experiments on piping in sandy gravels tests on internally unstable sandy gravels show that a significant proportion of the sand content is washed out by piping at hydraulic gradients far lower than the critical gradient given by a classical theory the probable explanation is that a major part of the overburden load is carried on a framework of gravel particles leaving the sand under relatively small pressures by contrast piping of the sand from stable sandy gravels occurs at approximately the full theoretical gradient the tests broadly confirm kenney s criterion for the internal stability of granular materials des essais realises sur des graves sableuses a instabilite interne importante montrent qu une proportion non negligeable du sable est lessivee pour des gradients hydrauliques bien inferieurs au gradient critique donne par les theories classiques l explication la plus probable est que la majeure partie de la surcharge des couches subjacentes est transmise au reseau des particules graveleuses le sable n etant alors plus soumis qu

the isostatic state of mead crater abstract we have analyzed high resolution magellan doppler tracking data over mead crater using both line of sight and spherical harmonic methods and have found a negative gravity anomaly of about 4 5 mgal at spacecraft altitude 182 km this is consistent with no isostatic compensation of the present topography the uncertainty in the analysis allows perhaps as much as 30 compensation at shallow depths 25 km this is similar to observations of large craters on earth which are not generally compensated but contrasts with at least some lunar basins which are inferred to have large moho uplifts and corresponding positive bouguer anomalies an uncompensated load of this size requires a lithosphere with an effective elastic lithosphere thickness greater than 30 km in order for the crust mantle boundary not to have participated in the deformation associated with the collapse of the transient cavity during the creation of the crater the yield strength near the top of the mantle must have been significantly higher on earth and venus than on the moon at the time of basin formation this might be due to increased strength against frictional sliding at the higher confining pressures within the larger planets alternatively the thinner crusts of earth and venus compared to that of the moon may result in higher creep strength of the upper mantle at shallower depths

floor subsidence and rebound of large venus craters the topography and geology of large craters on venus reveal no evidence for floor rebound or relaxation rather the floors have subsided depressions of the floor centers relative to the margins are evident in topography and floor faulting is interpreted as contractional failure of the likely processes responsible only subsolidus thermal contraction applies to craters that both have and have not been infilled by lavas assuming volcanism occurred within a few tens of millions of years after the impact thermal subsidence satisfies the measured floor depressions for reasonable scaling of impact energies and temperature distributions in the lithosphere further the predicted stresses are generally consistent with observed floor fracturing we constrain the impact heat deposited in the lithosphere to be less than roughly 5 1023 j for diameters of 100 km the absence of perceptible floor subsidence at craters this size on the moon and icy satellites is readily explained by the scaling dependence of impact energy not only on transient crater diameter but also on gravity and target density the unfractured melt sheets of three large young bright floored craters imply sufficient lithospheric rigidity to support the crater cavities an elastic flexural rebound model restricts the elastic plate thickness to at least 10 15 km for the three craters corresponding to maximum geotherms of 20 30 k km 1 structural evidence for early rebound in older dark floored craters may have been buried by subsequent volcanism

incipient motion of riverbank sediments with outflow seepage based on a force analysis an expression is derived to describe the critical shields number for incipient motion of uniform cohesionless sediment particles on a riverbank slope in terms of flow parameters outflow seepage and physical and mechanical properties of sediments parametric studies were conducted to investigate quantitatively the effects of hydraulic gradient of seepage slope angle and flow direction on the critical shields number the results show that the critical shields number decreases with an increase in the hydraulic gradient where bank collapse is concerned the most dangerous direction of hydraulic gradient of outflow seepage is at an angle equal to the effective internal angle of friction of the sediment mass with respect to slope surface at a certain value of hydraulic gradient the critical shields number decreases with increasing slope angle open flow becomes more erosive when the current direction changes from horizontally parallel with the riverbank line to turning downward

deep down at chicxulub the best preserved large impact crater on earth is overlain by a kilometre of sediment it is possible to look not only through that wrapping but also beyond at the effects of the impact at the crust mantle boundary

