a long term study of stable isotopes as tracers of processes governing water flow and quality in a lowland river basin the upper thames uk a long term study of o h and c stable isotopes has been undertaken on river waters across the 7000 km2 upper thames lowland river basin in the southern uk during the period flow conditions ranged from drought to flood a 10 year monthly record 2003 2012 of the main river thames showed a maximum variation of 3 18o and 20 2h though inter annual average values varied little around a mean of 6 5 18o and 44 2h the 2h 18o slope of 5 3 suggested a degree of evaporative enrichment consistent with derivation from local rainfall with a weighted mean of 7 2 18o and 48 2h for the period a tendency towards isotopic depletion of the river with increasing flowrate was noted but at very high flows 100 m3 s a reversion to the mean was interpreted as the displacement of bank storage by rising groundwater levels corroborated by measurements of specific electrical conductivity a shorter quarterly study october 2011 april 2013 of isotope variations in 15 tributaries with varying geology revealed different responses to evaporation with a high inverse correlation between 18o and baseflow index bfi for most of the rivers a comparison with aquifer waters in the basin showed that even at low flow rivers rarely consist solely of isotopically unmodified groundwater long term monitoring 2003 2007 of carbon stable isotopes in dissolved inorganic carbon dic in the thames revealed a complex interplay between respiration photosynthesis and evasion but with a mean inter annual 13c dic value of 14 8 0 5 exchange with atmospheric carbon could be ruled out quarterly monitoring of the tributaries october 2011 april 2013 indicated that in addition to the above factors river flow variations and catchment characteristics were likely to affect 13c dic comparison with basin groundwaters of different alkalinity and 13c dic values showed that the origin of river baseflow is usually obscured the findings show how long term monitoring of environmental tracers can help to improve the understanding of how lowland river catchments function

nitrogen isotope hydrochemistry and denitrification within the chalk aquifer system of north norfolk uk abstract although there has been much debate over the potential health risks of nitrate in drinking water there is a real issue of the costs associated with removing nitrate from drinking water supplies in the chalk aquifer system of north east norfolk modern contaminants of a mainly agricultural origin produce high levels of nitrate 15 mg l no3 n in the unconfined valley areas whereas in confined regions the levels of nitrate are low and commonly below detection limits

geochemical evolution of groundwater beneath mexico city abstract the geochemical evolution of groundwaters along a 24 km flow beneath central mexico city path from the sierra de las cruces towards lake texcoco has been investigated using stable isotopes radiocarbon and major and trace elements to determine the natural baseline conditions the extent of any contamination and the effectiveness of the overlying aquitard seal modern groundwaters of low salinity 1 are found up to 11 km from the outcrop area and groundwater ages of up to 6000 yr bp occur in the middle part of the section groundwater stable isotope ratios 18 o and 2 h lie close to the global meteoric water line indicating that the groundwater originates from local rainfall the groundwater chemistry may be interpreted as the result of inputs from the source area with progressive water rock interaction down the horizontal flow gradient a redox boundary is found at 9 km along the line of section coincident with the start of the confined section relatively low nitrate concentrations below 9 mg l 1 no 3 n are found in the aerobic waters low concentrations of no 3 in the aerobic waters and low cl reflect inputs prior to the modern development some elements cr u as se sb increase their concentration with distance time as far as the redox boundary but low concentrations occur in the reducing aquifer section the chemistry of several major ions mg na cl k as well as trace elements such as li rb ba reflect the weathering of the basaltic mineral assemblage feldspars and mafic minerals and their increases are generally proportional to residence time phosphate f and i concentrations indicate a probable source from apatite in the basaltic or rhyolitic rocks a borehole in the east of the city some 17 km downgradient intercepted thermal water si geothermometry indicates 163 c at depth this water gives a distinctive composition indicating possible addition of metamorphic co 2 which has then reacted with the igneous rocks increases in b and cl are derived from volatiles trapped in the glass or vesicular basalt a thermal anomaly found in the middle section of the heavily pumped aquifer is interpreted as the up coming of warmer water from medium to greater depth mainly from basalts rhyolites and possibly limestones the geochemistry indicates that groundwater beneath mexico city is of good quality and there is no obvious evidence of leakage of inorganic compounds from surface sources of contamination through the aquitard the younger groundwater drawn from the western outcrop area is generally of good inorganic quality increased drawdowns in the confined aquifer have induced flow of warmer water with higher cl from depth the resources in the aquifer represent an important reserve of good quality water which need to be properly managed as a high quality resource as part of integrated plans for the city s future supplies

groundwater composition hydrochemical evolution and mass transfer in a regional detrital aquifer baza basin southern spain abstract the physical chemical characteristics of the groundwater in the baza caniles detrital aquifer system indicate that a wide diversity of hydrochemical conditions exists in this semiarid region defining geochemical zones with distinct groundwater types the least mineralized water is found closest to the main recharge zones and the salinity of the water increases significantly with depth towards the center of the basin geochemical reaction models have been constructed using water chemistry data along flow paths that characterize the different sectors of the aquifer system namely quaternary aquifer unconfined sector and shallow and deep confined sectors of the mio pliocene aquifer geochemical mass balance calculations indicate that the dominant groundwater reaction throughout the detrital system is dedolomitisation dolomite dissolution and calcite precipitation driven by gypsum dissolution this process is highly developed in the central part of the basin due to the abundance of evaporites apart from this process there are others which influence the geochemical zoning of the system in the quaternary aquifer which behaves as a system open to gases and which receives inputs of co 2 gas derived from the intensive farming in the area the interaction of the co 2 with the carbonate matrix of the aquifer produces an increase in the alkalinity of the water in the shallow confined sector of the mio pliocene aquifer the process of dedolomitisation evolves in a system closed to co 2 gas ca 2 na cation exchange and halite dissolution processes are locally important which gives rise to a relatively saline water finally in the deep confined sector a strongly reducing environment exists in which the presence of h 2 s and nh 4 in the highly mineralized groundwater can be detected in this geochemical zone the groundwater system is considered to be closed to co 2 gas proceeding from external sources but open to co 2 from oxidation of organic matter the geochemical modeling indicates that the chemical characteristics of this saline water are mainly due to so 4 dissolution dedolomitisation and so 4 reduction coupled with microbial degradation of lignite

quantifying regional groundwater flow between continental intercalaire and djeffara aquifers in southern tunisia using isotope methods large scale interaction between the continental intercalaire and the djeffara aquifer systems in the southeast of tunisia has been investigated with the aid of chemical and isotopic tracers two distinct groundwater types have been identified 1 the continental intercalaire groundwater characterized by elevated temperatures 50 61 4 c low 18o 8 4 to 7 87 and 2h 67 2 to 59 values and negligible radiocarbon content both testifying its great age dating from the late pleistocene period and 2 the djeffara groundwater with distinctly heavier isotopic composition 18o 8 31 to 5 80 2h 65 9 to 31 9 the djeffara groundwaters reveal a distinct changes of physico chemical and isotopic parameters near el hamma faults in the northwestern part of the djeffara basin these changes could possibly be explained by a vertical leakage from the continental intercalaire aquifer through el hamma faults the mixing proportions inferred from stable isotope mass balance prove that the contribution of the continental intercalaire to the recharge of djeffara aquifer is very significant and may reach 100 in the el hamma region and in the northern part of gabes isotope tracers strongly suggest that recent recharge to the djeffara aquifer system is very limited its current yield particularly in its central and northern parts can be maintained only thanks to large scale underground inflow from the continental intercalaire aquifer system which carries late pleistocene palaeowater consequently current exploitation of groundwater resources of the djeffara aquifer has non sustainable character

crustal structure of the diablo and gabilan ranges central california a reinterpretation of existing data the compressional wave velocity structure of the crust of the coast ranges of central california was modeled from seismic refraction data reported previously for both the diablo range east of the san andreas fault and the gabilan range west of the fault two alternative velocity models were derived for each range by iterative two dimensional ray tracing each pair of models shows a sedimentary layer and an underlying crust composed of three or four layers for the diablo range the velocities in the sediments range from 2 9 to 4 8 km sec and the depth to basement varies from 0 2 km within the central diablo range to a maximum of 3 4 km north of the livermore valley in the gabilan range the velocities in the sediments overlying the granitic basement are higher north of the gabilan range 3 6 to 4 6 km sec than to the south 2 2 to 3 8 km sec and the depth to basement both north and south of the range is less than 2 km below the sediments and fractured near surface material a resolvable difference in the crustal velocity structure on opposite sides of the san andreas fault indicates compositional differences at depth the upper crust has an average velocity of 5 7 km sec at depths between 3 and 16 3 km in the diablo range and an average velocity of 6 1 km sec at depths between 2 and 9 1 km in the gabilan range the lower crust has an average velocity of 6 9 km sec at depths between 16 3 and 30 km in the diablo range and an average velocity of 6 5 km sec at depths between 10 and 24 km in the gabilan range the models also show that the depth to moho differs by several kilometers between the two ranges in the diablo range models the crust mantle boundary becomes shallower from south to north rising from a depth of 30 to 26 km in the gabilan range models the moho is at a depth of 24 to 26 km depending on the velocity assumed at the base of the crust laboratory measurements of rock velocities and the mapped surface geology allow us to interpret the velocity models in terms of crustal composition we conclude that the diablo range probably consists largely of metagraywacke to a depth of 16 3 km and gabbroic material below this depth the crust of the gabilan range probably consists of granitic material to a depth of 9 1 km and gneissic material below this depth franciscan rocks are not regionally present in the crust of the gabilan range if the gneissic lower crust consists of the same rocks as are found at the surface in the gabilan range then the presumed large scale lateral motion of the salinian block has taken place at or below the crust mantle boundary rather than along a mid crustal slip plane

