continental rifting as a function of lithosphere mantle strength abstract the role of the uppermost mantle strength in the pattern of lithosphere rifting is investigated using a thermo mechanical finite element code in the lithosphere the mantle crust strength ratio s m s c that decreases with increasing moho temperature t m allows two strength regimes to be defined mantle dominated s m s c and crust dominated s m s c the transition between the two regimes corresponds to the disappearance of a high strength uppermost mantle for t m 700 c 2d numerical simulations for different values of s m s c show how the uppermost mantle strength controls the style of continental rifting a high strength mantle leads to strain localisation at lithosphere scale with two main patterns of narrow rifting coupled crust mantle at the lowest t m values and deep crustal decollement for increasing t m values typical of some continental rifts and non volcanic passive margins the absence of a high strength mantle leads to distributed deformations and wide rifting in the upper crust these numerical results are compared and discussed in relation with series of classical rift examples

modeling susceptibility to landslides using the weight of evidence approach western colorado usa abstract the paonia mcclure pass area of colorado is well known for active mass movements we examined 735 active shallow movement features including debris flows debris slides rock slides and soil slides in this area identification of the hazardous areas is a fundamental component of disaster management and an important basis for promoting safe human occupation and infrastructure development in landslide prone areas bayes theorem based on the weight of evidence woe was used to create a map of landslides that could be hazardous the modeling was accomplished by employing a geographical information system gis and a statistical package seventeen factors that cause landslides were measured and weighted using the woe method to create a map of areas susceptible to landslides the maps of weighted factors were summed on a pixel by pixel basis after performing chi square tests to determine factors that are conditionally independent of each other by combining factors that represent topography hydrology geology land cover and human influences six models were developed the performance of each model was evaluated by the distribution of the observed landslides the validity of the best map was checked against landslides which were not entered in the analysis the resulting map of areas susceptible to landslides has a prediction accuracy of 78

pedogenic origin of dolomite in a basaltic weathering profile kohala peninsula hawaii we document stoichiometric dolomite occurring in a nonsaline quaternary soil on the kohala peninsula northwestern hawaii geologic constraints and geochemical and isotopic data confirm that this dolomite is not the result of marine influence or wind blown dust the strontium isotopic composition of the dolomite 87sr 87sr 0 7045 0 7048 is indicative of its derivation primarily from the weathering of basaltic parent material rather than from meteoric water or seawater infiltration of soil waters with elevated mg ca 1 derived from alteration of ferromagnesian minerals such as olivine likely led to dolomitization of early precipitated soil calcite and or to direct dolomite precipitation in the profile this demonstrates that well ordered dolomite can form in a nonmarine environment at temperatures 100 c without undergoing burial diagenesis

itrf2008 plate motion model 1 the itrf2008 velocity field is demonstrated to be of higher quality and more precise than past itrf solutions we estimated an absolute tectonic plate motion model made up of 14 major plates using velocities of 206 sites of high geodetic quality far from plate boundaries deformation zones and glacial isostatic adjustment gia regions derived from and consistent with itrf2008 the precision of the estimated model is evaluated to be at the level of 0 3 mm a wrms no gia corrections were applied to site velocities prior to estimating plate rotation poles as our selected sites are outside the fennoscandia regions where the gia models we tested are performing reasonably well and far from gia areas where the models would degrade the fit antarctica and north america our selected velocity field has small origin rate bias components following the three axis x y z respectively 0 41 0 54 0 22 0 64 and 0 41 0 60 95 per cent confidence limits comparing our model to nnr nuvel 1a and the newly available nnr morvel56 we found better agreement with nnr morvel56 than with nnr nuvel 1a for all plates except for australia where we observe an average residual rotation rate of 4 mm a using our selection of sites we found large global x rotation rates between the two models 0 016 ma and between our model and nnr morvel56 of 0 023 ma equivalent to 2 5 mm a at the earth surface

direct and indirect evaluation of denudation rates in central italy abstract this paper presents the main results of a series of geomorphological studies aimed to the quantitative direct and indirect evaluation of denudation processes in central italy these studies which started in some sample areas since long ago were further deepened and extended to a wider number of drainage basins representative of a variety of morphostructural conditions the complex cause effect relationships among factors influencing both the morphogenesis and the plano altimetric configurations of drainage basins resulted in a large variability in the values of the denudation index tu which ranged from 200 to 2500 t km2 year very high values tu 10 000 t km2 year were obtained for small catchments belonging to the wider basins of ombrone river and tevere river where fast morphological modifications occur due to the action of surface running waters and gravity in the drainage basins affected by the most powerful denudation processes direct measurements of denudation were performed several monitoring stations were equipped with iron stakes and disks to record the local modifications of the topographic surface with time whereas some of these stations have been working continuously since 1993 some others have been running only periodically direct measurements pertinent to periods longer than a decade indicated that mean annual values of denudation range between 1 and 2 5 cm year for slopes affected by sharp edged and or rounded edged badlands higher denudation rates 3 4 cm year were obtained for shorter observation periods still higher rates were recorded for short periods at the gully bottom or in coincidence with mass movements before bench marks were turned up or damaged denudation processes are likely to occur discontinuously they show a step like trend with time and are triggered by rainfall events distributed over a number of consecutive days though not greatly intense particularly their amount should overcome the threshold of 60 mm per 5 consecutive days below this threshold the surface runoff does not seem to reach the power necessary to induce significant modifications of the topographic surface in the study area

observation of glacial isostatic adjustment in stable north america with gps 1 motions of three hundred and sixty global positioning system gps sites in canada and the united states yield a detailed image of the vertical and horizontal velocity fields within the nominally stable interior of the north american plate by far the strongest signal is the effect of glacial isostatic adjustment gia due to ice mass unloading during deglaciation vertical velocities show present day uplift 10 mm yr near hudson bay the site of thickest ice at the last glacial maximum the uplift rates generally decrease with distance from hudson bay and change to subsidence 1 2 mm yr south of the great lakes the hinge line separating uplift from subsidence is consistent with data from water level gauges along the great lakes showing uplift along the northern shores and subsidence along the southern ones horizontal motions show outward motion from hudson bay with complex local variations especially in the far field although the vertical motions are generally consistent with the predictions of gia models the horizontal data illustrate the need and opportunity to improve the models via more accurate descriptions of the ice load and laterally variable mantle viscosity

dolomite formation and biogeochemical cycles in the phanerozoic summary based on present knowledge of the purely chemical controls on the kinetics of massive dolomite formation the abundance and distribution of dolomite throughout the phanerozoic remains an enigma sometimes referred to as the dolomite problem comparing dolomite abundance to secular variation in seawater chemistry indicates that some changes in seawater chemistry are more likely to have resulted from extensive dolomitization rather than to have caused it the recently formulated microbial dolomite model provides the opportunity to view the geological history of dolomite formation from a new perspective a biogeochemical approach to the dolomite problem reveals a plausible connection between phanerozoic geochemical cycles and dolomite formation in particular periods of more extensive dolomitization broadly correlate with diverse indicators of decreased oxygen levels in the atmosphere and oceans lowered oxygen levels would have fostered a more active community of anaerobic microbes including sulphate reducing bacteria which in turn could have led to more extensive dolomitization of marine carbonates

