the influence of fluid type on elastic wave velocity and attenuation in volcanic rocks abstract volcano seismic signatures are the convolution of source and path effects the source signature provides important information about the dynamic rock deformation and fluid resonance processes within the volcano but path effects are the result of the volcanic plumbing the edifice physical conditions and the complex geological structure complicating the inversion of seismic data further is the influence of fluid properties here we use ultrasonic experiments to understand the effect of variable fluid viscosity and bulk modulus on p wave attenuation and velocity for volcanic rocks from white island volcano whakaari new zealand our experimental conditions for high porosity ash tuff and low porosity lava resemble shallow and deep volcano facies respectively p wave velocity vp and quality factor qp increase with the viscosity and bulk modulus of the saturating fluid and decrease with porosity and fracture volume tuffs are highly sensitive to saturating fluid with variations in vp of up to 67 and qp of 383 vp and qp in fractured lavas are slightly less sensitive to fluids 24 and 296 respectively but vp can be used to identify lithology for these tuff vs lavas comparison of the experimental data with rock physics models suggests that squirt flow is the dominant attenuation mechanism for viscosities greater than that of water while scattering losses may be important in gas saturated rocks our results have significant implications for the interpretation of seismic tomography studies and for volcano hazard monitoring based on the characteristics of detected seismicity

quantifying damage saturation and anisotropy in cracked rocks by inverting elastic wave velocities crack damage results in a decrease of elastic wave velocities and in the development of anisotropy using non interactive crack effective medium theory as a fundamental tool we calculate dry and wet elastic properties of cracked rocks in terms of a crack density tensor average crack aspect ratio and mean crack fabric orientation from the solid grains and fluid elastic properties using this same tool we show that both the anisotropy and shear wave splitting of elastic waves can be derived two simple crack distributions are considered for which the predicted anisotropy depends strongly on the saturation reaching up to 60 in the dry case comparison with experimental data on two granites a basalt and a marble shows that the range of validity of the non interactive effective medium theory model extends to a total crack density of approximately 0 5 considering symmetries up to orthorhombic in the isotropic case kachanov s 1994 non interactive effective medium model was used in order to invert elastic wave velocities and infer both crack density and aspect ratio evolutions inversions are stable and give coherent results in terms of crack density and aperture evolution crack density variations can be interpreted in terms of crack growth and or changes of the crack surface contact areas as cracks are being closed or opened respectively more importantly the recovered evolution of aspect ratio shows an exponentially decreasing aspect ratio and therefore aperture with pressure which has broader geophysical implications in particular on fluid flow the recovered evolution of aspect ratio is also consistent with current mechanical theories of crack closure in the anisotropic cases both transverse isotropic and orthorhombic symmetries were considered anisotropy and saturation patterns were well reproduced by the modelling and mean crack fabric orientations we recovered are consistent with in situ geophysical imaging

combination of precise leveling and insar data to constrain source parameters of the mw 6 5 26 december 2003 bam earthquake we used new precise leveling data acquired 40 days after the bam earthquake in combination with radar interferometry observations from both ascending and descending orbits to investigate static deformation associated with the 2003 bam earthquake we invert this geodetic data set to gain insight into the fault geometry and slip distribution of the rupture the best fitting dislocation model is a steeply east dipping right lateral strike slip fault that has a size of 11 by 8 km and strikes n2 w we find that such smooth geometry fits available geodetic data better than previously proposed models for this earthquake our distributed slip model indicates a maximum strike slip of 3 m occurring about 3 to 5 km deep the slip magnitude and depth of faulting taper to the north where the fault approaches the bam city inclusion of crustal layering increases the amount of maximum slip inferred at depth by about 4

