lapse time dependence of coda q anisotropic multiple scattering models and application to the pyrenees abstract the coda quality factor of short period s waves q c excited by local earthquakes in the pyrenees has been measured as a function of the length of the coda window l w for different choices of the onset time of the coda t w in the 2 16 hz frequency band we observe a transient regime characterized by an increase of q c with l w followed by a stabilization around a plateau the value of which depends on the central frequency of the signal using monte carlo simulations of wave transport in a variety of random media 1200 models we demonstrate that the lapse time dependence of q c in the pyrenees may be modeled by multiple anisotropic scattering of seismic waves without invoking any depth dependence of the attenuation properties in the crust in our model anisotropic scattering is quantified by the ratio between the transport mean free path and the mean path l l at 6 hz the data require an anisotropy factor l l 5 a transport mean free path l 400 km and an intrinsic quality factor q i 800 from the frequency dependent plateau of q c at large lapse time we infer an intrinsic quality factor of the form q i 400 f 0 4 in the pyrenees we also show how the rapid increase of the lapse time dependence of q c with frequency may be exploited to put constraints on the power spectrum of heterogeneities in the crust

the rock physics and geochemistry of carbonates exposed to reactive brines when carbonate rich rocks are brought into contact with an acidic brine their mechanical and acoustic responses depend on many factors including ph porosity permeability effective stress and time these complexities hinder the understanding of processes such as hydrothermal fluid circulation seismicity and deep burial diagenesis the present study addresses how different lithofacies exposed to the same reactive brine undergo varying degrees of transformation and whether it is possible to remotely detect these phenomena in the earth results are presented from fluid injections carried out on a large and varied set of calcareous rocks under hydrostatic stress the output brine was analyzed for dissolved mineral concentrations and the rock porosity permeability axial strain ultrasonic velocity and images from electron microscopy were contrasted before and after injection microbialites were found to be the lithofacies most vulnerable to changes in their transport properties however all samples irreversibly compacted with the greatest strain in the most porous and permeable cores the most extreme structural changes discovered through imaging were the welding of microporous zones grain sliding and the fracturing of various phases observations are consistent with a chemically enhanced weakening of the rock frame that generated compliant pores the associated decrease in velocity of the dry rock can be approximated with linear relations that depend on both porosity and effective stress

attenuation of coda waves in new england abstract seismic wave attenuation was measured in new england from the time domain decay of coda wave amplitudes on narrow bandpass filtered seismograms of local earthquakes the frequency band of interest was 0 75 to 10 hz q c f was found to increase with frequency across this band but there was also a difference between the q c f values for short t t 100 sec lapse times of coda wave propagation for the short lapse time data corresponding to wave paths primarily in the upper crust q c f increases from 400 at 3 hz to 1300 at 10 hz for the large lapse time data corresponding to wave paths in the lower crust and upper mantle q c f was found to vary from 660 at 1 hz to 1500 at 10 hz if we interpret this dataset in terms of a model incorporating both scattering and anelastic attenuation we find that the mean free path of seismic waves over this frequency band is 80 km for short lapse times and 400 km for long lapse times if we assume that scattering is entirely responsible for the observed attenuation we find that the minimum mean free path for short lapse times is about 75 km over all frequencies whereas for long lapse times the minimum mean free path decreases from 400 km at 0 75 hz to 90 km at 10 hz

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

petrology and chemistry of the new shergottite dar al gani 476 in 1998 dar al gani dag 476 was found in the libyan desert the meteorite is classified as a basaltic shergottite and is only the 13th martian meteorite known to date it has a porphyritic texture consisting of a fine grained groundmass and larger olivines the groundmass consists of pyroxene and feldspathic glass minor phases are oxides and sulfides as well as phosphates the presence of olivine orthopyroxene and chromite is a feature that dag 476 has in common with lithology a of elephant moraine eet a79001 however in dag 476 these phases appear to be early phenocrysts rather than xenocrysts shock features such as twinning mosaicism and impact melt pockets are ubiquitous terrestrial weathering was severe and led to formation of carbonate veins following grain boundaries and cracks with a molar mgo mgo feo of 0 68 dag 476 is the most magnesian member among the basaltic shergottites compositions of augite and pigeonite and some of the bulk element concentrations are intermediate between those of lherzolitic and basaltic shergottites however major elements such as fe and ti as well as lree concentrations are considerably lower than in other shergottites noble gas concentrations are low and dominated by the mantle component previously found in chassigny a component similar to that representing martian atmosphere is virtually absent the ejection age of 1 35 0 10 ma is older than that of eeta79001 and could possibly mark a distinct ejection dar al gani 476 is classified as a basaltic shergottite based on its mineralogy it has a fine grained groundmass consisting of clinopyroxene pigeonite and augite feldspathic glass and chromite ti chromite ilmenite sulfides and whitlockite isolated olivine and single chromite grains occur in the groundmass orthopyroxene forms cores of some pigeonite grains shock features such as shock twinning mosaicism cracks and impact melt pockets are abundant severe weathering in the sahara led to significant formation of carbonate veins crosscutting the entire meteorite dar al gani 476 is distinct from other known shergottites chemically it is the most magnesian member among known basaltic shergottites and intermediate in composition for most trace and major elements between iherzolitic and basaltic shergottites unique are the very low bulk ree element abundances the ci normalized abundances of lrees are even lower than those of iherzolitic shergottites the overall abundance pattern however is similar to that of que 94201 textural evidence indicates that orthopyroxene as well as olivine and chromite crystallized as phenocrysts from a magma similar in composition to that of bulk dag 476 whether such a magma composition can be a shergottite parent melt or was formed by impact melting needs to be explored further at this time it cannot entirely be ruled out that these phases represent relics of disaggregated xenoliths that were incorporated and partially assimilated by a basaltic melt although the texture does not support this possibility trapped noble gas concentrations are low and dominated by a chassigny like mantle component virtually no martian atmosphere was trapped in dag 476 whole rock splits the exposure age of 1 26 0 09 ma is younger than that of most shergottites and closer to that of eeta79001 the ejection age of 1 35 0 1 ma could mark another distinct impact event

