dynamic modeling suggests terrace zone asymmetry in the chicxulub crater is caused by target heterogeneity we investigate the cause of terrace zone asymmetry in the chicxulub impact crater using dynamic models of crater formation marine seismic data acquired across the crater show that the geometry of the crater s terrace zone a series of sedimentary megablocks that slumped into the crater from the crater rim varies significantly around the offshore half of the crater the seismic data also reveal that at the time of impact both the water depth and sediment thickness varied with azimuth around the impact site to test whether the observed heterogeneity in the pre impact target might have affected terrace zone geometry we constructed two end member models of upper target structure at chicxulub based on the seismic data at different azimuths one model representing the northwest sector had no water layer and a 3 km thick sediment layer the other model representing the northeast sector had a 2 km water layer above a 4 km sediment layer numerical models of vertical impacts into these two targets produced final craters that differ substantially in terrace zone geometry suggesting that the initial water depth and sediment thickness variations affected the structure of the terrace zone at chicxulub moreover the differences in terrace zone geometry between the two numerical models are consistent with the observed differences in the geometry of the terrace zone at different azimuths around the chicxulub crater we conclude that asymmetry in the pre impact target rocks at chicxulub is likely to be the primary cause of asymmetry in the terrace zone

global distribution of lunar impact melt flows abstract in this study we analyzed the distribution and properties of 146 craters with impact melt deposits exterior to their rims many of these craters were only recently discovered due to their unusual radar properties in the near global mini rf data set we find that most craters with exterior deposits of impact melt are small 20 km and that the smallest craters have the longest melt flows relative to their size in addition exterior deposits of impact melt are more common in the highlands than the mare this may be the result of differing target properties in the highlands and mare the difference in titanium content or the greater variation of topography in the highlands we find that 80 of complex craters and 60 of simple craters have melt directions that are coincident or nearly coincident with the lowest point in their rim implying that pre existing topography plays a dominant role in melt emplacement this is likely due to movement during crater modification complex craters or breached crater rims simple craters we also find that impact melt flows have very high circular polarization ratios compared to other features on the moon this suggests that their surfaces are some of the roughest material on the moon at the centimeter to decimeter scale even though they appear smooth at the meter scale

polygonal impact craters in the argyre region mars evidence for influence of target structure on the final crater morphology impact craters that in plan view are distinctly polygonal rather than circular or elliptical are common on mars and other planets ohman et al 2005 their actual formation mechanism however is somewhat debatable we studied the polygonal craters of different degradational stages in the region of the argyre impact basin mars the results show that in the same areas heavily degraded moderately degraded and fresh polygonal craters display statistically similar strike distributions of the straight rim segments the fact that the strike distributions are not dependent on lighting conditions was verified by using two data sets viking and moc wa having different illumination geometries but similar resolutions in addition there are no significant differences in the amount of polygonality of craters in different degradational stages these results clearly imply that large scale polygonality is not caused by degradation but originates from the cratering process itself concurring with the findings regarding lunar craters by eppler et al 1983 the straight rims of polygonal craters apparently reflect areal fracture patterns that prevail for a geologically long time

vesta s shape and morphology vesta s surface is characterized by abundant impact craters some with preserved ejecta blankets large troughs extending around the equatorial region enigmatic dark material and widespread mass wasting but as yet an absence of volcanic features abundant steep slopes indicate that impact generated surface regolith is underlain by bedrock dawn observations confirm the large impact basin rheasilvia at vesta s south pole and reveal evidence for an earlier underlying large basin veneneia vesta s geology displays morphological features characteristic of the moon and terrestrial planets as well as those of other asteroids underscoring vesta s unique role as a transitional solar system body

