active deformation and relief evolution in the western lurestan region of the zagros mountain belt new insights from tectonic geomorphology analysis and finite element modeling 2 d finite element modeling of both coseismic and interseismic deformation was performed along a transect across the seismogenic fault of the mw 7 3 november 2017 lurestan earthquake zagros mount

slip distribution of the 1997 umbria marche earthquake sequence joint inversion of gps and synthetic aperture radar interferometry data 1 in september october 1997 a seismic sequence struck the southern part of the umbria marche region in central italy the three largest earthquakes took place on 26 september 0033 ut mw 5 7 09 40 gu mw 6 0 near colfiorito and on 14 october mw 5 6 near sellano we present a slip model for the main sequence over two separate fault planes we use previously published global positioning system gps and differential interferometric synthetic aperture radar dinsar data as well as new dinsar data covering the sellano event as input to a simulated annealing solution for the distribution of fault slip the combination of both types of geodetic data as well as the combination of sar interferograms from both ascending and descending satellite tracks allows us to make a more complete geodetically based assessment of the fault slip for these earthquakes for the solutions presented here we required the slip distribution to match the observed surface displacements while maintaining a total scalar seismic moment approximately equal to the seismologically inferred moments for this sequence we find the slip was concentrated in a zone at 4 5 5 km depth with a shallower tail extending to near the surface at the northern end of the colfiorito sequence for both the second colfiorito event and the sellano event individual patches were calculated with maximum slip of 2 m implying stress drops as high as 20 mpa coulomb stress calculations show that the coseismic slip distribution for the colfiorito events facilitated slip of the adjacent sellano earthquake

alongshore momentum balances in the nearshore the one dimensional time averaged over many wave periods along shore momentum balance between forcing by wind and breaking waves and the bottom stress is examined with field observations spanning a wide range of con ditions on a barred beach near bottom horizontal currents were measured for 2 months at 15 locations along a cross shore transect extending 750 m from the shoreline to 8 m water depth the hourly averaged bottom stress was estimated from observed currents using a quadratic drag law the wave radiation stress was estimated in 8 m depth from an array of pressure sensors and the wind stress was estimated from an anemometer at the seaward end of a nearby pier the combined wind and wave forcing integrated over the entire cross shore transect is balanced by the integrated bottom stress the wind stress contributes about one third of the forcing over the transect analysis of the momentum balances in different cross shore regions shows that in the surf zone wave forcing is much larger than wind forcing and that the bottom drag coefficient is larger in the surf zone than farther seaward consistent with earlier studies

analysis of seismological and geological observations formoderate size earthquakes the colfiorito fault system central apennines italy to contribute to the understanding of the relationships between moderate earthquakes and the faults that are recognisable in the geological record we analysed seismological and geological data related to the 1997 98 umbria marche central italy earthquake swarm the seismological recordings collected by local networks allowed accurate location of about 1000 events whereas the geological field observations provided a picture of the structural features and the ground surface deformations we also re examined and utilised some already published data and results mostly about the fault plane solutions and the geology on the basis of earthquake locations fault plane solutions and geological mapping we explored the possible correlation between the earthquake causative fault planes and the normal faults exposed in the area our results show that the two mainshocks that occurred on september 26 1997 mw 5 7 and mw 6 0 originated on the same structure reactivating at depth the colfiorito normal faults both ruptures did not propagate up to the ground surface but triggered gravitational sliding that occurred along pre existing fault scarps the earthquake that occurred on october 14 1997 mw 5 6 originated on another fault branch at a much shallower depth in spite of the lower magnitude this earthquake produced tectonic ruptures where the fault plane projects to the surface in an area where no faults were previously mapped by comparing the paleostress reconstruction based on slickenside lineations analysis and the focal mechanism solutions we also suggest a possible correlation between the long term early middle pleistocene cumulative effects of the colfiorito fault system and the short term behaviour of the fault planes observed during this earthquake swarm favouring the idea of a seismogenic source producing clustered moderate size earthquakes rather than large events scattered in time our results suggest that the integration of geological and seismological observations can constrain the seismotectonic interpretations in regions of low level seismicity and that this integration can pose a reliable basis in the seismic hazard assessment

aeration due to breaking waves part i bubble populations abstract the population of bubbles produced by breaking waves in 10 m winds of up to 12 m s 1 is analyzed using calibrated images from a vertical pencil beam sonar system placed on the seabed near the dutch coast the structure in the images is parameterized and the volumetric bubble backscatter is inverted to yield bubble concentrations data were obtained at three acoustic frequencies with inversion effected by prescribing a bubble spectrum with two free variables leaving a redundant measurement to test the robustness of the model median concentrations may in this way be obtained up to the sea surface measurements are multiply regressed on wind and dominant wave variables bubbles penetrate to a depth of about a factor of 6 1 times the significant wave height hs where is the wave age or ratio of dominant wave phase speed to wind speed the measured mean bubble radius decreases weakly with depth unless waves are gently sloping at about 5 m 1 at 0 4 m the mean radius ranges from 30 to 80

textural and mineralogical biosignatures in an unusual microbialite from death valley california abstract for in situ astrobiological studies of mars or other planets we must employ strategies that will enable us to verify whether our approach and prototype instruments are actually capable of distinguishing life from non life this must be done against a background of rigorously conducted scientific characterization of the environment or sample types being considered for measurement by the instruments under development in this study we show how a combination of mineralogical and textural features can be considered a biosignature in an early mars analogue environment death valley california we propose that it is a combination of features in context of the geologic matrix which allows determination of biogenicity to be made polymineralic microbialites organosedimentary formations constructed by microorganisms from a spring pool at badwater within death valley national park are composed of alternating biogenic and abiogenic minerals in a distinct triplet sequence related to wet and dry seasons a microbial community occurring as a black biofilm produced paired layers of two different mineral types manganese oxyhydroxides and calcite these biogenic layers are separated from the next pair by a gypsum layer and appear to be laid down in the wet season with the gypsum a mineral positively identified on mars precipitating in the dry part of the year abiogenically i e not dependent on microbial metabolic activity for its deposition in addition textural features smaller grain size and less geometric morphology unique to the biogenic vs the abiogenic layers were consistently observed so that texture served as a biosignature in this environment

inversion of synthetic geodetic data for dip slip faults clues to the effects of lateral heterogeneities and data distribution in geological environments typical of the apennines italy

an urban model for dolomite precipitation authigenic dolomite on weathered building stones abstract formation of authigenic dolomite within alteration crusts developing on limestone surfaces of a historical building is confirmed by xrd polarising microscopy and sem with edx data two different types of authigenic dolomite occur limpid stoichiometric dolomite and ca rich protodolomite the presence of gypsum calcite pollution derived particles clay minerals and organic material within the crusts confirms their recent formation together with that of dolomite in a micro environment of high evaporation and ionic concentrations such environments are typically found in many urban centres on the basis of these findings an urban model for dolomite precipitation is proposed there are two sources of mg 1 dissolution of nearby dolostones overlying the limestones as a result of leaching by atmospheric so2 oxidised and hydrolysed as h2so4 and 2 mg rich metallic atmospheric particles elevated mg ca values are achieved by precipitation of gypsum which removes ca from the solution protodolomite then precipitates and later recrystallises as limpid dolomite due to changes in the pore fluids related with the environmental conditions co32 and co3h are provided by leaching of both the limestone support and the nearby dolostones additional sources of co2 are provided both by the polluted urban atmosphere rain water and the degradation of organic material within the crust organic matter fungi and bacteria pollution derived particulate matter and clays seem to play a key role in promoting dolomite precipitation in this micro environment by altering kinetic barriers and providing active sites for dolomite nucleation finally the formation of urban dolomite is compared with recent dolomites forming in natural environments with alternating evaporative fresh water conditions

