seismic image quality beneath strongly scattering structures and implications for lower crustal imaging numerical simulations summary the aim of this paper is to analyse how the scattered wavefield in a highly heterogeneous structure influences the image quality of structures below it and how the velocity control during processing of data from highly heterogeneous areas is important in the imaging problem statistical 2 d two layer models are built based on deep borehole data the layers are characterized by a fractal dimension hurst exponent and by the standard deviation of the velocity fluctuations over a constant background velocity value shot gathers are generated in these models with a 2 d elastic and viscoelastic finite difference simulator the synthetic data are first stacked and migrated using an average background velocity function as would be done in a realistic situation during which only a smooth version of the velocity field can be resolved second the full heterogeneous velocity models are applied to the migration scheme the final sections are compared using a semblance based technique to quantify the amount of contamination from an upper heterogeneous structure of a lower heterogeneous structure in data that are not properly migrated multiple scattering in the upper layer seems to dominate the lower part of the section this contamination is controlled by the standard deviation of the velocity fluctuations and it is reduced when viscoelasticity is introduced in the simulations counterintuitively a low q value may improve deep imaging when the seismograms are migrated with the real complex velocity field this contamination is reduced to acceptable levels residual contamination cannot be corrected completely because of the single scattering assumption inherent to all migration techniques

fractal density modeling of crustal heterogeneity from the ktb deep hole fractal or multifractal concepts have significantly enlightened our understanding of crustal heterogeneity much attention has focused on 1 f scaling natures of physico chemical heterogeneity of earth crust from fractal increment perspective in this study fractal density model from fractal clustering point of view is used to characterize the scaling behaviors of heterogeneous sources recorded at german ktb main hole and of special contribution is the local and global multifractal analysis revisited by using haar wavelet transform hwt fractal density modeling of mass accumulation generalizes the unit of rock density from integer e g g cm3 to real numbers e g g cm so that crustal heterogeneities with respect to source accumulation are quantified by singularity strength of fractal density in dimensional space from that perspective we found that the bulk densities of metamorphic rocks exhibit fractal properties but have a weak multifractality decreasing with the depth the multiscaling natures of chemical logs also have been evidenced and the observed distinct fractal laws for mineral contents are related to their different geochemical behaviors within complex lithological context accordingly scaling distributions of mineral contents have been recognized as a main contributor to the multifractal natures of heterogeneous density for low porosity crystalline rocks this finally allows us to use de wijs cascade process to explain the mechanism of fractal density in practice the proposed local singularity analysis based on hwt is suggested as an attractive high pass filtering to amplify weak signatures of well logs as well as to delineate micro lithological changes

rare earth element concentrations and nd isotopes in the southeast pacific ocean 1 three vertical profiles of rare earth element concentrations and nd isotopic compositions have been measured in the remote southeast pacific ocean the three stations represent contrasting environments the oligotrophic center of the gyre station gyr the transition zone east of the south tropical front station egy and the peru chile upwelling marked by a pronounced oxygen minimum station upx rare earth concentrations display nutrient like vertical profiles except at upx where surface waters are enriched at this station nd isotopic compositions are clearly more radiogenic than in the open ocean suggesting that boundary exchange process is releasing lithogenic rare earth element from the volcanic andes unexpected radiogenic values end reaching 3 7 are also observed at 2000 m at station gyr in the upper circumpolar deep water that commonly have end values around 6 exchange processes related to hydrothermal activity are suspected to produce this increase in end in the vicinity of the east pacific rise these results provide some guidance for higher resolution studies planned in this region by the international geotraces program

the statistical nature of the upper continental crystalline crust derived from in situ seismic measurements summary in situ measurements in the main borehole of the german continental deep drilling project ktb point to the statistical nature of the continental crystalline crust between 286 and 6000 m depth p wave s wave and density logs display deviations from gaussian distribution functions that may be partly due to the approximately bimodal nature of the lithology because the crust consists mainly of metabasites and paragneisses the autocovariance functions and power spectra of the logs indicate that the velocity and density perturbations have a complex statistical nature but the autocovariance functions can be approximated by a superposition of two exponential functions with correlation lengths of 1 m and 20 m the associated relative standard deviations for each exponential function are about 3 per cent of the mean for the sonic logs and nearly 6 per cent of the mean for the density a vertical seismic profile measured between 3000 and 6000 m depth shows small traveltime fluctuations which can be explained by a generalization of a recently published scattering theory for transverse wavefield fluctuations to include the case of longitudinal fluctuations the theory is valid for harmonic scalar plane wave propagation in random media with isotropic statistics and scattering mainly in the forward direction one important theoretical result is that although longitudinal and transverse autocovariance functions of amplitudes and phases differ the expectations of their respective autovariances are the same the observed traveltime fluctuations agree with theoretical predictions based on normally distributed velocity perturbations that are described by the average of the autocovariance functions of the two p wave logs measured from 286 to 3000 m and between 3000 and 6000 m depth owing to the lack of traveltime information that can be averaged and because the traveltime fluctuations predicted by the theory do not differ sufficiently for 2 d and 3 d random perturbations no statement can be made on how anisotropic the observed random velocity perturbations are the observed heterogeneities are however consistent with the fact that reflection seismic profiles reveal a nearly transparent upper crystalline crust

heterogeneity spectrum and scale anisotropy in the upper crust revealed by the german continental deep drilling ktb holes crustal heterogeneities and their statistical characteristics bear important information about the dynamic processes and evolution of the crust the velocity well log data from the german continental deep drilling project ktb offer a rare opportunity to measure directly the properties of crustal heterogeneities in this study we first estimated the power spectrum of crustal heterogeneities from the p velocity well logs of the two holes for the first time a power law spectrum of crustal heterogeneities was directly observed in the spatial wavelength range from a few meters to a few kilometers the slope of the vertical 1d power spectrum of the random velocity perturbations is about 1 1 corresponding to a flicker noise random medium the scale anisotropy ratio aspect ratio and the horizontal spectral slope of crustal heterogeneities were also estimated by cross correlation analysis between these two holes to be about 1 8 and 2 0 respectively

the importance of small scale faulting in regional extension a recurring observation in many studies of extensional basins has been that the amount of extension visible on normal faults for example on seismic reflection profiles is significantly less than the amount of extension indicated by crustal thickness and thermal subsidence1 5 one mechanism suggested to account for this discrepancy is small scale faulting with offsets too small to be resolved seismically6 7 but earthquake studies8 10 indicate that small faults are responsible for only a small fraction of the total seismic moment in an active area scholz and cowie11 have recently attempted to extend this approach to the total strain at the end of a finite deformation interval by combining scaling laws describing the distributions of fault lengths and displacements here we present fault displacement data that directly conflict with scholz and cowie s conclusions and imply that up to 40 of the extension may be missed by summing fault offsets on basin profiles the fault population at the end of a long deformation interval may differ substantially from that responsible for the earthquake population at any one time

multiscaling nature of sonic velocities and lithology in the upper crystalline crust evidence from the ktb main borehole the observed scaling of sonic logs is generally described using a monofractal model fractional brownian motion with hurst exponent typically between 0 1 and 0 2 or fractional levy motion even though such a description recognizes the existence of the self similarity of the logs it offers only a limited account of the actual symmetry as it misses the displayed heterogeneous fractality intermittency of the velocity increments is here observed and calls for the use of a multifractal description we quantify such a multifractality in the case of the p wave sonic log recorded at the ktb main borehole we also show that the associated lithology inferred from the gamma log has a multifractal distribution as well though characterized by a stronger intermittency it can be expected that the multifractality of the sonic log is partially induced by the lithology though the observed discrepancy in the degree of intermittency between the two logs indicates that the scaling symmetry of the seismic velocity is probably due to many different contributions such statistics for both sonic and gamma logs have important implications on our understanding of wave propagation and rock strength and permeability in the crystalline crust as they show the crust to be more heterogeneous than is usually modeled

