3 d imaging of marlborough new zealand subducted plate and strike slip fault systems summary we present a 3 d seismic velocity model of the northern south island new zealand using several combined passive and active source data sets this area is the transition from hikurangi subduction in the north island to oblique continental collision along the alpine fault and the southern alps and geodetically observed deformation is consistent with plate motion being primarily taken up on a series of rotating strike slip faults we carry out simultaneous inversion for vp and vp vs and hypocentres using earthquake data recorded by the permanent seismic network and three temporary seismic arrays also using active source marine airgun data recorded at onshore stations we image the subducted hikurangi slab as a continuous unbroken feature extending from the active subduction zone to the north beneath the marlborough region the 3 d hypocentres define the subducted slab as a smooth curved feature to over 250 km depth whereas below the junction of the awatere and alpine faults the seismicity abruptly ends at 100 km depth the subducting pacific plate has a thick crust including greywacke upper crust which slows subduction the interaction of the subducted plate with the translating overlying plate forms a 50 km long zone of apparent crustal thickening with vp 7 0 km s 1 observed to 40 km depth the australian plate has a high velocity block to 65 km depth aligned with the separation point pluton and trending oblique to the subducted slab this zone of thicker australian lithosphere may also hinder subduction the marlborough faults trend about 25 to the strike of the underlying subducted slab so that the relation of faults to the slab varies along the fault strikes and the overlying plate ranges in thickness from 20 to 50 km along the faults thus the fault interaction with the subducted slab varies from translating material directly above the subducting plate to bottoming into a thick ductile region the lower crust has high vp vs under the marlborough faults except for a region of haast schist which may indicate excess fluid released by the subducted plate

empirical relationships among seismic velocity effective pressure porosity and clay content in sandstone we use a multivariate analysis to investigate the influence of effective pressure pe porosity and clay content c on the compressional velocity vp and shear velocity vs of sandstones laboratory measurements on water saturated samples of 64 different sandstones provide a large data set that was analyzed statistically for each sample relationships between effective pressure and vp and vs have been determined all samples were well fit by relationships that have an exponential increase in velocity at low pe tapering to a linear increase with pe for pe greater than 0 2 kbar there are differences in the pressure dependences of velocity for different rocks particularly at very low pressures however the differences cannot be attributed to or c for the combined set of measurements from all samples the best fitting formulations are vp 5 77 6 94 1 73c 0 446 pe e 16 7pe and vs 3 70 4 94 1 57c 0 361 pe e 16 7pe while this is admittedly a very simplified parameterization it is remarkable how well

method of estimating the amount of in situ gas hydrates in deep marine sediments abstract the bulk volume of gas hydrates in marine sediments can be estimated by measuring interval velocities and amplitude blanking of hydrated zones from true amplitude processed multichannel seismic reflection data in general neither velocity nor amplitude information is adequate to independently estimate hydrate concentration a method is proposed that uses amplitude blanking calibrated by interval velocity information to quantify hydrate concentrations in the blake ridge area of the us atlantic continental margin on the blake ridge blanking occurs in conjunction with relatively low interval velocities the model that best explains this relation linearly mixes two end member sediments hydrated and unhydrated sediment hydrate concentration in the hydrate end member can be calculated from a weighted equation that uses velocity estimated from the seismic data known properties of the pure hydrate and porosity inferred from a velocity porosity relationship amplitude blanking can be predicted as the proportions of hydrated and unhydrated sediment change across a reflection boundary our analysis of a small area near dsdp 533 indicates that the amount of gas hydrates is about 6 in total volume when the interval velocity is used as a criterion and about 9 5 when amplitude information is used this compares with a calculated value of about 8 derived from the only available measurement in dsdp 533

compressional and shear wave velocities as a function of confining stress in dry sandstones a laboratory study was carried out to investigate the influence of confining stress on compressional and shear wave velocities for a set of rock samples from gas producing sandstone reservoirs in the cooper basin south australia the suite of samples consists of 22 consolidated sublitharenites with helium porosity ranging from 2 6 to 16 6 we used a pulse echo technique to measure compressional and shear wave velocities on dry samples cylindrical 4 6 2 cm at room temperature and at elevated confining stress 60 mpa compressional and shear wave velocities in samples increase non linearly with confining stress a regression equation of the form v a be dp gives a good fit to the measured velocities with improved prediction of velocities at high confining stresses compared with equations suggested by other studies the predicted microcrack closure stresses of the samples show values ranging from 70 mpa to 95 mpa and insignificant correlation with porosity permeability or clay content there is a positive correlation between change in velocity with core porosity and permeability but this association is weak and diminishes with increasing confining stress experimental results show that pore geometry grain contact type and distribution and location of clay particles may be more significant than total porosity and clay content in describing the stress sensitivity of sandstones at in situ reservoir effective stress the stress dependence of cooper basin sandstones is very large compared with data from other studies the implication of our study for hydrocarbon exploration is that where the in situ reservoir effective stress is much less than the microcrack closure stress of the reservoir rocks the variation of reservoir effective stress could cause significant changes in velocity of the reservoir rocks the velocity changes induced by effective stress in highly stress sensitive rocks can be detected at sonic log and probably surface seismic frequencies

geophysical and geochemical logs from a copper oxide deposit santa cruz project casa grande arizona in support of an in situ leaching experiment five holes drilled into a copper oxide deposit have been logged with geophysical and geochemical tools developed for use in the petroleum industry when combined with geological description chemical analyses and mineralogical data from core and cuttings the logs provide information regarding the alteration fracturing copper distribution porosity and permeable zones correlations among sonic velocity rock strength from mechanical tests on core and alteration indicators from neutron and potassium logs demonstrate a close link between the state of alteration and the mechanical state of the rock neutron activation natural gamma ray and density logs in combination correlate so well with copper assays that log based prediction of copper content is possible in addition an estimate of whole rock mineralogy is presented in log format based on comparisons of flow logs and acoustic logs obtained in the same holes reductions in acoustic velocity appear t

understanding of elastic anisotropy of shale under triaxial loading porosity deformation approach abstracttheoretical models for the description of stress dependencies for anisotropic rocks are important for building velocity models and the interpretation of seismic data with respect to stress lithology and pore content especially important is the accurate description of the change of anisotropy due to applied anisotropic stress by means of a quantitative model to aid the interpretation the porosity deformation approach pda originally introduced as the piezosensitivity theory describes stress induced changes of elastic properties without any knowledge about the geometry and orientation of the microcracks we have developed a formulation of the theory for a transverse isotropic rock which was loaded parallel to the bedding plane and we found that it can be described theoretically as an orthorhombic rock we also found out how properties that described the velocity change due to hydrostatic loading can be used to predict elastic anisotropy under additional axial loading the number of free para

