rheological properties of water ice applications to satellites of the outer planets 1 abstract the icy moons of the outer solar system have not been quiescent bodies in part because many have a substantial water component and have experienced significant internal heating we can begin to understand the thermal evolution of the moons and the rate of viscous relaxation of surface topography because we now have good constraints on how ice in several of its polymorphic forms flows under deviatoric stress at planetary conditions details of laboratory derived flow laws for pure polycrystalline ice are reviewed in detail one of the more important questions at hand is the role of ice grain size grain size may be a dynamic quantity within the icy moons and it may or may not significantly affect rheology one recent beneficiary of revelations about grain size sensitive flow is the calculation of the rheological structure of europa s outer ice shell which may be no thicker than 20 km

rheology of ices a key to the tectonics of the ice moons of jupiter and saturn the polymorphic varieties of water ice are important rock forming minerals in the outer solar system the voyager 1 and 2 missions have shown that most of the ice moons of jupiter and saturn have had some form of tectonic or internal activity understanding of the tectonics and building reasonable models of the interior of these planets depend on our knowledge of the theological properties and viscosity of high pressure and low temperature forms of ice

strained craters on ganymede high resolution images of jupiter s satellite ganymede obtained by the galileo spacecraft reveal several elliptical craters that are transected by sets of subparallel ridges and troughs oriented roughly orthogonal to the long axis of the crater implying that these craters have been extensionally strained we analyze five such craters four in the ancient dark terrain and one in bright grooved terrain inferring their strain histories by assuming each crater was originally circular these strained craters have been elongated by amounts ranging from 5 to 50 all are deformed by extension near perpendicular to subparallel ridges and troughs and some are also deformed by distributed simple shear parallel to these tectonic structures the rift zones that deform these craters show extensions of 5 up to 180 for a well defined fault zone that rifts saltu crater within dark terrain of nicholson regio extensional fault zones consisting of domino style normal faults and representing strains of several tens of percent may be common on ganymede and strains of this order can alter pre existing surface features beyond recognition through the process of tectonic resurfacing

flooding of ganymede s bright terrains by low viscosity water ice lavas large regions of the jovian moon ganymede have been resurfaced but the means has been unclear suggestions have ranged from volcanic eruptions of liquid water or solid ice to tectonic deformation but definitive high resolution morphological evidence has been lacking here we report digital elevation models of parts of the surface of ganymede derived from stereo pairs combining data from the voyager and galileo spacecraft which reveal bright smooth terrains that lie at roughly constant elevations 100 to 1 000 metres below the surrounding rougher terrains these topographic data together with new images that show fine scale embayment and burial of older features indicate that the smooth terrains were formed by flooding of shallow structural troughs by low viscosity water ice lavas the oldest and most deformed areas the reticulate terrains in general have the highest relative elevations whereas units of the most common resurfaced type the grooved terrain lie at elevations between those of the smooth and reticulate terrains bright terrain which accounts for some two thirds of the surface probably results from a continuum of processes including crustal rifting shallow flooding and groove formation volcanism plays an integral role in these processes and is consistent with partial melting of ganymede s interior

atmospheric boundary layer structure and turbulence during sea fog on the southern china coast abstractsmall scale turbulence has an essential role in sea fog formation and evolution but is not completely understood this study analyzes measurements of the small scale turbulence together with the boundary layer structure and the synoptic and mesoscale conditions over the life cycle of a cold advection fog event and a warm advection fog event both off the coast of southern china the measurement data come from two sites one on the coast and one at sea these findings include the following 1 for cold advection fog the top can extend above the inversion base but formation of an overlaying cloud causes the fog to dissipate 2 for warm advection fog two layers of low cloud can merge to form deep fog with the depth exceeding 1000 m when strong advection of warm moist air produces active thermal turbulence mixing above the thermal turbulence interface 3 turbulence near the sea surface is mainly thermally driven for cold advection fog but mechanically driven for warm advection fog 4 the mo

dark halo craters and the thickness of grooved terrain on ganymede dark halo craters in grooved terrain on ganymede represent potential probes of the subsurface geology these craters are surrounded by a broad diffuse low albedo annulus or halo halo radius is linearly proportional to crater radius indicating that the halo is related to the continuous ejecta deposit of the crater and is not removed by natural aging processes such as regolith development and exposure to the space environment the halos have orange violet albedo ratios that are intermediate between ratios associated with grooved terrain and cratered terrain we propose that halos result from the incorporation of cratered terrain material into crater ejecta in uruk sulcus only craters greater than 12 km in diameter have halos indicating that the cratered terrain material there forms a stratigraphic horizon buried at depth in the grooved terrain into which only larger craters can excavate this depth can be calculated from the transition diameter by reconstructing the transient crater we calculate a depth of excavation corresponding to the depth of burial of cratered terrain of 1 0 to 1 6 km this shallow burial is inconsistent with deep subsidence and burial stoping into the interior or lateral spreading apart of ancient cratered terrain units but is consistent with a filled graben model for grooved terrain where relatively clean ice has been emplaced over downdropped blocks of cratered terrain

holocene paleoearthquake history on the qingchuan fault in the northeastern segment of the longmenshan thrust zone and its implications abstract although much work has been performed for faults with high slip rates little attention has been paid to low slip rate faults such as the longmenshan thrust zone ltz on which the wenchuan earthquake occurred the ltz is a long and matured fault that evolved during the mesozoic as a structural boundary but its quaternary activity had been considered insignificant the wenchuan earthquake on the central segment of the ltz and the following lushan earthquake on the southwestern segment illustrate the necessity of assessing the regional seismic potential around the northeastern extension of the ltz however little is known about its activity and paleoearthquake history to solve these problems we conducted paleoseismological trench excavations at two sites on the qingchuan fault to establish its paleoearthquake history only one and the latest event that occurred in the holocene is identified based on the radiocarbon dating the faulting event is constrained to occur between 4115 and 3820 b c and a long recurrence interval of greater than 6000 years is thus estimated judging from the matured fault structure of the qingchuan fault the latest event was likely to have ruptured the full length of the fault according to the empirical scaling laws between magnitude and rupture length the magnitude of the event is estimated to be mw 7 6 7 9 on the basis of the slip rate from gps measurements and the elapsed time since the last event it is estimated that a seismic moment equivalent to mw 7 5 has been accumulated on the qingchuan fault considering the increased coulomb failure stress and the shortened time of earthquake recurrence triggered by the wenchuan earthquake it is suggested a high seismic risk along the qingchuan fault and its neighboring area furthermore the slow strain buildup unadapted geometry and matured fault structure of the ltz may be the reason why it produces rare but large intraplate earthquakes

metastable stratus tops previously it has been shown that a saturated or near saturated mixture of cloud top air with cloud free air which has a somewhat lower wet bulb potential temperature w will be denser than the surrounding cloud air and will descend through the cloud layer this has been referred to as entrainment instability it is often presumed that this mechanism results in the rapid entrainment of dry air which may lead to the breakup of a continuous stratocumulus deck airborne observations of the marine planetary boundary layer are presented these along with previously published observations indicate that w at cloud top may exceed that of the air above by as much as 5 c without strong entrainment being active the fact that potential instability is not always accompanied by rapid entrainment suggests that the process is in a metastable state until sufficiently disturbed these observations show the vertical transfer mechanisms in stratus cloud and reveal the presence of a case with a drop free region between cloud top and the base of the inversion theoretical arguments are proffered to explain these phenomena and to account for the fact that entrainment episodes are delayed and intermittent

