the impact cratering rate in recent time data on the recent cratering rate in the earth moon system is somewhat ambiguous with respect to whether the rate has been constant over the last 3 b y rate estimates based on the present population of earth crossing bodies are higher than estimates based on crater counts at the apollo 12 and 15 sites while some estimates based on terrestrial crater counts are intermediate in value the terrestrial data base for structures with diameter d 20 km on the north american and european cratons has been investigated for variations in the rate with time there appear to be two populations with a 0 120 m y age group suggesting a higher cratering rate than an older 200 360 m y age group reexamination of the preservation levels of these structures indicates that the topography of a 20 km sized structure may be removed by erosion in 34 to 273 m y and the geologic anomaly resulting from structural uplift in 79 to 630 m y this suggests that the relatively lower rate for the 200 360 m y group may reflect problems in crater recognition associated with crater retention if rate estimates are restricted to the possibly more complete sample of 0 120 m y craters on the cratons the recalculated rate is 5 4 2 7 0 15 km 2 y 1 for d 20 km this is comparable to that based on earth crossers and reinforces previous suggestions that the recent cratering rate may be a factor of 2 3 higher than the average rate over the last 3 0 b y this rate estimate when extrapolated back in time is a better fit to lunar data from tycho and copernicus than a constant rate based on apollo 12 and 15 data and may be interpreted to suggest that the relatively higher recent rate has been in effect for 1 b y given the uncertainties however this must be regarded as speculative

landslide hazard evaluation and zonation mapping in mountainous terrain abstract landslide hazard zonation lhz maps are of great help to planners and field engineers for selecting suitable locations to implement development schemes in mountainous terrain as well as for adopting appropriate mitigation measures in unstable hazard prone areas a new quantitative approach has been evolved based on major causative factors of slope instability a case study of landslide hazard zonation in the himalaya adopting a landslide hazard evaluation factor lhef rating scheme has been presented

terrestrial mantle siderophiles and the lunar impact record a simple analytical fit to the lunar cratering record scaled from final to transient crater diameters then to impactor masses implies a total mass 1 0 1020kg incident on the moon subsequent to the solidification of the lunar crust 4 4 gyr ago about half this mass would be retained and a comparable lunar mass would be eroded these results are in good agreement with geochemical estimates of the meteoritic component mixed into the lunar crust which give 0 4 1 5 1020 kg gravitationally scaling to earth and taking account of the statistical probability that the largest impactors incident on earth were more massive than the largest incident on the moon gives an estimate of 1 5 1022 kg of material accumulated by earth subsequent to 4 4 gyr ago this result is in excellent accord with geochemical estimates of post core formation meteoritic input these estimates based on abundances of highly siderophile elements in the terrestrial mantle lie in the range 1 4 1022 kg the significant result is the approximate agreement of the lunar cratering record scaling with both lunar and terrestrial geochemical constraints numerous uncertainties render exact comparisons pointless nevertheless the close agreement suggests the model developed here may credibly be used to estimate exogenous volatile and prebiotic organic delivery

assessing landslide potential using gis soil wetness modeling and topographic attributes payette river idaho this study utilizes gis modeling to determine if the location of 559 landslides in the 875 km2 catchment of the middle fork of the payette river idaho can be predicted based on topographic attributes and a wetness index generated by the dynwet model slope and elevation were significantly related to landslide occurrence at this landscape scale aspect was also retained as a variable for further analysis because despite a non significant chi square relation to landslide occurrence graphical analysis suggested a relation between aspect and mass wasting chi square analysis indicated that plan and profile curvature flow path length upslope contributing area and the dynwet based moisture index were not significantly related to landsliding a bayesian probability model based on combinations of elevation slope aspect and wetness indicates that elevation exhibits the closest relation to landsliding followed by slope but that neither aspect nor wetness index values help in prediction the bayesian probability model using elevation and slope generates a map of relative landslide risk that can be used to direct activities away from mass wasting prone areas the association between elevation and landslides is perplexing but is perhaps due to the location of logging road at specific elevations roads could not be included in the input data for analysis because they have not been adequately mapped the lack of explanation provided by the dynwet wetness index was also surprising and may be due to the 30 m digital elevation model dem and the soils data having resolutions too coarse to adequately portray local variations key to mass wasting we believe the inadequacy of data to drive the models is typical of the majority of catchment scale setting for now the ability of researchers to effectively model landscape scale landsliding is more limited by the type resolution and quality of available data than by the quality of the landslide models

gis techniques and statistical models in evaluating landslide hazard geographical information systems gis and numerical cartography may greatly facilitate the development and use of statistical models for the assessment of regional landslide hazard from a small drainage basin located in central italy relevant geological and geomorphological factors were collected and processed by applying gis technology in particular modules were used which both generate high fidelity digital terrain models and automatically partition the terrain into main slope units the resulting information was then analysed by discriminant analysis which enabled landslide hazard and risk to be evaluated in each slope unit although not lacking drawbacks the method proved to be a feasible and cost effective approach to landslide susceptibility assessment and mapping

