diurnal shear instability the descent of the surface shear layer and the deep cycle of equatorial turbulence a new theory of shear instability in a turbulent environment is applied to eight days of velocity and density profiles from the upper equatorial pacific this period featured a regular diurnal cycle of surface forcing together with a clear response in upper ocean mixing during the day a layer of stable stratification and shear forms at the surface during late afternoon and evening this stratified shear layer descends leaving the nocturnal mixing layer above it using high resolution current measurements the detailed structure of the descending shear layer is seen for the first time linear stability analysis is conducted using a new method that accountsfortheeffectsofpreexistingturbulenceoninstabilitygrowth shearinstabilityfollowsadiurnalcycle linked to the afternoon descent of the surface shear layer this cycle is revealed only when the effect of turbulence is accounted for in the stability analysis the cycle of instability leads the diurnal mixing cycle typically by 2 3h consistent with the time needed for instabilities to grow and break late at night the resulting turbulence suppresses further instabilities lending an asymmetry to the mixing cycle that has not been noticed in previous measurements deep cycle mixing is triggered by instabilities formed as the descending shear layer merges with the marginally unstable shear of the equatorial undercurrent in the morning turbulence decays and the upper ocean restratifies wind accelerates the near surface flow to form a new unstable shear layer and the cycle begins again

crustal evolution of the ktb drill site from oldest relics to the late hercynian granites the crustal unit penetrated during the german continental deep drilling program ktb the zone of erbendorf vohenstrauss zev comprises an association of metabasites and paragneisses and orthogneisses that underwent high and medium pressure metamorphic cycles during the early palaeozoic in this summary of the structural petrological geochemical and geochronological information from borehole and surface rocks we show that geological models proposed prior to drilling have had to be significantly modified features of the zev such as the dominant nw se trending structures devonian 370 ma medium pressure amphibolite facies metamorphism 0 6 0 8 gpa 720 c and earlier eclogite stage are directly comparable with those of the nearby bohemicum unit in western bohemia intervening units in contrast exhibit ne sw trending structures and carboniferous 315 325 ma low pressure metamorphism all units are cut by predominantly posttectonic granites mostly 320 ma earlier models to explain this contrast by means of a nappe emplacement of the zev in the narrow time interval between the younger regional metamorphism and granite intrusion could not be substantiated because contrary to predictions the same rock association was present in the whole of the drilled 9 1 km and therefore no nappe boundary was drilled instead it is interpreted that shallow crustal levels reached by the zev subsequent to the devonian event shielded most of it from the effects of the carboniferous metamorphism a lack of expected thermal and baric gradients within the drilled metamorphic pile is a result of repeated stacking of an original 3 km depth section in mesozoic times an important result of the geological investigations of the ktb project is the recognition that the present day geometry of the zev is a result of cold shallow level thin skinned tectonics that in the absence of the view into the third dimension offered by the drill hole could not have been accurately predicted from the fossil high grade assemblages and structures seen at the surface

evidence for rapid fault healing derived from temporal changes in s wave splitting 1 tadokoro et al 1999 had made an s wave splitting analysis on the nojima fault zone that ruptured during the 1995 hyogo ken nanbu earthquake for a period 9 12 months after the mainshock the direction of faster shear wave polarization had been parallel to the fault strike suggesting fractures of shear fault origin in this study we made an additional s wave splitting analysis for a period 33 45 months after the mainshock and detected the rotation of that is the direction was parallel to the regional maximum horizontal compressional stress which is oblique to the fault strike this temporal change suggests that all the fractures of shear fault origin had completely healed and cracks of tectonic stress origin recovered between the two periods this is strong evidence for rapid fault healing which completed within 33 months after the mainshock

instability of baroclinic tidal flow in a stratified fjord abstract the taylor goldstein equation is used to investigate the stability of a baroclinic tidal flow observed in a stratified fjord the flow is analyzed at hourly intervals when turbulent dissipation measurements were made the critical gradient richardson number is often close to the miles howard limit of 0 25 but sometimes it is substantially less although during 8 of the 24 periods examined the flow is marginally stable it is either very stable or very unstable in others for the unstable flow the e folding period of the fastest growing disturbances is 83 455 s about 46 of the buoyancy period at the levels where the fastest growing disturbances have their maximum amplitude these disturbances to the flows have wavelengths about 20 72 of the water depth and have mostly a second mode structure simultaneous measurements of the flow and turbulence allow for testing of the hypothesis that the growth rates of the most unstable disturbances are related to the turbulent dissipation rates dissipati

grain boundary graphite in rocks and implications for high electrical conductivity in the lower crust the origin of zones of high electrical conductivity in the lower continental crust is a long standing mystery possible explanations include the presence of brines1 2 partial melt3 serpentine4 and graphite5 when discussing the occurrence of graphite in the crust many petrologists have considered phase relations as they would have existed at the peak of metamorphism or during igneous emplacement6 10 here we show that a fine film of graphite is present on the grain boundaries in three rocks from the laramie anorthosite complex in two of these rocks graphite was stable during igneous crystallization but in the other it was not we maintain that in all of the rocks the grain boundary graphite precipitated from a co2 rich fluid during cooling the chemical processes that produced the grain boundary graphite in these rocks are likely to operate in many lower crustal rocks we therefore contend that because the films we observe are capable of producing the high conductivity that is seen in the lower crust grain boundary graphite should be considered as a possible cause for some conductivity anomalies

magnetic and electric fields associated with changes in high pore pressure in fault zones application to the loma prieta ulf emissions we determined the electric and magnetic fields generated during failure of faults containing sealed compartments with pore pressures ranging from hydrostatic to lithostatic levels exhumed fault studies and strain measurement data limit the possible size of these compartments to less than 1 km in extent rupture of seals between compartments produces rapid pore pressure changes and fluid flow and may create fractures that propagate away from the high pressure compartment along the fault face nonuniform fluid flow results from pressure decrease in the fracture from crack generated dilatancy partial blockage by silica deposition and clearing as pressure increases a direct consequence of this unsteady fluid flow may be associated transient magnetic signals caused by electrokinetic piezomagnetic and magnetohydrodynamic effects models of these processes for fault geometries with 1 km high pressure compartments show that electrokinetic effects are several orders of magnitude larger than the other mechanisms the electrokinetic signals produced by this unsteady flow are comparable in magnitude and frequency to the magnetic signals observed prior to the ml 7 1 loma prieta earthquake of october 18 1989 provided fracture lengths are less than 200 m

the 2004 parkfield earthquake test of the electromagnetic precursor hypothesis 1 a controversy has existed for 30 years concerning the possibility of earthquake prediction using electromagnetic precursors long term electromagnetic monitoring prior to during and after the m6 0 earthquake at parkfield california on 28 september 2004 now provides a definitive test of this hypothesis during the earthquake our instruments recorded clearly documented electrical signals from an earthquake impulsive changes of up to 2 5 mv at an electrode located 250 m from the rupture zone followed by a transient decay lasting at least 3 1 4 hours similar signals 1 5 mv were recorded with the only two m 5 aftershocks but their transient decays lasted for only 17 min these signals are unambiguously a result of the earthquake and can be useful in studies of fluid flow in faults a major current topic in earthquake physics patterns in the distribution of transient voltages differ from static stress changes but are consistent with a small coseismic pressure drop on the fault and fluid flow inward signals at a distance of 1 km from the fault are less than 1 mv and are statistically no different from zero in our analysis transient voltages for the aftershocks have opposite polarity from those recorded with the main shock and are again maximal close to the fault suggesting subsequent outward flow from the fault finally there is no evidence of any precursory signal strongly calling into question previously suggested signals preceding smaller or more distant earthquakes

fracture surface energy of the punchbowl fault san andreas system the energetics of earthquake rupture slip weakening and rupture surface formation are poorly understood by measuring the energy associated with fracture damage along the punchbowl fault in the devil s punchbowl los angeles county park part of the san andreas system chester et al show that the fracture surface energy for rupture along a mature fault of this type accounts for only a small fraction of the energy released during large earthquakes as determined by seismologists this suggests that mechanisms such as melt lubrication and thermal pressurization are responsible for slip weakening fracture energy is a form of latent heat required to create an earthquake rupture surface and is related to parameters governing rupture propagation and processes of slip weakening1 2 3 fracture energy has been estimated from seismological and experimental rock deformation data4 5 6 7 8 yet its magnitude mechanisms of rupture surface formation and processes leading to slip weakening are not well defined8 9 10 here we quantify structural observations of the punchbowl fault a large displacement exhumed fault11 12 in the san andreas fault system and show that the energy required to create the fracture surface area in the fault is about 300 times greater than seismological estimates would predict for a single large earthquake if fracture energy is attributed entirely to the production of fracture surfaces then all of the fracture surface area in the punchbowl fault could have been produced by earthquake displacements totalling 1 km but this would only account for a small fraction of the total energy budget and therefore additional processes probably contributed to slip weakening during earthquake rupture