finite element modelling of stress field perturbations and interseismic crustal deformation in the val d agri region southern apennines italy abstract the val d agri area provides the opportunity to analyse active structures in a seismic region for which a large amount of subsurface data is available this area which was struck in 1857 by one of the most destructive earthquakes in italy mw 7 03 represents a unique natural laboratory to gain new insights into geometry modes and rates of faulting controlling crustal deformation in an actively extending orogen in this study a crustal geological section through the southern apennines is discretized into a finite element model fem we present a 2d elastoplastic fem that reproduces stress perturbations and strain field around the val d agri active fault system the influence of fault strand activity on interseismic crustal deformation is tested by a series of computer models whose predictions are compared with the horizontal velocity components of continuous gps sites in the region and with stress directions and geological data the best fit with available geological and geophysical constraints is obtained with a 300 km long 29 km deep model formed by a multilayer including three components having different rheological characteristics and including several shallow locked fault segments which branch into a freely slipping major basement fault at depth finite element modelling provides new insights into the controversial and widely debated active tectonic setting of the study area pointing out the fundamental role played by a structural reactivation process involving inherited long lived mature fault systems at depth our fem reconciling apparently contrasting geological and geophysical constraints from the study area points to maximum stress build up and strain accumulation at a depth of 15 5 km such a depth range is suggested as the most likely one for the nucleation of large events such as the 1857 val d agri earthquake

compositional controls on early diagenetic pathways in fine grained sedimentary rocks implications for predicting unconventional reservoir attributes of mudstones diagenesis significantly impacts mudstone lithofacies processes operating to control diagenetic pathways in mudstones are poorly known compared to analogous processes occurring in other sedimentary rocks selected organic carbon rich mudstones from the kimmeridge clay and monterey formations have been investigated to determine how varying starting compositions influence diagenesis the sampled kimmeridge clay formation mudstones are organized into thin homogenous beds composed mainly of siliciclastic detritus with some constituents derived from water column production e g coccoliths s depleted type ii kerogen as much as 52 6 total organic carbon toc and others from diagenesis e g pyrite carbonate and kaolinite the sampled monterey formation mudstones are organized into thin beds that exhibit pelleted wavy lamination and are predominantly composed of production derived components including diatoms coccoliths and foraminifera in addition to type iis kerogen as much as 16 5 toc and apatite and silica cements during early burial of the studied kimmeridge clay formation mudstones the availability of detrital fe iii and reactive clay minerals caused carbonate and silicate buffering reactions to operate effectively and the pore waters to be fe ii rich these conditions led to pyrite iron poor carbonates and kaolinite cements precipitating preserved organic carbon being s depleted and sweet hydrocarbons being generated in contrast during the diagenesis of the sampled monterey formation mudstones sulfide oxidation coupled with opal dissolution and the reduced availability of both fe iii and reactive siliciclastic detritus meant that the pore waters were poorly buffered and locally acidic these conditions resulted in local carbonate dissolution apatite and silica cements precipitation natural kerogen sulfurization and sour hydrocarbons generation differences in mud composition at deposition significantly influence subsequent diagenesis these differences impact their source rock attributes and mechanical properties

presence of sulfate does not inhibit low temperature dolomite precipitation abstract the hypothesis that sulfate inhibits dolomite formation evolved from geochemical studies of porewaters from deep sea sedimentary sequences and has been tested with hydrothermal experiments we examined the sulfate inhibition factor using aerobic culture experiments with virgibacillus marismortui and halomonas meridiana two moderately halophilic aerobic bacteria which metabolize independent of sulfate concentration the culture experiments were conducted at 25 and 35 c using variable so42 concentrations 0 14 28 and 56 mm and demonstrate that halophilic aerobic bacteria mediate direct precipitation of dolomite with or without so42 in the culture media which simulate dolomite occurrences commonly found under the earth s surface conditions hence we report that the presence of sulfate does not inhibit dolomite precipitation further we hypothesize that if sedimentary dolomite is a direct precipitate as in our low temperature culture experiments the kinetic factors involved are likely to be quite different from those governing a dolomite replacement reaction such as in hydrothermal experiments consequently the occurrence and presumably growth of dolomite in so42 rich aerobic cultures may shed new light on the long standing dolomite problem

vertical structure of dissipation in the nearshore abstract the vertical structure of the dissipation of turbulence kinetic energy was observed in the nearshore region 3 2 m mean water depth with a tripod of three acoustic doppler current meters off a sandy ocean beach surface and bottom boundary layer dissipation scaling concepts overlap in this region no depth limited wave breaking occurred at the tripod but wind induced whitecapping wave breaking did occur dissipation is maximum near the surface and minimum at middepth with a secondary maximum near the bed the observed dissipation does not follow a surfzone scaling nor does it follow a log layer surface or bottom boundary layer scaling at the upper two current meters dissipation follows a modified deep water breaking wave scaling vertical shear in the mean currents is negligible and shear production magnitude is much less than dissipation implying that the vertical diffusion of turbulence is important the increased near bed secondary dissipation maximum results from a decrease in the tu

calcium isotope evidence for suppression of carbonate dissolution in carbonate bearing organic rich sediments pore fluid calcium isotope calcium concentration and strontium concentration data are used to measure the rates of diagenetic dissolution and precipitation of calcite in deep sea sediments containing abundant clay and organic material this type of study of deep sea sediment diagenesis provides unique information about the ultra slow chemical reactions that occur in natural marine sediments that affect global geochemical cycles and the preservation of paleo environmental information in carbonate fossils for this study calcium isotope ratios 44 40ca of pore fluid calcium from ocean drilling program odp sites 984 north atlantic and 1082 off the coast of west africa were measured to augment available pore fluid measurements of calcium and strontium concentration both study sites have high sedimentation rates and support quantitative sulfate reduction methanogenesis and anaerobic methane oxidation the pattern of change of 44 40ca of pore fluid calcium versus depth at sites 984 and 1082 differs markedly from that of previously studied deep sea sites like 590b and 807 which are composed of nearly pure carbonate sediment in the 984 and 1082 pore fluids 44 40ca remains elevated near seawater values deep in the sediments rather than shifting rapidly toward the 44 40ca of carbonate solids this observation indicates that the rate of calcite dissolution is far lower than at previously studied carbonate rich sites the data are fit using a numerical model as well as more approximate analytical models to estimate the rates of carbonate dissolution and precipitation and the relationship of these rates to the abundance of clay and organic material our models give mutually consistent results and indicate that calcite dissolution rates at sites 984 and 1082 are roughly two orders of magnitude lower than at previously studied carbonate rich sites and the rate correlates with the abundance of clay our calculated rates are conservative for these sites the actual rates could be significantly slower because other processes that impact the calcium isotope composition of sedimentary pore fluid have not been included the results provide direct geochemical evidence for the anecdotal observation that the best preserved carbonate fossils are often found in clay or organic rich sedimentary horizons the results also suggest that the presence of clay minerals has a strong passivating effect on the surfaces of biogenic carbonate minerals slowing dissolution dramatically even in relation to the already slow rates typical of carbonate rich sediments

the solubility of calcite and aragonite in sulfate free seawater and the seeded growth kinetics and composition of the precipitates at 25 c the influence of dissolved sulfate ions on the precipitation kinetics and composition of calcite and aragonite overgrowths was investigated in artificial seawater solutions at 25 c using a constant disequilibrium technique the solubility of both minerals in sulfate free seawater was determined to allow the expression of the saturation state of precipitating solutions as the ratio of the caco3 ion concentration product to their stoichiometric solubility constant so2 4 ions inhibit both calcite and aragonite precipitation the inhibition in seawater is not selective and therefore whether in the presence or absence of 0 028 m so2 4 aragonite precipitates more rapidly on aragonite seeds than calcite does on calcite seeds from supersaturated solutions srco3 incorporation in aragonite is independent of the precipitation rate and unaffected by so2 4 ions in seawater the distribution coefficient of sr2 in aragonite overgrowths precipitated from seawater is 0 97 0 08 while a value of 1 05 0 09 is obtained in sulfate free seawater in contrast mgco3 incorporation in calcite overgrowths is influenced significantly by the presence or absence of so2 4 ions in seawater while the distribution coefficient of mg2 in calcite is also independent of the precipitation rate its value increases from 0 0172 0 0022 in seawater to 0 0230 0 0026 in sulfate free seawater corresponding respectively to the precipitation of 8 1 1 and 10 5 1 mole magnesian calcites