seismic attenuation and velocity dispersion in fractured rocks the role played by fracture contact areas the presence of fractures in fluid saturated porous rocks is usually associated with strong seismic p wave attenuation and velocity dispersion this energy dissipation can be caused by oscillatory wave induced fluid pressure diffusion between the fractures and the host rock an intrinsic attenuation mechanism generally referred to as wave induced fluid flow geological observations suggest that fracture surfaces are highly irregular at the millimetre and sub millimetre scale which finds its expression in geometrical and mechanical complexities of the contact area between the fracture faces it is well known that contact areas strongly affect the overall mechanical fracture properties however existing models for seismic attenuation and velocity dispersion in fractured rocks neglect this complexity in this work we explore the effects of fracture contact areas on seismic p wave attenuation and velocity dispersion using oscillatory relaxation simulations based on quasi static poroelastic equations we verify that the geometrical and mechanical details of fracture contact areas have a strong impact on seismic signatures in addition our numerical approach allows us to quantify the vertical solid displacement jump across fractures the key quantity in the linear slip theory we find that the displacement jump is strongly affected by the geometrical details of the fracture contact area and due to the oscillatory fluid pressure diffusion process is complex valued and frequency dependent by using laboratory measurements of stress induced changes in the fracture contact area we relate seismic attenuation and dispersion to the effective stress the corresponding results do indeed indicate that seismic attenuation and phase velocity may constitute useful attributes to constrain the effective stress alternatively knowledge of the effective stress may help to identify the regions in which wave induced fluid flow is expected to be the dominant attenuation mechanism

gassmann s fluid substitution and shear modulus variability in carbonates at laboratory seismic and ultrasonic frequencies carbonates have become important targets for rock property research in recent years because they represent many of themajoroilandgasreservoirsintheworld someareundergoing enhanced oil recovery most laboratory studies to understand fluid and pressure effects on reservoir rocks have been performed on sandstones but applying relations developed for sandstones to carbonates is problematic at best we measure in the laboratory nine carbonate samples from the same reservoir at seismic 3 3000 hz and ultrasonic 0 8 mhz frequencies samples are measured dry humidified and saturated with liquid butane and brine our carbonate samples showed typical changes in moduli as a function of porosity andfluid saturation however we explore the applicability of gassmann s theory on limestone and dolomite rocks in the context of shear and bulk modulus dispersion andgassmann stheoryassumptions forourcarbonatesetat high differential pressures and seismic frequencies the bulk modulus of rocks with high aspect ratio pores and dolomite mineralogy is predicted by gassmann s relation we also explore in detail some of the assumptions of gassmann s relation especiallyrock framesensitivitytofluidsaturation our carbonate samples show rock shear modulus change from dry to brine saturation conditions and we investigate several rock fluid mechanisms responsible for this change to our knowledge these are the first controlled laboratory experimentsoncarbonatesintheseismicfrequencyrange

deep downward fluid percolation driven by localized crust dilatation in iceland from a detailed seismic survey on a transform like plate setting in iceland we propose a spatial relationship between highly deformed crustal columns and areas of low vp vs ratio which are best explained by high fluid pressures at the base of the seismogenic crust combined with geological observations our seismic data suggest transient and local increases in crust permeability at specific highly dilating areas triggered by dynamical stresses from high magnitude regional earthquakes fluids are then trapped at supercritical conditions in the deep brittle crust which in turn increases the capacity of the rocks to deform through cracking and faulting

micromechanics of brittle faulting and cataclastic flow in mount etna basalt understanding how the strength of volcanic rocks varies with stress state pressure and microstructural attributes is fundamental to understanding the dynamics and tectonics of a volcanic system and also very important in applications such as geothermics or reservoir management in volcanic environments in this study we investigated the micromechanics of deformation and failure in basalt focusing on samples from mount etna we performed 65 uniaxial and triaxial compression experiments on nominally dry and water saturated samples covering a porosity range between 5 and 16 at effective pressures up to 200 mpa dilatancy and brittle faulting were observed in all samples with porosity of 5 water saturated samples were found to be significantly weaker than comparable dry samples shear enhanced compaction was observed at effective pressures as low as 80 mpa in samples of 8 porosity microstructural data revealed the complex interplay of microcracks pores and phenocrysts on dilatant failure and inelastic compaction in basalt the micromechanics of brittle failure is controlled by wing crack propagation under triaxial compression and by pore emanated cracking under uniaxial compression especially in the more porous samples the mechanism of inelastic compaction in basalt is cataclastic pore collapse in agreement with a recent dual porosity model

