vivianite formation and its role in phosphorus retention in lake orn denmark abstract vivianite fe 3 po 4 2 8h 2 o may precipitate in anoxic lake sediments affecting the porewater orthophosphate concentration and thereby the trophic status of lakes we have investigated changes in lake diagenesis of fe and p 1969 2009 with particular attention focused on vivianite formation with sediment depth 0 20 cm in an iron silica carbon rich lake sediment ornso denmark porewaters were supersaturated for vivianite by two to five orders of magnitude upper 10 cm with porewater phosphate concentrations ranging between 0 69 and 10 mol l 1 in winter and summer concentrations ranging between 9 8 and 40 mol l 1 significant formation of vivianite was confirmed by x ray diffraction while scanning electron microscopy and electron dispersive x ray spectroscopy indicated an increase in vivianite crystal size with depth 20 to 70 m across variations in elemental composition of vivianite crystals in relation to at p and fe were especially seen going from 9 5 cm to 24 5 cm the total sediment fe pool was very large 3000 mol g 1 and total p increased from 200 mol g 1 to 400 mol g 1 descending down the sediment profile differential extraction experiments of p release at ph 3 estimated that vivianite amounts to between 3 and 5 of the total fe pool the total p burial fluxes estimate that 38 mol cm 2 yr 1 or 26 of sedimentary p in the lower sediments is sequestered as vivianite there are seasonal variations in the porewater composition with lower fe orthophosphate and higher sulfate concentrations during winter 5 c than during summer 15 c this suggests that temperature modulates the rate of organic matter degradation which in turns affects the rate of fe iii phase reduction release of phosphate and thereby the porewater fe 2 and orthophosphate concentrations and hence vivianite formation this work highlights the role vivianite can play for p retention in a si fe c rich lake sediment

conductivity distribution beneath lascar volcano northern chile and the puna inferred from magnetotelluric data abstract during two field campaigns in 2007 and 2010 long period and broadband magnetotelluric measurements were conducted in the central andes of northern chile and northwestern argentina at a latitude of 23 7 s the study area spans from the precordillera over the active volcanic arc of the western cordillera until the western part of the puna a special focus was on lascar a subduction related stratovolcano with an historical activity characterized by fumarolic emissions and occasional sub plinian eruptions like the one occurred on 1993 the broadband instruments covering a period range between t 0 005 s and 1000 s were installed in the proximities of lascar volcano while the long period devices t 10 s 10 000 s were installed on a profile slightly south of lascar crossing the salar de atacama basin the volcanic arc and reaching the western border of the puna remote reference and robust techniques were used for data processing induction vectors phase tensor ellipses and strike direction of the conductivity distribution were calculated showing some 3 d behavior for the lascar sites at shallower depths with induction vectors close to the edifice influenced partially by the topography 3 d modeling and inversion revealed conductive anomalies beneath lascar volcano but also beneath the puntas negras volcanic chain for the long period transect the behavior is closer to a 2 d case with more stable strike direction coherent with induction vectors and phase tensor ellipses the major result of 2 d inversion is a vast high conductivity zone in the backarc crust which seems to be the southern extension of a large highly conductive anomaly observed in prior studies beneath the altiplano

crustal heterogeneity in the 2007 noto hanto earthquake area and its geodynamical implications abstract to understand the genesis of the 25 march 2007 noto hanto earthquake mw 6 6 we determined high resolution 3 d seismic velocity vp and vs and poisson s ratio images in the epicenter area using 24 698 p wave and 22 927 s wave arrival times from 809 earthquakes and 265 sp depth phase data collected from seismograms of 162 earthquakes beneath the japan sea the sub oceanic events are relocated accurately by using p s and sp depth phase arrival time data jointly our results demonstrate that the seismic velocity vp and vs and poisson s ratio vary markedly in the source area in and around the main shock hypocenter low velocity and high anomalies are revealed which are apt for accumulation of differential strain to bring the brittle failure we infer that the zone with pronounced low velocity and high poisson s ratio beneath the source area reflects fluid related anomalies derived either from the dehydration of the subducting pacific slab or from permeation of sea water through deep seated active faults or both to the main shock hypocenter which in turn may have facilitated the rupture initiation of the main shock and its aftershock sequence by weakening the overlying seismogenic layer beneath the region our study reinforces the concept of fluid driven earthquakes in the peninsular regions elsewhere in the world

electrical image of subduction zone beneath northeastern japan we conducted long period magnetotelluric observations in northeastern japan from 2010 to 2013 to investigate the three dimensional electrical resistivity distribution of the subduction zone incorporating prior information of the subducting slab into the inversion scheme we obtained a three dimensional resistivity model in which a vertically continuous conductive zone is imaged from the subducting slab surface to the lower crust beneath the ou backbone range the conductive body indicates a saline fluid and or melt pathway from the subducting slab surface to the lower crust the lower crust conductor is less than 10 m and we estimate a saline fluid and or melt fraction of at least 0 7 vol other resistivity profiles in the across arc direction reveal that the conductive body segregates from the subducting slab surface at 80 100 km depth and takes an overturned form toward the backarc the head of the conducting body reaches the lower crust just beneath mt gassan one of the prominent backarc volcanoes in the system

one dimensional resistivity modeling of ne japan from stationary wide band magnetotelluric data abstract stationary magnetotelluric mt systems were set up at the esashi station and the mizusawa geodetic observatories of geographical survey institute gsi in ne japan since 1996 continuous 24 h resistivity and phase data have been acquired by the wide band mt measurement devices the data from the two sites were processed by the remote reference technique to minimize the effect of local noise data quality at the mizusawa was sometimes poor but use of the data as reference improved the mt data of the esashi station as a result extremely stable apparent resistivity and phase curves were obtained from the esashi station the resistivity structure of ne japan was estimated using two ways of 1 d modelling procedure by evaluating the stability of apparent resistivity and phase data the modelling suggests the existence of anomalous layers which represent anisotropic or inhomogeneous crust and or upper mantle structures of the ne japan of fore arc these features may relate with cretaceous tectonic events

mt and reflection an essential combination summary at many localities in the world there have been coincident comprehensive electromagnetic em studies and seismic reflection profiles conducted unfortunately over many more regions the seismic reflection images are interpreted without the constraints afforded by electrical conductivity information this paper is an attempt to convince the reader that a collocated magnetotelluric mt study should in almost every case be made wherever a seismic reflection survey is undertaken examples are shown from six studies in which the em results aided the geological tectonic interpretations of the seismic sections also difficulties with the mt technique are discussed and the interpretations of conducting zones within the lower crust are examined finally a generalised model is proposed for the continental crust that may account for both the reflectivity and conductivity of the zone at the top of the lower crust

magnetotelluric imaging of the median tectonic line in western shikoku southwest japan implications of the fault related low resistivity zone abstract we carried out a magnetotelluric mt survey along a profile crossing the median tectonic line mtl in western shikoku japan the mtl is a terrane boundary that formed during the cretaceous between the sanbagawa belt consisting of high pressure temperature p t metamorphic rocks and the ryoke belt of granites and low p t metamorphic rocks the mt image shows a zone of remarkably low resistivity dipping northward at 40 at the surface coincides with the surface trace of the mtl the low resistivity zone probably corresponds to a fluid filled damaged zone of porous media composed of clay minerals and cracked rocks formed by repeated faulting of the mtl since late cretaceous time the calculated maximum porosity of the damaged zone is 7 1 which is clearly higher than that of the non damaged crystalline rocks

