determining the damping factor of sedimentary rocks required for seismically designed structures abstract relationships for the shear damping ratio d s a function of shear quality factor q s and modulus decay curve g seis g max as a function of shear strain for mudrocks have been developed field experiments to determine damping ratio and elastic moduli should be performed at frequencies as close as possible to the bandwidth 0 100 hz of interest for building design estimates of these parameters made from extrapolating laboratory core mhz or wireline khz data to lower frequencies can be highly unreliable field estimates of damping ratio are very dependent on and often totally dominated by the effects of scattering of p and s waves by inhomogeneities in the rock mass structure this is particularly the case when open fractures or cracks are present in near surface rocks

critical degree of saturation a control factor of freeze thaw damage of porous limestones at castle of chambord france abstract the paper analyzes the petrophysical and mechanical properties of two porous limestones that were used in the construction and restoration works at the castle of chambord in france a unesco world heritage site the original construction material the tuffeau limestone with a total porosity of 45 0 6 and the replacement stone of later restorations the richemont limestone with a total porosity of 29 0 7 were subjected to freeze thaw tests under laboratory conditions to evaluate the role of critical degree of saturation and pore size distribution in frost damage laboratory tests were coupled with in situ measurements of temperature and relative humidity at stone surface at the castle of chambord in situ data show that the stones in the castle experienced several freezing thawing cycles annually the limestone samples under laboratory conditions were subjected to up to 50 freeze thaw cycles under eight different degrees of saturations the total porosity tensile strength ultrasonic pulse velocity the mercury intrusion porosimetry and scanning electron microscopy techniques were employed to analyze the conditions of samples during the cycles the experimental results show that when the degree of saturation of the two studied limestones exceeds 80 85 the freeze thaw damage occurs even after a few freeze thaw cycles the effect of freezing is very fast if the water saturation is sufficient moreover results indicate that these stones have the same critical degree of saturation of about 85 despite the differences in porosity finally the results indicate that the increase in the number of freezing thawing cycles has no effect on the critical degree of saturation but the frost damage is mostly controlled by pore size distribution rather than by total porosity accordingly critical degree of saturation can be defined as an intrinsic stone property

near surface temperature cycling of stone and its implications for scales of surface deterioration abstract many previous studies into internal temperature gradients within stone have assumed smooth exponential increases and decreases in sub surface temperatures in response for example to diurnal patterns of heating and cooling and these have been used to explain phenomena such as large scale contour scaling this high resolution experimental study in which a porous limestone block was subjected to alternate surface heating and cooling using an infrared lamp demonstrates that internal temperature gradients in response to short term environmental cycles measured in minutes can in fact be complex and inconsistent results confirm the significance of very steep temperature stress gradients within the outer 10 mm or less of exposed stone below this the data indicate complex patterns of temperature reversals the amplitudes of which are attenuated with depth and which are influenced in their intensity and location by variations in the relative duration of heating and cooling phases it is suggested that the reversals might represent interference patterns between incoming and outgoing thermal waves but whatever their origin they are potentially important because they occur within the zone in which many stone decay processes especially salt weathering operate these processes invariably respond to temperature and moisture fluctuations and short term interruptions to insolation could for example trigger these fluctuations on numerous occasions over a day in particular the reversals occur at a scale that is commensurate with decay by multiple flaking and could indicate an underlying control on this previously little researched pattern of weathering in the context of this publication however the main lesson to be learned from this study is that differing scales of behaviour require different scales of enquiry

anisotropy in seismic velocities and amplitudes from multiple parallel fractures many rock structures include multiple near parallel planar discontinuities such as bedding planes or joints the effects of these nonwelded interfaces on seismic wave propagation are often analyzed using effective moduli in terms of which seismic wave propagation is independent of frequency and without loss unless the moduli include imaginary terms an alternative approach is to treat these interfaces as a boundary condition in the seismic wave equation across which seismic stress is continuous but seismic particle displacements are discontinuous the ratio of the stress to displacement is called the specific stiffness of the interface and characterizes the elastic properties of a fracture for a completely elastic system this results in frequency dependent reflection and transmission coefficients for each interface as well as a frequency dependent group time delay using multiple parallel displacement discontinuities and ignoring converted and reflected waves expressions derived for transmitted wave amplitudes and group velocities show that these depend on frequency angle of incidence and polarization in the case of shear waves measurements on a laminated steel block show that shear pulses propagating parallel to the laminations and polarized parallel and perpendicular to the plane of the laminations both travel at the velocity for solid steel although the spectra of these pulses differ considerably however the energy of the pulse polarized perpendicular to the laminations may propagate as an interface wave between each pair of laminations predictions of the displacement discontinuity model have features quite distinct from many crustal observations to date we suggest that we are able to model dense populations of coplanar cracks that cannot be treated by effective moduli methods which require a dilute concentration of cracks

