environmental isotopes meet 3d geological modelling conceptualising recharge and structurally controlled aquifer connectivity in the basalt plains of south western victoria australia summary to develop a conceptual model of recharge and inter aquifer connectivity for a complex aquifer system in southwestern victoria australia a three dimensional 3d geological model was constructed and used to examine the influence of the regional geology on groundwater composition and age as well as recharge mechanisms the major aquifers are three basalts differentiated on age and geomorphological features and an underlying palaeovalley deep lead system the upper fine grained sediments of the deep lead form an aquitard that separates the basalt from the permeable sands and gravels beneath recharge calculations chloride mass balance and water table fluctuation methods salinity stable isotope tritium and radiocarbon data show that volcanoes and the youngest basalts although volumetrically minor form preferential recharge areas for all the basalts up to 30 mm year and also recharge the deep lead sediments through volcanic necks that penetrate the aquitard infiltration through the thick clay rich soils on the older basalts is small typically 1 2 mm year and saline resulting in a progressive increase of groundwater salinity along the flow path in these basalts the comparison of fault location with groundwater age in the deep lead aquifer suggests that in some areas faults exert significant structural control on groundwater flow this study demonstrates the value of integrating geological hydrogeological and hydrochemical data to identify preferential recharge areas inter aquifer connectivity and the influence of faults on groundwater flow in a complex aquifer system

a simple kinematic model for crustal deformation along two and three dimensional listric normal faults derived from scaled laboratory experiments abstract we have derived a simple kinematic model of the deformation that results from extension accommodated by movement of a crustal block along two and three dimensional listric fault surfaces the model accurately reproduces deformation observed in a series of scaled analogue models the kinematic model is based on the simple assumption that lines within the hangingwall that are normal to the fault surface before deformation remain so following deformation an additional constraint built into the model is that of incompressibility deformation in the hangingwall block as observed in the laboratory experiments and predicted by the kinematic model is characterized by 1 a key stone structure or crestal collapse graben at some finite distance from the fault tip and 2 pure solid body rotation of the hangingwall head area near the tip of the fault in three dimensions the central region of the model undergoes extension in a direction normal to the direction of imposed displacement in such a way that the direction of dip of the upper surface of the hangingwall is aligned with the direction of extension this result provides quantitative support for the use of dip analysis to infer tectonic transport direction we also show how the distribution of extension within the hangingwall is affected when the constraint of constant displacement along the fault is relaxed

the importance of small scale faulting in regional extension a recurring observation in many studies of extensional basins has been that the amount of extension visible on normal faults for example on seismic reflection profiles is significantly less than the amount of extension indicated by crustal thickness and thermal subsidence1 5 one mechanism suggested to account for this discrepancy is small scale faulting with offsets too small to be resolved seismically6 7 but earthquake studies8 10 indicate that small faults are responsible for only a small fraction of the total seismic moment in an active area scholz and cowie11 have recently attempted to extend this approach to the total strain at the end of a finite deformation interval by combining scaling laws describing the distributions of fault lengths and displacements here we present fault displacement data that directly conflict with scholz and cowie s conclusions and imply that up to 40 of the extension may be missed by summing fault offsets on basin profiles the fault population at the end of a long deformation interval may differ substantially from that responsible for the earthquake population at any one time

structures in segment boundary zones of the lost river and lemhi faults east central idaho geologic mapping and structural analysis of the lost river and lemhi normal faults in east central idaho suggest that many rupture segment boundaries previously inferred from geomorphic data coincide with two classes of structural complexities 1 zones of distributed faults and steps or jogs in the range front faults and 2 intersections with preexisting eocene to oligocene cross faults at 10 15 km depth segment boundaries contain as many as 13 fault splays and are as much as 13 km long and 5 6 km wide in plan view in contrast simple fault traces characterize the range front faults in the interiors of segments thus segment boundaries of normal faults are broad zones of intersecting faults not discrete points the structural data further imply that segment boundaries contain large volumes of fractured and faulted rock and that zones of distributed normal faults have influenced rupture propagation and arrest along these two normal faults intersections of preexisting cross faults and range front faults may also have influenced the locations of rupture boundaries along the lost river and lemhi faults downdip projections of preexisting eocene to oligocene normal faults in the footwall of the lost river and lemhi faults may coincide with four or five segment boundary zones at about 15 km depth the depth at which large earthquakes nucleate in the basin and range province structural analyses also show that some cross faults which coincide with segment boundary zones at the surface are distant from these zones at depth conversely some potentially significant structures present at depth are far removed from the segment boundary zone at the surface thus a close spatial relationship between cross faults and segment boundary zones at the surface cannot prove or disprove a genetic relationship between these features because the near surface geometry of segment boundary zones may differ dramatically from the subsurface geometry of the zones where cross faults define segment boundaries the enhanced fracture toughness of preexisting fault planes and their damage zones may impede or arrest rupture on younger crosscutting faults

oblique slip deformation in extensional terrains a case study of the lakes tanganyika and malawi rift zones the east african rift system ear is the archetypal continental rift and a widely proposed analogue for the early stages of evolution of passive continental margins the three dimensional structure of parts of the ear has been recently elucidated by a multifold seismic mfs survey of lakes tanganyika and malawi project probe analysis of fault geometries displayed on the probe mfs data coupled with the more extensive 28 khz echosounder data has improved understanding of the geometry and kinematics of the linked fault systems that underlie the lakes in particular it has been recognized that profiles across i e at high angles to the rift elongation commonly display fault geometries that are not readily retrodeformable there must therefore be significant displacement out of the plane of what would conventionally be regarded as dip lines that is perpendicular to rift elongation and parallel to the tectonic transport or extension direction careful determination of fault plane dip and the dip of synrift reflectors in the hanging wall demonstrates that the dip directions of the shallowest faults and the steepest hanging wall sediment dips are oriented either nw or se this defines the direction of maximum fault block rotation and therefore the direction of extension or tectonic transport as nw se oblique to the trend of the regional rift axis and to the apparent strike of many of the major border faults in the survey area the border faults and many other faults imaged on the probe mfs data must therefore have significant components of strike slip motion and the tanganyika and malawi rift zones have undergone extension oblique to and not perpendicular to their axes near dip slip normal faults steeply dipping oblique slip faults and subvertical strike slip or transfer faults have all been recognized in a complex linked fault system that accomplishes the extension the overall orientation of the rift lakes and their internal segmentation are influenced by major preexisting subvertical fault zones within the basement complex accommodation zones act principally as transfer zones that allow switches in gross polarity of the border fault system the detailed geometries of the accommodation zones result from the specific relations between juxtaposed half graben and the strike and internal geometry of the influencing basement structure the variations in fault geometry subsidence water depth and basin or rift morphology can be better explained by an oblique slip extensional model influenced by basement structures than by a simple orthogonal extensional model

3 d mapping of segmented active faults in the southern vienna basin abstract in this paper we present novel data on the location and kinematics of seismically active fault segments of the vienna basin transfer fault system in the southern vienna basin spatial mapping of active faults and kinematical analyses are based on commercial 3 d reflection seismic data geomorphological features such as tilted quaternary river terraces and fault scarps the geometry of subsided quaternary basins and published geodetic data accordingly active faulting in the southern vienna basin occurs partly by reactivation of the miocene fault system related to the formation of the vienna pull apart basin between c 17 and 8 ma two domains of quaternary and active faults can be distinguished with 1 predominantly strike slip and 2 mainly normal faulting 1 a seismically active ne striking sinistral strike slip fault zone with large negative flower structures is mapped at the south eastern margin of the basin subsidence within the reflection seismically imaged flower structure is documented by up to 1000 m of throw since pannonian times and the accumulation of up to 150 m thick quaternary gravels at the surface the fault zone is characterized by en echelon faults with some prominent scarps 2 major e dipping normal faults branch off from the transfer strike slip fault system the normal faults extend into the central and western part of the basin as well as into the urban area of vienna close to vienna the normal offset along such a normal fault is at minimum 300 m since pannonian times surface expressions of active normal faulting are tilted quaternary terraces of the danube river and tilted ancient land surfaces in the hanging wall of the normal faults the mapped active normal faults are kinematically linked by a common detachment horizon which is in contact with the seismically active strike slip zone along the south eastern border of the basin northeast of the vienna basin the seismically active zone continues as a straight line indicating a rather linear transfer fault zone than a pull apart step over geometry

the relationship between the geometry of normal faults and that of the sedimentary layers in their hanging walls abstract we derive an analytical expression that relates the shape of a fault in cross section to the shape of the bedding horizons in its hanging wall block the expression assumes that the hanging wall deforms by simple shear and that the footwall remains undeformed throughout although this paper concentrates on normal faults the expression is equally valid and applicable to thrust faults the direction of simple shear in the hanging wall block is arbitrary and has a dramatic effect on the predicted fault or bedding geometry there is no reason to believe that the simple shear occurs on vertical planes as is commonly assumed in graphical approaches to this problem and ignoring the presence of inclined simple shear is likely to lead to considerable underestimates of the amount of extension across normal faults and in the amount of shortening across thrusts similar though more complicated expressions can be obtained when compaction within the hanging wall block is taken into account for a planar normal fault such compaction may result in the development of a hanging wall syncline

geomorphic and structural variations along the doruneh fault system central iran 1 this paper focuses on the analysis of geomorphic structural and behavioral characteristics along the doruneh fault system dfs east of longitude 56 45 e detailed geomorphic and structural analyses of different scale satellite images and digital topographic data accompanied with field surveys allowed us to establish a fault segmentation model in which three discrete fault zones have been recognized 1 the western fault zone wfz characterized by reverse left lateral mechanism with left handed step over geometry 2 the central fault zone cfz which is pure left lateral strike slip and comprises nearly parallel faults and 3 the eastern fault zone efz that is a trailing imbricate fan fault termination characterized by reverse faulting and fault related folding each fault zone shows discrete geometry and kinematics implying that deformation is not uniformly accommodated along the dfs we propose a new kinematic model to explain how the dfs accommodate the arabia eurasia convergence normal to the overall fault orientation according to this model the dfs takes up the northward motion between central iran lut block relative to eurasia by a complex kinematics varying from pure reverse to pure left lateral strike slip faulting the kinematics of the wfz and efz corresponds to the direction of the ne trending regional compression while the partitioning of slip into strike slip and reverse component of faulting on parallel faults strain partitioning allows the cfz to remain pure left lateral strike slip such a model propose a way to explain how large strike slip faults such as the dfs accommodate tectonic block motions perpendicular to strike of the faults

detecting subtle hydrochemical anomalies with multivariate statistics an example from homogeneous groundwaters in the great artesian basin australia the major ion composition of great artesian basin groundwater in the lower namoi river valley is relatively homogeneous in chemical composition traditional graphical techniques have been combined with multivariate statistical methods to determine whether subtle differences in the chemical composition of these waters can be delineated hierarchical cluster analysis and principal components analysis were successful in delineating minor variations within the groundwaters of the study area that were not visually identified in the graphical techniques applied hydrochemical interpretation allowed geochemical processes to be identified in each statistically defined water type and illustrated how these groundwaters differ from one another three main geochemical processes were identified in the groundwaters ion exchange precipitation and mixing between waters from different sources both statistical methods delineated an anomalous sample suspected of being influenced by magmatic co2 input the use of statistical methods to complement traditional graphical techniques for waters appearing homogeneous is emphasized for all investigations of this type copyright 2006 john wiley sons ltd