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

temporal change in coda q before the tangshan earthquake of 1976 and the haicheng earthquake of 1975 a new earthquake precursor called coda q is demonstrated for the tangshan earthquake of 1976 and for the haicheng earthquake of 1975 the precursor is based on the measurement of coda decay rate for small local earthquakes in the general area that is preparing for a major earthquake during the 3 year period preceding the tangshan earthquake the coda q was about 3 times lower than it was before or after this period a comparable change also occured at the time of the haicheng earthquake the observed change cannot be due to the change in the source parameters such as the focal depth or the source spectrum the coda q precursor appears to detect the same physical process detected by other precursors such as b value quiescence radon water quality vp vs and animal behavior but has advantages over them in its clearer physical mechanism easier sampling and better defined anomalous region

integrating palynological and geochemical data in a new approach to palaeoecological studies upper cretaceous of the banterwick barn chalk borehole berkshire uk abstract the dinoflagellate cyst record from an upper cretaceous uppermost cenomanian upper coniacian chalk core drilled at banterwick barn berkshire is described and statistically correlated with elemental and stable isotope bulk sediment geochemical data from the same core seventy two dinocyst species and subspecies are recorded and stable carbon and oxygen isotopic 13 c 18 o trends are documented lithostratigraphy and chemostratigraphic correlation of the 13 c curve with an expanded section at dover kent are used to identify stratigraphically significant marls and determine the positions of macrofossil zones and stage boundaries in the banterwick barn core these data indicate that 30 m of chalk at dover are represented by senoniasphaera rotundata alveolata is proposed which has a fad in the lower turonian and last appears lad in the lower coniacian senoniasphaera rotundata rotundata autonym herein has its fad in the middle turonian first common occurrence in the uppermost turonian and lad in the upper coniacian an extremely impoverished assemblage of dinocysts in the highest cenomanian to lowest turonian is considered to be largely a preservational artefact of intraclastic nodular and calcarenitic chalks and is not related directly to the well documented global oceanic anoxic event oae2 occurring at that time 93 5 ma a sharp increase in dinocyst abundance in the lower turonian corresponds with a change in lithology to more marly chalks a gradual decrease in the number of species is observed through the middle turonian to upper coniacian 18 o records show that this was associated with global climatic cooling cluster analysis of the dinocyst abundance record with geochemical data indicates four distinct species groups with characteristic geochemical associations i e groups 1 4 groups 1 and 2 are associated with phases of increased siliciclastic supply a positive correlation with higher 13 c values differentiates the latter group 3 is independent of carbonate and detrital input and group 4 is associated with high carbonate flux and low detrital supply these groupings suggest that cyst forming dinoflagellates exhibited a range of ecological niches in the late cretaceous although the relationship between the encystment process and the geochemical associations is unclear key environmental factors are likely to be sea level and climate related including water depth turbidity nutrient supply sea surface temperature and environmental stability predictability integrated geochemical and palynological studies have great potential for inter regional correlation and palaeoenvironmental interpretation

transport of radionuclides in an unconfined chalk aquifer inferred from u series disequilibria abstract u series disequilibria measured in waters and rocks from a chalk aquifer in france have been used as an analog for long term radionuclide migration drill core samples from a range of depths in the vadose zone and in the saturated zone as well as groundwater samples were analyzed for 238 u 234 u 232 th and 230 th to determine transport mechanisms at the water rock interface and to quantify parameters controlling the migration of radionuclides isotope measurements in rocks were done by tims whereas 234 u 238 u and 230 th 232 th activity ratios in water samples were measured by multi collector icp ms both depletion and enrichment in 234 u relative to 238 u were observed in carbonate rock samples resulting from chemical weathering in the unsaturated zone and calcite precipitation in the zone of water table oscillation respectively the correlation between 230 th 232 th activity ratios and 87 sr 86 sr ratios found in the chalk samples indicates that thorium is mainly contained in a minor silicate phase whose abundance is variable in chalk samples water samples are all characterized by 234 u 238 u 1 resulting from recoil effect of 234 th groundwaters are characterized by a more radiogenic signature in 87 sr 86 sr than the rocks moreover 230 th 232 th activity ratios in the waters are lower than in the rocks and increase with distance from the water divide which suggests that th transport is controlled by colloids formed during water infiltration in the soil a 1 d transport model has been developed in order to constrain the u series nuclide transport considering a transient behavior of radionuclides in the aquifer and a time dependent composition for the solid phase this model permits a prediction of the time scale of equilibration of the system and an estimation of parameters such as weathering rate distribution coefficients and recoil fractions retardation factors of 10 35 and from 1 10 4 to 2 10 5 were predicted for u and th respectively and can be used to predict the migration of radionuclides released as contaminants in the environment at the scale of our watershed 32 km 2 a characteristic migration time from recharge to riverine discharge of 200 600 yr for u and 0 2 3 7 myr for th was obtained

regional change of coda q in the oceanic lithosphere coda q of 22 local earthquakes recorded on islands located in young and old oceanic lithosphere areas has been measured we found that the q values at periods of from 1 to 2 seconds increase from young to old ocean lithosphere in the same way as for the continent where the intensity of current tectonic activity shows a strong negative correlation with the coda q the q values increase with frequency proportional to fn where n was found to be 0 46 0 61 with the higher values for younger oceanic lithosphere which is again similar to the continents where the active regions have higher n values

geochemical characterization of groundwater from an arid region in india a study on the geochemical processes in arid region of western india kachchh district was carried out using major minor trace metal data and isotopic composition 2h 18o of groundwaters results indicate that the distribution of chemical species in groundwater of this district is controlled by leaching of marine sediments dissolution of salts in root zone and incongruent dissolution of carbonate minerals common inorganic contaminants such as fluoride nitrate and phosphate are within drinking water permissible limits however most of the samples analyzed contain total dissolved salts more than desirable limits and fall in doubtful to unsuitable category with regard to irrigational purpose trace metal data indicates no contamination from toxic elements such as arsenic and lead an increased salt content is observed in groundwater at shallower depths indicating mixing with surface water sources the chemical characteristics of the groundwater have found to be strongly dependent on the local lithological composition environmental isotopic data indicates that the groundwater is of meteoric origin and has undergone limited modification before its recharge the processes responsible for observed brackishness are identified using chemical and isotope indicators which are in agreement with subsurface lithology and hydrochemistry these data though represent hydrochemical scenario of 2001 can still be used for understanding the long term fluctuations in water chemistry and would be quite useful for the planners in validating groundwater quality models

the relation of crustal scattering to seismicity in southern california dense regional array recordings of 377 teleseismic events are used to map geographic variability in upper crustal p to s scattering in southern california scattered wave energy is sensitive to short wavelength heterogeneity and maps of scattering potential offer a powerful complement to travel time tomography in characterizing seismic crustal heterogeneity the scale length of resolved scattering variability is commensurate with the scale lengths of surface fault trace length and microseismicity variations and both mapped faults and seismicity are concentrated in regions of strong scattering fault proximal scattering averaged across strike of predominately strike slip fault zones is highly correlated with microseismicity levels and is predictive of the pattern of microseismicity variation but not of absolute scale north south profiles through the transverse ranges reveal coincident strong gradients in microseismicity and scattering whereas mapped segment bounds along the san andreas fault zone from san francisco to the salton sea coincide with strong along strike gradients in the level of scattering the overall correlation of microseismicity and scattering potential is consistent with structural control of aftershock and background microseismicity production strain energy control of scattering or both prior evidence for fault offset in the pattern of scattering intensity revenaugh and reasoner 1997 favors the former

syn rift geofluids in fractures related to the early middle miocene evolution of the valles penedes half graben ne spain abstract the valles penedes half graben located in the central part of the catalan coastal ranges is ne sw oriented 10 14 km wide and up to 100 km long and is filled mainly with continental to marine siliciclastic deposits ranging from late oligocene early miocene to late miocene the syn rift burdigalian continental deposits are well stratified s 0 approx 090 15n red beds affected by nnw sse trending nearly vertical extensive fractures middle burdigalian early langhian in age these extensive fractures which cut quasi perpendicularly the stratification are filled with calcite veins presenting two filling stages the first stage is formed by millimetric to centrimetric thick bands of crystalline calcite consisting of palisade calcite cement anhedral spar texture and rhombic calcite cement non to dull orange luminescent with 18 o values ranging from 9 0 to 5 2 pdb 13 c values varying from 9 3 to 6 7 pdb 87 sr 86 sr ratios ranging from 0 71088 to 0 71361 relatively high values of mg and variable values of mn sr and fe this stage is interpreted as subaerial speleothems rimstones which developed in meteoric vadose conditions the second stage is formed by euhedral spar megaspar cement and coconut meat cement with zoned bright yellow to orange luminescence with 18 o values ranging from 16 2 to 9 9 pdb 13 c values varying from 7 4 to 1 9 pdb 87 sr 86 sr ratios ranging from 0 71608 to 0 71800 and relatively low values of mg mn sr and fe this stage is interpreted as subaquatic cements developed in meteoric phreatic conditions the two stages of calcite fillings reflect successive circulation of two meteoric fluids with very different geochemical compositions and represent the change from vadose to phreatic environment during the evolution of the syn rift stage middle late burdigalian to late langhian the meteoric fluid producing the first filling stage was a superficial fluid proceeding directly from the surface influenced by soil co 2 the meteoric fluid generating the second stage was a more evolved fluid which had previously undergone interaction with sediments and reservoir effect the beginning of the thermal subsidence coupled with a change from a more arid to a hotter and perhaps wetter climate could had been the ultimate reasons for the observed evolution