an integrated study of seismic anisotropy and the natural fracture system at the conoco borehole test facility kay county oklahoma a significant body of published work has developed establishing fracture related seismic anisotropy as an observable effect to further the understanding of seismic birefringence techniques in characterizing natural fracture systems at depth an integrated program of seismic and geologic measurements has been conducted at conoco s borehole test facility in kay county oklahoma birefringence parameters inferred from the seismic data are consistent with a vertical fracture model of density 0 04 striking east northeast that direction is subparallel to a fracture set mapped both on the surface and from subsurface data to the in situ maximum horizontal stress and to the inferred microfabric

intraplate deformation and closure of the australia antarctica africa plate circuit to determine the current motion between the australian antarctic and african plates and to test whether this plate circuit obeys closure all plate motion data available along the southeast southwest and central indian ridges are analyzed and reduced to 67 spreading rates 38 transform fault azimuths and 135 earthquake slip vectors carlsberg ridge data were excluded because they record india africa not australia africa motion new data include 10 new transform azimuths along the southwest indian ridge many slip vectors and a dense aeromagnetic survey along the southeast indian ridge all published and many unpublished magnetic profiles are modeled to determine rates consistently over a 3 m y time averaging interval for three reasons 1 magnetic profiles from the southeast and central indian ridges suggest recent spreading rate changes 2 some published rates differ for identical profiles and 3 prior studies have not used identical criteria and time scales to determine spreading rates the new rates differ from published rates by as much as 5 mm yr transform fault azimuths are estimated from bathymetry seasat altimetric data epicenter distributions and offsets of magnetic lineations azimuths of plate motion are also estimated from the horizontal projections of slip vectors from the centroid moment tensor solutions and other focal mechanism studies our new australia antarctica and australia africa euler vectors differ from all prior euler vectors at the 95 confidence level along the southeast and central indian ridges our model gives rates differing by 4 7 mm yr from those of prior models from a systematic analysis of the plate motion data we find no evidence for a nubia somalia antarctica triple junction along the southwest indian ridge we also find no evidence for a triple junction previously proposed to be at 80 e along the southeast indian ridge any deformation within this seismically active region of the australian plate adds up to less than a few millimeters per year along each boundary data are fit well by a single euler vector except for a 5 systematic misfit to azimuthal data along the eastern southeast indian ridge near a seismically active region of the australian plate south of tasmania although seismicity and the azimuthal misfit suggest the australian plate is deforming measurably possibly by distributed deformation or by the westward motion of a small microplate southeast of tasmania the significance of the misfit is marginal and is small enough that systematic errors may cause it these alternative explanations could be distinguished by surveying these transform faults with modern seafloor mapping techniques prior studies found that enforcing plate circuit closure causes systematic misfits to rates along the southeast indian ridge here we find that enforcing closure causes no systematic misfits to any data moreover only insignificant nonclosure is found by an f ratio test which numerical experiments suggest could detect deformation exceeding 2 mm yr we conclude that indian ocean plate circuit nonclosure and the deformation it suggests are much smaller than thought before the absence of significant nonclosure argues against the usefulness of a model of deformation distributed throughout an indo australian plate but favors a model in which the significant deformation occurs in a diffuse plate boundary along the equatorial indian ocean between the central indian ridge and the sumatra trench

magnetic and bathymetric investigations over the vema region of the central indian ridge tectonic implications abstract magnetic and bathymetric data were collected along n50 e profiles in the vema region 7 12 s 64 70 e across five ridge segments of the central indian ridge cir anomalies up to a5 10 ma identified by generating synthetics for each profile show asymmetric spreading though inter segmental variations in spreading rate have been observed the mean half spreading rate increases from 1 8 cm yr in the region north of vema transform to 2 1 cm yr south of the vema transform the average spreading rate for the last 10 ma has not always been symmetric the interpretation of magnetic and bathymetric data shows the complex nature of this part of the cir which could probably be attributed to i the short ridge segment ii interaction with fracture zone and iii interaction between the cir and the wide boundary zone wbz separating the indian and australian plates