3d geological modeling of the kasserine aquifer system central tunisia new insights into aquifer geometry and interconnections for a better assessment of groundwater resources summary the challenge of this study was to create a 3d geological and structural model of the kasserine aquifer system kas in central tunisia and its natural extension into north east algeria this was achieved using an implicit 3d method which honors prior geological data for both formation boundaries and faults a current model is presented which provides defendable predictions for the spatial distribution of geology and water resources in aquifers throughout the model domain this work has allowed validation of regional scale geology and fault networks in the kas and has facilitated the first ever estimations of groundwater resources in this region by a 3d method the model enables a preliminary assessment of the hydraulic significance of the major faults by evaluating their influence and role on groundwater flow within and between four compartments of the multi layered kas hydrogeological system thus a representative hydrogeological model of the study area is constructed the possible dual nature of faults in the kas is discussed in the context that some faults appear to be acting both as barriers to horizontal groundwater flow and simultaneously as conduits for vertical flow also discussed is the possibility that two flow directions occur within the kas at a small syncline area of near feriana in summary this work evaluates the influence of aquifer connectivity and the role of faults and geology in groundwater flow within the kas aquifer system the current kas geological model can now be used to guide groundwater managers on the best placement for drilling to test and further refine the understanding of the groundwater system including the faults connectivity as more geological data become available the current model can be easily edited and re computed to provide an updated model ready for the next stage of investigation by numerical flow modeling

three dimensional structure along the inverted palaeoproterozoic fiery creek fault system mount isa terrane australia abstract the nw dipping fiery creek fault system located in the northern mount isa terrane comprises numerous sub parallel faults that record multiple episodes of palaeo to mesoproterozoic movement hanging wall wedge shaped stratal geometries and marked stratal thickness variation across the fault system indicate that the earliest movement occurred during episodic intracontinental extension mount isa rift event ca 1710 1655 ma reactivation of the fault system during regional shortening and basin inversion associated with the mesoproterozoic isan orogeny ca 1590 1500 ma resulted in complex three dimensional hanging wall geometries and highly variable strain in the hanging wall strata along the fault system this has resulted in the development of discrete hanging wall deformation compartments that are characterised by different structural styles high strain compartments are characterised by relatively intense folding and the development of break back thrusts whereas low strain compartments are only weakly folded variations in hanging wall strain are attributed to selective reactivation of normal fault segments controlled by the pre inversion fault dip and lithological contrasts across the faults variation of the pre inversion fault dip is interpreted to have been caused by episodic tilt block rotation during crustal extension moderately dipping faults active early in the mount isa rift event show the greatest degree of reactivation whereas younger and steeper normal faults have behaved as buttresses during inversion with strain focussed in zones of upright folding in the hanging wall

structural framework of the edwards aquifer recharge zone in south central texas the edwards aquifer the major source of water for many communities in central texas is threatened by population growth and development over its recharge zone the location of the recharge and confined zones and the flow paths of the aquifer are controlled by the structure of and deformation processes within the balcones fault system a major system of predominantly down to the southeast normal faults we investigate the geologic structure of the edwards aquifer to assess the large scale aquifer architecture analyze fault offset and stratigraphic juxtaposition relationships evaluate fault zone deformation and dissolution and fault system architecture and investigate fault block deformation and scaling of small scale intrablock normal faults characterization of fault displacement shows a pattern of aquifer thinning that is likely to influence fault block communication and flow paths flow path constriction may be exacerbated by increased fault segment connectivity associated with large fault displacements also increased fault zone deformation associated with larger displacement faults is likely to further influence hydrologic properties overall faulting is expected to produce strong permeability anisotropy such that maximum permeability is subhorizontal and parallel to fault bedding intersections at all scales aquifer permeability is either unchanged or enhanced parallel to faults and in many cases decreased perpendicular to faults

development of pull apart basins a comparative study of well mapped active and ancient pull apart basins suggests a qualitative model for their continuous development pull aparts evolve from incipient to extremely developed basins through a sequence of closely related states new and compiled map data from several areas including the northern caribbean and turkey suggests the following stages in pull apart development 1 in rigid intracontinental strike slip plate boundary zones larger pull aparts nucleate at releasing fault bends along segments of the principal displacement strike slip fault zone which are oblique to the theoretical interplate slip lines 2 initial opening across releasing fault bends produces spindle shaped basins defined and often bisected by oblique slip faults connecting the discontinuous ends of the strike slip faults 3 increased strike slip offset produces basin shapes which we colloquially call lazy s shape for basins between sinistral faults and lazy z shape for basins between dextral faults 4

analysis of scale exaggeration on seismic profiles 1 seismic profiles have become an important medium for illustrating interpreted structural geometry and style in areas of steep dip and complex geologic structure however these profiles often yield distorted structural views due to vertical or horizontal exaggeration geological misinterpretation may result if the effects of this exaggeration are not recognized seismic profiles from the central rocky mountain basins illustrate the geometrical distortion produced by significant scale exaggeration to assist in analysis of these profiles three nomograms have been constructed the nomograms show graphically the relationships between exaggeration factors exaggerated dips unexaggerated dips and correction factors which are derived from the ratio of exaggerated orthogonal thicknesses to true orthogonal thicknesses with knowledge of the horizontal scale the nomograms also can be used to estimate average velocities on exaggerated profiles in areas of steep dip and uniform stratigraphic thicknesses

normal faulting in the upper continental crust observations from regions of active extension abstract observations of present day normal faulting in regions of active continental extension may be helpful when interpreting the geological record in older extensional basins the most obvious manifestation of active extension is normal faulting in earthquakes earthquake foci are mostly confined to the upper seismogenic continental crust whose thickness imposes a scale on the observed deformation large earthquakes move faults with lengths similar or large compared with the thickness of the seismogenic layer large seismogenic normal faults on the continents appear to be restricted to a dip range of around 30 60 dips significantly gentler than 20 have not been observed in fault plane solutions of large earthquakes large seismographic normal faults are approximately planar in cross section and cut through the base of the upper seismogenic layer rotating about a horizontal axis as they move a reasonable estimate of the regional extension can often be made from the dip of the large normal faults and the tilt of the blocks they bound the domino model such faults are rarely continuous for more than 15 20 km but commonly change strike or step in an en echelon fashion this segmentation may occur on a scale controlled by the thickness of the seismogenic layer and is an important influence on sedimentation and drainage these observations are common to large seismogenic normal faults from a variety of tectonic settings and suggest that the kinematics of normal faulting may not be strongly influenced by the forces responsible for the extension which can vary widely in nature and magnitude small earthquakes which move faults that are small compared with the seismogenic layer thickness show no simple pattern and often can be interpreted as internal deformation of blocks bounded by large faults in some places the seismogenic basement faults do not reach the surface but are decoupled from the sedimentary cover by layers of weak lithology faults in the sedimentary cover may be strongly curved in cross section requiring their hangingwalls to deform internally estimating extension from such faults is not straightforward and requires a knowledge of the hangingwall deformation estimates made in this way are often very non unique and prone to large errors we postulate that the thickness of the seismogenic upper crust controls both the maximum length of large normal fault segments along strike and the maximum size of blocks that can rotate coherently about a horizontal axis

study of hydrochemical characteristics of cbm co produced water of the shizhuangnan block in the southern qinshui basin china on its implication of cbm development abstract coalbed methane cbm co produced water is primarily coal seam water it may be mixed with fracturing fluids especially during the early drainage stage or with other aquifer water if the coal seam is connected with an aquifer via artificial or natural fractures faults if the impacts of fracturing fluids and other aquifer water can be removed the chemical characteristics of cbm co produced water can act as effective indicators for cbm exploration and development based on the water chemistry analyses of 119 samples collected from 47 cbm wells over four years quarterly sampling in the shizhuangnan block qinshui basin the dynamic characteristics of the cbm co produced water chemistry that were influenced by fracturing fluids were studied in this study relationships between the major cbm co produced water ions were determined and the relationship between the cbm co produced water ions and gas production were investigated the results suggest that the cbm co produced water chemical signature of the shizhuangnan block is similar to that of other coal seam waters from around the world being characterized by the sodium chloride bicarbonate water types that are depleted in calcium and magnesium ions and exhibit highly lowered sulfate concentrations due to the mixing with the fracturing fluids and coal seam water the tds sodium chloride and calcium and magnesium ion concentrations decrease during the early drainage stage following a power law function however bicarbonate and sulfate concentrations do not significantly vary the na and cl na cl and alkalinity cl and na cl and na alkalinity ratios exhibit a positive linear relationship strong positive linear relationship and exponentially decaying relationship respectively additionally 10 meq l of cl may serve as a dividing line for the presence or absence of the fracturing fluid affect na and cl may release organic bound chlorine complexes from the coal during coal metamorphism the tds and bicarbonate concentration of the cbm co produced water produced by the gas production wells are all 1000 mg l and 8 meq l respectively the bicarbonate concentration is influenced by both the lch which is the height of the liquid level compared to the coal bed surface at the onset of water production at a cbm well and hydraulic conductivity fault and its distribution controls the distribution of the high gas yield wells

significance of the connection between bedrock alluvium and streams a spatial and temporal hydrogeological and hydrogeochemical assessment from queensland australia abstract catchment scale hydrological and hydrogeological investigations commonly conclude by finding that particular stream reaches are either gaining or losing they also often assume that the influence of bedrock aquifers on catchment water balances and water quality is insignificant however in many cases such broad findings are likely to oversimplify the spatial and temporal complexity of the connections between the different hydrological system components particularly in regions dominated by cycles of droughts and flooding from a modelling perspective such oversimplifications can have serious implications on the process of identifying the magnitude and direction of the exchange fluxes between the surface and groundwater systems in this study we use 3d geological modelling and historic water chemistry and hydraulic records to identify the origins of groundwater at different locations in the alluvium and along the course of streams in the lockyer valley queensland australia a catchment impacted by a severe drought millennium drought from 1998 to 2009 followed by extensive flooding in 2011 we also demonstrate how discharge from the sub alluvial regional scale volcanic and sedimentary bedrock influences the water balance and water quality of the alluvium and streams the investigation of aquifer geometry via development of a three dimensional geological model combined with an assessment of hydraulic data provided important insights on groundwater flow paths and helped to identify areas where bedrock aquifers interact with shallow alluvial aquifers and streams multivariate statistical techniques were then applied as an additional line of evidence to groundwater and surface water hydrochemical data from large historical datasets this confirmed that most sub catchments within the lockyer valley have distinct water chemistry patterns which result from mixing of different water sources including discharge from the sub alluvial bedrock importantly in addition to the observed spatial variability time series hydrochemical groundwater and surface water data further demonstrated that the hydraulic connection between alluvial aquifers streams and sub alluvial bedrock aquifers is temporally dynamic with very significant changes occurring at the transition from normal to drought conditions and following flooding affecting both catchment water quality and water balances

dip analysis as a tool for estimating regional kinematics in extensional terranes abstract in basin analyses that rely almost solely on seismic reflection data to configure the underlying structure it has become common practice to use extensional fault geometries to infer kinematic histories this procedure relies on the existence of fault geometries predicted by ideal orthogonal extension and assumes the structure is well constrained in areas where data are sparse or of equivocal quality this often leads to circular analysis that is ideal orthogonal extension is assumed to have been operative then under constrained fault geometries are mapped according to model predictions fault geometries so derived are subsequently used as evidence that orthogonal extension was operative and that the direction of extension is determinable we develop an alternative tool for inferring kinematics which is independent of fault geometries the method relies on the empirical evidence that the dip of the hangingwall s is systematic and predictable in extensional systems even when fault geometries are non ideal although not without significant limitations dip analysis can provide additional constraints for structural and kinematic interpretations especially where seismic reflection data are the main source of information and dip domains define discrete crustal blocks

