the temperature of europa s subsurface water ocean a 100 km deep liquid water ocean probably underlies the icy exterior of jupiter s satellite europa the long term persistence of a liquid ocean beneat ha n ice shell presents a thermal conundrum is the temperature of the ocean equal to the freezing point of water at the bottom of the ice shell or is it equal t o the somewhat warmer temperature at which water attains its maximum density we argue that most of the ocean is at the temperature of maximum density and that the bulk of the vigorously convecting ocean is separated from the bottom of the ice shell by a thin stratosphere of stably stratified water whi ch is at the freezing point and therefore buoyant if europa s subsurface water ocean is warm it could explain the widespread geologic evidence for app arent melt through events observed on its surface and may constrain the overall age of its surface

the landscape of titan as witness to its climate evolution we investigated the range of titan climate evolution hypotheses regulated by the role sources and availability of methane we analyzed all available image data principally synthetic aperture radar sar of titan s landscape through the t 86 encounter starting with focused examinations of terrains that carry the markers of climate evolution traditional geologic and geomorphic landscape analysis was used to perform morphometric characterization establish time stratigraphic relationships and interpret local and regional geologic process oriented evolutionary histories we then assayed the distribution of terrains we identified with respect to both their latitudinal and altimetric occurrence our analysis of the terrain types and distributions was used to evaluate and rank the various climate evolution scenarios we favor progressive hypotheses which include a relatively brief period in which precipitation was able to affect geomorphic change in low latitudes at scales perceivable in sar data with subsequent gradual decline of precipitation intensity coupled with an increasing poleward restriction

simulating the failure process of the xinmo landslide using discontinuous deformation analysis abstract the xinmo landslide slope in sichuan china was stable during the intensive wenchuan earthquake in 2008 but failed on june 24 2017 landslide debris buried xinmo village and blocked the songpinggou river at the slope toe this study aims to clarify the post failure behavior of the landslide using two dimensional discontinuous deformation analysis 2d dda the simulation results provide comprehensive information on the initiation and the evolution of the landslide the failure process determined by the dda correlates well with the seismic signal analysis results in addition the location of the calculated rock deposit is similar to that shown by the topographic map after the landslide the maximum rock velocity in the landslide is 65 4 m s therefore the impacts of the high velocity blocks and the buildings in xinmo village must be considered to simulate the burial of xinmo village by rocks and the transport of additional rocks across the songpinggou river this xinmo landslide study demonstrates that the dda accurately simulates the post failure behavior and determines the impact area of a landslide with complicated failure processes and topography

the long term stability of a possible aqueous ammonium sulfate ocean inside titan we model the thermal evolution of a subsurface ocean of aqueous ammonium sulfate inside titan using a parameterized convection scheme the cooling and crystallization of such an ocean depends on its heat flux balance and is governed by the pressure dependent melting temperatures at the top and bottom of the ocean using recent observations and previous experimental data we present a nominal model which predicts the thickness of the ocean throughout the evolution of titan after 4 5 ga we expect an aqueous ammonium sulfate ocean 56 km thick overlain by a thick 176 km heterogeneous crust of methane clathrate ice i and ammonium sulfate underplating of the crust by ice i will give rise to compositional diapirs that are capable of rising through the crust and providing a mechanism for cryovolcanism at the surface we have conducted a parameter space survey to account for possible variations in the nominal model and find that for a wide range of plausible conditions an ocean of aqueous ammonium sulfate can survive to the present day which is consistent with the recent observations of titan s spin state from cassini radar data lorenz r d stiles b w kirk r l allison m d del marmo p p iess l lunine j i ostro s j hensley s 2008 science 319 1649 1651

effects of near fault seismic loadings on run out of large scale landslide a case study this study presents the run out analysis of the daguangbao landslides subjected to near fault multi direction earthquake forces using discontinuous deformation analysis dda the daguangbao landslide is the largest landslide induced by the 2008 wenchuan earthquake in order to investigate the effects of near fault seismic force on landslide run out kinematic behavior of sliding mass is simulated by a dynamic discrete numerical analysis method called dda in this simulation based on the shape of failure surface and the feature of slope geology the whole slope is divided into three parts base block upper sliding mass and lower sliding mass then two sliding masses are divided into the smaller discrete deformable blocks based on pre existing discontinuities size effect of the huge landslide is also considered baseline corrected real horizontal and vertical ground motions are taken as volume force acting to the base block the results show that seismic force has a significant influence on the landslide progression sliding distance and shape of post failure results of the horizontal and vertical situation are in good agreement with those obtained from post earthquake field investigation remote sensing image and description from the survivors

shape topography gravity anomalies and tidal deformation of titan abstract gravity measurements and elevation data from the cassini mission have been used to create shape global topography and gravity anomaly models of titan that enable an improved understanding of its outer ice i shell structure we provide constraints on the averaged ice shell thickness and its long wavelength lateral variations as well as the density of the subsurface ocean using gravity anomalies the tidal love number k2 measurement and long wavelength topography we found that titan s surface topography is consistent with an approximate isostatically compensated ice shell of variable thickness likely in a thermally conductive or in a subcritical convective state overlying a relatively dense subsurface ocean

influence of kinematics on landslide mobility and failure mode geometry of discontinuities greatly influences the kinematic behavior of slopes and landslides discontinuous deformation analysis dda is used here to analyze two typical examples of slope failure demonstrating that accurate representation of the geometry of the discontinuities is essential for identification of kinematically correct failure modes then static stability analyses of the vaiont italy landslide of october 9 1963 are used to show that the dda results compare favorably with previously published limit equilibrium studies using similar geometries and that the location and number of discontinuities have a significant effect on the predicted stability and failure velocities of the landslide dynamic dda simulations of the vaiont landslide show that the peak velocity increases up to 50 as the number of blocks increases indicating that internal disintegration of the landslide mass results in increasing acceleration and higher peak velocity dda analyses simulating pore pressure rise resulting from frictional heating of the basal slide plane show that the peak velocity similarly increases up to 50 as the number of blocks increases the magnitude of the increase in peak velocity as a result of disintegration i e increasing number of blocks suggests that as much attention should be paid to the geometry of discontinuities as is typically paid to shear strength and pore pressure

a numerical study of tides in titan s northern seas kraken and ligeia maria abstract the tidal response of titan s two largest northern seas ligeia mare and kraken mare is studied by means of a two dimensional depth averaged shallow water model slim http www climate be slim kraken mare is formed of two basins the northern one being assumed to be linked by a single strait trevize fretum to ligeia mare the tidal motions tend to be independent of each other in each basin i e ligeia mare kraken 1 and kraken 2 which results in sharp transitions in the straits our results are overall rather similar to those of tokano et al 2014 suggesting that a 2d model such as slim is adequate for modelling titan s tides and since it is presumably less computationally demanding may be better for sensitivity studies for instance the maximum tidal range in kraken and ligeia maria respectively are 0 29 m and 0 14 m which is within the range predicted by lorenz et al 2014 although smaller by 0 07 m and larger by 0 04 m than the estimates of tokano et al 2014 but it occurs at the same location the tidal currents are faster by about one order of magnitude in the straits linking those maria than in the basins themselves with a maximum of 0 36 m s in the strait linking kraken 1 and kraken 2 seldon fretum a decomposition of the tidal history into different harmonic components is carried out except in specific areas such as the straits and the amphidromic point s the main tidal component has a period of 1 titan day we also briefly studied the eigenmodes of the northern seas whose period is close to the tidal period such modes are very local indeed their magnitude is significant with respect to the magnitude of the modes elsewhere in the seas in small bay s or near the islands of kraken 2 and ligeia mare they are not excited by the tides as they do not appear in the tidal motion a sensitivity analysis to poorly constrained parameters bottom friction coefficient depth of trevize fretum and attenuation factor the latter is briefly discussed with respect to the values of the love numbers found in the literature is also conducted the model parameters are seen to have a significant impact on the liquid exchanges between the basins and consequently on the tidal range and phase fluid velocity and location of amphidromic point s