the role of sulphate reducing bacteria and cyanobacteria in dolomite formation in distal ephemeral lakes of the coorong region south australia abstract the dolomitic distal ephemeral lakes of the coorong region of south australia are dynamic systems in which the concentrations of solutes generally increase during late spring and summer when the rate of evaporation greatly exceeds aqueous input during late evaporation active bacterial sulphate reduction occurs in uppermost anoxic lake sediments as rising salinity and then h2s toxicity kills off the macrobiota these hypersaline lakewaters are characterised by high ph and elevated concentrations of carbonate and sulphate ions magnesium concentrated in cyanobacterial cells and sheaths is released into the strongly electrolytic alkaline lake brines from lake margin stromatolites and mats during desiccation and may explain the remarkable increase in mg levels recorded at this time continued evaporation of the lakewaters produces a halite crust overlying the dolomite sulphate free residual puddles and the absence of gypsum indicates that all sulphate is removed by sulphate reducing bacteria dolomite forms in situ as a primary precipitate from these microbially mediated lake porewaters and both the morphology and size distribution of dolomite grains is identical to bacterial cells it is not proven exactly when dolomite precipitation occurs but the submicron sized grains and multiple defects in a disordered lattice indicate that precipitation is rapid and follows bacterial removal of sulphate which is known to inhibit dolomite formation bacterial sulphate reduction and cyanobacterial degradation may thus lead to the removal of all kinetic inhibitors to dolomite formation and provide a mechanism for dolomite precipitation around bacterial cells in shallow subsurface sediments during the late stages of evaporation in adjacent non dolomitic lakes sulphate is present throughout evaporation so that other minerals principally aragonite and hydromagnesite are precipitated

a gis based approach for gully erosion susceptibility modelling a test in sicily italy the aim of this study is to analyze the susceptibility conditions to gully erosion phenomena in the magazzolo river basin and to test a method that allows for driving the factors selection the study area is one of the largest 225 km2 watershed of southern sicily and it is mostly characterized by gentle slopes carved into clayey and evaporitic sediments except for the northern sector where carbonatic rocks give rise to steep slopes in order to obtain a quantitative evaluation of gully erosion susceptibility statistical relationships between the spatial distributions of gullies affecting the area and a set of twelve environmental variables were analyzed stereoscopic analysis of aerial photographs dated 2000 and field surveys carried out in 2006 allowed us to map about a thousand landforms produced by linear water erosion processes classifiable as ephemeral and permanent gullies the linear density of the gullies computed on each of the factors classes was assumed as the function expressing the susceptibility level of the latter a 40 m digital elevation model dem prepared from 1 10 000 scale topographic maps was used to compute the values of nine topographic attributes primary slope aspect plan curvature profile curvature general curvature tangential curvature secondary stream power index topographic wetness index ls usle factor from available thematic maps and field checks three other physical attributes lithology soil texture land use were derived for each of these variables a 40 m grid layer was generated reclassifying the topographic variables according to their standard deviation values in order to evaluate the controlling role of the selected predictive variables one variable susceptibility models based on the spatial relationships between each single factor and gullies were produced and submitted to a validation procedure the latter was carried out by evaluating the predictive performance of models trained on one half of the landform archive and tested on the other large differences of accuracy were verified by computing geometric indexes of the validation curves prediction and success rate curves roc curves drawn for each one variable model in particular soil texture general curvature and aspect demonstrated a weak or a null influence on the spatial distribution of gullies within the studied area while on the contrary tangential curvature stream power index and plan curvature showed high predictive skills hence predictive models were produced on a multi variable basis by variously combining the one variable models the validation of the multi variables models which generally indicated quite satisfactory results were used as a sensitivity analysis tool to evaluate differences in the prediction results produced by changing the set of combined physical attributes the sensitivity analysis pointed out that by increasing the number of combined environmental variables an improvement of the susceptibility assessment is produced this is true with the exception of adding to the multi variables models a variable as slope aspect not correlated to the target variable the addition of this attribute produces effects on the validation curves that are not distinguishable from noise and as a consequence the slope aspect was excluded from the final multi variables model used to draw the gully erosion susceptibility map of the magazzolo river basin in conclusion the research showed that the validation of one variable models can be used as a tool for selecting factors to be combined to prepare the best performing multi variables gully erosion susceptibility model

strain accumulation in the new madrid and wabash valley seismic zones from 14 years of continuous gps observation the mechanical behavior and hence earthquake potential of faults in continental interiors is an issue of critical importance for the resultant seismic hazard but no consensus has yet been reached on this controversial topic the debate has focused on the central and eastern united states in particular the new madrid seismic zone struck by four magnitude 7 or greater earthquakes in 1811 1812 and to a lesser extent the wabash valley seismic zone just to the north a key aspect of this issue is the rate at which strain is currently accruing on those plate interior faults a quantity that remains debated here we address this issue with an analysis of up to 14 6 years of continuous gps data from a network of 200 sites in the central united states centered on the new madrid and wabash valley seismic zones we find that the high quality sites in these regions show motions that are consistently within the 95 confidence limit of zero deformation these results place an upper bound on strain accrual on faults of 0 2 mm yr and 0 6 mm yr in the new madrid and wabash valley seismic zones respectively for the new madrid region where a paleoseismic record is available for the past 5000 years we argue that strain accrual if any does not permit the 500 900 year repeat time of paleo earthquakes observed in the upper mississippi embayment these results together with increasing evidence for temporal clustering and spatial migration of earthquake sequences in continental interiors indicate that either tectonic loading rates or fault properties vary with time in the new madrid seismic zone and possibly plate wide

badland susceptibility assessment in volterra municipality tuscany italy by means of gis and statistical analysis badlands can be defined as complex and peculiar types of erosional formations that develop in clayey environments and are mainly favoured by lithological and topographic features as well as by markedly seasonal climate this work aims at assessing badland susceptibility in volterra municipality located in tuscany region italy by means of bivariate statistical analysis implemented in a geographic information system the volterra municipality is affected by intense soil erosion processes including rill and gully erosion usually turned out as badland forms mostly occurring on pliocene pleistocene clayey sediments firstly an inventory of 234 badland areas was produced on the basis of an available pre existing database integrated with the interpretation of aerial photographs and supported by a field survey badlands were distinguished in type a and type b according to different evolutional stage vegetation presence and consequently different landforms then nine geoenvironmental factors supposed to be predisposing for badland occurrence were chosen and combined with the spatial frequency of badland areas derived from the inventory through information value statistic approach the result was a badland susceptibility map that highlights a strong control of lithology slope gradient and land use in conditioning badland development in the investigated area the effectiveness of the performed model was demonstrated by a validation test computed through a receiver operating characteristics analysis the outcomes of this work provide an updated badland database that is useful for soil erosion management and further land use planning within the volterra municipality

morphological analysis and erosion rate evaluation in badlands of radicofani area southern tuscany italy abstract since 1988 geomorphologic research based on field surveys and photo geological analysis has been conducted in southern tuscany italy in areas characterised by very rapid morphological evolution in the area outcrop pliocene marine claystones uplifted during the quaternary up to 750 m above sea level now undergoing intense erosion processes leading to considerable badlands formation morphodynamic analysis conduced by direct and indirect measurements in a sample area were taken in order to quantify the erosion rate in badland areas the torrente piantrafolla sample area was chosen as representative of the study area it was most recently monitored during the period nov 2000 feb 2004 at this time morphographic and morphometric analyses carried out in selected measurement stations located on slopes identified gravity as the main morphogenetic process responsible for slope shaping the calanchi badland areas are characterised by constant and rapid shrinking of their edges resulting from landslides which occur in autumn and winter as a consequence of intense rainstorms selected measurement stations indicate an erosion rate value range from 5 to 7 5 cm y the comparison between 1976 and 1994 digital elevation models dem obtained from photogrammetric restitution indicated a mean erosion rate of about 5 cm y in a nineteen year period this value considerably higher than the values measured in other italian basins indicate a very rapid evolution of the slopes due mainly to small earth flows inside calanchi badlands