three dimensional high resolution fluvio glacial aquifer analog part 2 geostatistical modeling summary the heterogeneity of sedimentary structures at the decimeter scale is crucial to the understanding of groundwater flow and transport in a series of two papers we provide a detailed analysis of a fluvio glacial aquifer analog the herten site the geological data along a series of 2d sections in a quarry the corresponding gpr measurements and their sedimentological interpretation are described in the companion paper in this paper we focus on the three dimensional reconstruction of the heterogeneity the resulting numerical model is provided as an electronic supplementary material for further studies furthermore the geostatistical parameters derived from this analysis and the methodology described in the paper could be used in the future for the simulation of similar deposits where less data would be available to build the 3d model we propose a hierarchical simulation method which integrates various geostatistical techniques first we model the subdivision of the domain into regions corresponding to main sedimentological structures e g a sedimentation event within these volumes we use multiple point statistics to describe the internal heterogeneity what is unusual here is that we do not try to use a complex training image for the multiple point algorithm accounting for all the non stationarity and complexity but instead use a simple conceptual model of heterogeneity ellipsoidal shapes as a training image and constrain the multiple point simulations within the regions by a detailed interpolation of orientation data derived from the 2d sections this method produces realistic geological structures the analysis of the flow and transport properties hydraulic conductivity and tracer breakthrough curves of the resulting model shows that it is closer to the properties estimated directly from the 2d geological observations rather than those estimated from a model of heterogeneity based on probability of transitions and not including the modeling of the large scale structures

multivariate statistical analysis of geochemical data as indicative of the hydrogeochemical evolution of groundwater in a sedimentary rock aquifer system summary the study of groundwater hydrogeochemistry of the paleozoic basses laurentides sedimentary rock aquifer system in quebec produced a large geochemical dataset groundwater samples were collected at 153 sites over a 1500 km2 study area and analyzed for major and minor ions the large number of data can lead to difficulties in the integration interpretation and representation of the results two multivariate statistical methods hierarchical cluster analysis hca and principal components analysis pca were applied to a subgroup of the dataset to evaluate their usefulness to classify the groundwater samples and to identify geochemical processes controlling groundwater geochemistry this subgroup consisted of 144 samples and 14 parameters ca2 mg2 na k hco 3 cl so 4 2 fe2 mn2 br sr2 f ba2 hs seven geochemically distinct clusters c1 c7 resulted from the hca samples from clusters c3 c4 c6 and c7 are mostly located in preferential recharge areas the majority of these samples have ca mg hco3 recharge groundwater c3 c6 c7 and na hco3 evolved groundwater c4 samples from the other three clusters c1 c2 c5 are characteristic of an aquifer system under confined conditions the majority of these samples have na hco3 evolved groundwater c1 c5 and na cl ancient groundwater that exhibits elevated concentrations in br c2 in addition to recognizing the importance of hydrogeological conditions on groundwater geochemistry the distribution of clusters also showed the importance of the geological formations on minor and trace elements such as fe2 mn2 sr2 f and ba2 the first five components of the pca account for 78 3 of the total variance in the dataset component 1 is defined by highly positive loadings in na cl and br and is related to groundwater mixing with champlain sea water and solute diffusion from the marine clay aquitard the high positive loadings in ca2 and mg2 of component 2 suggest the importance of dissolution of carbonate rocks in this aquifer system from their characteristic loadings the first two components are defined as the salinity and hardness components respectively components 3 5 are related to more local and geological effects the integration of the hca and the pca with conventional classification of groundwater types as well as with the hydrogeological and geological contexts allowed the division of the region into four main geochemical areas providing an improved regional picture of the aquifer system dynamics and hydrogeochemical evolution of groundwater the following factors were recognized as influencing the evolution of groundwater identified in every geochemical area 1 geological characteristics including sedimentary rock type and till mineralogy 2 hydrogeological characteristics represented by the level of confinement and the hydraulic gradient and 3 the geological history including the latest glaciation and the champlain sea invasion with its integrated approach this hydrogeochemical study contributes to the characterization and understanding of complex groundwater flow systems and provides an example of the long term geochemical evolution of hydrogeological systems after a major perturbation in this case seawater invasion

structural analysis of the brigham city weber segment boundary zone wasatch normal fault utah implications for fault growth and structure we investigate the history kinematics principal stress orientations and geometry of deformation at the end of a bent normal fault segment of the wasatch fault zone utah three fault types developed in archean crystalline rocks reflect progressive uplift of fault related footwall rocks chlorite breccias and phyllonites reflect deep level reaction assisted plastic deformation along the north striking part of the segment planar fretted faults which formed by cataclasis cut the phyllonites and breccias and are developed throughout the footwall of the segment youngest faults are hematitecoated extremely narrow polished surfaces slip vectors and kinematic analyses of small faults developed in the footwall indicate oblique normal slip along the north striking portion of the segment slip vectors and fault orientation along the northwest striking portion of the segment reflect complexly oriented slip on faults which strike subparallel and at high angles to the main fault trace yet slip is confined to a broad fault parallel zone small faults at the southernmost tip of the segment indicate a strong influence of the north striking weber segment to the south inversion of fault data for principal stress orientations document complexly oriented principal stresses through the segment boundary zone and suggest that 3 may have reoriented approximately 60 over the life of the segment subsurface structure combined with small fault data indicate the segment boundary is comprised of a southwest plunging bedrock high which is reflected by a sharp bend in the brigham city segment the southern end of the brigham city segment may have started as a straight north striking fault which has bent due to changes in stress orientations and or interaction with the adjacent weber segment

analysis of tilting near normal faults using calculus of variations implications for upper crustal stress and rheology abstract an initially horizontal surface in the surroundings to a normal fault will after extension tilt towards the fault if in the hanging wall or away from it if in the footwall coseismic deformation of these surroundings can be validly modelled as flexure cumulative deformation on geological time scales has been regarded as flexure also but this has led to the apparent paradox that many observed structures require the effective elastic thickness of the brittle upper crust to be much smaller than its seismogenic thickness this article presents a possible alternative that cumulative deformation of the upper crust near some active normal faults may be regarded instead as partitioned into separation of the blocks that comprise their surroundings through the horizontal component of dip slip on the fault and distributed vertical simple shear in their surroundings which causes them to tilt and takes up the vertical slip on the fault a generalized profile of tilting near a normal fault which approximates a parabola can be derived following two assumptions first the brittle layer retains an elastic term in its rheology on geological time scales such that it resists arbitrary length changes second the brittle layer minimizes its overall vertical deflection thus minimizing the buoyancy force acting on it maximum stress and total strain energy associated with observed profiles of tilting are typically smaller for distributed vertical simple shear favouring this mechanism over flexure

groundwater visualisation system gvs a software framework for integrated display and interrogation of conceptual hydrogeological models data and time series animation summary management of groundwater systems requires realistic conceptual hydrogeological models as a framework for numerical simulation modelling but also for system understanding and communicating this to stakeholders and the broader community to help overcome these challenges we developed gvs groundwater visualisation system a stand alone desktop software package that uses interactive 3d visualisation and animation techniques the goal was a user friendly groundwater management tool that could support a range of existing real world and pre processed data both surface and subsurface including geology and various types of temporal hydrological information gvs allows these data to be integrated into a single conceptual hydrogeological model in addition 3d geological models produced externally using other software packages can readily be imported into gvs models as can outputs of simulations e g piezometric surfaces produced by software such as modflow or feflow boreholes can be integrated showing any down hole data and properties including screen information intersected geology water level data and water chemistry animation is used to display spatial and temporal changes with time series data such as rainfall standing water levels and electrical conductivity displaying dynamic processes time and space variations can be presented using a range of contouring and colour mapping techniques in addition to interactive plots of time series parameters other types of data for example demographics and cultural information can also be readily incorporated the gvs software can execute on a standard windows or linux based pc with a minimum of 2 gb ram and the model output is easy and inexpensive to distribute by download or via usb dvd cd example models are described here for three groundwater systems in queensland northeastern australia two unconfined alluvial groundwater systems with intensive irrigation the lockyer valley and the upper condamine valley and the surat basin a large sedimentary basin of confined artesian aquifers this latter example required more detail in the hydrostratigraphy correlation of formations with drillholes and visualisation of simulation piezometric surfaces both alluvial system gvs models were developed during drought conditions to support government strategies to implement groundwater management the surat basin model was industry sponsored research for coal seam gas groundwater management and community information and consultation the virtual groundwater systems in these 3d gvs models can be interactively interrogated by standard functions plus production of 2d cross sections data selection from the 3d scene rear end database and plot displays a unique feature is that gvs allows investigation of time series data across different display modes both 2d and 3d gvs has been used successfully as a tool to enhance community stakeholder understanding and knowledge of groundwater systems and is of value for training and educational purposes projects completed confirm that gvs provides a powerful support to management and decision making and as a tool for interpretation of groundwater system hydrological processes a highly effective visualisation output is the production of short videos e g 2 5 min based on sequences of camera fly throughs and screen images further work involves developing support for multi screen displays and touch screen technologies distributed rendering gestural interaction systems to highlight the visualisation and animation capability of the gvs software links to related multimedia hosted online sites are included in the references

three dimensional hydrogeological reconstruction based on geological depositional model a case study from the coastal plain of arborea sardinia italy abstract this study presents a novel approach for the hydrogeological assessment of sedimentary coastal aquifers specifically the methodology is tailored for modeling groundwater flow and nitrates contamination in typical mediterranean coastal plains with high anthropogenic pressures as exemplified by the arborea plain central western sardinia italy the study started with development of an updated geological depositional model based on sequential stratigraphy geological and geophysical data processed in a geographic information system gis environment supported the definition of a 3d hydrogeological conceptual model and provided a solid basis for the interpretation of groundwater flow directions the 3d hydrogeological model allowed constraining groundwater circulation flow paths and distribution of nitrate concentrations in the aquifers the methodology appears as a valid tool applicable in other coastal areas to determine geological and hydrogeological settings the definition of a quantitative hydrogeological framework will support the effective management of local water resources

cenozoic and mesozoic structure of the eastern basin and range province utah from cocorp seismic reflection data cocorp seismic reflection data collected from the eastern basin and range in west central utah provide information on cenozoic extensional tectonics mesozoic thrusting and their interrelationships those data show a series of remarkably continuous low angle reflectors that extend more than 120 km perpendicular to strike and can be traced as deep as 15 20 km over that distance none of these events are significantly cut by any high angle normal faults a major detachment beneath the sevier desert can be traced from a surface zone of normal faulting to a depth of 12 15 km with a regional apparent westward dip of 12 tentative correlation of upper and lower plate events suggests 30 60 km of extensional displacement on this detachment whether this structure is a reactivated mesozoic thrust is uncertain west steepening splays off the end of the detachment reach depths of 20 km and may represent a major mesozoic ramp or zones of distributed ductile shearing during extension some events are interpreted to be mesozoic thrusts of which at least one beneath the house range has been reactivated during the cenozoic the snake range decollement dips gently east and has a sense of cenozoic displacement opposite to that of other cenozoic detachments farther east deep events are most numerous beneath the east side of the sevier desert where they occur to depths of 30 km at the top of or perhaps partly within the anomalously low velocity upper mantle