poroelastic model to relate seismic wave attenuation and dispersion to permeability anisotropy a transversely isotropic model with a horizontal axis of symmetry based on the biot and squirt flow mechanisms predicts seismic waves in poroelastic media the model estimates velocity dispersion and attenuation of waves propagating in the frequency range of crosswell and high resolution reverse vertical seismic profiling vsp 250 1250 hz for vertical permeability values much greater than horizontal permeability parameters the model assumes the principal axes of the stiffness constant tensor are aligned with the axes of the permeability and squirt flow tensors in addition the unified biot and squirt flow mechanism bisq model is adapted to simulate cracks in permeable media under these conditions the model simulations demonstrate that the preferential direction of fluid flow in a reservoir containing fluid filled cracks can be determined by analyzing the phase velocity and attenuation of seismic waves propagating at different azimuth and incident angles as a result the fast compressional wave

tube wave suppression in single well seismic acquisition single well seismic imaging is significantly hampered by the presence of borehole tube waves a tube wave suppressor has been tested using single well seismic equipment at the lost hills california oil field the suppressor uses a gas filled bladder kept slightly above borehole fluid pressure field tests show a measurable reduction in tube wave energy as compared to body waves propagating in the surrounding reservoir rock when using a high frequency 500 4000 hz piezoelectric source the p wave tube wave amplitude ratio was increased by 33 db when using a lower frequency 50 350 hz orbital vibrator source the s wave tube wave amplitude ratio was increased by 21 db while the p wave tube wave amplitude ratio was increased by 23 db these reductions in tube wave amplitudes significantly improve single well data quality

radiation from seismic sources in cased and cemented boreholes far field stationary phase approximations are often used to study the radiation of p and s waves from seismic sources located in boreholes usually with an assumption of low frequency and in application to uncased boreholes these two assumptions allow explicit analytical results for the radiation patterns to be derived as boundary condition equations can be solved analytically in fairly simple forms applying the same methodology to cased and cemented boreholes however is much more difficult because of the increased number of simultaneous boundary condition equations i circumvent this difficulty by solving the boundary condition equations numerically using propagator matrices as is generally done in the calculation of synthetic full waveform acoustic logs in this way the assumption of low frequency is also avoided and a generalized stationary phase solution for sources in general concentrically layered borehole models is easily obtained computation of the radiation patterns for cased and uncased boreholes in various formations shows that the amplitude reduction because of the introduction of casing is a function of both source type and of formation velocities axial stress sources are less affected by the casing than either radial stress or volume injection sources and as formation velocity decreases the effect of the casing becomes more significant as the impedance contrast between steel and the formation becomes larger the new generalized stationary phase solution also shows that as frequency approaches 1000 hz the results obtained by low frequency approximations for stress sources can be inaccurate and that the energy radiated from the source becomes more highly directed in the horizontal directions the radiation pattern begins to change relatively rapidly as a function of frequency so that the resulting observations from broad band sources will show changes in waveforms that mimic the effects of attenuation these changes occur because the length of the source becomes important as wavelength decreases demonstrating the need to consider the influence of frequency as well as casing and cement on source radiation

development of a joint hydrogeophysical inversion approach and application to a contaminated fractured aquifer this paper presents a joint inversion approach for combining crosshole seismic travel time and borehole flowmeter test data to estimate hydrogeological zonation the approach is applied to a complex fractured department of energy field site located at the oak ridge national laboratory in tennessee united states we consider seismic slowness the inverse of seismic velocity and hydrogeological zonation indicators as unknown variables and use a physically based model with unknown parameters to relate the seismic slowness to the zonation indicators we jointly estimate all the unknown parameters in the model by conditioning them to the crosshole seismic travel times as well as the borehole flowmeter data using a bayesian model and a markov chain monte carlo sampling method the fracture zonation estimates are qualitatively compared to bromide tracer breakthrough data and to uranium biostimulation experiment results the comparison suggests that the joint inversion approach adequately estimated the fractured zonation and that the fracture zonation influenced biostimulation efficacy our study suggests that the new joint hydrogeophysical inversion approach is flexible and effective for integrating various types of data sets within complex subsurface environments and that seismic travel time data have the potential to provide valuable information about fracture zonation

the possible role of clay minerals in salt weathering abstract results of a salt weathering experiment on a laminated sandstone are reported it is observed that laminae which contain smectite clays break down more readily than those with little clay this preferential breakdown may be related to the swelling of the clays which assists salt weathering processes per se and or secondary microporosity created by the clays which could enhance salt weathering effects it is not possible at this point in time to state definitively the effects that the presence of clay has upon salt weathering but suggestions for future research are made

