quaternary tectonics of the outer west carpathians poland abstract quaternary tectonic activity in the polish segment of the outer west carpathians has been relatively weak and can be reconstructed on the basis of indirect evidence provided by geomorphological mapping the construction of various morphometric maps based on mathematical transformation of the present day topography and the use of some mathematical techniques to model the theoretical longitudinal river profiles and the valley network and to process statistically the drainage pattern parameters morphological evidences of tectonic movements include deformed strath terraces differentiated amounts and rates of fluvial incision in individual geomorphic units which occurred despite of regionally consistent quaternary climatic conditions throughout the west carpathians and more or less uniform bedrock resistance to erosion as well as changes in the drainage network the values of some morphometric indices like abnormally high river bed gradients and bifurcation ratios or low valley floor width valley height ratios differ throughout that part of the carpathian arc and cluster into a number of zones that are aligned subparallel to the mountain belt and coincide with geomorphic units showing upwarped strath terraces these zones become more numerous from the west to the east and some of them are located at or in front of the present day carpathian frontal thrust cutting it obliquely and passing into the eastern carpathian foredeep the spatial arrangement of such zones showing alternatively uplifting subsiding tendencies suggests that one of the main driving forces leading to quaternary tectonic deformations is that resulting from the relaxation of remnant horizontal stresses built up during the late neogene thrusting

interferometric daylight seismic imaging summary claerbout s daylight imaging concept is generalized to a theory of interferometric seismic imaging ii interferometric seismic imaging is defined to be any algorithm that inverts correlated seismic data for the reflectivity or source distribution as examples we show that ii can image reflectivity distributions by migrating ghost reflections in passive seismic data and generalizes the receiver function imaging method used by seismologists interferometric seismic imaging can also migrate free surface multiples in common depth point cdp data and image source distributions from passive seismic data both synthetic and field data examples are used to illustrate the different possibilities of ii the key advantage of ii is that it can image source locations or reflectivity distributions from passive seismic data where the source position or wavelet is unknown in some cases it can mitigate defocusing errors as a result of statics or an incorrect migration velocity the main drawback with ii is that severe migration artefacts can be created by partial focusing of virtual multiples

retrieval of super virtual refraction by cross correlation topography and severe variations of near surface layers lead to travel time perturbations for the events in seismic exploration usually these perturbations could be estimated and eliminated by refraction technology the virtual refraction method is a relatively new technique for retrieval of refraction information from seismic records contaminated by noise based on the virtual refraction this paper proposes supervirtual refraction interferometry by cross correlation to retrieve refraction wavefields by summing the cross correlation of raw refraction wavefields and virtual refraction wavefields over all receivers located outside the retrieved source and receiver pair this method can enhance refraction signal gradually as the source receiver offset decreases for further enhancement of refracted waves a scheme of hybrid virtual refraction wavefields is applied by stacking of correlation type and convolution type super virtual refractions our new method does not need any information about the near surface velocity model which can solve the problem of directly unmeasured virtual refraction energy from the virtual source at the surface and extend the acquisition aperture to its maximum extent in raw seismic records it can also reduce random noise influence in raw seismic records effectively and improve refracted waves signal to noise ratio by a factor proportional to the square root of the number of receivers positioned at stationary phase points based on the improvement of virtual refraction s signal to noise ratio using results from synthetic and field data we show that our new method is effective to retrieve refraction information from raw seismic records and improve the accuracy of first arrival picks

finite difference modeling experiments for seismic interferometry in passive seismic interferometry new reflection data can be retrieved by crosscorrelating recorded noise data the quality of the retrieved reflection data is among others dependent on the duration and number of passive sources present during the recording time the source distribution and the source strength to investigate these relations we set up several numerical modeling studies to carry out the modeling in a feasible time we design a finite difference algorithm for the simulation of long duration passive seismic measurements of band limited noise signatures in the subsurface novel features of the algorithm include the modeling of thousands of randomly placed sources during one modeling run the modeling experiments explore the dependency relation between the retrieved reflections and source signature length source positions number of sources and source amplitude variations from these experiments we observed that the positions of the passive sources and the length of the source signals are of direct influence on the quality of the retrieved reflections random amplitude variations among source signals do not seem to have a big impact on the retrieved reflections

anomalous radar backscatter from titan s surface abstract since cassini arrived at saturn in 2004 its moon titan has been thoroughly mapped by the radar instrument at 2 cm wavelength in both active and passive modes some regions on titan including xanadu and various bright hummocky bright terrains contain surfaces that are among the most radar bright encountered in the solar system this high brightness has been generally attributed to volume scattering processes in the inhomogeneous low loss medium expected for a cold icy satellite surface we can test this assumption now that the emissivity has been obtained from the concurrent radiometric measurements for nearly all the surface with unprecedented accuracy janssen et al and the cassini radar team 2009 icarus 200 222 239 kirchhoff s law of thermal radiation relates the radar and radiometric properties in a way that has never been fully exploited in this paper we examine here how this law may be applied in this case to better understand the nature of titan s radar bright regions we develop a quantitative model that when compared to the observational data allows us to conclude that either the reflective characteristics of the putative volume scattering subsurface must be highly constrained or more likely organized structure on or in the surface is present that enhances the backscatter

seismic refraction interferometry with a semblance analysis on the crosscorrelation gather crosscorrelating wavefields recorded at two receivers to produce data as if one receiver was a source is commonly referred to as seismic interferometry or the virtual source method an artifact in seismic interferometry related to critically refracted waves allowed us to estimate the velocity in the refracting layer in addition we devised a new semblance analysis on the crosscorrelation of reflection and refraction energy to robustly estimate the depth and velocity of the slow layer tested with a numerical example and field data from the boise hydrogeophysical research site