case history using time lapse vertical seismic profiling data to constrain velocity saturation relations the frio brine pilot co2 injection author s al hosni m caspari e pevzner r daley tm gurevich b abstract 2016 european association of geoscientists a engineers co2 sequestration projects benefit from quantitative assessment of saturation distribution and plume extent for field development and leakage prevention in this work we carry out quantitative analysis of time lapse seismic by using rock physics and seismic modelling tools we investigate the suitability of gassmann s equation for a co2 sequestration project with 1600 tons of co2 injected into high porosity brine saturated sandstone we analyze the observed time delays and amplitude changes in a time lapse vertical seismic profile dataset both reflected and transmitted waves are analyzed qualitatively and quantitatively to interpret the changes obtained from the vertical seismic profile we perform a 2 5d elastic finite difference modelling study the results show a p wave velocity reduction of 750 m s in the proximity of the injection well evident by the first arrivals travel time delays and amplitude change and reflected wave amplitude changes these results do not match with our rock physics model using gassmann s equation predictions even when taking uncertainty in co2 saturation and grain properties into account we find that time lapse vertical seismic profile data integrated with other information e g core and well log can be used to constrain the velocity saturation relation and verify the applicability of theoretical models such as gassmann s equation with considerable certainty the study shows that possible nonelastic factors are in play after co2 injection e g co2 brine rock interaction and pressure effect as gassmann s equation underestimated the velocity reduction in comparison with field data for all three sets of time lapse vertical seismic profile attributes our work shows the importance of data integration to validate the applicability of theoretical models such as gassmann s equation for quantitative analysis of time lapse seismic data

stress dependent anisotropy in transversely isotropic rocks comparison between theory and laboratory experiment on shale understanding the effect of stress and pore pressure on seismic velocities is important for overpressure prediction and for 4d reflection seismic interpretation a porosity deformation approach originally called the piezosensitivity theory and its anisotropic extension describe elastic moduli of rocks as nonlinear functions of the effective stress this theory assumes a presence of stiff and compliant parts of the pore space the stress dependent geometry of the compliant pore space predominantly controls stress induced changes in elastic moduli we show how to apply this theory to a shale that is transversely isotropic ti under unloaded conditions the porosity deformation approach shows that components of the compliance tensor depend on exponential functions of the principal components of the effective stress tensor in the case of a hydrostatic loading of a ti rock only the diagonal elements of this tensor expressed in contracted notation are significantly stress dependent two equal shear compo

seismic wave attenuation determined from tectonic tremor in multiple subduction zones abstract tectonic tremor provides a new source of observations that can be used to constrain the seismic attenuation parameter for ground motion prediction and hazard mapping traditionally recorded earthquakes of magnitude 3 8 are used to develop ground motion prediction equations however typical earthquake records may be sparse in areas of high hazard in this study we constrain the distance decay of seismic waves using measurements of the amplitude decay of tectonic tremor which is plentiful in some regions tectonic tremor occurs in the frequency band of interest for ground motion prediction i e 2 8 hz and is located on the subducting plate interface at the lower boundary of where future large earthquakes are expected we empirically fit the distance decay of peak ground velocity from tremor to determine the attenuation parameter in four subduction zones nankai japan cascadia united states canada jalisco mexico and southern chile with the large amount of data available from tremor we show that in the upper plate the lower crust is less attenuating than the upper crust we apply the same analysis to intraslab events in nankai and show the possibility that waves traveling from deeper intraslab events experience more attenuation than those from the shallower tremor due to ray paths that pass through the subducting and highly attenuating oceanic crust this suggests that high pore fluid pressure is present in the tremor source region these differences imply that the attenuation parameter determined from intraslab earthquakes may underestimate ground motion for future large earthquakes on the plate interface

pore pressure distribution of a mega splay fault system in the nankai trough subduction zone insight into up dip extent of the seismogenic zone we use the pore pressure distribution predicted from a waveform tomography wt velocity model to interpret the evolution of the mega splay fault system in the nankai trough off kumano japan to map pore pressure around the mega splay fault and plate boundary decollement we integrate the high resolution wt velocities with laboratory data and borehole well log data using rock physics theory the predicted pore pressure distribution shows that high pore pressures close to lithostatic pressure along the footwall of the mega splay fault extend seaward to the trough region and the normalized pore pressure ratio is nearly constant over that extent this continuity of the overpressured zone indicates that a coseismic rupture can potentially propagate nearly to the trough axis we interpret a high pressure belt within an accretionary wedge on the landward side of the present mega splay fault as evidence of the ancient mega splay fault because the ancient mega splay fault soles into the active mega splay fault the active mega splay fault may function as a basal detachment fault and is directly connected to the seaward plate boundary decollement

elastic piezosensitivity of porous and fractured rocks understanding the stress dependencies of seismic velocities is important for interpreting a variety of seismic data ranging from amplitude versus offset avo and velocity analysis to overpressure prediction and 4d seismic monitoring of reservoirs sometimes rather complex forms of these dependencies based on specific models of porous space geometry are used for example spherical contacts models duffy and mindlin 1957 merkel et al 2001 duffy merkel 2001 and crack contacts models gangi and carlson 1996 carcione and tinivella 2001 have been used in different studies gangi96 however usually the pore pressure velocity dependence along with the velocity dependence on the confining pressure are phenomenologically described by the following simple relationship zimmerman et al 1986 eberhart phillips et al 1989 freund 1992 jones 1992 prasad and manghnani 1997 khaksar et al 1999 carcione and tinivella 2001 kirstetter and macbeth 2001

stress induced seismic azimuthal anisotropy in the upper crust across the north west shelf australia seismic azimuthal anisotropy saa is observed in many areas of the earth and fast polarized directions have been mapped using earthquake surface waves and teleseismic s wave splitting over large regional and tectonic scales higher resolution petroleum exploration data including 3 d seismic surveys and dipole shear logs often exhibit azimuthal anisotropy however we are unaware of any published studies mapping saa from exploration scale data to study large scale regional and tectonic saa trends the physical mechanisms causing saa in earthquake data are a subject of great interest comparing regional trends to the higher resolution exploration trends may help understand these mechanisms we present a saa analysis using seismic exploration data across the north west shelf nws of australia we map the fast polarization directions from 34 dipole shear logs and two 3 d seismic surveys and compare them to in situ maximum horizontal stress orientations h our results show that the and h trends correlate across a geographical area spanning almost 2000 km and are similar to published results in the region from earthquake seismology these results suggest that differential horizontal stress is the likely mechanism causing saa at a wide range of spatial scales on the nws of australia we also show that saa is not observed at exploration scales in some areas of the nws and propose a lithology dependent stress sensitivity model in which saa is strongest in clean unconsolidated quartz dominated sandstones and weaker or nonexistent in well consolidated cemented rocks and shale dominated sediments

