fault interaction may generate multiple slip vectors on a single fault surface slip vectors of multiple orientations on a single fault surface may be explained by the interaction of crustal scale faults in response to nearby earthquakes field observations of at least five sets of striae on a single planar fault surface can be reproduced in numerical experiments these experimental results suggest that slip vectors having variable orientations may reflect a highly transient local stress state in an otherwise constant regional stress field our results suggest that stress inversion techniques should be applied with caution to areas with complex regional scale fault patterns

can flat ramp flat fault geometry be inferred from fold shape a comparison of kinematic and mechanical folds the inference of fault geometry from suprajacent fold shape relies on consistent and verified forward models of fault cored folds e g suites of models with differing fault boundary conditions demonstrate the range of possible folding results of kinematic fault parallel flow and mechanical boundary element method models are compared to ascertain differences in the way the two methods simulate flexure associated with slip along flat ramp flat geometry these differences are assessed by systematically altering fault parameters in each model and observing subsequent changes in the suprajacent fold shapes differences between the kinematic and mechanical fault fold relationships highlight the differences between the methods additionally a laboratory fold is simulated to determine which method might best predict fault parameters from fold shape although kinematic folds do not fully capture the three dimensional nature of geologic folds mechanical models have non unique fold fault relationships predicting fault geometry from fold shape is best accomplished by a combination of the two methods

tectonic hydrothermal brecciation associated with calcite precipitation and permeability destruction in mississippian carbonate reservoirs montana and wyoming the mississippian madison formation contains abundant fracture zones and breccias that are hydrothermal in origin based on their morphology distribution and geochemical signature the hydrothermal activity is related to crustal shortening during the laramide orogeny brecciation is accompanied by dedolomitization late stage calcite precipitation and porosity occlusion especially in outcrop dolomites the tectonic hydrothermal late stage calcite reduces permeability in outcrops and potentially high quality subsurface reservoir rocks of the subsurface madison formation bighorn basin the reduction of permeability and porosity is increased along the margins of the bighorn basin but not predictable at outcrop scale the destruction of porosity and permeability by hydrothermal activity in the madison formation is unique in comparison to studies that document enhanced porosity and permeability and invoke hydrothermal dolomitization models hydrothermal breccias from the owl creek thrust sheet are classified into four categories based on fracture density calcite volume and clast orientation shattered breccias dominate the leading edge of the tip of the owl creek thrust sheet in the eastern owl creek mountains where tectonic deformation is greatest whereas fracture mosaic and chaotic breccias occur throughout the bighorn basin the breccias are healed by calcite cements with 18o values ranging between 26 5 and 15 1 peedee belemnite pdb indicating that the cements were derived from isotopically depleted fluids with elevated temperatures in the chaotic and mosaic breccia types large rotated and angular clasts of the host rock float in the matrix of coarse and nonzoned late stage calcite this appearance combined with similar 18o values across even large calcite veins indicates that the calcite precipitated rapidly after brecciation values for 13c 5 12 pdb from the frontal part of the owl creek thrust sheet indicate equilibrium between methane and co2 bearing fluids at about 180c fluid inclusions from the eastern basin margin show that these cements are in equilibrium with fluids having minimum temperatures between 120 and 140c and formed from relatively low salinity fluids less than 5 wt nacl strontium isotope ratios of these hydrothermal fluids are more radiogenic than proposed values for mississippian seawater suggesting that the fluids mixed with felsic rich basement before migrating vertically into the madison formation we envisage that the tectonic hydrothermal late stage calcite cemented breccias and fractures originated from undersaturated meteoric groundwaters that migrated into the burial environment while dissolving and incorporating ca2 and and radiogenic sr from the dissolution of the surrounding carbonates and the felsic basement respectively in the burial environment these fluids were heated and mixed with hypersaline brines from deeply buried parts of the basement expulsion of these fluids along basement rooted thrust faults into the overlying strata including the madison formation occurred most likely during shortening episodes of the laramide orogeny by earthquake induced rupturing of the host rock the fluids were injected forcefully and in an explosive manner into the madison formation causing brecciation and fracturing of the host rock whereas the subsequent and sudden decrease in the partial pressure of co2 caused the rapid precipitation of calcite cements the explosive nature of hydrothermal fluid migration ultimately produces heterogeneities in reservoir quality carbonates in general flow units in the madison formation are related to sequence boundaries which create vertical subdivisions in the porous dolomite the late stage calcite cement surrounds hydrothermal breccia clasts and invades the dolomite reducing porosity and permeability of the reservoir quality rock as a consequence horizontal flow barriers and compartments are established that are locally unpredictable in their location and extent and regionally predictable along the margins of the bighorn basin

strained craters on ganymede high resolution images of jupiter s satellite ganymede obtained by the galileo spacecraft reveal several elliptical craters that are transected by sets of subparallel ridges and troughs oriented roughly orthogonal to the long axis of the crater implying that these craters have been extensionally strained we analyze five such craters four in the ancient dark terrain and one in bright grooved terrain inferring their strain histories by assuming each crater was originally circular these strained craters have been elongated by amounts ranging from 5 to 50 all are deformed by extension near perpendicular to subparallel ridges and troughs and some are also deformed by distributed simple shear parallel to these tectonic structures the rift zones that deform these craters show extensions of 5 up to 180 for a well defined fault zone that rifts saltu crater within dark terrain of nicholson regio extensional fault zones consisting of domino style normal faults and representing strains of several tens of percent may be common on ganymede and strains of this order can alter pre existing surface features beyond recognition through the process of tectonic resurfacing

fold evolution matrices and axial surface analysis of fault bend folds application to the medina anticline eastern cordillera colombia the medina anticline is a fault bend fold located in the hanging wall of the aguaclara fault along the southeastern thrust front of the eastern cordillera of colombia a petroleum province with giant fields we employ a modified technique of axial surface analysis using fold evolution matrices which helps define the subsurface geometry and thereby provides important constraints on trap geometry modeling of hydrocarbon migration pathways and prediction of reservoir quality

kinematics of fault related folding derived from a sandbox experiment we analyze the kinematics of fault tip folding at the front of a fold and thrust wedge using a sandbox experiment the analog model consists of sand layers intercalated with low friction glass bead layers deposited in a glass sided experimental device and with a total thickness h 4 8 cm a computerized mobile backstop induces progressive horizontal shortening of the sand layers and therefore thrust fault propagation active deformation at the tip of the forward propagating basal decollement is monitored along the cross section with a high resolution ccd camera and the displacement field between pairs of images is measured from the optical flow technique in the early stage when cumulative shortening is less than about h 10 slip along the decollement tapers gradually to zero and the displacement gradient is absorbed by distributed deformation of the overlying medium in this stage of detachment tip folding horizontal displacements decrease linearly with distance toward the foreland vertical displacements reflect a nearly symmetrical mode of folding with displacements varying linearly between relatively well defined axial surfaces when the cumulative slip on the decollement exceeds about h 10 deformation tends to localize on a few discrete shear bands at the front of the system until shortening exceeds h 8 and deformation gets fully localized on a single emergent frontal ramp the fault geometry subsequently evolves to a sigmoid shape and the hanging wall deforms by simple shear as it overthrusts the flat ramp system as long as strain localization is not fully established the sand layers experience a combination of thickening and horizontal shortening which induces gradual limb rotation the observed kinematics can be reduced to simple analytical expressions that can be used to restore fault tip folds relate finite deformation to incremental folding and derive shortening rates from deformed geomorphic markers or growth strata

dark halo craters and the thickness of grooved terrain on ganymede dark halo craters in grooved terrain on ganymede represent potential probes of the subsurface geology these craters are surrounded by a broad diffuse low albedo annulus or halo halo radius is linearly proportional to crater radius indicating that the halo is related to the continuous ejecta deposit of the crater and is not removed by natural aging processes such as regolith development and exposure to the space environment the halos have orange violet albedo ratios that are intermediate between ratios associated with grooved terrain and cratered terrain we propose that halos result from the incorporation of cratered terrain material into crater ejecta in uruk sulcus only craters greater than 12 km in diameter have halos indicating that the cratered terrain material there forms a stratigraphic horizon buried at depth in the grooved terrain into which only larger craters can excavate this depth can be calculated from the transition diameter by reconstructing the transient crater we calculate a depth of excavation corresponding to the depth of burial of cratered terrain of 1 0 to 1 6 km this shallow burial is inconsistent with deep subsidence and burial stoping into the interior or lateral spreading apart of ancient cratered terrain units but is consistent with a filled graben model for grooved terrain where relatively clean ice has been emplaced over downdropped blocks of cratered terrain

structural analysis of seismically mapped horizons using the developable surface model a new method for the analysis of folding of seismically mapped horizons is described based on a model of developable surfaces the local geometrical properties are determined by analyzing the variation of dip and strike along linear strips on the surface by considering strips in different directions a plunge line the approximation to the generatrix of a developable fold is identified as the direction associated with the least variation of surface attitude the map pattern obtained by analyzing the plunge and trend of plunge lines across an area allows the identification of domains where folding accords with a developable geometry such domains are recognized from straight plunge lines defining convergent or parallel patterns deviations from these patterns correspond to regions of structural complexity associated with ductile or brittle straining of the horizon we suggest that plunge line analysis may offer a useful technique for automatic fault recognition

annual replenishable ground water potential of india an estimate based on injected tritium studies abstract natural recharge is a vital parameter to be known for ground water budgeting management and modelling percolation of a portion of the rainfall through the vadose zone is the principal source of natural recharge to the aquifer systems in india the tritium injection method based on piston flow model is particularly suitable for quantifying the downward flux of moisture in the vadose zone and for measuring natural recharge in indian climatic condition where about 80 of the annual rainfall is received as pulses and occurs during the four monsoon months from june to september natural recharge measurements using the tritium injection method have been carried out in india during the last 25 years in several basins and watersheds located in varying climatic and hydrogeological situations the mean natural recharge values for 35 study areas well distributed over 17 major river basins are presented the recharge rates range from 24 to 198 mm yr 1 or 4 1 to 19 7 of the local average seasonal rainfall the natural recharge data are grouped into four main hydrogeological provinces namely granitic basaltic sedimentary and alluvial and the regression equations between rainfall and natural recharge are derived for each province these equations enable one to determine the approximate value of natural recharge in any watershed basin from the rainfall data for any year the regression equations are used to compute the total annual replenishment of ground water reserves of the country for an average rainfall year the calculated annual input is about 476 10 9 m 3 yr 1 this can be considered as a minimal quantity as it represents the natural recharge due to precipitation alone and does not account for seepage from ponds lakes stream bed canals and return flow from surface water irrigation