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

the role of undercooling in producing igneous zoning trends in pyroxenes and maskelynites among basaltic martian meteorites abstract pyroxene and maskelynite are major minerals in basaltic martian meteorites shergotty zagami eeta79001 and que94201 they are chemically zoned in both major and minor elements offering useful information on their crystallization history pigeonite and augite show two distinct textural occurrences of zoning patterns in shergotty and zagami pigeonite and augite are usually present as separate grains that are zoned from mg rich core to fe rich rim respectively both pigeonite and augite usually have homogeneous cores considered to be cumulus phases zagami pyroxenes are not zoned as extensively as those in shergotty but their mineralogy is quite similar on the other hand pigeonite and augite in eeta79001 and que94201 are both present in individual composite grains these pyroxenes are complexly zoned and typically the cores are mg rich pigeonites mantled by mg rich augite and the rims are fe rich pigeonite pyroxenes in lithology a of eeta79001 are small and show irregular zoning patterns but most of them show similar zoning patterns to lithology b of eeta79001 and que94201 maskelynite compositions also correspond to differences in pyroxene zoning maskelynites in shergotty and zagami are more alkali rich than those in eeta79001 and que94201 shergotty and zagami maskelynites apparently nucleated on pyroxene crystals and grew outward to lower an content into interstitial melts whereas eeta79001 and que94201 maskelynites have the most an rich portions in the centers of grains showing normal core to rim zoning feo in the maskelynite cores is different between shergotty and zagami 0 5 0 6 wt and eeta79001 and que94201 0 3 0 4 wt the lower fe content of eeta79001 and que94201 maskelynite cores reflects earlier crystallization of plagioclase al zoning in pyroxenes also marks the beginning of plagioclase crystallization decrease of the al ti ratios observed in al ti plots of pyroxenes further suggests plagioclase crystallization and the al ti distribution shows a clear difference between shergotty and zagami on one hand and eeta79001 and que94201 on the other such mineralogical differences of eeta79001 and que94201 from shergotty and zagami can be understood by undercooling of the magmas from which they have crystallized we believe that shergotty and zagami experienced only slight undercooling resulting initially in cotectic growth of pigeonite and augite later joined by plagioclase on the other hand eeta79001 and que94201 experienced significant undercooling of their melts and their crystallization sequence was pigeonite augite plagioclase and then fe rich pigeonite with each phase crystallizing metastably alone because the melt compositions did not follow the equilibrium phase boundaries lithology a of eeta79001 also experienced undercooling effects but they are not so extensive as in lithology b inasmuch as lithology a shows some features similar to shergotty and zagami all of these inferences concerning supercooling are consistent with field emission gun scanning electron microscopy feg sem observation of pyroxene microstructures if we consider that magmatic cooling rates are related to subsolidus cooling rates that is the pyroxene cores of shergotty and zagami have fine exsolution lamellae a few tens to a few hundreds nm whereas those of eeta79001 and que94201 do not contain such exsolution lamellae indicating faster cooling rate even at subsolidus

estimates of q in central asia as a function of frequency and depth using the coda of locally recorded earthquakes digital recordings of microearthquake codas from shallow and intermediate depth earthquakes in the hindu kush region of afghanistan were used to determine the attenuation factors of the s wave coda qc and primary s waves q an anomalously rapid decay of the coda shortly after the s wave arrival observed also in a study of coda in central asia by rautian and khalturin 1978 seems to be due primarily to depth dependent variations in qc in particular we deduce the average qc in the crust and uppermost mantle 100 km depth is approximately four times lower than the deeper mantle 400 km depth over a wide frequency range 0 4 to 24 hz further while qc generally increases with frequency at any depth the degree of frequency dependence of qc depends on depth except at the highest frequency studied here 48 hz the magnitude of qc at a particular frequency increases with depth while its frequency dependence decreases for similar depths determinations of q and qc agree suggesting a common wave composition and attenuation mechanism for s waves and codas comparison of these determinations of qc in afghanistan with those in other parts of the world shows that the degree of frequency dependence of qc correlates with the expected regional heterogeneity such a correlation supports the prejudice that qc is primarily influenced by scattering and suggests that tectonic processes such as folding and faulting are instrumental in creating scattering environments

temporal variation of body wave attenuation as related to two earthquake doublets in w greece in this research four earthquakes which are considered to compose two earthquake doublets recorded prior to and after a magnitudem s 5 0 and a magnitudem s 4 8 event in w greece are used to derive temporal variations ofp wave attenuation in the region

changes of shear moduli in carbonate rocks implications for gassmann applicability in laboratory experiments we measured the saturation effects on the acoustic properties in carbonates and the results question some theoretical assumptions in particular these laboratory experiments under dry and wet conditions show that shear moduli do not remain constant during saturation this change in shear modulus puts gassmann s assumption of a constant shear modulus into question and also explains why velocities predicted with the gassmann equation can be lower or higher than measured velocities

acoustic measures of partial gas saturation in tight sandstones the acoustic properties of tight sandstones are very sensitive to partial gas water saturation measurements at 5 khz show that compressional velocity drops sharply with undersaturation extensional and shear losses at 5 khz are large in both fully and partially saturated sands the shear loss qs 1 declines linearly with increasing gas content the extensional loss qe 1 peaks at 0 80 water saturation q 1 is frequency dependent the attenuation is well explained by hydrodynamic relaxation in the grain contacts the measurements indicate velocity dispersions consistent with this mechanism ultrasonic velocities at 500 khz are roughly 10 25 higher than acoustic velocities at 5 khz the ultrasonic velocities exhibit a weak dependence on saturation frame moduli are unrelaxed at these frequencies

olivine in antarctic micrometeorites comparison with other extraterrestrial olivine abstract antarctic micrometeorite particles range from porous unmelted samples to completely melted spheres of approximately 175 particles examined twenty six contain 5 m or larger mg rich olivine with compositions similar to those found in unequilibrated meteorites electron probe analyses for minor elements show high levels of cr in micrometeorite olivine above those found in c3 and uoc olivines but closely matching levels found in c2 olivines very mg rich feo