reduced north atlantic deep water flux to the glacial southern ocean inferred from neodymium isotope ratios the global circulation of the oceans and the atmosphere transports heat around the earth broecker and denton1 suggested that changes in the global ocean circulation might have triggered or enhanced the glacial interglacial cycles but proxy data for past circulation taken from sediment cores in the south atlantic ocean have yielded conflicting interpretations of ocean circulation in glacial times 13c variations in benthic foraminifera2 3 4 5 6 support the idea of a glacial weakening or shutdown of north atlantic deep water production whereas other proxies such as cd ca ba ca and 231pa 230th ratios show little change from the last glacial maximum to the holocene epoch7 8 9 here we report neodymium isotope ratios from the dispersed fe mn oxide component of two southeast atlantic sediment cores both cores show variations that tend towards north atlantic signatures during the warm marine isotope stages 1 and 3 whereas for the full glacial stages 2 and 4 they are closer to pacific ocean signatures we conclude that the export of north atlantic deep water to the southern ocean has resembled present day conditions during the warm climate intervals but was reduced during the cold stages an increase in biological productivity may explain the various proxy data during the times of reduced north atlantic deep water export

deep water formation in the north pacific and deglacial co2 rise deep water formation in the north atlantic and southern ocean is widely thought to influence deglacial co 2 rise and climate change here we suggest that deep water formation in the north pacific may also play an important role we present paired radiocarbon and boron isotope data from foraminifera from sediment core md02 2489 at 3640 m in the north east pacific these show a pronounced excursion during heinrich stadial 1 with benthic planktic radiocarbon offsets dropping to 350 years accompanied by a decrease in benthic 11 b we suggest that this is driven by the onset of deep convection in the north pacific which mixes young shallow waters to depth old deep waters to the surface and low ph water from intermediate depths into the deep ocean this deep water formation event was likely driven by an increase in surface salinity due to subdued atmospheric monsoonal freshwater flux during heinrich stadial 1 the ability of north pacific deep water npdw formation to explain the excursions seen in our data is demonstrated in a series of experiments with an intermediate complexity earth system model these experiments also show that breakdown of stratification in the north pacific leads to a rapid 30 ppm increase in atmospheric co 2 along with decreases in atmospheric 13 c and 14 c consistent with observations of the early deglaciation our inference of deep water formation is based mainly on results from a single sediment core and our boron isotope data are unavoidably sparse in the key hs1 interval so this hypothesis merits further testing however we note that there is independent support for breakdown of stratification in shallower waters during this period including a minimum in 15 n younging in intermediate water 14 c and regional warming we also re evaluate deglacial changes in north pacific productivity and carbonate preservation in light of our new data and suggest that the regional pulse of export production observed during the bolling allerod is promoted by relatively stratified conditions with increased light availability and a shallow potent nutricline overall our work highlights the potential of npdw formation to play a significant and hitherto unrealized role in deglacial climate change and co 2 rise

microscale neodymium distribution in sedimentary planktonic foraminiferal tests and associated mineral phases neodymium isotopic ratios recorded in calcareous foraminiferal tests shells and associated authigenic minerals were used to trace past water masses although the origin of preserved nd signals is still a matter of debate we determined for the first time the microscale nd distribution in two planktonic foraminifera species globigerinoides ruber and neogloboquadrina dutertrei and coexisting authigenic minerals from two selected time slices 15 6 and 129 kyr of a marine sediment core in the panama basin elemental mapping of nd ca fe mn and si was performed using nanosims ion probe and electron probe microanalysis epma on uncleaned tests together with scanning electron microscopy sem imagery epma and sem images revealed the presence of fe rich framboidal minerals inside test pores and inner chambers particularly in the old samples the young sample presented fe and mn rich patches on the inner test wall the nd intensity in fe mn rich patches and in some framboids was much higher than in foraminiferal calcite where the nd distribution was randomly heterogeneous with no systematic features such as an ontogenic nd rich layer or species specific differences the relationship between nd fe and mn confirmed a significant role of fe mn oxides as a nd carrier the high nd enrichment in some framboids could be explained by nd adsorption onto oxidized surface of fe sulfides particles rather than direct incorporation since the authigenic precipitates are major nd carrier phases the nd isotopic signals in sedimentary foraminiferal tests likely reflect bottom pore water values rather than surface water ones

the broad band fractal nature of heterogeneity in the upper crust from petrophysical logs in situ measurements of petrophysical properties of the upper crust from wire line logs provide a direct means of assessing fluctuations in these properties with depth and thus allow for the statistical characterization of crustal heterogeneity wire line logs from a cluster of nine boreholes 1000 1500 m deep have been analysed using four different techniques autocorrelation semi variogram rescaled range and power spectra six of the boreholes are vertical the remainder inclined all penetrate clastic and pyroclastic rock the analysis techniques have been tested on synthetic data for which we have precise control on the scaling in order to assess their robustness the results for the borehole data show broad band fractal scaling with a fractal dimension of 1 62 to 1 97 autocorrelation 1 59 to 1 79 rescaled range and 1 61 to 2 0 power spectra the use of different techniques to estimate the fractal dimension provides an excellent constraint on the results furthermore it allows us to determine which model for crustal heterogeneity best describes the data a band limited von karman function or unbounded fractal scaling in order to test the possible anisotropy in the scaling parameters the horizontal scaling properties for this area have been calculated by correlation spectra analysis of neighbouring wells this suggests that upper crustal correlation lengths are of the order of kilometres and anisotropic being over four times greater in the horizontal direction the origins of the observed power law scaling are complex analysis of long term correlations between logs and televiewer data points towards the influence of fracture porosity within the pyroclastics but a fractal distribution of pore spaces within the clastics also controls the log fluctuations separating the logs into clastic and pyroclastic subsets reveals slight differences in fractal scaling as determined by autocorrelation and semi variogram these differences are attributed to the dominance of either primary or fracture porosity within each geological unit

the isotopic composition of neodymium in the north pacific abstract we have determined the isotopic composition of neodymium in two water column profiles in the western north pacific and in bottom waters from three other locations in the north pacific the vertical profiles reveal that the water column is stratified with respect to isotopic composition mid depths associated with pacific deep water are uniform having nd 0 3 shallow waters are variable but deep waters are less radiogenic having md 0 4 4 to 5 in the western basin the more negative bottom waters in the western north pacific provide evidence for the advective transport of rare earth elements from antarctic sources to this region bottom waters in the eastern north pacific are more radiogenic nd 0 3 3 to 3 8 indicating very little transport of ree from antarctic sources to this basin overall the isotopic composition of nd in pacific bottom waters appears to be conservative when compared to the silica distribution in spite of evidence for nd removal the findings are generally compatible with other parameters such as temperature salinity and nutrient distributions the presence of nd isotopic signatures associated with antarctic sources in these waters provides evidence for a small component of rare earth elements of north atlantic origin in the bottom waters of the north pacific this is the first tracer evidence to corroborate the suggestion of reid and lynn 1971 that some of the temperature and salinity properties of the deep waters of the north pacific originated in the norwegian and greenland seas

neodymium isotopic composition in foraminifera and authigenic phases of the south china sea sediments implications for the hydrology of the north pacific ocean over the past 25 kyr end and normalized rare earth elements ree patterns of benthic and planktonic foraminifera and fe mn coatings precipitated on sediments have been investigated for the south china sea scs to 1 assess the reliability of the extraction of past seawater end in the scs and to 2 reconstruct past hydrological changes during the last 25 kyr reductively cleaned mono specific planktonic foraminifera globigerinoides ruber and mixed benthic foraminifera in core top sediments from 1500 to 2400 m display similar end values to those of the modern pacific deep water pdw end of 3 9 to 4 4 furthermore the end of the reductive cleaning solutions shows similar end values to ones obtained on cleaned foraminifera combined with paas normalized ree patterns these results confirm that the oxidative and reductive cleaning procedure applied to foraminifera does not totally remove all of the fe mn coatings and that end values yielded by cleaned planktonic foraminifera retain the end imprint of the bottom and or pore water end values obtained from a leaching procedure carried out on the bulk non decarbonated sediments are comparable to the end values of the modern pdw whereas a similar leaching procedure applied to decarbonated sediments reveals a bias due to contamination with nd deriving from lithogenic particles in core md05 2904 seawater end reconstructed from planktonic foraminifera indicates that the last glacial period is characterized by lower end 5 2 0 2 to 6 4 0 3 than the late holocene 4 1 0 2 assuming that nd input from river does not change strongly the end of the pdw of the northern scs these end variations suggest a higher relative proportions of southern sourced water in the deep water of the western subtropical pacific ocean during the last glacial period