patterns of folding and fold interference in oblique contraction of layered rocks of the inverted cobar basin australia abstract the inverted cobar basin within the lachlan fold belt of new south wales australia comprises a mid palaeozoic cover sequence originally deposited in a nnw trending basin the pattern of f1 folding in the layered cover rocks changes from east to west from tight well cleaved folds parallel to the nnw trending basin margin on the east to open poorly cleaved en echelon folds at about 35 to the margin further to the west the change in fold trend and strain intensity has been repeatedly ascribed to the differing behaviour of discrete zones decoupled across a north trending strike slip fault boundary new field data show that the changes in orientation and strain intensity of f1 structures are progressively developed that an abrupt boundary between discrete zones cannot be substantiated and that interpretations involving decoupled blocks are not supported by the evidence conversely the data require coherent behaviour across the basin such that the overall pattern of f1 folding must be explained by strain compatible processes this new interpretation of the f1 deformation pattern has been modelled and quantitatively analysed theoretical predictions of the orientation of structures in unlayered isotropic material undergoing oblique contraction are inapplicable to layered anisotropic material the style of deformation in layered material will reflect the interaction of the bulk strain pattern due to convergence together with the influence of the layering anisotropy the orientations of the finite strain axes inferred from the folding need not match those of the bulk deformation the amount of strain recorded by folding may be unrepresentative of that developed in the deformed tract oblique contraction at a range of convergence angles was simulated by models employing layers of wet tissue paper quantitative analysis of the strain patterns in this layered anisotropic material showed consistent departures from the theoretical predictions for isotropic material the orientations of the principal finite horizontal extension proximal to the margin yielded higher convergence angles than those which were imposed the orientations distal from the margin yielded substantially lower apparent convergence angles this is because the layering anisotropy results in tight folds dissipating the normal component of the oblique convergence vector close to the margin whereas more open structures further from the margin show orientations controlled by the progressively more dominant shear component of the vergence vector modelling of d1 the cobar basin shows that the f1 pattern is consistent with dextral oblique convergence at 60 to the eastern margin of the basin the deformation patterns in both the model and the cobar basin yield higher proximal and substantially lower distal apparent convergence angles this is as expected from theoretical considerations and quantitative analysis of oblique contraction over a range of convergence angles the rheological anisotropy of the cover sequence of the basin is replicated by that of the layered wet tissue paper wet tissue modelling of the superposition of the second period of deformation d2 on f1 demonstrates the way in which the tightness and orientation of early folds influence the type of fold interference pattern at the eastern margin of the cobar basin where d1 was most intense this resulted in major swings of the strike of bedding and cleavage and of the trend of f1 folds further west open basin and dome patterns developed where d1 was least intense principles developed in relation to the inversion of the cobar basin are equally applicable to other basins in which layered cover rocks have undergone inversion by oblique contraction many basins in the lachlan fold belt and in general would fall within this category

constraints on the expansion of ganymede and the thickness of the lithosphere grooves and furrows have been interpreted as grabens resulting from extension of ganymede s lithosphere geologically reasonable estimates of the dip 90 60 and displacement less than 1 km to a few hundred meters of faults bounding grooves on ganymede allow calculation of the extension and surface area increase 0 04 2 required for the formation of all grooved terrain the implied radius increase is thus limited between 0 02 and 1 1 planetary expansion is the maximum possible since formation of the grooved terrain began similar estimates for faults bounding furrows the oldest preserved tectonic features on ganymede indicate a maximum surface area increase of 0 5 for the best developed furrow system which is located in galileo regio if equivalent furrow systems existed on all of the cratered terrain then a maximum of 0 5 increase in surface area of ganymede is possible after the formation of the lithosphere and prior to the formation of grooved terrain faults bounding simple graben originate at a subsurface mechanical discontinuity and propagate upwards resulting in grabens with similar widths and similar spacings between members of a set the depth to this mechanical discontinuity for furrows and grooves on ganymede must give at least a minimum lithosphere thickness because it is impossible for faults to originate and propagate upwards from a point below the lithosphere therefore the minimum lithosphere thickness on ganymede is 5 km and 9 km in marius and galileo regiones respectively at the time of furrow formation and 4 km at the time of groove formation

mechanical analysis of the geometry of forced folds a mechanical model of forced folding comprised of an anisotropic cover overlying displaced rigid basement blocks is used to investigate the influence of various parameters on theoretical fold form shape and dip of basement fault strength of basement cover contact and degree of anisotropy of the cover we show that the degree of anisotropy in the cover largely influences the geometry of the forelimb of the forced fold folds produced in isotropic cover display forelimbs that taper from large dip angles near the basement cover contact to low dip angles at the ground surface in contrast dips in the forelimbs of folds in anisotropic cover are nearly uniform with depth we show that the basement cover contact and the shape of the basement fault largely influence the geometry of the backlimb backlimb rotation occurs in cover welded to the basement and in cover underlying curved basement faults in addition the kinematic features of the theoretical folds are compared with the fold geometry generated by parallel kink and trishear models folds in isotropic cover overlying straight basement faults closely resemble the fold forms produced by the trishear kinematic model while fold forms in anisotropic cover more closely resemble folds produced by parallel kink geometric constructions

determination of the conduit structure in a karst aquifer based on tracer data lurbach system austria a structure model was used to analyse solute transport parameter estimates based on tracer breakthrough curves in the model system groundwater flow is envisioned to be organised in a complex conduit network providing a variety of short circuits with relative small carrying capacities along different erosion levels the discharge through the fully filled conduits is limited owing to void geometries and turbulent flow thus a hierarchic overflow system evolves where conduits are re activated or dried up depending on the flow condition exemplified on the lurbach tanneben karst aquifer the applicability of the model approach was tested information derived from multi tracer experiments performed at different volumetric flow rates enabled to develop a structural model of the karst network under constraint of the geomorphological and hydrological evolution of the site depending on the flow rate groundwater is divided into up to eight flow paths the spatial hierarchy of flow paths controls the sequence of flow path activation conduits of the topmost level are strongly influenced by reversible alteration processes sedimentation or blocking causes an overflow of water to the next higher conduit flow path specific dissolutional denudation rates were estimated using the temporal development of the partial discharge copyright 2012 john wiley sons ltd

global geological mapping of ganymede abstract we have compiled a global geological map of ganymede that represents the most recent understanding of the satellite based on galileo mission results this contribution builds on important previous accomplishments in the study of ganymede utilizing voyager data and incorporates the many new discoveries that were brought about by examination of galileo data we discuss the material properties of geological units defined utilizing a global mosaic of the surface with a nominal resolution of 1 km pixel assembled by the usgs with the best available voyager and galileo regional coverage and high resolution imagery 100 200 m pixel of characteristic features and terrain types obtained by the galileo spacecraft we also use crater density measurements obtained from our mapping efforts to examine age relationships amongst the various defined units these efforts have resulted in a more complete understanding of the major geological processes operating on ganymede especially the roles of cryovolcanic and tectonic processes in the formation of might materials they have also clarified the characteristics of the geological units that comprise the satellite s surface the stratigraphic relationships of those geological units and structures and the geological history inferred from those relationships for instance the characteristics and stratigraphic relationships of dark lineated material and reticulate material suggest they represent an intermediate stage between dark cratered material and light material units

evidence of transpressional tectonics on the uruk sulcus region ganymede abstract the surface of ganymede is characterized by intense tectonic deformation the two terrains light and dark show morphotectonic features namely grooves and furrows these represent kilometric systems at the regional scale interpreted as extensional structures e g horst and graben systems currently evidence of significant compression has not yet been recognized leaving open the opportunity to clarify the tectonic balance of ganymede s surface debate still exists on the geodynamics responsible for surface deformation and the investigation of these features contributes to understanding the internal processes to understand the deformation that shapes the surface of the satellite we explore the tectonic setting of the light terrain region of uruk sulcus using structural geology methodologies by remote sensing and systematic analysis of grooves we recognize three groove systems within the sulcus and one furrow system in the neighboring dark terrain uruk sulcus is also characterized by the presence of two domains of lineaments subtle linear texture anisotropies related to the influence of tectonic processes on morphology comparison of the combined results from the analyses of the recognized groove systems with the lineament domains allowed us to infer the stress field responsible for their development in the studied area according to these results an evolutionary tectonic scenario for uruk sulcus is proposed a tectonic corridor characterized by dextral transpression with 58 of the internal compressional component approximately n s oriented and responsible for localized e w extensional features among crustal blocks of the shear zone

large impact features on europa results of the galileo nominal mission the galileo orbiter examined several impact features on europa at considerably better resolution than was possible from voyager the new data allow us to describe the morphology and infer the geology of the largest impact features on europa which are probes into the crust we observe two basic types of large impact features 1 classic impact craters that grossly resemble well preserved lunar craters of similar size but are more topographically subdued e g pwyll and 2 very flat circular features that lack the basic topographic structures of impact craters such as raised rims a central depression or central peaks and which largely owe their identification as impact features to the field of secondary craters radially sprayed about them e g callanish our interpretation is that the classic craters all 30 km diameter formed entirely within a solid target at least 5 to 10 km thick that exhibited brittle behavior on time scales of the impact events some of the classic craters have a more subdued topography than fresh craters of similar size on other icy bodies such as ganymede and callisto probably due to the enhanced viscous relaxation produced by a steeper thermal gradient on europa pedestal ejecta facies on europa and ganymede may be produced by the relief flattening movement of plastically deforming but otherwise solid ice that was warm at the time of emplacement callanish and tyre do not appear to be larger and even more viscously relaxed versions of the classic craters rather they display totally different morphologies such as distinctive textures and a series of large concentric structural rings cutting impact feature related materials impact simulations suggest that the distinctive morphologies would not be produced by impact into a solid ice target but may be explained by impact into an ice layer 10 to 15 km thick overlying a low viscosity material such as water the very wide near antipodal separation of callanish and tyre imply that 10 15 km may have been the global average thickness of the rigid crust of europa when these impacts occurred the absence of detectable craters superposed on the interior deposits of callanish suggests that it is geologically young 108years hence it seems likely that our preliminary conclusions about the subsurface structure of europa apply to the current day