the occurrence of gypsum in the scaling of stones at the castle of chambord france the main cause of degradation in tuffeau a soft siliceous and clayey limestone extensively used in the construction of the castles of the loire valley in france is scaling the most damaging form of weathering is spalling over time a plaque several centimetres in thickness gradually forms under the stone surface and eventually falls away leaving the resulting new surface powdered hypotheses regarding the initiation and development of such degradation have not yet met scientific consensus the objective of the present paper is to improve existing knowledge of scaling degradation by analysing in situ samples representing different stages of the same degradation process the analysis of the stones at the castle of chambord revealed the presence of gypsum caso4 2h2o mainly located in cracks parallel to the stone surface this gypsum was then studied in terms of its crystal morphology and distribution with depth for comparison purposes another form of scaling identified at the castle of chambord but rarely studied flaking was also examined a first attempt at explaining the origin and formation of the observed gypsum in both scaling processes was conducted by interacting and comparing the characterisation results with historical and environmental data

urban and rural limestone weathering the contribution of dust to black crust formation a novel approach of studying dust black crust and host limestones by using various techniques is presented in this paper samples were collected from limestone monuments located in rural urban and industrial areas in germany and hungary the paper focuses on differences in the mineralogical composition major and trace element distribution of materials and their total polyaromatic hydrocarbons pah concentration having different exposure to air pollutants high concentration of gypsum was found in laminar and dendritic black crusts and even in the dust of both urban and rural areas despite the low concentration of so2 in rural atmospheric environments the black crusts show a typical microfabric with distinct layers of various gypsum calcite mineral associations silt sized mineral fragments and black particle content in dust newly formed gypsum crystals were found along with mineral fragments and siliceous and less frequently carbonaceous fly ash particles high concentration of lead was found both in the samples of urban and rural areas of germany and hungary lead mostly accumulates in dust and also in the black crust highest lead concentrations were found not on the surface of the black crust but close to the crust limestone boundary according to la icpms analyses it indicates that despite the ban of leaded petrol lead is still present in the dust and the in the soiled zones of the built environment similarly to lead no significant difference in the total pah content of dust and crust samples were found in the two countries dusts are equally enriched in pah in both countries whereas black crusts contain fewer amounts most of the aqueous extracts of the samples were saturated with respect to sulphate which also indicate the presence of gypsum whilst in some german samples unsaturated conditions were detected in summary by using a combination of these analytical techniques it was possible to distinguish rural and urban samples and to outline the role of dust in bringing pollutants to the stone surface it is suggested that the analysed dust and stone samples indicate not only present but also the past pollution fluxes and as a consequence stones similar to sediments or surface waters can be used as environment indicators

discrete dual porosity model for electric current flow in fractured rock the identification of fractures and the characterization of their properties are of critical importance in a wide variety of research fields and applications to this end geophysical methods are of significant interest as they can provide information regarding the spatial distribution of a number of subsurface physical properties in a rapid and noninvasive manner electrical resistivity surveying in particular has been shown in several previous investigations to exhibit sensitivity to the presence of fractures suggesting that geoelectrical experiments may contain important information regarding how fractures are distributed and connected in the subsurface however a lack of suitable numerical modeling tools for electric current flow in fractured media has prevented a detailed and systematic exploration of this concept to address this issue we present a novel discrete dual porosity modeling approach that is specifically tailored to the electrical resistivity problem with our approach an analytical formulation for fracture matrix current flow exchange at the fracture scale is integrated into a discrete fracture network model which is then combined with a block scale finite volume representation of the rock matrix our methodology allows for low cost and accurate simulation of electric current flow through both the fractures and matrix and is readily applicable to complex fracture networks at relatively large scales although formulated here in two dimensions this work represents an important first step toward investigating the effect of fracture network characteristics on bulk electrical properties as well as toward the simulation of geoelectrical survey data in realistic fractured rock environments

underlying issues on the selection use and conservation of building limestone an argument is presented that despite popular assumptions many limestones especially the wide range of clastic and in general granular limestones do not decay in a steady and predictable pattern in response to slow dissolution instead these stones especially when used in construction in polluted environments invariably decay episodically through physical breakdown most commonly this is accomplished through a variety of salt weathering mechanisms that if unconstrained can lead to the rapid catastrophic decay of building blocks and their complete loss a process that has driven the extensive programmes of stone replacement that are typical of buildings constructed of these stones in polluted environments especially those rich in sulphur and particulates the most common constraint on accelerated decay has been the rapid development of gypsum crusts that for example could rapidly heal the scars left by contour scaling it is ironic therefore that any reduction in pollution could conceivably lead to increased erosion by retarding this healing process because of this temporal variability of decay and its translation into spatial complexity it is important that further research is undertaken to understand controls on the decay of these important building stones so that future conservation strategies can be appropriately informed on the predictability of decay and the role