application of super virtual seismic refraction interferometry to enhance first arrivals a case study from saudi arabia complex near surface anomalies are one of the main onshore challenges facing seismic data processors refraction tomography is becoming a common technology to estimate an accurate near surface velocity model this process involves picking the first arrivals of refracted waves one of the main challenges with refraction tomography is the low signal to noise ratio characterizing the first break waveform arrivals especially for the far offset receivers this is especially evident in data recorded using reflection acquisition geometry this low signal to noise ratio is caused by signal attenuation due to geometrical spreading of the seismic wavefield near surface generated noise and amplitude absorption super virtual refraction interferometry improves the quality of the first break picks by enhancing the amplitude of the refracted waves and attenuating the amplitude of the random noise

the geology and geophysics of kuiper belt object 486958 arrokoth the cold classical kuiper belt a class of small bodies in undisturbed orbits beyond neptune is composed of primitive objects preserving information about solar system formation in january 2019 the new horizons spacecraft flew past one of these objects the 36 kilometer long contact binary 486958 arrokoth provisional designation 2014 mu69 images from the flyby show that arrokoth has no detectable rings and no satellites larger than 180 meters in diameter within a radius of 8000 kilometers arrokoth has a lightly cratered smooth surface with complex geological features unlike those on previously visited solar system bodies the density of impact craters indicates the surface dates from the formation of the solar system the two lobes of the contact binary have closely aligned poles and equators constraining their accretion mechanism

stability of polar frosts in spherical bowl shaped craters on the moon mercury and mars following svitek martian water frost control of global distribution by small scale processes ph d thesis california institute of technology 1992 analytic solutions are presented for the effective albedo the effective emissivity and the radiative equilibrium temperature in the shadowed portions of a spherical bowl shaped crater the model assumes that the surface is a lambert scatterer with visual albedo and infrared emissivity each independent of wavelength across their respective spectral ranges absorption emission and multiple scattering from the walls of the crater are treated rigorously to all orders for airless bodies whose surfaces are in radiative equilibrium all shadowed portions of any individual crater have the same temperature whose value depends on four quantities the insolation product of the solar constant and the sine of the solar elevation angle the depth diameter ratio of the crater the visual albedo and the infrared emissivity as long as the crater is deep enough to have shadows the lowest temperatures are for the shallowest crater those with the smallest depth diameter ratio the model is applied first to the moon and mercury using a depth diameter ratio of 0 2 which is typical of the lunar highlands according to pike geophys res lett 1 291 294 1974 in impact and explosion cratering roddy et al eds pp 489 509 pergamon new york 1977 for mercury and the moon temperatures in shadows in polar craters are below 102 k so the sublimation rate of water ice calculated according to the model of watson et al j geophys res 66 3033 3015 1961 is less than 1 cm per byr the latitudinal extent of the cold zone on the moon is greater than that on mercury although temperatures at the poles of the two planets are similar the other application is to polar frosts on mars illuminated water frosts in radiative equilibrium grow rougher because the average temperature of a depression is greater than that of flat ground subliming co 2 frosts which are always at the same temperature grow rougher at low solar elevation angles because the heat flux absorbed by a depression is greater than that for a flat surface at high insolation rates high sun near perihelion the average heat flux to a depression is less than for a flat surface the latter evaporates faster which makes the average surface smoother and leads to a high average albedo this behavior helps explain the fact that the south co 2 cap which receives its greatest insolation near perihelion has a higher effective albedo and therefore can survive the summer whereas the north co 2 cap has a lower effective albedo and disappears each year around summer solstice

multifractal analysis applied to the study of the accuracy of dem based stream derivation abstract a correct description of river network morphology is very important when it is used to study different features of a river s morphology as well as phenomena related to it such as erosion nitrogen retention or sediment pollution in recent years different algorithms have been developed to extract drainage networks directly from digital elevation models in this paper the suitability of archydro extension developed for arcgis desktop and based on the d8 algorithm to generate river networks has been studied by using multifractal analysis the river networks generated by archydro tools were compared to those provided by photogrammetric restitution for different flow accumulation threshold values one limitation of the d8 algorithm in order to generate the most appropriate river networks is the correct choice of the flow accumulation threshold value multifractal analysis has shown itself to be an efficient approach to determine the most suitable flow accumulation threshold values moreover this approach has allowed characterizing the morphology of river networks and testing the quality of archydro results according to the multifractal spectra the main difference between the networks considered here is the lesser stream density with a low channel order detected for archydro results compared to photogrammetric restitution in addition the relationship between ruggedness number for the largest contributing area and fractal dimensions in each study area has been explored the use of multifractal analysis has been extended to drainage network simulation going beyond the descriptive aim of previous works

seismic interferometry reconstructing the earth s reflection response in1968 jonclaerboutshowedthatthereflectionresponseofa 1dacousticmediumcanbereconstructedbyautocorrelatingthe transmission response since then several authors have derived relationships for reconstructing green s functions at the surface using crosscorrelations of noise recordings that were taken at thesurfaceandthatderivedfromsubsurfacesources foracousticmedia wereviewrelationsbetweenthereflection response and the transmission response in 3d inhomogeneous lossless media these relations are derived from a one way wavefield reciprocity theorem we use modeling results to show howtoreconstructthereflectionresponseinthepresenceoftransientsubsurfacesourceswithdistinctexcitationtimes aswellas inthepresenceofsimultaneouslyactingnoisesourcesinthesubsurface weshowthatthequalityofreconstructedreflectionsdepends on the distribution of the subsurface sources for a situation with enough subsurface sources that is for a distribution that illuminates the subsurface area of interest from nearly all directions the reconstructed reflection responses and the migrated depth image exhibit all the reflection events and the subsurface structures of interest respectively with only a few subsurface sources that is with insufficient illumination the reconstructed reflection responses are noisy and can even become kinematically incorrect at the same time however the depth image which was obtained from their migration still shows clearly all the illuminated subsurface structures at their correct positions for the elastic case we review a relationship between the reflection green s functions and the transmission green s functionsderivedfromatwo waywavefieldreciprocitytheorem usingmodelingexamples weshowhowtoreconstructthedifferent components of the particle velocity observed at the surface and resulting from a surface traction source this reconstruciton is achievedusingcrosscorrelationsofparticlevelocitycomponents measured at the surface and resulting from separate p and s wavesourcesinthesubsurface