microstructural and crystal fabric evolution during shear zone formation abstract the microstructures and crystal fabrics associated with the development of an amphibolite facies quartzo feldspathic mylonitic shear zone torridon nw scotland have been investigated using sem electron channelling our results illustrate a variety of microstructures and fabrics which attest to a complex shear zone deformation history microstructural variation is particularly pronounced at low shear strains significant intragranular deformation occurs via a domino faulting style process whilst mechanical incompatibilities between individual grains result in characteristic grain boundary deformation accommodation microstructures a sudden reduction in grain size defines the transition to medium shear strains but many of the boundaries inherited from the original and low shear strain regions can still be recognized and define distinctive bands oriented at low angles to the shear zone margin grains within these bands have somewhat steeper preferred dimensional orientations these domains persist into the high shear strain mylonitic region where they are oriented subparallel to the shear zone margin and consist of sub 20 m grains the microstructures suggest that the principal deformation mechanism was intracrystalline plasticity with contributions from grain size reduction via dynamic recrystallization grain boundary migration and grain boundary sliding crystal fabrics measured from the shear zone vary with position depending on the shear strain involved and are consistent with the operation of several crystal slip systems e g prism basal rhomb and acute rhomb planes in a consistent direction probably parallel to a and or m they also reveal the presence of dauphine twinning and suggest that this may be a significant process in quartz deformation a single crystal fabric evolution path linking the shear zone margin fabric with the mylonitic fabric was not observed rather the mylonitic fabric reflects the instantaneous fabric which developed at a particular location for a particular shear strain and original parental grain orientation the mature shear zone therefore consists of a series of deformed original grains stacked on top of each other in a manner which preserves original grain boundaries and intragranular features which develop during shear zone evolution the stability of some microstructures to higher shear strains the exploitation of others at lower shear strains and a continuously evolving crystal fabric mean that the strain gradient observed across many shear zones is unlikely to be equivalent to a time gradient

stochastic characterization and seismic response of upper and middle crustal rocks based on the lewisian gneiss complex scotland summary we have developed statistical models of upper and middle crustal seismic velocity heterogeneity based on geologic maps and petrophysical data from the lewisian gneiss complex scotland the level of heterogeneity we have measured is relevant to seismic exploration of the crystalline crust using conventional reflection and refraction techniques we digitized two 1 10560 geologic maps of laxfordian archean age lewisian rocks on a 26 8m grid both maps are believed to be representative of the upper and middle crust in north western scotland and both are believed to provide cross sectional views of parts of the crust the digital maps were characterized by the statistics of their lithologic populations and by their 2 d spatial autocorrelation functions different lithologies were assigned seismic velocities appropriate for the mid crust using petrophysical data three lithologies are dominant silicic gneisses vp 6 2 km s 1 mafic amphibolites vp 6 75 kms 1 and intermediate composition schists vp 6 5kms 1 both maps have self affine spatial fabrics the first map covers the core of a syncline its autocorrelation function defines a medium with a fractal dimension of 2 78 a horizontal characteristic length of about 244m and a vertical correlation of about 133m aspect ratio is 2 1 it has an essentially trimodal velocity lithology population consisting of 37 per cent silicicgneiss 43 per cent mafic amphibolites and 20 per cent schists this map is representative of 30 40 per cent of laxfordian rocks the second map is a plan view which can be rotated 90 about an axis perpendicular to strike to give a cross section this map is characterized by a fractal dimension of 2 55 with a horizontal correlation length of about 111m and a vertical correlation of about 38m aspect ratio 3 1 it has a nearly bimodal population consisting of 77 per cent silicic gneisses and 22 per cent mafic amphibotites it is representative of 60 70 per cent of laxfordian rocks lastly we examine the seismic response of an upper to middle crust based on our statistical models using acoustic and elastic 2 d finite difference synthetic seismograms short offset shot records demonstrate that a lewisian upper crust produces scattered waves which significantly disrupt signals reflecting from deeper levels measurements of transmission scattering q and coda decay rates confirm that seismic scattering in lewisian type crust is strong the migrated cmp response of a lewisian crustal model shows the characteristic salt and pepper pattern often observed in the upper crust and described incorrectly as transparent we suggest that translucent is a more appropriate descriptor

triggering of seismicity at short timescales following californian earthquakes 1 a method for measuring seismicity rate changes caused by the occurrence of major earthquakes in the surrounding crust is proposed it is based on a nonstationary poisson modeling of earthquake activity an estimate of the seismicity rate change and a probability measure of seismicity triggering following a large shock are derived and the removal of the influence of independent aftershock sequences of other nearby previous earthquakes is attempted without using more traditional declustering techniques the seismicity rate change estimator is corrected for its natural bias in favor of positive changes at short timescales that has so far strongly hindered measures of seismicity quiescences three californian earthquakes are examined using this method the 1989 m7 1 loma prieta the 1992 m7 3 landers and the 1994 m6 7 northridge earthquakes positive triggering is very commonly observed as expected but quiescence is however more seldomly obtained for timescales up to 100 days after the main shock this relative absence of quiescence as compared to typical predictions of coulomb modeling for example is also independently observed through direct correlation analyses of californian seismicity the possibility that the stresses caused by the main shock are spatially highly variable may explain these observations

deep south china sea circulation 1 the analysis of an updated monthly climatology of observed temperature and salinity from the u s navy generalized digital environment model reveals a basin scale cyclonic circulation over the deep south china sea scs the cyclonic circulation lies from about 2400 m to the bottom the boundary current transport of the cyclonic circulation is around 3 0 sv our results suggest that the cyclonic circulation is mainly forced by the luzon overflow with bottom topography playing an important role the structures of potential temperature salinity and potential density in the deep scs are consistent with the existence of the cyclonic circulation specifically low salinity water is found in the interior region west of luzon island and surrounded by saline pacific water in boundary current regions to the north west and southwest our results show the potential density distribution and the corresponding cyclonic circulation in deep scs are primarily controlled by salinity variations in the deep basin

nature and origin of upper crustal seismic velocity fluctuations and associated scaling properties combined stochastic analyses of ktb velocity and lithology logs the main borehole of the german continental deep drilling program ktb extends over 9000 m into a crystalline upper crust consisting primarily of interlayered gneiss and metabasite we present a joint analysis of the velocity and lithology logs in an effort to extract the lithology component of the velocity log covariance analysis of lithology log approximated as a binary series indicates that it may originate from the superposition of two brownian stochastic processes fractal dimension 1 5 with characteristic scales of 2800 m and 150 m respectively covariance analysis of the velocity fluctuations provides evidence for the superposition of four stochastic process with distinct characteristic scales the largest two scales are identical to those derived from the lithology confirming that these scales of velocity heterogeneity are caused by lithology variations the third characteristic scale 20 m also a brownian process is probably related to fracturing based on correlation with the resistivity log the superposition of these three brownian processes closely mimics the commonly observed 1 k decay fractal dimension 2 0 of the velocity power spectrum the smallest scale process characteristic scale 1 7 m requires a low fractal dimension 1 0 and accounts for 60 of the total rms velocity variation a comparison of successive logs from 6900 7140 m depth indicates that such variations are not repeatable and thus probably do not represent true velocity variations in the crust the results of this study resolve disparity between the differing published estimates of seismic heterogeneity based on the ktb sonic logs and bridge the gap between estimates of crustal heterogeneity from geologic maps and borehole logs

isotopic composition of neodymium in waters from the drake passage the isotopic composition of neodymium has been determined in seawaters from the drake passage the antarctic circumpolar current which controls interocean mixing flows through this passage the parameter e nd 0 which is a function of the ratio of neodymium 143 to neodymium 144 is found to be uniform with depth at two stations with a value which is intermediate between the values for the atlantic and the pacific and indicates that the antarctic circumpolar current consists of about 70 percent atlantic water cold bottom water from a site in the south central pacific has the neodymium isotopic signature of the waters in the drake passage by using a box model to describe the exchange of water between the southern ocean and the ocean basins to the north together with the isotopic results an upper limit of approximately 33 million cubic meters per second is calculated for the rate of exchange between the pacific and the southern ocean concentrations of samarium and neodymium were also determined and found to increase approximately linearly with depth these results suggest that neodymium may be a valuable tracer in oceanography and may be useful in paleo oceanographic studies

on the use of fractal surfaces to understand seismic wave propagation in layered basalt sequences the aim of this study is to better understand how a layered basalt sequence affects the propagation of a seismic wave which has implications for sub basalt seismic imaging this is achieved by the construction of detailed realistic models of basalt sequences using data derived directly from outcrop analogues field data on the surface roughness of basaltic lava flows were captured using terrestrial laser scanning and satellite remote sensing the fractal properties of the surface roughness were derived and it can be shown that the lava flow surface is fractal over length scales up to approximately 2 km the fractal properties were then used to construct synthetic lava flow surfaces using a von karman power spectrum and the resulting surfaces were then stacked to create a synthetic lava flow sequence p wave velocity data were then added and the resulting model was used to generate synthetic seismic data the resulting stacked section shows that the ability to resolve the internal structure of the lava flows is quickly lost due to scattering and attenuation by the basalt pile a further result from generating wide angle data is that the appearance of a lower velocity layer below the basalt sequence may be caused by destructive interference within the basalt itself