integrated reservoir petrophysical and seismic simulation of co2 storage in coal beds in this paper we present results of an integrated simulation study to assess the effectiveness of seismic imaging for monitoring co2 sequestration we considered two scenarios in the first injected co2 remained confined within a shallow coal formation in the second the sequestered co2 gas leaked through a semi permeable shale layer to an overlying sand unit sealed above in both scenarios the co2 injection process resulted in enhanced production of coal bed methane the reservoir and seismic simulations required the construction of 3d geologic and facies models the estimations of seismic velocities based on rock physics correlations and the development of geostatistical dual porosity reservoir descriptions of the coal and overlying shale and sand units we ran the 3d reservoir simulations with gem 2008 10 an equation of state compositional reservoir simulator from computer modeling group with the capability to model adsorption of injected co2 in coal desorption of ch4 and matrix shrinkage swel

weathering effects in an urban environment a case study of tuffeau a french porous limestone abstract a case study is carried out on a highly porous limestone called tuffeau located in an urban environment weathering effects are characterized by several complementary techniques mechanical resistance compressive test imbibition capillarity test mercury intrusion porosimetry chemical analysis inductively coupled plasma optical emission spectrometer icp oes scanning electron microscope sem image analysis and x ray diffraction xrd the results show the different composition of the deteriorated zone of the stone and mainly the presence of high gypsum content in the black crust surface the analysis also shows that the natural penetration of water into this stone under environmental conditions atmospheric precipitation relative humidity and temperature is limited to 20 mm moreover the presence of gypsum is only detected in this limited zone which demonstrates the depth of alteration in this stone finally this study clearly highlights the important role of water movements in the deterioration of stone

effect of thermal stress condensation and freezing thawing action on the degradation of stones on the castle of chambord france this work consists in estimating the role of climatic conditions in the degradation of two french limestones tuffeau and richemont stone used in the construction and the restoration of the castle of chambord the largest castle in the loire valley france meteorological data air temperature air relative humidity and rainfall were statistically analysed in combination with stone data from thermal humidity sensors inserted into the walls the climatic conditions of the surrounding area were described to assess their role in enhancing the degradation of the stones through three weathering processes thermal stress condensation and freezing thawing the damage risks due to the weathering processes were taken into account not only through the bulk effects on the stone surfaces but also their effects were extended to investigate the damage that occurs within the porous structure of the stone field observations showed that the main patterns of degradation affecting the stones of the castle are biological colonization and stone detachment in the form of stone spalling and exfoliation the results of the analysis show that there is no risk of damage to the stones due to thermal stress moreover the two stones experience similar overall trends against freezing thawing processes finally this study clearly highlights the important role of condensation in the degradation of the stones of the castle

joint cross well and single well seismic studies of co2 injection in an oil reservoir a series of time lapse seismic cross well and single well experiments were conducted in a diatomite reservoir to monitor the injection of co2 into a hydrofracture zone based on p and s wave data a high frequency piezo electric p wave source and an orbital vibrator s wave source were used to generate waves that were recorded by hydrophones as well as 3 component geophones during the first phase the set of seismic experiments was conducted after the injection of water into the hydrofractured zone the set of seismic experiments was repeated after a time period of seven months during which co2 was injected into the hydrofractured zone the questions to be answered ranged from the detectability of the geological structure in the diatomic reservoir to the detectability of co2 within the hydrofracture furthermore it was intended to determine which experiment cross well or single well is best suited to resolve these features during the pre injection experiment the p wave velocities exhibited relatively low values between 1700 and 1900 m s which decreased to 1600 1800 m s during the post injection phase 5 the analysis of the pre injection s wave data revealed slow s wave velocities between 600 and 800 m s while the post injection data revealed velocities between 500 and 700 m s 6 these velocity estimates produced high poisson s ratios between 0 36 and 0 46 for this highly porous 50 material differencing post and pre injection data revealed an increase in poisson s ratio of up to 5 both velocity and poisson s ratio estimates indicate the dissolution of co2 in the liquid phase of the reservoir accompanied by an increase in pore pressure the single well data supported the findings of the cross well experiments p and s wave velocities as well as poisson s ratios were comparable to the estimates of the cross well data the cross well experiment did not detect the presence of the hydrofracture but appeared to be sensitive to overall changes in the reservoir and possibly the presence of a fault in contrast the single well reflection data revealed an arrival that could indicate the presence of the hydrofracture between the source and receiver wells while it did not detect the presence of the fault possibly due to out of plane reflections