landslide hazard spatial analysis and prediction using gis in the xiaojiang watershed yunnan china abstract the xiaojiang watershed in southwest china has high landslide hazard and has been given the title of the museum of geohazards in china however the available information on landslides in the xiaojiang watershed is still limited we constructed the essential spatial database of landslides using the gis techniques the quantitative relationships between landslides and factors affecting landslides are established by the certainty factor model cf the affecting factors such as lithology structure slope angle slope aspect elevation and off fault distance are recognized by applying cf value integration and landslide zonation the most significant affecting factors are selected the widespread landslide activities in the xiaojiang watershed are caused and triggered by heavy rain a promising approach to modeling the spatial distribution of rainfall triggered landslide is combining the mechanistic infinite slope stability model with a hydrological model a model modified from stability index mapping sinmap is used to prepare the landslide susceptibility maps for different rainfall conditions information on these maps could be useful for explaining the known existing landslide making emergency decisions and relieving the efforts on the avoidance and mitigation of future landslide hazards

structural analysis of supracrustal faults in the charlevoix area quebec relation to impact cratering and the st laurent fault system the charlevoix area which is host to an impact structure of devonian age straddles the boundaries among crystalline rocks of the grenville province the cambrian ordovician sedimentary succession of the st lawrence platform and accreted units of the appalachian orogen the area features well developed supracrustal fault systems attributed to impact cratering a major fault system oriented from northeast to northwest consists of normal faults marked by cataclastic and gouge breccias and less frequently by pseudotachylyte detailed mapping of faults both within and outside the charlevoix impact crater suggests that brittle faulting occurred both before and after impact cratering polymictic fault breccias occurring along some supracrustal faults are the clearest evidence of impact related fault rocks in the charlevoix area the st laurent fault trending to the northeast represents a major structure interpreted as being related to late proterozoic early paleozoic rifting of the iapetus ocean howev

assessment of calanchi and rill interrill erosion susceptibilities using terrain analysis and geostochastics a case study in the oltrepo pavese northern apennines italy

present day 3d velocity field of eastern north america based on continuous gps observations the saint lawrence river valley in eastern canada was studied using observations of continuously operating gps cgps stations the area is one of the most seismically active regions in eastern north america characterized by many earthquakes which is also subject to an ongoing glacial isostatic adjustment we present the current three dimensional velocity field of eastern north america obtained from more than 14 years 9 years on average of data at 112 cgps stations bernese gnss and gitsa software were used for cgps data processing and position time series analysis respectively the results show the counterclockwise rotation of the north american plate in the no net rotation model with the average of 16 8 0 7 mm year constrained to itrf 2008 we also present an ongoing uplift model for the study region based on the present day cgps observations the model shows uplift all over eastern canada with the maximum rate of 13 7 1 2 mm year and subsidence to the south mainly over northern usa with a typical rate of 1 to 2 mm year and the minimum value of 2 7 1 4 mm year we compared our model with the rate of radial displacements from the ice 5g model both models agree within 0 02 mm year at the best stations however our model shows a systematic spatial tilt compared to ice 5g the misfits between two models amount to the maximum relative subsidence of 6 1 1 1 mm year to the east and maximum relative uplift of 5 9 2 7 mm year to the west the intraplate horizontal velocities are radially outward from the centers of maximum uplift and are inward to the centers of maximum subsidence with the typical velocity of 1 1 6 0 4 mm year that is in agreement with the ice 5g model to the first order

msi morphometric slope index for analyzing activation and evolution of calanchi in italy article i nfo the calanchi singular calanco are a typical example of italian badlands widespread in areas with hills of clay rich sediments and rocks they appear as a very dense and rapidly evolving drainage system characterized by an alternating pattern of narrow furrows and sharp crests the calanchi can be considered as small hydrographical basins characterized by two possible drainage patterns parallel and dendritic the two patterns show both linear and areal erosion processes in this study calanchi with dendritic drainage patterns were analyzed in three different areas representative of the italian peninsular atri in the abruzzi region mount ascensione in the marche region and orcia valley in the tuscany region for each calanchi the pre erosion topographic surface was reconstructed and the value of msi morphometric slope index was calculated for the surface the volume of eroded material was estimated by comparing the pre calanchi and present surfaces we assumed that slope morphometry influences the type of erosion processes and the efficacy of these processes with respect to the amount of eroded material is a func tion of their duration we deduced that calanchi inception was contemporaneous because the duration of the processes was common to all landforms and probably due to a common climate input moreover the relations among msi eroded volume and erosion processes indicate that over a long period areally distributed surface processes contribute more to total sediment yields than channel flows

gis based landslide susceptibility mapping using analytical hierarchy process and bivariate statistics in ardesen turkey comparisons of results and confirmations abstract the ardesen area is prone to landslides because of the climate conditions geologic and geomorphologic characteristics of the region as in previous years in 2001 due to heavy rainfall there were many landslides resulting in damage and human casualties there is still a great danger of further landslides in the region therefore it is vitally important to prepare a landslide susceptibility map of the region in this study the analytical hierarchy process ahp the statistical index wi and weighting factor wf methods were used to produce and later compare three susceptibility maps for this purpose thematic layers including landslide inventory lithology weathering slope aspect land cover distance to stream drainage density and distance to road were used in this study area 98 of landslides occurred in highly or completely weathered units lithology weathering land cover and slope data layers were found to be important factors in the study area to confirm the practicality of the three susceptibility maps were compared with a landslide activity map containing 16 active landslide zones the outcome was that the active landslide zones do not completely fit into the high and very high susceptibility classes but 81 3 of these landslide zones fall into the high and very high susceptibility zones of the ahp method while this is 62 5 in the case of wi method and 68 8 with the wf method in spite of the results obtained in this study the development of a susceptibility map is usually determined by the needs and available resources the results showed that the ahp method gave a more realistic picture of the actual distribution of landslide susceptibility than the wi and wf methods

a typical calanchi landscape on the eastern apennine margin atri central italy geomorphological features and evolution abstract the surroundings of the town of atri abruzzo region central italy situated about 10 km from the adriatic shoreline can be considered as representative of most part of the italian seaward peninsular landscape the subject of this research the calanchi landscape often generally considered as badlands by non italian authors is in fact made up of many singular landforms each of which calanco corresponds to a more or less extended hydrographic unit the dynamics are mainly the result of the action of the particularly aggressive climatic factors such as the mediterranean rainfall regime on weak substrata clay silt and sand of the plio pleistocene marine cycles the morphogenetic activity is not only limited to channel erosion but it is also due to repeated superficial slides so that it should in fact be better to consider the calanco as the result of a combined erosion process sensu zachar d 1982 soil erosion elsevier amsterdam since the mechanism regulating this process remains unclear this work wants to offer a contribution to this research field multitemporal geomorphological analysis has helped us to distinguish the different areas in which the calanchi evolution has been more or less important in the past in such a way it has been possible to characterize the landscape evolution as a function of the parameters that influence soil loss especially in areas such as that of atri where calanchi like landforms are highly developed moreover this analysis coupled with the processing of 40 years rainfall data also taking into account the concurrent land use changes has clearly shown that the areas affected by calanchi erosion on the eastern apennine margin still tectonically active are progressively diminishing

digital terrain modelling a review of hydrological geomorphological and biological applications the topography of a catchment has a major impact on the hydrological geomorphological and biological processes active in the landscape the spatial distribution of topographic attributes can often be used as an indirect measure of the spatial variability of these processes and allows them to be mapped using relatively simple techniques many geographic information systems are being developed that store topographic information as the primary data for analysing water resource and biological problems furthermore topography can be used to develop more physically realistic structures for hydrologic and water quality models that directly account for the impact of topography on the hydrology digital elevation models are the primary data used in the analysis of catchment topography we describe elevation data sources digital elevation model structures and the analysis of digital elevation data for hydrological geomorphological and biological applications some hydrologic models that make use of digital representations of topography are also considered