lame parameters of common rocks in the earth s crust and upper mantle 1 lame parameter and shear modulus are the most important intrinsic elastic properties of rocks the lame parameter which relates stresses and strains in perpendicular directions is closely related to the incompressibility and contains a high proportion of information about the resistance to a change in volume caused by a change in pressure recent studies have emphasized the roles played by in the discrimination of gas sands from carbonates and shale in sedimentary basins and in the seismic reflection of crustal fault zones here we analyze the equivalent isotropic elastic data of 475 natural rocks in order to characterize values for common types of crystalline rocks in the earth s crust and upper mantle and their variations with pressure p temperature t and mineralogical composition when no partial melting metamorphic reaction dehydration or phase transformation occurs of a crystalline rock as a function of p and t can be described by a d dp p c exp kp d dt t where a is the projected value at zero pressure if microcracks were fully closed d dp is the pressure derivative in the linear elastic regime c is the initial drop caused by the presence of microcracks at zero pressure k is a decay constant of the drop in the nonlinear poroelastic regime and d dt is the temperature derivative the parameter increases nonlinearly and linearly with increasing pressure at low 300 mpa pressures respectively in the regime of high pressures decreases quasi linearly with increasing temperature with d dt values in the range of 1 10 10 3 gpa c approaching the quartz transition temperature quartzite displays negative values in the density and plots the main categories of lithology can be clearly distinguished the ultramafic rocks display systematic decreases in both and with increasing the degree of serpentinization eclogites mafic rocks gabbro diabase mafic granulite and mafic gneiss and felsic rocks granite diorite felsic gneiss intermediate gneiss and metasediments are characterized by high moderate and low and values respectively for pyroxene and olivine both and increase but decreases with increasing the fe mg ratios in the plagioclase series both and increases with increasing the anorthite content increases in the contents of garnets sillimanite rutile zircon ilmenite and spinel result systematically in an increase in rock s and values the present results provide improved constraints on the discrimination of composition for crustal and upper mantle rocks in terms of and

effective stress coefficient for seismic velocities in carbonate rocks effects of pore characteristics and fluid types the concept of effective stress is key for understanding the dependence of rock elastic and compaction behaviors on stress and pore fluid pressure previous studies on the concept largely used data acquired on siliciclastic rocks carbonate rocks however display elastic and compaction behaviors that can be very different than those of siliciclastic rocks for example applying most velocity to pore pressure transforms in the context of carbonate reservoirs can be quite challenging our study used an experimental approach a disequilibrium compaction scenario to assess effective stress coefficient n for velocities in three carbonate samples displaying comparable porosities but different dominant pore types in terms of shape and compliance different saturating fluids nitrogen and distilled water were used one at a time which allowed us to compare both pore and fluid type effects on the coefficient n between these rocks we found that n is generally bounded by unity the exception is with nvs n derived from shear wave velocities obtained under nitrogen saturated conditions nvs is higher than 1 on the three studied samples under nitrogen saturated conditions the less compliant the main pore types in a given rock are the higher the value of nvs is higher than unity values of nvs indicate a deviation from the behavior predicted by existing theories this could stem from i the fact that theoretical analyses assume a pore fluid whose properties are not comparable to those of nitrogen and or ii the way the bulk volumetric strain a main factor in elastic wave propagation is incorporated into those theories

crustal heterogeneity and subduction processes 3 d vp vp vs and q in the southern north island new zealand summary along the southern hikurangi subduction zone in the southern north island new zealand the subduction zone changes from volcanic with moderately weak interseismic coupling to non volcanic with strong coupling in wellington to investigate how material heterogeneity relates to subduction processes we compute 3 d seismic properties using 342 earthquakes and 2 shots recorded by a 165 station seismic array the time base for some telemetered temporary stations was not stable which required revising the inversion code to allow an additional origin time related to the telemetered stations progressive inversions from 2 d to fine 3 d were carried out for vp vp vs and qp combined interpretation of these three seismic properties highlights features of the subduction zone the subducted slab is imaged as a high velocity high q feature in the overlying crust from southeast to northwest there is low velocity in the accretionary wedge high velocity in the axial ranges and low velocity in the wanganui basin high vp vs and low qp characterize the crust east of the north island dextral fault belt high vp vs is imaged above the subducted slab to 40 km depth in the northern half of the study area low qp is also prominent above the slab particularly trenchwards of the volcanic region in marked contrast to the high vp vs the low qp above the slab extends as a continuous feature up to the low qp in the shallow crust underlying the volcanic region the low qp and high vp vs are correlated with the region of weaker coupling and are consistent with significant subducted sediments with associated fluid release vp vs is particularly sensitive to overpressured fluid in the compressional forearc whereas qp also images the hydrostatically pressured fluid transport in the more permeable extensional volcanic region the rheology of the lower crust of the overlying plate is a factor in large scale subduction coupling as evidenced by the terrane boundaries and haast schist in the section near wellington the changing rheology of the lower crust of the overlying plate in the southern north island also provides a possible explanation for the southward cessation of volcanism

composition microstructures and petrophysics of the mozumi fault japan in situ analyses of fault zone properties and structure in sedimentary rocks from shallow crustal levels 1 we characterize the chemical microstructural and geophysical properties of fault related rock samples from the 80 100 m wide mozumi fault zone north central honshu japan the fault is exposed in a research tunnel 300 400 m below the ground and we combine geological data with borehole geophysical logs to determine the elastic and seismic properties of the fault zone detailed mapping within the tunnel reveals that the fault zone consists of two zones of breccia to foliated cataclasites 20 and 50 m thick two narrow tens of centimeters wide principal slip zones on which most of the slip occurred bound the central fault zone the dominant deformation mechanisms within the fault zone were brittle fracture brecciation slip localization plastic deformation and vein formation in a sericite calcite rich matrix clay alteration patterns are complex within the fault zone with clay rich fault breccia enriched in smectite illite and kaolinite relative to the kaolinite and illite dominant in the host rock whole rock geochemical analyses show that the fault related rocks are depleted in fe na k al mg and si relative to the host rock the fault zone exhibits depressed electrical resistivity values by 10 100 ohm m relative to the wall rock values of vp and vs values that are 0 30 and 0 40 km s 10 20 less than protolith values the spontaneous potential logs indicate that the fault zone has increased freshwater content relative to formation waters wellbore based measurements of vp and vs in fault related rocks to enable us to calculate values of young s modulus from 16 2 to 44 9 gpa and poisson s ratio for the fault zone of 0 263 to 0 393 the protolith has young s modulus of 55 4 gpa and a poisson s ratio of 0 242 lowest calculated values of young s modulus and highest calculated values of poisson s ratio correspond to fault breccia with increased porosity high fluid content and low resistivity values taken together these data show that the shallow portion of the mozumi fault consists of a complex zone of anastomosing narrow slip zones that bound broad zones of damage fluid rock alteration and deformation created altered fault related rocks which have resulted in overall reduced interval velocities of the fault zone these data indicate that seismic waves traveling along the interface or internally reflected in the fault zone would encounter rocks of differing and reduced elastic properties relative to the host rocks but that in detail material properties within the fault may vary