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

isotopic and hydrochemistry spatial variation of sulfate for groundwater characterization in karstic aquifers the sierra gorda aquifer is one of the most extensive of southern spain the main groundwater discharge is produced at its northern boundary through several high flow springs in this study stable isotopes of dissolved sulfate 34s and 18o and groundwater chemistry were used to determine the origin of the sulfate and to characterize the groundwater flow we sampled the main springs as well as other minor outlets related to perched water tables in order to determine the different sources of so42 e g dissolution of evaporites atmospheric deposition etc the substantial difference in the amount of dissolved so42 between the springs located in its northwestern part 25 mg l and those elsewhere in the northern part 60 mg l suggests zones with separate groundwater flow systems a third group of springs far from the northeastern boundary of the permeable outcrops shows higher so42 content than the rest 125 mg l the isotopic range of sulfate 0 3 to 14 82 v ctd points to several sources including dissolution of triassic or miocene evaporites atmospheric deposition and decomposition of organic material in the soil among these the dissolution of triassic gypsum which overlies the saturated zone as a consequence of the folds and faults that deform the aquifer is the main source of so42 range from 12 79 to 14 82 v ctd this range is typical for triassic gypsum the higher karstification in the western sector together with important differences in the saturated thickness between the western and eastern sectors would also be due to the tectonic structure and could explain the difference in so42 contents in the water this singular arrangement may cause a higher residence time of groundwater in the eastern sector thus a higher contact time with triassic evaporitic rocks is inferred accordingly the stable isotopes of so42 are found to be a valuable tool for identifying areas with different flow systems in the saturated zone of karstic aquifers as well as for evaluating aspects such as the degree of karstification

geochemistry and14c dating of groundwaters from jurassic aquifers of north aquitaine basin france twenty seven samples from a confined lower middle jurassic aquifer and an unconfined oxfordian aquifer of the north aquitaine basin france have been analysed for their major elements br 18o 2h 13c and14c contents hydrochemistry indicates 1 a dissolution of carbonate and anhydrite near the recharge zone and 2 a dilution of a saline water derived from a seawater halite mixing in the deeper part of the aquifer the mixing is also visible in a 18o vs cl diagram in which two different groups appear recent waters and old waters indicating a mixing process between fresh and saline groundwaters the composition of the saline water is likely to be 34 100 11 200 ppm in cl 70 20 ppm in br and more than 3 5 07 vs smow in18o 13c contents indicate 1 a c exchange with caco3 matrix for groundwaters near the recharge zone and 2 a participation of organic matter in the deep part of the aquifer residence times for waters near the area of the aquifer outcrop correspond to holocene and late pleistocene periods the depletion in stable isotopes of 10 to 15 000 y b p waters show a late glacial period infiltration to the aquifer after a distance of about 10 km in the aquifer the14c activities are 0 pmc showing the presence of old groundwaters

local magnitude tomography in california lateral variation in crustal attenuation of california is calculated by inverting 25 330 synthetic wood anderson amplitudes from the california integrated seismic network cisn for site source and path effects two dimensional attenuation q or 1 q is derived from the path term which is calculated via an iterative least squares inversion that also solves for perturbations to the site and source terms source terms agree well with initial cisn m l s and site terms agree well with a prior regression analysis q ranges from low attenuation at 0 001 q 1000 to high attenuation at 0 015 q 66 with an average of 0 07 q 143 the average q is consistent with an amplitude decay function log a for california when q is combined with a simple geometrical spreading rate attenuation in california is consistent with the tectonic structure of california with low attenuation in the sierra batholith and high attenuation at the geysers at long valley and in the salton trough possibly due to geothermal effects also path terms are an order of magnitude smaller than site and source terms suggesting that they are not as important in correcting for m l

application of regional phase amplitude tomography to seismic verification we have applied tomographic techniques to amplitude data to quantify regional phase path effects for use in source discrimination studies tomography complements interpolation kriging methods by extending our ability to apply path corrections into regions devoid of calibration events as well as raising levels of confidence in the corrections because of their more physical basis our tomography technique solves for resolvable combinations of attenuation source generation site and spreading terms first difference regularization is used to remove singularities and reduce noise effects in initial tests the technique was applied to a data set of 1488 1 0 hz p g l g amplitude ratios from 13 stations for paths inside a 30 by 40 box covering western china and surrounding regions tomography reduced variance 60 relative to the power law distance correction traditionally applied to amplitude ratios relative p g l g attenuation varied with geologic region with low values in tibet intermediate values in basins and high values for platforms and older crust spatial patterns were consistent with previous path effect studies in asia especially local earthquake coda q relative spreading was consistent with expected values for p g and l g relative site terms were similar to one another yet some tradeoff with attenuation was evident tomography residuals followed systematic trends with distance which may result from the evolution from direct to coda phases focusing model tradeoff or data windowing effects examination of the residuals using a kriging interpolator showed coherent geographical variations indicating unmodeled path effects the residual patterns often follow geological boundaries which could result from attenuating zones or minor blockages that are too thin to be resolved or that have anisotropic effect on regional phases these results will guide efforts to reparameterize tomography models to more effectively represent regional wave attenuation and blockage the interpolated residuals also can be combined with predictions of the tomographic model to account for path effects in discrimination studies on a station by station basis

isotopic and noble gas study of chalk groundwater in the london basin england abstract the chemical and isotopic composition of groundwater from 52 sites in the london u k area was determined as part of a project aimed at assessing the spatial variation in the age of chalk groundwater and in determining the relationship between fracture and matrix groundwater in this dual porosity system systematic changes in groundwater chemistry take place in the downgradient direction in response to several chemical processes these processes include early concentration by evaporation and congruent dissolution of calcite followed by widespread incongruent dissolution and ion exchange in addition to local oxidation reduction reactions gypsum dissolution and saline intrusion as a result of the above processes chalk groundwater follows an evolutionary path from ca bicarbonate type to na bicarbonate type the age of chalk groundwater was modelled using14c 13c 3h 2h and 180 there is a general increase in the groundwater age in a downgradient direction with the oldest water found in n central areas of the basin groundwater in the unconfined zones and in areas s of the greenwich fault is almost entirely of unevolved modem composition carbon 14 modelling suggests that chalk groundwater in the s basin is generally less than 10000 a old while that in the north is generally between 10000 and 25000 a old the presence of3h in concentrations of up to 7 tu in groundwater which yields ages of several 1000 a however indicates that mechanisms exist for the rapid introduction of recent groundwater to the confined aquifer results of palaeorecharge temperature determinations using 2h 180 and noble gas analytical results suggest that significant devensian recharge did indeed occur in the aquifer a model of the development of the chalk recognizes that it is a classic dual porosity aquifer in which groundwater flow occurs predominantly in the fracture system the upper 50 m of the aquifer was flushed with fresh water during the 2 3 106 a of the quaternary and therefore meteoric water largely replaced the tertiary and cretaceous marine water that previously saturated the system most processes which control the chemistry of the groundwater occur in the matrix where the surface area is exceptionally high although fracture flow dominates the flow regime diffusion from the matrix into the fracture porosity controls the chemistry of chalk groundwater

the isotopic composition of radiogenic helium and its use to study groundwater movement in confined aquifers abstract the 3 he 4 he ratio for radiogenic he is shown to be primarily determined by the abundance of li and neutron absorbing elements in the host formations and is almost independent of the radioelement abundance the 3 he 4 he ratios have been computed for various li contents in rock matrices with average abundances of other elements the 3 he 4 he ratio is specific for each formation and may therefore be used to study crustal diffusion of he it is shown however that both the 3he and 4he contents of continental basements are likely to exceed those of the mantle so that diffusion of mantle he through continental crust is not likely to occur changes in the 3 he 4 he ratio for dissolved he have potential for studying groundwater movement and mixing processes atmospheric he which was dissolved at recharge is progressively diluted by radiogenic he with an isotopic ratio characteristic of the aquifer as the groundwater migrates down dip mixing proportions for formation he and atmospheric he in aquifers for which there is admixture of fracture borne water and interstitially stored water can also be estimated from isotopic measurements these processes are discussed in relation to two aquifers in eastern england

hydrochemical and isotopic characterisation of the bathonian and bajocian coastal aquifer of the caen area northern france abstract this paper describes the geochemical evolution of groundwater in the bathonian and bajocian aquifer along its flowpath since this aquifer represents one of the main sources of fresh water supply in the caen area and has been subjected to a holocene marine intrusion its management requires a sound knowledge of 1 the primary conditions and 2 the potential influence of either natural or anthropogenic pressures groundwater vertical sampling validity is discussed with the contribution of high resolution temperature logging the main processes of geochemical evolution along a groundwater flow line and the sea water intrusion characteristics are discussed using ionic concentrations br f and major elements and isotopes water 2 h and 18 o tdic 13 c and a 14 c sulphate 18 o and 34 s as the 13 c content of tdic is used as a tracer of water rock interaction it shows evidence of specific chemical and isotopic evolutions of groundwater within the aquifer both related to water rock interaction and mineral equilibria in groundwater all the above mentioned tracers evolve downflow cation concentrations are modified by exchange with clay minerals allowing a high f concentration in groundwater whereas br and so 2 4 concentrations appear to be redox condition dependant superimposed on these geochemical patterns 18 o and 2 h compositions indicate that aquifer recharge has varied significantly through time the chemical evolution of groundwater is locally affected by a salty water intrusion that is characterised by mixing between flandrian fresh water and sea water which has interacted with peat as evidenced by a high br cl ratio and so 2 4 reduction

finite difference simulations of seismic scattering implications for the propagation of short period seismic waves in the crust and models of crustal heterogeneity synthetic seismograms produced by the finite difference method are used to study the scattering of elastic and acoustic waves in two dimensional media with random spatial variations in seismic velocity the results of this study provide important insights about the propagation of short period 5 the self similar medium is characterized by a scattering q that is constant with frequency whereas theory predicts that the apparent q in an exponential medium is proportional to frequency these alternative models of crustal heterogeneity can thus be tested by improved measurements of the frequency dependence of crustal q at frequencies greater than about 1 hz assuming that scattering is responsible for most of the attenuation at these frequencies measurements of the time decay of the synthetic coda waves clearly show that the single scattering model of coda decay is not appropriate in the presence of moderate amounts of scattering attenuation scattering q 200 in these cases q values derived from the coda decay rate using the single scattering theory do not correspond to the transmission q of the medium the cross correlation of synthetic waveforms observed for an array of receivers along the free surface is observed to be dependent on the correlation distance of the medium the self similar random medium proposed here for the crust produces waveform variations at high frequencies 15 30 hz similar to those reported for actual small scale seismic arrays with apertures of hundreds of meters

the effects of historic abstraction of groundwater from the london basin aquifers on groundwater quality abstract the basal sands and chalk aquifers in the lee valley and enfield haringey areaas of north london have considerable potential for artificial recharge having been dewatered by groundwater abstraction since the late 1800s trials have been undertaken periodically since the mid 1950s however one of the drawbacks is the potential for developing poor quality groundwater as a result of pyrite oxidation in the basal sands analysis of pumped groundwaters from the basal sands has confirmed the presence of relatively high concentrations of dissolved so4 along with k ca total fe and li porewater chemistry profiles have been obtained from fresh cores through the basal sands and underlying chalk at four sites the site with the highest so4 concentration up to 33 000 mg 1 1 had a porewater ph of 3 45 and has remained dewatered owing to overpumping for more than 70 a water pumped from the chalk showed little evidence of these extreme conditions there was no overall correlation between the bulk pyrite or gypsum content of the sediment and the porewater so4 concentration within the sediment the principal mechanism governing the generation of so4 is the oxidation of pyrite which is present in small amounts the extremely high concentrations of so4 in the porewaters indicate that the extent of oxidation is controlled by the entry of air rather than the input of dissolved oxygen or nitrate in the groundwater or recharge water abstraction from the chalk aquifer over many decades has resulted in the dewatering of the overlying basal sands aquifer allowing air entry and has led to the localized oxidation of pyrite and the accumulation of poor quality porewater in the basal sands the rate of oxidation is probably greatest near to wells and boreholes which allow ready access of air the solutes produced are only available for abstraction after the water table has risen dilution with native chalk groundwater will tend to minimize potential water quality problems future oxidation will be minimized by maintaining a high water table