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

structural characteristics of the sudbury impact structure canada impact induced versus orogenic deformation a review orogenic deformation both preceding and following the impact event at sudbury strongly hinders a straightforward assessment of impact induced geological processes that generated the sudbury impact structure central to understanding these processes is the state of strain of the sudbury igneous complex the solidified impact melt sheet its underlying target rocks overlying impact breccias and post impact sedimentary rocks this review addresses 1 major structural metamorphic and magmatic characteristics of the impact melt sheet and associated dikes 2 attempts that have been made to constrain the primary geometry of the igneous complex 3 modes of impact induced deformation as well as 4 mechanisms of pre and post impact orogenic deformation the latter have important consequences for estimating parameters such as magnitude of structural uplift tilting of pre impact huronian strata and displacement on major discontinuities which collectively have not yet been considered in impact models in this regard a mechanism for the emplacement of offset dikes is suggested that accounts for the geometry of the dikes and magmatic characteristics as well as the occurrence of sulfides in the dikes moreover re interpretation of published paleomagnetic data suggests that orogenic folding of the solidified melt sheet commenced shortly after the impact uncertainties still exist as to whether the sudbury impact structure was a peak ring or a multi ring basin and the deformation mechanisms of rock flow during transient cavity formation and crater modification

overview of the shuttle imaging radar b preliminary scientific results the shuttle imaging radar b experiment consisted of a large number of scientific investigations in the earth sciences nine oceanographic experiments were conducted to study the generation and propagation of surface waves the dynamics of internal waves oil slick detection and the properties of southern polar ice stereo imaging from space allowed three dimensional viewing of surface features geologic experiments were conducted to study subsurface penetration structural mapping and lithologic classification imaging radar angular scatterometry was used in the vegetation cover forest type and urban areas classification experiments this article provides an overview of the scientific results some of which are also presented in this issue

analysis of seasat l band radar imagery of the west bay indin lake fault system northwest territories seasat l band 23 5 cm synthetic aperture radar sar images of the yellowknife area in the northwestern canadian shield have been digitally processed and correlated with geologic maps of the region we specifically analyze the distribution of faults of the west bay indin lake system and conclude from cross cutting geological relationships that this fault system formed at circa 1964 pm 36 ma in response to a sinistral oblique component of extension which led to rifting of the coronation continental margin by 1961 pm 5 ma through this analysis we show that spaceborne sar is a useful tool for delineation of brittle tectonic features such as faults joints and dikes on a regional scale enabling field geologists to place their observations in a broader context when coupled with field surveys of small representative areas thousands of square kilometers can be quickly and efficiently analyzed in a statistically uniform manner broad coverage of the planet and other bodies in the solar system by sp

the equilibrium size frequency distribution of small craters reveals the effects of distal ejecta on lunar landscape morphology abstract small craters of the lunar maria are observed to be in a state of equilibrium in which the rate of production of new craters is on average equal to the rate of destruction of old craters crater counts of multiple lunar terrains over decades consistently show that the equilibrium cumulative size frequency distribution sfd per unit area of small craters of radius r is proportional r 2 and that the total crater density is a few percent of so called geometric saturation which is the maximum theoretical packing density of circular features while it has long been known that the primary crater destruction mechanism for these small craters is steady diffusive degradation there are few quantitative constraints on the processes that determine the degradation rate of meter to kilometer scale lunar surface features here we combine analytical modeling with a monte carlo landscape evolution code known as the cratered terrain evolution model to place constraints on which processes control the observed equilibrium size frequency distribution for small craters we find that the impacts by small distal ejecta fragments distributed in spatially heterogeneous rays is the largest contributor to the diffusive degradation which controls the equilibrium sfd of small craters other degradation or crater removal mechanisms such cookie cutting ejecta burial seismic shaking and micrometeoroid bombardment likely contribute very little to the diffusive topographic degradation of the lunar maria at the meter scale and larger

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

shuttle imaging radar sir b investigations of the canadian shield initial report two of the 43 shuttle imaging radar sir b experiments carried out from the 41 g shuttle mission in 1984 involved a 2600 km swath across the canadian shield with the objectives of studying the structure of province boundaries and developing techniques for the geologic use of orbital radar despite degraded single incidence angle imagery resulting from system problems valuable experience has been obtained with data over a test site near bancroft ontario it has been found that even subdued glaciated topography can be effectively imaged variations in backscatter being caused by variations in local incidence angle rather than shadowing it has been demonstrated that small incidence angles are more sensitive to topography than large angles backscatter is extremely sensitive to look direction topographic features nearly normal to the illumination being highlighted and those nearly parallel to it being suppressed it is concluded that orbital radar can provide a valuable tool for geologic studies of the canadian shield and similar areas if suitable look angles and at least two look directions can be utilized for each area

