coupled caldera subsidence and stirring inferred from analogue models analogue modelling of caldera forming eruptions suggests that sinking of the magma chamber roof is variable in space and time leading to substantial stirring and mixing of magma this can explain the common occurrence of geochemical zonation and magma mingling in deposits erupted from calderas

seismic depth imaging of iron oxide deposits and their host rocks in the ludvika mining area of central sweden abstract the development of cost effective and environmentally acceptable geophysical methods for the exploration of mineral resources is a challenging task seismic methods have the potential to delineate the mineral deposits at greater depths with sufficiently high resolution in hardrock environments which typically host the majority of metallic mineral deposits seismic depth imaging workflows are challenged by steeply dipping structures strong heterogeneity and the related wavefield scattering in the overburden as well as the often limited signal to noise ratio of the acquired data in this study we have developed a workflow for imaging a major iron oxide deposit at its accurate position in depth domain while simultaneously characterizing the near surface glacial overburden including surrounding structures like crossing faults at high resolution our workflow has successfully been showcased on a 2d surface seismic legacy data set from the ludvika mining area in central sweden acquired in 2016 we applied focusing prestack depth imaging techniques to obtain a clear and well resolved image of the mineralization down to over 1000 m depth in order to account for the shallow low velocity layer within the depth imaging algorithm we carefully derived a migration velocity model through an integrative approach this comprised the incorporation of the tomographic near surface model the extension of the velocities down to the main reflectors based on borehole information and conventional semblance analysis in the final step the evaluation and update of the velocities by investigation of common image gathers for the main target reflectors were used although for our data set the reflections from the mineralization show a strong coherency and continuity in the seismic section reflective structures in a hardrock environment are typically less continuous in order to image the internal structure of the mineralization and decipher the surrounding structures we applied the concept of reflection image spectroscopy to the data which allows the imaging of wavelength specific characteristics within the reflective body as a result conjugate crossing faults around the mineralization can directly be imaged in a low frequency band while the internal structure was obtained within the high frequency bands

seismic imaging of the waltham canyon fault california comparison of ray theoretical and fresnel volume prestack depth migration abstract near vertical faults can be imaged using reflected refractions identified in controlled source seismic data often theses phases are observed on a few neighboring shot or receiver gathers resulting in a low fold data set imaging can be carried out with kirchhoff prestack depth migration in which migration noise is suppressed by constructive stacking of large amounts of multifold data fresnel volume migration can be used for low fold data without severe migration noise as the smearing along isochrones is limited to the first fresnel zone around the reflection point we developed a modified fresnel volume migration technique to enhance imaging of steep faults and to suppress noise and undesired coherent phases the modifications include target oriented filters to separate reflected refractions from steep dipping faults and reflections with hyperbolic moveout undesired phases like multiple reflections mode conversions direct p and s waves and surface waves are suppressed by these filters as an alternative approach we developed a new prestack line drawing migration method which can be considered as a proxy to an infinite frequency approximation of the fresnel volume migration the line drawing migration is not considering waveform information but requires significantly shorter computational time target oriented filters were extended by dip filters in the line drawing migration method the migration methods were tested with synthetic data and applied to real data from the waltham canyon fault california the two techniques are applied best in combination to design filters and to generate complementary images of steep faults

elastoviscoplastic relaxation of impact crater topography with application to ganymede and callisto 1 we use an elastoviscoplastic rheological model to study the long term relaxation of impact crater topography on ganymede and callisto we employ a complete set of rheological parameters for ductile creep in ice ih and implement a new shallower initial shape model under high heat flow conditions stresses are relieved in deeper less viscous material and the remainder concentrates as flexural bending stresses in a viscously stiffer near surface layer essentially a mechanical lithosphere forms that focuses stresses but with uplifts and stress levels that are always greater than those obtained for a purely viscous half space we discuss how classic elastic flexure and purely viscous relaxation are special cases of this more generalized rheological model stress concentration in the flexing i e bending layer can exceed the plastic yield strength of ice for high enough heat flows weakening the layer somewhat and increasing the total amount of relaxation these plastic strains tend to be limited to small magnitudes 1 mm permits both retention and relaxation of topography at the lower and higher ends respectively of the anticipated heat flow range consideration of relaxed craters in marius regio and of the palimpsests and penepalimpsests suggests ancient heat flows in excess of 10 mw m 2 consistent with other estimates

atmospheric effects on ejecta emplacement laboratory experiments allow the investigation of complex interactions between impacts and an atmosphere although small in scale they can provide essential first order constraints on the processes affecting late stage ballistic ejecta and styles of ejecta emplacement around much larger craters on planetary surfaces the laboratory experiments involved impacting different fine grained particulate targets under varying atmospheric pressure and density different gas compositions during crater formation ballistic ejecta form the classic cone shaped profile observed under vacuum conditions as atmospheric density increases for a given pressure however the ejecta curtain bulges at the base and pinches above this systematic change in the ejecta curtain reflects the combined effects of deceleration of ejecta smaller than a critical size and entrainment of these ejecta within atmospheric vortices created as the outward moving wall of ejecta displaces the atmosphere additionally a systematic change in emplacement style occurs as a function of atmospheric pressure largely independent of density contiguous ejecta rampart superposing ballistically emplaced deposits 0 06 to 0 3 bar ejecta flow lobes 0 3 to 0 7 bar and radial patterns 0 8 bar underlying processes controlling such systematic changes in emplacement style were revealed by observing the evolution of the ejecta curtain by changing target materials including layered targets and low density particulates by varying atmospheric density by changing impact angle and by comparing the ejecta run out distances with first order models of turbidity flows three distinct ejecta emplacement processes can be characterized ejecta ramparts result from coarser clasts sorted and driven outward by vortical winds behind the outward moving ejecta curtain this style of wind modified emplacement represents minimal ejecta entrainment and is enhanced by a bimodal size distribution in the ejecta such eddy supported flows are observed to increase in run out distance scaled to crater size with increasing atmospheric pressure by analogy with turbidity flows this scaled distance should increase as r1 2 for a given atmospheric pressure and degree of entrainment ejecta flows with much greater run out distances develop as the turbulent power in atmospheric response winds increase such flows overrun and scour the inner ejecta facies thereby producing distinct inner and outer facies the degree of ejecta entrainment depends on the dimensionless ratio of drag to gravity forces acting on individual ejecta and the intensity of the winds created by the outward moving curtain entrainment increases with increasing atmospheric density and ejection velocity crater size but decreases with ejecta density and size the intensity of curtain generated winds increases with ejection velocity crater size the dimensionless drag ratio characterizing the laboratory experiments can be applied to mars since the reduced atmospheric density is offset by the increased ejection velocities for kilometer scale events for a given crater size ejection velocity and atmospheric conditions a wide range of nonballistic ejecta emplacement styles could occur simply by varying ejecta sizes even without the presence of water alternatively the onset crater diameter for nonballistic emplacement styles can reflect the range of ejecta sizes possible from the diverse martian geologic history massive basalts to fine grained aeolian deposits scaling considerations further predict that ejecta run out distances scaled to crater size on mars should increase as r1 2 hence long run out flows dependent on crater diameter need not reflect depth to a buried reservoir of water on venus however the dense atmosphere maximizes entrainment and results in ejecta flow densities approaching a constant fraction of the atmospheric density under such conditions ejecta run out distances should decrease as r 1 2