testing the extraction of past seawater nd isotopic composition from north atlantic deep sea sediments and foraminifera neodymium isotopes provide a paleoceanographic proxy for past deep water circulation and local weathering changes and have been measured on various authigenic marine sediment components including fish teeth ferromanganese oxides extracted by acid reductive leaching cleaned foraminifera and foraminifera with fe mn oxide coatings here we compare nd isotopic measurements obtained from ferromanganese oxides leached from bulk sediments and planktonic foraminifera as well as from oxidatively reductively cleaned foraminiferal shells from sediment cores in the north atlantic sedimentary volcanic ash contributes a significant fraction of the nd when the ferro manganese fe mn oxide coatings are leached from bulk sediments reductive leachates of marine sediments from north atlantic core tops near iceland or directly downstream from iceland scotland overflow waters record nd values that are significantly higher than seawater indicating that volcanic material is easily leached by acid reductive methods the nd values from sites more distal to iceland are similar to modern seawater values showing little contamination from iceland derived volcanogenic material in all comparisons core top planktonic foraminifera nd values more closely approximate modern deep seawater than the bulk sediment reductive leached value suggesting that the foraminifera provide a route toward quantifying the nd isotopic signature of deep north atlantic water masses

alkaline earth metal and rare earth element incorporation control by ionic radius and growth rate on a stalagmite from the chauvet cave southeastern france abstract a multi element study involving major alkaline earth cations mg ca sr ba and trace elements like na u mn y and rare earth elements ree in calcite of a stalagmite from the chauvet cave se of france was carried out using icp qms analysis this study focused on the chau stm6 stalagmite which displays a record of the last deglaciation until the end of the younger dryas with ages ranging from 33 kyr to 11 5 kyr bp in this study profiles of the alkaline earth elements sr and ba show concentrations increasing sharply at the beginning of the deglaciation while mg and u show a decreasing trend rey ree y concentrations decrease sharply during early deglaciation the clear record of the onset of the younger dryas by stable isotopes is not well marked by these elements the absence of a significant correlation between rey and mn suggests that ree were here not strongly bound to particulate colloidal phases but were mainly controlled by limestone groundwater interaction shale normalized ree patterns in stalagmite characterized by a negative ce anomaly and hree enrichment compared to lree is thought to mainly arise from the dissolution of bedrock since chau stm6 patterns are similar to those of the bedrock chau stm6 rey patterns are even more depleted in lree than those of the bedrock showing that part of the lree were removed from groundwater upstream from the stalagmite some particular rey pattern changes were observed for the different climatic conditions 1 glacial samples often display a more marked negative ce anomaly 0 3 and a high y ho ratio 0 6 2 bolling allerod and younger dryas samples display a variable and less pronounced anomaly 0 5 0 8 and a lower y ho ratio 0 35 0 55 climatic changes modified the rate of the stalagmite growth which likely caused a change in the properties of element incorporation in the calcite lattice consequently the concentration variations of mg ca sr ba u and rey would be directly controlled by ionic radii of each element

radiocarbon and stable isotope constraints on last glacial maximum and younger dryas ventilation in the western north atlantic 1 foraminiferal abundance 14c ventilation ages and stable isotope ratios in cores from high deposition rate locations in the western subtropical north atlantic are used to infer changes in ocean and climate during the younger dryas yd and last glacial maximum lgm the 18o of the surface dwelling planktonic foram globigerinoides ruber records the present day decrease in surface temperature sst of 4 c from gulf stream waters to the northeastern bermuda rise if during the lgm the modern 18o salinity relationship was maintained this sst contrast was reduced to 2 c with lgm to interglacial 18o changes of at least 2 2 ssts in the western subtropical gyre may have been as much as 5 c colder above 2 3 km glacial 13c was higher than today consistent with nutrient depleted younger bottom waters as identified previously below that 13c decreased continually to 0 5 about equal to the lowest lgm 13c in the north pacific ocean seven pairs of benthic and planktonic foraminiferal 14c dates from cores 2 5 km deep differ by 1100 340 years with a maximum apparent ventilation age of 1500 years at 4250 m and at 4700 m apparent ventilation ages are presently unavailable for the lgm 2 5 km because of problems with reworking on the continental slope when sea level was low because lgm 13c is about the same in the deep north atlantic and the deep north pacific and because the oldest apparent ventilation ages in the lgm north atlantic are the same as the north pacific today it is possible that the same water mass probably of southern origin flowed deep within each basin during the lgm very early in the yd dated here at 11 25 0 25 n 10 conventional 14c kyr bp equal to 12 9 calendar kyr bp apparent ventilation ages 2 3 km water depth were about the same as north atlantic deep water today below 2 3 km four yd pairs average 1030 400 years the oldest apparent ventilation age for the yd is 1600 years at 4250 m this strong contrast in ventilation which indicates a front between water masses of very different origin is similar to glacial profiles of nutrient like proxies this suggests that the lgm and yd modes of ocean circulation were the same

source to sink transport processes of fluvial sediments in the south china sea the south china sea offers an excellent case for studying source to sink transport processes of fluvial sediments among the global marginal seas this study synthesizes existing clay mineralogical and geochemical data from similar to 1500 samples from the seafloor and surrounding rivers deepwater mooring observation results and high resolution glacial cyclic clay mineralogy records from six high quality sediment cores source to sink sediment transport from the river mouth to the continental shelf and then to the abyssal basin is investigated at two time scales modern process and late quaternary glacial cycles the results firstly show the high diversity of clay mineralogical and geochemical compositions in riverbed surface sediments surrounding the south china sea e g dominant illite and chlorite in taiwan overwhelming majority of smectite in luzon dominant kaolinite in south china and similar amounts of the four clay mineral species in red and mekong river systems the formation of these fluvial sediments through chemical weathering in surrounding drainage systems is controlled principally by the east asian monsoon climate with warm temperature and high precipitation and subordinately by tectonic activity and specific lithological character the basin wide distribution of clay mineral assemblages combined with neodymium and strontium isotopic compositions reflects strong provenance control and differential settling effects the differential settling of kaolinite in slightly saline and proximal regions relative to smectite in more saline and distal regions is well demonstrated in the south china sea through combining clay mineralogical distributions on the seafloor with observed oceanic current systems the modern transport pathways can be well established e g in the northern south china sea illite and chlorite from taiwan are mainly carried by contour currents with the strong influence of mesoscale eddies high resolution sediment dynamic analysis for the late quaternary reveals different sediment transport patterns in the northern western and southern south china sea when the land sea configuration dramatically changed during glacial conditions in the north the terrigenous dispersal is mainly controlled by provenance supply and oceanic current transport in the west the clay mineral assemblage reflects variations of the prevailing surface current influenced by monsoon winds in the south the clay mineral input indicates intensive chemical weathering during interglacial periods and strengthened physical erosion during glacial periods the transport of terrigenous sediments since the last glaciation is quantitatively reconstructed through studying two deepwater sediment cores located in the northern south china sea the relative contributions from three provenances south china luzon and taiwan highlight their distinct variability over the last 28 ka implying that the southward shift of the inter tropical convergence zone itcz at 16 ka bp caused an increased sediment contribution from south china the intensified influence of the kuroshio current intrusion controls more efficient westward transport of luzon sediments and the stronger deepwater current transports taiwan sourced sediments further westward from the last glaciation to the holocene c 2015 elsevier b v all rights reserved