near infrared spectral mapping of titan s mountains and channels 1 we investigate the spectral reflectance properties of channels and mountain ranges on titan using data from cassini s visual and infrared mapping spectrometer vims obtained during the t9 encounter 26 december 2005 we identify the location of channels and mountains using synthetic aperture radar maps obtained from cassini s radar instrument during the t13 30 april 2006 flyby channels are evident even in vims imaging with spatial resolution coarser than the channel size the channels share spectral characteristics with titan s dark blue terrain e g the huygens landing site that is consistent with an enhancement in water ice content relative to the rest of titan we use this fact to measure widths of 1 km for the largest channels comparison of the data sets shows that in our study area within the equatorial bright spectral unit east of xanadu mountains are darker and bluer than surrounding smooth terrain these results are consistent with the equatorial bright terrain possessing a veneer of material that is thinner in the regions where there are mountains and streambeds that have likely undergone more recent and extensive erosion we suggest a model for the geographic relationship of the dark blue dark brown and equatorial bright spectral units based on our findings

virtual shear source makes shear waves with air guns we demonstrate a novel application of the virtual source method to create shear wave sources at the location of buried geophones these virtual downhole sources excite shear waves with a different radiation pattern than known sources they can be useful in various shear wave applications here we focus on the virtual shear check shot to generate accurate shear velocity profiles in offshore environments using typical acquisition for marine walkaway vertical seismic profiling vsp the virtual source method is applied to walkaway vsp data to obtain new traces resembling seismograms acquired with downhole seismic sources at geophone locations thus bypassing any overburden complexity the virtual sources can be synthesized to radiate predominantly shear waves by collecting converted wave energy scattered throughout the overburden we illustrate the concept in a synthetic layered model and demonstrate the method by estimating accurate p and s wave velocity profiles below salt using a walkaway vsp from the deepwater gulf of mexico

channel initiation and the problem of landscape scale since the 1940s it has been proposed that landscape dissection into distinct valleys is limited by a threshold of channelization that sets a finite scale to the landscape this threshold is equal to the hillslope length that is just shorter than that necessary to support a channel head a field study supports this hypothesis by showing that an empirically defined topographic threshold associated with channel head locations also defines the border between essentially smooth undissected hillslopes and the valley bottoms to which they drain this finding contradicts assertions that landscapes are scale independent and suggests that landscape response to changes in climate or land use depends on the corresponding changes in the threshold of channelization

using the density of kuiper belt objects to constrain their composition and formation history telescopic observations of kuiper belt objects have enabled bulk density determinations for 17 objects these densities vary systematically with size perhaps suggesting systematic variations in bulk composition we find this trend can be explained instead by variations in porosity arising from the higher pressures and warmer temperatures in larger objects we are able to match the density of 14 of 17 kbos within their 2 errors with a constant rock mass fraction of 70 suggesting a compositionally homogeneous rock rich reservoir because early 26al would have removed too much porosity in small 100 km kbos we find the minimum formation time to be 4 myr after solar system formation this suggests that coagulation and not gravitational collapse was the dominant mechanism for kbo formation we also use this model to make predictions for the density of makemake 2007 or10 and mu69

evidence for a polar ethane cloud on titan spectra from cassini s visual and infrared mapping spectrometer reveal the presence of a vast tropospheric cloud on titan at latitudes 51 to 68 north and all longitudes observed 10 to 190 west the derived characteristics indicate that this cloud is composed of ethane and forms as a result of stratospheric subsidence and the particularly cool conditions near the moon s north pole preferential condensation of ethane perhaps as ice at titan s poles during the winters may partially explain the lack of liquid ethane oceans on titan s surface at middle and lower latitudes

physical state and distribution of materials at the surface of pluto from new horizons leisa imaging spectrometer abstract from earth based observations pluto is known to be the host of n2 ch4 and co ices and also a dark red material very limited spatial distribution information is available from rotational visible and near infrared spectral curves obtained from hemispheric measurements in july 2015 the new horizons spacecraft reached pluto and its satellite system and recorded a large set of data the leisa spectro imager of the ralph instruments are dedicated to the study of the composition and physical state of the materials composing the surface in this paper we report a study of the distribution and physical state of the ices and non ice materials on pluto s illuminated surface and their mode and degree of mixing principal component analysis as well as various specific spectral indicators and correlation plots are used on the first set of 2 high resolution spectro images from the leisa instrument covering the whole illuminated face of pluto at the time of the new horizons encounter qualitative distribution maps have been obtained for the 4 main condensed molecules n2 ch4 co h2o as well as for the visible dark red material based on specific spectral indicators using either the strength or the position of absorption bands these 4 molecules are found to indicate the presence of 3 different types of ices n2 rich ch4 co ices ch4 rich co n2 ices and h2o ice the mixing lines between these ices and with the dark red material are studied using scatter plots between the various spectral indicators ch4 is mixed at the molecular level with n2 most probably also with co thus forming a ternary molecular mixture that follows its phase diagram with low solubility limits the occurrence of a n2 rich ch4 rich ices mixing line associated with a progressive decrease of the co ch4 ratio tells us that a fractionation sublimation sequence transforms one type of ice to the other forming either a n2 rich ch4 rich binary mixture at the surface or an upper ch4 rich ice crust that may hide the n2 rich ice below the strong ch4 rich h2o mixing line witnesses the subsequent sublimation of the ch4 rich ice lag left behind by the n2 co sublimation n spring summer or a direct condensation of ch4 ice on the cold h2o ice s autumn the weak mixing line between ch4 containing ices and the dark red material and the very sharp spatial transitions between these ices and this non volatile material are probably due to thermal incompatibility finally the occurrence of a h2o ice red material mixing line advocates for a spatial mixing of the red material covering h2o ice with possibly a small amount intimately mixed in water ice from this analysis of the different materials distribution and their relative mixing lines h2o ice appears to be the substratum on which other ices condense or non volatile organic material is deposited from the atmosphere n2 rich ices seem to evolve to ch4 dominated ices possibly still containing traces of co and n2 as n2 and co sublimate away the spatial distribution of these materials is very complex the high spatial definition of all these composition maps as well as those at even higher resolution that will be soon available will allow us to compare them with pluto s geologic features observed by lorri panchromatic and mvic multispectral imagers to better understand the geophysical processes in action at the surface of this astonishingly active frozen world