structure and dynamics of titan s outer icy shell constrained from cassini data abstract the cassini huygens mission has brought evidence for an internal ocean lying beneath an outer icy shell on titan the observed topography differs significantly from the reference hydrostatic shape while the measured geoid anomalies estimated up to degree three remain weak this suggests compensation either by deflections of the ocean ice interface or by density variations in an upper crust however the observed degree three gravity signal indicates either that the topography is not perfectly compensated or that mass anomalies exist in the deep interior or a combination of both to investigate the compensation mechanisms we developed an interior structure model satisfying simultaneously the surface gravity and long wavelength topography we quantified the excess deflection of ocean ice i interface the density anomalies in the upper crust or the deflection of the ice rock interface needed to explain the observed degree three anomalies finally we tested the long term mechanical stability of the internal mass anomalies by computing the relaxation rate of each internal interface in response to interface mass load we showed that the computed deflection of the ocean ice i interface is stable only for a conductive highly viscous layer above a relatively cold ocean t

tidal dissipation surface heat flow and figure of viscoelastic models of io abstract the distribution of hot spots on io s surface and io s figure constrain models of io s interior voyager observations indicate that most hot spots and volcanic plumes are close to the equator recently however it has been proposed that a large low albedo feature in the south polar region may be the source of 40 of the surface heat flow we calculate spatial distributions of the dissipation rate surface heat flow and the figures of three and four layer maxwell rheology models of io by using the correspondence principle the models are required to satisfy the observed surface heat flow constraint and are consistent with the composition of a dehydrated c2 chondrite they consist of an inviscid fe fes core and viscoelastic silicate mantle and lithosphere layers a comparison of the calculated equilibrium figure with the observed figure of io supports the chosen core radius of 980 km in addition the four layer model has a partially molten asthenosphere a few tens of kilometers thick the preferred three layer model has a mantle shear modulus of 10 10 pa and a viscosity of 2 10 16 pa s consistent with rock properties the tidal dissipation rate for this model is largest along the polar axis integration of the dissipation rate over radius gives a surface heat flow with maxima at the poles and minima near the sub jovian and anti jovian points in contrast the dissipation rate in a molten or partially molten incompressible asthenosphere has maxima near the equator and is close to zero at the poles the asthenosphere dissipation rate is mainly a function of asthenosphere viscosity and thickness the thinner the asthenosphere the smaller is the required viscosity a 50 km thick asthenosphere requires a viscosity of about 10 8 pa s a strong south polar hot spot if it can be confirmed by infrared observation favors dissipation in the mantle but does not exclude dissipation in a partially molten asthenosphere equatorial hot spots and the concentration of prometheus type plumes near the equator favor asthenosphere heating but do not rule out deep mantle dissipation both asthenosphere and deep mantle heating may contribute to io s surface heat flow the properties of magma transport through the lithosphere and the planform of mantle convection might exert a control on the surface expression of heating at greater depth

runout simulation of seismic landslides using discontinuous deformation analysis dda with state dependent shear strength model the reliable numerical simulation of the landslide process contributes to the establishment of evidence based disaster mitigation measures in seismically active zones to achieve this goal a simpl

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

tidal heating in icy satellite oceans abstract tidal heating plays a significant role in the evolution of many satellites in the outer solar system however it is unclear whether tidal dissipation in a global liquid ocean can represent a significant additional heat source tyler tyler r h 2008 nature 456 770 772 tyler r h 2009 geophys res lett 36 doi 10 1029 2009gl038300 suggested that obliquity tides could drive large scale flow in the oceans of europa and enceladus leading to significant heating a critical unknown in this previous work is what the tidal quality factor q of such an ocean should be the corresponding tidal dissipation spans orders of magnitude depending on the value of q assumed to address this issue we adopt an approach employed in terrestrial ocean modeling where a significant portion of tidal dissipation arises due to bottom drag with the drag coefficient o 0 001 being relatively well established from numerical solutions to the shallow water equations including nonlinear bottom drag we obtain scalings for the equivalent value of q as a function of this drag coefficient in addition we provide new scaling relations appropriate for the inclusion of ocean tidal heating in thermal orbital evolution models our approach is appropriate for situations in which the ocean bottom topography is much smaller than the ocean thickness using these novel scalings we calculate the ocean contribution to the overall thermal energy budgets for many of the outer solar system satellites although uncertainties such as ocean thickness and satellite obliquity remain we find that for most satellites it is unlikely that ocean tidal dissipation is important when compared to either radiogenic or solid body tidal heating of known satellites triton is the most likely icy satellite to have ocean tidal heating play a role in its present day thermal budget and long term thermal evolution

near surface heating on enceladus and the south polar thermal anomaly 1 strike slip motion is predicted to be a consequence of diurnal tidal stresses in most satellites of the outer solar system such motion can lead to near surface heating through friction or viscous dissipation here we discuss the effect of near surface shear heating on convection in the underlying ice shells of icy satellites we present models of convection in spherical shells including tidal and shear heating and show that localized near surface heating enhances convective upwelling beneath it the near surface heating promotes regional melting of the ice shell which likely results in subsidence of the surface topography the long wavelength geoid resulting from the subsidence plume buoyancy and dynamic topography may lead to small 4 per ma amounts of true polar wander potentially contributing to the south polar location of the observed thermal anomaly however compositional effects are likely required in addition to thermal effects to generate larger degrees of reorientation

mountains on titan modeling and observations 1 we have developed a thermal model of titan s interior to study changes in volume during partial freezing or melting of a subsurface ocean due to heat flux variations from the interior we find that the long term cooling of titan can cause global volume contraction v v 0 01 we then simulate two dimensional contractional deformation of titan s icy lithosphere finding that contractional deformation can produce tectonic activity and fold formation folds could potentially achieve a topographic height of several kilometers for high local strain 0 16 and for high temperature gradients in the ice i shell order of 10 k km 1 corresponding to an ancient high heat flux from the interior order of 0 02 0 06 w m 2 examination of synthetic aperture radar sar imagery obtained by cassini radar shows possible evidence of contractional tectonism in the equatorial regions of titan although the moderate resolution of the cassini sar imagery does not permit an unambiguous geological interpretation

the size distribution and mobility of landslides caused by the 2015 mw7 8 gorkha earthquake nepal abstract coseismic landslides pose immediate and prolonged hazards to mountainous communities and provide a rare opportunity to study the effect of large earthquakes on erosion and sediment budgets by mapping landslides using high resolution satellite imagery we find that the 25 april 2015 m w 7 8 gorkha earthquake and aftershock sequence produced at least 25 000 landslides throughout the steep himalayan mountains in central nepal despite early reports claiming lower than expected landslide activity our results show that the total number area and volume of landslides associated with the gorkha event are consistent with expectations when compared to prior landslide triggering earthquakes around the world the extent of landsliding mimics the extent of fault rupture along the east west trace of the main himalayan thrust and increases eastward following the progression of rupture in this event maximum modeled peak ground acceleration pga and the steepest topographic slopes of the high himalaya are not spatially coincident so it is not surprising that landslide density correlates neither with pga nor steepest slopes on their own instead we find that the highest landslide density is located at the confluence of steep slopes high mean annual precipitation and proximity to the deepest part of the fault rupture from which 0 5 2 hz seismic energy originated we suggest that landslide density was determined by a combination of earthquake source characteristics slope distributions and the influence of precipitation on rock strength via weathering and changes in vegetation cover determining the relative contribution of each factor will require further modeling and better constrained seismic parameters both of which are likely to be developed in the coming few years as post event studies evolve landslide mobility in terms of the ratio of runout distance to fall height is comparable to small volume landslides in other settings and landslide volume runout scaling is consistent with compilations of data on larger slope failures in general the size ratios of landslide source area to full landslide area are smaller than global averages and hillslope length seems to largely control runout distance which we propose reflects a topographic control on landslide mobility in this setting we find that landslide size dictates runout distance and that more than half of the landslide debris was deposited in direct connection with stream channels connectivity which is defined as the spatial proximity of landslides to fluvial channels is greatest for larger landslides in the high relief part of the high himalaya although these failures are less abundant than those at lower elevations they may have a disproportionate impact on sediment dynamics and cascading hazards such as landslide reactivation by monsoon rainfall and landslide dams that lead to outburst floods the overall high fluvial connectivity of coseismic landsliding in the gorkha event suggests coupling between the earthquake cycle and sediment geochemical budgets of fluvial systems in the himalaya