micropiping processes and biancana evolution in southeast tuscany italy abstract biancane badlands consisting of small domes dissected by rills and micropipes with rough disordered microrehef can be found along the apennines in italy the dominant processes forming biancane differ from those of badlands formed on smectite rich mudrocks as micropipes associated with pseudokarstic enlargement of pores and cracks predominate and form the main routes for evacuation of eroded material biancana evolution is controlled by water infiltration into intact bedrock producing an erodible weathering rind which is more porous than intact rock this rind is easily removed by rill or micropipe flow and erosion is therefore weathering controlled depending on rind production by infiltrating water infiltration is initially slow and stepped due to slow water movement through very small capillary pores in intact rock alternating with rapid filling of macropores and cracks this occurs due to rapid matrix pore enlargement by dispersion and or dissolution the infiltration pattern is accurately reproduced by a model built on progressive development of weathering layers by moisture penetration model results are consistent with weathering rind depths and erosion observed in the field and show that a pipe network can be generated on newly exposed rock by the rainfall of one year propagation of the pipe network diverts a progressively larger proportion of runoff into micropipes expanding weathering rind production within the biancana as well as on the surface internal weathering and flow progressively dominate with few unweathered corestones and the biancana gradually collapses into a penultimate souffle like form

noise in gps displacement measurements from southern california and southern nevada 1 time series of position changes estimated from data from 236 continuously recording gps receivers operating in southern california and southern nevada are evaluated for noise models that characterize their temporal correlations the lengths of the time series range between 3 5 and 10 years after adjusting these data for postseismic deformation offsets and annual periodicities i find that about one half of the time series have temporal correlations that are categorized as either flicker or random walk noise the remaining time series can be best categorized as either a combination of flicker and random walk power law noise first order gauss markov plus random walk noise or power law plus broadband seasonal noise a variety of geodetic monuments are used in southern california and nevada including deeply braced designs cement piers pins drilled in outcrop and buildings when i evaluate the noise for each time series in terms of an estimate of the standard error in velocity i find that the sites with the smallest errors are those located in nevada using deeply braced monuments sites that are installed within regions of active pumping both for groundwater and oil had the largest standard errors in velocity comparison of monument stability as measured by standard error in rate with average annual rainfall nearby indicates a marginally significant correlation in addition even though regional filtering removed much of the common mode signals in these time series there still remains a common mode seasonal signal which can and should be removed

microbial precipitation of dolomite in methanogenic groundwater we report low temperature microbial precipitation of dolomite in dilute natural waters from both field and laboratory experiments in a freshwater aquifer microorganisms colonize basalt and nucleate nonstoichiometric dolomite on cell walls in the laboratory ordered dolomite formed at near equilibrium conditions from groundwater with molar mg ca ratios of 1 dolomite was absent in sterile experiments geochemical and microbiological data suggest that methanogens are the dominant metabolic guild in this system and are integral to dolomite precipitation we hypothesize that the attached microbial consortium reacts with the basalt surface releasing mg and ca into solution which drives dolomite precipitation via nucleation on the cell wall these findings provide insight into the long standing dolomite problem and suggest a fundamental role for microbial processes in the formation of dolomite across a wide range of environmental conditions

dolomitization a critical view of some current views perspectives abstract the principal models in vogue today for dolomitization are the mixing zone and the sabkha models despite the wide acceptance of these models there has been little critical assessment of their validity such an assessment is the objective of the present paper a close look at the dorag mixing zone model badiozamani 1973 reveals several serious weaknesses 1 the range of freshwater seawater mixtures that meet the dorag requirement for dolomitization shrinks to a small window if the geologically more realistic disordered dolomite is used in the calculations instead of the ordered dolomite on which the model is based 2 in none of the known modern coastal mixing zones in limestone or lime sediments has replacement by dolomite been observed 3 in a number of dolomites interpreted to be of mixing zone origin dolomite has precipitated without dissolution of the calcite substrate evidence that negates the fundamental premise of the dorag model in addition to these weaknesses isotope and trace element data used to identify mixed water olomite are inadmissible because 1 isotopic fractionation factors for dolomites remain unresolved 2 isotope values uncorrected for temperature for a host of dolomites interpreted to be of different origins overlap 3 nonisomorphous trace elements such as na in dolomite cannot on theoretical grounds be relied on to identify dolomitizing fluids similar overall objections can be brought against folk and land s 1975 schizohaline version of mixing zone dolomitization in summary mixing zone models have such weak underpinnings that they should be questioned as viable explanations for massive dolomitization contemporaneous dolomite formation in modern sabkhas is well documented but the important question of whether the mechanism of dolomite formation is replacement or direct precipitation remains to be resolved in the well studied sabkha at abu dhabi brine chemistry changes have been used as evidence of a replacement origin for the dolomite but it is shown here that this evidence is far from unequivocal an alternative origin of direct precipitation of dolomite is offered an origin in keeping with dolomite precipitation known from other modern sabkhas and saline lakes and in line with our laboratory experience with dolomite synthesis moreover it is suggested here that in general contemporaneous dolomite will form at low temperatures only by direct precipitation a mechanism tha requires special conditions of highly super saturated waters of high mg ca ratio and elevated co3 hco3 concentrations this may explain why modern dolomite is mainly restricted to evaporitic environments a bias not shared by ancient dolomites in contrast replacement dolomite appears to require at low temperatures long reaction times 104 yr a requirement that is mainly to be met in large regional groundwater flow systems both marine and nonmarine a third dolomitization model considered here is that of baker and kastner 1981 based on the experimental finding that sulfate ions inhibit or retard dolomitization a number of modern sedimentary dolomites are not in accord with this model in that they are forming from brines with large sulfate concentrations 2 to 70 times that of seawater thus the baker kastner model should be held in abeyance until these serious contradictions are resolved the current emphasis on mixing zone and sabkha dolomitization has diverted attention from other promising avenues of approach to the dolomite problem four of these avenues each of which deemphasizes the special water approach are briefly addressed and are as follows 1 influence of temperature and time 2 mass transfer processes 3 burial diagenesis of epigenetic dolomites 4 fluid inclusion studies at elevated temperatures the dolomite problem essentially disappears ordered dolomite can be made in the laboratory in days at 100 c what is more at temperatures above 60 c ca rich waters become dolomitizing fluids which makes most natural subsurface waters capable of dolomitization at low temperatures time may be the key element so that seawater will become a ma or dolomitizing fluid only where stable circulation systems such as kohout convention can drive seawater through carbonate platforms for many thousands to millions of years this paper has tried to show that currently favored models of dolomitization carry serious uncertainties enough to warn us to look more critically at the validity of these models and also it is hoped enough to spur new efforts to find new solutions to the problems of dolomitization

the plate tectonic approximation plate nonrigidity diffuse plate boundaries and global plate reconstructions the central assumption of plate tectonics that plate interiors are rigid remains a useful but uncertain approximation strain rates of stable plate interiors are bounded between 10 i12 10 i11 year i1 and 4 10 i10 year i1 the narrowness of all plate boundaries the other main assumption of plate tectonics as originally conceived is contradicted by many observations both in the continents and in the oceans some diffuse plate boundaries in both continents and oceans exceed dimensions of 1000 km on a side diffuse plate boundaries cover 15 of earth s surface the maximum speed of relative plate motion across any one diffuse plate boundary ranges from 2t o 15 mm year which is faster than some upper bounds on intraplate motion across stable plate interiors 2m m year i1 strain rates in diffuse plate boundaries can be as high as 10 i8 year i1 25 times higher than the upper bound on strain rates of stable plate interiors but 600 times lower than the lowest strain rates across typical narrow plate boundaries the poles of rotation of the plates flanking a diffuse oceanic plate boundary tend to be located in the diffuse boundary which is a consequence of the strong coupling across the boundary