incidence angle considerations for spacecraft imaging radar the value of radar imagery for most geologic applications is greatest when obtained with relatively large incidence angles it is infeasible to attain these large angles from spacecraft altitudes a study is being conducted to assess the usefulness of imagery collected at smaller angles radar image simulation is employed to create imagery for platform scenarios at numerous angles of incidence for specific geologic features preliminary analyses and results are provided

the geology and geomorphology of the venus surface as revealed by the radar images obtained by veneras 15 and 16 a region by region condensed description of almost all of the area that was radar photographed by veneras 15 and 16 is presented using some generalizations the diversity of terrain was reduced to a discrete set from which a geological morphological map was constructed the predominant type of terrain of the studied area is a plain that was tentatively subdivided into five morphological types ridge and band patchy rolling plain dome and butte plain smooth plain and high smooth plain stratigraphically the ridge and band plains are the oldest and the smooth plains are the youngest the stratigraphic position of the other types is yet to be determined large sections of the plains show similarities to the mare type basaltic plains of the moon mercury and mars other types of terrain are combinations of ridges and grooves in various patterns linear parallel orthogonal diagonal or chevron like and chaotic in some places the ridge and groove terrain is stratigraphically below the plain material but in other places it appears to be plain material that has been subsequently deformed near the eastern and western boundaries of ishtar terra large several hundred kilometers in diameter ring like features can be seen that are named coronae or ovoids evidence of tectonic deformation and the presence of flow like patterns support their designation as volcano tectonic features beta regio seems to be an uplifted plain showing evidence of rifting and volcanism all types of terrain are sparesely peppered with craters of obvious impact morphology their average density gives the plain an age range of 0 5 to 1 109 years the fact that many impact craters are still in the pristine state indicates a very low rate of surface reworking at least for the last 0 5 to 1 109 years no evidence for water erosion sedimentation processes has been found the tectonic activity of venus has no equivalent on the moon mercury or even mars and can be compared only with that of the earth intensive horizontal deformation previously known only on earth occurs on venus but in a characteristic venusian style

groundwater favorability map using gis multicriteria data analysis on crystalline terrain sao paulo state brazil summary this paper presents the groundwater favorability mapping on a fractured terrain in the eastern portion of sao paulo state brazil remote sensing airborne geophysical data photogeologic interpretation geologic and geomorphologic maps and geographic information system gis techniques have been used the results of cross tabulation between these maps and well yield data allowed groundwater prospective parameters in a fractured bedrock aquifer these prospective parameters are the base for the favorability analysis whose principle is based on the knowledge driven method the multicriteria analysis weighted linear combination was carried out to give a groundwater favorability map because the prospective parameters have different weights of importance and different classes of each parameter the groundwater favorability map was tested by cross tabulation with new well yield data and spring occurrence the wells with the highest values of productivity as well as all the springs occurrence are situated in the excellent and good favorability mapped areas it shows good coherence between the prospective parameters and the well yield and the importance of gis techniques for definition of target areas for detail study and wells location

constructional volcanic edifices on mercury candidates and hypotheses of formation mercury a planet with a predominantly volcanic crust has perplexingly few if any constructional volcanic edifices despite their common occurrence on other solar system bodies with volcanic histories using image and topographical data from the mercury surface space environment geochemistry and ranging messenger spacecraft we describe two small 15 km diameter prominences with shallow summit depressions associated with volcanically flooded impact features we offer both volcanic and impact related interpretations for their formation and then compare these landforms with volcanic features on earth and the moon though we cannot definitively conclude that these landforms are volcanic the paucity of constructional volcanic edifices on mercury is intriguing in itself we suggest that this lack is because volcanic eruptions with sufficiently low eruption volumes rates and flow lengths suitable for edifice construction were highly spatiotemporally restricted during mercury s geological history we suggest that volcanic edifices may preferentially occur in association with late stage post impact effusive volcanic deposits the esa jaxa bepicolombo mission to mercury will be able to investigate further our candidate volcanic edifices search for other as yet unrecognized edifices beneath the detection limits of messenger data and test our hypothesis that edifice construction is favored by late stage low volume effusive eruptions