using supervirtual first arrivals in controlled source hardrock seismic imaging well worth the effort varied applications of seismic interferometry have arisen in the last decade however the potential of the method to improve reflection seismic processing in hardrock environments has not explicitly been regarded therefore in this paper we investigate the potential of retrieving the first arrivals originally hindered by high noise level in the exploitation of controlled source data acquired over the iron oxide apatite rich deposit at grangesberg sweden and its mining induced structures the supervirtual first arrivals retrieved using interferometry methodologies allowed first breaks to be picked more extensively than in the original data revised static corrections significantly improved the linearity of the first arrivals and continuity of reflections in the source gathers especially reflections considerably enhanced in the source gathers stacked constructively in the final section comparison with geological data supported by traveltime forward modelling indicates that these reflections represent the unmined part of the deposit other reflections at shallower depth are interpreted as anthropogenic faults possibly located at lithological contacts tomographic inversion was also run using the augmented traveltime data the greater resolution and penetration of this new tomographic image allowed better bridging with the results of the reflection seismic section velocity anomalies depict the presence of mining induced structures and a potential brewery fault which is believed to put at risks an urban area even though the potential of first arrival retrieval seems to be case dependent this study illustrates that interferometry may substantially improve the accuracy of static corrections and subsequent stack for hardrock imaging as well as in the penetration and resolution of traveltime tomograms

large heterogeneities in comet 67p as revealed by active pits from sinkhole collapse pits have been observed on many cometary nuclei mapped by spacecraft1 2 3 4 it has been argued that cometary pits are a signature of endogenic activity rather than impact craters such as those on planetary and asteroid surfaces impact experiments5 6 and models7 8 cannot reproduce the shapes of most of the observed cometary pits and the predicted collision rates imply that few of the pits are related to impacts8 9 alternative mechanisms like explosive activity10 have been suggested but the driving process remains unknown here we report that pits on comet 67p churyumov gerasimenko are active and probably created by a sinkhole process possibly accompanied by outbursts we argue that after formation pits expand slowly in diameter owing to sublimation driven retreat of the walls therefore pits characterize how eroded the surface is a fresh cometary surface will have a ragged structure with many pits while an evolved surface will look smoother the size and spatial distribution of pits imply that large heterogeneities exist in the physical structural or compositional properties of the first few hundred metres below the current nucleus surface

identification of bedrock lithology using fractal dimensions of drainage networks extracted from medium resolution lidar digital terrain models geologists know that drainage networks can exhibit different drainage patterns depending on the hydrogeological properties of the underlying materials geographic information system gis technologies and the increasing availability and resolution of digital elevation data have greatly facilitated the delineation quantification and study of drainage networks this study investigates the possibility of inferring geological information of the underlying material from fractal and linear parameters describing drainage networks automatically extracted from 5 m resolution lidar digital terrain model dtm data according to the lithological information scale 1 25 000 the study area is comprised of 30 homogeneous bedrock lithologies the lithological map units lmus these are mostly igneous and metamorphic rocks but also include some sedimentary rocks a statistical classification model of the lmus by rock type has been proposed based on both the fractal dimension and drainage density of the overlying drainage networks the classification model has been built using 16 lmus and it has correctly classified 13 of the 14 lmus used for its validation results for the study area show that lmus with areas ranging from 177 83 0 01 to 3 16 0 01 km2 can be successfully classified by rock type using the fractal dimension and the drainage density of the drainage networks derived from medium resolution lidar dtm data with different flow support areas these results imply that the information included in a 5 m resolution lidar dtm and the appropriate techniques employed to manage it are the only inputs required to identify the underlying geological materials

