sand dune patterns on titan controlled by long term climate cycles linear sand dunes on equatorial titan are shaped by winds the morphologies of smaller dunes that have been reoriented with respect to the linear dune crests suggest that winds shift with long term orbitally driven climate cycles on titan

measuring volcanic plume and ash properties from space the remote sensing of volcanic ash plumes from space can provide a warning of an aviation hazard and knowledge on eruption processes and radiative effects in this paper new algorithms are presented to provide volcanic plume properties from measurements by the michelson interferometer for passive atmospheric sounding mipas the advanced along track scanning radiometer aatsr and spinning enhanced visible and infrared imager seviri a challenge of remote sensing is to provide near real time methods to identify and so warn of the presence of volcanic ash to achieve this a singular vector decomposition method has been developed for the mipas instrument on board the environmental satellite envisat this method has been applied to observations of the ash clouds from the eruptions of nabro and the puyehue cordon caulle in 2011 and lead to a more sensitive volcanic signal flag which was capable of tracking changes in the volcanic signal spectra as the plume evolved a second challenge for remote sensing is to identify the ash plume height this is a critical parameter for the initialisation of algorithms that numerically model the evolution and transport of a volcanic plume as mipas is a limb sounder the identification of ash also provides an estimate of height provided the plume is above about 6 km this is complemented by a new algorithm stereo ash plume height retrieval algorithm saphra that identifies plume height using the parallax between images provided by along track scanning radiometer type instruments the algorithm was tested on an image taken at 14 01 gmt on 6 june 2011 of the puyehue cordon caulle eruption plume and gives a height of 11 9 1 4 km which agreed with the value derived from the location of the plume shadow 12 7 1 8 km this plume height was similar to the height observed by mipas 12 1 5 km at 02 56 gmt on 6 june the quantitative use of satellite imagery and the full exploitation of high resolution spectral measurements of ash depends upon knowing the optical properties of the observed ash laboratory measurements of ash from the 1993 eruption of mt aso japan have been used to determine the refractive indices from 1 to 20 m these preliminary measurements have spectral features similar to ash values that have been used to date albeit with slightly different positions and strengths of the absorption bands the refractive indices have been used to retrieve ash properties plume height optical depth and ash effective radius from aatsr and seviri instruments using two versions of oxford ral retrieval of aerosol and cloud orac algorithm for aatsr a new ash cloud type was used in orac for the analysis of the plume from the 2011 eyjafjallajokull eruption for the first 500 km of the plume orac gave values of plume height 2 5 6 5 km optical depth 1 2 5 and effective radius 3 7 m which are in agreement with other observations a weakness of the algorithm occurs when underlying cloud invalidates the

descriptive nomenclature and classification of pyroclastic deposits and fragments recommendations of the iugs subcommission on the systematics of igneous rocks

characterization of tephra deposits with limited exposure the example of the two largest explosive eruptions at nisyros volcano greece explosive eruptions associated with tephra deposits that are only exposed in proximal areas are difficult to characterize in fact the determination of physical parameters such as column height mass eruption rate erupted volume and eruption duration is mainly based on empirical models and is therefore very sensitive to the quality of the field data collected we have applied and compared different modeling approaches for the characterization of the two main tephra deposits the lower pumice lp and upper pumice up of nisyros volcano greece which are exposed only within 5 km of the probable vent isopach and isopleth maps were compiled for two possible vent locations on the north and on the south rim of the caldera and different models were applied to calculate the column height the erupted volume and the mass eruption rate we found a column height of about 15 km above sea level and a mass eruption rate of about 2 107 kg s for both eruptions regardless of the vent location considered in contrast the associated wind velocity for both up and lp varied between 0 and 20 m s for the north and south vent respectively the derived erupted volume for the south vent considered as the best vent location ranges between 2 and 27 108 m3 for the lp and between 1 and 5 108 m3 for the up based on the application of four different methods integration of exponential fit based on one isopach line integration of exponential and power law fit based on two isopach lines and an inversion technique combined with an advection diffusion model the eruption that produced the up could be classified as subplinian discrepancies associated with different vent locations are smaller than the discrepancies associated with the use of different models for the determination of erupted mass plume height and mass eruption rate proximal outcrops are predominantly coarse grained with 90 wt of the clasts ranging between 6 and 0 the associated total grainsize distribution is considered to result from a combination of turbulent fallout from both the plume margins and the umbrella region and as a result it is fines depleted given that primary deposit thickness observed on nisyros for both lp and up is between 1 and 8 m if an event of similar scale were to happen again it would have a significant impact on the entire island with major damage to infrastructure agriculture and tourism neighboring islands and the continent could also be significantly affected

the correction for sediment loading on the seafloor available measurements of sediment velocity and density indicate that a factor of 600 m s 1 of two way sediment reflection time will correct seafloor depth to yield basement depth in the absence of sediment loading this simple linear relation is derived from the results of six deep drill holes in abyssal sediments of the north and south atlantic oceans the relation predicts the sediment correction with an accuracy of about 50 m regardless of the lithology sampled down to a depth of 1 5 s of reflection time the cost wells on the u s continental shelf and empirical relations among velocity density porosity and depth provide estimates of the deeper behavior of abyssal sediments and suggest that the 600 m s 1 factor continues to provide a satisfactory sediment correction to a depth of 3 s

titan s surface composition and atmospheric transmission with solar occultation measurements by cassini vims abstract solar occultation measurements by the cassini visual and infrared mapping spectrometer vims reveal the near infrared transmission of titan s atmosphere down to an altitude of 40 km by combining these observations with vims reflectance measurements of titan s surface and knowledge of haze and gas opacity profiles from the huygens probe we constrain a simple model for the transfer of radiation in titan s atmosphere in order to derive surface reflectance in the methane windows used for compositional analysis the advantages of this model are twofold 1 it is accurate enough to yield useful results yet simple enough to be implemented in just a few lines of code and 2 the model parameters are directly constrained by the vims occultation and on planet measurements we focus on the 2 0 2 7 2 8 and 5 0 m windows where haze opacity is minimized and diagnostic vibrational bands exist for water ice and other candidate surface species a particularly important result is the strong atmospheric attenuation at 2 7 m compared to 2 8 m resulting in a reversal of apparent spectral slope in a compositionally diagnostic wavelength range these results show that titan s surface reflectance is much bluer and more closely matched by water ice than the uncorrected spectra would indicate although the majority of titan s surface has a spectrum consistent with mixtures either intimate or areal of water ice and haze particles precipitated from the atmosphere compositions of geologic units can be accurately modeled as mixtures ranging from predominantly water ice sinlap crater ejecta and margins of dark equatorial terrain to predominantly organic rich tui regio and hotei regio with particles in the size range 10 20 m in distinguishing between hypothesized formation mechanisms for tui and hotei regio their organic rich composition favors a process that concentrates precipitated haze particles such as playa lake evaporite deposition barnes j w bow j schwartz j brown r h soderblom j m hayes a g vixie g le mouelic s rodriguez s sotin c jaumann r stephan k soderblom l a clark r n buratti b j baines k h nicholson p d 2011 icarus 216 136 140 in other places kilometer scale exposures of nearly pure water ice bedrock on titan s surface indicate relatively locally rapid erosion compared to rates of accumulation of solid hydrocarbons precipitated from the atmosphere somewhat surprisingly titan s vast equatorial dune fields appear slightly enriched in water ice compared to the surrounding bright regions but the spectrum of the dune material itself may nonetheless be consistent with a predominantly organic haze derived composition

