity and turbulence intensity profiles the results indicate that velocity is nearly constant within the short and tall dowel array and increases significantly at the top of the arrays the velocity profile behind a dowel is characterized by multiple inflection points and velocity spikes near the bed especially for locations directly behind a tall dowel where a bulge in the velocity at the top of the short dowel array is present followed by a significant drop in velocity the region immediately behind a tall dowel where the highest turbulence intensities are found is very unstable especially at the dowel boundaries where significant mass and momentum exchange occurs the better known case of submerged single layer flow is included for comparison

high frequency analysis of seismic background noise as a function of wind speed and shallow depth we used a deep 1500 m cased borehole near the town of datil in west central new mexico to study high frequency 1 hz seismic noise characteristics the remote site had very low levels of cultural noise but strong winds winter and spring made the site an excellent candidate to study the effects of wind noise on seismograms along with a three component set of surface sensors teledyne geotech gs 13 a vertical borehole seismometer gs 28 was deployed at a variety of depths 5 43 and 85 m to investigate signal and noise variations wind speed was measured with an anemometer event triggered and time triggered data streams were recorded on a reftek 72 02 data acquisition system located at the site our data show little cultural noise and a strong correlation between wind speed and seismic background noise the minimum wind speed at which the seismic background noise appears to be influenced varies with depth 3 m sec at the surface 3 5 m sec at 43 m in depth and 4 m sec at 85 m in depth for wind speed below 3 to 4 m sec we observe omni directional background noise that is coherent at frequencies below 15 hz this coherence is destroyed when wind speeds exceed 3 to 4 m sec we use a test event md 1 6 and superimposed noise to investigate signal to noise ratio snr improvement with sensor depth for the low q valley fill of the datil borehole dbh site we have found that snr can be improved by as much as 20 to 40 db between 23 and 55 hz and 10 to 20 db between 10 and 20 hz by deploying at a 43 m depth rather than at the surface at the surface there is little signal above noise in the 23 to 55 hz frequency band for wind speeds greater than 8 m sec thus high frequency signal information that is lost at the surface can be recorded by deploying at the relatively shallow depth of 40 m because we observe only minor further reductions in seismic background noise sbn at deeper depths 40 m is likely to be a reasonable deployment depth for other high frequency monitoring sites in similar environmental and geologic conditions

particle size distribution of main channel bed sediments along the upper mississippi river usa abstract in this study we compared pre lock and dam ca 1925 with a modern longitudinal survey of main channel bed sediments along a 740 km segment of the upper mississippi river umr between davenport ia and cairo il this comparison was undertaken to gain a better understanding of how bed sediments are distributed longitudinally and to assess change since the completion of the umr lock and dam navigation system and missouri river dams i e mid twentieth century the comparison of the historic and modern longitudinal bed sediment surveys showed similar bed sediment sizes and distributions along the study segment with the majority 90 of bed sediment samples having a median diameter d50 of fine to coarse sand the fine tail d10 of the sediment size distributions was very fine to medium sand and the coarse tail d90 of sediment size distribution was coarse sand to gravel coarsest sediments in both surveys were found within or immediately downstream of bedrock floored reaches statistical analysis revealed that the particle size distributions between the survey samples were statistically identical suggesting no overall difference in main channel bed sediment size distribution between 1925 and present this was a surprising result given the magnitude of river engineering undertaken along the study segment over the past 90 years the absence of substantial differences in main channel bed sediment size suggests that flow competencies within the highly engineered navigation channel today are similar to conditions within the less engineered historic channel

acoustic signature of thunder from seismic records thunder the sound wave through the air associated with lightning transfers sufficient energy to the ground to trigger seismometers set to record regional earthquakes the acoustic signature recorded on seismometers in the form of ground velocity as a function of time contains the same type features as pressure variations recorded with microphones in air at a seismic station in kislovodsk ussr a nearly direct lightning strike caused electronic failure of borehole instruments while leaving a brief impulsive acoustic signature on the surface instruments the peak frequency of 25 55 hz is consistent with previously published values for cloud to ground lightning strikes but spectra from this station are contaminated by very strong wind noise in this band a thunderstorm near a similar station in karasu triggered more than a dozen records of individual lightning strikes during a 2 hour period the spectra for these events are fairly broadband with peaks at low frequencies varying from 6 to 13 hz the spectra were all computed by multitaper analysis which deals appropriately with the nonstationary thunder signal these independent measurements of low frequency peaks corroborate the occasional occurrences in traditional microphone records but a theory concerning the physical mechanism to account for them is still in question examined separately the individual claps in each record have similar frequency distributions discounting a need for multiple mechanisms to explain different phases of the thunder sequence particle motion determined from polarization analysis of the three component records is predominantly vertical downward with smaller horizontal components indicative of the direction to the lightning bolt in three of the records the azimuth to the lightning bolt changes with time confirming a significant horizontal component to the lightning channel itself

enhanced stage and stage variability on the lower missouri river benchmarked by lewis and clark data from the 1803 1806 lewis and clark expedition and nineteenth century stage records are used to quantitatively benchmark natural premanagement hydrology of the lower missouri river and assess the magnitude and timing of hydrologic change over nearly two centuries data show doubling in daily stage variability from the nineteenth century to 2005 annual maximum stages have at some sites become more extreme and their seasonality is less regular observed changes adversely affect riverine habitat and flood levels their timing beginning as early as 1900 suggests that channelization is the major driver