cellular neural network for automated detection of geological lineaments on radarsat images the analysis of natural linear structures termed lineaments in satellite images provides important information to the geologist in the satellite imaging process important features of the observed tridimensional scene including geological lineaments are mapped into the resulting 2d image as sharp radiation variations or edge elements edgels edgels are detected by a first order differentiation operator and are linked together with those in the vicinity on a basis of orientation continuity lineaments are mapped into remotely sensed satellite images as long and continuous quasilinear features and can be described as a connected sequence of edgels whose direction may change gradually along the sequence parts of the same lineament can be occluded by geomorphological features and must be linked together a major drawback with local and small neighborhood detectors the authors propose a cellular neural network cnn architecture to offer a large directional neighborhood to the lineament detection algorithm the cnn uses a large circular neighborhood coupled with a directional induced gradient field to link together edgels with similar and continuous orientation missing edgels are restored if a surrounding lineament is detected

impact cratering on slopes abstract the majority of impact craters have circular outlines and axially symmetric morphologies deviation from crater circularity is caused by either target heterogeneity a very oblique impact incidence post impact deformation or by topography here we investigate the effect of topography on crater formation and systematically study impact cratering processes on inclined hillsides up to 25 slope utilizing analogue experiments a spring driven air gun mounted in a vertical position shoots into three different types of granular bulk solids two sorts of glass beads quartz sand to emulate impact cratering on slopes in all 170 experiments were conducted the transient crater develops roughly symmetrically perpendicular to the slope plane resulting in higher ejection angles uphill than downhill when measured with respect to a horizontal plane craters become increasingly elliptical with increasing slope angle at slope angles close to angle of repose of the respective bulk solids aspect ratios of the craters reach 1 7 uphill downhill cross sections become increasingly asymmetric the depth diameter ratio of the craters decreases and the deepest point shifts downhill with increasing slope angle mass wasting is initiated both in the uphill and downhill sectors of the crater rim for steep slopes the landslides that emanate from the uphill rim can overshoot the crater cavity and superpose the downhill crater rim in a narrow tongue mass wasting initiated at the downhill sector forms broader and shallower tongues and is triggered by the deposition of ejecta on the inclined slope our experiments help to explain asymmetric crater morphologies observed on asteroids such as ceres vesta lutetia and also on mars

use of synthetic aperture radar sar for geologic reconnaissance in arctic regions an example from the arctic national wildlife refuge alaska satellite based synthetic aperture radar sar can provide an additional remote sensing tool for regional geologic studies in arctic regions although sar data do not yield direct information on rock type and do not replace traditional optical data sar data can provide useful geologic information in arctic regions where the stratigraphic column includes a wide range of lithologies and bedrock exposures have been reduced to rubble by frost action for example in ers 1 sar data from the arctic national wildlife refuge anwr of the northeastern brooks range alaska carbonate and clastic rocks can give remarkably different radar responses on minimally reprocessed sar data the different radar response of different lithologies can be attributed to variations in surface roughness specifically the size and angularity of scree in talus slopes additional postacquisition processing can both remove many of the negative terrain effects common in sar data and enhance contrasts in bedrock lithology because of this ability to discriminate between gross lithologic packages the ers 1 sar data can be used to provide a regional view of anwr and a detailed look at specific areas a mosaic of ers 1 sar data from all of anwr provides a synoptic copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received august 30 1995 revised manuscript received march 11 1996 final acceptance august 15 1996 2geophysical institute university of alaska fairbanks alaska 99775 3alaska sar facility geophysical institute university of alaska fairbanks alaska 99775 this study was supported by sponsors of the tectonics and sedimentation research group of the university of alaska fairbanks including arco alaska bp alaska chevron exxon japan national oil co mobil phillips and unocal the alaska sar facility provided support for richard guritz and reprocessing of the ers 1 sar data ers 1 sar data were provided by the european space agency under a research agreement with nasa we would like to thank steve ahlgren lyn mcnutt and ken dean for stimulating discussions on sar and its potential geologic applications in the arctic wes wallace for discussions on the regional geology of northeastern alaska and weathering characteristics of the different stratigraphic units and wes wallace ken dean bill stringer larry lane m c erskine jr h r hopkins and k biddle for helpful reviews of the manuscript