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

latitudinal and altitudinal controls of titan s dune field morphometry dune fields dominate 13 of titan s surface and represent an important sink of carbon in the methane cycle herein we discuss correlations in dune morphometry with altitude and latitude these correlations which have important implications in terms of geological processes and climate on titan are investigated through the microwave electromagnetic signatures of dune fields using cassini radar and radiometry observations the backscatter and emissivity from titan s dune terrains are primarily controlled by the amount of interdune area within the radar footprint and are also expected to vary with the degree of the interdunal sand cover using sar derived topography we find that titan s main dune fields shangri la fensal belet and aztlan tend to occupy the lowest elevation areas in equatorial regions occurring at mean elevations between 400 and 0 m relative to the geoid in elevated dune terrains we show a definite trend towards a smaller dune to interdune ratio and possibly a thinner sand cover in the interdune areas a similar correlation is observed with latitude suggesting that the quantity of windblown sand in the dune fields tends to decrease as one moves farther north the altitudinal trend among titan s sand seas is consistent with the idea that sediment source zones most probably occur in lowlands which would reduce the sand supply toward elevated regions the latitudinal preference could result from a gradual increase in dampness with latitude due to the asymmetric seasonal forcing associated with titan s current orbital configuration unless it is indicative of a latitudinal preference in the sand source distribution or wind transport capacity

cassini sar radiometry scatterometry and altimetry observations of titan s dune fields large expanses of linear dunes cover titan s equatorial regions as the cassini mission continues more dune fields are becoming unveiled and examined by the microwave radar in all its modes of operation sar radiometry scatterometry altimetry and with an increasing variety of observational geometries in this paper we report on cassini s radar instrument observations of the dune fields mapped through may 2009 and present our key findings in terms of titan s geology and climate we estimate that dune fields cover 12 5 of titan s surface which corresponds to an area of 10 million km 2 roughly the area of the united states if dune sand sized particles are mainly composed of solid organics as suggested by vims observations cassini visual and infrared mapping spectrometer and atmospheric modeling and supported by radiometry data dune fields are the largest known organic reservoir on titan dune regions are with the exception of the polar lakes and seas the least reflective and most emissive features on this moon interestingly we also find a latitudinal dependence in the dune field microwave properties up to a latitude of 11 dune fields tend to become less emissive and brighter as one moves northward above 11 this trend is reversed the microwave signatures of the dune regions are thought to be primarily controlled by the interdune proportion relative to that of the dune roughness and degree of sand cover in agreement with radiometry and scatterometry observations sar images suggest that the fraction of interdunes increases northward up to a latitude of 14 in general scattering from the subsurface volume scattering and surface scattering from buried interfaces makes interdunal regions brighter than the dunes the observed latitudinal trend may therefore also be partially caused by a gradual thinning of the interdunal sand cover or surrounding sand sheets to the north thus allowing wave penetration in the underlying substrate altimetry measurements over dunes have highlighted a region located in the fensal dune field 5 latitude where the icy bedrock of titan is likely exposed within smooth interdune areas the hemispherical assymetry of dune field properties may point to a general reduction in the availability of sediments and or an increase in the ground humidity toward the north which could be related to titan s asymmetric seasonal polar insolation alternatively it may indicate that either the wind pattern or the topography is less favorable for dune formation in titan s northern tropics

petrographical and petrophysical properties of sandstones statistical analysis as an approach to predict material behaviour and construction suitability most studies dealing with material properties of sandstones are based on a small data set the present study utilizes petrographical and petrophysical data from 22 selected sandstones and 300 sandstones from the literature to estimate predict the material and weathering behaviour of characteristic sandstones composition and fabric properties were determined from detailed thin section analyses statistical methods applied consist of data distributions with whisker plots and linear regression with confidence regions for the petrophysical and weathering properties to identify similarities between individual sandstones and to define groups of specific sandstone types principal component and cluster analyses were applied the results confirm an interaction between the composition depositional environment stratigraphic association and diagenesis which leads to a particular material behaviour of sandstones three different types of pore radii distributions are observed whereby each is derived from different pore space modifications during diagenesis and is associated with specific sandstone types 1 bimodal with a maximum in capillary and micropores 2 unimodal unequal with a maximum in smaller capillary pores and 3 unimodal equable with a maximum in larger capillary pores each distribution shows specific dependencies to water absorption salt loading and hygric dilatation the strength porosity relationship shows dependence on the content of unstable lithic fragments grain contact and type of pore radii distribution cementation and degree of alteration sandstones showing a maximum of capillary pores and micropores bimodal exhibit a distinct hygric dilatation and low salt resistance these sandstones are highly immature sublitharenites litharenites characterized by altered unstable rock fragments which show pointed elongated grain contacts and some pseudomatrix quartz arenites and sublitharenites litharenites which are strongly compacted and cemented show unimodal unequal pore radii distributions low porosity high strength and a high salt resistance the presence of swellable clay minerals in sublitharenites litharenites leads to a medium to high hygric dilatation whereas quartz arenites show little hygric dilatation sandstones with unimodal equal pore radii distribution mostly belong to weakly compacted and cemented mature quartz arenites these are characterized by high water absorption and high porosity low to medium strength and a low salt resistance the data compiled in this study are used to create a sandstone quality catalogue since material properties are dependent on many different parameters of influence the transition between different lithotypes is fluent

controls on acoustic properties of upper jurassic siliciclastic rocks boulonnais northern france more than 200 plugs from outcrop and a nearby borehole in a carbonaceous siliciclastic interval of late jurassic kimmeridgian to tithonian age were quantitatively analyzed for texture mineralogy and acoustic properties our primary goal was to study the effect of clay fraction smaller than 8 m silt sand fraction larger than 8 m and carbonate on the acoustic properties the quantitative nature and volume of the data made it possible to observe four dimensional relationships in contoured ternary diagrams primary control on the acoustic properties is exerted by porosity but the trend of this relationship significantly deviates from popular velocity transforms the contribution of clay silt sand and carbonate particular material and cement explains the remaining variation in acoustic properties although no clear linear thresholds are defined a general trend is that clay and carbonate content have opposite and overlapping effects on acoustic properties the influence of clay content progressively increases with decreasing carbonate content and visa versa with increasing carbonate content the variation of acoustic velocity at a given porosity value increases to nearly twice of that in the clay dominated sediment traditional classification boundaries are present but strongly overprinted by this interplay between clay and carbonate this study may have important implications for porosity and lithofacies prediction from wireline logs in similar mixtures of sediment in addition the quantitative character of the textural and mineralogical data may provide a direct link from acoustic properties to the primary depositional system and sequence stratigraphy

high resolution ultrasonic measurements as proxies to resolve clastic reservoir heterogeneity in a salt cemented gas reservoir petrophysical properties and their heterogeneity within sandstone bodies are key parameters in the evaluation of hydrocarbon and geothermal reservoirs however common tools applied to constrain the porosity distribution pattern in borehole cores are commonly time consuming and destructive or suffer from a resolution limited to the meter to decimeter scale we examine the applicability of nondestructive high resolution sonic hrs logging of well core sections in the ultrasonic frequency range as a method providing porosity proxy data at the centimeter scale in a clastic sedimentary sequence the middle solling sandstone member a gas bearing reservoir offshore from the netherlands is used as a test sample it consists almost entirely of clean cross bedded to massive eolian dune and dry sand flat deposits that are salt plugged to variable degrees plots of hrs logging data versus core plug porosity values show a positive linear relationship that develops the highest coefficient of determination r2 0 86 in structureless eolian dune sands most probably caused by the lack of bedding related anisotropies there once calibrated for a particular facies type this correlation enables the calculation of porosity proxy data from sonic transit time values acquired at centimetric steps high resolution sonic logging thus contributes a reliable and time efficient highly spatially resolving quantification of reservoir heterogeneities at centimeter scale and turns out to be a suitable tool for the nondestructive in situ detection of high porosity zones in otherwise uniform sandstone successions moreover plots of closely spaced hrs logging derived porosity proxy data significantly improve interpolation between single wider spaced core plug porosity data points

modeling microwave backscatter and thermal emission from linear dune fields application to titan we present an electromagnetic model that relates the microwave backscatter and thermal emission from linear dune fields to their compositional physical roughness subsurface porosity heterogeneity and geometrical slope orientation properties this model shows the value of exploring these highly directional and geometrical features in light of both their backscattering cross section and emissivity compared to cassini concurrent radar and radiometry data acquired from october 2004 to june 2011 over titan s dune fields it provides clues to understand variations among dune regions on the largest saturn s moon in particular it brings a formal support to the idea first advanced in le gall et al le gall a janssen m a wye l c hayes a g radebaugh j savage c zebker h lorenz r d lunine j i kirk r l lopes r m c wall s callahan p stofan e r farr t and the cassini radar team 2011 icarus 213 608 624 that the size of the interdune valleys relative to that of the dunes varies across titan as well as the diffuse scattering properties of these interdune areas due to different thickness of sand cover i e bedrock contribution or degree of compaction heterogeneity of the sand cover the fensal and belet dune fields in particular are quite different in terms of these properties the comparison between the model and cassini data also reveals the potential presence of structures possibly small superposed dunes oriented perpendicular to the dune crests in the aztlan region