electrical conductivity of fluid bearing quartzite under lower crustal conditions abstract the electrical conductivity of fluid bearing quartzite was determined as function of temperature and fluid fraction at 1 gpa in order to assess the origin of the high conductivity anomalies observed in the middle to lower crustal levels dihedral angles of quartz fluid quartz determined from recovered samples were below 60 suggesting that fluid forms an interconnected network through the quartz aggregate the electrical conductivity of quartzite increases with increasing temperature which can be approximately expressed by arrhenius equation the apparent activation enthalpy decreases from 0 70 to 0 25 ev with increasing fluid fraction in volume from 0 00043 to 0 32 the electrical conductivity of the fluid bearing quartzite increased with fluid fraction proportionally to a power law 0 56 0 71 within the temperature range of 900 1000 k the electrical conductivity of the aqueous fluid bearing quartzite with the maximum fluid fraction 0 32 was found to be about three orders of magnitude higher than that of dry quartzite at 1000 k however its electrical conductivity was definitely lower than the geophysically observed values of high conductivity anomalies even if the quartzite contained large fluid fractions 0 32 the present results suggest that fluid bearing quartzite is unable to account for the high conductivity anomalies in terms of fluid fraction a significant amount of other ionic species such as na cl and al in aqueous fluid in addition to silica phases dissolved in fluid is required to increase conductivity

flat slab thermal structure and evolution beneath central mexico recent seismic and magnetotelluric experiments aimed at better characterizing the shape and state of the subducting slab and continental crust beneath central mexico exposed significant differences with conclusions of previous studies a new slab geometry is revealed in which the subducting cocos slab is perfectly flat between 120 to 290 km from the trench after which it plunges into the asthenosphere at a dip angle of 65 in sharp contrast with the previously proposed 20 dip angle seismic tomography studies show negative p wave velocity anomalies 2 to 4 in the mantle wedge beneath the mexican volcanic belt and positive anomalies 2 to 3 for the subducted cocos slab magnetotelluric experiments exposed a very low resistivity area 1 10 m located within the continental crust just below the mexican volcanic arc finally several spots of non volcanic tremors nvts have been recorded inside the continental crust above the flat slab segment while all these experiments provide a better picture of the subduction system beneath central mexico several key processes need further investigation in this study we take advantage of these new observations to better constrain the thermal structure beneath central mexico two different thermal models are computed for a mantle potential temperature t p of 1 350 and 1 450 c respectively the new thermal structures are then converted into p wave velocity anomalies and compared with the observed v p anomalies we found that a t p of 1 450 c produced larger v p anomalies that do not fit the observations however using a t p of only 1 350 c our predicted v p anomalies are positive 2 to 3 for the cold slab and negative 2 to 4 in the mantle wedge these v p estimates are consistent with the observed seismic tomography from p wave arrivals and therefore we conclude that a t p of 1 350 c is a better estimate for the mantle potential temperature beneath central mexico the new thermal model in conjunction with phase diagrams for sediments hydrated basalt and lithospheric mantle have been used to estimate the amount and location of fluids released from the subducting cocos slab several dehydration pulses have been identified along the slab interface where most of the fluids stored in sediments and oceanic crust are released into the overlying continental crust above the flat slab we found a good correlation between the pattern of these dehydration pulses and the location of nvts suggesting that slab dehydration is responsible for triggering the tremors we suggest that nvt bursts localized above the flat slab segment represent the manifestation of ongoing continental crust hydration and weakening a process that has been going on since 15 ma ago when the cocos slab entered into a flat slab regime such continuous weakening would have reduced the suction forces that kept the slab in a flat regime in the last 15 ma allowing the slab to easily roll back the continuous low resistivity region recorded beneath the volcanic front in central mexico might represent the evidence of slab dehydration and crust weakening over time

magnetotelluric evidence for thick skinned tectonics in central taiwan taiwan is the type example of an arc continent collision numerous tectonic models have been proposed for this orogen and include both thin skinned and thick skinned lithospheric deformation these models predict very different structures at middle and lower crustal depths but insuffi cient geophysical data exist to unequivocally distinguish between them long period magnetotelluric mt data were collected in central taiwan in 2006 2007 to constrain the crustal resistivity structure a two dimensional inversion of these mt data revealed a prominent electrical conductor that extends across the decollement predicted by the thin skinned model this feature is interpreted to be due to 1 2 saline fl uids and is inconsistent with the thin skinned model in contrast the thick skinned model predicts this feature since fl uids are generated in the crustal root through metamorphism quantitative correlation of the resistivity and seismic velocity models supports small volume high salinity fl uids in a thickened crust as the cause of this conductor

role of microbial processes in linking sandstone diagenesis with organic rich clays abstract numerous chemical reactions within clay sequences have been proposed to produce dissolved material for diagenesis of deeply buried sands however reactions responsible for solubilizing inorganic and organic constituents in clays at intermediate depths and their importance to sandstone diagenesis have not been evaluated results from this study show that the processes of microbial organic acid production via fermentation in clays and microbial organic acid consumption via sulfate reduction in sands effectively link organic rich clays to sandstone diagenesis in the black creek formation of south carolina diagenetic processes have resulted in the formation of 10 volume percent calcite cement 0 1 volume percent authigenic pyrite and 1 5 volume percent secondary porosity in black creek sands however the distribution of these diagenetic processes is not uniform resulting in net destruction of porosity in some parts of the sand and net porosity enhancement in other parts mass balance derived rates of microbial organic acid production 10 5 mmole carbon 1 1 yr 1 and microbial co2 production 4 10 5 mmole l 1 yr 1 show that microbial processes can account for all organic carbon in the calcite cements at least 11 of carbonate carbon based on isotope balance calculations all observed authigenic pyrite and all observed secondary porosity these findings show that microbial processes can serve to link organic rich clays with sandsto e diagenesis at intermediate depths

two dimensional electrical section beneath the eastern margin of japan sea 1 four ocean bottom electromagnetometers provided seafloor geoelectromagnetic data for more than nine months in order to reveal mantle dynamics beneath the eastern margin of japan sea where several large and hazardous earthquakes have repeatedly occurred so far high quality magnetotelluric mt data from the seafloor array together with those of four additional land sites in northeast japan were analyzed and carefully corrected for topographic bathymetric effects to extract two dimensional 2d mt responses at each site here we show how the 2d electrical section derived by inverting the corrected 2d mt responses depicts fluid injection deep into the wedge and back arc mantle by the cold and fast subducting pacific plate a high conductivity anomaly found beneath the sado ridge at depths ranging from 150 to 200 km may be direct field evidence that supports water transportation from the earth s surface to the wedge and back arc mantle in the form of serpentinite

metal fixation and mobilisation in the sediments of the afon goch estuary dulas bay anglesey abstract the surface drainage waters of parys mountain anglesey wales a site of former mining for base metals are highly acidic and metal rich due to the oxidation of sulphide minerals these acid waters mix with more neutral waters in the afon goch downstream of parys mountain allowing the formation of ochre precipitates which are found throughout the length of the afon goch and dulas bay x ray fluorescence xrf analysis of the ochres that settle where the afon goch enters dulas bay fe 2 o 3 18 wt reveals that they are heavily contaminated with cu 13 000 g g and zn 7700 g g these sediments are black immediately below the surface and porewater analysis confirms that sulphate reduction is taking place samples of both stream ochre and anoxic black mud have been analysed by exafs spectroscopy data from the exafs analysis of the ochre sample reveals that the fe cu and zn are bonded to oxygen in poorly ordered or amorphous solids in the anoxic black mud however fe cu and zn are all present as sulphides the fe sulphide is either amorphous or poorly ordered whereas zn forms a discrete sulphide phase similar to sphalerite the cu sulphide has short range order with a chalcopyrite like structure sequential extraction analysis of the same samples was also performed for the ochre sample cu and zn release is controlled by the fe hydrated oxides being recovered primarily in the mildly acid carbonate and more strongly acid and reducing reducible fractions fe and zn are also recovered in these fractions from the black mud indicating that these metals are present as acid soluble sulphides cu however is almost exclusively recovered in the oxidisable fraction indicating that it is incorporated into a more stable sulphide such as chalcopyrite