impact features on europa results of the galileo europa mission gem during the galileo europa mission gem impact features on europa were observed with improved resolution and coverage was compared with voyager or the galileo nominal mission we surveyed all primary impact features 4 km in diameter seen on europa through orbit e19 the transition from simple to complex crater morphology occurs at a diameter of about 5 km we calculated the transient crater dimensions and excavation depths of all craters surveyed the largest impact feature tyre probably had a transient crater depth between 5 and 10 km and transported material to the surface from a depth of not greater than 4 km craters 30 km in diameter such as manannan and pwyll formed within targets whose immediate subcrater materials exhibited nonfluid behavior on time scales of the impact event and that are capable especially in the case of pwyll of supporting significant local topographic loads such as a central peak these craters are nevertheless quite shallow with very subdued floors and we suspect that manannan and pwyll s small depth to diameter ratios are due to the isostatic adjustment of large scale topography facilitated by warm plastically deformable ice at depth morphological similarities between callanish and tyre strongly imply that conclusions reached regarding callanish in j moore et al 1998 icarus135 127 145 also apply to tyre which was that callanish is the consequence of impact into target materials that are mechanically very weak at depth new evidence that callanish s circumferential rings formed before the proximal ejecta became immobile implies a low viscosity substrate at the time of impact we also report additional evidence that a component of the proximal ejecta of callanish was emplaced as a fluid our observations of pwyll secondaries support the conclusions stated in alpert and melosh 1999 that impacts on icy bodies eject smaller fragments and that fragment size decreases more gradually as velocity increases than observed for impacts on silicate bodies at equivalent ejection velocities examination of pwyll s secondary craters reveals azimuthal variations with ejecta fragment sizes being larger near the center of a ray than off the ray our initial analysis of the characteristic size distribution of pwyll s secondary craters shows that they form a differential slope slightly shallower than 4 similar steep slopes for small craters on ganymede imply that small craters there are mostly formed by secondary impact and the jovian system may thus be deficient in small impacts relative to the environment of the terrestrial planets

viscous relaxation of ganymede s impact craters constraints on heat flux abstract measurement of crater depths in ganymede s dark terrain have revealed substantial numbers of unusually shallow craters indicative of viscous relaxation see companion paper singer k n schenk p m bland m t mckinnon w b 2017 relaxed impact craters on ganymede regional variations and high heat flow icarus submitted these viscously relaxed craters provide insight into the thermal history of the dark terrain the rate of relaxation depends on the size of the crater and the thermal structure of the lithosphere here we use finite element simulations of crater relaxation to constrain the heat flux within the dark terrain when relaxation occurred we show that the degree of viscous relaxation observed cannot be achieved through radiogenic heating alone even if all of the relaxed craters are ancient and experienced the high radiogenic fluxes present early in the satellite s history for craters with diameter 10 km heat fluxes of 40 50 mw m 2 can reproduce the observed crater depths but only if the fluxes are sustained for 1 gyr these craters can also be explained by shorter lived heat pulses with magnitudes of 100 mw m 2 and timescales of 10 100 myr at small crater diameters 4 km the observed shallow depths are difficult to achieve even when heat fluxes as high as 150 mw m 2 are sustained for 1 gyr the extreme thermal conditions required to viscously relax small craters may indicate that mechanisms other than viscous relaxation such as topographic degradation are also in play at small crater diameters the timing of the relaxation event s is poorly constrained due to the sparsity of adequate topographic information though it likely occurred in ganymede s middle history neither recently nor shortly after satellite formation the consistency between the timing and magnitude of the heat fluxes derived here and those inferred from other tectonic features suggests that a single event caused both ganymede s tectonic deformation and its crater relaxation future observations should permit more robust determination of the relative timing of the heating event that caused viscous relaxation

ganymede and callisto complex crater formation and planetary crusts new depth diameter d d rim and peak height and width measurements of fresh craters on ganymede and callisto are utilized to explore not only crater mechanics on icy satellites but intersatellite crater scaling and crustal properties and composition significant systematic differences in crater morphology on icy and rocky planets are confirmed simple to complex transition diameters on icy satellites including ganymede and callisto are much lower than those on rocky planets also complex crater depths and rim heights on ganymede and callisto are inherently 60 70 shallower than lunar complex craters despite similar surface gravity hence viscous relaxation is not as important as is generally assumed central peaks on most icy satellites are 1 2 km higher and considerably wider with respect to diameter than for similar sized lunar craters terracing and rim slumping is also rare in these craters central peaks in craters on ganymede and callisto larger than 15 km however are relatively small in both width and height however correlating with the occurrence of rim slumping thus central peak dimensions are an indirect indicator of the degree of rim slumping transition diameters for the occurrence of central peaks and rim slumps and for d d curve inflections for icy satellites scale approximately with the inverse of surface gravity except possibly at very low g the transition diameters for central peaks and for rim slumping differ however by 5 15 km on ganymede and callisto but by 50 or more km on the smaller icy satellites these large differences suggest that d d curves on icy satellites are comprised of three segments of decreasing slope one for smaller simple craters a second for central peak craters and a third for larger true complex craters with both central peaks and rim slumping the shallow slopes of d d curves on ganymede and callisto resemble that of the moon consistent with the occurrence of both central peaks and rim failure the high slopes of d d curves on the middle sized icy satellites indicate that they are middle segments consistent with the dominance of central peaks in those craters complex crater depths on icy satellites in general scale with the inverse of surface gravity the depths of all the observed large basin scale craters on these small satellites when scaled to ganymede gravity are very similar to those of complex craters on ganymede and callisto these large craters including odysseus 425 km diameter on tethys are probably true complex craters that have not undergone significant viscous relaxation ithaca chasma on tethys probably formed during the prompt collapse of the transient odysseus crater crater morphology is clearly controlled by both gravity and by large variations in material properties i e composition and should be useful in constraining bulk crustal composition i e ice rock ratios the similarity of various morphological transition diameters and complex crater depths on ganymede and callisto two geophysically very similar but geologically divergent large icy satellites indicates that the crusts of both bodies are dominated by water ice with only a minor rocky component

the distribution of bright and dark material on ganymede in relationship to surface elevation and slopes abstract the unique high resolution digital terrain data set available for ganymede s uruk sulcus area and galileo regio is analyzed by quantitative image analysis techniques to identify relationships between surface brightness elevation and slopes broad and narrow ridges and grooves of the uruk sulcus terrain model are found to be aligned with bright and dark lineament patterns visible in images these prominent lineaments represent areas covered by bright and dark albedo material not effects of photometric shading there is a strong correlation between material locations and elevation bright material is found on topographic highs whereas dark material is located in depressions the relative abundance of the dark material increases with lower elevation in galileo regio we find that bright material is also located on slopes facing north we suggest that the bright material in uruk sulcus and galileo regio was emplaced or exposed during or after formation of the terrain in its present location whereas the dark material was eroded and redistributed down slope effects of net solar illumination may play a role in the peculiar azimuthal distribution of bright and dark material on slopes

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

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

seismic exploration scale velocities and structure from ambient seismic noise 1 hz the successful surface waves retrieval in solid earth seismology using long time correlations and subsequent tomographic images of the crust have sparked interest in extraction of subsurface information from noise in the exploration seismology subsurface information in exploration seismology is usually derived from body wave reflections 1 hz which is challenging for utilization of ambient noise we use 11 h of noise recorded in the sirte basin libya first we study the characteristics of the noise we show that the bulk of the noise is composed of surface waves at frequencies below 6 hz some noise panels contain nearly vertically traveling events we further characterize these events using a beamforming algorithm from the beamforming we conclude that these events represent body wave arrivals with a fairly rich azimuthal distribution having body wave arrivals in the noise is a prerequisite for body wave reflections retrieval we crosscorrelate and sum the recorded ambient noise panels to retrieve common source gathers following two approaches using all the noise and using only noise panels containing body wave arrivals likely to contribute to the reflections retrieval comparing the retrieved gathers with active seismic data we show that the two way traveltimes at short offsets of several retrieved events coincide with those of reflections in the active data and thus correspond to apexes of reflections we then compare retrieved stacked sections of the subsurface from both approaches with the active data stacked section and show that the reflectors are consistent along a line the results from the second approach exhibit the reflectors better