in situ and space based observations of the kelud volcanic plume the persistence of ash in the lower stratosphere volcanic eruptions are important causes of natural variability in the climate system at all time scales assessments of the climate impact of volcanic eruptions by climate models almost universally assume that sulfate aerosol is the only radiatively active volcanic material we report satellite observations from the cloud aerosol lidar with orthogonal polarization caliop on board the cloud aerosol lidar and infrared pathfinder satellite observations calipso satellite after the eruption of mount kelud indonesia on 13 february 2014 of volcanic materials in the lower stratosphere using these observations along with in situ measurements with the compact optical backscatter aerosol detector cobald backscatter sondes and optical particle counters opcs made during a balloon field campaign in northern australia we find that fine ash particles with a radius below 0 3 m likely represented between 20 and 28 of the total volcanic cloud aerosol optical depth 3 months after the eruption a separation of 1 5 2 km between the ash and sulfate plumes is observed in the caliop extinction profiles as well as in the aerosol number concentration measurements of the opc after 3 months the settling velocity of fine ash with a radius of 0 3 m in the tropical lower stratosphere is reduced by 50 due to the upward motion of the brewer dobson circulation resulting a doubling of its lifetime three months after the eruption we find a mean tropical clear sky radiative forcing at the top of the atmosphere from the kelud plume near 0 08 w m2 after including the presence of ash a value 20 higher than if sulfate alone is considered thus surface cooling following volcanic eruptions could be affected by the persistence of ash and should be considered in climate simulations

effects of diagenesis and clays on compressional velocities in rocks experimental results at ultrasonic frequencies in brine or water saturated samples cut perpendicular to bedding demonstrate that compressional velocities vary linearly with porosity and volume fraction clay in detrital silicate rocks characterized by pores with low aspect ratios p wave velocity is more sensitive to porosity than clay content obeying the empirically derived expression vp 2 4c 8 6 5 8 at 800 bars confining pressure and 400 bars pore pressure where the units of vp are kilometers per second is the volume fraction pores and c is the volume fraction clay deviations from this equation are less than 2 with the exception of the high pore aspect ratio st peter sandstone which has a compressional velocity that is 17 higher than the predicted value the equation is insensitive to the chemical compostion of the dominant clay mineral and apparently insensitive to the location of the clay grains with respect to the mineral framework e g in free pore space or in contact zones between mineral grains of lower compressibilities

evidence of titan s climate history from evaporite distribution abstract water ice poor 5 m bright material on saturn s moon titan has previously been geomorphologically identified as evaporitic here we present a global distribution of the occurrences of the 5 m bright spectral unit identified with cassini s visual infrared mapping spectrometer vims and examined with radar when possible we explore the possibility that each of these occurrences are evaporite deposits the 5 m bright material covers 1 of titan s surface and is not limited to the poles the only regions with extensive long lived surface liquid we find the greatest areal concentration to be in the equatorial basins tui regio and hotei regio our interpretations based on the correlation between 5 m bright material and lakebeds imply that there was enough liquid present at some time to create the observed 5 m bright material we address the climate implications surrounding a lack of evaporitic material at the south polar basins if the south pole basins were filled at some point in the past then where is the evaporite

reference data set of volcanic ash physicochemical and optical properties uncertainty in the physicochemical and optical properties of volcanic ash particles creates errors in the detection and modeling of volcanic ash clouds and in quantification of their potential impacts in this study we provide a dataset that describes the physicochemical and optical properties of a representative selection of volcanic ash samples from nine different volcanic eruptions covering a wide range of silica contents 50 80 wt sio2 we measured and calculated parameters describing the physical size distribution complex shape and dense rock equivalent mass density chemical bulk and surface composition and optical complex refractive index from ultra violet to near infrared wavelengths properties of the volcanic ash and classified the samples according to their sio2 and total alkali contents into the common igneous rock types basalt to rhyolite we found that the mass density ranges between 2 49 and 2 98 g cm3 for rhyolitic to basaltic ash types and that the particle shape varies with changing particle size d 100 m the complex refractive indices in the wavelength range between 300 nm and 1500 nm depends systematically on the composition of the samples the real part values vary from n 1 38 to 1 66 depending on ash type and wavelength and the imaginary part values from k 0 00027 to 0 00268 we place our results into the context of existing data and thus provide a comprehensive dataset that can be used for future and historic eruptions when only basic information about the magma type producing the ash is known

temporal variations of titan s surface with cassini vims abstract we analyze cassini vims data of several areas on titan s surface looking for variations with time three of these locations are near the equator 10 30 s namely hotei regio tui regio and sotra patera in some cases changes in brightness and or in appearance were reported therein we also investigate a portion of the undifferentiated plains areas relatively homogeneous and dark in radar observations located near 20 25 n this is a follow up on a previous paper in which we had inferred surface albedos for some distinct regions of interest rois identified within the hotei tui and sotra areas through a principal component analysis pca and radiative transfer rt modeling solomonidou 2014 j geophys res 119 1729 1747 we apply the same methods here to a larger dataset looking for variations of the surface albedo with time and using the huygens landing site as the ground truth for calibration purposes as expected the undifferentiated plains remain unchanged from january 2010 to june 2012 our analysis of hotei regio data from march 2005 to march 2009 also does not show any significant surface albedo variations within uncertainties we note however that our rt retrievals are not optimal in this case because of the use of a plane parallel code and the unfavorable geometry of the associated datasets conversely tui regio and sotra patera show surface albedo fluctuations with time with pronounced trends for darkening and for brightening respectively the tui regio spectrum exhibits a surface albedo decrease from march 2005 to february 2009 at 0 94 1 08 2 03 and 5 m wavelengths while the spectrum shape remains the same over that time on the contrary the sotra patera area became at least two times brighter within a year april 2005 february 2006 at 1 58 m 2 03 m and 5 m we also retrieved surface albedo spectra for three reference regions surrounding hotei tui and sotra and for three additional regions we use as test cases that correspond to dune fields during the time periods explored here we find that as expected and contrary to tui regio and sotra patera the test cases did not show any significant changes in surface albedo we therefore suggest that temporal variations of surface albedo exist for some areas on titan but that their origin may differ from one region to the other they could be due to diverse past and or ongoing formation processes endogenic and or exogenic possibly cryovolcanic as discussed here

implications of dune pattern analysis for titan s surface history abstract analysis of large scale morphological parameters can reveal the reaction of dunes to changes in atmospheric and sedimentary conditions over 7000 dune width and 7000 dune spacing measurements were obtained for linear dunes in regions across saturn s moon titan from images t21 t23 t28 t44 and t48 collected by the synthetic aperture radar sar aboard the cassini spacecraft in order to reconstruct the aeolian surface history of titan dunes in the five study areas are all linear in form with a mean width of 1 3 km and mean crest spacing of 2 7 km similar to dunes in the african saharan and namib deserts on earth at the resolution of cassini sar the dunes have the morphology of large linear dunes and they lack evidence for features of compound or complex dunes the large size spacing and uniform morphology are all indicators that titan s dunes are mature features in that they have grown toward a steady state for a long period of time dune width decreases to the north perhaps from increased sediment stabilization caused by a net transport of moisture from south to north or from increased maturity in dunes to the south cumulative probability plots of dune parameters measured at different locations across titan indicate there is a single population of intermediate to large sized dunes on titan this suggests that unlike analogous dunes in the namib and agneitir sand seas dune forming conditions that generated the current set of dunes were stable and active long enough to erase any evidence of past conditions

global scale surface spectral variations on titan seen from cassini vims we present global scale maps of titan from the visual and infrared mapping spectrometer vims instrument on cassini we map at 64 near infrared wavelengths simultaneously covering the atmospheric windows at 0 94 1 08 1 28 1 6 2 0 2 8 and 5 m with a typical resolution of 50 km pixel or a typical total integration time of 1 s our maps have five to ten times the resolution of ground based maps better spectral resolution across most windows coverage in multiple atmospheric windows and represent the first spatially resolved maps of titan at 5 m the vims maps provide context and surface spectral information in support of other cassini instruments we note a strong latitudinal dependence in the spectral character of titan s surface and partition the surface into 9 spectral units that we describe in terms of spectral and spatial characteristics

tectonic signatures in centimeter scale velocity porosity relationships of costa rica convergent margin sediments 1 the costa rica convergent margin investigated during ocean drilling program leg 170 offers a unique opportunity to compare the tectonic effects of rapid subduction on incoming oceanic sediments to their laterally equivalent underthrust counterparts and to terrestrially derived wedge materials elevated pressure laboratory measurements of ultrasonic compressional and shear wave velocity and porosity are used to examine the importance of tectonic lithologic and diagenetic controls on physical and elastic properties of sediments in these three key tectonic domains depositional and stress path histories of the three domains for example can be distinguished by 1 trends of in situ velocity porosity and derived measurements correspondence and 2 the mechanical response of representative materials to isotropic consolidation a compressional wave velocity porosity model critical for the application of seismic imaging to margin wide physical property and mass balance estimates is developed from the laboratory measurements and shown to be consistent with the information derived from lwd bulk density and migrated seismic reflection data this consistency of the velocity porosity model over the large range of both frequency and length measurement scales is a key result supporting the assertion that core and borehole physical property measurements can be extrapolated to larger domains finally dewatering and overpressure effects critical factors in subduction zone and fault process dynamics and increasingly common multiphase converted wave imaging targets are discussed in terms of laboratory estimated in situ compressional and shear wave velocity relationships