acetate and propionate in landfill leachates implications for the recognition of microbiological influences on the composition of waters in sedimentary systems routine monitoring of landfill leachates provides information concerning aqueous systems in which anaerobic microbiological processes influence water chemistry propionate and acetate are substrate and product respectively of metabolism by bacteria that have an obligate syntrophic relationship with sulfate reducing bacteria the stoichiometry of the bacteriological metabolic reactions indicates a 1 1 molar proportionality for acetate and propionate this is observed for landfill leachates consistent with the known biological control on their organic acid anion contents similar data for oil field waters show the same 1 1 molar proportionality for reservoirs where bacterial sulfate reduction is known to take place at temperatures up to about 95 c in contrast to the 3 2 proportionality acetic acid propionic acid observed in higher temperature systems these observations suggest that 1 1 molar proportionality for acetate and propionate may be characteristic of natural systems where anaerobic bacterial activity occurs including bacterial sulfate reduction

a fault zone conductor beneath a compressional inversion zone northeastern honshu japan 1 a resistivity section based on magnetotelluric data was obtained for the shonai plain fault in northeastern honshu japan faults in this area were created as normal faults during the opening of the japan sea in the miocene but are now reactivated as high angle reverse faults under compressional tectonics geological interpretations of the resistivity section support the proposed fault reactivation an estimated east dipping conductor along a deep part of the shonai plain fault system probably represents a fluid rich zone around the fault zone the high 3he 4he ratio near the fault indicates transportation of mantle fluid through this fluid rich zone these evidences may reflect the development of pronounced fracture permeability after fault rupturing as in the fault valve hypothesis

rheological structure of northeastern japan lithosphere based on geophysical observations and rock mechanics abstract based on recent results on rock mechanics and geophysical observations i constructed rheological strength and viscosity profiles across the northeastern japan lithosphere the profiles well explain patterns of present day geodetic strain accumulation and shallow seismicity experimentally derived flow laws also predict the presence of weak zones by mechanisms likely operated in the lithosphere e g partial melting and shear zone development the strain localization into weak zones explains the estimates of low viscosity 1019 1020 pas from post seismic creep after a large inland earthquake the strain localization into weak zones also efficiently accumulates elastic strains at the base of upper seismogenic faults locked during interseismic periods resulting in the reactivation of pre existing fault systems in the northeastern japan

structural heterogeneity in northeast japan and its implications for the genesis of the 2004 and 2007 niigata earthquakes abstract we utilized 188 766 p wave and 179 328 s wave high quality arrival time data from 14 666 local earthquakes to determine the three dimensional 3d seismic velocity v p v s v p v s ratio crack density e and bulk velocity v structures in and around the source areas of the 2004 and 2007 niigata earthquakes japan meteorological agency magnitude m j 6 8 in japan in order to understand the generation mechanisms of the niigata mainshocks the aftershock hypocenters were relocated by applying the double difference location method simultaneously with the tomographic inversion indicating a complicated fault system that includes not only two parallel dominant faults dipping to the northeast but also some conjugate faults crossing the niigata mainshock hypocenters in general high velocity v p v s with low e at 11 km depth is visible in the southeastern part of this area in contrast to anomalous low velocity with high crack density in the northwestern part along the niigata kobe tectonic zone nktz these characteristics of the velocity and crack density are consistent with the spatial distribution of active faults along the nktz the surface geological features that indurated pre neogene rock outcrops were observed in the southeastern area whereas deep sedimentary basins were observed on the opposite side low v p and low v s zones with high v p v s anomalies were imaged in and or under the source areas showing agreement with those revealed by previous studies all the features of the velocity and v p v s structures together with the images of the crack density and bulk velocity suggest the presence of fluids under the source areas such fluids might have weakened the mechanical strength of the fault zone of the source areas thus triggering the 2004 and 2007 niigata earthquakes our present study together with other recent tomographic images reveals that fluids penetrated into the source rocks from the lower crust and uppermost mantle as a result of dehydration of the subducting pacific slab and thus may play a key role in the genesis of these large crustal earthquakes

developing the scientific framework for urban geochemistry abstract urban geochemistry is a unique discipline that is distinguished from general geochemistry by the complex infrastructure and intense human activities associated with concentrated population centers as stated by thornton 1991 this subject is concerned with the complex interactions and relationships between chemical elements and their compounds in the urban environment the influence of past and present human and industrial activities on these and the impacts or effects of geochemical parameters in urban areas on plant animal and human health urban areas present special challenges to geochemists attempting to understand geochemical states and fluxes on the 5 6 of august 2014 the first meeting of the reorganized urban geochemistry working group of the international association of geochemistry iagc was held in columbus ohio united states two goals of the meeting were to develop the overall scope and a general definition of urban geochemistry five grand themes were developed 1 recognizing the urban geochemical signature 2 recognizing the legacy of altered hydrologic and geochemical cycles in urban environments 3 measuring the urban geochemical signature 4 understanding the urban influence on geochemical cycles from the continuous development and erosion of physical infrastructure and episodic perturbations and 5 relating urban geochemistry to human and environmental health and policy after synthesizing the discussion of these themes we offer the following perspective on the science of urban geochemistry building on the work of thornton 1991 urban geochemistry as a scienti c discipline provides valuable information on the chemical composition of environments that support large populations and are critical to human health and well being research into urban geochemistry seeks to 1 elucidate and quantify the sources transport transformations and fate of chemicals in the urban environment 2 recognize the spatial and temporal including legacies variability in these processes and 3 integrate urban studies into global perspectives on climate change biogeochemical cycles and human and ecosystem health we hope that this discussion will encourage other geochemists to engage in challenges unique to urban systems as well as provide a framework for the future of urban geochemistry research

magnetotelluric imaging of fluids in intraplate earthquake zones ne japan back arc intraplate earthquake zones in the back arc of ne japan were imaged by wide band magnetotelluric mt soundings the 90km long mt profile of 34 stations extends over the two topographic features the dewa hills and the ou backbone range which were uplifted by thrust faults mt data show two dimensionality and strong te tm anisotropic responses at the periods around 100 s after tensor decompositions with regional strike of n12 e two dimensional inversion was carried out where static shift was also a model parameter the final model is characterized by conductive blocks in the mid crust to account for the anisotropic responses correlation of the conductors to the seismic scatterers and to the low velocity anomalies suggests that the conductors represent fluids high seismicity clustering near the rims of conductors suggests that the intraplate seismicity results either from the migration of the fluids to less permeable crust or from local stress concentration near the structural boundary

sediments porewaters and diagenesis in an urban water body salford uk impacts of remediation contaminated sediments deposited within urban water bodies commonly exert a significant negative effect on overlying water quality however our understanding of the processes operating within such anthropogenic sediments is currently poor this paper describes the nature of the sediment and early diagenetic reactions in a highly polluted major urban water body the salford quays of the manchester ship canal that has undergone remediation focused on the water column the style of sedimentation within salford quays has been significantly changed as a result of remediation of the water column pre remediation sediments are composed of a range of natural detrital grains predominantly quartz and clay and anthropogenic detrital material dominated by industrial furnace derived metal rich slag grains post remediation sediments are composed of predominantly autochthonous material including siliceous algal remains and clays at the top of the pre remediation sediments and immediately beneath the post remediation sediments is a layer significantly enriched in furnace derived slag grains input into the basin as a result of site clearance prior to water column remediation these grains contain a high level of metals resulting in a significantly enhanced metal concentration in the sediments at this depth porewater analysis reveals the importance of both bacterial organic matter oxidation reactions and the dissolution of industrial grains upon the mobility of nutrient and chemical species within salford quays minor release of iron and manganese at shallow depths is likely to be taking place as a result of bacterial fe iii and mn iv reduction petrographic analysis reveals that the abundant authigenic mineral within the sediment is manganese rich vivianite and thus fe ii and mn ii released by bacterial reactions may be being taken up through the precipitation of this mineral significant porewater peaks in iron manganese and silicon deeper in the sediment column are most probably the result of dissolution of furnace derived grains in the sediments these species have subsequently diffused into porewater above and below the metal enriched layer this study illustrates that the remediation of water quality in anthropogenic water bodies can significantly impact upon the physical and chemical nature of sedimentation additionally it also highlights how diagenetic processes in sediments derived from anthropogenic grains can be markedly different from those in sediments derived from natural detrital material copyright 2003 john wiley sons ltd