rare earth elements in cold seep carbonates from the southwestern dongsha area northern south china sea the circulation of methane rich fluids at cold seeps often leads to the precipitation of seep carbonates close to the seafloor along continental margins which can be used as records of past fluid seepage rare earth element ree concentrations in seep carbonates have been used to trace fluid sources and provide information on associated biogeochemical processes at cold seeps the ree concentrations of a series of carbonates collected from cold seeps in the southwestern dongsha area of the northern south china sea are analyzed in this study the total ree contents sigma ree of the seep carbonates analyzed show a wide variation from 17 ppm to 523 ppm with an average sigma ree value of 54 ppm which are higher than the carbonates from other cold seep areas a positive correlation between fe mn content and sigma ree was observed these results suggest that the seep carbonates of this study were primarily controlled by the methane derived fluid from which they precipitated the fe rich dolomite and siderite which are the main components of the carbonates are responsible for the enrichment of the ree a slight positive ce anomaly observed in the shale normalized ree patterns of the studied seep carbonates suggests that they formed in anoxic conditions and the correlations between ce ce and la n sm n ce ce and dy n sm n ce ce and sigma ree further reveal that the ree characteristics of most seep carbonate samples preserve the original redox conditions in which they precipitated and late diagenesis has had little effect on the ree however the ree characteristics of sub samples ds2 2b ds1 6a and ds1 7a are very different from those of the other sub samples indicating a greater impact of late diagenesis and post oxidation favored ree enrichment c 2014 elsevier ltd all rights reserved

directional attributes of the ocean surface wind stress vector in a recent paper by geernaert 1988 it was suggested that the stress and wind vectors are rarely aligned and that the deviation of the stress vector direction from the wind vector is related to the surface heat flux it was argued that since cold air advection over the open ocean generally corresponds to upward heat flux the consequent rotation of the winds to the right with height during cold air advection could be responsible for observations of the stress vector to be to the right of the wind flow for unstable stratifications conversely observations of the stress vector to the left of the flow for stable stratifications were suggested to be associated with the turning of the wind vector to the left of the flow for warm air advection or downward heat flux in that study only 30 of the statistical variance of the angle between the wind and wind stress vectors could be explained by air sea heat flux and it was suggested that the orbital velocity spectrum of surface waves i e data unavailable in that study could be important for explaining at least part of the remaining variance in this study we report on measurements of the wind stress vector and wave directional spectrum collected during the synthetic aperture radar x band ocean nonlinearities experiment conducted on the chesapeake light tower during 1988 the experiment yielded data reported herein that provide convincing evidence that the stress vector direction during light winds and near zero air sea heat flux is governed in large part by the direction of long waves on the ocean surface further the measurements suggest that the stress vector has a direction which is a blend between the wind direction and the swell direction

elastic modeling of the alto tiberina normal fault central italy geometry and lithological stratification influences on the local stress field abstract two dimensional elastic plane strain finite element models fems are generated to study the state of stress and failure induced by a low angle normal fault the alto tiberina fault of the northern apennines central italy it is beyond the scope of the present work to show that slip can occur on such a fault the numerical study was performed to evaluate the influences on the local stress field of the litho mechanical stratification of formations surrounding the fault and those induced by the geometry of the fault the performed models have shown the important role played by evaporites and basement formations of the umbria marche succession as seismogenetic layers the model results have also underlined that the flat ramp geometry of the fault induces high relative concentration of stresses in correspondence with the low angle east dipping synthetic normal faults observed today in shallow depth near the alto tiberina surface trace the stress regime predicted by the final model in which the behavior of the alto tiberina together with the antithetic normal fault of gubbio was simulated reconciles available geological and geophysical observable to a greater extent the numerical results can assist interpretation of the tectonic evolution of the region

evolution of the elastic moduli of seismogenic triassic evaporites subjected to cyclic stressing seismic cycles lead to variations in rock physical properties quantifying these changes is of key importance in building reliable crustal deformation models here we report laboratory measurements of the uniaxial compressive strength ucs young s modulus and poisson s ratio both static es s and dynamic ed d of the seismogenic triassic evaporites of the northern apennines triassic evaporites are composed of dolostones anhydrites and gypsum gypsum was the weakest lithology with ucs values ranging from 10 to 26 mpa anhydrite exhibited intermediate values from 52 to 144 mpa and dolostones were the strongest with a maximum ucs of 228 mpa during uniaxial cyclic stressing experiments we observed complex variations in es and s with large increases are observed in the early cycles stage 1 followed by essentially constant values stage 2 before es decreases and s increases approaching failure stage 3 complementary microseismicity acoustic emission ae data show no significant ae during stage 1 then the stress needed to induce ae remained essentially constant stages 2 and 3 integration of mechanical data with microstructural observations suggests a first stage dominated by compaction and strengthening a second stage characterised by quasi elastic behaviour associated with the development of randomly oriented microfractures and a third stage of weakening due to the growth of macrofractures parallel to the direction of the load laboratory dynamic elastic moduli are on average in agreement with dynamic elastic moduli used in crustal modelling however static values of young s modulus are about 50 lower than dynamic ones and static values of poisson s ratio are about 40 higher with respect to dynamic values these observations suggest that the frequency effect on the difference between laboratory and crustal scale dynamic moduli values is rather small and that static values of modulus are more appropriate for crustal deformation modelling than seismically derived values

diagenetic signatures of stratal surfaces in the upper jurassic fulmar formation central north sea ukcs sedimentation rate and changes in relative sea level affect early diagenetic cementation along key stratal surfaces within the deeply buried upper jurassic fulmar formation south central graben ukcs as a result of the bioturbated nature of the shallow marine strata variations in ichnofabrics and cross cutting relationships between trace fossils are important in identifying and correlating stratal surfaces two transgressive and two regressive surfaces sequence boundaries were studied using petrographical mineralogical and geochemical techniques cements including early diagenetic pyrite framboids grain rimming apatite microcrystalline dolomite and ankerite occur at above and immediately below both transgressive and forced regressive surfaces sequence boundaries breaks or subdued rates of sedimentation associated with both types of surfaces meant that the sediment package resided within early diagenetic zones for prolonged periods of time enhancing diagenetic reactions at and below the surfaces the distribution of ankerite despite being a deep burial cement was primarily controlled by concentrations of bioclasts that are particularly abundant at transgressive surfaces the diagenetic character of the forced regressive surfaces sequence boundaries is more complex than that of the transgressive surfaces both in terms of mineralogy and paragenesis this is attributed to the superimposition of diagenetic assemblages as a result of erosion re sedimentation and sediment by passing although the diagenetic signature of the surfaces has been modified by dissolution replacement reactions during deep burial early diagenetic signatures can still be distinguished

the september 26 1997 colfiorito italy earthquakes modeled coseismic surface displacement from sar interferometry and gps the largest events of the 1997 umbria marche seismic sequence were the two september 26 earthquakes of mw 5 7 00 33 gmt and mw 6 0 09 40 gmt which caused severe damage and ground cracks in a wide area around the epicenters we created an ers sar differential interferogram where nine fringes are visible in and around the colfiorito basin corresponding to 25 cm of coseismic surface displacement gps data show a maximum horizontal displacement of 14 1 8 cm and a maximum subsidence of 24 3 cm we used these geodetic data and the seismological parameters to estimate geometry and slip distribution on the fault planes modeled fault depths and maximum slip amplitudes are 6 5 km and 47 cm for the first event and 7 km and 72 cm for the second one in good agreement with those derived from the seismological data

origins of microbial microstructures in the neoproterozoic beck spring dolomite variations in microbial community and timing of lithification abstract microbialite microstructures form at the scale of microbial processes and can preserve evidence of growth degradation and lithification in microbial communities understanding how these processes are preserved in microstructures will provide insights into microbial ecosystems and how microbial communities have evolved through time microbialites in the neoproterozoic beck spring dolomite southern california u s a contain microstructures that record variations in the morphology of microbial communities as well as the timing of degradation versus lithification in the communities these processes are represented by five end member microbial microstructures 1 distinct laminated microstructure 2 diffuse laminated microstructure 3 distinct clotted microstructure 4 diffuse and regular clotted microstructure and 5 diffuse and irregular clotted microstructure these microstructures are distinguished by fabrics defined by organic inclusions in distinct microstructures organic inclusions sharply define microbial features such as laminae that are laterally continuous for millimeters or 50 200 micron diameter microdots the contacts between distinct microstructures are always sharp in diffuse microstructures zones of organic inclusions lack distinct boundaries neighboring laminae and clots grade into each other within tens of microns and boundaries between microbial structures and encasing cements are indistinct diffuse microstructures grade into each other and into distinct microstructures in a systematic way that suggests that differences are due to variations in the timing of mineralization relative to growth and degradation of microbial communities sharply defined textures in distinct microstructures suggest that lithification started during growth of the microbial community and the close spatial association but lack of intergrading between distinct laminated and distinct clotted microstructures suggests that they formed from two distinct microbial communities that lived in the same environment by contrast diffuse microstructures formed where lithification occurred after the onset of decay and degradation of the primary growth structure the continuum from distinct microbial textures through more diffuse and irregular textures documents variations in the timing of lithification relative to growth and decay of the microbial community thus where petrographic preservation is extremely good such as in the beck spring dolomite sub millimeter scale microbial microstructures record a gradation between growth and degraded microbial structures depending on the relative timing of lithification and heterotrophic decay