reflection characteristics of a mylonite zone based on compressional wave velocities of rock samples summary a combined field and laboratory study of the seismic reflection response and seismic properties of the mylonite zone capping the kettle dome metamorphic core complex provides important constraints on reflectivity of mylonites because of its structural and petrologic characteristics this mylonite zone can be regarded as a model for mid to deep crustal mylonite zones cdp reflection profiling revealed that the mylonite zone is reflective laboratory measurements of compressional wave velocities v at high confining pressures in samples collected directly up dip from the cdp reflection line revealed a wide variation of v in common mid crustal lithologies mafic and carbonate rock mean v values range from 6 67 to 7 31 km s at 600 mpa and quartzite and quartzo feldspathic values range from 6 16 to 6 52 km s seismic anisotropy at low pressures can be related to open microcracks and preferred mineral orientation whereas the latter effect controls anisotropy at high pressures the laboratory data provide the basis for a seismic model which indicates that the kettle dome mylonite zone can generate reflections from zones where high and low velocity lithologies are interlayered these reflections correlate with those observed on the cdp data thus demonstrating that the reflectivity of the mylonite zone is a direct result of its lithologic diversity and layered nature in this case it is not necessary to explain the reflections by the effects of anisotropy retrogression high pore pressure or constructive interference

ocean ventilation and sedimentation since the glacial maximum at 3 km in the western north atlantic 1 stable isotope sedimentological and radiocarbon data from cores at 3 km water depth on the blake ridge western subtropical north atlantic reveal the history of deep water ventilation since the last glacial maximum lgm bulk sediment accumulation rates varied locally by a factor of 2 under the influence of bottom currents in this sediment drift environment but the sand flux mostly foraminifera was nearly identical at a given time this suggests that the rain rate of foraminifera mostly planktonic was constant that transport of foraminifera was negligible and that current controlled differences in clay and silt transport drive bulk accumulation in two of the cores flux peaks in the benthic foraminifera cibicidoides and uvigerina peregrina occurred during the younger dryas yd cold event and at 18 2 19 6 21 1 25 0 and 28 1 ka radiocarbon measurements on those benthic foraminifera show the ventilation age of bottom waters was 1000 years during the yd and for older events it was as great as 2000 years these results contrast with holocene ventilation which was 500 years and 700 years at 1500 years and 7100 years before present respectively

glacial water mass geometry and the distribution of δ13c of σco2 in the western atlantic ocean 1 oxygen and carbon isotopic data were produced on the benthic foraminiferal taxa cibicidoides and planulina from 25 new piston cores gravity cores and multicores from the brazil margin the cores span water depths from about 400 to 3000 m and intersect the major water masses in this region these new data fill a critical gap in the south atlantic ocean and provide the motivation for updating the classic glacial western atlantic 13c transect of duplessy et al 1988 the distribution of 13c of co2 requires the presence of three distinct water masses in the glacial atlantic ocean a shallow 1000 m southern source water mass with an end member 13c value of about 0 3 0 5 vpdb a middepth 1500 m northern source water mass with an end member value of about 1 5 and a deep 2000 m southern source water with an end member value of less than 0 2 and perhaps as low as the 0 9 values observed in the south atlantic sector of the southern ocean ninnemann and charles 2002 the origins of the water masses are supported by the meridional gradients in benthic foraminiferal 18o a revised glacial section of deep water 13c documents the positions and gradients among these end member intermediate and deep water masses the large property gradients in the presence of strong vertical mixing can only be maintained by a vigorous overturning circulation

nd ca ratios in plankton towed and core top foraminifera confirmation of the water column acquisition of nd planktic foraminifera have been used as recorders of the neodymium nd isotopic composition of seawater although there is still controversy over the precise provenance of the nd signal we present an extensive multispecific plankton tow nd ca data set from several geographic locations se atlantic ne atlantic norwegian sea and western mediterranean together with core top samples from the mediterranean region the range of nd ca ratios in plankton towed foraminifera cleaned only of organic material from all regions 0 01 0 7 mol mol is similar to previously published analyses of sedimentary foraminifera cleaned using both oxidative and reductive steps with distribution coefficients kd ranging between 4 and 302 for the mediterranean where core top and plankton tow data are both available the range for plankton tows 0 05 0 7 mol mol is essentially identical to that for the core tops 0 1 0 5 mol mol readsorption of nd during cleaning is ruled out by the fact that the plankton tow samples underwent only an oxidative cleaning process we find a relationship between manganese mn and nd in plankton tow samples that is mirrored by a similar correlation in core top samples this relationship suggests that fe mn coatings are of negligible importance to the nd budgets of foraminifera as the nd mn ratio it implies is over an order of magnitude greater than that seen in other fe mn oxide phases rather since both plankton tows and core tops present a similar behavior the nd mn relationship must originate in the upper water column the data are consistent with the acquisition of nd and mn from the water column by binding to organic material and the fact that intratest organic material is shielded from both aggressive cleaning and diagenetic processes collectively the results help to explain two abiding puzzles about nd in sedimentary planktic foraminifera their high ree contents and the fact that they record a surface water nd isotopic signal regardless of the cleaning procedure used

deep borehole log evidence for fractal distribution of fractures in crystalline rock summary sonic velocity and electrical resistivity logs run to a depth of 3 5 km in crystalline rock near the san andreas fault at cajon pass in southern california correlate over scale lengths both small sub metre and large tens to hundreds of metres no such correlations are seen with the more lithologically sensitive natural gamma intensity log the correlation between the sonic velocity and electrical resistivity logs suggests that a non lithologic property of the crystalline rock controls fluctuations in situ fracture intensity is a logical candidate for the controlling rock property the fluctuations of the individual sonic velocity and electrical resistivity logs are examined with the hurst rescaled range parameter over borehole log intervals 1 5 m l 1500 m for log fluctuations arising from a scale invariant physical process the hurst rescaled range scales with data interval as lh 0 h 1 a purely random sequence of in situ fractures produces a scaling exponent h 0 50 fluctuations in the cajon pass sonic velocity and electrical resistivity logs yield h 0 70 evidence that in situ fracture sets tend to occur in clusters rather than at purely random intervals the tendency for fracture clustering over log intervals 1 5 m l 1500 m suggests that fracture formation is a fractal process independent of length scale in which larger fracture intervals form from clustering of numerous smaller fracture intervals seismic reflectivity derived from the borehole sonic velocity log is also scale independent over the range of data intervals 1 5m l 1500 m with a hurst exponent h 0 21 if we associate fracture clustering with crustal fault formation the cajon pass borehole sonic velocity and electrical resistivity logs predict that crustal faults scale fractally with fractal dimension d 2 30 the equivalent b value for earthquake size distribution is b d 2 1 15 on this hypothesis observed b values 1 15 indicate a tendency for earthquakes to cluster on existing weak faults a scale independent mechanics for crystalline rock fracture formation in which larger scale fractures form as clusters of smaller scale fractures provides a mechanical link between the small pervasive stress aligned flaws cracks and microfractures which can impart anisotropy to crystalline rock and the larger scale fractures associated with finite strain and faulting thus in crustal regions of active but low strain fracture anisotropy is observed to be aligned with the inferred maximum principal stress while in actively faulted crust fracture anisotropy is observed to be more nearly fault parallel as if the fractures are aligned by the finite strain faulting process

stochastic analysis of sonic logs from the upper crystalline crust methodology to relate local fluctuations observed in sonic logs to small scale velocity fabric along boreholes both filtering effects and noise introduced by the logging procedure must be taken into account sonic log velocities are represented as a time series consisting of a large scale deterministic and a small scale stochastic component the deterministic trend approximated by a low order polynomial best fit contains information on the average velocity structure whereas the small scale stochastic variations consist of noise plus in situ velocity variations convolved with the logging system response the velocity fluctuations of the sonic data considered here are zero mean and have quasi gaussian probability density functions therefore they are well characterised by their second statistical moment i e their autocovariance function tests on synthetic data indicate that the autocovariance function corresponding to this data model may be used to extract information on the second order statistics of the in situ velocity variations along the borehole and to constrain the level of white noise in sonic logs ignoring the presence of filtering effects and noise in sonic logs may result in seriously flawed estimates of the second order statistics of the actual velocity structure assuming a von karman autocovariance function for the in situ velocity variations this model provides a good match to the autocovariance functions of sonic log data from the siljan ring sweden and sudbury areas canada although differing significantly in their noise content these two data sets yield similar results for the small scale velocity structure which is modelled as a bandlimited self affine time series for the siljan ring borehole we found a close relation between small scale variations of the borehole diameter as determined from caliper logs and the level of uncorrelated noise present in the sonic log data