estimating the wet rock p wave velocity from the dry rock p wave velocity for pyroclastic rocks seismic methods are widely used for the geotechnical investigations in volcanic areas or for the determination of the engineering properties of pyroclastic rocks in laboratory therefore developing a relation between the wet and dry rock p wave velocities will be helpful for engineers when evaluating the formation characteristics of pyroclastic rocks to investigate the predictability of the wet rock p wave velocity from the dry rock p wave velocity for pyroclastic rocks p wave velocity measurements were conducted on 27 different pyroclastic rocks in addition dry rock s wave velocity measurements were conducted the test results were modeled using gassmann s and wood s theories and it was seen that estimates for saturated p wave velocity from the theories fit well measured data for samples having values of less and greater than 20 practical equations were derived for reliably estimating wet rock p wave velocity as function of dry rock p wave velocity

evidence of spatial variations of attenuation in the western pyrenean range summary spectral attenuation of coda waves has been studied in the range 2 40 hz from local events recorded in the western pyrenean range from 1980 to 1982 q was obtained using a single scattering model ol s waves for different segments of the coda an increase of q with lapse time was found and attributed to a rapid increase of qp with depth three groups of events were selected from distinct focal areas two data sets are mainly composed of aftershocks of moderate earthquakes of magnitude 5 1 and 4 8 respectively no moderate earthquake occurred in the third area in the few years preceding or following the selected events use of stations close to epicentres allowed sampling of the coda at very short lapse times and then study of small distinct scattering volumes noticeable differences were found between the three studied areas and attributed to spatial rather than temporal variations the q frequency dependence was studied according to q qfa y is found to range from 0 7 to 1 1 and q from 30 to 140 these values are in agreement with those found inother tectonic areas it is shown that scattering is the dominant attenuation process below 10 hz

a preliminary study of coda q in california and nevada the decay rate of local earthquake coda is characteristic of the area in which the epicenter and stations are located aki 1969 aki and chouet 1975 rautian and khalturin 1978 tsujiura 1978 aki 1980 interpreted the coda decay rate in terms of the attenuation property of s waves in the lithosphere under the area the q of s waves inferred from coda waves is called coda q recently several papers reported temporal changes in coda q prior to the occurrence of large earthquakes they are 1 the tangshan earthquake m 7 8 of 1976 and the haicheng earthquake m 7 4 of 1975 jin and aki 1986 2 three earthquakes m 8 in the kuril kamchatka region gusev and lemzikov 1985 3 the kalapana hawaii earthquake m 7 2 of 1975 wilson et al 1983 and 4 the eastern yamanashi japan earthquake m 6 0 of 8 august 1983 sato 1986 in all these cases the coda q was reported to be anomalously low before the occurrence of the earthquake however in a detailed study by chouet 1979 a strong fluctuation of coda q with time was observed in bear valley california which was not followed by a significant earthquake a recent coda q study in the adak seismic zone by scherbaum and kisslinger 1985 also did not find significant coda q changes that could be related to a mb 5 8 earthquake which occurred in the area of investigation in order to evaluate the feasibility of using coda q for earthquake prediction research in california and nevada we began a systematic study of coda q using digital waveform data from the regional microearthquake networks operated by the u s geological survey and the university of nevada

petrology and chemistry of the picritic shergottite north west africa 1068 nwa 1068 we report on the petrology and chemistry of north west africa 1068 nwa 1068 a shergottite recently recovered in morocco this meteorite has a total known mass of about 577 g and comprises 23 fragments the largest fragment is a greenish brown rock devoid of fusion crust it displays a porphyritic texture consisting of a fine grained groundmass and olivine grains excluding the impact melt pockets and the minor carbonate veins produced by terrestrial weathering modal analyses indicate the following mineral proportions 52 vol pyroxenes 22 maskelynite 21 olivine 2 phosphates merrillite and chlorapatite 2 opaque oxides mainly ilmenite and chromite and sulfides and 1 k rich mesostasis olivines with various habits occur as clusters often associated with chromite or single crystals ranging in size from 50 mum to 2 millimeters megacrysts these crystals originate probably from disrupted cumulates with strong affinities with peridotitic shergottites

the athens earthquake of 7 september 1999 based on detailed aftershock monitoring the first model of the athens earthquake is formulated which is consistent with global regional and local strong motion data of the mainshock and fits with geological setting the 30 station temporary network located 450 aftershocks during the first 20 observation days the aftershocks identified the mainshock fault plane dipping 52 and striking 117 consistently with the teleseismic fault plane solution a formal upward continuation of the fault plane intersects the surface close to the fili fault numerical modeling of the broadband regional data at 10 stations epicentral distances 140 to 370 km estimates the centroidal source depth of 10 km and yields an average source duration of 5 to 6 sec the interstation variability of the apparent duration indicates source directivity the empirical green9s function modeling at the closest broadband station suggests a fault length of 20 or 10 km both the numerical and empirical modelings give a very short rise time of 0 1 to 0 3 sec the short rise time seems to favor the nearly complete stress release of an asperity a 10 km asperity stress drop of 2 7 m pa is in agreement with a gap identified during the first 12 observation days between two aftershock clusters the strong motion accelerograms in athens also indicate a short apparent duration due to directivity about 3 sec and confirm an abrupt rupture beginning there is no evidence for an abrupt stopping the short rise time and short apparent source duration were two principal factors determining the damaging ground motions in athens

investigation of elastic weakening in limestone and sandstone samples from moisture adsorption summary elastic and mechanical weakening from water saturation are widely known to occur in sedimentary rocks and particularly in carbonate rocks to improve our understanding of the physics underlying this phenomenon ultrasonic f 0 5 mhz elastic properties are measured on a large suite of clean limestones and sandstones at very low saturations from relative humidity rh variations at ambient conditions measurements clearly highlight an elastic weakening i e decrease in elastic wave velocity from moisture adsorption p and s wave velocities are similarly affected by adsorption but in a different way for limestones and sandstone samples while the elastic properties of limestone samples show almost no rh dependence a large weakening is observed for samples of fontainebleau sandstone that increases with the samples porosity the main elastic weakening effect is likely to result from adsorption of fluid at grain contacts it thus affects particularly granular rocks such as sandstones while well cemented limestones are not affected the granular model from murphy et al accounting for surface energy effects proves to be appropriate applying this model it is shown that i p and s wave velocities have the same dependence on surface energy which is consistent with the measurements and ii surface energy values obtained from the ultrasonic data using this model correlate with rh and are consistent with the expected value for quartz crystals at vapour pressure yet porosity which relates to degree of cementation in the particular case of fontainebleau sandstone appears to be an additional parameter a modified model is thus derived using the cementation model from digby accounting for a bonding radius at grain contact it proves to apply well to the measured data the fundamental difference between limestones and sandstones dependence to rh appears to be related to a microstructural difference saturation variations from rh increase depend on specific surface area which is particularly low in fontainebleau sandstones and large in microporous limestones however elastic weakening from rh is more important in sandstones owing to their granular microstructure