structural and tidal models of titan and inferences on cryovolcanism titan saturn s largest satellite is subject to solid body tides exerted by saturn on the timescale of its orbital period the tide induced internal redistribution of mass results in tidal stress variations which could play a major role for titan s geologic surface record we construct models of titan s interior that are consistent with the satellite s mean density polar moment of inertia factor obliquity and tidal potential love number k2 as derived from cassini observations of titan s low degree gravity field and rotational state in the presence of a global liquid reservoir the tidal gravity field is found to be consistent with a subsurface water ammonia ocean more than 180 km thick and overlain by an outer ice shell of less than 110 km thickness the model calculations suggest comparatively low ocean ammonia contents of less than 5 wt and ocean temperatures in excess of 255 k i e higher than previously thought thereby substantially increasing titan s potential for habitable locations the calculated diurnal tidal stresses at titan s surface amount to 20 kpa almost comparable to those expected at enceladus and europa tidal shear stresses are concentrated in the polar areas while tensile stresses predominate in the near equatorial midlatitude areas of the sub and anti saturnian hemispheres the characteristic pattern of maximum diurnal tidal stresses is largely compliant with the distribution of active regions such as cryovolcanic candidate areas the latter could be important for titan s habitability since those may provide possible pathways for liquid water ammonia outbursts on the surface and the release of methane in the satellite s atmosphere

the shape of enceladus as explained by an irregular core implications for gravity libration and survival of its subsurface ocean 1 enceladus global shape is not consistent with a simultaneously hydrostatic and fully differentiated body but its geophysical hyperactivity strongly implies that it is differentiated enceladus surface conforms to a triaxial shape consistent with relaxation to a global geoid but its rocky core need not be hydrostatic a modestly irregular core either in terms of topography or density and dynamically aligned would act to enhance the global geoid explaining the full global shape of enceladus requires 10 km of excess core polar flattening and 4 km of excess core equatorial distortion for a uniform density core the stresses associated with this excess topography can be sustained indefinitely but because the rocky core is not hydrostatic enceladus degree 2 gravity coefficients j2 and c22 will not conform to the hydrostatic ratio of 10 3 testable by cassini gravity notably core polar axes could be depressed by up to 4 6 km with respect to internal isobars such a topographic variation could help preserve polar ocean remnants for example if enceladus ocean undergoes secular freezing it will first ground near the tidal axes polar seas would be the last to freeze and survival of a south polar sea may be one reason why enceladus activity today is concentrated at high southern latitudes isostatic variations in the thickness or density of a floating ice shell may also contribute to enceladus nonhydrostatic shape but a strength supported nonisostatic icy lithosphere is argued here to be unlikely given enceladus record of regional high heat flows faulting and viscous relaxation

dda validation of the mobility of earthquake induced landslides abstract this paper studies the run out of earthquake induced landslides there are more than 20 mechanical models to explain long run out of rapid landslides including some earthquake induced landslides however notably few of them considered the effect of seismic loading on the run out of landslides in a previous study we have proposed a model which is called the multiplex acceleration model mam to interpret the long run out mechanism and a shaking table test has been performed to verify the mam because the previous mam is a conceptual model and only a single stone has been examined under sine waves by the shaking table test the mam needs to be extended and further verified in this paper the mam was extended by introducing the movement change that was induced by the so called trampoline effect of earthquake loading and the latest practical numerical simulation program discontinuous deformation analysis dda was used to verify the mobility of earthquake induced landslides after a conceptual landslide model was used to verify the effect of seismic loading on the mobility the donghekou landslide which was a typical long run out landslide that was induced by the 2008 wenchuan earthquake was analyzed the results show that the seismic loading could be one of the factors that could eventually help increase the run out of landslides

hydrocarbon lakes on titan distribution and interaction with a porous regolith from 10 to more than 100 000 km 2 the size and location of lakes provide constraints on parameters associated with subsurface transport using porous media properties inferred from huygens probe observations timescales for flow into and out of observed lakes are shown to be in the tens of years similar to seasonal cycles derived timescales are compared to the time between collocated sar observations in order to considertheroleofsubsurfacetransportintitan shydrologic cycle citation hayes a et al 2008 hydrocarbon lakes on titan distribution and interaction with a porous regolith geophys res lett 35 l09204 doi 10 1029 2008gl033409

an experimental study to characterize the initiation of the seismic induced tsaoling rock avalanche abstract the tsaoling rock avalanche which had a sliding volume of 120 million m3 and a maximum thickness of 170 m was triggered by the chi chi earthquake in 1999 however the initiation mechanism has not been well understood because different friction models have been proposed to describe the triggering process using the newmark sliding model and numerical simulations in this study a new dynamic ring shear test with a maximum normal stress higher than 3400 kpa is applied as an alternative approach to investigate the initiation of the seismic induced rock avalanche along the wet sliding surface at the interface of the cholan sandstone and consolidated remold shale experimental results verify that the seismic stresses at the wet sliding surface touch the failure surface and generate significant cumulative shear displacements additionally the shear surface should have non linear failure criteria rather than the well known linear mohr coulomb failure criteria with a constant friction angle furthermore the initiation time of the tsaoling rock avalanche obtained from the dynamic ring shear test is strongly correlated with the available seismic signal interpretations and the interviews of witnesses who travelled with the sliding mass this is the first experiment clarifying the co seismic behavior of the sliding surface and the initiation of the tsaoling landslide during the chi chi earthquake additionally from the development of the ring shear test the integrations of high normal stress the wet sandstone shale interface and the dynamic test with seismic loadings greatly extend the use of ring shear tests to rock avalanches

crater topography on titan implications for landscape evolution abstract we present a comprehensive review of available crater topography measurements for saturn s moon titan in general the depths of titan s craters are within the range of depths observed for similarly sized fresh craters on ganymede but several hundreds of meters shallower than ganymede s average depth vs diameter trend depth to diameter ratios are between 0 0012 0 0003 for the largest crater studied menrva d 425 km and 0 017 0 004 for the smallest crater studied ksa d 39 km when we evaluate the anderson darling goodness of fit parameter we find that there is less than a 10 probability that titan s craters have a current depth distribution that is consistent with the depth distribution of fresh craters on ganymede there is however a much higher probability that the relative depths are uniformly distributed between 0 fresh and 1 completely infilled this distribution is consistent with an infilling process that is relatively constant with time such as aeolian deposition assuming that ganymede represents a close airless analogue to titan the difference in depths represents the first quantitative measure of the amount of modification that has shaped titan s surface the only body in the outer solar system with extensive surface atmosphere exchange

the landslide story the catastrophic wenchuan earthquake induced an unprecedented number of geohazards the risk of heightened landslide frequency after a quake with potential secondary effects such as river damming and subsequent floods needs more focused attention

convection in enceladus ice shell conditions for initiation 1 observations of enceladus by the cassini spacecraft indicate that this tiny saturnian moon is geologically active with plumes of water vapor and ice particles erupting from its southern polar region this activity suggests that tidal dissipation has become spatially localized perhaps due to a compositional rheological and or thermal anomaly in its ice shell here we examine the role that solid state convection may have played in enceladus prolific activity by creating a suitable rheological and thermal anomaly we find convection can only initiate in the pure water ice i shell of a differentiated enceladus if the ice grain size is less than 0 3 mm which is quite small but may be realistic if non water ice impurities and or tidal stresses keep grains from growing this grain size restriction becomes more severe for lower basal ice temperatures which implies that any ammonia present has not become strongly concentrated in a thin basal ocean while convection occurs for a maximally thick pure ice shell and underlying ocean convective heat flows are 7 11 mw m 2 for ice grain sizes of 0 1 0 3 mm compared with the 100 mw m 2 measured for enceladus south polar terrain from cassini cirs observations thus whereas solid state convection may be a prerequisite for enceladus geological activity the observed heat flow requires strong tidal dissipation within the convecting region and possibly that convection reaches the surface