measurements of the complex refractive index of volcanic ash at 450 546 7 and 650 nm the detection and quantification of volcanic ash is extremely important to the aviation industry civil defense organizations and those in peril from volcanic ashfall to exploit the remote sensing techniques that are used to monitor a volcanic cloud and return information on its properties the effective complex refractive index of the volcanic ash is required this paper presents the complex refractive index determined in the laboratory at 450 0 nm 546 7 nm and 650 0 nm for volcanic ash samples from eruptions of aso japan grimsvotn iceland chaiten chile etna italy eyjafjallajokull iceland tongariro new zealand askja iceland nisyros greece okmok alaska augustine alaska and spurr alaska the becke line method was used to measure the real part of the refractive index with an accuracy of 0 01 the values measured differed between eruptions and were in the range 1 51 1 63 at 450 0 nm 1 50 1 61 at 546 7 nm and 1 50 1 59 at 650 0 nm a novel method is introduced to derive the imaginary part of the refractive index from the attenuation of light by ash the method has a precision in the range 10 3 10 4 the values for the ash imaginary refractive index ranged 0 22 1 70 10 3 at 450 0 nm 0 16 1 93 10 3 at 546 7 nm and 0 15 2 08 10 3 at 650 0 nm the accuracy of becke and attenuation methods was assessed by measuring the complex refractive index of hoya neutral density glass and found to have an accuracy of 0 01 and 2 10 5 for the real and imaginary parts of the refractive index respectively

the effect of micrite content on the acoustic velocity of carbonate rocks abstractwe have demonstrated the effect of micrite content on the acoustic properties of well controlled microstructures that are created in the laboratory to closely mimic those of carbonate rocks in particular we examined the effect of micrite content on the acoustic velocity sensitivity of velocity to pressure and changes in velocity resulting from dissolution upon saturation with a reactive fluid we followed dunham s classification and fabricated the samples by mixing coarse sand sized and very fine micrite sized calcite grains in different ratios and then cold compressing the mixture the acoustic velocities were measured under benchtop conditions and as functions of confining pressure before and after the injection of a co2 aqueous solution the benchtop measurements indicated that the addition of micrite made the frame of the carbonate samples stiffer because the sensitivity of velocity to pressure decreases as the content of micrite increases we hypothesized a stiffer pore structure in

rock physics based estimation of critical clay volume fraction and its effect on seismic velocity and petrophysical properties abstractknowledge of the clay content in clastic reservoirs is important for predicting reservoir quality and properties we used a microgeometrical model for shaly sand and sandy shale to define the critical clay volume fraction and explain the dependence of the bulk modulus on clay content we found that the concept of the pore aspect ratio relating to the critical clay volume fraction was important to interpret the elastic behavior of shaly sandstone an abrupt decrease in pore aspect ratio from about 0 23 to about 0 04 was observed where the clay volume fraction was greater than the critical value of 32 for the studied data set at the critical clay volume fraction of 32 an increase in pore compressibility also occurred from about 0 6 to about 11 25 gpa 1 results revealed that the microgeometrical model compared to other models can better explain the existence of highly scattered compressional velocity porosity crossplots when the clay content is close to the critical amount we discovered that t

parameters controlling sonic velocities in a mixed carbonate siliciclastics permian shelf margin upper san andres formation last chance canyon new mexico we have measured the acoustic properties and mineralogic composition of 48 rock specimens from mixed carbonate siliciclastic outcrops of the permian upper san andres formation in last chance canyon new mexico the goals were 1 identify and model the parameters controlling the sonic velocities 2 assess the influence of postburial diagenesis on the acoustic velocities the variation in sonic velocity in the 0 to 25 porosity range is primarily controlled by porosity and secondly by the ratio of carbonate siliciclastic material linear multivariate fitting resulted in a velocity porosity carbonate content transform that accurately predicts sonic velocity at different effective stresses the slope of the velocity porosity transform steepens with increasing carbonate content which may be explained by the higher velocity of carbonate minerals another reason may be the property of carbonate minerals to form more perfect intercrystalline boundaries that improve the transmission properties of acoustic waves and are less sensitive to changes in effective stress the velocity ratio vp vs is an excellent tool to discriminate between predominantly calcitic lithologies ratio between 1 8 and 1 95 and predominantly dolomitic and quartz rich lithologies ratio between 1 65 and 1 8 gardner s experimental curve overestimates and the velocity porosity transforms by wyllie and raymer underestimate the observed sonic velocities probably because they do not account for variations in texture carbonate mineralogy and pore geometry petrographic observations show that postburial diagenesis is minor and does not seem to significantly affect porosity therefore the outcrop data set can be regarded as a proxy for the subsurface analog these findings underline the significantly more complex acoustic behavior in mixed carbonate siliciclastic sedimentary rocks than in pure siliciclastics where mineralogic composition explains most of the observed relationships between porosity and sonic velocity

velocity porosity clay content systematics of poorly consolidated sandstones compressional velocities have been measured as a function of confining pressure for 14 west delta block louisiana sandstone cores the dry velocity data for these poorly consolidated sandstones at 10 mpa confining pressure plot on a linear velocity density trend with well consolidated sandstones but not loose sands the dry velocity data also show linear trends of decreasing velocity with increasing porosity along contours of constant clay content similar to those obtained at 40 mpa by tosaya and nur 1982 for saturated sandstones the spacing between clay contours indicates that a large portion of the velocity variation with clay content is due to microporosity which is not included in point counting within the clays the slope of the velocity porosity trends indicates that cementation increases with decreasing porosity

environmental effects of ashfall in argentina from the 2008 chaiten volcanic eruption analyses of air water and vegetation samples collected in june 2008 offer new insights into the environmental effects of the may 2008 chaiten eruption on argentina which was subject to significant ashfall between 42 s and 46 s results from air filtration in the ash affected town of esquel with samples analysed by gravimetry and scanning electron microscopy show the total mass of resuspended ash in the air is well correlated with traffic activity however this variation is primarily related to varying amounts of the largest particles with little variation in the amounts of fine ash particles i e d results from water and vegetation sampling with samples analysed by inductively coupled plasma mass spectrometry and ion chromatography indicate that ashfall resulted in significant compositional changes in ephemeral lakes and coiron grass festuca pallescens for b cd zn tl cu and ni there are strong linear correlations between concentrations and ash thickness where 2 mm in both datasets these results suggest that the eruption of chaiten led to significant changes in the concentrations of trace volatile elements within the environment analysis of vegetation samples collected in january 2009 indicates that the elevated element concentrations in coiron grass persisted for 8 months these results offer insights into the environmental fate of volatile trace elements emitted during volcanic eruptions

laboratory measurements of the acoustic and transport properties of carbonate rocks and their link with the amount of microcrystalline matrix laboratory data and computer tomography ct scan image analysis of carbonate rocks were combined demonstrating a quantitative link between acoustic and transport properties the fraction of microcrystalline calcite micrite in the matrix and the grain to micrite matrix ratio samples from the monte acuto formation gargano italy a transgressive system tract tst whose microstructure ranges from basal pelagic mudstones to coarse calciturbidites were analyzed results indicate that high micrite rocks with low grain to micrite matrix ratios typical of low energy depositional settings are relatively stiffer and more impermeable in contrast lower amounts of micrite due to high energy depositional settings or its removal from intergranular macropores by progressive leaching of the matrix leads to high grain to micrite matrix ratios this process will increase porosity and reduce rock stiffness both of which reduce velocity decreasing micrite content correlates well with increasing macroporosity

cassini observations of flow like features in western tui regio titan 1 a large 3 104 km2 lobate 5 m bright region seen by cassini on titan s leading equatorial region is best explained as a flow field we discuss observations from the visual and infrared mapping spectrometer and imaging science subsystem of the feature and present a map of the field we establish relative ages of flow features and discuss possible formation mechanisms and the implications of this finding for the evolution of titan s surface