bounce rock a shergottite like basalt encountered at meridiani planum mars additional co authors thanasis economou steven p gorevan brian c hahn gostar klingelhofer timothy j mccoy harry y mcsween jr douglas w ming richard v morris daniel s rodionov steven w squyres heinrich wanke shawn p wright michael b wyatt albert s yen

velocities of compressional and shear waves in limestones carbonate rocks are important hydrocarbon reservoir rocks with complex textures and petrophysical properties porosity and permeability mainly resulting from various diagenetic processes compaction dissolution precipitation cementation etc these complexities make prediction of reservoir characteristics e g porosity and permeability from their seismic properties very difficult to explore the relationship between the seismic petrophysical and geological properties ultrasonic compressional and shear wave velocity measurements were made under a simulated in situ condition of pressure 50 mpa hydrostatic effective pressure at frequencies of approximately 0 85 mhz and 0 7 mhz respectively using a pulse echo method the measurements were made both in vacuum dry and fully saturated conditions in oolitic limestones of the great oolite formation of southern england some of the rocks were fully saturated with oil the acoustic measurements were supplemented by porosity and permeability measurements petrological and pore geometry studies of resin impregnated polished thin sections x ray diffraction analyses and scanning electron microscope studies to investigate submicroscopic textures and micropores it is shown that the compressional and shear wave velocities vp and vs respectively decrease with increasing porosity and that vp decreases approximately twice as fast as vs the systematic differences in pore structures e g the aspect ratio of the limestones produce large residuals in the velocity versus porosity relationship it is demonstrated that the velocity versus porosity relationship can be improved by removing the pore structure dependent variations from the residuals the introduction of water into the pore space decreases the shear moduli of the rocks by about 2 gpa suggesting that there exists a fluid matrix interaction at grain contacts which reduces the rigidity the predicted biot gassmann velocity values are greater than the measured velocity values due to the rock fluid interaction this is not accounted for in the biot gassmann velocity models and velocity dispersion due to a local flow mechanism the velocities predicted by the raymer and time average relationships overestimated the measured velocities even more than the biot model

a model for attenuation and scattering in the earth s crust the mechanisms contributing to the attenuation of earthquake ground motion in the distance range of 10 to 200 km are studied with the aid of laboratory data coda waves rg attenuation strong motion attenuation measurements in the northeast united states and canada and theoretical models the frequency range 1 10 hz has been studied the relative contributions to attenuation of anelasticity of crustal rocks constant q fluid flow and scattering are evaluated scattering is found to be strong with an albedo b 0 0 8 0 9 and a scattering extinction length of 17 32 km the albedo is defined as the ratio of the total extinction length to the scattering extinction length the rg results indicate that q increases with depth in the upper kilometer or two of the crust at least in new england coda q appears to be equivalent to intrinsic anelastic q and indicates that this q increases with frequency as q q 0 f n where n is in the range of 0 2 0 9 the intrinsic attenuation in the crust can be explained by a high constant q 500 q 0 2000 and a frequency dependent mechanism most likely due to fluid effects in rocks and cracks a fluid flow attenuation model gives a frequency dependence q q 0 f0 5 similar to those determined from the analysis of coda waves of regional seismograms q is low near the surface and high in the body of the crust

experimental investigation of camg exchange between olivine orthopyroxene and clinopyroxene potential for geobarometry abstract the distribution of ca and mg among coexisting olivine clinopyroxene and orthopyroxene has been studied in a piston cylinder apparatus in the temperature range 1100 1300 c and pressure range 9 41 kbar ca in olivine decreases with increasing pressure and decreasing temperature the pressure effect is the result of ca going into the higher coordination m2 site in clinopyroxene as pressure is increased for the ca mg exchange reaction between olivine and clinopyroxene v 0 249j bar 1 mole 1 this is sufficient for pressure estimates accurate to 3kbar if temperatures of equilibration are independently known ca mg exchange between olivine and orthopyroxene is not sufficiently pressure dependent to be used as a geobarometer application of the olivine clinopyroxene geobarometer to coarse garnet lherzolites from southern africa gives p t results consistent with a continental geotherm for spinel lherzolites from southwestern united states the geotherm appears to be displaced to higher temperatures indicating oceanic affinities application of the geobarometer to natural systems requires assumptions about activity relationships in clinopyroxene which should be checked by experiment

noble gases in mineral separates from three shergottites shergotty zagami and eeta79001 this study provides a complete data set of all five noble gases for bulk samples and mineral separates from three martian shergottites shergotty bulk pyroxene maskelynite zagami bulk pyroxene maskelynite and elephant moraine eet a79001 lithology a bulk pyroxene we also give a compilation of all noble gas and nitrogen studies performed on these meteorites our mean values for cosmic ray exposure ages from 3he 21ne and 38ar are 2 48 myr for shergotty 2 73 myr for zagami and 0 65 myr for eeta79001 lith a serious loss of radiogenic 4he due to shock is observed cosmogenic neon results for bulk samples from 13 martian meteorites new data and literature data are used in addition to the mineral separates of this study in a new approach to explore evidence of solar cosmic ray effects while a contribution of this low energy irradiation is strongly indicated for all of the shergottites spallation ne in chassigny allan hills alh 84001 and the nakhlites is fully explained by galactic cosmic ray spallation implanted martian atmospheric gases are present in all mineral separates and the thermal release indicates a near surface siting we derive an estimate for the 40ar 36ar ratio of the martian interior component by subtracting from measured ar in the k poor pyroxenes the small radiogenic component as well as the implanted atmospheric component as indicated from 129xe excesses unless compromised by the presence of additional components a high ratio of 2000 is indicated for martian interior argon similar to that in the martian atmosphere since much lower ratios have been inferred for chassigny and alh 84001 the result may indicate spatial and or temporal variations of 40ar 36ar in the martian mantle

