comment on effects of hydraulic roughness on surface textures of gravel bed rivers and effects of sediment supply on surface textures of gravel bed rivers by john m buffington and david r montgomery

factors controlling riffle scale hyporheic exchange flows and their seasonal changes in a gaining stream a three dimensional groundwater flow model 1 subsurface flow within a single riffle of a low gradient gravel bed stream was modeled in three dimensions using modflow a finite difference groundwater flow model model simulations showed that exchange flows can only occur in this low gradient gaining stream because of a zone of alluvial sediment around the stream that has much higher permeability than the surrounding catchment k 10 4 m s 1 compared with k 10 6 to 10 8 m s 1 the key factors controlling exchange flow within the alluvial zone were identified as the hydraulic conductivity of the alluvium the hydraulic gradient between upstream and downstream ends of the riffle and the flux of groundwater entering the alluvium from the sides and beneath in the study riffle each of these factors changes with season causing a reversal of flow paths in the alluvium and a reduction in exchange flows from about 0 2 0 5 m 3 d per meter stream length in summer to about 0 008 0 04 m 3 d 1 per meter stream length during fall to spring the model also revealed that exchange flows are up to twice as strong but more variable at the sides of the stream than near the center and that vertical flow paths beneath the channel are more persistent under the range of conditions modeled than lateral flow paths into the banks

assessing the reliability of the modified three component spatial autocorrelation technique summary analysis of seismic ambient vibrations is becoming a widespread approach to estimate subsurface shear wave velocity profiles however the common restriction to vertical component wavefield data does not allow investigations of love wave dispersion and the partitioning between rayleigh and love waves in this study we extend the modified spatial autocorrelation technique mspac to three component analysis 3c mspac by determination of love wave dispersion curves this technique provides additional information for the determination of shear wave velocity depth profiles furthermore the relative fraction of rayleigh waves in the total portion of surface waves on the horizontal components is estimated tests of the 3c mspac method are presented using synthetic ambient vibration waveform data different types of surface waves are simulated as well as different modes in addition different spatial distributions of sources are used we obtain rayleigh and love wave dispersion curves for broad frequency bands in agreement with the models used for waveform simulation the same applies for the relative fraction of rayleigh waves dispersion curves are observed at lower frequencies for love waves than for rayleigh waves while 3c mspac has clear advantages for determination of love waves velocities 3c mspac and conventional vertical frequency wavenumber analysis complement each other in estimating the rayleigh wave dispersion characteristics inversions of the dispersion curves for the shear wave velocity depth profile show that the use of love wave velocities confirms the results derived from rayleigh wave velocities in the presence of higher mode surface waves love waves even can improve results application of 3c mspac to ambient vibration data recorded during field measurements pulheim germany show dominance of love waves in the wavefield existing shear wave profiles for this site are consistent with models obtained from inversion of rayleigh and love wave dispersion curves

seismic waves estimation and wavefield decomposition application to ambient vibrations summary passive seismic surveying methods represent a valuable tool in local seismic hazard assessment oil and gas prospection and in geotechnical investigations array processing techniques are used in order to estimate wavefield properties such as dispersion curves of surface waves and ellipticity of rayleigh waves however techniques presently in use often fail to properly merge information from three components sensors and do not account for the presence of multiple waves in this paper a technique for maximum likelihood estimation of wavefield parameters including direction of propagation velocity of love waves and rayleigh waves and ellipticity of rayleigh waves is described this technique models jointly all the measurements and all the wavefield parameters furthermore it is possible to model the simultaneous presence of multiple waves the performance of this technique is evaluated on a high fidelity synthetic data set and on real data it is shown that the joint modelling of all the sensor components decreases the variance of wavenumber estimates and allows the retrieval of the ellipticity value together with an estimate of the prograde retrograde motion

seismic noise based strategies for emphasizing recent tectonic activity and local site effects the ferrara arc northern italy case study during the seismic crisis of may june 2012 that strongly affected the central sector of the ferrara arc relevant coseismic effects were observed such as ground deformations and amplification phenomena due to low quality mechanical characteristics of the shallow subsurface i e few hundreds of meters this portion of the subsurface is not investigated by neither hydrocarbon explorations too deep nor geotechnical surveys too shallow furthermore direct analysis is not cost effective to carry out over such a wide area to overcome these limitations we exploited seismic noise based strategies which are not invasive and do not require expensive equipment we carried out several single station and array measurements i e esac re mi and hvsr across some of the major tectonic structures of the eastern po plain belonging to the most advanced buried sector of the northern apennines such investigations were performed along two profiles about 27 km long and oriented ssw nne i e almost perpendicular to the regional trend of the ferrara arc structures our results clearly document lateral shear wave velocity variations and the occurrence of resonance phenomena between 0 52 and 0 85 hz additionally based on inversion procedures we were able to infer the depth of the resonant interface s and we associated such interface s to the major known stratigraphic discontinuities thus emphasizing the recent tectonic activity of the blind thrusts affecting this sector of the ferrara arc

comment on microtremor observations of deep sediment resonance in metropolitan memphis tennessee by paul bodin kevin smith steve horton and howard hwang abstract bodin et al eng geol 62 2001 159 reported three sets of maxima in observed h v particle motion spectra where the longest period set of peaks provided clear mapping information on the thickness of post cretaceous sediments in the mississippi embayment but the remaining peaks remained largely unexplained a review of microtremor array studies for similar sites and similar frequencies suggests that the microtremor field is best interpreted in terms of rayleigh wave energy use of this approach with modeling of particle motion h v ratios for realistic models of the mississippi embayment shows that the eng geol 62 2001 159 second set of spectral maxima can be associated with higher mode rayleigh wave energy and may contain information on a possible velocity inversion in the shear velocity profile of the site a third spectral maximum appears to be associated with soft soils loess and may be able to be used for mapping the near surface thickness order 15 m of this unit

mapping the palaeo piniada valley central greece based on systematic microtremor analyses the application of seismic noise based techniques has become particularly popular in the last decades as they are not invasive and do not require large teams or expensive equipments the horizontal to vertical spectral ratio hvsr is commonly used not only in seismic microzoning studies as far as from noise recording constraining the fundamental resonant frequency but it is also possible to infer the depth of the bedrock knowing the average shear wave velocity of the overlying sedimentary cover or viceversa i e resonance equation for the purposes of the present research more than 300 single station noise measurements were carried out across the piniada valley central greece along and between several transects planned roughly perpendicular to the mean valley trend to understand the palaeogeographic and tectonic evolution of this area we needed an estimation of the geometry at depth of the bedrock underlying the fluvial deposits of the present day pinios river as a result for each measured site we calculated the depth of the bedrock and afterwards such values were opportunely interpolated for obtaining a 3d model of the palaeo piniada valley documenting for the first time the recent late quaternary inversion of the topographic gradient