geological history of the tyre region of europa a regional perspective on europan surface features and ice thickness galileo images of the tyre macula region of europa at regional 170 m pixel and local 40 m pixel scales allow mapping and understanding of surface processes and landforms ridged plains doublet and complex ridges shallow pits domes chaos areas impact structures tilted blocks and massifs and young fracture systems indicate a complex history of surface deformation on europa regional and local morphologies of the tyre region of europa suggest that an impactor penetrated through several kilometers of water ice to a mobile layer below the surface morphology was initially dominated by formation of ridged plains followed by development of ridge bands and doublet ridges with chaos and fracture formation dominating the latter part of the geologic history of the tyre region two distinct types of chaos have been identified which along with upwarped dome materials appear to represent a continuum of features domes platy chaos knobby chaos resulting from increasing degrees of surface disruption associated with local lithospheric heating and thinning local and regional stratigraphic relationships block heights and the morphology of the tyre impact structure suggest the presence of low viscosity ice or liquid water beneath a thin several kilometers surface ice shell at the time of the impact the very low impact crater density on the surface of europa suggests that this thin shell has either formed or been thoroughly resurfaced in the very recent past

tyre and pwyll galileo orbital remote sensing of mineralogy versus morphology at two selected sites on europa observational data from the galileo orbiter s remote sensing instruments including solid state imaging ssi the near infrared mapping spectrometer nims and the ultraviolet spectrometer uvs are analyzed and interpreted in terms of the history of the tyre and pwyll impact sites and the nature of europa s crustal zonal structure material characterized by asymmetric 1 4 and 2 0 xm bands and visible coloration characterizes each site where morphologic evidence suggests disruption of the topmost crust the material is not h20 ice is endogenic and is common to the linea impact basins and dark trailing side terrain differences between tyre and 11 are interpreted in terms of europa s peculiar energy history while other evidence may suggest flooding of the endogenic material as a liquid the pure ice appearance of most of europa s crust is probably superficial while beneath a thin patina of sputtered h20 molecules the crust is everywhere laced with numerous generations of intrusions and extrusions of an aqueous phase our results together with numerous laboratory experiments and theoretical analysis suggest that the aqueous phase is dominated by the so2 anion nothing is rich but the inexhaustible wealth of nature she shows us only surfaces but she is a million fathoms deep

3d wavepath migration 3d kirchhoff migration km smears a trace s time sample along a quasi ellipsoid in the model space this is a costly and sometimes noisy process as reflection energy is smeared far away from the actual reflector position introducing far field migration artefacts as a reduced form of 3d km 3d wavepath migration wm smears a picked reflection arrival to a small fresnel zone portion centred about the specular reflection point leading to fewer migration artefacts and reduced computation time both the traveltime and the angle of incidence are required by wm for locating the specular reflection point our results with 3d prestack synthetic data show that wm generates fewer migration artefacts and can sometimes define complex structure better than km our results with 3d prestack field data show that wm can mostly suppress migration artefacts and can sometimes resolve reflection interfaces better than km the cpu comparison shows that for both the synthetic and field data examples wm can be more than an order of magnitude faster than km the limitation with 3d wm is that the angle of incidence calculation is sensitive to the recording geometry and the signal to noise s n ratio which can lead to blurred images

catastrophic caldera forming eruptions thermomechanics and implications for eruption triggering and maximum caldera dimensions on earth abstract approximately every 100 000 years the earth experiences catastrophic caldera forming supereruptions that are considered to be one of the most hazardous natural events on earth utilizing new temperature dependent viscoelastic numerical models that incorporate a mohr coulomb failure criterion we find that eruptive failure of the largest magma chambers is a function of the geometry of the overlying roof and the location of the brittle ductile transition in particular the ductile halo created around the hot magma chamber buffers increasing overpressures and prevents pressure relief via magmatic injection from the magma chamber the numerical results indicate that as chamber volume increases the higher temperatures in the host rock and the decrease in the roof aspect ratio cause a shift from reservoir triggered eruption to an external roof triggered mechanism specifically as overpressure increases within the largest magma chambers extensive uplift in the overlying roof promotes the development of through going faults that may trigger eruption and caldera collapse from above we find that for magma chamber volumes 103 km3 and roof aspect ratios depth width

does crater saturation equilibrium occur in the solar system abstract similarity is found in crater densities on the most heavily cratered surfaces throughout the solar system this is hypothesized to result from a steady state saturation equilibrium being approached or achieved by cratering processes this hypothesis conflicts with some recent interpretations however it accounts for 1 a similarity in maximum relative crater density below certain theoretically predicted values on all heavily cratered surfaces 2 a leveling off at this same relative density among 100 m scale secondary craters in populations on lunar maria and other sparsely cratered lunar surfaces 3 the approximate uniformity of maximum relative densities on saturn satellites in spite of dramatic variations predicted from nonsaturation models assuming heliocentric impactors the lunar frontside upland crater population sometimes described as a well preserved production function useful for interpreting other planetary surfaces is found not to be a production function it was modified by intercrater plains formed at least partly by early upland basaltic lava flooding recently confirmed spectrophotometrically consistent with this counts in pure uplands those lacking intercrater plains match the proposed saturation equilibrium density variations among large d 64 km crater populations are found but these may involve several hypothesized mechanisms that rapidly obliterate large craters especially on icy surfaces recent models in which different populations of interplanetary bodies hit different planets need further appraisal

volcanology volcanic bipolar disorder explained eruptions come in a range of magnitudes numerical simulations and laboratory experiments show that rare giant super eruptions and smaller more frequent events reflect a transition in the essential driving forces for volcanism

titan an exogenic world abstract all landforms on titan that are unambiguously identifiable can be explained by exogenic processes aeolian fluvial impact cratering and mass wasting previous suggestions of endogenically produced cryovolcanic constructs and flows have without exception lacked conclusive diagnostic evidence the modification of sparse recognizable impact craters themselves exogenic can be explained by aeolian and fluvial erosion tectonic activity could be driven by global thermal evolution or external forcing rather than by active interior processes a lack of cryovolcanism would be consistent with geophysical inferences of a relatively quiescent interior incomplete differentiation only minor tidal heating and possibly a lack of internal convection today titan might be most akin to callisto with weather an endogenically relatively inactive world with a cool interior we do not aim to disprove the existence of any and all endogenic activity at titan nor to provide definitive alternative hypotheses for all landforms but instead to inject a necessary level of caution into the discussion the hypothesis of titan as a predominantly exogenic world can be tested through additional cassini observations and analyses of putative cryovolcanic features geophysical and thermal modeling of titan s interior evolution modeling of icy satellite landscape evolution that is shaped by exogenic processes alone and consideration of possible means for supplying titan s atmospheric constituents that do not rely on cryovolcanism

formation of crater palimpsests on ganymede crater palimpsests on ganymede are circular features of high albedo apparently formed by impacts very early in the satellite s history some palimpsests have distinct outward facing slopes at their outer margins suggesting that they are distinct deposits of significant thickness this view is supported by observations of superimposed craters that excavate through palimpsest deposits into underlying materials of contrasting albedo we suggest that crater palimpsests may result from volcanic extrusions triggered by large impact events early in ganymede s history impact excavation that occurred to a sufficient depth would penetrate the satellite s thin primordial lithosphere allowing mobile buoyant material from a vigorously convecting mantle to rise to the surface upon reaching the surface the material would spread radially to produce a circular deposit of relatively high albedo as the lithosphere cooled and thickened palimpsest formation would have ceased consistent with the observed concentration of palimpsest formation in the earliest part of ganymede s recorded geologic history constraints on the nature of the extruded material may be derived from a simple model of emplacement we use an analytic model for axisymmetric viscous flow to constrain the flow viscosity in terms of the aspect height radius ratio of the palimpsest a measured value of 0 02 would imply a viscosity marginally consistent with glacial ice viscosities smaller values of which are likely would imply still lower viscosities more appropriate to partially liquid flow if such flows were described by a bingham rheology their yield strengths were of the order of 1 kpa this is lower than is typical for even very mobile silicate lavas but may be reasonable for a water ice slush ice extrusion could have been a slow process taking thousands of years while slush extension would have been essentially contemporaneous with the impact event for the case of either solid ice and slush extrusion our conclusions for the thermal structure of ganymede at the time of palimpsest formation are similar there was a thin 10 km conducting lithosphere underlain by a vigorously convecting mantle that was very close to the solidus temperature