hydraulic and acoustic properties as a function of porosity in fontainebleau sandstone laboratory measurements have been made of the permeability k free porosity l compressional velocities vp or ve and compressional attenuations qp or qe in fontainebleau sandstone over a continuous range of porosities from 3 to 28 this large variation was achieved without any composition change fontainebleau sandstone is made of fine quartz grains with regular grain size 250 m permeability was measured with a falling head permeameter velocities and attenuations were obtained either through an ultrasonic experiment for frequencies around 500 khz or through a resonant bar technique experiment for frequencies around 5 khz and in both cases with varying water saturation the results show an excellent correlation between permeability k and total porosity for all our samples for low porosities 3 to 9 permeability in millidarcies is 2 75 10 5 7 33 while for high porosities 9 to 28 permeability k in millidarcies is given by 0 303 3 05 the correlation is also excellent between free porosity and total porosity on the other hand the correlation between acoustic properties and total porosity is not as clear as for hydraulic properties whatever the frequency 500 khz or 5 khz or the water saturation on the average velocity decreases and attenuation roughly increases with increasing total porosity velocity and attenuation values are related to the variation of grain contact structure and two samples with the same porosity and permeability may exhibit different velocities and attenuations the clear correlation between hydraulic properties and porosity is related to constant grain size while the lack of correlation for acoustic properties emphasizes the importance of the microstructure

depth dependent seismic attenuation in western greece abstract coda q estimates for the seismically active region of western greece are obtained by analyzing earthquakes occurring within the borders of the recently established patras seismological network the data set is composed of 97 low magnitude local events coda q values obtained show a clear dependence of frequency according to the relation q q 0 f n where n ranges from 0 77 to 0 82 the data fit indicated an increase of q 0 with increasing lapse time which is interpreted as being due to attenuation variation with depth

attenuation of shear waves in the back arc region of the hellenic arc for frequencies from 0 6 to 16 hz abstract q for shear waves is determined for the inner part of the hellenic arc the back arc area as a function of frequency in the range 0 6 16 hz we used 314 digital records from 32 earthquakes with magnitudes m w ranging from 3 9 to 5 1 epicentral distances ranged from 65 to 515 km the data were obtained in 1997 during a 6 month operation of a digital portable network in greece the q estimates were made for five frequency bands centred at 0 8 1 5 3 0 6 0 and 12 0 hz and the q values obtained were 47 79 143 271 and 553 respectively the results show that q for s waves increases with frequency taking the form q 55 f 0 91 or q 1 0 018 f 0 91 the high attenuation and the strong frequency dependence found which is close to the frequency dependence of coda q for greece are characteristic of an area with high seismicity rapid extension and in agreement with other similar studies in greece

petrography and mineralogy of two basalts and olivine pyroxene spinel fragments in achondrite eeta79001 three lithologies occur in shocked achondrite eeta79001 a1 exotic irregular crystals and clusters of coarse grained olivine fo81 55 cao 0 2 cr2o3 0 06 nio 0 5 wt low ca pyroxene en82wo2 en58wo12 and low ti chromite cr2o3 59 feo 27 tio2 0 7 wt a2 basaltic host to a1 containing pyroxene mainly pigeonite en67wo12 en52wo13 maskelynite an61 55or0 7 high ti chromite some rimming low ti chromite whitlockite minor cl apatite ilmenite pyrrhotite and mesostasis and b a homogeneous basalt containing augite laths en40 50wo25 35 in a matrix of pigeohite augite maskelynite an62 56 or1 2 ulvospinelilmenite intergrowth whitlockite cl apatite and mesostasis mineral compositions indicate an oxidation state similar to that of shergottites lithology a1 represents an unmetamorphosed cumulate that was disrupted and partly resorbed by a basaltic magma incorporation of low ca magnesian pyroxenes and olivine increased the mg fe ratio of the basaltic magma responsible for a2 and resulted in abundant crystallization of pigeonite lithology b was generated from a distinct magma lacking fragments of a1 the parental spinel harzburgite of a1 was not annealed and is probably a near surface igneous cumulate from a shergottite type basalt ringwood and majorite were found in shock veins

acoustic properties of carbonates effects of rock texture and implications for fluid substitution more than 250 plugs from outcrops and three nearby boreholes in an undisturbed reef of miocene tortonian age were quantitatively analyzed for texture mineralogy and acoustic properties we measured the p and s waves of carbonate rocks under dry humidified and brine saturated conditions at 10 mpa effective pressure with an ultrasonic pulse transmission technique 1 mhz the data set was compared with an extensive database of petrophysical measurements of a variety of rock types encountered in carbonate sedimentary sequences two major textural groups were distinguished on the basis of trends in plots of compressional wave velocity versus poisson s ratio a specific ratio of p wave over s wave velocity in granular rocks the framework of depositional grains is the main medium for acoustic wave propagation in crystalline rocks this medium is provided by a framework of interlocking crystals formed during diagenesis rock textures are connected to primary depositionalparameters and a diagenetic ov