stream aquifer interactions and hyporheic exchange in gaining and losing sinuous streams 1 the irregular planform morphology of rivers leads to formation of hyporheic zones along its banks this study investigates how hyporheic exchange in stream banks whose planform is idealized as sinusoidal is affected by net gains from and net losses of water to the adjacent aquifer these effects are studied via numerical modeling of groundwater flow adjacent to sinuous channels across a broad range of sinuosity and gain loss magnitude hyporheic zone areas and fluxes both decrease exponentially with increasing magnitude of net gain or loss relative to the case where the stream has no net flux of water neutral residence time through the hyporheic zone also decreases with gain loss magnitude the hyporheic zones become constrained near the apex of bends indicating that these areas could be hot spots for mixing and biogeochemical processing hyporheic zones in channels with smaller sinuosity are more prone to hyporheic flux and area reduction while very sinuous channels are able to maintain a hyporheic zone even under largely losing or gaining conditions equations fitted to the suite of simulation results allow for prediction of hyporheic flux area and residence time on the basis of aquifer hydraulic conductivity channel sinuosity and the ratio of along valley and across valley mean head gradients

direct laboratory observation of patchy saturation and its effects on ultrasonic velocities maximizing the recovery of known hydrocarbon reserves is one of the biggest challenges facing the petroleum industry today optimal production strategies require accurate monitoring of production induced changes of reservoir saturation and pressure over the life of the field time lapse seismic technology is increasingly used to map these changes in space and time however until now interpretation of time lapse seismic data has been mostly qualitative in order to allow accurate estimation of the saturation it is necessary to know the quantitative relationship between fluid saturation and seismic characteristics elastic moduli velocity dispersion and attenuation the problem of calculating acoustic properties of rocks saturated with a mixture of two fluids has attracted considerable interest gist 1994 mavko and nolen hoeksema 1994 knight et al 1998 for a comprehensive review of theoretical and experimental studies of the patchy saturation problem see toms et al 2006

time lapse sonic logs reveal patchy co2 saturation in situ 1 based on time lapse sonic and neutron porosity logs from the nagaoka co2 sequestration experiment a p wave velocity saturation relation at reservoir depth is retrieved it does not coincide with either of the end member models of uniform and patchy saturation but falls in between even if realistic error estimates for the host rock properties are considered assuming a random distribution of co2 patches it is shown that the mechanism of wave induced flow can be evoked to explain this velocity saturation relation characteristic co2 patch size estimates range from 1 to 5 mm such mesoscopic heterogeneity can be responsible for attenuation and dispersion in the well logging frequency band

comparison of p wave attenuation models of wave induced flow abstract wave induced oscillatory fluid flow in the vicinity of inclusions embedded in porous rocks is one of the main causes for p wave dispersion and attenuation at seismic frequencies hence the p wave velocity depends on wave frequency porosity saturation and other rock parameters several analytical models quantify this wave induced flow attenuation and result in characteristic velocity saturation relations here we compare some of these models by analyzing their low and high frequency asymptotic behaviours and by applying them to measured velocity saturation relations specifically the biot rayleigh model considering spherical inclusions embedded in an isotropic rock matrix is compared with white s and johnson s models of patchy saturation the modeling of laboratory data for tight sandstone and limestone indicates that by selecting appropriate inclusion size the biot rayleigh predictions are close to the measured values particularly for intermediate and high water saturations

seismic exploration scale velocities and structure from ambient seismic noise 1 hz the successful surface waves retrieval in solid earth seismology using long time correlations and subsequent tomographic images of the crust have sparked interest in extraction of subsurface information from noise in the exploration seismology subsurface information in exploration seismology is usually derived from body wave reflections 1 hz which is challenging for utilization of ambient noise we use 11 h of noise recorded in the sirte basin libya first we study the characteristics of the noise we show that the bulk of the noise is composed of surface waves at frequencies below 6 hz some noise panels contain nearly vertically traveling events we further characterize these events using a beamforming algorithm from the beamforming we conclude that these events represent body wave arrivals with a fairly rich azimuthal distribution having body wave arrivals in the noise is a prerequisite for body wave reflections retrieval we crosscorrelate and sum the recorded ambient noise panels to retrieve common source gathers following two approaches using all the noise and using only noise panels containing body wave arrivals likely to contribute to the reflections retrieval comparing the retrieved gathers with active seismic data we show that the two way traveltimes at short offsets of several retrieved events coincide with those of reflections in the active data and thus correspond to apexes of reflections we then compare retrieved stacked sections of the subsurface from both approaches with the active data stacked section and show that the reflectors are consistent along a line the results from the second approach exhibit the reflectors better

s wave velocity structure of sediments in anchorage alaska estimated with array measurements of microtremors the array measurements of microtremors were carried out at nine sites to estimate the subsurface s wave velocity structures of the sedimentary deposits beneath the metropolitan area of anchorage alaska the data were recorded by ten three component accelerometers arranged in a triangular manner for three different array sizes the phase velocities c f were estimated at each site from the vertical component of the recorded microtremor data by using the frequency wavenumber technique the c f data from different arrays were combined after checking their consistency for a series of overlapped frequency bands from different arrays and were inverted using a stochastic least squares inversion technique to estimate the 1d structure underneath each site the inversion results show that the engineering basement 750 m sec lies at a relatively shallower depth 40 m in the eastern part of the basin along the foothills of the chugach mountains cm and at deeper depths toward the southcentral 100 m and western 150 m parts of the basin in accord with the general dip of the basin below the engineering basement a well developed low velocity zone lvz with values in the range of 900 1040 m sec is found to be present in the eastern as well as along the knik arm side in the western part of the basin at a depth of 200 m and 900 m respectively moreover the central part of the basin is associated with a weakly developed lvz below the engineering basement depth in the rest of the basin the value increases gradually with depth the spatial variations of in the basin at different depths from 20 to 500 m are represented by using 2d interpolation of the structures obtained from the inversion of c f data the depth to the crystalline basement of the basin however could not be ascertained and it seems to be much deeper than the maximum depth 2000 m resolved by the data gathered in this study to validate the results of inversion the spectral ratio between the horizontal and vertical components h v of the recorded microtremor data at each site has been compared with the computed h v of rayleigh waves based on the respective structure the results showed good agreement in the frequency range of about 0 4 6 0 hz in this frequency range the h v peaks are due to the overall effect of the velocity contrasts between layers representing the subsurface structure

semianalytical analysis of hyporheic flow induced by alternate bars 1 we investigate the effects of alternate bar morphology on the hyporheic flow in gravel bed rivers our goal is to investigate the relations between residence time distribution of a conservative tracer and the parameters controlling bed form morphology we assume homogeneous isotropic or anisotropic hydraulic properties of the streambed sediment and constant flow regime in equilibrium with the bed form which is considered fixed because its formation timescale is much longer than that of the subsurface flow under these assumptions we solve the in stream and hyporheic flow fields analytically in a three dimensional domain we approximate the former with the shallow water equations and model the latter as a darcian flow the two systems are linked through the hydraulic head distribution which is predicted at the streambed by the surface model and applied as a boundary condition to the hyporheic flow model we solve the solute transport equation in the hyporheic zone for a conservative tracer by means of particle tracking our model predicts that the mean value and variance of the hyporheic residence time depend on the alternate bar amplitude at equilibrium this result is found to be applicable also to discharges that are lower 70 in our simulations than the formative and submerge the bars entirely moreover our analysis shows that 95 of the hyporheic flow is confined in a near bed layer whose depth is about the width of the channel and shallows from low to steep gradient streams this causes the hyporheic mean residence time to reach a threshold when the alluvial depth is deeper than the channel width our results also show that as the stream slope increases the streamlines compact near to the streambed thereby reducing the mean residence time and its variance finally we observe that the hyporheic residence time of pulse injections of passive solutes is lognormally distributed with the mean value depending in a simple manner on the amplitude of the alternate bars