the influence of a grain shape fabric on the mechanical behaviour of rock salt results from deformation experiments abstract in order to assess the effect of shape preferred orientation spo of halite grains on deformation of rock salt ductile plane strain deformation experiments have been conducted natural halite cubes with and without an spo from the asse mine of northern germany were deformed at 345 c atmospheric pressure and a strain rate of 10 7 s 1 the spo was oriented at different angles s 0 45 and 90 to the main shortening direction z the sample is confined in the y direction and can freely move to the principal stretching direction x most of the strain was accommodated by dislocation creep the qualitative analysis of the stress strain data shows the clear influence of the spo on the mechanical data at a shortening strain of ca 10 the samples with 0 and 45 are weaker than the samples without an spo in contrast the sample with 90 is stronger than the samples without an spo a new spo is formed in all samples with the long axis of the grain shape fabric being subparallel to the principal stretching axis x at these larger shortening strains the samples show similar strength with an exception of the 90 oriented sample that is still stronger than the samples without an spo even though the experimental set up has to be improved to obtain quantitative results on the influence of spo on mechanical strength of rock salt the results show that the spo of rock salt likely has to be taken into account when building a repository for nuclear waste and could have an effect on the stability of caverns

rheology of rocksalt abstract we review progress in experimental determinations of transient and steady state flow properties and processes of natural rocksalt aggregates focusing primarily on results from avery island louisiana domal salt the steady state flow field established from constant stress and constant strain rate tests at temperatures from 50 to 200 c strain rates from 10 5 to 10 9 s 1 and differential stresses from 20 7 to 2 5 mpa has been separated into two flow regimes each fit by a power law relation at the higher stresses and strain rates this relation is e 1 6 10 4 exp 68 1 rt 10 3 5 3 for which the pre exponential constant is expressed in mpa 5 3 s 1 and the apparent activation energy is in j mol 1 creep rates predicted by equation a do not differ appreciably from those predicted previously the relatively low stress low strain rate data are very well fit by e 8 1 10 5 exp 51 6 rt 10 3 2 4 which is comparable conditions predicts creep rates higher and equivalent viscosities lower than does equation a by two orders of magnitude the change in behavior from a to b is ascribed to a change in rate limiting mechanism from cross slip of screw dislocations to the climb of edge dislocations in this dry material subgrain formation dominates microstructural development during steady state flow of salt and from determinations of average subgrain diameters in crystals from 20 different rocksalt bodies flow stress levels between 0 6 and 1 4 mpa have been estimated these values do not bear directly on arguments concerning the nature of forces initiating salt pillow growth because apparently evidence relating to the early deformational history has been overprinted at that stage fluid assisted grain boundary diffusional processes might dominate dislocation creep leading to a linear stress strain rate mechanical response considering buoyancy forces alone behavior described by equation b rather than a reduces the relief necessary to initiate pillow growth but a 1000 fold amplification is required to produce stress differences near 1 mpa that forces other than buoyancy are important is indicated by the occurrence of these same paleostress levels in bedded salts and in shallow offshore concordant intrusions differential loading generally provides the most plausible initial driving force for the growth of diapiric salt structures

a physically based model for the topographic control on shallow landsliding a model for the topographic influence on shallow landslide initiation is developed by coupling digital terrain data with near surface through flow and slope stability models the hydrologic model topog o loughlin 1986 predicts the degree of soil saturation in response to a steady state rainfall for topographic elements defined by the intersection of contours and flow tube boundaries the slope stability component uses this relative soil saturation to analyze the stability of each topographic element for the case of cohesionless soils of spatially constant thickness and saturated conductivity the steady state rainfall predicted to cause instability in each topographic element provides a measure of the relative potential for shallow landsliding the spatial distribution of critical rainfall values is compared with landslide locations mapped from aerial photographs and in the field for three study basins where high resolution digital elevation data are available tennessee valley in marin county california mettman ridge in the oregon coast range and split creek on the olympic peninsula washington model predictions in each of these areas are consistent with spatial patterns of observed landslide scars although hydrologic complexities not accounted for in the model e g spatial variability of soil properties and bedrock flow control specific sites and timing of debris flow initiation within areas of similar topographic control