cassini radar observations of enceladus tethys dione rhea iapetus hyperion and phoebe cassini 2 2 cm radar and radiometric observations of seven of saturn s icy satellites yield properties that apparently are dominated by subsurface volume scattering and are similar to those of the icy galilean satellites average radar albedos decrease in the order enceladus tethys hyperion rhea dione iapetus and phoebe this sequence most likely corresponds to increasing contamination of near surface water ice which is intrinsically very transparent at radio wavelengths plausible candidates for contaminants include ammonia silicates metallic oxides and polar organics ranging from nitriles like hcn to complex tholins there is correlation of our targets radar and optical albedos probably due to variations in the concentration of optically dark contaminants in near surface water ice and the resulting variable attenuation of the high order multiple scattering responsible for high radar albedos our highest radar albedos for enceladus and tethys probably require that at least the uppermost one to several decimeters of the surface be extremely clean water ice regolith that is structurally complex i e mature enough for there to be high order multiple scattering within it at the other extreme phoebe has an asteroidal radar reflectivity that may be due to a combination of single and volume scattering iapetus 2 2 cm radar albedo is dramatically higher on the optically bright trailing side than the optically dark leading side whereas 13 cm results reported by black et al black g j campbell d b carter l m ostro s j 2004 science 304 553 show hardly any hemispheric asymmetry and give a mean radar reflectivity several times lower than the reflectivity measured at 2 2 cm these iapetus results are understandable if ammonia is much less abundant on both sides within the upper one to several decimeters than at greater depths and if the leading side s optically dark contaminant is present to depths of at least one to several decimeters as argued by lanzerotti et al lanzerotti l j brown w l marcantonio k j johnson r e 1984 nature 312 139 140 a combination of ion erosion and micrometeoroid gardening may have depleted ammonia from the surfaces of saturn s icy satellites given the hypersensitivity of water ice s absorption length to ammonia concentration an increase in ammonia with depth could allow efficient 2 2 cm scattering from within the top one to several decimeters while attenuating 13 cm echoes which would require a six fold thicker scattering layer if so we would expect each of the icy satellites average radar albedos to be higher at 2 2 cm than at 13 cm as is the case so far with rhea black g campbell d 2004 bull am astron soc 36 1123 as well as iapetus

channel morphometry sediment transport and implications for tectonic activity and surficial ages of titan basins abstract fluvial features on titan and drainage basins on earth are remarkably similar despite differences in gravity and surface composition we determined network bifurcation r b ratios for five titan and three terrestrial analog basins tectonically modified earth basins have r b values greater than the expected range 3 0 5 0 for dendritic networks comparisons with r b values determined for titan basins in conjunction with similarities in network patterns suggest that portions of titan s north polar region are modified by tectonic forces sufficient elevation data existed to calculate bed slope and potential fluvial sediment transport rates in at least one titan basin indicating that 75 mm water ice grains observed at the huygens landing site should be readily entrained given sufficient flow depths of liquid hydrocarbons volumetric sediment transport estimates suggest that 6700 10 000 titan years 2 0 3 0 10 5 earth years are required to erode this basin to its minimum relief assuming constant 1 m and 1 5 m flows these lowering rates increase to 27 000 41 000 titan years 8 0 12 0 10 5 earth years when flows in the north polar region are restricted to summer months

natural experiments in landscape evolution a natural experiment in landscape evolution is a case study of landform development in which only one element varies significantly and for which the driving forces initial conditions and or boundary conditions are well constrained natural experiments provide a means of testing landscape evolution theory on the large space and time scales to which that theory applies natural experiments can involve either steady or transient conditions cases with steady conditions allow one to test predictions about the relationships among topography erosion rates and various attributes related to climate and material properties transient cases are valuable for distinguishing between models whose predictions might be similar and therefore indistinguishable under steady conditions essential ingredients of a natural experiment include minimal variation in all but one factor good constraints on timing and or rates well characterized processes and high quality topographic data other useful ingredients include information about intermediate topographic states such as a former valley profile revealed by strath terraces and knowledge of the time history of erosion rates in order to deepen our understanding of the physics and chemistry of long term landscape evolution there is a pressing need to identify natural experiments and develop the necessary databases to take advantage of them copyright 2009 john wiley sons ltd

tectonic and climatic controls on rift escarpments erosion and flexural rebound of the dhofar passive margin gulf of aden oman we investigate the respective roles of climatic parameters and the flexural rigidity of the lithosphere in the erosion history and behavior of two adjacent rift escarpments along the northern coast of the gulf of aden in oman at this 25 myr old passive margin we define a type 1 scarp which is high sharp crested and has retreated 25 30 km inland from its master fault and a type 2 scarp which exhibits a more rounded profile lower relief and still coincides with its mapped normal fault trace since about 15 ma the margin has been seasonally affected by monsoon precipitation but with contrasting effects at the type 1 and type 2 escarpments depending on the position of the intertropical convergence zone in the geologic past during peak monsoon conditions both scarps experienced heavy rainfall and runoff whereas during monsoon starved conditions such as today the type 2 scarp experienced a foggy moist climate while the type 1 scarp remained much drier in order to assess the relative effects of climate and flexural parameters on the present day morphology of the dhofar margin we present onedimensional numerical models of erosion and flexure along two profiles representative of the type 1 and type 2 scarps unlike most surface process models previously published where present day topography is the only criterion by which to evaluate the quality of model outputs model behavior here is additionally constrained by independent estimates of denudation provided by geological cross sections well defined fault traces and other stratigraphic markers the best fitting models indicate that the type 1 escarpment formed under relatively arid climatic conditions and was affected by significant erosion recession and flexural uplift due to a low 7 km effective elastic thickness in contrast the morphology of the type 2 fault scarp was smoothed by a more humid climate but a high effective elastic thickness 15 km prevented it from uplifting or receding in addition we show that the sedimentary load acting at the foot of the escarpments exerts significant influence on their morphological evolution though this parameter is often neglected in other scarp evolution models

updated global map of martian valley networks and implications for climate and hydrologic processes 1 martian valley networks have long been viewed as some of the best evidence of prolonged surface water on mars analysis from viking data showed that valleys were primarily contained on the ancient crust drainage networks were immature and large undissected regions occurred in between individual systems these observations led many to propose that they formed primarily by groundwater processes and limited or no climate change from the present state was required using more recent and higher resolution data sets including visible infrared and topographic data we have manually remapped valleys on a global scale more than eight times as many valleys have been identified on the surface and calculated drainage densities are on average higher by a factor of 2 further regions previously thought to be undissected have significant incision by fluvial processes most of these systems seem to have formed around the noachian hesperian boundary 3 8 3 6 ga minor valley formation continued through the hesperian and into the early amazonian epoch approximately 2 8 ga ago the new data reveal characteristics of sustained precipitation and surface runoff including inner braided channels terraces multiple periods of formation complex network morphology and correlation with other fluviosedimentary features and chloride salts on mars groundwater processes or a transient steam atmosphere generated by impacts played at most a minor role these new results imply that mars had a long lived period or periods of clement conditions toward the end of the noachian epoch that supported a hydrologic cycle and potentially a biosphere