grabens basin tectonics and the maximum total expansion of the moon the presence of grabens and wrinkle ridges indicates that stresses sufficient to deform or fault crustal rocks have existed for at least part of lunar history these structures have been explained as due to global expansion and contraction basin subsidence or both even if the extension implied by all lunar grabens were due to global expansion the total radius increase permissible after terminal bombardment would be much less than that predicted by the most conservative models of lunar thermal evolution the obvious areal association of most grabens and wrinkle ridges with impact basins suggests that a genetic relationship exists also but it is necessary to develop either kinematic or dynamic models to determine if basin subsidence alone can account for these structures kinematic models are the most useful because fewer assumptions regarding material properties are needed than for dynamic models for both types the grabens and wrinkle ridges provide the data that must be predicted by the models considerations of geometry kinematics and mechanics suggest that the simple grabens on the moon are reliable indicators of crustal extension two end member kinematic models of postimpact basin modification are derived one assuming that subsidence is accomplished entirely by an increase in radius of curvature of the basin floor the other assuming that subsidence is accomplished without any change in radius of curvature of the basin floor any combination of the two also would be possible both models predict enough extension to account completely for basin related grabens and thus they indicate that virtually all of the extension implied by lunar grabens can be provided by modest amounts of basin subsidence in addition both models also predict total radial and hoop shortening of the basin floor of about the correct magnitude to explain wrinkle ridges if these features are structures resulting from compression consequently almost all extension and shortening of the lunar crust implied by grabens and wrinkle ridges can be explained by basin subsidence alone significant global expansion after 3 9 b y is unlikely and significant global contraction is unnecessary

bedding plane slip in initial stages of fault related folding abstract frictional slip along bedding planes contributes to fault related folding of layered rocks we use numerical experiments to investigate the deformation of frictional bedding planes near dipping faults under layerparallel contraction and extension within the numerical experiments contraction boundary conditions produce asymmetric anticlines and extension produces asymmetric synclines the fold shape may be used to infer dip of the underlying fault in situations where the fault may not be observable additionally sense of slip along bedding planes may indicate proximity to the fault tip under uniform remote tectonic strain fault slip induces deformation in both the hangingwall and the footwall at depths as shallow as 1 km there is no significant difference between fold amplitudes in the hangingwall and the footwall this result is contrary to many kinematic models currently in use kinematic models of fault related folds commonly include the development of flat ramp and flat ramp flat fault geometries which may be attributed to initial ramp thrusting and later flat development our mechanical models show that fault flats may be produced from fault ramps due to slip along frictional bedding planes near the thrust fault tips our numerical experiments also evaluate joint initiation joints perpendicular to bedding are promoted in extensional environments we compare the results of the mechanical model to kinematic models of fault propagation folds and conclude that mechanical models offer important insights to better understand the folding process

three layered models of ganymede and callisto compositions structures and aspects of evolution abstract three layered structural models are determined for ganymede and callisto each consists of a rock core a mixed ice rock lower mantle and a pure ice upper mantle this structure results from differentiation subsequent to accretional melting attention is given to evaluating various candidates for the rock component and three alternatives representing various degrees of silicate hydration and oxidation are modeled and incorporated structures are calculated on the basis of a 250 k isotherm which is a reasonablev approximation to the gentle adiabats expected to occur in icy satellites differentiation of an ice rock satellite generally involves an increase in radius and the three layered approach allows this process to be examined in some detail it is determined that satellite expansion is most significant early in the process and much less so as differentiation proceeds to completion if tectonics are due to global expansion distinguishing on this basis between a completely differentiated satellite and one that is only partially differentiated is difficult the postaccretional global expansion of ganymede which may have left a tectonic record was probably limited to 1 in radius in agreement with observed limits useful quantities such as silicate mass and volume fraction uncompressed density j2 c22 binding energy and surface heat flow are also determined nonhydrostatic contributions to j2 and c22 are estimated and shown to be nonnegligible encounters with jupiter orbiting spacecraft are unlikely to determine callisto s degree of central condensation we conclude by calculating the relative likelihood of postaccretional melting caused by radiogenic heating three layered satellites have generally hotter interiors because additional thermal boundary layers divide the separately convecting upper and lower mantles inhibiting heat transport ganymedes and callistos that are less than about 1 3 differentiated by mass should experience a second episode of melting as these boundary layers are either above the level of the water ice minimum melting temperature or intersect the melting curve at deeper levels runaway differentiation to at least a depth corresponding to a pressure in the ice v stability field is likely the main point here is that if satellite tectonics are tied to differentiation by melting or its aftermath as in the instability following ocean closure of kirk and stevenson moderate or small amounts of accretional differentiation are unlikely to explain an absence of tectonics as in callisto because extensive differentiation ultimately occurs

topographic wavelengths of ganymede groove lanes from fourier analysis of galileo images galileo images have shown that grooved terrain on ganymede consists of pervasive ridges and grooves at a variety of spatial scales which complicates visual interpretation we use fourier analysis to separate complex surface deformation into its component dominant wavelengths closely correlated to topographic wavelengths to determine spatial relationships within and among grooved terrain units we analyze groove lanes in four galileo target sites uruk sulcus byblus sulcus tiamat sulcus and nicholson regio spanning a range of resolutions and lighting geometries and we find multiple dominant wavelengths in each fourier analysis of the complexly deformed uruk sulcus shows both similarities and differences in wavelength distribution among its tectono stratigraphic subunits a range of 0 5 to 6 km with a concentration at 1 2 km favorable comparison is made to a stereo derived topographic model of the dominant wavelengths displayed by byblus sulcus 1 3 3 and 10 km the longest wavelength is revealed by profiles across both high and low resolution images with very different lighting geometries tiamat sulcus displays different dominant wavelengths north 5 to 10 km and south 3 to 5 km of the orthogonally trending kishar sulcus groove lanes in nicholson regio are significantly different from the other sites because they are isolated within dark terrain fourier analysis of these dark terrain groove lanes shows dominant wavelengths 2 1 3 2 and 8 0 km that are similar to those in lanes of more typical grooved terrain this suggests that the tectonic style and lithospheric characteristics in this portion of ganymede s dark terrain were similar to those in bright grooved terrain at the time of deformation our results support the hypothesis that longer topographic wavelengths in ganymede s groove lanes formed by means of extensional necking of the lithosphere while multiple shorter wavelengths formed by normal faulting of the brittle lithosphere in both bright and dark terrains the similar wavelengths of deformation seen in several groove lanes in both bright and dark terrain suggest similarity in lithospheric thickness composition and mechanical structure at these disparate sites a global process such as differentiation could be responsible for creating a similar planet wide strain and thermal regime during the time of grooved terrain formation

the effect of non parallel thrust fault interaction on fold patterns the geometry of two subsurface non parallel thrust faults are systematically altered within mechanical models to determine the range of resulting fold map patterns and the effect of fault interaction on these fold patterns and ultimately to infer fault geometry from complex fold shapes multiple faults can create both complex fold patterns with more than one fold axis and single folds without evidence of a second fault fold length may not correlate to fault length when remote contraction is oblique to the faults thus contraction direction should be determined before fault length is inferred the influence of fault interaction is studied by comparing the fold pattern created by interacting faults to the fold pattern created from the superposition of folds produced by equivalent but isolated faults under small strains larger faults tend to have greater interaction but even interacting faults may not produce fold patterns notably distinct from the superposed fold patterns this suggests that fault interaction need not necessarily be considered when inferring fault geometry from fold shape in the field however under non coaxial strain conditions fold patterns may differ from those presented here

estimating aquifer recharge and parameters from water level observations this paper is concerned with the development of a technique to estimate recharge from rainfall and to estimate aquifer parameters using groundwater level records and available climatological data the methodology combines a hydrometeorological model which links rainfall and evapotranspiration to the effective groundwater recharge and a geohydrologic model which links the recharge to the water level in the aquifer results of field application are presented to illustrate the usefulness of the technique

from excess infiltration to aquifer recharge a derivation based on the theory of flow of water in unsaturated soils an approximate unit hydrograph of aquifer recharge due to effective percolation is derived from a theory describing flow of water in unsaturated soils the parameters appearing in the expression of the unit hydrograph have physical meaning comparison of the theory with field observations indicates that the theory works well a new tool for estimation of the temporal variation of aquifer recharge from that of excess infiltration is now available the tool is practical simple and physical and apparently works well as evidenced by comparisons with field observations

discontinuities in the shallow martian crust at lunae syria and sinai plana detailed photoclinometric profiles across 125 erosional features and 141 grabens in the western equatorial region of mars indicate the presence of three discontinuities within the shallow crust pits troughs and wall valleys tributary canyons within noctis labyrinthus and valles marineris and escarpments within the fretted terrain of sacra fossae and kasei valles show distinct erosional base levels at depths of 0 3 0 6 km 1 km and 2 3 km the shallowest discontinuity corresponds to thickness estimates for the ridged plains unit in this region and thus the discontinuity probably is the contact between a sequence of layered rock making up this unit and the underlying megaregolith the 1 km discontinuity is reflected in the base levels of erosion of all the features studied and it may correspond to the base of the proposed layer of ground ice model calculations using photoclinometric profiles of simple grabens corrected for the effects of mass wasting and the 60 dip of bounding faults measured from the exposed traces of faults on trough walls show that graben bounding faults consistently intersect at the mechanical discontinuity at about 1 km depth this discontinuity may represent an interface between ice laden and dry regolith ice laden and water laden regolith or pristine and cemented regolith a correlation between wall valley head depth and local thickness of the faulted layer suggests that the 1 km discontinuity also controlled the depth of the heads of sapping canyons there is no apparent relation between the pit and trough depths and the local thickness of the faulted layer which can be explained if pits and troughs developed by subsidence into underlying tension cracks that disrupted the 1 km discontinuity the data do suggest however that erosion of shallow pits and troughs was influenced by the 1 km discontinuity the third discontinuity at a depth of 2 3 km corresponds to the proposed base of the martian megaregolith and is probably the interface between overlying ejected breccia and in situ fractured basement rocks