electrical conductivity and carbon in metamorphic rocks of the yukon tanana terrane alaska electrical conductivity of a water saturated quartz mica garnet schist collected from a surface outcrop near the denali fault zone in the yukon tanana terrane of east central alaska increases slightly with pressure to about 200 mpa this behavior is unlike that exhibited by other yukon tanana samples or by most rocks from other locations detailed petrographic examination of the sample revealed the presence of a stringer of carbonaceous material generally less than 10 m thick enclosed in and intergrown with one of the muscovite layers and extending for about 2 cm along the foliation the stringer is probably responsible for the anomalous conductivity change with pressure making the sample the first for which anomalous electrical conductivity behavior can be attributed to carbon associated with a specific feature the carbonaceous stringer together with its host muscovite layer are deformed and broken around a rotated garnet porphyroclast the deformation was accommodated by plastic deformation of quartz and therefore occurred in the ductile regime under conditions at least equivalent to greenschist facies metamorphism we interpret the textural relations to indicate that the carbonaceous material was formed by fluid deposition in a fracture formed within the muscovite layer possibly during the main phase of metamorphism and deformation and that the mica and carbon stringer were then deformed by the noncoaxial deformation responsible for rotation of the garnet porphyroclasts together the facts that the deformation resulting in garnet rotation was ductile and that the garnet rotation disrupted the stringer demonstrate that the carbonaceous stringer was present at depth i e 10 km brittle deformation on the microscopic scale is observed to have broken the connectivity of the carbon stringer explaining in part why the rock does not exhibit anomalously high conductivity at 0 1 mpa 1 atm pressure the brittle deformation is interpreted to have been caused by unloading due to uplift the observations indicate that carbonaceous material may exert a primary control on crustal electrical conductivity because it may be present as interconnected arrays in grain boundaries or microfractures or in megascopic throughgoing fractures

instability and hydraulics of turbulent stratified shear flows nerc ne f002432 national natural science foundation of china 41006017 41076001 fundamental research funds for the central universities 2010121031 bangor university us national science foundation 1030772

the turbulent transition of a supercritical downslope flow sensitivity to downstream conditions blocked continuously stratified crest controlled flows have hydraulically supercritical downslope flow in the lee of a ridge like obstacle the downslope flow separates from the obstacle and depending on conditions further downstream transitions to a subcritical state a controlled stratified overflow and its transition to a subcritical state are investigated here in a set of three dimensional numerical experiments in which the height of a second downstream ridge is varied the downslope flow is associated with an isopycnal and streamline bifurcation which acts to form a nearly uniform density isolating layer and a sharp pycnocline that separates deeper blocked and stratified fluid between the ridges from the flow above the height of the downstream obstacle is communicated upstream via gravity waves that propagate along the density interface and set the separation depth of the downslope flow the penetration depth of the downslope flow its susceptibility to shear instabilities and the amount of energy dissipated in the turbulent outflow all increase as the height of a downstream ridge which effectively sets the downstream boundary conditions is reduced

open ocean regimes of relative dispersion as two fluid particles separate in time the entire spectrum of eddy motions is being sampled from the smallest to the largest scales in large scale geophysical systems for which the earth rotation is important it has been conjectured that the relative diffusivity should vary respectively as d2 and d4 3 for distances respectively smaller and larger than a well defined forcing scale of the order of the internal rossby radius with d the r m s separation distance particle paths data from a mid latitude float experiment in the central part of the north atlantic appear to support these statements partly two particles initially separated by a few km within two distinct clusters west and east of the mid atlantic ridge statistically dispersed following a richardson regime d2 t3 asymptotically for r m s separation distances between 40 and 300 km in agreement with a d4 3 law at early times and for smaller separation distances an exponential growth in agreement with a d2 law was briefly observed but only for the eastern cluster with an e folding time around 6 days after a few months or separation distances greater than 300 km the relative dispersion slowed down naturally to the taylor absolute dispersion regime

carbon deposition during brittle rock deformation changes in electrical properties of fault zones and potential geoelectric phenomena during earthquakes 1 to investigate potential mechanisms for geoelectric phenomena accompanying earthquakes we have deformed hollow cylinders of sioux quartzite to failure in the presence of carbonaceous pore fluids and investigated the resulting changes in electrical conductivity and carbon distribution samples were loaded at room temperature or 400 c by a hydrostatic pressure at their outer diameter increasing pressure at a constant rate to 290 mpa pore fluids consisted of pure co co2 and ch4 and a 1 1 mixture of co2 and ch4 each with pore pressures of 2 0 to 4 1 mpa failure occurred by the formation of mode ii shear fractures transecting the hollow cylinder walls radial resistivities of the cylinders fell to 2 9 to 3 1 m m for co tests and 15 2 to 16 5 m m for co2 ch4 tests compared with 23 m m for dry undeformed cylinders carbonaceous fluids had no discernable influence on rock strength on the basis of mapping using electron microprobe techniques carbon occurs preferentially as quasi continuous films on newly formed fracture surfaces but these films are absent from preexisting surfaces in those same experiments the observations support the hypothesis that electrical conductivity of rocks is enhanced by the deposition of carbon on fracture surfaces and imply that electrical properties may change in direct response to brittle deformation they also suggest that the carbon films formed nearly instantaneously as the cracks formed carbon film deposition may accompany the development of microfracture arrays prior to and during fault rupture and thus may be capable of explaining precursory and coseismic geoelectric phenomena

lateral dispersion over the continental shelf analysis of dye release experiments lateral dispersion over the continental shelf was examined using dye studies performed as a part of the coastal mixing and optics experiment four experiments performed at intermediate depths each lasting 2 5 5 days were examined in some cases the dye patches remained fairly homogeneous both vertically and horizontally throughout an experiment in other cases significant patchiness was observed on scales ranging from 2 to 10 m vertically and a few hundred meters to a few kilometers horizontally the observations showed that the dye distributions were significantly influenced by shearing and straining on scales of 5 10 m in the vertical and 1 10 km in the horizontal superimposed on these larger scale distortions were simultaneous increases in the horizontal second moments of the dye patches with corresponding horizontal diffusivities based on a fickian diffusion model of 0 3 4 9 m 2 s 1 analysis of the dye data in concert with shear estimates from shipboard acoustic doppler current profiler observations showed that the existing paradigms of shear dispersion and dispersion by interleaving water masses cannot account for the observed diffusive spreading of the dye patches this result suggests that some other mechanisms provided an additional diffusivity of order 0 2 4 6 m 2 s 1 an alternative mechanism dispersion by vortical motions caused by the relaxation of diapycnal mixing events may explain the observed dispersion in some cases

significant resistivity changes in the fault zone associated with the 1999 chi chi earthquake west central taiwan abstract the purpose of this paper is to demonstrate the possible influence of an earthquake on the resistivity distribution in a fault zone we collected resistivity image profiles across a proposed fault trace prior to the 7 3 magnitude 1999 shallow earthquake in the chi chi area of taiwan significant positive resistivity anomalies were observed in the hanging wall after the earthquake however there were negligible resistivity changes in the footwall from an examination of geoelectric phenomena and surface rupture in the fault zone it is believed that geoelectric anomalies are associated with abrupt displacement along the active chelungpu fault this result indicates a potential for resistivity methods to provide a basis for the monitoring of an active fault