integrating deterministic lithostratigraphic models in stochastic realizations of subsurface heterogeneity impact on predictions of lithology hydraulic heads and groundwater fluxes realistic representations of geological complexity are important to address several engineering and environmental challenges the spatial distribution of properties controlling physical and geochemical processes can be effectively described by the geological structure of the subsurface in this work we present an approach to account for geological structure in geostatistical simulations of categorical variables the approach is based on the extraction of information from a deterministic conceptualization of the subsurface which is then used in the geostatistical analysis for the development of models of spatial correlation and as soft conditioning data the approach was tested to simulate the distribution of four lithofacies in highly heterolithic quaternary deposits a transition probability based stochastic model was implemented using hard borehole data and soft data extracted from a 3 d deterministic lithostratigraphic model simulated lithofacies distributions were also used as input in a flow model for numerical simulation of hydraulic head and groundwater flux the outputs from these models were compared to corresponding values from models based exclusively on borehole data results show that soft lithostratigraphic information increases the accuracy and reduces the uncertainty of these predictions the representation of the geological structure also allows a more precise definition of the spatial distribution of prediction uncertainty here quantified with a metric based on shannon information entropy correlations between prediction uncertainties for lithofacies hydraulic heads and groundwater fluxes were also investigated the results from this analysis provide useful insights about the incorporation of soft geological data into stochastic realizations of subsurface heterogeneity and emphasize the critical importance of this type of information for reducing the uncertainty of simulations considering flux dependent processes

half graben structures balanced models of extensional fault bend folds one common structural style in extensional regimes is a half graben bounded on one side by a master normal fault and on the other side by a domain of beds dipping toward the master fault this geometry is modeled as being caused by a bend in the master fault the hanging wall beds dipping toward the master fault are bounded by axial surfaces formed as the hanging wall moves past the bend resulting in an extensional fault bend fold the footwall beds remain undeformed and unrotated the major assumptions used in the derivation are that the geometry is area balanced and that the axial surfaces in the hanging wall have dips equal and opposite to the dip of the master fault above the bend important consequences of the model include a relationship between master fault dip above and below a bend and the amount of hanging wall dip the horizontal width of the dipping beds in the hanging wall is twice the heave on the master fault above the bend the asymmetry of the axial surfaces in the hanging wall requires that the rotated beds be strained hanging wall beds dipping toward the master fault are predicted for a fault bend wherein the dip decreases downward hanging wall beds dipping away from the master fault are predicted for a bend wherein the dip increases downward the model fits measurements taken from a published ramp and flat clay model by e cloos and is used to develop a balanced and restorable cross section of the schell creek fault a basin and range structure in nevada

quasi three dimensional modelling of the jurassic cretaceous sediments hydrogeochemical conditions in the central part of the west siberian megabasin abstract this paper presents the method and results of the hydrogeochemical spatial pattern modelling in the cretaceous and jurassic sediments of the koltogor and tolkin megatroughs and the surrounding areas of the west siberian megabasin the method is based on the preliminary calculation of two dimensional radial profiles that provide the assessment of hydrogeochemical parameter changes with depth at the given points set within the study area using the results of the calculations a model of hydrogeochemical conditions is constructed as a series of maps of the groundwater salinity in formations as well as ns and ew oriented cross sections the method is relatively simple reliable and ensures result consistency the analysis of the results indicates a significant variability of groundwater salinity both as a whole in the jurassic cretaceous sediments and within individual aquifer on cross sections areas with relatively constant salinity appear both in the form of separate thin and inconsistent layers and in the form of thick extended zones the geometry of the zones is not fully defined by the boundaries of the aquifers such variability is also reflected in the significant differences of hydrogeochemical conditions in different formations and subformations of the sedimentary cover of the west siberian megabasin the revealed substantial heterogeneity of hydrogeochemical conditions in the jurassic cretaceous sediments indicates a complex genesis of the groundwater chemical composition and in particular the absence of a clear impact of the powerful pre jurassic tectonics including those that have formed the regional vast koltogor tolkin trough zone

the principal components statistical method as a complementary approach to geochemical methods in water quality factor identification application to the coastal plain aquifer of israel abstract in general schoeller and piper diagrams as well as other classical techniques facilitate the description of the various geochemical groups of water and help to explain quality changes in an aquifer we propose the use mainly of principal components analysis for identification of relevant groups of water and the factors that bring about a change in their quality the major advantage of this method is its suitability for simultaneous analysis of a great number of variables and observations it is here being applied for the investigation of the dan metropolitan region of israel s coastal plain the variables involved include major ions as well as the physical factors of depth of the well intake filter below sea level distance from the sea and aquifer recharge the primary purpose of this work is to demonstrate the use and reliability of principal components analysis pca as a method complementary to classical approaches for hydrogeochemical research subsidiary purposes involve determination of the major water groups characterizing the coastal plain aquifer identification of some of the principal variables that influence changes in water quality in the aquifer and description of some of the geochemical phenomena contributing to change in aquifer water quality the following results were achieved for the test area 1 1 two major groups of water were identified a low salinity calcium bicarbonate water occurring in the phreatic portion of the coastal plain aquifer and a more saline sodium chloride water characterizing the neighboring cenomanian aquifer and the confined portions of the coastal plain aquifer 2 2 the major water input sources such as rain injection water waste water irrigation etc may vary in their influence upon resulting water quality this water quality is affected by such physical factors as distance from the sea depth of well intake filters below sea level proximity to streams and the lithology of the saturated and unsaturated zones 3 3 the evolutionary alteration in content of specific ions with time can be clearly visualized on the same graph by means of pca the universal applicability of such a statistical approach to other hydrological settings is noted

structural and fluid chemical properties of seismogenic normal faults abstract structures in extensional fault zones can be classified using the configuration of fault branch lines and tip lines important classes include the segment bend segment termination segment branch cross fault intersection and segment offset the effect of these structures on rupture history is not necessarily consistent neither between individual earthquakes nor between different fault zones rupture behavior is dependent on several other factors including loading conditions regional and localized rupture tip stress fields fluid mechanical processes and chemical processes fracture toughness is partly controlled by the angular discordance between slip directions on adjacent fault segments greater discordance between slip directions and intersection lines of fault segments results in greater strain incompatibility an internal fracture network generally evolves within a segment boundary to maintain compatibility and transfer slip between the segments the dimensions and structure of this fracture network may also partly control rupture propagation presumably activation of a fault network with large angular discordances between slip directions and intersection lines will generate numerous asperities as the subsidiary faults mutually interact and offset each other the geometry of a segment boundary may change with depth and the three dimensional nature of the structure may be important in controlling rupture history fluids influence rupturing via fluid pressure effects and time dependent chemical processes fracture propagation by stress corrosion may favor instability and chemical alteration may produce minerals of lower strengths allowing time dependent creep sealing and healing of fractures however may remove damage and increase strength elementary computations indicate that representative times for sealing and chemical alteration are between 1 and 1000 years for reasonable physical conditions well within the recurrence intervals of most large earthquakes time to failure for stress corrosion cracking is more highly variable and strongly sensitive to applied stress and fluid pressure

current tufa sedimentation in a changing slope valley the river anamaza iberian range ne spain abstract a three year study of modern carbonate sedimentation was conducted through analysis of sedimentological and hydrochemical parameters measured every six months at 10 sites along a high slope river in northeastern spain river anamaza three stretches of the river were characterised the dominant water inputs from the upstream karstic springs primarily from the jurassic rock aquifer determined the so4 hco3 ca composition of the river water from this area decreasing trends in alkalinity calcium and total dissolved inorganic carbon occurred downstream in both the warm and cool periods as a result of calcite precipitation tufa thickness variations were consistent with such hydrochemical evolution deposition rates increased downstream primarily where the gradient is steeper middle stretch and subsequently decreased at the downstream gently sloped stretch therefore the slope along the river and the distance from the main upstream springs conditioned the spatial distribution of tufa deposits by determining the chemical characteristics of the water the monitored sites represent four primary fluvial subenvironments with distinct sedimentary facies the highest carbonate deposition rates were measured in fast flow conditions stromatolites facies a deposits with calcite coated algae and mosses facies c formed in cascades and small jumps with very fast flowing water exhibited lower deposition rates and typical erosion lower rates corresponded to slow flow conditions in which thin stromatolite crusts and or filamentous and calcareous algae and tufa fragments facies b accumulated in slow flowing water areas near springs upstream stretch calcite was absent linked to the higher pco2 of water microbial films and aquatic flora composed the biofacies facies d in such subenvironment therefore tufa deposition rates in each fluvial subenvironment were controlled by the amount of co2 outgassing linked to local flow conditions the biological substrate type and the chemical attributes of the water along each stretch a six month pattern of deposition rates best marked in the steeper stretch was recorded from thickness measurements spring summer periods 4 30 mm autumn winter periods 1 22 mm parallel variations were recorded using pwp plummer wigley parkhurst and calcite mass balance calculations multivariate statistical analyses hca and pca clearly separated hydrochemical and sedimentological attributes in samples from warm and cool periods exceptions to this pattern were related to changes in the water discharge high discharge events caused the dilution of the chemical composition and erosion of the tufa deposits therefore temperature dependent factors i e physico chemical and biological processes coupled with discharge changes controlled the seasonal variations in deposition rates the stable isotope composition of calcite and river water also reflected the discharge effects however the seasonal variation signature of temperature was preserved in the 18o of sediment

detachment faulting and the evolution of passive continental margins major detachment faults play a key role in the lithospheric extension process in the basin and range province and may also be important in other continental extension terranes such detachment faulting leads to an inherent asymmetry of extensional structure and of uplift subsidence patterns detachment models developed for the formation of metamorphic core complexes can also be applied to the formation of passive continental margins we therefore suggest the existence of upper plate and lower plate passive margins these give rise to a complementary asymmetry of opposing margins after continental breakup transfer faults offset marginal features and allow margins to switch from upper plate to lower plate characteristics along strike

the geometry of listric normal faults and deformation in their hangingwalls abstract in cross sections containing listric extensional faults area balancing techniques for depth to decollement are usually based on either bed length conservation or displacement conservation listric fault geometry may be constructed from a hangingwall roll over profile using the chevron construction this construction based on conservation of heave necessitates a reduction in fault displacement with decreasing fault dip a modification of this construction utilizing conservation of fault displacement predicts a listric fault that detaches at a shallower depth a new construction based on slip lines uses fault perpendicular displacement segments to generate listric fault shape fault propagation strain may be responsible for anomalous hangingwall geometries and these can be predicted by forward modelling using either a modified chevron construction or a slip line construction

dip domain method applied to the mesozoic connecticut valley rift basins this paper presents a new approach to structural analysis of u s east coast mesozoic basins a contoured compilation of numerical values of dip data for the connecticut valley rift basins reveals distinct domains related to their broader tectonic development additional more standard geologic constraints are then used to interpret the dip domain patterns most of the tilt deformation involved and hence postdated early jurassic basaltic flow units and overlying jurassic thick alluvial deposits normal drag characterizes the attitude of mesozoic strata along the western border fault of the main hartford basin whereas reverse drag is common along its larger listric eastern border fault strata within the basin mostly along its eastern margin include several subgrabens and or strongly tilted zones associated with early subbasins marked by local changes in strike of the early border fault the meriden cross graben may be a similar structure that extended much farther southwestward across the basin within the hartford basin linear domains of steeper dips are interpreted as surface expressions of the edges of a 5 to 15 km wide late stage central graben that trends n15 e diagonally across the basin possibly a reflection of very late strike slip stress systems