3 d finite element modelling of deformation and stress associated with faulting effect of inhomogeneous crustal structures summary modelling of deformation and stress caused by earthquake faulting or fault motion based on a homogeneous elastic half space model does not include crustal rigidity layering and lateral variations geological data and seismic surveys indicate that the crust is elastically inhomogeneous and that rigidity layering and heterogeneities are likely to affect the magnitude and pattern of deformation and stress we use the finite element method fem to investigate deformation and stress generated by strike slip tensile and thrust faulting considering rigidity layering in the crust for a fault with a dimension of 25 10 km and a slip value of 0 5 m cutting through the top 10 km of the crust the deformation and stress change associated with the three modes of faulting are calculated for an island arc crustal structure represented by three models of rigidity layering the results indicate i the maximum effect in horizontal displacements due to crustal layering for the investigated models is 19 7 mm and 28 8 mm for strike slip and tensile faulting respectively for thrust faulting the effect is up to 58 3 mm this remarkable effect is due to the offset of layers by thrust faulting which dynamically changes the crustal structure both horizontally and vertically ii the maximum effect in vertical deformation due to crustal rigidity layering for strike slip and tensile faulting is 5 mm in contrast the effect for thrusting is 30 3 mm iii the effect in the shear stress change at a depth of 7 5 km for the different styles of faulting ranges from 0 02 mpa to 0 10 mpa an additional modelling analysis of subduction thrusting at the japan trench with a detailed structural model based on seismic surveys further confirms the significant distortion caused by a homogeneous model that ignores crustal structural information overall the effect of crustal rigidity layering is at least 20 per cent for surface deformation and 15 per cent for stress changes at depth in light of the present accuracy of global positioning system gps observations 2 mm and the estimate of stress change required for earthquake hazard analysis ca 0 01 mpa the results from the numerical experiments indicate that crust inhomogeneity rigidity layering and lateral variations should be included in any quantitative models of faulting

a low angle normal fault in the umbria region central italy a mechanical model for the related microseismicity abstract in the northern apennines the upper crust is thinned by a set of east dipping low angle normal faults lanfs the easternmost and more recent of these lanfs is the altotiberina fault atf located in northern umbria the geometry of the atf has been reconstructed matching surface geology with seismic reflection profiles and borehole data the fault whose average dip is 20 borders the upper pliocene quaternary tiber basin and has a displacement of about 8 km the deeper portion of the atf is located below the axial zone of the northern apennines where the strongest instrumental and historical seismicity is recorded the microseismicity of the region m 1 to evaluate the boundary conditions for the brittle activity of the atf the fault can be reactivated for low values of differential stress 1 3 t 10 mpa and tensile fluid overpressure p f 3 e g v 0 93 in the peculiar situation of the northern apennines the deep emissions of large amounts of co 2 documented in the area can be entrapped in their ascent by structural seals e g atf favouring localised fluid overpressures the impossibility of sustaining p f 3 for wide fault portions counteracted by hydraulic fracturing increased permeability under low effective stress and load weakening behaviour for normal faulting would prevent the nucleation of moderate ruptures along the fault the short lived attainment of p f 3 along small fault portions can account for the microseismic activity located along the atf which occurs on rupture surfaces in the range of 10 1 10 3 km 2

upper crust tomographic structure of the central apennines italy from local earthquakes abstract we derived a three dimensional p and s waves velocity model of the first 9 km of crust in the central apennine from local earthquakes the data set used for the tomographic inversion was recorded from three component regional and local networks which operated in the region from 1979 to 1998 and consists of 984 earthquakes for these earthquakes we have at least eight phases a gap smaller than 200 and a total rms residual smaller than 0 6 s giving a total of 13190 p and 10257 s phases first arrivals the inversion is performed using the simulps12 code this technique iterates the estimated velocity model parameters defined at the nodes of a grid relocating the earthquakes with an approximate 3 d ray tracing a large positive p and s wave velocity anomaly is observed in correspondence to the main seismogenetic volume of the central apennines a synthetic test demonstrates that this anomaly is not artificially produced by the substantially higher density of earthquakes within the seismic velocity anomaly this anomaly corresponds to the carbonatic rocks that form the core of the fold and thrust central apennines belt these rocks are underlain by ductile evaporite formations which were justaposed during the tectonic evolution of the belt we suggest that the evaporite layers effectively decouple the upper crustal seismogenetic volume from the middle and lower crust we conclude that the accumulation of seismic energy could be induced by gravitational tectonic processes explaining the fact that most of the seismicity is confined above the evaporites

synsedimentary diagenesis in a cryogenian reef complex ubiquitous marine dolomite precipitation abstract analysis of the synsedimentary diagenetic phases from a pervasively dolomitised cryogenian 650 ma reef complex south australia reveals a fundamentally different style of marine diagenesis to that of phanerozoic carbonates textural evidence from dolomitised and undolomitised lithologies of the oodnaminta reef complex indicates that depositional components were precipitated initially as calcium carbonate aragonite and calcite dissolution textures and preserved fabrics in ooids indicate an originally aragonitic mineralogy early fibrous marine cements that have well preserved fibrous crystallographic fabrics with a length fast optical character are likely to have precipitated as high magnesium calcite however following this very early phase of diagenesis the dominant marine process occurring in these reefs was dolomite precipitation this involved the dolomitisation of earlier depositional and diagenetic phases as well as the precipitation of fibrous dolomite cements these fibrous marine cements include the newly described radial slow fascicular slow radiaxial slow and rhombic dolomite cements the cements have optical properties chemical zonation and cathodoluminescent characteristics indicating that they were direct marine precipitates dolomite precipitation during marine diagenesis in this reef complex suggests that the oceans of the cryogenian were chemically different to those of the phanerozoic abundant dolomite formation appears to be linked to anoxic magnesium rich seawater during this time marine dolomite precipitation under these conditions may explain the abundance of dolomite in the precambrian sedimentary record

fem based inversion for heterogeneous fault mechanisms application at etna volcano by dinsar data summary a procedure based on the finite element method fem for high resolution geodetic data inversion was developed to estimate non uniform slip distribution during the 2002 september 22 m3 7 earthquake rupture occurring only one month before the 2002 2003 eruption of etna volcano fem generated synthetic green s functions are combined with an inverse algorithm to simulate deformation of the earthquake for a 3 d problem domain that takes into account heterogeneity of material properties in the volcanic edifice the inversion of dinsar data shows complex kinematics of the northeastern flank of the etna volcano involving the pernicana fault system we detailed the coseismic shear rupture mechanism and highlighted a tensile mechanism never observed before related to a first attempt of magma intrusion which preceded the following october 26 eruption

some evidence of colinear wind stress and wave breaking abstract data collected during the surface waves and processes program are employed to investigate a possible interrelation between wind stress and surface wave breaking from comparison of data from 15 half hour long time segments the directions of the wind stress and the whitecap motion are observed to be generally colinear with both lying between the mean wind and the swell as well a nondimensionalized whitecap speed is found to correlate with the drag coefficient these results suggest that the magnitude and direction of the wind stress might be estimated from wave breaking information

authigenic carbonates in sediments from the gulf of mexico abstract the carbon isotopic composition of diagenetic dolomite and calcite in some sediments of the gulf of mexico varies between normal marine 13 c ca 0 and 14 6 which suggests that biogenic co 2 contributed to the carbonate formation the 13 o values of dolomite and coexisting calcite are very similar but variable down core dolomite and calcite precipitated early from pore water where so 4 2 was not reduced however during and after so 4 2 reduction dolomite and calcite still formed and there are at least two generations of carbonate minerals present