a proposed origin for palimpsests and anomalous pit craters on ganymede and callisto palimpsests and anomalous pit craters are two classes of craters found on the icy satellites ganymede and callisto that have no obvious counterparts among the crater populations found on rocky planets the distinct characteristics of palimpsests and anomalous pit craters in morphology morphometry and population statistics which differentiate them from the more numerous normal craters and basins on the icy satellites also preclude their origin as normal craters that have nearly vanished through viscous relaxation an alternate origin is proposed palimpsests are formed when the flow of material during the modification stage of crater formation is dominated by wet fluid flow as opposed to dry granular flow which forms normal craters conditions of wet modification flow occur when the volume of melt remaining in the crater attains a volume comparable to the volume of the transient crater by use of an impact model that includes 1 plausible impact velocity distributions 2 crater scaling in ice 3 shock melting in ice 4 thermal profiles as a function of time in ganymede and 5 cratering flow field constraints conditions for wet modification flow are found to occur for sufficiently large impacts or high velocity impactors the range of normal crater palimpsest transition diameters and the morphologic characteristics inferred from the impact model are consistent with the observed characteristics of palimpsests thus normal craters are inferred to result from the majority of impactors which have impact velocities near the average of 15 km s anomalous pit craters inferred to be transitional forms from intermediate velocity impactors at about 30 km s and palimpsests by impactors travelling in excess of about 40 km s the thermal state of the crust at the time of impact is a second order effect but sufficient to account for the difference in palimpsest population between ganymede and callisto if ganymede once had a liquid mantle while callisto remained unmelted and undifferentiated or solidified prior to the formation of the presently observed crater population

pedestal craters on ganymede abstract the high resolution voyager images of ganymede show a class of fresh craters 6 89 km in diameter which is distinguished by an ejecta blanket similar to those seen for some types of martian craters one hundred and eighty five were identified and studied for trends with respect to latitude longitude and terrain type no correlation of the ratio of ejecta diameter to crater diameter was found as a function of latitude or longitude and there is only a suggestion of a trend in this ratio with respect to major terrain types central peak frequency is greatest for the smaller crater diameters central pit occurrence dominates central peak occurrence at crater diameters 35 km we conclude that the ejecta morphology probably results from impact into an icy target the question of whether atmospheric ejecta particle drag contributes to ejecta blanket morphologies on planets with an atmospheric cannot be resolved entirely from the voyager images the image resolution is insufficient to show diagnostic flow features on the ejecta if they exist or to detect evidence of any other ejecta deposits which would lie beyond the pedestal predicted by some researchers to exist only on bodies with an atmosphere

standardizing the nomenclature of martian impact crater ejecta morphologies the mars crater morphology consortium recommends the use of a standardized nomenclature system when discussing martian impact crater ejecta morphologies the system utilizes nongenetic descriptors to identify the various ejecta morphologies seen on mars this system is designed to facilitate communication and collaboration between researchers crater morphology databases will be archived through the u s geological survey in flagstaff where a comprehensive catalog of martian crater morphologic information will be maintained

focusing in prestack isochrone migration using instantaneous slowness information prestack migration finds increasing application in processing crustal seismic data however less effort has been made to incorporate slowness information in the imaging process the combination of slowness information with migration leads to an improved image in the depth domain especially by reducing migration artefacts and noise a slowness driven isochrone migration scheme is introduced for migration of 2 d seismic data instantaneous slowness information p x t is extracted from the data using correlation analysis in moving time and space windows slowness values resulting from spatial coherent energy signal and incoherent background noise are distinguished by the simultaneous evaluation of an instantaneous coherence criterion g x t in slowness driven isochrone migration this information is used for locally weighting the amplitude a x t smearing on the isochrone surface in particular slowness p and coherence criterion g determine position and sharpness of a gaussian weighting function the method is demonstrated using two synthetic data examples and is subsequently applied to two deep crustal data sets one wide angle along dekorp4 and one steep angle reflection seismic observation ktb8506 both data sets were collected in the surroundings of the ktb drill site oberpfalz as part of the german dekorp project

seismic imaging using microseismic events results from the san andreas fault system at safod 1 we have developed a new passive seismic imaging approach that consists of two steps first the hypocenter of the microseismic event is precisely located second this event is treated as a pseudo active seismic source and the reflections within the recorded wavefield are processed by using a directional migration algorithm in order to construct a high resolution image of the illuminated subsurface region in this paper we demonstrate the application of our approach to a number of microseismic events recorded by a borehole array in the san andreas fault observatory at depth main hole results obtained were high resolution 3 d images of different se nw oriented reflectors related to the san andreas fault saf system in the close vicinity of the borehole to support our approach we compared our findings with other active and passive seismic images and analyzed the correlation with borehole lithology we revealed a predominantly satisfactory agreement for both juxtapositions furthermore the stacked image of several microearthquakes provides a spatial characterization of the complex internal structure of the saf with much higher resolution than can be obtained from surface seismic reflection data

advanced seismic imaging techniques characterize the alpine fault at whataroa new zealand the plate bounding alpine fault in new zealand is a 850 km long transpressive continental fault zone that is late in its earthquake cycle we have acquired and processed reflection seismic data to image the subsurface around the main drill site of the deep fault drilling project dfdp 2 the resulting velocity models and seismic images of the upper 5 km show complex subsurface structures around the alpine fault zone the most prominent feature is a strong reflector at depths of 1 5 2 2 km with an apparent dip of 48 to the southeast below the dfdp 2 borehole which we assume to be the main trace of the alpine fault above the main reflector parallel reflectors suggest the presence of a 600 m wide damage zone additionally subparallel reflectors are imaged that we interpret as secondary branches of the main fault zone conjugate faults imaged by the data show the complexity of the subsurface the derived p wave velocity model reveals a 300 600 m thick sedimentary layer with velocities of 2 3 km s above a schist basement with velocities of 4 5 5 5 km s a low velocity layer can be observed within the basement at 0 8 2 km depth a small scale low velocity anomaly appears at the top of the basement that can be correlated to the fault zone the results provide a reliable basis for a seismic characterization of the dfdp 2 drill site that can be used for further structural and geological investigations of the architecture of the alpine fault in this area

crustal structure of the eratosthenes seamount cyprus and s turkey from an amphibian wide angle seismic profile abstract in 2010 project cococo incipient continent continent collision recorded a 650 km long amphibian n s wide angle seismic profile extending from the anatolian plateau across southern turkey and cyprus to just south of the eratosthenes seamount esm the aim of the project is to reveal the impact of the transition from subduction to continent continent collision of africa with anatolia arrival picking finite differences ray tracing and inversion of the offshore and on offshore data produced a tomographic model across southern cyprus the accretionary wedge and the esm the main features of this model are 1 crustal p velocities predominantly lower than 6 5 km s beneath the esm 2 crustal thickness between 28 and 37 km 3 an upper crustal reflection at 5 km depth beneath the esm 4 the likely presence of oceanic crust south of the esm and a transform margin north of it and 5 a 12 km thick ophiolite sequence on cyprus land shots on turkey also recorded on cyprus gravity data and geological and previous seismic investigations allow to derive a layered velocity model beneath anatolia and the northern part of cyprus the main features of this model are 1 moho depths of 38 45 km beneath the anatolian plateau 2 an upper and lower crust with large lateral changes in velocity and thickness 3 a north dipping subducting plate below cyprus with a steepening of the dip angle of the plate at about 45 km depth thus the wide angle seismic and gravity data provide detailed insights into the 2 d geometry and velocity structures associated with the cyprus arc collision zone finally integrated analysis of the geophysics and geology allows a comprehensive interpretation of the crustal structure related to the collision process