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

geologic interpretation of space shuttle radar images of indonesia the national aeronautics and space administration nasa space shuttle mission in november 1981 acquired images of parts of the earth with a synthetic aperture radar system at a wavelength of 23 5 cm 9 3 in and spatial resolution of 38 m 125 ft this report describes the geologic interpretation of 1 250 000 scale images of irian jaya and eastern kalimantan indonesia where the all weather capability of radar penetrates the persistent cloud cover the inclined look direction of radar enhances subtle topographic features that may be the expression of geologic structures on the indonesian images the following terrain categories are recognizable for geologic mapping carbonate clastic volcanic alluvial and coastal melange and metamorphic as well as undifferentia ed bedrock regional and local geologic structures are well expressed on the images in the vogelkop region of irian jaya the major tectonic elements tamrau mountains sorong fault kemum block bintuni basin and lengguru foldbelt are readily mapped on the image of the sorong fault geomorphic features offset drainage shutterridges aligned notches provide clear evidence for left lateral strike slip displacement several lineaments on the image correlate with previously mapped faults other lineaments may be the expression of previously unrecognized faults on the image of the mainland of irian jaya a belt of metamorphic and melange terrain marks the zone of collision between the pacific plate and the australian plate the high central range of irian jaya is located south of the metamorphic and melange belt the generally homoclinal structure of the central range is interrupted in the paniai lake region by a series of southward directed thrust plates indicated by belts of carbonate terrain new guinea limestone group that alternate with belts of clastic terrain kembelangan formation in the image of eastern kalimantan several major foldbelts are clearly expressed these limited examples of space shuttle radar images demonstrate their value for geologic interpretation of indonesia it is recommended that future shuttle missions acquire complete radar coverage of the main islands of indonesia for use in geologic mapping and energy exploration shuttle radar images would also be valuable for other cloud covered forested regions

the role of tilted heating in the evolution of the mjo there has been much discussion about the role of tilted heating in the evolution of the mjo it is believed that the inability of many general circulation models to produce a robust mjo is directly related to deficiencies in the model produced tropical heating distributions given the mjo s importance in tropical climate we need to better understand what heating distributions are required in climate models to produce strong mjos this study addresses the role of tilted heating in the community atmospheric model version 4 cam4 idealized and observed heating distributions are added to the tropical atmosphere in cam4 these include heating that tilts westward with height in the lower and upper atmosphere as well as various tilted and untilted heating in the form of either idealized blobs or observations derived from the tropical rainfall measuring mission precipitation radar and the international satellite cloud climatology project we find that low level heating ahead of the mjo convective center is critical for the initial strengthening and later maintenance of the mjo however tilted heating is not necessary to simulate a realistic mjo in addition excess upper level heating whether tilted or not appears to degrade the mjo signal although rossby wave modes are evident only in runs with additional upper level heating kelvin waves are evident during strong mjos for all simulations but are only visible over the central pacific results suggest that accurate shallow convective parameterizations may be more important than deep convective ones in the evolution of the mjo