enceladus s and dione s floating ice shells supported by minimum stress isostasy enceladus gravity and shape have been explained in terms of a thick isostatic ice shell floating on a global ocean in contradiction of the thin shell implied by librations here we propose a new isostatic model minimizing crustal deviatoric stress and demonstrate that gravity and shape data predict a 38 4km thick ocean beneath a 23 4km thick shell agreeing with but independent from libration data isostatic and tidal stresses are comparable in magnitude south polar crust is only 7 4km thick facilitating the opening of water conduits and enhancing tidal dissipation through stress concentration enceladus resonant companion dione is in a similar state of minimum stress isostasy its gravity and shape can be explained in terms of a 99 23km thick isostatic shell overlying a 65 30km thick global ocean thus providing the first clear evidence for a present day ocean within dione

titan s impact crater population after cassini abstract titan is saturn s largest moon and has a dynamic surface with methane rivers carved by an active hydrological cycle and sand seas shaped by aeolian processes one way to study the rates of these processes is by examining titan s impact craters because they provide quantitative constraints on the level of degradation with the end of the cassini mission in september 2017 we have reassessed the crater population using the entire cassini synthetic aperture radar sar dataset including 30 additional craters since the last assessment in 2012 for a total of 90 certain to possible impact craters on titan we adjust for incomplete coverage 69 of the moon by sar imaging using a monte carlo approach and find no major change in titan s inferred surface age from prior studies we then used the sartopo and stereo topography data sets to measure crater depths and diameters for the first time rim heights for twelve craters were also reported on average titan s craters are shown to be shallower with lower rims than those observed on similarly sized icy moons e g ganymede this suggests that the observed modification is due to a combination of sand and sediment infilling onto the crater floor and fluvial erosion of the rims with fluvial erosion playing a larger role than previously thought in crater degradation on titan

determination of ocean tides from the first year of topex poseidon altimeter measurements an improved geocentric global ocean tide model has been determined using 1 year of topex poseidon altimeter measurements to provide corrections to the cartwright and ray 1991 model cr91 the corrections were determined on a 3 3 grid using both the harmonic analysis method and the response method the two approaches produce similar solutions the effect on the tide solution of simultaneously adjusting radial orbit correction parameters using altimeter measurements was examined four semidiurnal n2 m2 s2 and k2 four diurnal q1 o1 p1 and k1 and three long period ssa mm and m constituents along with the variation at the annual frequency were included in the harmonic analysis solution the observed annual variation represents the first global measurement describing accurate seasonal changes of the ocean during an el nino year the corrections to the m2 constituent have an rms of 3 6 cm and display a clear banding pattern with regional highs and lows reaching 8 cm the improved tide model reduces the weighted altimeter crossover residual from 9 8 cm rms when the cr91 tide model is used to 8 2 cm rms comparison of the improved model to pelagic tidal constants determined from 80 tide gauges gives rms differences of 2 7 cm for m2 and 1 7 cm for k1 comparable values when the cr91 model is used are 3 9 cm and 2 0 cm respectively examination of topex poseidon sea level anomaly variations using the new tide model further confirms that the tide model has been improved

titan s gravity field and interior structure after cassini since its arrival at saturn in 2004 cassini performed nine flybys devoted to the determination of titan s gravity field and its tidal variations here we present an updated gravity solution based on the final data set collected during the gravity dedicated passes before cassini s plunge into saturn s atmosphere the data set includes an additional flyby t110 march 2015 primarily devoted to imaging titan s north polar lakes carried out with the low gain antenna this flyby was particularly valuable because the closest approach occurred at a high latitude 75 n over an area not previously sampled previously published gravity results iess et al 2012 indicated that titan is subject to large eccentricity tides in response to the time varying perturbing potential exerted by saturn the magnitude of the response quadrupole field expressed in the tidal love number k 2 was used to infer the existence of an internal ocean the new gravity field determination provides an improved estimate of k 2 of about 0 62 accurate to a level of a few percent the value is higher than the simplest models of titan suggest and the interpretation is unclear possibilities include a high density ocean as high as 1300 kg m 3 a partially viscous response of the deeper region or a dynamic contribution to the tidal response the new solution includes higher degree and order harmonic coefficients up to 5 and offers an improved map of gravity anomalies the geoid is poorly correlated with the topography implying strong compensation in addition the updated geoid and its associated uncertainty could be used to refine the gravity altimetry correlation analysis and for improved interpretation of radar altimetric data

insights into the catastrophic xinmo rock avalanche in maoxian county china combined effects of historical earthquakes and landslide amplification abstract a large and catastrophic rock avalanche occurred at the xinmo village in the maoxian county of the sichuan province of china on june 24 2017 the avalanche destroyed 64 houses and killed 10 people and 73 people were reported to be missing in this study we focused on the contributions of six historical earthquakes to the collapse of rocks in the source area and the landslide amplification caused by the entrainment of pre existing deposits on the landslide path the historical earthquakes in this area contributed different levels of damage on the source rocks particularly the 1933 diexi earthquake induced a few initial cracks in rocks at the crest of the steep hillslope under the combined time effects of long term weathering and gravity the rock blocks in the source area were detached from the crest along the intersecting cracks and over dip soft layer namely the sliding surface the avalanche was amplified by the entrainment of colluvium on its path the influence of the colluvium on the movement process of the xinmo landslide was modelled by the gpu based parallel discontinuous deformation analysis dda method and the effect of the impact and entrainment in the debris flow was rigorously analysed the results indicate that the impact and entrainment can continuously increase the volume of debris flow and the thickness of the colluvium was established to be in the range of 25 9 33 9 m based on the analysis of the deposit pattern and movement duration of the avalanche there were numerous unstable rocks induced by historical earthquakes at the crests of steep hill slopes in the earthquake stricken area with long term damage caused by environmental factors and gravity the failure of unstable rocks with high potential energy is likely to cause severe disasters the excess pore water pressure likely to be present in the colluvium or deposits during impact and entrainment can considerably reduce the effective stress and degrade friction resistance along the runout path as a result the landslide can be intensively amplified owing to the effect of impact and entrainment under a lower friction resistance

stresses generated in cooling viscoelastic ice shells application to europa 1 a cooling viscoelastic ice shell overlying an ocean develops stresses due to two effects thermal contraction of the ice due to cooling and the expansion of the shell due to the ice water volume change the former effect generates near surface compression and deeper extension the second effect generates extension only in both cases stresses are smaller at depth due to viscous creep the resulting combined stresses are extensional except at shallow 1 km depths in thin ice shells for ice shells thicker than 45 km stresses are extensional throughout the extensional stresses exceed 10 mpa for shells thicker than 20 km and thus dominate all other likely sources of stress as long as shell cooling occurs the dominantly extensional nature of the stresses may help to explain the puzzling lack of compression observed on europa and other large icy satellites however after 100 myr of conductive cooling the maximum theoretical elastic strains for europa are 0 35 which are probably insufficient to explain the total amount of observed extension

global contraction expansion and polar lithospheric thinning on titan from patterns of tectonism we investigate the underlying physical processes that govern the formation and evolution of titan s tectonic features this is done by mapping mountain chains and hills using cassini radar data obtained during titan flybys t3 to t69 our mapping of mountain chains and hills reveals a global pattern east west orientations within 30 of the equator and north south between 60 latitude and the poles this result makes titan one of the few solar system bodies where global processes rather than regional processes dominate tectonism after comparison with five global stress models showing theoretical mountain chain orientations we suggest that either global contraction coupled with spin up or global expansion coupled with despinning could explain our observations if coupled with a lithosphere thinner in titan s polar regions