comparison of historical and modern river surveys reveal changes to waterhole characteristics in an australian dryland river abstract human activities are known to impact the physical template of river channels these impacts can result from deliberate direct modifications as well as via indirect processes linked to broadscale landscape change this study examined changes in the physical template of the barwon darling river a dryland river in southeastern australia historical longitudinal profiles from the late 1800s were compared with contemporary profiles derived from high definition side scanning sonar comparisons focused on characterising waterhole features as they are a critical biophysical component of dryland rivers the use of historical data presented several challenges related to small sample size and suspected sampling bias in the historical survey however this study demonstrates that these issues are not insurmountable providing the limitations and uncertainties with the data are acknowledged and data analyses are limited to parameters that can distinguish genuine landscape change the findings revealed a dramatic change in the physical template of the barwon darling river over a 120 yr period waterhole depths and distances between waterholes have been altered significantly the magnitude and trajectory of change was found to be scale dependent with the greatest observable change aligned with the presence or absence of low level weirs waterholes influenced by low level weirs have increased in depth because of localised impoundment whilst the distance between deep waterholes 4 m in depth has declined substantially in contrast the maximum depths of waterholes located outside the influence of weir pools has declined by 1 6 m and the distance between deep waterholes has more than doubled in several reaches these declines are likely to be caused by sediment accumulation in waterholes associated with anthropogenic increases in sediment flux and a decline in the river s capacity to entrain and transport sediment throughout the system

modeling effects of bank friction and woody bank vegetation on channel flow and boundary shear stress in the rio puerco new mexico 1 we have applied a physically based model for steady horizontally uniform flow to calculate reach averaged velocity and boundary shear stress distributions in a natural stream with woody vegetation on the channel banks the model calculates explicitly the form drag on woody plant stems and includes the effects of vegetation on the boundary shear stress velocity and turbulence fields average channel shapes bed gradients and shrub characteristics were determined for four long internally similar reaches covering an 81 km segment of the lower rio puerco in north central new mexico hydraulic geometries for each of three flow events were determined from reach average channel shapes slopes and measured silt line heights above the bed model results show that friction on the lateral boundaries reduced the boundary shear stress in the center of the rio puerco channel by as much as 20 in reaches with moderate to dense bank shrubs perimeter averaged boundary shear stresses were reduced by almost 40 during near bankfull flows model calculated discharges for all three flow events indicate there was a loss of about 40 of the upstream discharge through the 81 km river segment infiltration rates estimated from discharge losses during the quasi steady peak flows and areas of the bed and banks suggest rates of flow loss into the silty sand of the upper banks are about 8 times greater than rates of loss into the clayey silt covered bed and lower banks

flow and form in rehabilitation of large river ecosystems an example from the lower missouri river abstract on large intensively engineered rivers like the lower missouri the template of the physical habitat is determined by the nearly independent interaction of channel form and flow regime we evaluated the interaction between flow and form by modeling four combinations of modern and historical channel form and modern and historical flow regimes the analysis used shallow slow water shallow water habitat swh defined as depths between 0 and 1 5 m and current velocities between 0 and 0 75 m s as an indicator of habitat that has been lost on many intensively engineered rivers and one that is thought to be especially important in rearing of young fishes two dimensional hydrodynamic models for modern and historical channels of the lower missouri river at hermann missouri indicate substantial differences between the two channels in total availability and spatial characteristics of swh in the modern channel swh is maximized at extremely low flows and in overbank flows whereas the historical channel had substantially more swh at all discharges and swh increased with increasing discharge the historical channel form produced 3 7 times the swh area of the modern channel regardless of flow regime the effect of flow regime is evident in increased within year swh variability with the natural flow regime including significant seasonal peaks of swh associated with spring flooding comparison with other reaches along the lower missouri river indicates that a channel form is the dominant control of the availability of habitat even in reaches where the hydrograph is more intensively altered and b rehabilitation projects that move toward the historical condition can be successful in increasing topographic diversity and thereby decreasing sensitivity of the availability of habitat to flow regime the relative efficacy of managing flow and form in creating swh is useful information toward achieving socially acceptable rehabilitation of the ecosystem in large river systems

high broadband seismoacoustic signature of vulcanian explosions at popocatepetl volcano mexico author s matoza robin samuel arciniega ceballos a sanderson r w mendo perez g rosado fuentes a chouet b a

are restored side channels sustainable aquatic habitat features predicting the potential persistence of side channels as aquatic habitats based on their fine sedimentation dynamics abstract the restoration of side channels also referred to as abandoned channels former channels floodplain channels or side arms is increasingly implemented to improve the ecological integrity of river floodplain systems however the design of side channel restoration projects remains poorly informed by theory or empirical observations despite the increasing number of projects moreover feedback regarding the hydromorphological adjustment of restored channels is rarely documented making it difficult to predict channel persistence as aquatic habitats in this study we analyze the spatial and temporal patterns of fine sediment deposition 1 and reached 90 3 cm y 1 locally some channels exhibited a significant decline of sedimentation rates through time whereas others maintained rather constant rates scouring processes i e self rejuvenation capacity were occasionally documented in 15 channels six of the 16 studied channels appeared to be self sustaining the 10 others accumulated more and more fine sediment deposits after restoration parametric modeling of sedimentation rates suggested that among these 10 channels four have long life durations i e more than a century three have intermediate life durations i e likely between three and nine decades and three others have short life durations i e likely between two and five decades observed channel averaged sedimentation rates can be predicted from the frequency and magnitude i e maximum shear stress of upstream overflow events and the maximum intensity of backflow events i e maximum backflow capacity these predictors reflect the dominant role of side channel geometry i e morphology of the upstream alluvial plug slope conditions in controlling their flooding regime these models applied successfully to a wide range of channel morphologies and can be used to quantify a priori the likely effects and the sustainability of side channel restoration