strontium isotopes as tracers of groundwater induced floods the somme case study france major ions trace elements and o h and sr isotopes have been determined for surface water and groundwater in the somme catchment northern france the present study using a coupled hydrological and geochemical stable and sr isotopes approach focuses on the interactions between ground and surface water stable water isotopes 18o 2h show that all waters have a purely local origin from precipitation without significant evaporation or water rock interaction as all points plot close to the general meteoric water line water chemistry in the different catchments shows large variations in major element contents plotting na vs cl contents and mg2 no3 k so42 sr2 concentrations reveals a slight variations in groundwater composition b agricultural input into surface waters and c some similarities between ground and surface waters suggesting the former to be responsible for the chemical signature of the dissolved river load strontium isotope ratios measured in groundwater range from 0 70769 to 0 70808 clearly higher than that of chalk matrix water 0 707337 variations of sr isotope signatures in groundwater from the chalk aquifer are significant and help identifying different groundwater bodies the different signatures in groundwater are better explained by matrix heterogeneity which can present lateral facies variations than by a strong anthropogenic influence the sr isotope compositional range in surface waters is very wide varying from 0 70775 to 0 70816 and defining a trend towards a more radiogenic sr isotope signature with high sr contents and high mg sr ratios the relationship between 87sr 86sr and the mg sr ratios allows different end members to be defined the rivers are influenced by anthropogenic disturbance even during flood periods and river water has geochemical characteristics very similar to those of groundwater indicating a strong influence from groundwater feeding the rivers

baseline geochemical conditions in the chalk aquifer berkshire u k a basis for groundwater quality management the chalk aquifer is the most important british aquifer and is also important over much of northern europe aquifer protection requires a sound knowledge of the baseline conditions and how these might vary or have varied with time this detailed geochemical study of a representative area of chalk in berkshire u k includes a consideration of several components 1 the inputs from the atmosphere 2 the interstitial water of the soil and the unsaturated zone 3 the interstitial water in the confined and unconfined sections of the aquifer and 4 the saturated mainly fissure flow along the hydraulic gradient which forms an important water supply of the thames valley region atmospheric inputs form an important source of some elements but the dominant chemical characteristics of the chalk groundwater are acquired during percolation through the soil and the upper unsaturated zone during saturated flow downgradient the chemistry is modified mainly by incongruent reactions of the carbonate matrix and by redox reactions and only to a minor extent by exchange reactions and mixing with residual saline connate water the incongruent reaction of carbonate results in a marked increase in the mg ca ratio and the sr and 13c contents of the groundwater with increased residence time oxygen concentrations are reduced mainly by oxidation of fe2 and the onset of reducing conditions allows dissolved fe2 to increase and rapid denitrification to occur the salinity profile through the confined chalk confirms that residual connate water up to one fifth sea water concentration still remains at depth and this accounts for some salinity increase in the confined groundwater resulting from fissure water pore water diffusional exchange timescales for groundwater movement have been established using tritium radiocarbon and indirectly using inert gas ratios and stable isotope ratios on balance it is concluded that all abstracted water is of holocene age although inert gas temperatures indicate cooler climatic conditions for recharge for some of the confined groundwater the implications for development and aquifer protection are discussed especially the prospect of natural in situ denitrification problems of fe solubility and the recognition of groundwater of different maturities

chemical characteristics of groundwater in parts of mountainous region alvand hamadan iran eighty seven groundwater samples have been collected from a mountainous region alvand iran for hydrochemical investigations to understand the sources of dissolved ions and assess the chemical quality of the groundwater most water quality parameters are within world health organization acceptable limits set for drinking water the least mineralized water is found closest to the main recharge zones and the salinity of water increased towards the north of the basin the most prevalent water type is ca hco3 followed by water types ca no3 ca cl ca so4 and mg hco3 the ca no3 water type is associated with high nitrate pollution agricultural and industrial activities were associated with elevated level of no3 mineral dissolution weathering of evaporites dominates the major element hydrochemistry of the area chemical properties of groundwater in alvand region are controlled both by natural geochemical processes and anthropogenic activities

helium accumulation in groundwater ii a model for the accumulation of the crustal 4he degassing flux abstract a model of 4 he accumulation in a confined aquifer is presented which includes in situ production and a crustal degassing flux of 4 he into the bottom of a confined aquifer the model is consistent with the measurements of 4 he concentration in the great artesian basin australia torgersen and clarke 1985 and also with the measurements of 4 he concentration in the auob sandstone of namibia heaton 1981 the measured value of the crustal degassing flux of 4 he from these two areas is comparable with the 4 he degassing flux calculated from the atmospheric budget of 4 he wasserburg et al 1963 ozima and podosek 1983 a literature review suggests that a crustal degassing 4 he source may account for the 4 he accumulation in many other groundwater systems it is concluded from the literature review the detailed modelling of 4 he accumulation in gab and the auob sandstone and the atmospheric budget that crustal degassing of 4 he may be a common and widespread phenomena

carbon isotope exchange rate of dic in karst groundwater abstract the kinetics of isotopic exchange between dissolved inorganic carbon dic of groundwater and calcite of the matrix of karst aquifers of cyrenaica libya can be deduced from 13 c and 14 c data the aquifers are mostly confined and the majority of the wells do not show any occurrence of modern recharge in 1976 1980 in fact the tritium content was below 1 tritium unit tu in most sites assuming that the isotopic exchange takes place through a first order reaction such as 14 c radioactive decay it can be shown that a linear correlation occurs between ln a and ln m e p where a is the 14 c activity m and are the 13 c contents of matrix calcite and dic respectively and e p is the 13 c enrichment in caco 3 precipitation the slope of the correlation provides the half life of the isotopic exchange process for cyrenaica karst groundwater a half life of about 11 000 years is obtained i e about double that of 14 c radioactive decay the isotopic exchange kinetics also depends on the ratio between groundwater volume and the calcite surface exposed to the exchange process thus other aquifers will show different exchange half life values the cretaceous chalk aquifers of the paris basin france and lagerdorf germany give a half life of about 4000 years much shorter than that of cyrenaica which may be due to the high porosity i e to the large surface available for the isotope exchange process the berkshire chalk aquifer uk gives a half life of about 10 000 years much higher half lives above 20 000 years are obtained for two sandy aquifers in flevoland the netherlands and texas usa which could be explained by the low caco 3 content of the aquifer matrix the highest half life value about 40 000 years is obtained in an artesian limestone aquifer in florida usa

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

vanadium geochemistry along groundwater flow paths in contrasting aquifers of the united states carrizo sand texas and oasis valley nevada aquifers abstract vanadium v concentrations were measured along the flow paths in two contrasting aquifer systems to study how changing solution composition and redox conditions affect v cycling and transport in groundwater flow systems the oasis valley groundwater system in nevada is an unconfined system where groundwaters generally remain oxic along the flow path whereas the carrizo sand aquifer is a deep confined coastal plain aquifer in texas that contains well defined fe iii and so 4 2 reduction zones along the flow path speciation modeling predicts that in groundwaters from the oasis valley v chiefly occurs as the vanadate oxyanion e g h 2 vo 4 hvo 4 2 which is mobile along the entire flow path because of vanadate s solubility in oxic and alkaline waters furthermore the data indicate that v concentrations increase in groundwaters along the flow path suggesting that mineral dissolution and or desorption reactions progressively contribute v to groundwaters of the oasis valley system geochemical modeling is consistent with dissolution of mafic phenocrysts that are common in the local tuffaceous aquifer rocks as a probable source of v to oasis valley groundwaters within the carrizo sand aquifer groundwater v concentrations decrease with flow beyond the recharge zone and into the confined portion of the aquifer thereafter total v concentrations remain low and relatively constant along the remainder of the studied flow path exhibiting no systematic variations across the fe iii and so 4 2 reduction zones groundwaters from the carrizo sand aquifer are generally reducing and as such geochemical modeling suggests that both v v and v iv species occur in carrizo sand groundwaters and furthermore that the proportion of v iv species increases concurrent with the decrease in total v concentrations along the flow path results from sequential extraction experiments on carrizo sand aquifer sediment samples suggest that v adsorption onto fe iii mn iv oxides oxyhydroxides acts to decrease the aqueous v concentrations in carrizo sand groundwater furthermore geochemical modeling is consistent with complexation of v iv with dissolved organic matter dom within the carrizo sand aquifer groundwaters which owing to the low dom concentrations appears to buffer v at low but relatively constant concentrations within the confined and reducing carrizo sand groundwaters these results support previous reports of v iv dom binding and imply that aquifer material maintains an essential role in not only determining the availability of v to enter aqueous solution but also in influencing partitioning between solid and aqueous phases

site amplification of coda waves from local earthquakes in central california the goals of this study are two fold 1 to examine the site effect of coda waves believed to be the average site effect of shear waves in order to understand its spatial and frequency dependent behavior and 2 to learn what we can about the processes that generate the coda itself we use digital data from over 90 earthquakes each recorded by a subset of some 150 stations in the coast ranges of central california between san francisco and san luis obispo results from the band 1 5 to 24 hz indicate that site amplification depends strongly on surface geology and frequency at low frequencies 1 5 to 3 0 hz changes in amplification up to a factor of 20 are observed amplification generally varies inversely with deposit age at sediment sites and is lowest at granite and franciscan basement sites at high frequencies 6 to 24 hz the pattern changes many granite sites the majority in the gabilan range exhibit increasing amplification with frequency relative to the average station this behavior differs strikingly from that observed at sediment and franciscan sites which roll off at an intermediate rate and many sediment sites adjacent to the san andreas fault zone which decay away even more rapidly with frequency these results can be explained qualitatively by appealing to variable near site impedance and attenuation however complicating phenomena such as mode excitation in valley sediments must exist at low frequencies peaked behavior at a few hard rock sites at high frequency 12 hz currently lacks explanation at a few sediment sites the low frequency excitation is so strong that the coda envelopes begin to take on different shapes this contradicts the assumption based on previous observations that the coda shape is independent of source receiver location thus some site measurements may be artificially high the working model of coda waves as body wave energy backscattered from randomly distributed inhomogeneities must be modified to include the possibility of efficient near site resonance excited by incident direct and coda wave energy