detection of overpressure zones and a statistical model for pore pressure estimation from well logs in the krishna godavari basin india abnormally high pressures measured by repeat formation tester rft and detected by well log data from 10 wells in the krishna godavari k g basin occur in the vadaparru shale of miocene and raghavapuram shale of early cretaceous age overpressures generated by disequilibrium compaction and pore pressures have been estimated using the conventional eaton sonic equation with an exponent of 3 0 the observed abnormal pore pressure gradient ranges from 11 85 to 13 10 mpa km whereas fracture pressure gradient varies from 17 40 to 19 78 mpa km the magnitude of vertical stress sv has a gradient from 21 00 to 23 10 mpa km the minimum horizontal principal stress sh magnitude is found to vary from 64 to 77 of the sv in normally pressured to overpressured sediments a multiple linear regression model with a squared multiple correlation coefficient r2 of 0 94 is proposed for pore pressure prediction from gamma ray density and sonic logs to focus on efficient drilling operations and to prevent borehole instability the statistical model has been calibrated with the rft data from five wells covering about 3400 sq km area of the onshore k g basin the model predicted pore pressure values are in close agreement with the actual rft data for another four wells including a well in the offshore k g basin hence the proposed regression model may be useful for predicting pore pressure from other well logs in the k g basin

estimation of rock frame weakening using time lapse crosswell the frio brine pilot project abstractco2 injection into subsurface reservoirs leads to pressure and saturation changes furthermore co2 brine minerals interaction could result in dissolution or reprecipitation of rock frame forming minerals observed time lapse seismic associated with co2 injection into poorly consolidated sandstone at the frio co2 injection site texas usa could not be predicted using classical rock physics models i e models involving elastic changes in the rock frame due to saturations and or pressures changes only and assuming no changes in the rock microstructure that and the changes in the fluid chemistry after co2 injection suggests that the assumption of a constant rock microstructure might be violated using high resolution time lapse crosswell data we have developed a methodology for estimating changes in the rock frame by quantifying the rock frame drained moduli before and after co2 injection based on rock microstructure diagnostics we found that the changes in the drained frame elastic prope

velocities and quality factors of sedimentary rocks at low and high effective pressures summary techniques for measuring acoustic velocities and quality factors q of sedimentary rocks in the laboratory are sufficiently accurate to establish closely fitting regression curves which represent the variation of these acoustic properties with pressure ultrasonic p and s wave measurements of velocity v v and q q q were made on 16 different water saturated sandstone samples at various effective pressures using an ultrasonic reflection technique and the data were fitted using a simple regression equation containing a constant plus linear and exponential pressure dependent terms the redundancy of the linear term in the regression of q data suggests that microcracks alone govern the pressure variation of q whereas velocities are additionally dependent on another mechanism consistent with the changes in elastic moduli caused by intergranular compression causing small reductions in porosity the implied rates of microcrack closure with increasing effective pressure in all samples were found to be comparable the regression equations describe the data closely enough to enable the extrapolation of acoustic properties to both low and high effective pressures this is of practical use since laboratory techniques can produce uncertain results at low pressures due to coupling problems and low signal strengths whilst high pressures require large confining vessels low pressure and high pressure data are applicable to shallow seismic surveys and hydrocarbon exploration respectively

shear wave velocities and anisotropy in the barbados accretionary complex s wave velocities at the base of the barbados accretionary wedge were determined from mode converted s waves in two vertical seismic profiles in ocean drilling program boreholes at hole 949c the profile extends from 92 to 397 m below seafloor mbsf ending 17 m into the decollement zone separating the wedge from the underthrust sediment on the subducting plate beneath at hole 948d the profile extends from 105 to 471 mbsf ending 19 m above the decollement zone s wave velocities are 303 549 m s at hole 949c and 453 679 m s at hole 948d the profiles show that the lowest 70 m of the accreted sediment just above the decollement has lower s wave velocity 379 26 m s at hole 949c and 453 11 m s at hole 948d and higher ratio of p wave to s wave velocity vp vs 4 59 0 31 at hole 949c and 3 99 0 10 at hole 948d than in the overlying layer this coincides with high clay content that has a high proportion of smectite shear wave splitting observed in records from the lowest 100 m of the accretionary wedge at both sites indicates little or no anisotropy in the low velocity zone a single measurement at hole 949c of the horizontal component of polarization of the leading split s wave from an ocean bottom shot is n68 e 20 at hole 949c split shear wave delays in the downward propagating s wave originating at a fault at 275 mbsf indicate strong anisotropy in the range 275 306 mbsf and little or no anisotropy in the range 306 380 mbsf the rate of increase of delay between 275 and 306 mbsf 0 52 0 16 ms m can be modeled by either a hudson cracked medium with crack density 0 186 0 054 or preferably a hornby model of shale with 44 of clay particles aligned within 5 of the symmetry plane this strong anisotropy is attributed to scaly fabric alignment of clay particles by pervasive shear in the fault zone which is observed in core the low anisotropy in the remainder of the section shows that there is very little overall alignment of pore space in the lower part of the accreted sediments supporting the hypothesis that the sediments are undercompacted rather than hydrofractured the low s wave velocities and high vp vs ratios indicate undercompaction and low effective stress despite the tectonic burial of the lowermost accreted sediments

prediction of elastic wave velocities in sandstones using structural models elastic wave propagation in fluid saturated sandstones depends upon two sets of rock features 1 the volume fractions and elastic constants of the rock constituents quartz clay water etc and 2 microstructural geometry grain contacts pore aspect ratios while the former data are usually obtainable the latter are relatively inaccessible we present a new method for determining microstructural data using idealized but physically representative models of sandstone the key to the method is the simulation of certain depositional and diagenetic processes in a manner that completely specifies the geometry of the resulting models hence the geometric features of the grain space and void space required for various theories of elastic propagation can be calculated directly from the models we find good agreement between predictions and measurements of compressional and shear wave velocities in both clean and clay bearing saturated sandstones in contrast with previous efforts at predicting velocitie

simultaneous core sample measurements of elastic properties and resistivity at reservoir conditions employing a modified triaxial cell a feasibility study adaptations of existing triaxial cells for ultrasonic p and s wave measurements are well documented this paper proposes further modification of such a cell so that also resistivity measurements can be carried out simultaneously at reservoir conditions by employing the top cap and the pedestal of the cell as electrodes axial resistivity measurements are now feasible in order to minimize the polarization effect of this two electrode arrangement careful analyses have been carried out to optimize the choice of electrode coating and measurement frequency band radial resistivity measurements are also included in the system by introducing a strap electrode system in a reservoir under production changes in both saturations temperature if steam injection and stresses can take place therefore the modified triaxial system should be able to measure the integrated effects on the acoustic parameters and electric responses caused by variations in each of these parameters the feasibility of the system to obtain such reliable information is demonstrated employing a small selection of core samples in the future such combined measurements on reservoir core samples can be used to link both seismic and electromagnetic observations to the actual earth model and constrain both modelling and inversion

in situ calibrated velocity to stress transforms using shear sonic radial profiles for time lapse production analysis abstract borehole acoustic waves are affected by near and far field stresses within rocks that exhibit stress sensitivity typically in medium to high porosity formations nonlinear or third order elastic constants are obtained from the inversion of borehole sonic shear radial profiles with an elastic wellbore stress model the stress to velocity relationship determined from these profiles in the elastic region surrounding the wellbore is used for calibration to compare with empirical laboratory data traditionally used in time lapse seismic feasibility studies to assess simulated production this analysis enables rock physicists to use the wellbore as a laboratory and to examine the stress dependence of the acoustic velocities from in situ field data in their zone of interest laboratory experiments on core samples can yield both empirical and mathematical rock physics models to describe the relationship between stress and velocity to link rock properties to in situ measurements of acoustic data seis