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

fluid distribution effect on sonic attenuation in partially saturated limestones extensional and torsional wave attenuation measurements are obtained at a sonic frequency around 1 khz on partially saturated limestones using large resonant bars 1 m long to study the influence of the fluid distribution we use two different saturation methods drying and depressurization when water saturation sw is higher than 70 the extensional wave attenuation is found to depend on whether the resonant bar is jacketed this can be interpreted as the biot gardner white effect the experimental results obtained on jacketed samples show that during a drying experiment extensional wave attenuation is influenced strongly by the fluid content when sw is between approximately 60 and 100 this sensitivity to fluid saturation vanishes when saturation is obtained through depressurization using a computer assisted tomographic ct scan we found that during depressurization the fluid distribution is homogeneous at the millimetric scale at all saturations in contrast during drying heterogeneous s

noninvasive techniques for site characterization of alberta seismic stations based on shear wave velocitynoninvasive techniques for site characterization of alberta seismic stations based on shear wave velocity

azimuthal anisotropy of rayleigh waves in the crust in southern tohoku area japan to reveal seismic anisotropy within the crust in the southern tohoku area japan we analyze the azimuthal anisotropy of rayleigh waves in the frequency range of 40 65 mhz rayleigh wave anisotropy is estimated by array analysis of 102 teleseismic events that occurred between 2007 and 2014 the frequency variation of the estimated azimuthal anisotropy indicates depth variation of the seismic anisotropy within the crust 1 north south fast velocity direction around the upper crust and 2 trench normal fast velocity direction in the deeper crust we also conduct a time lapse analysis of rayleigh wave anisotropy to demonstrate the stability of the estimated anisotropy in time and to estimate possible changes in seismic anisotropy associated with the 2011 tohoku oki earthquake we demonstrate that the azimuthal location of teleseismic events influences the accuracy of time lapse analysis moreover a decrease of azimuthal anisotropic ratio in time lapse results might be related to changes in the velocity structure associated with release of crustal stress during the tohoku oki earthquake

a generic formulation for microtremor exploration methods using three component records from a circular array summary we present a generic formulation for analysis methods that estimate phase velocities of rayleigh and love waves by way of intermediary quantities called spectral ratios using three component records of microtremors from a circular array of sensors at each time instant the set of records are expanded in a fourier series with respect to azimuth so that we obtain a set of fourier coefficients that are represented in the form of complex time histories we then estimate power and cross spectral densities of those fourier coefficients the spectral densities thus obtained generally contain information on the phase velocities powers and arrival directions of individual modes of rayleigh and love waves by taking the quotient of two different sorts of such spectral densities we can cancel out information on their powers and arrival directions and extract information on their phase velocities alone the spectral ratios have to be estimated in practice on the basis of records from a finite number of seismic sensors that are either evenly or unevenly spaced around a circumference we describe a general procedure for their estimation and discuss the effects of directional aliasing that the finite number of sensors and their configuration have on the estimates of spectral ratios we also discuss biases in the estimates of spectral ratios caused by the presence of incoherent noise by using our method it is also possible to estimate the central arrival direction of the microtremors the ellipticity of the rayleigh waves and whether the rayleigh waves are prograde or retrograde

deblurring of frequency wavenumber images from small scale seismic arrays summary temporary arrays installed in urban areas for investigating the upper most geological structure typically comprised of a limited number of stations and are arranged in geometries constrained by environmental boundaries therefore it is expected that the frequency wavenumber images are significantly blurred by the array transfer function and are corrupted by noise in this paper the effect of the richardson lucy regularization method applied to the problem of deblurring frequency wavenumber images is investigated the images are computed by analysing data from two small aperture 2 d arrays installed with different configurations in a test site within the town of potenza southern italy for near surface investigations we show that removing the effects of the array response from the frequency wavenumber images improve the phase velocity estimation reducing the relevant level of uncertainty furthermore the richardson lucy regularization method is effective in reducing the level of noise related to spatial aliasing by eliminating spurious peaks allowing the maxima related to different seismic sources to be better discriminated

compressional wave dispersion due to rock matrix stiffening by clay squirt flow the standard biot gassmann theory of poroelasticity fails to explain strong compressional wave velocity dispersion experimentally observed in 12 tight siltstone with clay filled pores in order to analyze and understand the results we developed a new double porosity model of clay squirt flow where wave induced local fluid flow occurs between the micropores in clay aggregates and intergranular macropores the model is validated based on the combined study of ultrasonic experiments on specimens at different saturation conditions and theoretical predictions the presence of a sub pore scale structure of clay micropores contained in intergranular macropores where the fluid does not have enough time to achieve mechanical equilibrium at ultrasonic frequencies and thus stiffens the rock matrix provides a suitable explanation of the experimental data moreover the model provides a new bound for estimating the compressional wave velocity of tight rocks saturated with two immiscible liquids the theoretical predictions indicate that the velocity variation between gas and liquid saturated specimens is predominantly induced by the clay squirt stiffening effect on the rock matrix and not by fluid substitution the effect contributes more than 90 to the variation in the porosity range of 0 5 thus clay squirt flow dominates the relationships between compressional wave velocity and pore fluid in tight rocks

basin delineation with a 40 hour passive seismic record several geophysical methods exist to delineate the lower interface of a sedimentary basin most popularly employed are gravity and magnetic surveys and surface wave inversion while all three methods are successful overall in estimating an average basin depth they fail to find a more detailed depth variation as an alter native we consider three passive seismic techniques using especially body waves we analyze 40 hours of data recorded with 110 stations installed over the abu gharadig basin in egypt in an earlier study we found the frequency band of 0 09 1 0 hz to be dominated by body waves as a first method we apply body wave seismic interfero metry si using body wave noise we extract pp and ss reflections from the basin floor we estimate the depth of the basin to be around 4 8 km as a second technique we estimate the resonance spectra of the basin using the horizontal to vertical h v spectral ratio using surface wave noise we find an extremum that is probably related to the complete sedimentary package using this peak we find a basin depth of 5 4 km using s phase arrivals we find two extrema in the h v which are probably related to the s wave resonances of two distinct layers in the basin as a third method we compute receiver functions rfs based on the rfs we can confirm the presence of a large interface in the upper crust but we cannot well constrain its depth

seismic attenuation in porous rocks with random patchy saturation saturation of porous rocks with a mixture of two fluids has a substantial effect on seismic wave propagation in particular partial saturation causes significant attenuation and dispersion of the propagating waves due to the mechanism of wave induced fluid flow such flow arises when a passing wave induces different fluid pressures in regions of rock saturated by different fluids most models of attenuation and dispersion due to mesoscopic heterogeneities imply that fluid heterogeneities are distributed in a regular way however recent experimental studies show that mesoscopic heterogeneities have less idealized distributions and that the distribution itself affects attenuation and dispersion based on an approximation for the coherent wavefield in random porous media we develop a model which assumes a continuous distribution of fluid heterogeneities as this continuous random media approach assumes that there will be a distribution of different patch sizes it is expected to be better suited to modelling experimental data we also show how to relate the random functions to experimentally measurable parameters