fluid control of localized mineral domains in limestone pressure solution structures grain to grain and stylolitic solution structures in two central appalachian siluro devonian limestone macroscale folds contain one of four distinct mineral assemblages that are characterized by the dominant iron phase mineral present 1 chloritegillitegpyritegcalciteg quartzgtio2ggoethite 2 chloritegillitegpyrite altered to iron oxide hydroxidegcalcite gquartzgtio2 3 chloritegilliteg magnetitegcalcitegquartz and 4 chloritegilliteggoethitegcalcitegquartzgtio2 optical reflectance microscopy and sem eds was used to characterize the mineralogy and mineral morphology of these structures geochemical modeling was used to constrain the conditions of formation and preservation the primary control on solution structure mineral assemblage was the redox conditions present in the solution structures during burial and deformation the redox conditions on the microscale may have been controlled by the local fluid chemistry and the presence absence of hydrocarbons and organic acids within the formation fluids and the influx of externally derived fluids by fracture formation during the folding process the wide variation in mineralogy of the solution structures shows that they were chemical factories where a variety of chemical reactions took place during rock dissolution in particular the formation of authigenic magnetite in solution structures has significant implications for paleomagnetic applications and use of anisotropy of anhysteretic remanent magnetization and anisotropy of magnetic susceptibility fabrics q 2005 elsevier ltd all rights reserved

heterogeneous behaviour of unconfined chalk aquifers infer from combination of groundwater residence time hydrochemistry and hydrodynamic tools chalk groundwater is an important aquifer resource in france and also in much of northwestern europe large areas between the paris basin the london basin denmark and the northwest of germany as it is intensively exploited for human use with a large proportion reserved for drinking water the improvement of the knowledge on chalk aquifer hydrodynamical functioning and groundwater geochemistry is essential for the management of this resource to achieve this aim we developed a methodology based on a combination of hydrodynamic hydrochemistry and groundwater dating tools a study site of about 500 km2 was selected in ne france where chalk outcrops at 15 sampling points including boreholes and rivers mainly from chalk aquifer drainage groundwater geochemistry were monitored monthly for 2 years from june 2017 to june 2019 groundwater level in boreholes were monitored hourly with in situ water loggers in addition two sampling campaigns for the analysis of cfcs and sf6 have been conducted in boreholes in high and low water level periods to define the groundwater residence time the aquifer at the majority of sampling sites has an inertial behavior with respect to recharge as no impact of individual rainfall event was observed rapid piezometric response following rainfalls was observed at one site suggesting the presence of locally highly developed fracture network contrariwise high spatial and temporal heterogeneities of geochemistry was observed on the study area according to the mixing process piston flow exponential or binary mixing defined at each sampling site groundwater dating indicated rather heterogeneous ages ranging from less than 20 years to more than 50 years a combination of hydrogeological setting residence time and land use information was used to explain the hydrochemical heterogeneities highlighting the main factors governing the chalk groundwater geochemistry including water level fluctuation thickness of the unsaturated zone superficial formations distribution of fracture network aquifer river relations and human activities a conceptual model was proposed to clarify the hydrogeosystem functioning of unconfined chalk aquifers the proposed methodology can be used for the study of other worldwide aquifers chalk or not with the aim to provide appropriate recommendations in terms of water management

spatial heterogeneity of high resolution chalk groundwater geochemistry underground quarry at saint martin le noeud france chalk groundwater is an important aquifer resource in france because it accounts for a production of 12 million m3 y 1 with a large proportion reserved for drinking water processes occurring in the unsaturated zone uz and the overlying superficial formations have a high impact on chalk groundwater geochemistry and require better understanding the study site is a former underground chalk quarry located near beauvais france that extends over 1200 m in length at a depth ranging from 20 to 30 m the water table intersects the cavity creating 15 underground lake that give access to the chalk groundwater lakes geochemistry has been studied water samples were collected in july 2013 and major ion concentrations were analyzed uz and clay with flints thickness above each lake were estimated qualitatively using an electromagnetic sensor em31 and underground gps the results unexpectedly showed that groundwater quality varied widely in spatial terms for both allochthonous and autochthonous ions e g hco3 ranged from 2 03 to 4 43 meq l 1 no3 ranged from 0 21 to 1 33 meq l 1 principal component analysis indicated the impact of agricultural land use on water quality with the intake of no3 as well as so42 cl and ca2 chalk groundwater geochemistry is compared with the nature and structure of the uz we highlight correlations 1 between thick clay with flints layers and the ions mg2 and k and 2 between uz thickness and na in conclusion this paper identifies various ion sources agriculture clay with flints and chalk and demonstrates different processes in the uz dissolution ionic exchange and solute storage

a seismic refraction study of the santa clara valley and southern santa cruz mountains west central california abstract two seismic refraction profiles were recorded in the santa clara valley region of central california to determine the upper crustal seismic velocity structure a reversed 8 km long profile was recorded across the valley near gilroy and an unreversed 38 km long profile was recorded in the southern santa cruz mountains the data indicate that the valley is wedge shaped in cross section with the basement dipping 10 to the east the alluvial fill of the valley has a maximum thickness of 1 5 km and has an average compressional wave velocity of 2 3 km sec the top of the basement has a velocity of 4 3 km sec the velocity reaches 6 0 km sec at a depth of 2 km the calaveras fault zone located due east of the valley was crossed by a short unreversed profile it appears to be characterized by a low velocity v p 2 7 km sec to a depth of 2 5 km the southern santa cruz mountain profile indicates a 4 6 km sec near surface refractor and a layer with a velocity of 6 1 km sec at 2 km depth thus considered together the similarity in velocity structure determined from the two profiles indicates that the franciscan rocks of the santa cruz mountains continue beneath the valley the presence of high compressional wave velocities 6 0 km sec at 2 km depth in this franciscan terrain can best be explained by an abundance of metabasalts greenstones at that depth these seismic observations indicate that an area of at least 120 km 2 is underlain by this high velocity basaltic material therefore the upper crustal structure in the study area differs dramatically from the franciscan terrain of the diablo range where greywackies and metagreywackies v p 5 4 km sec dominate in the uppermost crust

isotopic evidence for palaeowaters in the british isles before the 20th century groundwater circulation in the aquifers of the british isles had largely adjusted to the temperate maritime climate and sea levels established over the past 10 ka since the end of the pleistocene however in the last 100 a this natural regime has been disturbed by abstraction of water for public supply and industrial use and palaeowaters from earlier recharge episodes are now becoming a factor to be considered in water balance estimates this paper presents a synthesis of the existing palaeowater distribution in the british isles based on isotopic evidence 18o 2h and and14c as such it has relevance to palaeoclimatic studies in addition to the water resource implications the triassic basins of england and northern ireland contain saline waters beyond the range14c dating 40 ka stable isotopic ratios show enrichment in some basins and depletion in others without an overall pattern that would explain all the observed compositions the results for the wessex basin suggest recharge in pre quaternary times but for the other basins some flushing by pleistocene or holocene meteoric waters is indicated isolated occurrences of apparently long residence waters are found elsewhere throughout the british isles for example from carboniferous and lower palaeozoic strata in such cases environmental isotopes are more useful as constraints on hydrogeological models than as indicators of palaeoconditions major water supply aquifers are restricted almost entirely to england the two sandstone formations triassic sherwood sandstone and cretaceous lower greensand have a greater range of stable isotopic values between phreatic and confined conditions than the two carbonate formations jurassic lincolnshire limestone and cretaceous chalk this indicates that the sandstone aquifers are better archives of information on palaeoconditions than the carbonate aquifers they show that atmospheric circulation patterns over britain have probably remained the same since the late pleistocene however 14c data from all four of the major aquifers emphasise the hiatus in recharge during periglacial conditions which occurred between the late pleistocene and early holocene

attenuation of coda waves in northern greece the single scattering model has been applied for the estimation of codaq values for local earthquakes that occurred in northern greece during the period 1983 1989 and recorded by the telemetered network of the geophysical laboratory of the university of thessaloniki codaq estimations were made for four frequency bands centered at 1 5 hz 3 0 hz 6 0 hz and 12 0 hz and for the lapse time windows 10 20 sec 15 30 sec 20 45 sec 30 60 sec and 50 100 sec the codaq values obtained show a clear frequency dependence of the formq c q 0 f n whileq 0 andn depend on the lapse time window q 0 was found equal to 33 andn equal to 1 01 for the time window of 10 to 20 sec while for the other windowsq 0 increased from 60 to 129 withn being stable close to 0 75 this lapse time dependence is interpreted as due to a depth dependent attenuation the high attenuation and the strong frequency dependence found are characteristic of an area with high seismicity in agreement with studies in other seismic regions

spatial variation of crustal coda q in california coda wave data from california microearthquakes were studied in order to delineate regional fluctuations of apparent crustal attenuation in the band 1 5 to 24 hz apparent attenuation was estimated using a single back scattering model of coda waves the coda wave data were restricted to 30 s following the origin time this insures that crustal effects dominate the results as the backscattered shear waves thought to form the coda would not have had time to penetrate much deeper results indicate a strong variation in apparent crustal attenuation at high frequencies between the franciscan and salinian regions of central california and the long valley area of the sierra nevada although the coda q measurements coincide at 1 5 hz q c 100 at 24 hz there is a factor of four difference between the measurements made in franciscan q c 525 and long valley q c 2100 with the salinian midway between q c 900 these are extremely large variations compared to measures of seismic velocities of comparable resolution demonstrating the exceptional sensitivity of the high frequency coda q measurement to regional geology in addition the frequency trend of the results is opposite to that seen in a compilation of coda q measurements made worldwide by other authors which tend to converge at high and diverge at low frequencies however the worldwide results generally were obtained without limiting the coda lengths and probably reflect upper mantle rather than crustal properties our results match those expected due to scattering in random media represented by von karman autocorrelation functions of orders 1 2 to 1 3 the von karman medium of order 1 3 corresponding to the franciscan coda q measurement contains greater amounts of high wavenumber fluctuations this indicates relatively large medium fluctuations with wavelengths on the order of 100 m in the highly deformed crust associated with the franciscan however the influence of scattering on the coda q measurement is currently a matter of controversy