seismic anisotropy and its impact on imaging the shallow alpine fault an experimental and modeling perspective the transpressional alpine fault in new zealand has created a thick shear zone with associated highly anisotropic rocks low seismic velocity zones lvz and high seismic reflectivity are recorded in the alpine fault zone but no study has explored the underlying physical rock parameters of the shallow crust that control these observations protomylonites are the volumetrically dominant lithology of the fault zone here we combine experimental measurements of p wave speeds with numerical models of elastic wave anisotropy of protomylonite samples to explore how the fault zone can be seismically imaged numerical models that account for the porosity free real samples fabric elastic tensors from ebsd are calculated by mtex and a finite element model fem while microfractures are modeled with differential effective media dem theory at effective pressures representative of the alpine fault brittle zone experimental wave speeds are lower than those predicted by mtex fem a possible dem model suggests that a combination of random and aligned microfractures with aspect ratios increasing with pressure can explain the experimental wave speeds for pressures 70 mpa such micro porosity in the form of foliation and mica basal plane parallel microfractures and grain boundaries is validated with synchrotron x ray microtomography and tem images finally by modeling anisotropy of seismic reflection coefficients with angle of incidence we demonstrate that the high reflectivity and lvz observed at the alpine fault can only be explained if this microporosity is accounted for throughout the brittle fault zone even at depths of 7 10 km

stress induced elastic anisotropy of the etnean basalt theoretical and laboratory examination 1 a theory the stress sensitivity approach has been developed which relates the elastic moduli of anisotropic rocks to the stress tensor and pore pressure for an arbitrary symmetry of the applied load the theory explains the stress induced changes of seismic velocities in terms of stress induced changes of the pore space geometry the stress dependent anisotropy is described in terms of thomsen s anisotropy parameters e and to test the theory we analyze the laboratory high frequency results of deformation of an isotropically crack damaged dry lava flow basalt from mt etna volcano the theory states that under an anisotropic i e axisymmetric triaxial load and in the case of an initially isotropic rock 1 the anisotropy parameters are linear functions of the stress exponentials i e exponential functions of principal stress components and 2 the ratio of these anisotropy parameters as a function of the stress is constant in order to verify these relationships the stress exponentials and the anisotropy parameters based on the measured velocities are computed as well as the expected ratio of the thomsen s parameters our experimental results are in very good agreement with the theoretically predicted relations

linking preferred orientations to elastic anisotropy in muderong shale australia the significance of shales for unconventional hydrocarbon reservoirs nuclear waste repositories and geologic carbon storage has opened new research frontiers in geophysics among many of its unique physical properties elastic anisotropy had long been investigated by experimental and computational approaches here we calculated elastic properties of cretaceous muderong shale from australia with a self consistent averaging method based on microstructural information the volume fraction and crystallographic preferred orientation distributions of constituent minerals were based on synchrotron x ray diffraction experiments aspect ratios of minerals and pores determined from scanning electron microscopy were introduced in the self consistent averaging our analysis suggested that phyllosilicates i e illite mica illite smectite kaolinite and chlorite were dominant with 70 vol the shape of clay platelets displayed an average aspect ratio of 0 05 these platelets were aligned parallel to the bedding plane with a high degree of preferred orientation the estimated porosity at ambient pressure was 17 vol and was divided into equiaxial pores and flat pores with an average aspect ratio of 0 01 our model gave results that compared satisfactorily with values derived from ultrasonic velocity measurements confirming the validity and reliability of our approximations and averaging approach

variations in petrophysical properties along a mixed siliciclastic carbonate ramp upper jurassic ricla ne spain abstract a multi scale petrophysical study was performed on an upper jurassic siliciclastic carbonate ramp system near the village of ricla spain a combination of textural field observations thin section and grain size analysis chemical mineralogical thermo gravimetric analysis and physical porosity gamma ray and velocity measurements properties was used to capture the heterogeneity of this mixed sedimentary system subsequently synthetic seismic sections with varying resolution were created to show the characteristics of the internal ramp structures the translation from the measured petrophysical properties to a synthetic seismic section helps to better understand subsurface seismic although upscaling problems are a recurring issue the homogeneity of the samples and the continuity of the outcrop and facies reduce the number of uncertainties acoustic properties are generally controlled by the amount and type of pore spaces due to the low porosities the ramp geometry is characterized by an overall lateral homogeneity and vertical heterogeneity textural sedimentological and stratigraphic transitions in the outcrop are related to the defined facies each has its own unique mineralogical signature amplitude variations in the synthetic seismic profile are primarily caused by changes in mineral composition thus facies transitions

temporal change of upper crustal vp vs ratios with volcanic evolution in redoubt volcano abstract volcanic activities accompany changes in the physical and chemical properties of the medium the ratio between p and s wave velocities v p v s is sensitive to the medium property changes we investigate temporal variations of the v p v s ratios in the upper crust around redoubt volcano in the 1989 2014 time period using the traveltimes of local earthquakes the v p v s ratios reached 2 0 immediately prior to the 1989 1990 and 2009 eruptions these high v p v s ratios may be associated with partial melts in the edifice the v p v s ratios rapidly decreased to 1 7 during the 1989 1990 and 2009 eruptions due to decreasing temperatures fluids and pore pressures and increasing effective stresses after melt eruptions and gas emission the change rates of the v p v s ratios showed evident spatial distributions the v p v s ratios increased at a rate of 0 025 0 003 yr 1 below the 2009 vent during the inter eruption period between the 1989 1990 and 2009 eruptions due to an increase in the temperature which may be associated with the recharge of the magma in the lower crust the increase rate of the v p v s ratios was as low as 0 005 0 001 yr 1 in the regions located away from the eruption site the v p v s ratios appear to have increased consistently at a rate of 0 017 0 004 yr 1 since the 2009 eruption

overburden 4d time shifts indicating undrained areas and fault transmissibility in the reservoir abstract production induced geomechanical stress changes cause velocity changes in the overburden that might be detected as 4d seismic time shifts the strength of the velocity changes depends on the degree of pressure changes and the elastic properties of the reservoir and overburden layers even small velocity changes less than 1 might accumulate into detectable seismic time shifts at the top reservoir since the overburden thickness typically ranges from one to several kilometers reservoir pressure changes inducing seismic time shifts are observed in the overburden of the snorre heidrun and statfjord fields all located on the norwegian continental shelf the strong correlation between overburden time shifts geomechanics and reservoir pressure changes is used to indicate undrained areas and transmissibility across faults which is useful information for increased oil recovery well planning and reservoir model updating 4d geomechanical models are built with input from simulated reservoir pres