discrimination between pressure and fluid saturation changes from time lapse seismic data explicit expressions for computing saturation and pressure related changes from time lapse seismic data have been derived and tested on a real time lapse seismic data set necessary input is near and far offset stacks for the baseline seismic survey and the repeat survey the method has been tested successfully in a segment where pressure measurements in two wells verify a pore pressure increase of 5 to 6 mpa between the baseline survey and the monitor survey estimated pressure changes using the proposed relationships fit very well with observations between the baseline and monitor seismic surveys 27 of the estimated recoverable hydrocarbon reserves were produced from this segment the estimated saturation changes also agree well with observed changes apart from some areas in the water zone that are mapped as being exposed to saturation changes which is unlikely saturation changes in other segments close to the original oil water contact and the top reservoir interface are also estimated and conf

effect of seepage flow on incipient motion of sand particles in a bed subjected to surface flow abstract understanding the interaction of the groundwater seepage flow and sediment transport along permeable boundaries is essential for managing soil beds and bank erosion a significant bank failure may occur due to sediment transport under the boiling condition in the present study an experiment is conducted to investigate the effects of injection or upward seepage on the critical shear stress of a cohesionless soil bed subjected to surface flow the upward seepage force acting on the soil bed particles may reduce the virtual weight of the particles in turn it may also reduce the critical shear stress acting on the particles a theoretical analysis examines how the upward seepage force acts to modify the critical shear stress for the sediment entrainment due to the increase in the hydraulic gradient of the seepage flow a force analysis reveals that the ratio of the critical shear stress with seepage to that without seepage is dependent on the ratio of the hydraulic gradient of seepage to its value at the quicksand condition a test apparatus was built and the effects of injection on the critical shear stress of cohesionless soil bed particles were measured an acrylic channel with a rectangular cross section was prepared and a section of a cohesionless soil bed subjected to an upward seepage flow was installed at the bottom of the channel the experiment demonstrates that the induced seepage affects the dynamics of the channel flow even though the magnitude of the seepage flow velocity is significantly smaller than that of the free surface water flow the test results show that the dimensionless critical shear stress of the cohesionless soil bed particles decreases slightly as the hydraulic gradient of the seepage flow is increased when critical shear stress is determined at the upstream edge of the seepage zone furthermore the dimensionless critical shear stress decreases sharply with the increment of the hydraulic gradient of the seepage flow when critical shear stress is determined in the seepage zone however it does not decrease in either case as was theoretically assumed even when the hydraulic gradient approaches to the critical hydraulic gradient or the quicksand condition

direct correlation of 4d seismic with well activity for a clarified dynamic reservoir interpretation a method to provide an improved time lapse seismic attribute for dynamic interpretation is presented this is based on the causal link between the time lapse seismic response and well production activity taken over time the resultant image is obtained by computing correlation coefficients between sequences of time lapse seismic changes extracted over different time intervals from multiply repeated seismic and identical time sequences of cumulative fluid volumes produced or injected from the wells maps of these cross correlations show localized spatially contiguous signals surrounding individual wells or a specific well group these may be associated with connected regions around the selected well or well group application firstly to a synthetic data set reveals that hydraulic compartments may be delineated using this method a second application to a field data set provides empirical evidence that a connected well centric fault block and active geobody can be detected it is concluded that uniting well data and time lapse seismic using our proposed method delivers a new attribute for dynamic interpretation and potential updating of the model for the producing reservoir

basement structural architecture and hydrocarbon conduit potential of polygonal faults in the cooper eromanga basin australia abstract a thorough and complete understanding of the structural geology and evolution of the cooper eromanga basin has been hampered by low resolution seismic data that becomes particularly difficult to interpret below the thick permian coal measures as a result researchers are tentative to interpret the basement fault architecture within the basin which is largely undefined to provide a better understanding of the basement fault geometry all available two dimensional seismic lines together with 12 three dimensional seismic surveys were structurally interpreted with assistance from seismic attribute analysis the upper cretaceous cadna owie formation and top permian reflectors were analysed using a common seismic attribute technique incoherency that was used to infer the presence of faults that may have otherwise been overlooked detailed basement fault maps for each seismic survey were constructed and used in conjunction with two dimensional seismic data interpretation to produce a regional basement fault map large north northeast south southwest striking sinistral strike slip faults were identified within the patchawarra trough appearing to splay from the main northeast southwest striking ridge these sinistral north northeast south southwest striking faults together with field scale southeast northwest striking dextral strike slip faults are optimally oriented to have potentially developed as a conjugated fault set under a south southeast north northwest oriented strike slip stress regime geomechanical modelling for a regionally extensive system of cretaceous polygonal faults was performed to calculate the leakage factor and dilation tendency of individual faults faults that extend into lower cretaceous oil rich reservoirs with strikes of between 060 n and 140 n and a high to near vertical dip angle were identified to most likely be acting as conduits for the tertiary migration of hydrocarbons from known lower cretaceous hydrocarbon reservoirs into shallow cretaceous sediments this research provides valuable information on the regional basement fault architecture and a more detailed exploration target for the cooper eromanga basin which were previously not available in literature

