impact cratering in sandstone the memin pilot study on the effect of pore water abstract planetary surfaces are subjected to meteorite bombardment and crater formation rocks forming these surfaces are often porous and contain fluids to understand the role of both parameters on impact cratering we conducted laboratory experiments with dry and wet sandstone blocks impacted by centimeter sized steel spheres we utilized a 40 m two stage light gas gun to achieve impact velocities of up to 5 4 km s 1 cratering efficiency ejection velocities and spall volume are enhanced if the pore space of the sandstone is filled with water in addition the crater morphologies differ substantially from wet to dry targets i e craters in wet targets are larger but shallower we report on the effects of pore water on the excavation flow field and the degree of target damage we suggest that vaporization of water upon pressure release significantly contributes to the impact process

analytical solutions of seawater intrusion in sloping confined and unconfined coastal aquifers sloping coastal aquifers in reality are ubiquitous and well documented steady state sharp interface analytical solutions for describing seawater intrusion in sloping confined and unconfined coastal aquifers are developed based on the dupuit forchheimer approximation specifically analytical solutions based on the constant flux inland boundary condition are derived by solving the discharge equation for the interface zone with the continuity conditions of the head and flux applied at the interface between the freshwater zone and the interface zone analytical solutions for the constant head inland boundary are then obtained by developing the relationship between the inland freshwater flux and hydraulic head and combining this relationship with the solutions of the constant flux inland boundary it is found that for the constant flux inland boundary the shape of the saltwater interface is independent of the geometry of the bottom confining layer for both aquifer types despite that the geometry of the bottom confining layer determines the location of the interface tip this is attributed to that the hydraulic head at the interface is identical to that of the coastal boundary so the shape of the bed below the interface is irrelevant to the interface position moreover developed analytical solutions with an empirical factor on the density factor are in good agreement with the results of variable density flow numerical modelling analytical solutions developed in this study provide a powerful tool for assessment of seawater intrusion in sloping coastal aquifers as well as in coastal aquifers with a known freshwater flux but an arbitrary geometry of the bottom confining layer this article is protected by copyright all rights reserved

folding within seconds hypervelocity impacts of cosmic projectiles larger than 200 m diameter are capable of forming complex craters on earth at these craters shock loading shock damage and excavation flow are followed by a gravity driven collapse of the deep transient cavity such impact structures are characterized by a central uplift a flat crater floor and a terraced crater rim collapse induced deformation features like folds and brittle fault zones have many similarities to tectonic structures typical deformation patterns of complex terrestrial impact craters of 5 15 km diameter are compiled and analyzed with respect to their kinematic development unlike their tectonic counterparts deformation structures are always the result of non plane strain deformation and are formed in a single event that takes place in seconds to minutes to understand the high strain rate processes the microstructure of an impact induced fold of the crooked creek impact crater 7 km diameter missouri united states is investigated in detail a period of 20 30 s at the most is determined for the collapse phase of this crater the gross plastic deformation behavior of the fold is achieved by localized brittle deformation along millimeter to centimeter spaced fault zones forming a network of veins shock damage has fractured 40 of grain boundaries the onset of collapse and associated deformation started in rocks with a reduced cohesion and is friction controlled

a correction factor to account for mixing in ghyben herzberg and critical pumping rate approximations of seawater intrusion in coastal aquifers 1 the classic ghyben herzberg estimate of the depth of the freshwater saltwater interface together with the dupuit approximation is a useful tool for developing analytical solutions to many seawater intrusion problems on the basis of these assumptions strack 1976 developed a single potential theory to calculate critical pumping rates in a coastal pumping scenario the sharp interface assumption and in particular this analytical solution are widely used to study seawater intrusion and the sustainable management of groundwater resources in coastal aquifers the sharp interface assumption neglects mixing and implicitly assumes that salt water remains static consequently this approximation overestimates the penetration of the saltwater front and underestimates the critical pumping rates that ensure a freshwater supply we investigate the error introduced by adopting the sharp interface approximation and we include the effects of dispersion on the formulation of strack 1976 to this end we perform numerical three dimensional variable density flow simulations we find that strack s equations can be extended to the case of mixing zone if the density factor is multiplied by an empirically derived dispersion factor 1 t b 1 6 where t is transverse dispersivity and b is aquifer thickness we find that this factor can be used not only to estimate the critical pumping rate but also to correct the ghyben herzberg estimate of the interface depth its simplicity facilitates the generalization of sharp interface analytical solutions and good predictions of seawater penetration for a broad range of conditions

constraints on central uplift structure from the manicouagan impact crater recent drilling operations at the 90 km diameter late triassic manicouagan impact crater of quebec canada have provided new insight into the internal structure of a complex craters central region previous work had indicated that the impact event generated a 55 km diameter sheet of molten rock of relatively consistent originally 400 m thickness floran et al 1978 the drilling data reveals melt sheet thicknesses of up to 1500 m with kilometer scale lateral and substantial vertical variations in the geometry of the crater floor beneath the melt sheet the thickest melt section occurs in a 1500 m deep central trough encircled by a horseshoe shaped uplift of precambrian basement the uplift constitutes a modified central peak structure at least part of which breached the melt sheet mineralogical and compositional segregation differentiation of the thicker melt sheet section coupled with a lack of fractionation in the thinner units shows that the footwall geometry and associated trough structure were in place prior to melt sheet solidification marked lateral changes in sub melt sheet basement relief support the existence of a castellated footwall that was created by high angle impact related offsets of 100s to 1000s of meters this indicates that deformation during the modification stage of the cratering process was primarily facilitated by large displacement fault systems this work suggests that manicouagan is a central peak basin with rings which does not appear to fit with current complex crater classification schemes

effect of climate change on sea water intrusion in coastal aquifers there is increasing debate these days on climate change and its possible consequences much of this debate has focused in the context of surface water systems in many arid areas of the world rainfall is scarce and so is surface runoff these areas rely heavily on groundwater the consequences of climate change on groundwater are long term and can be far reaching one of the more apparent consequences is the increased migration of salt water inland in coastal aquifers using two coastal aquifers one in egypt and the other in india this study investigates the effect of likely climate change on sea water intrusion three realistic scenarios mimicking climate change are considered under these scenarios the nile delta aquifer is found to be more vulnerable to climate change and sea level rise copyright 1999 john wiley sons ltd

crater floor topography and impact melt sheet geometry of the sudbury impact structure canada terra nova 00 000 000 2010 abstract based on high resolution topography data and the geometry of geological contact traces at the surface we determined the orientation of layer interfaces of the sudbury igneous complex sic our analysis provides for the first time quantitative structural evidence for the thickness variation of its layers which supports an impact melt origin of the sic the present crater floor topography varies up to 400 m over distances of hundreds of metres to a few kilometres and up to 1500 m over a distance of about 25 km crater floor depressions are spatially associated with economically important sulphide mineral deposits which points to a viable exploration strategy finally observed variations in the width of the thermal aureole imparted by the sic on its host rocks are due to primary thickness variations of the sic rather than post impact deformation

the dynamic strength of an ordinary chondrite abstract dynamic and quasistatic unconfined compression experiments were performed on samples of the l5 ordinary chondrite macalpine hills mac 88118 the dynamic compressive strength measurements are the first of its kind for a stony meteorite and indicate that the material tested here exhibits significant increase in compressive strength with increasing strain rate this increase in compressive strength is larger than the increases typically observed in terrestrial rock specimens compressed over a similar range of strain rates the details of the failure process are investigated by recording images of the experiments in real time specifically the crack growth speeds in the dynamic compression experiments are measured from ultrahigh speed images these speeds are significantly lower than the speeds observed in terrestrial analogs that are typically used in numerical investigations of large scale impacts the implications of these measurements of strength and failure process are explored in the contexts of atmospheric disruption of meteors and impact cratering disruption of asteroids

chicxulub multiring impact basin size and other characteristics derived from gravity analysis the buried chicxulub impact structure in mexico which is linked to the cretaceous tertiary k t boundary layer may be significantly larger than previously suspected reprocessed gravity data over northern yucatan reveal three major rings and parts of a fourth ring spaced similarly to those observed at multiring impact basins on other planets the outer ring probably corresponding to the basin s topographic rim is almost 300 kilometers in diameter indicating that chicxulub may be one of the largest impact structures produced in the inner solar system since the period of early bombardment ended nearly 4 billion years ago

observations and interpretations at vredefort sudbury and chicxulub towards an empirical model of terrestrial impact basin formation the structural topographic and other characteristics of the vredefort sudbury and chicxulub impact structures are described assuming that the structures originally had the same morphology the observations interpretations for each structure are compared and extended to the other structures this does not result in any major inconsistencies but requires that the observations be scaled spatially in the case of vredefort and sudbury this is accomplished by scaling the outer limit of particular shock metamorphic features in the case of chicxulub scaling requires a reasoned assumption as to the formation mechanism of an interior peak ring the observations interpretations are then used to construct an integrated empirical kinematic model for a terrestrial peak ring basin the major attributes of the model include a set of outward directed thrusts in the parautochthonous rocks of the outermost environs of the crater floor some of which are pre existing structures that have been reactivated during transient cavity formation inward directed motions along the same outermost structures and along a set of structures at intermediate radial distances during transient cavity collapse structural uplift in the center followed by a final set of radially outward directed thrusts at the outer edges of the structural uplift during uplift collapse the rock displacements on the intermediate inward and innermost outward sets of structures are consistent with the assumption that a peak ring will result from the convergence of the collapse of the transient cavity rim area and the collapse of the structural uplift