a geometric analysis of surface deformation implications for the tectonic evolution of ganymede abstract a visual nonalignment of the furrows and the circularity of impact craters are used to study surface deformation on ganymede the furrow system is examined to test the hypothesis that lateral motion has taken place between areas of dark terrain results show that while lateral motion cannot be ruled out it may not be required to explain the geometry of the system initial nonconcentricity of the furrows or an early period of penetrative deformation shortly after furrow formation could also account for the present configuration centers of curvature of the furrows in galileo and marius regiones are numerically determined and it is shown that if lateral movement did occur it is not possible to determine the amount of displacement the axial ratios of impact craters in the uruk sulcus region which separates galileo and marius regiones are determined and show that large scale shear deformation has not occured in that area since bright terrain was emplaced deformation of impact craters within galileo regio suggests that ganymede s lithosphere has behaved rigidly throughout most of the satellite s evolution the shapes and orientations of impact craters in dark terrain around wedges of bright terrain are used to place an upper limit on the amount of extension associated with bright terrain formation

constraints on the expansion of ganymede and the thickness of the lithosphere grooves and furrows have been interpreted as grabens resulting from extension of ganymede s lithosphere geologically reasonable estimates of the dip 90 60 and displacement less than 1 km to a few hundred meters of faults bounding grooves on ganymede allow calculation of the extension and surface area increase 0 04 2 required for the formation of all grooved terrain the implied radius increase is thus limited between 0 02 and 1 1 planetary expansion is the maximum possible since formation of the grooved terrain began similar estimates for faults bounding furrows the oldest preserved tectonic features on ganymede indicate a maximum surface area increase of 0 5 for the best developed furrow system which is located in galileo regio if equivalent furrow systems existed on all of the cratered terrain then a maximum of 0 5 increase in surface area of ganymede is possible after the formation of the lithosphere and prior to the formation of grooved terrain faults bounding simple graben originate at a subsurface mechanical discontinuity and propagate upwards resulting in grabens with similar widths and similar spacings between members of a set the depth to this mechanical discontinuity for furrows and grooves on ganymede must give at least a minimum lithosphere thickness because it is impossible for faults to originate and propagate upwards from a point below the lithosphere therefore the minimum lithosphere thickness on ganymede is 5 km and 9 km in marius and galileo regiones respectively at the time of furrow formation and 4 km at the time of groove formation

global geological mapping of ganymede abstract we have compiled a global geological map of ganymede that represents the most recent understanding of the satellite based on galileo mission results this contribution builds on important previous accomplishments in the study of ganymede utilizing voyager data and incorporates the many new discoveries that were brought about by examination of galileo data we discuss the material properties of geological units defined utilizing a global mosaic of the surface with a nominal resolution of 1 km pixel assembled by the usgs with the best available voyager and galileo regional coverage and high resolution imagery 100 200 m pixel of characteristic features and terrain types obtained by the galileo spacecraft we also use crater density measurements obtained from our mapping efforts to examine age relationships amongst the various defined units these efforts have resulted in a more complete understanding of the major geological processes operating on ganymede especially the roles of cryovolcanic and tectonic processes in the formation of might materials they have also clarified the characteristics of the geological units that comprise the satellite s surface the stratigraphic relationships of those geological units and structures and the geological history inferred from those relationships for instance the characteristics and stratigraphic relationships of dark lineated material and reticulate material suggest they represent an intermediate stage between dark cratered material and light material units

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

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

topographic wavelengths of ganymede groove lanes from fourier analysis of galileo images galileo images have shown that grooved terrain on ganymede consists of pervasive ridges and grooves at a variety of spatial scales which complicates visual interpretation we use fourier analysis to separate complex surface deformation into its component dominant wavelengths closely correlated to topographic wavelengths to determine spatial relationships within and among grooved terrain units we analyze groove lanes in four galileo target sites uruk sulcus byblus sulcus tiamat sulcus and nicholson regio spanning a range of resolutions and lighting geometries and we find multiple dominant wavelengths in each fourier analysis of the complexly deformed uruk sulcus shows both similarities and differences in wavelength distribution among its tectono stratigraphic subunits a range of 0 5 to 6 km with a concentration at 1 2 km favorable comparison is made to a stereo derived topographic model of the dominant wavelengths displayed by byblus sulcus 1 3 3 and 10 km the longest wavelength is revealed by profiles across both high and low resolution images with very different lighting geometries tiamat sulcus displays different dominant wavelengths north 5 to 10 km and south 3 to 5 km of the orthogonally trending kishar sulcus groove lanes in nicholson regio are significantly different from the other sites because they are isolated within dark terrain fourier analysis of these dark terrain groove lanes shows dominant wavelengths 2 1 3 2 and 8 0 km that are similar to those in lanes of more typical grooved terrain this suggests that the tectonic style and lithospheric characteristics in this portion of ganymede s dark terrain were similar to those in bright grooved terrain at the time of deformation our results support the hypothesis that longer topographic wavelengths in ganymede s groove lanes formed by means of extensional necking of the lithosphere while multiple shorter wavelengths formed by normal faulting of the brittle lithosphere in both bright and dark terrains the similar wavelengths of deformation seen in several groove lanes in both bright and dark terrain suggest similarity in lithospheric thickness composition and mechanical structure at these disparate sites a global process such as differentiation could be responsible for creating a similar planet wide strain and thermal regime during the time of grooved terrain formation

trenching exposures of the surface rupture of 2008 mw 7 9 wenchuan earthquake china implications for coseismic deformation and paleoseismology along the central longmen shan thrust fault abstract the may 12 2008 mw 7 9 wenchuan earthquake was induced by failure of two of the major faults of the longmen shan thrust fault zone along the eastern margin of tibet plateau our study focused on trenches across the yingxiu bichuan fault the central fault in the longmen shan belt that has a coseismic surface break of more than 200 km long trenching excavation across the 2008 earthquake rupture on three representative sites reveals the styles and amounts of the deformation and paleoseismicity along the longmen shan fault styles of coseismic deformation along the 2008 earthquake rupture at these three sites represent three models of deformation along a thrust fault two of the three trench exposures reveal one pre 2008 earthquake event which is coincident with the pre existing scarps based on the observation of exposed stratigraphy and structures in the trenches and the geomorphic expressions on ground surface we interpret the 2008 earthquake as a characteristic earthquake along this fault the interval of reoccurrence of large earthquake events on the central longmen shan fault the yingxiu beichuan fault can be inferred to be about 11 000 years according to 14c and osl dating the amounts of the vertical displacement and shortening across the surface rupture during the 2008 earthquake are determined to be 1 0 2 8 m and 0 15 1 32 m respectively the shortening rate and uplift rate are then estimated to be 0 09 0 12 mm yr and 0 18 0 2 mm yr respectively it is indicated that the deformation is absorbed mainly not by shortening but by uplift along the rupture during the 2008 earthquake

dynamics of cumulus rising into stratocumulus as observed during the first lagrangian experiment of astex the atlantic stratocumulus transition experiment took place during june 1992 in the eastern atlantic ocean in an area extending south east of the azores to madeira one of the goals of this experiment was to study the physical processes responsible for the transition from stratocumulus to shallow cumulus clouds the cloud type most frequently observed was cumulus rising into stratocumulus two lagrangian experiments were carried out to study the evolution of the boundary layer and to observe any transition in the cloud characteristics downstream here we concentrate on the last flight of the first lagrangian experiment during which cumulus cloud was penetrating thin and broken stratocumulus from below the immediate cause of the cumulus convection was condensation at the top of the well mixed surface based boundary layer the lifting condensation level was observed to be at about 500 m and above this height there was a conditionally unstable layer up to 1600 m in the upper part of the conditionally unstable layer the horizontally averaged thermodynamical variables showed that the air was very close to saturation indicating that the upper part of the cloud deck consisted of broken clouds the vertical structure of mean variables variances fluxes and turbulent kinetic energy budget is discussed one of the findings is that the cumulus convection is an important factor in counteracting the gradual dissipation of the stratocumulus deck in that it supplies moisture to the latter furthermore the net longwave radiative loss at cloud top was observed to be about 40 15 w m 2 which tended to destabilize the cloud layer from above the skewness factor s showed that the upward convection was quite intense owing to the rising cumuli the factor s reaching a maximum of about 2 0 7 in the middle of the cloud layer the skewness was found to be slightly negative near the cloud top