flood disturbance recovery and inter flood incision on a large sand bed river abstract the lower 800 km of the missouri river has been incising for decades however the 2011 flood scoured more sediment than the previous 12 yr combined the river rebounded in the following two years re depositing over 70 of the sediment scoured during the 2011 flood historic evidence suggests that past missouri river floods may have followed similar scour rebound patterns this paper analyzes 16 channel surveys from 1987 to 2014 including 50 723 total cross sections to document the morphological history of the lower 800 km of the missouri river over the last thirty years including flood disturbance and long term trends the last thirty years on the missouri river included two basic morphologic regimes steady incision during low to moderate flow periods and rapid scour rebound responses to floods surveys collected during the 2011 flood demonstrate that the river scoured throughout the flood including the falling limb and did not begin a rebound phase until after the flood the analysis also identifies sediment sinks associated with each of these scour regimes flood scour and incision between floods that exceed the total volume eroded from the bed during those periods results suggest that floodplain deposition may induce the supply limitation that drives flood scour on this large sand bed river additionally aggregate mining removes substantially more sediment than the total river incision between floods and the reaches with maximum scour during the 1993 and 2011 floods correspond to the zones of aggregate mining

calibrating infrasonic to seismic coupling using the stardust sample return capsule shockwave implications for seismic observations of meteors 1 shock waves produced by meteoroids are detectable by seismograph networks but a lack of calibration has limited quantitative analysis of signal amplitudes we report colocated seismic and infrasound observations from reentry of nasa s stardust sample return capsule ssrc on 15 january 2006 the velocity of the ssrc initially 12 5 km s was the highest ever for an artificial object lying near the low end of the 11 2 72 km s range typical of meteoroids our infrasonic seismic recordings contain an initial n wave produced by the hypersonic shock front followed 10 s later by an enigmatic series of weak secondary pulses the seismic signals also include an intervening dispersed wave train with the characteristics of an air coupled rayleigh wave we determine an acoustic seismic coupling coefficient of 7 3 0 2 m ms 1 pa this represents an energy admittance of 2 13 0 15 several orders of magnitude larger than previous estimates derived from earthquake or explosive analogs theoretical seismic response was computed using in situ vp and vs measurements together with laboratory density measurements from samples of the clay rich playa treatment of the air ground interface as an idealized air solid contact correctly predicts the initial pulse shape but underestimates its seismic amplitude by a factor of 2 full wave synthetic seismograms simulate the air coupled rayleigh wave and suggest that the secondary arrivals are higher order airy phases part of the infrasound signal appears to arise from coupling of ground motion into the air much like earthquake induced sounds

vertical seismic profiling of oroville microearthquakes velocity spectra and particle motion as a function of depth direct evidence of site distortion of p and s wave microearthquake source spectra at oroville california is presented the data were gathered by placing vertical and three component seismometers at 90 m intervals in a 500 m borehole through the cleveland hill normal fault on which the 1975 ml 5 7 oroville earthquake took place high pressure hydraulic locking mechanisms were used to firmly lock the seismometer packages against the borehole wall digital event triggering geos recorders were used to receive the data some 30 seismic events including 12 microearthquakes were recorded during the 4 months the seismometers were deployed by comparing the velocity spectra of microearthquake waves at the different depths it can be seen that scattering and attenuation in the shallow crust around the borehole dominantly affect high frequency s waves above 15 hz the value of the apparent s wave quality factor qas for the upper 500 m of crust at this site is 9 one feature of this low qas is a gross difference between s wave corner frequencies observed at ground level and 500 m downhole for example the uphole and downhole s wave corner frequencies for the mcoda 0 4 microearthquake of julian day 259 differ by a factor of 2 or more low quality factors and depth dependent corner frequencies were also observed for p waves but these data are less definitive due to lower signal to noise ratios based on their three component particle motions and polarizations the direct s waves of the microearthquakes appear to be composed of two phases which have similar amplitudes but different apparent velocities it is possible that the velocity differences are a result of anisotropy in the underlying rock

continuous catchment scale monitoring of geomorphic processes with a 2 d seismological array 1 distributed activity of geomorphic processes with different spatiotemporal scales is hard to monitor in detail with conventional methods but might be detected with seismometers from july to september 2010 we deployed 14 seismometers to evaluate the ability of a two dimensional array with small interstation distances 11 km to continuously monitor geomorphic processes in a mountain catchment 370 km2 in taiwan spectral analysis of seismic records highlights different sources with high frequency content 1 hz consistent with hillslope and river processes using a common detection algorithm and a location technique based on the timing of seismic amplitude we have located 314 near surface events most of which 69 occurred during daily convective storms event activity was positively correlated with the precipitation intensity but this relation was not uniform in the catchment high resolution satellite images and air photos did not show geomorphic change during the study which did not have any episodes of extreme precipitation a majority of events 61 were collocated with preexisting geomorphic features landslide scars gullies within the uncertainty on location 9 of interstation distance the combination of event location and timing suggests a geomorphic source of recorded signals and most events had the seismic characteristics of rockfall debris avalanches or slides reactivation of prior erosion sites by such processes is difficult to detect with imagery but can possibly be resolved by seismic monitoring when proven this approach will allow a spatially comprehensive survey of geomorphic activity at the catchment scale with temporal detail sufficient to evaluate the exact meteorological conditions under which process events occur