structural analysis and fault segment boundary identification along the hurricane fault in southwestern utah abstract long normal fault zones are common in extending regions and can be divided into segments with different geometries and faulting histories based on surface observations the boundaries between fault segments are important because they may be the sites of significant strain may impede rupture propagation and may greatly influence the locations of earthquakes because large geometric bends exist at some fault segment boundaries throughout the history of the boundary we suggest that such bends can last throughout much of the life of the fault we use fault segmentation concepts to define a segment boundary and parts of two fault segments along the active hurricane normal fault southwestern utah u s a we use fault geometry slip direction shortening structures in the hanging wall and footwall and fault scarp morphology to identify the fault segments and segment boundary the fault strikes n13 w south of the boundary and n21 e north of the boundary stratigraphic separation of geochemically identical quaternary basalt in the footwall and the hanging wall suggests that the slip vector of quaternary displacement trends between n70 w and s18 w and slickenlines earthquake rakes and dip analysis on syndeformational basalt further constrains the slip direction to n75 85 w relative motion on the northern segment termed here the ash creek segment is purely dip slip and on the southern anderson junction segment is dominantly dip slip with a small dextral slip component fault scarps along the ash creek segment compared with offset gravels lacking scarps along the anderson junction segment suggest that the two segments have different late quaternary faulting histories which is indicative of discrete fault segments the ash creek segment is about 24 km long and the anderson junction segment is 19 45 km long although the non adjacent segment terminations remain poorly defined the segment boundary zone consists of 1 a small scale hanging wall anticline that trends roughly normal to the fault 2 a small offset footwall thrust fault and 3 space filling imbricate normal faults in the hanging wall secondary structures suggest the segment boundary is a non conservative boundary

relationships between major ions in coal seam gas groundwaters examples from the surat and clarence moreton basins abstract using a combination of multivariate statistical techniques and the graphical assessment of major ion ratios the influences on hydrochemical variability of coal seam gas or coal bed methane groundwaters from several sites in the surat and clarence moreton basins in queensland australia were investigated several characteristic relationships between major ions were observed 1 strong positive linear correlation between the na cl and alkalinity cl ratios 2 an exponentially decaying trend between the na cl and na alkalinity ratios 3 inverse linear relationships between increasing chloride concentrations and decreasing ph for high salinity groundwaters and 4 high residual alkalinity for lower salinity waters and an inverse relationship between decreasing residual alkalinity and increasing chloride concentrations for more saline waters the interpretation of the hydrochemical data provides invaluable insights into the hydrochemical evolution of coal seam gas csg groundwaters that considers both the source of major ions in coals and the influence of microbial activity elevated chloride and sodium concentrations in more saline groundwaters appear to be influenced by organic bound chlorine held in the coal matrix a sodium and chloride ion source that has largely been neglected in previous csg groundwater studies however contrastingly high concentrations of bicarbonate in low salinity waters could not be explained and are possibly associated with a number of different factors such as coal degradation methanogenic processes the evolution of high bicarbonate nahco 3 water types earlier on in the evolutionary pathway and variability in gas reservoir characteristics using recently published data for csg groundwaters in different basins the characteristic major ion relationships identified for new data presented in this study were also observed in other csg groundwaters from australia as well as for those in the illinois basin in the usa this observation suggests that where coal maceral content and the dominant methanogenic pathway are similar and where organic bound chlorine is relatively abundant distinct hydrochemical responses may be observed comparisons with published data of other nahco 3 water types in non csg environments suggest that these characteristic major ion relationships described here can i serve as an indicator of potential csg groundwaters in certain coal bearing aquifers that contain methane and ii help in the development of strategic sampling programmes for csg exploration and to monitor potential impacts of csg activities on groundwater resources

structure of a fault segment boundary in the lost river fault zone idaho and possible effect on the 1983 borah peak earthquake rupture abstract the 1983 borah peak earthquake m s 7 3 initiated within the southern part of the thousand springs segment in the lost river fault zone east central idaho the earthquake rupture propagated unilaterally to the northwest over a distance of 36 km and was accompanied by sinistral normal slip within the fault zone at the surface the southern most part of the rupture zone is marked by a bend in the lost river fault zone at the intersection between the thousand springs segment to the north and the mackay segment of the fault zone to the southeast the intersection between the two fault segments is a lens shaped area that contains numerous nw and ne striking faults that cut the paleozoic bedrock several of the faults within the intersection zone ruptured at the surface during the 1983 earthquake a three dimensional geometrical model of the intersection zone between the thousand springs and mackay fault segments was constructed from geological mapping in conjunction with previously published interpretations of geodetic and seismological data the longitudinal axis of the intersection zone plunges to the southwest where its projected position in the subsurface roughly coincides with the location of the 1983 earthquake9s hypocenter at a depth of 15 to 16 km the intersection zone between the two fault segments may have played a dual role during the borah peak earthquake both marking the site of rupture nucleation but also acting to arrest spread of the rupture to the southeast onto the adjacent mackay segment

south virgin white hills detachment fault system of se nevada and nw arizona applying apatite fission track thermochronology to constrain the tectonic evolution of a major continental detachment fault the south virgin white hills detachment svwhd in the central basin and range province with an along strike extent of similar to 60 km is a major continental detachment fault system displacement on the svwhd decreases north to south from similar to 17 to 6 km this is accompanied by a change in fault and footwall rock type from mylonite overprinted by cataclasite to chlorite cataclasite and then fault breccia reflecting decreasing fault displacement and footwall exhumation apatite fission track aft thermochronology was applied both along strike and across strike to assess this displacement gradient the overall thermal history reflects laramide cooling similar to 75 ma and then rapid cooling beginning in the late early miocene age patterns reflect some complexity but extension along the svwhd appears synchronous with rapid cooling initiated at similar to 17 ma due to tectonic exhumation slip rate is more rapid similar to 8 6 km ma in the north compared to similar to 1 km ma in the south the displacement gradient results from penecontemporaneous along strike motion and formation of the svwhd by linkage of originally separate fault segments that have differential displacements and hence differential slip rates east west transverse structures likely play a role in linkage of different fault segments the preextension paleogeothermal gradient is well constrained in the gold butte block as 18 20 degrees c km we present a new thermochronologic approach to constrain fault dip during slip treating the vertical exhumation rate and the slip as vectors with the angle between them used to constrain fault dip during slip through the closure temperature of a particular thermochronometer aft data from the western rim of the colorado plateau citation fitzgerald p g e m duebendorfer j e faulds and p o sullivan 2009 south virgin white hills detachment fault system of se nevada and nw arizona applying apatite fission track thermochronology to constrain the tectonic evolution of a major continental detachment fault tectonics 28 tc2001 doi 10 1029 2007tc002194

soil liquefaction induced uplift of underground structures physical and numerical modeling abstractunderground structures located in liquefiable soil deposits are susceptible to floatation following a major earthquake event such failure phenomenon generally occurs when the soil liquefies and loses its shear resistance against the uplift force from the buoyancy of the underground structure numerical modeling accompanied with centrifuge experiments with shallow circular structures has been carried out to investigate the floatation failure at different buried depths of the structure the influence of the magnitude of input sinusoidal earthquake shaking was also studied both numerical and experimental results showed matching uplift response of the structures and acceleration and pore pressure measurements in the liquefied soil deposit a higher uplift displacement of the structure was observed for shallower buried depth thereby indicating the influence of overlying soil weight against floatation results also showed that the structures commenced floatation in the presence of high excess pore pr

effect of height and orientation microclimate on geomorphic degradation rates and processes late glacial terrace scarps in central idaho terrace scarps can serve as a nearly ideal natural laboratory for the study of the evolution of slopes this paper examines the effects of scarp size height and orientation microclimate by keeping constant variables such as age lithology and regional climate if a scarp degrades as a closed system and downslope movement is directly proportional to surface gradient the evolution of the scarp is modeled by the diffusion equation for a group of scarps of same age and known starting angle the diffusion equation model predicts the relation between maximum scarp angle and scarp height h late pleistocene terrace scarps now as steep as 33 25 as well as measured angles of repose for sand and gravel require a starting angle as steep as 33 5 for latest pleistocene idaho and utah scarps as h increases is gentler more degraded than modeled by the diffusion equation with a constant rate coefficient the degradation rate coefficient c increases tenfold with scarp height it should not change with scarp height if downslope movement is solely determined by surface gradient to the first power soil wash appears to be responsible for this departure from the diffusion equation model for transport rate by soil wash is a function of scarp size height south facing scarps are less vegetated and more degraded than north facing scarps for scarps 2 m high the degradation rate c on s facing scarps is 2 times that on n facing scarps for 10 m scarps it is 5 times the observed dependence of the rate coefficient c on scarp height can be removed by normalizing c to values for west facing scarps of the same height the residual c values calculated by this method correlate well with differences in incident solar radiation resulting from the different scarp orientations and maximum gradients this correlation demonstrates the importance of orientation on slope processes and their rates through the differences in freeze thaw cycles soil moisture and vegetative cover scarp morphology may be used to estimate age if one accounts for the effects of climate and for scarp height orientation and lithology for example using the dated bonneville shoreline scarps for calibration and comparing only scarps of equal height we estimate the drum mountains fault scarps to be 9 000 yr old this age is about twice that produced by previous diffusion equation calculations that have not accounted for the height as we have here but it is the same as independent geologic estimates of their age

evaluation of simulation models of lateral spread sites treated with prefabricated vertical drains abstractfinite element analyses are performed of centrifuge tests consisting of untreated and drain treated lateral spread sites with the goal of evaluating the ability of numerical simulations to predict the response of sites improved with prefabricated vertical drains finite element models of varying complexity are analyzed a two dimensional model of the full centrifuge test a three dimensional unit cell model around a single drain and a two dimensional unit cell model all the finite element models predict pore pressures consistent with the centrifuge tests the deformation responses of the finite element models show that unit cell analyses produce significantly larger deformations than those observed in the centrifuge this result is caused by the fact that the centrifuge test geometry is not well represented by the infinite slope condition assumed in a unit cell the full two dimensional model predicts deformations that are more consistent with those of the centrifuge because it can capture the

lithospheric dismemberment and magmatic processes of the great basin colorado plateau transition utah implied from magnetotellurics 1 to illuminate rifting processes across the transition zone between the extensional great basin and stable colorado plateau interior we collected an east west profile of 117 wideband and 30 long period magnetotelluric mt soundings along latitude 38 5 n from southeastern nevada across utah to the colorado border regularized two dimensional inversion shows a strong lower crustal conductor below the great basin and its transition zone in the 15 35 km depth range interpreted as reflecting modern basaltic underplating hybridization and hydrothermal fluid release this structure explains most of the geomagnetic variation anomaly in the region first measured in the late 1960s hence the transition zone while historically included with the colorado plateau physiographically possesses a deep thermal regime and tectonic activity like that of the great basin the deep crustal conductor is consistent with a rheological profile of a brittle upper crust over a weak lower crust in turn on a stronger upper mantle jelly sandwich model under the incipiently faulted transition zone the conductor implies a vertically nonuniform mode of extension resembling early stages of continental margin formation colorado plateau lithosphere begins sharply below the western boundary of capitol reef national park as a resistive keel in the deep crust and upper mantle with only a thin and weak moho level crustal conductor near 45 km depth several narrow steep conductors connect conductive lower crust with major surface faulting some including modern geothermal systems and in the context of other great basin mt surveying suggest connections between deep magma sourced fluids and the upper crustal meteoric regime the mt data also suggest anisotropically interconnected melt over a broad zone in the upper mantle of the eastern great basin which has supplied magma to the lower crust consistent with extensional mantle melting models and local shear wave splitting observations we support a hypothesis that the transition zone location and geometry ultimately reflect the middle proterozoic suturing between the stronger yavapai lithosphere to the east and the somewhat weaker mojave terrane to the west we conclude that strength heterogeneity is the primary control on locus of deformation across the transition zone with modulating force components