velocity saturation relation in partially saturated rocks modelling the effect of injection rate changes the relationship between p wave velocity and fluid saturation in a porous medium is of importance for reservoir rock characterization forced imbibition experiments in the laboratory reveal rather complicated velocity saturation relations including rollover like patterns induced by injection rate changes poroelasticity theory based patchy saturation models using a constant fluid patch size are not able to describe these velocity saturation relations therefore we incorporate a saturation dependent patch size function into two models for patchy saturation this recipe allows us to model observed velocity saturation relations obtained for different and variable injection rates the results reveal an increase in patch size with fluid saturation and show a reduction in the patch size for decreasing injection rate this indicates that there can exist a distinct relation between patch size and injection rate we assess the relative importance of capillarity on velocity saturation relations and find that capillarity stiffening impairs the impact of patch size changes capillarity stiffening appears to be a plausible explanation when a decrease in the injection rate is expected to boost the importance of capillarity

static and dynamic characterization of alluvial deposits in the tiber river valley new data for assessing potential ground motion in the city of rome 1 the paper presents the results of a case study conducted on the holocene alluvial deposits of the tiber river valley in the city of rome the main test site selected for the study valco s paolo is located about 2 km south of rome s historical centre the alluvial deposits were dynamically characterized in a comprehensive way via site investigations and geotechnical laboratory tests normalized shear modulus decay and damping curves g g0 and d d0 vs were obtained for the dominantly fine grained levels the curves demonstrate that these levels have a more marked shear stiffness decay if compared with the underlying pliocene bedrock decay curves from laboratory tests for the tiber alluvia correlated well with the trend of the function proposed by hardin and drnevich making it possible to derive their specific interpolation function coefficients use was made of the extrapolation of the findings from the valco s paolo test site to a large part of rome s historical centre by means of two other test sites supported by an engineering geology model of the complex spatial distribution of the tiber alluvia the experimental valco s paolo vs profile was extrapolated to the other test sites on the basis of a stratigraphic criterion the analysis of seismic noise measurements obtained for the three test sites validated the engineering geology based extrapolation and showed that the main rigidity contrast occurs inside the alluvial body at the contact with the underlying basal gravel level g and not between the alluvia and the plio pleistocene bedrock composed of highly consistent clay marne vaticane the 1d modeling of local seismic response to the maximum expected earthquakes in the city of rome confirms that the deposits have one principal mode of vibration at about 1 hz however the simulation also evidenced that the silty clay deposits level c making up the most part of the tiber alluvial body play a key role in characterizing the soil column deformation profile since it can be affected by non linear effects induced by the maximum expected earthquake when some stratigraphic conditions are satisfied

suitability of 10 hz vertical geophones for seismic noise array measurements based on frequency wavenumber and extended spatial autocorrelation analyses microzonation studies using ambient noise measurements constitute a promising way for seismic hazard evaluation in urban areas among the existing techniques seismic noise array measurements have become a valuable tool for estimating vs profiles and thus the characteristics of a soil structure although methods based on analysis of seismic noise are simpler cheaper and faster than borehole drilling and down hole or cross hole logs to derive shear wave velocity profiles array deployment requires the use of several stations broadband or short period sensors that are not always available in this paper we have compared the results obtained by 10 hz vertical geophone arrays with the results provided by 1 hz sensor arrays two sites in the bajo segura basin se spain with different soil characteristics were chosen for array deployment the comparison is carried out in terms of dispersion curves by using frequency wavenumber f k and extended spatial autocorrelation esac techniques both analyses show a good agreement using either 1 hz sensors or 10 hz geophones moreover they demonstrate that it is possible to extend the analysis in a frequency range much below the natural frequency of the geophones the results of our study confirm the suitability of standard seismic refraction reflection equipment also for ambient noise array measurements which constitutes a cheaper and faster way for investigating soil characteristics

numerical studies of effects of dipping structures on horizontal vertical spectral ratios shallow s wave velocity structures commonly have been estimated from phase velocity curves and horizontal to vertical h v spectral ratios in microtremor exploration techniques however such estimations assume that underground structures are horizontally stratified therefore if the structures were irregular instead the estimations would have errors owing to perturbations in the wavefield from the irregular boundary in this study we examined the influence of the dipping structure on the observed wavefield and the h v spectral ratios based on numerical calculations as a result we observed that the peak frequency in the h v spectral ratios shifted toward lower frequencies along the dipping structure as the structure deepened we also observed a complex amplitude change in the h v spectral ratios along the dipping structure the peak became obscure near and on the dipping structure it was likely that the waves reflected within one wavelength of the issued receiver were likely to have significant effects on the observed wavefield and to disturb the h v spectral ratios according to a sensitivity analysis our result indicates that dipping structures could be estimated by the peak shift in h v spectral ratios derived from a spatially dense observation however it should be noted that the peaks sometimes become obscure due to the wavefield perturbation from the dipping structure mainly within one wavelength

a patch hierarchy approach to modeling surface and subsurface hydrology in complex flood plain environments geomorphology interacts with surface and ground water hydrology across multiple spatial scales nonetheless hydrologic and hydrogeologic models are most commonly implemented at a single spatial scale using an existing hydrogeologic computer model we implemented a simple hierarchical approach to modeling surface and ground water hydrology in a complex geomorphic setting we parameterized the model to simulate ground and surface water ow patterns through a hierarchical three dimensional quantitative representation of an anabranched montane alluvial ood plain the nyack flood plain middle fork flathead river montana usa comparison of model results to eld data showed that the model provided reasonable representations of spatial patterns of aquifer recharge and discharge temporal patterns of ood water storage on the ood plain and rates of ground water movement from the main river channel into a large lateral spring channel on the ood plain and water table elevation in the alluvial aquifer these results suggest that a hierarchical approach to modeling ground and surface water hydrology can reproduce realistic patterns of surface and ground water ux on alluvial ood plains and therefore should provide an excellent quantitative laboratory for studying complex interactions between geomorphology and hydrology at and across multiple spatial scales copyright 2004 john wiley sons ltd

ambient noise analysis in the eastern sea of marmara region in northwest turkey lateral variations of the crustal velocity field abstract we analyze the ambient seismic noise field in order to investigate the crustal structure at the north anatolian fault zone nafz in northwest turkey we focus on the eastern sea of marmara section where the nafz is in the final phase of the seismic cycle prior to an expected major m 7 earthquake we apply cross correlation analysis of the seismic ambient noise to determine the spectral dependence of the seismic velocity in order to image the crustal structure at seismogenic depth time domain cross correlations are calculated for available station pairs in the target area interstation distances span 0 3 90 km here the vertical component is analyzed in order to recover fundamental mode rayleigh waves in the 0 05 1 1 hz frequency range group velocity dispersion curves are obtained for selected correlation paths in particular to address the azimuthal dependence of the velocity field in the frequency band of interest average group velocities range between 1 8 and 3 5 km s dispersion curves corresponding to the north south trending paths crossing the main nafz fault branch below the eastern sea of marmara show low group velocities between 1 5 and 1 8 km s which is well explained by the 3 4 km deep cinarcik basin located between the two major fault branches the princes islands and armutlu fault segments in contrast ray paths restricted to within the mainland of istanbul and the armutlu peninsulas primarily trending east west show higher group velocities up to 3 2 km s by averaging the dispersion curves we determine an optimized 1d s wave velocity model for the eastern sea of marmara region allowing for a significant improvement in hypocenter determination for local seismicity