electrical structure of the himalaya of central nepal high conductivity around the mid crustal ramp along the mht twelve broadband magnetotelluric mt soundings were performed across the himalaya of central nepal in 1996 in order to determine the electrical structure of the crust and its relation to geological structures and active tectonics the mt impedance tensors were obtained for frequencies between 0 001 and 500 hz the 2 d section derived from joint inversion of te and tm mode after rri and groom bailey decomposition shows high conductivity in the foreland basin 30 m that contrasts with the resistive indian basement 300 m and lesser himalaya 1000 m in addition our mt sounding reveals a major conductive feature beneath the front of the higher himalaya also characterized by intense microseismic activity and the position of a mid crustal ramp along the major active thrust fault mht this high conductivity zone probably reflects metamorphic fluids released during underthrusting of the indian basement and pervading well connected microcracks induced by interseismic stress build up or distributed brittle deformation around the ramp

electrical resistivity structure of the xiaojiang strike slip fault system sw china and its tectonic implications abstract it is widely accepted that large scale strike slip faults play an important role in accommodating the india eurasia convergence but the relationships between surface displacements and deep deformation along the faults remain largely uncertain to address this issue new magnetotelluric mt images were obtained along two profiles across the xiaojiang strike slip fault system xjfs one of the most tectonically active areas in southwest china although different in details these two profiles show similar overall crustal structures the upper crust is generally resistive but separated by several narrow subvertical conductors that broadly coincide with the surface traces of the xjfs these fault zone conductors fzcs are interpreted to represent fault damage zones that formed by strike slip faulting shearing along the faults and filled with deeply sourced magmatic and or metamorphic fluids the lower crust is broadly characterized by enhanced conductivity and likely associated with partial melting at high temperatures these observations are consistent with other geophysical measurements in this area and in favor of the development of ductile flow along the xjfs although the pattern of flow is more complex than previously suggested based on these observations we propose that active deformation along the xjfs can be better described in the brittle upper crust by strike slip motion along the fluid weakened faults and by shear enhanced ductile flow in the partially molten lower crust these two mechanisms are not mutually exclusive but rather can be complementary to each other

s wave attenuation structure on the western side of the nankai subduction zone implications for fluid distribution and dynamics we estimated the s wave attenuation structure in southwestern japan and the western nankai trough by analyzing maximum s wave amplitudes at 4 8 8 16 and 16 32 hz with a correction term for apparent amplitude attenuation due to multiple forward scattering because the estimated attenuation q 1 in our tomographic study was much larger than q 1 due to wide angle scattering our estimated q 1 was composed mainly of intrinsic attenuation high attenuation areas q 1 1 300 at 4 8 hz were imaged beneath quaternary volcanoes and south off shikoku low 1 1500 at 4 8 hz or moderate q 1 1 500 1 1000 at 4 8 hz was imaged beneath shikoku and nonvolcanic areas of chugoku high and moderate q 1 in and around shikoku are located near the top of subducting philippine sea plate this correspondence implies that these high and moderate q 1 reflect fluid in the subducting slab by applying a theoretical model of attenuation in water saturated porous random media we examined wave induced fluid flow induced by lower frequency 1 hz seismic waves that may be related with triggering of nonvolcanic tremor by surface waves even though q 1 structure in this study cannot fully explain the tremor triggering by wave induced fluid flow large uncertainties of q 1 in tremor zone suggest that high resolution imaging of q 1 and random inhomogeneities would give some constraints for the spatial variation of permeability and other medium properties

authigenesis of vivianite as influenced by methane induced sulfidization in cold seep sediments off southwestern taiwan abstract authigenesis of iron rich phosphate nodules occurs in iron rich cold seep sediments md052911 core at yung an ridge offshore southwestern taiwan raman ftir and quantitative x ray energy dispersive spectroscopic analyses indicate that the phosphate mineral is vivianite or baricite and shows fe mg molar ratios spanning from ca 0 6 to 4 0 and a general down core trend of increasing fe mg ratios the formation of vivianite is limited to a depth interval of 13 17 mbsf meters below seafloor and is most prominent at 16 mbsf in association with high dissolved iron concentrations and depleted dissolved sulfide below a peak sulfidization zone enriched in mackinawite and greigite alternate growths of vivianite and iron monosulfides and compositional zoning with mg enriched towards the peripheries of individual nodules occur in the transition from the zone of vivianite mineralization to the sulfidization zone the crystallization of vivianite below the sulfidization front could have been favored by scavenging of downward diffusive dissolved sulfide from pore waters in the sulfidization zone alternate growths and overlapping of the zones of iron monosulfides and vivianite can be attributed to fluctuations of the sulfidization front and methane flux the discovery of vivianite in the yung an ridge sediments implies that authigenic vivianite can be an important sink for phosphorus burial in cold seep sediments that have high reactive iron contents and high sedimentation rates

regional metamorphic dehydration and seismic hazard we use a one dimensional model of coupled heat transport fluid transport porosity feedback and metamorphism to investigate how dehydration reactions proceeding during burial of hydrous rocks in the footwall of thrusts or the hanging wall of normal faults may influence the temporal evolution of pore fluid pressure pf based on a new interpretation of existing kinetic data for the dehydration of model serpentinite we advance the hypothesis that pf buildup to tensile failure may be possible within decades of the onset of dehydration in low permeability metamorphic rocks of the middle crust this model contrasts with both 1 typical earthquake nucleation models which involve preexisting fluids that play a passive role responding to tectonic stresses rather than generating them and 2 conventional treatments of pf generation based on equilibrium thermodynamics and constant rates of dehydration which require 10 106 years to produce significant pf increases our results suggest that repeated cycles dehydration induced seismicity are plausible in low permeability areas of the mid crust and can be sustained throughout an orogenic episode if fresh hydrous minerals descend into the metamorphic zone along the downgoing face of a thrust or normal fault system

electromagnetic heterogeneity of the seismogenic region of 1962 m6 5 northern miyagi earthquake northeastern japan magnetotelluric surveys were carried out to in vestigate the electrical resistivity structure of the seismo genic region of the 1962 northern miyagi earthquake m6 5 in miyagi prefecture northeastern japan a 2 d inversion reveals the existence of a deep conductive zone and overly ing re sistivezonein theuppe r crust a positiveae romag netic anomaly is also recognized above the resistive zone which is interpreted as a buried kitakami granitoid pluton by comparison with these ismicity wefound that themi croearthquakes occur just above the deep conductor and in the resistive zone and that several s wave reflectors are just above the deep conductor since the s wave reflectors sug gest the existence of fluid beneath them the deep conduc tor can be interpreted as a fluid filled zone moreover we suggest that the seepage of the fluid from the conductive fluid filled zone to the resistive granitoid pluton can become a trigger of the earthquakes

aqueous fluids derived from a subducting slab observed high 3he emanation and conductive anomaly in a non volcanic region kii peninsula southwest japan abstract it has long been recognized that the kii peninsula in the southwest japan arc is peculiar in a non volcanic region indicated by the presence of high temperature hot springs high terrestrial heat flow and high 3 he content in hot spring gases geophysical and geochemical studies were carried out to understand the geotectonic environment in the southern part of the kii peninsula most of the measured 3 he 4 he ratios are similar or higher than air indicating wide spread incorporation of mantle derived helium into meteoric water a region with rather high 3 he 4 he ratios 4 r a on the west side of the omine mountains coincides with the occurrence of high temperature hot springs a deep crustal resistivity structure across the omine mountains was imaged by wide band magnetotelluric soundings a 2 d inversion with n s strike using both tm and te modes reveals two conductors one in the upper 3 7 km depth and the other in lower crust 25 35 km depth to the west of the omine mountains the distribution of microearthquakes and low frequency tremors and the existence of seismic reflectors indicate that the large conductor in the lower crust is related to aqueous fluids derived from the philippine sea plate the upper crustal conductive zone may also reflect the aqueous fluids trapped in the upper crust which are presumably derived from the subducting slab considering the occurrence of seismic events in the subducting slab beneath the southern kii peninsula the aqueous fluids generated by dehydration of the slab mantle could plausibly include morb type helium derived from the residual lithospheric mantle therefore the high temperature hot springs and high 3 he emanations in hot spring gases and other geotectonic events in the southern kii peninsula may be due to heat flux and mantle derived helium discharged from aqueous fluid in the upper crust