finite extension and low angle normal faulting andersonian theory for infinitesimal strains predicts that normal faults will form at high angles to the surface in extensional terranes in contrast low angle normal faults are sometimes observed on which tens of kilometers of slip has occurred and moderate angle faults with slip of 5 to 15 km are common a simple extension of the theory to account for the stresses required to drive finite deformation shows that low angles are preferred for large extension on individual faults the formation of low angle faults may require inhomogeneities in stress or material properties but once slip begins on a low angle fault it is likely to continue whereas slip on high angle faults is likely to end after modest slip to be replaced by the formation of new high angle faults

nature of the s reflector beneath the galicia banks rifted margin preliminary results from prestack depth migration beneath the tilted fault blocks of the galicia rifted margin a bright reflection termed s has been interpreted as the master detachment fault controlling the extension of the margin however on time migrated sections s appears to be locally offset by the steep faults of the upper section we investigate the true geometry of s and its relation to the overlying faults through iterative prestack depth migration we conclude that it is not significantly offset by the faults which instead appear to stop abruptly at s thus we interpret s as the master detachment and consider its role during extension

stability of scour protection due to earthquake induced liquefaction centrifuge modelling abstract a key aspect of permanent offshore structures is protection against scour this is typically in the form of a blanket of coarse gravel or cobbles surrounding the structure these coarse particles are selected for their high resistance to being displaced by strong currents and thus protect the underlying finer sand particles from scour however in the event of an earthquake the foundation sand may be susceptible to some degree of liquefaction this research investigates the effects of seismic induced liquefaction over a scour blanket and if sinking is inhibited by some combination of the additional effective stress imposed by the gravel together with the interlocking resistance that develops when coarse particles are subjected to relative displacements in order to evaluate the stability of scour protection blankets a programme of physical modelling was carried out involving the assessment of different configurations of stone layers over a liquefiable material and a monopile type foundation models were subjected to scaled base shaking equivalent to earthquake loading a mass balance of particle sinkage showed that a filter layer was critical for maintaining the integrity of the armour stones based on displacement and pore water pressure measurements it was found that the presence of the scour protection blankets improved the response of the liquefiable sand under seismic loading and even inhibited the occurrence of liquefaction this implies that a well designed scour protection blanket can assist in protecting against earthquake effects also

towards incorporating uncertainty of structural data in 3d geological inversion abstract all geological models are subject to several kinds of uncertainty these can be classified into three different types data imprecision and quality inherent randomness and incomplete knowledge with our approach we address uncertainties introduced by input data quality in complex three dimensional 3d models of subsurface structures geological models as input data we consider parameters of geological structures i e formation and fault boundary points and orientation measurements our method consists of five steps construction of an initial geological model with an implicit potential field method assignment of probability distributions to data positions and orientation measurements simulation of several input data sets construction of several model realisations based on these simulated data sets and finally the visualisation and analysis of the uncertainties we test our approach in two generic models a simple graben setting and a complex dome structure the first model shows that our approach can evaluate uncertainties from different structures and their interaction furthermore it indicates that the final uncertainty of the model is not simply the sum of all input data uncertainties but complex interactions exist the second example demonstrates that our approach can handle full three dimensional settings with overturned surfaces results of the uncertainty simulation can be visualised and analysed in several ways ranging from borehole histograms to uncertainty maps for complex 3d visualisation and analysis we use indicator functions when we apply these we can treat the visualisation of uncertainties in complex settings in a self consistent manner with our simulation method it is possible to analyse and visualise the uncertainties directly introduced by imprecision in the input data our approach is intuitive and straight forward and suitable in both simple and complex geological settings it enables detailed insights into the model quality even for the non expert in cases where a geological model is the basis for geophysical simulation it opens up the way to geological data driven ensemble modelling and inversion

experimental investigation of drainage during earthquake induced liquefaction earthquake induced liquefaction is typically viewed as an undrained phenomenon with undrained element tests forming the core of knowledge built around it however there is evidence to suggest that

using multivariate statistical analysis of groundwater major cation and trace element concentrations to evaluate groundwater flow in a regional aquifer groundwater samples were collected from 11 springs in ash meadows national wildlife refuge in southern nevada and seven springs from death valley national park in eastern california concentrations of the major cations ca mg na and k and 45 trace elements were determined in these groundwater samples the resultant data were subjected to evaluation via the multivariate statistical technique principal components analysis pca to investigate the chemical relationships between the ash meadows and death valley spring waters to evaluate whether the results of the pca support those of previous hydrogeological and isotopic studies and to determine if pca can be used to help delineate potential groundwater flow patterns based on the chemical compositions of groundwaters the results of the pca indicated that groundwaters from the regional paleozoic carbonate aquifers all of the ash meadows springs and four springs from the furnace creek region of death valley exhibited strong statistical associations whereas other death valley groundwaters were chemically different the results of the pca support earlier studies where potentiometric head levels 18o and d geological relationships and rare earth element data were used to evaluate groundwater flow which suggest groundwater flows from ash meadows to the furnace creek springs in death valley the pca suggests that furnace creek groundwaters are moderately concentrated ash meadows groundwater reflecting longer aquifer residence times for the furnace creek groundwaters moreover pca indicates that groundwater may flow from springs in the region surrounding scotty s castle in death valley national park to a spring discharging on the valley floor the study indicates that pca may provide rapid and relatively cost effective methods to assess possible groundwater flow regimes in systems that have not been previously investigated copyright 1999 john wiley sons ltd

space time patterns and tectonic controls of tertiary extension and magmatism in the great basin of the western united states structural and stratigraphic relations in the great basin indicate widespread pre middle miocene crustal extension that appears to define two north trending belts most extension in these belts was oligocene age but locally it began earlier or lasted into early miocene time the eastern belt straddles the nevada utah border and includes the snake range nevada area with its southern end near 37 5 n and its western edge at the seaman butte mountains breakaway the southern boundary of the eastern belt is occupied by the 26 15 ma caliente caldera complex and approximately coincides with the present east west trending margin of the great basin north of saint george utah crust north of this boundary extended approximately east west before volcanism began at 30 32 ma but to the south extension began after about 15 ma this boundary may have been a rooted zone of left slip faults that allowed the footwall of the stampede detachment to move west relative to unextended terrain to the south the eastern margin of the eastern belt is probably located near the present eastern edge of the great basin but its northern end is poorly defined the western belt runs from the funeral and grapevine mountains california to the ruby mountains nevada and north northeast to the albion range idaho tens of kilometers of crustal extension occurred at least locally in both belts but magnitude of extension is poorly known for large areas of each tertiary volcanism in the great basin began in the north in eocene time with predominantly effusive volcanism and swept southward ending with voluminous oligocene miocene ignimbrite eruptions from calderas in an irregular discontinuous belt between marysvale utah and reno nevada a result of the south ward migration of volcanism is that the onset of extension in both belts was syn or post volcanic in the north but was pre volcanic in the south late paleogene extension and crustal magmatism coincided in both time and space only locally where south migrating magmatism overlapped active north south trending extensional belts most calderas in the southern great basin formed in previously extended belts or on their margins southward migration of ignimbrite sources was apparently blocked by unextended crust to the south in contrast volcanism north of the ignimbrite province was dominated by nonexplosive effusion of lava prior to or during crustal extension this is consistent with observations in the southern basin and range where volcanism and crustal extension were generally synchronous and volcanism was dominantly effusive thus caldera formation may be controlled by the distribution of upper crustal extension although the physical mechanism for this control remains speculative the space time patterns of late paleogene extension in the great basin are consistent with extension being triggered by thermal weakening of subducted oceanic lithosphere rather than by effects transmitted from the plate margin but being driven by gravitational collapse of thick crust space time patterns of tertiary volcanism in the basin and range also appear to conform to patterns of thermal weakening or destruction of the subducted slab both active and passive rifting mechanisms are inapplicable on the scale of the extensional belts because both predict close spatial and temporal association of extension and magmatism which is not generally observed

relations between normal fault geometry tilting and vertical motions in extensional terrains an example from the southern gulf of suez abstract earthquakes and data from subsurface oil exploration suggest that large active normal faults in the southern gulf of suez are approximately planar with dips of 30 40 from the surface to around 10 km depth these faults and the blocks they bound appear to rotate about a horizontal axis as they move causing tilting this tilting is seen both in young vertical movements of the coastline such as raised beaches and marshlands and in the distribution of middle miocene marine rocks which are uplifted to elevations of 400 500 m in footwalls of faults and found at depths of around 3500 m in the adjacent grabens the absolute amplitude of the observed vertical motions can be approximately modelled by planar rotating normal faults that impose a saw tooth topography on a regional subsidence caused by crustal and lithospheric thinning the observations required for this simple model are the present day fault dip the amount of tilting and the width of the rotating blocks the virtues of the model are its simplicity and its compatibility with our knowledge of how large active normal faults move elsewhere on the continents

three dimensional geological modelling and multivariate statistical analysis of water chemistry data to analyse and visualise aquifer structure and groundwater composition in the wairau plain marlborough district new zealand summary concerns regarding groundwater contamination with nitrate and the long term sustainability of groundwater resources have prompted the development of a multi layered three dimensional 3d geological model to characterise the aquifer geometry of the wairau plain marlborough district new zealand the 3d geological model which consists of eight litho stratigraphic units has been subsequently used to synthesise hydrogeological and hydrogeochemical data for different aquifers in an approach that aims to demonstrate how integration of water chemistry data within the physical framework of a 3d geological model can help to better understand and conceptualise groundwater systems in complex geological settings multivariate statistical techniques e g principal component analysis and hierarchical cluster analysis were applied to groundwater chemistry data to identify hydrochemical facies which are characteristic of distinct evolutionary pathways and a common hydrologic history of groundwaters principal component analysis on hydrochemical data demonstrated that natural water rock interactions redox potential and human agricultural impact are the key controls of groundwater quality in the wairau plain hierarchical cluster analysis revealed distinct hydrochemical water quality groups in the wairau plain groundwater system visualisation of the results of the multivariate statistical analyses and distribution of groundwater nitrate concentrations in the context of aquifer lithology highlighted the link between groundwater chemistry and the lithology of host aquifers the methodology followed in this study can be applied in a variety of hydrogeological settings to synthesise geological hydrogeological and hydrochemical data and present them in a format readily understood by a wide range of stakeholders this enables a more efficient communication of the results of scientific studies to the wider community

geometric pattern rupture termination and fault segmentation of the dixie valley pleasant valley active normal fault system nevada u s a abstract active fault systems of both interplate and intraplate settings clearly show patterns of segmentation fault segmentation therefore is very important for understanding fault behavior and assessing seismic hazard the complexity of geometric patterns along fault systems has a strong influence on the propagation of earthquake ruptures because it can form structural heterogeneities that tend to inhibit rupture propagation this implies that there should be relations between fault segmentation and the complexity of fault geometry the active normal faults of the dixie valley pleasant valley system provide an excellent example to study such relations and to establish the geometric method of normal fault segmentation in the basin and range province studies of fault segmentation in the dixie valley pleasant valley fault system indicate that there are changes of both geometric pattern and geomorphic character in the area of the segment boundary the characteristics of segment boundaries on normal faults of the dixie valley pleasant valley system can be explained in terms of the nature of rupture propagation and termination these changes may be helpful criteria for distinguishing normal fault segmentation at least in the basin and range province