mechanisms of dynamic recrystallization in naturally deformed dolomite inferred from ebsp analyses abstract in order to investigate the mechanisms of dynamic recrystallization in dolomite single grain orientation measurements on a mantled porphyroclast have been carried out by means of electron back scattered patterns ebsps the local orientations in the grain fabric were analysed to establish meaningful orientation families in addition to a twinned grain the porphyroclast consists of two domains each with a specific orientation pattern both domains are polygonized by subgrain rotation which gives great and small circle dispersion patterns of the crystal orientation data in the pole figures however even the simple and well defined dispersion patterns for which one can assume a single slip system are not consistent with any of the theoretical dispersion patterns of the known slip systems additional mechanisms like rigid body rotation nucleation and or combinations of different slip systems are the likely explanation no definitive orientation relationship has been found between the porphyroclast and the mantle the lack of such a relationship together with the shape of the grain boundary point to grain boundary migration the texture of the mantle agrees with the global texture of the sample indicating that mechanisms of crystal plasticity were active during flow around the clast the results demonstrate the potential of ebsp data for the deduction of active mechanisms but a proper interpretation requires a better theoretical foundation this could be achieved by modelling dispersion patterns for different mechanisms and different combinations and by including orientation correlations

extraterrestrial influences on mantle plume activity abstract we use time series analysis to compare the impact histories of the earth and moon with the record of mantle plume activity we use events with errors in their ages of 150 ma the terrestrial and lunar impact records when smoothed at a 45 ma interval correlate at a 97 confidence level this high confidence level suggests that we have an adequate sampling of most of the major impact events on the earth we then test the idea that existing mantle plumes may be strengthened by impacts when smoothed at a 45 ma interval strong plumes correlate with the terrestrial impact record at better than a 99 confidence level no time lag is discernible between the data sets which is expected given their present error level when the time series are smoothed at a 30 ma interval there are 10 major peaks in impact activity nine out of ten of these peaks have a counterpart in either or both of the strong mantle plume or the mantle plume time series as a result the strong mantle plume and the impact time series correlate at the 97 confidence level the mantle plume and the impact time series correlate at the 90 confidence level finally the deccan plume showed greatly increased activity immediately after the chixculub impact the results of our analysis suggest that large meteorite and cometary impacts may well increase the amount of volcanism from already active mantle plumes

direct evidence of ancient shock metamorphism at the site of the 1908 tunguska event abstract shock metamorphism is rarely found at the surface of the earth the most used structures to identify shock metamorphism are true planar deformation features pdfs in quartz now accepted as diagnostic indicators of a meteorite impact here we present several lines of evidence for shock metamorphism and pdfs developed in quartz occurring on samples centered on a circular geological structure on mount stojkovic 60 54 06 n 101 55 40 e which lies within southern surface exposures of the siberian traps the shock event appears to have occurred during the eruption of the surface siberian traps basalts that cover this region curiously mount stojkovic lies within 3 km of the tree fall epicenter of the 1908 tunguska event based on current estimates of the phanerozoic impact distribution there is at most a 1 in 17 000 chance that the 1908 bolide would randomly fall on the site of a previous impact structure capable of creating shocked quartz just as improbable would be an airbust event incapable of creating a small crater that could have produced shock metamorphism our preferred least implausible hypothesis is that the shock metamorphism here was associated with a terrestrial event a hyperexplosive volcanic gas eruption called verneshot

structural characteristics of the halite fabric type kristallbrocken from the zechstein basin with regard to its development the kristallbrocken are a characteristic centimetre to decimetre sized laminated halite fabric type occurring in the stassfurt formation in the zechstein basin up to now the nature of the kristallbrocken i e if they are relics of fine grained polycrystalline halite beds or clasts of single crystal layers as well as the deformation mechanisms of this halite type were not clear from the literature drill core material from the salt deposit teutschenthal at the southern rim of the zechstein basin now allowed investigating less intensely deformed samples for the first time the deformational behaviour of these kristallbrocken ranges from brittle to ductile which is evidenced by fractured kristallbrocken on the one hand and weakly bent or even folded kristallbrocken on the other hand local x ray texture measurements demonstrated that the kristallbrocken are definitely single crystals and that they can be regarded as relics of formerly larger single crystal layers of up to several dm2 in size the folded kristallbrocken clearly display by their single grain texture characteristics that their crystal lattice is bent which was most likely enabled by a kind of flexural shear folding and did not develop after deformation from a fine grained aggregate by recrystallisation due to their monocrystallinity their originally large size and the solid inclusions forming the internal lamination the kristallbrocken have clearly stronger rheological properties than the surrounding fine to coarse grained polycrystalline rock salt and thus also deform by fracturing

microfabrics and 3d grain shape of gorleben rock salt constraints on deformation mechanisms and paleodifferential stress abstract the permian knauel and streifensalz formations z2hs1 and z2hs2 are main constituents of the gorleben salt dome northern germany and show different amounts and distributions of anhydrite the reconstruction of 3d halite grain shape ellipsoids reveals small grain size 3 4 0 6 mm and heterogeneous grain shapes in both formations the latter attributed to the polyphase deformation of the rock salt during diapirism the halite microfabrics of both formations indicate that strain induced grain boundary migration was active during deformation crystal plastic deformation of halite is further documented by lattice bending subgrain formation and minor subgrain rotation evidence for pressure solution of halite has not been found but cannot be excluded because of the small grain size the lack of lpo and the low differential stress 1 1 1 3 mpa as deduced from subgrain size piezometry anhydrite has been deformed in the brittle ductile regime by solution precipitation creep minor dislocation creep and brittle boudinage no continuous anhydrite layers are preserved and halite has acted as a sealing matrix embedding the disrupted anhydrite fragments prohibiting any potential migration pathways for fluids thus anhydrite should not have a negative effect on the barrier properties of the gorleben rock salts investigated in this study