karstification below dam sites a model of increasing leakage from reservoirs unnaturally steep hydraulic gradients below foundations or across abutments of dams may cause solutional widening of fractures in karstifiable rocks of carbonates or gypsum this could cause increasing leakage which may endanger the performance of the construction to investigate this problem recent models on natural karstification have been applied we have performed numerical simulations of leakage below a model dam with a grouting curtain reaching down to 100 m below its impermeable foundation of 100 m width water is impounded to a depth of 100 m the dam is located on a terrane of fractured rock dissected by two perpendicular sets of fractures with spacing of 5 m and with a log normal distribution of their initial aperture widths of about 0 02 cm in the first state of karstification these fractures widen slowly until a pathway of widened fractures below the grouting has reached the downstream side with exit widths of about 1 mm this causes a dramatic increase of leakage and turbulent flow sets in after this breakthrough at time t in the second state of karstification dissolution rates become even along these fractures and cause widening of about 0 1 cm year 1 for limestone and at least of 1 cm year 1 for gypsum this leads to an increase in leakage to excessive rates within 25 years for limestone but only 5 years for gypsum we have performed a sensitivity analysis of breakthrough time t for the various parameters which determine the problem the result shows breakthrough times in the order of several tens of years for both limestone and gypsum we have also modelled leakage to caves or karst channels 200 m below the bottom of the reservoir which could induce the formation of sinkholes the model can be extended to more realistic settings in conclusion our results support the prediction that increasing leakage at dam sites can be caused by recent karstification which is activated after filling the reservoir possibly leading to serious problems within its lifetime

carbon enhanced electrical conductivity during fracture of rocks changes in electrical resistance during rock fracture in the presence of a carbonaceous atmosphere have been investigated using nugget sandstone and westerly granite the experiments were performed in an internally heated gas pressure vessel with a load train that produced strain rates between 10 6 and 10 5 s 1 samples were deformed at temperatures of 354 to 502 c and pressures of 100 to 170 mpa in atmospheres of ar or mixtures of 95 co2 with 5 co or 5 ch4 compositions that are well within the field of graphite stability at the run conditions in experiments using nugget sandstone resistance reached a minimum value when the maximum temperature was achieved and good electrode contact was made the resistance then increased as the experiment continued probably due to dry out of the sample a change in the oxidation state of the fe oxide associated with the cement or destruction of current bearing pathways at approximately 200 mpa end load the rock sample failed plots of load and resistance versus time show several interesting features in one experiment for example as the end load reached about 175 mpa resistance stopped increasing and remained fairly constant for a period of approximately 0 5 hour during loading the end load displayed small decreases that were simultaneous with small decreases in resistance when the end load and the displacement indicated rock failure resistance decreased dramatically from 150 m to 100 m in a single experiment the westerly granite also showed a decrease in resistance during dilatancy the nature and distribution of carbon in the run products were studied by electron microprobe and time of flight secondary ion mass spectroscopy top sims carbon observed by mapping with the former is clearly observed on micro cracks that based on the microtexture are interpreted to have formed during the deformation the tof sims data confirm the electron probe observations that carbon is present on fracture surfaces these observations and experimental results lead to the hypothesis that as microfractures open in the time leading up to failure along a fracture carbon is deposited as a continuous film on the new reactive mineral surfaces and this produces a decrease in resistance subsequent changes in resistance occur as connectivity of the initial fracture network is altered by continued deformation such a process may explain some electromagnetic effects associated with earthquakes

sequential tracer tests for determining water seepage paths in a large rockfill dam nakdong river basin korea the rockfill dam of this study has a clay core filter zone and sandy gravel shell and it is located in the nakdong river basin in korea filling the reservoir began in august 1994 and it was full by april 1998 when the reservoir level was approximately 150 m three settlement holes were found in the dam crest to determine possible seepage paths and potential damaged areas within the rockfill dam 15 tracer tests were performed during two periods during the two test periods six and nine tracer tests were conducted when the average water levels of the reservoir were 145 m and 142 m respectively rhodamine wt rwt and bromide ion were used as tracers for each test 1800 to 4000 l of tracer solution were injected into the riprap for about 5 h the 15 injection points were uniformly distributed from the right to left sides of the embankment and the two tracers were injected alternately tracer concentrations were monitored at 26 observation wells which were divided into four groups by their geographical positions right side of the crest left side of the crest right side of the dam toe and left side of the dam toe for each tracer test more than 30 water samples were taken during a period of 96 h at each observation well based the breakthrough curves obtained from the sequential tracer tests it was inferred that the most probable seepage paths and potential damaged area were in the left side of the crest tongue wing zone and to a lesser extent in the right side of the dam abutment

hydrogeochemistry of sodium bicarbonate type bedrock groundwater in the pocheon spa area south korea water rock interaction and hydrologic mixing the pocheon spa land area south korea occurs in a topographically steep fault bounded basin and is characterized by a hydraulic upwelling flow zone of thermal water up to 44 c in its central part hydrogeochemical and environmental isotope data for groundwater in the study area suggested the occurrence of two distinct water types a ca hco3 type and a na hco3 type the former water type is characterized by relatively high concentrations of ca so4 and no3 which show significant temporal variation indicating a strong influence by surface processes in contrast the na hco3 type waters have high and temporally constant temperature ph tds na cl hco3 and f indicating the attainment of a chemical steady state with respect to the host rocks granite and gneiss oxygen hydrogen and tritium isotope data also indicate the differences in hydrologic conditions between the two groups the relatively lower 18o d and tritium values for na hco3 type waters suggest that they recharged at higher elevations and have comparatively long mean residence times considering the geologic and hydrogeologic conditions of the study area na hco3 type waters possibly have evolved from ca hco3 type waters mass balance modeling revealed that the chemistry of na hco3 type water was regulated by dissolution of silicates and carbonates and concurrent ion exchange particularly low ca concentrations in na hco3 water was mainly caused by cation exchange multivariate mixing and mass balance modeling m3 modeling was performed to evaluate the hydrologic mixing and mass transfer between discrete water masses occurring in the shallow peripheral part of the central spa land area where hydraulic upwelling occurs based on q mode factor analysis and mixing modeling using phreeqc an ideal mixing among three major water masses surface water shallow groundwater of ca hco3 type deep groundwater of na hco3 type was proposed m3 modeling suggests that all the groundwaters in the spa area can be described as mixtures of these end members after mixing the net mole transfer by geochemical reaction was less than that without mixing therefore it is likely that in the hydraulic mixing zone geochemical reactions are of minor importance and therefore that mixing regulates the groundwater geochemistry

electrical properties of granite with implications for the lower crust the electrical properties of granite appear to be dominantly controlled by the amount of free water in the granite and by temperature minor contributions to the electrical properties are provided by hydrostatic and lithostatic pressure structurally bound water oxygen fugacity and other parameters the effect of sulfur fugacity may be important but is experimentally unconfirmed in addition to changing the magnitude of electrical properties the amount and chemistry of water in granite significantly changes the temperature dependence of the electrical properties with increasing temperature changes in water content retain large but lessened effects on electrical properties near room temperature a monolayer of water will decrease the electrical resistivity by an order of magnitude several weight percent water may decrease the electrical resistivity by as much as 9 orders of magnitude and decrease the thermal activation energy by a factor of 5 at elevated temperatures just below granitic melting a few weight percent water may still decrease the resistivity by as much as 3 orders of magnitude and the activation energy by a factor of 2 above the melting temperature 650 to 1100 c depending upon water pressure a few weight percent water will decrease the resistivity by less than an order of magnitude and will barely change the activation energy remarkably the few weight percent water must be present as free water experiments with hydrated hornblende schist with structural water indicate an electrical resistivity very similar to that for dry granite the implications of these results together with the findings of deep magnetic sounding and magnetotelluric surveys suggest much more free water than is commonly associated with the lower crust and possibly into the upper mantle

electrical resistivity changes not observed with the 28 september 2004 m6 0 parkfield earthquake on the san andreas fault california 1 an 18 a long experiment to capture changes in electrical resistivity prior to during and after a m6 earthquake on the san andreas fault at parkfield california culminated with an event of that magnitude on 28 september 2004 resistivity was monitored with a telluric array giving precisions in measured parameters of 0 2 or less no coseismic resistivity changes greater than 5 could have occurred or they would have been detected by the array and any precursory changes would have been much smaller because maximum possible precursory strains were 4000 times smaller than the coseismic strain given that the earthquake ruptured directly beneath the telluric array this experiment places a bound on the amount resistivity might change at the hypocentral location changes measured with instruments farther from earthquakes can only be smaller it is still possible that a measurable change with a larger earthquake or other fault geometries are capable of generating larger signals but our results show clearly that future experiments should be designed with precisions of much better than 0 1 if they are to be successful