elastic wave velocities and permeability of cracked rocks abstract cracks play a major role in most rocks submitted to crustal conditions mechanically cracks make the rock much more compliant they also make it much easier for fluid to flow through any rock body relying on fracture mechanics and statistical physics we introduce a few key concepts which allow to understand and quantify how cracks do modify both the elastic and transport properties of rocks the main different schemes which can be used to derive the elastic effective moduli of a rock are presented it is shown from experimental results that an excellent approximation is the so called non interactive scheme the main consequences of the existence of cracks on the elastic waves is the development of elastic anisotropy due to the anisotropic distribution of crack orientations and the dispersion effect due to microscopic local fluid flow at a larger scale macroscopic fluid flow takes place through the crack network above the percolation threshold two macroscopic fluid flow regimes can be distinguished the percolative regime close to the percolation threshold and the connected regime well above it experimental data on very different rock types show both of these behaviors

a composite analysis of winter season overrunning precipitation bands over the southern plains of the united states abstract this investigation presents an extensive analysis of precipitation bands associated with winter season over running events in the southern plains of the united states the primary motivation is an investigation of the relevance of conditional symmetric instability csi theory to overrunning precipitation events this is accomplished by means of a statistical composite study of events of differing degrees of bandedness using synoptic sounding and national weather service radar data the composite study shows that it is difficult to distinguish between the environments of banded and nonbanded cases on the basis of individually examined shear and buoyancy parameters some statistically significant differences do occur when shear and buoyancy effects are combined in an evaluation of csi with more strongly banded events showing greater instability

effects of fluid shear resistance and squirt flow on velocity dispersion in rocks abstractlaboratory measurements of rocks saturated with high viscosity fluids such as heavy oil bitumen magma kerogen etc often exhibit considerable seismic velocity dispersion which is usually underestimated by the biot theory over the years grain scale dispersion mechanisms such as squirt local flow and shear relaxation nonzero shear stress in the pore fluid have been more successful in explaining the measured dispersion we developed a new method to quantify the combined high frequency effects of squirt and shear dispersion on the effective moduli of rocks saturated with viscous fluids viscous fluid at high frequencies was idealized as an elastic solid of finite shear modulus hydraulically locked in stiff and soft pores this method entailed performing solid substitution in stiff pores of a dry rock frame which itself was unrelaxed due to solid filled soft pores the unrelaxed frame stiffness solutions required information on the pressure dependency of the rock stiffness and porosity

ultrasonic velocities acoustic emission characteristics and crack damage of basalt and granite acoustic emissions ae compressional p shear s wave velocities and volumetric strain of etna basalt and aue granite were measured simultaneously during triaxial compression tests deformation induced ae activity and velocity changes were monitored using twelve p wave sensors and eight orthogonally polarized s wave piezoelectric sensors volumetric strain was measured using two pairs of orthogonal strain gages glued directly to the rock surface p wave velocity in basalt is about 3 km s at atmospheric pressure but increases by 50 when the hydrostatic pressure is increased to 120 mpa in granite samples initial p wave velocity is 5 km s and increases with pressure by 20 the pressure induced changes of elastic wave speed indicate dominantly compliant low aspect ratio pores in both materials in addition etna basalt also contains high aspect ratio voids in triaxial loading stress induced anisotropy of p wave velocities was significantly higher for basalt than for granite with vertical velocity components being faster than horizontal velocities however with increasing axial load horizontal velocities show a small increase for basalt but a significant decrease for granite using first motion polarity we determined ae source types generated during triaxial loading of the samples with increasing differential stress ae activity in granite and basalt increased with a significant contribution of tensile events close to failure the relative contribution of tensile events and horizontal wave velocities decreased significantly a concomitant increase of double couple events indicating shear suggests shear cracks linking previously formed tensile cracks