low frequency exchange of mass between ocean basins 1 we examine the gravity recovery and climate experiment grace data and output from an ocean model to quantify mass fluctuations for the pacific atlantic and indian ocean basins from august 2002 until december 2008 the monthly spatial mean is removed to study interbasin mass exchange we find a seasonal exchange of mass between the atlantic and pacific that is similar to one documented previously although the amplitude observed by grace is about 20 lower than that simulated by an ocean model there are also significant fluctuations with periods longer than 1 year we find large interannual exchanges in 2005 and 2007 with grace observing yearly averaged mass anomalies in the pacific that are about 30 40 larger than simulated by a model this is shown to be from significant interannual mass losses from the indian ocean that are observed by grace but not simulated by the model a longer run of the model from 1976 to 2008 suggests that such interbasin mass exchanges are a regular occurrence and can last for as long as a couple of decades

slow wavespeeds and fluid overpressure in a region of shallow geodetic locking and slow slip hikurangi subduction margin new zealand abstract travel times recorded onshore from active source marine seismic surveys were used to determine hikurangi forearc wavespeeds ray path midpoints sample forearc crust above the shallow v p from the seabed to 4 km depth consistent with rapidly deposited clastic sediments and near constant v p 5 0 0 2 km s at depths of 4 10 km within the forearc the northern region has slow slip events at shallow depths of c 5 15 km beneath the volume sampled by our analysis average travel times at offsets of 20 80 km are 1 s more than at equivalent offsets in the south and v p increases with depth within the forearc from 3 5 0 1 km s at 4 km depth to 4 5 0 2 km s at 10 km depth we interpret the low wavespeeds in terms of compaction disequilibrium and compare seismic inferences of anomalously high porosity 10 with hydrostatic reference compaction models to show effective stress is low in both the north 27 10 mpa and south 36 14 mpa in the south pore space and conduits have a high chance of being localized on faults or sand layers the wedge is clearly compressionally critical and we suggest the higher seismic velocities recorded primarily reflect higher effective stress levels transmitted through the rock framework the observed wedge geometry and our estimate of fluid pressure within the wedge 0 87 0 05 suggest a weak overpressured subduction thrust in the north we suggest high fluid pressure is maintained by a large fluid inventory from subducting sediment a pore space geometry characterized by pervasively fractured rock and mudstone and a lower mean stress due to its stable and non critical wedge geometry we consider both end member assumptions of convergent and tensile failure the latter of which reveals the possibility of near lithostatic fluid pressure on the north hikurangi subduction interface although this remains unproven our observations are consistent with high fluid pressures encountered in petroleum wells at depths

surface seismic and electrical methods to detect fluids related to faulting in the absence of drilling surface based geophysical methods are necessary to observe fault zones and fault zone physical properties at seismogenic depths these in situ physical properties can then be used to infer the presence and distribution of fluids along faults although such observations are by nature indirect and become less exact with greater depth multiple observations of a range of such geophysical properties as compressional and shear seismic velocity vp and vs vp v5 ratio related to poisson s ratio resistivity and attenuation in and adjacent to fault zones offer the greatest hope of making inferences of the fault zone geometry fluids in the fault zone and fluid reservoirs in the surrounding crust for simple geometries fault zone guided waves can provide information on fault zone width and velocities for faults of the order of 200 m wide to address the question of whether a narrow fault zone can be imaged well enough at depths of seismic rupture to infer the presence of anomalously high fluid rock ratios we present synthetic seismic tomography and magnetotelluric examples for an ideal case of a narrow fault zone with a simple geometry large changes in material properties and numerous earthquakes within the fault zone a synthetic 0 5 km wide fault zone with 20 velocity reduction is well imaged using local earthquake tomography when sequential velocity inversions are done the true fault width is found even to 9 km depth although the calculated amplitude of the velocity reduction is lower than the actual amplitude vp vs is as well determined as vp magnetotelluric imaging of a synthetic fault zone shows that a conductive fault zone can be well imaged within the upper 10 km further a narrow 1 km very low resistivity 3 ohm m fault core can be imaged within a broad 5 km low resistivity 10 ohm m fault zone illustrating that regions of a fault containing large quantities of interconnected fluids within a broader conductive fault zone should be detectable thus variations in fluid content and fluid pressure can be inferred from electrical and seismic methods but there will always be uncertainty in these inferences due to the trade off with other factors such as intrinsic variations in porosity mineralogy and pore geometry the best approach is combined modeling of varied seismic and electrical data

plateau uplift forcing climate change around 8 6 ma on the northeastern tibetan plateau evidence from an integrated sedimentary sr record abstract the uplift of the northern tibetan plateau tp has long been regarded as one of major factors accounting for both the enhanced process of aridification recorded in central asia and the shifts in the asian monsoonal circulations that are known to have occurred at approximately 8 ma until now there have been few sedimentary records reported on which can directly and in an integrated fashion shed light on the region s tectonic and climate regimes this can be largely attributed to the fact that the influence exerted by the presence of source materials and subsequent sedimentary sorting in this tectonically active region would be likely to bias significantly any paleoclimatic interpretation of silicate derived proxies based on detailed investigations of strontium sr distributions revealed by multi step leaching in a fluvial sequence from the linxia basin which includes paleosols we reconstructed the long term late miocene regional climatic and environmental changes likely to have occurred on the northeastern tp from 12 1 to 5 2 ma we investigated sr related proxies in two typical paleosol profiles to constrain sr mobility in paleosol weathering and thus to further prompt the interpretation of sr related proxies along the whole section we would suggest that carbonate derived sr concentrations and sr ca ratios are suitable proxies for tracing regional climate change associated with weathering and pedogenesis together they exhibit weakened chemical weathering intensity and pedogenesis at 8 6 ma the concomitant appearance of immature sediments through poor sedimentary sorting revealed by silicate derived rb sr 87 sr 86 sr and eu anomaly eu eu alongside a sharp increase in sedimentation rates noted at this time suggests that it was indeed tectonic uplift that principally controlled the dramatic climatic and environmental changes this multi proxy record of concomitant tectonic uplift and climate change in the linxia basin provides direct geological evidence for uplift driven climate change in the northeastern tp region

the inverse correlations between methane content and elastic parameters of coal bed methane reservoirs we investigated three coal bed methane cbm reservoirs in which there exist when we are careful about data quality and reduce environmental variations inverse correlations between methane content and the elastic properties of the coal beds such inverse correlations may exist in general in high and medium rank cbm reservoirs there is evidence that supports the generalization of such inverse correlations and factors that distort them these distorting factors may prevent identification of such inverse correlations in certain cbm prospects however they cannot negate the underlying inverse correlations such inverse correlations may play a role in cbm amplitude versus offset avo similar to the role played by gassmann biot theory gassmann 1951 biot 1956 1962 in avo technology for conventional gas reservoirs this may lay the first brick for a theoretical basis of cbm avo

practical seismic petrophysics the effective use of log data for seismic analysis a quick scan of the seg web site shows that the phrase seismic petrophysics has been used explicitly in the title of a paper or abstract six times the earliest of which was by williams et al in 1996 the hugoton cross well survey a direct look at stratigraphy seismic petrophysics and shale anisotropy however the first attempt at a definition and an expanded description of seismic petrophysics was published by wayne pennington in the leading edge in 1997 seismic petrophysics an applied science for reservoir geophysics he defines seismic petrophysics as follows the purposeful application of rock physics theory as calibrated by laboratory and well measurements to the interpretation of seismic data