high electrical conductivity in a model lower crust with unconnected conductive seismically reflective layers summary in this paper we derive the electrical conductivity for a model lower crust containing unconnected highly conductive lamellae within a highly resistive matrix lateral overlap with small vertical separation of lamellae of the dimensions imaged by seismic reflection profiling a few hundred metres thick and a few kilometres across could increase lower crustal conductivity from the low values predicted by laboratory measurements on dry rocks to the high values observed in field experiments the model does not depend on the cause of high conductivity within the lamellae however lamellation of the lower crust may provide a way of lithologically trapping saline water in permeable conductive lamellae within an impermeable non conductive matrix and so resolve the apparent contradiction between the low crustal permeabilities required for maintenance of high pore pressure over geological time periods and the high degree of pore interconnection required for the high observed conductivity the permeable lamellae and impermeable matrix would be of very different lithologies as implied by the high amplitudes of the lower crustal reflections for a typical example the model gives resistivities that compare favourably with the modified archie s law the model can also give anisotropic resistivity effects which are quantitatively compatible with results from field experiments

nature and origin of carbon in the archaean witwatersrand basin south africa the nature and origin of the carbonaceous matter carbon in the gold bearing reefs of the archaean witwatersrand basin of south africa has long been a subject of controversy and debate the importance of the carbon results from its direct association with the gold grade the studies reported here were directed at resolving the nature and origin of carbon techniques used include stope scale macroscopic mapping mesoscopic hand specimen examination and microscopic studies incorporating the use of optical reflectance measurement macroscopic mapping has demonstrated the braided habit of carbon bodies over tens of square metres with a close parallel to sedimentology mesoscopic observations however show the vein like carbon seams are often cross cutting sedimentary features with the carbon occupying an anastomosing set of bed parallel fractures microscopic observations show a globular form for the carbon and inclusions of uraninite particles in seam carbon the globules are generally modified into elongated spindles oriented perpendicular to bedding optical properties are dominated by generally high reflectance and anisotropy with a swirling liquid crystal structure classifying seam carbon as carbonaceous mesophase it is this fine mesophase texture that has previously been wrongly attributed to plant algal morphology highly significantly the optical anisotropy is bed perpendicular rather than bed parallel as in normal sedimentary burial indicating mesophase formation during fracture opening both reflectance and bireflectance of the seam mesophase show a range of values at all scales no stratigraphic or depth trends were apparent though geographic variation points to localization of the maximum temperature event s given high anisotropies maximum reflectance values in the 4 8 r o range and minima in the 1 2 r o range give arithmetic mean reflectance values of about 4 0 r o kinetic modelling equates these values with short term 50 000 years temperature events of c 400 c or burial temperatures of c 280 c lower reflectance values of c 2 0 r o obtained from the shales suggests thermal detachment of permeable and impermeable beds a characteristic of pulsed hydrothermal flux the included uraninite grains influence the orientation of the surrounding anisotropic mesophase demonstrating that uraninite predated the mesophase formation event regional palaeo stress frozen into the mesophase anisotropy indicates a nw se deviatoric stress the combination of hydrocarbon radiation and hydrothermal fluid flow marks witwatersrand basin pyrobitumens out as being different from conventional oil putative source rocks for the oil are identified in the intra basinal witwatersrand shale units lithological control in carbon seams is explained by the poro perm and mechanical properties of the unconformity sequence of footwall reef conglomerates and hanging wall quartzites favouring fracture along the unconformity surfaces an overpressured oxidizing fluid created the fracture network that hosted the oil and also introduced uranium as uranyl ion on meeting a reducing agent oil uraninite precipitated stabilizing the oil by polymerization further hotter hydrothermal flux then coked the bitumen to often fibrous spindle shaped mesophase continued flow deposited gold in the available pore spaces most notably those formed by lateral contraction between mesophase spindles the speculative role of methane in the reductive precipitation of gold is indicated by the presence of gold in any co eval porosity largely independent of the mineral matrix

mechanisms of fracture propagation in experimentally extended sioux quartzite abstract notched samples of sioux quartzite have been extended to failure at temperatures t between 25 and 710 c strain rates e from 5 2 10 6 to 6 7 10 4 s 1 and 100 mpa confining pressure and fracture morphologies examined by optical and scanning electron microscopy in all the extension tests performed sample failure occurred by the formation of a tensile fracture in or near the notch mid plane differential stress magnitudes at failure are insensitive to variations in t and e and calculated tensile strengths are comparable to previously reported values for unconfined tests at room temperature force displacement records show a change in mechanical response from linear elastic behavior at temperatures between 25 and 412 c to significant yielding in compression prior to failure in the 500 to 710 c tests in all cases fractures consist almost entirely of intragranular cracks igc which exhibit characteristic surface features which can be used to infer local crack propagation directions in one test in which fracturing was initiated at an edge flaw igc propagation directions show no overall trend the observations indicate that the mechanism of fracture propagation involves nucleation growth and coalescence of igc which are themselves propagating in all directions in the plane of the main fracture the onset of inelastic yielding prior to failure at elevated temperatures is attributed to the formation of thermally induced gbc which act as nucleation sites for igc during extension

geoelectric signals in china and the earthquake generation process we present original apparent resistivity records for stations located in the chinese provinces of hebei and sichuan along with seismicity patterns fault maps and limited hydrologic data these records are part of a 30 year database of geoelectric signals that have been recorded in china by a nationwide network of more than 100 stations set up by the state seismological bureau of the people s republic of china the database includes the time period during which the m 7 8 1976 tangshan and m 7 2 1976 songpan earthquakes occurred resistivity data recorded in and around the epicentral region of the tangshan event show coherent changes both temporal and in areal distribution years and months before and after the earthquakes a regional change in water table occurred more than 3 years prior to the tangshan earthquake the resistivity and water table signals appear to correlate in the 2 to 3 year period prior to the earthquake rainfall records from the region around tangshan extending to the cities of beijing and tianjin do not appear to account for the resistivity changes regional seismicity and active fault patterns in north china indicate that deformation occurs mainly along the borders of large tectonic blocks the source region for the geoelectric signals appears to lie within a large shear zone at the edge of a tectonic block undergoing rotation the tangshan epicentral area is thus only part of a larger zone of deformation we suggest that dilational strain associated with the opening of fractures may lower resistivity and water table for shallow crustal depths such as those monitored by the chinese geoelectric network dilation and resistivity changes are expected to begin at stress levels well below the peak values of the seismic cycle our study suggests that in some cases the areal extent of geoelectric signals may be significantly larger than that of the eventual earthquake source dimension the chinese geoelectric database offers an opportunity to improve our understanding of possible geoelectric precursors to earthquakes

laboratory study of fault healing and lithification in simulated fault gouge under hydrothermal conditions abstract seismic data geologic observations and laboratory friction studies suggest that faults lithify and strengthen heal during the interseismic period of the earthquake cycle we report on experiments to investigate the influence of healing duration and temperature on the strength and healing rate of simulated faults layers of m sized quartz powder were used to simulate granular fault gouge gouge layers were sheared within sioux quartzite in a triaxial pressure vessel at elevated pressures p c 250 mpa elevated temperatures 230 636 c and in the presence of water p h 2 o 75 mpa we performed hold slide experiments in which samples were subjected to a period of healing under hydrostatic load followed by shear deformation healing times ranged from a few hundred s to 10 5 s to isolate the effects of lithification and temperature on friction we ran two types of hold slide experiments 1 samples were subjected to healing and shear deformation at elevated temperature and 2 following healing at elevated temperature temperature was reduced prior to shear we also ran slide hold slide experiments in which samples were healed under shear load at elevated temperature 636 c experiments in which deformation was carried out at a lower temperature than healing show that both the static and sliding coefficient of friction increase with heal time samples healed and deformed at higher temperature showed lower peak strengths and within the scatter of our data did not exhibit time dependent strengthening these data are interpreted to result from enhanced lithification rates at elevated temperature samples healed under shear load exhibited a log linear decrease in friction with hold time modeling using rate and state dependent friction laws indicates velocity strengthening behavior with friction a b values of 0 05 to 0 08 our data indicate that at high temperature the effective state evolution term b is negative moreover the data indicate the rate of frictional strengthening varies significantly for hydrostatic and non hydrostatic load conditions our measurements of healing are consistent with seismic estimates of fault healing rates if stress drop is a fraction of the total shear stress and effective fault normal stress is 60 to 100 mpa

experimental diagenesis exploratory results we conducted experiments in which a granular mixture of quartz and labradorite was deformed in compression at elevated temperatures 200 350 c and pressures 100 mpa in the presence of deionized water following initial consolidation of the material by application of the loads at room temperature a second hydrothermal phase of consolidation was observed when the temperature was increased with the loads fixed the strain rate during this hydrothermal consolidation decayed approximately exponentially with time and was accompanied by only minor porosity reduction the sample permeability decreased rapidly during the hydrothermal consolidation and continued to decrease following cessation of the deformation the rate of this self sealing process was a complex function of temperature scanning electron microscopy and microprobe analysis of the indurated post experimental material showed albitization of the feldspar especially in highly deformed regions analysis of post experimental fluids show that si in solution increased with increasing flow and temperature fluid rock equilibrium was not achieved within the short durations of the experiments 50 60 hours our interpretation is that deformation occured by grain boundary sliding aided by solution and reaction at high stress contacts and sealing occurred by precipitation in low stress regions in the throats of pores