pumping management of coastal aquifers using analytical models of saltwater intrusion 1 analytical models of saltwater intrusion in coastal aquifers of finite size are developed and utilized in an optimization methodology for determining the optimal pumping rates the models are based on the sharp interface approximation and the ghyben herzberg relation the governing equations are expressed in terms of a single potential and are solved analytically using the method of images to account for the aquifer boundaries the analytical models consider ambient flow and surface recharge the results are compared to numerical simulations indicating a good match as the number of images is increased the objective of optimization is to maximize the total pumping from the aquifer and a set of constraints protect the wells from saltwater intrusion the constraints are expressed using the analytical saltwater intrusion models two different constraint formulations are investigated the toe constraint formulation protects the wells from saltwater intrusion by not allowing the toe of the interface to reach the wells this formulation results in a nonlinear optimization problem which is solved using sequential quadratic programming sqp the potential constraint formulation on the other hand protects the wells by maintaining a potential at the wells larger than the toe potential this formulation results in a linear optimization problem which is solved using the simplex method several simulation runs indicate that the optimal solution is very sensitive to variations of recharge rates hydraulic conductivity heterogeneities etc the linear programming formulation besides being computationally simpler provides a safer solution than the nonlinear formulation

tidal influence on seawater intrusion in unconfined coastal aquifers studies of seawater intrusion in unconfined coastal aquifers typically neglect oceanic oscillations such as tides and assume a static seaward boundary condition defined by the mean sea level laboratory experiments and numerical simulations were conducted to investigate the influence of tidal oscillations on the behavior of the saltwater wedge for the conditions examined the experiments showed that an upper saline plume formed in the intertidal zone due to tide induced seawater circulation the presence of the upper saline plume shifted the fresh groundwater discharge zone seaward to the low tide mark and restricted the intrusion of the saltwater wedge the overall seawater intrusion extent as indicated by the wedge toe location was reduced significantly compared with the nontidal static case results from the numerical model matched these experimental observations and further demonstrated the similar type of tidal influence on the saltwater wedge in a field scale aquifer system the glover 1959 solution for predicting the saltwater wedge was modified to account for the tidal effect by including the tide induced circulation as a recharge to the aquifer the findings highlight the significant impact of the tide in modulating the groundwater behavior and salt freshwater dynamics not only within but also landward of the intertidal zone

structural geology of impact craters abstract the formation of impact craters is a highly dynamic and complex process that subjects the impacted target rocks to numerous types of deformation mechanisms understanding and interpreting these styles of micro meso and macroscale deformation has proved itself challenging for the field of structural geology in this paper we give an overview of the structural inventory found in craters of all size ranges on earth and look into the structures of craters on other planetary bodies structural features are discussed here that are caused by i extremely high pressures and temperatures that occur during the initial passage of the shock wave through the target rock and projectile ii the resulting flow field in the target that excavates and ejects rock materials and iii the gravitationally induced modification of the crater cavity into the final crater form a special focus is put on the effects that low angle impacting bodies have on crater formation we hope that this review will help both planetary scientists and structural geologists understand the deformation processes and resulting structures generated by meteorite impact

groundwater pumping in head controlled coastal systems the role of lateral boundaries in quantifying the interface toe location and maximum pumping rate summary the current study explores quantitatively the impact of lateral impermeable boundaries on groundwater pumping in head controlled coastal systems based on the potential theory and the image well superposition method we compare the interface toe location and maximum pumping rate among three scenarios that assume s1 an infinite domain width and a finite domain length s2 a finite domain width and length and ss an infinite domain width and length focusing exclusively on boundary effects the upstream freshwater discharge is assumed the same for all scenarios regardless of the variation in domain size it is found that the impact from both inland and lateral boundaries could play a significant role on the interface toe location and maximum pumping rate defined as the maximum allowable pumping rate that will not lead to pumping saltwater depending on sizes of domain length and width since the impacts of inland fixed head boundary and lateral impermeable boundaries are contrary on the maximum interface toe location defined as the farthest inland point of the interface toe under pumping condition and maximum pumping rate they can be offset under certain critical conditions such that the results of the two quantitative indictors i e the maximum interface toe location and maximum pumping rate in s2 are close to those in ss in particular a linear equation is derived to reflect the relationship between the domain width and length under such critical conditions and expressed as l 0 87 w 0 62 w 1 or l 1 5 in which w and l are the domain width and length normalized by the distance between the coastline and pumping well when l 0 87 w 0 62 the impact from lateral overcomes that from inland producing a larger maximum interface toe location and a lower maximum pumping rate than those in ss when l w 0 62 by contrast the impact from inland exceeds that from lateral and hence resulting in a smaller maximum interface toe location and a higher maximum pumping rate it is expected that the results developed in the current study could support the design of numerical models and 3d laboratory experiments as well as the assessment of domain size impact on pumping in head controlled coastal groundwater systems

complex craters relationship of stratigraphy and rings to impact conditions one of the key issues associated with the understanding of large scale impacts is how the observable complex crater structural features e g central peaks and pits flat floors ring shaped ridges and depressions stratigraphic modifications and faults relate to the impactor s parameters e g radius velocity and density and the nonobservable transient crater measures e g depth of penetration and diameter at maximum penetration we have numerically modeled large scale impacts on planets for a range of impactor parameters gravity and planetary material strengths from these we found that the collapse of the transient cavity results in the development of a tall transient central peak that oscillates and drives surface waves that are arrested by the balance between gravitational forces and planetary strength to produce a wide range of the observed surface features in addition we found that the underlying stratigraphy is inverted outside of the transient cavity diameter overturned flap region but not inside this change in stratigraphy is observable by remote sensing drilling seismic imaging and gravity mapping techniques we used the above results to develop scaling laws and to make estimates of the impact parameters for the chicxulub impact and also compared the calculated stratigraphic profile with the internal structure model developed by hildebrand et al 1998 using gravity seismic and other field data for a stratigraphy rotation diameter of 90 km the maximum depth of penetration is 43 km the impactor diameter was also calculated from the scaling relationships we get for a 2 7 g cm 3 asteroid impacting at 20 km s or a 1 0 g cm 3 comet impacting at 40 km s an impactor diameter of 13 km and for a comet impacting at 60 km s an impactor diameter of 10 km

the canyon diablo impact event 2 projectile fate and target melting upon impact abstract despite its centennial exploration history there are still unresolved questions about meteor crater the first recognized impact crater on earth this theoretical study addresses some of these questions by comparing model results with field and laboratory studies of meteor crater our results indicate that meteor crater was formed by a high velocity impact of a fragmented projectile ruling out a highly dispersed swarm as well as a very low impact velocity projectile fragmentation caused many fragments to fall separately from the main body of the impactor making up the bulk of the canyon diablo meteorites most of these fragments were engulfed in the expansion plume as they approached the surface without suffering high shock compression and were redistributed randomly around the crater thus the distribution of canyon diablo meteorites is not representative of projectile trajectory as is usual for impactor fragments in smaller strewn fields at least 50 of the main impactor was ejected from the crater during crater excavation and was dispersed mostly downrange of the crater as molten particles spheroids and highly shocked solid fragments shrapnel when compared with the known distribution model results suggest an impactor from the sw overall every model case produced much higher amounts of pure projectile material than observed the projectile target mixing was not considered in the models however this process could be the main sink of projectile melt as all analyzed melt particles have high concentrations of projectile material the fate of the solid projectile fragments is still not completely resolved model results suggest that the depth of melting in the target can reach the coconino sandstone formation however most of the ejected melt originates from 30 40 m depth and thus is limited to moenkopi and upper kaibab material some melt remains in the target based on the estimated volume of the breccia lens at meteor crater our models suggest at most a 2 content of melt in the breccia finally a high water table at the time of impact could have aided strong dispersion of target and projectile melt

ries and chicxulub impact craters on earth provide insights for martian ejecta blankets terrestrial impact structures provide field evidence for cratering processes on planetary bodies that have an atmosphere and volatiles in the target rocks here we discuss two examples that may yield implications for martian craters 1 recent field analysis of the ries crater has revealed the existence of subhorizontal shear planes detachments in the periphery of the crater beneath the ejecta blanket at 0 9 1 8 crater radii distance their formation and associated radial outward shearing was caused by weak spallation and subsequent dragging during deposition of the ejecta curtain both processes are enhanced in rheologically layered targets and in the presence of fluids detachment faulting may also occur in the periphery of martian impacts and could be responsible for the formation of lobe parallel ridges and furrows in the inner layer of double layer and multiple layer ejecta craters 2 the ejecta blanket of the chicxulub crater was identified on the southeastern yucatn peninsula at distances of 3 0 5 0 crater radii from the impact center abundance of glide planes within the ejecta and particle abrasion both rise with crater distance which implies a ground hugging erosive and cohesive secondary ejecta flow systematic measurement of motion indicators revealed that the flow was deviated by a preexisting karst relief in analogy with martian fluidized ejecta blankets it is suggested that the large runout was related to subsurface volatiles and the presence of basal glide planes and was influenced by eroded bedrock lithologies it is proposed that ramparts may result from enhanced shear localization and a stacking of ejecta material along internal glide planes at decreasing flow rates when the flow begins to freeze below a certain yield stress

analytical single potential sharp interface solutions for regional seawater intrusion in sloping unconfined coastal aquifers with pumping and recharge summary contamination of groundwater by intruding seawater is a major problem in many parts of the world this work derives novel analytical solutions for addressing this problem by extending the girinskii strack concept of discharge potential to represent regional steady state sharp interface seawater intrusion in a sloping unconfined coastal aquifer the aquifer has hydraulic conductivity k is recharged uniformly at the rate r receives an inflow at its land boundary and has a collector trough or well gallery idealised as line sink located at the distance lw from the coastline that penetrates the aquifer and draws groundwater at the rate qw the theory rests on the approximation of a linearised gravity part of the hydraulic potential analytical solutions for the discharge potential are derived through which the hydraulic head the flow depth and the sharp interface and particularly the location of the interface toe lt are also determined these solutions simplify to known results for the horizontal aquifer case the utility and robustness to uncertainty regarding the base slope of the results in applications is demonstrated in the regional example of the akrotiri coastal aquifer cyprus recasting the problem in non dimensional form provides a relationship for the dependence of the relative interface toe location lt lw on the appropriately normalised difference between the groundwater flow just up gradient of the collector trough qo and the pumping rate qw given values of the base slope r k and hsea lw where hsea is the sea surface elevation above the aquifer base at the coastline that relationship frames a common groundwater management problem in coastal aquifers subject to a certain exploitation scheme with lt as decision variable in an exploratory demonstration study non dimensional sets of performance curves are calculated for the regional akrotiri aquifer in general the derived analytical solutions can be used for first order assessments of seawater intrusion vulnerability and management possibilities across a wide range of current regional coastal aquifer conditions and or projected water demand groundwater management and climatic change scenarios