the geochronology of large igneous provinces terrestrial impact craters and their relationship to mass extinctions on earth the relationship between sudden catastrophic events and sudden mass extinctions on earth has attracted a great deal of research effort including measurements of the absolute and relative ages of these events the result has been a rapid improvement in the precision and accuracy of radiometric dates for large igneous provinces lips for which there is now a consensus on the peak eruption times over the last 250 ma in parallel there has been a more gradual improvement in the radiometric dates for craters formed by hypervelocity impacts hvis of asteroids and comets with earth the absolute ages of the largest craters are known to within a few million years but the ages of many smaller craters are poorly constrained in addition whereas relatively few lips have formed in the last 250 ma at least one hvi crater larger than 20 km diameter has formed on earth every million years only 25 such craters have been discovered so coincidence between the ages of hvi crater formation and ages of mass extinctions is related as much to crater preservation as to coincidence of the events the difference in quality of geochronology between hvis and lips is the result of differing availability of samples lips cover large areas and present an array of basalt samples suitable for dating whereas hvi craters are often poorly preserved and present few datable samples the radiometric data for preserved hvis and lips are now sufficiently precise and accurate for us to be confident that there is no one to one correlation between either lips or hvis and global mass extinctions of life on earth however there is a close association between a significant number of lips and sudden environmental change and a very close association between at least one massive hvi crater formation and a mass extinction further there is no apparent correlation between hvis and lips and thus no reason to suggest a causative relationship finally the radiometric dating of hvi craters indicates several clusters in the geological record but the correlation with sudden environmental change is no better than for large craters

evaluation of multispectral fine scale digital imagery as a tool for mapping stream morphology abstract multispectral digital imagery acquired from soda butte and cache creeks montana and wyoming was used in conjunction with field data to classify and map hydrogeomorphic stream units on four stream reaches the morphologic units that were field mapped were eddy drop zones glides low gradient riffles high gradient riffles lateral scour pools attached bars detached bars and large woody debris unsupervised and supervised classifications of the imagery were used to develop a maximum joint probability classification and an alternative joint probability classification of the stream reaches the maximum joint probability classification allowed only one of the image classes to represent each hydrogeomorphic unit on the field map and resulted in relatively low overall accuracies for identification of these units of 10 to 50 the alternative joint probability classification allowed each image class to represent any geomorphic unit where the probability of a correct classification was greater than random in this technique two or three image classes were assigned to represent each hydrogeomorphic unit resulting in higher overall accuracies of 28 to 80 accurate classification of hydrogeomorphic units was hampered by poor rectification of imagery with the field maps because of inadequate ground control points in general the largest hydrogeomorphic units were most accurately classified whereas units that were small in area or spatially linear were least likely to be accurately classified the results of this study demonstrated that multispectral digital imagery has the potential to be a useful tool for mapping hydrogeomorphic stream units at fine scales imagery to be an effective tool however careful measures such as accurate documentation of ground control points must be taken to ensure accurate rectification of the imagery with field maps

bromide distribution characteristics of different zechstein 2 rock salt sequences of the southern permian basin a comparison between bedded and domal salts the bromide profile of the bedded zechstein 2 rock salts in the southern permian basin is characterized by a continuous increase in the bromide contents from base to top indicating progressive evaporation of sea water former studies have suggested that the bromide distribution in domal salts is more irregular raising such questions as whether there is a causal relationship between bromide distribution and deformation related processes or whether various halite types with different primary bromide contents account for such irregularities in this study the bromide distribution of a defined stratigraphic section hauptsalz of the zechstein 2 was investigated in three salt deposits with bedded salt teutschenthal compared with domal salts morsleben and gorleben furthermore two different halite types kristallbrocken matrix were distinguished during sampling comparison between the locations reveals that i the characteristic trend of the bromide profile was generally preserved in both the bedded and the more intensely deformed domal salts ii the dispersion of bromide contents along the running average curve is lower in domal salt especially in the lower half of the hauptsalz and iii the kristallbrocken are absent in the lower half of the hauptsalz of morsleben and gorleben the absence of the kristallbrocken and the lower dispersion of the bromide contents in the domal salts are clear indications for the influence of salt migration related processes on the bromide distribution characteristics it shows that these processes are associated with a redistribution of bromide which eventually results in a homogenization of the originally varying bromide contents on the other hand preservation of the characteristic trend in the bromide profiles indicates that large scale brecciation folding processes or circulating bromide rich fluids played only a minor role during the formation of the salt domes selective sampling of the kristallbrocken and matrix halite displays a disparity in bromide content that is not consistent between the studied locations these specific phenomena might be related to different depositional locations in the zechstein basin or to post depositional processes