subsurface structure at the insight landing site from compliance measurements by seismic and meteorological experiments measurements of ground compliance at the insight landing site describing the surface response to pressure loading are obtained from seismic and meteorological data compliance observations show an increase with frequency indicating the presence of a stiffer rock layer beneath the exposed regolith we performed a markov chain monte carlo inversion to investigate the vertical profile of the elastic parameters down to 20 m below insight compliance was inverted both freely and assuming prior knowledge of compaction in the regolith and the limitations and strengths of the methods were assessed on the basis of theoretical considerations and synthetic tests the inverted young modulus exhibits an increase by a factor of 10 100 over the first 10 15 m compatible with a structural discontinuity between 0 7 and 7 m the proposed scheme can be used for joint inversion of other seismic geological or mechanical constraints to refine the resulting vertical section

high frequency 1 100 hz noise and signal recorded at different depths in a mine northwest adirondacks ny seismograms of noise recorded simultaneously at the surface and at two subsurface stations 335m and 945m below surface level show that high frequency 1 100 hz background noise is reduced at the subsurface stations seismometers at all three stations are well coupled to hard crystalline bedrock most of the noise reduction occurs between the surface and 335m depth between 1 and 3 hz seismic noise correlates well with wind speed at all levels above 3 hz wind speed up to 8 m sec does not influence high frequency noise levels at 335m or 945m depths at the surface however high frequency noise is associated with wind speeds in excess of 2 m s a site resonance is characteristic of the surface spectra but is not characteristic of the subsurface sites spectral signal to noise s n ratios measured for s waves from a regional earthquake delta 530 km m sub b 4 1 are roughly equal from 1 10 hz at all depths above 10 hz however s n is greater at the subsurface stations with s n greater than 1 up to 30 hz for the surface station approx 50 hz for the 335m station and approx 70 hz for the 945m station results indicate the advantage of employingmore high frequency sensors sufficiently below the surface to reduce the level of noise and to improve the s n ratio in the high frequency range such an advantage could be critically important for nuclear test detection and discrimination less

acoustic waveform inversion with application to seasonal snow covers the amplitude and waveform shape of atmospheric acoustic pulses propagating horizontally over a seasonal snow cover are profoundly changed by the air forced into the snow pores as the pulses move over the surface this interaction greatly reduces the pulse amplitude and elongates the waveform compared to propagation above other ground surfaces to investigate variations in snow cover effects acoustic pulses were recorded while propagating horizontally over 11 different naturally occurring snow covers during two winters two inversion procedures were developed to automatically match the observed waveforms by varying the snow cover parameters in theoretical calculations a simple frequency domain technique to match the dominant frequency of the measured waveform suffered from multiple solutions and poor waveform matching while a time domain minimization method gave unique solutions and excellent waveform agreement results show that the effective flow resistivity and depth of the snow are the parameters controlling waveform shape with the pore shape factor ratio of secondary importance inversion estimates gave flow resistivities ranging from 11 to 29 kn s m 4 except for two late season cases where values of 60 and 140 were determined compared to 345 for the vegetation covered site in the summer acoustically determined snow depths agreed with the measured values in all but one case when the depth to a snow layer interface instead of the total snow depth was determined except for newly fallen snow the pore shape factor ratio values clustered near two values that appear to correspond to wet 1 0 or dry 0 8 snow

observations of low frequency acoustic to seismic coupling in the summer and winter experiments were conducted at a site in northern vermont to investigate low energy acoustic to seismic coupling in the 5 to 500 hz frequency band for propagation distances between 1 and 274 m pistol shots were used as the source of the acoustic waves with geophones and microphones serving as the receivers the strongest coupling into the ground occurred as the air wave passed with measured ratios of about 7 and 6 10 6 m s 1 pa 1 in the summer and winter respectively compressional waves induced in the ground immediately under the source were observed as first arrivals since they travel at the higher subsurface seismic wave velocity but their amplitudes were one to two orders of magnitude lower than those of the later arriving air wave a comparison of the summer and winter recordings revealed a number of effects caused by the introduction of a 0 25 m thick snow cover the peak amplitude of the seismic arrival induced by the passage of the acoustic wave was more strongly attenuated in the winter wi

assessment of chevron dikes for the enhancement of physical aquatic habitat within the middle mississippi river usa summary blunt nosed chevron dikes a new invention now being widely constructed on the middle mississippi river mmr have been justified as a tool for enhancing physical aquatic habitat chevron dikes were initially designed to concentrate flow induce channel scour and thus facilitate river navigation more recently these structures have been justified in part for promoting habitat heterogeneity the ability of chevrons to create and diversify physical aquatic habitat however has not been empirically evaluated to assess the ability of chevrons to create and diversify physical aquatic habitat we compiled hydrologic and geospatial data for three channel reference conditions along a 2 0 km 140 ha reach of the mmr where three chevrons were constructed in late 2007 we used the hydrologic and hydraulic data to construct detailed 2 d hydrodynamic models for three reference condition historic circa 1890 pre chevron and post chevron channel conditions these models documented changes in depths and flow dynamics for a wide range of in channel discharges depth velocity habitat classes were used to assess change in physical aquatic habitat patches and spatial statistical tools in order to evaluate the reach scale habitat patch diversity comparisons of pre and post chevron conditions revealed increases in deep to very deep 3 0 m areas of slow moving 3 0 m low velocity constructing chevrons dikes or other dike like structures in the river channel can change the physical aquatic habitat patch mosaic and likely contribute to small increases in physical aquatic habitat heterogeneity however differences in the types quantity and diversity of physical aquatic habitat patches created by chevron dikes in comparison to the physical aquatic habitat patch mosaic of historic channel underscore the need for additional research to determine which physical aquatic habitat patches are critical for the recovery of endangered or threatened aquatic organisms