steady state freshwater seawater mixing zone in stratified coastal aquifers summary the mixing zone between freshwater and intruding seawater which controls regional groundwater flow dynamics and reactive transport processes is the most important component in coastal aquifers laboratory experiments and numerical simulations were conducted to investigate the effects of aquifer stratification on the thickness of a steady state freshwater seawater mixing zone a series of experiments were implemented in a laboratory tank packed with three layers of coastal sands and manipulated by two flow cells for maintaining constant head boundary conditions packed aquifers included a homogenous aquifer a high hydraulic conductivity k low k high k stratified aquifer and a low k high k low k stratified aquifer both tank scale and field scale density dependent models were developed to simulate the laboratory experiments and to systematically investigate aquifer stratification effects on the thickness of a steady mixing zone with varying layer configurations results showed that when an aquifer layer with a low k overlies a layer with a relatively high k slanting upward flow of diluted saltwater and re circulated seawater flow are refracted at the interface between the two layers resulting in streamline separation and a broad mixing zone in the low k layer by contrast the mixing zone in a high k layer is slightly narrowed when it overlies a layer with a relatively low k because flow refraction squeezes the streamlines within the mixing zone the mixing zone profile in head controlled systems is a function of k contrast but independent of the magnitude of k our results demonstrated the significant impact of aquifer stratification on controlling groundwater flow and solute transport in coastal subsurface environments and would have significant implications for studying physical chemical and biological processes in coastal subsurface environments as aquifer stratification is naturally prevalent

dynamic fracture by large extraterrestrial impacts as the origin of shatter cones a large impact by a comet or meteorite releases an enormous amount of energy which evaporates melts and fractures the surrounding rocks distinctive features of such impacts are shatter cones deformed rocks characterized by hierarchical striated features although such features have been used for decades as unequivocal fingerprints of large body impacts the process by which shatter cones form has remained enigmatic here we show that the distinctive shatter cone striations naturally result from nonlinear waves front waves that propagate along a fracture front this explains the observed systematic increase of striation angles with the distance from the impact shatter cone networks typically spanning many scales can be understood as hierarchical bifurcations of the fracture front which is generated by the immense energy flux carried by the initial impact generated shock waves our quantitative predictions based on this theory are supported by field measurements at the kentland and vredefort impact sites these measurements indicate that shatter cones near to the impact site were formed by fractures propagating at nearly the rayleigh wave speed of the host rocks whereas the furthest shatter cones observed about 40 km from the impact site were formed by fronts moving more slowly these results provide insight into impact dynamics as well as dissipative mechanisms in solids subjected to sudden extremely intense fluxes of energy

post impact structural crater modification due to sediment loading an overlooked process post impact crater morphology and structure modifications due to sediment loading are analyzed in detail and exemplified in five well preserved impact craters mjolnir chesapeake bay chicxulub montagnais and bosumtwi the analysis demonstrates that the geometry and the structural and stratigraphic relations of post impact strata provide information about the amplitude the spatial distribution and the mode of post impact deformation reconstruction of the original morphology and structure for the mjolnir chicxulub and bosumtwi craters demonstrates the long term subsidence and differential compaction that takes place between the crater and the outside platform region and laterally within the crater structure at mjolnir the central high developed as a prominent feature during post impact burial the height of the peak ring was enhanced and the cumulative throw on the rim faults was increased the original chicxulub crater exhibited considerably less prominent peakring and inner ring crater rim features than the present crater the original relief of the peak ring was on the order of 420 570 m currently 535 575 m the relief on the inner ring crater rim was 300 450 m currently 700 m the original bosumtwi crater exhibited a central uplift high whose structural relief increased during burial current height 101 110 m in contrast to the original height of 85 110 m whereas the surrounding western part of the annular trough was subdued more that the eastern part exhibiting original depths of 43 68 m currently 46 m and 49 55 m currently 50 m respectively furthermore a quantitative model for the porosity change caused by the chesapeake bay impact was developed utilizing the modeled density distribution the model shows that compared with the surrounding platform the porosity increased immediately after impact up to 8 5 in the collapsed and brecciated crater center currently 6 due to post impact compaction in contrast porosity decreased by 2 3 currently 3 to 4 5 due to post impact compaction in the peak ring region the lateral variations in porosity at chesapeake bay crater are compatible with similar porosity variations at mjolnir crater and are considered to be responsible for the moderate chesapeake bay gravity signature annular low of 8 mgal instead of 15 mgal the analysis shows that the reconstructions and the long term alterations due to post impact burial are closely related to the impact disturbed target rock volume and a brecciated region of laterally varying thickness and depth varying physical properties the study further shows that several crater morphological and structural parameters are prone to post impact burial modification and are either exaggerated or subdued during post impact burial preliminary correction factors are established based on the integrated reconstruction and post impact deformation analysis the crater morphological and structural parameters corrected from post impact loading and modification effects can be used to better constrain cratering scaling law estimates and impact related consequences

tectonics of complex crater formation as revealed by the haughton impact structure devon island canadian high arctic the results of a systematic field mapping campaign at the haughton impact structure have revealed new information about the tectonic evolution of mid size complex impact structures these studies reveal that several structures are generated during the initial compressive outward directed growth of the transient cavity during the excavation stage of crater formation 1 sub vertical radial faults and fractures 2 sub horizontal bedding parallel detachment faults and 3 minor concentric faults and fractures uplift of the transient cavity floor toward the end of the excavation stage produces a central uplift compressional inward directed deformation results in the duplication of strata along thrust faults and folds it is notable that haughton lacks a central topographic peak or peak ring the gravitational collapse of transient cavity walls involves the complex interaction of a series of interconnected radial and concentric faults while the outermost concentric faults dip in toward the crater center the majority of the innermost faults at haughton dip away from the center complex interactions between an outward directed collapsing central uplift and inward collapsing crater walls during the final stages of crater modification resulted in a structural ring of uplifted intensely faulted sub vertical and or overturned strata at a radial distance from the crater center of 5 0 6 5 km converging flow during the collapse of transient cavity walls was accommodated by the formation of several structures 1 sub vertical radial faults and folds 2 positive flower structures and chaotically brecciated ridges 3 rollover anticlines in the hanging walls of major listric faults and 4 antithetic faults and crestal collapse grabens oblique strike slip i e centripetal movement along concentric faults also accommodated strain during the final stages of readjustment during the crater modification stage it is clear that deformation during collapse of the transient cavity walls at haughton was brittle and localized along discrete fault planes separating kilometer size blocks

shock metamorphism of ordinary chondrites a revised petrographic classification of progressive stages of shock metamorphism of ordinary chondrites is proposed six stages of shock s1 to s6 are defined based on shock effects in olivine and plagioclase as recognized by thin section microscopy the characteristic shock effects of each shock stage are s1 unshocked sharp optical extinction of olivine s2 very weakly shocked undulatory extinction of olivine s3 weakly shocked planar fractures in olivine s4 moderately shocked mosaicism in olivine s5 strongly shocked isotropization of plagioclase maskelynite and planar deformation features in olivine and s6 very strongly shocked recrystallization of olivine sometimes combined with phase transformations ringwoodite and or phases produced by dissociation reactions s6 effects are always restricted to regions adjacent to melted portions of a sample which is otherwise only strongly shocked in stages s3 to s6 localized melting results from stress and temperature peaks which locally deviate from the equilibration shock pressure due to differences in shock impedance these melting effects are a opaque melt veins shock veins b melt pockets with interconnecting melt veins c melt dikes and d troilite metal deposits in fractures based on a critical evaluation of data from shock recovery experiments a shock pressure calibration for the six shock stages is proposed which defines the s1 s2 s2 s3 s3 s4 s4 s5 and s5 s6 transitions at 5 5 10 15 20 30 35 and 45 55 gpa respectively whole rock melting and formation of impact melt rocks or melt breccias occurs at about 75 90 gpa the symbol for the shock stage may be used in combination with the symbol for the petrologic type to abbreviate the complete classification of a chondrite e g h5 s3 we propose this new shock classification and pressure calibration system to replace previous systems which are out of date with respect to the pressure calibration nominally restricted to l chondrites and based on incomplete and in part illdefined sets of shock effects we have classified seventy six ordinary chondrites using the new classification system and conclude the following 1 1 shock effects and the sequence of progressively increasing degrees of shock metamorphism are very similar in h l and ll groups differences in the frequency distribution of shock stages are relatively minor e g l chondrites appear to have the largest fraction with stages s5 and s6 this suggests that the collisional histories of the h l and ll parent bodies were similar 2 2 petrologic type 3 chondrites are deficient in stages s4 to s6 and with increasing petrologic type the frequency of stages s4 to s6 increases we suggest that the more porous and volatile rich type 3 chondrites are subject to melting at a lower shock pressure than the nonporous chondrites of higher petrologic type volatiles trapped in pores cause shock induced dispersal of the shocked and melted material into small particles which are not expected to survive as meteorites 3 3 stage s3 is the most abundant in nearly all petrologic types 4 4 at shock pressures in excess of about 35 gpa s5 and s6 4he and 40ar are almost completely lost pressures below 10 gpa s1 and s2 do not cause noble gas losses