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

coupled effects of impact and orogeny is the marine lockne crater sweden pristine our current understanding of marine impact cratering processes is partly inferred from the geological structure of the lockne crater we present results of a mapping campaign and structural data indicating that this crater is not pristine in the western part of the crater pre impact impact and post impact rocks are incorporated in caledonian thrust slices and are subjected to folding and faulting a nappe outlier in the central crater depression is a relic of the caledonian nappe cover that reached a thickness of more than 5 km the overthrusted crater is gently deformed strike of strata and trend of fold axes deviate from standard caledonian directions northeast southwest radially oriented crater depressions which were previously regarded as marine resurge gullies formed when resurging seawater erosively cut through the crater brim are interpreted to be open synclines in which resurge deposits were better preserved the presence of the impact structure influenced orogenesis due to morphological and lithological anomalies of the crater i a raised crater brim zone acted as an obstacle during nappe propagation ii the occurrence of a central crater depression caused downward sagging of nappes and iii the lack of an appropriate detachment horizon alum shale within the crater led to an enhanced mechanical coupling and internal deformation of the nappe and the overthrusted foreland preliminary results of 3 danalogue experiments suggest that a circular high friction zone representing the crater locally hinders nappe propagation and initiates a circumferentially striking ramp fault that delineates the crater crustal shortening is also partitioned into the crater basement and decreases laterally outward deformation of the foreland affected the geometry of the detachment and could be associated with the activation of a deeper detachment horizon beneath the crater strain gradients both vertically and horizontally result in non plane strain deformation in the vicinity of the crater the strain tensors in the hanging and foot walls may deviate up to 90 from each other and rotated by up to 45 with respect to the standard regional orientation the observed deflection of strata and fold axes within the lockne crater area as revealed by field mapping is in agreement with the pattern of strain partitioning shown in the analogue models

the planforms of low angle impact craters in the northern hemisphere of mars we have surveyed martian impact craters greater than 5 km in diameter using viking and thermal emission imaging system themis imagery to evaluate how the planform of the rim and ejecta changes with decreasing impact angle we infer the impact angles at which the changes occur by assuming a sin2 dependence for the cumulative fraction of craters forming below angle at impact angles less than 40 from horizontal the ejecta become offset downrange relative to the crater rim as the impact angle decreases to less than 20 the ejecta begin to concentrate in the crossrange direction and a forbidden zone that is void of ejecta develops in the uprange direction at angles less than 10 a butterfly ejecta pattern is generated by the presence of downrange and uprange forbidden zones and the rim planform becomes elliptical with the major axis oriented along the projectile s direction of travel the uprange forbidden zone appears as a v curving outward from the rim but the downrange forbidden zone is a straight edged wedge although fresh martian craters greater than 5 km in diameter have ramparts indicative of surface ejecta flow the ejecta planforms and the angles at which they occur are very similar to those for lunar craters and laboratory impacts conducted in a dry vacuum the planforms are different from those for venusian craters and experimental impacts in a dense atmosphere we interpret our results to indicate that martian ejecta are first emplaced predominantly ballistically and then experience modest surface flow

sources of shape variation in lunar impact craters fourier shape analysis r mode factor analysis of fourier harmonics that describe the shape in plan view of 716 large diameter 15 km nearside lunar craters shows that two factors explain 84 3 of shape variance observed in the sample factor i accounts for 68 2 of the sample variance and describes moderate scale roughness defined by harmonics 7 through 10 shape variation described by these harmonics is related to surficial lunar processes of degradation that modify crater shape in plan dominant among these processes are ejecta scour from large impact events and ongoing aging factor ii accounts for 16 1 of the observed shape variance and describes polygonal shape elements related to harmonics 2 3 4 and 6 variation in these harmonics is tied to variables that distort the spherical symmetry of crater forming processes the dominant contributor among these variables is the nature of geologic structural patterns in impacted material unlike transient features described by factor i polygonal shape elements described by factor ii do not change appreciably with time the permanence of these features and their relation to lunar geologic structure suggest that the shape of old craters carries the imprint of geologic structural relationships present in early lunar crust

effect of stratiform heating on the planetary scale organization of tropical convection abstractit is widely recognized that stratiform heating contributes significantly to tropical rainfall and to the dynamics of tropical convective systems by inducing a front to rear tilt in the heating profile precipitating stratiform anvils that form from deep convection play a central role in the dynamics of tropical mesoscale convective systems the wide spreading of downdrafts that are induced by the evaporation of stratiform rain and originate from in the lower troposphere strengthens the recirculation of subsiding air in the neighborhood of the convection center and triggers cold pools and gravity currents in the boundary layer leading to further lifting here aquaplanet simulations with a warm pool like surface forcing based on a coarse resolution gcm of approximately 170 km grid mesh coupled with a stochastic multicloud parameterization are used to demonstrate the importance of stratiform heating for the organization of convection on planetary and intraseasonal scales when the model paramet