dunes on titan observed by cassini radar thousands of longitudinal dunes have recently been discovered by the titan radar mapper on the surface of titan these are found mainly within 30 of the equator in optically near infrared and radar dark regions indicating a strong proportion of organics and cover well over 5 of titan s surface their longitudinal duneform interactions with topography and correlation with other aeolian forms indicate a single dominant wind direction aligned with the dune axis plus lesser off axis or seasonally alternating winds global compilations of dune orientations reveal the mean wind direction is dominantly eastwards with regional and local variations where winds are diverted around topographically high features such as mountain blocks or broad landforms global winds may carry sediments from high latitude regions to equatorial regions where relatively drier conditions prevail and the particles are reworked into dunes perhaps on timescales of thousands to tens of thousands of years on titan adequate sediment supply sufficient wind and the absence of sediment carriage and trapping by fluids are the dominant factors in the presence of dunes

hydraulic and acoustic properties as a function of porosity in fontainebleau sandstone laboratory measurements have been made of the permeability k free porosity l compressional velocities vp or ve and compressional attenuations qp or qe in fontainebleau sandstone over a continuous range of porosities from 3 to 28 this large variation was achieved without any composition change fontainebleau sandstone is made of fine quartz grains with regular grain size 250 m permeability was measured with a falling head permeameter velocities and attenuations were obtained either through an ultrasonic experiment for frequencies around 500 khz or through a resonant bar technique experiment for frequencies around 5 khz and in both cases with varying water saturation the results show an excellent correlation between permeability k and total porosity for all our samples for low porosities 3 to 9 permeability in millidarcies is 2 75 10 5 7 33 while for high porosities 9 to 28 permeability k in millidarcies is given by 0 303 3 05 the correlation is also excellent between free porosity and total porosity on the other hand the correlation between acoustic properties and total porosity is not as clear as for hydraulic properties whatever the frequency 500 khz or 5 khz or the water saturation on the average velocity decreases and attenuation roughly increases with increasing total porosity velocity and attenuation values are related to the variation of grain contact structure and two samples with the same porosity and permeability may exhibit different velocities and attenuations the clear correlation between hydraulic properties and porosity is related to constant grain size while the lack of correlation for acoustic properties emphasizes the importance of the microstructure

compositional and spatial variations in titan dune and interdune regions from cassini vims and radar dunes cover about 15 of titan s visible surface and represent one of the largest reservoirs of hydrocarbon solids on titan and herein we use data from the cassini spacecraft to derive constraints on the compositional and regional variability of titan s dune and interdune regions by combining spectral information from the visual and infrared mapping spectrometer vims and spatial information from synthetic aperture radar sar data using the combined datasets we extract pure infrared spectra of dune and interdune regions by extrapolating linear correlations between vims reflectance and dune area fraction calculated in each vims footprint from sar images we applied the same method using the cassini radar radiometer dataset to extract the microwave surface emissivity of the dune and interdune regions globally the dune spectra show little variation but we find that the interdune spectra exhibit several different behaviors similarly we extract from passive radiometry a mean dune emissivity of 0 98 0 01 while interdune emissivity varies from 0 86 to 0 98 we find that the interdune regions are often spectrally similar to other titan terrain units namely caladan planitia the adiri mountains and sinlap crater while the dunes are spectrally distinct from all terrain units around sinlap crater the interdune regions correspond to the dark blue vims unit the dunes could be forming on top of the ejecta or the material corresponding to the blue unit could be depositing preferentially in the interdunes areas there was one region in the belet sand sea where we were unable to extract the dune and interdune spectra and emissivities in spite of high quality data which we interpret to result from a thick sand cover in the interdune regions implying inactive or saturated dune fields however the fact that we were able to extract distinct dune and interdune spectra and emissivities in most of titan s dune fields makes a strong case for sand free interdune areas of varying composition in these regions on depths from micrometers to decimeters this would imply that the sand dunes have been active recently on geologic timescales

empirical estimation of viscoelastic seismic parameters from petrophysical properties of sandstone viscoelastic seismic parameters are expressions of underlying petrophysical properties theoretical and empirically derived petrophysical seismic relations exist but each is limited in the number and the range of values of the variables used to provide a more comprehensive empirical model we combined lab measurements from 18 published data sets and well log data for sandstone samples and determined least squares coefficients across them all the dependent variables are the seismic parameters of bulk density compressional and shear wave velocities vp and vs and compressional and shear wave quality factors qp and qs the independent variables are effective pressure porosity clay content water saturation permeability and frequency as the derived expressions are empirical correlations no causal relations should be inferred prediction of is based on volumetric mixing of the constituents for vp and vs predictions separate sets of coefficients are fitted for three water saturation condi

titan s surface at 2 18 cm wavelength imaged by the cassini radar radiometer results and interpretations through the first ten years of observation abstract a comprehensive calibration and mapping of the thermal microwave emission from titan s surface is reported based on radiometric data obtained at 2 18 cm wavelength by the passive radiometer included in the cassini radar instrument compared to previous work the present results incorporate the much larger data set obtained in the approximately ten years following saturn orbit insertion brightness temperature data including polarization were accumulated by segments in titan passes from ta october 2004 through t98 february 2014 the observational segments were analyzed to produce a mosaic of effective dielectric constant based on the measurement of thermal polarization covering 76 of the surface and brightness temperature at normal incidence covering titan s entire surface as part of the mosaicking process we also solved for the seasonal variation of physical temperature with latitude which we found to be smaller by a factor of 0 87 0 05 in relative amplitude compared to that reported in the thermal infrared by cassini s composite infrared spectrometer cirs we used the equatorial temperature obtained by the huygens probe and the seasonal dependence with latitude from cirs to convert the brightness mosaic to absolute emissivity from which we could infer global thermophysical properties of the surface in combination with the dielectric mosaic we see strong evidence for subsurface volume scattering as a dominant cause of the radar reflectivity in bright regions and elsewhere a surface composition consistent with the slow deposition and processing of organic compounds from the atmosphere the presence of water ice in the near subsurface is strongly indicated by the high degree of volume scattering observed in radar bright regions e g hummocky mountainous terrains constituting 10 of titan s surface a thermal analysis allowed us to infer a mean 2 18 cm emission depth in the range 40 100 cm for the dominant radar dark terrains the remainder of titan s surface at all latitudes of titan consistent with the deposition and possible processing and redistribution of tholin like atmospheric photochemical products

fallout and distribution of volcanic ash over argentina following the may 2008 explosive eruption of chaiten chile 1 the major explosive eruption of chaiten volcano chile in may 2008 provided a rare opportunity to track the long range dispersal and deposition of fine volcanic ash the eruption followed 10 000 years of quiescence was the largest explosive eruption globally since hudson chile in 1991 and was the first explosive rhyolitic eruption since novarupta alaska in 1912 field examination of distal ashfall indicates that 1 6 1011 kg of ash dense rock equivalent volume of 0 07 km3 was deposited over 2 105 km2 of argentina during the first week of eruption the minimum eruption magnitude estimated from the mass of the tephra deposit is 4 2 several discrete ashfall units are identifiable from their distribution and grain size characteristics with more energetic phases showing a bimodal size distribution and evidence of cloud aggregation processes ash chemistry was uniform throughout the early stages of eruption and is consistent with magma storage prior to eruption at depths of 3 6 km deposition of ash over a continental region allowed the tracking of eruption development and demonstrates the potential complexity of tephra dispersal from a single eruption which in this case comprised several phases over a week long period of intense activity

a 3 km atmospheric boundary layer on titan indicated by dune spacing and huygens data abstract some 20 of titan s surface is covered in large linear dunes that resemble in morphology size and spacing 1 3 km those seen on earth although gravity atmospheric density and sand composition are very different on these two worlds this coincident size scale suggests that the controlling parameter limiting the growth of giant dunes namely the boundary layer thickness andreotti et al 2009 nature 457 1120 1123 is similar we show that a 3 km boundary layer thickness is supported by huygens descent data and is consistent with results from global circulation models taking the distinctive thermal inertia and albedo of the dune sands into account while the boundary layer thickness on earth controlling dunes can vary by an order of magnitude depending on the proximity of oceans which have very different thermal properties from dry land the relative invariance of dune spacing on titan is consistent with relatively uniform thermal properties near the dunes and no prominent variation with latitude is seen

optical properties of the ash from el chichon volcano we have measured visible wavelength optical properties of the ash from the 1982 el chichon eruptions these measurements were made on ash samples collected at three surface sites at distances between 12 and 80 km from the volcano the most distant sample is taken as most representative of the silicate ash injected into the stratosphere the measured optical properties are expressed as a complex refractive index n with the aerosol absorption expressed as the imaginary component of the refractive index nim each of these samples showed quite low values of absorption with nim at 500 nm ranging from 1 5 10 3 for the 12 km sample to 1 0 10 3 for the 80 km sample based on these measurements we estimate that n for the stratospheric silicate ash is given by n 1 53 0 001i