supracrustal faults of the st lawrence rift system quebec kinematics and geometry as revealed by field mapping and marine seismic reflection data abstract the st lawrence rift system from the laurentian craton core to the offshore st lawrence river system is a seismically active zone in which fault reactivation is believed to occur along late proterozoic to early paleozoic normal faults related to the opening of the iapetus ocean the rift related faults fringe the contact between the grenvillian basement to the nw and cambrian ordovician rocks of the st lawrence lowlands to the se and occur also within the grenvillian basement the st lawrence rift system trends ne sw and represents a se dipping half graben that links the nw se trending ottawa bonnechere and saguenay river grabens both interpreted as iapetan failed arms coastal sections of the st lawrence river that expose fault rocks related to the st lawrence rift system have been studied between quebec city and the saguenay river brittle faults marking the st lawrence rift system consist of ne and nw trending structures that show mutual crosscutting relationships fault rocks consist of fault breccias cataclasites and pseudotachylytes field relationships suggest that the various types of fault rocks are associated with the same tectonic event high resolution marine seismic reflection data acquired in the st lawrence river estuary between rimouski the saguenay river and forestville identify submarine topographic relief attributed to the st lawrence rift system northeast trending seismic reflection profiles show a basement geometry that agrees with onshore structural features northwest trending seismic profiles suggest that normal faults fringing the st lawrence river are associated with a major topographic depression in the estuary the laurentian channel trough with up to 700 m of basement relief a two way travel time to bedrock map based on seismic data from the st lawrence estuary and comparison with the onshore rift segment suggest that the laurentian channel trough varies from a half graben to a graben structure from sw to ne it is speculated that natural gas occurrences within both the onshore and offshore sequences of unconsolidated quaternary deposits are possibly related to degassing processes of basement rocks and that hydrocarbons were drained upward by the rift faults

significant motions between gps sites in the new madrid region implications for seismic hazard position time series from global positioning system gps stations in the new madrid region were differenced to determine the relative motions between sta tions uncertainties in rates were estimated using a three component noise model con sisting of white flicker and random walk noise following the methodology of langbein 2004 significant motions of 0 37 0 07 one standard error mm yr were found between sites ptgvand stle for which the baseline crosses the inferred deep portion of the reelfoot fault baselines between stle and three other sites also show significant motion site mcty adjacent to stle also exhibits significant motion with respect to ptgv these motions are consistent with a model of interseismic slip of about 4 mm yr on the reelfoot fault at depths between 12 and 20 km if constant over time this rate of slip produces sufficient slip for an m 7 3 earthquake on the shallow portion of the reelfoot fault using the geologically derived recurrence time of 500 years this model assumes that the shallow portion of the fault has been pre viously loaded by the intraplate stress a gps site near little rock arkansas shows significant southward motion of 0 3 0 4 mm yr 0 08 mm yr relative to three sites to the north indicating strain consistent with focal mechanisms of earthquake swarms in northern arkansas

oxygen and carbon isotopic composition of marine carbonate concretions an overview abstract compilation of stable isotope data 18o and 13c for marine calcite siderite and dolomite concretions from a large number of studies reveals consistent and unanticipated isotopic trends although many of the dolomites have 18o values that are compatible with precipitation from unaltered seawater at low temperatures most of the calcites and siderites are far too depleted in 12o for such an origin this is surprising as most of the concretions appear to have formed very early in the diagenetic history of the sediments often within several meters of the sediment water interface the most likely cause of the anomalously depleted oxygen values is a decrease in pore water 18o values during early diagenesis a result perhaps of a significant influx of meteoric water into the marine shelf environment or water mineral interaction e g precipitation of 18o enriched minerals the carbon isotopic field for dolomite is quite different from that for calcite and siderite highly positive 13c values are fairly common only for dolomites this indicates that while dolomite concretions often form in sediments where methanogenesis is rapid precipitation of calcite and siderite concretions is restricted to sediments where either n methanogenesis takes place or where methanogenesis is not extensive enough to generate highly positive pore fluid 13c values this variation in carbon isotopic composition among the different minerals suggests that the rates of organic carbon oxidation and sedimentation may control the mineralogy of carbonate concretions high organic carbon oxidation rates favor dolomite and lower oxidation rates favor calcite or siderite

space geodesy constrains ice age terminal deglaciation the global ice 6g_c vm5a model a new model of the last deglaciation event of the late quaternary ice age is here described and denoted as ice 6g c vm5a it differs from previously published models in this sequence in that it has been explicitly refined by applying all of the available global positioning system gps measurements of vertical motion of the crust that may be brought to bear to constrain the thickness of local ice cover as well as the timing of its removal additional space geodetic constraints have also been applied to specify the reference frame within which the gps data are described the focus of the paper is upon the three main regions of last glacial maximum ice cover namely north america northwestern europe eurasia and antarctica although greenland and the british isles will also be included if peripherally in the discussion in each of the three major regions the model predictions of the time rate of change of the gravitational field are also compared to that being measured by the gravity recovery and climate experiment satellites as an independent means of verifying the improvement of the model achieved by applying the gps constraints several aspects of the global characteristics of this new model are also discussed including the nature of relative sea level history predictions at far field locations in particular the caribbean island of barbados from which especially high quality records of postglacial sea level change are available but which records were not employed in the development of the model although ice 6g c vm5a is a significant improvement insofar as the most recently available gps observations are concerned comparison of model predictions with such far field relative sea level histories enables us to identify a series of additional improvements that should follow from a further stage of model iteration

bacterially induced dolomite precipitation in anoxic culture experiments to study the process of microbial mediated dolomite formation growth experiments were carried out with selected bacterial cultures under anoxic environmental conditions simulating those found in lagoa vermelha a hypersaline lagoon in brazil where dolomite precipitation occurs specifically we report the isolation of a particular strain of sulfate reducing bacteria lvform6 from lagoa vermelha sediment which apparently promotes the formation of nonstoichiometric dolomite sulfate reducing bacteria grown in a synthetic liquid medium produced dolomite during 30 days incubation at 30 c the precipitates have morphologies similar to those observed in lagoa vermelha sediment our results demonstrate that sulfate reducing bacteria can influence dolomite precipitation under controlled lowtemperature anoxic conditions and imply that anaerobic microorganisms can play an important role in carbonate sedimentation they may have been particularly significant in earth s earliest history when a more reducing atmosphere existed

rates and uncertainties on seismic moment and deformation in eastern canada 1 on the basis of earthquake statistics from the canadian earthquake hazard model we estimate the rates of seismic moment and deformation in seismic zones of eastern canada we use a logic tree approach to derive median values and 66 confidence intervals for models based on earthquake cluster distributions and geological and tectonic structures typical moment rates are low 0 1 1 1017 n m yr 1 equivalent to a magnitude mw 7 earthquake every 350 3500 years in each seismic zone in a few zones such as baffin bay moment rates reach 2 10 1017 n m yr 1 expressed in terms of relative velocity between zone boundaries seismic deformation rates are typically 0 2 0 5 mm yr 1 for a few regions of high seismicity such as baffin bay charlevoix or grand banks the relative velocities reach 1 2 mm yr 1 strain rates are typical of the intraplate environment 10 13 10 10 yr 1 with values locally as high as 10 8 yr 1 these rates give some insight into geodynamic aspects of the northeastern north america plate assuming that the seismic deformation rates represent long term deformation of the lithosphere they provide some constraint to the amplitude and variability of intraplate strain on a shorter timescale seismic strain rates can be compared with postglacial rebound predictions and might help constrain some aspects of these models because they reflect the seismic energy released over the last few hundred years our estimates in combination with geodetic measurements can also help constrain models of earthquake dynamics in eastern north america