modified logarithmic law for velocity distribution subjected to upward seepage a modified logarithmic law is derived to describe the velocity distribution in open channel flow with an upward seepage the derived function agrees well with the experimental measurements conducted in a laboratory flume the roughness function included in the modified logarithmic law is found to be dependent on the boundary reynolds number and the ratio of the seepage velocity to the shear velocity with the integration of the modified logarithmic law the bed shear stress subjected to upward seepage can be computed based on the depth averaged velocity water depth boundary roughness and seepage velocity using this method variations of the bed shear stress over the seepage zone are studied the results show that the bed shear stress decreases rapidly from the leading section of the seepage zone and then increases gradually toward the downstream end of the seepage zone

an automated cross validation method to assess seismic time to depth conversion accuracy a case study on the cooper and eromanga basins australia selecting a seismic time to depth conversion method can be a subjective choice that is made by geophysicists and is particularly difficult if the accuracy of these methods is unknown this study presents an automated statistical approach for assessing seismic time to depth conversion accuracy by integrating the cross validation method with four commonly used seismic time to depth conversion methods to showcase this automated approach we use a regional dataset from the cooper and eromanga basins australia consisting of 13 three dimensional 3d seismic surveys 73 two way time surface grids and 729 wells approximately 10 000 error values predicted depth vs measured well depth and associated variables were calculated the average velocity method was the most accurate overall 7 6 m mean error however the most accurate method and the expected error changed by several metres depending on the combination and value of the most significant variables cluster analysis tested the significance of the associated variables to find that the seismic survey location potentially related to local geology i e sedimentology structural geology cementation pore pressure etc processing workflow or seismic vintage formation potentially associated with reduced signal to noise with increasing depth or the changes in lithology distance to the nearest well control and the spatial location of the predicted well relative to the existing well data envelope had the largest impact on accuracy importantly the effect of these significant variables on accuracy were found to be more important than choosing between the four methods highlighting the importance of better understanding seismic time to depth conversions which can be achieved by applying this automated cross validation method

three dimensional focused seismic imaging for geothermal exploration in crystalline rock near schneeberg germany we present the results of a 3d seismic survey acquired near the city of schneeberg in the western erzgebirge germany the main objective of this survey was to use reflection seismic exploration methods to image a major fault zone in crystalline rock which could serve as a geothermal reservoir at a target depth of about 5 km 6 kmwith expected temperatures between 160 c 180 c for this purpose a high resolution 3d vibroseis survey was performed in late 2012 covering an area of about 10 km 12 km the 3d survey was complemented by a wide angle seismic survey for obtaining velocity information from greater depths using explosives along ten profile lines radially centred at the target area the region itself is dominated by the northwestsoutheast striking gera j achymov fault system and the southwest northeast striking l ossnitz zw onitz syncline the main geological features in the survey area are well known from intensive mining activities down to a depth of about 2 km the seismic investigations aimed at imaging the partly steeply dipping fault branches at greater depths in particular a dominant steeply northeast dipping fault roter kamm in the central part of the survey area in addition to this main structure the gera j achymov fault zone consists of a series of steeply southwest dipping conjugate faults for imaging these structures we used a focusing pre stack depth migration technique where the wavefield coherency at neighbouring receivers is used for weighting the amplitudes during migration this method delivers a clear focused image of the 3d structures within the target area a 3d velocity model for depth imaging was obtained by first arrival tomography of the wide angle survey data with this approach we were able to image several pronounced structures interpreted as faults within the crystalline rock units which partly reach the target depth where the temperatures for a geothermal usage would be sufficient in general the results show a complex three dimensional image of the geological structures with different reflection characteristics which can serve as a basis for a detailed characterization of the potential deep geothermal reservoir