magnetotelluric imaging beneath the taiwan orogen an arc continent collision 1 the taiwan orogen has formed since the late miocene by oblique collision between the luzon volcanic arc on the philippine sea plate and the eurasian continental margin this oblique collision has produced an orogen that decreases in age from north to south and permits study of the temporal evolution of an arc continent collision these factors make taiwan a favorable location to study the process of arc continent collision the first long period magnetotelluric mt measurements were recorded in taiwan as part of the taiwan integrated geodynamics research taiger project in 2006 7 measurements were made at 82 sites on three transects across south central and north taiwan that span the breadth of the orogen and cross all major tectonic boundaries robust remote reference processing of the mt time series data resulted in high quality soundings that were modeled in both 2 and 3 dimensions these mt models support predictions of lithospheric deformation i e thick skinned tectonics beneath the central ranges in south and central taiwan but are inconsistent with predictions of orogen scale thin skinned models the mt resistivity model for northern taiwan is consistent with dewatering of the subducting philippine slab and with deformation described by the subducting indenter tectonic model modeling the taiger mt data has definitively shown that conductive and seismically active crustal structures exist to 30 km beneath the orogen these conductive regions interpreted as interconnected fluid map pervasive zones of collisional deformation that are lithospheric in scale

high resolution electromagnetic imaging of the san andreas fault in central california although there is increasing evidence that fluids may play a significant role in the earthquake rupture process direct observation of fluids in active fault zones remains difficult since the presence of an electrically conducting fluid such as saline pore water strongly influences the overall conductivity of crustal rocks electrical and electromagnetic methods offer great potential for overcoming this difficulty here we present and compare results from high resolution magnetotelluric mt profiles across two segments of the san andreas fault saf which exhibit very different patterns of seismicity parkfield which has regular small earthquakes and creep events and in the carrizo plain where the fault is seismically quiescent and apparently locked in both surveys electric fields were sampled continuously with 100 m long dipoles laid end to end across the fault from 100 to 0 1 hz the data from both profiles are consistent with a two dimensional 2 d fault parallel resistivity model when both transverse electric and magnetic te and tm mode data are included in the interpretation narrow approximately 300 endash 600 m wide zones of low resistivity extending to depths of 2 endash 4 km in the core of the fault are required at both locations however at parkfield the conductance conductivity thickness product of the anomalous region ismore an order of magnitude larger than at carrizo plain suggesting much higher concentrations of fluids for the more seismically active parkfield segment we also image structural differences between the two segments at carrizo plain resistive presumably crystalline rocks are present on both sides of the fault at depths below 3 endash 4 km in particular we clearly image resistive basement extending approximately 10 km or more east of the saf beneath the elkhorn hills and temblor range at parkfield the situation is quite different with a resistive block of salinian granite west of the fault and an electrically conductive presumably fluid rich franciscan complex to the east it is possible that these structural differences control the difference in mechanical behavior of the fault either directly by affecting fault strength or indirectly by controlling fluid supply copyright 1999 american geophysical union less

effect of mining and related activities on the sediment trace element geochemistry of lake coeur d alene idaho usa part i surface sediments during the summer of 1990 12 gravity cores were collected in lake coeur d alene idaho at various depths and in a variety of depositional environments all core subsamples were analysed to determine the bulk sediment chemistry selected subsamples were analysed for trace element partitioning and 137cs activity the purpose of these analyses was to determine the trace element concentrations and distributions in the sediment column and to try to establish a trace element geochemical history of the lake in relation to mining and mining related discharge operations in the area substantial portions of the near surface sediments in lake coeur d alene are markedly enriched in ag as cd hg pb sb and zn and slightly enriched in cu fe and mn variations in the thickness of the trace element rich sediments which range from more than 119 cm to as little as 17 cm indicate that the source of much of this material is the coeur d alene river an estimated 75 million tonnes of trace element rich sediments have been deposited on or in the lake bed estimated trace element masses in excess of those considered representative of background conditions range from a high of 468 000 tonnes of pb to a low of 260 tonnes of hg the similarity between the trace element rich surface and subsurface sediments with respect to their location their bulk chemistry their interelement relations and their trace element partitioning indicate that the sources and or concentrating mechanisms causing the trace element enrichment in the lake sediments have probably been the same through out their depositional history based on a mt st helens ash layer from the 1980 eruption ages estimated from 137cs activity and the presence of 80 discernible and presumably annual layers in a core collected near the coeur d alene river delta indicate that deposition rates for the trace element rich sediments have ranges from 2 1 to 1 3 cm year these data also indicate that the deposition of trace element rich sediments began at least in the coeur d alene river delta some time between 1895 and 1910 dates consistent with the onset of mining and ore processing activities that began in the area in the 1880s

vertical collapse origin of las canadas caldera tenerife canary islands revealed by 3 d magnetotelluric inversion tenerife island geology is one of the most complexes of the canaries archipelago this complexity is evidenced by the existing controversy regarding the lateral or vertical collapse origin of the las canadas caldera the resistivity structure of the las canadas caldera has been determined by the 3 d inversion of 188 broadband magnetotelluric data the resistivity distribution obtained in the final model shows clear evidences of the presence of a vertical structure under the teide associated to the buried northern wall of the caldera additionally the characteristics of the main resistivity structure a ring shaped low resistivity body 10 m interpreted as a hydrothermal clay alteration cap would point out the presence of a handwall for the icod valley lateral landslide located under the teide but not in the southern caldera wall current wall all these support the vertical collapse hypothesis to explain the origin of the las canadas caldera

extensional structure in northern honshu arc as inferred from seismic refraction wide angle reflection profiling a recent extensive seismic wide angle experiment revealed a new image of crustal and uppermantle structure across northern honshu arc japan the western part of the arc recorded the crustal deformation by the miocene back arc spreading of the sea of japan the crust is composed of highly deformed tertiary sedimentary layers a relatively low velocity 5 75 5 9 km s crystalline basement and a 15 km thick lower crust with a velocity of 6 6 7 0 km s clear westward crustal thinning from 32 to 27 km represents the extensional deformation by the backarc spreading the crust attains the maximum thickness 32 35km east of the backbone range for which the magmatic intrusion underplating since 10 15 ma is a predominant factor the eastern part of the arc has a less deformed upper crust and a reflective middle lower crust probably remaining a stable block since the time of the backarc spreading

electrical conductivity of albite quartz water and albite water nacl systems and its implication to the high conductivity anomalies in the continental crust abstract the electrical conductivities of albite water albite quartz water and albite water nacl systems have been measured in terms of impedance spectroscopy at 1 gpa and 400 1000 k the relationship between electrical conductivity and temperature in the albite quartz water system cannot be expressed by the arrhenian formula whereas that in the brine bearing system follow the arrhenian law showing small temperature dependence the electrical conductivity of the albite quartz water samples decreased with decreasing temperature from 1000 to 800 k then increased rapidly upon further cooling from 800 to around 550 k the bulk conductivities of the albite quartz water system are consistent with variation of the total concentration of the dissolved electric charge carriers of h oh na alo 2 and hsio 3 in aqueous fluid with temperature based on the thermal dynamic calibration there is a small negative dependence of bulk conductivity on aqueous fluid fraction electrical conductivity of the albite water nacl samples is higher than that of the albite quartz water samples which shows the following features 1 small dependence of conductivity on the temperature 2 increase of electrical conductivity with the fluid fraction and the salinity our results suggest that the high conductivity anomalies of 10 1 s m typically observed in the continental crust can be explained by the presence of albite and quartz with fluid fraction as low as 0 014 at temperatures lower than 650 k in the case that the geotherm is higher than 650 k the observed value of 10 1 s m can be explained by the brine bearing albite with a fluid fraction of 1 vol if the salinity is similar to the seawater