periodicity in the accretion process on the southeast indian ridge at 27 40 s abstract image processing of a seabeam bathymetric grid on the southeast indian ridge seir at 27 40 s has been used to analyse the morphotectonics of the ridge flanks steep topographic slopes indicating inward facing or outward facing faults and those representing tilted blocks were automatically separated an autocorrelation process allows an estimation of the periodicity of the fault spacing the outward facing faults first appear at 16 18 km from the axial valley are more common on bathymetric highs and correspond to tilted block zones in adjacent deeper areas the tilting of the blocks is 4 the transformation of the rift valley into the smooth undulating relief of the flanks is accomplished by these outward facing faults and tilted blocks inward facing faults appear either as large faults with major throws or as a series of smaller faults with minor throws the minor faults are mainly localized on bathymetric highs and are densely organized the major faults continuous and symmetrically spaced on each side of the axis zone are organized with a periodicity of 8 2 km these faults seem to be old inner walls which have been moved outwards periodically during the spreading process they alternate with positive magnetic lineaments reflecting old neovolcanic zones linked to intense magmatic periods considering a mean half spreading rate of 31 km m y during the past million years this would mean the development of a major fault each 0 26 m y we propose a model for the evolution of the seir at 27 40 s controlled by a periodic succession of magmatic and tectonic episodes 1 1 faulting and volcanism are concentrated in the axial zone above the melt reservoir where the crust is weakened magmatic period outside this zone the external relief is frozen in supported by the finite strength of the plate 2 2 the axial valley is enlarged fills up with lavas and bulges due to thermal effects 3 3 at the end of the magmatic period this bulged zone collapses by thermal subsidence along lines of weakness such as the faults forming the inner walls 4 4 when the melt reservoir is empty tectonic period the processes are no longer concentrated and active faulting extends over tens of kilometres from the axis the lithosphere is thinned a new axial valley is created the flanks are uplifted and outward facing faults and block tilting are induced

moment tensor solutions of earthquakes in the indian ocean from surface waves and their tectonic implications rayleigh and love waves generated by sixteen earthquakes which occurred in the indian ocean and were recorded at 13 wwssn stations of asia africa and australia are used to determine the moment tensor solution of these earthquakes a combination of thrust and strike slip faulting is obtained for earthquakes occurring in the bay of bengal thrust strike slip or normal faulting or either of the combination is obtained for earthquakes occurring in the arabian sea and the indian ocean the resultant compressive and tensional stress directions are estimated from more than 300 centroid moment tensor cmt solution of earthquakes occurring in different parts of the indian ocean the resultant compressive stress directions are changing from north south to east west and the resultant tensional stress directions from east west to north south in different parts of the indian ocean the results infer the counterclockwise movement of the region 0 33 s and 64 e 94 e stretching from the rodriguez triple junction to the intense deformation zone of the central indian ocean and the formation of a new subduction zone island arc beneath the intense deformation zone of the central indian ocean and another at the southern part of the central indian basin the compressive stress direction is along the ridge axis and the extensional stress manifests across the ridge axis the north south to northeast south west compression and east west to northwest southeast extension in the indian ocean suggest the northward underthrusting of the indian plate beneath the eurasian plate and the subduction beneath the sunda arc region in the eastern part the focal depth of earthquakes is estimated to be shallow varying from 4 to 20 km and increasing gradually in the age of the oceanic lithosphere with the focal depth of earthquakes in the indian ocean

cross borehole geological interpretation model based on a fuzzy neural network and geotomography this paper demonstrates a method of predicting subsurface geological characteristics in the region between boreholes using a fuzzy neural network fnn inverted geophysical data geotomogram and fuzzy geological knowledge traditionally geological interpretations are often of inadequate reliability in cross borehole regions because of the scarcity of quantitative data hence geological interpretation has been a subjective process although there is a paucity of data a fair amount of information exists in the form of human perception summarized as either rough maps or vague descriptions here a method based on fuzzy set theory that can extract rough information from conventional geological interpretations is described the extracted data can be used with geophysical tomography data in a fnn to improve geological interpretation the proposed method was applied to the geological evaluation of a site where construction of an underground hydroelectric power generation facility was being considered

channel waves in cross borehole data layered geological formations with large seismic velocity contrasts can effectively create channel waves in cross borehole seismic data the existence of channel waves for such waveguides can be confirmed by ray tracing wave equation modeling and modal analysis channel wave arrivals are identified in cross borehole data recorded at conoco s newkirk test facility for these data where velocity contrasts are about 2 to 1 tomography based on first arrival traveltimes is limited due to problems with extreme ray bending and seismic shadow zones however it may be possible to extract geological information using channel wave information the seismometer differencing method appears to be a promising approach for detecting waveguide boundaries by use of cross borehole data