deformation across the rupture zone of the 1964 alaska earthquake 1993 1997 a linear array of 15 geodetic monuments was installed in 1993 across the rupture zone of the 1964 alaska earthquake mw 9 2 the array extends from middleton island at the edge of the continental shelf and 80 km from the alaska aleutian trench to north of palmer alaska 380 km from the trench in the approximate direction of pacific north american plate convergence n15 5 w the array was surveyed in june 1993 may 1995 and june 1997 the changes between surveys are a measure of the deformation of the continental margin across the subduction zone in southern alaska measured relative to the interior of the north american plate the horizontal velocities on the outer plate margin are parallel to the direction of plate convergence n15 5 w and reach a maximum 58 mm yr 1 about 150 km from the trench beyond about 300 km from the trench the observed horizontal velocities are small a narrow halfwidth 50 km zone of significant uplift 10 mm yr 1 maximum is observed about 300 km from the trench coinciding roughly with the locus of maximum coseismic subsidence associated with the 1964 alaska earthquake although the deformation is roughly described by the conventional model of deformation at a subduction zone deformation due to virtual back slip on the main thrust zone at the 55 mm yr 1 plate convergence rate a better fit is given with a 65 mm yr 1 virtual back normal slip rate this higher rate is attributed to continued postseismic relaxation the model does not explain the relatively high uplift rate and low n15 5 w velocity observed at middleton island that anomalous motion is attributed to continued thrusting on postulated upward trending splays from the subduction zone beneath the island

anaerobic methane oxidation and the formation of dolomite abstract we examine the link between organic matter degradation anaerobic methane oxidation amo and sulfate depletion and explore how these processes potentially influence dolomitization we determined rates and depths of amo and dolomite formation for a variety of organic rich sites along the west african margin using data from ocean drilling program odp leg 175 rates of amo are calculated from the diffusive fluxes of ch4 and so4 and rates of dolomite formation are calculated from the diffusive flux of mg we find that the rates of dolomite formation are relatively constant regardless of the depth at which it is forming indicating that the diffusive fluxes of mg and ca are not limiting based upon the calculated log iap values log ksp values for dolomite were found to narrowly range between 16 1 and 16 4 dolomite formation is controlled in part by competition between amo and methanogenesis which controls the speciation of dissolved co2 amo increases the concentration of co32 through sulfate reduction favoring dolomite formation while methanogenesis increases the pco2 of the pore waters inhibiting dolomite formation by regulating the pco2 and alkalinity methanogenesis and amo can regulate the formation of dolomite in organic rich marine sediments in addition to providing a mechanistic link between amo and dolomite formation our findings provide a method by which the stability constant of dolomite can be calculated in modern sediments and allow prediction of regions and depth domains in which dolomite may be forming

the major event of the 1997 umbria marche italy sequence what could we learn from dinsar and gps data summary the main event of the umbria marche central italy sequence was an m w 6 earthquake following another m w 5 7 event that had occurred a few hours before two kinds of geodetic data enable us to image the coseismic displacement field related to these two earthquakes gps measurements over several points in the area and the vertical displacement field provided by dinsar interferometry with respect to a preseismic stage both measurements were taken approximately 15 days after the main shock other two m w 5 earthquakes occurred nearby 6 and 9 days after the main shock also contributed to the observed displacement field the present study of the main structure involved in this sequence is based on the comparison between a dislocation model that is as simplified as possible and both kinds of deformational data the seismogenic structures involved in the four events were described by several studies made before the present one where reference is also made to seismological evidence the previously obtained inferences of fault geometry length width and slip heterogeneity concerning the main event of the umbria marche sequence are used here as a starting model compared with previous analyses of the same measurements the present study identifies to what extent each fault parameter is constrained by the data quantifying the uncertainties associated with its estimated value

geochemistry and petrology of a middle tithonian limestone marl rhythmite in the neuquen basin argentina depositional and burial history

the 1997 umbria marche central italy earthquake sequence insights on the mainshock ruptures from near source strong motion records a small size foreshock and the two mainshocks of the umbria marche earthquake sequence which occurred on september 26 1997 have been recorded by two digital 3c accelerometers located at near source distances the close epicentral distance and azimuthal location relative to the fault orientation and geometry make these records relevant to look at the detail of the rupture kinematics s wave polarizations apparent source time duration and waveforms from strong motion records are used to constrain the location of the fracture origin point the fault geometry the final slip distribution size and mechanism of the events the final model shows that the seismic ruptures occurred along two adjacent sub parallel low angle dipping normal faults the relative timing location and geometry of the mainshock faults suggest the presence of a transfer zone barrier which has probably controlled the amplitude increase of local stress released by the first rupture at its nw edge which triggered about 9 hours later the second rupture

dolomite occurrence evolution and economically important associations abstract dolomite is not a simple mineral it can form as a primary precipitate a diagenetic replacement or as a hydrothermal metamorphic phase all that it requires is permeability a mechanism that facilitates fluid flow and a sufficient supply of magnesium dolomite can form in lakes on or beneath the shallow seafloor in zones of brine reflux and in early to late burial settings it may form from seawater from continental waters from the mixing of basinal brines the mixing of hypersaline brine with seawater or the mixing of seawater with meteoric water or via the cooling of basinal brines bacterial metabolism may aid the process of precipitation in settings where sulfate reducing species flourish and microbial action may control primary precipitation in some hypersaline anoxic lake settings dolomite is a metastable mineral early formed crystals can be replaced by later more stable phases with such replacements repeated a number of times during burial and metamorphism each new phase is formed by the partial or complete dissolution of an earlier dolomite this continual re equilibration during burial detracts from the ability of trace elements to indicate depositional conditions and resets the oxygen isotope signature of the dolomite at progressively higher temperatures because subsurface dolomite evolves via dissolution and reprecipitation a bed of dolomite can retain or create porosity and permeability to much greater burial depths and into higher temperature realms than a limestone counterpart dolomitization also creates new crystals with new rhomb growth following the dissolution of less stable precursors repetition of this process without complete pore cementation can generate intercrystalline porosity a number of times in the rock s burial history intercrystalline porosity is a highly interconnected style of porosity that gives dolomite reservoirs their good fluid storage capacity and efficient drainage the fact that many dolomite reservoirs formed via brine reflux means that they sit beneath an evaporite seal in both platform and basinwide evaporite settings the same association of evaporites sulfate source and entrained hydrocarbons means that burial conditions are also suitable for thermochemical sulfate reduction and the precipitation of base metals this tends to occur at higher temperatures 60 c 80 c and so the resulting dolomites tend to be ferroan and consist of saddle shaped crystals

an advanced slip model for the umbria marche earthquake sequence coseismic displacements observed by sar interferometry and model inversion summary we report an improved slip model for the 1997 september october umbria marche earthquake sequence in central italy the model is based on coseismic displacements estimated by differential synthetic aperture radar dinsar interferometry using an advanced inverse modelling approach that enables the characteristics of the sar data especially their dense spatial sampling to be fully exploited the paper first looks at dinsar analysis using the simplest configuration that is a single image pair that temporally covers the earthquake sequence yet given that this dinsar configuration is often used for coseismic studies and the limited availability of sar data we duly consider the limitations of the dinsar results and discuss the rigorous dinsar procedure carried out highlighting key errors associated with such observations we then focus on the inversion of the estimated dinsar displacements and on our advanced heterogeneous slip model for this earthquake sequence s main shocks emphasizing its most significant features

3700 ma pre metamorphic dolomite formed by microbial mediation in the isua supracrustal belt w greenland simple evidence for early life chemical meta sedimentary rocks in the amphibolite facies 3700 ma isua supracrustal belt w greenland are mostly strongly deformed so there is only a small chance of the survival of features such as stromatolites or microfossils that would be direct proof of a 3700 ma biosphere therefore the search for evidence of 3700 ma life in isua rocks has focused on chemical signatures particularly c isotopes the new approach presented here is based on whole rock chemistry rather than isotopic signatures isua chemical sedimentary rocks have ca mg fe bulk compositions that coincide with ferroan dolomite siderite fe oxide mixtures most have low al2o3 tio2 contents 0 5 and 0 05 wt respectively showing minimal contamination from terriginous materials identical seawater like ree y shale normalised trace element signatures with la ce eu and y positive anomalies are found in magnetite rich banded iron formation bif such as the geochemical standard if g dolomite rich rocks and quartz carbonate calcsilicate rocks additionally from a rare small area of low deformation in isua there are 3700 ma pillow lava interstices consisting of quartz tremolite calcite derived from pre metamorphic dolomite silica thus the dolomite in the chemical sediments and the pillow interstice was part of the pre metamorphic assemblage and was deposited from seawater and or low temperature groundwater as shown by the ree y chemistry therefore at least some isua carbonate rocks are sedimentary or diagenetic in origin rather than being formed by metasomatism at 600 500