rupture termination and jump on parallel offset faults proper evaluation of seismic hazard depends on accurate estimates of potential earthquake size in areas with complex multisegment fault systems such an estimate in turn depends on an ability to predict the circumstances under which rupture may jump between fault segments many observational and numerical studies have analyzed the phenomenon of jumping rupture but none has focused on how the process of rupture termination on the primary nucleating fault segment affects the ability of rupture to jump to a secondary fault segment in the current study i model the dynamics of a simple 2d strike slip fault system with two parallel segments arranged with either a compressional or extensional stepover i vary the suddenness with which the initial shear stress tapers to zero on the primary section if the initial shear stress goes to zero over a very small 100 m distance rupture readily jumps both compressional and extensional stepovers of 1 km if the initial shear stress tapers to zero over 1 km rupture can jump the compressional stepover but not the extensional stepover if the initial shear stress tapers to zero over 2 5 km rupture cannot jump either the compressional or the extensional stepover the results illustrate the importance of the slip gradient and the resultant static stress field and the acceleration of the rupture front and the resultant generation of stopping phases in determining the probability of jumping rupture

locations and types of ruptures involved in the 2008 sichuan earthquake inferred from sar image matching 1 we have detected detailed ground displacements in the proximity of the longmen shan fault zone lmsfz by applying a sar offset tracking method in the analysis of the 2008 sichuan earthquake an elevation dependent correction is indispensable for achieving sub meter accuracy a sharp displacement discontinuity with a relative motion of 1 2 m appears over a length of 200 km along the lmsfz which demonstrates that the main rupture has proceeded on the beichuan fault bf among several active faults composing the lmsfz and a new active fault is detected on the northeastward extension of the bf the rupture on the bf is characterized by a right lateral motion in the northeast while in the southwest an oblique right lateral thrust slip is suggested in contrast to the northeast where a major rupture proceeded on the bf only in the southwest multiple thrust ruptures have occurred in the southeastern foot of the pengguan massif

global reorientation and its effect on tectonic patterns on ganymede the basins of ganymede are studied in order to examine the effects of global reorientation on the grooves and furrows of the satellite an impact basin and the global reorientation of ganymede were modeled the damping time the time for relaxation of tidal bulge and the time for isostatic adjustment of craters are significant in calculating the duration and amount of global reorientation the regional global control of groove orientation is examined the data reveal that the tidal despinning and furrow formation created the reactivated zones of weakness in which the groove sets were formed it is observed that the grooved terrain emplacement caused a 15 deg shift in the paleopole

early thermal profiles and lithospheric strength of ganymede from extensional tectonic features abstract estimates of the brittle lithosphere thickness derived from the width and spacing of extensional tectonic features coupled with lithospheric strength envelopes brittle and ductile yield stress versus depth appropriate for ice allow the quantitative determination of early thermal profiles and lithospheric strength and stability on ganymede furrows and grooves indicate brittle lithospheric thicknesses of 5 10 and 2 5 km respectively assuming that their spacing is controlled by an extensional instability or that their width is controlled by the intersection depth of their bounding faults plots of the brittle and ductile yield stress versus depth for the icy lithosphere of ganymede show a linear increase in brittle strength with depth to a maximum at the brittle ductile transition followed by an exponential decrease in ductile yield stress with depth because the depth to the brittle ductile transition depends primarily on the thermal gradient the thickness of the brittle lithosphere can be used to calculate early thermal profiles of 1 5 6 and 4 5 20 km during the formation of the furrows and grooves respectively lithospheric strength the integral of the yield stress versus depth curve varied from 30 125 gpa m when the furrows formed to 5 30 gpa m when the grooves formed which correspond to maximum yield stresses of 6 11 and 2 5 6 mpa respectively these results indicate that the thermal gradient and lithospheric strength varied laterally by as much as a factor of 5 and that ganymede cooled in a highly inhomogeneous manner with significant lateral thermal anomalies finally this analysis provides a straightforward explanation for the stability of large remnants of cratered terrain such as galileo regio that had a low thermal gradient and strong lithosphere in contrast to small remnants of cratered terrain that were fractured and broken up by grooved terrain as a result of higher thermal gradients and weaker lithospheres

a unified nomenclature for tectonic structures on the surface of enceladus abstract enceladus has experienced widespread and diverse tectonic deformation the diversity and nonuniform distribution of structures visible on the surface attests to a complicated and perhaps long lived tectonic history currently no fundamental classification scheme based on morphology exists for the tectonic structures on enceladus which limits analysis and discussion of tectonic structures and regional and global tectonic histories characterization and classification of structures on enceladus is an important first step in understanding its tectonic history here we propose a global morphologic i e nongenetic classification scheme for tectonic structures on enceladus five classes of tectonic structures on enceladus have been identified based on images and limited topographic data troughs scarps chasmata ridges and bands morphological variation of structures exists within these classes reinforcing the complicated tectonic history of this small body

grooved terrain on ganymede first results from galileo high resolution imaging abstract high resolution galileo imaging has provided important insight into the origin and evolution of grooved terrain on ganymede the uruk sulcus target site was the first imaged at high resolution and considerations of resolution viewing geometry low image compression and complementary stereo imaging make this region extremely informative contrast variations in these low incidence angle images are extreme and give the visual impression of topographic shading however photometric analysis shows that the scene must owe its character to albedo variations a close correlation of albedo variations to topography is demonstrated by limited stereo coverage allowing extrapolation of the observed brightness and topographic relationships to the rest of the imaged area distinct geological units are apparent across the region and ridges and grooves are ubiquitous within these units the stratigraphically lowest and most heavily cratered units lineated grooved terrain generally show morphologies indicative of horst and graben style normal faulting the stratigraphically highest groove lanes parallel ridged terrain exhibit ridges of roughly triangular cross section suggesting that tilt block style normal faulting has shaped them these extensional tectonic models are supported by crosscutting relationships at the margins of groove lanes thus a change in tectonic style with time is suggested in the uruk sulcus region varying from horst and graben faulting for the oldest grooved terrain units to tilt block normal faulting for the latest units the morphologies and geometries of some stratigraphically high units indicate that a strike slip component of deformation has played an important role in shaping this region of grooved terrain the most recent tectonic episode is interpreted as right lateral transtension with its tectonic pattern of two contemporaneous structural orientations superimposed on older units of grooved terrain there is little direct evidence for cryovolcanic resurfacing in the uruk sulcus region instead tectonism appears to be the dominant geological process that has shaped the terrain a broad wavelength of deformation is indicated corresponding to the voyager observed topography and may be the result of ductile necking of the lithosphere while a finer scale of deformation probably reflects faulting of the brittle near surface the results here form a basis against which other galileo grooved terrain observations can be compared

finescale structure and microphysics of coastal stratus observations were made of unbroken marine stratus off the coast of oregon using the combined capabilities of in situ probes and a 95 ghz radar mounted on an aircraft reflectivity and doppler velocity measurements were obtained in vertical and horizontal planes that extend from the flight lines data from three consecutive days were used to examine echo structure and microphysics characteristics the clouds appeared horizontally homogeneous and light drizzle reached the surface in all three cases radar reflectivity is dominated by drizzle drops over the lower two thirds to four fifths of the clouds and by cloud droplets above that cells with above average drizzle concentrations exist in all cases and exhibit a large range of sizes the cells have irregular horizontal cross sections but occur with a dominant spacing that is roughly 1 2 1 5 times the depth of the cloud layer doppler velocities in the vertical are downward in all but a very small fraction of the cloud volumes the cross correlation between reflectivity and vertical doppler velocity changes sign at or below the midpoint of the cloud indicating that in the upper parts of the clouds above average reflectivities are associated with smaller downward velocities this correlation and related observations are interpreted as the combined results of upward transport of drizzle drops and of downward motion of regions diluted by entrainment the in situ measurements support these conclusions