recharge characteristics of an unconfined aquifer from the rainfall water table relationship the determination of recharge levels of unconfined aquifers recharged entirely by rainfall is done by developing a model for the aquifer that estimates the water table levels from the history of rainfall observations and past water table levels in the present analysis the model parameters that influence the recharge were not only assumed to be time dependent but also to have varying dependence rates for various parameters such a model is solved by the use of a recursive least squares method the variable rate parameter variation is incorporated using a random walk model from the field tests conducted at tomago sandbeds newcastle australia it was observed that the assumption of variable rates of time dependency of recharge parameters produced better estimates of water table levels compared to that with constant recharge parameters it was observed that considerable recharge due to rainfall occurred on the very same day of rainfall the increase in water table level was insignificant for subsequent days of rainfall the level of recharge very much depends upon the intensity and history of rainfall isolated rainfalls even of the order of 25 mm day 1 had no significant effect on the water table levels

a review of aridity and groundwater surface hydrological studies are seen as inadequate in hyperarid and arid areas to provide reliable estimates of recharge in most such areas surface discharges are not present so that assessments of groundwater resources are dependent upon ground interpretation and denied the flow control found in assessments elsewhere groundwater models show that gradients are sustained by long term dewatering and very small amounts of modern indirect recharge recharge indications are well within the error of a hydrological balance discharges appear equally small the development of groundwater in arid areas frequently faces problems of salination due to recycling of irrigation water and rising groundwater heads abstraction is often inadequately managed so that uncontrolled mining of groundwater occurs the advantage that groundwater has however is that it offers staged development and staged appraisal

using vertical rock uplift patterns to constrain the three dimensional fault configuration in the los angeles basin comparison of geologic uplift patterns with results of three dimensional mechanical models provides constraints on the fault geometry compiled by the south ern california earthquake center community fault model in the northern los angeles basin california the modeled uplift matches well the geologic pattern of uplift as sociated with the santa fe springs and coyote hills segments of the puente hills thrust fault but does not match structures to the west of the san gabriel river to better match the geologic patterns in this area alternative fault configurations were tested the best match to geologic uplift is attained with a model incorporating 1 a steep blind thrust fault at the location of the los angeles segment of the puente hills thrust system following interpretations of the las cienegas fault geometry at this location 2 removal of an inferred linking fault between the raymond and holly wood faults and 3 lateral continuation of the lower elysian park fault a blind low angle detachment at 10 km depth along strike to the northwest these geometric revisions alter the connectivity of northern los angeles basin faults and significantly improve the match of model uplift pattern to geologic data model results suggest that fault connectivity may be more important in governing fault slip rate than are fault dip and fault area the preferred model alters slip rates by 0 2 mm yr for the upper elysian park hollywood lower elysian park raymond sierra madre west and verdugo faults additionally the preferred model alters the surface area of several faults in the northern los angeles basin such as the puente hills thrust and the lower elysian park fault which may have important implications for seismic hazard assess ment in the northern los angeles basin

early thermal profiles and lithospheric strength of ganymede from extensional tectonic features abstract estimates of the brittle lithosphere thickness derived from the width and spacing of extensional tectonic features coupled with lithospheric strength envelopes brittle and ductile yield stress versus depth appropriate for ice allow the quantitative determination of early thermal profiles and lithospheric strength and stability on ganymede furrows and grooves indicate brittle lithospheric thicknesses of 5 10 and 2 5 km respectively assuming that their spacing is controlled by an extensional instability or that their width is controlled by the intersection depth of their bounding faults plots of the brittle and ductile yield stress versus depth for the icy lithosphere of ganymede show a linear increase in brittle strength with depth to a maximum at the brittle ductile transition followed by an exponential decrease in ductile yield stress with depth because the depth to the brittle ductile transition depends primarily on the thermal gradient the thickness of the brittle lithosphere can be used to calculate early thermal profiles of 1 5 6 and 4 5 20 km during the formation of the furrows and grooves respectively lithospheric strength the integral of the yield stress versus depth curve varied from 30 125 gpa m when the furrows formed to 5 30 gpa m when the grooves formed which correspond to maximum yield stresses of 6 11 and 2 5 6 mpa respectively these results indicate that the thermal gradient and lithospheric strength varied laterally by as much as a factor of 5 and that ganymede cooled in a highly inhomogeneous manner with significant lateral thermal anomalies finally this analysis provides a straightforward explanation for the stability of large remnants of cratered terrain such as galileo regio that had a low thermal gradient and strong lithosphere in contrast to small remnants of cratered terrain that were fractured and broken up by grooved terrain as a result of higher thermal gradients and weaker lithospheres

grooved terrain on ganymede first results from galileo high resolution imaging abstract high resolution galileo imaging has provided important insight into the origin and evolution of grooved terrain on ganymede the uruk sulcus target site was the first imaged at high resolution and considerations of resolution viewing geometry low image compression and complementary stereo imaging make this region extremely informative contrast variations in these low incidence angle images are extreme and give the visual impression of topographic shading however photometric analysis shows that the scene must owe its character to albedo variations a close correlation of albedo variations to topography is demonstrated by limited stereo coverage allowing extrapolation of the observed brightness and topographic relationships to the rest of the imaged area distinct geological units are apparent across the region and ridges and grooves are ubiquitous within these units the stratigraphically lowest and most heavily cratered units lineated grooved terrain generally show morphologies indicative of horst and graben style normal faulting the stratigraphically highest groove lanes parallel ridged terrain exhibit ridges of roughly triangular cross section suggesting that tilt block style normal faulting has shaped them these extensional tectonic models are supported by crosscutting relationships at the margins of groove lanes thus a change in tectonic style with time is suggested in the uruk sulcus region varying from horst and graben faulting for the oldest grooved terrain units to tilt block normal faulting for the latest units the morphologies and geometries of some stratigraphically high units indicate that a strike slip component of deformation has played an important role in shaping this region of grooved terrain the most recent tectonic episode is interpreted as right lateral transtension with its tectonic pattern of two contemporaneous structural orientations superimposed on older units of grooved terrain there is little direct evidence for cryovolcanic resurfacing in the uruk sulcus region instead tectonism appears to be the dominant geological process that has shaped the terrain a broad wavelength of deformation is indicated corresponding to the voyager observed topography and may be the result of ductile necking of the lithosphere while a finer scale of deformation probably reflects faulting of the brittle near surface the results here form a basis against which other galileo grooved terrain observations can be compared

spectral analysis of groove spacing on ganymede grooves on ganymede are interpreted as extensional tectonic features whose regular spacing is an indicator of the thickness of a brittle surface layer or lithosphere at the time of deformation we have performed a statistical analysis of groove spacing on ganymede taking fourier transforms of 157 photometric profiles across sets of grooves and examining the resultant power spectra for peaks representing the dominant topographic periodicities the distribution of groove spacing on ganymede is approximately lognormal with a minimum of 3 5 km a maximum of 17 km and a mean of 8 4 km there is no correlation of groove spacing with latitude or longitude the most striking feature of the geographic distribution is that while groove spacing tends to be quite constant within a given groove set it can vary substantially from one groove set to another in a geographic region an exception is the uruk sulcus region with a mean groove spacing of 6 5 km and very little variability we examine several models that relate the observed groove spacing to lithospheric thicknesses the most important conclusion is that lithospheric thickness varied significantly from one groove set to the next while the grooves were being formed we examine four possible causes for the heterogeneous distribution variation in time of formation during a period in which the global mean heat flow was changing variation in strain rate from one groove set to the next local excursions in geothermal gradient caused by variations in the vigor of underlying convective upwellings and local excursions in geothermal gradient caused by resurfacing events the first three appear viable while the fourth requires very rapid groove formation due to the short cooling times involved

recharge from an ephemeral stream following wetting front arrival to water table after the infiltration wetting front from a river bed of an ephemeral stream in flood reaches the shallow water table the rate of recharge which is also that of infiltration is affected by the development of a groundwater mound the effect is practically immediate if the water content behind the wetting front is close to saturation an approximate analytical solution is developed in that case which predicts the time dependence of the recharge rate comparison with experimental results in the laboratory shows that the solution is excellent in spite of the assumptions necessary in the derivations as long as the ratio of river width over depth to water table exceeds 2 and as long as the ratio of initial saturated thickness over depth to the water table exceeds 2 5 the analytical solution is essentially exact under most field conditions these ratios are largely exceeded consequently the predictive equation for the time dependence of the recharge is both quite simple to use and adequately accurate for field applications

a possible stress interaction between large thrust and normal faulting earthquakes in the mexican subduction zone abstract a large nearly vertical normal faulting earthquake mw 7 1 took place in 1997 in the subducting cocos plate just beneath the ruptured fault zone of the 1985 michoacan mexico earthquake mw 8 1 we investigate the possibility of stress interaction between the two large events through a 3d analysis of coseismic stress change that was due to the first event taking into consideration the postseismic change and the dynamic rupture process of the second event in the middle portion of the subducting plate at depths below 30 km the calculated coseismic increase in the vertical shear stress and in the coulomb failure stress beneath the high stress drop zones of the 1985 earthquake is in the order of 0 4 to 0 8 mpa it was also found that the 1997 earthquake took place in the zone of maximum coseismic stress increase possible postseismic stress changes due to the subduction process or to the loading of the overriding continental lithosphere and from aseismic slip would enhance the coseismic stress change and hence the possibility of occurrence of a normal faulting earthquake in the subducting plate the dynamic rupture pattern of the 1997 event seems to be consistent with the inferred stress interactions introduction a large nearly vertical normal faulting earthquake mw 7 1 occurred on 11 january 1997 beneath the mi choacan segment of the mexican subduction zone santoyo

ice covered water volcanism on ganymede eruption of liquid h2o magmas along extensional fractures and graben bounding normal faults may have played a critical role in the development of ganymede s grooved terrain the resurfacing potential of a water magma is dependent on a variety of factors including the areal extent of the source region the rate of discharge the thickness of the flow and the time that it takes the flow to completely freeze to its base in this paper the thermal evolution of such a flow is considered in detail the minimum unfrozen lifetime of a 5 m flow is approximately 12 5 days while a 10 m flow would survive for at least 50 days heating resulting from factional head loss could reasonably extend these lifetimes by 50 or more with a discharge rate of the order of 1 10 km3 d 1 an individual volcanic water flow could flood an area of 104 km2 before freezing as the flow solidifies its volume will increase thus lifting and arching its protective ice cover extensional fractures may then develop in the ice subparallel to the graben walls these fractures could result in grooves directly given a sufficiently thick 1 km flow or they may simply act to concentrate various tectonic forces that could initiate groove producing faults