gps crustal strain postglacial rebound and seismic hazard in eastern north america the saint lawrence valley example 1 we present global positioning system gps measurements that constrain the amplitude pattern and origin of crustal deformation in the saint lawrence valley quebec one of the most seismically active regions of eastern north america the gps network shows coherent southeastward motion of 0 6 0 2 mm yr 1 relative to north america and uplift of 2 6 0 4 mm yr 1 network average horizontal strain rates are mostly ese wnw shortening at 1 7 1 0 10 9 yr 1 the shortening rate across the charlevoix seismic zone is about twice as big as the regional average these measurements are consistent with both postglacial rebound pgr models and the deformation style indicated by earthquake focal mechanisms although the gps data do not discriminate between various models of crustal deformation they provide important constraints on large earthquake recurrence assuming that the gps strain estimates are representative of seismic moment release they constrain the maximum magnitude of truncated gutenberg richter recurrence statistics in the charlevoix seismic zone to mx 7 8 0 6 one m 7 earthquake per 400 1300 years the remarkable agreement between the gps strain rates seismic catalogue statistics and pgr predictions suggests that in charlevoix most of the pgr driven crustal strain may be released by large m 7 earthquakes in the rest of the saint lawrence valley pgr strain rates are significantly larger than seismic strain rates suggesting either that pgr deformation remains mostly elastic or that large events are more frequent than indicated by small earthquake statistics i e characteristic earthquakes

can deglaciation trigger earthquakes in n america a spherical self gravitating viscoelastic earth model is used to calculate the spatial and temporal evolution of the glacially induced lithospheric stress and fault stability in north america the predicted onset time of a pulse of earthquake activities the mode of failure and the magnitude of instability are investigated for three sites with different distance from the former ice margin it is found that glacial unloading is able to trigger paleo earthquakes within the ice margin near charlevoix 47 5 n 70 1 w and in wabash valley 38 5 n 87 w outside the ice margin however rebound stress decays away from the former ice margin thus glacial unloading is unlikely to have triggered the large m8 earthquakes in new madrid 36 6 n 89 5 w

indentor corner tectonics in the yakutat st elias collision constrained by gps the yakutat st elias collision in se alaska and adjacent canada represents a prime example of present day tectonics associated with an indentor corner its eastern syntaxis is marked by high exhumation a sharp structural bend and strain concentration at the transition from shortening to oblique transpression here we present gps velocity and strain rate fields that cover the syntaxis including 11 new stations in the core of the st elias mountains these data are corrected for transient deformation glacial isostatic adjustment and postseismic and interseismic loading to produce residual velocities and strain rates representative of long term tectonics the main features of these velocity and strain rate fields are a peak in strain rates strain knot in the syntaxis at the junction between the main fault systems and a rapid rotation from convergence parallel to convergence normal orientations of the velocities and shortening axes around the syntaxis leading to shortening across the southern denali fault these features are consistent with the strain and tectonic patterns expected near an indentor corner at the transition from shortening to transpression with a combination of diffuse and localized deformation the gps velocities and strain rates show diffuse deformation around the syntaxis from pure convergence parallel shortening in the orogenic wedge to oblique extension that accommodates the strain rotation at the front of the syntaxis this indentor corner model also results in a near zero strike slip rate on the southern denali fault and shows no clear evidence for a throughgoing fault hypothesized to link the fairweather and totschunda faults

troposphere mapping functions for gps and very long baseline interferometry from european centre for medium range weather forecasts operational analysis data 1 in the analyses of geodetic very long baseline interferometry vlbi and gps data the analytic form used for mapping of the atmosphere delay from zenith to the line of site is most often a three parameter continued fraction in 1 sin elevation using the 40 years reanalysis era 40 data of the european centre for medium range weather forecasts for the year 2001 the b and c coefficients of the continued fraction form for the hydrostatic mapping functions have been redetermined unlike previous mapping functions based on data from numerical weather models isobaric mapping functions niell 2000 and vienna mapping functions vmf boehm and schuh 2004 the new c coefficients are dependent on the day of the year and unlike the niell mapping functions niell 1996 they are no longer symmetric with respect to the equator apart from the opposite phase for the two hemispheres compared to vmf this causes an effect on the vlbi or gps station heights that is constant and as large as 2 mm at the equator and that varies seasonally between 4 mm and 0 mm at the poles the updated vmf based on these new coefficients and called vmf1 hereinafter yields slightly better baseline length repeatabilities for vlbi data the hydrostatic and wet mapping functions are applied in various combinations with different kinds of a priori zenith delays in the analyses of all vlbi international vlbi service for geodesy and astrometry ivs r1 and ivs r4 24 hour sessions of 2002 and 2003 the investigations concentrate on baseline length repeatabilities as well as on absolute changes of station heights

identification characterisation and analysis of the oltrepo pavese calanchi in the northern apennines italy abstract badlands are characteristic erosional forms distributed along the entire apennines in the italian context badland areas are called calanchi the plural of the word calanco in this paper we present the first calanchi inventory map of the oltrepo pavese area northern apennines italy in total 263 calanchi were mapped using remote sensing techniques like orthophotos google earth images as well as field recognition moreover calanchi were characterised from a geomorphologic geologic and a morphometric point of view the calanchi of the oltrepo pavese have been categorised in two geomorphological classes based on process related morphologies in the study area calanchi mainly occur in soft sedimentary bedrock materials such as melanges marls claystones and interstratified rocks the results show that calanchi formations are often related to faults and tectonic lineaments present in the study area moreover we analyse a 5 m cell size digital terrain model to detect correlations between calanchi and morphometric indices the calanchi defined and categorised for the first time in the study area show typical morphometric characteristics of apennine calanchi forms and features in particular they occur on concave south facing slopes on soft bedrock formations finally a multitemporal air photo interpretation over a 40 years period indicated a general decrease in calanchi areas the area reduction is mainly correlated to intensive land use changes combined with variations of precipitation pattern the revegetation trend was also confirmed by ndvi analysis based on landsat satellites images the calanchi were digitized and stored in a gis database providing the information for future quantitative modelling assessments

composition of the crust in the grenville and appalachian provinces of north america inferred from v p v s ratios we use the ratios between p and s wave velocities vp vs derived from seismic refraction data to infer the composition of the crust in the grenville and the appalachian provinces of north america the crust exhibits vp vs increasing with depth from 1 64 to 1 84 there is a clear distinction between the grenville province average vp vs 1 81 and the appalachian province average vp vs 1 73 which persists at all depths the boundary between these provinces is east dipping extending for 100 km east of the champlain thrust in the appalachian province the increase in vp vs ratios with depth from 1 67 to 1 74 0 02 may reflect a normal decrease of silica content in the continental crust in the grenville province beneath the central granulite terrane an anomalous vp vs ratio of 1 82 0 02 is observed extending to a depth of 10 km this correlates with the abundance of ca plagioclase in the marcy anorthosite at greater depth 15 20 km where seismic lamination and high electrical conductivity is observed vp vs is 1 84 0 02 and correlates with the tahawus complex a layered mafic intrusion within the 25 km thick lower crust of the grenville province the vp vs is 1 84 0 02 and p velocity is 7 0 0 1 km s which are typical for plagioclase bearing rocks gabbro norite the high vp vs ratio in the grenville province has not been reported in crust of any other age since the grenville province contains 75 of the world s known anorthosites high vp vs ratio is related to high plagioclase we suggest that the composition of the grenville lower crust was significantly modified by the emplacement of the anorthosites in the mid proterozoic

seismology tectonic strain in plate interiors arising from r smalley jr m a ellis j paul r b van arsdale nature 435 1088 1090 2005 r smalley et al reply it is not fully understood how or why the inner areas of tectonic plates deform leading to large although infrequent earthquakes smalley et al 1 offer a potential breakthrough by suggesting that surface deformation in the central united states accumulates at rates comparable to those across plate boundaries however we find no statistically significant deformation in three independent analyses of the data set used by smalley et al and conclude therefore that only the upper bounds of magnitude and repeat time for large earthquakes can be inferred at present