an experimental and petrographic investigation of elephant moraine 79001 lithology a implications for its petrogenesis and the partitioning of chromium and vanadium in a martian basalt a composition approximating the lithology a groundmass ofthe elephant moraine eet 79001 martian basalt eg mcsween and jarosewich 1983 has been used to investigate the petrogenesis ofthe meteorite and the behavior ofcr and v at different oxygen fugacities crystallization experiments were carried out over a range of temperatures and oxygen fugacities of either iron wustite iw or iw 2 i e 1 5 log units below the quartz fayalite magnetite qfm buffer comparison oftrace element concentrations obtained by secondary ion mass spectrometry sims analysis in experimental silicates with those of natural silicates supports the fe ti oxide derived oxygen fugacity of qfm 1 8 0 3 for this basalt herd et al 2001 experimental distribution coefficients in conjunction with sims analyses of rims from the olivine and pyroxene xenocrysts in lithology a as well as analyses of lithology a groundmass pigeonite cores are used to calculate coexisting liquid concentrations of v and cr liquid compositions derived from pigeonite xenocryst rims and groundmass pigeonite cores are similar suggesting that the rims of orthopyroxene xenocrysts are overgrowths which have not previously been accounted for when reconstructing the groundmass composition this implies that the eg composition requires modification a similar exercise for the ferroan rims on olivine xenocrysts yields very different liquid compositions indicating that these rims are not overgrowths but are part of the xenocryst assemblage these results are shown to be consistent with the petrography of lithology a xenocrysts

crystallization of the basaltic shergottites insights from crystal size distribution csd analysis of pyroxenes quantitative petrographic analysis using the crystal size distribution csd method provides a novel approach for examining the crystallization histories of basaltic shergottites grain number densities at different sizes are plotted against grain size and the resulting curve relates to the geologic processes involved with the crystallization of the grain population most basaltic shergottites are dominated by pigeonite and augite and because plagioclase is primarily interstitial and therefore constrained in its growth by the surrounding pyroxenes we limited our size measurements to the pyroxene phases the groundmasses of elephant moraine eet a79001 lithology a and dar al gani dag 476 are fine grained with cumulus pyroxene and interstitial plagioclase glass their simple linear csd plots record a single stage of pyroxene crystallization under steady state conditions of continuous nucleation and growth the textures of queen alexandra range que 94201 and eeta79001 lithology b are quite different from the other shergottites with intergrown pyroxene and plagioclase likewise their csd plots are also distinct with curved trends that suggest a lack of large grains most likely because of interference between simultaneously growing silicate phases however the csd plot shapes are smooth also implying a single stage of growth shergotty and zagami with coarser cumulus textures display csd plots that are generally linear over most grain sizes this implies that conditions of nucleation and growth were dominant during formation of the pyroxene populations both plots however also display kinks implying multiple stages of growth a similar kink is also visible in a csd plot of only the mg rich cores of shergotty pyroxenes which suggests the feature represents changes in conditions during core crystallization rather than an event coincident with the change in composition to the fe rich rims the plot may be interpreted as representing two stages of core growth with an intervening short hiatus of nucleation with continued crystallization associated with ascent of the magma eruption onto the surface probably triggered the compositional change to fe rich rims the csd analysis of products from a controlled crystallization study agree with experimental and petrologic estimates that cooling rates for zagami were on the order of a few tenths of a degree per hour growth rates derived from these cooling rates suggest crystallization of shergotty and zagami pyroxenes occurred over a period of a few weeks to months

sulfide mineralogy and redox conditions in some shergottites magmatic sulfide mineralogy has been studied in 2 olivine phyric shergottites dag 476 and sau 005 and 4 basaltic shergottites zagami shergotty los angeles and nwa 480 modal abundances of magmatic sulfides as estimated by image analysis on thin section are high 0 16 to 0 53 area percent and correlate positively with abundances of fe ti oxides sulfides are mesostasis minerals being mostly interstitial grains or locally enclosed in post cumulus melt inclusions e g sau 005 in olivine sulfides in shergottites are composed of major pyrrhotite containing pentlandite exsolutions associated with minor amounts of cu sulfides chalcopyrite and or cubanite hot desert finds e g dag 476 show abundant fracture filling iron oxy hydroxides of probable terrestrial origin unaltered sulfides show metal rich hexagonal pyrrhotite compositions with metal sulfur m s ratio ranging between 0 936 0 005 and 0 962 0 01 this compositional range corresponds to the two phase structural domain 2c nc of the fe s system however the high temperature disordered hexagonal 1c pyrrhotite structure would be in better agreement with magnetic properties of shergottites ni contents in pyrrhotite increase from los angeles 0 05 at to shergotty zagami and nwa 480 0 2 0 5 at and dag 476 and sau 005 up to 3 at the higher ni values of pyrrhotite in olivine phyric shergottites correlate with the abundance of pentlandite exsolutions both reflecting more primitive ni rich sulfide liquids where abundant olivine crystallized this result and the strong correlation between sulfide abundances and fe ti oxides argue for a primary magmatic origin of these sulfides although they reproduce the trend of magmatic oxygen fugacity conditions determined from fe ti oxide pairs observed pyrrhotite compositions are systematically more metaldeficient compared to those calculated from the fe s o system this suggests post magmatic oxidation during cooling on mars followed by terrestrial weathering for hot desert finds

depth dependent seismic attenuation in the granada zone southern spain abstract coda q estimates for the granada basin southern spain are obtained by analyzing earthquakes occurring within or close to the borders of this area the data set is composed of 54 earthquakes with local magnitudes ranging between 2 2 and 4 0 and with epicentral distances to the nearest station smaller than 10 km a single scattering process is assumed coda q values obtained show a clear dependence on frequency according to the relationship q q o f n where n ranges from 0 81 to 0 89 after removing the main site effects and discussing the possible multiple scattering influence the lapse time dependence is interpreted as due to attenuation variations with depth this result agrees with the variation of coda q obtained by using different sets of events with increasing hypocentral depth ranges

energy flux model of seismic coda separation of scattering and intrinsic attenuation a new model of seismic coda is presented based on the balance between the energy scattered from the direct wave and the energy in the seismic coda this energy flux model results in a simple formula for the amplitude and time decay of the seismic coda that explicitly differentiates between the scattering and intrinsic anelastic attenuation of the medium this formula is valid for both weak and strong scattering and implicitly includes multiple scattering the model is tested using synthetic seismograms produced in finite difference simulations of wave propagation through media with random spatial variations in seismic velocity some of the simulations also included intrinsic dissipation the energy flux model explains the coda decay and amplitude observed in the synthetics for random media with a wide range of scattering q in contrast the single scattering model commonly used in the analysis of microearthquake coda does not account for the gradual coda decay observed in the simulations for media with moderate or strong scattering attenuation scattering q less than or equal to 150 the simulations demonstrate that large differences in scattering attenuation cause only small changes in the coda decay rate as predicted by the energy flux model the coda decay rate is sensitive however more to the intrinsic q of the medium the ratio of the coda amplitude to the energy in the direct arrival is a measure of the scattering attenuation thus analysis of the decay rate and amplitude of the coda can in principle produce separate estimates for the scattering and intrinsic q values of the crust we analyze the coda from two earthquakes near anza california intrinsic q values determined from these seismograms using the energy flux model are comparable to coda q values found from the single scattering theory the results demonstrate that coda q values are at best measures of the intrinsic attenuation of the lithosphere and are unrelated to the scatteing q less