dolomitization of holocene shallow marine deposits mediated by sulfate reduction and methanogenesis in normal salinity seawater northern belize abstract dolomite constitutes an average of 12 of the holocene organic rich sediments over a 15 km2 area of the cangrejo shoals mudbank in northern belize although it defines a laterally persistent stratiform body that averages 3 m thick it is present throughout the 7 6 m thick sediment section these transgressive sediments are less than 6400 years old and were deposited in shallow marine environments of normal salinity the dolomite is dominantly cement and average crystal size is 7 m there are no significant correlations among amount of dolomite vs sediment texture mineralogy porosity or mole mgco3 in associated particulate high mg calcite depth or location on the shoals the dolomites are poorly ordered and calcic 39 5 44 5 mole mgco3 with low mean mn 210 ppm and relatively high mean sr 1034 ppm concentrations there is no evidence of recrystallization or geochemical alteration of the dolomite 18o values of the dolomites range from 0 5 to 2 8o oopdb and the mean value 2 1o oo suggests that the dolomite precipitated from normal salinity pore water dolomite 13c values range from 5 2o oo to 11 6o oopdb mean seawater 13c 0 5o oo which suggests dolomitization promoted by both bacterial sulfate reduction and methanogenesis in environments with anoxic pore water dolomitization attending these organodiagenetic reactions apparently was reversible over time and episodic rather than continual precipitation is indicated requisite mg and ca were provided by seawater and by some dissolution of host sediments the most rapid period of dolomitization may have been during early transgression when relatively high sedimentation rates sustained high levels of organodiagenesis and pore water alkalinities

strontium isotope stratigraphy of kita daito jima atoll north philippine sea implications for neogene sea level change and tectonic history abstract a detailed chronology of a 432 m core from kita daito jima an atoll on the philippine sea plate has been obtained by strontium isotope stratigraphy the atoll carbonate extends to late oligocene age the top 100 m plio pleistocene section of the core has been dolomitized and dolomite also extends to middle miocene sediments sr isotopes identify two dolomitization events at 2 and 5 ma atoll growth appears to have been continuous between 18 8 and 24 3 ma and the fit of the growth history to a standard model provides a successful confirmation of darwin s subsidence theory the atoll growth appears to have commenced about 42 ma ago 6 ma after volcanism producing a 2 km column of atoll carbonate in agreement with bathymetry the subsidence model defines an apparent loss of 360 m of the sedimentary record since the early middle miocene boundary the amount in excess of the 100 m associated with sea level fall is attributed to plio pleistocene uplift at rates of 20 30 m ma associated with the forebulge of the philippine sea plate prior to its subduction uplift rates have also been estimated using a the heights of dated last interglacial coral reefs on kita daito jima and nearby minami daito jima 17 m ma and 29 m ma b sr isotope ages of calcites from surface samples on minami daito jima 21 m ma and c contrasts in elevation with okino daito jima 100 km away 22 m ma the locations of hiatuses and ages of dolomitization indicate sea level falls of 80 m at 17 16 ma 30 m at 16 15 ma 125 m at 11 ma and 90 m at 5 ma and at 2 ma the data have been combined with those from enewetak atoll to produce a curve of sea level change for the neogene

observed directional characteristics of the wind wind stress and surface waves on the open ocean sonic anemometer data were taken during the surface waves processes program swapp in march 1990 in the north pacific measurements of the wind stress vector span several strong wind events significant angles between the wind stress vector and the mean wind vector are seen simultaneous measurements of the directional wave field were made with a surface scanning doppler sonar the data suggest that the wind stress direction is influenced by the direction of the surface waves especially for stronger winds overall the stress vector lies between the mean wind and the mean wave directions at the higher wind speeds over 8 6 m s there is a nonzero correlation between the variations in wave directions and stress directions as well finally the stress and wave component directions have similar frequency dependence over the frequency band where wave energy is nonnegligible suggesting a dynamic link

effects of geological complexities on coseismic displacement hints from 2d numerical modelling by means of a 2d finite element procedure we tested how heterogeneities at the scale of seismogenic fault affect the displacement we defined one or more slip distributions for two typical normal faulting earthquakes in the central apennines computed the displacement occurred within different structures including lateral heterogeneities and compared the different displacement profiles to isolate the effect of the crustal structure to understand at what magnitude the heterogeneities affect the observation significantly we compared the predicted coseismic displacement with gps and dinsar data for the colfiorito 1997 earthquake we find that heterogeneities significantly affect the observable horizontal coseismic displacement for the larger magnitudes whereas for smaller quakes they affect horizontal displacement close to the fault trace only

systematic sequence scale controls on carbonate cementation in a siliciclastic sedimentary basin examples from upper cretaceous shallow marine deposits of utah and coloradao usa whilst the relationship between stratigraphic development and carbonate cementation within siliciclastic succession has been documented through a number case studies these studies have been generally restricted to observations upon individual sequences and or limited sub surface data in this paper long term 5 million years large scale 200 km stratigraphic controls on carbonate cementation patterns are documented from the upper cretaceous panther tongue member blackhawk formation and castlegate sandstone exposed in the book cliffs in utah and colorado usa together these comprise eight progradational wedges of sandstones which interfinger with the mancos shale deposited within the western interior seaway foreland basin petrographic analyses of ferroan dolomite cement bodies within these sandstone wedges show that the ferroan dolomite cements are all early relative to burial diagenesis within the host sandstones stable isotope analyses indicates that a significant meteoric component was present in precipitating fluids and this is consistent with the observation that cements are always present down dip of sequence boundaries and or leached whitecaps beneath coals in addition the lateral distribution of cement bodies increases consistently up succession from less than 5 km in extent in the older sequences to 30 km in extent in the youngest sequences these changes in distribution are in response to the increased progradation and increased and more aerially extensive sequence boundary development in younger sequences the implications of these data are that whilst localized spatial patterns of diagenesis and in particular carbonate cementation are predictable and controlled by the nature and presence of individual stratal surfaces systematic diagenetic alteration patterns are also present at the sedimentary basin scale and controlled by the nature of larger scale stratigraphic development and basin evolution this evolution may be driven by eustatic shifts or through tectonic or climatic driven base level shifts these observations allow an improved insight into the basin scale processes that control the macroscopic diagenetic properties of sedimentary successions and sub surface hydrocarbon reservoirs

loading of a seismic zone to failure deforms nearby volcanoes a new earthquake precursor the south iceland seismic zone sisz was loaded to failure in june 2000 resulting in two m6 6 earthquakes the sisz is an e w trending zone with an overall sinistral movement numerical models indicate that when the sisz is loaded to failure there are stress concentrations at its ends tensile in the north east and south west quadrants and compressive in the north west and south east quadrants these model predictions fit well with observations geodetic measurements indicate considerable compression uplift and associated intense seismicity in recent years in the volcanoes of hengill and eyjafjallajokull located in the quadrants of compression whereas there have been unusually frequent eruptions in the past decades in the hekla volcano located in one of the quadrants of extension the models predict that following the large june 2000 earthquakes stress relaxation within the sisz should lead to stopping of the intense seismicity and deformation in the volcanoes of hengill and eyjafjallajokull again in agreement with observations however when similar episodes of deformation and seismicity start again particularly in the hengill volcano a large earthquake would be expected within several years in the sisz the numerical models and the deformation and seismic data indicate that monitoring of soft inclusions such as volcanoes many with magma chambers in the vicinity of a seismic zone may serve as precursors to large earthquakes

trends in oolite dolomitization across the neoproterozoic cambrian boundary a case study from death valley california abstract changes in dolomite fabric within the neoproterozoic cambrian stratigraphic succession in death valley california preserve evidence for a first order biogeochemical change in early diagenetic environments through the neoproterozoic cambrian transition oolite forms the primary focus of the study so that the general paleoenvironmental setting and presumed susceptibility to early diagenesis and fluid flow can be kept relatively constant across geologic time two key generalizations can be made 1 late neoproterozoic dolomitization in death valley occurred very early in the paragenetic sequence was volumetrically significant and preserved fine detail of the original aragonite or calcite precursor and 2 early cambrian dolomitization in death valley occurred late in the paragenetic sequence with burial was commonly incomplete and obliterated details of the calcite or aragonite precursor early diagenetic dolomitization of any kind was absent the dolomitization fabrics in death valley parallel the presumed pattern of seawater mg ca with respect to mimetic dolomitization in the paleozoic low mg ca little no mimetic dolomitization and cenozoic higher mg ca more common mimetic dolomitization however the volume of neoproterozoic mimetic dolomitization is immense compared to the cenozoic examples we speculate that a fundamental shift in the early diagenetic environment occurred in late neoproterozoic time perhaps in association with secular variation in the sulfate concentration of seawater and the advent and proliferation of penetrative bioturbation that destroyed sediment capping microbial mats an oscillatory trend in the fabric and volume of dolomite through the phanerozoic has been suggested but the termination of volumetrically significant mimetic dolomitization across the neoproterozoic cambrian transition a critical time in earth history for many reasons dwarfs the oscillatory trends noted in the phanerozoic