rock anelasticity due to patchy saturation and fabric heterogeneity a double double porosity model of wave propagation heterogeneity of rock s fabric can induce heterogeneous distribution of immiscible fluids in natural reservoirs since the lithological variations mainly permeability may affect fluid migration in geological time scales resulting in patchy saturation of fluids therefore fabric and saturation inhomogeneities both affect wave propagation to model the wave effects attenuation and velocity dispersion we introduce a double double porosity model where pores saturated with two different fluids overlap with pores having dissimilar compressibilities the governing equations are derived by using hamilton s principle based on the potential energy kinetic energy and dissipation functions and the stiffness coefficients are determined by gedanken experiments yielding one fast p wave and four slow biot waves three examples are given namely muddy siltstones clean dolomites and tight sandstones where fabric heterogeneities at three different spatial scales are analyzed in comparison with experimental data in muddy siltstones where intrapore clay and intergranular pores constitute a submicroscopic double porosity structure wave anelasticity mainly occurs in the frequency range 104 107 hz while in pure dolomites with microscopic heterogeneity of grain contacts and tight sandstones with mesoscopic heterogeneity of less consolidated sands it occurs at 103 107 hz and 101 103 hz seismic band respectively the predicted maximum quality factor of the fast compressional wave for the sandstone is the lowest approximately 8 and that of the dolomite is the highest the results of the diffusive slow waves are affected by the strong friction effects between solids and fluids the model describes wave propagation in patchy saturated rocks with fabric heterogeneity at different scales and the relevant theoretical predictions agree well with the experimental data in fully and partially saturated rocks

near surface shear wave velocity structure of the chiayi area taiwan this paper uses microtremor array measurements to obtain an overall view of s wave velocity structure in the chiayi area taiwan the rayleigh wave dispersion curves are calculated using the frequency wavenumber graphic 1 spectrum method and then the s wave velocity structure of the area is estimated by surface wave inversion according to the inversion results the s wave velocities decrease from east to west if the s wave velocity of the bedrock is assumed to be 1500 m s the depths of the alluvium are between 560 and 1400 m gradually increasing from east to west in order to understand the variations of the shallow s wave velocity in the area we sketch 2d and 3d maps using the imaging techniques based on interpolation algorithms from the 3d results the thickness of the sediments having an s wave velocity in the range 270 1500 m s increases from east to west whereas the thickness of the layers having an s wave velocity in the range 1500 2370 m s decreases from east to west the results are also in good agreement with the geological and geophysical information of the chiayi area therefore microtremor array measurement provides a good alternate to estimate shallow s wave velocity structure online material figures showing observed and calculated phase velocities f k spectra dispersion curves inverted velocity models sensitivity kernels and v s contour maps and electric resistivity maps 1 embed inline graphic 1 gif

seismic attenuation due to heterogeneities of rock fabric and fluid distribution jing ba 1 2 jose m carcione3 and weitao sun4 1school of mathematics and statistics xi an jiaotong university 710049 xi an china e mail jba uh edu 2department of earth and atmospheric sciences university of houston houston tx 77204 usa 3istituto nazionale di oceanografia e di geofisica sperimentale ogs borgo grotta gigante 42c sgonico trieste i 34010 italy 4zhou pei yuan center for applied mathematics tsinghua university 100083 beijing china

sound velocity of a sandstone saturated with oil and brine at different concentrations we have measured the velocity of sound in a sandstone saturated with oil and brine at different concentrations the velocity variations with the concentration depend drastically on the way of entering the fluids in the sample injection of non wetting fluid in a sandstone fully saturated with a totally wetting fluid drainage or vice versa imbibition we interpret our measurements with an extension of the biot gassmann theory to a wetted frame of the sandstone saturated with an effective oil brine fluid

effects of stream discharge alluvial depth and bar amplitude on hyporheic flow in pool riffle channels 1 hyporheic flow results from the interaction between streamflow and channel morphology and is an important component of stream ecosystems because it enhances water and solute exchange between the river and its bed hyporheic flow in pool riffle channels is particularly complex because of three dimensional topography that spans a range of partially to fully submerged conditions inducing both static and dynamic head variations hence these channels exhibit transitional conditions of streambed pressure and hyporheic flow compared to previous studies of fully submerged two dimensional bed forms here we conduct a series of three dimensional simulations to investigate the effects of bed topography depth of alluvium and stream discharge on hyporheic flow in pool riffle reaches with variable bed form submergence and we propose three empirical formulae to predict the mean depth of hyporheic exchange and characteristic values of the residence time distribution mean and standard deviation hyporheic exchange is predicted with a three dimensional pumping model and hyporheic flow is modeled as a darcy flow we find that the hyporheic residence time is well approximated by a lognormal distribution for both partially and entirely submerged pool riffle topography with the parameters of the distribution defined by the mean and variance of the log transformed residence time depth of alluvium has a substantial effect on hyporheic flow when alluvial depth is less than a third of the bed form wavelength for the conditions examined

a new method to determine phase velocities of rayleigh waves from microseisms we have developed a new method to determine phase velocities from the vertical component of microseisms recorded with an array of seismic sensors spaced around the circumference of a circle we calculate two different time histories by taking the average of the seismograms with differing sets of weights for the sensor stations the spectral ratio of these two time histories contains no information on the arrival directions or on the amplitudes of the incoming waves but depends solely on the phase velocities of the arriving modes theoretical considerations indicate that the effects of directional aliasing caused by the use of a finite number of sensors in the field implementation of our method are small in most situations except for short wavelengths the presence of incoherent noise limits the efficacy of our method for long wavelengths in field tests using arrays of three seismic sensors we obtained appropriate estimates of phase velocities in the wavelength range from 5r to 30r where r the array radi

miniature array analysis of microtremors we suggest observing microtremors by using a miniature array consisting of vertical component seismometers that are placed at the center andon the circumferenceofa circlewith a radius of several tens of centimeters for identifying the phase velocities of rayleigh waves with wavelengths exceeding several tens or a hundred meters we present as tools for the analysis a set comprised of the analysis methods for the phase velocity and the evaluation method for the analysis limit which were recently developed by the authors on the basis of a rigorous theory derived by generalizing a spatial autocorrelation method we conducted miniature array observations using four or six servo type seismometers ju 215 manufactured by hakusan corporation at about 50 observation points throughout a test site and urban areas in tsukuba city and its surroundings which have various topographical and geologic environments the time required from arrival at an observation point to retrieval averaged about 30 min we could determine the phase velocities of rayleigh waves with wavelengths of 40 and 100 m at 91 and 51 of all the observation points respectively miniature array analyses can significantlyimprovethemobilityofobservationtoinfershallow subsurface velocity structures to the depth of several tens of meters

uncertainty of linear earthquake site amplification via bayesian inversion of surface seismic data abstractwe examine uncertainty in predicted linear 1d site amplification due to uncertainty in shear wave velocity vs structure quantified from bayesian probabilistic inversion of microtremor array dispersion data based on a sample of vs profiles drawn from the posterior probability density of the microtremor inversion probability distributions are computed for common predictors of site amplification including vsz traveltime average vs to a depth z and amplification spectra based on seismic impedance variations and full transverse shear wave effects these methods are applicable for any site but the resulting probabilistic site amplification analyses are specific to the two sediment sites studied here with strongly contrasting geology in high population centers of british columbia canada the site amplification probability distributions for the two sites are shown to be more informative than amplification estimated for a single best fit vs profile by characterizing the uncertainty and therefore