an investigation of the spectral properties of primary reflection coefficients this paper investigates the form of the nonwhiteness found in the reflection coefficients from a wide variety of rock sequences around the world in all but one case densities are taken as constant due to the paucity of suitable density data the reflection sequences are pseudo white only above a corner frequency below which their power spectrum falls away according to a power law f where is between 0 5 and 1 5 this spectrum can be adequately modelled in practice very simply with an arma 1 1 process which acts on a white innovation sequence the corollary of this is that before wavelet estimation methods are applied all of which except those based on synthetic seismograms presuppose white reflection sequences or deconvolution filters estimated seismic traces should be filtered with the inverse of this process interestingly the estimated arma processes group themselves into two clearly differentiated categories having very different indices of predictability or strictly indices of linear determinism the two categories apparently correlate precisely with two kinds of sedimentation one which consists largely of sequences of rocks with repeating properties called repetitive in this paper but perhaps loosely describable as cyclic and the other which is randomly bedded with no apparent pattern of components the former has indices of predictability which are two to four times as great as those of the latter another probably related property is that for the repetitive sequences tends to be greater than that for non repetitive rock columns the observed power spectra are shown to be consistent with a simple model for the logarithm of acoustic impedance consisting of a mixture of processes where the distribution of time scale parameters is reciprocal detailed effects of block averaging and sampling the logs are shown to depend on the type of sequence under examination

fracture network characterization using 1d and 2d data of the moragy granite body southern hungary abstract a disposal system for low and medium level nuclear waste in hungary is being constructed inside the fractured rock body of the lower carboniferous moragy granite previous studies proved that the granitoid massif is rather heterogeneous in terms of lithological composition brittle structure and hydrodynamic behaviour a significant part of the body consists of monzogranite while other portions are more mafic in composition and are monzonites as a result of at least three significant brittle deformation events the area is at present crosscut by wide shear zones that separate intensively fractured zones and poorly deformed domains among them due to late mineralization processes some of these fractured zones are totally sealed and cannot conduct fluids while others are excellent migration pathways the spatial distribution of these two types nevertheless does not show any systematics hydrodynamic behaviour clearly reflects this heterogeneous picture in some places hydraulic jumps as great as 25 m at compartment boundaries can be detected in this study the fracture network of the moragy granite body is evaluated from a geometric aspect using datasets measured at a wide range of scales 2d digitized images of a hand specimen one large 20 60 m and 12 smaller subvertical wall rocks outcrops and 120 images from tunnel faces representing the ground level of the underground repository site were analysed moreover 1d data from 13 wells that all penetrate the granitoid massif were studied based on measured geometric data spatial position length orientation and aperture fracture networks are simulated to study connectivity relations and for computing the fractured porosity and permeability at different scales the results prove the scale invariant geometry of the fracture system geostatistical calculations indicate that measurable fracture geometry parameters behave as regionalized variables and so can be extended spatially estimated localities of connected subsystems fit very well with fault zones mapped previously moreover the spatial position of regimes of different hydrodynamic behaviours can be explained by connectivity relations both regionally and within wells

from the subtropics to the central equatorial pacific ocean neodymium isotopic composition and rare earth element concentration variations 1 neodymium isotopic compositions end and rare earth element ree concentrations were measured for filtered surface to deep waters 112 samples in the southern tropical pacific the relatively detailed picture of these tracer distributions allowed us to refine the areas where oceanic end variations occur end values increase for most of the water masses flowing from samoa to the solomon sea and in the papua new guinea png area as already observed furthermore water masses arriving from the eastern equatorial pacific 200 550 m depth also revealed radiogenic values possibly acquired in the vicinity of the south american coasts and galapagos islands these end variations affect the whole water column the most likely process causing such variations is boundary exchange between the numerous radiogenic slopes margins located in this area and seawater flowing past dissolution of atmospheric deposition and or diffuse streaming of volcanic ash are also suggested to explain the radiogenic end observed at the surface in the png area interestingly a positive europium eu anomaly characterizes the normalized ree patterns of most of the studied water masses this anomaly is consistent with the ree patterns of sediment and rock samples that are potential sources for the local waters such consistency reinforces the hypothesis that lithogenic sources play a major role in the oceanic ree budget thanks to boundary exchange the data set presented here is a good basis for further sampling that will be realized in the framework of the ongoing geotraces program www geotraces org

the use of foraminifera as a record of the past neodymium isotope composition of seawater 1 we present new isotopic data for sedimentary planktonic foraminifera as well as for potential water column and sedimentary sources of neodymium nd which confirm that the isotopic composition of the foraminifera is the same as surface seawater and very different from deep water and sedimentary nd the faithfulness with which sedimentary foraminifera record the isotopic signature of surface seawater nd is difficult to explain given their variable and high nd ca ratios ratios that are often sedimentary foraminifera ratios that are often much higher than is plausible for direct incorporation within the calcite structure we present further data that demonstrate a similarly large range in nd ca ratios in plankton tow foraminifera a range that may be controlled by redox conditions in the water column cleaning experiments reveal in common with earlier work that large amounts of nd are released by cleaning with both hydrazine and diethylene triamine penta acetic acid but that the nd released at each step is of surface origin while further detailed studies are required to verify the exact location of the surface isotopic signature and the key controls on foraminiferal nd isotope systematics these new data place the use of planktonic foraminifera as recorders of surface water nd isotope ratios and thus of variations in the past supply of nd to the oceans from the continents via weathering and erosion on a reasonably sure footing

fault scaling and 1 f noise scaling of seismic velocity fluctuations in the upper crystalline crust sonic logs are detailed measurements of the in situ seismic velocity along borehole walls power spectra of sonic logs typically decay approximately as the reciprocal of spatial frequency f regardless of the chemical composition geologic age and tectonic history of the probed lithologies data sequences of this type are fractal or scale invariant the origins of this uniform 1 f scaling of seismic structure are not clear particularly in low porosity crystalline rocks but faults fractures and cracks are considered to be important fault structures also follow fractal scaling laws and have significant effects on seismic velocity this paper presents a quantitative model that evaluates the role played by faults in determining the scaling laws of seismic velocity fluctuations the model is based on current knowledge of the structure and scaling properties of brittle faults and of associated regions of microcracking by approximating the relationship between crack density and velocity variation as linear this model yields a brownian power spectrum 1 f 2 for velocity perturbations across a single fault zone in a medium of otherwise constant velocity the power spectrum of velocity fluctuations induced by a population of faults is then obtained by superposing the corresponding brownian power spectra weighted according to the observed frequency size scaling relationship of brittle faults the results of this study indicate that the uniform 1 f scaling of velocity fluctuations in crystalline rocks seems to be linked to the correspondingly uniform scaling properties of fault structures

some remarks on the estimation of fractal scaling parameters from borehole wire line logs well logging provides a direct means of assessing fluctuations in petrophysical properties with depth and thus allows for the statistical characterisation of crustal heterogeneity using records from three super deep boreholes ktb and cajon pass and synthetic data we assess three different techniques for estimating fractal dimension and correlation length inaccurate correlation lengths may result from the way in which the autocorrelation is calculated for well logs leading to an incorrect application of the von karman function analysis of the rescaled range power spectra and autocorrelation allow us to model the data as k where k wavenumber and exponent 5 2d for fractal dimension d process with values of fractal dimension displaying anti persistence

rock as a critical point system and the inherent implausibility of reliable earthquake prediction summary the statistical mechanics of critical point thermodynamic systems provide a powerful conceptual tool with which to examine the plausibility of reliable earthquake prediction the issue turns on how rock is heterogeneous if the correlation range of a spatially fluctuating rock property is bounded by a characteristic length then the spatial average of that property over dimensions greater than may be regarded as defining an effective continuum value for that property ideas about earthquake preparation in rock with an effective continuum mechanical strength can plausibly focus on failure that is initiated at small anomalous zones and grows to instability with access to a continuous volume of strain energy the dimensions and temporal evolution of the growing anomaly can then be expected to relate to the size location and timing of the impending seismic event borehole log evidence indicates however that rock heterogeneity correlation lengths are unbounded and hence that the effective continuum approximation for rock must be applied with discretion an infinite correlation length indicates a statistical mechanical critical point system in which the correlation length is related to a singularity in a physical property in thermodynamic critical systems the singularity occurs at the critical system temperature tc 1 t tc in rock the singularity occurs at the critical percolation probability pc 1 p pc statistical physics descriptions of critical point spatial correlations are based on nearest neighbour inter actions at every scale length nearest neighbour interactions at one scale say that of large failure structures the loci of large earthquakes involve minimal coupling to structures at other scales in particular small scale failure structures the loci of small earthquakes the mechanics of nearest neighbour interactions plausibly form a fundamental constraint on the role of small scale failure or related nucleating activity as a prelude to large scale failure in light of 1 the evidence against rock being an effective medium notionally supporting localized precursory activity that reliably grows to large scale mechanical failure and 2 the history of failure to identify reliable precursors to major earthquakes the onus should now be on advocates of earthquake prediction schemes to evaluate their claims for precursory activity in terms of rock as a critical point system