geometry of sand bed channels with seepage literature suggests that apart from a significant percentage of water loss from seepage downward seepage from the channel causes an increase in the mobility of channel bed materials and thus changes the channel stability consequently regime conditions which provide the relationship among hydraulic parameters should also be revised by incorporating downward seepage as an additional parameter in the present work regime conditions for the prediction of channel geometry in alluvial channels affected by downward seepage have been formulated on the basis of experimental observations c 2011 elsevier b v all rights reserved

on the origin of mascon basins on the moon and beyond 1 mascon basins on the moon are large craters that display significant positive free air and bouguer gravity anomalies an important question is why is not every large crater a mascon as less than half have been previously determined to be we detrend the free air topographic and bouguer gravity anomalies and find that most large basins 28 of 41 display mascon characteristics e g strong positive bouguer anomalies narrower than the surface rims negative free air gravity annuli surrounding the central highs generally are absent in the bouguer gravity implicating surface topography we propose that beneath a forming large basin the relatively narrow transient crater drives mantle uplift while upward and inward collapse forms the surface topography furthermore the nonmascon basins are all ancient and heavily degraded indicating a postimpact evolutionary process our results suggest that mascon formation is the standard for large impacts on the moon and by extension on other terrestrial planets

structural evolution of horst and half graben structures proximal to a transtensional fault system determined using 3d seismic data from the shipwreck trough offshore otway basin australia abstract using a three dimensional 3d seismic reflection dataset from the shipwreck trough offshore otway basin southern australia we aim to characterise and understand the structural evolution of the shipwreck fault zone sfz and associated extensional structures the sfz is a key structural element of the otway basin which is a nw striking upper jurassic cenozoic rift to passive margin basin that formed due to the breakup of australia and antarctica the sfz marks the transition from the major southern margin rift system to the west and the oceanic continental transform margin to the se the sfz formed and bounds the shipwreck trough on the eastern side and is interpreted as a n s striking transtensional fault zone representing the northern en echelon extension of the transform margin to the south the shipwreck trough is the downward thrown western side of the sfz and is host to an array of horst and half graben structures two of which contain the producing geographe and thylacine gas fields the shipwreck trough and sfz are imaged by the investigator 3d seismic dataset which has previously been studied to conduct 2d restorations and interpret the timing magnitude orientation and nature of the structural events of the shipwreck trough our study adds to this previous research by using spectral decomposition and coherence volumes to further characterise the sfz and associated igneous features basement structural elements and late cretaceous horst and half graben structures we have identified examples of releasing bend releasing jog and restraining jog structures along the sfz that are indicative of sinistral transtensional deformation and have highlighted areas of increased basement fault block relief which have driven extensional faulting in the cover we have also conducted throw distance and throw depth analysis on four horst and half graben structures and shown that the associated normal faults have had continuous late cretaceous growth with the structures being formed through incidental linkage of normal fault segments finally our two way time twt and isochronal mapping of the entire 3d survey shows the development of the late cretaceous rifting event in the shipwreck trough and highlights numerous other structural closures similar to and with close vicinity of the thylacine and geographe gas fields providing implications for prospectivity

geometry and evolution of low angle normal faults lanf within a cenozoic high angle rift system thailand implications for sedimentology and the mechanisms of lanf development 1 at least eight examples of large 5 35 km heave low angle normal faults lanfs 20 30 dip occur in the cenozoic rift basins of thailand and laterally pass into high angle extensional fault systems three large displacement lanfs are found in late oligocene miocene onshore rift basins suphan buri phitsanulok and chiang mai basins they have 1 developed contemporaneous with or after the onset of high angle extension 2 acted as paths for magma and associated fluids and 3 impacted sedimentation patterns displacement on low angle faults appears to be episodic marked by onset of lacustrine conditions followed by axial progradation of deltaic systems that infilled the lakes during periods of low or no displacement the chiang mai lanf is a low angle 15 25 high displacement 15 35 km heave ese dipping lanf immediately east of the late early miocene doi inthanon and doi suthep metamorphic core complexes early cenozoic transpressional crustal thickening followed by the northward motion of india coupled with burma relative to east burma and thailand 40 30 ma caused migmatization and gneiss dome uplift in the late oligocene of the core complex region followed by lanf activity lanf displacement lasted 4 6 ma during the early miocene and possibly transported a late oligocene early miocene high angle rift system 35 km east other lanfs in thailand have lower displacements and no associated metamorphic core complexes the three lanfs were initiated as low angle faults not by isostatic rotation of high angle faults the low angle dips appear to follow preexisting low angle fabrics thrusts shear zones and other low angle ductile foliations predominantly developed during late paleozoic and early paleogene episodes of thrusting and folding