wave velocities in sandstones from elastic network simulations an elastic network model is used to calculate compressional and shear wave velocities in a model sandstone the model consists of mineral components and pores distributed at random on a regular cubic lattice springs are used to represent compressional shear and rotational forces between neighboring grains we have used the network model to calculate the dependence of wave velocities on porosity and clay content in sandstones the calculated velocities are a linear function of both porosity and total clay content the coefficients in this bilinear relationship are in quantitative agreement with published experimental correlations for sandstone velocities this result provides theoretical support for the linear velocity porosity clay content relationship commonly assumed in empirical correlations the rotational forces between grains are necessary to obtain quantitative agreement with experimental data wave velocities calculated using the continuum self consistent imbedding approximation agree with the elastic network for quartz water mixtures but not for quartz clay mixtures this disagreement demonstrates the importance of a granular elastic model with rotational forces for calculating velocities in rocks with multiple mineral components

porosity and elastic anisotropy of rocks under tectonic stress and pore pressure changes elastic properties of rocks depend on tectonic stress using the theory of poroelasticity as a constraint we analyze features of these dependencies related to changes in rock pore space geometry we develop a formalism describing elastic moduli and anisotropy of rocks as nonlinear functions of confining stress and pore pressure this formalism appears to agree with laboratory observations to a first approximation elastic moduli and seismic velocities as well as porosity depend only on the difference between the confining tectonic stress and pore pressure however in general both the confining stress tensor and the pore pressure must be taken into account as independent variables the stress dependent geometry of the pore space fully controls the stress induced changes in elastic moduli and seismic velocities specifically the compliant porosity plays the most important role despite the fact that in many rocks the compliant porosity is a very small part of total porosity changes in compliant porosi

the ability of rock physics models to infer marine in situ pore pressure pore fluid pressure is an important parameter defining the mechanical strength of marine sediments obtaining high spatial resolution in situ pore pressure measurements in marine sediments however is a challenge and as a result only a handful of in situ pore pressure measurements exist at scientific drill sites integrating rock physics models with standard iodp odp measurements provides a potentially widely applicable approach for calculating in situ pore pressure here we use a rock physics approach to estimate in situ pore pressure at two scientific ocean drill sites where in situ pressure is well constrained odp site 1173 used as reference for normal hydrostatic fluid pressures and odp site 948 where previous studies infer high fluid pressures 0 45 0 95 where the pore pressure ratio is defined as the pore pressure above hydrostatic divided by the difference between the largest principal stress and hydrostatic stress our analysis indicates that the rock physics method provides an accurate low precision method for estimating in situ pore pressure at these drill sites and sensitivity analysis indicates this method can detect modestly high 0 6 pore pressure at the 95 confidence level this approach has broad applicability because it provides an inexpensive high resolution meter scale method for retrospectively detecting and quantifying high pore pressure at any drill site where quality wireline logs and ocean drilling data exist

newly observed deep slow slip events at the central hikurangi margin new zealand implications for downdip variability of slow slip and tremor and relationship to seismic structure 1 we present previously undocumented deep 25 45 km depth moderate duration 2 3 months slow slip events sses directly downdip of known shallow 15 km depth short term 2 3 weeks sses at the central hikurangi margin new zealand the moderate duration sses produce 2 6 mm of horizontal displacement at continuous global positioning system stations in 2006 and 2008 similar to cascadia sses they involve 2 5 cm of slip over 5000 km2 of the subduction interface tremor occurs just downdip of the deep sse source area we also present results from a large shallow 12 km sse in 2013 just updip of the 2006 2008 sses the location of deep sses between shallow short term sses and tremor indicates strong downdip variation of subduction interface slip behavior at central hikurangi the deep sses occur where qp and vp vs data suggest an accumulation of fluid rich underplated sediment at the interface consistent with the idea that sses occur under high fluid pressure

acoustic and petrophysical relationships in low shale sandstone reservoir rocks this paper describes the measurements of the acoustic and petrophysical properties of two suites of low shale sandstone samples from north sea hydrocarbon reservoirs under simulated reservoir conditions the acoustic velocities and quality factors of the samples saturated with different pore fluids brine dead oil and kerosene were measured at a frequency of about 0 8 mhz and over a range of pressures from 5 mpa to 40 mpa the compressional wave velocity is strongly correlated with the shear wave velocity in this suite of rocks the ratio v p v s varies significantly with change of both pore fluid type and differential pressure confirming the usefulness of this parameter for seismic monitoring of producing reservoirs the results of quality factor measurements were compared with predictions from biot flow and squirt flow loss mechanisms the results suggested that the dominating loss in these samples is due to squirt flow of fluid between the pores of various geometries the contribution of the biot flow loss mechanism to the total loss is negligible the compressional wave quality factor was shown to be inversely correlated with rock permeability suggesting the possibility of using attenuation as a permeability indicator tool in low shale high porosity sandstone reservoirs

saturation pore pressure and effective stress from sandstone acoustic properties 1 acoustic velocity and vp vs ratio show different responses in saturated and dry rocks under increasing differential pressures velocity is also shown to be sensitive to pore pressure not just differential pressure under identical low differential pressure conditions velocity is higher in sandstones when pore pressure is high during simulation of inflationary overpressure conditions vp vs ratios of sandstones with high fluid pressures are shown to lie between dry conditions and saturated conditions with constant and low pore pressure thus the velocity differential pressure relationship is not unique however the use of the measured biot effective stress coefficient results in a unique relationship it is postulated that higher velocity and different vp vs ratios are caused by loss of compliance in microfractures due to stiffening by increasing fluid pressure

comparative tomography of reverse slip and strike slip seismotectonic provinces in the northern south island new zealand abstract actively deforming crust and upper mantle around the obliquely convergent pacific australia plate boundary in the northern south island of new zealand have been investigated by seismic tomography using data from a temporary c 50 station network plus geonet the alpine wairau fault principal component of the plate boundary at the surface transects the study area separating the buller nelson bn province of active compressional inversion involving steep reverse faulting to the northwest from the marlborough fault system ma dominated by dextral strike slip faulting to the southeast in the course of this study ma hosted the 2013 seddon earthquake sequence m5 9 6 6 and the 2016 m7 8 kaikoura earthquake active fault structures and present seismicity are associated with a heterogeneous distribution of low velocity and vp vs anomalies elsewhere there is a general association between crustal seismicity and low velocity zones along major fault structures within both the ma and bn seismotectonic provinces along which high vp vs anomalies are locally conspicuous areas of active crustal seismicity are also generally characterized by high vp vs for instance the hypocentre and aftershocks of the 2016 m7 8 kaikoura earthquake overlie a low velocity region with high vp vs the coincidence of anomalously low vp and vs and anomalously high vp vs with zones of high electrical conductivity defined by a previous mt transect is consistent with the notion that upward migration of overpressured hydrothermal fluid from the subducting slab at depth leads to a heterogeneous distribution of overpressured fluid in and around the base of the crustal seismogenic zone weakening the overlying crust and promoting seismic rupture along major fault systems it seems possible that the association of mid crustal low velocity zones with anomalously high vp vs may diagnose rupture preparation zones where frictional strength is being lowered by the build up of fluid overpressure concurrent with accumulating shear stress so that eventual fault failure is dual driven