retro modeling the middle mississippi river summary a one dimensional 1 d unsteady flow retro model was developed using historic c 1900 hydrologic and geospatial data and implemented using hec ras the objective of this investigation was to create a 1 d unsteady flow model for the middle mississippi river for the beginning of the 20th century in order to assess the magnitude and types of changes in flood stages associated with 20th century river engineering the retro model was constructed from survey data dating to 1888 1889 and hydrologic data from 1900 to 1904 the late 19th century survey data was supplemented by a modern high resolution dem used to fill gaps in the historic data land cover data recorded during this historic survey was used to establish floodplain roughness values based on published manning s n for the various land cover types and these roughness values were then adjusted to calibrate the model comparison of the retro model results with the 2004 upper mississippi river system flow frequency study umrsffs flood stages showed increases in flood stages of 2 3 4 7 m for large events 50 year recurrence interval these results confirm previous research results showing large scale reductions in flood conveyance on the middle mississippi during the 20th century increased roughness of the floodway coupled with reduction in channel and floodplain area due to wing dike and levee construction are the likely explanation for the observed increases in flood stages between 1889 and 1998 channel widths through the study reach decreased 40 and floodplain area for the 100 year flood decreased by 60 in addition manning s n values in the retro model were lower than the values used in the umrsfss suggesting that 1 the modern floodway is rougher than the historic floodway 2 this increased roughness is not a result of explicit changes in land cover but rather 3 the increase is a result of implicit roughness changes such as wing dike construction the retro model developed in this investigation provides a framework for modeling hydrodynamic and ecological responses to altered hydrologic regimes during more than a hundred years of channel modification

ground coupled airwaves at pavlof volcano alaska and their potential for eruption monitoring an abnormally high number of explosion quakes were noted during the monitoring effort for the 2007 eruption of pavlof volcano on the alaska peninsula in this study we manually cataloged the explosion quakes from their characteristic ground coupled airwaves this study investigates how the ground coupled airwaves might be used in a monitoring or analysis effort by estimating energy release and gas mass release over 3 104 quakes were recorded the energy release from the explosions is approximated to be 3 1011 j and the total gas mass assuming 100 water released was 450 t the tracking of explosion quakes has the potential to estimate relative eruption intensity as a function of time and is thus a useful component of a seismic monitoring program

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

analysis of high frequency seismic noise in the western united states and eastern kazakhstan seismographic stations were operated for several months during 1987 at three sites within 250 km of the kazakh test site in the u s s r and through most of 1988 and early 1989 at three sites within 250 km of the nevada test site in the united states we have analyzed surface and borehole noise levels at these sites as a function of wind speed using nearly 2000 recordings of ambient ground noise collected at the u s stations and several hundred noise measurements from the u s s r sites at the surface wind did not become a noticeable source of noise until a minimum speed of 4 to 5 m sec in the boreholes noise levels were affected by wind conditions to a much smaller degree than at the surface between 3 and 10 hz surface and borehole noise levels were typically comparable and western u s sites were generally quieter than kazakh sites in the 10 to 80 hz band surface noise in the western united states was much higher than in kazakhstan but downhole noise levels in both regions were similar and greatly reduced compared to surface noise we suspect that this is due to differences in surface vault quality between the two sets of stations

seasonal variations of seismic velocities in the san jacinto fault area observed with ambient seismic noise s u m m a r y we observe seasonal seismic wave speed changes dv v in the san jacinto fault area and investigate several likely source mechanisms velocity variations are obtained from analysis of 6 yr data of vertical component seismic noise recorded by 10 surface and six borehole stations we study the interrelation between dv v records frequency dependent seismic noise properties and nearby environmental data of wind speed rain ground water level barometric pressure and atmospheric temperature the results indicate peak to peak seasonal velocity variations of 0 2 per cent in the 0 5 2 hz frequency range likely associated with genuine changes of rock properties rather than changes in the noise field phase measurements between dv v and the various environmental data imply that the dominant source mechanism in the arid study area is thermoelastic strain induced by atmospheric temperature variations the other considered environmental effects produce secondary variations that are superimposed on the thermal based changes more detailed work with longer data on the response of rocks to various known external loadings can help tracking the evolving stress and effective rheology at depth

temporal variations of seismic velocity at paradox valley colorado using passive image interferometry in our recent article ugalde et al 2014 we applied the passive image interferometry technique of sens schonfelder and wegler 2006 to monitor seismic velocity changes in paradox valley southwestern colorado for this purpose we computed the autocorrelation

flow characteristics within different configurations of submerged flexible vegetation summary the effects of three configurations aligned staggered and columnar of submerged flexible vegetation on flow structure are investigated experimentally in the laboratory time averaged flow velocity and turbulence behavior are evaluated at different positions in each configuration by using a 3d acoustic doppler velocimeter adv according to the hydrodynamic regimes in experimental results the vertical distribution of streamwise velocity can be separated into three layers the upper non vegetated layer middle vegetation layer and lower sheath layer this three layer model which is associated with different logarithmic equations can be applied to describe the vertical distribution of streamwise velocity the local maximum velocity within vegetation occurs at the sheath section of a plant clump 0 10 0 15 vegetation height h v where the frontal width is minimal turbulent intensities in the streamwise u rms and spanwise v rms directions peak at the sheath section and at the approximate top of the canopy 0 9 1 2 h v the maximum reynolds stresses exist at roughly 0 9 1 2 h v which may be migrated vertically as the frontal width of a plant clump is increased this high frontal width also increases streamwise velocity above vegetation leading to increase variations in reynolds stresses around the canopy top on the vertical turbulent velocity scale w rms the vortices above a still canopy rotate faster than those above a waving canopy therefore the experimental results demonstrate that the flow field can vary significantly at the sheath section and at the top of a plant clump due to altered flow pass these analytical findings will likely prove useful when designing ecological habitats and preventing riverbed erosion