multi disciplinary approach to fault and top seal appraisal pyrenees macedon oil and gas fields exmouth sub basin australian northwest shelf abstract the pyrenees macedon p m fields in the exmouth sub basin of the northern carnarvon basin australian northwest shelf are currently under filled relative to available closure despite being a regional focal point for cretaceous to recent charge late structural development of the p m trap with respect to charge was thought to be the reason for under filling however seismic amplitude anomalies and gas shows above the reservoir suggest vertical leakage may have controlled column heights hydrodynamic analysis of pressure data also suggests that faults separating the fields act as barriers to the migration of hydrocarbons and water whilst faults within the macedon field do not the reasons for hydrocarbon leakage and the difference in fault seal capacities are investigated by integrating field observations analysis of pressure and stress data the appraisal of top mercury porosimetry measurements and fault shale gouge ratios sgr membrane seal capacities constraining geomechanical properties top and fault seals and well based fracture analysis the top seals are at a low risk of capillary failure but vertical leakage is possible via dynamic failure along pre existing faults and conductive fractures and lateral leakage across reservoir against thief zone fault juxtapositions the difference in observed fault seal capacities between different faults is explained by a combination of the spatial distributions of sgr and buoyancy pressure the procedure presented delivers a robust description of the key risks concerning reservoir connectivity and the integrity and capacity of seals where static geological timescale migration and dynamic tectonically related flow conditions must be considered

studying lower crustal flow beneath mead basin implications for the thermal history and rheology of venus abstract mead the largest crater on venus has low topographic relief at the surface and at the crust mantle boundary due to high surface temperatures viscous deformation could play an important role in crustal structure using the finite element method we simulate the long term viscoelastic deformation of mead crater and investigate the role of lower crustal flow in the evolution of the surface and subsurface topography we examine the thermal states that allow this evolution to occur and determine the background heat flux our study constrains the background heat flux in the vicinity of mead basin to 55 90 mw m 2 this surface heat flow is generally higher than the average venusian global values suggested by recent thermal models in addition by applying hydrous and anhydrous creep rheological parameters we demonstrate that the venus s interior is rheologically dry and that the crust near mead could be relatively high in plagioclase

mapping permeable subsurface fracture networks a case study on the cooper basin australia abstract the spatial distribution of permeable fracture networks is constrained in the subsurface cooper basin australia through the integration of most positive curvature k analysis of five three dimensional 3d seismic surveys wellbore fracture data and geomechanical modelling the k provides the likely distribution of subsurface extensional fractures based on the stress redistribution along the outer arc of an anticline these results are reprocessed into the semblance similarity attribute to improve the signal noise ratio prior to being extracted along the gas rich and low permeability patchawarra formation the subsurface fracture distribution maps show the geometry and density of extensional fractures that have been shown to facilitate fluid migration in this province particularly those striking se nw and e w as these are properly oriented to undergo tensile reactivation the density of these permeable se nw and e w striking fracture sets is predicted to significantly increase along e w elongate anticlines and may contribute to improved hydrocarbon recovery in this low permeability stratigraphic interval we show that wellbore fracture data n 917 in the patchawarra formation presents a close relationship to k results and can be used to generate high density structural data in this basin with the methodology applicable to other subsurface and offshore provinces

3d seismic analysis investigating the relationship between stratigraphic architecture and structural activity in the intra cratonic cooper and eromanga basins australia abstract this research uses four three dimensional 3d seismic surveys located in australia s largest onshore hydrocarbon province the intra cratonic cooper and eromanga basins to present an approach that extracts important structural and stratigraphic information from geophysical data that can then be used to define the tectonostratigraphic evolution of subsurface provinces the methodology consists of 1 analysing isopach maps 2 cross section interpretation of stratigraphic features erosional surfaces and faults and 3 constraining the evolution of fault activity most faults within this province are basement involved with high dip angles the primary fault set is ne sw striking with secondary sets striking n s e w and nw se these high angle faults most likely developed as normal faults before being reactivated by five of the six major tectonic events field scale nw se strike slip faults are prolific and can often be overlooked due to the low seismic resolution a close relationship between on lapping features and present day structural highs was found during each of the major structural events particularly within hydrocarbon rich permian stratigraphy inferring that present day structures were present throughout basin development and intermittently reactivated significant stratal package thinning and a high presence of on lapping features were associated with regional basement involved faults particularly along the gidgealpa merrimelia innamincka and murteree nappacoongee ridges initial structural trap development occurred during the early permian but was most significant during the late triassic hydrocarbon accumulations were unaffected by structural growth after the critical moment in the petroleum system 90 ma as the final period of fault activity was during the late cretaceous this research constrains the tectonostratigraphic evolution of the intra cratonic cooper and eromanga basins while detailing an approach that extracts and analyses important structural and stratigraphic information from geophysical data where outcrop is not accessible