stress channelling and partitioning of seismicity in the charlevoix seismic zone quebec canada summary the charlevoix seismic zone csz in the st lawrence valley of quebec is historically the most active in eastern canada the structurally complex region comprises rift faults formed during the opening of the iapetus ocean superimposed by a 350 ma meteorite impact structure resulting in a circular highly fractured zone although seismicity is localized along two steeply dipping planar rift parallel zones previous work indicates that most of the large scale rift faults bound the low magnitude background seismicity rather than generate earthquakes themselves in order to gain insight into the mechanics of the partitioning of this seismicity a 2 d model of the csz was built using the stress analysis code flac the rift faults are represented by frictional discontinuities the heavily fractured impact structure is represented by an elastic continuum of reduced modulus boundary displacements are used to generate a regional stress field with the major horizontal component in the direction of tectonic loading given a high strength the rift faults have little effect on the stress patterns stress trajectories naturally flow around the crater of reduced elastic modulus leaving the fractured area with lower stresses than the background level however when the rift faults have low strength they are unable to support stress trajectories inclined to them due to the resolved shear stress exceeding their strength this prevents trajectories from flowing out of the rift effectively channelling higher magnitude stresses into the region of the impact structure between the faults low strength bounding faults can thus explain the localization of seismicity into linear bands rather than distributed seismicity throughout the impact structure it also explains how the rift faults act as boundaries to regions of low magnitude seismicity these results indicate that the interplay between faults of varying strength and zones of differing elastic modulus can give rise to complicated stress patterns and can explain many of the seismicity patterns observed in the csz this has implications for other intraplate seismic zones as it shows an example of how regional weak faults can modify stress conditions around local structures and drive seismicity the results are particularly relevant for other regions located within rifted crust such as the new madrid seismic zone which possibly display evidence of stress channelling

structural inheritance control on intraplate present day deformation gps strain rate variations in the saint lawrence valley eastern canada structural inheritance is one of the key factors commonly proposed to control the localization of strain and seismicity in continental intraplate regions primarily on the basis of a first order spatial correlation between seismicity and inherited tectonic structures in this paper we present new gps global positioning system velocity and strain rate analyses that provide strong constraints on the magnitude and style of present day strain localization associated with the inherited tectonic structures of the saint lawrence valley eastern canada we analyze 143 continuous and campaign gps stations to calculate velocity and strain rate patterns with specific emphases on the combination of continuous and campaign velocity uncertainties and on the definition of robustness categories for the strain rate estimations within the structural inheritance area strain rates are on average 2 11 times higher than surrounding regions and display strong lateral variations of the style of deformation these gps velocity and strain rate fields primarily reflect ongoing glacial isostatic adjustment gia their comparison with gia model predictions allows us to quantify the impact of the structural inheritance and the associated lithosphere rheology weakening outside of the major tectonic inheritance area gps and gia model strain rates agree to first order both in style and magnitude in contrast the saint lawrence valley displays strong strain amplification with gps strain rates 6 28 times higher than model predicted gia strain rates our results provide the first quantitative constraints on the impact of lithospheric scale structural inheritance on strain localization in intraplate domains

the impact of the farming practice of remodelling hillslope topography on badland morphology and soil erosion processes abstract badland landforms created in plio pleistocene clay landscapes of the basilicata region of southern italy form marginal features in a semi arid landscape dominated by the widespread cultivation of subsidised cereals these badland features are high relative relief forms exhibiting a high drainage density and steep slopes with slope angles typically in excess of 35 economic incentives to increase agricultural productivity have resulted in the practice of remodelling these marginal areas using heavy earth moving equipment remodelling the badland features creates longer slopes at lower angles which can be cultivated using conventional farm machinery these changes in hillslope morphology have altered the degree to which soil erosion processes operating in these areas are spatially coupled in the badland areas erosion and deposition are strongly localised with minimal sediment delivery to ephemeral or perennial channel systems the economically driven change in land use from visually striking badland areas to newly remodelled fields for agricultural use results in an increase in the coupling of drainage networks and a net increase in soil erosion

ice 3g a new global model of late pleistocene deglaciation based upon geophysical predictions of post glacial relative sea level change a new high resolution global model of late pleistocene deglaciation is inferred on the basis of geophysical predictions of postglacial relative sea level variations in which the ice ocean solid earth interaction is treated in a gravitationally self consistent fashion for the purpose of these analyses the radial viscoelastic structure of the planet is assumed known on the basis of previously published sensitivity tests on solutions of the forward problem only radiocarbon controlled relative sea level histories from sites that were actually ice covered with one or two additions are employed to constrain the model leaving relative sea level rsl data from sites that were not ice covered to be employed to confirm its consistency results for these confirmatory analyses are reported elsewhere here the new deglaciation model referred to as ice 3g is compared to previous models derived by several independent means and tested against a number of additional observations other than sea level histories including geologically controlled retreat isochrones oxygen isotope data from deep sea sedimentary cores and coral terrace elevations the latter two observations strongly constrain the net sea level rise that has occurred since the onset of deglaciation and therefore the mass of ice that melted during the last glacial interglacial transition

iron reduction in the sediments of a hydrocarbon contaminated aquifer abstract sediments sampled at a hydrocarbon contaminated glacial outwash sandy aquifer near bemidji minnesota were analyzed for sediment associated fe with several techniques extraction with 0 5 m hcl dissolved poorly crystalline fe oxides and small amounts of fe in crystalline fe oxides and extracted fe from phyllosilicates use of ti citrate edta bicarbonate results in more complete removal of crystalline fe oxides the average hcl extractable fe iii concentration in the sediments closest to the crude oil contamination 16 2 mol g has been reduced by up to 30 from background values 23 8 mol g as a result of fe iii reduction in contaminated anoxic groundwater iron ii concentrations are elevated in sediments within an anoxic plume in the aquifer iron ii values under the oil body 19 2 mol g are as much as 4 times those in the background sediments 4 6 mol g indicating incorporation of reduced fe in the contaminated sediments a 70 increase in total extractable fe at the anoxic oxic transition zone indicates reoxidation and precipitation of fe mobilized from sediment in the anoxic plume scanning electron microscopy detected authigenic ferroan calcite in the anoxic sediments and confirmed abundant fe iii oxyhydroxides at the anoxic oxic boundary the redox biogeochemistry of fe in this system is coupled to contaminant degradation and is important in predicting processes of hydrocarbon degradation

comparison of gully erosion estimates using airborne and ground based lidar on santa cruz island california abstract gully erosion removes comparatively large volumes of soil from small areas it is often difficult to quantify the loss of soil because the footprint of individual gullies is too small to be captured by most generally available digital elevation models dems such as the usgs national elevation dataset airborne lidar light detection and ranging has the potential to provide the required data density but an even newer class of ground based sensors may provide better local resolution at lower cost in this study we compared digital elevation models produced by airborne and ground based lidar systems with ground based geomorphic and geodetic survey data to determine their utility in quantifying volumetric soil loss due to gully erosion in a heavily degraded watershed 7 55 10 2 km 2 on southwestern santa cruz island in southern california volumetric estimates of the eroded sediment were produced by comparing the lidar derived dems of the gully system to a modeled pre erosion surface average point densities were significantly higher for the ground based lidar system and provided more detailed information however its limited scanning footprint and side looking orientation presented serious challenges in collecting continuous data from deeply incised gullies making the airborne system preferable for this type of investigation and likely for most applications where heavy topographic shadowing is prevalent

comparison of gis based gullying susceptibility mapping using bivariate and multivariate statistics northern calabria south italy abstract this paper presents gis aided procedures for the evaluation of gullying susceptibility on a statistical basis field surveys and air photo interpretation allowed us to identify gullies geology and land use while some predisposing factors were derived from a 7 5 m cell size dem in order to investigate the role of each instability factor in controlling the spatial distribution of gullies we implemented four models that differ in the types of method bivariate vs multivariate training set sampling polygon or point based and variables continuous or categorical the models were applied to the turbolo river catchment a tributary of the crati river northern calabria italy the susceptibility values were classified into five categories model performance was evaluated using prediction rate curves and by comparing the proportion of each susceptibility class with gully distribution in the validation set although all models showed relatively good performances the bivariate method overestimated the extent of the high susceptibility classes the multivariate logistic regression model using continuous variables was found to be the best model in predicting gullying susceptibility of the study area the area classified as stable increased with dem cell size meaning that a reasonably fine dem should be used