rupture mechanism and seismotectonics of the ms6 5 ludian earthquake inferred from three dimensional magnetotelluric imaging a three dimensional 3 d resistivity model around the 2014 ms6 5 ludian earthquake was obtained the model shows that the aftershocks were mainly distributed in a shallow inverse l shaped conductive angular region surrounded by resistive structures the presences of this shallow conductive zone may be the key factor leading to the severe damage and surface rupture of the ludian earthquake a northwest trending local resistive belt along the baogunao xiaohe fault interrupts the northeast trending conductive zone at the zhaotong lianfeng fault zone in the middle crust which may be the seismogenic structure of the main shock based on the 3 d electrical model combining with gps thermal structure and seismic survey results a geodynamic model is proposed to interpret the seismotectonics deep seismogenic background and deformation characterized by a sinistral strike slip with a tensile component of the ludian earthquake

cenozoic remagnetization of the paleozoic rocks in the kitakami massif of northeast japan and its tectonic implications abstract secondary remanent magnetization is identified in the paleozoic igneous and sedimentary rocks of the kitakami massif the secondary nature is shown by a negative fold test for the permo carboniferous sedimentary rocks the northwesterly paleomagnetic declination with moderate inclination d 321 2 i 56 5 95 5 2 n 18 of this secondary remanent magnetization is almost parallel to the primary magnetization reported for the cenozoic welded tuffs of northeast japan indicating that the paleozoic rocks were subjected to remagnetization at any period between 62 and 16 ma the secondary magnetization of the serpentinized ultramafic rocks is carried by magnetite which grew in veins and mesh rims of serpentine whereas the carrier of the magnetization in limestones is fine grained pyrrhotite combining this with the previously reported remagnetization of the kitakami granitic rocks it is suggested that rocks in the kitakami massif were subjected to crystallization remanent magnetization at low temperature conditions since serpentinization requires fluid migration one of the most likely events is the eastward lateral migration of water into the kitakami massif we postulate a cenozoic suturing of the kitakami massif with the asian continent as a plausible tectonic event for this fluid migration

the relationship between late cenozoic tectonic events and stress field and basin development in northeast japan the regional tectonic stress field basin development and crustal deformation of the ne japan arc in the interval between 32 ma to the quaternary can be synthesized based on dike vein and fault orientation data as well as on the compilation of the regional geology an extensional stress field became prevalent from 32 ma and major normal faulting started at 25 20 ma which resulted from back arc rifting normal faulting trending nearly parallel to the arc propagated from the present japan sea coast to the forearc side following the trenchward migration of the main volcanic field from 20 to 15 ma normal faults with an oblique trend to the arc developed due to the counterclockwise rotation of ne japan the rapid clockwise rotation of sw japan since 16 ma produced a nw se directed transtensional stress regime in the ne japan arc due to crustal stretching associated with this pull apart movement the back arc side of the ne japan arc subsided rapidly to middle bathyal environments after the termination of the opening of the japan sea at about 14 ma a neutral stress regime prevailed which included phases of both weak extension and compression lithospheric cooling eventually led to thermal subsidence of the back arc region and igneous underplating caused uplift of the axial zone of the volcanic arc the increase in velocity of the westward motion of the pacific plate at around 4 ma produced strong compression across the arc reactivating most of the miocene normal faults and uplifting the volcanic arc the greatest crustal shortening occurred in areas that were stretched the most in the miocene within the volcanic arc which implies tectonic inversion

magnetotelluric imaging of crustal magma storage beneath the mesozoic crystalline mountains in a nonvolcanic region northeast japan mesozoic crystalline mountains iide mountains in a nonvolcanic region of the northeast japan arc were imaged by wide band magnetotelluric soundings a two dimensional model shows that an anomalous conductive body 10 m is clearly visible beneath the iide mountains the conductor widens with increasing depth and extends from the near surface down to the base of the crust and perhaps into the upper mantle the location of the conductive body correlates with high temperature hot springs with high 3he 4he ratio thinning of the brittle seismogenic layer and anomalies of low seismic velocity we conclude that the conductor reflects the presence of partial melts in the crust related to renewed magmatism in the present day subduction system

formation of ferric iron crusts in quaternary sediments of lake baikal russia and implications for paleoclimate phosphate bearing ferric iron and siliceous crusts ranging in age from recent to approximately 65 000 yr b p are observed in sediments of lake baikal in younger sediments the crusts are at the base of a spectrum of secondary iron and manganese oxides that accumulate near the sediment water interface in the zone of positive oxidation potential beneath an oxygenated water column in areas where the average quaternary sedimentation rates have been slow e g 0 026 mm yr the crusts are more common and span a wider range of ages no crusts have been found where the quaternary sedimentation mode has been deltaic and rapid 0 15 mm yr independent core correlation based on magnetic properties of the sediment suggests that crusts can be correlated over most of academician ridge an area that is particularly sensitive to climatic events affecting the concentration of suspended sediment these crusts may be indicative of periods of low suspended sediment concentration which occur during sustained transitions from glacial periods of high detrital input to interglacial periods of high diatom sedimentation the crusts are dominated by iron rich and siliceous amorphous mineral phases with an feo sio2by weight of 3 1 regardless of age or location in the lake the fe phase always includes ca p and mn extensive microprobe data for these four elements recast as normalized elemental weight percent reveal linear trends of ca p and fe p with increasing p ca also increases such that the two elements maintain a linear relationship passing very close to the origin and with a mean molar ca p 0 3 too low for well characterized apatite conversely with increasing p fe decreases mean molar fe p 3 4 there is no correlation between mn and p molar fe p ratios for vivianite an fe ii phosphate mineral observed in sediments closely below some crusts are clustered around a stoichiometric composition the covariant increase in ca p and the corresponding decrease in fe p may be explained by 1 coupled adsorption of aqueous ca and p by a colloidal ferric hydrous oxide 2 loss of fe from a ca p fe phase or 3 oxidation of vivianite to a metastable mineral phase that gradually loses ca and gains fe the first explanation is favored because there is no petrographic evidence for either the existence of an originating ca p fe phase or for the oxidation of vivianite further it is suggested that by continually equalizing surface charge ca allows more phosphate to be adsorbed leading to thicker crusts and longer preservation after burial

seismic structure and magmatism of the young kyushu subduction zone seismic tomography shows that slow velocity anomalies exist in the mantle wedge and extend to the forearc region down to the subducting philippine sea slab under northern kyushu we also conducted numerical simulations with petrologic data to estimate the fluid distribution in the mantle wedge the seismic and simulation results indicate that regimes of melting and magmatism in a subduction zone with a young slab are different from those with old slabs dehydration and melting occur beneath the arc and forearc above a young and warm slab such as in northern kyushu 26 ma while fluids aqueous solution and melt occur mainly beneath the back arc above old slabs

magnetotelluric transect across the niigata kobe tectonic zone central japan a clear correlation between strain accumulation and resistivity structure 1 we obtained an electrical transect image of the niigata kobe tectonic zone nktz several major active faults are located in this zone of concentrated deformation the main features of the final two dimensional model are a thick resistive block in the upper crust with a thinned out portion beneath the atotsugawa fault and a strong conductor in the lower crust that intrudes upward into the upper resistor the upper crustal resistive zone corresponds well to the spatiality of the nktz and relatively conductive zones sandwiching this resistor may contribute to observed changes in displacement rates the overlapping locations of the conductor and the low velocity body in the lower crust indicate that the conductor represents a zone that was weakened by fluids given that microearthquakes are localized in the regions between the resistive and conductive zones we suggest that the distribution of earthquakes is influenced by intrusions of fluid derived from the conductor