color composition and thermal environment of kuiper belt object 486958 arrokoth introduction the new horizons spacecraft flew past 486958 arrokoth provisional designation 2014 mu69 on 1 january 2019 arrokoth is a member of the subclass of trans neptunian or kuiper belt objects kbos known as the cold classical kbos cckbos most kbos formed in a disk of planetesimals that extended to about 30 au from the sun neptune eventually disrupted that disk by migrating outward through it with the migration halted by the sparseness of the disk beyond 30 au that event eliminated most members of the planetesimal disk but a minority were emplaced into dynamically excited orbits in the present day kuiper belt cckbos differ from those objects in having formed well beyond the 30 au edge of the main planetesimal disk they remain approximately where they formed on low inclination near circular orbits between 42 and 47 au from the sun relicts of the early solar system their distributions of colors albedos sizes and binarity differ from those of the more excited kbos rationale initial results from the exploration of arrokoth were published previously more data have since been received from the spacecraft allowing a more detailed analysis we analyze a high spatial resolution color imaging observation near infrared spectral imaging and microwave radiometry of arrokoth the infrared spectral data have been processed to compensate for the changing range and scale during the observation our multiple scattering radiative transfer models provide compositional constraints from the infrared spectral imagery microwave thermal radiometry at 4 2 cm wavelength is combined with heat transport models that account for the bilobate shape of arrokoth and for self radiation results at visual wavelengths arrokoth s reflectance rises toward longer wavelengths this red coloration is typical of the broader cckbo population that has been studied using telescopic observations color differences across the surface of arrokoth correspond to geological features these color differences are subtle with deviations of just a few percent around the prevailing red coloration some of the color variations are associated with albedo markings such as the bright neck between the two lobes bright splotches associated with a large pit or crater on the smaller lobe and poorly resolved small bright spots methanol ice ch3oh and complex organic tholins dominate the near infrared reflectance spectrum with h2o ice contributing little or no detectable absorption at the 4 2 cm microwave wavelength of new horizons radio system arrokoth s winter night side glows with an average brightness temperature of 29 5 k this emission probably emerges from below the cold winter surface at depths where warmth from the previous summer lingers our models show that self radiation more than compensates for self shadowing in the neck region between the two lobes resulting in warmer temperatures in that region by up to a few kelvin conclusion the nearly uniform coloration across arrokoth is consistent with expectations for an object that accreted too quickly for the composition of the available nebular solids to have changed during the course of its accretion radiolysis and photolysis from long exposure to space radiation would be expected to result in a dark space weathered surface veneer that is distinct from the more pristine interior but there is little evidence for such a coating perhaps because radiolytically processed material is eroded away faster than it accumulates the abundance of ch3oh ice and apparent scarcity of h2o ice appear to be signatures of a distinct environment in the cold dust shaded midplane of the outer nebula during formation of the solar system in this region temperatures would have been low enough that volatile co and ch4 could freeze onto dust grains enabling production of ch3oh and perhaps also destruction of h2o when the nebular dust dissipated some time after arrokoth s formation exposure to sunlight would have raised its temperature rapidly driving off condensed co and ch4 the temperature has remained too cold to crystallize amorphous h2o volatile species may remain trapped in amorphous h2o ice within arrokoth s interior but the infrared spectrum shows little evidence for such ice at the surface although the neck region gets slightly warmer than the rest of arrokoth s surface this effect is small relative to the winter summer temperature contrast and is thus unlikely to account for the distinctly higher albedo and slightly less red material that is seen there a more plausible explanation for the neck s albedo and color contrasts involves texture changes induced by the merger of the two lobes or subsequent downslope movement of material there

a modified delay time method for statics estimation with the virtual refraction topography and near surface heterogeneities lead to traveltime perturbations in surface land seismic experiments usually these perturbations are estimated and removed prior to further processing of the data a common technique to estimate these perturbations is the delay time method we have developed the modified delay time method wherein we isolate the arrival times of the virtual refraction and estimate receiver side delay times the virtual refraction is a spurious arrival found in wavefields estimated by seismic interferometry the new method removes the source term from the delay time equation is more robust in the presence of noise and extends the lateral aperture compared to the conventional delay time method we tested this in an elastic 2d numerical example where we estimated the receiver delay times above a horizontal refractor taking advantage of reciprocity of the wave equation and rearranging the common shot gathers into common receiver gathers isolated source delay times could also be obtained

enhanced refractor imaging by supervirtual interferometry refraction surveys are a well established method of imaging subsurface velocities both in terms of the deep crustal structure at global scales and in the shallow near surface these surveys generally involve deploying an array of receivers on the surface or water bottom and recording arrivals from a seismic source initiated at or near the surface

titan s inventory of organic surface materials 1 cassini radar observations now permit an initial assessment of the inventory of two classes presumed to be organic of titan surface materials polar lake liquids and equatorial dune sands several hundred lakes or seas have been observed of which dozens are each estimated to contain more hydrocarbon liquid than the entire known oil and gas reserves on earth dark dunes cover some 20 of titan s surface and comprise a volume of material several hundred times larger than earth s coal reserves overall however the identified surface inventories 3 104 km3 of liquid and 2 105 km3 of dune sands are small compared with estimated photochemical production on titan over the age of the solar system the sand volume is too large to be accounted for simply by erosion in observed river channels or ejecta from observed impact craters the lakes are adequate in extent to buffer atmospheric methane against photolysis in the short term but do not contain enough methane to sustain the atmosphere over geologic time unless frequent resupply from the interior buffers this greenhouse gas at exactly the right rate dramatic climate change on titan is likely in its past present and future