extensional tilt blocks on miranda evidence for an upwelling origin of arden corona subparallel ridges and troughs in the outer belt of arden corona on the uranian satellite miranda are interpreted as tilt blocks formed by extension and normal faulting fault scarps generally face outward from the corona exposing dark material in the subsurface reconstruction of faults along a deep rift zone bounding the corona suggests initial dips of 50 local extension reaches 70 extremely high in comparison to previous estimates of strain on icy satellites a rise adjacent to the rift zone is modeled as flexural and indicates an effective elastic lithospheric thickness of 2 km at the time of flexure the assumption that faulting has significantly weakened the lithosphere suggests a mechanical lithosphere thickness of 5 to 10 km corresponding thermal gradients in a frictionally controlled ice lithosphere are 8 to 20 k km 1 and lithospheric tensional strength is 0 4 to 1 8 mpa normal faulting in arden corona indicates that internal upwelling likely formed the corona and the outward facing direction of faults is consistent with such a model an upwelling origin of miranda s coronae eliminates the need to invoke catastrophic breakup and reaccretion of the satellite as an explanation for its surface geology

structures of the zagros fold thrust belt in iran the zagros fold thrust belt in iran forms the external part of the zagros active orogenic wedge it includes a sequence of heterogeneous latest neoproterozoic phanerozoic sedimentary cover strata 7 to 12 km thick and composed of alternating incompetent and competent layers overlying precambrian crystalline basement with a complex pre zagros structural fabric balancing structures of the cover statigraphic units in the zagros fold thrust belt requires in sequence and out of sequence involvement of the precambrian basement in the deformation six detailed balanced and retrodeformable cross sections which are constructed based on geological and geophysical data across various sectors of the belt show fault bend and fault propagation folds interpreted to have formed by slip on their subjacent thrusts out of sequence basement rooted thrusts as the interpretations in the constructed cross sections suggest have breached the cover basement interface and using incompetent cover strata for propagation cut across the cover structures and have created associated new folds superimposed upon the pre existing structures this style of deformation which has resulted in structural complexity of the belt characterizes a 200 to 300 km wide zone of distributed partly synchronous deformation with along strike and across strike variations it also implies that the zagros fold thrust belt as the external part of the orogenic wedge is still in its subcritical condition with internal deformation to achieve a critical taper in creating structural complexity in addition to out of sequence thrusting mechanically weak layers evaporites and mudstones of the cover strata have played a significant role by providing several detachment horizons shortening estimates across the belt are variable based on the constructed cross sections and their restorations minimum shortening estimates range from 16 percent to 30 percent in different sectors of the belt

global contraction expansion and polar lithospheric thinning on titan from patterns of tectonism we investigate the underlying physical processes that govern the formation and evolution of titan s tectonic features this is done by mapping mountain chains and hills using cassini radar data obtained during titan flybys t3 to t69 our mapping of mountain chains and hills reveals a global pattern east west orientations within 30 of the equator and north south between 60 latitude and the poles this result makes titan one of the few solar system bodies where global processes rather than regional processes dominate tectonism after comparison with five global stress models showing theoretical mountain chain orientations we suggest that either global contraction coupled with spin up or global expansion coupled with despinning could explain our observations if coupled with a lithosphere thinner in titan s polar regions

from infiltration to recharge use of a parametric transfer function abstract the recharge of a water table aquifer involves transfer of the infiltration effective rainfall through the unsaturated zone in certain areas the depth at which the water table lies and the properties of the unsaturated zone can vary greatly and thus the determination as a function of time of the recharge actually arriving in the saturated aquifer can be rather difficult however we need to know this recharge in order to simulate the true behaviour of the aquifer in transient state in a regional digital model of the aquifer for the purpose of calibration or prediction the resolution of the exact flow equations in the unsaturated zone is possible but seems still to be far too complex for practical applications in this paper we first propose a methodology for the identification of the spatial variability of the infiltration transfer function using common climatic and piezometric data a parametrisation of these transfer functions using gamma distributions as basic functions is then suggested two practical examples make it possible to check the applicability of the procedure

possible breakup of dark terrain on ganymede by large scale shear faulting a system of arcuate furrows in galileo regio and marius regio two large blocks of ancient dark terrain has previously been proposed to be the remnant of an originally more concentric furrow set that was disrupted by shear estimates of the two regions poles of furrow concentricity indicate a considerable westward offset of the galileo regio pole these measurements suggest the possibility of about 500 km of left lateral offset of the two areas four additional independent structural indicators support this hypothesis there is evidence that shear deformation was concentrated along a major structural lineament which closely follows a small circle about 45 of arc of radius which encloses galileo regio and that a smaller amount of distributed shear occurred across an adjacent 500 to 1500 km wide band there is also morphologic evidence for zones of minor right lateral shear between central and southern marius regio and between barnard and nicholson regio and for a zone of minor left lateral shear in nun sulci stratigraphic relations indicate that any major shear offsets occurred before and during the earliest stages of grooved terrain formation before most grooves had formed and before virtually all light material had been emplaced however regionally dominant groove orientations are generally consistent with orientations expected for transtensional features either shear strain or the shear s driving mechanism may have had a long term effect on patterns of deformation of ganymede s lithosphere

fault type predictions from stress distributions on planetary surfaces importance of fault initiation depth faults on planetary surfaces initiate at depth where stresses due to the weight of overburden are important consequently the prediction of fault type from calculated stresses at depth can yield different faults than those predicted using the surface criteria commonly employed in geophysical models for elastic plate flexure models of mascon loading on the moon stresses calculated at the surface predict that the most likely faulting is strike slip for which there is no direct evidence at a distance from the basin center where grabens are found modifying these plate flexure calculations to account for the weak surface layer of ejecta megaregolith 1 3 km thick that overlies the relatively strong lunar lithosphere results in model stresses in the outer layers of the moon tens of bars that are an order of magnitude lower than in the lithosphere hundreds of bars because faults bounding lunar grabens initiate at the mechanical discontinuity between the megaregolith and lithosphere and because the reverse faults likely responsible for wrinkle ridges probably initiate at the basalt basin floor contact 0 5 2 km deep model stresses must be calculated at these depths superposing nonisotropic stresses due to the weight of the overburden at the depths of these mechanical discontinuities with plate flexure model stresses correctly predicts maximum stress differences in an interior zone of expected wrinkle ridges surrounded by a zone of concentric normal faults or grabens and effectively eliminates the strike slip zone in agreement with observations the absence of strike slip faults from almost all planetary and satellite surfaces may be explainable if lithospheric deformation model stresses are calculated at important shallow crustal mechanical discontinuities where the maximum compressive stress is vertical thereby favoring the formation of normal faults if true mechanical discontinuities in the shallow crusts of planets and satellites play an extremely important and hitherto unrecognized role in the formation of structures observed on their surfaces

ring geometry on ganymede and callisto abstract arguments have been made based on geometry for both an impact and an internal origin for the ancient partially preserved major furrow system of ganymede zuber and parmentier concluded that furrows are not concentric but could be impact related if multiringed structures on icy satellites are initially noncircular we examine the geometry of the valhalla ring structure on callisto in order to assess the circularity of an unmodified ring system despite prominent local meandering the only gross deviations from concentricity in the valhalla system are found in the outer northeast quadrant of the system here a number of ring segments intersect small circles about the center at angles up to 30 the ganymede furrow system was remapped to make use of improvements in coordinate control the least squares center of curvature determined using natural weighting for all furrows in marius and galileo regio is 20 7 1 1 s 179 2 1 1 w 2 uncertainty furrows in marius and galileo regio are reasonably concentric are much more circular than previously estimated and probably once covered at least an entire hemisphere of ganymede in addition at least three other multiring systems of varying size are identified on ganymede indicative of a projectile population thus we find furrow geometry and occurrence are consistent with an impact origin deviations of some furrows from concentricity about the center of curvature on the scale of those found at valhalla do exist as in the case of valhalla these variations are principally confined to outer regions of the structure and are interpreted as inherent properties of multiringed structures on icy satellites the cause s of this may be in the ring formation mechanism itself but are more likely due to variations in preexisting lithospheric mechanical properties the perceived present nonalignment of the assumed originally concentric furrows has been used to argue for large scale lateral motion of dark terrain blocks in ganymede s crust presumably in association with bright terrain formation the overall alignment of furrows as well as the inherent scatter in centers of curvature for subregions of galileo and marius regio do not support this hypothesis

fold geometry at sheep mountain anticline wyoming constructed using airborne laser swath mapping data outcrop scale geologic mapping and numerical interpolation 1 constraints available at the earth s surface on the geometry of geologic folds often are discontinuous consisting of scattered bedding surface outcrops representing the position and orientation of different stratigraphic surfaces for this reason characterization of fold geometry from surface data by methods such as sequential balanced cross sections remains a subjective and interpretive process we present a new method for modeling the geometry of kilometer scale folds using dense precise topographic data available from airborne laser swath mapping alsm outcrop scale geologic mapping and a reproducible numerical interpolation method that is free of subjectivity geologic mapping at sheep mountain anticline wyoming enables the association of hundreds of thousands of alsm data points with 14 weathering resistant bedding surfaces from seven different stratigraphic units ranging in age from mississippian to cretaceous these data supplemented by several hundred strike and dip measurements constraining local orientation of folded strata are projected to the stratigraphic position of a single surface and used as constraint for a smoothed minimum curvature spline interpolation to generate a continuous representation of fold geometry both strengths and weaknesses of the new method are discussed in the context of comparison between the new surface model and an existing model constructed by traditional methods

terrain types and local scale stratigraphy of grooved terrain on ganymede grooved terrain is subdivided on the basis of pervasive morphology into 1 groove lanes elongate parallel groove bands 2 grooved polygons polygonal domains of parallel grooves 3 reticulate terrain polygonal domains of orthogonal grooves and 4 complex grooved terrain polygons with several complexly cross cutting groove sets detailed geologic mapping of select areas employing previously established conventions for determining relative age relations reveals a general three stage sequence of grooved terrain emplacement first dissection of the lithosphere by throughgoing grooves and pervasive deformation of intervening blocks second extensive flooding and continued deformation of the intervening blocks third repeated superposition of groove lanes concentrated at sites of initial throughgoing grooves this sequence is corroborated by crater density measurements dominant orientations of groove sets are parallel to relict zones of weakness that probably were reactivated during grooved terrain formation groove lane morphology and development consistent with that predicted for passive rifts suggests a major role of global expansion in grooved terrain formation