the carancas meteorite impact crater peru geologic surveying and modeling of crater formation and atmospheric passage the recent carancas meteorite impact event caused a worldwide sensation an h4 5 chondrite struck the earth south of lake titicaca in peru on september 15 2007 and formed a crater 14 2 m across it is the smallest youngest and one of two eye witnessed impact crater events on earth the impact violated the hitherto existing view that stony meteorites below a size of 100 m undergo major disruption and deceleration during their passage through the atmosphere and are not capable of producing craters fragmentation occurs if the strength of the meteoroid is less than the aerodynamic stresses that occur in flight the small fragments that result from a breakup rain down at terminal velocity and are not capable of producing impact craters the carancas cratering event however demonstrates that meter sized stony meteoroids indeed can survive the atmospheric passage under specific circumstances we present results of a detailed geologic survey of the crater and its ejecta to constrain the possible range of impact parameters we carried out numerical models of crater formation with the isale hydrocode in two and three dimensions depending on the strength properties of the target the impact energies range between approximately 100 1000 mj 0 024 0 24 t tnt by modeling the atmospheric traverse we demonstrate that low cosmic velocities 12 1 4 kms 1 and shallow entry angles 20 are prerequisites to keep aerodynamic stresses low 10 mpa and thus to prevent fragmentation of stony meteoroids with standard strength properties this scenario results in a strong meteoroid deceleration a deflection of the trajectory to a steeper impact angle 40 60 and an impact velocity of 350 600 ms 1 which is insufficient to produce a shock wave and significant shock effects in target minerals aerodynamic and crater modeling are consistent with field data and our microscopic inspection however these data are in conflict with trajectories inferred from the analysis of infrasound signals

when a cosmic impact strikes the sea bed most bolides that collide with the earth hit the sea limited knowledge about marine target impacts hampers predictions about their perilousness this study presents geological features that are particular to craters formed at sea the features are most likely a result of the influence of the target on the cratering process marine target craters form only if the target sea is shallow enough to admit sufficient kinetic energy into the sea bed when the crater diameter is large compared to the water depth the crater resembles its counterparts that are formed on land craters formed in deeper water are concentric and often lack melt sheets and rim walls but have deposits and radial gullies formed by the resurge of the sea impacts on the deep shelf are probably much more energetic than is suggested by the dimensions of the preserved crater

effects of kinetic mass transfer and transient flow conditions on widening mixing zones in coastal aquifers 1 the width of a mixing zone between freshwater and seawater is important primarily because it directly reflects the extent of mixing and the growth and decay of the mixing zone indicates changes of the flow regime and water exchange between freshwater and coastal seawater wide mixing zones have been found in many coastal aquifers all over the world however the mechanisms responsible for wide mixing zones are not well understood this work examines the hypothesis that kinetic mass transfer coupled with transient conditions which create the movement of the mixing zone may widen mixing zones in coastal aquifers the hypothesis is tested by conducting two dimensional numerical simulations based on a variable density groundwater model for a scaled tank model and a field scale model periodic water levels representing periodic tidal motion and freshwater table fluctuations are imposed at the seaward and landward boundary respectively which cause the movement of the mixing zone both the scaled tank model and the field model show that the combination of the moving mixing zone and kinetic mass transfer may significantly enhance the extent of mixing and create a wider mixing zone than the models without kinetic mass transfer in addition sensitivity analyses indicate that a larger capacity ratio immobile porosity mobile porosity of mass transfer leads to a wider mixing zone and the maximum width of the mixing zone may be reached for a given capacity ratio when the mean retention time scale in the immobile domain the reciprocal of mass transfer rate and the period of water level fluctuations are comparable

a formulation for vertically integrated groundwater flow in a stratified coastal aquifer we present the comprehensive discharge potential for steady three dimensional flow in horizontally stratified coastal aquifers with a horizontal base and a vertical coastline the gradient of this comprehensive potential gives the vertically integrated discharge throughout the aquifer i e the specific discharge vector as a function of three dimensional space integrated over the saturated portion of the aquifer the boundary values of the comprehensive potential along the coast can be computed precisely given the geometry of the aquifer the hydraulic conductivities of the strata the elevations of the horizontal planes that separate the strata and the elevation of the impermeable base of the aquifer relative to sea level boundary conditions of the comprehensive potential may either be given in terms of its gradient or computed from given heads along the boundaries the governing equation of the comprehensive potential is the poisson equation in areas of infiltration and the laplace equation elsewhere the computation of interface elevations piezometric heads and the vertical distribution of flow requires that an assumption be made regarding the relation between the comprehensive potential and piezometric heads we adopt the dupuit forchheimer approximation for this purpose and make use of the ghyben herzberg equation we present several applications of the approach and find that the stratification may have a significant effect on the boundary value of the comprehensive potential and thus on the flow rates in the aquifer this article is protected by copyright all rights reserved

shock experiments with the h6 chondrite kernouve pressure calibration of microscopic shock effects shock recovery experiments were carried out on samples of the h6 chondrite kernouve at shock pressures of 10 15 20 25 30 35 45 and 60 gpa and preheating temperatures of 293 k low temperature experiments and 920 k high temperature experiments using a calculated equation of state of kernouve pressure pulse durations of 0 3 to 1 2 s were estimated the shocked samples were investigated by optical microscopy to calibrate the various shock effects in olivine orthopyroxene oligoclase and troilite the following pressure calibration is proposed for silicates 1 undulatory extinction of olivine gpa 2 weak mosaicism of olivine from 10 15 gpa to 20 25 gpa 3 onset of strong mosaicism of olivine at 20 25 gpa 4 transformation of oligoclase to diaplectic glass completed at 25 30 gpa low temperature experiments and at 20 25 gpa high temperature experiments 5 onset of weak mosaicism in orthopyroxene at 30 35 gpa low temperature experiments and at 25 30 gpa high temperature experiments and 6 recrystallization or melting of olivine starting at 45 60 gpa low temperature experiments and at 35 45 gpa high temperature experiments and completed above 45 60 gpa in the high temperature experiments troilite displays distinct differences between the samples shocked at low and high temperatures in the low temperature experiments the following effects can be observed in troilite 1 undulatory extinction up to 25 gpa 2 twinning up to 45 gpa 3 partial recrystallization from 30 to 60 gpa and 4 complete recrystallization 35 gpa whereas in the high temperature experiments troilite shows 1 complete recrystallization from 10 up to 45 gpa and 2 melting and crystallization above 45 gpa localized shock induced melting is observed in samples shocked to pressures 15 gpa in the high temperature experiments and 30 gpa for the low temperature experiments in the form of feni metal and troilite melt injections and intergrowths and as pockets and veins of whole rock melt obviously the onset and abundance of shock induced localized melting strongly depends on the initial temperature of the sample

impact related dike breccia lithologies in the icdp drill core yaxcopoil 1 chicxulub impact structure mexico petrographic descriptions of three dike breccia lithologies from drill core yaxcopoil 1 yax 1 are presented they occur within allochthonous units of displaced sedimentary megablocks of the chicxulub impact structure the suevitic dike breccias are the uppermost dike lithology they contain melt rock particles and melt injections into the dike groundmass shock features occur ubiquitously and indicate a strong thermal annealing flow textures suggest a highly energetic emplacement process possibly during the excavation stage as a ground surge related deposit the impact melt rock dikes are present in a strongly brecciated megablock interval as flow textured anastomozing veinlets of impact melt rock that were altered to clay minerals the melt impregnated a dolomitic host rock indicating a low viscosity and thus high initial temperatures brecciation of the impact melt rock dikes occurred while they were still below the glass transition temperature suggesting that dynamic conditions prevailed shortly after the emplacement process major element data indicates that the impact melt rock dikes differ in composition from the homogenized impact melt rock of chicxulub this could point to an emplacement during the late compression or early excavation stages of cratering the clastic polymict dike breccias are coeval with pervasive brittle fracturing of the host rocks they bear clasts including some crystalline basement and possible melt rock particles in a fine grained dolomite matrix with turbulent flow textures fabric and texture indicate a granular flow at ambient pressures such conditions could be envisaged for the excavation phase while the transient cavity grew and fractures opened

radial transpression ridges a new structural feature of complex impact craters the gravity driven collapse of complex impact craters induces the mass transfer of large rock volumes in distal parts of a crater inward movements dominate whereas in the centre of an impact structure outward movements occur if the central uplift collapses the particle trajectory field is centro symmetric which signifies that the conditions for plane strain deformation are not fullfilled converging particle trajectories can be compensated either by a bulk thickening of inward sliding masses folding repetition of rock units along thrust faults plastic flow or by the formation of localised radial transpression ridges rtr at the edges of individual landslides in these transpression ridges material is uplifted to accommodate the converging mass flow different modes of uplift are possible including radial folding lateral overthrusting and the formation of positive flower structures a simple geometric model is used to estimate the amount of transpression thickening and bulk thickening of inward sliding masses on the base of volumetric considerations the existence of rtrs is confirmed by structural investigations at the siljan impact structure sweden as well as at other complex impact craters on earth

theoretical and conceptual models of subsurface hillslope flows 1 theoretical and conceptual models for predicting the subsurface flow in a sloping aquifer are presented one category of models is of the lumped conceptual type that is based on combining the continuity equation with discharge storage relationships derived from the steady state solutions of the linearized boussinesq equation the second categories of models are derived from the linearized unsteady boussinesq equation using the method of green s function the green s function solution determines the water table profile and the aquifer outflow for nonuniform and nonsteady recharge distribution arbitrary initial water table profile and time varying stream level at the downstream end the latter theoretical models pertain to a finite domain and to a semi infinite domain and are of two types depending on the linearization approach the conceptual and theoretical models are used to derive the outflow and the cumulative outflow expressions for a particular set of conditions and a comparative analysis is carried out semi infinite aquifer models generate almost the same results as the more complicated finite aquifer models and the quasi steady state models perform as well as the nonsteady ones for long recharge events the kinematic wave model is also shown to provide a good approximation of boussinesq models for steep slopes and high hydraulic conductivity the application of the various models is also illustrated for three published experimental data the present models can be easily incorporated in catchments models and can provide a suitable framework for aquifer parameter estimation base flow separation and recession analysis and analysis of drainage in landfills

crater features diagnostic of oblique impacts the size and position of the central peak using magellan data we investigated two crater characteristics that have been cited as diagnostic of oblique impacts an uprange offset of the central peak in complex craters and an increasing central peak diameter relative to crater diameter with decreasing impact angle we find that the offset distribution is random and very similar to that for high angle impacts and that there is no correlation between central peak diameter and impact angle accordingly these two crater characteristics cannot be used to infer the impact angle or direction