modelling the baseline geochemistry of groundwater in a chalk aquifer considering solid solutions for carbonate phases the chalk aquifer of champagne france baseline geochemistry has been determined using a solid solution approach for the modelling of calcite dissolution the water rock interactions are modelled by the speciation code chess from field data and ca mg and sr aqueous concentrations in groundwater the stoichiometries of solid solutions are defined in each stratigraphic unit of the chalk aquifer from bulk geochemistry and chalk mineralogy of samples taken from boreholes the initial mineralisation of water at the bottom of the unsaturated zone and the characterisation of the theoretical evolution of groundwater chemistry along the flow lines associated with incongruent calcite dissolution are calculated from this approach

residence time of chalk groundwaters in the paris basin and the north german basin a geochemical approach the comparative geochemical and isotopic study of confined and unconfined chalk groundwaters of the paris basin and the n german basin proves a significant chemical evolution during groundwater flow from the recharge zones to the deep confined aquifer different time dependent geochemical parameters have been tested as dating tools cation ratios sr2 ca2 mg2 ca2 n no 3 noble gas contents as paleotemperature indicators ne ar kr xe radiogenic he 13c 14c 18o 2h 3h cation ratios and 13c show the importance of incongruent dissolution processes in the chalk aquifer water rock interactions were taken into account in a multi step dissolution model to determine radiocarbon groundwater ages the oldest waters in the confined part of the paris basin chalk with maximum 14c ages of 14 000 a b p contain pleistocene recharge components as can be shown by a stable isotope depletion and noble gas temperatures significantly lower than in recent groundwaters chalk waters at the lagerdorf site in northern germany show a distinct stratification with respect to residence times and hydrochemistry

frequency dependent characteristics of coda wave quality factor in central and southcentral alaska coda wave quality factor q c was investigated by using digital data 100 sample sec 1 recorded by a vertical component short period station installed for this study the station was located in the greater fairbanks area in central alaska from several hundred earthquakes recorded by this station in about a year 27 earthquakes were selected for the above study 7 of these selected earthquakes were located along the alaska wadati benioffzone pacific plate the other 20 earthquakes were located in the area of intraplate seismicity north american plate the data was filtered using 9 pass bands with center frequency varying from 1 5 hz to 16 hz with octave bandwidth the values of q c obtained from the coda amplitude decay rates measured on the filtered data after corrections due to the recording instrument and source receiver separation show appreciable frequency dependence the value of q c varies in the range of 253 and 1190 corresponding to the frequency interval from 1 5 hz to 16 hz for the study area this variation is close to that reported by others for the kanto region of japan moreover the characteristics of q c obtained in the present case seem to be independent of epicentral distance and hypocentral depth

kinematics of rotating panels of e w faults in the san andreas system what can we tell from geodesy summary sets of e to ne trending sinistral and or reverse faults occur within the san andreas system and are associated with palaeomagnetic evidence for clockwise vertical axis rotations these structures cut across the trend of active dextral faults posing questions as to how displacement is transferred across them geodetic data show that they lie within an overall dextral shear field but the data are commonly interpreted to indicate little or no slip nor any significant rate of rotation we model these structures as rotating by bookshelf slip in a dextral shear field and show that a combination of sinistral slip and rotation can produce the observed velocity field this allows prediction of rates of slip rotation fault parallel extension and fault normal shortening within the panel we use this method to calculate the kinematics of the central segment of the garlock fault which cuts across the eastern california shear zone at a high angle we obtain a sinistral slip rate of 6 1 1 1mmyr 1 comparable to geological evidence but higher than most previous geodetic estimates and a rotation rate of 4 0 0 7 myr 1 clockwise the western transverse ranges transect a similar shear zone in coastal and offshore california but at an angle of only 40 as a result the faults which were sinistral when they were at a higher angle to the shear zone have been reactivated in a dextral sense at a low rate and the rate of rotation of the panel has decreased from its long term rate of 5 to 1 6 0 2 myr 1 clockwise these results help to resolve some of the apparent discrepancies between geological and geodetic slip rate estimates and provide an enhanced understanding of the mechanics of intracontinental transform systems

the curved 14c vs δ13c relationship in dissolved inorganic carbon a useful tool for groundwater age and geochemical interpretations abstract determination of the 14c content of dissolved inorganic carbon dic is useful for dating of groundwater however in addition to radioactive decay the 14c content in dic 14cdic can be affected by many geochemical and physical processes and numerous models have been proposed to refine radiocarbon ages of dic in groundwater systems changes in the 13c content of dic 13cdic often can be used to deduce the processes that affect the carbon isotopic composition of dic and the 14c value during the chemical evolution of groundwater this paper shows that a curved relationship of 14cdic vs 13cdic will be observed for groundwater systems if 1 the change in 13c value in dic is caused by a first order or pseudo first order process e g isotopic exchange between dic and solid carbonate 2 the reaction process progresses with the ageing of the groundwater i e with decay of 14c in dic and 3 the magnitude of the rate of change in 13c of dic is comparable with that of 14c decay in this paper we use a lumped parameter method to derive a model based on the curved relationship between 14cdic and 13cdic the derived model if used for isotopic exchange between dic and solid carbonate is identical to that derived by gonfiantini and zuppi 2003 the curved relationship of 14cdic vs 13cdic can be applied to interpret the age of the dic in groundwater results of age calculations using the method discussed in this paper are compared with those obtained by using other methods that calculate the age of dic based on adjusted initial radiocarbon values for individual samples this paper shows that in addition to groundwater age interpretation the lumped parameter method presented here also provides a useful tool for geochemical interpretations e g estimation of apparent rates of geochemical reactions and revealing the complexity of the geochemical environment

geochemistry s vital contribution to solving water resource problems abstract as part of the events celebrating 40 a of iagc it is fitting to trace the modern evolution and development of hydrogeochemistry however fascination with water quality can be traced back more than 2 ka in the post war years hydrogeochemistry was influenced heavily by the advances in other disciplines including physical chemistry metallurgy and oceanography hydrological applications of isotope science also developed rapidly at this time and important advances in analytical chemistry allowed multi element and trace element applications to be made experimental studies on equilibrium processes and reaction kinetics allowed bench scale insight into water rock interaction consolidation of knowledge on processes in groundwaters and the current awareness of hydrogeochemistry by water professionals owe much to the work of robert garrels john hem and co workers in the early 1960s studies of down gradient evolution enabled a field scale understanding of groundwater quality and geochemical processes as a function of residence time dissolution and precipitation processes in carbonate and non carbonate aquifers redox processes cation exchange and salinity origins emerging water resource and water quality issues in the 1960s and 70s permitted the application of hydrogeochemistry to contaminant and related problems and this trend continues the impacts of diffuse pollution from intensive agriculture waste disposal and point source pollution from urban and industrial sources relied on geochemistry to solve questions of origin and attenuation in semi arid regions facing water scarcity geochemical approaches have been vital in the assessment of renewability and characterising palaeowaters the protection and new incoming regulation of water resources will rely increasingly on a sound geochemical basis for management

nature and origin of authigenic rhodochrosite and siderite from the paleozoic aquifer northeast mississippi u s a abstract botryoidal rhodochrosite siderite and pyrite are the principal authigenic phases in fractured chert comprising the paleozoic aquifer of northeast mississippi locally alternating bands of near end member composition rhodochrosite and siderite occur in veinlets up to 2 mm wide in the fractured chert carbon isotope data for the carbonates 13c values ranging from 9 6 to 11 3 pdb indicate that both inorganic and organic c were incorporated into the authigenic phases the paleozoic aquifer is hydraulically connected with the overlying upper cretaceous coastal plain strata groundwater in the coastal plain units is undersaturated with respect to calcite and has relatively high fe and mn contents the latter apparently caused by the dissolution of fe mn oxyhydroxides the natural downward recharge of these waters into the paleozoic aquifer causes calcite dissolution in limestone at the base of the chert which in turn leads to the precipitation of rhodochrosite and siderite additionally pyrite is precipitated as so4 reduction occurs in the same zone rhodochrosite has not been previously documented as an authigenic phase in a fresh water aquifer system suggesting that the geochemical environment necessary for its precipitation is not common the alternating bands of rhodochrosite and siderite observed in this study coupled with available thermodynamic data indicate that the groundwater a mn2 afe2 ratio must have fluctuated over time variations in the ratio are best explained by variable eh conditions at the site where fe mn oxyhydroxide dissolution occurs

a precursorlike change in coda excitation before the western nagano earthquake ms 6 8 of 1984 in central japan temporal variations of coda duration were studied in relation to a crustal earthquake september 14 1984 which took place near the nw corner of the kanto tokai microearthquake observation network of the national research center for disaster prevention in japan vertical seismograms recorded at station ger close to the main shock epicenter 24 km between february 1982 and december 1984 were analyzed a precursorlike change was found in the relation between coda duration and average magnitude for 185 earthquakes which occurred in a small volume in the middle of the aftershock region the average magnitude is the arithmetic mean of station magnitudes which are calculated from the maximum amplitudes of direct waves coda durations for earthquakes of the same average magnitude were significantly longer during the 16 month period preceding the main shock than those before and after this period with a confidence level of 99 9 the increase in coda durations was about 3 s on average in this period the coda duration anomaly was significant for lapse time shorter than 30 s which corresponds to a travel radius less than 50 km although no clear temporal change was found in the residuals of station magnitude measured at ger from average magnitude an attenuation change in the preevent period can not be ruled out due to the large scatter of data crack formation however is the most plausible mechanism for an increase in scattering intensity around the focal region in the stress accumulation stage and is consistent with other precursory observations clusters of cracks in the heterogeneous earth medium might be big enough to scatter high frequency seismic waves even though each individual crack may be very small