estimating the quality of landslide susceptibility models we present a landslide susceptibility model for the collazzone area central italy and we propose a framework for evaluating the model reliability and prediction skill the landslide susceptibility model was obtained through discriminant analysis of 46 thematic environmental variables and using the presence of shallow landslides obtained from a multi temporal inventory map as the dependent variable for statistical analysis by comparing the number of correctly and incorrectly classified mapping units it is established that the model classifies 77 0 of 894 mapping units correctly model fitting performance is investigated by comparing the proportion of the study area in each probability class with the corresponding proportion of landslide area we then prepare an ensemble of 350 landslide susceptibility models using the same landslide and thematic information but different numbers of mapping units this ensemble is exploited to investigate the model reliability including the role of the thematic variables used to construct the model and the model sensitivity to changes in the input data by studying the variation of the model s susceptibility estimate the error associated with the susceptibility assessment for each mapping unit is determined this result is shown on a map that complements the landslide susceptibility map prediction skill of the susceptibility model is then estimated by comparing the forecast with two recent event inventory maps the susceptibility model is found capable of predicting the newly triggered landslides a general framework for testing a susceptibility model is proposed including a scheme for ranking the quality of the susceptibility assessment

quantitative impact of structural inheritance on present day deformation and seismicity concentration in intraplate deformation zones abstract structural inheritance i e paleo tectonic areas acting as weakened domains appear to be a key element localizing the seismicity in intraplate deformation zones however the impact of structural inheritance on the observed present day seismicity and strain rate concentration remains to be quantified in this study we quantify through 2d numerical modeling the localization and amplification factor of upper crustal strain rates induced by structural inheritance our 2d models are constrained by intraplate velocity boundary conditions and include rheology laws that accounts for inherited strain weakening in both the brittle and ductile layers of the lithosphere the role of structural inheritance is investigated for different localization of the weakened domain in the lithosphere for an average intraplate geotherm moho temperature ca 500 c brittle weakening i e inherited faults alone induces a limited amplification factor of upper crustal strain rates of ca 4 ductile weakening can increase the amplification factor to ca 7 when localized in the lower crust but has no effect when localized in the lithospheric mantle overall the amplification factors of upper crustal strain rates vary between 1 and 27 depending on the location of the weakened area in the lithosphere and on the different possible net driving forces crustal strengths amounts of weakening and geotherms these model amplification factors are in reasonable agreement with those derived from gps and seismicity data over large spatial scale several hundreds of kilometers in north america

gully erosion impacts factors and control gully erosion attracts increasing attention from scientists as reflected by two recent international meetings poesen and valentin eds catena 50 2 4 87 564 li et al 2004 gully erosion under global change sichuan science technology press chengu china 354 pp this growing interest is associated with the increasing concern over off site impacts caused by soil erosion at larger spatial scales than the cultivated plots the objective of this paper is to review recent studies on impacts factors and control of gully erosion and update the review on dgully erosion and environmental change importance and research needst poesen et al 2003 catena 50 2 4 91 134 for the farmers the development of gullies leads to a loss of crop yields and available land as well as an increase of workload i e labour necessary to cultivate the land gullies can also change the mosaic patterns between fallow and cultivated fields enhancing hillslope erosion in a feedback loop in addition gullies tend to enhance drainage and accelerate aridification processes in the semi arid zones fingerprinting the origin of sediments within catchments to determine the relative contributions of potential sediment sources has become essential to identify sources of potential pollution and to develop management strategies to combat soil erosion in this respect tracers such as carbon nitrogen the nuclear bomb derived radionuclide 137 cs magnetics and the strontium isotopic ratio are increasingly used to fingerprint sediment recent studies conducted in australia china ethiopia and usa showed that the major part of the sediment in reservoirs might have come from gully erosion gullies not only occur in marly badlands and mountainous or hilly regions but also more globally in soils subjected to soil crusting such as loess european belt chinese loess plateau north america and sandy soils sahelian zone north east thailand or in soils prone to piping and tunnelling such as dispersive soils most of the time the gullying processes are triggered by

southern california permanent gps geodetic array spatial filtering of daily positions for estimating coseismic and postseismic displacements induced by the 1992 landers earthquake the june 28 1992 m w 7 3 landers california earthquake was the first earthquake to be surveyed by a continuously operating global positioning system gps array the coordinate time series of seven sites are evaluated for station displacements during an interval of 100 days centered on the day of the earthquake we employ a new spatial filtering technique that removes common mode errors from the coordinate time series this approach provides precise estimates of site specific displacements compared to the cumbersome method of analyzing baselines between pairs of stations all sites indicate significant coseismic horizontal displacements of 5 65 mm with uncertainties of 1 2 mm horizontal displacements are in general agreement with elastic dislocation models in particular for sites closer to the epicenter vertical displacements range from 13 to 7 mm with uncertainties of 2 4 mm the observed vertical displacements in all cases show 5 10 mm more subsidence than expected from geodetic and seismic geologic models significant postseismic horizontal displacements totaling 6 2 mm 10 20 of the coseismic displacement are detected at the three sites closest to the epicenter these displacements are modeled as a short term exponential relaxation with a decay time of 22 10 days superimposed on a longer term linear interseismic trend scaling the observed coseismic and postseismic displacements at one of the sites with the distance to the epicenter provides a measure of site strain which agrees well with the direction and magnitude determined from more precise laser strain meter data the time series do not show any detectable preseismic displacements

control of tectonic inheritance on continental intraplate strain rate and seismicity abstract present day deformation and seismicity of continental lithosphere are characterized by a first order dichotomy between plate boundary zones pbz and stable continental regions scr whereas the former are associated with high strain and seismicity rates the latter tend to remain un deformed except in localized regions of higher strain and seismicity commonly related to fossilized paleo pbz acting as locally weaker domains because of their low amplitudes these intraplate strain and seismicity rates are particularly difficult to measure and characterize in this study we propose a simple model to explain and quantify first order continental strain rate variations focusing on intraplate regions assuming near failure equilibrium on 1d lithosphere profiles we derive steady state strain rates driven by tectonic forces as a function of rheological models that include new strain weakening rheologies in order to simulate tectonic inheritance within this framework inherited strain weakening plays a fundamental role in allowing for and explaining strain and seismicity concentration in intraplate weak zones our model predicts strain rates in intraplate weak zones up to two to three orders of magnitude higher compared to stable cratons due to the effect of tectonic inheritance on rheology weakening these model predictions are in agreement with empirical estimations in intraplate regions and can provide a conceptual framework for characterization of scr strain and seismicity rates

landslide susceptibility mapping in the damrei romel area cambodia using frequency ratio and logistic regression models this study applied tested and compared a probability model a frequency ratio and statistical model a logistic regression to damre romel area cambodia using a geographic information system for landslide susceptibility mapping landslide locations were identified in the study area from interpretation of aerial photographs and field surveys and a spatial database was constructed from topographic maps geology and land cover the factors that influence landslide occurrence such as slope aspect curvature and distance from drainage were calculated from the topographic database lithology and distance from lineament were extracted and calculated from the geology database land cover was classified from landsat tm satellite imagery the relationship between the factors and the landslides was calculated using frequency ratio and logistic regression models the relationships frequency ratio and logistic regression coefficient were overlaid to make landslide susceptibility map then the landslide susceptibility map was compared with known landslide locations and tested as the result the frequency ratio model 86 97 and the logistic regression 86 37 had high and similar prediction accuracy the landslide susceptibility map can be used to reduce hazards associated with landslides and to land cover planning