influence of turbulence on bed load sediment transport this paper summarizes the results of an experimental study on the influence of an external turbulence field on the bed load sediment transport in an open channel the external turbulence was generated by 1 a horizontal pipe placed halfway through the depth ih 2 a series of grids with a clearance of about one third of the depth from the bed and extending over a finite length of the flume and 3 a series of grids with a clearance in the range 0 1 1 0 ih from the bed but extending over the entire length of the flume two kinds of experiments were conducted plane bed experiments and ripple covered bed experiments in the former case the flow in the presence of the turbulence generator was adjusted so that the mean bed shear stress was the same as in the case without the turbulence generator in order to single out the effect of the external turbulence on the sediment transport in the ripple covered bed case the mean and turbulence quantities of the streamwise component of the velocity were measured and the shields parameter due to skin friction was determined the shields parameter together with the rms value of the streamwise velocity fluctuations was correlated with the sediment transport rate the sediment transport increases markedly with increasing turbulence level

seepage effects on dune dimensions this note presents an experimental study of seepage effects on the dimensions of a dune its height length and lee side slope the critical slope of a cohesionless material was found to be related to the ratio of the hydraulic gradient of seepage to its critical value under the quick condition the theoretical relationship is successfully used to predict seepage effects on the lee side slope of dunes measured laboratory data support the assumption that the effect of seepage on the lee side slope of dunes is the same as that on the critical slope of the sediment the data reveal that the slope is reduced and increased with injection and suction respectively additionally the study explores seepage effects on the development of dune height and length experimental results show that suction and injection increase and decrease the equilibrium height of dunes by 25 and 40 respectively on the other hand the dune length is found to increase by approximately 30 and decrease by 20 under the influence of suction and injection respectively

particle densimetric froude number for estimating sediment transport it has been established that for ratios of flow depth to bed particle diameter less than ten flow on very rough boundaries neither the reynolds number of the solid loose particles at a stream bed

terrestrial and planetary gravity fields the determination of the gravity field together with knowledge of the surface topography provides one of the primary means of inferring the density structure and dynamics of planetary interiors phillips and lambeck 1980 hager 1985 after removing the topographic gravity signal the distribution of internal density anomalies caused by thermal or compositional differences can be studied gravity field models can also be used to study the compensation of surface topography which can provide information on the mechanical properties and state of stress of the lithosphere the determination of these models has been accomplished using a wide variety of different measurement types and solution techniques the near earth measurement types can be divided into satellite tracking measurements surface gravity measurements and satellite altimeter measurements in both near earth and interplanetary contexts tracking data are used to measure gravitational perturbations affecting satellites with the accuracy and spatial temporal distribution of the data being the most important factors in the resulting field accuracy and resolution surface gravity data provide a more direct measurement of the gravity field but acquiring data uniformly over the earth has always been difficult satellite altimetry provides precise measurements of the marine gravity field provided that satellite orbit errors and non geoidal sea surface height variations can be adequately modeled comprehensive gravity field solutions must incorporate these disparate data types in order to estimate mathematical parameters describing the gravity field such as spherical harmonic coefficients the proper combination of these data along with the desire to acquire an accurate representation of the model errors require that complex procedures be developed for computing these solutions

bed shear stress and scour over bed type river intake laboratory experiments are carried out to determine the increase in bed shear stress and local scour over the zone of suction associated with a bed type river intake in a channel with a mobile bed bed shear stress is estimated first by observing the movement of indicator grains whose threshold shear stress in uniform flow was already known and second by observing the rate at which local scour takes place evaluation of the two sets of results indicates that at the onset of scour when particles are lifted from the bed by increased bed shear stress they do not strike the bed again until they are clear of the scour zone the final scour depth is found to be directly proportional to the difference between the initial bed shear stress because of suction and the threshold bed shear stress for the bed grains in the presence of suction