rate laws for water assisted compaction and stress induced water rock interaction in sandstones mineral water interactions under conditions of nonhydrostatic stress play a role in subjects as diverse as ductile creep in fault zones phase relations in metamorphic rocks mass redistribution and replacement reactions during diagenesis and loss of porosity in deep sedimentary basins as a step toward understanding the fundamental geochemical processes involved using naturally rounded st peter sand we have investigated the kinetics of pore volume loss and quartz water reactions under nonhydrostatic hydrothermal conditions in flow through reactors rate laws for creep and mineral water reaction are derived from the time rate of change of pore volume sand water dissolution kinetics and flow rate independent steady state silica concentrations and reveal functional dependencies of rates on grain size volume strain temperature effective pressure confining minus pore pressure and specific surface areas together the mechanical and chemical rate laws form a self consistent model for coupled deformation and water rock interaction of porous sands under nonhydrostatic conditions microstructural evidence shows a progressive widening of nominally circular and nominally flat grain grain contacts with increasing strain or equivalently porosity loss and small quartz overgrowths occurring at grain contact peripheries the mechanical and chemical data suggest that the dominant creep mechanism is due to removal of mass from grain contacts termed pressure solution or solution transfer with a lesser component of time dependent crack growth and healing the magnitude of a stress dependent concentration increase is too large to be accounted for by elastic or dislocation strain energy induced supersaturations favoring instead the normal stress dependence of molar gibbs free energy associated with grain grain interfaces

effects of temperature and sliding rate on frictional strength of granite layers of artificial granite gouge have been deformed on saw cut granite surfaces inclined 30 to the sample axes samples were deformed at a constant confining pressure of 250 mpa and temperatures of 22 to 845 c the velocity dependence of the steady state coefficient of friction ss was determined by comparing sliding strengths at different sliding rates the results of these measurements are consistent with those reported bysolberg andbyerlee 1984 at room temperature andstesky 1975 between 300 and 400 c stesky found that the slip rate dependence of ss increased above 400 c in the present study however the velocity dependence of ss was nearly independent of temperature

magnetotelluric evidence for layered mafic intrusions beneath the voring and exmouth rifted margins abstract marine magnetotelluric mt surveys at two volcanic passive margins have revealed an enigmatic layer of extremely high conductivity 0 1 m at 10 km depth at the voring plateau off the northwest shelf of norway 2d inversion of data from nine sites along a 54 km line resolves a layer with a conductance of 10 4 s at the exmouth plateau off the northwest shelf of australia 2d inversion of 122 sites in 17 lines finds a similar layer at similar depth but an order of magnitude higher conductance at both plateaus the depth of the high conductivity layer coincides roughly with what seismic studies have identified as an assemblage of sills we propose that the extremely high conductance is due to well connected conductive cumulates e g magnetite precipitated in layered mafic intrusions in contrast to sill emplacement the nature of layered intrusion formation requires connection to a magma source over time such a connection would not be likely during rifting when the rift provides a preferential pathway for pressure release this implies emplacement prior to or during a pause in the early stage of continental breakup

review of wave turbulence interactions in the stable atmospheric boundary layer flow in a stably stratified environment is characterized by anisotropic and intermittent turbulence and wavelike motions of varying amplitudes and periods understanding turbulence intermittency and wave turbulence interactions in a stably stratified flow remains a challenging issue in geosciences including planetary atmospheres and oceans the stable atmospheric boundary layer sabl commonly occurs when the ground surface is cooled by longwave radiation emission such as at night over land surfaces or even daytime over snow and ice surfaces and when warm air is advected over cold surfaces intermittent turbulence intensification in the sabl impacts human activities and weather variability yet it cannot be generated in state of the art numerical forecast models this failure is mainly due to a lack of understanding of the physical mechanisms for seemingly random turbulence generation in a stably stratified flow in which wave turbulence interaction is a potential mechanism for turbulence intermittency a workshop on wave turbulence interactions in the sabl addressed the current understanding and challenges of wave turbulence interactions and the role of wavelike motions in contributing to anisotropic and intermittent turbulence from the perspectives of theory observations and numerical parameterization there have been a number of reviews on waves and a few on turbulence in stably stratified flows but not much on wave turbulence interactions this review focuses on the nocturnal sabl however the discussions here on intermittent turbulence and wave turbulence interactions in stably stratified flows underscore important issues in stably stratified geophysical dynamics in general

constraints on melting and magma production in the crust major intrusions of granitic rocks are found in several tectonic settings and in all cases crustal melts may contribute to the volumes of granitic magma high grade metamorphism and partial melting of the crust take place predominantly under fluid absent conditions we present a model for calculating the amounts of melt that may be formed by fluid absent breakdown of micas and amphiboles in common crustal rock types pelitic quartzofeldspathic intermediate and mafic melt proportions depend mainly on the kind of source rock the pressure at which melting takes place the temperature and the hydrous mineral h2o content of the source as a consequence of the pressure dependence of water solubility in silicate melts any given source rock will produce more melt by a given fluid absent reaction at lower pressure at a given pressure higher temperature reactions can produce more melt from a given source rock based on a survey of the compositions of common rock types we show that the amounts of melt can vary from 50vol thus crustal rocks vary widely in their fertility as magma sources depending on the types and amounts of hydrous phases they contain in general muscovite breakdown in pelites will yield only small quantities of melt and lead to migmatite formation biotite breakdown in pelites occurs at higher temperature and because most high grade pelites below granulite grade are biotite rich can yield up to about 50 vol of granitoid melt rocks of intermediate composition and hornblende rich mafic rocks are potentially highly fertile magma sources also provided that the high temperatures necessary for biotite and hornblende breakdown are realized pyroxene rich mafic rocks and quartzofeldspathic rocks are much less potentially fertile data suggest that mechanisms exist for the efficient segregation of melt and restite in systems with 30and probably 20vol melt the pressure temperature history of a region can greatly influence crustal source fertility through its control over the occurrence of subsolidus dehydration and melting equilibria

a thermodynamic assessment of the potential synthesis of condensed hydrocarbons during cooling and dilution of volcanic gases the possibility for abiotic synthesis of condensed hydrocarbons in cooling diluting terrestrial volcanic gases has been evaluated on the basis of the consideration of metastable chemical equilibria involving gaseous co co2 h2 and h2o the stabilities of n alkanes and polycyclic aromatic hydrocarbons pahs have been evaluated for several typical volcanic gas compositions under various conditions for cooling diluting of quenched volcanic gas the modeling shows that n alkanes and pahs have a thermodynamic potential to form metastably from h2 and co below 250 c within the stability field of graphite despite the predominance of co2 in volcanic gases synthesis of hydrocarbons from co2 and h2 is less favored energetically than from co and h2 both low temperature and a high h c atomic ratio in volcanic gas generally favor stability of hydrocarbons with higher h c ratios pahs are thermodynamically stable at temperatures 10 50 c higher than large n alkanes however at lower temperatures pahs and n alkanes have similar stabilities and are likely to form metastable mixtures both the energetic drive to form hydrocarbons and possible temperatures of formation increase as the oxidation state o2 of the volcanic gases decreases and as the cooling dilution ratios of volcanic gases increase synthesis of hydrocarbons is energetically more likely in cooling trapped gases than in ashcloud eruptive columns mechanisms for hydrocarbon formation may include fischer tropsch type synthesis catalyzed by magnetite from solid volcanic products on the early earth mars and jupiter s satellite europa several factors would have provided more favorable conditions for hydrocarbon synthesis in volcanic gases than under current terrestrial conditions and might have contributed to the production of organic compounds required for the emergence of life