viscous relaxation as a prerequisite for tectonic resurfacing on ganymede insights from numerical models of lithospheric extension abstract ganymede s bright terrain formed during a near global resurfacing event or events that produced both heavily tectonized and relatively smooth terrains the mechanism s by which resurfacing occurred on ganymede e g cryovolcanic or tectonic and the relationship between the older dark and the younger bright terrain are fundamental to understanding the geological evolution of the satellite using a two dimensional numerical model of lithospheric extension that has previously been used to successfully simulate surface deformation consistent with grooved terrain morphologies we investigate whether large amplitude preexisting topography can be resurfaced erased by extension i e tectonic resurfacing using synthetically produced initial topography we show that when the total relief of the initial topography is larger than 25 50 m periodic groove like structures fail to form instead extension is localized in a few individual isolated troughs these results pose a challenge to the tectonic resurfacing hypothesis we further investigate the effects of preexisting topography by performing suites of simulations initialized with topography derived from digital terrain models of ganymede s surface these include dark terrain fresh relatively deep impact craters smooth bright terrain and a viscously relaxed impact crater the simulations using dark terrain and fresh impact craters are consistent with our simulations using synthetic topography periodic groove like deformation fails to form in contrast when simulations were initialized with bright smooth terrain topography groove like deformation results from a wide variety of heat flow and surface temperature conditions similarly when a viscously relaxed impact crater was used groove like structures were able to form during extension these results suggest that tectonic resurfacing may require that the amplitude of the initial topography be reduced before extension begins we emphasize that viscous relaxation may be the key to enabling tectonic resurfacing as the heat fluxes associated with groove terrain formation are also capable of reducing crater topography through viscous relaxation for long wavelength topography large craters viscous relaxation is unavoidable we propose that the resurfacing of ganymede occurred through a combination of viscous relaxation tectonic resurfacing cryovolcanism and at least in a few cases band formation variations in heat flow and strain magnitudes across ganymede likely produced the complex variety of terrain types currently observed

spectral analysis of groove spacing on ganymede grooves on ganymede are interpreted as extensional tectonic features whose regular spacing is an indicator of the thickness of a brittle surface layer or lithosphere at the time of deformation we have performed a statistical analysis of groove spacing on ganymede taking fourier transforms of 157 photometric profiles across sets of grooves and examining the resultant power spectra for peaks representing the dominant topographic periodicities the distribution of groove spacing on ganymede is approximately lognormal with a minimum of 3 5 km a maximum of 17 km and a mean of 8 4 km there is no correlation of groove spacing with latitude or longitude the most striking feature of the geographic distribution is that while groove spacing tends to be quite constant within a given groove set it can vary substantially from one groove set to another in a geographic region an exception is the uruk sulcus region with a mean groove spacing of 6 5 km and very little variability we examine several models that relate the observed groove spacing to lithospheric thicknesses the most important conclusion is that lithospheric thickness varied significantly from one groove set to the next while the grooves were being formed we examine four possible causes for the heterogeneous distribution variation in time of formation during a period in which the global mean heat flow was changing variation in strain rate from one groove set to the next local excursions in geothermal gradient caused by variations in the vigor of underlying convective upwellings and local excursions in geothermal gradient caused by resurfacing events the first three appear viable while the fourth requires very rapid groove formation due to the short cooling times involved

evidence for europa like tectonic resurfacing styles on ganymede 1 very high resolution imaging and stereo topographic data obtained during the galileo g28 encounter with ganymede show 1 evidence for europa like crustal spreading and resurfacing to form portions of the bright terrain and 2 bright terrain that appears smooth at voyager resolution and thus a strong candidate for cryovolcanism but instead is tectonically deformed and lacks embayment relationships when viewed at high resolution in contrast to previous views these new data show that tectonism has been the dominant process in shaping some very smooth areas and that ganymede appears to have experienced europa like crustal spreading during its previous history

the evolution of tectonic features on ganymede the bands of bright resurfaced terrain on ganymede are probably broad grabens formed by global expansion and filled with deposits of ice grooves within the bands are thought to be extensional features formed during the same episode of expansion the crust of ganymede is modeled as a viscoelastic material subjected to extensional strain with sufficiently high strain rates and stresses deep normal faulting will occur creating broad grabens that may then be filled continuing deformation at high strain rates and stresses will cause propagation of deep faults up into the flood deposits and normal faulting at the surface while lower strain rates and stresses will cause formation of open extension fractures or if the crustal strength is very low grabens at the surface the spacing between adjacent fractures may reflect the geothermal gradient at the time of deformation surface topography resulting from fracturing and normal faulting will decay with time as a result of viscous relaxation and mass wasting

fault geometries and structures associated with the rupture endpoints of the 2008 mw 7 9 wenchuan earthquake eastern tibet plateau china

tectonic framework of grooved terrain on ganymede abstract an analysis of the tectonic features grooves and prominent troughs comprising grooved terrain on ganymede shows a global tectonic framework domains of grooves bordered by deep structural boundaries that controlled their extent and orientation developed along preferred orientations some of these directions are much more prominent than others and appear to coincide with at least two great circles with pole locations at 152 long 55 lat and 65 long and 50 lat the great circle hypothesis is in good agreement with several statistical tests of the data set several mechanisms for the emplacement of grooved areas along great circles are discussed a plausible mechanism is a pattern of equatorial symmetric rising and descending convection cells because the studied areas represent only a small portion of ganymede interpretations of global tectonic patterns and models of formation must remain tentative

ice covered water volcanism on ganymede eruption of liquid h2o magmas along extensional fractures and graben bounding normal faults may have played a critical role in the development of ganymede s grooved terrain the resurfacing potential of a water magma is dependent on a variety of factors including the areal extent of the source region the rate of discharge the thickness of the flow and the time that it takes the flow to completely freeze to its base in this paper the thermal evolution of such a flow is considered in detail the minimum unfrozen lifetime of a 5 m flow is approximately 12 5 days while a 10 m flow would survive for at least 50 days heating resulting from factional head loss could reasonably extend these lifetimes by 50 or more with a discharge rate of the order of 1 10 km3 d 1 an individual volcanic water flow could flood an area of 104 km2 before freezing as the flow solidifies its volume will increase thus lifting and arching its protective ice cover extensional fractures may then develop in the ice subparallel to the graben walls these fractures could result in grooves directly given a sufficiently thick 1 km flow or they may simply act to concentrate various tectonic forces that could initiate groove producing faults

formation of ganymede s grooved terrain by convection driven resurfacing the heat flux and strain rate inferred for grooved terrain formation on ganymede can be produced in a convecting ice shell 10 100 km thick with weak near surface ice smooth linear grooves may have formed by convection driven lithospheric spreading and long wavelength compressional folds may form atop convective downwellings and would possibly be detectable with mapping from esa s upcoming jupiter icy moon explorer mission

a field study of nocturnal stratocumulus ii turbulence structure and entrainment tethered balloon borne instrumentation has been used to study the small scale air motion and temperature variations occurring within a layer of nocturnal stratocumulus the observations indicate a very sharp and intermittently turbulent entrainment interfacial layer with some evidence for a characteristic entrainment scale of about 10m within the cloud layer convective motions are apparent and these take the form of cold downward moving plumes which increase in scale away from cloud top they are generated by the large radiative loss from the upper part of the cloud some statistical features of the turbulence field in cloud are discussed and compared with other observations from stratocumulus and the daytime convective boundary layer