p wave seismic attenuation by slow wave diffusion effects of inhomogeneous rock properties recent research has established that the dominant p wave attenuation mechanism in reservoir rocks at seismic frequencies is because of wave induced fluid flow mesoscopic loss the p wave induces a fluid pressure difference at mesoscopic scale inhomogeneities larger than the pore size but smaller than the wavelength typically tens of centimeters and generates fluid flow and slow diffusion biot waves continuity of pore pressure is achieved by energy conversion to slow p waves which diffuse away from the interfaces in this context we consider a periodically stratified medium and investigate the amount of attenuation and velocity dispersion caused by different types of heterogeneities in the rock properties namely porosity grain and frame moduli permeability and fluid properties the most effective loss mechanisms result from porosity variations and partial saturation where one of the fluids is very stiff and the other is very compliant such as a highly permeable sandstone at shallow depths saturated with small amounts of gas around 10 saturation and water grain and frame moduli variations are the next cause of attenuation the relaxation peak moves towards low frequencies as the background permeability decreases and the viscosity and thickness of the layers increase the analysis indicates in which cases the seismic band is in the relaxed regime and therefore when the gassmann equation can yield a good approximation to the wave velocity

seismic wave attenuation and dispersion resulting from wave induced flow in porous rocks a review one major cause of elastic wave attenuation in heterogeneous porous media is wave induced flow of the pore fluid between heterogeneities of various scales it is believed that for frequencies below 1 khz the most important cause is the wave induced flow between mesoscopic inhomogeneities which are large compared with the typical individual pore size but small compared to the wavelength various laboratory experiments in some natural porous materials provide evidence for the presence of centimeter scale mesoscopic heterogeneities laboratory and field measurements of seismic attenuation in fluid saturated rocks provide indications of the role of the wave induced flow signatures of wave induced flow include the frequency and saturation dependence of p wave attenuation and its associated velocity dispersion frequency dependent shear wave splitting and attenuation anisotropy during the last four decades numerous models for attenuation and velocity dispersion from wave induced flow have been developed with varying degrees of rigor and complexity these models can be categorized roughly into three groups according to their underlying theoretical framework the first group of models is based on biot s theory of poroelasticity the second group is based on elastodynamic theory where local fluid flow is incorporated through an additional hydrodynamic equation another group of models is derived using the theory of viscoelasticity though all models predict attenuation and velocity dispersion typical for a relaxation process there exist differences that can be related to the type of disorder periodic random space dimension and to the way the local flow is incorporated the differences manifest themselves in different asymptotic scaling laws for attenuation and in different expressions for characteristic frequencies in recent years some theoretical models of wave induced fluid flow have been validated numerically using finite difference finite element and reflectivity algorithms applied to biot s equations of poroelasticity application of theoretical models to real seismic data requires further studies using broadband laboratory and field measurements of attenuation and dispersion for different rocks as well as development of more robust methods for estimating dissipation attributes from field data

site specific issues for strong ground motions during the kocaeli turkey earthquake of 17 august 1999 as inferred from array observations of microtremors and aftershocks array observations of microtremors and aftershocks were carried out near the permanent strong motion observation sites and the damaged areas after the kocaeli turkey earthquake of 17 august 1999 the major objectives were to determine s wave velocity structures at the sites and to understand the site effects on strong motion or damage array observation of microtremors is a useful method for determining the s wave velocity structures in a sedimentary basin with less practical restriction than the other geotechnical methods the spatial autocorrelation method spac was applied to array data of microtremors for determining s wave velocity structures the spac method generally provides an equivalent result with that of the frequency wavenumber method using fewer array sites and a smaller array size most strong motion sites near the fault are classified into stiff and or very hard soils the records cannot directly be used for interpreting damage to buildings in the sedimentary basin records of long durations of strong motion at ats near avcilar west of istanbul are closely related to the low velocity v s 200 m sec of the surface layers the s wave velocity structure at avcilar where there was severe damage during the mainshock is similar to that of the lowland ats and it differs significantly from that of cna located 4 km northeast of avcilar where the strong motion record was obtained from the mainshock the strong ground motion at avcilar during the mainshock is estimated to be similar to that at ats of the strong motion sites sakarya skr is located on very hard soil whereas thick and soft sediments cover downtown adapazari it is plausible that strong ground motions during the mainshock in the damaged area adc were significantly different from those of skr a large difference between the strong motions of a hillside and the lzmit bay area in and around golcuk is also indicated by a comparison of aftershock records

s wave velocity structure of the taiwan chelungpu fault drilling project tcdp site using microtremor array measurements the taiwan chelungpu fault drilling project tcdp drilled a 2 km deep hole 2 4 km east of the surface rupture of the 1999 chi chi earthquake mw 7 6 near the town of dakeng geophysical well logs at the tcdp site were run over depths ranging from 500 to 1 900 m to obtain the physical properties of the fault zones and adjacent damage zones these data provide good reference material for examining the validity of velocity structures using microtremor array measurement therefore we conduct array measurements for a total of four arrays at two sites near the tcdp drilling sites the phase velocities at frequencies of 0 2 5 hz are calculated using the frequency wavenumber f k spectrum method then the s wave velocity structures are estimated by employing surface wave inversion techniques the s wave velocity from the differential inversion technique gradually increases from 1 52 to 2 22 km s at depths between 585 and 1 710 m this result is similar to those from the velocity logs which range from 1 4 km s at a depth of 597 m to 2 98 km s at a depth of 1 705 m the stochastic inversion results are similar to those from the seismic reflection methods and the lithostratigraphy of tcdp a borehole comparatively these results show that microtremor array measurement provides a good tool for estimating deep s wave velocity structure

instrumental evidence of normal mode rock slope vibration summary a unique field experiment was performed to constrain the seismic response of a large potentially unstable rock slope in the southern swiss alps small aperture seismic arrays were deployed to record ambient vibrations both inside and outside of the mapped instability boundary the recordings were analysed by means of the high resolution f k method site to reference spectral ratios and time frequency dependent polarization analysis all three methods indicated that the wavefield within the potentially unstable rock mass is dominated by normal mode motion standing waves rather than horizontal propagation of seismic waves both fundamental frequency and relative amplification could be recovered from ambient noise data the observed amplification is strongly directional and the maximum amplification is oriented perpendicular to open tension cracks mapped at the ground surface our results highlight site response characteristics relevant for analysis of earthquake triggered rock slope failures