seismic albedo from the total seismic energy dependence on hypocentral distance in southern california abstract scattering and absorption of seismic waves have been studied in southern california to determine their respective contributions to the measured apparent attenuation we measured the total seismic energy from the onset of the s waves for local earthquakes recorded at stations on granitic rock reduced to a common source by eliminating the source and site effect by the coda method then applied wu s method based on the radiative transfer theory which has the facility to separate the intrinsic absorption from the scattering effect the observed total energy as a function of hypocentral distance exhibits a striking behavior increasing to a maximum at about 50 km then decreasing exponentially as a function of hypocentral distance decay of the total energy as a function of distance is remarkably similar for all frequency bands centered at 1 5 3 0 6 0 and 12 0 hz in good agreement with earlier results on q of coda and s waves in southern california comparison with wu s theoretical plots which shows curves that differ in shape because of differences in seismic albedo if b 0 s s a where s and a are the scattering and absorption coefficients respectively leads to the conclusion that the s wave energy is primarily redistributed in space by scattering rather than intrinsically absorbed by the earth our results from southern california agree with those of toksoz et al who found seismic albedo b0 to be 0 8 0 9 in eastern north america coda q in southern california however closely agrees with scattering q using wu s model in disagreement with the conclusions of toksoz et al for eastern north america where coda q is close to the absorptive q obtained from the total energy study the agreement between wu s theoretical curves and our observations is not perfect departure of the observed curves from the theory may be due in part to inhomogeneous distribution of scatterers and absorbers as well as non isotropic scattering we need more realistic models which can also account for inhomogeneous bounded media

properties of scattered elastic waves in the lithosphere of kamchatka parameters and temporal variations abstract records of near earthquakes from the shipunsky station were used to estimate s wave absorption for seven frequency bands ranging from 0 4 to 24 hz three techniques were employed and three rows of consistent estimates were obtained two of the three techniques give estimates that are independent of q anisotropic scattering was studied by observing the broadening of the s wavelet the estimates obtained show that anisotropic scatter may be significant the time variation of the coda envelope shape was studied using the records of 1 s regional seismographs three epicentral regions were chosen in the kurile kamchatka zone where m 8 earthquakes have occurred time series of the parameter which is the anomaly of the logarithmic steepness of coda envelope were constructed for vertical and horizontal channels of several stations pronounced forerunner type variations of were revealed we show that the probable cause of these variations is a qs decrease in the vicinity of impending m 8 earthquake this decrease is about 20 with a lead time of about a year the forerunner anomaly is not of the bay type and recovers 1 2 years after a large earthquake

stability of coda q in the region of parkfield california view from the u s geological survey parkfield dense seismograph array many investigators have proposed that changes in the rate at which the coda decays may be an intermediate term precursor to moderate to large earthquakes parkfield california on the san andreas fault is a promising location for studying premonitory changes in coda q qc because a large earthquake is likely to occur there we have investigated qc using recordings from the u s geological survey parkfield dense seismograph array which is a digital array with 14 triaxial sensors and an aperture of about 1 km for each earthquake we can measure qc from up to 42 recordings their average is more stable than the measurement from a single station using clustered seismicity we have developed criteria for selecting events and reducing scatter in the measurement the qc value determined from a seismogram depends on the position and length of the analysis window thus qc should always be measured from the same length window starting at the same lapse time regardless of the source location in addition the band limited signal to noise ratio at the end of the analysis window is important qc determined in two frequency bands 4 8 hz and 8 16 hz from a tight cluster of 26 events which occurred between december 1989 and january 1994 has not changed despite m 4 7 and m 4 6 events in october 1992 and november 1993 qc measured from local events 60 km in three frequency bands shows larger scatter but has also not changed during this period for monitoring qc observations should include array averaged measurements from a single lapse time because qc measurements made using an analysis window that starts at a constant multiple of the s wave lapse time depend on epicentral distance a procedure combining the evaluation of the time and distance dependences of qc also gives stable observations

chemical evolution of groundwater in the river danube deposits in the southern part of the pannonian basin hungary processes controlling the groundwater chemical composition were studied in the river danube deposits in the southeastern part of hungary phreeqm a combined geochemical and one dimensional transport model and phreeqe netpath and wateqf geochemical computer codes were used to simulate these processes the main processes controlling water chemistry are equilibrium with calcite undersaturation in dolomite and albite weathering in the recharge area ion exchange along the flow path and ion exchange and mixing with old water at the end of the flow path ion exchange seems to be the most important process controlling groundwater chemistry along the flowpath in the fluvial sediments studied isotopic data support the geochemical model the groundwater ages adjusted for the modeled c mass transfer range from 3300 to 20 200 a b p cation exchange suggests that displacement of a former aqueous solution by the present groundwater occurred this displacement is attributed to tectonic and paleoclimatic events at the end of the pleistocene

the influence of pre devensian glacial deposits on the hydrogeochemistry of the chalk aquifer system of north norfolk uk the distribution of hydrochemical facies in the chalk aquifer system of north norfolk uk is interpreted to reveal the hydraulic and hydrogeochemical processes operating in the area the occurrence of two distinct glacial tills covering the chalk aquifer is shown to dominate aquifer conditions chalk groundwater in the interfluve regions covered by chalky boulder clay is characteristically of the order of 10 000 years old and compares with chalk groundwater of about 1000 2000 years old in areas covered by north sea drift the difference in age reflects the different mechanical compositions of the two glacial tills with the chalky boulder clay containing a higher clay content and lower sand content than the north sea drift hydrochemically chalk groundwater from beneath chalky boulder clay is distinguished from groundwater associated with north sea drift by a hco3 concentration of 300 mgl 1 with higher values occurring beneath chalky boulder clay the reason for the difference is that recharge water entering the carbonatedepleted soils developed on north sea drift attains calcite saturation for low values of soil pco2 in the range 10 2 5 10 2 0 whereas recharge entering carbonate rich soils developed on chalky boulder clay achieves calcite saturation for higher values of soil pco2 in the range 10 2 1 10 2 0 additionally pyrite oxidation and so4 reduction associated with the chalky boulder clay interfluve regions evolve further hco3 and to maintain calcite equilibrium increase the dissolved pco2 of the chalk groundwater in the interfluve regions mg sr and sio2 are able to increase because of the groundwater residence time which favours incongruent dissolution of the rock carbonate and breakdown of clay minerals contained in the glacial deposits and the chalk in contrast modern valley zone chalk groundwaters contain high concentrations of no3 up to 120 mgl 1 so4 up to 130 mgl 1 and cl up to 100 mgl 1 contributed by contamination mainly from an agricultural source the hydrochemical interpretation demonstrates that the varying glacial deposits are important in controlling recharge and groundwater flow within the chalk aquifer the chalk aquifer in the interfluvial areas experiences minor recharge whereas the chalk in the valley zone receives direct modern recharge water at the fluvial margin glacial sands and gravels control the storage and release of water transferred laterally through the glacial tills to the high transmissivity chalk in the valley zone

coda q before the 1983 hawaii ms 6 6 earthquake abstract coda q values were derived for more than 300 microearthquakes that occurred in a 6 yr period before the 16 november 1983 kaoiki hawaii earthquake m s 6 6 the sources were located within a 14 16 km rectangular region surrounding the main shock epicenter and most of them occurred at depths between 5 and 10 km digital recordings from three stations at epicentral distances ranging from 0 to 18 km were used coda q was calculated from the amplitude decay rate of the s wave coda in nine frequency bands from 4 5 to 27 hz the average q of the nw part of the studied area is about 15 per cent higher than that of the se part these two subregions also showed differences in seismicity b value and microearthquake source mechanisms in the high q volume the b value was 1 0 and the rate of earthquakes per unit volume was about 50 per cent of the rate in the low q volume where b 1 3 one interpretation of these observations is that more extensive faulting in the se kaoiki fault zone leads to lower q higher b value and a higher seismicity rate during the 5 to 6 yr before the mainshock the 1 yr average q values were stable no significant q change could be identified as a precursor to the main shock

temporal change in coda associated with the round valley california earthquake of november 23 1984 seven thousand seismograms of small earthquakes in the mammoth lakes bishop area were used to measure values of q from the decay of the earthquake coda these measurements were compared between events that occurred before and after the round valley earthquake m 5 7 we found that in regions near the main shock epicenter measurements of coda q 1 for earthquakes that occurred after the main shock were higher than for those earthquakes that occurred prior to the main shock the opposite behavior was found for regions farther away from the main shock namely lower coda q 1 after the main shock than before measurements of coda q 1 in the long valley caldera outside of the immediate source region of the earthquake were higher than in surrounding areas before the main shock but the difference disappeared after the occurrence of the main shock this indicates that the temporal variation in coda q 1 is comparable to its spatial variation the doughnut model seismicity quiescence surrounded by a zone of activity which was invoked for explaining the precursory seismicity pattern appears to be similar with the observed coda q 1 variation associated with the round valley earthquake the observed spatial variations in coda q 1 also help to reconcile conflicting results published in previous studies of the coda q 1 precursor

recent localised sulphate reduction and pyrite formation in a fissured chalk aquifer reply reduction oxidation reactions in the london basin aquifer system how may they be investigated

regionalization of crustal coda q in the continental united states a contour map of crustal q sub 0 values for the entire united states is presented based on a scattering model to explain the coda waves of local and near regional earthquakes these coda q sub 0 values are in good agreement with q of lg waves data are obtained from over 250 local earthquakes with most magnitudes between 3 0 and 5 0 recorded by 25 wwssn and 27 lrsm stations throughout the continental united states these two sets of data provide a range of frequencies from 0 5 to 3 5 hz a frequency dependence of q is observed in the range of frequencies considered a power law dependence of the form q q sub 0 f f sub 0 sup eta is assumed the value of frequency dependence eta is found to be maximum in the tectonically active western united states and least in the stable regions of the central and south central united states the lowest q sub 0 values are obtained in the western united states with values ranging from 140 to 200 in the coastal plains average crustal q sub 0 values for the basin and range province vary from 200 to 300 increasing gradually to 400 in the colorado plateau region q sub 0 valuesmore in the columbia plateau vary from 200 to 400 q sub 0 values increase very rapidly along the central and southern rocky mountains from 400 to 800 east of the rocky mountains q sub 0 values increase gradually in the interior plains to a maximum value of around 1300 in the mississippi embayment region farther east q sub 0 values decrease gradually to an almost constant value of 1000 along the appalachian mountains coastal regions of eastern and northeastern united states have a crustal q sub 0 value between 900 to 700 regions of north central and gulf coastal plains show low q sub 0 values ranging from 600 to 400 and less the source factor b f sub p a measure of the intensity of scattering was obtained for several different regions of the continental united states regions of high q sub 0 values exhibit low intensity of scattering less