a generalized 3 d geological and hydrogeological conceptual model of granite aquifers controlled by single or multiphase weathering summary the weathered layers of crystalline rocks form aquifers that are of prime interest for water supply in hard rock areas these weathering profiles generally develop under both stable geodynamic conditions weathering rate erosion rate and a hydrolysing climate they are composed of thick stratiform layers that follow the paleo landscape paleotopography and thus present a gently dipping sequence at a regional scale the structure and the hydrodynamic properties of the weathering profile of a granitic area 53 km 2 maheshwaram catchment state of andhra pradesh india were characterized in detail and mapped from observations on outcrops 80 vertical electric soundings and lithologs from 45 borewells in which flowmeter measurements and injection tests were also performed to characterize the hydraulic conductivities of the conductive fissure zones the structure of the weathering profile results from a multiphase process an ancient weathering profile was partly eroded down to its fissured layer it was later re weathered more or less parallel to the current topographic surface this peculiar structure is linked to the geodynamic history of the indian peninsula that underwent alternate weathering and erosion dominated phases the profile is thus composed from top to bottom up to a total depth of 35 m of sandy regolith saprolite 1 3 m 10 15 m of laminated saprolite containing unusual preserved fissures and a 15 20 m thick fissured layer by comparing various case studies in similar terrain a generalized 3 d geological and hydrogeological conceptual model of granite type aquifers granites gneisses etc is proposed in granite type rocks single weathering or multiphase weathering and erosion processes induce similar geological structures a few main geological differences arise from the comparison of single phase and multiphase weathering profiles i in the later the respective thicknesses of the various layers can be deeply modified ii the ancient fissured layer can be re weathered and the resulting new laminated layer may contain quite well preserved and conductive ancient fissures and iii the upper part of the fissured layer is more densely fissured as a result of the same weathering processes the fissures from the fissured layer of single phase or multi phase profiles exhibit very similar hydraulic conductivities and show both a higher density of conductive fissures at the top of the layer the preserved ancient fissures within the laminated layer of a multiphase profile are partly obliterated by the recent weathering their hydraulic conductivity is thus significantly reduced nevertheless they do significantly contribute to borewell yield these weathering induced fissures provide most of the aquifer permeability the use of such a conceptual model for the precise geological mapping of the weathering structure appears to be a prerequisite for groundwater development and management in hard rock areas as it answers to several key issues

estimating aquifer recharge due to rainfall abstract an existing dynamic model of the annual water balance is modified to account for two phenomena peculiar to arid climates i e variable rainy season length and soil dessication during the dry season model parameter values are estimated for two locations in the central zone of saudi arabia and the cumulative distribution function of annual recharge from precipitation is found for two of the primary sedimentary aquifers outcripping in this zone results quantify the large uncertainty of annual recharge in such climates and confirm the accepted notion that these aquifers are being mined

proteus geology shape and catastrophic destruction abstract proteus with a mean radius of 209 8 km is the largest irregular shaped icy body in the solar system it has a primitive heavily cratered surface its most prominent feature is an impact crater 255 km in diameter and 10 to 15 km deep relatively one of the largest craters in the solar system this prominent crater is similar in relative size to giant impacts on several other planets and satellites all of which are larger than a recent theoretical limit for catastrophic disruption consistency is obtained by inclusion of reaccumulation in the disruption analysis based on this reanalysis proteus was not brought to the brink of catastrophic destruction by the giant impact but only to the limit beyond which the surface of the impacted body and the form of the disrupting crater are modified beyond recognition a network of large streaks interpreted as troughs are also discernable this network too extensive to be explained by strains produced in traditional thermal history calculations may represent the onset of significant internal disruption in near catastrophic impacts proteus sphericity is near unity but it has one of the roughest surfaces known thus proteus is a transitional object in the irregular spherical shape spectrum for icy satellites its global figure is relaxed but its surface features are unrelaxed proteus intermediate relaxation state requires relatively high internal temperatures the required temperatures and the observed radius of the shape transition for icy bodies is consistent with radiogenic heating in bodies with deep porous regoliths

estimating infiltration recharge using a response function model abstract rainfall infiltration influences both the quantity and quality of groundwater systems the knowledge of the process of infiltration recharge is of great importance to the management of groundwater systems and the hydraulically connected streams in this study a response function model is developed to estimate soil water flux at the water table or the process of infiltration recharge from rainfall and evaporation data the gamma probability density function is modified to represent the travel time distribution of infiltrating water by rainfall events the travel time distribution is used to determine the recharge process according to the effective infiltration of a rainfall event the effective infiltration is the amount of soil water pushed down into groundwater by infiltrating water of a rainfall event and is evaluated based on the vadose zone soil water balance superposition is employed to compute the recharge rate produced by a sequence of rainfall events estimations of soil water flux at different groundwater depths are compared with lysimetric observations in the field good agreements between the estimated and observed results confirm the reliability of the response function model for predicting infiltration recharge processes

slip distributions on intersecting normal faults abstract slip distributions on normal faults often are asymmetric and display multiple local maxima numerically computed slip distributions from elastic models indicate that such irregular slip distributions can be caused by mechanical interaction between intersecting faults that produce local perturbations of the stress field resolved on the faults a three dimensional boundary element model based on the displacement discontinuity method has been used to analyze the mechanical interaction of faults that form y or t shaped intersections slip distributions are asymmetric with a steeper slip gradient toward the line of intersection multiple slip maxima occur depending on the angle between the faults but generally they are not located along the intersections nor at the fault centers examples of intersecting normal faults taken from oil reservoir seismic surveys and sandbox experiments have been used to confirm the application of the theoretical results despite considerable simplifications in terms of geometry and boundary conditions the computed slip distributions capture the characteristics of the observed slip distributions

viscoelastic models of tidal heating in enceladus abstract tidal heating in enceladus is investigated using multilayered viscoelastic models of the satellite dissipation in a homogeneous maxwell model of enceladus at the current eccentricity can be as large as 920 gw nearly a factor of 2000 greater than previously thought reflecting the fact that the dynamic love number can approach unity the elastic love number 10 3 the theoretical tidal heating maximum violates an upper bound based on saturn s q and models with this much heating are unreasonable plausible multilayered models are shown to be thermally stable at the current eccentricity with 10 km thick lithosphere and surface heat flow 5 mw m 2 the models require a combination of near surface insulation subsurface solar heating or anomalously low lithosphere conductivity to simultaneously fit dynamic and geologic constraints a two layer model with a conductive lithosphere over a maxwell mantle has mantle viscosity of about 10 13 pa sec and mantle temperature about 210 k a three layer model with an internal ocean of accumulated nh 3 h 2 o eutectic melt that decouples the lithosphere from a maxwell core has slightly lower internal viscosity and slightly higher temperature than the two layer model dissipation in the ocean layer may be significant if the tidally forced flow is turbulent the models suggest that enceladus thermal and dynamical evolution may have been relatively simple involving only dione in a 2 1 resonance the current eccentricity could have been maintained since resonance onset with recurring surface activity due to a thermally active interior

sedimentary and diagenetic controls on the multiscale fracturing pattern of a carbonate reservoir the madison formation sheep mountain wyoming usa a multidisciplinary approach has been applied to characterize the madison formation in the sheep mountain anticline at different scales in order to illustrate the relationship between sedimentology diagenesis and fracturing pattern sedimentary facies are organized into three types of elementary facies sequences showing different vertical evolutions of their petrophysical properties this is controlled by the double influence of the initial sedimentary facies and the diagenetic evolution three main sets of fractures related to the sevier and laramide compressive phases and to the folding of sheep mountain have been described at three orders of scale at small scale the sevier related set i and folding related set iii are the most abundant set ii dated from the early stage of the laramide compression exhibits the highest fracture intensity there is also a clear faciologic control on the fracture intensity small scale mechanical units correspond to entire facies sequences when no or little petrophysical property contrasts between beds are observed conversely small scale mechanical units correspond to each bed of a facies sequence in the case of high contrasts of petrophysical properties between beds at intermediate scale set ii is not present and sets i and iii show the highest fracture intensities the latter are partly controlled by the mechanical unit thickness intermediate and large scale mechanical unit distribution is mainly controlled by the overall faciologic vertical stacking pattern and by the position across the sheep mountain anticline forelimb or backlimb sheep mountain outcrops provide a good spatial representation of the carbonate reservoir heterogeneities from the micro to the field scale illustrating the complexity of fractured carbonate reservoirs

the hydrogeology and groundwater resources development of the cambro ordovician sandstone aquifer in saudi arabia and jordan abstract the saq cambro ordovician sandstones form the major national aquifer in saudi arabia and jordan significant abstraction of groundwater has taken place since the early 1950s and monitoring of the aquifer responses indicates a moderate transmissivity but high specific yield the groundwater quality is excellent for irrigation which is the present major use and is also good for potable purposes although large drawdowns are being experienced locally in confined areas of the aquifer the unconfined area responses show the aquifer to have an excellent potential for development under groundwater mining principles that may be considered for use outside the areas of occurrence

the topography of ganymede s grooved terrain abstract using the technique of photoclinometry topographic profiles across areas of grooved terrain and several other features on ganymede have been constructed the grooved terrain examined consists of subparallel grooves spaced 3 10 km apart topographic amplitudes are typically 300 400 m with a maximum of about 700 m slopes are very gentle and tend to be primarily concave upward very few major positive relief features exist on ganymede the most important of these is a broad gently sloping dome shaped feature 260 km in diameter and over 2 km high

the formation of ganymede s grooved terrain numerical modeling of extensional necking instabilities abstract ganymede s grooved terrain likely formed during an epoch of global expansion when unstable extension of the lithosphere resulted in the development of periodic necking instabilities linear infinitesimal strain models of extensional necking support this model of groove formation finding that the fastest growing modes of an instability have wavelengths and growth rates consistent with ganymede s grooves however several questions remain unanswered including how nonlinearities affect instability growth at large strains and what role instabilities play in tectonically resurfacing preexisting terrain to address these questions we numerically model the extension of an icy lithosphere to examine the growth of periodic necking instabilities over a broad range of strain rates and temperature gradients we explored thermal gradients up to 45 k km 1 and found that at infinitesimal strain maximum growth rates occur at high temperature gradients 45 k km 1 and moderate strain rates 10 13 s 1 dominant wavelengths range from 1 8 to 16 4 km post extension our infinitesimal growth rates are qualitatively consistent with but an order of magnitude lower than previous linearized calculations when strain exceeds 10 growth rates decrease limiting the total amount of amplification that can result from unstable extension this fall off in growth occurs at lower groove amplitudes for high temperature gradient thin lithosphere simulations than for low temperature gradient thick lithosphere simulations at large strains this shifts the ideal conditions for producing large amplitude grooves from high temperature gradients to more moderate temperature gradients 15 k km 1 we find that the formation of periodic necking instabilities can modify preexisting terrain replacing semi random topography up to 100 m in amplitude with periodic ridges and troughs assisting the tectonic resurfacing process despite this success the small topographic amplification produced by our model presents a formidable challenge to the necking instability mechanism for groove formation success of the necking instability mechanism may require rheological weakening or strain localization by faulting effects not included in our analysis