three dimensional focused seismic imaging for geothermal exploration in crystalline rock near schneeberg germany we present the results of a 3d seismic survey acquired near the city of schneeberg in the western erzgebirge germany the main objective of this survey was to use reflection seismic exploration methods to image a major fault zone in crystalline rock which could serve as a geothermal reservoir at a target depth of about 5 km 6 kmwith expected temperatures between 160 c 180 c for this purpose a high resolution 3d vibroseis survey was performed in late 2012 covering an area of about 10 km 12 km the 3d survey was complemented by a wide angle seismic survey for obtaining velocity information from greater depths using explosives along ten profile lines radially centred at the target area the region itself is dominated by the northwestsoutheast striking gera j achymov fault system and the southwest northeast striking l ossnitz zw onitz syncline the main geological features in the survey area are well known from intensive mining activities down to a depth of about 2 km the seismic investigations aimed at imaging the partly steeply dipping fault branches at greater depths in particular a dominant steeply northeast dipping fault roter kamm in the central part of the survey area in addition to this main structure the gera j achymov fault zone consists of a series of steeply southwest dipping conjugate faults for imaging these structures we used a focusing pre stack depth migration technique where the wavefield coherency at neighbouring receivers is used for weighting the amplitudes during migration this method delivers a clear focused image of the 3d structures within the target area a 3d velocity model for depth imaging was obtained by first arrival tomography of the wide angle survey data with this approach we were able to image several pronounced structures interpreted as faults within the crystalline rock units which partly reach the target depth where the temperatures for a geothermal usage would be sufficient in general the results show a complex three dimensional image of the geological structures with different reflection characteristics which can serve as a basis for a detailed characterization of the potential deep geothermal reservoir

advanced three dimensional seismic imaging of deep supercritical geothermal rocks in southern tuscany the seismic k horizon is the key to gaining understanding on the deep supercritical geothermal rocks in southern tuscany the k horizon is hosted in metamorphic rocks which cause strong seismic wavefield scattering resulting in a poor signal to noise ratio our study aims to reveal high resolution seismic images of the k horizon below a geothermal field in southern tuscany using an advanced threedimensional seismic depth imaging approach the key seismic pre processing steps in the time domain include muting a large amount of persistent noise based on the statistical analysis of the seismic amplitudes and tomostatics technique to correct for static effects we carried out seismic depth imaging using kirchhoff pre stack depth migration and fresnel volume migration techniques each migration technique was tested with constant and heterogeneous three dimensional velocity models due to the difficulties in determining emergent angles for this low signal to noise ratio data set the migration results with the heterogeneous three dimensional velocity model show less coherent reflections compared to the migration results using the constant velocity model both velocity models however lead to relatively the same structure and depth of the k horizon indicating the similarity of the average velocities along the wave propagation paths in both velocity models with both velocity models fresnel volume migration yields the k horizon with better reflection coherency and higher signal to noise ratio than standard kirchhoff pre stack depth migration nevertheless both migration techniques have been able to reveal the k horizon with relatively high resolution and provide a reliable basis for geothermal rock characterization as well as steering of the first geothermal well penetrating the k horizon

microseismic reflection imaging and its application to the basel geothermal reservoir we have developed a new approach for reflection seismic imaging using microseismic waveform data we took the specific character of microseismic downhole data into account and were able to image regions in the direct vicinity or inside of a seismically active zone we used a directional migration method that reduced imaging artifacts caused by the low aperture of the data but required estimation of the wavefield polarization we also used hodogram analysis to identify parts of data that provided reliable polarization estimates only these parts were then used for imaging whereas the rest of the data are excluded the approach was successfully applied to microseismic waveforms recorded during and after the stimulation of the enhanced geothermal system in basel switzerland this data set included more than 2000 events recorded at five sparsely distributed borehole sensors the reflection images revealed a distinct network of reflectors in the vicinity of the open hole section within the injection well the results were compared with the injection borehole ultrasonic image revealing a quite good agreement combined analysis of imaged reflectors event locations and event focal mechanisms indicated that the approach resolved mostly aseismic highly permeable fluid pathways whereas most of the seismicity occurred in the second order fractures

parsimonious migration of 3 c 3d vsp data conventional kirchhoff migration can be made much faster by a priori calculation of wave arrival directions and tracing rays back only along the measured directions this is known as parsimonious migration for surface seismic data where acquisition with 2d arrays is common the wave arrival directions can be measured by using local slant stacking to calculate the two horizontal slowness components the vertical slowness is then deduced by using the dispersion relation for vertical seismic profile vsp data where multiline acquisition is not possible only the vertical component of the slowness vector can be measured which is insufficient to constrain the wave arrival direction we overcome this limitation for three component vsp data by polarization analysis of the incident waves polar and azimuth anglesare calculated at the receivers by estimating the data covariance matrix and the vertical slowness assuming isotropic media and linear polarization of both p and s waves for p waves the data co

imaging salt with turning seismic waves turning seismic waves which first travel downward and then upward before and after reflection have been recorded in a 3 d seismic survey conducted over an overhanging salt dome careful processing of these turning waves enables the imaging of the underside of the salt dome and of intrusions of salt into vertical faults radiating from the dome when seismic wave velocity increases with depth waves that initially travel downward are reflected and may turn so as to travel upward before reflection a simple geometrical argument suggests that these turning waves are likely to exhibit abnormal moveout in com mon midpoint cmp gathers in that reflection time decreases with increasing source receiver offset this abnormal moveout and the attenuation of turning waves by most migration methods suggest that conventional seismic processing does not properly image turning waves the most important step in imaging turning waves assuming that they have been recorded is the migration process simple and inexpensive modifications to the conventional phase shift migration method enable turning waves to be imaged for little additional computational cost the examples provided in this paper suggest that these and other such modifications to conventional processing should be used routinely when imaging salt domes

the effect of viscosity on impact cratering and possible application to the icy satellites of saturn and jupiter impact experiments in newtonian fluids with a range of viscosities of 10 3 to 60 pa s demonstrate that transient crater volume and shape depth to diameter ratio depend on target viscosity as well as on gravity volume is reduced and depth to diameter ratio is increased for cratering events in which viscosity plays a dominant role in addition to being affected by target kinematic viscosity viscous scaling is most strongly influenced by projectile diameter less strongly by projectile velocity and least strongly by gravity in a planetary context viscous effects can occur for craters formed by small or slow moving impacting bodies low planetary surface densities high surface viscosities and low gravity values conditions all likely for certain impacts into the icy satellites of saturn and jupiter especially if liquid mantles were still present beneath solid crusts age dating based on crater counts and size frequency distributions for these icy bodies may have to be modified to account for the possibility that viscosity dominated craters were initially smaller and deeper than their gravity controlled counterparts

a global system of furrows on ganymede indicative of their creation in a single impact event abstract furrows are a concentric system of tectonic troughs and are the oldest recognizable surface feature on ganymede we analyzed the distribution of furrows utilizing voyager and galileo images and found that furrows over ganymede s surface are part of a global concentric circular structure if this multi ring structure is impact origin this is the largest impact structure identified so far in the solar system deviations of the shapes of the furrows from the concentricity are small everywhere which implies that the relative location of the blocks of the dark terrains over the entire surface of ganymede has not changed appreciably even during formation of the bright terrains the estimate of the impactor size is difficult but an 150 km radius impactor is consistent with the observed properties of furrows the furrow forming impact should have significant effects on the satellite s geological and internal evolution which are expected to be confirmed by future explorations of jupiter s icy moons such as the juice jupiter icy moon explorer or europa clipper mission

the global magnitude frequency relationship for large explosive volcanic eruptions abstract for volcanoes as for other natural hazards the frequency of large events diminishes with their magnitude as captured by the magnitude frequency relationship assessing this relationship is valuable both for the insights it provides about volcanism and for the practical challenge of risk management we derive a global magnitude frequency relationship for explosive volcanic eruptions of at least 300 mt of erupted mass or m4 5 our approach is essentially empirical based on the eruptions recorded in the lameve database it differs from previous approaches mainly in our conservative treatment of magnitude rounding and under recording our estimate for the return period of super eruptions 1000 gt or m8 is 17 ka 95 ci 5 2 ka 48 ka which is substantially shorter than previous estimates indicating that volcanoes pose a larger risk to human civilisation than previously thought