deep seismic reflection profiling across the ou backbone range northern honshu island japan knowledge of the crustal structure especially the geometry of seismogenic faults is key to understanding active tectonic processes and assessing the size and frequency of future earthquakes to reveal the relationship between crustal structure and earthquake activity in northern honshu island common midpoint cmp deep reflection profiling and earthquake observations by densely deployed seismic stations were carried out across the active reverse faults that bound the ou backbone range the 40 km long cmp profiles portray a relatively simple fault geometry within the seismogenic layer the reverse faults merge at a midcrustal detachment just below the base of the seismogenic layer producing a pop up structure that forms the ou backbone range the top of the reflective middle to lower crust 4 5 s in travel time twt nearly coincides with the bottom of seismogenic layer the p wave velocity structure and surface geology suggest that the bounding faults are miocene normal faults that have been reactivated as reverse faults

magnetotelluric survey for exploration of a volcanic rock reservoir in the yurihara oil and gas field japan the yurihara oil and gas field is located on the southern edge of akita prefecture northeastern japan in this area drilling surface geological surveys and many seismic surveys have been used to investigate the geological structure wells drilled into the nishikurosawa basalt group nbg of miocene age found oil and gas reservoirs at depths of 1 5 2km oil and gas are now being produced commercially and further exploration is required in the surrounding areas however since the neighbouring areas are covered with young volcanic products from the chokai volcano and have a rough topography the subsurface distribution of the nbg must be investigated using other methods in addition to seismic reflection according to the well data the resistivity of the nbg is comparatively higher than that of the overlying sedimentary formations and therefore the magnetotelluric mt method is expected to be useful for the estimation of the distribution of the nbg an mt survey was conducted along three survey lines in this area each line trended east west perpendicular to the regional geological strike and was composed of about 25 measurement sites induction vectors evaluated from the magnetic field show that this area has a two dimensional structure the evaluated resistivity sections are in agreement with the log data in conclusion we were able to detect resistive layers the nbg below conductive layers the results indicate that the nbg becomes gradually less resistive from north to south in the centre of the northern line an uplifted resistive area is interpreted as corresponding to the reservoir by comparison with a seismic section we prove the effectiveness of the integration of seismic and mt surveys for the investigation of the morphology and internal structure of the nbg on other survey lines the resistive uplifted zones are interpreted as possible prospective areas

imaging the fault zones of the 2000 western tottori earthquake by a new inversion method to estimate three dimensional distribution of the scattering coefficient 1 we developed an inversion method to estimate the spatial variation of scattering coefficient from observed envelopes of s coda waves synthetic envelopes are calculated on the basis of the single scattering theory assuming double couple sources and a one dimensional depth dependent velocity structure in our algorithm we evaluated scattering attenuation taking spatial variation of scattering coefficient into consideration in order to model energy attenuation by passing through the localized anomalous zones with high scattering coefficients the inversion method was applied to the seismograms in and around the focal area of the 2000 western tottori earthquake with m 7 3 obtained results show that there exist several zones with large scattering coefficient zones lszs one of the most predominant lsz is located along and around the fault zone of the m 7 3 earthquake in the upper crust this lsz suggests the existence of damaged zones in the main shock fault within this lsz an exceptionally small scattering coefficient area was detected this area corresponds to an asperity with a large amount of coseismic slip of the main shock other prominent lszs are detected in the mid to lower crust below the northwestern part of the main shock fault in addition lszs are distributed in a seismic low velocity zone near quaternary volcanoes and near hypocenters of deep low frequency microearthquakes some of the imaged lszs are probably related to local concentration of fluid in the crust

the role of grain dissolution and diagenetic mineral precipitation in the cycling of metals and phosphorus a study of a contaminated urban freshwater sediment this paper describes the detrital mineralogy early diagenetic reactions and authigenic mineral precipitates for freshwater contaminated sediments deposited in an urban water body the salford quays of the manchester ship canal greater manchester uk these sediments contain a mix of natural and anthropogenic detrital grains detrital grains are dominated by quartz and clay grains whilst anthropogenic grains are dominated by metal rich glass grains concentrated at a depth of 12 17 cm in the sediment as a result of historical inputs sediment porewaters contain significant concentrations of fe mn zn and phosphate bacterial fe iii and mn iv reduction are hypothesised to supply fe2 and mn2 to porewaters with phosphate released from fe oxide reduction or organic matter oxidation petrographic observations indicate that the metal rich glass grains are undergoing chemical dissolution during early diagenesis supplying fe and zn to porewaters the most abundant authigenic mineral in the sediments is vivianite fe3 po4 2 8h2o containing a significant level of redlingite with minor framboidal pyrite fes2 electron microprobe analysis shows the vivianite to contain zn cu and pb suggesting that vivianite acts as a long term sink for these metals in this sediment this implies that authigenic vivianite in freshwater sediments may act as a long term sink for metals in a similar manner to sulphides in marine sediments this study highlights that the nature of detrital and diagenetic mineralogy in addition to porewater and sediment chemistry needs to be considered in assessing contaminated sediments

2000 years of sediment borne heavy metal storage in the yorkshire ouse basin ne england uk floodplain overbank sediments are often used to evaluate the influence of environmental change on sediment and chemical fluxes within river basins this paper presents the results of an investigation of heavy metal storage in seven floodplain reaches in the yorkshire ouse basin in north east england floodplain heavy metal storage has been greatest since c 1750 and many of the post 1750 sedimentary units exhibit heavy metal values that exceed recommended trigger and guideline values for contaminated land relatively high heavy metal storage occurs from ad 1250 1750 in most of the reaches these patterns are related to 2000 years of pb and zn mining in the yorkshire dales and c 250 300 years of industrial and urbanization activity around leeds and bradford and increased delivery of fine grained sediment during the last millennium possibly owing to factors such as population growth and agricultural expansion during the middle ages and climate change during the little ice age copyright 1999 john wiley sons ltd

microbial acetogenesis as a source of organic acids in ancient atlantic coastal plain sediments field and laboratory evidence shows that deeply buried 90 888 m fine grained sediments of the atlantic coastal plain contain viable acetogenic microorganisms and that these microorganisms actively produce organic acids concentrations of formate acetate and propionate in pore waters extracted from fine grained sediments ranged from 50 m to 5 m m and were much higher than in adjacent pore waters associated with sandy sediments m laboratory studies showed that asceptically cored fine grained sediments incubated under a h 2 atmosphere produced formate and acetate and that h 14 co 3 was converted to 14 c acetate and 14 c formate over time an enrichment culture of these acetogenic microorganisms was recovered from one long term incubation that showed the presence of several morphologically distinct gram positive rod shaped bacteria these microorganisms were capable of growth under autotrophic h 2 co 2 heterotrophic syringate and mixotrophic h 2 co 2 syringate conditions these results suggest that microbial acetogenesis rather than abiotic processes is the most important organic acid producing mechanism during low temperature 30 c diagenesis of atlantic coastal plain sediments

decoupling of as and fe release to bangladesh groundwater under reducing conditions part i evidence from sediment profiles this study reexamines the notion that extensive as mobilization in anoxic groundwater of bangladesh is intimately linked to the dissolution of fe oxyhydroxides on the basis of analyses performed on a suite of freshly collected samples of aquifer material detailed sediment profiles extending to 40 to 70 m depth below the surface were obtained at six sites where local groundwater as concentrations were known to span a wide range the sediment properties that were measured include 1 the proportion of fe ii in the fe fraction leached in hot 1 2 n hcl 2 diffuse spectral reflectance and 3 magnetic susceptibility in parallel with local concentrations of dissolved as ranging from 5t o 600g l fe ii fe ratios in shallow gray holocene sands tended to gradually increase with depth from values of 0 3 to 0 5 to up to 0 9 in deeper orange aquifers of presumed pleistocene age that were separated from shallow sands by a clay layer and contained 5 g l dissolved as leachable fe ii fe ratios averaged 0 2 there was no consistent relation between sediment fe ii fe and dissolved fe concentrations in groundwater in nearby wells the reflectance measurements indicate a systematic linear relation r 2 of 0 66 n 151 between the first derivative transform of the reflectance at 520 nm and fe ii fe the magnetic susceptibility of the shallow aquifer sands ranged from 200 to 3600 x 10 9 m 3 kg si and was linearly related r 2 of 0 75 n 29 to the concentrations of minerals that could be magnetically separated 0 03 to 0 79 dry weight no systematic depth trends in magnetic susceptibility were observed within the shallow sands although the susceptibility of deeper low as aquifers was low up to 200 10 9 m 3 kg si