global pattern of titan s dunes radar survey from the cassini prime mission 1 we present a map of the orientation and extent of titan s sand dunes derived from the complete radar imaging dataset from the cassini prime mission the 16 000 dune segments we have mapped cover 8 of the titan s surface suggesting a total coverage of 20 are confined within 30 of the equator and show local and regional deviations of dune orientation of up to about 40 from due eastwards there is no obvious global longitudinal pattern although some divergence with latitude is apparent the most striking pattern is one of collimation by and divergence around bright and or high terrain obstacles 100 300 m high obstruct dunes when the local slope is 1 50 or steeper while slopes 1 200 or shallower cause dunes to thin out as they climb or to deviate around the obstacles

predicting lithology and transport properties from acoustic velocities based on petrophysical classification of siliciclastics based on the recently developed petrophysical classification of siliciclastics which takes into account the amount of the volumetric clay content c and textural position of clay it is shown that acoustic velocities can be fairly accurate tools in predicting lithology porosity and ultimately transport properties of these rocks four major petrophysical groups of carbonate and organic poor siliciclastics are distinguished 1 clean arenites c 35 percent the compressional velocity versus porosity relation for consolidated rocks in each of these groups is found to be linear with very high correlation coefficients this allows for remarkably accurate porosity estimates or lithology prediction in consolidated siliciclastics from acoustic velocities compared to the widely used time average wyllie equation or its improved modification raymer equations both of which neglect textural factors

are the basins of titan s hotei regio and tui regio sites of former low latitude seas 1 features observed in the low latitude basins of hotei regio and tui regio on titan have attracted the attention of the cassini era investigators at both locations visual infrared mapping spectrometer vims observed isolated 5 m bright 500 km wide features described as lobate in shape several studies have proposed that these materials are cryo volcanic flows we propose an alternative explanation recently published topographic profiles across hotei regio and tui regio indicate these features appear to occur in large regional basins at least along the direction of the profiles cassini synthetic aperture radar sar images show that the terrains surrounding both topographically low lying 5 m bright features exhibit fluvial networks that appear to converge into the probable basins the 5 m bright features themselves correspond to fields of discrete radar bright depressions whose bounding edges are commonly rounded and cumulate in planform in sar images these fields of discrete radar bright depressions strongly resemble fields of features seen at titan s high latitudes identified as dry lakes thus the combination of 1 the resemblance to high latitude dry lakes 2 location in the centers of regional depressions and 3 convergence of fluvial networks are inferred by us to best explain the features of hotei regio and tui regio as sites of paleolake clusters and perhaps former now dry seas these low latitude paleolake clusters or former seas if real may be evidence of substantially larger inventories of liquid alkanes in titan s past

titan dune heights retrieval by using cassini radar altimeter abstract the cassini radar is a ku band multimode instrument capable of providing topographic and mapping information during several of the 93 titan fly bys performed by cassini the radar collected a large amount of data observing many dune fields in multiple modes such as sar altimeter scatterometer and radiometer understanding dune characteristics such as shape and height will reveal important clues on titan s climatic and geological history providing a better understanding of aeolian processes on earth dunes are believed to be sculpted by the action of the wind weak at the surface but still able to activate the process of sand sized particle transport this work aims to estimate dunes height by modeling the shape of the real cassini radar altimeter echoes joint processing of sar altimeter data has been adopted to localize the altimeter footprints overlapping dune fields excluding non dune features the height of the dunes was estimated by applying maximum likelihood estimation along with a non coherent electromagnetic em echo model thus comparing the real averaged waveform with the theoretical curves such analysis has been performed over the fensal dune field observed during the t30 flyby may 2007 as a result we found that the estimated dunes peak to trough heights difference was in the order of 60 120 m estimation accuracy and robustness of the mle for different complex scenarios was assessed via radar simulations and monte carlo approach we simulated dunes interdunes different composition and roughness for a large set of values verifying that in the range of possible titan environment conditions these two surface parameters have weak effects on our estimates of standard dune heights deviation results presented here are the first part of a study that will cover all titan s sand seas

the sand seas of titan cassini radar observations of longitudinal dunes the most recent cassini radar images of titan show widespread regions up to 1500 kilometers by 200 kilometers of near parallel radar dark linear features that appear to be seas of longitudinal dunes similar to those seen in the namib desert on earth the ku band 2 17 centimeter wavelength images show 100 meter ridges consistent with duneforms and reveal flow interactions with underlying hills the distribution and orientation of the dunes support a model of fluctuating surface winds of 0 5 meter per second resulting from the combination of an eastward flow with a variable tidal wind the existence of dunes also requires geological processes that create sand sized 100 to 300 micrometer particulates and a lack of persistent equatorial surface liquids to act as sand traps

cryovolcanism on titan new results from cassini radar and vims 1 the existence of cryovolcanic features on titan has been the subject of some controversy here we use observations from the cassini radar including synthetic aperture radar sar imaging radiometry and topographic data as well as compositional data from the visible and infrared mapping spectrometer vims to reexamine several putative cryovolcanic features on titan in terms of likely processes of origin fluvial cryovolcanic or other we present evidence to support the cryovolcanic origin of features in the region formerly known as sotra facula which includes the deepest pit so far found on titan now known as sotra patera flow like features mohini fluctus and some of the highest mountains on titan doom and erebor montes we interpret this region to be a cryovolcanic complex of multiple cones craters and flows however we find that some other previously supposed cryovolcanic features were likely formed by other processes cryovolcanism is still a possible formation mechanism for several features including the flow like units in hotei regio we discuss implications for eruption style and composition of cryovolcanism on titan our analysis shows the great value of combining data sets when interpreting titan s geology and in particular stresses the value of radar stereogrammetry when combined with sar imaging and vims

velocity porosity relationships for water saturated siliciclastic sediments seeking a global empirical relationship between compressional wave velocity and porosity for siliciclastic sediments we have brought together an extensive suite of both new and published log and core based data we undertook a detailed statistical analysis of ocean drilling program data from amazon fan to examine variables affecting compressional velocity in shallow unconsolidated sediments we identify three dominant variables porosity shale fraction and consolidation history and present two empirically determined boundary curves one for normally consolidated sediments and a second for highly consolidated environments e g accretionary prisms these two empirical relationships predict the compressional velocity of siliciclastic sedimentary rocks with water filled pores as a function of porosity and clay content for the full range of observed porosities velocities of siliciclastic sedimentary rocks decrease rapidly with both increasing porosity and increasing clay content at fractional porosities higher than about 0 4 fluid dominates the elastic properties and velocity exhibits a subtle dependence on porosity remarkably the amazon fan data show that clay content has no direct influence on velocity at high porosities both clay content and sorting do indirectly affect velocity through their control of porosity burial affects velocity not only by compaction related porosity decrease but also by pressure induced increase of intergrain coupling because of the sensitivity of velocity to consolidation history particularly at intermediate fractional porosities of about 0 30 0 40 no single velocity porosity relationship can apply to all high porosity sediments the two proposed relationships fit the majority of published and new data they are applicable however only for normally pressured in situ conditions and water filled pores

surface albedo spectral properties of geologically interesting areas on titan we investigate the nature and possible formation processes of three areas on titan s surface which have been suggested as geologically interesting hotei regio tui regio and sotra patera we also reanalyze the spectral characteristics of the huygens landing site we apply a statistical principal component analysis pca and a radiative transfer rt method on the visual and infrared mapping spectrometer datacubes in order to retrieve the surface albedo of distinct spectral units in the near infrared we have been able to exploit only a subset of the currently available hotei regio data which are in general not optimal in terms of geometry for an analysis with a plane parallel rt code our inferred surface albedos present generally higher values from 1 to 2 m and lower ones at 0 94 and in the 2 6 5 m region the regions of interest rois within hotei regio tui regio and sotra patera are always significantly brighter than the surrounding areas the largest variations are found longward of 2 m and mainly at 5 m this higher surface albedo with respect to the surrounding area and in general the fact that the spectral behavior is different for each of these areas is probably indicative of diverse chemical compositions and origins we compare the spectral albedos with some suggested surface candidates on titan such as h2o co2 and ch4 ices as well as tholin and discuss possible chemical composition variations as well as other interpretations