effects of superficial layers on coseismic displacements for a dip slip fault and geophysical implications summary we study the effect of a superficial layer overlying a half space on the surface displacements created by a dip slip dislocation on a planar rectangular fault using a 2 d finite element model the effect of the density and poisson s ratio is negligible on the other hand the contrast in young s modulus between the top layer and the half space below significantly affects the modelled coseismic displacements the horizontal displacements are more sensitive than the vertical displacements to the existence of the top layer near the fault a low rigidity layer with a young s modulus of 10 gpa can increase the horizontal displacements by up to 40 per cent an analytical 3 d half space model is used to interpret this effect in terms of an equivalent homogeneous model the presence of a top layer can be partly simulated in a homogeneous half space by perturbing the depth and the slip on the fault from their real values to equivalent values for a given displacement field observed at the surface the perturbations in fault depth and slip can reach 1 km and 25 per cent respectively the fault dip angle is not model dependent we conclude that for the accurate estimation of fault depth and slip from coseismic geodetic data rigidity contrasts existing within the upper crust must be taken into account not taking into account the effect of an existing low rigidity layer also leads to an underestimation of seismic moment release this may in part be the cause of apparent discrepancies between seismic and geodetic moment releases in particular areas such as the gulf of corinth greece

physical and chemical growth conditions of ordovician organogenic deep water dolomite concretions implications for the δ18o of early palaeozoic sea water the estimated depth of formation of authigenic dolomite concretions in the middle ordovician cloridorme formation quebec ranges from 350 mbsf 25 17 porosity in the lower ordovician levis formation outward decreasing 13cvpdb values 10 2 0 8 suggest precipitation in the methane generation zone with an increasing contribution of light carbonate derived by advection from thermocatalytic reactions at depth anomalously low 18ovpdb values centre to margin variations of 0 4 to 7 5 give reasonable temperatures for the concretion centres only if the 18o of ordovician sea water was negative 6 and the bottom water was warm 15 c the 3 5 lower values for the concretion margins compared with the centres can be explained if in addition volcanic ash alteration organic matter decomposition and or advection of 18o depleted water lowered the 18o of the pore water further by 2 0 4 0 during the first 25 200 m of burial reasonable growth temperatures for the margins of 17 20 c are compatible with a lowering of the isotopic ratios by 1 to 1 3 as a temperature effect the systematic concentric isotope zonation of the concretions suggests that the well ordered near stoichiometric dolomite is a primary feature and not the result of recrystallization diagenetic dolomite beds of the cloridorme formation appear to have formed by coalescence of concretions as shown by randomly sampled traverses that indicate formation at different subsurface depths growth of the cloridorme dolomites was probably limited by calcium availability at least 50 of which was derived from connate water and the remainder by diffusion from sea water dolomite precipitation was favoured over calcite by very high sedimentation rates the abundance of marine organic matter in the host sediment and a correspondingly thin sulphate reduction zone deep seated concretion growth in the levis formation required either internal sources for the participating ions carbonate dissolution event or porewater advection along faults

repeated occurrences of methanogenic zones diagenetic dolomite formation and linked silicate alteration in southern bering sea sediments bowers ridge iodp exp 323 site u1341 abstract diagenetic precipitates such as dolomite and the chemistry of residual deeply buried porewater often represent the only traces of past biogeochemical activity in marine sediments a 600 m thick sedimentary section recently drilled at integrated ocean drilling program iodp site u1341 on bowers ridge southern bering sea provides insight into such a 4 3 ma old paleo diagenetic archive hard lithified calcite dolomite layers and laminae of disseminated carbonate were recovered in diatom rich sediments over a depth range of 400 m carbon isotope values of the diagenetic carbonates between 16 6 and 14 4 vpdb and strontium isotope ratios of dolomites close to past seawater values suggest carbonate precipitation induced by the production of dissolved inorganic carbon dic during elevated rates of organic carbon mineralization primarily via sulfate reduction at shallow sediment depth below the paleo seafloor diagenetic carbonates at 280 440 m below seafloor were likely also produced by the intermittent onset of sulfate reduction coupled to the anaerobic oxidation of methane aom at sulfate methane transition zones smtz these microbially mediated processes do not occur in the sediment at this site at present but were likely connected to the presence of a methanogenic zone at 2 58 2 51 ma a minimum in sulfate concentrations in modern porewaters and low sedimentary ba al ratios resulting from former sulfate depletion are reminiscent of the presence of this large methanogenic zone the minimum in sulfate concentrations is reflected in a minimum in magnesium concentrations less radiogenic strontium and isotopically light calcium in the porewater it is proposed that magnesium was removed from the porewater during carbonate precipitation and volcanic ash alteration which occurred in the former methanogenic zone and also released strontium with a less radiogenic isotope ratio and isotopically light calcium into the porewater the isotopic composition of porewater calcium was also influenced by ammonium calcium exchange on clay minerals and carbonate recrystallization our study elucidates the response of porewater element concentrations and isotopic profiles interlinked with the formation of diagenetic carbonates to changes in the deposition of organic carbon in sediments of deeper water sites 2000 m water depth over prolonged timescales it shows that variations in biogeochemical processes in response to changes in oceanographic conditions and a dynamic subseafloor biogeochemical zonation have to also be taken into account at these deep water sites for a global assessment of organic carbon burial fluxes and remineralization

moment tensor analysis of the central italy earthquake sequence of september october 1997 the larger earthquakes in the umbria marche central italy seismic sequence of september october 1997 are analyzed using long period seismograms from the mediterranean seismographic network mednet and additional data from the global seismographic network gsn we modify the harvard centroid moment tensor cmt algorithm to allow moment tensor inversion of long period waveforms primarily rayleigh and love waves for small earthquakes at local to regional distances 5 5 in the sequence moment tensors have previously been determined using teleseismic waveforms and standard methods of analysis our results agree well with those of earlier studies we determine additional moment tensors for the largest foreshock and 10 aftershocks with mw 4 2 the earthquakes are characterized by normal faulting mechanisms with a ne sw tension axis and the presumed fault plane dips towards the sw only one of the fourteen events studied has a different faulting geometry indicating instead right lateral strike slip faulting on a plane oriented approximately e w or left lateral faulting on a plane oriented n s the september 26 mainshock 09 40 ut accounts for only approximately 50 of the total moment release in the sequence

kinematics and source zone properties of the 2004 sumatra andaman earthquake and tsunami nonlinear joint inversion of tide gauge satellite altimetry and gps data 1 we re analyzed the source of the 26 december 2004 sumatra andaman earthquake and tsunami through a nonlinear joint inversion of an inhomogeneous data set made up of tide gauges satellite altimetry and far field gps recordings the purpose is twofold 1 the retrieval of the main kinematics rupture parameters slip rake and rupture velocity and 2 the inference of the rigidity of the source zone we independently estimate the slip from tsunami data and the seismic moment from geodetic data to derive the rigidity our results confirm that the source of the 2004 sumatra andaman earthquake has a complex geometry constituted by three main slip patches with slip peaking at 30 m in the southern part of the source the rake direction rotates counterclockwise at the northern part of the source according to the direction of convergence along the trench the rupture velocity is higher in the deeper than in the shallower part of the source consistent with the expected increase of rigidity with depth it is also lower in the northern part consistent with known variations of the incoming plate properties and shear velocity our model features a rigidity 20 30 gpa that is lower than the preliminary reference earth model prem average for the seismogenic volume the source rigidity is one of the factors controlling the tsunami genesis for a given seismic moment the lower the rigidity the higher the induced seafloor displacement the general consistence between our source model and previous studies supports the effectiveness of our approach to the joint inversion of geodetic and tsunami data for the rigidity estimation