hydrochemical trends palaeorecharge and groundwater ages in the fissured chalk aquifer of the london and berkshire basins uk the hydrochemical radiochemical stable isotope 14c and dissolved noble gas composition of groundwaters has been determined along two profiles across the confined fissured chalk aquifer of the london basin of southern england and for selected sites in the adjacent berkshire basin during downgradient flow in the london basin aquifer the groundwater chemistry is modified by water rock interactions congruent and incongruent reaction of the carbonate lithology resulting in enhanced mg ca and sr ca ratios and 13c contents with increased residence times redox and ion exchange reactions and towards the centre of the basin mixing with a residual saline connate water stored in the chalk matrix there is evidence from anomalous water chemistries for a component of vertical leakage from overlying tertiary beds into the confined aquifer as a result of historical dewatering of the aquifer dissolved noble gas contents indicate the climate was up to 4 5 c cooler than at present during recharge of the waters now found in the centres of both basins stable isotope 2h and 18o depletions correspond to this recharge temperature change for evolved waters having 13c 8 pdb a negative linear correlation is demonstrated between derived recharge temperatures and 13c values which is interpreted as mixing between relatively warm light isotopic fracture borne waters and cooler stored waters of the matrix having a 13c signature more or less equilibrated with the chalk from geochemical 14c 4he age estimates the abstracted water is interpreted as being either of wholly holocene post devensian glacial origin or an admixture of holocene and late pleistocene pre glacial cold stage interstadial recharge devensian pleniglacial stage waters of the last glacial maximum are not represented

identification of connate water in interstitial solution of chalk sediment interstitial solution was recovered from core samples of a borehole through 472 m of the upper cretaceous chalk formation in eastern england the solution has been analysed for major and some minor components and also for oxygen and hydrogen isotopic composition samples of the carbonate rock have also been analysed following acid dissolution the general feature of interstitial solution chemistry is a progressive dilution of dissolved species with decreasing depth from a near marine composition found in the deepest samples which are identified as connate water departures from the expected dilution trend are interpreted as evidence for diagenetic reactions during burial or as a result of freshwater circulation following subaerial uplift sr2 li and f have been enriched in interstitial solution and k has been slightly depleted the profile of chalk chemistry with depth shows no conclusive evidence for changes in the mg and sr content of the bulk carbonate due to freshwater diagenesis the 18o and d of the interstitial water reflect the same mixing as that shown by dissolved species however an apparent depletion of 18o and d in the deepest fluids with respect to the expected marine isotopic composition is tentatively explained as a result of the differences in diffusion rates of aqueous oxygen and hydrogen and of ionic solutes

hydrochemical and stable isotope evidence for the extent and nature of the effective chalk aquifer of north norfolk uk in eastern england the chalk aquifer is covered by extensive pleistocene deposits which influence the hydraulic conditions and hydrochemical nature of the underlying aquifer in this study the results of geophysical borehole logging of groundwater temperature and electrical conductivity and depth sampling for major ion concentrations and stable isotope compositions 18o and 2h are interpreted to reveal the extent and nature of the effective chalk aquifer of north norfolk it is found that the chalk aquifer can be divided into an upper region of fresh groundwater with a cl concentration of typically less than 100 mg l 1 and a lower region of increasingly saline water the transition between the two regions is approximately 50 m below sea level and results in an effective aquifer thickness of 50 60 m in the west of the area but less than 25 m where the eocene london clay boundary is met in the east of the area hydrochemical variations in the effective aquifer are related to different hydraulic conditions developed in the chalk where the chalk is confined by low permeability chalky boulder clay isotopically depleted groundwater 18o less than 7 5 is present in contrast to those areas of unconfined chalk where glacial deposits are thin or absent 18o about 7 0 the isotopically depleted groundwater is evidence for groundwater recharge during the late pleistocene under conditions when mean surface air temperatures are estimated to have been 4 5 c cooler than at the present day and suggests long groundwater residence times in the confined aquifer elevated molar mg ca ratios of more than 0 2 resulting from progressive rock water interaction in the confined aquifer also indicate long residence times a conceptual hydrochemical model for the present situation proposes that isotopically depleted groundwater occupying areas where confined groundwater dates from the late pleistocene is being slowly modified by both diffusion and downward infiltration of modem meteoric water and diffusive mixing from below with an old saline water body

kinetics of incongruent dissolution of carbonates in a chalk aquifer using reverse flow modelling s u m m a r y water rock interactions are major processes that control the solute transfer from natural or anthropo genic sources in aquifers in carbonate aquifers these water rock interactions are mainly characterised by the incongruent dissolutions of carbonates the in situ quantification of these reactions is few studied in the present paper we provide a new quantification of the kinetic rates of simultaneous incongruent dissolution of composite carbonate and dolomite in a chalk aquifer the approach is based on a mass balance model used to calculate the rates of mineral dissolution and precipitation along a 500 m to 4 km flow path starting at the groundwater divide line the groundwater transfer times between the groundwater divide line and the wells are calculated thanks to flow and transport modelling used in a backward particle tracking mode the uncertainties on porosity dispersivity and transmissivity are taken into account the rates are found ranging between 1 5 10 a5 and 1 5 10 a4 mol c5 chalk l a1 w yr a1 for the composite carbonate dissolution between 1 0 10 a7 and 3 0 10 a6 mol dolomite l a1 w yr a1 for the dolomite dissolution and between 1 0 10 a5 and 1 5 10 a4 mol calcite l a1 w yr a1 for the calcite precipitation the results highlight the importance of physical and geological properties of the aquifer

tracking selenium in the chalk aquifer of northern france sr isotope constraints groundwater at the southern and eastern edges of france s paris basin has a selenium content that at times exceeds the european framework directive s drinking water limit value of 10 g l to better understand the dynamics of the chalk groundwater being tapped to supply the city of lille and the se origins we used a combination of geochemical and isotopic tools strontium isotopes coupled with ca sr mg sr and se sr ratios were used to identify the main groundwater bodies and their mixings with the mg sr ratio constraining a ternary system groundwater in the agricultural aquifer recharge zone represents a first end member and displays the youngest water ages of the catchment along with the highest strontium isotopic signature 0 7084 and low se contents anaerobic groundwater constitutes a second major end member affected by water rock interactions over a long residence time with the lowest strontium isotopic signature 0 7079 and the lowest se content its low sf6 content confirming the contribution of old water se rich groundwater containing up to 30 g l of se represents a third major end member with an intermediate sr isotopic ratio and is mainly constrained by the clayey se rich formation overlying the chalk aquifer the spatial and temporal se variability in the groundwater is clearly linked to the presence of this formation identified as tertiary and also to the hydrological conditions saturation of the se rich clays by oxygenated groundwater enhances se mobility and also sr adsorption onto the clays this multi tool study including sr isotopes successfully identified the se origins in the aquifer and has led to a better understanding of the regional mixing and processes affecting the chalk groundwater

a finite difference simulation of wave propagation in two dimensional random media a finite difference algorithm is used to generate synthetic seismograms for waves propagating through two dimensional random media the media have a significant component of their material properties varying randomly over length scales smaller than the seismic wavelength and are meant to approximate the heterogeneity of the crust and upper mantle the finite difference technique retains all multiply scattered and diffracted waves and also accounts for transmission losses the synthetic seismograms clearly exhibit coda and apparent attenuation caused by scattering for a medium with a white wavenumber spectrum of velocity fluctuations the coda is higher frequency than the initial pulse the apparent attenuation is greatest when the scatterer size is comparable to the seismic wavelength the spectra of the coda generally increase in frequency as the scatterers decrease in size examples demonstrate how scattering can produce spectra with broad peaks and sharp fall offs that can make the determination of the source spectra and corner frequencies of small earthquakes extremely difficult

the contribution of topographic scattering to teleseismic coda in southern california given that seismic coda is largely the result of scattering near the receiver a tie to geological complexity i e to crustal heterogeneity is expected but a systematic and predictive understanding of the important aspects of geology is lacking we have developed a technique for mapping the origins of coda energy as recorded by regional networks that provides insight into the proximal generation of seismic coda here the role of topography in the production of surface propagating coda energy both as a scatterer and as a proxy of shallow geologic structure is examined for the portion of the san andreas fault system within the southern california seismic network we find significant correlation of p to rg scattering potential with topographic roughness that extends to relatively subtle topography the correlation peaks at a migration velocity of 2 9 km s confirming the identification of scattered rg energy and offering an alternative means of estimating regional shallow velocity structure

source parameters of two ml 5 earthquakes near anza california and a comparison with an imperial valley aftershock strong motion records were used to determine the seismic moments source dimensions and stress drops for two earthquakes near the proposed anza seismic gap thatcher et al 1975 along the san jacinto fault the 25 february 1980 m l 5 5 event and the shock of 15 june 1982 m l 4 8 seismic moments determined for the two events were 2 5 10 23 and 1 1 10 23 dyne cm respectively the source radii were estimated from the displacement pulse widths using the source model of madariaga 1976 static stress drops for the 1980 and 1982 earthquakes were calculated as 110 and 100 bars respectively stress drops determined from the rms accelerations using the method of hanks and mcguire 1981 were 220 bars for the 1980 earthquake and 180 bars for the 1982 event the long period seismic moments for these events derived from regional recordings of 30 to 40 sec love waves were a factor of two to three greater than the moments estimated from the strong motion records as a comparison to the anza events source parameters were also determined from strong motion records for an immediate aftershock m l 5 0 of the 1979 imperial valley earthquake the seismic moment of this aftershock was calculated as 4 2 10 23 dyne cm and its static stress drop was 130 bars static stress drops calculated from the displacement pulse shapes for the three events studied in this paper as well as for an aftershock of the oroville earthquake reported by fletcher et al 1980 exhibit a relatively narrow range between about 100 and 180 bars this result indicates that the stress drops of the two main shocks near anza were not unusually high relative to those of certain aftershocks in other tectonic settings in california