impact craters on titan five certain impact craters and 44 additional nearly certain and probable ones have been identified on the 22 of titan s surface imaged by cassini s high resolution radar through december 2007 the certain craters have morphologies similar to impact craters on rocky planets as well as two with radar bright jagged rims the less certain craters often appear to be eroded versions of the certain ones titan s craters are modified by a variety of processes including fluvial erosion mass wasting burial by dunes and submergence in seas but there is no compelling evidence of isostatic adjustments as on other icy moons nor draping by thick atmospheric deposits the paucity of craters implies that titan s surface is quite young but the modeled age depends on which published crater production rate is assumed using the model of artemieva and lunine 2005 suggests that craters with diameters smaller than about 35 km are younger than 200 million years old and larger craters are older craters are not distributed uniformly xanadu has a crater density 2 9 times greater than the rest of titan and the density on equatorial dune areas is much lower than average there is a small excess of craters on the leading hemisphere and craters are deficient in the north polar region compared to the rest of the world the youthful age of titan overall and the various erosional states of its likely impact craters demonstrate that dynamic processes have destroyed most of the early history of the moon and that multiple processes continue to strongly modify its surface the existence of 24 possible impact craters with diameters less than 20 km appears consistent with the ivanov basilevsky and neukum 1997 model of the effectiveness of titan s atmosphere in destroying most but not all small projectiles

the taxonomic distribution of asteroids from multi filter all sky photometric surveys abstract the distribution of asteroids across the main belt has been studied for decades to understand the current compositional distribution and what that tells us about the formation and evolution of our solar system all sky surveys now provide orders of magnitude more data than targeted surveys we present a method to bias correct the asteroid population observed in the sloan digital sky survey sdss according to size distance and albedo we taxonomically classify this dataset consistent with the bus and binzel bus s j binzel r p 2002 icarus 158 146 177 and bus demeo et al demeo f e binzel r p slivan s m bus s j 2009 icarus 202 july 160 180 systems and present the resulting taxonomic distribution the dataset includes asteroids as small as 5 km a factor of three in diameter smaller than in previous work such as by mothe diniz et al mothe diniz t carvano j m a lazzaro d 2003 icarus 162 march 10 21 because of the wide range of sizes in our sample we present the distribution by number surface area volume and mass whereas previous work was exclusively by number while the distribution by number is a useful quantity and has been used for decades these additional quantities provide new insights into the distribution of total material we find evidence for d types in the inner main belt where they are unexpected according to dynamical models of implantation of bodies from the outer solar system into the inner solar system during planetary migration levison h f bottke w f gounelle m morbidelli a nesvorn d tsiganis k 2009 nature 460 july 364 366 we find no evidence of s types or other unexpected classes among trojans and hildas albeit a bias favoring such a detection finally we estimate for the first time the total amount of material of each class in the inner solar system the main belt s most massive classes are c b p v and s in decreasing order excluding the four most massive asteroids 1 ceres 2 pallas 4 vesta and 10 hygiea that heavily skew the values primitive material c p types account for more than half main belt and trojan asteroids by mass most of the remaining mass being in the s types all the other classes are minor contributors to the material between mars and jupiter

relative rates of fluvial bedrock incision on titan and earth 1 observations of likely fluvial channels on the surface of titan along with titan s geologically youthful surface motivate this study of comparative fluvial erosion rates on titan and the earth the roles of bedload abrasion suspended load abrasion plucking and cavitation are considered despite orders of magnitude differences in some of the physical parameters that control fluvial incision on titan and the earth incision rates on titan are likely to be similar to terrestrial rates given similar conditions of slope discharge and sediment supply

modeling of ice pinnacle formation on callisto callisto s pinnacle terrain has been interpreted to form through sublimation weathering of bedrock and subsequent deposition of the sublimated ice in local cold traps on peaks and crater rims to investigate how these processes are affected by environmental parameters including solar illumination and the composition and concentration of ices in the crust we employ the marssim landform evolution model and advance its treatment of the physics that underlies the relevant processes both ice sublimation and deposition are controlled by surface temperature which we calculate based on energy contributions from both insolation and thermal reradiation from the surrounding landscape we perform 4 5 gyr duration simulations whereby we separately consider and model co2 and h2o as the crustal ice species we find that sublimating a crustal content of 10 co2 ice a reasonable but arbitrarily selected value yields present day landform degradation and regolith coverage that is comparable to what is observed on callisto in our h2o ice simulations we reproduce the essential features of pinnacle ice distribution at both the equator and midlatitudes our present nominal crustal h2o ice content is 33 which produces a maximum pinnacle ice thickness of 64 m pinnacle height is likely limited by collapse or mass wasting of the ice once it reaches a certain thickness

size and shape of saturn s moon titan cassini observations show that saturn s moon titan is slightly oblate a fourth order spherical harmonic expansion yields north polar south polar and mean equatorial radii of 2574 32 0 05 kilometers km 2574 36 0 03 km and 2574 91 0 11 km respectively its mean radius is 2574 73 0 09 km titan s shape approximates a hydrostatic synchronously rotating triaxial ellipsoid but is best fit by such a body orbiting closer to saturn than titan presently does titan s lack of high relief implies that most but not all of the surface features observed with the cassini imaging subsystem and synthetic aperture radar are uncorrelated with topography and elevation titan s depressed polar radii suggest that a constant geopotential hydrocarbon table could explain the confinement of the hydrocarbon lakes to high latitudes