structure and formation of the lunar farside highlands the formation of the lunar farside highlands has long been an open problem in lunar science we show that much of the topography and crustal thickness in this terrain can be described by a degree 2 harmonic no other portion of the moon exhibits comparable degree 2 structure the quantified structure of the farside highlands unites them with the nearside and suggests a relation between lunar crustal structure nearside volcanism and heat producing elements the farside topography cannot be explained by a frozen in tidal bulge however the farside crustal thickness and the topography it produces may have been caused by spatial variations in tidal heating when the ancient crust was decoupled from the mantle by a liquid magma ocean similar to europa s present ice shell

travel distance angle for rapid landslides in constructed and natural soil slopes rapid landslides in constructed and natural soil slopes have the potential to cause loss of life destruction of property and damage to the natural environment because the velocity of the slide

polar motion of titan forced by the atmosphere 1 titan s atmosphere possesses an equatorial component of angular momentum which can be transferred to the surface and can excite polar motion of titan the atmospheric excitation of titan s polar motion is calculated using the wind and pressure data prediction from a general circulation model the polar motion equation is solved considering titan s triaxial shape and different hypothetical interior models titan s polar motion basically consists of a superposition of small diurnal wobbles and larger semiannual and annual wobbles caused by seasonal redistribution of wind and pressure pattern if the entire interior of titan is solid the polar motion has total amplitudes of a few meters but the diurnal and seasonal wobble may be intermingled due to preferential damping of the seasonal wobble by saturn s gravitational torque if instead there is a subsurface ocean underneath the crust the wobble amplitude could be larger by an order of magnitude if the crust is thin a resonance between the seasonal and chandler wobble further increases the polar motion amplitude and makes the polar motion path elliptical the seasonal wobble of a crust lying on a subsurface ocean experiences damping by either gravitational and pressure torque or elastic torque but the relative reduction of the polar motion amplitude by these torques is likely to be smaller than that of the length of day variations

the tidal response of europa the tidal response of europa to a time varying potential is determined by solving the quasi static equilibrium equations for a body composed of several uniform maxwell viscoelastic layers models in which europa s surface ice extends all the way to the silicate mantle have weak tidal responses 1 m vertical deflection while models in which a liquid ocean underlies the ice have about 30 m peak vertical deflection the phase lag of the tidal response is very small 2 in the case of an ocean but may be large if there is no ocean and the ice has a viscosity around 1013 pa s for models with an ocean the product of the thickness and strength of the ice determines the tidal response making it difficult to determine the thickness of the ice by observing the tidal deflection of europa

interior structure models and tidal love numbers of titan 1 interior models of a differentiated titan with an internal ammonia water ocean and chondritic radiogenic heat production in an undifferentiated rock iron core have been calculated we assume thermal and mechanical equilibrium and calculate the structure of the interior as a function of the thickness of an ice i layer on top of the ocean as well as the moment of inertia factor and the tidal love numbers for comparison with cassini gravity data the love numbers are linearly dependent on the thickness of the ice i shell at constant rheology parameters but decrease by one order of magnitude in the absence of an internal ocean ice shell thicknesses are between 90 and 105 km for models with 5 wt ammonia and for core densities between 3500 and 4500 kg m 3 for 15 wt ammonia the shell is 65 to 70 km thick we use a strongly temperature dependent viscosity parameterization of convective heat transport and find that the stagnant lid comprises most of the ice i shell tidal heating in the warm convective sublayer is of minor importance the internal ocean is several hundred kilometers thick and its thickness decreases with increasing thickness of the ice shell core sizes vary from 1500 to 1800 km radius with associated moment of inertia factors of 0 30 0 01

the relationship between topography and gravity on earth and venus abstract the measurement of the admittance between the topography and the gravity of a planet as a function of wavelength provides important constraints on its interior processes a detailed discussion of the influence of noise on such measurements shows that at long wavelengths the admittance is best determined in the frequency domain using gravity as input and topography as output this procedure is used to estimate the admittance in the pacific and indian oceans the observed values are reduced by volcanism above plumes which produces a contribution to the long wavelength compensated topography when this effect is taken into account there is little evidence that the admittance is reduced by the presence of a low viscosity zone in the upper mantle a similar study of venus shows an excellent correlation between gravity g and topography h for wavelengths greater than 700 km with an admittance of about 50 mgal km 1 this value agrees well with that expected from numerical axisymmetric models of plumes and can be used to construct maps of residual topography by calculating h g 50 where h is in kilometers and g in milligals the power spectrum of the gravity field and its skewness with positive anomalies covering a smaller area but being larger than the negative ones are also in agreement with those of the numerical models of the major topographic features only aphrodite and ishtar terrae behave differently with a value of admittance of about one third of other large structures this difference requires their topography to be partly supported by variations in crustal thickness by analogy with similar structures on earth both are likely to be supported by volcanically thickened crust on top of rising plumes though the observed relationships do not rule out other models the behavior of the admittance at long wavelengths is important because it can constrain the thickness of the convecting layer at wavelengths of more than 3000 km the gravity data provides some evidence that the layer depth is about 1000 km over the center of beta and phoebe regiones there are short wavelength anomalies of residual topography produced by crust that is thinner than that elsewhere flanked by positive anomalies of thicker crust the regions of thin crust occur beneath rift zones this behavior can be explained if crust flows down the flanks of elevated regions above plumes and can generate coronae when the plume support disappears

tidal heating and the long term stability of a subsurface ocean on enceladus abstract tidal dissipation has been suggested as the heat source for the south polar thermal anomaly on enceladus we find that under present day conditions and assuming maxwellian behavior tidal dissipation is negligible in the silicate core dissipation may be significant in the ice shell if the shell is decoupled from the silicate core by a subsurface ocean we have run a series of self consistent convection and conduction models in 2d axisymmetric and 3d spherical geometry in which we include the spatially variable tidal heat production we find that in all cases the shell removes more heat from the interior than can be produced in the core by radioactive decay resulting in cooling of the interior and the freezing of any ocean under likely conditions a 40 km thick ocean made of pure water would freeze solid on a 30 ma timescale an ocean containing other chemical components will have a lower freezing point but even a water ammonia eutectic composition will only prolong the freezing not prevent it if the eccentricity of enceladus were higher e 0 015 in the past the increased dissipation in the ice shell may have been sufficient to maintain a liquid layer we cannot therefore rule out the presence of a transient ocean as a relic of an earlier era of greater heating if the eccentricity is periodically pumped up the ocean may have thickened and thinned on a similar timescale as the orbital evolution provided the ocean never froze completely we conclude that the current heat flux of enceladus and any possible subsurface ocean is not in steady state and is the remnant of an epoch of higher eccentricity and tidal dissipation

global drainage patterns and the origins of topographic relief on earth mars and titan rivers have eroded the topography of mars titan and earth creating diverse landscapes however the dominant processes that generated topography on titan and to some extent on early mars are not well known we analyzed drainage patterns on all three bodies and found that large drainages which record interactions between deformation and erosional modification conform much better to long wavelength topography on titan and mars than on earth we use a numerical landscape evolution model to demonstrate that short wavelength deformation causes drainage directions to diverge from long wavelength topography as observed on earth we attribute the observed differences to ancient long wavelength topography on mars recent or ongoing generation of long wavelength relief on titan and the creation of short wavelength relief by plate tectonics on earth