geology and mapping of dark terrain on ganymede and implications for grooved terrain formation geological mapping of regional and high resolution galileo images reveals a variety of units and structures within ganymede s dark terrain we have made a detailed study of areas within galileo marius and nicholson regiones in order to investigate the style of tectonic deformation experienced by dark terrain adjacent to swaths of grooved terrain dark terrain appears to become fractured as a precursor to grooved terrain formation in places dark fractured swaths are recognized which have similar characteristics to brighter grooved terrain swaths tectonic deformation may be but is not always focused through preexisting weaknesses caused by impact craters and furrows a prominent groove lane anshar sulcus is inferred to have formed by the process of hanging wall rollover accompanied by a small amount of right lateral horizontal shear offset resulting from ne sw extension

possible breakup of dark terrain on ganymede by large scale shear faulting a system of arcuate furrows in galileo regio and marius regio two large blocks of ancient dark terrain has previously been proposed to be the remnant of an originally more concentric furrow set that was disrupted by shear estimates of the two regions poles of furrow concentricity indicate a considerable westward offset of the galileo regio pole these measurements suggest the possibility of about 500 km of left lateral offset of the two areas four additional independent structural indicators support this hypothesis there is evidence that shear deformation was concentrated along a major structural lineament which closely follows a small circle about 45 of arc of radius which encloses galileo regio and that a smaller amount of distributed shear occurred across an adjacent 500 to 1500 km wide band there is also morphologic evidence for zones of minor right lateral shear between central and southern marius regio and between barnard and nicholson regio and for a zone of minor left lateral shear in nun sulci stratigraphic relations indicate that any major shear offsets occurred before and during the earliest stages of grooved terrain formation before most grooves had formed and before virtually all light material had been emplaced however regionally dominant groove orientations are generally consistent with orientations expected for transtensional features either shear strain or the shear s driving mechanism may have had a long term effect on patterns of deformation of ganymede s lithosphere

crustal structure beneath the eastern margin of the tibetan plateau and its tectonic implications 1 two crustal cross sections through the eastern margin of the tibetan plateau are jointly determined from deep seismic sounding the e w trending line aa passes through the western sichuan plateau including the songpan garze terrane and the longmenshan fault belt and ends in the sichuan basin a part of the yangtze craton line bb has a trend of nne and crosses the songpan garze terrane two dimensional crustal structures along the profiles were jointly determined by the additional use of existing deep seismic sounding data our seismic velocity models indicate that the western sichuan plateau and the sichuan basin have crustal thicknesses of 62 and 43 km average crustal p wave velocities of 6 27 and 6 45 km s and lower crustal vp 6 5 km s thicknesses of 27 and 15 km respectively density models constructed from the seismic velocity models are consistent with observed bouguer gravity anomalies we infer that collision between the tibetan plateau and the yangtze craton has caused thickening of the lower crust and uplift of the western sichuan plateau we detect a low velocity layer in the upper crust of the western sichuan plateau but observe no equivalence in the sichuan basin west dipping thrusts may detach into this low velocity layer the seismic phase pmp in the western sichuan plateau has low amplitude suggesting high attenuation in the lower crust qp of 100 300 we suggest that the high attenuation is a consequence of lower crustal flow caused by the large lower crustal thickness beneath the western sichuan plateau

planetary science icing ganymede much of jupiter s moon ganymede is covered in comparatively young ice images from spacecraft are providing clues about whether this resurfacing occurred primarily through tectonic or volcanic events

ring geometry on ganymede and callisto abstract arguments have been made based on geometry for both an impact and an internal origin for the ancient partially preserved major furrow system of ganymede zuber and parmentier concluded that furrows are not concentric but could be impact related if multiringed structures on icy satellites are initially noncircular we examine the geometry of the valhalla ring structure on callisto in order to assess the circularity of an unmodified ring system despite prominent local meandering the only gross deviations from concentricity in the valhalla system are found in the outer northeast quadrant of the system here a number of ring segments intersect small circles about the center at angles up to 30 the ganymede furrow system was remapped to make use of improvements in coordinate control the least squares center of curvature determined using natural weighting for all furrows in marius and galileo regio is 20 7 1 1 s 179 2 1 1 w 2 uncertainty furrows in marius and galileo regio are reasonably concentric are much more circular than previously estimated and probably once covered at least an entire hemisphere of ganymede in addition at least three other multiring systems of varying size are identified on ganymede indicative of a projectile population thus we find furrow geometry and occurrence are consistent with an impact origin deviations of some furrows from concentricity about the center of curvature on the scale of those found at valhalla do exist as in the case of valhalla these variations are principally confined to outer regions of the structure and are interpreted as inherent properties of multiringed structures on icy satellites the cause s of this may be in the ring formation mechanism itself but are more likely due to variations in preexisting lithospheric mechanical properties the perceived present nonalignment of the assumed originally concentric furrows has been used to argue for large scale lateral motion of dark terrain blocks in ganymede s crust presumably in association with bright terrain formation the overall alignment of furrows as well as the inherent scatter in centers of curvature for subregions of galileo and marius regio do not support this hypothesis

galileo s first images of jupiter and the galilean satellites the first images of jupiter io europa and ganymede from the galileo spacecraft reveal new information about jupiter s great red spot grs and the surfaces of the galilean satellites features similar to clusters of thunderstorms were found in the grs nearby wave structures suggest that the grs may be a shallow atmospheric feature changes in surface color and plume distribution indicate differences in resurfacing processes near hot spots on io patchy emissions were seen while io was in eclipse by jupiter the outer margins of prominent linear markings triple bands on europa are diffuse suggesting that material has been vented from fractures numerous small circular craters indicate localized areas of relatively old surface pervasive brittle deformation of an ice layer appears to have formed grooves on ganymede dark terrain unexpectedly shows distinctive albedo variations to the limit of resolution

terrain types and local scale stratigraphy of grooved terrain on ganymede grooved terrain is subdivided on the basis of pervasive morphology into 1 groove lanes elongate parallel groove bands 2 grooved polygons polygonal domains of parallel grooves 3 reticulate terrain polygonal domains of orthogonal grooves and 4 complex grooved terrain polygons with several complexly cross cutting groove sets detailed geologic mapping of select areas employing previously established conventions for determining relative age relations reveals a general three stage sequence of grooved terrain emplacement first dissection of the lithosphere by throughgoing grooves and pervasive deformation of intervening blocks second extensive flooding and continued deformation of the intervening blocks third repeated superposition of groove lanes concentrated at sites of initial throughgoing grooves this sequence is corroborated by crater density measurements dominant orientations of groove sets are parallel to relict zones of weakness that probably were reactivated during grooved terrain formation groove lane morphology and development consistent with that predicted for passive rifts suggests a major role of global expansion in grooved terrain formation

simple approach to dynamics of entrainment interface layers and cloud holes in stratocumulus clouds this paper presents simple conceptual models of phenomena essential to the entrainment processes at the top of inversion capped stratocumulus clouds mixing processes lead to formation of an interface layer between pure cloud and the top of the inversion as well as downdraughts of dry air that penetrate the cloud interior and form cloud holes spaces that have reduced liquid water content or are completely devoid of it these processes are illustrated with one dimensional models permitting estimation of interface layer thickness as well as the cloud hole parameters and conditions of formation results are in rough agreement with observations copyright 2009 royal meteorological society

fault steps and the dynamic rupture process 2 d numerical simulations of a spontaneously propagating shear fracture fault steps may have controlled the sizes of the 1966 parkfield 1968 borrego mountain 1979 imperial valley 1979 coyote lake and the 1987 superstition hills earthquakes this project investigates the effect of fault steps of various geometries on the dynamic rupture process we have used a finite difference code to simulate spontaneous rupture propagation in two dimensions we employ a slip weakening fracture criterion as the condition for rupture propagation and examine how rupture on one plane initiates rupture on parallel fault planes the geometry of the two parallel fault planes allows for stepover widths of 0 5 to 10 0 km and overlaps of 5 to 5 km our results demonstrate that the spontaneous rupture on the first fault segment continues to propagate onto the second fault segment for a range of geometries for both compressional and dilational fault steps a major difference between the compressional and dilational cases is that a dilational step requires a longer time delay between the rupture front reaching the end of the first fault segment and initiating rupture on the second segment therefore our dynamic study implies that a compressional step will be jumped quickly whereas a dilational step will cause a time delay leading to a lower apparent rupture velocity we also find that the rupture is capable of jumping a wider dilational step than compressional step