three dimensional p velocity image of the oroville reservoir area california from local earthquake tomography this study images the p velocity structure of a region in the vicinity of the large artificial reservoir at oroville california the velocity structure of the upper crust to a depth of 12 km was obtained by simultaneous inversion of p arrivals of 168 aftershocks of the 1975 oroville earthquake a decrease in p wave velocity by 7 to 8 was observed across a known fault zone the hypocenters of the 1975 sequence are associated with a southwest dipping structure characterized by low velocity with most of the deeper activity occurring in adjacent regions of higher velocity resolution of the velocity structure was examined through inversions of synthetic travel times using different starting velocity models although the role of the reservoir in generating the low velocities remains speculative the structure is comparable to that of some active segments of the san andreas fault where fluid pressures are thought to be high

resolution limits of fluid overpressures from mineralogy porosity and sonic velocity variations in north sea mudrocks pore pressure identification in mudrocks largely relies on indirect methods including analyses of sonic velocity data the magnitude of pore pressure changes that can be resolved from such data depends on the impact of fluid pressures on well log responses and on the velocity responses to lithological variations that could be mistaken for indications of pore pressure changes analysis of relationships between sonic velocity mineralogy and porosity from 11 north sea wells demonstrated porosity variations of up to 5 from the mean value in mudrocks at any given depth between 1 and 3 5 km 3300 11 500 ft comparisons of these wells with seven wells from the norwegian sea demonstrated that the sonic velocity and density variations are influenced by the content of silica with a biogenic origin but that they can otherwise not in general be related to mineralogy and pore pressure variations the sonic velocity deviations from the mean value are of the same magnitude as those that would be caused by porosity changes of 8 in mudrocks of uniform lithology furthermore the deviations are not significantly reduced when the velocity data are compensated for changes in density porosity detection limits for mechanically compacting mudrocks that are at their maximum effective stress are equivalent to static mud density changes of 0 1 0 15 g cm3 these numbers apply to mudrocks with similar lithological variability to those analyzed in our data set but should be much higher when significant amounts of silica with a biogenic origin are present the impact of effective stress changes on the sonic velocities of chemically compacting as well as of mechanically unloading rocks is much less because small or no porosity changes follow from the effective stress changes in such cases the velocity responses for mechanically unloading and stress insensitive chemical compaction can only be identified from four dimensional time lapse seismic data unless the rocks are close to the fracturing limit these observations imply that reasonably accurate velocity based pore pressure identification in north sea mudrocks requires a knowledge of local mudrock heterogeneity and compaction that cannot easily be obtained as a result sonic velocity data should be treated with considerable caution in pore pressure evaluation

seismic velocities for hydrate bearing sediments using weighted equation a weighted equation based on the three phase time average and wood equations is applied to derive a relationship between the compressional wave p wave velocity and the amount of hydrates filling the pore space the proposed theory predicts accurate p wave velocities of marine sediments in the porosity range of 40 80 and provides a practical means of estimating the amount of in situ hydrate using seismic velocity the shear s wave velocity is derived under the assumption that the p to s wave velocity ratio of the hydrated sediments is proportional to the weighted average of the p to s wave velocity ratios of the constituent components of the sediment in the case that all constituent components are known a weighted equation using multiphase time average and wood equations is possible however this study showed that a three phase equation with modified matrix velocity compensated for the clay content is sufficient to accurately predict the compressional wave velocities for the marine sediments this theory was applied to the laboratory measurements of the p and s wave velocities in permafrost samples to infer the amount of ice in the unconsolidated sediment the results are comparable to the results obtained by repeatedly applying the two phase wave scattering theory the theory predicts that the poisson s ratio of the hydrated sediments decreases as the hydrate concentration increases and the porosity decreases in consequence the amplitude versus offset avo data for the bottom simulating reflections may reveal positive negative or no avo anomalies depending on the concentration of hydrates in the sediments

fundamentals of seismic rock physics during the past 50 years or so tremendous progress has been made in studying physical properties of rocks and minerals in relation to seismic exploration and earthquake seismology during this period many theories have been developed and many experiments have been carried out some of these theories and experimental results have played important roles in advancing earth sciences and exploration technologies this tutorial paper attempts to summarize some of these results

a feasibility study of co2 geologic sequestration integrating reservoir simulation rock physics theory and seismic modeling abstractco2 capture and sequestration is a promising approach to reduce carbon emission and mitigate the greenhouse effect we have developed a methodology combining reservoir simulation rock physics theory and seismic modeling to simulate the co2 sequestration and monitoring process based on an idealized geologic model of the sleipner field first we simulated a constant rate co2 injection into the idealized geologic model to study the basics of the two phase flow involved in co2 sequestration the main features of the co2 plume evolution and pressure build up are captured in the simulation results in any co2 sequestration project an important part is monitoring co2 distribution using seismic methods the seismic response of the injected co2 is controlled by its effect on elastic properties of the reservoir rock we built a rock physics model to assess the effect of co2 on wave properties for unconsolidated sand a sensitivity study found that co2 saturation and effective pressure can strongly aff

correlations between seismic parameters em parameters and petrophysical petrological properties for sandstone and carbonate at low water saturations empirical relations are found between measured petrophysical petrologic seismic and electrical properties of sandstone and carbonate samples by least squares fitting at room pressure and ambient saturation the measured parameters include porosity fluid permeability k clay content c grain density g bulk density b p wave velocity vp electrical conductivity and dielectric constant the samples are from reservoir analog sites in the ferron sandstone in central utah and the ellenburger carbonate in central texas crossplots and regression analysis are done separately for the sandstone and the carbonate samples for the sandstone samples predictions with correlation coefficients r2 greater than 0 75 include b from ln k from and c from ln k and from b and c and from ln k predictions with 0 65 r2 0 75 include from vp and b from vp and vp from ln k and c from ln and from b in general is difficult to predict with the best r2 0 48 obt

detailed fault structure highlighted by finely relocated aftershocks arthur s pass new zealand 1 more than 6000 aftershocks were recorded following the 1994 arthur s pass mw6 7 earthquake in south island new zealand here we relocate over 3500 of the aftershocks using double difference tomography to map detailed fault structures and obtain a 3 d model of p wave velocity and vp vs ratio in the volume around the aftershock region waveform cross correlation methods are used to calculate high quality differential times for event pairs two parallel clusters in particular are very well defined after the double difference relocation with a dip of 70 80 and n60e 10 strike a third nw dipping cluster aligns very closely with one of the preferred fault planes for the mainshock corroborating previous interpretations of the mainshock source mechanism results from the double difference tomography indicate p wave velocities and vp vs change markedly immediately above the upper bound of the seismicity with a vp of 4 5 to 5 5 km s and elevated vp vs found in the top 2 km