mid jurassic volcanic structures in the outer moray firth basin uk 3d seismic mapping in the southern part of quadrant 15 in the outer moray firth basin reveals an array of circular to oval downthrown blocks bound by steep ring faults these lows affect triassic and older strata are approximately 1 5 2 km in diameter and 0 5 1 km deep the footwall crests of the structures now lie at a depth of c 2 5 km several alternative causal mechanisms for these circular fault blocks are examined including salt dissolution strike slip pull apart and impact cratering but in terms of geological and geometrical criteria the most likely mechanism appears to be small calderas or diatreme conduit collapse seismic data indicates that the circular structures cut triassic permian and devono carboniferous strata and are infilled with pre upper oxfordian sediments therefore they are broadly synchronous with mid jurassic volcanism local well control demonstrates the presence of several thousand feet of basalt tuffs and lavas the model proposed here to account for the circular structures consists of an initial phase of diatreme maar cratering as magmas associated with the rattray volcanics member intruded shallow aquifers in the pentland formation fluviodeltaic rocks these maars enlarged and deepened via conduit wall collapse supplemented by downsag faulting due to magma withdrawal the post volcanic evolution of the structures included 1 differential erosion creating accommodation space which may have been infilled with oxfordian reservoir sands and 2 local reactivation by underlying basement faults in the kimmeridgian

creep of rocksalt abstract a review is presented of the fundamental flow properties and processes in experimentally deformed natural and synthetic halite single crystals and polycrystalline aggregates included in the summary are discussions of a microstructures induced during steady state creep b creep rupture of rocksalt c experiments associated with project salt vault and more recent field studies and d brine migration a representative steady state flow law determined for natural aggregates and maximum natural deviatoric stresses deduced from subgrain sizes are applied briefly to considerations of creep in waste repositories and of salt dome dynamics while the mechanical behavior of rocksalt is probably better understood than for all other rock types further investigations especially on load path stress history and creep rupture are clearly mandated furthermore additional investigations of brine migration and of bench and field scale deformations are needed the latter incorporating realistic rocksalt flow properties into numerical simulations of natural rock mass response

landslide hazard zoning using the gis approach a case study from the ramganga catchment himalayas abstract this paper deals with the development of a technique for risk assessment of landslide hazards using the geographic information system gis approach the method has been applied to the ramganga catchment lying in the lower himalayas and the investigations are based on multi data sets the landslide activity is related to a number of parameters viz lithology land use distance from major tectonic shear zone and azimuth direction based on the data for 522 landslides in four selected sub basins an index value called landslide nominal risk factor lnrf is defined and developed for each of the important factors different weights have been assigned to the terrain depending upon the lnrf and integrated in an ordinal scale to help locate areas of high moderate and low landslide risk

volcanism impact and mass extinctions incredible or credible coincidences massive continental volcanism and or bolide impacts are considered by many authors to have caused three major mass extinction events during the last 300 million years the end permian end cretaceous and end triassic extinctions however reevaluation of the frequency of bolide impacts and plume related flood basalt provinces indicates that both types of event occur much more frequently than mass extinctions and so in isolation may not be responsible for the largest extinctions furthermore the kill mechanisms associated with either flood basalts or impacts do not appear to be sufficiently powerful to cause worldwide collapse of ecosystems leading to the largest mass extinctions contemporaneous flood basalts and bolide impact may be prerequisites for the largest mass extinctions we present a statistical analysis of the probability of coincidence between volcanism and impact and show that three random coincidences of these events in the last 300 m y are likely no causal relationship between impact and volcanism is necessary the lesser mass extinctions on the other hand may not require juxtaposition of two such catastrophic events such coincidences occurring on more than three occasions during the last 300 m y become increasingly unlikely d 2004 elsevier b v all rights reserved