lunar floor fractured craters evidence for viscous relaxation of crater topography in this paper we evaluate quantitatively the hypothesis that topographic modification of floor fractured craters on the moon was accomplished predominantly by viscous relaxation adopting the simple assumption that the moon may be modeled as having a uniform newtonian viscosity we compare the observed topographic profiles for a number of floor fractured craters with the profiles predicted from the viscous relaxation of topography of fresh craters of similar diameter despite the simplicity of the rheological model the comparison is quite good the floor uplift the rim subsidence and the apparent subsidence outside the rim for the several floor fractured craters considered are well matched by the viscous relaxation hypothesis floor fractures while indicating that a purely viscous model is not strictly valid can be explained by the effects of isostatic adjustment on a thin brittle lithosphere the association of many floor fractured craters with impact basins and with the time of mare volcanism can be understood in terms of a pronounced acceleration of crater relaxation in local regions of anomalously high near surface temperatures and therefore of low effective viscosity and thin lithosphere the quantitative extent of relaxation of floor fractured craters can be interpreted in terms of a limited time interval of substantial relaxation for each crater that time interval ended for each crater after local cooling had been sufficient for the viscosity to rise for the lithosphere to thicken and for the present topographic relief to be frozen in thus viscous relaxation is a viable hypothesis to explain the topographic profiles of a number of lunar floor fractured craters and the extent of viscous relaxation of crater topography may serve as a tool to map lateral and temporal variations in the shallow thermal structure of the moon and of other planets and satellites

super volcanic investigations multi disciplinary analyses of earth s most destructive volcanic systems show that continuous monitoring and an understanding of each volcano s quirks rather than a single unified model are key to generating accurate hazard assessments

ignimbrite morphology and the effects of erosion a new zealand case study ignimbrite morphology previously generalised using aspect ratios is here quantified as the relationships between the various thicknesses of material forming an ignimbrite and the areas and volumes represented by those thicknesses the morphology can be measured for the deposit in its present day eroded condition or reconstructed for the original deposit the reconstructed morphology of the 22 500 year bp ca 11 500 km2 ca 300 km3 oruanui ignimbrite in new zealand is documented to illustrate the latter approach the oruanui ignimbrite is an intermediate aspect ratio deposit and shows broadly linear relationships between 1 in thickness and the cumulative area occupied by that thickness or less of material and 2 thickness and the volume represented by that thickness or less of material two theoretical morphologies one where thicknesses exponentially decay with distance from a maximum and the other of uniform thickness slab are compared with the oruanui data limited comparative data suggest that low aspect ratio violently emplaced ignimbrites will show upward concave curves at one extreme following the exponential decay model and high aspect ratio gently emplaced ignimbrites downward concave curves with the slab model as an extreme when plotted on diagrams where the oruanui data show linear trends the effects of erosion on oruanui and model ignimbrite morphologies are modelled using two theoretical erosion scenarios 1 material is evenly removed from the land surface and 2 thinner non welded material is preferentially removed for the oruanui ignimbrite data area is lost much more rapidly in the first instance than volume for example 5 m of erosion is sufficient to remove 50 area whereas 40 m scenario 1 or 120 m scenario 2 of erosion is required to remove 50 volume in old ignimbrites volume estimates may be reasonably accurate even after strong erosion provided the original thicknesses of ponded landscape forming material can be inferred but estimates of original area and aspect ratio will be inaccurate an envelope enclosing all known outcrops of an ignimbrite will give a better estimate of original area and aspect ratio than simply summing the areas of known outcrops

from the hagedoorn imaging technique to kirchhoff migration and inversion the seminal 1954 paper by j g hagedoorn introduced a heuristic for seismic reflector imaging that heuristic was a construction technique a string construction or ruler and compass method for finding reflectors as an envelope of equal traveltime curves defined by events on a seismic trace later kirchhoff migration was developed this method is based on an integral representation of the solution of the wave equation for decades kirchhoff migration has been one of the most popular methods for imaging seismic data parallel with the development of kirchhoff wave equation migration has been that of kirchhoff inversion which has as its objectives both structural imaging and the recovery of angle dependent reflection coefficients the relationship between kirchhoff migration inversion and hagedoorn s constructive technique has only recently been explored this paper addresses this relationship presenting the mathematical structure that the kirchhoff approach adds to hagedoorn s constructive method and showing the relationship between the two

fresnel volume migration of single component seismic data standard implementations of kirchhoff prestack depth migration psdm distribute the recorded wavefield along two way traveltime isochrons and an image is generated by constructive interference of these isochrons along the actual reflector elements beside the recent developments of wave equation based approaches kirchhoff psdm is still considered widely as a state of the art technique in obtaining high quality images of the subsurface particularly for highly irregular survey layouts and target oriented imaging tasks however for sparse sampling or limited aperture the resulting image is affected by significant migration noise as a result of limited constructive interference of the back propagated wavefield some modifications have been proposed to reduce these artifacts these modifications include constructing a specular path of wave propagation derived from estimates of the emergent angle of coherent phases in the seismogram section and the mainly heuristic restriction of the imaging operator to the neighborhood of that wavepath our approach uses fresnel volumes to restrict the migration operator in a physically frequency dependent way using the emergent angle at the receiver determined by a local slowness analysis a ray is propagated into the subsurface the back propagation of the wavefield is restricted to the vicinity of this ray according to its approximated fresnel volume this so called fresnel volume migration approach enhances image quality significantly compared with standard kirchhoff psdm because of the inherent focusing and the restriction of the back propagation to the region around the actual reflection point

central pit and dome craters exposing the interiors of ganymede and callisto central pit craters on the large icy satellites ganymede and callisto are an unusual crater class perhaps related to the unusual properties of water ice the detailed morphology and dimensions of pit crater features differ from those of smaller normal complex craters on these two satellites pit crater depths appear to be constant regardless of diameter rim collapse is also restricted relative to that in lunar craters or smaller ganymede craters the floors of pits in craters larger than 60 km are occupied by smooth bright domes pit to crater and dome to crater diameter ratios increase linearly with crater diameter and are indistinguishable on ganymede and callisto and with terrain type or surface longitude the floors and central structures of young bright rayed pit craters such as osiris are covered by a thin uniformly bright impact melt or frost deposit thus domes and pits form rapidly on the time scale of the impact itself rather than by long term postimpact intrusion or extrusion the bright domes in pit craters are most simply explained as the uplift and exposure of relatively ice rich material from depths of 3 5 to 5 km during impact this process is almost directly analogous to the uplift and exposure of anamolous deep seated material observed in terrestrial and lunar craters the unusual pit morphology on icy satellites may be the result of impact into crust that is mechanically much weaker at shallow depth than on rocky bodies such as the moon because crater morphology is strongly dependent on ice rock composition the similarity of pit and dome dimensions on ganymede and callisto indicates that the structure and rheology of the crusts of these bodies down to depths of 10 km are very similar and have been for several b y pit crater morphology indicates that the crusts of both satellites are probably ice rich and differentiated

high resolution microseismic imaging abstract we examine the feasibility of high resolution microseismic imaging of unconventional reservoirs given frequencies in typical downhole microseismic data that are almost an order of magnitude higher than in seismic reflection data a comparable increase in image resolution might be expected bringing potential resolution of downhole microseismic images to a few meters we demonstrate that such a resolution is indeed achievable and present two case studies illustrating the reservoir features that can be imaged our first example constructed with p waves recorded in the woodford field reveals internal fabric of the woodford reservoir and formations surrounding it allowing us to discriminate the stimulated and unstimulated zones of the lower woodford shale encouraged by those results in our second example this time from the bakken field we use the slow shear waves which are more sensitive to fluids than p waves to find out whether hydraulic fractures themselves could be imaged our seismic v