bayesian inversion of microtremor array dispersion data in southwestern british columbia summary this paper applies bayesian inversion with evaluation of data errors and model parametrization to produce the most probable shear wave velocity profile together with quantitative uncertainty estimates from microtremor array dispersion data generally the most important property for characterizing earthquake site response is the shear wave velocity vs profile the microtremor array method determines phase velocity dispersion of rayleigh surface waves from multi instrument recordings of urban noise inversion of dispersion curves for vs structure is a non unique and non linear problem such that meaningful evaluation of confidence intervals is required quantitative uncertainty estimation requires not only a non linear inversion approach that samples models proportional to their probability but also rigorous estimation of the data error statistics and an appropriate model parametrization this paper applies a bayesian formulation that represents the solution of the inverse problem in terms of the posterior probability density ppd of the geophysical model parameters markov chain monte carlo methods are used with an efficient implementation of metropolis hastings sampling to provide an unbiased sample from the ppd to compute parameter uncertainties and inter relationships nonparametric estimation of a data error covariance matrix from residual analysis is applied with rigorous a posteriori statistical tests to validate the covariance estimate and the assumption of a gaussian error distribution the most appropriate model parametrization is determined using the bayesian information criterion which provides the simplest model consistent with the resolving power of the data parametrizations considered vary in the number of layers and include layers with uniform linear and power law gradients parameter uncertainties are found to be underestimated when data error correlations are neglected and when compressional wave velocity and or density nuisance parameters are fixed in the inversion bayesian inversion of microtremor array data is applied at two sites in british columbia the area of highest seismic risk in canada to study the ability to recover an accurate vs profile in relatively deep and shallow geological settings on the fraser river delta in greater vancouver and in victoria respectively a well resolved vs profile to at least 110 m depth is determined at the fraser river delta site for a power law gradient parametrization at the victoria site a layer with low vs and a weak linear gradient is indicated to 15 18 m depth above much higher velocity material invasive vs measurements from seismic cone penetration testing and or surface to downhole methods are used to assess the reliability of the bayesian microtremor inversion results with excellent agreement obtained at both sites

reduction of the hyporheic zone volume due to the stream aquifer interaction 1 pore water in stream sediments is continuously exchanged with the surface water from the overlying stream this exchange of water and solutes that occurs across the stream sediment interface plays an important role for fluvial ecology because of the unique biochemical conditions rich biodiversity and high rates of metabolism while many studies have observed the extent of the hyporheic zone to be modified by changes in the level of the groundwater table the actual importance of this interaction is still difficult to quantify here we focus on the case of bedform induced hyporheic exchange to show how the the volume of hyporheic sediments that receive water from the stream is significantly reduced by the upwelling of subsurface water a simple scaling relationship for the assessment of maximum depth of the hyporheic zone is proposed by relating hyporheic flow to the groundwater discharge in an aquifer with given hydraulic properties and head difference between the stream and the aquifer

the structure of the onega downthrown block and adjacent geological objects according to the microseismic sounding method the geological structure of the major part of the arkhangelsk region in the north west russia has been poorly studied in the present work the microseismic sounding method was for the first time used to carry out a detailed geological geophysical survey in the region the particles motion study confirmed the results of mathematical modeling of the smallest imaged heterogeneity and resolution of the method the microseism stability study allowed to determine the amount of error of the microseismic sounding method which is 1 2 db two geophysical cross sections of the north eastern and south western boundaries of the onega downthrown block were studied the method was shown to allow obtaining seismic images with a high precision in the horizontal direction at relatively low costs in terms of time and finances the obtained data provided additional information about the structure of the crust which was consistent with the known geological and geophysical information for the surveyed area based on the data it was concluded that the main reasons of the dissonance of geological information were most likely the division of the downthrown block into the northern and southern blocks and horizontal displacement of the layer to the north at a depth ranging from 3 to 5 km it was suggested that the most active tectonic processes including eruptions of ancient volcanoes occurred in the northern block two benches at the studied downthrown block were allocated at the depths of 5 and 10 km

effect of instream wood on vertical water flux in low energy sand bed flume experiments 1 in streams interaction of current with bed forms and solid objects can produce vertical water flux across the streambed instream wood is a major obstacle to flow and alters the bed topography of natural sand bed streams in the present experimental study in large circulating flumes simulating sand bed streams with low constant slope we compared systems with and without natural quantities of wood the introduction of wood resulted in the production of irregular bed forms as a result flow resistance tripled and vertical water flux across the streambed increased by a factor of 1 8 to 2 5 the mixing depth was spatially variable and seemed unrelated to the local bed form after the addition of wood surface water mixed deeper into the sediments and the total sediment pore water volume involved in mixing increased by factors of 1 2 to 1 5 the practice of increasing instream wood should be a valuable tool for hyporheic rehabilitation of degraded sand bed streams

deriving wavefield characteristics and shear velocity profiles from two dimensional small aperture arrays analysis of ambient vibrations in a small size alluvial basin colfiorito italy we analyze the dispersion characteristics of ambient noise vibrations for this purpose two dimensional 2d seismic array data were acquired in four different sites in the colfiorito plain an alluvial intramountain basin that exhibits strong site effects assuming seismic noise being mainly composed of surface waves we derive one dimensional 1d shallow shear velocity profiles through the inversion of dispersion curves measured by frequency wavenumber f k methods the inverted shear wave velocity profiles are consistent with a priori information for those sites that can be approximated by 1d simple models in these cases the use of passive records of seismic vibrations can be a valuable tool for determining the shallow velocity profile if a detailed depiction of velocity structure is not required the theoretical dispersion curves for rayleigh and love waves were compared with the measured dispersion curves for vertical and horizontal components respectively this allows us to discuss qualitatively the composition of ambient vibrations outlining a large proportion of love waves in the noise wave field and the effects of higher modes we also use the single station method for investigating the origin of the horizontal to vertical h v peak in the plain of colfiorito in terms of ellipticity of the fundamental rayleigh mode

hyporheic exchange with heterogeneous streambeds laboratory experiments and modeling 1 hyporheic exchange is generally analyzed with the assumption of a homogeneous hyporheic zone in reality streambed sediments have a heterogeneous structure and this natural heterogeneity produces spatially variable interfacial fluxes and complex hyporheic exchange patterns to assess the basic effects of sediment structure on hyporheic exchange we performed salt and dye injection experiments in a recirculating laboratory flume with two heterogeneous sediment beds characterized by negative exponential correlated random hydraulic conductivity fields dye injections showed that the hyporheic flow structure was controlled by the spatial relationship of bed forms to high and low permeability regions of the streambed as no existing model could represent these effects we developed a new finite element model to calculate the pore water flow field resulting from the interaction of the bed form induced boundary head distribution and the heterogeneous sediment structure a numerical particle tracking approach was then used to assess the resulting hyporheic exchange the combined flow transport model did an excellent job of predicting the complex hyporheic flow pathways in the heterogeneous bed and the net hyporheic exchange up to t 30 hours the heterogeneous hydraulic conductivity field caused both greater spatial variability in the water flux through the bed surface and a greater average interfacial flux than would have occurred with a homogeneous bed the layered correlation structure of the streambed produced an effective anisotropy that favored longitudinal pore water flow and caused a relatively rapid decrease of the mean pore water velocity with depth as a result solute penetration into the bed was confined to a more shallow region than would have occurred with a homogeneous bed the combination of faster near surface transport and shallower solute penetration produced a shorter mean hyporheic residence time on the basis of the combination of experimental results and model simulations we conclude that the structural heterogeneity of streambed sediments produces more spatially limited hyporheic exchange that occurs with greater spatial variability and at a higher overall rate

ground motion in the presence of complex topography earthquake and ambient noise sources to study the influence of topography on ground motion eight seismic recorders were deployed for a period of one year over poverty ridge on the east side of the san francisco bay area california this location is desirable because of its proximity to local earthquake sources and the significant topographic relief of the array 439 m topographic amplification is evaluated as a function offrequency using a variety of methods including reference site based spectral ratios and single station horizontal to vertical spectral ratios using both shear waves from earthquakes and ambient noise field observations are compared with the predicted ground motion from an accurate digital model of the topography and a 3d local velocity model amplification factors from the theoretical calculations are consistent with observa tions the fundamental resonance of the ridge is prominently observed in the spectra of data and synthetics however higher frequency peaks are also seen primarily for sources in line with the major axis of the ridge perhaps indicating higher resonant modes excitations of lateral ribs off of the main ridge are also seen at frequencies consistent with their dimensions the favored directions of resonance are shown to be transverse to the major axes of the topographic features