dynamic and static moduli static and dynamic bulk moduli ks and kd are measured as continuous functions of pressure from zero to 2 3 kilobars for two sandstones a tuff limestone granite and oil shale results for the sandstones and granite are in good agreement with previously reported data with ks kd varying from about 0 5 at atmospheric pressure to close to unity at pressures 2 kilobars and above for rocks behaving elastically under static loading the ks kd ratio is inversely related to the microcrack density for the limestone time dependent deformation associated with pore collapse results in ks kd ratios approaching 0 1 at high pressure upon unloading while initially high 1 0 at high pressures ks kd becomes lower than values obtained during loading at low pressures 1 kilobar due to opening of microcracks generated during pore collapse for the oil shale in which few microcracks exist ks kd remains relatively constant with pressure at a value of about 0 7

titan s surface and atmosphere from cassini vims data with updated methane opacity abstract we present an analysis of titan data acquired by the cassini visual and infrared mapping spectrometer vims making use of recent improvements in methane spectroscopic parameters in the region 1 3 5 2 m we first analyzed vims spectra covering a 8 10 km2 area near the huygens landing site in order to constrain the single scattering albedo 0 of the aerosols over all of the vims spectral range our aerosol model agrees with that derived from huygens probe descent imager spectral radiometer disr in situ measurements below 1 6 m at longer wavelengths 0 steadily decreases from 0 92 at 1 6 m to about 0 70 at 2 5 m and abruptly drops to about 0 50 near 2 6 m a spectral variation that differs from that of khare et al s khare b n sagan c arakawa e t suits f callcott t a williams m w 1984 icarus 60 127 137 laboratory tholins our analysis shows that the far wings of the strong methane bands on both sides of the transparency windows provide a significant source of opacity in these windows and that their unknown sub lorentzian behavior limits our ability to determine precisely the surface albedos below 1 6 m the retrieved surface albedos agree with those derived from huygens disr the vims spectrum at 2 0 m indicates a surface albedo of 0 11 0 01 larger than derived in previous studies and inconsistent with the signature of water ice a series of vims data taken from 2004 to 2010 between 40 s and 40 n were then analyzed to monitor the latitudinal and temporal evolution of the atmospheric aerosol content in the 2004 2008 period the haze extinction is larger at northern mid latitudes by 20 with respect to the huygens site whereas southern mid latitudes are depleted by 15 20 in 2009 2010 a progressive decline of the haze content in the northern hemisphere is observed but no reversal of the north to south asymmetry is seen till mid 2010 finally data from five regions in tui regio and fensal that show markedly different spectral behaviors and morphologies were analyzed to investigate the wavelength dependence of their surface albedo the difference between bright and dark regions can be explained by different contents of small sized tholins at the surface brighter regions being more tholin rich than dark regions including the huygens landing site on the other hand the albedo spectrum of the so called blue regions either dark or bright can be explained by an excess of water ice particles compared with the huygens landing site the spectrum of a 5 m bright region in tui regio indicates a large excess of small sized tholins relative to the huygens site but does not point to any particular surface composition

mapping and interpretation of sinlap crater on titan using cassini vims and radar data 1 only a few impact craters have been unambiguously detected on titan by the cassini huygens mission among these sinlap is the only one that has been observed both by the radar and vims instruments this paper describes observations at centimeter and infrared wavelengths which provide complementary information about the composition topography and surface roughness several units appear in vims false color composites of band ratios in the sinlap area suggesting compositional heterogeneities a bright pixel possibly related to a central peak does not show significant spectral variations indicating either that the impact site was vertically homogeneous or that this area has been recovered by homogeneous deposits both vims ratio images and dielectric constant measurements suggest the presence of an area enriched in water ice around the main ejecta blanket since the ku band sar may see subsurface structures at the meter scale the difference between infrared and sar observations can be explained by the presence of a thin layer transparent to the radar an analogy with terrestrial craters in libya supports this interpretation finally a tentative model describes the geological history of this area prior during and after the impact it involves mainly the creation of ballistic ejecta and an expanding plume of vapor triggered by the impact followed by the redeposition of icy spherules recondensed from this vapor plume blown downwind subsequent evolution is then driven by erosional processes and aeolian deposition

spectroscopy morphometry and photoclinometry of titan s dunefields from cassini vims fine resolution 500 m pixel cassini visual and infrared mapping spectrometer vims t20 observations of titan resolve that moon s sand dunes the spectral variability in some dune regions shows that there are sand free interdune areas wherein vims spectra reveal the exposed dune substrate the interdunes from t20 are variously materials that correspond to the equatorial bright 5 m bright and dark blue spectral units our observations show that an enigmatic dark red spectral unit seen in t5 in fact represents a macroscopic mixture with 5 m bright material and dunes as its spectral endmembers looking more broadly similar mixtures of varying amounts of dune and interdune units of varying composition can explain the spectral and albedo variability within the dark brown dune global spectral unit that is associated with dunes the presence of interdunes indicates that titan s dunefields are both mature and recently active the spectrum of the dune endmember reveals the sand to be composed of less water ice than the rest of titan various organics are consistent with the dunes measured reflectivity we measure a mean dune spacing of 2 1 km and find that the dunes are oriented on the average in an east west direction but angling up to 10 from parallel to the equator in specific cases where no interdunes are present we determine the height of one set of dunes photoclinometrically to be between 30 and 70 m these results pave the way for future exploration and interpretation of titan s sand dunes

geophysical properties of cap rocks in qiongdongnan basin south china sea abstract based on measured petrophysical properties and statistical methods relationship between petrophysical properties and well log and seismic parameters are established empirically to evaluate the quality of cap rocks in qiongdongnan basin good cap rocks show high density and low sonic travel time four zones can be divided vertically according to displacement pressures in qiongdongnan basin best seal quality is found in the depth range of 2000 4000 m the ya 13 1 structure has excellent cap rock which contributes to its abundant gas accumulation

experimental mechanical compaction of clay mineral aggregates changes in physical properties of mudstones during burial dry and brine saturated clay aggregates ranging from pure smectite to pure kaolinite were compacted in the laboratory experiments were conducted by increasing vertical effective stress up to 50 mpa to study the changes in physical properties of mudstones during burial the results suggest that the physical properties porosity density acoustic velocity etc of mudstones vary greatly with increasing effective stress clay mineralogy and fluid content kaolinite aggregates are much more compressible than those composed of smectite brine saturated clay mixtures are much more compressible than dry clay mixtures brine may soften and lubricate the clay matrix compared to dry clays resulting in higher compressibility in the brine saturated state the lesser degree of compaction of dry smectite compared to dry kaolinite aggregates can be explained by the differences in grain size as kaolinitic clays have much larger grains than smectitic clays the extremely fine grained nature of smectite implies that the imposed vertical stress is distributed over a very large number of grain contacts so that the force per contact area is very low in smectite compared to that in coarse grained kaolinite at 20 mpa effective stress corresponding to about 2 km burial depth with hydrostatic pore pressure brine saturated pure kaolinite compacted to 20 porosity while pure smectite retained 41 porosity brinesaturated clay mixtures show higher vp and lower vs than dry clay mixtures a pronounced difference in vs was observed among the brinesaturated clay mixtures the lowest vs as a function of vertical effective stress was found for pure smectite for a given porosity value smectitic clays have higher velocities and elastic moduli than the kaolinitic clays the vp vs ratio is significantly higher in smectite than in kaolinite aggregates treating mudstones as a uniform class of rocks introduces significant errors in estimates of physical properties which are strongly affected by the clay mineralogy grain size the amount of other minerals present and fluid content our results have implications for well log interpretation and mudstone and shale property determinations from seismic data at shallow burial depth o 2k m 801c above depths where significant chemical compaction takes place r 2007 elsevier ltd all rights reserved

rapid and extensive surface changes near titan s equator evidence of april showers although there is evidence that liquids have flowed on the surface at titan s equator in the past to date liquids have only been confirmed on the surface at polar latitudes and the vast expanses of dunes that dominate titan s equatorial regions require a predominantly arid climate we report the detection by cassini s imaging science subsystem of a large low latitude cloud system early in titan s northern spring and extensive surface changes spanning more than 500 000 square kilometers in the wake of this storm the changes are most consistent with widespread methane rainfall reaching the surface which suggests that the dry channels observed at titan s low latitudes are carved by seasonal precipitation

coseismic landsliding during the mw 7 1 darfield canterbury earthquake implications for paleoseismic studies of landslides abstract the head scarp of the harper hills landslide consists of ground cracks with vertical displacement and extension that opened during the 2010 darfield canterbury mw 7 1 earthquake the geomorphology of the cracks regional geology and ground penetrating radar indicate that the landslide formed by bedding controlled translation and joint controlled toppling and suggest incipient deep seated movement crack depth and displacement along the head scarp vary along the ridge maximum values are located where the head scarp is closest to the local ridge line increased seismic shaking due to topographic and geometric amplification of seismic waves is suggested as an explanation for this relationship an excavation across the head scarp revealed no evidence of prior slip events over a time period that is likely to exceed the return period 1000 2500 years of peak ground accelerations experienced at this location in the darfield earthquake we suggest that specific seismologic attributes of the darfield earthquake may have influenced the location of landsliding in this instance studies of paleo landslides must consider crack preservation potential as well as complex source site effects that may complicate estimates of acceleration return periods from the subsurface investigation of individual landslide head scarps