on the location of frequencies of maximum acoustic to seismic coupling measurements of the acoustic to seismic transfer function ratio of the normal soil particle velocity at a depth d to the acoustic pressure at the surface for outdoor ground surfaces quite typically reveal a series of maxima and minima in a publication sabatier et al j acoust soc am 80 646 649 1986 the location and magnitude of these maxima are measured and predicted for several outdoor ground surfaces using a layered poroelastic model of the ground surface in this paper the seismic transfer function for a desert site is compared to the seismic transfer function for holes dug in the desert floor which were filled with pumice volcanic rock the hole geometry was rectangular and the hole depths varied from 0 25 2 0 m the p and s wave speeds densities porosities and flow resistivities for the desert floor and pumice were all measured by varying the hole depth and the fill material the maxima in the seismic transfer function can be shifted in frequency and the locations of the maxima

high frequency seismic noise at lajitas texas a preliminary analysis of high frequency 1 to 20 hz ambient seismic noise at a very quiet site in southwest texas is presented at frequencies greater than 1 hz the displacement noise power decreases at a rate between f 4 and f 5 the ambient seismic noise is also characterized by persistent narrow band peaks f 0 2 hz of unknown origin the noise appears to be propagating at phase velocities 2 5 to 4 km sec or greater which suggests higher mode surface or body waves estimates of coherence and degree of polarization of three component array data indicate that the high frequency ambient noise is relatively well organized over distances of at least 600 to 700 m for a single component but is relatively unorganized in a three component sense a principal result of this preliminary analysis is that the use of three component high frequency 1 to 20 hz arrays at very quiet sites coupled with three component processors may result in substantial improvement of the thresholds for detection and discrimination of weak seismic events

1 min in the life of a river selecting the optimal record length for the measurement of turbulence in fluvial boundary layers in the analysis of instantaneous velocity measurements it is important to consider carefully the properties of the instruments as well as the sampling frequency and the record length although several studies have examined the influence of instrument settings on velocity measurements in rivers little information is available on the effects of the record length on these measurements and on the turbulence parameters that can be extracted from the time series decisions on the record length are often made ad hoc here we quantify the effects of the sampling period on the precision of turbulence statistics e g mean standard deviation skewness reynolds stress quadrant analysis obtained from velocity measurements in fluvial turbulent boundary layers a bootstrapping method is used to determine the standard errors s e of turbulence statistics from 19 time series the time series were sampled in three gravel bed rivers using both electromagnetic current meters ecm and acoustic doppler velocimeters adv the record lengths ranged between 20 and 60 min the sampling frequencies were 20 and 25 hz for the ecms and advs respectively we show that for most turbulence statistics the optimal record length minimum sampling effort to achieve low standard errors ranges between 60 and 90 s we discuss the implication of these record lengths for standard errors estimates and variance losses

thunder induced ground motions 1 observations 1 acoustic pressure from thunder and its induced ground motions were investigated using a small array consisting of five three component short period surface seismometers a three component borehole seismometer and five infrasound microphones we used the array to constrain wave parameters of the incident acoustic and seismic waves the incident slowness differences between acoustic pressure and ground motions suggest that ground reverberations were first initiated somewhat away from the array using slowness inferred from ground motions is preferable to obtain the seismic source parameters we propose a source equalization procedure for acoustic seismic deconvolution to generate the time domain transfer function a procedure similar to that of obtaining teleseismic earthquake receiver functions the time domain transfer function removes the incident pressure time history from the seismogram an additional vertical to radial ground motion transfer function was used to identify the rayleigh wave propagation mode of induced seismic waves complementing that found using the particle motions and amplitude variations in the borehole the initial motions obtained by the time domain transfer functions suggest a low poisson s ratio for the near surface layer the acoustic to seismic transfer functions show a consistent reverberation series at frequencies near 5 hz this gives an empirical measure of site resonance that depends on the ratio of the layer velocity to layer thickness for earthquake p and s waves the time domain transfer function approach by transferring a spectral division into the time domain provides an alternative method for studying acoustic to seismic coupling

synthetic river valleys creating prescribed topography for form process inquiry and river rehabilitation design abstract the synthesis of artificial landforms is complementary to geomorphic analysis because it affords a reflection on both the characteristics and intrinsic formative processes of real world conditions moreover the applied terminus of geomorphic theory is commonly manifested in the engineering and rehabilitation of riverine landforms where the goal is to create specific processes associated with specific morphology to date the synthesis of river topography has been explored outside of geomorphology through artistic renderings computer science applications and river rehabilitation design while within geomorphology it has been explored using morphodynamic modeling such as one dimensional simulation of river reach profiles two dimensional simulation of river networks and three dimensional simulation of subreach scale river morphology to date no approach allows geomorphologists engineers or river rehabilitation practitioners to create landforms of prescribed conditions in this paper a method for creating topography of synthetic river valleys is introduced that utilizes a theoretical framework that draws from fluvial geomorphology computer science and geometric modeling such a method would be valuable to geomorphologists in understanding form process linkages as well as to engineers and river rehabilitation practitioners in developing design surfaces that can be rapidly iterated the method introduced herein relies on the discretization of river valley topography into geometric elements associated with overlapping and orthogonal two dimensional planes such as the planform profile and cross section that are represented by mathematical functions termed geometric element equations topographic surfaces can be parameterized independently or dependently using a geomorphic covariance structure between the spatial series of geometric element equations to illustrate the approach and overall model flexibility examples are provided that are associated with mountain lowland and hybrid synthetic river valleys to conclude recommended advances such as multithread channels are discussed along with potential applications