going quantitative with 4d seismic analysis it is demonstrated that time lapse seismic signatures can be directly calibrated with historical data from producing and injecting wells via a reservoir simulator material balance calculation or simply using the hard data when this procedure is applied to a field over which two or more repeat surveys have been shot at different calendar times the correlation coefficients that link the seismic difference signatures to the reservoir s pressure and saturation variations are determined by utilizing several seismic attributes that respond differently to reservoir perturbations pressure and saturation changes are then independently estimated the approach is tested on synthetic data and then on data from the schiehallion field on the uk continental shelf with favourable results

time depth relationships for multilayer depth conversion the conversion of seismic time to depth through the use of analytical functions has been a common procedure in seismic work for many decades with the exception of recent examples dealing with the linear function none of the published time depth relationships corresponding to these functions is applicable to multilayer depth conversion the present work redresses this situation it presents formulae applicable to multilayer depth conversion for a large number of analytical functions the derivation is based on a procedure generally similar to that presented by japsen 1993 most of the functions considered date back to a publication by kaufman in 1953 and earlier publications a number of other functions hitherto not known in the industry are also presented

global mapping of crustal and lithospheric thickness on venus 1 we have produced a high resolution global admittance map of venus using a spatiospectral localization technique calculating 64 800 admittance spectra evenly spaced in latitude and longitude we grouped the admittance spectra into 35 classes that we inverted for elastic crustal and lithospheric thickness using bottom loading top loading and short wavelength top loading models with long wavelength bottom loading hot spot models our best fit models identify 17 classes consistent with top loading 40 of the surface 7 with bottom loading 39 and 4 with a long wavelength bottom loading model 15 the remaining seven classes 6 of the surface generally had large amplitude top loading signatures that could not be fit with our models for the classes that were successfully modeled the estimated range of crustal 0 90 km and elastic thickness 0 100 km is larger than results for most previous studies primarily because of the incorporation of bottom loading nearly half of the planet has elastic thickness 20 km which we cannot distinguish from isostasy suggesting that these regions are tectonically inactive a key finding is that the lithospheric properties typically vary over scales of 1000 km or less except in some plains and crustal plateau regions both the scale and range of crustal and elastic thickness variations indicate that venus remains an active planet and that geologic processes may be more complex than previously recognized in many regions the correlation with surface geology is not obvious and this suggests that deformation of the lower lithosphere and crust may occur with little surface manifestation

constraints on deformation mechanisms during folding provided by rock physical properties a case study at sheep mountain anticline wyoming usa summary the sheep mountain anticline wyoming usa is a well exposed asymmetric basementcored anticline that formed during the laramide orogeny in the early tertiary in order to unravel the history of strain during folding we carried out combined anisotropy of magnetic susceptibility ams anisotropy of p wave velocity apwv and fry strain analyses the results are compared to previously published stress strain data from calcite twins at the microscopic scale and from fracture sets at the mesoscopic scale and are used to discuss the kinematics and mechanics of forced folding the results obtained in sandstone and carbonate lithologies demonstrate a good agreement between 1 the principal axes of the ams and apwv tensors 2 stress strain tensors derived from calcite twins 3 fry strain axes and mesoscopic fracture sets furthermore these tensors are coaxial with the main structural trends of the anticline the differences between ams and apwv fabrics on one hand and the differential stress values of the forelimb and the backlimb on the other hand emphasize how the macroscopic asymmetry of sheep mountain anticline affects the strain pattern at the microscopic scale the data set presented in this paper offers a consistent mechanical scenario for the development of sheep mountain anticline

inflow seepage influence on straight alluvial channels a flume study was conducted to identify and analyze the effects of inflow seepage on flow in straight alluvial open channels the effect of inflow seepage on energy slope water surface depth velocity sediment transport scour bed forms and resistance to flow was investigated the results of this investigation indicated that inflow seepage increases localized mean channel velocity energy slope and stream power in the zone of inflow the water surface depth decreased for subcritical flow and remained nearly constant for supercritical flow during inflow conditions sediment transport was slightly increased when inflow was introduced in the bed inflow seepage did not appear to enhance channel scour inflow seepage significantly enhanced bed form transformation and the bed roughness inflow seepage also caused dunes to become longer flatter and move more erratically in the reach where inflow occurred it was concluded that inflow seepage could significantly influence the channel hydraulics stream po