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

the formation of ganymede s grooved terrain numerical modeling of extensional necking instabilities abstract ganymede s grooved terrain likely formed during an epoch of global expansion when unstable extension of the lithosphere resulted in the development of periodic necking instabilities linear infinitesimal strain models of extensional necking support this model of groove formation finding that the fastest growing modes of an instability have wavelengths and growth rates consistent with ganymede s grooves however several questions remain unanswered including how nonlinearities affect instability growth at large strains and what role instabilities play in tectonically resurfacing preexisting terrain to address these questions we numerically model the extension of an icy lithosphere to examine the growth of periodic necking instabilities over a broad range of strain rates and temperature gradients we explored thermal gradients up to 45 k km 1 and found that at infinitesimal strain maximum growth rates occur at high temperature gradients 45 k km 1 and moderate strain rates 10 13 s 1 dominant wavelengths range from 1 8 to 16 4 km post extension our infinitesimal growth rates are qualitatively consistent with but an order of magnitude lower than previous linearized calculations when strain exceeds 10 growth rates decrease limiting the total amount of amplification that can result from unstable extension this fall off in growth occurs at lower groove amplitudes for high temperature gradient thin lithosphere simulations than for low temperature gradient thick lithosphere simulations at large strains this shifts the ideal conditions for producing large amplitude grooves from high temperature gradients to more moderate temperature gradients 15 k km 1 we find that the formation of periodic necking instabilities can modify preexisting terrain replacing semi random topography up to 100 m in amplitude with periodic ridges and troughs assisting the tectonic resurfacing process despite this success the small topographic amplification produced by our model presents a formidable challenge to the necking instability mechanism for groove formation success of the necking instability mechanism may require rheological weakening or strain localization by faulting effects not included in our analysis

lithospheric stresses due to radiogenic heating of an ice silicate planetary body implications for ganymede s tectonic evolution thermal evolution models of differentiated and undifferentiated ice silicate bodies containing longlived radiogenic heat sources are examined lithospheric stresses arise due to volume change of the interior and temperature change in the lithosphere for an undifferentiated body the surface stress peaks early in the evolution while in the differentiated case stresses peak later and continue to accumulate for longer periods of time the variation of near surface stress with depth shows that stresses for the undifferentiated body initially penetrate to great depths but rapidly concentrate within a few kilometers of the surface for the differentiated body elastic stresses never accumulate at a depth greater than a few kilometers these models are applied to consider long term radioactive heating as a possible mechanism of tectonic activity and bright terrain formation on ganymede

coseismic deformation from the 2008 wenchuan china earthquake derived from alos palsar images abstract we analyzed alos palsar images along eight paths acquired before and after the mainshock of an earthquake in wenchuan in the sichuan province of china may 12 2008 we found entire coseismic deformation features and detected many fringes in an approximately 100 km wide region surrounding the longmen shan fault zone we found 6 7 broad elliptic fringes north of the epicenter which indicated around 70 80 cm increase in range distance between the ground and satellite this pattern corresponded to subsidence or eastward shift of ground which is often seen above the lower margin of a low angled thrust we also counted 8 9 fringes i e 90 100 cm range decrease between the fault zone and chengdu chengdu is located roughly 50 km away from the pengguan fault which is the southernmost trace of the longmen shan fault zone as this area is located on the footwall side the pattern suggested a westward shift of the earth s surface however we could not obtain high correlations due to large displacements in the about 240 km long belt along the surface faults several concentric fringes were found along the beichuan fault which is the central trace of the longmen shan fault zone this implied that the rupture process of this earthquake was complicated we also performed pixel matching to estimate offsets in the region of low correlation positive and negative range offsets larger than 2 m were found on the north and south sides of the beichuan fault respectively we observed a belt of negative range and azimuth offsets between the beichuan and pengguan faults we calculated an interferogram using a multi segment fault model with uniform slip along the beichuan and pengguan faults and estimated the slip distribution based on previous seismological studies we assumed that the southwestern part dipped toward the northwest by 33 degrees whereas the central and northeastern parts had a much steeper dip angle we found two regions of slips larger than 4 m in the southwest and central parts of the beichuan fault the pengguan segments may have much smaller slips around 1 m the southwestern segments of the beichuan fault and the entire pengguan fault had dominant thrust components whereas dextral slip prevailed in the central and northeastern segments of the beichuan fault the estimated geodetic moment was 5 87 1020nm mw 7 78

viscous relaxation of impact craters on icy planetary surfaces determination of viscosity variation with depth spacecraft images show that the icy galilean satellites have surfaces with very low topographic relief impact craters on ganymede and callisto are anomalously shallow and are characterized by sharp well defined rims and domed floors these morphological characteristics can be explained by viscous relaxation of topography on an icy crust in which the viscosity is uniform or decreases with depth under these conditions large craters relax more rapidly than small craters therefore explaining a possible underabundance of large craters viscous relaxation on an icy crust that is thin compared to the crater diameter or on a thick icy crust in which viscosity increases with depth could not produce this crater morphology and would result in the more rapid relaxation of small craters rather than large craters the results of this study suggest that more detailed analysis of relaxing impact crater morphology may resolve the rate of viscosity decrease with depth and so provide evidence on the interior thermal evolution of icy planetary bodies

on the resurfacing of ganymede by liquid water volcanism abstract a long popular model for producing ganymede s bright terrain involves flooding of low lying graben with liquid water slush or warm soft ice the model suffers from major problems however including the absence of obvious near surface heat sources the negative buoyancy of liquid water and the lack of a mechanism for confining the flows to graben floors we present new models for cryovolcanic resurfacing to overcome these difficulties tidal heating within an ancient laplace like orbital resonance showman and malhotra 1997 icarus 127 93 showman et al 1997 icarus 129 367 provides a plausible heat source and could allow partial melting to occur as shallow as 5 10 km depth our favored mechanism for delivering this water to the surface invokes the fact that topography such as a global set of graben causes subsurface pressure gradients that can pump water or slush upward onto the floors of topographic lows graben despite the negative buoyancy of the liquid these eruptions can occur only within the topographic lows furthermore as the low areas become full the pressure gradients disappear and the resurfacing ceases this provides an explanation for the observed straight dark bright terrain boundaries water cannot overflow the graben so resurfacing rarely embays craters or other rough topography pure liquid water can be pumped to the surface from only 5 10 km depth but macroscopic bodies of slush ascending within fractures can reach the surface from much greater depths due to the smaller negative buoyancy of slush a challenge for these models is the short predicted gravitational relaxation timescale of topographic features at high heat flows the resurfacing must occur before the graben topography disappears we also evaluate alternate resurfacing mechanisms such as pumping of liquid water to the surface by thermal expansion stresses and buoyant rise of water through a silicate contaminated crust that is denser than liquid water and conclude that they are unlikely to explain ganymede s bright terrain