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

ocean worlds in the outer solar system many outer solar system bodies are thought to harbor liquid water oceans beneath their ice shells this article first reviews how such oceans are detected we then discuss how they are maintained when they formed and what the oceans likely characteristics are we focus in particular on europa ganymede callisto titan and enceladus bodies for which there is direct evidence of subsurface oceans we also consider candidate ocean worlds such as pluto and triton

analysis of landsliding by earthquake shaking using a block on slope thermo mechanical model example of jiufengershan landslide central taiwan the jiufengershan rock and soil avalanche is one of the largest landslides triggered by the chi chi taiwan earthquake september 21 1999 in order to study landslide triggering and propagation by seismic shaking we propose a method that combines features of the classic newmark approach with mechanical relations involving mohr coulomb failure criteria pore water pressure and shear heating during the sliding process the effective shear strength is affected by shear heating and by pore pressure variations during the sliding process the shaking process was simulated using strong motion accelerograms of the three nearest free field stations which surrounded the landslide the initiation and propagation of earthquake induced landslides are mainly controlled by the peak and residual shear strengths respectively the increase in temperature in the shear zone increases the pore water pressure and weakens the shear strength rock avalanches are generated when mechanical parameters achieve critical threshold values such that the residual shear strength is less than the tangential projection of body forces

shell thickness variations and the long wavelength topography of titan the long wavelength topography of titan has an amplitude larger than that expected from tidal and rotational distortions at its current distance from saturn this topography is associated with small gravity anomalies indicating a high degree of compensation both observations can be explained if titan has a floating isostatically compensated ice shell with a spatially varying thickness the spatial variations arise because of laterally variable tidal heating within the ice shell models incorporating shell thickness variations result in an improved fit to the observations and a degree two tidal love number h2t consistent with expectations without requiring titan to have moved away from saturn our preferred models have a mean shell thickness of 100 km in agreement with the observed gravity anomalies and a heat flux appropriate to a chondritic titan shell thickness variations are eliminated by convection we therefore conclude that titan s ice shell is not convecting at the present day

objective delineation of lahar inundation hazard zones a new method of delineating lahar hazard zones in valleys that head on volcano flanks provides a rapid objective reproducible alternative to traditional methods the rationale for the method derives from scaling analyses of generic lahar paths and statistical analyses of 27 lahar paths documented at nine volcanoes together these analyses yield semiempirical equations that predict inundated valley cross sectional areas a and planimetric areas b as functions of lahar volume v the predictive equations a 0 05v 2 3 and b 200v 2 3 provide all information necessary to calculate and plot in

obliquity of the galilean satellites the influence of a global internal liquid layer abstract the obliquity of the galilean satellites is small but not yet observed studies of cycloidal lineaments and strike slip fault patterns on europa suggest that europa s obliquity is about 1 although theoretical models of the obliquity predict the obliquity to be one order of magnitude smaller for an entirely solid europa here we investigate the influence of a global liquid layer on the obliquity of the galilean satellites io most likely has a fully liquid core while europa ganymede and callisto are thought to have an internal global liquid water ocean beneath an external ice shell we use a model for the obliquity based on a cassini state model extended to the presence of an internal liquid layer and the internal gravitational and pressure torques induced by the presence of this layer we find that the obliquity of io only weakly depends on the different internal structure models considered because of the weak influence of the liquid core which is therefore almost impossible to detect through observations of the obliquity the obliquity of europa is almost constant in time and its mean value is smaller 0 033 0 044 with an ocean than without 0 055 an accuracy of 0 004 about 100 m on the spin pole location at the surface would allow detecting the internal ocean the obliquity of ganymede and callisto depends more on their interior structure because of the possibility of resonant amplifications for some periodic terms of the solution their ocean may be easily detected if at the measuring time the actual internal structure model lead to a very different value of the obliquity than in the solid case a long term monitoring of their shell obliquity would be more helpful to infer information on the shell thickness

thermal orbital evolution of io and europa coupled thermal orbital evolution models of europa and io are presented it is assumed that io europa and ganymede evolve in the laplace resonance and that tidal dissipation of orbital energy is an internal heat source for both io and europa while dissipation in io occurs in the mantle as in the mantle dissipation model of segatz et al 1988 icarus 75 187 two models for europa are considered in the first model dissipation occurs in the silicate mantle while in the second model dissipation occurs in the ice shell in the latter model ice shell melting and variations of the shell thickness above an ocean are explicitly included the rheology of both the ice and the rock is cast in terms of a viscoelastic maxwell rheology with viscosity and shear modulus depending on the average temperature of the dissipating layer heat transfer by convection is calculated using a parameterization for strongly temperature dependent viscosity convection both models are consistent with the present orbital elements of io europa and ganymede it is shown that there may be phases of quasi steady evolution with large or small dissipation rates in comparison with radiogenic heating phases with runaway heating or cooling and oscillatory phases during which the eccentricity and the tidal heating rate will oscillate europa s ice thickness varies between roughly 3 and 70 km dissipation in the silicate layer or 10 and 60 km dissipation in the ice layer suggesting that europa s ocean existed for geological timescales the variation in ice thickness including both convective and purely conductive phases may be reflected in the formation of different geological surface features on europa both models suggest that at present europa s ice thickness is several tens of km thick and is increasing while the eccentricity decreases implying that the satellites evolve out of resonance including lithospheric growth in the models makes it impossible to match the high heat flux constraint for io other heat transfer processes than conduction through the lithosphere must be important for the present io

ocean tidal heating in icy satellites with solid shells abstract as a long term energy source tidal heating in subsurface oceans of icy satellites can influence their thermal rotational and orbital evolution and the sustainability of oceans we present a new theoretical treatment for tidal heating in thin subsurface oceans with overlying incompressible elastic shells of arbitrary thickness the stabilizing effect of an overlying shell damps ocean tides reducing tidal heating this effect is more pronounced on enceladus than on europa because the effective rigidity on a small body like enceladus is larger for the range of likely shell and ocean thicknesses of enceladus and europa the thin shell approximation of beuthe 2016 is generally accurate to less than about 4 explaining enceladus endogenic power radiated from the south polar terrain by ocean tidal heating requires ocean and shell thicknesses that are significantly smaller than the values inferred from gravity and topography constraints the time averaged surface distribution of ocean tidal heating is distinct from that due to dissipation in the solid shell with higher dissipation near the equator and poles for eccentricity and obliquity forcing respectively this can lead to unique horizontal shell thickness variations if the shell is conductive the surface displacement driven by eccentricity and obliquity forcing can have a phase lag relative to the forcing tidal potential due to the delayed ocean response for europa and enceladus eccentricity forcing generally produces greater tidal amplitudes due to the large eccentricity values relative to the obliquity values despite the small obliquity values obliquity forcing generally produces larger phase lags due to the generation of rossby haurwitz waves if europa s shell and ocean are respectively 10 and 100 km thick the tide amplitude and phase lag are 26 5 m and

landslide mobility analysis for design of multiple debris resisting barriers multiple debris resisting barriers have been commonly used worldwide to mitigate debris flows in drainage lines however a well developed methodology to assess the mobility of debris flows with co

mountain torque and its influence on the atmospheric angular momentum on titan abstract the impact of titan s large scale topography and surface roughness on the atmospheric angular momentum budget is investigated by the cologne titan general circulation model that is run with and without topography constrained by cassini on seasonal timescales the angular momentum exchange is dominated by the friction torque which oscillates semi annually topography gives rise to a large diurnal and small seasonal mountain torque the diurnal mountain torque is caused by surface pressure variations associated with saturn s tide but has no net effect on the atmospheric angular momentum the seasonal mountain torque is mainly contributed by low latitude mountains that are hit by easterly surface winds the seasonal mountain torque causes a net transfer of angular momentum from the surface to the atmosphere which is counterbalanced by an opposite angular momentum transfer by the friction torque the atmospheric angular momentum is larger if topography is included

stability of ice rock mixtures with application to a partially differentiated titan titan s moment of inertia calculated assuming hydrostatic equilibrium from gravity field data obtained during the cassini huygens mission implies an internal mass distribution that may be incompatible with complete differentiation this suggests that titan may have a mixed ice rock core possibly consistent with slow accretion in a gas starved disk which may initially spare titan from widespread ice melting and subsequent differentiation a partially differentiated titan however must still efficiently remove radiogenic heat over geologic time we argue that compositional heterogeneity in the major saturnian satellites indicates that titan formed from planetesimals with disparate densities the resulting compositional anomalies would quickly redistribute to form a vertical density gradient that would oppose thermal convection we use elements of the theory of double diffusive convection to create a parameterized model for the thermal evolution of ice rock mixtures with a stabilizing compositional gradient to account for large uncertainties in material properties and accretionary processes we perform simulations for a wide range of initial conditions ultimately for realistic density gradients double diffusive convection in the ice rock interior can delay but not prevent ice melting and differentiation even if a substantial fraction of potassium is leached from the rock component consequently titan is not partially differentiated

dynamic stability analysis of jointed rock slopes using the dda method king herod s palace masada israel abstract a dynamic two dimensional stability analysis of a highly discontinuous rock slope is demonstrated in this paper the studied rock slope is the upper terrace of king herod s palace in masada situated on the western margins of the seismically active dead sea rift the slope consists of sub horizontally bedded and sub vertically jointed stiff dolomite blocks the dynamic deformation of the slope is calculated using a fully dynamic version of dda in which time dependent acceleration is used as input the analytically determined failure modes of critical keyblocks in the jointed rock slope are clearly predicted by dda at the end of the dynamic calculation it is found however that for realistic displacement estimates some amount of energy dissipation must be introduced into the otherwise fully elastic un damped dda formulation comparison of predicted damage with actual slope performance over a historic time span of 2000 years allows us to conclude that introduction of 2 kinetic damping should suffice for realistic damage predictions this conclusion is in agreement with recent results of tsesarsky et al in y h hatzor ed stability of rock structures proceedings of the fifth international conference of analysis of discontinuous deformation balkema publishers lisse 2002 pp 195 203 who compared displacements of a single block on an inclined plane subjected to dynamic loading obtained by dda and by shaking table experiments using dynamic dda it is shown that introduction of a simple rock bolting pattern completely stabilizes the slope