an overview of laboratory apparatuses to measure seismic attenuation in reservoir rocks intrinsic wave attenuation at seismic frequencies is strongly dependent on rock permeability fluid properties and saturation however in order to use attenuation as an attribute to extract information on rock fluid properties from seismic data experimental studies on attenuation are necessary for a better understanding of physical mechanisms that are dominant at those frequencies an appropriate laboratory methodology to measure attenuation at seismic frequencies is the forced oscillation method but technical challenges kept this technique from being widely used there is a need for the standardization of devices employing this method and a comparison of existing setups is a step towards it here we summarize the apparatuses based on the forced oscillation method that were built in the last 30 years and were used to measure frequency dependent attenuation in fluid saturated and or dry reservoir rocks under small strains 10 8 10 5 we list and discuss important technical aspects to be taken into account when working with these devices or in the course of designing a new one we also present a summary of the attenuation measurements in reservoir rock samples performed with these apparatuses so far

a simple hydromechanical approach for simulating squirt type flow abstractthe deformations caused by an acoustic wavefield in subsurface rock can induce fluid flow within hydraulically interconnected mesoscopic fractures from one fracture into the other the viscous friction associated with this squirt type fluid flow parallel to the fracture walls results in energy dissipation and velocity dispersion we have developed a quasi static hydromechanical approach that is suitable for simulating squirt type flow in the mesoscopic scale range and microscopic squirt flow our approach couples navier stokes equation with hooke s law to describe the laminar flow of a viscous compressible fluid in conduits embedded in an elastic solid background results from the proposed method were compared with those obtained with biot s equations for a model containing interconnected mesoscopic fractures embedded in a background of very low porosity and permeability despite significant differences in the flow and dissipation spatial patterns we have observed an essentially perfect agreemen

monitoring fluid substitution in rock samples from noise correlation an alternative laboratory technique to measure the elastic constants of solid samples based on the analysis of the cross correlation spectra of the vibratory response of randomly excited short solid cylinders has been recently proposed the aim of this paper is to check the ability of the technique called passive ultrasonic interferometry to monitor fluid substitution in different rock samples velocity variations due to fluid substitution are easily measured if the wave attenuation in the fluid saturated rock is not too large typically in rocks with few cracks or microfractures the experimental results are in agreement with the predictions of biot gassmann poroelastic theory the effect of substituting water with a stiffer saturating fluid such as ethylene glycol is to increase the overall bulk modulus of the rock without any substantial effect on shear modulus furthermore the experimental results compare well with those obtained independently with conventional pulse transmission technique using ultrasonic transducers however the measured pulse transmission bulk moduli are slightly larger than the corresponding measured ultrasonic interferometry moduli with the deviation increasing with increasing fluid viscosity this can be explained by dispersion due to wave induced flow of the viscous fluid since pulsetransmission experiments involve higher frequencies than ultrasonic interferometry experiments

characteristics of anisotropy and dispersion in cracked medium abstract in upper crustal conditions where effective pressure is not high enough to close them all rocks contain cracks understanding the effect of cracks on both the elastic anisotropy and the elastic waves frequency dependence dispersion is of major interest to underground storage monitoring reservoir monitoring and fault mechanics the challenge is to extract from geophysical data the maximum information with a minimal number of assumptions and model parameters this is possible if reference data exist at the laboratory scale and if extrapolation from laboratory to field scale is not biased in order to check that investigating few basic idealized cases can provide useful guidelines let us consider an isotropic rock matrix and assume that dispersion is the result of squirt flow in this paper we will not consider crack to pore but rather focus on crack to crack squirt flow three basic cracks configurations are quantitatively investigated for which the elastic symmetry is transverse isotropy ti our aim is to check if from first principles high frequency laboratory data can be used for field data interpretation in these three cases the first case is that of identical cracks aligned in the same direction a sufficiently strong deviatoric stress field in a given plane is expected to induce such a distribution at the field scale 1 2 3 we show that it results in a maximum anisotropy but with virtually no dispersion because there is no dispersion high frequency data obtained in the laboratory mhz ultrasonic range are directly applicable to field data hz to khz range interpretation thomsen parameters provide then a direct proxy for crack density a second case is that of identical cracks with random orientations isotropic distribution such a situation could exist at the field scale if cracks result from the superposition of several independent tectonic episodes associated with different directions of principal stresses in that case 1 2 3 this configuration could also result from thermal cracking in an initially isotropic metamorphic rock obviously there is no overall anisotropy then but we show that dispersion may be large due to dispersion ultrasonic laboratory data are not directly applicable to field data interpretation unless the medium is dry a third intermediate case is that of cracks randomly distributed in zone with a given axis the corresponding symmetry is that of a so called axi symmetric triaxial test which in fact is biaxial it is of interest because it represents a classical laboratory experiment situation it can also exist at the field scale if one principal stress is much larger than both others 1 2