geology and distribution of impact craters on venus what are they telling us magellan has revealed an ensemble of impact craters on venus that is unique in many important ways we have compiled a data base describing the 842 craters on 89 of venus surface mapped through orbit 2578 the craters range in diameter from 1 5 to 280 km we have studied the distribution size density morphology geology and associated surface properties of these craters both in the aggregate and for some craters in greater detail we find that 1 the spatial distribution of craters is highly uniform 2 the size density distribution of large craters diameters 35 km is similar to the young crater populations on other terrestrial planets but at a much lower density that indicates an average age of only about 0 5 ga based on the estimated population of venus crossing asteroids 3 unlike the case on other planets the density of small craters diameters 35 km declines rapidly with decreasing diameters because of atmospheric filtering 4 the spectrum of crater modification differs greatly from that on other planets 62 of all craters are pristine only 4 are embayed by lavas and the remainder are affected by tectonism but none are severely and progressively depleted as extrapolated from the size density distribution of larger craters 5 large craters have a progression of morphologies generally similar to those on other planets but small craters are typically irregular or multiple rather than bowl shaped 6 diffuse radar bright or dark features surround some craters and 367 similar diffuse splotches with no central crater are observed and 7 other crater features unique to venus include radar bright or dark parabolic arcs opening westward and extensive outflows originating in crater ejecta the first three of these observations are entirely unexpected we interpret them as indicating that the planet s cratering record was erased by a global resurfacing event or events the latest ending about 0 5 ga after which volcanic activity declined but did not cease entirely since the last resurfacing event a maximum of 10 of the planet has been resurfaced and only about 4 of the craters have been obliterated convective thermal evolution models support this interpretation arkani hamed and toksoz 1984 observations 3 7 confirm quantitatively the expectation that the dense atmosphere of venus has strongly affected the production of craters large impactors have been relatively unaffected intermediate sized ones have been fragmented and have produced overlapping or multiple craters a narrow size range has produced shock induced splotches but no craters and the smallest bodies have had no observable effect on the surface the number of craters eliminated by the atmospheric filter is enormous about 98 of the craters between 2 and 35 km in diameter that magellan might have observed on a hypothetical airless venus unique crater related features such as parabolas and outflow deposits demonstrate the roles of venus high atmospheric density and temperature in modifying the crater formation process finally heavily fractured craters and lava embayed craters are found to have higher than average densities along the major fracture belts and rifted uplands connecting aphrodite terra and atla beta themis and phoebe regiones these craters thus provide physical evidence for recent volcanic and tectonic activity at a low level

high temperature texture in naturally deformed carrara marble from the alpi apuane italy abstract from deformation experiments and numerical modelling a large type variety of crystallographic preferred orientations textures are known for calcite in contrast naturally deformed samples usually show the low temperature lt texture type with only minor texture variations the high temperature ht texture type is rarely described and mostly not very well defined based on neutron diffraction measurements and a quantitative texture analysis by means of the iterative series expansion method and the texture component model this study gives evidence for the ht texture type in a deformed marble from the alpi apuane in italy the microstructure of the sample shows elongated grains with long short axis ratios of up to 10 1 the long axes of the grains are oriented parallel to the general direction of transport indicating prolate strain but no shear sense from the texture a shear sense can be deduced that cannot be fully brought in line with the regional deformation and thermal history the results indicate a larger texture variety of naturally deformed calcite rocks than generally assumed this should stimulate further systematic texture studies for a better understanding of the texture forming mechanisms and the closely connected understanding of the kinematic significance of textures for the analysis of regional deformation histories

estimates of yet to find impact crater population on earth abstract one hundred and seventy six craters on earth are currently accepted as resulting from bolide impact this list is growing at a rate of approximately two craters per year because of new discoveries and revised interpretations here we take the subset of craters most relevant to sedimentary basin exploration and utilization phanerozoic kilometre scale craters and tackle the question of how many remain to be found in phanerozoic strata on earth a surprising range in predictions of crater numbers is obtained from published crater population functions reaching two orders of magnitude variation for craters in the range 1 5 km diameter this range in predictions is largely due to variations in treatment of impactor breakup in the atmosphere also required is quantification of the total area and timespan of phanerozoic sediment currently preserved on earth an estimate of 8 87 10 15 km 2 a is derived here together with a relatively conservative crater population function this yields a prediction of 845 craters subtracting the 131 known phanerozoic craters larger than 1 km leaves a predicted population yet to find of 714 of which 228 are larger than 2 5 km uncertainties subsets of this population and spatial distribution are also considered