brine volcanism and the interior structures of asteroids and icy satellites abstract cryovolcanism is among the foremost processes responsible for modifying the surfaces of icy satellites volcanic brine petrogenesis in ammonia deficient satellites should mainly involve eutectic melting in relevant salt water systems carbonaceous chondrites provide useful insights into the compositions of salts and aqueously altered rock in icy satellites and asteroids c1 chondrites contain about one fifth by mass of salts in various states of hydration many aspects of the petrogenesis and physical volcanology of icy satellite brines should be well described in the system h2o mgso4 na2so4 minor components include sulfates of k ni mn and ca chondrites also contain abundant carbonates but these are probably not very important in brine magmatism due to their low solubilities under expected conditions chlorides are also unimportant under most circumstances because of the low cosmic abundance ratio of cl s soluble salts may have profound effects on the geology and structure of icy satellites and asteroids in some models late episodes of water volcanism are facilitated by high buoyant forces due to the relatively high densities of sulfate rich mantle and crustal layers in other models early hypersaline brine volcanism quickly yields to plutonic magmatism due to low crustal densities europa probably has a layered crust composed of anhydrous mg na sulfates near the base and a frozen or partially molten eutectic mixture of ice and hydrated mg and na sulfates near the surface ganymede may have a crust about 300 km thick composed of a 10 1 ratio of ice mirabilite and a mantle 500 km thick composed of 50 ice phases plus 50 hydrated mg and na sulfates

volcanic constructs on ganymede and enceladus topographic evidence from stereo images and photoclinometry paul m schenklunar and planetary institute houston texasjeffrey m moorespace sciences division and the seti institute nasa ames research center moffett field californiaabstract the morphology of volcanic features on ganymede differs significantly from that onthe terrestrial planets few if any major volcanic landforms such as thick flows or shieldvolcanoes have been identified to date using new stereo voyager images we have searchedganymede for relief generating volcanic constructs we observed seven major types of volcanicstructures including several not previously recognized the oldest are broad flat topped domespartially filling many older craters in dark terrain similar domes occur on enceladus togetherwith smooth dark deposits these domes indicate that the volcanic history of the dark terrain iscomplex bright terrain covers vast areas although the style of emplacement remains unclear smooth bright materials embay and flood older terrains and may have been emplaced as low viscosity fluids associated with smooth bright material are a number of scalloped shaped semi enclosed scarps that cut into preexisting terrain in planform these structures resemble terrestrialcalderas the youngest volcanic materials identified are a series of small flows that may haveflooded the floor of the multiring impact structure gilgamesh forming a broad dome theidentification of volcanic constructs up to 1 km thick is the first evidence for extrusion ofmoderate to high viscosity material on ganymede viscosity and yield strength estimates for thesematerials span several orders of magnitude indicating that volcanic materials on ganymede have arange of compositions and or were extruded under a wide range of conditions and or eruptive styles introductionthe voyager survey of the outer solar system has revealedan astonishing variety of endogenic landforms on the surfacesof icy satellites despite extensive endogenic resurfacing ofsomc satellites for example ganymede enceladus andtriton volcanism on these surfaces has little topographicexpression we do not see massive volcanic edifices similarto olympus mons or mauna kea even the best putativeexamples of volcanic landforms seen on ariel miranda triton and enceladus exhibit rarely more than 1 2 km ofrelief jankowski and squyres 1988 pozio and kargel 1989 schenk 1991a croft et al 1995 this may berelated to the soft theology of ice see poirier 1982 durham et al 1983 and kirby et al 1987 or torheology and volcanic styles peculiar to icy petrologicsystems e g kargel 1991 kargel et al 1991 well over half of the surface of ganymede radius 2634 kin has been covered by endogenic effusions it is now consideredlikely that ganymede experienced one or more episodes ofchaotic orbital behavior malhotra 1991 possiblyresulting in tidal heating volcanic resurfacing constitutes arecord of ganymede s compositional and thermal evolution andmay record some of these putative tidal heating events yetthis satellite has been the subject of morphological study for15 years without the unambiguous detection of relief copyright 1995 by the american geophysical union paper number 95je01854 0148 0227 95 95je 01854505 00generating volcanic constructions on its landscape the styleof emplacement and composition of those volcanic depositsthat have been identified remains unclear on any planetary surface volcanic and other nonimpactconstructs can be difficult to recognize in spacecraft images particularly those obtained under high sun conditions e g malin 1978 topography is especially low on the galileansatellites and imaging resolution is at best 500 m pixel major local albedo variations on ganymede further complicategeologic and topographic mapping with these problems inmind we have undertaken the production of stereo pairs ofvoyager images where coverage permits to aid in the searchfor and characterization of volcanic landforms on ganymede ssurface in addition to an examination of previously identifiedvolcanic materials we report the discovery of severalpreviously unrecognized volcanic landforms and at least twotypes with substantial relief and describe their morphologyand geologic setting morphology of volcanic depositsindicates that ganymede extrusions probably had a range oftheologies and may be compositionally variable we concludewith speculations and predictions regarding their mode ofemplacement and the implications of volcanic landforms forthe geologic evolution of ganymede stereo imaging with voyagerthis study was motivated by the recognition that asignificant fraction of the surfaces of most of the outer planetsatellites were imaged by voyager in stereo e g croft andsoderblom 1991 schenk and moore 1993 we can usestereo imaging to detect subtle topographic features that were19 009

the galilean satellites nasa s galileo mission to jupiter and improved earth based observing capabilities have allowed major advances in our understanding of jupiter s moons io europa ganymede and callisto over the past few years particularly exciting findings include the evidence for internal liquid water oceans in callisto and europa detection of a strong intrinsic magnetic field within ganymede discovery of high temperature silicate volcanism on io discovery of tenuous oxygen atmospheres at europa and ganymede and a tenuous carbon dioxide atmosphere at callisto and detection of condensed oxygen on ganymede modeling of landforms seen at resolutions up to 100 times as high as those of voyager supports the suggestion that tidal heating has played an important role for io and europa

rupture imaging of the mw 7 9 12 may 2008 wenchuan earthquake from back projection of teleseismic p waves 1 the mw 7 9 wenchuan earthquake of 12 may 2008 was the most destructive chinese earthquake since the 1976 tangshan event tens of thousands of people were killed hundreds of thousands were injured and millions were left homeless here we infer the detailed rupture process of the wenchuan earthquake by back projecting teleseismic p energy from several arrays of seismometers this technique has only recently become feasible and is potentially faster than traditional finite fault inversion of teleseismic body waves therefore it may reduce the notification time to emergency response agencies using the iris dmc we collected 255 vertical component broadband p waves at 30 95 from the epicenter we found that at periods of 5 s and greater nearly all of these p waves were coherent enough to be used in a global array we applied a simple down sampling heuristic to define a global subarray of 70 stations that reduced the asymmetry and sidelobes of the array response function arf we also considered three regional subarrays of seismometers in alaska australia and europe that had apertures less than 30 and p waves that were coherent to periods as short as 1 s individual arfs for these subarrays were skewed toward the subarrays however the linear sum of the regional subarray beams at 1 s produced a symmetric arf similar to that of the groomed global subarray at 5 s for both configurations we obtained the same rupture direction rupture length and rupture time we found that the wenchuan earthquake had three distinct pulses of high beam power at 0 23 and 57 s after the origin time with the pulse at 23 s being highest and that it ruptured unilaterally to the northeast for about 300 km and 110 s with an average speed of 2 8 km s it is possible that similar results can be determined for future large dip slip earthquakes within 20 30 min of the origin time using relatively sparse global networks of seismometers such as those the usgs uses to locate earthquakes in near real time