ecoulement sature et non sature de l eau souterraine vers des drains en aquifere a nappe libre the drainage of sports fields highways farm lands and covers for wastes corresponds to the drainage of a shallow unconfined aquifer resting on a horizontal or sloping impervious substratum the seepage partly saturated and partly unsaturated is thus described by nonlinear equations that are not easy to solve a few analytical solutions exist they were obtained after several simplifying assumptions are they realistic in this paper comparisons are made between predictions from analytical solutions and those from numerical resolutions for saturated and unsaturated seepage under steady and transient states the analytical solutions predict a water table and flow rates that differ significantly from those of the numerical resolutions and are sometimes unrealistic corrections to the analytical solutions have already been proposed to account for the vadose zone despite such corrections the published solutions to drainage problems may be inaccurate in engineering projects where the duration of dra

morphological mapping of ganymede investigating the role of strike slip tectonics in the evolution of terrain types abstract the heavily fractured surface of ganymede displays many morphologically distinctive regions of inferred distributed shear and strike slip faulting that may be important to the structural development of its surface to better understand the role of strike slip tectonism in shaping this complex icy surface we perform detailed mapping at nine sites using galileo and voyager imagery noting key examples of strike slip morphologies where present these four morphological indicators are en echelon structures strike slip duplexes laterally offset pre existing features and possible strained craters we map sites of both light grooved terrain nun sulci dardanus sulcus tiamat sulcus uruk sulcus and arbela sulcus and terrains that are transitional from dark to light terrains nippur and philus sulci byblus sulcus anshar sulcus and the transitional terrain of northern marius regio at least one if not more of the four strike slip morphological indicators are observed at every site suggesting strike slip tectonism is indeed important to ganymede s evolutionary history byblus sulcus is the only mapped site where the presence of strike slip indicators is limited to only a few en echelon structures every other mapped site displays examples of at least two types with arbela sulcus containing candidate examples of all four in addition quantification of morphological characteristics suggests related rotation between sites as evidenced by the predominant nw se trend of mapped features within the light terrain present in five different sites nun tiamat uruk nippur philus byblus and anshar sulcus moreover incorporation of strike slip tectonism with pre existing observations of extensional behavior provides an improved synoptic representation of ganymede s tectonic history

estimation of fault propagation distance from fold shape implications for earthquake hazard assessment a numerical grid search using the trishear kinematic model can be used to extract both slip and the distance that a fault tip line has propagated during growth of a fault propagation fold the propagation distance defines the initial position of the tip line at the onset of slip in the santa fe springs anticline of the los angeles basin we show that the tip line of the underlying puente hills thrust fault initiated at the same position as the 1987 magnitude 6 0 whittier narrows earthquake

elastic modeling of fault driven monoclinal fold patterns abstract the traces of buried dip slip faults are often reconstructed by assuming that they follow the plan view patterns of the overlying monoclines and by interpolating between seismic profiles to place constraints on such reconstructions the uplift pattern produced by prescribed slip on a set of buried reverse faults is calculated assuming that the overall plan view fold pattern is determined by faulting induced elastic strain while inelastic relaxation and gravitation only modify the details of the finite cross sectional geometry of the folds faults are represented by dislocation planes embedded in an elastic medium which is otherwise continuous and uniform these assumptions are applied to the monoclines of the negev israel driven by high angle reverse faults a first model closely follows the existing structural map which is based on field mapping and seismic profiles and is characterized by long continuous faults slip is taken as uniform and proportional to fault length such a model does not produce either the pattern or the relative structural elevation of the overlying monoclines and in particular the observed fold axis variations in a second model we introduce fault en echelon discontinuities and slip gradients at fault terminations relative slip on faults underlying various structures is proportional to their observed structural elevations these features produce a reasonable approximation of the overall observed structural configuration of the monoclines it can thus be concluded that 1 the overall patterns of fault driven folds are determined by the coseismic elastic strain field 2 fault segmentation is a major cause of observed axis undulations of fault driven folds 3 finite dip slip offset at depth is proportional to the observed structural elevation and 4 along strike slip gradients account for variations of the structural elevation in that direction

lithologically constrained rainfall lcr method for estimating spatio temporal recharge distribution in crystalline rocks summary a lithologically constrained rainfall lcr method has been developed to estimate the spatial and temporal natural recharge distribution a complex and high variable hydrological parameter in hard rocks the lithological constraints are coupled to the rainfall in terms of soil resistivity s and vadose zone thickness h in the absence of a bore well in an over exploited area with deep water table it is difficult to get the water table precisely from any surface exploration methods such as remote sensing and geophysics however water table variation being close to the basement in this situation depth to basement was used as an alternative to the vadose zone thickness which yielded equally reliable estimate the method facilitates to estimate temporal due to time varying rainfall and spatial due to lithological variability distribution of natural recharge for many numbers of years say 50 by inputting the precipitation of corresponding years provided once hydrogeophysical s and h parameters are known the method has been successfully validated and applied to study the watershed scale in a granitic terrain and found that the variability is much higher than otherwise expected or estimated by a single method

lithospheric stresses due to radiogenic heating of an ice silicate planetary body implications for ganymede s tectonic evolution thermal evolution models of differentiated and undifferentiated ice silicate bodies containing longlived radiogenic heat sources are examined lithospheric stresses arise due to volume change of the interior and temperature change in the lithosphere for an undifferentiated body the surface stress peaks early in the evolution while in the differentiated case stresses peak later and continue to accumulate for longer periods of time the variation of near surface stress with depth shows that stresses for the undifferentiated body initially penetrate to great depths but rapidly concentrate within a few kilometers of the surface for the differentiated body elastic stresses never accumulate at a depth greater than a few kilometers these models are applied to consider long term radioactive heating as a possible mechanism of tectonic activity and bright terrain formation on ganymede

two dimensional modelling of water table fluctuation in response to localised transient recharge abstract an analytical solution of the linearised boussinesq equation is presented and used to predict the spatio temporal variation of the water table in a finite aquifer system in response to a transient recharge from an overlying rectangular basin the boundary conditions of the finite aquifer are taken as fixed heads which would apply when the aquifer system is surrounded by open water bodies application of the solution is illustrated with the help of a numerical example the results would also have applications in studying stream aquifer interaction in the presence of transient recharge

the orbital thermal evolution and global expansion of ganymede article history the tectonically and cryovolcanically resurfaced terrains of ganymede attest to the satellite s turbulent geologic history yet the ultimate cause of its geologic violence remains unknown one plausible scenario suggests that the galilean satellites passed through one or more laplace like resonances before evolving into the current laplace resonance passage through such a resonance can excite ganymede s eccentricity leading to tidal dissipation within the ice shell to evaluate the effects of resonance passage on ganymede s thermal history we model the coupled orbital thermal evolution of ganymede both with and without passage through a laplace like resonance in the absence of tidal dissipation radiogenic heating alone is capable of creating large internal oceans within ganymede if the ice grain size is 1 mm or greater for larger grain sizes oceans will exist into the present epoch the inclusion of tidal dissipation significantly alters ganymede s thermal history and for some parameters e g ice grain size tidal q of jupiter a thin ice shell 5 to 20 km can be maintained throughout the period of resonance passage the pulse of tidal heating that accompanies laplace like resonance capture can cause up to 2 5 volumetric expansion of the satellite and contemporaneous formation of near surface partial melt the presence of a thin ice shell and high satellite orbital eccentricity would generate moderate diurnal tidal stresses in ganymede s ice shell larger stresses result if the ice shell rotates non synchronously the combined effects of satellite expansion its associated tensile stress rapid formation of near surface partial melt and tidal stress due to an eccentric orbit may be responsible for creating ganymede s unique surface features

insights into fold growth using fold related joint patterns and mechanical stratigraphy despite how common folds are as structural features along strike fold propagation has proven elusive to document however if a fold grows laterally along its axis early formed fold related joints may differ significantly in orientation from joints that form later in this paper we integrate mechanical stratigraphy with joint pattern analysis to determine relative timing of jointing additionally we demonstrate that joint patterns can be related to stresses on both the top and bottom of the bed during flexure we present joint data from eight sedimentary beds on the fold terminus at sheep mountain anticline wyoming usa the joint patterns around the terminus show two distinct patterns joints in six of the beds show a radial pattern around the terminus whereas joint patterns in the two remaining beds differ from proximal units despite being in the same structural position fracture resistance calculations confirm that the beds with mis oriented fractures are less resistant to fracturing than other units in the study and therefore would have fractured earlier in fold growth history we present a plate bending model that illustrates potential joint patterns around a plunging fold nose from stresses along both the top and bottom of the bed the joint strike predictions for the area in front of the inflection line on the fold nose match the orientations in our less resistant beds which are now positioned behind the inflection line suggesting that the fold grew laterally the combined analysis of fracture pattern and mechanical stratigraphy provides a new way to investigate fold evolution

estimation of duration of subaerial exposure in shallow marine limestones an isotopic approach abstract subaerial exposure surfaces in shallow marine limestones may represent a significant period of nondeposition and or erosion the minimum duration of subaerial exposure is estimated through modeling the maximum whole rock 13c depletion toward exposure surfaces in vadose meteorically altered limestones the model simulates the water rock interaction that caused the depletion and calculates the volume of meteoric water needed to achieve the observed 13c value then the duration of vadose meteoric diagenesis which approximates exposure duration is the volume of water divided by the infiltration rate of vadose water sensitivity tests indicate that estimated duration is moderately sensitive to many input parameters particularly the isotope composition and concentration of total dissolved carbon in vadose water sediment porosity and infiltration rate of vadose water the method is mostly effective in estimating exposure durations of less than 400 ky the estimated durations of nine subaerial exposures in pleistocene reef tracts of barbados west indies agree well with available radiometric dates application of the method to subaerial exposures in mississippian pennsylvanian and cretaceous shallow marine limestones confines their durations to 21 54 ky and distinguishes exposures of different durations the proposed method offers a potential tool and direction in estimating minimum duration of stratal hiatuses in meter scale stratigraphic studies