landslide susceptibility mapping of the slopes in the residual soils of the mengen region turkey by deterministic stability analyses and image processing techniques abstract the aim of the present study is to prepare a landslide susceptibility map of a region of about 120 km2 between gokcesu and pazarkoy around mengen nw turkey at approximately 10 km north of the north anatolian fault zone where frequent landslides occur for this purpose mechanisms of the landslides were studied by two dimensional stability analyses together with field observations and the parameters controlling the development of such slides were identified field observations indicated that the failures generally developed within the unconsolidated and or semiconsolidated soil units in forms of rotational successive shallow landslides within the weathered zone in mengen cukurca and sazlar formations although consisting of residual soils capak and gokdag formations do not exhibit landslides as the natural slopes formed on these do not exceed the critical slope angles statistical evaluations and distribution of the landslides on the topographical map showed that such parameters as cohesion angle of internal friction slope relative height orientation of slopes proximity to drainage pattern vegetation cover and proximity to major faults were the common features on the landslides digital images were obtained to represent all these parameters on gray scale on the spot image and on the digital elevation model dem of the area using image processing techniques soil mechanics tests were carried out on 36 representative samples collected from different units and parameters were determined for two dimensional stability analyses basing on sensitivity approach and for the preparation of digital shear strength map in order to determine the critical slope angle values for the residual soils a series of sensitivity analyses were realized by using two dimensional deterministic slope stability analyses techniques for varying values of cohesion angle of internal friction and slope height along with varying saturation conditions according to the results of the sensitivity analyses the mengen formation was found to be most susceptible unit to landslides covering about 33 5 of the region studied in terms of surface area the distribution of the critical slopes were determined by superimposing the critical slope values from sensitivity analyses on slope map of the study area on the other hand iso cohesion and iso friction maps were produced by locating the values of cohesion and internal friction angles in a geographic coordinate system such that they coincide with sample locations on the dem and by further interpolation of the values concerned the pixel values were evaluated in gray scale from 0 to 255 0 representing the lowest pixel value and 255 representing the highest sensitivity analyses on cohesion and angle of internal friction to investigate the effects of these parameters only on stability revealed that cohesion was effective at a rate of 70 by itself while angle of internal friction alone controlled the stability by a rate of 30 the iso cohesion and iso friction maps previously obtained were digitally combined in these rates and a shear strength map was prepared the geographic setting of the study area is such that northern slopes usually receive dense precipitation in relation to this fact about 42 of the landslides are due north thus a slope orientation map was prepared using the dem and slopes facing north were evaluated as being more susceptible to sliding proximity to the drainage pattern was another important factor in the evaluation as streams could adversely affect the stability by either eroding the toe or saturating the slope or both when considered together in conjunction with the field observations faults and landslides showed a close association in the area about 88 of the landslides were detected within an area closer than 250 m to major faults therefore a main discontinuity map was produced using the spot image of the region and proximity to major faults was evaluated as a parameter as most of the landslides developed in areas where the vegetation was rather sparse a vegetation cover map was therefore obtained from the spot image and the areas with denser vegetation were considered to be less susceptible to sliding with respect to the areas with less or no vegetation having prepared the maps accounting for the distribution of critical slopes shear strength properties relative height slope angle orientation of the slopes vegetation cover proximity to the drainage pattern geographic corrections were carried on each of these and a potential failure map was obtained for the residual soils by superimposing all these maps next a classification was performed on the final map and five relative zones of susceptibility were defined when compared with this map all of the landslides identified in the field were found to be located in the most susceptible zone the performance of the method used in processing the images appears to be quite high the zones determined on the map being the zones of relative susceptibility

geological and tectonic investigations in the former morsleben salt mine germany as a basis for the safety assessment of a radioactive waste repository abstract the safety assessment of a repository for radioactive waste is based on the results of model simulations and scenario analysis to obtain a well founded geological basis for this extensive geological and structural studies have been carried out for the morsleben repository the morsleben repository for radioactive waste was constructed in zechstein strata the location of the werra formation z1 was located in boreholes and the stassfurt z2 leine z3 and aller z4 formations are exposed in the repository mine the zechstein salt has a total thickness in the western part of the salt body of 580 m in the eastern part it is only 380 m thick the morsleben repository is in the allertal zone salt structure the root zone of a deeply eroded salt body this is evidenced by the relatively small thickness of the zechstein salt as well as by the many blocks of the hauptanhydrit z3ha in the salt which are present mostly in the synclinal hinge zones i e in the deeper parts of the structure as a result of tectonic separation of ductile salt from competent anhydrite the tectonics of the structure are documented by polyphase folds characteristic of the deformation of ductile material the general trend of the fold axes is horizontal nw se parallel to the trend of the allertal zone the western part of the salt structure is characterised by high ne vergent isoclinal folds the z2 to z4 strata involved in the folding extend from the salt table top of the salt body down to the lowest synclinal trough in the eastern part the folds are open and symmetric with considerably smaller amplitude correspondingly z4 strata mostly occur just below the salt table z3 at the repository level and z2 below that the different styles of folding in the east and west are due to the structure of the rocks beneath the zechstein salt the boundary between the two types of folds lies above a major fault in the rocks below the zechstein salt separating a downthrown block in the west from an upthrown block in the east ne vergent isoclinal folds occur above the downthrown block where the major ascent of the salt occurred in contrast the folding in the upthrown eastern block has hardly been affected by the ascending salt hence the wide open symmetrical folds thus the structure of the rocks beneath the zechstein determined the folding style in the overlying salt the present day fold structures chiefly result from late cretaceous compression that affected the north german basin the salt body is therefore primarily a tectonic structure and is not halokinetic