fracture detection using crosswell and single well surveys we recorded high resolution 1 to 10 khz crosswell and single well seismic data in a shallow 15 to 35 m water saturated fractured limestone sequence at conoco s borehole test facility near newkirk oklahoma our objective was to develop seismic methodologies for imaging gas filled fractures in naturally fractured gas reservoirs the crosswell 1 4 m receiver spacing 50 to 100 m well separation surveys used a piezoelectric source and hydrophones before during and after an air injection that we designed to displace water from a fracture zone our intent was to increase the visibility of the fracture zone to seismic imaging and to confirm previous hydrologic data that indicated a preferred pathway for the single well seismic imaging a piezoelectric source and an eight element hydrophone array at 1 4 m spacing we also recorded data before and after the air injection the crosswell results indicate that the air did follow a preferred pathway that was predicted by hydrologic modeling in addition

centroid depths of mid ocean ridge earthquakes dependence on spreading rate from inversions of teleseismic p and sh waveforms we have determined the source parameters of 50 large earthquakes that occurred during 1962 1983 on slowly spreading mid ocean ridges all events are characterized by predominantly normal faulting on planes that dip at approximately 45 and strike parallel to the local trend of the ridge axis centroid depths range from 1 to 6 km beneath the seafloor the p waves from these earthquakes show strong water column reverberations suggesting that fault rupture extended to the seafloor under the assumption that the centroid depth marks the mean depth of fault slip earthquake faulting extended to a depth of 2 10 km for these earthquakes the water depths inferred from the predominant periods of the water column reverberations constrain the epicenters of these earthquakes to lie within the relatively deep inner floor of the median valley the maximum centroid depths of ridge crest earthquakes decrease with increasing spreading rate and the maximum seismic moment may also decrease with increasing spreading rate these results indicate a general decrease with spreading rate in maximum thickness of the mechanically strong layer beneath the ridge axis region the concentration of large earthquakes within the deepest parts of the median valley and the depth extent of seismic faulting support lithospheric necking models for the origin of the median valley

cyclic wetting drying ageing test and patina formation on tuffeau limestone this paper presents the results of an ageing test based on cycles of wetting drying of a french building limestone named tuffeau during 3 years 50 complete wetting drying cycles with pure distilled water were carried out on the side of a cylindrical sample the characterization of the stone shows that the ageing test applied induces changes in the surface appearance with the formation of a patina with decrease in porosity and mineralogical changes due to dissolution transport and recrystallization of the dissolved mineralogical component of the rock as calcite the decrease in the imbibition kinetics confirms the alteration of the tested stone sample after 50 wetting drying cycles imbibition coefficients are almost halved this alteration is not homogeneous as the patina covers only some sections of the exposed surface of the stone on the well formed parts of the patina with a brownish and varnished aspect which represent about 20 of the total surface measurements show a decrease in porosity and roughness of about 25 the physico chemical characterization shows that the patina formed in the laboratory is fully comparable to natural patina observed on monuments built of tuffeau

the motion and boundary between the capricorn and australian plates the motions between the somalian antarctic and australian plates the three plates believed to meet at the rodrigues triple junction in the indian ocean are inconsistent with the assumption that all three plates are rigid the discrepancy is best explained if the australian plate contains two component plates thus the traditionally defined indo australian plate consists of three component plates and multiple diffuse plate boundaries the pattern of present deformation indicates that the boundaries between the three component plates are two unconnected zones accommodating divergence and a larger zone which we interpret as three diffuse convergent plate boundaries and a diffuse triple junction

weathering of limestone on al ziggurat walls in the ancient al nimrud city iraq diagnosing the weathering of stones used in built heritage is essential for their preservation samples taken from the surface and the core stones of al ziggurat walls in the archaeological city of al nimrud north iraq were characterized stone samples from a quarry believed to be the origin of the stones used in the construction of al nimrud were also characterized physical properties pore space system mineralogical and chemical compositions and microstructural properties of historic fresh and weathered stones were determined by various complementary techniques at the microscopic level results show that the main damage observed on the stone surface of al ziggurat walls is due to salt weathering gypsum is the predominant salt and probably originated from the soil in contact with the stones during burial of the walls results also indicate that the characteristics of samples of the core of historic stone are quite similar to those of the fresh stone extracted from the quarry demonstrating that the core of the historic stone is unweathered and that this quarry was probably the source of the construction material for al ziggurat this means that these fresh stones could be used in future restoration work