tectonic climatic and lithologic influences on landscape fractal dimension and hypsometry implications for landscape evolution in the san gabriel mountains california east west variation in tectonic activity and strong north south climatic gradients provide a unique opportunity to study tectonic climatic and lithologic influences on landscape evolution in the san gabriel mountains california the competing tendencies of constructive tectonic and degradational climatic effects act against lithologic resistance to influence fluvial systems and thus the nature of adjacent and nested drainage basins landscape fractal dimension d a measure of surface roughness over a variety of scales and the hypsometric integral i a measure of the distribution of landmass volume above a reference plane are useful measures of altitudinal variation with scale as such they may provide clues as to the relative influences of tectonism climate and rock type topographic analyses of the san gabriel mountains clearly indicate that tectonism strongly influences d at range wavelength scales while rock type variation apparently influences d and i at smaller scales tectonism is also shown to influence i across the mountain piedmont junction at all scales investigated tectonic activity shows strong negative correlation with both i and d because tectonically active portions of the mountain front do not allow time for much landscape dissection by lower order streams three dimensional topographic modeling suggests climatic parameters exert a stronger influence on d than does tectonism this modeling also suggests an inverse correlation between range scale d and i with varying climate and uplift rate a positive correlation is observed in the san gabriel mountains we suggest this difference results from 1 differences in uplift style between the san gabriel mountains and the models and or 2 variation in rock type erodibility present in the san gabriel mountains but which was not modeled we postulate that the interaction of tectonic climatic and lithologic parameters influences the stable i and d to which a landscape evolves key questions remaining include 1 the time required to reach a stable i or d after a climatic or tectonic change 2 what does the fractal nature of topography tell us about the scaling characteristics of major landforming processes 3 how does climate influence range scale i and both range and small scale d and 4 what are the effects on i and d of range scale lithologic variation both in the models and in real landscapes

variation in the reference shields stress for bed load transport in gravel bed streams and rivers 1 the present study examines variations in the reference shear stress for bed load transport r using coupled measurements of flow and bed load transport in 45 gravel bed streams and rivers the study streams encompass a wide range in bank full discharge 1 2600 m3 s average channel gradient 0 0003 0 05 and median surface grain size 0 027 0 21 m a bed load transport relation was formed for each site by plotting individual values of the dimensionless transport rate w versus the reach average dimensionless shear stress the reference dimensionless shear stress r was then estimated by selecting the value of corresponding to a reference transport rate of w 0 002 the results indicate that the discharge corresponding to r averages 67 of the bank full discharge with the variation independent of reach scale morphologic and sediment properties however values of r increase systematically with average channel gradient ranging from 0 025 0 035 at sites with slopes of 0 001 0 006 to values greater than 0 10 at sites with slopes greater than 0 02 a corresponding relation for the bank full dimensionless shear stress bf formulated with data from 159 sites in north america and england mirrors the relation between r and channel gradient suggesting that the bank full channel geometry of gravel and cobble bedded streams is adjusted to a relatively constant excess shear stress bf r across a wide range of slopes

the virtual refraction useful spurious energy in seismic interferometry seismic interferometry is rapidly becoming an established technique to recover the green s function between receivers but practical limitations in the source energy distribution inevitably lead to spurious energy in the results instead of attempting to suppress all such energy we use a spurious wave associated with the crosscorrelation of refracted energy at both receivers to infer estimates of subsurface parameters we named this spurious event the virtual refraction illustrated by a numerical two layer example we found that the slope of the virtual refraction defines the velocity of the faster medium and that the stationary phase point in the correlation gather provides the critical offset with the associated critical time derived from the real shot record this approach includes all of the necessary information to estimate wave speeds and interface depth without the need of inferences from other wave types

lithologic control on the multifractal spectrum of river networks previous observations on some natural river networks showed the similar values of the support fractal dimension and the information entropy in basins having similar source rocks in the present work lithologic control on river network multifractality is investigated through the reconstruction of the spectra belonging to two classes of different lithology the plutonic metamorphic class and the coherent sedimentary one two computational methods of the generalised fractal dimensions and multifractal spectra are illustrated and applied to river networks of the calabria region southern italy it is shown that an increment of both the fractal dimensions and the lipschitz holder exponents of singularity occurs when passing from a coherent sedimentary to a plutonic metamorphic river network the importance of this finding emerges from the direct link between flood hydrographs and multifractal spectra as expressed in the multifractal instantaneous unit hydrograph miuh the increment of the multifractal parameters produces an increment of the flood peaks

determining titan surface topography from cassini sar data a technique referred to as sartopo has been developed for obtaining surface height estimates with 10 km horizontal resolution and 75 m vertical resolution of the surface of titan along each cassini synthetic aperture radar sar swath we describe the technique and present maps of the co located data sets a global map and regional maps of xanadu and the northern hemisphere hydrocarbon lakes district are included in the results a strength of the technique is that it provides topographic information co located with sar imagery having a topographic context vastly improves the interpretability of the sar imagery and is essential for understanding titan sartopo is capable of estimating surface heights for most of the sar imaged surface of titan currently nearly 30 of the surface is within 100 km of a sartopo height profile other competing techniques provide orders of magnitude less coverage we validate the sartopo technique through comparison with known geomorphological features such as mountain ranges and craters and by comparison with co located nadir altimetry including a 3000 km strip that had been observed by sar a month earlier in this area the sartopo and nadir altimetry data sets are co located tightly within 5 10 km for one 500 km section have similar resolution and as expected agree closely in surface height furthermore the region contains prominent high spatial resolution topography so it provides an excellent test of the resolution and precision of both techniques