structural record of an oblique impact abstract most impactors strike their target at an oblique angle the common criterion for identifying craters formed by an oblique impact is the pattern of the ejecta blanket on earth however ejecta blankets are rarely preserved and other morphological structural or geophysical criteria are needed here we present structural details from the central uplift of the upheaval dome impact structure that are diagnostic of the kinematics during crater collapse and central uplift formation a characteristic imbrication of thrust slices towards the se the pattern of strata orientation within the central uplift dominant radial faults that accommodated nw se shortening and an elliptical bedding outline indicate that the displacement field during crater collapse has not been axial symmetric instead an additional lateral component roughly towards the se is preserved in the internal structure of the central uplift the structural asymmetries are largest in the core of the central uplift and disappear outwards thereby preserving the large scale circular shape of the main structural elements rim monocline ring syncline comparison with numerical models of oblique impacts suggests that the additional lateral displacement component reflects a downrange material transport during the initial stages of central uplift formation similar patterns are identified in other impact structures and may serve as general criteria for identifying the impact direction of deeply eroded impact structures in sedimentary targets

tidal effects on sea water intrusion in unconfined aquifers abstract a variable density groundwater model is used to analyse the effects of tidal fluctuations on sea water intrusion in an unconfined aquifer it is shown that the tidal activity forces the sea water to intrude further inland and it also creates a thicker interface than would occur without tidal effects moreover the configuration of the interface is radically changed when the tidal fluctuations are included this is because of the dramatic changes in the flow pattern and velocity of the groundwater near the shoreline for aquifer depths much larger than tidal amplitudes the tidal fluctuation does not have much effect on how far the sea water intrudes into the aquifer nevertheless a significant change in the configuration of concentration contours because of the effect of tidal fluctuations is observed this change is more noticeable at the top of the aquifer near the water table than at the bottom of the aquifer and is caused by the infiltration of salt water into the top of the aquifer at higher tidal levels a flatter beach slope therefore intensifies this phenomenon the interface configurations do not change noticeably over the course of a tidal cycle neglecting tidal fluctuation effects results in an inaccurate evaluation of the water table elevation at the land end of the aquifer although no distinguishable difference is seen between the water tables near the shoreline where the landward boundary condition is a constant head the effects of tidal fluctuations on sea water intrusion are more pronounced than for cases where the landward boundary condition is a specified flux also it is shown that the effects of tidal fluctuations are more significant for a sloping beach than for a vertical shoreline and the salt water intrudes further inland for the sloping case

asymmetric signatures in simple craters as an indicator for an oblique impact direction in oblique impacts with an impact angle under 45 the bilateral shape of the distal ejecta blanket is used as the strongest indicator for an impact vector this bilateral symmetry is attenuated and is superimposed by radial symmetry towards the crater rim which remains circular for impact angles down to 10 15 the possibility that remnants of bilateral symmetry might still be present in the most proximal ejecta the overturned flap and the crater rim was explored with the intention of deducing an impact vector a model is presented that postulates bilateral patterns using proximal ejecta trajectories and predicts these patterns in the orientation of bedding planes in the crater rim this model was successfully correlated to patterns described by radial grooves in the proximal ejecta blanket of the oblique tooting crater on mars a new method was developed to detect structural asymmetries by converting bedding data into values that express the deviation from concentric strike orientation in the crater rim relative to the crater center termed concentric deviation the method was applied to field data from wolfe creek crater western australia bedding in the overturned flap implies an impactor striking from the east which refines earlier publications while bedding from the inner rim shows a correlation with the crater rim morphology

assessment of the impact of sea level rise on seawater intrusion in sloping confined coastal aquifers abstract previous studies of the impact of sea level rise on seawater intrusion slr swi are mostly based on horizontal coastal aquifers despite that most coastal aquifers are sloping a recent study has shown that the effect of aquifer slope can not be neglected when assessing slr swi in unconfined coastal aquifers however the effect of slope in confined aquifers has not been evaluated in this study we apply existing analytical solutions to quantify the effect of the slope of both upper and lower confining layers on slr swi the results show that for flux controlled sloping confined coastal aquifer systems slr does not change the steady state interface location consistent with previous findings for horizontal aquifers therefore our analysis focuses on head controlled sloping confined coastal aquifer systems for which we find the assumption of horizontal confining units causes significant errors we demonstrate this by assessing the sensitivities of the seawater toe location and seawater volume to slr for various combinations of sloping confining layers the results indicate that the influence of the slope on slr swi is small in thin confined aquifers however the slope is an important factor in thick confined aquifers the influence of the slope in the lower confining layer on slr swi is much greater than that of the upper confining layer aquifers that thin towards the sea are most susceptible to slr swi whereas those that thin towards inland are least susceptible the assessment of slr swi in sloping confined coastal aquifers in the current study demonstrates application of a rapid first order assessment tool that can be applied to a wide range of other sloping coastal confined aquifer problems

steady state phreatic surfaces in sloping aquifers 1 steady state groundwater flow driven by constant recharge in an unconfined aquifer overlying sloping bedrock is shown to be represented using the dupuit approximation by an ordinary differential equation of the abel type y x y x a y x x 0 whose analytical solution is derived in this work this article first investigates the case of zero saturated thickness at the upstream boundary a flow system reminiscent of perched groundwater created by percolation of precipitation or irrigation in a sloping aquifer fully draining at its downstream boundary a variant of this flow system occurs when the phreatic surface mounds and produces groundwater discharge toward the upstream boundary this variant is a generalization of the classical groundwater flow problem involving two lakes connected by an aquifer the latter being on sloping terrain in this instance analytical solutions for the phreatic surface s steady state geometry are derived for the case of monotonically declining hydraulic head as well as for the case of a mounded phreatic surface these solutions are of practical interest in drainage studies slope stability and runoff formation investigations it is shown that the flow factor a tan where k n and tan are the hydraulic conductivity vertical recharge and aquifer slope respectively has a commanding role on the phreatic surface s solutions two computational examples illustrate the implementation of this article s results

shock veins in the central uplift of the manicouagan impact structure context and genesis we describe the development of shock veins that penetrate the anorthositic central uplift of the manicouagan impact structure they occur as thin 2 5 mm wide linear micro fault systems that can be traced for several meters in length and which predominantly trend radially from the point of impact the shock veins are distinguished by the development of maskelynite along vein margins and stishovite in vein matrices which are otherwise absent in non veined regions these phases define a shock excursion of up to 30 gpa in contrast to bulk shock effects of 12 gpa defined by development of shatter cones planar fractures and planar deformation features in various minerals the shock veins at manicouagan share many similarities with vein systems developed in meteorites they also provide an in situ context with which to better understand meteoroid source and lofting conditions in addition to containing high pressure phases the shock veins exhibit evidence for high temperature partial melting of host silicate clasts with the generation of flow textured fragments and glasses the formation of microcrystallites and dendrites from some melts indicates rapid cooling we propose a two stage generation mechanism comprising an initial high pressure shock excursion estimated to last 0 5 s based on projectile size considerations followed by a longer high temperature pulse of a few seconds duration we suggest that the shock excursion is initiated by target heterogeneities that cause distortions in the hemispherically propagating shock front this results in radially oriented tearing and vein formation with shock amplification occurring via intra vein shock reverberation high speed displacement along the veins is driven by stress release on rarefaction which results in frictional melting via adiabatic heating

modeling the ries steinheim impact event and the formation of the moldavite strewn field using detailed geological petrographic geochemical and geographical constraints we have performed numerical modeling studies that relate the steinheim crater apparent diameter da 3 8 km the ries crater da 24 km in southern germany and the moldavite tektite strewn field in bohemia and moravia czech republic lusatia east germany and lower austria the moldavite strewn field extends from 200 to 450 km from the center of the ries to the east northeast forming a fan with an angle of 57 an oblique impact of a binary asteroid from a west southwest direction appears to explain the locations of the craters and the formation and distribution of the moldavites the impactor must have been a binary asteroid with two widely separated components some 1 5 and 0 15 km in diameter respectively we carried out a series of three dimensional hydrocode simulations of a ries type impact the results confirm previous results suggesting that impacts around 30 50 from the horizontal are the most favorable angles for near surface melting and consequently for the formation of tektites finally modeling of the motion of impact produced tektite particles through the atmosphere produces in the downrange direction a narrow angle distribution of the moldavites tektites in a fan like field with an angle of 75 an additional result of modeling the motion of melt inside and outside the crater is the preferred flow of melt from the main melt zone of the crystalline basement downrange towards the east northeast rim this explains perfectly the occurrence of coherent impact melt bodies some tens of meters in size in a restricted zone of the downrange rim of the ries crater the origin of these melt bodies which represent chemically a mixture of crystalline basement rocks similar to the main melt mass contained as melt particles 0 5 m in size in the suevite do not occur at any other portion of the ries crater rim and remained enigmatic until now although the calculated distribution of moldavites still deviates to some degree from the known distribution our results represent an important step toward a better understanding of the origin and distribution of the high velocity surface melts and the low velocity deep seated melt resulting from an oblique impact on a stratified target