improved structural characterization of the earth s crust at the german continental deep drilling site using advanced seismic imaging techniques this paper describes the principles of three novel seismic imaging techniques and their application to two deep seismic reflection data sets from the vicinity of the german continental deep drilling site ktb these imaging techniques are based on kirchhoff prestack depth migration and use an inherent restriction of the migration operator to focus the wavefield to its actual reflection point for fresnel volume migration the emergent angle at the receivers is estimated and then used to propagate the wavefield back into the subsurface along which the fresnel volume is determined the migration operator is restricted to this volume thereby focusing the image to the part of the isochrone which physically contributes to the reflection for coherency migration the coherency of the wavefield at neighboring traces is calculated and used as a weighting factor within the migration integral leading to a comparable focusing to the reflection point for coherency based fresnel volume migration both approaches are combined resulting in an even more focused seismic image with significantly increased image quality we applied these methods to two seismic data sets from the area around the ktb a survey with standard split spread geometry ktb8502 and a sparse data set with a small number of source points in combination with short receiver lines instruct93 the focusing approaches yield major improvements in the final images for both data sets incoherent noise and migration artifacts are reduced and the visibility of crustal structures is strongly enhanced allowing for an improved geologic and tectonic characterization

parsimonious 3d post stack kirchhoff depth migration parsimonious post stack migration is extended to three dimensions by tracing single rays back along each incident wave direction as determined by a local slant stack at the receivers the ray tracing can be embedded in the migration this approach significantly reduces the computer time and disk space needed because it is not necessary to build and save image time maps 3d migration can be performed on a workstation or personal computer rather than using a supercomputer or cluster the location of a reflector in the output image is defined by tracing a zero offset ray to the one way traveltime the image condition the orientation of the reflector is defined as a surface perpendicular to the raypath the migration impulse response operator is confined to the first fresnel zone around the estimated reflection point which is much smaller than the large isochronic surface in traditional kirchhoff depth migration additional efficiency is obtained by applying an amplitude threshold to reduce the amount of data to be migrated tests on synthetic data show that the proposed implementation of parsimonious 3d post stack kirchhoff depth migration is at least two orders of magnitude faster than traditional kirchhoff migration at the expense of slightly degraded migration image coherence the proposed migration is expected to be a useful complement to conventional time migrations for fast initial imaging of subsurface structures and for real time imaging of near offset sections during data acquisition for quality control

seismic depth imaging of a geothermal system in southern tuscany this work represents a case study concerning the application of reflection seismic imaging methods in the context of geothermal exploration our goal is to obtain accurate structural images of a geothermal active area in southern tuscany these images will be required in subsequent studies as the input for geological model building and numerical simulation of the heat transport and fluid flow the target region exhibits great geologic complexity including strong velocity contrasts lateral nearsurface inhomogeneities fracture zones and significant topography those features are typical for a volcanic hard rock environment and pose significant challenges to conventional seismic imaging methodology therefore we apply a sophisticated and robust depth imaging workflow to previously acquired surface seismic data within our workflow we focus on estimating the seismic velocities of the predominant rock units and subsequently carry out kirchhoff pre stack depth migration and fresnel volume migration to obtain high resolution images of the subsurface our results demonstrate that the applied methodology provides a valueable tool for imaging in a complex environment such as a volcano geothermal area in detail the resulting reflector images show the main horizons that delineate the tuscan sedimentary rocks in the target region the images from standard kirchhoff migration can be significantly enhanced by utilizing fresnel volume migration which eliminates migration artefacts and provides a better result moreover we obtain the migration velocities and depths for an important regional reflector known as the k horizon which is of major interest for geothermal characterization

are eruptions from linear fissures and caldera ring dykes more likely to produce pyroclastic flows turbulent volcanic jets are produced by highly energetic explosive eruptions and may form buoyant plumes that rise many tens of kilometres into the atmosphere to form umbrella clouds or collapse to generate ground hugging pyroclastic flows ash injected into the atmosphere can be transported for many hundreds of kilometres with the potential to affect climate disrupt global air travel and cause respiratory health problems pyroclastic flows by contrast are potentially catastrophic to populations and infrastructure close to the volcano key to which of these two behaviours will occur is the extent to which the mechanical entrainment and mixing of ambient air into the jet by large entraining eddies forming the jet edge changes the density of the air ash mixture low entrainment rates lead to pyroclastic flows and high entrainment rates give rise to buoyant plumes recent experiments on particle laden multi phase volcanic jets from flared and straight sided circular openings suggest that the likelihood for buoyant plumes will depend strongly on the shape and internal geometry of the vent region this newly recognised sensitivity of the fate of volcanic jets to the structure of the vent is a consequence of a complex dynamic coupling between the jet and entrained solid particles an effect that has generally been overlooked in previous studies building on this work here we use an extensive series of experiments on multi phase turbulent jets from analogue linear fissures and annular ring fractures to explore whether the restrictive vent geometry during cataclysmic caldera forming ccf eruptions will ultimately lead a relatively greater frequency of pyroclastic flows than eruptions from circular vents on stratovolcanoes our results understood through scaling analyses and a one dimensional theoretical model show that entrainment is enhanced where particle motions contribute angular momentum to entraining eddies however because the size of the entraining eddies scales approximately with vent width the extent of entrainment is reduced as the vent width becomes small in comparison to its length consequently our work shows that for specified mass eruption rates the high length to width ratio vents typical of ccf events are more likely to produce pyroclastic flows we suggest that the enigmatic trend in the geological record for the largest ccf eruptions to produce pyroclastic flows is an expected consequence of their being erupted through continuous or piece wise continuous caldera ring fractures

a 25 myr chronostratigraphy of ignimbrites in south peru implications for the volcanic history of the central andes with an area exceeding 25 000 km 2 and volumes c 5000 km 3 south peru hosts the andes second largest neogene ignimbrite field we document the extent stratigraphy and chronology of 12 ignimbrite sheets in the rio ocona cotahuasi maran and colca deep canyons based on 74 40 ar 39 ar and u pb age determinations ignimbrite forming episodes span 25 myr prior to 9 ma eight large volume ignimbrites were produced every 2 4 myr after 9 ma average lulls between small to moderate volume ignimbrites decreased to 0 85 myr the refined volcanic stratigraphy reveals three main features 1 larger volume ignimbrites were emplaced by punctuated flare ups between 25 and 9 ma during uplift of the western cordillera 2 numerous smaller ignimbrites were emplaced after 9 ma as the ignimbrite production rate decreased threefold this decrease may be due to the declining crustal melting rate decreasing plate convergence rate after 9 ma or more magma stagnation in the shallow crust which promoted the growth of composite cones 3 growth of two volcanic arcs has added twice as much volume c 53 km 3 ma 1 to the rio ocona cotahuasi maran volcanic field than the ignimbrites after 2 27 ma estimated linear arc magma output has however decreased twofold 0 15 0 08 km 3 km 1 ma 1 from the early quaternary to the pleistocene holocene supplementary materials supplementary text tables 1 3 and figures 1 4 are available at http doi org 10 6084 m9 figshare c 3147100