reconstructing deglacial north and south atlantic deep water sourcing using foraminiferal nd isotopes during the last few decades neodymium isotopes have been increasingly used as a paleoceanographic and paleoclimate proxy on million year through millennial time scales the widespread use of the nd isotope proxy depends on whether the nd isotopic composition of past seawater can be reliably extracted from authigenic sediment phases here we show evidence that planktonic foraminifera with authigenic coatings preserve a deep water nd isotopic signature and thus can be used to reconstruct past deep water nd isotopes applying this method downcore on south atlantic deep cape basin core tno57 21 41 1 s 7 9 e 4981 m the nd isotopic composition of the planktonic foraminiferal fe mn oxide coatings is identical with and confirms that of the reductively leached bulk sediment fraction piotrowski et al 2004 2005 2008 as reflecting changes in bottom water sourcing in the case of northeastern north atlantic core bofs 8k 52 5 n 22 1 w 4045 m the planktonic foraminiferal fe mn oxide coatings have different nd isotopes from reductive sediment leaches clearly acid reductive leaching must be tested in more detail we observe that the nd isotopic composition of the deep northeastern atlantic core shifted during the deglaciation from glacial values similar to the south atlantic cape basin towards holocene values similar to the bermuda rise roberts et al 2010 taken as a whole the nd isotope record from foraminiferal authigenic coatings suggests large scale changes in the proportion of northern and southern deep water sources occurred throughout the atlantic ocean with substantial chemical gradients at times during the last deglaciation

deep water exchanges between the south china sea and the pacific since the last glacial period deep ocean circulation is widely considered as one of the important factors for increasing co2 concentration and decreasing radiocarbon activity 14c of the atmosphere during the last deglaciation the ams 14c ages of benthic and planktonic foraminifers from 18 samples of core md05 2904 water depth of 2066 m in the northern south china sea scs and 15 samples of core md05 2896 water depth of 1657 m in the southern scs were analyzed in this study for reconstructing the intrabasin deep oceanic processes and hence exploring the deep water exchanges between the scs and the pacific since the last glacial period the results show that during the holocene the average apparent ventilation age of deep water was younger in the southern scs 1350 years than in the northern scs 1850 years due to relatively strong vertical mixing and advection consistent with modern observations however during the last glacial period and deglaciation the deep water was older in the southern scs 2050 years and 1800 to 1200 years respectively than in the northern scs 1600 years and 670 years respectively indicating reduced deep mixing and advection moreover the northern scs deep water was significantly younger during the last deglaciation than during the holocene and the last glacial period implying the existence of northern sourced newly formed and relatively young north pacific deep water our records do not support the intrusion of anomalously 14c depleted deep water to the middepth of the low latitude western pacific and the scs during the mystery interval 17 5 14 5 kyr b p

manganese carbonate overgrowths on foraminifera tests below the zone where manganese is remobilized as mn2 aq reductively cleaned foraminifera in deep sea sediments have much higher mnca than those in core tops and sediment traps mnca ranges from less than 20 10 6 in and above the mno2 maximum to as high as 700 10 6 in reducing panama basin sediments the most plausible explanation for this enrichment is that the tests are coated with mn carbonate overgrowths these coatings can account for a significant proportion of the mn in reduced deep sea sediments uptake of manganous ion by carbonate may explain the absence of mn nodules in areas of high carbonate accumulation extreme degrees of overgrowth can alter foram trace element values but this artifact can be avoided by avoiding foraminifera with high mn ca

power law scaling behavior of crustal density and gravity 1 the scale invariant nature of crustal heterogeneity has been established through direct measurements of rock properties and inferences from geophysical observations we examine the behavior of crustal density variations over length scales from centimeters to hundreds of kilometers using well logs surface rock samples and observed gravity data the three data types support a simple model of an isotropic scaling crust with density characterized by a power law spectral behavior

upper crustal seismic velocity heterogeneity as derived from a variety of p wave sonic logs sonic log measurements provide detailed 1 d information on the distribution of elastic properties within the upper crystalline crust at scales from about one metre to several kilometres 10 p wave sonic logs from six upper crustal drill sites in europe and north america have been analysed for their second order statistics the penetrated lithological sequences comprise archean volcanic sequences proterozoic mafic layered intrusions and precambrian to phanerozoic gneisses and granites despite this variability in geological setting tectonic history and petrological composition there are notable similarities between the various data sets after removing a large scale deterministic component from the observed velocity depth function the residual velocity fluctuations of all data sets can be described by autocovariance functions corresponding to band limited self affine stochastic processes with quasi gaussian probability density functions depending on the maximum spatial wavelength present in the stochastic part of the data the deterministic trend can be approximated either by a low order polynomial best fit or by a moving average of the original sonic log data the choice of the trend has a significant impact on the correlation length and on the standard deviation of the residual stochastic component but does not affect the hurst number for trends defined by low order polynomial best fits correlation lengths were found to range from 60 to 160 m whereas for trends defined by a moving average the correlation lengths are dominated by the upper cut off wavenumber of the corresponding filter regardless of the trend removed the autocovariance functions of all data sets are characterised by low hurst numbers of around 0 1 0 2 or equivalently by power spectra decaying as 1 k a possible explanation of this statistical uniformity is that sonic log fluctuations are more sensitive to the physical state in particular to the distribution of cracks than to the petrological composition of the probed rocks

on the cause of 1 f power spectral scaling in borehole sonic logs borehole logs provide in situ information about the scaling of fluctuations in the elastic properties of rock a surprising finding has been the widespread 1 f type 0 5 1 5 scaling of borehole sonic log power spectra yielding no clear correlation with geological age type or history raising questions about the reliability and origin of these findings ubiquitous fractures for example have been evoked as the most likely explanation of these results firstly we show that the smoothing effects of the logging tool must be taken into account in order to obtain reliable values of we then investigate the scaling properties of lithology only in perfectly exposed metamorphic rock by explicitly excluding fractures we find clear 1 f scaling for reconstructed velocity data based solely on lithological variations although fractures are certainly important in contributing to 1 f fluctuations in borehole logs intrinsic geology may also play a significant role

abrupt changes of intermediate water properties on the northeastern slope of the bering sea during the last glacial and deglacial period 1 millennial scale variability in the behavior of north pacific intermediate water during the last glacial and deglacial period and its association with dansgaard oeschger d o cycles and heinrich events are examined based on benthic foraminiferal oxygen and carbon isotopes 18obf and 13cbf and caco3 using a sediment core recovered from the northeastern slope of the bering sea a suite of positive 18obf excursions at intermediate depths of the bering sea which seem at least in part associated with increases in the 18obf gradients between the bering and okhotsk seas suggest the bering sea as a proximate source of intermediate water during several severe stadial episodes in the last glacial and deglacial period absence of such 18obf gradients during periods of high surface productivity in the bering and okhotsk seas which we correlate to d o interstadials suggests a reduction in intermediate water production in the bering sea and subsequent introduction of nutrient rich deep waters from the north pacific into intermediate depths of the bering sea we argue that a reorganization of atmospheric circulation in the high latitude north pacific during severe cold episodes in the last glacial and deglacial period created favorable conditions for brine rejection in the northeastern bering sea the resulting salinity increase in the cold surface waters could have initiated intermediate and deep water formation that spread out to the north pacific

climatic and tectonic controls on weathering in south china and indochina peninsula clay mineralogical and geochemical investigations from the pearl red and mekong drainage basins 1 results of clay mineralogy major element geochemistry and sr and nd isotopes in 93 argillaceous samples collected from drainage basins of the pearl red and mekong rivers reveal different degrees of chemical weathering in southeast asia despite similar climate conditions across these regions the kaolinite illite ratio illite chemistry index and illite crystallinity can be used as indicators of chemical weathering intensity these mineralogical proxies combined with the k2o na2o cao molar ratio chemical index of alteration cia and weathering trends observed from major element results indicate intensive silicate weathering in the pearl river basin moderate to intensive in the mekong river basin and moderate in the red river basin although a significant modification of epsilon nd 0 values in our riverine sediments during chemical weathering and transport is unlikely sr 87 sr 86 ratios are controlled by various states of chemical weathering of high sr minerals such as plagioclase rich in na and ca with a linear decrease trend from the pearl mekong to red river basins our results suggest that it is not the warm climate with heavy monsoon precipitation but tectonics playing the most significant role in controlling weathering and erosion processes in south china and indochina peninsula strong physical erosion caused by tectonic activities and river incision along the eastern margin of the tibetan plateau and along the red river fault system is responsible for high contents of primary minerals in the lowlands of red and mekong river basins