vegetative impacts on hydraulics and sediment processes across the fluvial system summary vegetation creates a complicated system of feedbacks and linkages across the fluvial system that is realized through river planform shape interactions occur among flow hydraulics sediment deposition and erosion and plant morphology density and biomechanics interest in the interactions and feedback loops between vegetation and the fluvial system has grown extensively in the past few years this interest is partially driven by the popularity of stream restoration activities worldwide that include re vegetation of stream banks and formation of an ecosystem that is intended to encourage the growth of aquatic macrophytes we present a review of the research into the interactions and dependencies between vegetation and the fluvial system to identify hydraulic and sediment dynamics that are consistent around vegetation located in the channel on channel banks and over the floodplain we illustrate process commonalities operating across spatial locations within the fluvial system and highlight some of the current research opportunities and challenges to encourage research collaborations between those working in areas of the fluvial system traditionally viewed as disparate

reciprocal interactions and adjustments between fluvial landforms and vegetation dynamics in river corridors a review of complementary approaches abstract until recently one way relationships between flow dynamics geomorphology and plant ecology were considered dominantly when studying the functioning of river systems whereby fluvial landforms and hydrogeomorphic processes drive the evolution of riparian plant communities however biological communities may significantly control geomorphic processes and have strong impacts on landform dynamics in order to fully identify the processes linked to river dynamics changes in time and space of fluvial landforms and associated plant communities conceptual multidisciplinary progress is clearly needed to understand the mutual interactions and feedbacks between fluvial landforms and vegetation community dynamics this paper presents a detailed literature review of fluvial geomorphology riparian plant ecology and hydraulic engineering knowledge the historical and recent development of ecological plant succession theory toward the integration of hydrogeomorphic disturbances is discussed as well as the integration of vegetation within geomorphology as a significant landform control factor incorporating both hydrogeomorphic controls on riparian vegetation dynamics and mechanical impacts of vegetation structures on flow properties and sediment dynamics recent progress in ecology hydraulic engineering and fluvial geomorphology emphasises interdependence between biological and physical forms and processes based on this literature review a fluvial biogeomorphic succession concept is proposed to link fluvial landform and riparian vegetation community evolution within a bi directional model the succession of fluvial landforms and associated vegetation communities is composed of four main critical phases that represent a shift in the relative dominance of hydrogeomorphic and ecological processes as a response to biostabilisation and passive bioconstruction processes the positive feedbacks associated with this shift lead to the development of characteristic biogeomorphic structures such as vegetated banks islands or floodplains which are moderated by the biogeomorphic functional roles of ecosystem engineers that induce or reinforce the positive feedbacks this fluvial biogeomorphic succession concept relates the natural darwinian selection and ecological succession theories to fluvial geomorphology

determining snow water equivalent by acoustic sounding the possibility of determining snow water equivalent swe by the use of an acoustic impulse was assessed at two field locations in saskatchewan and british columbia canada these sites represent cold windswept prairie and temperate deep mountain snowcovers a continuous frequency swept acoustic wave was sent into the snowpack and received signal processing was then subsequently used to estimate the depth and density of each snow layer by a recursive relationship involving frequency modulated continuous wave fmcw radar and seismological techniques from this method it is also shown that the tortuosity of snow can be estimated data collected by gravimetric sampling was used as comparison to the swe values determined by the use of acoustic sounding the results showed that for the saskatchewan sites the correlation between the measured and the modeled values of swe was 0 86 whereas at the british columbia sites the correlation was 0 78 the difference in the correlations was interpreted as being due to additional acoustic measurement error at the british columbia sites caused by higher liquid water contents and more layers in the snowpack the measured and the modeled swe for saskatchewan snowpacks with high liquid water contents were found to be weakly associated with correlations of 0 30 the acoustically determined values of tortuosity were close to unity 1 which is in agreement with the values characteristic of snow as a porous substance further research is necessary to determine whether this technique can be applied to snow in other environmental conditions copyright 2007 john wiley sons ltd

variations in noise and signal levels in a pair of deep boreholes near amarillo texas to better understand the depth dependence of improvements in signal to noise ratio for borehole seismic data we have collected and analyzed a data set recorded from a pair of high fidelity broadband 1 to 80 hz seismometers sited in two closely separated deep boreholes near amarillo texas the total decrease surface to 1951 m in minimum noise level is up to 30 db the total decrease in maximum noise level is up to 35 db and the range of noise values maximum to minimum at a given depth decreases from 30 to 10 db the majority of the noise reduction occurs within the first few hundred meters below the surface but the decrease continues with depth and there is no indication that even lower noise levels do not exist below our deepest recording depth 1951 m cultural work day noise prominent during normal working hours from 0 to 40 hz is observed at all depths suggesting a strong body wave component wind generated 15 to 60 hz noise is strongest at the surface and is observed as deep as 367 m without a properly shielded hole with the addition of shielding to reduce the coupling between the borehole casing and or cable with the wind wind generated noise above 40 hz can be eliminated at 367 m events with near vertical propagation paths and signal power above 1 hz show signal strength decreasing uphole with a steady winnowing of high frequencies that can be fit by a simple frequency independent q of 35 5 8 for the material between 1951 and 367 m