carbonaceous matter in peridotites and basalts studied by xps sali and leed abstract carbonaceous matter in peridotite xenoliths and basalt from the hualalai volcano in a basalt glass collected directly from an active lava lake on the east rift of kilauea in garnet and diopside megacrysts from the jagersfontein kimberlite and in gabbros from the stillwater and bushveld complexes has been studied by x ray photoelectron spectroscopy xps thermal desorption surface analysis by laser ionization sali and low energy electron diffraction leed the basalt and two of the four xenoliths from hualalai and both jagersfontein megacrysts yielded trace quantities 10 nanomoles of organic compounds on heating to 700 c organics were not detected in the rocks from the layered intrusions and neither carbonaceous matter nor organics were detected in the glass from the lava lake where detected organics appear to be associated with carbonaceous films on microcrack surfaces carbonaceous matter exists as films less than a few nm thick and particles up to 20 m across both of which contain elements expected to be present in significant quantities in magmatic vapors namely si alkalis halogens n and transition metals leed studies suggest that the carbonaceous films are amorphous the data suggest two possible mechanisms for the formation of the organics one is that they are a product of abiotic heterogeneous catalysis of volcanic gas on new chemically active mineral surfaces formed by fracturing during cooling alternatively organics may have been assimilated into the volcanic gases prior to eruption and then deposited on cracks formed during eruption and cooling in any case there is no evidence to suggest that the organics represent laboratory or field biogenic contamination

possible evidences of earthquake lightning accompanying the 1995 kobe earthquake inferred from the nojima fault gouge the kobe earthquake of january 17 1995 which had a magnitude of 7 2 was accompanied by earthquake lightning eql the fault gouge near ground level at the nojima fault near where the eql was witnessed was highly lithified and anomalously mag netized the characterization of the fault gouge and the mudstone near the fault suggests that the anomalies might have been induced by an intense eql current which passed through the fault plane

carbonaceous films in midcrustal rocks from the ktb borehole germany as characterized by time of flight secondary ion mass spectrometry 1 amphibolites from 4 6 and 9 1 km depth in the kontinentales tiefbohrprogramm der bundesrepublik deutschland ktb borehole have developed extensive interconnected networks of carbonaceous films on cracks and grain boundaries as determined by electron probe and time of flight secondary ion mass spectrometry in the sample from 9 1 km depth the carbon is dominantly to completely elemental in contrast the carbonaceous matter in the samples from 4 6 km depth comprises a mixture of elemental carbon and simple hydrocarbons such as alkanes and possibly c o h compounds the microcracks within the 4 6 km sample also contain a retrograde micro assemblage consisting of ferri oxy hydroxide calcite and possibly clay minerals suggesting that the carbonaceous matter and retrograde minerals formed together at relatively high crustal levels and at a time much later than the peak metamorphism because the carbon films likely influence the electrical conductivity of the rocks in situ it is proposed that production of hydrocarbons during retrograde metamorphism of grain boundary and microcrack carbon tends to increase the resistivity of the rocks this chemical destruction of the interconnectivity of electrical pathways may contribute to the observed diminished conductivity of the shallow crust relative in relation to thto the deep crust

low frequency magnetic field measurements near the epicenter of the ms 7 1 loma prieta earthquake the authors report the results of measurements of low frequency magnetic noise by two independent monitoring systems prior to the occurrence of the m sub s 7 1 loma prieta earthquake of 17 october 1989 their measurements cover 25 narrow frequency bands in the more than six decade frequency range 0 01 hz 32 khz with a time resolution varying from a half hour in the ulf range 0 01 10 hz to one second in the elf vlf range 10 hz 32 khz the ulf system is located near corralitos about 7 km from the epicenter the elf vlf system is located on the stanford campus about 52 km from the epicenter analysis of the elf vlf system is located on the stanford campus about 52 km from the epicenter analysis of the elf vlf data has revealed no precursor activity that they can identify at this time however the ulf data have some distinctive and anomalous features first a narrow band signal appeared in the range 0 05 0 2 hz around september 12 and persisted until the appearance of the second anomalous feature which consisted of a substantial increase in the noise background starting on 5 october and covering almost the entire frequency range of the ulf system third there was an anomalousmore dip in the noise background in the range 0 2 5 hz starting one day ahead of the earthquake finally and perhaps most compelling there was an increase to an exceptionally high level of activity in the range 0 01 0 5 hz starting approximately three hours before the earthquake there do not appear to have been any magnetic field fluctuations originating in the upper atmosphere that can account for this increase further while the systems are sensitive to motion seismic measurements indicate that there were no significant shocks preceding the quake thus the various anomalous features in the data and in particular the large amplitude increase in activity starting three hours before the quake may have been magnetic precursors less

fault stability inferred from granite sliding experiments at hydrothermal conditions seismicity on crustal faults is concentrated in the depth interval 1 3 to 12 15km tse and rice 1986 suggested that the lower bound on seismicity is due to a switch with increasing temperature from velocity weakening destabilizing to velocity strengthening stabilizing friction they inferred this transition from friction data for dry granite however pore fluids exist at elevated temperatures throughout the crust and may strongly influence strength and sliding behavior we present new data from sliding experiments on granite at elevated t 23 to 600 plus elevated ph2o 100 mpa our results show velocity strengthening at room temperature but velocity weakening from 100 to 350 c except at 250 from 350 to 600 there are systematic trends from velocity weakening to strong velocity strengthening and from high to low friction neither trend was seen in tests on dry granite the velocity dependence data imply the potential for unstable slip in the interval 100 to 350 using a geotherm to map temperature to depth this interval closely matches the observed earthquake distribution

earthquake nucleation on model faults with rate and state dependent friction effects of inertia laboratory studies suggest that earthquake nucleation involves a transition from quasi static slip when inertial effects are negligible to inertia driven dynamic motion this transition occurs via quasi dynamic motion during which the effects of inertia become increasingly important the characteristics of this transition which depend on frictional properties of the fault determine the observability of earthquake nucleation by seismic geodetic or other means by investigating the role of inertia during nucleation we obtain a quantitative definition of the limiting velocity vin which marks the end of quasi dynamic motion and the onset of instability for reasonable friction parameters and fault widths we obtain estimates of vin for crustal faults to study the roles of inertia stiffness and friction parameters on preseismic motion we simulate triggered instabilities in a one dimensional model of a homogeneous fault with rate and state variable friction in most of our simulations triggering is achieved by applying a stress perturbation to an initially creeping fault under steady state friction we also investigate triggering on faults which are initially locked and overstressed compared to their nominal frictional strength due to time dependent healing we study the amount up and duration tp of preseismic slip as a function of system mass m and other model parameters for crustal faults we interpret the relevant mass as a product of density and fault width and find that wider fault zones result in smaller up and larger tp both up and tp are proportional to the system stiffness k the characteristic slip distance dc and the friction constitutive parameter a and inversely proportional to the size of the triggering event we find greater up and tp for constitutive laws which allow strengthening at zero velocity compared to laws that require slip or a combination of slip and aging for state evolution in contrast to quasi static modeling our simulations suggest a minimum stress perturbation criterion for instability which may be interpreted in terms of a strain threshold for triggered seismicity

evaluation and rehabilitation of dam seepage problems a case study kafrein dam abstract the intention of this study is to locate the probable sources of the kafrein dam seepage problem a methodology known as excitation response analysis will be considered analytical expressions depicting the groundwater level response in the underlying aquifer as a result of changes in the reservoir water level were derived from a linearized groundwater flow equation for one dimensional semi infinite isotropic and homogeneous porous media the results revealed that a large proportion of the seepage water originates from a site at a distance about 1 km from the observation point m1 and streamlines along the existing faults emphasis in this work was also placed on controling and mitigating the seepage problem

hydrologic characteristics of a large rockfill dam implications for water leakage abstract the unmun dam a rockfill dam with a clay core filter zone and sandy gravel shell is located in the nakdong river basin near cheongdo gun in korea in the dam area the cretaceous gyeongsang supergroup andesite lies over intrusive granite these form the intrusive contact near the main dam and cofferdam areas the stratigraphic units in upward sequence consist of cretaceous granite and andesite weathered soft rock and a soil layer of silty clay with gravel the reservoir was first filled in august 1994 and was full by april 1998 right after complete filling three sinkholes were found in the dam crest near stations 2 12 and 10 when the reservoir level was at around 150 m the amount of leakage increased with rise of the reservoir level mainly caused by rainfall events as a countermeasure for the abnormal leakage and dam rehabilitation comprehensive surveys were performed on the dam including observational drillings grouting geophysical surveys and tracer tests by korea water resources corporation kowaco there were also further investigations for hydrologic characterization of the dam to identify water leakages the groundwater levels at the 26 observation wells installed on the crest and dam toe were measured to evaluate the relationship between the reservoir level and groundwater level and the influences on the dam leakage groundwater level at the left side of the embankment was high compared with a normal phreatic line it was only 4 m lower than the reservoir level while 6 65 m lower than that at its right side fluctuation of the groundwater levels in the crest wells coincided well with the reservoir level without a significant lag time which reflected a good hydraulic connection between the reservoir and the dam interior hydraulic conductivity estimated from 149 hydraulic tests at 9 monitoring wells constructed in the dam core showed a wide range between 1 42 10 4 and 4 35 10 8 cm s with a geometric mean of 3 13 10 6 cm s furthermore water quality at the monitoring wells were much different from that of the reservoir high levels of turbidity and electrical conductivity were observed at the monitoring wells in the left side of the bank all these hydrologic characteristics reflected possible occurrence of the leakage on the dam especially in the left embankment this paper presents a summary of several investigation studies on the hydrologic characteristics of the rockfill dam which implied abnormal water leakage