shock experiments on pre heated α and β quartz i optical and density data abstract discs of single crystal quartz unheated and pre heated to 275 c and 540 c i e quartz and 630 c i e quartz were experimentally shocked to pressures ranging from 20 to 40 gpa with the shock front propagating parallel to either 10 1 0 or 0001 refractive indices density and the orientation of planar deformation features pdfs were determined on the recovered quartz samples refractive indices of pre heated quartz are unaffected up to 25 gpa but density starts to decrease slightly up to this pressure above 25 gpa pre heating causes drastic variations refractive indices and birefringence of quartz shocked at ambient temperature decrease continuously until complete isotropization is reached at 35 gpa in quartz shocked at 630 c refractivity drops discontinuously in the interval from 25 to 26 gpa and complete transformation to diaplectic glass is reached at 26 gpa density follows the trends demonstrated by the optical parameters with higher pre shock temperatures yielding lower density at a given shock pressure these results indicate that the threshold pressure for the onset of transformation to diaplectic quartz glass is largely temperature invariant lying at 25 gpa whereas the pressure limit for complete transformation decreases with increasing pre shock temperature from 35 to 26 gpa quartz shocked parallel to 0001 always has a higher density and refractivity than that shocked parallel to 10 1 0 indicating a significant influence of the structural anisotropy this is also evident from the distribution of pdf orientations pressures 25 gpa cause in quartz shocked parallel to 10 1 0 pdfs that are predominantly oriented parallel to 10 1 2 while quartz shocked to the same pressures but parallel to 0001 contains almost exclusively pdfs parallel to 10 1 3 pdf orientations in quartz shocked at ambient temperature parallel to 10 1 0 show the following characteristics i the frequency of 10 1 3 is high at 20 gpa declines with increasing pressure and finally is totally absent at 32 gpa ii 10 1 3 begins to occur at 25 gpa increases and finally is the only remaining orientation at 32 gpa and iii 10 1 2 and 11 2 2 are only present at 20 and 25 gpa in contrast quartz shocked at 630 c parallel to 10 1 0 displays a broad pdf distribution with indistinct maxima and 10 1 3 is totally absent the small structural difference between and quartz which is reflected in the pdf distribution should allow in principle evaluation of the pre shock temperature in naturally impacted metamorphic rocks the results substantiate that formation of shock effects in quartz is dependent on i shock pressure ii pre shock temperature and iii shock wave direction so far the latter two parameters have not been considered in the application of experimental results to impact sites

pumping optimization in saltwater intruded coastal aquifers this paper investigates the hydraulic issues of pumping well optimization in saltwater intruded coastal aquifers the well field includes freshwater outflow pumping wells and a recharge canal the objective is to maximize the total pumping rate subject to the constraint of no intrusion of the saltwater front into the wells analytical solutions are presented for one well two well and one well with recharge canal problems for problems involving multiple pumping wells a structured messy genetic algorithm is used to search for the optimal solution

terrace width variations in complex lunar craters the widths of terrace structures in complex craters on the moon are compared to existing theoretical models of their origin terrace widths in an individual crater increase monotonically outward toward the crater rim similarly the width w of the terraces lying closest to the rim of a crater of diameter d increases monotonically obeying a least squares power law relation w km 0 09d0 87 km a simple model of slumping that ignores inertial forces and assumes a constant bedrock yield strength is in good agreement with the observations

origin of the structure and planform of small impact craters in fractured targets endurance crater at meridiani planum mars we present observations and models that together explain many hallmarks of the structure and growth of small impact craters forming in targets with aligned fractures endurance crater at meridiani planum on mars diameter 150 m formed in horizontally layered aeolian sandstones with a prominent set of wide orthogonal joints a structural model of endurance crater is assembled and used to estimate the transient crater planform the model is based on observations from the mars exploration rover opportunity a bedding plane orientations and layer thicknesses measured from stereo image pairs b a digital elevation model of the whole crater at 0 3 m resolution and c color image panoramas of the upper crater walls this model implies that the crater s current shape was mostly determined by highly asymmetric excavation rather than long term wind mediated erosion we show that modal azimuths of conjugate fractures in the surrounding rocks are aligned with the square component of the present day crater planform suggesting excavation was carried farther in the direction of fracture alignments this was previously observed at barringer crater in arizona and we show the same relationship also holds for tswaing crater in south africa we present models of crater growth in which excavation creates a stellate transient cavity that is concave cuspate in planform these models reproduce the lenticular crescentic layering pattern in the walls of some polygonal impact craters such as endurance and barringer craters and suggest a common origin for tear faults and some crater rays we also demonstrate a method for detailed error analysis of stereogrammetric measurements of bedding plane orientations

exact versus dupuit interface flow in anisotropic coastal aquifers the dupuit solution for interface flow toward the coast in a confined aquifer is compared to a new exact solution which is obtained with the hodograph method and conformal mapping the position of the toe of the interface is a function of two dimensionless parameters the ratio of the hydraulic gradient upstream of the interface where flow is one dimensional over the dimensionless density difference and the ratio of the horizontal hydraulic conductivity over the vertical hydraulic conductivity the dupuit interface which neglects resistance to vertical flow is a very accurate approximation of the exact interface for isotropic aquifers the difference in the position of the toe between the exact and dupuit solutions increases when the vertical anisotropy increases for highly anistropic aquifers it is proposed to add an effective resistance layer along the bottom of the sea in dupuit models the resistance of the layer is chosen such that the head in the dupuit model is equal to the head in the exact solution upstream of the interface where flow is one dimensional

the subsurface character of meteor crater arizona as determined by ground probing radar ground probing radar has provided new two dimensional stratigraphic and structural information on meteor crater arizona four 50 mhz transects inside the crater and one 100 mhz transect on a northeast radial across the exterior ejecta blanket were carried out the frequencies used were in relation to the desired depth of investigation greater than 50 m at 50 mhz and 30 m for 100 mhz the results obtained inside the crater show that the water table can be clearly detected at depths of 65 m as can the contact between the crater wall and the infilling allochthonous breccia lens in addition we were able to detect 1 point reflectors from relatively coherent blocks 1 5m within the breccia lens 2 a zone 7 m thick relatively free of point reflectors from the immediate fall back unit 3 a series of subhorizontal reflectors a few meters apart due to bedding in the post impact crater sediments and 4 five separate subhorizontal reflectors from what we interpret to be a series of postimpact paleo water table levels in the breccia lens the ejecta blanket transect indicates a 4 10 m thick ejecta layer and the underlying moenkopi formation sandstone as well as the moenkopi kaibab contact and bedding within the kaibab formation in addition reverse faults with displacements up to 4 m were detected in the bedrock as well as changes from subhorizontal to 30 in the dip of the bedrock as the crater rim is approached from the northeast beneath the ejecta blanket the total uplift observed at the crater rim is around 55 m the radar data indicate uplift effects out to a radial distance of 400 m from the rim farther than that determined from drilling 300 m the results demonstrate the utility of continuous ground probing radar cross sections in studying the near subsurface 50 m character at meteor crater this relatively rapid low cost technique can be extended to other structures but confident interpretation requires supplemental ground truth constraints

friction melt distribution in a multi ring impact basin it is generally accepted that multi ring basins are the consequence of very large impacts but the mechanism by which they form is still a matter of contention1 2 most of what is currently known about multi ring basins is based on remote studies of the moon3 5 and to a lesser extent mars and mercury4 6 but at least two multi ring impact basins have been recognized on earth7 the sudbury8 canada and vredefort9 south africa impact structures providing an opportunity to study their properties directly here we describe the distribution of friction melt pseudotachylyte in the floor of the sudbury impact basin although the veins and dykes of pseudotachylyte decrease in both thickness and frequency of occurrence towards the basin periphery the greatest volumes of friction melt appear to define four rings around the central impact melt sheet field evidence indicates that the rings originated as zones of large displacement which facilitated localized frictional melting of the basin floor during the modification collapse stage of the cratering process by analogy we argue that the rings of other multi ring impact basins are also likely to be the remnants of such large displacement fault zones

groundwater flow to a pumping well in a sloping fault zone unconfined aquifer this study develops a mathematical model for simulating the hydraulic head distribution in response to pumping in a sloping fault zone aquifer under a water table boundary condition a two dimensional equation with a sink term representing the pumping is used for describing the head distribution in the aquifer in addition a first order free surface equation is adopted to represent the change in water table at the outcrop the analytical solution of the model derived by the laplace and finite fourier cosine transforms is expressed in terms of a double series a finite difference solution within a deformable grid framework is developed to assess the solution obtained by specifying the free surface equation at the outcrop based on the analytical solution we have found that the model s prediction tends to overestimate drawdown in a late pumping period the temporal head distribution is independent of the aquifer slope if the water table change is small and exhibits a double humped shape due to the effect of the free surface the temporal drawdown predicted from the analytical solution is further compared with those measured from a pumping test conducted in northern portugal

generation of fragment rich pseudotachylite bodies during central uplift formation in the vredefort impact structure south africa abstract target rocks underlying the central portions of large terrestrial impact structures are characterized by the pervasive presence of fragment rich pseudotachylite bodies debates regarding the formation of these bodies include the origin of pseudotachylitic melts i e friction versus shock induced melting melt mobility causes of target rock fragmentation and timing of fragmentation and melt emplacement with respect to stages of cratering comprehensive structural analysis of pre impact mineral fabrics and properties of fragment rich pseudotachylite in the vredefort dome suggests that melt is allochthonous and was emplaced at an advanced stage of cratering into tensional fracture zones within the crater floor both concentration of bending strains imparted on target rocks during central uplift formation and thermal stresses induced by the emplacement of allochthonous melt led to fragmentation of target rock tensional fracture zones formed in an overall dilational strain field towards the end of cratering likely during collapse of the central uplift and constitute low pressure zones into which melt was forcefully drawn melt may have been drained from the overlying impact melt sheet or from sites within the crater floor and transported into fragment rich dilation zones our field based analysis failed to identify the presence of bona fide shear faults that could potentially have generated in situ frictional melts and fragments rather target rock fragmentation and melt generation that resulted in fragment rich pseudotachylite bodies are processes separated in space and time during cratering

shock metamorphic features and their zoning and orientation in the precambrian rocks of the manicouagan structure quebec canada abstract the manicouagan structure of impact origin is located in eastern quebec about 300 km north of the st lawrence river the complex is of triassic age the shock deformation of the more important rock forming minerals of the autochthonous or at least parautochthonous rocks within the structure is described four zones of shock metamorphism are delineated based on the deformation features of plagioclase 1 plagioclase without planar features 2 plagioclase with planar features 3 first occurrence of plagioclase with partial isotropization and 4 first occurrence of plagioclase with total isotropization these four zones are more or less concentric and indicate a general increase in the grade of shock metamorphism towards the centre of the structure however several small areas probably underlain by allochthonous rocks appear not to fit this general picture biotite and garnet show evidence of a shock orientation of their deformation features an impact origin for the structure is favoured the impact possibly triggering volcanism