flow resistance in open channel flows with sparsely distributed bushes the paper faces the problem of the resistance due to vegetation in a river characterized by fully submerged vegetation formed by concentrated colonies of bushes the flow presents strong spatial variations between plants that make unreliable the traditional approach based on time averaging of turbulent fluctuations a more useful model based on time and spatial averaging is proposed in the paper the necessary closure hypotheses are also discussed the vertical distribution of mean velocity and turbulence stress have been measured with laser doppler anemometry techniques by means of spatial and time averaging rules based on the double averaged velocity and reynolds stress profiles an analytical two layer model is proposed in order to describe uniform flow conditions in the whole flow depth theoretical results are compared with the results of a series of experimental tests carried out in a laboratory flume

acoustically induced seismic waves when an airborne acoustic wave is incident at the ground surface energy is coupled into the ground as seismic motion in a previous publication sabatier et al j acoust soc am 78 1345 1352 1986 the ground surface was modeled as an air filled poroelastic layer overlying a semi infinite nonporous elastic substrate in this work the model is extended to include calculations of the normal seismic transfer function ratio of the normal soil particle velocity at a depth d to the acoustic pressure at the surface measurements of the seismic transfer function for three sites are considered and compared to the predicted values generally good agreement between theory and experiment is achieved by best fits assuming the soil or seismic attenuation this is accomplished by specifying the ratio of the imaginary to real part of the measured seismic p and s wave speeds the seismic transfer functions quite typically exhibit minima and maxima which are associated with the seismic layering of the ground su

an experimental study of flow through rigid vegetation 1 better understanding of the role of vegetation in the transport of fluid and pollutants requires improved knowledge of the detailed flow structure within the vegetation instead of spatial averaging this study uses discrete measurements at multiple locations within the canopy to develop velocity and turbulence intensity profiles and observe the changes in the flow characteristics as water travels through a vegetation array simulated by rigid dowels velocity data was collected with a one dimensional laser doppler velocimeter under emergent and submerged flow conditions the effects of dowel arrangement density and roughness were also examined the results show that the velocity within the vegetation array is constant with depth and the velocity profile is logarithmic above it however the boundaries are marked by inflection points the strongest vortices and turbulence intensities can be found there especially in the region immediately downstream of a dowel these results support the idea that the flow in the region near the bed and at the top of the dowel array is very unstable leading to the formation of coherent structures and are areas of significant mass and momentum exchange

a description of water and sediment flow in the presence of obstacles with a two dimensional lattice bgk cellular automata model 1 the spatial distribution of water and sediment flow in the presence of obstacles on the soil surface is described with a coupled two dimensional lattice bgk the bhatnagar groos and krook version of the lattice boltzmann equation cellular automata model the model reproduces the main water flow characteristics of the bunte and poesen 1993 experiment well as well as the mean runoff velocity the model also approximates the main features of local scouring and sediment yield of the experiment although the results obtained in two dimensions are encouraging the consideration of the erosive action of the vortexes on a plane perpendicular to the bed would improve the characterization of the scouring patterns in the stagnation points developed upstream from the obstacles index terms 1815 hydrology erosion and sedimentation 1860 hydrology runoff and streamflow 1869 hydrology stochastic processes keywords flow erosion obstacles lattice bgk model cellular automata model

spectral analysis of seismic noise induced by rivers a new tool to monitor spatiotemporal changes in stream hydrodynamics to 20 db relative to m s 2 hz for all the stations located along a steep 30 km long narrow and deeply incised channel of the trisuli river a major trans himalayan river the early summer increase in high frequency energy is modulated by a 24 h periodicity where the minimum of seismic noise level is reached around noon and the maximum is reached late in the evening a detailed study of seismic noise amplitude reveals a clear correlation with both regional meteorological and hydrological data along the trisuli river seasonal increase in ambient noise coincides with the strong monsoon rainfall and a period of rapid melting of snow and ice in the high elevations the observed 24 h cyclicity is consistent with the daily fluctuation of the precipitation and river discharge in the region river induced seismic noise is partly generated by stream turbulence but this mechanism fails to explain the observed clockwise hysteresis of seismic noise amplitude versus water level this pattern is better explained if a significant part of the observed seismic noise is caused by ground vibrations generated by bed load transport this points out the potential of using background seismic noise to quantify in continuous river bed load and monitor its spatial variations which remain difficult with classical approaches

high frequency borehole seismograms recorded in the san jcinto fault zone southern california part 2 attenuation and site effects we examine surface and downhole p and s wave spectra from local earthquakes recorded at two borehole seismometer arrays knw bh and pfo bh installed in the southern california batholith region of the san jacinto fault zone by the u s geological survey to assess the influence of the weathered layer on the spectral content of high frequency 2 to 200 hz seismic signals earthquake signals recorded downhole at both sites show significantly improved seismic bandwidth due to both a reduction in ambient noise levels and especially to dramatically increased levels of high frequency signal significant seismic signal is observed up to approximately 190 hz for p waves at knw bh stacked spectral ratios from these signals indicate that the highly weathered near surface between 0 and 150 m at knw bh and pfo bh exerts a much larger influence on seismic signals than deeper between 150 and 300 m material modeling of uphole downhole spectral ratio data suggests q 6 5 and q 9 between 0 and 150 m increasing to q 27 and q 26 between 150 and 300 m an outcrop mounted anza network station deployed approximately 0 4 km from knw bh displays roughly similar high frequency content to the knw bh downhole sensors but it exhibits spectra that are significantly colored by directional resonances low q and low velocity near surface material forms a lossy boundary layer at these borehole sites that is advantageous to the high frequency downhole environment not only are noise levels reduced but reflections from the surface and near surface are greatly attenuated as a result high frequency recordings from below the weathered zone more nearly resemble those recorded in a whole space than would otherwise be expected