investigation of groundwater chemistry at a dam site during its construction a case study of xiangjiaba dam china water quality can be used to reflect the hydro geological features and seepage restrictions around grout curtains xiangjiaba dam a large hydropower station constructed in southwest of china was investigated as a case study groundwater samples were collected and analysed qualitatively using hydrochemistry diagrams after which the presence of four major water groups was determined by hierarchical cluster analysis and saturation indices of each group were calculated finally inverse geochemical models of the groups were developed using phreeqc to elucidate the dissolution precipitation quality of different minerals and the relative contributions of different seepage sources the hydro geochemical methods used were found to be useful for revealing seepage behaviour within the domain during construction of a hydropower station

reduction of co2 during serpentinization of olivine at 300 c and 500 bar co 2 reduction processes occurring during experimental serpentinization of olivine at 300 c and 500 bar confirm that ultramafic rocks can play an important role in the generation of abiogenic hydrocarbon gas data reveal that conversion of fe ii in olivine to fe iii in magnetite during serpentinization leads to production of h 2 and conversion of dissolved co 2 to reduced c species including methane ethane propane and an amorphous carbonaceous phase hydrocarbon gases generated in the process fit a schulz flory distribution consistent with catalysis by mineral reactants or products magnetite is inferred to be the catalyst for methanization during serpentinization because it has been previously shown to accelerate fischer tropsch synthesis of methane in industrial applications involving mixtures of h 2 and co 2 the carbonaceous phase was predominantly aliphatic but had a significant aromatic component although this phase should ultimately be converted to hydrocarbon gases and graphite if full thermodynamic equilibrium were established its formation in these experiments indicates that the pathway for reduction of co 2 during serpentinization processes is complex and involves a series of metastable intermediates

grain boundary graphite in kapuskasing gneisses and implications for lower crustal conductivity surface electromagnetic measurements commonly reveal that the intermediate and lower continental crust has an appreciable electrical conductivity much higher than that found for laboratory analogues of deep crustal rocks or for upper crustal rocks either formed at shallow depths or uplifted from deeper levels conducting films at grain boundaries are thought to play an important part in enhancing deep crustal conductivity with brines and graphite being the main candidates1 at present however there is a lack of direct evidence for such films frost et al 2 have reported an enhancement in conductivity of igneous lower crustal rocks from the la ramie complex apparently owing to the presence of graphite films but the possible role of brines was not clear from this work here we present a study of the grain surface composition of metamorphic and one igneous rocks exhumed from 20 km depth by the kapuskasing uplift of the canadian shield3 we expect these samples to be representative of metamorphic and igneous rocks of the deep archaean crust auger spectroscopy provides evidence for graphite films at grain boundaries which can account for the present electrical signature of the kapuskasing crust4 6 we also detect traces of chlorine sulphur and iron which suggest that brines and solid conductors other than graphite may have helped to enhance the conductivity but their abundance suggests at best a minor role relative to graphite

mixing of a tracer in the pycnocline a patch of sulfur hexafluoride was released in may 1992 in the eastern north atlantic on an isopycnal surface near 300 m depth and was surveyed over a period of 30 months as it dispersed across and along isopycnal surfaces the diapycnal eddy diffusivity k estimated for the first 6 months was 0 12 0 02 cm2 s while for the subsequent 24 months it was 0 17 0 02 cm2 s the vertical tracer distribution remained very close to gaussian for the full 30 months as the root mean square rms dispersion grew from 5 to 50 m lateral dispersion was measured on several scales the growth of the rms width of the tracer streaks from less than 100 m to approximately 300 m within 2 weeks implies an isopycnal diffusivity of 0 07 m2 s at scales of 0 1 to 1 km larger than expected from the interaction between vertical shear of the internal waves and diapycnal mixing teasing of the overall patch initially about 25 km across into streaks with an overall length of 1800 km within 6 months supports predictions of exponential growth by the mesoscale strain field at a rate of 3 0 5 10 7 s 1 the rms width of these streaks estimated as 3 km and maintained in the face of the streak growth indicates an isopycnal diffusivity of 2 m2 s at scales of 1 to 10 km much greater than expected from internal wave shear dispersion the patch was painted in albeit streakily by 12 months confirming expectations from analytical and numerical models homogenization of the patch continued during the subsequent 18 months while the patch continued to spread with an effective isopycnal eddy diffusivity on the order of 1000 m2 s acting at scales of 30 to 300 km

experimental simulation of plagioclase diagenesis at p t conditions of 3 5 km burial depth dissolution of plagioclase under the physical conditions at shallow to intermediate burial depths is a prime candidate for secondary porosity generation in feldspathic siliciclastic sediments the diagenetic behavior of granular aggregates of plagioclase feldspar and quartz has been investigated by experimentation performed in a bridgeman type pressure vessel the experiments each of two weeks duration simulated pressure temperature conditions approximating 3 5 km burial depth by using a double acting pore fluid reservoir solutions of various chemistries were cycled through samples composed of oligoclase or labradorite feldspar and quartz 90 10 wt respectively

reconnaissance electromagnetic induction study of the kapuskasing structural zone implications for lower crustal conductivity abstract a large scale electromagnetic induction study has been carried out over the kapuskasing structural zone ksz an upthrust section of lower crustal rocks in north central ontario the absence of an overall anomalous response from the ksz even though the lower crust in this region of the canadian shield is known to be anomalously conductive implies that enhanced lower crustal conductivity is related to intrinsic conditions at lower crustal depths and not to mineralogical composition

streaming potential properties of westerly granite with applications this paper reports on laboratory measurements of the streaming potential properties of common minerals and in particular of westerly granite data are presented for these solids in contact with simple electrolytic solutions and in one case for temperature variation in the range 5 70 c for 1 1 electrolytes the ratio of the streaming potential coupling coefficient to fluid resistivity was approximately 4 mv atm m and for 2 1 electrolytes 2 mv atm m the effect of temperature was small 0 05 mv c temperature increase and indicates that the zeta potential was independent of temperature preliminary experimental results using mixed electrolytic solutions nacl cacl2 and two phase fluid flow are also described two phase flow can enhance streaming potentials by as much as a factor of 3 or 4 the laboratory data are used to interpret streaming potentials in geological problems such as earthquake prediction geothermal prospecting using the self potential method and surface conductivity contribution to the electrical resistivity of rocks

flow and hydraulics near the sill of hood canal a strongly sheared continuously stratified fjord abstract hood canal a long fjord in washington state has strong tides but limited deep water renewal landward of a complex constriction tide resolving hydrographic and velocity observations at the constriction with a depth cycling towed body varied markedly during three consecutive years partly because of stratification variations to determine whether hydraulic control is generally important and to interpret observations of lee waves blocking and other features hydraulic criticality is estimated over full tidal cycles for channel wide internal wave modes 1 2 and 3 at five cross channel sections using mode speeds from the extended taylor goldstein equation these modes were strongly supercritical during most of ebb and flood on the gentle seaward sill face and for part of flood at the base of the steep landward side examining local criticality along the thalweg found repeated changes between mode 1 being critical and supercritical approaching the sill crest during flood unsurprising given l

factor and cluster analyses of water chemistry in and around a large rockfill dam implications for water leakage based on water chemistry data a rockfill dam in south korea was investigated to identify major parts of substantial dam water leakage sinkholes in the dam crest and abnormal water leakage through the dam were observed since the first impounding of the dam previous investigations including observational drillings hydraulic tests geophysical surveys and tracer tests revealed the development of a high permeability zone in the clay core and an abnormally high phreatic line zone in the left embankment sequential tracer tests provided further evidence of locations of preference and rapid water leakage pathways in this study we examined the usefulness of water chemistry data to confirm previous findings of water leakage factor analysis of the water chemistry data revealed major processes controlling the chemical composition which include the wash out and successive dissolution of fill materials in the dam interior interaction between percolating water and dam core materials and contamination of seeping water by grouting materials and previous tracer tests distinct spatial distribution of similar chemical groups was illustrated by cluster analysis and confirmed the location of major water leakage at the left abutment adjoining the spillway