landslide processes and landslide susceptibility analysis from an upland watershed a case study from st andrew jamaica west indies abstract rainfall induced landslides are common geomorphic events on the steeper slopes of upper st andrew and cause severe environmental engineering social and economic repercussions in the area a geotechnical study was initiated to identify a past present and potential landslide types and sites for landslides b to examine the nature of geological geomorphological and geotechnical conditions under which failures can take place and c the potential landslide hazard in the area 886 failures were mapped more than 80 of which were located in soils a total of 1 55 km2 9 80 of the total area had failed approximately 59 failures per km2 were mapped with the highest density within elastic sedimentary units and weathered granodiorite 789 failure were mapped on slopes between 20 45 with no failure on slope less than 10 481 failures were mapped along twelve major roadways 46 6 km of road with approximately 10 failures km of road analysis of eighteen geotechnical units within nine geological formations revealed that the highest susceptibility for failure was within old landslide deposits with granular nonplastic to low plasticity soils and on slopes between 20 and 30 the lowest susceptibility was found within white limestones and recent alluvium and terrace deposits granular nonplastic to low plasticity soils are generally more susceptible than fine soils especially on slopes between 30 and 45 while granular and expansive clay soils demonstrate similar susceptibilities but on slopes between 30 and 45 and 20 and 45 respectively clastic sedimentary rocks are more susceptible that igneous lithologies an increase in slope angle increases the susceptibility to failures but only on slopes up to 45 an increase in the degree of weathering of soils and bedrock and fracturing of bedrock as well as road construction increases the landslide susceptibility in the area

structural evolution of continental and marine permian rock salt of the north german basin constraints from microfabrics geochemistry and u pb ages analyzing the dynamics of microstructural response on natural deformation in rock salt we present microfabric ebsd geochemical and u pb data obtained from permian salt formations of the kiel honigsee salt wall in northern germany the samples were recovered from deep drillings which penetrated through an overturned rock salt sequence of both rotliegend and zechstein deposits the bromide concentration in halite indicates a continental and marine origin for the rotliegend and zechstein deposits respectively despite intense deformation relics of early diagenetic fabrics are still preserved deformation of the impure rotliegend rock salt was accommodated by pressure solution and hydrofracturing as is indicated by the microfabrics and bromide concentration in halite fractures in siliciclastic domains were filled with fibrous halite and deformed by subgrain rotation recrystallization sgr fluid rich zechstein rock salt on the other hand was deformed by formation of subgrains and grain boundary migration gbm the distribution of mineral phases and fluids had a significant impact on the fabric evolution and on strain localization u pb dating of carbonate phases of the rotliegend sequence yielded permian depositional ages and jurassic to cretaceous deformation ages the latter related to diapiric ascent the combination of results traces a dynamic evolution of the rock fabric inside the diapir structure driven by locally active deformation processes that can be correlated with early stages of halite deposition and diagenesis and syntectonic fabric reorganization related to diapirism in an extensional setting

texture and anisotropy the study of preferred orientation of minerals in rocks dates back to omalius d halloy 1833 who attributes a special significance to the alignment of crystals as an indicator of the formation process much later the influence of crystal alignment on physical properties was quantified e g weissenberg 1922 voigt 1928 reuss 1929 only recently has this field emerged as a coherent part of earth science research linking such branches as mineralogy petrology structural geology geodynamics and seismology the reason for this was the emergence of quantitative methods to analyze preferred orientation or texture as it was first called by naumann 1850 these methods were largely developed in collaboration with materials science and mechanics quantitative measurements detailed field studies rigorous data analysis theories to predict textures and improvements in characterizing seismic anisotropy in the earth are leading to a coherent picture that is now being refined though seismologists have long accepted that there is a causal relationship between anisotropic propagation of seismic waves the deformation field and crystal orientation the prevailing view is still largely the mythological concept that seismic fast directions align with the flow direction while this may be approximately the case for olivine deformed under certain conditions it is certainly no universal law as we will try to illustrate in this review the fast direction of a crystal depends on the mineral species and its crystal structure the alignment of crystals depends on microscopic intra crystalline deformation systems and the deformation history both relationships are complex and not intuitive but there are well established theories to compute single crystal physical properties as well as orientation patterns simulations can be compared with experimental data and then applied with some caution to the macroscopic earth this review is intended to provide a brief introduction highlighting some of the issues with

evolution of dilatancy and permeability in rock salt during hydrostatic compaction and triaxial deformation combined gas permeability and p and s wave velocity measurements were carried out on rock salt samples from the gorleben salt dome and the morsleben salt mine under hydrostatic and triaxial loading condions mostly at room temperature permeabilities in the as received samples vary between 10 16 and 2x10 20 m 2 the initial permeability is primarily due to decompaction induced by drilling core retrieval and sample preparation hydrostatic loading gives rise to a marked decrease of permeability and a coeval significant increase of p and s wave velocities due to progressive closure of grain boundary cracks tending to approach the in situ matrix permeability 18 mpa differential stress at 10 mpa confining pressure to similar to 30 mpa at confining pressures above similar to 70 mpa dilatancy is due to the opening of grain boundary and 100 cleavage cracks and depends on the applied confining pressure the orientation of the open cracks is primarily controlled by the loading geometry system compression extension as a consequence permeability increases dramatically with progressive dilatancy followed by a period of plus minus constant permeability during strain hardening up to 10 axial strain or even more this suggests that the evolution of permeability is not only a function of dilatancy but also of microcrack linkage importantly the anisotropic crack array within the samples causes a strong directional dependence of permeability