fault properties from seismic q summary a previously published investigation of seismic q from a north sea vertical seismic profiling data set has revealed an abrupt increase in attenuation to a q value of 45 which is associated with a region between 1000 and 2000 m depth where the borehole intersects a major fault zone dipping at approximately 50 this q anomaly is modelled using a linear slip theory fractures are considered to be imperfectly bonded interfaces where displacement is not required to be continuous the resulting apparent attenuation of the vertically propagating incident p wave is shown to be very dependent on the dip angle of the fault due to the relatively high predicted values of shear compliance compared to the normal compliance of fluid filled fractures at 30 60 mpa confining pressure the observed frequency independence of q is satisfactorily reproduced in addition to the low pass filtering of the downgoing p wave a difference in the frequency content of the first arriving p wave on the vertical compared to the horizontal components has been observed this difference is interpreted as resulting from rayleigh scattering from 3 d inhomogeneities within the fault zone no assumptions are required concerning the existence of intrinsic q although our results do not preclude this possibility

experimental development of low frequency shear modulus and attenuation measurements in mated rock fractures shear mechanics due to asperity contact area changes with normal stress abstractreservoir core measurements can help guide seismic monitoring of fluid induced pressure variations in tight fractured reservoirs including those targeted for supercritical co2 injection we have developed the first seismic frequency room dry measurements of fracture specific shear stiffness using artificially fractured standard granite samples with different degrees of mating a well mated tensile fracture from a dolomite reservoir core as well as simple roughened polymethyl methacrylate pmma surfaces we have adapted a low frequency 0 01 100 hz shear modulus and attenuation apparatus to explore the seismic signature of fractures and understand the mechanics of asperity contacts under a range of normal stress conditions our instrument is unique in its ability to measure at low normal stresses 0 5 20 mpa simulating open fractures in shallow or high fluid pressure reservoirs the accuracy of our instrument is demonstrated by calibration and comparison with ultrasonic measurements and

using seismic crosswell surveys to determine the aperture of partially water saturated fractures an air injection experiment in a shallow fractured limestone at conoco s borehole test facility near newkirk oklahoma has shown large effects on the amplitude but small effects on the traveltime of the transmitted seismic waves we have analyzed data from a seismic monitor survey in the kilohertz range performed during the experiment and have modeled the fracture zone as a single fracture the large amplitude decrease during the experiment is mainly attributable to the impedance contrast between the small velocities of gas water mixtures inside the fracture and the formation the intrinsic attenuation of the fracture fluid seems to be a second order effect for small apertures during the experiment the seismic wavelengths inside the fracture become comparable to the aperture dimension which allows an estimation of fracture apertures we also have analyzed a crosswell survey acquired shortly after the experiment and computed aperture and gas concentration profiles our aperture estimates range from 1 m

redatuming through a salt canopy and target oriented salt flank imaging we describe a new shortcut strategy for imaging the sediments and salt edge around a salt flank through an overburden salt canopy we tested its performance and capabilities on 2d synthetic acoustic seismic data from a gulf of mexico style model we first redatumed surface shots using seismic interferometry from a walkaway vertical seismic profile survey as if the source and receiver pairs had been located in the borehole at the positions of the receivers this process creates effective downhole shot gathers by completely moving surface shots through the salt canopy without any knowledge of overburden velocity structure after redatuming we can apply multiple passes of prestack migration from the reference datum of the bore hole in our example first pass migration using only a simple vertical velocity gradient model reveals the outline of the salt edge a second pass of reverse time prestack depth migration using full two way wave equation was performed with an updated velocity model that consisted of the velocity gradient and salt dome the second pass migration brings out dipping sediments abutting the salt flank because these reflectors were illuminated by energy that bounced off the salt flank forming prismatic reflections in this target oriented strategy the computationally fast redatuming process eliminates the need for the traditional complex process of velocity estimation model building and iterative depth migration to remove effects of the salt canopy and surrounding overburden this might allow this strategy to be used in the field in near real time

gypsum and spalling decay mechanism of tuffeau limestone the general form of degradation of tuffeau is the progressive spalling of the surface of the stone over time thick plates 1 to 3 cm thick form gradually on the surface of the stone once the plate drops the resulting stone surface turns into powder at the castle of chambord mineralogical analysis of the degraded stone throughout its depth shows the presence of gypsum caso4 2h2o located mainly within a crack network parallel to the surface the objective of this research is to study different hypotheses of gypsum formation to improve the understanding of the damaging process of spalling fresh stones were subjected to artificial ageing in the laboratory through imbibition drying tests to study the resulting distribution of gypsum as a function of several parameters the source of gypsum initial stone cracking drying conditions and analysis after different measurement sequences tested samples were analysed at different stages of ageing by using x ray diffraction and ion chromatography to localise and quantify the amount of gypsum throughout the depth results indicate that gaseous so2 can lead to a distribution of gypsum very similar to that observed in stones subjected to spalling in situ at the castle of chambord