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

laboratory scale investigation of the 3 d geometry of landslide dams in a u shaped valley abstract landslide dams form when a landslide obstructs narrow and steep valleys in mountainous areas since these dams may fail over a short time and cause secondary geological disasters in the downstream area the stability of such dams must be assessed in an accurate and timely manner the three dimensional 3 d geometry of a landslide dam which is one of the essential indices for stability analyses is highly influenced by the landslide dam formation conditions including the sliding surface dip angle and the valley topography however few studies have focused on the correlation between the 3 d geometry and formation conditions of a landslide dam a photogrammetric system was used to develop a laboratory apparatus to simulate the formation process of a landslide dam and construct a digital model for the 3 d geometry of a landslide dam in a u shaped valley then a series of experiments were designed to systematically investigate the formation process and the 3 d geometry of landslide dams under different combinations of valley bed inclinations 0 4 8 and 12 and sliding surface dip angles 30 45 60 and 75 the results indicate that the sliding surface dip angle has a significant effect on the length and height of a landslide dam whereas the valley bed inclination has a limited effect on the length and height compared with its effect on the relative angles of a landslide dam in addition the cross sectional profiles of landslide dams can be classified into three categories namely symmetric asymmetric and flat shapes and these profiles are predominantly affected by the sliding surface dip angle instead of the valley bed inclination subsequently a mathematical model for predicting the 3 d geometry of a landslide dam was presented according to the experimental results and it was verified by the experimental data and 42 historical cases of landslide dams based on the proposed model the predicted 3 d geometry of the tangjiashan landslide dam triggered by the wenchuan earthquake of 2008 was consistent with its actual geometry which confirmed the reliability of the prediction model in practical applications the findings of our study contribute to the establishment of evidence based disaster prevention and mitigation measures for landslide dams

runout analysis and mobility observations for large open pit slope failures objectively forecasting the runout of a potential open pit slope failure in addition to identifying the failure itself is a critical component of a mine s risk management plan recent losses arising from large open pit slope failures demonstrate shortcomings in current practice a dataset of 105 pit slope failures was compiled to compare open pit runout trends against established empirical runout relationships for natural landslides fahrboschung angle versus volume and fahrboschung angle versus slope angle relationships provide reasonable runout estimates open pit slopes have the advantage of removing the influence of morphological features vegetation and liquefiable substrates while controlling the travel path angle and roughness in such a controlled environment landslide mobility has a strong sensitivity to slope angle material properties and fall height and is only modestly sensitive to volume a grouping of highly mobile open pit slope cases involving weathered saturated collapsible rock

a rigid and weathered ice shell on titan a strong inverse correlation between gravity and topography leads to the conclusion that saturn s largest moon titan must have a rigid ice shell with an elastic thickness exceeding 40 kilometres titan saturn s largest moon may have a stronger ice shell than previously thought several lines of evidence suggest that titan has a global subsurface ocean beneath an outer ice shell 50 200 km thick with a rigid portion that is thin and weak here hemingway et al report a strong inverse correlation between gravity and topography at long wavelengths that are not dominated by tides and rotation this finding is not compatible with a geologically active low rigidity ice shell suggesting that titan s ice shell must be substantially rigid with an elastic thickness of greater than 40 km several lines of evidence suggest that saturn s largest moon titan has a global subsurface ocean beneath an outer ice shell 50 to 200 kilometres thick1 2 3 4 if convection5 6 is occurring the rigid portion of the shell is expected to be thin similarly a weak isostatically compensated shell has been proposed7 8 to explain the observed topography here we report a strong inverse correlation between gravity3 and topography9 at long wavelengths that are not dominated by tides and rotation we argue that negative gravity anomalies mass deficits produced by crustal thickening at the base of the ice shell overwhelm positive gravity anomalies mass excesses produced by the small surface topography giving rise to this inverse correlation we show that this situation requires a substantially rigid ice shell with an elastic thickness exceeding 40 kilometres and hundreds of metres of surface erosion and deposition consistent with recent estimates from local features10 11 our results are therefore not compatible with a geologically active low rigidity ice shell after extrapolating to wavelengths that are controlled by tides and rotation we suggest that titan s moment of inertia may be even higher that is titan may be even less centrally condensed than is currently thought12

geophysical implications of the long wavelength topography of the saturnian satellites 1 we use limb profiles to quantify the long wavelength topography of the saturnian satellites the degree 2 shapes of mimas enceladus and tethys are not consistent with hydrostatic equilibrium we derive 2 d topographic maps out to spherical harmonic degree 8 there is a good correlation with topography derived from stereo techniques if uncompensated topography at degree 3 and higher is large enough to be detectable during close spacecraft flybys if not properly accounted for this topography may bias estimates of a satellite s degree 2 gravity coefficients which are used to determine the moment of inertia we also derive a one dimensional variance spectrum a measure of how roughness varies with wavelength for each body the short wavelength spectral slope is 2t o 2 5 similar to silicate bodies however unlike the terrestrial planets each satellite spectrum shows a reduction in slope at longer wavelengths if this break in slope is due to a transition from flexural to isostatic support the globally averaged elastic thickness te of each satellite may be derived we obtain te values of 5 km 1 5 5 km 5 km and 5 km for tethys dione rhea and iapetus respectively for europa we obtain te 1 5 km these estimates are generally consistent with estimates made using other techniques for enceladus intermediate wavelengths imply te 0 5 km but the variance spectrum at wavelengths greater than 150 km is probably influenced by long wavelength processes such as convection or shell thickness variations impact cratering may also play a role in determining the variance spectra of some bodies citation nimmo f b g bills and p c thomas 2011 geophysical implications of the long wavelength topography of the saturnian satellites j geophys res 116 e11001 doi 10 1029 2011je003835

the tectonics of titan global structural mapping from cassini radar abstract the cassini radar mapper has imaged elevated mountain ridge belts on titan with a linear to arcuate morphology indicative of a tectonic origin systematic geomorphologic mapping of the ridges in synthetic aperture radar sar images reveals that the orientation of ridges is globally e w and the ridges are more common near the equator than the poles comparison with a global topographic map reveals the equatorial ridges are found to lie preferentially at higher than average elevations we conclude the most reasonable formation scenario for titan s ridges is that contractional tectonism built the ridges and thickened the icy lithosphere near the equator causing regional uplift the combination of global and regional tectonic events likely contractional in nature followed by erosion aeolian activity and enhanced sedimentation at mid to high latitudes would have led to regional infilling and perhaps covering of some mountain features thus shaping titan s tectonic landforms and surface morphology into what we see today

titan s topography and shape at the end of the cassini mission with the conclusion of the cassini mission we present an updated topographic map of titan including all the available altimetry sartopo and stereo photogrammetry topographic datasets available from the mission we use radial basis functions to interpolate the sparse dataset which covers only 9 of titan s global area the most notable updates to the topography include higher coverage of the poles of titan improved fits to the global shape and a finer resolution of the global interpolation we also present a statistical analysis of the error in the derived products and perform a global minimization on a profile by profile basis to account for observed biases in the input dataset we find a greater flattening of titan than measured additional topographic rises in titan s southern hemisphere and better constrain the possible locations of past and present liquids on titan s surface