direct ventilation of the north pacific did not reach the deep ocean during the last deglaciation 1 despite its tremendous size the deep north pacific has received relatively little attention by paleoceanographers it was recently suggested that the deep north pacific was directly ventilated by dense waters formed in the subarctic pacific during heinrich stadial 1 hs1 of the early deglaciation here we present new redox sensitive trace metal data from a sediment core at 2393 m in the subarctic pacific in comparison with previously published data from elsewhere in the region the combined picture shows no sign of ventilation during the early deglaciation in any available core from water depths of 2393 m and deeper while the deepest core to display clear signs of enhanced ventilation during hs1 was raised from 1366 m water depth thus it appears likely that although the north pacific was well ventilated to intermediate depths during hs1 the deep ocean did not receive a significant input of dense waters from a local source but remained isolated from the surface waters above

southern ocean evidence for reduced export of north atlantic deep water during heinrich event 1 deep sea corals form unique high resolution archives of ocean circulation that can be dated using the decay of uranium to thorium they are abundant in the southern ocean and can provide unprecedented insights into ocean circulation and ocean chemistry on sub millennial time scales in areas where application of traditional paleoceanographic proxies is difficult here we present the first coupled neodymium nd isotope and radiocarbon data from deep sea corals in the drake passage southern ocean adding new constraints on ocean circulation during the last heinrich event h1 16 7 ka the modern day drake passage water column is homogeneous with respect to nd isotopes expressed in epsilon units nd its isotopic value of close to 9 is largely controlled by the mixture of north atlantic deep water and pacific deep water the aragonite of modern drake passage corals reflects this water column value whereas a fossil coral from h1 is significantly higher at 6 4 0 4 we interpret this 2 5 unit shift as a reduction in the influence of north atlantic sourced nd in the southern ocean during h1 this interpretation is supported by a series of radiocarbon analyses on the same sample and is consistent with a twofold or greater reduction in export of north atlantic waters from the atlantic basin combining analyses of radiocarbon and nd isotopes on u series dated deep sea coral skeletons holds great potential for quantification of past ocean ventilation rates

neodymium isotopic composition of intermediate and deep waters in the glacial southwest pacific abstract neodymium nd isotopes tracers of deep water mass source and mixing were measured on sedimentary planktic foraminifera with authigenic coatings from a depth transect of cores 1400 4800 m from chatham rise in the southwest pacific over the past 30 ka we observe deglacial variations in the nd isotopic composition which showed an average glacial composition of e nd 5 0 1 0 3 n 4 for cores sites below 3200 mbsl no significant deglacial variation was observed in the nd isotopic composition of intermediate depth waters 1400 mbsl in contrast with benthic foraminifera c 13 data the deglacial e nd shift of cdw in the southwest pacific is consistent with changes observed in the deep south atlantic and equatorial indian ocean but e nd values are offset by 1 e nd unit to more radiogenic values throughout the deglacial records likely due to admixture of a nd isotope signal which was modified in the southern ocean or pacific perhaps by boundary exchange however this modification did not overprint the deglacial nd isotope change the consistent deglacial evolution of e nd in the south atlantic equatorial indian and southwest pacific cdw is evidence for the connection of cdw during the glacial and propagation of diminished north atlantic deep water export to the glacial southern ocean in contrast spatial heterogeneities in the benthic foraminifera c 13 of cdw have been observed in the atlantic indian and pacific basins of the deep glacial southern ocean the nd isotope data implies a well connected deep southern ocean which transported waters from the atlantic to the indian and pacific oceans during the glacial this suggests that basin scale variability in the glacial c 13 composition of cdw was unrelated to circulation changes

scaling geology and seismic deconvolution the reflection seismic signal observed at the surface is the convolution of a wavelet with a reflection sequence representing the geology deconvolution of the observations without prior knowledge of the wavelet can be done by making assumptions about the statistics of the reflection sequence in particular the widely used prediction error filter is obtained by assuming that the power spectra of reflection sequences are white however evidence from well logs suggests that the power spectra are in fact proportional to a power of the frequency f that is to f with equal approximately to 1

power law random behaviour of seismic reflectivity in boreholes and its relationship to crustal deformation models abstract there is good evidence for the fractal nature of some fault systems both from field observations and the frequency magnitude distribution of earthquakes recently two models with fundamentally different dynamics have been employed to explain seismicity low order non linear slider block models have successfully explained activity on part of the san andreas fault system and in the nankai trough while high dimensional self organised critical cellular automaton models convincingly reproduce the gutenberg richter frequency magnitude relationship output variables from these two models fall respectively into two distinct data classes chaotic deterministic and random using a predictability algorithm which can distinguish between random and chaotic datasets we examine the distribution class of in situ fractures as inferred from borehole seismic reflectivity logs in three chalk layers off the south coast of ireland we find that fractures are distributed in a non deterministic manner consistent with self organised critical dynamics therefore we may infer that deterministic seismicity should not occur on structures over the scale range covered by the logs at least in the end member case where the frequency magnitude distribution of earthquakes is controlled by the fractal distribution of faults

a review of shear wave splitting in the crack critical crust summary over the last 15 years it has become established that crack induced stress aligned shear wave splitting with azimuthal anisotropy is an inherent characteristic of almost all rocks in the crust this means that most in situ rocks are pervaded by fluid saturated microcracks and consequently are highly compliant the evolution of such stress aligned fluid saturated grain boundary cracks and pore throats in response to changing conditions can be calculated in some cases with great accuracy using anisotropic poro elasticity ape ape is tightly constrained with no free parameters yet dynamic modelling with ape currently matches a wide range of phenomena concerning anisotropy stress shear waves and cracks in particular ape has allowed the anisotropic response of a reservoir to injection to be calculated predicted with hindsight and the time and magnitude of an earthquake to be correctly stress forecast the reason for this calculability and predictability is that the microcracks in the crust are so closely spaced that they form critical systems this crack critical crust leads to a new style of geophysics that has profound implications for almost all aspects of pre fracturing deformation of the crust and for solid earth geophysics and geology we review past present and speculate about the future of shear wave splitting in the crack critical crust shear wave splitting is seen to be a dynamic measure of the deformation of the rock mass there is some good news and some bad news for conventional geophysics many accepted phenomena are no longer valid at high spatial and temporal resolution a major effect is that the detailed crack geometry changes with time and varies from place to place in response to very small previously negligible changes however at least in some circumstances the behaviour of the rock in the highly complex inhomogeneous earth may be calculated and the response predicted opening the way to possible control by feedback the need is to devise ways to exploit these new opportunities in the crack critical crust recent observations from the smsites project at husavik in northern iceland gathered while this review was being written display the extraordinarily sensitivity of in situ rock to small changes at great distances the effects are far too large to occur in a conventional elastic brittle crust and their presence confirms the highly compliant nature of the crack critical crust

thermohaline circulation in the deep south china sea basin inferred from oxygen distributions 1 on the basis of the historical oxygen data available distributions of dissolved oxygen were analyzed in detail to investigate the thermohaline circulation in the south china sea scs the analyses confirmed the existence of a layer of minimal oxygen content at intermediate depths of the basin which shows a low oxygen 1 6 ml l 1 core in the southern basin with water ages shorter than 100 years after entering the scs and which appears isolated from its counterpart of the western philippine sea north to the core along the northern slope there is a band of oxygen rich water in both upper and intermediate layers above 700 m the band can be attributed to the intrusion of high oxygen water through the luzon strait while vertical flux appears to be responsible between 700 and 1500 m the oxygen distribution provides additional evidence for a sandwiched vertical structure in transports through the luzon strait with outflows in the intermediate layer and inflows above and below while the abyssal water of the scs is being replenished by the deep inflows an abrupt change of water properties was observed in both upper and intermediate layers across the luzon strait suggesting possible domination of local vertical mixing over horizontal spreading of inflows in the northern scs a four cell conceptual model was proposed for the thermohaline circulation which consists of a three layer cross basin exchange cell in the luzon strait an active ventilation cell in the upper and intermediate layers along the northern slope an abyssal replenishment cell in the deep and a cyclonic recirculation cell in the interior basin