insights into titan s geology and hydrology based on enhanced image processing of cassini radar data the cassini synthetic aperture radar has been acquiring images of titan s surface since october 2004 to date 59 of titan s surface has been imaged by radar with significant regions imaged more than once radar data suffer from speckle noise hindering interpretation of small scale features and comparison of reimaged regions for change detection we present here a new image analysis technique that combines a denoising algorithm with mapping and quantitative measurements that greatly enhance the utility of the data and offers previously unattainable insights after validating the technique we demonstrate the potential improvement in understanding of surface processes on titan and defining global mapping units focusing on specific landforms including lakes dunes mountains and fluvial features lake shorelines are delineated with greater accuracy previously unrecognized dissection by fluvial channels emerges beneath shallow methane cover dune wavelengths and interdune extents are more precisely measured a significant refinement in producing digital elevation models is shown interactions of fluvial and aeolian processes with topographic relief is more precisely observed and understood than previously benches in bathymetry are observed in northern sea ligeia mare submerged valleys show similar depth suggesting that they are equilibrated with marine benches these new observations suggest a liquid level increase in the northern sea which may be due to changes on seasonal or longer timescales

multiple origins of linear dunes on earth and titan the formation of dunes is controlled by the direction of the prevailing winds and the characteristics of the sediments linear dunes in the qaidam basin china are shown to form from cohesive sediments a model that could be applicable to dunes on titan

experimental investigation of factors affecting compressional and shear wave velocities in shale and limestone of ewekoro formation of southern nigeria sedimentary basin compressional vp and shear vs velocities measurements were taken out on fluid saturated shale and limestone obtained from the ewekoro quarry of southern nigeria sedimentary basin at constant differential pressure of 50 mpa with porosities ranging from 0 32 to 0 53 and 0 01 to 0 35 for limestone and shale respectively while the volume of clay content c ranges from 0 to 60 and 0 to 40 for limestone and shale respectively correlation coefficient for the velocities of both clean samples and those with clay minerals ranged from 0 972 to 1 000 and 0 971 to 1 000 respectively with limestone having the lesser for both a very small amount of clay about 0 21 and 0 23 reduced the elastic modulus of limestone and shale respectively for water saturated shaly samples vs was more sensitive to porosity and clay content than vp consequently velocity ratios vp vs also showed a reasonable degree of correlations with clay content and porosity for both limestone and shale studied the presence of porosity is the most important parameter in reducing velocities followed by clay content due to the softening of its matrix this study established that wave velocities are functions of porosity and clay content of porous shale and limestone of ewekoro formations

the respiratory health hazards of volcanic ash a review for volcanic risk mitigation studies of the respiratory health effects of different types of volcanic ash have been undertaken only in the last 40 years and mostly since the eruption of mt st helens in 1980 this review of all published clinical epidemiological and toxicological studies and other work known to the authors up to and including 2005 highlights the sparseness of studies on acute health effects after eruptions and the complexity of evaluating the long term health risk silicosis non specific pneumoconiosis and chronic obstructive pulmonary disease in populations from prolonged exposure to ash due to persistent eruptive activity the acute and chronic health effects of volcanic ash depend upon particle size particularly the proportion of respirable sized material mineralogical composition including the crystalline silica content and the physico chemical properties of the surfaces of the ash particles all of which vary between volcanoes and even eruptions of the same volcano but adequate information on these key characteristics is not reported for most eruptions the incidence of acute respiratory symptoms e g asthma bronchitis varies greatly after ashfalls from very few if any reported cases to population outbreaks of asthma the studies are inadequate for excluding increases in acute respiratory mortality after eruptions individuals with pre existing lung disease including asthma can be at increased risk of their symptoms being exacerbated after falls of fine ash a comprehensive risk assessment including toxicological studies to determine the long term risk of silicosis from chronic exposure to volcanic ash has been undertaken only in the eruptions of mt st helens 1980 usa and soufriere hills montserrat 1995 onwards in the soufriere hills eruption a long term silicosis hazard has been identified and sufficient exposure and toxicological information obtained to make a probabilistic risk assessment for the development of silicosis in outdoor workers and the general population a more systematic approach to multi disciplinary studies in future eruptions is recommended including establishing an archive of ash samples and a website containing health advice for the public together with scientific and medical study guidelines for volcanologists and health care workers

ultrasonic compressional and shear velocities in dry clastic rocks as a function of porosity clay content and confining pressure summary for clastic silicate rocks sampled from a rotliegendes well core the velocities up and us were obtained at 10 pressures up to 300mpa using a pulse transmission technique the porosities of all rocks 57 sandstones 26 siltstones five claystones ranged from 0 01 and 0 15 by volume fraction and the clay content varied from less than 0 01 to 0 88 by volume fraction both velocities increase with pressure in the low pressure range the rate of increase is large non linear and is greater for up than for us above 120 mpa both velocities increase linearly velocities porosity and clay content were fitted by least squares regression for pressures of 8 24 60 120 200 and 300 mpa the fractional effect of porosity and clay on the velocities for dry clastic silicate rocks can be described above 120 mpa by u a b ccluy where v is the velocity of the p wave or s wave is the volume fraction of pores and clay is the volume fraction of clay from this it is possible to obtain pressure dependent velocity functions u a pb c exp dp where u is the crack free velocity linear in porosity and clay b is the velocity slope under high pressure u c is the zero pressure velocity and d is related to closure of cracks

methane storms as a driver of titan s dune orientation titan s equatorial dunes propagate eastwards whereas titan s surface winds blow towards the west atmospheric simulations suggest that tropical methane storms generate strong eastward gusts that may dominate sand transport on titan s surface

correlations between seismic parameters em parameters and petrophysical petrological properties for sandstone and carbonate at low water saturations empirical relations are found between measured petrophysical petrologic seismic and electrical properties of sandstone and carbonate samples by least squares fitting at room pressure and ambient saturation the measured parameters include porosity fluid permeability k clay content c grain density g bulk density b p wave velocity vp electrical conductivity and dielectric constant the samples are from reservoir analog sites in the ferron sandstone in central utah and the ellenburger carbonate in central texas crossplots and regression analysis are done separately for the sandstone and the carbonate samples for the sandstone samples predictions with correlation coefficients r2 greater than 0 75 include b from ln k from and c from ln k and from b and c and from ln k predictions with 0 65 r2 0 75 include from vp and b from vp and vp from ln k and c from ln and from b in general is difficult to predict with the best r2 0 48 obt

compressional velocity and porosity in sand clay mixtures laboratory measurements of porosity and compressional velocity were conducted on unconsolidated brine saturated clean ottawa sand pure kaolinite and their mixtures at various confining pressures a peak in p velocity versus clay content in unconsolidated sand clay mixtures at 40 percent clay by weight was found the peak in velocity is 20 30 percent higher than for either pure clay or clean sand a minimum in porosity versus clay content at 20 40 percent clay by weight is also observed such behavior is explained using a micro geometrical model for mixtures of sand and clay in which two classes of sediments are considered 1 sands and shaley sands in which clay is dispersed in the pore space of load bearing sand and thus reduces porosity and increases the elastic moduli of the pore filling material and 2 shales and sandy shales in which sand grains are dispersed in a clay matrix for these sediments the model reproduces the extrema in velocity and porosity and accounts for much of the scatter in

growth mechanisms and dune orientation on titan dune fields on titan cover more than 17 of the moon s surface constituting the largest known surface reservoir of organics their confinement to the equatorial belt shape and eastward direction of propagation offer crucial information regarding both the wind regime and sediment supply herein we present a comprehensive analysis of titan s dune orientations using automated detection techniques on nonlocal denoised radar images by coupling a new dune growth mechanism with wind fields generated by climate modeling we find that titan s dunes grow by sediment transport on a nonmobile substratum to be fully consistent with both the local crestline orientations and the eastward propagation of titan s dunes the sediment should be predominantly transported by strong eastward winds most likely generated by equinoctial storms or occasional fast westerly gusts additionally convergence of the meridional transport predicted in models can explain why titan s dunes are confined within 30 latitudes where sediment fluxes converge