diapir induced reorientation of saturn s moon enceladus the recent discovery of active water venting from the surface of saturn s icy moon enceladus has caused a ripple of excitement as it suggests the possibility of subsurface liquid water geologically enceladus poses problems one the reason why the hotspot of geological activity is centred precisely on the south pole has been tackled by francis nimmo and robert t pappalardo they identify reorientation of enceladus s rotation axis as the likely cause and an upwelling of low density material to the surface as the cause of that reorientation comparison of the distribution of impact craters on the leading and trailing hemispheres will be a good test of the reorientation part of the theory enceladus is a small icy satellite of saturn its south polar region consists of young tectonically deformed terrain and has an anomalously high heat flux1 2 this heat flux is probably due to localized tidal dissipation within either the ice shell3 or the underlying silicate core4 the surface deformation is plausibly due to upwelling of low density material diapirism5 as a result of this tidal heating here we show that the current polar location of the hotspot can be explained by reorientation of the satellite s rotation axis because of the presence of a low density diapir if the diapir is in the ice shell then the shell must be relatively thick and maintain significant rigidity elastic thickness greater than 0 5 km if the diapir is in the silicate core then enceladus cannot possess a global subsurface ocean because the core must be coupled to the overlying ice for reorientation to occur the reorientation generates large 10 mpa tectonic stress patterns6 that are compatible with the observed deformation of the south polar region2 we predict that the distribution of impact craters on the surface will not show the usual leading hemisphere trailing hemisphere asymmetry a low density diapir also yields a potentially observable negative gravity anomaly

error analysis of empirical ocean tide models estimated from topex poseidon altimetry an error budget is proposed for the topex poseidon t p empirical ocean tide models estimated during the primary mission the error budget evaluates the individual contribution of errors in each of the altimetric range corrections orbit errors caused by errors in the background ocean tide potential and errors caused by the general circulation of the oceans to errors in the ocean tide models of the eight principal diurnal and semidiurnal tidal components and the two principal long period tidal components the effect of continually updating the t p empirical ocean tide models during the primary t p mission is illustrated through tide gauge comparisons and then used to predict the impact of further updates during the extended mission both the tide gauge comparisons and the error analysis predict errors in the tide models for the eight principal diurnal and semidiurnal constituents to be of the order of 2 3 cm root sum square the dominant source of errors in the t p ocean tide models appears to be caused by the general circulation of the oceans observed by the t p altimeter further updates of the t p empirical ocean tide models during the extended mission should not provide significant improvements in the diurnal and semidiurnal ocean tide models but should provide significant improvements in the long period ocean tide models particularly in the monthly mm tidal component

fluvial erosion as a mechanism for crater modification on titan abstract there are few identifiable impact craters on titan especially in the polar regions one explanation for this observation is that the craters are being destroyed through fluvial processes such as weathering mass wasting fluvial incision and deposition in this work we use a landscape evolution model to determine whether or not this is a viable mechanism for crater destruction on titan we find that fluvial degradation can modify craters to the point where they would be unrecognizable by an orbiting spacecraft such as cassini given enough time and a large enough erosion rate a difference in the erosion rate between the equator and the poles of a factor of a few could explain the latitudinal variation in titan s crater population fluvial erosion also removes central peaks and fills in central pits possibly explaining their infrequent occurrence in titan craters although many craters on titan appear to be modified by aeolian infilling fluvial modification is necessary to explain the observed impact crater morphologies thus it is an important secondary modification process even in titan s drier equatorial regions

does titan s long wavelength topography contain information about subsurface ocean dynamics abstract the long wavelength topography of titan is characterized by relatively small amplitudes about 1 km peak to peak an anomalous equatorial bulge the poles are about 300 m lower than the equator and small gravity anomalies indicating a high degree of compensation in the past years the nature of titan s non hydrostatic topography has been addressed in several studies the topography has been interpreted in terms of isostatic or viscous models and discussed in connection with tidal heating in the ice shell and surface erosion here we present a model of the shape evolution of titan s ice shell driven by tidal heating in the shell and spatial variations of the heat flux from a subsurface ocean the model is obtained by solving a general set of equations coupling the viscoelastic flow of ice with the thermal evolution of the ice shell and phase transitions at the ice water interface the equations are solved in a domain with radially varying material properties and moving boundaries the motion of the boundaries is a consequence of ice flow within the shell melting and crystallization at the bottom boundary and erosion and deposition at the surface our model suggests that titan s anomalous topographic bulge can be explained by lateral variations of ocean heat flux of the order of 0 1 1 mw m 2 provided that the heat flux is stable over a period of at least 10 myr and the ice shell has a sufficiently high viscosity exceeding 1016 pa s at the base of the shell such a high value of viscosity implies that either the ice grains are coarse 10 mm or the temperature of the ocean is significantly by more than 40 k lower than the melting temperature of pure water ice the heat flux pattern predicted on top of the ocean is consistent with a flow characterized by upwelling of warm water in polar regions and downwelling of cold water at low latitudes the negative correlation between the topography and geoid at degree 3 reported in a previous study but not confirmed at higher degrees yet is shown to be compatible with erosion and deposition occurring at a rate of 0 01 0 1 mm yr 1 our results underline the importance of gravity and topography measurements for understanding titan s surface and deep interior processes

a global topographic map of titan abstract cassini radar sartopo and altimetry data are used to construct a global gridded 1 1 elevation map for use in global circulation models hydrological models and correlative studies the data are sparse and so most of the map domain 90 is populated with interpolated values using a spline algorithm the highest 520 m gridded point observed is at 48 s 12 w the lowest point observed 1700 m below a 2575 km sphere is at 59 s 317 w this may be a basin where liquids presently in the north could have resided in the past if the deepest point were once a sea with the areal extent of present day ligeia mare it would be 1000 m deep we find four prominent topographic rises each 200 km wide radar bright and heavily dissected distributed over a 3000 km arc in the southeastern quadrant of titan 40 60 s 15 150 w

is titan s shape caused by its meteorology and carbon cycle 1 titan s shape is characterized by a difference between the long equatorial radius and the polar radius that is several hundred meters larger than that predicted by the flattening due to its spin rate the north polar region is covered by large mare filled with hydrocarbons including ethane moreover global circulation models predict ethane precipitation on the polar areas this study shows that the shape of titan can be explained by the subsidence associated with the substitution of methane with ethane rich liquids percolating into the crust which as suggested by evolution models may be composed of methane clathrate hydrates such substitutions have been observed in laboratory experiments this process would provide an additional methane source as required for sustaining the presence of this constituent in titan s atmosphere through its history a 270 m subsidence of the polar caps is explained by the circulation of 1 5 to 6 1018kg of ethane in the top three kilometers of an initially methane clathrate crust this process would have operated during the last 300 1200 myr at the present ethane production rate

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

dynamic discrete analysis of an earthquake induced large scale landslide abstract the chiu fen erh shan landslide estimated to have a volume of 36 million cubic meters was triggered by the m w 7 6 taiwan chi chi earthquake of 1999 the debris covered an area of 1 95 km 2 and claimed 36 lives during the sliding the landslide mass disintegrated with its debris acquiring high speeds to reach over 1 km of travel distance the main objectives of the study were to investigate if it was possible to numerically model the landslide progression including slope disintegration and to reproduce the post failure configuration toward these goals the study employed a discrete element method called discontinuous deformation analysis for the dynamic analysis by incorporating the spacing and orientation information of the joints and bedding planes the slope was modeled as an assemblage of discrete deformable blocks horizontal and vertical ground motions were simultaneously applied the near field digital strong records were affected by the large uplift of the hanging wall of the reverse thrust fault and corrections were made to address this issue the study showed that the methodology adopted was able to capture essential characteristics of the landslide and gave a post failure configuration resembling that observed in the field