interrelations of the petrophysical sedimentological and microstructural properties of the oolithe blanche formation bathonian saline aquifer of the paris basin abstract the paris basin seems a suitable location for co2 capture and storage given both the amount of co2 produced and the availability of depleted fields and deep saline aquifers this study investigates the petrophysical properties in relation to the sedimentary and diagenetic environment of the oolithe blanche formation middle jurassic a deep saline aquifer considered a potential candidate for co2 storage because of the scarcity of core data in the paris basin our investigation was based on the study of field analogues in the south east part of the paris basin the oolithe blanche formation bathonian is 70 80 m thick eighteen oriented blocks were collected from three outcrops selected for the different sedimentological facies identified in the formation their petrophysical properties were measured porosity pore size distribution derived from mercury injection tests permeability and capillary imbibition parameters the sedimentary and diagenetic facies were defined by using optical microscopy coupled with image analysis on thin sections and sem the oolithe blanche formation is composed of oolitic and bioclastic limestones deposited in a shallow marine setting three main sedimentological facies were defined the oolitic shoal facies the tide dominated facies and the prograding oolitic facies they exhibit subtle variations in composition and in the distribution of carbonate textures porosity measured using the water saturation triple weight method ranges from 6 to 34 permeability values are low between 0 1 md and 9 md the data from mercury intrusion porosimetry show that the distribution of the pore throat diameter is either unimodal microporosity only or bimodal macro and microporosity microporosity is intraparticle intraooid and macroporosity is interparticle and is related to dolo dedolomitization variations of petrophysical parameters can be explained by the microstructure now these latter results calibrated by studying field analogues must be extended to borehole data and core data to optimize our knowledge of the deep saline aquifer of the oolithe blanche formation without such investigations it will be impossible to estimate the suitability of this deep saline aquifer for co2 storage

laboratory measurements of porosity permeability resistivity and velocity on fontainebleau sandstones the relations among the resistivity elastic wave velocity porosity and permeability in fontainebleau sandstone samples from the ile de france region around paris france were experimentally revisited these samples followed a permeability porosity relation given by kozeny carman s equation for the resistivity measurements the samples were partially saturated with brine archie s equation was used to estimate resistivity at 100 water saturation assuming a saturation exponent n 2 using self consistent sc approximations modeling with grain aspect ratio 1 and pore aspect ratio between 0 02 and 0 10 the experimental data fall into this theoretical range the sc curve with the pore aspect ratio 0 05 appears to be close to the values measured in the entire porosity range the elastic wave velocity was measured on these dry samples for confining pressure between 0 and 40 mpa aloading and unloading cycle was used and did not produce any significant hysteresis in the velocity pressure behavior for the velocity data using the sc model with a grain aspect ratio 1 and pore aspect ratios 0 2 0 1 and 0 05 fit the data at 40 mpa pore aspect ratios ranging between 0 1 0 05 and 0 02 were a better fit for the data at 0 mpa both velocity and resistivity in clean sandstones can be modeled using the sc approximation in addition a linear fit was found between the p wave velocity and the decimal logarithm of the normalized resistivity with deviations that correlate with differences in permeability combining the stiff sand model and archie for cementation exponents between 1 6 and 2 1 resistivity was modeled as a function of p wave velocity for these clean sandstones

elastic wave velocities during evaporative drying laboratory measurements of drying rates and elastic wave velocities are made on limestone dolomite and sandstone samples during evaporative drying the drying rate data are very similar in form there is a constant rate period at higher saturations and a falling rate period below saturation levels of approximately 0 2 the falling rate period marks the transition in the sample from hydraulically connected to disconnected water there is a strong link between elastic wave velocities and the drying process because different pore geometries drain at different stages in drying the drainage of these different geometries results in specific changes in the moduli and velocities simple models of the pore geometries and the drying process are used to model the velocity data the velocity saturation relationship for each of the three samples is very different in form because of differences in pore space microgeometry of particular interest is the velocity response during the falling rate period of drying in the limestone and the sandstone there is a significant decrease in bulk and shear moduli and elastic wave velocities because of the drainage of crack like pores and grain contacts in contrast the absence of these pore geometries in the dolomite results in essentially no changes in the moduli at low saturations an understanding of the drying process and resulting pore scale fluid distribution provides useful insights into the observed form of the velocity saturation relationship

coda attenuation analysis in the west bohemia vogtland earthquake swarm area seismic coda represents a valuable source of information about the attenuation of the high frequency waves in the studied region the quality factor q derived from coda is an integral parameter of the volume surrounding the hypocenter and seismic station and according to the applied method represents the total attenuation or the intrinsic and scattering parts we analyzed records of 13 selected earthquakes in the magnitude range 1 7 2 9 of the 2011 swarm from west bohemian vogtland area central europe which were recorded at epicentral distances from 7 to 50 km two methods were applied coda method for estimation of the qc and the multiple lapse time windows analysis for separation of the scattering and intrinsic loss by estimation of qi and qsc careful selection of the analyzed events was necessary due to the frequent contamination of coda decays by the running seismic swarm activity the resulting coda qc is relatively high with respect to the geodynamic activity and varies between 100 and 2500 within the analyzed frequency range of 1 18 hz the intrinsic loss dominates over scattering attenuation with qi increasing from 100 and 1850 and qsc from 300 to 3400 in the same frequency range which is consistent with the geodynamic activity of the region we find that the intrinsic attenuation in west bohemia vogtland is higher that in neighboring germany which could be attributed to the heterogeneity of the crust in central europe