one dimensional random patchy saturation model for velocity and attenuation in porous rocks porous rocks encountered in hydrocarbon reservoirs are often saturated with a mixture of two or more fluids generation of synthetic seismograms as well as interpretation of in situ attenuation measurements require a theoretical understanding of the relation between the heterogeneous distribution of fluid patches and the acoustic properties of rocks thus the problem of calculating acoustic properties of rocks saturated with a mixture of two fluids has attracted considerable interest white 1975 murphy 1982 gist 1994 mavko and mukerji 1998 pride et al 2004 at the same time this problem is also interesting from the theoretical point of view because partially saturated rocks represent a particularly interesting situation when the effects of dynamic poroelasticity may be significant at seismic or sonic frequencies indeed it is a radical departure from the situation with a porous material fully saturated with a single fluid such a fully saturated material exhibits frequency dependent effects only at frequencies comparable with biot9s characteristic frequency bourbie et al 1987 c f where f is the fluid density is fluid viscosity is permeability and is porosity for frequencies much lower than c the dynamic effects can be ignored and gassmann theory applies

dynamic poroelasticity a unified model with the squirt and the biot mechanisms the velocities and attenuation of seismic and acoustic waves in rocks with fluids are affected by the two most important modes of fluid solid interaction 1 the biot mechanism where the fluid is forced to participate in the solid s motion by viscous friction and inertial coupling and 2 the squirt flow mechanism where the fluid is squeezed out of thin pores deformed by a passing wave traditionally both modes have been modeled separately with the biot mechanism treated in a macroscopic framework and the squirt flow examined at the individual pore level we offer a model which treats both mechanisms as coupled processes and relates p velocity and attenuation to macroscopic parameters the biot poroelastic constants porosity permeability fluid com pressibility and viscosity and a newly introduced microscale parameter a characteristic squirt flow length the latter is referred to as a fundamental rock property that can be determined experimentally we show that the squirt flow mechanism dominates the biot mechanism and is responsible for measured large velocity dispersion and attenuation values the model directly relates p velocity and attenuation to measurable rock and fluid properties therefore it allows one to realistically interpret velocity dispersion and or attenuation in terms of fluid properties changes e g viscosity during thermal enhanced oil recovery eor or to link seismic measurements to reservoir properties as an example of the latter transformation we relate permeability to attenuation and achieve good qualitative correlation with experimental data

squirt flow in fully saturated rocks we estimate velocity frequency dispersion and attenuation in fully saturated rocks by employing the squirt flow mechanism of solid fluid interaction in this model pore fluid is squeezed from thin soft cracks into the surrounding large pores information about the compliance of these soft cracks at low confining pressures is extracted from high pressure velocity data the frequency dependence of squirt induced pressure in the soft cracks is linked with the porosity and permeability of the soft pore space and the characteristic squirt flow length these unknown parameters are combined into one expression that is assumed to be a fundamental rock property that does not depend on frequency the appropriate value of this expression for a given rock can be found by matching our theoretical predictions with the experimental measurements of attenuation or velocity the low frequency velocity limits as given by our model are identical to those predicted by gassmann s formula the high frequency limits may sign

s wave velocity profiling by joint inversion of microtremor dispersion curve and horizontal to vertical h v spectrum a joint inverse analysis using both microtremor dispersion curve and horizontal to vertical h v spectrum is proposed for estimating the s wave velocity vs profiles of subsurface soils in the inversion both microtremor dispersion and h v data are assumed to be the rayleigh wave dispersion curve and the surface both rayleigh and love wave h v spectrum that have been theoretically derived by taking into account the effects of their fundamental and higher modes the proposed joint inversion as well as the conventional one using dispersion data alone is per formed at four sites where shallow vs profiles down to engineering bedrock are available the vs profiles estimated by the proposed joint inversion are more con sistent with available down hole velocity logs than those by the conventional method in particular the proposed inversion shows significant improvement in estimating bedrock vs structures compared to the conventional inversion sensitivity analyses indicate that the surface wave h v ratio is sensitive to the bedrock vs structure more than the rayleigh wave phase velocity confirming that the proposed joint inversion including h v spectrum is promising

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

application of acoustic noise and self potential localization techniques to a buried hydrothermal vent waimangu old geyser site new zealand a seismo acoustic and self potential survey has been performed in the hydrothermal area of the old waimangu geyser new zealand which was violently erupting a century ago nowadays no surface activity is visible there we set up an array of 16 geophones and recorded a high and steady acoustic ambient noise we applied the matched field processing mfp approach to the acoustic data to locate the sources responsible for the ambient noise the white noise constraint processor reveals the presence of a unique and well focused acoustic source at a depth of 1 5 m below the seismic array for this very shallow source the application of mfp enabled the determination of both the source location and the dispersion curve of seismic velocity the study was completed by self potential sp measurements on several profiles around the acoustic noise source which displayed a large positive anomaly above it the results of the sp inversion gave an electric streaming current density source very close to the acoustic one both sources likely belong to a shallow hydrothermal structure interpreted as a small convective cell of boiling water beneath an impermeable layer the joint application of these methods is a promising technique to recognize hydrothermal structures and to study their dynamics

shear wave velocity structure of the izmit bay area turkey estimated from active passive array surface wave and single station microtremor methods summary to provide quantitative information on the shear wave velocity structure of the izmit bay area we conduct active passive array surface wave and single station microtremor measurements at 60 sites we process these array measurements to produce combined rayleigh wave dispersion curves that span a broad frequency range 0 5 20 hz we also make use of horizontal to vertical spectral ratio hvsr curves obtained from the single station microtremor measurements to benefit from their close relation to the ellipticity of rayleigh waves using the dispersion curve sensitivity to the absolute velocities and the shape of the hvsr curve sensitivity to the velocity contrasts of the velocity depth model we have applied a combined inversion technique to derive better constrained shear velocity models at each site the derived shear velocity models are used to provide a vs30 site classification map and information on the sediment bedrock structure for the izmit bay area the vs30 map shows that the entire shoreline regions including artificial infill areas of the izmit bay have vs30 values less than 200 m s 1 locally as low as 80 m s 1 the older sediment areas of the izmit basin have vs30 values ranging between 250 and 350 m s 1 the highest vs30 values are associated with rock sites reaching about 950 1300 m s 1 we also present a high correlation between the vs30 values and the phase velocity of rayleigh wave corresponding to the 40 m wavelength c40 the important implication of this correlation is that vs30 may be estimated from c40 without inverting the dispersion curve the inferred sediment bedrock interface along a cross section shows an antisymmetric v shaped basin with a sedimentary cover thickness reaching about 1200 m at the deepest part of the izmit basin this deepest part coincides in the map view where the north anatolian fault zone crosses the basin in the east west direction the sedimentary cover thickness is found to be 750 m in the golcuk derince basin

combined role of advective pumping and mechanical dispersion on time scales of bed form induced hyporheic exchange this study analyzes the effect of advective pumping and pore scale dispersion on bed form induced hyporheic exchange advection and dispersion play a competitive role in the exchange dynamics betwe