lower crustal fluid distribution in the northeastern japan arc revealed by high resolution 3d seismic tomography abstract the ou backbone range strikes northwards through the central northeastern japan arc and is bounded on both sides by the active reverse uwandaira and sen ya faults we have applied a traveltime inversion method seismic tomography with spatial velocity correlation to active and passive seismic data in order to investigate a three dimensional 3 d velocity structure the data set contains 33 993 p and 18 483 s wave arrivals from 706 natural sources and 40 blasts as well as 2803 p wave traveltime data from 10 explosions detonated during the 1997 controlled source experiment the traveltime inversion reveals a zone beneath the ou backbone range in which p wave velocities vp are approximately 6 8 lower than the average velocity at equivalent depths the low vp and a low vp to s wave velocity vs ratio vp vs of about 1 65 suggest the presence of aqueous fluids in the middle crust

the occurrence identification and environmental relevance of vivianite in waterlogged soils and aquatic sediments abstract in this article we review the nature occurrence and environmental relevance of the authigenic ferrous iron phosphate mineral vivianite fe 3 po 4 2 8h 2 o in waterlogged soils and aquatic sediments we critically discuss existing work from freshwater and marine systems laboratory studies and microbial batch culture experiments aiming to deduce common characteristics of the mineral s occurrence and the processes governing its formation vivianite regularly occurs in close association with organic remains in iron rich sediments simultaneously it is a biogenic mineral product of metal reducing bacteria these findings suggest that vivianite nucleation in natural systems is directed by the activity of such bacteria and crystal growth is particularly favoured within protected microzones taking into account recent findings from coastal marine sediments where vivianite authigenesis has been shown to be coupled to the anaerobic oxidation of methane small scale microbially mediated reactions appear to be crucial for the formation of vivianite small scale heterogeneity within the sediment matrix may also explain why saturation calculations based upon bulk pore water constitutions often fail to accurately predict the occurrence of the mineral vivianite is not restricted to a specific trophic state of a system the mineral forms in oligotrophic as well as in eutrophic waters however depending on the iron inventory the production supply and degradation of organic matter determine the relative contribution of iron sulphide formation to the iron pool and the concentration of inorganic phosphate and fe 2 in pore waters thus vivianite authigenesis is also governed by bulk chemical conditions such as the rate of sulphide formation relative to that of fe 2 production this situation allows stimulation of vivianite formation by iron supplementation aimed at restoring eutrophic lakes recent results from coastal marine sediments suggest that vivianite authigenesis is of significance for p burial in the marine realm vivianite authigenesis is likely important at the global scale but has so far largely been ignored

magnetotelluric imaging of the fault rupture area of the 1999 izmit turkey earthquake abstract wide band 320 0 001 hz and long period 0 01 0 0001 hz magnetotelluric mt data were acquired along two profiles crossing the western part of the north anatolian fault zone nafz turkey which consists of two main fault branches the first profile izmit profile crosses the epicentral area of the 17 august 1999 izmit earthquake in fact the mt measurements along this profile started just a few weeks before the occurrence of the mainshock and four instruments happened to be in operation in the vicinity of the fault when the earthquake took place the second profile adapazari profile is located about 30 km east of the first profile two dimensional modeling shows the following results first the hypocenters of mainshock and aftershocks are located on the highly resistive side near the edge of a conductive zone second the long period mt data show a low resistivity zone extending down to 50 km between the two fault branches such a deep conductive zone is interpreted as representing partial melting resulted from the past complex tectonics in this region and it is related to the non seismic after slip in the layer below the seismogenic zone characterized by the highly resistive layer

evidence for middle triassic to miocene dual subduction zones beneath the shan thai terrane western thailand from magnetotelluric data abstract kanchanaburi province western thailand is in the middle of shan thai terrane paleomagnetic and geological data support the hypothesis of dual subduction zones beneath the shan thai terrane during the late triassic there was a westward subduction in the east where the lampang chiang rai block subducted beneath the shan thai terrane in addition in the early tertiary the western burma terrane subducted underneath the shan thai in the west resulting in an eastward subduction a pioneer survey of this region was therefore conducted using magnetotelluric mt techniques with the aim of finding deep structures associated with these ancient subduction zones 39 mt stations were deployed to cover most of the province resistivity structures are obtained from the 3 d inversion the near surface resistivity structures correspond well with the surface geology the mid and lower crusts are conductive and this is interpreted as the crusts being composed of mafic granulites of 3 porosity in which the remnant dehydrated fluid was accumulated during the subduction in addition the westward and eastward subduction zones generated mafic ultramafic intrusions which appear as two conductive zones on the east and west respectively these two conductors and the conductive lower crust support the hypotheses of the middle triassic to miocene dual subduction zones

large heterogeneous structure beneath the atotsugawa fault central japan revealed by seismic refraction and reflection experiments abstract a high strain rate zone termed the niigata kobe tectonic zone is located in central japan and contains an active right lateral fault called the atotsugawa fault we present the results of an explosive source seismic experiment that focused on identifying the formation mechanisms of the fault the experiment used seven explosive sources and 1108 seismic stations and was undertaken during october 2007 in the area of the atotsugawa fault the seismic stations were set up on a survey line with a length of 170 km oriented orthogonal to the strike of the fault the linear array was used to identify the seismic structure of the fault zone and the deeper parts of the crust in the study area yielding fine details of the seismic structure of the crust along the profile line including lateral variations in p wave velocity and the configuration of layers in the crust a relatively low p wave velocity reflective zone was detected beneath the fault at depths of 15 25 km this zone also has extremely low s wave velocities directly underlies three active faults and contains three low resistivity zones that underlie these faults these reflective and low resistivity zones are thought to represent fluid within the crust and the data obtained during this study are consistent with a weak zone model for the formation of the active faults in the study area this suggests that the reflective layer represents a weak zone in the lower crust that is responsible for the concentration of deformation within the upper crust the presence of abundant fluids beneath the atotsugawa fault could also reduce the strength of the lower crust again focusing deformation related to the regional stress regime in areas that overlie these fluid containing zones the results suggest that the reflective layer was an important factor in the formation of the atotsugawa fault

mineralogical and geochemical signature of mine waste contamination tresillian river fal estuary cornwall uk the mineralized district of sw england was one of the world s greatest mining areas with mining commencing in the bronze age peaking in the 1850s to 1890s but still continuing to the present day consequently it is not surprising that mining has had a major impact on the environmental geochemistry of sw england in this study the mineralogical and geochemical signature of mine waste contamination within the fal estuary at tresillian cornwall has been examined a pulse of mine waste contamination is recognized at approximately 50 cm below present day sediment surface sn as cu pb and zn are all enriched within this contaminated interval with up to 1800 mg kg 1 sn 290 mg kg 1 as 508 mg kg 1 pb 2210 mg kg 1 zn and 1380 mg kg 1 cu within this interval the dominant minerals present include chalcopyrite arsenopyrite pyrite cassiterite fe ti oxides ilmenite and rutile wolframite sphalerite baryte zircon monazite tourmaline and xenotime in addition man made slag products commonly occur the exact timing of the release of mine waste into the estuary is poorly constrained but probably occurred during or immediately following the peak in mining activity in the nearby camborne redruth district which was between 1853 and 1893 the mine waste may have entered the estuary either via the tresillian river and its tributaries or via calenick creek and the truro river and or the carnon river which flows into rostronguet creek