experimental approach to generate shock veins in single crystal olivine by shear melting a shock experiment has been devised to produce large shear in a single crystal sample of olivine the recovered sample exhibits macroscopic shear faults resembling shock veins in ordinary chondrites examination with transmission electron microscopy reveals a high density of dislocations in the bulk olivine the shear faults appear as thin veins containing small grains of olivine and pockets of glass the microstructure and composition of the material in the veins point to fractional crystallization of a melt an order of magnitude calculation is consistent with the idea that the veins were produced by shear melting these results support the view that shock veins in meteorites are the result of shear heating rather than of pressure heterogeneities

a 3d model of first order structural elements of the vredefort dome south africa importance for understanding central uplift formation of large impact structures abstract based on detailed structural mapping geophysical information and structural consideration we generated a 3d structural model of a segment of the vredefort dome this model provides insight into the mechanism of mass transfer during central uplift formation of large impact structures the model consists of geometrically and kinematically linked km scale radial and concentric faults that affected the overturned limb of the rim syncline to the vredefort dome the faults accomplished constrictional centripetal rock flow followed by radial spreading of uplifted and gravitationally unstable rocks in the crater centre more specifically concentric faults formed likely as normal faults during transient crater rim collapse steepened and were transformed to reverse faults during central rock uplift and finally were overturned during gravitational collapse of the central uplift radial faults by contrast formed at a later stage of convergent rock flow towards the crater centre and retained largely their orientation during central uplift formation displacement on individual faults is up to 2 km cumulative displacement notably on concentric faults can account for the large displacement magnitudes predicted by numerical models

the complex impact structure serra da cangalha tocantins state brazil abstract serra da cangalha is a complex impact structure with a crater diameter of 13 700 m and a central uplift diameter of 5800 m new findings of shatter cones planar fractures feather features and possible planar deformation features are presented several ring like features that are visible on remote sensing imagery are caused by selective erosion of tilted strata the target at serra da cangalha is composed of devonian to permian sedimentary rocks mainly sandstones that are interlayered with siltstone and claystones nne ssw and wnw ese striking joint sets were present prior to the impact and also overprinted the structure after its formation as preferred zones of weakness these joint sets partly controlled the shape of the outer perimeter of the structure and in particular affected the deformation within the central uplift joints in radial orientation to the impact center did not undergo a change in orientation during tilting of strata when the central uplift was formed these planes were used as major displacement zones the asymmetry of the central uplift with preferred overturning of strata in the northern to western sector may suggest a moderately oblique impact from a southerly direction buckle folding of tilted strata as well as strata overturning indicates that the central uplift became gravitationally unstable at the end of crater formation

some analytical solutions of the linearized boussinesq equation with recharge for a sloping aquifer subsurface flow from a hillslope can be described by the hydraulic groundwater theory as formulated by the boussinesq equation several attempts have been made to solve this partial differential equation and exact solutions have been found for specific situations in the case of a sloping aquifer brutsaert 1994 suggested linearizing the equation to calculate the unit response of the hillslope in this paper we first apply the work of brutsaert by assuming a constant recharge to the groundwater table the solution describes the groundwater table levels and the outflow in function of time then an analytical expression is derived for the steady state solution by allowing time to approach infinity this steady state water table is used as an initial condition to derive another analytical solution of the boussinesq equation this can then be used in a quasi steady state approach to compute outflow under changing recharge conditions subsurface flow from a hillslope can be described by the hydraulic groundwater theory as formulated by the boussinesq equation several attempts have been made to solve this partial differential equation and exact solutions have been found for specific situations in the case of a sloping aquifer brutsaert 1994 suggested linearizing the equation to calculate the unit response of the hillslope in this paper we first apply the work of brutsaert by assuming a constant recharge to the groundwater table the solution describes the groundwater table levels and the outflow in function of time then an analytical expression is derived for the steady state solution by allowing time to approach infinity this steady state water table is used as an initial condition to derive another analytical solution of the boussinesq equation this can then be used in a quasi steady state approach to compute outflow under changing recharge conditions

rim uplift and crater shape in meteor crater effects of target heterogeneities and trajectory obliquity 1 we have analyzed the rim structure of meteor crater arizona in order to understand the mechanism of rim uplift in simple craters and the causes of the shape of polygonal impact craters for this purpose we systematically determined bedding orientation of the autochthonous crater wall and overturned flap and analyzed the kinematics of major radial faults we found that rim uplift correlates with the crater shape and increases in the corners of the crater the two main mechanisms of differential uplift are the formation of horizontal interthrust wedges leading to the doubling of strata in the rim and radial corner faults or tear faults that vertically displace bedrock the development of meteor crater s quadrangular shape is caused by more effective crater excavation flow parallel to major joint sets additionally we infer the impact direction with a newly developed technique the two corners model and review the arguments in favor of an oblique trajectory while the data set is ambiguous several indicators suggest an impact direction from the nnw we conclude that oblique impacts should have an effect on early cratering and excavation flow whereas target heterogeneities like joints start to play a prominent role in later stages when the stresses induced by the excavation flow are in the same order of strength as the material involved

low angle collision with earth the elliptical impact crater matt wilson northern territory australia nearly all meteorite impact craters on earth are circular however 4 of craters should be formed by impacts at angles lower than 12 from the horizontal which should result in elongated crater structures the crater forming process that produces elliptical shapes is poorly understood we document the first elliptical crater on earth that contains a central uplift and that provides insights into the mechanisms of crater formation at a critical threshold angle of 10 15 the dimensions of the proterozoic matt wilson impact structure northern territory australia are 7 5 by 6 3 km corresponding to an aspect ratio of 1 2 with its long axis trending northeast southwest the exposed crater floor shows a preferred stacking of thrust sheets within the central uplift and in the surrounding syncline indicating northeast southwest shortening and a material transport top to the sw this is consistent with an up range to down range motion of rock caused by remnant horizontal momentum transferred from the impacting projectile to the target this preferential deformation interferes with a radially oriented convergent material flow characteristic for crater collapse the matt wilson crater provides evidence for the usefulness of structural asymmetries as a diagnostic tool to infer impact vectors the new impact crater is confirmed by the presence of planar deformation features planar fractures in quartz grains and its structural inventory

experimental generation of shock induced pseudotachylites along lithological interfaces to understand the mechanism of formation of shock induced pseudotachylites and particularly the role that rock heterogeneities and interfaces play in their formation shock recovery experiments were carried out on samples consisting of two distinct lithologies dunite and quartzite it was possible to generate melt veins of 1 6 m width along lithological interfaces at moderate shock pressures 6 to 34 gpa the magnitudes of displacement along the interface strain rate and the kinetic heat production indicate that friction is an important heat source that largely contributes to the energy budget of the melt veins the experimentally produced veins resemble natural s type pseudotachylites the geometry of the veins depends on the orientation of the interface with respect to the shock front and includes strong variations in thickness formation of melt pockets and injection veins sudden changes in vein orientation and sharp vein margins two types of melt were observed vesicle free and vesicular melts dense vesicle free melt rock is likely to represent high pressure melts vesicular melts were also generated during shock compression but they remained in a molten state during pressure release and continued shearing intermingling of comminuted olivine and melt suggests that ultracataclasis of olivine induced by a dynamic tensile failure is a precursor stage to frictional melting shock wave interferences at the lithological interface provide the necessary stress conditions to start dynamic failure of olivine the composition of the frictional melts ranges from olivine normative to enstatite normative and is thus largely determined by olivine melting the validity of the sequence of friction melting susceptibilities of rock forming minerals inferred from tectonically produced pseudotachylites is confirmed and can now be applied to ultra high strain rates during shock compression

a 20 km diameter multi ringed impact structure in the north sea most craters found on earth are highly eroded poorly preserved and only exposed on land here we describe a multi ringed impact structure discovered in the north sea from the analysis of three dimensional seismic reflection data the structure is 20 km in diameter and has at least ten distinctive concentric rings located between 2 and 10 km from the crater centre the structure affects cretaceous chalk and jurassic shales and is well preserved below several hundred metres of post impact tertiary strata which constrains its age to be 60 65 myr old the formation of concentric ringed impact structures at this relatively small scale had not previously been thought possible especially on the terrestrial planets we have mapped the ring structures at a resolution of tens of metres both laterally and in depth and show that the rings are fault bounded graben structures similar to fault arrays formed in low strain rate detachment tectonic settings strata deeper than 500 m palaeodepth appear unfaulted and we infer that the concentric ring structures may have accommodated post impact extension towards the excavated crater through detachment on weak layers within the chalk

seawater intrusion in response to sea level rise in a coastal aquifer with a general head inland boundary seawater intrusion in response to sea level rise has been studied extensively in recent years by assuming largely a constant head or constant flux inland boundary condition however these two types of boundary conditions are not sufficient when the inland edge of the model domain is neither natural groundwater nor known hydraulic boundaries under these circumstances a general head inland boundary condition capable of characterizing the hydraulic response of model boundaries is needed previous studies adopting the general head inland boundary condition to assess coastal aquifer vulnerability to sea level rise are limited and all based on numerical modeling in this study we derive analytical solutions of the interface toe location in both confined and unconfined coastal systems with a general head inland boundary condition comparison among the performances of the three different types of inland boundary conditions in evaluating the sea level rise impact on aquifer salinization is carried out by assuming the same initial system condition it is found that the displacement of the interface toe predicted using a general head inland boundary is between those of using a constant head upper bound and constant flux lower bound inland boundary depending on the values of two general head boundary parameters i e hydraulic conductance and reference head more importantly analytical solutions developed could serve as a tool for calibrating the two boundary parameters defined in the general head boundary condition for site specific assessments