ultrasonic monitoring of spontaneous imbibition experiments acoustic signature of fluid migration capillary rise experiments spontaneous imbibition tests were conducted in the laboratory with ultrasonic and x ray monitoring on the sherwood sandstone and the majella grainstone the aim was to provide a direct comparison between the variation in seismic attributes amplitude velocity spectral content and energy and the actual fluid distribution in the rock two pairs of ultrasonic p wave sensors located at different heights on a cylindrical rock specimen recorded every 5 s the waveforms when capillary forces make water rise up into the rock from the bottom in contact with a water tank simultaneously computerized tomography scan images of a vertical cross section were also recorded two important results were found i the amplitude of the first p wave arrival is impacted by the upward moving fluid front before the p wave velocity is while the fluid front has not yet reached the sensors level in contrast the p wave velocity decreases when the fluid front reaches the fresnel clearance zone the spectral analysis of the waveforms shows that the peak frequency amplitude is continuously decreasing without noticeable frequency shift ii a methodology based on the calculation of the analytical signal and instantaneous phase was designed to decompose each waveform into discrete wavelets associated with direct or reflected waves the energy carried by the wavelets is very sensitive to the fluid substitution process the coda wavelets related to reflections on the bottom end face of the specimen are impacted as soon as imbibition starts and can be used as a precursor for the arriving fluid

new method for measuring compressibility and poroelasticity coefficients in porous and permeable rocks over the last decades a large understanding has been gained on the elastic properties of rocks rocks are however porous materials which properties depend on both response of the bulk material and of the pores because in that case both the applied external pressure and the fluid pressure play a role different poroelasticity coefficients exist while theoretical relations exist measuring precisely those different coefficients remains an experimental challenge accounting for the different experimental complexities a new methodology is designed that allows attaining accurately a large set of compressibility and poroelasticity coefficients in porous and permeable rocks this new method relies on the use of forced confining or pore fluid pressure oscillations in total seven independent coefficients have been measured using three different boundary conditions because the usual theories predict only four independent coefficients this overdetermined set of data can be checked against existing thermodynamic relations measurements have been performed on a bentheim sandstone under water and glycerine saturated conditions for different values of confining and pore fluid pressure consistently with the poroelasticity theory the effect of the fluid bulk modulus is observed under undrained conditions but not under drained ones using thermodynamic relations i the unjacketed quartz and skeleton zimmerman s relation bulk moduli fit ii the drained and undrained properties fit and iii it is directly inferred from the measurements that the pore skeleton compressibility c phi is expected to be constant with pressure and to be exceedingly near the bulk skeleton c s and mineral c m compressibility coefficients plain language summary poroelastic properties of rocks are a major information for a large variety of applications linked to rupture processes in saturated media theories exist to link the properties to measurable parameters yet only little measurements exist to confront those theories this article aims at providing a method for accurately measuring those properties moreover for one particular rock a large amount of compressibility and poroelastic coefficients is measured and used to confront those theories

thermoluminescence and the shock and reheating history of meteorites iii the shergottites abstract the thermoluminescence tl sensitivities of the four shergottites are extremely low and display a 10 fold range values are 0 15 to 1 8 where dhajala 1000 with the tl sensitivity decreasing with increasing peak temperature from about 140 to 180 c and peak width from about 100 to 150 c a mineral separation experiment indicates that the mineral producing the tl is associated with the maskelynite presumably nanogram per gram quantities of crystalline feldspar are present in the maskelynite samples of shergotty allan hills a77005 and elephant moraine a79001 were annealed at 400 900 c for 24 98 h for shergotty the peak increased in width and moved to higher temperatures in the glow curve while for allan hills a77005 and elephant moraine a79001 whose tl peaks were already broad and at high temperatures remained unchanged all samples showed a significant increase in tl sensitivity when annealed at 600 700 c apparently the feldspar is present in varying proportions of high to low temperature form and in amounts which vary from meteorite to meteorite we conclude that the shergottites underwent post shock recrystallization at a variety of cooling rates and that the order of increasing cooling rate was shergotty allan hills a77005 zagami and elephant moraine a79001 the presence of a high temperature phase implies peak post shock cooling temperatures 600 c and that the size of the ejecta was

intrinsic and scattering seismic attenuation in w greece intrinsic q i 1 and scattering q s 1 attenuation parameters have been determined in the seismically active region of w greece which is continuously monitored by the university of patras microearthquake network one hundred and twenty three local and shallow earthquakes close to the recording stations have been used and wennerberg s 1993 approach has been adopted results for 1 to 12 hz range show that q i 1 is higher than q s 1 and coda q values are close to q i indicating that coda q can be a reasonable estimate of intrinsic q

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

multiple origins of xenoliths and xenocrysts in the elephant moraine 79001 lithology a olivine phyric shergottite

enhanced deformation of limestone and sandstone in the presence of high fluids 1 geological repositories subject to the injection of large amounts of anthropogenic carbon dioxide will undergo chemical and mechanical instabilities for which there are currently little experimental data this study reports on experiments where low and high 8 mpa aqueous fluids were injected into natural rock samples the experiments were performed in flow through triaxial cells where the vertical and confining stresses temperature and pressure and composition of the fluid were separately controlled and monitored the axial vertical strains of two limestones and one sandstone were continuously measured during separate experiments for several months with a strain rate resolution of 10 11 s 1 fluids exiting the triaxial cells were continuously collected and their compositions analyzed the high fluids induced an increase in strain rates of the limestones by up to a factor of 5 compared to the low fluids injection of high fluids into the sandstone resulted in deformation rates one order of magnitude smaller than the limestones the creep accelerating effect of high fluids with respect to the limestones was mainly due to the acidification of the injected fluids resulting in a significant increase in solubility and reaction kinetics of calcite compared to the limestones the much weaker response of the sandstone was due to the much lower solubility and reactivity of quartz in high fluids in general all samples showed a positive correlation between fluid flow rate and strain rate x ray tomography results revealed significant increases in porosity at the inlet portion of each core the porosity increases were dependent on the original lithological structure and composition the overall deformation of the samples is interpreted in terms of simultaneous dissolution reactions in pore spaces and intergranular pressure solution creep