enhanced dynamic interpretation from correlating well activity to frequently acquired 4d seismic signatures quantitative 4d seismic interpretation can be successfully achieved by exploiting the causal link between the temporal variation in well activity and the 4d seismic signatures they induce this is achieved by capturing in mathematical form the common interpretational practice of identifying the origin of dynamic signals in the 4d seismic volumes or maps on the basis of their association with a particular injector or producer thus for example a region of reservoir hardening impedance increase around a producer may be interpreted as a signal of pressure decrease similarly an area of softening impedance decrease around an injector is interpreted as a signal of pressure increase when pressures are above bubble point in the literature a hardwired integration between the seismic and engineering domain has been obtained to some extent using methods such as seismic history matching where the observed seismic and well production history data are simultaneously fit by predictions from a common simulation model however this approach is computationally expensive and suffers from nonuniquenesses inaccuracies in the petroelastic model and is ultimately only as accurate as the model itself as an alternate approach we reconcile here the well production history and time lapse seismic data in the data domain without the need for a model this approach involves the use of many frequently repeated seismic surveys shot over the same field and mathematically correlates changes in the mapped seismic attributes directly to the fluid volumes injected and produced from the wells thus well data normally used exclusively for history matching in the reservoir engineering domain can now also be directly integrated with the time lapse seismic data

3d seismic imaging of the lalor volcanogenic massive sulphide deposit manitoba canada a three component three dimensional seismic data set was acquired over the lalor volcanogenic massive sulphide deposit near snow lake manitoba canada to assess the reflectivity of the ore and further validate the potential of three dimensional reflection seismic methods for deep mineral exploration the lalor deposit was chosen as a test site as it provided an intact well characterized 25 mt deep ore deposit with a rich catalogue of geological and geophysical data as well as extensive drill core and drill hole geophysical and geological logs an analysis of physical rock properties from borehole logging data indicates that massive sulphides associated with the zincrich zones could produce prominent reflections whereas acoustic impedances of zones with disseminated gold do not sufficiently differ from the impedances of the host rocks to produce reflections the interpretation of the seismic data is constrained with a detailed three dimensional lithofacies model constructed from the categorical kriging of 15 lithological units identified in borehole intersections processing of the seismic data included prestack dip moveout and poststack time migration final images reveal some strong reflections associated with the zinc rich massive sulphide zones the most prominent reflection results from the constructive interference of thin and closely spaced massive sulphide zones and felsic mafic volcanic rock contacts above and below the mineralization contacts between felsic and mafic volcanic rocks including those that were hydrothermally altered and subsequently metamorphosed produced prominent and continuous reflections that are used to map the main architecture of the footwall rocks at depth a series of continuous and conformable reflections indicate the general geometry of the volcanic sequences in the area of the three dimensional seismic survey

stress and strain patterns kinematics and deformation mechanisms in a basement cored anticline sheep mountain anticline wyoming 1 in order to characterize and compare the stress strain record prior to during and just after folding at the macroscopic and the microscopic scales and to provide insights into stress levels sustained by folded rocks we investigate the relationship between the stress strain distribution in folded strata derived from fractures striated microfaults and calcite twins and the development of the laramide basement cored sheep mountain anticline wyoming tectonic data were mainly collected in lower carboniferous to permian carbonates and sandstones in both rock matrix and veins calcite twins recorded three different tectonic stages the first stage is a pre laramide sevier layer parallel shortening lps parallel to fold axis the second one is a laramide lps perpendicular to the fold axis and the third stage corresponds to laramide late fold tightening with compression also perpendicular to the fold axis stress and strain orientations and regimes at the microscale agree with the polyphase stress evolution revealed by populations of fractures and striated microfaults testifying for the homogeneity of stress record at different scales through time calcite twin analysis additionally reveals significant variations of differential stress magnitudes between fold limbs our results especially point to an increase of differential stress magnitudes related to laramide lps from the backlimb to the forelimb of the fold possibly in relation with motion of an underlying basement thrust fault that likely induced stress concentrations at its upper tip this result is confirmed by a simple numerical model beyond regional implications this study highlights the potential of calcite twin analyses to yield a representative quantitative picture of stress and strain patterns related to folding