the evolution of enceladus saturn s small icy moon enceladus shows evidence of several episodes of geologic resurfacing and extensional tectonism spread over much of its history freezing of liquid in the interior caused global expansion and fracturing of the crust resurfacing took place by eruption of fresh material perhaps containing nh3 to the surface solid state convection could take place in enceladus for a crustal thickness greater than about 30 km assuming thermal properties like those of pure h2o ice melting in the interior may have been made more likely by the presence of nh3 as the h2o nh3 system has a eutectic point at 173 k tidal dissipation seems to be the only heating mechanism capable of melting enceladus for the thermal properties of pure h2o the orbital eccentricity would have to be higher by a factor of 5 7 than the present value of 0 0044 to maintain a molten interior and may have to be greater by as much as a factor of 20 to cause melting in an initially frozen body if the thermal conductivity is diminished by inclusion of clathrate hydrates a significant enhancement over the present eccentricity would still be required to initiate melting but it might be possible to maintain a molten interior and allow geologic activity with the present eccentricity removal of eccentricity forcing would result in rapid eccentricity damping freezing and cessation of tectonic activity

the marine boundary layer in the vicinity of an ocean front abstract aircraft observations obtained during the frontal air sea interaction experiment fasinex are used to investigate the structure of the marine atmospheric boundary layer in the vicinity of an ocean front a quasi stationary sea surface temperature sst discontinuity of 2 c was maintained across the frontal zone throughout the duration of the experiment the primary response of the atmosphere to changes in the sst was observed in the surface related turbulence fluxes in the case of warm air flowing over cold water the boundary layer appears to develop an internal boundary layer ibl in response to the sudden change in the sea surface temperature the organized updrafts and downdrafts within this layer collapse with entrainment detrainment processes in these cells dominating the turbulence statistics the ibl grows in response to the wind shear in this layer although the surface shear stress is much smaller on the colder side of the front than on the warm the depth of the ibl and in the abse

dynamics of rifting and modes of extension on icy satellites 1 a simple numerical model of extension in icy satellite shells is developed thinning of the ice weakens the shell promoting further extension if lateral flow in the lower part of the shell is unimportant extension is opposed and wide rifts are generated if lateral flow is rapid localized extension is favored and narrow rifts are produced thick shells or high strain rates favor the development of narrow rifts low strain rates favor wide rifting it is proposed that bands extensional features on europa are narrow rifts while groove lanes on ganymede are wide rifts the existence of wide rifting on ganymede is consistent with previous estimates of a conductive shell thickness at the time of rifting of 4 8 km and a strain rate of 10 15 s 1 strain rates at the time of rifting whether this shell thickness applies to present day europa depends on the age of band formation which is poorly known the difference between rifting behavior on ganymede and europa is due to either higher strain rates or higher shell thicknesses on europa during rifting the mean stresses required to cause the observed rifting are 0 2 mpa for ganymede and 0 3 mpa for europa these values are comparable to estimates derived from flexural features index terms 5475 planetology solid surface planets tectonics 8149 6218 planetology solar system objects jovian satellites 8109 tectonophysics continental tectonics extensional 0905 8160 tectonophysics rheology general keywords europa ganymede extension faulting ice

aircraft observations of boundary layer rolls off the coast of california abstract large scale horizontal rolls can have a significant influence on turbulent transport across the atmospheric boundary layer the formation and maintenance of such rolls is dependent on the thermal and dynamic stability of the boundary layer bl the authors present aircraft observations of boundary layers both with and without roll circulations off the coast of california the contribution of the rolls to the turbulent fluxes of heat moisture and momentum and the variances of the three velocity components are determined for four cases the fractional roll contributions to the u and w variances and the sensible heat and along wind momentum fluxes show a near linear increase with altitude from less than 10 at 30 m to more than 70 at the top of the bl the variance in and crosswind momentum flux are more scattered although the variance shows a slight increase with altitude from about 40 to 60 the latent heat flux also shows a great deal of scatter especially in the lower third of th

the tectonics of ganymede the surface of ganymede the largest icy jovian satellite is composed of two distinct terrain types showing abundant evidence of global scale tectonics there is geological evidence consistent with the formation of younger bright terrain by the emplacement of relatively clean ice into rift zones developed in the more silicate rich dark terrain

forming ganymede s grooves at smaller strain toward a self consistent local and global strain history for ganymede abstract the ubiquity of tectonic features formed in extension and the apparent absence of ones formed in contraction has led to the hypothesis that ganymede has undergone global expansion in its past determining the magnitude of such expansion is challenging however and extrapolation of locally or regionally inferred strains to global scales often results in strain estimates that exceed those based on global constraints here we use numerical simulations of groove terrain formation to develop a strain history for ganymede that is generally consistent at local regional and global scales these simulations reproduce groove like amplitudes wavelengths and average slopes at modest regional extensions 10 15 the modest strains are more consistent with global constraints on ganymede s expansion yet locally we also find that surface strains can be much larger 30 60 in the same simulations consistent with observations of highly extended impact craters thus our simulations satisfy both the smallest scale and largest scale inferences of strain on ganymede the growth rate of the topography is consistent with or exceeds predictions of analytical models and results from the use of a non associated plastic rheology that naturally permits localization of brittle failure plastic strain into linear fault like shear zones these fault like zones are organized into periodically spaced graben like structures with stepped steeply dipping faults as in previous work groove amplitudes and wavelengths depend on both the imposed heat flux and surface temperature but because our brittle strength increases with depth we find for the parameters explored that the growth rate of topography is initially faster for lower heat flows we observe a transition to narrow rifting for higher heat flows and larger strains which is a potential pathway for breakaway margin or band formation

the geology of callisto the geology of callisto is not boring although cratered terrain dominates callisto a key end member of the jovian satellite system a number of more interesting features are apparent cratered terrain is broken into irregular mappable bright and dark subunits that vary in albedo by a factor of 2 and several relatively smooth units are depleted of small craters some of these areas may have been volcanically resurfaced lineaments including parallel and radial sets may be evidence for early global tectonism frost deposition occurs in cold traps and impact scars have formed from tidally disrupted comets geologic evidence suggests that callisto does have a chemically differentiated crust central pit and central dome craters and palimpsests are common the preferred interpretation is that a relatively ice rich material at depths of 5 km or more has been mobilized during impact and exposed as domes or palimpsests the close similarity in crater morphologies and dimensions indicates that the outermost 10 km or so of callisto may be as differentiated as on ganymede the geology of cratered terrain on callisto is simpler than that of cratered terrain on ganymede however orbital evolution and tidal heating may provide the answer to the riddle of why callisto and ganymede are so different malhotra 1991 we should expect a few surprises and begin to answer some fundamental questions when callisto is observed by galileo in late 1996

a common origin for ridge and trough terrain on icy satellites by sluggish lid convection abstract ridge and trough terrain is a common landform on outer solar system icy satellites examples include ganymede s grooved terrain europa s gray bands miranda s coronae and several terrains on enceladus the conditions associated with the formation of each of these terrains are similar heat flows of order tens to a hundred milliwatts per meter squared and deformation rates of order 10 16 10 12 s 1 our prior work shows that the conditions associated with the formation of these terrains on ganymede and the south pole of enceladus are consistent with vigorous solid state ice convection in a shell with a weak surface we show that sluggish lid convection an intermediate regime between the isoviscous and stagnant lid regimes can create the heat flow and deformation rates appropriate for ridge and trough formation on a number of satellites regardless of the ice shell thickness for convection to deform their surfaces the ice shells must have yield stresses similar in magnitude to the daily tidal stresses tidal and convective stresses deform the surface and the spatial pattern of tidal cracking controls the locations of ridge and trough terrain