the galilean satellites nasa s galileo mission to jupiter and improved earth based observing capabilities have allowed major advances in our understanding of jupiter s moons io europa ganymede and callisto over the past few years particularly exciting findings include the evidence for internal liquid water oceans in callisto and europa detection of a strong intrinsic magnetic field within ganymede discovery of high temperature silicate volcanism on io discovery of tenuous oxygen atmospheres at europa and ganymede and a tenuous carbon dioxide atmosphere at callisto and detection of condensed oxygen on ganymede modeling of landforms seen at resolutions up to 100 times as high as those of voyager supports the suggestion that tidal heating has played an important role for io and europa

assessing the work budget and efficiency of fault systems using mechanical models 1 we examine the work energy budget of actively deforming fault systems in order to develop a means of examining the systemic behavior of complex fault networks work done in the deformation of a faulted area consists of five components 1 work done against gravity in uplift of topography wgrav 2 internal energy of the strained host rock wint 3 work done resisting friction during slip on faults wfric 4 seismic energy released in earthquake events as ground shaking wseis and 5 work done in initializing new faults and propagating existing faults wprop the energy budget of a fault system can be expressed as wtot wgrav wint wfric wseis wprop for a balanced energy budget the total of these five components will equal the external tectonic work applied to the system we examine the work balance within hypothetical and simulated two dimensional static fault systems using mechanical models the boundary element method models produce a balanced work budget for both simple and complex fault system models the presence of slipping faults reduces the internal strain energy of the faulted area wint at a cost of work done against friction and gravity and propagation and seismic energy where applicable calculations of minimum work deformation match expected deformation paths indicating the usefulness of this approach for evaluating efficiency in more complex systems the partitioning of various work terms may express the relative efficiency or maturity of fault systems furthermore calculation of potential seismic energy release can provide an upper bound to earthquake seismic moment assessments

sequential development of grooved terrain and polygons on ganymede grooves on ganymede have been interpreted as fractures that result from extensional tectonics which accompanied by some type of resurfacing changed relatively low albedo heavily cratered terrain to higher albedo less cratered grooved terrain the formation of grooves involved initial fracturing of cratered terrain resurfacing confined within these fractures and subsequent fracturing of resurfacing material crosscutting and terminating or t structural relationships among grooves groove sets and cratered terrain indicate that grooved terrain developed in three stages the formation of primary grooves marks the initial breakup of cratered terrain secondary grooves generally terminate against primary grooves and complete the breakup of cratered terrain into polygons that are mechanically isolated from adjacent polygons in the final stage 3 polygons of cratered terrain are fractured resurfaced and the resurfacing material is subsequently fractured by a set of closely spaced parallel to subparallel grooves that terminate against the older primary and or secondary grooves in each of these stages the groove forming process occurs in the same sequence fracturing resurfacing and subsequent fracturing of resurfacing material but most of the area of grooved terrain is resurfaced during stage 3 the process may stop during any of the three stages yielding areas of fractured cratered terrain polygons of cratered terrain polygons which have been resurfaced but not subsequently fractured smooth terrain or completely grooved terrain regardless of place or time of development grooved terrain appears to have evolved according to the same sequential order of stages because the development of grooves within each stage created smaller isolated polygons out of larger areas this process has resulted in the break up of the surface of ganymede into progressively smaller and more equidimensional mechanical units

modeling the effects of unsaturated stratified sediments on groundwater recharge from intermittent streams abstract unsaturated stratified sediments beneath intermittent stream channels affect groundwater recharge from these streams using four different cases of sediment stratification we simulate transient variably saturated flow in a two dimensional 2 d vertical cross section between the stream and the underlying water table these cases include homogeneous sediments low permeability streambed sediments narrow low permeability lenses and extensive low permeability layers the permeability of the sediments in these cases greatly affects the timing and rate of channel loss and groundwater recharge flow patterns and the style of stream water table connection are controlled by the location and geometry of low permeability sediments in cases with homogeneous sediments and narrow low permeability lenses stream water table connection occurs by a saturated column advancing from above in cases with low permeability streambed sediments and extensive low permeability layers connection occurs by a water table mound building from below the style of stream water table connection suggests simplified physically based interaction models that may be appropriate for these settings we compared channel loss and groundwater recharge computed using two simplified models a darcian seepage equation and the green ampt infiltration equation with the results from our 2 d simulations simplified models using parameters from the 2 d simulations appear to perform well in cases with homogeneous and low permeability streambed sediments in cases with low permeability lenses or layers the simplified models require calibrated parameters to perform well

the role of fractures in the structural interpretation of sheep mountain anticline wyoming the development of fractures in the sedimentary layers of sheep mountain anticline a laramide asymmetric fault cored fold of the bighorn basin is documented and interpreted to constrain the kinematic evolution of the fold the fracture pattern is interpreted to identify five main fracture sets a fracture set striking 110 set i oblique to the future fold trend is interpreted as a regional fracture set that predates laramide compression a joint set set ii striking 045 and present in the hinge and backlimb is related to the ne oriented laramide compression just prior to and during initial anticline growth joints striking 135 set iii parallel to the fold trend are found within the hinge and are interpreted to have developed in response to the bending of layers the two youngest fracture sets are attributed to a late stage of fold growth a joint set set iv in the backlimb striking parallel to the set i fractures but vertical and a fracture set in the forelimb consisting of set i fractures reactivated as reverse faults the relative chronology mode of formation opening vs shearing and structural locations of these fractures suggest the following kinematics of folding at sheep mountain anticline little or no lateral fold propagation no hinge migration and limb rotation with only minor limb flexure and stretching

the tectonics of ganymede the surface of ganymede the largest icy jovian satellite is composed of two distinct terrain types showing abundant evidence of global scale tectonics there is geological evidence consistent with the formation of younger bright terrain by the emplacement of relatively clean ice into rift zones developed in the more silicate rich dark terrain

the geology of callisto the geology of callisto is not boring although cratered terrain dominates callisto a key end member of the jovian satellite system a number of more interesting features are apparent cratered terrain is broken into irregular mappable bright and dark subunits that vary in albedo by a factor of 2 and several relatively smooth units are depleted of small craters some of these areas may have been volcanically resurfaced lineaments including parallel and radial sets may be evidence for early global tectonism frost deposition occurs in cold traps and impact scars have formed from tidally disrupted comets geologic evidence suggests that callisto does have a chemically differentiated crust central pit and central dome craters and palimpsests are common the preferred interpretation is that a relatively ice rich material at depths of 5 km or more has been mobilized during impact and exposed as domes or palimpsests the close similarity in crater morphologies and dimensions indicates that the outermost 10 km or so of callisto may be as differentiated as on ganymede the geology of cratered terrain on callisto is simpler than that of cratered terrain on ganymede however orbital evolution and tidal heating may provide the answer to the riddle of why callisto and ganymede are so different malhotra 1991 we should expect a few surprises and begin to answer some fundamental questions when callisto is observed by galileo in late 1996

stress and strain patterns kinematics and deformation mechanisms in a basement cored anticline sheep mountain anticline wyoming 1 in order to characterize and compare the stress strain record prior to during and just after folding at the macroscopic and the microscopic scales and to provide insights into stress levels sustained by folded rocks we investigate the relationship between the stress strain distribution in folded strata derived from fractures striated microfaults and calcite twins and the development of the laramide basement cored sheep mountain anticline wyoming tectonic data were mainly collected in lower carboniferous to permian carbonates and sandstones in both rock matrix and veins calcite twins recorded three different tectonic stages the first stage is a pre laramide sevier layer parallel shortening lps parallel to fold axis the second one is a laramide lps perpendicular to the fold axis and the third stage corresponds to laramide late fold tightening with compression also perpendicular to the fold axis stress and strain orientations and regimes at the microscale agree with the polyphase stress evolution revealed by populations of fractures and striated microfaults testifying for the homogeneity of stress record at different scales through time calcite twin analysis additionally reveals significant variations of differential stress magnitudes between fold limbs our results especially point to an increase of differential stress magnitudes related to laramide lps from the backlimb to the forelimb of the fold possibly in relation with motion of an underlying basement thrust fault that likely induced stress concentrations at its upper tip this result is confirmed by a simple numerical model beyond regional implications this study highlights the potential of calcite twin analyses to yield a representative quantitative picture of stress and strain patterns related to folding

thermal stress tectonics on the satellites of saturn and uranus most of the major saturnian and uranian satellites have undergone some form of extensional tectonism and or resurfacing early in their histories we examine the stresses created by the early thermal evolution of these satellites and consider the geologic implications of these stresses starting from an initial accretional temperature profile we calculate the satellites temperature profiles as they evolve by conduction solid state convection when it occurs is handled using a simple parameterized convection scheme the effects of radiogenic heating and release of heat of phase change are included the thermal stresses built up in the satellites are then calculated assuming the satellites to have a maxwell viscoelastic rheology the stress calculation takes into account both the effects of thermal stresses and of shifts in the position of the ice i ice ii phase boundary in some satellites if accretion takes place in a cold gas free environment the stresses that build up in the smaller satellites mimas miranda and enceladus are minor in the larger satellites however stresses are large enough to cause fracturing and extensional tectonism under these circumstances the stresses result largely from rapid cooling contraction of a thin outer shell the ice ii ice i phase transition also contributes significantly for the largest satellites if accretion occurs in a warm gaseous nebula that dissipates rapidly stresses large enough to cause failure are attained in all of the satellites in all cases the material immediately underlying the zone of failure is the warmest in the satellite and hence may be buoyant and mobile enough to be extruded to the surface through fractures created by the extension we conclude that thermal stresses following accretion led to a substantial early episode of extensional tectonism and perhaps also associated resurfacing on many of the saturnian and uranian satellites if evidence of this early episode of extensional tectonism has survived subsequent impacts then the process may have been responsible for much of the early tectonism and resurfacing observed on these satellites if not then it may only be responsible for the very early global resurfacing that some of the satellites are inferred to have undergone