frequency and fluid effects on elastic properties of basalt experimental investigations 1 in order to investigate the effects of fluid and frequency on the elastic properties we performed hydrostatic experiments on an icelandic basalt specimen under both dry and saturated conditions this basalt is characterized by a bimodal porosity i e cracks and equant pores the elastic properties bulk moduli in our case were investigated under high pressure through two experimental methods 1 a classical one using ultrasonic p and s waves velocities frequency 106 hz 2 and a new one using oscillation tests frequency 10 2 hz in dry condition experimental data show no significant difference between high hf and low lf frequency bulk moduli however in saturated conditions two effects are highlighted a physico chemical effect emphasized by a difference between drained and dry moduli and a squirt flow effect evidenced by a difference between hf and lf undrained moduli

elastic laboratory measurements and modeling of saturated basalts 1 understanding the elastic behavior of basalt is important to seismically monitor volcanoes subsea basalts and carbon sequestration in basalt we estimate the elastic properties of basalt samples from the snake river plain idaho at ultrasonic 0 8 mhz and seismic 2 300 hz frequencies to test the sensitivity of seismic waves to the fluid content in the pore structure measurements are performed at three saturation conditions saturated with liquid co2 water and dry when co2 replaces water the p wave velocity drops on average by 10 vesicles and cracks observed in the rock microstructure control the relaxation of pore fluid pressures in the rock as a wave propagates the bulk and shear moduli of basalts saturated with liquid co2 are not frequency dependent suggesting that fluid pore pressures are in equilibrium between 2 hz and 0 8 mhz however when samples are water saturated the bulk modulus of the rock is frequency dependent modeling with gassmann s equations predicts the measured saturated rock bulk modulus for all fluids for frequencies below 20 hz but underpredicts the water saturated basalt bulk modulus for frequencies greater than 20 hz the most likely reason is that the pore fluid pressures are unrelaxed instead the ultrasonic frequency rock moduli are modeled with high frequency elastic theories of squirt flow and kuster toksoz kt although kt s model is based on idealized pore shapes a combination of spheres vesicles and penny shaped cracks fractures interpreted and quantified from petrographical data predicts the ultrasonic dry and saturated rock moduli for the measured basalts

p wave velocity and anisotropy of lawsonite and epidote blueschists constraints on water transportation along subducting oceanic crust p wave velocity vp and the anisotropy of lawsonite and epidote blueschists were measured up to 1 0 gpa and 400 c using the ultrasonic pulse transmission technique the slowest vp in the direction normal to foliation is similar between lawsonite and epidote blueschists 7 0 7 2 km s at 1 0 gpa and room temperature while the fastest vp in the direction parallel to lineation markedly differs between lawsonite blueschists 7 4 7 6 km s at 1 0 gpa and room temperature and epidote blueschist 7 9 km s at 1 0 gpa and room temperature crystallographic orientation measurements for main constituent min erals revealed that both epidote 0 1 0 axes fastest vp direction in epidote single crystal and amphibole 0 0 1 axes fastest vp direction in amphibole single crystal are preferentially oriented parallel to lin eation to enhance vp anisotropy of the epidote blueschist in contrast lawsonite 0 0 1 axes fastest vp direction in lawsonite single crystal are oriented subnormal to foliation whereas amphibole 0 0 1 axes are oriented subparallel to lineation so that relatively weak vp anisotropy was observed in the lawsonite blueschist our experimental results in conjunction with recent seismological observations suggest that the vp of the subducting oceanic crust at 50 km has been observed in several subducting slabs however the high vp values at 50 km depth are difficult to be explained by blueschists this indicates that the blueschist would be at least partially transformed to hydrous mineral bearing eclogite at 50 km depth in subducting oceanic crusts