origin of large volume pseudotachylite in terrestrial impact structures large volume pseudotachylite bodies in impact structures are dike like and consist of angular and rounded wall rock fragments enveloped by a microcrystalline and sporadically glassy matrix that crystallized from a melt knowledge of the formation of pseudotachylite bodies is important for understanding mechanics of complex crater formation most current hypotheses of pseudotachylite formation inherently assume that fragmentation and melt generation occur during a single process based on the structure of pseudotachylite bodies at sudbury canada and vredefort south africa we show that these processes differ in time and space we demonstrate that the centimeter to kilometer scale bodies are effectively fragment and melt fi lled tension fractures that formed by differential rotation of target rock during cratering highly variable pseudotachylite characteristics can be accounted for by a single process i e drainage of initially superheated impact melt into tension fractures of the crater fl oor

formation of pseudotachylitic breccias in the central uplifts of very large impact structures scaling the melt formation abstract the processes leading to formation of sometimes massive occurrences of pseudotachylitic breccia ptb in impact structures have been strongly debated for decades variably an origin of these pseudotachylite friction melt like breccias by 1 shearing friction melting 2 so called shock compression melting with or without a shear component immediately after shock propagation through the target 3 decompression melting related to rapid uplift of crustal material due to central uplift formation 4 combinations of these processes or 5 intrusion of allochthonous impact melt from a coherent melt body has been advocated our investigations of these enigmatic breccias involve detailed multidisciplinary analysis of millimeter to meter sized occurrences from the type location the vredefort dome this complex archean to early proterozoic terrane constitutes the central uplift of the originally 250 km diameter vredefort impact structure in south africa previously results of microstructural and microchemical investigations have indicated that formation of very small veinlets involved local melting likely during the early shock compression phase however for larger veins and networks it was so far not possible to isolate a specific melt forming mechanism macroscopic to microscopic evidence for friction melting is very limited and so far chemical results have not directly supported ptb generation by intrusion of impact melt on the other hand evidence for filling of dilational sites with melt is abundant herein we present a new approach to the mysterium of ptb formation based on volumetric melt breccia calculations the foundation for this is the detailed analysis of a 1 5 3 0 04 m polished granite slab from a dimension stone quarry in the core of the vredefort dome this slab contains a 37 5 dm3 breccia zone the pure melt volume in 0 1 m3 ptb bearing granitic target rock outside of the several decimeter wide breccia zone in the granite slab was estimated at 5 2 dm3 this amount can be divided into 4 6 dm3 melt 88 for which we have evidenced a limited material transport at maximum 20 cm and 0 6 dm3 melt 12 with at most grain scale material transport which we consider in situ formed shock melt the breccia zone itself contains about 10 dm3 of matrix melt assuming melt exchange over 20 cm at the slab surface between breccia zone and surrounding melt bearing host rock volume the outer melt volume is calculated to contain the same amount of melt as contained by the massive breccia zone meso and microscopic observations indicate melt transport is more prominent from larger into smaller melt occurrences thus melt of the breccia zone could have provided the melt fill for all the small scale ptb veins in the surrounding target rock extrapolating this melt capacity calculation for 1 m3 ptb bearing host rock shows that a host rock volume of this dimension is able to take up some 52 dm3 melt scaling up 1000 fold to the outcrop scale reveals that exchange between a host rock volume of 2 m radius around a 37 m3 breccia zone could involve some 10 m3 melt these results demonstrate that large melt volumes i e large breccia zones can be derived in principle from local reservoirs however strong decompression would have to apply in order to exchange these considerable melt volumes which would only be realistic during the decompression phase of impact cratering upon central uplift formation or locally where compressive regimes acted during the subsequent down and outward collapse of the central uplift

modeling damage and deformation in impact simulations numerical modeling is a powerful tool for investigating the formation of large impact craters but is one that must be validated with observational evidence quantitative analysis of damage and deformation in the target surrounding an impact event provides a promising means of validation for numerical models of terrestrial impact craters particularly in cases where the final pristine crater morphology is ambiguous or unknown in this paper we discuss the aspects of the behavior of brittle materials important for the accurate simulation of damage and deformation surrounding an impact event and the care required to interpret the results we demonstrate this with an example simulation of an impact into a terrestrial granite target that produces a 10 km diameter transient crater the results of the simulation are shown in terms of damage a scalar quantity that reflects the totality of fragmentation and plastic strain both total plastic strain the accumulated amount of permanent shear deformation regardless of the sense of shear and net plastic strain the amount of permanent shear deformation where the sense of shear is accounted for damage and plastic strain are both greatest close to the impact site and decline with radial distance however the reversal in flow patterns from the downward and outward excavation flow to the inward and upward collapse flow implies that net plastic strains may be significantly lower than total plastic strains plastic strain in brittle rocks is very heterogeneous however continuum modeling requires that the deformation of the target during an impact event be described in terms of an average strain that applies over a large volume of rock large compared to the spacing between individual zones of sliding this paper demonstrates that model predictions of smooth average strain are entirely consistent with an actual strain concentrated along very narrow zones furthermore we suggest that model predictions of total accumulated strain should correlate with observable variations in bulk density and seismic velocity

ejecta formation and crater development of the mjolnir impact crater ejecta correlation is an important element in the analysis of crater formation and its influence on the geological evolution in this study both the ejecta distribution and the internal crater development of the jurassic cretaceous mjolnir crater 40 km in diameter located in the barents sea are investigated through numerical simulations the simulations show a highly asymmetrical ejecta distribution and underscore the importance of a layer of surface water in ejecta distribution as expected the ejecta asymmetry increases as the angle of impact decreases the simulation also displays an uneven aerial distribution of ejecta the generation of the central high is a crucial part of crater formation in this study peak generation is shown to have a skewed development from approximately 50 90 sec after impact when the peak reaches its maximum height of 1 1 5 km during this stage the peak crest is moved about 5 km from an uprange to a downrange position ending with a final central position which has a symmetrical appearance that contrasts with its asymmetrical development

generation and crystallization of an amphibolite shear melt an investigation using radial friction welding apparatus a cylinder of amphibolite comprising the assemblage amphibole clinozoisite albite has been frictionally melted using radial friction welding apparatus this was achieved by rotating a steel ring at 750 rpm and a force of 98 kn for 10 s against a stationary steel casing which housed the rock sample the ring penetrated the casing then proceeded to rotate and compress the sample to 95 of its original volume until it cracked at right angles to its length this generated a whole rock silicate melt which injected the crack and on cooling produced glass crystallites and vesicles melting occurred in two stages an initial low pressure melting event with crystallization to augite fe rich anorthite followed by a high pressure melting event with crystallization to fassaitic clinopyroxene it is estimated that pressures of 0 5 gpa rising to 1 gpa were realized at the ring rock interface under these conditions fassaite superseded augite anorthite crystallization due to the increased solubility of ca tschermak s component in clinopyroxene the high pressure event provides a crude analogue for the frictional melting of basic rock at depths of 15 30 km in a seismogenic fault a situation realized along the slip zone between cold descending lithosphere and overlying mantle during subduction

a correction for dupuit forchheimer interface flow models of seawater intrusion in unconfined coastal aquifers interface flow models that use the dupuit forchheimer df approximation for assessing the freshwater lens and the seawater intrusion in coastal aquifers lack representation of the gap through whic

effects of wave forcing on a subterranean estuary wave and tide are important forcing factors that typically co exist in coastal environments a numerical study was conducted to investigate individual and combined effects of these forces on flow and mixing processes in a near shore subterranean estuary a hydrodynamic model based on the shallow water equations was used to simulate dynamic sea level oscillations driven by wave and tide the oscillating sea levels determined the seaward boundary condition of the coastal aquifer where variably saturated variable density flow was modeled the simulation results showed that waves induced an onshore upward tilt in the phase averaged sea level wave set up the resulting hydraulic gradient generated pore water circulations in the near shore zone of the coastal aquifer which led to formation of an upper saline plume usp similar to that due to tides however mixing of recirculating seawater in the usp with underlying fresh groundwater was less intensive under the high frequency wave oscillations in the case of combined forcing wave induced circulations coupled with the intra tidal flows strengthened the averaged circulating pore water flows in the near shore zone over the tidal period the circulating flows increased exchange between the subterranean estuary and ocean contributing 61 of the total submarine groundwater discharge for the simulated condition in comparison with the 40 and 49 proportions caused by the same but separate tidal and wave forcing respectively the combined forces also created a more extensive usp with the freshwater discharge zone shifted further seaward the freshwater flow paths in the intertidal subterranean estuary were altered with a significant increase of associated transit times the interplay of wave and tide led to increased mixing between discharging fresh groundwater and recirculating seawater these results demonstrated the complexity of near shore groundwater systems and have implications for future investigations on the fate of land sourced chemicals in the subterranean estuary prior to discharge to the ocean

coseismic deformation field observations and seismic fault of the 17 november 2015 m 6 5 lefkada island greece earthquake abstract on november 17 2015 07 10 07 utc a strong shallow mw6 5 earthquake occurred on the island of lefkada along a strike slip fault with right lateral sense of slip the event triggered widespread environmental effects at the south and western part of the island while the intensity and severity of these earthquake induced deformations is substantially decreased towards the eastern part of the island relocation of seismicity and inversion of geophysical gps insar data indicate that the seismic fault runs parallel to the west coast of lefkada along the aegean apulia plate boundary the fault plane strikes n20 5 e and dips to east with an angle of about 70 5 coseismic deformation was measured in the order of tens of centimeters of horizontal motion by continuous gps stations of noanet the noa gps network and by insar sentinel 1 a image pairs a coseismic uniform slip model was produced from inversion of insar data and permanent gps stations the earthquake measured mw 6 5 using both the geodetic moment produced by the slip model as well as the pgd relation of melgar et al 2015 grl in the field we observed no significant vertical motion of the shoreline or surface expression of faulting this is consistent with the predictions of the model the interferograms show a large decorrelation area that extends almost along all the western coast of lefkada this area correlates well with the mapped landslides the 2003 2015 pattern of seismicity in the ionian sea region indicates the existence of a 15 km seismic gap offshore nw cephalonia