graphite ch4 h2o co2 equilibria at low grade metamorphic conditions equilibrium calculations and published phase equilibria are used to show that at temperatures below 400 c and pressures above 300 bar the fluids coexisting with graphite in the c o h system consist either of co2 h2o mixtures or ch4 h2o mixtures bulk fluid compositions consisting of ch4 h2o will unmix to methane rich fluid and h2o rich liquid at temperatures below about 325 c compositions on the co2 h2o join will unmix only at temperatures below about 275 c oxygen fugacity in the ch4 h2o graphite three phase region is fixed at constant p and t and approximately equal to that of the quartz magnetite fayalite assemblage in the co2 h2o graphite three phase region oxygen fugacity is about three orders of magnitude greater from the end stages of diagenesis to temperatures of 300 c and possibly 400 c in salt rich systems many metamorphic rocks may contain ch4 h2o fluids rather than co2 h2o mixtures thus metamorphic reactions involving carbonate minerals would involve ch4 graphite and h2o rather than co2 the immiscibility between ch4 and h2o could result in the common occurrence of methane natural gas in low grade metamorphic terrains

unstable graphite films on grain boundaries in crustal rocks abstract the origin of high electrical conductive anomalies in the lower crust is a long standing and controversial problem although it has been proposed that saturated saline water or partial melt increases electrical conductivity graphite film has also been recognized as a potential cause of high conductivity since the discovery of fine graphite films on the grain boundaries of high grade metamorphic rocks to investigate the stability of graphite film on grain boundary of silicate minerals under lower crustal conditions electrical conductivity of graphite film on synthetic grain boundaries of quartz bicrystals was measured by means of impedance spectroscopy at 1 gpa and up to 1200 k in a multianvil apparatus at first heating the electrical conductivity of the thin graphite film with thickness less than 100 nm was initially very high but decreased with time during annealing under high temperature conditions 1000 k the conductivity of a thin carbon film rapidly decreases and approaches the quartz conductivity this indicates that graphite film on a grain boundary between two quartz crystals is not stable at high temperatures optical microscopic observation of the run products suggested a disconnected feature of graphite on a quartz grain boundary disconnection of graphite film can be caused by higher interfacial energy between graphite and silicate minerals than that of the grain boundary energy therefore a thin graphite film is not a likely candidate to account for high conductivity anomalies in the middle and lower continental crust

electrical conductivity variations around the palmdale section of the san andreas fault zone our analysis of a decade of observations from the palmdale california telluric array is presented the array is a system of large scale telluric field measurements used for the passive monitoring of electrical conductivity variations over a large region centered over the san andreas fault zone northeast of los angeles since 1985 systematic changes in the relationships between the telluric field measurements around the array have been observed these changes amounted to 1 to 2 by the time the array was closed down in 1989 with the fields measured along the fault and northeast of the fault showing signal decreases relative to the fields southwest of the fault because of the possible implications of these changes for conductivity variations related to tectonic activity on the san andreas we have attempted to sort out the geography of the zones that could cause the changes the simplest though nonunique interpretation of the observed variations in the telluric relationships is a steady increase in the conductivity of the lower crustal region of the fault zone from two dimensional models of the telluric response around the array we infer that an increase of about 60 milli siemens in the conductance of the lower crustal fault zone could account for the changes seen over the period 1985 to 1989 assuming changes were in a kilometer wide zone and that the lower crustal fluids were very conductive this could represent a strain of about 0 4 10 6 the surface strain would be much smaller and would be lost in surface strain noise because of the possibility that fluid pressure changes are involved these small strains could still be significant for earthquake cycle phenomena alternatively the observed changes could have been produced by increases in the conductivity of the upper crust of the mojave desert northeast of the fault or by decreases in the conductivity of the upper crust in the san gabriel mountains southwest of the fault to produce the observed telluric changes however the additional conductivity and the associated strain changes would have to be much larger the strain needed to accommodate the increased conductivity on the mojave side would have to be of the order of 6 10 4 which seems unrealistically high smaller strains could account for conductivity changes in the san gabriel mountains but these strains would have to be compressive water level changes are not considered to be a possible cause of the conductivity changes because the measurement scale is much larger than the typical scale of water level changes and no seasonally correlated changes in the telluric fields were observed

stirring by small scale vortices caused by patchy mixing evidence is presented that lateral dispersion on scales of 1 10 km in the stratified waters of the continental shelf may be significantly enhanced by stirring by small scale geostrophic motions caused by patches of mixed fluid adjusting in the aftermath of diapycnal mixing events dye release experiments conducted during the recent coastal mixing and optics cmo experiment provide estimates of diapycnal and lateral dispersion microstructure observations made during these experiments showed patchy turbulence on vertical scales of 1 10 m and horizontal scales of a few hundred meters to a few kilometers momentum scaling and a simple random walk formulation were used to estimate the effective lateral dispersion caused by motions resulting from lateral adjustment following episodic mixing events it is predicted that lateral dispersion is largest when the scale of mixed patches is on the order of the internal rossby radius of deformation which seems to have been the case for cmo for parameter values relevant to cmo lower bound estimates of the effective lateral diffusivity by this mechanism ranged from 0 1 to 1 m 2 s 1 revised estimates after accounting for the possibility of long lived motions were an order of magnitude larger and ranged from 1 to 10 m 2 s 1 the predicted dispersion is large enough to explain the observed lateral dispersion in all four cmo dye release experiments examined

hydrogeochemical modeling of the water seepages through tannur dam southern jordan this paper reveals the geochemical processes of dissolution precipitation and cation exchange that took place during water rock interaction between water seepages through the tannur dam the schoeller diagram indicates that there are three major water types originating during water rock interaction the first water type is characterized by low salinity that ranges from 1 300 to 2 800 s cm which represents the reservoir water and the water in the right side of the central gallery the second water type is in the left side of the central gallery which exhibits medium salinity that reaches about 4 400 s cm the third water type is characterized by very high salinity that reaches a value of around 8 500 s cm and represents the water in the right existing adit the increase of salinity can be explained due to the dissolution of carbonate and sulfate minerals that form the matrix of the foundation and the abutment rocks and the dissolution of the grout curtain which is composed of cement and bentonite hydrogeochemical modeling using a computer code phreeqc was used to obtain the saturation indices of specific mineral phases which might be related to interaction with water seepages and to identify the chemical species of the dissolved ions the thermodynamic calculations indicate that most of the water samples were undersaturated with respect to gypsum anhydrite and halite and were saturated and or supersaturated with respect to calcite and dolomite ca hco3 2 is the primary water type as a result of dissolution of carbonate minerals such as calcite and dolomite prevailing at the dam site however cation exchange processes are responsible for the formation of the na2so4 water type from the caso4 type that formed due to the dissolution of gypsum

causes of the catastrophic failure of an earth dam built on gypsiferous alluvium and dispersive clays altorricon huesca province ne spain this paper analyses the causes of the catastrophic failure of an earth dam that took place on 21 january 2001 during the first filling test in the ne of spain altorricon village huesca province the san juan reservoir with a capacity of 850 000 m3 was built in 1999 on gypsiferous mantled pediment deposits overlying tertiary dispersive clay sediments the basin of the reservoir was excavated in the alluvial cover and tertiary bedrock an earth dam was constructed on the pediment surface along the perimeter of the artificial basin the dam has a core of compacted clay material derived from the excavation which is indented 1 m in the tertiary shales of the bedrock cutting the highly pervious alluvial mantle field observations analysis of the basin and dam materials and eyewitnesses accounts have helped to infer the processes involved in the failure of the earth dam these processes include 1 subsidence and ravelling suffosion processes induced by the dissolution of the 4 m thick detrital cover with a gypsum content of around 40 2 piping processes affecting the embankments and core of the dam built with dispersive clays that have high exchangeable sodium percentage esp and show active pipes and 3 water circulation through biogenic burrows in the pediment deposits this case study demonstrates the frequently hidden limitations that evaporite sediments and dispersive clay materials pose to the construction of dams it also shows that highly permeable surficial deposits should be stripped before the construction of the dam structure