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

stress associated intrinsic and scattering attenuation from laboratory ultrasonic measurements on shales seismic attenuation is sensitive to stress induced subtle changes in the physical state of rocks in this study the stress and frequency associated attenuation is quantified through ultrasonic measurements on three differently oriented cylindrical shale samples under various axial stresses as an improvement to the single scattering model the elastic monte carlo method is employed to investigate multiple scattering attenuations by incorporating the boundary reflections and wave conversions our results show that as the axial stress increases the intrinsic attenuation decreases in all directions while the scattering attenuation decreases slightly in the direction perpendicular to the bedding but increases largely and nonlinearly in other directions these discrepancies result from different attenuation mechanisms both the intrinsic and scattering attenuation are found to be largest in the direction 45 to the bedding but least in the perpendicular direction the s wave attenuation is larger and more sensitive to stress changes than p wave attenuation due to its shorter wavelength as expected from sandstone examples the scattering attenuation in shales is significantly larger and more sensitive to stress changes than the intrinsic attenuation the frequency dependence of scattering attenuation suggests that the peak frequency with the maximum scattering attenuation is independent of axial stresses but varies in different directions of an individual rock with different heterogeneity and anisotropy scales the peak frequency of s coda is smaller and its peak scattering attenuation is larger than p coda in conclusion the stress and frequency dependence of ultrasonic attenuations in shales differ largely in various directions indicating significant anisotropy and heterogeneity

dispersion and anisotropy of elastic waves in cracked rocks 1 rocks in the earth s crust contain variable amount of cracks depending on the deviatoric and confining stress levels pore pressure and temperature conditions crack damage results in effects that have been investigated for a long time in particular a decrease in elastic wave velocity and the development of anisotropy in this paper we focus on cracked rocks and develop a method to calculate both the elastic wave anisotropy and the dispersion in a fluid saturated cracked rock we show that analytic expressions can be derived for both properties in terms of the crack density tensor components two fundamental theoretical tools are used in this purpose the first one is the effective medium theory and the second one is the anisotropic poroelastic theory using both it is possible from first principles to predict anisotropy and dispersion results are shown to be valid up to a total crack density of 0 5 the failure threshold appears close to a total crack density of 1 between 0 5 and 1 the model still gives reasonably good results anisotropy can increase up to 60 and dispersion up to 30 depending on the crack distribution these results point out important differences that could exist in fluid saturated rocks between laboratory high frequency data and field low frequency results

geomorphic effectiveness of check dams in a debris flow catchment using multi temporal topographic surveys abstract torrent control works such as grade control dams and sediment retention dams are structural measures for controlling debris flows and debris floods in spite of the widespread presence of such hydraulic structures in steep mountain streams worldwide there are still few studies monitoring the effects of check dams on sediment dynamics the use of repeated topographic surveys allows us to characterize debris flow activity at multiple temporal and spatial scales and its interaction with torrent control works structure from motion sfm technique paired with multi view stereo mvs algorithms represents a low cost opportunity to conduct such multi temporal surveys this enables us to better study the effects of individual debris flows track geomorphic changes and evaluate the effectiveness of torrent control works e g check dams the effect of check dams on sediment dynamics is investigated by means of multi temporal topographic surveys before and after debris flow events in the moscardo torrent eastern italian alps where two check dams have recently been built multi temporal sfm based on images taken from the ground in combination with imagery taken by an unmanned aerial vehicle uav is used to obtain dems and to study topographic changes through the comparison of repeat dems dem of difference i e dod the results show that the new check dams considerably modified sediment dynamics in the studied channel but their performance cannot be considered satisfactory the sediment flowed around the upstream check dam on the right wing while deep erosion observed downstream of the check dam threatened to undermine the foundation s stability moreover debris flow lobes deposited upstream of the check dams could act as sources of sediment further increasing downstream debris flow volume the analysis proposed in this work could help improve design strategies and permitting the identification of a proper site for check dam building