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

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

morphology and scaling of ejecta deposits on icy satellites 1 continuous ejecta deposits on ganymede consist of two major units or facies a thick inner hummocky pedestal facies and a relatively thin outer radially scoured facies defined also by the inner limit of the secondary crater field both ejecta facies have a well defined power law relationship to crater diameter for craters ranging from 15 to 600 km across this relationship can be used to estimate the nominal crater diameter for impact features on icy satellites such as palimpsests and multiring basins for which the crater rim is no longer recognizable ejecta deposits have also been mapped on 4 other icy satellites although morphologically similar to eject deposits on the moon ejecta deposits for smaller craters are generally significantly broader in extent on the icy satellites in apparent defiance of predictions of self similarity a greater degree of rim collapse and enlargement on the moon may explain the observed difference

gaussian beam migration of common shot records gaussian beam migration is a depth migration method whose accuracy rivals that of migration by wavefield extrapolation so called wave equation migration and whose efficiency rivals that of kirchhoff migration this migration method can image complicated geologic structures including very steep dips in areas where the seismic velocity varies rapidly however applications of prestack gaussian beam migration either have been limited to common offset common azimuth data volumes and thus are inflexible or suffer from multiarrival inaccuracies in a common shot implementation in order to optimize both the flexibility and accuracy of gaussian beam migration i present a common shot implementation that handles multipathing in a natural way this allows the migration of data sets that can include a variety of azimuths and it allows a simplified treatment of near surface issues application of this method to model data typical of canadian foothills structures and to model data that includes a complicate

fresnel volume migration of multicomponent data if the aperture of a seismic reflection experiment is strongly limited kirchhoff migration suffers from strong artifacts attributable to incomplete summation this can be overcome by restricting the migration operator to the region that physically contributes to a reflection event examples of such limited aperture experiments include data acquisition in boreholes tunnels and mines we present an extension to three component 3c kirchhoff prestack depth migration where the migration operator is restricted to the fresnel volume of the specular reflected raypath we use the measured polarization direction at a 3c receiver to determine points of specular reflection in homogeneous media the polarization angle of 3c data can be used directly to decide whether a certain image point belongs to the fresnel volume of a specular reflection in heterogeneous media the fresnel volume around an image point is approximated by means of paraxial ray tracing the method is tested on a synthetic vertical seismic profiling experiment with strongly limited aperture migration artifacts and crosstalk effects from converted waves are strongly reduced compared with standard migration schemes the method is successfully applied to seismic data acquired in a tunnel

relaxed impact craters on ganymede regional variation and high heat flows abstract viscously relaxed craters provide a window into the thermal history of ganymede a satellite with copious geologic signs of past high heat flows here we present measurements of relaxed craters in four regions for which suitable imaging exists near anshar sulcus tiamat sulcus northern marius regio and ganymede s south pole we describe a technique to measure apparent depth or depth of the crater with respect to the surrounding terrain elevation measured relaxation states are compared with results from finite element modeling to constrain heat flow scenarios see companion paper bland et al 2017 the presence of numerous substantially relaxed craters indicates high heat flows in excess of 30 40 mw m 2 over 2 gyr with many small

seismic imaging in the krafla high temperature geothermal field ne iceland using zero and far offset vertical seismic profiling vsp data abstract among geothermal exploration methods active surface seismic methods have played only a minor role to date especially in high temperature volcanic systems reflection seismic data often reveal poor delineation of volcanic features due to the internal heterogeneity of volcanic sequences to enhance the vertical resolution one possibility is the application of downhole seismic methods like vertical seismic profiling vsp a test experiment was carried out in the krafla high temperature geothermal field ne iceland to assess the ability of vsp to image subsurface structures such as fractures zones of high permeability magmatic bodies and zones of supercritical fluids and steam logging in such hostile environments is technical challenging in many aspects but mainly due to the high temperature impact on the downhole electronic components of the measuring equipment this requires a thorough pre examination and implementation of the measurement especially to avoid delays and tool failures this paper presents results of zero and far offset vsp data from the k 18 borehole from within the krafla caldera which reveal good correlation with the surrounding lithology the raw three component seismic data display a good signal to noise ratio and dominant signal frequencies between 20 and 40 hz down to c 2200 m depth for air gun and explosive sources respectively a zero offset source comparison was also conducted to assess the use of different impulsive sources for future vsp surveys in similar settings by applying a standard vsp processing we identified stratigraphic boundaries between lavas hyaloclastites and intrusions which are in good agreement with existing well data for the zero offset vsp both p and s wave velocity models were calculated and a depth converted corridor stack was determined in addition multicomponent kirchhoff depth migration and fresnel volume migration were tested around the borehole the 3d results are promising but the specific shape and lateral extent of the reflectors could not be determined due to the restriction to only two sources and the insufficient spatial coverage aperture our study demonstrates that vertical seismic profiles can clearly detect variations in the subsurface volcanic stratigraphy in high temperature geothermal fields a more detailed reservoir characterization can be achieved by further data integration enhanced survey design including more source positions and improved processing and imaging techniques such as full waveform inversion

morphology and origin of palimpsests on ganymede based on galileo observations palimpsests are large circular low relief impact scars on ganymede and callisto these structures were poorly understood based on voyager era analysis but high resolution galileo images allow more detailed inspection we analyze images of four ganymedean palimpsests targeted by galileo memphis and buto faculae epigeus and zakar ganymedean craters and europan ring structures are used as tools to help better understand palimpsests based on morphologic similarities from analysis of galileo images palimpsests consist of four surface units central plains an unoriented massif facies a concentric massif facies and outer deposits using as a tie point the location in these structures where secondary craters begin to appear outer deposits of palimpsests are analogous to the outer ejecta facies of craters the concentric massif facies of palimpsests are analogous to the pedestal facies of craters and the unoriented massif facies and central plains are analogous to crater interiors these analogies are supported by the presence of buried preexisting structure beneath the outer two and absence of buried structure beneath the inner two units our observations indicate that palimpsest deposits represent fluidized impact ejecta rather than cryovolcanic deposits or ancient crater interiors

predicted crater morphologies on ceres probing internal structure and evolution the detailed internal structure of the dwarf planet ceres target of nasa s dawn mission has not been unequivocally determined from ground based data whereas ceres is most likely differentiated with a near surface ice layer tens to one hundred kilometers thick the possibility of a homogenous ice poor interior structure cannot be completely eliminated these two internal structural end members have profoundly different implications for ceres origin and evolution here we demonstrate that observations of ceres impact craters by the dawn spacecraft will permit unambiguous distinction between the two internal structural models using finite element simulations of crater relaxation we show that if ceres does contain a water ice layer its relatively warm diurnally averaged surface temperature ensures extensive viscous relaxation of even small impact craters at likely equatorial temperatures craters as small as 4km in diameter can be relaxed to the point where complete crater erasure is plausible thus decreasing the overall crater density in the equatorial region at mid latitudes crater relaxation is less extensive but still sufficient to completely relax all craters older than 10 ma and larger than 16 km in diameter as well as smaller ancient craters only in ceres cold polar regions are some crater morphologies expected to be pristine in contrast if ceres is primarily a rocky body we expect crater relaxation to be negligible these basic conclusions are generally independent of ice grain size salt dust contamination of the ice the presence of a thin undifferentiated ice rock crust and the total thickness of the ice layer all of which produce second order modifications to the relaxation process that can be used to better constrain such ice layer properties thus the morphology of impact craters on ceres as revealed by the dawn spacecraft will provide direct insight into the internal structure and evolution of the dwarf planet

three dimensional seismic imaging of tunnels abstract we present the recent results of our work which is concerned with the determination of the spatial locations of faults fractures and heterogeneities around a tunnel by advanced seismic imaging techniques so far we have extended existing 2d imaging techniques to 3d we have implemented 3d versions of kirchhoff prestack depth migration kpsdm fresnel volume migration fvm and reflection image spectroscopy ris the 3d p and s velocity models required for the calculation of the green s functions have been generated by using the 2d first break tomography velocity models and rotating them around the tunnel axis the 3d images were obtained by stacking the migrated data taking into account either the true phase or the absolute value the application of the mentioned imaging techniques to data from the gotthard base tunnel piora adit shows significant improvements compared to standard kpsdm processing the 3d ris approach suppresses scattering effects in the low frequency band and increases resolution in the high frequency band so that some of the geological structures are much better visible the 3d fvm technique uses slowness and polarization based estimates of the emergence angles at the receivers and restricts the imaging to the region around the actual reflection or diffraction point we observe less spatial ambiguity and a higher resolution of most structures the integration of both approaches ris and fvm exploits their advantages and delivers an even more pronounced and clear image of the tunnel environment