kinematic implications of joint zones and isolated joints in the navajo sandstone at zion national park utah evidence for cordilleran relaxation 1 at zion national park znp the landscape is a consequence of differential weathering of the navajo sandstone where closely spaced vertical joints constitute joint zones that erode to form regularly spaced half kilometer slot canyons striking 351 between these joint zones is a set of isolated joints striking 339 fracture interaction and horsetail wing crack development indicate that the 339 striking joint set is younger than the 351 striking joint zones despite the lateral extent of stress reduction shadows in the vicinity of the large scale joint zones in addition to an older less pervasive 020 joint set this sequence of jointing records a counterclockwise rotation of the regional extension directed from wnw to wsw in the navajo sandstone at znp znp is located at the western margin of the colorado plateau 100 km east of the major normal faults of the northeastern central basin and range subprovince extension within the eastern central basin and range initiated during the miocene and exhibited a wsw extension direction anderson 1971 wernicke et al 1988 snow and wernicke 2000 the correlation between nearby basin and range extension and the extension direction for the 351 tending joint zones of znp is so close that the jointing at znp is interpreted as evidence for modest yet pervasive basin and range extension in the western margin of the colorado plateau

fault behavior and characteristic earthquakes examples from the wasatch and san andreas fault zones paleoseismological data for the wasatch and san andreas fault zones have led to the formulation of the characteristic earthquake model which postulates that individual faults and fault segments tend to generate essentially same size or characteristic earthquakes having a relatively narrow range of magnitudes near the maximum analysis of scarp derived colluvium in trench exposures across the wasatch fault provides estimates of the timing and displacement associated with individual surface faulting earthquakes at all of the sites studied the displacement per event has been consistently large measured values range from 1 6 to 2 6 m and the average is about 2 m on the basis of variability in the timing of individual events as well as changes in scarp morphology and fault geometry six major segments are recognized along the wasatch fault on the basis of the most likely number of surface faulting events 18 that have occurred on segments of the wasatch fault zone during the past 8000 years an average recurrence interval of 400 666 years with a preferred average of 444 years is calculated for the entire zone geologic data on the distribution of slip associated with prehistoric earthquakes and slip rates along the south central segment of the san andreas fault suggest that the m 8 1857 earthquake is a characteristic earthquake for this segment comparisons of earthquake recurrence relationships on both the wasatch and san andreas faults based on historical seismicity data and geologic data show that a linear constant b value extrapolation of the cumulative recurrence curve from the smaller magnitudes leads to gross underestimates of the frequency of occurrence of the large or characteristic earthquakes only by assuming a low b value in the moderate magnitude range can the seismicity data on small earthquakes be reconciled with geologic data on large earthquakes the characteristic earthquake appears to be a fundamental aspect of the behavior of the wasatch and san andreas faults and may apply to many other faults as well

speculations on the geometry of the initiation and termination processes of earthquake rupture and its relation to morphology and geological structure earthquake initiation and termination processes are commonly described in terms of barriers and asperities barriers fall into two classes geometric barriers are associated with places where the orientation of a failure surface changes and relaxation barriers where stress is low because aseismic creep processes outpace tectonic loading geometric barriers fall into conservative and nonconservative subgroups according to whether finite fault motion can proceed without the creation of new structures or whether it demands the creation of new faulting or void space the multiple faulting or fragmentation associated with some nonconservative barriers can disrupt fault planes and form asperities by means of selected examples it is shown that a description in terms of these barriers can help one to visualise the processes of earthquake rupture and its relation to the geological environment

environmental tritium and 18o applied in a hydrological study of the wairau plain and its contributing mountain catchments marlborough new zealand abstract isotope data tritium and 18 o for rivers and ground water acquired since 1968 are combined with geological hydrological and hydrochemical evidence to determine sources and flow patterns of ground water in gravel aquifers of the wairau coastal plain and its southern tributary valleys determination of the components of groundwater origin depends on a strong west east gradient of 18 o concentration between mountain catchment precipitation feeding rivers flowing to the plain and rainwater falling directly on the plain the main aquifer is postglacial alluvial material deposited by wairau river deriving its water from that river locally infiltrated precipitation contributes at most only a few percent to the flow in the shallowest gravels downstream of the infiltration zone in the south of the plain the unconfined aquifer comprises material deposited during the last glaciation its ground water has both local precipitation and inflow from southern tributary streams as appreciable sources the main aquifer is confined near the coast where it is overlain by up to 60 m of marine sediments deposited during postglacial marine transgression and subsequent coastal progradation tritium concentrations show that ground water in the shallowest geological stratum rapaura gravels reaches the confined zone boundary less than 1 year after recharge from the river with much shallow flow being discharged at the surface just upstream of the boundary in contrast ground water in the underlying unit speargrass gravels requires at least 10 years to reach this point analysis of tritium concentrations in the confined zone shows a central zone through which the faster flowing rapaura component dominates as far as the coast but also areas to the north and south where ground water in the rapaura gravels has a dominant older component the combined evidence reveals that the confined ground water is leaking into the overlying sediments allowing water to flow from the lower speargrass gravels into the rapaura gravels because wairau river is the dominant source of ground water for the main aquifer its response to bomb tritium input to its mountain catchments is given detailed consideration much of the river water derives promptly from bare catchment areas but the analysis suggests that about 50 is retained for about 8 years on average before release to the river large deposits of scree in higher lying formerly glacial catchments appears to be the major factor in the surprisingly large quantity of stored water implied by this result

normal vs strike slip faulting during rift development in east africa the malawi rift kinematic analysis of neogene and quaternary faults demonstrates that the direction of extension in the malawi rift rotated from east northeast to southeast rift development commenced with the formation of half grabens bounded by northwest north and northeast striking normal faults owing to slightly oblique rifting the northwest striking faults in the northernmost rift segment show a small dextral oblique slip component whereas north and northeast oriented faults in the central part of the rift display a sinistral oblique slip component this first event resulted in block faulting and basin subsidence which is largely responsible for the present day basin morphology of lake malawi a major change in fault kinematics occurred because of rotation of the extension direction and permutation of the principal compressive and intermediate axes the structural pattern inherited from the first rifting phase was no longer suitably oriented to accommodate extensional deformation and strike slip faulting assumed a major role the strike slip regime amplified uplift of basement ridges within the rift in regions of local transpression but it also created alluvial basins because of local transtension this new kinematic style is compatible with the recent seismicity older faults that show mainly the first deformational increment are restricted to the outermost parts of the rift toward the center the faults depict an increase in strike slip components of movement suggesting deformation propagation toward the rift center which results in a narrowing of the active rift environments with time

new age determinations of central colorado plateau laccoliths utah recognizing disturbed k ar systematics and re evaluating tectonomagmatic relationships published k ar ages of laccoliths of the henry and la sal mountains range from 23 to 56 ma with a bimodal distribution in the eocene and late oligocene epochs eocene ages require a period of magmatism during the laramide orogeny a time of little or no igneous activity in the western united states at these latitudes on the basis of 40 ar 39 ar and fission track ages we conclude that intrusive activity occurred during middle to late oligocene and early miocene time 31 20 ma in the henry la sal and abajo mountains these results imply a genetic link to magmatism in the reno marysvale and san juan volcanic fields which lie to the west and east of the colorado plateau respectively we interpret the small volume of the laccoliths relative to the surrounding volcanic fields to reflect differences in crustal composition and tectonic history of the plateau and adjacent areas eocene k ar ages result from excess 40 ar or contamination by xenocrysts excess argon is manifested by trapped argon with 40 ar 36 ar ratios greater than atmosphere 295 5 resulting in total gas or apparent k ar ages that are too old laser fusion experiments and microprobe data show that some samples with eocene or older total gas ages and uncorrelated inverse correlation plots are affected by radiogenic argon residing in incompletely outgassed hornblende xenocrysts all such samples contain middle to late oligocene magmatic hornblende crystals as revealed by laser fusion experiments xenocrysts may be derived from amphibolite xenoliths common in these rocks mixing calculations indicate that only 1 4 contamination may be required to increase k ar ages by 10 15 ma for xenocrysts outgassed as much as 75 the 40 ar 39 ar method is capable of identifying small degrees of magmatic contamination by older k bearing phases

the geological and hydrogeological framework of the panabako kodjari and bimbilla formations of the voltaian supergroup revelations from groundwater hydrochemical data abstract this research demonstrates the utility of groundwater hydrochemical data for facilitating lithological mapping in a sedimentary terrain factor analysis and q mode hierarchical cluster analysis hca were applied to groundwater hydrochemical data from the nasia basin in northern ghana to determine the major sources of hydrochemical variation and the main spatial groundwater associations groups these analyses were complemented by mass balance hydrochemical modeling from phreeqc and petrographical analysis of rock samples from the area rock samples from the study area were subjected to petrographical and geochemical analyses from a petrographic microscope and scanning electron microscope sem respectively four principal factors were distinguished from the factor analysis highlighting four principal processes responsible for the observed hydrochemistry in the area these four factors cumulatively account for over 79 of the total variance in the dataset factor scores were computed from the factor loadings matrix through a regression process to highlight the spatial variations in the significance of each of the factors in the terrain on the basis of the parameter loadings the first factor which has been noted to be pervasive throughout the terrain has been interpreted to represent silicate mineral weathering both the geochemical data and petrographical analysis indicate the presence of silicate minerals indicating the plausibility of silicate mineral weathering the process of silicate mineral weathering appears to be highly pervasive throughout the basin indicating high factor scores in places the trend of spatial variations in the scores of factor 1 clearly mimics the known geology of the terrain indicating that the geology is the main controlling factor in the hydrochemistry of groundwater in the basin this pattern exhibited by the factor scores indicates that where adequate groundwater hydrochemical data is available factor analysis would prove useful in mapping out lithological variations in an area two of the remaining factors have been observed to represent other specific geogenic processes mass balance hydrochemical modeling suggests that albite may be in active dissolution presenting pervasively negative saturation indices undersaturation while kaolinite is extensively supersaturated five groundwater associations distinguished from the q mode hca display a spatial pattern which identifies with the underlying geology

modelling the behaviour of large gravity wharf structure under the effects of earthquake induced liquefaction abstract gravity wharf structures are widely used worldwide to form shallow and deep water ports they are large structures with a height of 25 50 m depending on the water depth when these structures are to be sited on loose to medium dense sand earthquake induced liquefaction settlements present a significant risk this often requires expensive soil replacement or other ground improvement techniques in this paper the dynamic behaviour of these large structures that exert very high bearing pressures on the foundation soil was investigated for the first time the level of settlements they can suffer due to soil liquefaction was investigated using dynamic centrifuge testing it will be shown that the full liquefaction does not occur below the structure even when the free field soil fully liquefies during strong earthquakes however there will be some stiffness degradation owing to excess pore pressure generation and consequent structural settlements the level of these settlements are considered to be acceptable from a service limit state sls perspective in addition to this the hydro dynamic pressures that act on the gravity wharf structure were also investigated

paleoseismology and neotectonics of the shivwits section of the hurricane fault northwestern arizona the shivwits section of the hurricane fault in northwestern arizona has been largely ignored in evaluating the seismic hazard posed to the rapidly growing populations of southwestern utah to assess this hazard we conducted studies along the shivwits section using field observations and geomorphic modeling to understand the quaternary tectonism of this portion of the hurricane fault we have found evidence that it ruptured with up to 2 to 3 m of vertical displacement per event and likely produced m 7 earthquakes our results suggest that the slip rate along the southern hurricane fault has not decreased during the quaternary the moriah knoll basalt offset 150 to 200 m along the hurricane fault yielded a maximum long term slip rate of 0 15 to 0 25 mm yr estimated using a new 40ar 39ar age of 0 85 0 06 ma the late quaternary slip rates on alluvial fan surfaces offset 2 to 7 4 m were estimated using pedogenic carbonate rind thickness as a calibrated proxy for age these observations yielded slip rates of 0 05 to 0 3 mm yr paleoseismic trench investigations showed that two surface rupturing events occurred in the past 15 78 k y a radiocarbon sample from a most recent event mre fissure yielded a calibrated age of 8900 10 400 years b p the penultimate event was likely 10 k y before the most recent event slip rate estimates using the moriah knoll basalt 0 15 0 24 mm yr 850 ka surface offset 0 05 0 3 mm yr 100 ka morphologic modeling 0 06 0 21 mm yr 100 ka and observations from the trench 0 06 0 34 mm yr 15 75 ka suggest that there has been no detectable change in slip rate in the past 1 million years or so this implies a constant deformation rate for this portion of the colorado plateau margin therefore basin and range extension is actively encroaching manuscript received 24 november 2003