fluid mobility and frequency dependent seismic velocity direct measurements the influence of fluid mobility on seismic velocity dispersion is directly observed in laboratory measurements from seismic to ultrasonic frequencies a forceddeformation system is used in conjunction with pulse transmission to obtain elastic properties at seismic strain amplitude 10 7 from 5 hz to 800 khz varying fluid types and saturations document the influence of pore fluids the ratio of rock permeability to fluid viscosity defines mobility which largely controls pore fluid motion and pore pressure in a porous medium high fluid mobility permits pore pressure equilibrium either between pores or between heterogeneous regions resulting in a low frequency domain where gassmann s equations are valid in contrast low fluid mobility can produce strong dispersion even within the seismic band here the low frequency assumption fails since most rocks in the general sedimentary section have very low permeability and fluid mobility shales siltstones tight limestones etc most rocks are not in the lowfrequency domain even at seismic frequencies only those rocks with high permeability porous sands and carbonates will remain in the low frequency domain in the seismic or sonic band

frequency dependent seismic attenuation in shales experimental results and theoretical analysis claudio delle piane 1 joel sarout 1 claudio madonna 2 erik h saenger 2 david n dewhurst1 and mark raven3 1csiro earth science and resource engineering australian resources research centre 26 dick perry avenue kensington wa 6151 australia e mail claudio dellepiane csiro au 2geological department eth sonneggstrasse 5 ch 8092 zurich switzerland 3csiro land and water waite rd urrbrae sa 5064 australia

how cracks modify permeability and introduce velocity dispersion examples of glass and basalt the porosity of igneous rocks is usually very small although for some basalts it can be nonnegligible due to gas exsolution in the case of glass it is vanishingly small why is it of any interest to look at this kind of material from the point of view of rock physics two series of reasons indeed motivate such investigations

wave velocities in hydrocarbon saturated rocks experimental results this paper contains laboratory measurements of the temperature dependence of velocities determined by ultrasonic pulse transmission methods in hydrocarbon liquids and rock samples saturated by the liquids the samples discussed include 26 hydrocarbons of varying molecular weight nine mixtures of these hydrocarbons four heavy oils tar three saturated sandstones and a saturated sand the data provide encouragement that high frequency high resolution seismic techniques may infer formation temperature changes thereby detecting the progress of thermal enhanced oil recovery processes

modelling the drained undrained transition effect of the measuring method and the boundary conditions abstract the dependence of fluid saturated rocks elastic properties to the measuring frequency is related to fluid flow phenomena at different scales in the frequency range of 10 3 106 hz for fully saturated rocks two phenomena have been experimentally documented i the drained undrained transition i e global flow and ii the relaxed unrelaxed transition i e local flow when investigating experimentally those effects or comparing different measurements in rocks one needs to account for both the boundary conditions involved and the method of measurement used a one dimensional poroelastic model is presented which aims at calculating the expected poroelastic response during an experiment the model is used to test different sets of boundary conditions as well as the role of the measuring setup i e local strain gauges or global linear variable differential transformer strain measurement four properties are predicted and compared with the measurements i e bulk modulus bulk attenuation pseudo skempton coefficient and pore pressure phase shift for the drained undrained transition because fluid pressure may not be homogeneous in the sample local and global measurements are predicted to differ furthermore the existence of a dead volume at both sample s ends is shown to be important due to the existence of the dead volume an interplay between sample s and dead volumes storage capacity determines both the magnitudes and the frequency dependence of the dispersion attenuation measurements the predicted behaviours are shown to be consistent with the measurements recently reported on very compressible and porous sandstone samples