vp and vp vs images in the mw 6 0 colfiorito fault region central italy a contribution to the understanding of seismotectonic and seismogenic processes 1 in 1997 the umbria marche apennines central italy was struck by a series of moderate magnitude normal faulting earthquakes accompanied by a prolonged sequence of aftershocks seismological analysis revealed a 40 km long nw trending structure composed by several low angle normal fault segments in this paper we present the three dimensional 3 d vp and vp vs structure of the fault zone determined by the inversion of p and s wave arrival times from 1982 aftershocks the high resolution tomographic images reveal strong heterogeneity along and across the fault zone and allow us along with the 3 d location of earthquakes to define the fault geometry at depth and to improve our understanding on the seismotectonics of this part of the northern apennines thrust and fold belt the relocated aftershocks suggest that the main ruptures occurred on planes slightly steeper than previously hypothesized and at depths shallower than those evidenced by 1 d locations we find that the preexisting structure which developed during the neogene compressional tectonics plays an important role in the earthquake generation and rupture evolution of the normal faulting events we propose that the main shocks whose hypocenters are all located at 6 km depth originated along a shallow decollement of the meso cenozoic cover thrust over the metamorphic basement geometrical discontinuities and lateral steps along the inherited structures control the lateral fault extent and determine fault segmentation this study offers a good example of how lithological heterogeneities and the complexity of the upper crust structure strongly affect the faulting process

the hydromagnesite playas of atlin british columbia canada a biogeochemical model for co2 sequestration abstract anthropogenic greenhouse gas emissions may be offset by sequestering carbon dioxide co2 through the carbonation of magnesium silicate minerals to form magnesium carbonate minerals the hydromagnesite mg5 co3 4 oh 2 4h2o playas of atlin british columbia canada provide a natural model to examine mineral carbonation on a watershed scale at near surface conditions co2 is biogeochemically sequestered by microorganisms that are involved in weathering of bedrock and precipitation of carbonate minerals the purpose of this study was to characterize the weathering regime in a groundwater recharge zone and the depositional environments in the playas in the context of a biogeochemical model for co2 sequestration with emphasis on microbial processes that accelerate mineral carbonation regions with ultramafic bedrock such as atlin represent the best potential sources of feedstocks for mineral carbonation elemental compositions of a soil profile show significant depletion of mgo and enrichment of sio2 in comparison to underlying ultramafic parent material polished serpentinite cubes were placed in the organic horizon of a coniferous forest soil in a groundwater recharge zone for three years upon retrieval the cube surfaces as seen using scanning electron microscopy had been colonized by bacteria that were associated with surface pitting degradation of organic matter in the soil produced chelating agents and acids that contributed to the chemical weathering of the serpentinite and would be expected to have a similar effect on the magnesium rich bedrock at atlin stable carbon isotopes of groundwater from a well situated near a wetland in the southeastern playa indicate that 12 of the dissolved inorganic carbon has a modern origin from soil co2 the mineralogy and isotope geochemistry of the hydromagnesite playas suggest that there are three distinct depositional environments 1 the wetland characterized by biologically aided precipitation of carbonate minerals from waters concentrated by evaporation 2 isolated wetland sections that lead to the formation of consolidated aragonite sediments and 3 the emerged grassland environment where evaporation produces mounds of hydromagnesite examination of sediments within the southeastern playa wetland suggests that cyanobacteria sulphate reducing bacteria and diatoms aid in producing favourable geochemical conditions for precipitation of carbonate minerals the atlin site as a biogeochemical model has implications for creating carbon sinks that utilize passive microbial geochemical and physical processes that aid in mineral carbonation of magnesium silicates these processes could be exploited for the purposes of co2 sequestration by creating conditions similar to those of the atlin site in environments artificial or natural where the precipitation of magnesium carbonates would be suitable given the vast quantities of mg rich bedrock that exist throughout the world this study has significant implications for reducing atmospheric co2 concentrations and combating global climate change

sequence stratigraphic distribution of diagenetic alterations in coal bearing paralic sandstones evidence from the rio bonito formation early permian southern brazil linking siliciclastic diagenesis to sequence stratigraphy allows a better understanding of the parameters controlling the spatial and temporal distribution of diagenetic alterations and hence of reservoir quality a study of the coal bearing alluvial deltaic estuarine and shallow marine sandstones of the rio bonito formation early permian parana basin southern brazil reveals that the distribution of diagenetic alterations and of related reservoir quality evolution can be constrained within a sequence stratigraphic framework calcite dolomite siderite kaolinite and pyrite cementation is consistently linked to sequence and parasequence boundaries transgressive and maximum flooding surfaces and is systematically distributed within lowstand transgressive and highstand systems tracts diagenesis of coal layers at parasequence boundaries has promoted the formation of stratabound calcite detectable in resistivity wire line logs concretionary pyrite and kaolinite and of silicate grain dissolution in sandstones located above and below these boundaries particularly in the transgressive systems tract meteoric water diagenesis caused grain dissolution and the formation of kaolinite in sandstones below sequence boundaries and in lowstand systems tract sandstones carbonate bioclasts and low sedimentation rates in lag deposits at parasequence boundaries transgressive and maximum flooding surfaces favoured the formation of grain rimming siderite the results of this study are relevant to the exploration of coal bed methane and other coal bearing reservoirs where it is crucial to unravel and predict the distribution and quality of reservoirs and compartments

monte carlo inversion of dinsar data for dislocation modeling application to the 1997 umbria marche seismic sequence central italy the study of surface deformation due to seismic activity is often made using dislocations with uniform slip and simple geometries a better modeling of coseismic and postseismic surface displacements can be obtained by using dislocations with variable slip and nonregular shapes this is consistent with the asperity model of fault surfaces assuming a friction distribution on faults made of locked zones with much higher friction than surrounding zones in this paper we consider the 1997 1998 colfiorito seismic sequence the coseismic surface displacements in the colfiorito zone are used in order to infer the slip distribution on the fault surface at different stages of the sequence the displacement field has been modeled varying the slip distribution on the fault and comparing the deformation observed by sar and gps techniques with model results the slip distribution is calculated by monte carlo simulations on a normal fault with the dip angle equal to 40 a good approximation is obtained by using square asperity units of 1 5 1 5 km2 in the first stage we employed a simplified model with uniform slip in which each asperity unit is allowed to slip a constant amount or not to slip at all and in the second stage we evaluate the slip distribution in the dislocation area determined by the monte carlo inversion in this case we allow unit cells to undergo different values of slip in order to refine the initial dislocation model the results show that the 1997 seismic events of the sequence can be modeled by irregular dislocations obtaining a good fit to the dinsar and gps observations the model also confirms the results of previous studies by a different methodology defining the distribution of asperities on the fault plane using the fault geometry the geodetic data and the seismic moment of the 1997 1998 colfiorito seismic sequence furthermore the analysis of 1997 aftershocks in the seismogenic region shows a strong correlation between most events and the asperity distribution which can be considered as an independent test of the validity of the model

long duration asynchronous ground motions in the colfiorito plain central italy observed on a two dimensional dense array 1 in winter 1998 a small aperture 200 m four station array was operating in the middle of the colfiorito plain waveforms of seven small magnitude 2 1 m 3 7 local earthquakes are analyzed in this study the peculiarity of the array seismograms is a 2 min long duration of the horizontal ground motion the predominant frequency in the plain is around 1 hz in this frequency band earthquake induced ground shaking is synchronous for a few seconds during direct s waves after this time window wave trains show an increasingly chaotic behavior within the array the energy variation of the horizontal ground shaking between the array and a nearby rock outcrop exceeds a factor of 500 at 1 hz in order to help understanding of observations and construct models for future numerical simulations the buried structure of the colfiorito plain has been investigated through seismic refraction profiles and geoelectric measurements a three dimensional reconstruction of the basin structure reveals an extremely complex bedrock topography which is probably a recurrent feature for intermontane basins in tectonically active regions apparent velocities and backazimuths in the frequency band 0 5 1 5 hz indicate that a 180 m deep depression nw of the array is responsible for the generation of edge diffracted surface love waves their arrival to the array breaks the synchronism of vertically reverberating waves which predominate in the first seconds of the s wave window

three dimensional imaging of the p and s wave velocity structure and earthquake locations beneath southwest iceland three dimensional imaging of the p and s wave velocity structure and earthquake locations beneath southwest iceland