geochemical and palaeohydrological controls on the composition of shallow groundwater in the netherlands with the exception of the south of the country the netherlands has a strong bipartite hydrogeology the holocene part with a coastal dune belt and confining top layer of clay and peat further inland and the pleistocene where thick phreatic aquifers dominate this research aimed to ascertain the geochemical and palaeohydrological controls on the composition of shallow groundwater in 27 regions close to 6000 groundwater analyses were grouped and interpreted in terms of 1 salinity 2 redox status 3 acid base and carbonate status and 4 natural nutrients nh4 and po4 the a priori classification into geographical regions and geological formations revealed many statistically significant differences in medians even for geologically or geographically related data groups the compound specific interpretation indicates that there are geogenically controlled systematic differences in groundwater composition at the regional scale the imprint of the geological sediments on the groundwater composition decreases in the order marine estuarine via limnological fluvial to aeolian the imprints with respect to ph and carbonate status natural nutrients and redox status are not necessarily interrelated the vertical stratification in groundwater composition turns out to be often limited at the regional scale due to mutual occurrence of infiltrating and exfiltrating groundwater in regions and either the presence of a highly reactive holocene confining top layer or temporal changes in contamination in the holocene part the salinity is controlled by the palaeoenvironmental conditions during the holocene and by the recharge origin the average cl concentration decreases from estuarine via lagoonal to the former zuider sea which was a bay the most reduced states and also the highest nutrient concentrations and highest co2 pressure are related to the presence of holocene marine sediments in the confining top layer degradation of marine derived organic matter as a nutrient source is likely more intense in the holocene deposits than that of peat and sedimentary remnants of terrestrial plants a broad range in ph carbonate status and redox status is encountered in the pleistocene part here the palaeohydrological evolution in terms of carbonate leaching together with the geological controls on the calcareous nature of the shallow sedimentary deposits cause regional differences in ph calcite saturation and silicate weathering one region with late pleistocene limnological deposits has deviating groundwater characteristics and appears more similar to the holocene part of the netherlands furthermore reactive fe is not abundant in all pleistocene fluvial sediments nor is it maximally mobilised as not all anoxic groundwater in these sediments is siderite saturated this leads to considerable intra and inter region variability 2013 elsevier ltd

parameterization of training images for aquifer 3 d facies modeling integrating geological interpretations and statistical inference we develop a stochastic approach to construct channelized 3 d geological models constrained to borehole measurements as well as geological interpretation the methodology is based on simple 2 d geologist provided sketches of fluvial depositional elements which are extruded in the 3rd dimension multiple point geostatistics mps is used to impair horizontal variability to the structures by introducing geometrical transformation parameters the sketches provided by the geologist are used as elementary training images whose statistical information is expanded through randomized transformations we demonstrate the applicability of the approach by applying it to modeling a fluvial valley filling sequence in the maules creek catchment australia the facies models are constrained to borehole logs spatial information borrowed from an analogue and local orientations derived from the present day stream networks the connectivity in the 3 d facies models is evaluated using statistical measures and transport simulations comparison with a statistically equivalent variogram based model shows that our approach is more suited for building 3 d facies models that contain structures specific to the channelized environment and which have a significant influence on the transport processes

compositional multivariate statistical analysis of thermal groundwater provenance a hydrogeochemical case study from ireland abstract thermal groundwater is currently being exploited for district scale heating in many locations world wide the chemical compositions of these thermal waters reflect the provenance and circulation patterns of the groundwater which are controlled by recharge rock type and geological structure exploring the provenance of these waters using multivariate statistical analysis msa techniques increases our understanding of the hydrothermal circulation systems and provides a reliable tool for assessing these resources hydrochemical data from thermal springs situated in the carboniferous dublin basin in east central ireland were explored using msa including hierarchical cluster analysis hca and principal component analysis pca to investigate the source aquifers of the thermal groundwaters to take into account the compositional nature of the hydrochemical data compositional data analysis coda techniques were used to process the data prior to the msa the results of the msa were examined alongside detailed time lapse temperature measurements from several of the springs and indicate the influence of three important hydrogeological processes on the hydrochemistry of the thermal waters 1 salinity and increased water rock interaction 2 dissolution of carbonates and 3 dissolution of sulfides sulfates and oxides associated with mineral deposits the use of msa within the coda framework identified subtle temporal variations in the hydrochemistry of the thermal springs which could not be identified with more traditional graphing methods or with a standard statistical approach the msa was successful in distinguishing different geological settings and different annual behaviours within the group of springs this study demonstrates the usefulness of the application of msa within the coda framework in order to better understand the underlying controlling processes governing the hydrochemistry of a group of thermal springs in a low enthalpy setting

current tufa sedimentation in a high discharge river a comparison with other synchronous tufa records in the iberian range spain abstract the results from sedimentological isotopic and hydrochemical analyses of current tufa sedimentation conducted in a high discharge river ebron river northeastern spain 1 49 m 3 s through six month monitoring over 3 5 years are discussed in terms of the factors that control local carbonate deposition through space and time and compared with results from other synchronous tufa records in the same climatic domain the findings allow for discerning the influence of the riverbed slope hydrochemistry discharge and groundwater inputs on tufa attributes and assess the significance of tufa as archives of certain climatic events on a regional scale in the ebron river the dominant upstream karstic springs from a jurassic rock aquifer determined the river s hco 3 ca composition two river stretches were differentiated according to localised increments in both pco 2 resulting from additional groundwater inputs and so 4 content influenced by evaporite bearing units the variations in tufa s thickness through space were strongly controlled by co 2 rich springs and local slope variations the monitored sites represent four primary subenvironments with distinct sedimentary facies whose attributes suggest that 1 the tufa deposition rates in each fluvial subenvironment are mainly controlled by the co 2 outgassing intensity linked to local flow conditions and the biological substrate type and 2 stromatolites represent the thickest and most complete record the six month variations in tufa thickness and calculated calcite mass in the ebron river were controlled by temperature dependent physico chemical and biological parameters coupled with high discharge events that provoked tufa erosion the smaller deposition of the ebron river compared to two other synchronous tufa records in the iberian range is linked to 1 the absence of long areas of increased slope 2 the occurrence of significant co 2 rich groundwater springs in the middle reach and 3 the higher discharge and water depth certain high discharge events were recorded as lower deposition rates concurrent in the three rivers moreover anomalous water temperatures calculated from the calcite 18 o in the three rivers for a coincident time span support a regional anomaly in the precipitation 18 o thus the evolution of the short term tufa deposition rates and calcite 18 o composition through time can detect regional climate and hydrology changes and therefore can be robust criteria for correlation in the geological record

extension in high grade terranes of the southern omineca belt british columbia evidence from paleomagnetism paleomagnetic observations are used to construct a map of structural tilts in metamorphic and plutonic rocks of the southern omineca belt in southeastern british columbia during eocene extension midcrustal rocks were exhumed in footwalls of low to moderate angle normal faults that dip east and west in the eastern and western parts of the study area respectively tilts averaging 30 to 40 are consistent over large areas and generally antithetic to the major faults in the central part of the study area however the eastern half of the coryell pluton is untilted and its western half in the hanging wall of the east dipping kettle river fault is tilted down to the east in the opposite sense to that expected north of the pluton these eastward tilted rocks are juxtaposed against westward tilted rocks to explain the anomalous tilts a major west dipping eocene normal fault arrow lake fault is inferred and a revised kinematic history for the area proposed observations of magnetic polarity 86 normal laboratory unblocking temperatures and isotopic age data suggest that magnetizations in the west were acquired during chron 23n and in the east in chron 23n and or chron 24n unless extension postdated the acquisition of magnetization tilts would not be observed thus it is argued that extension in the west occurred after 50 6 ma and in the east between 51 6 possibly 53 3 and 50 6 ma these time intervals do not correspond to any known global plate reorganization event indicating that the last phase of eocene extension in the southern omineca belt was governed by regional rather than global processes

delineation of hydrochemical facies distribution in a regional groundwater system by means of fuzzy c means clustering 1 in this paper classification of a large hydrochemical data set more than 600 water samples and 11 hydrochemical variables from southeastern california by fuzzy c means fcm and hierarchical cluster analysis hca clustering techniques is performed and its application to hydrochemical facies delineation is discussed results from both fcm and hca clustering produced cluster centers prototypes that can be used to identify the physical and chemical processes creating the variations in the water chemistries there are several advantages to fcm and it is concluded that fcm as an exploratory data analysis technique is potentially useful in establishing hydrochemical facies distribution and may provide a better tool than hca for clustering large data sets when overlapping or continuous clusters exist index terms 1806 hydrology chemistry of fresh water 1829 hydrology groundwater hydrology 1831 hydrology groundwater quality 1871 hydrology surface water quality keywords clustering techniques fuzzy logic fuzzy c means hydrochemical facies hydrochemistry inverse modeling

growth of faults by accumulation of seismic slip the accommodation of large strains in the upper crust is largely achieved by the accumulation of displacement on faults observation shows that as a fault accumulates displacement it grows in size i e its surface area and its length increase here we address the question for an increase in the amount of displacement on a fault by how much would the length of the fault change it is argued by cowie and scholz 1992a that the displacement on a fault is linearly related to the length of the fault this simple result is expanded upon in this paper by assuming that a fault accumulates displacement by repeated earthquakes two different approaches are presented the first approach considers the balance that must be achieved between the energy available for deformation and the work involved in creating new fault surface area as the fault grows the available energy is provided by changes in strain energy when the fault slips the second approach is to construct a geometrical model for fault growth using the scaling relationship between the slip during a single earthquake and the length of the rupture the total displacement on a fault is the sum of the slips contributed by many earthquakes the usefulness of these two approaches is that the growth of a fault over geologic time can be described by parameters that can be obtained from earthquake and fault data the models presented here predict that 1 the maximum amount a fault can grow in a single earthquake that ruptures the entire fault is of the order of 1 of its previous length and 2 the work of faulting may account for 10 of the total energy available during an earthquake the energy lost from the system is accounted for by work done against friction and seismic radiation consequences of fault growth for the segmentation and thus seismogenic potential of a fault over geologic time are discussed using predictions of the theory

permeability and stiffness of sands at very low effective stresses loose saturated sandy soils may undergo liquefaction under cyclic loading generating positive excess pore pressures due to their contractile nature and inability to dissipate pore pressures rapidly during earthquake loading these liquefied soils have a near zero effective stress state and hence have very low strength and stiffness causing severe damage to structures founded upon them the duration for which this near zero effective stress state persists is a function of the rate of reconsolidation of the liquefied soil which in turn is a function of the permeability and stiffness of the soil at this very low effective stress existing literature based on observation of physical model tests suggests that the consolidation coefficient cv associated with this reconsolidation of liquefied sand is significantly lower than that of the same soil at moderate stress levels in this paper the results of a series of novel fluidisation tests in which permeability k and coefficient of consolidation cv were indep