stress strain paradox plate coupling and forearc seismicity at the cascadia and nankai subduction zones abstract in the continental forearcs of the cascadia and nankai subduction zones geodetic strain measurements indicate crustal contraction in the direction of plate convergence nearly margin normal but earthquake focal mechanisms and other stress indicators show maximum compression along strike margin parallel it is evident that the geodetic strain signals reflect the temporal fluctuations of elastic stress associated with subduction earthquake cycles not the absolute stresses the absolute margin normal stress is not only much less than the margin parallel stress but also no greater than the lithostatic value indicating a very weak subduction thrust fault weak subduction faults are also consistent with geothermal data which require very low frictional heating along the faults great subduction earthquakes occur at very low shear stresses and cause small perturbations to the forearc stress regime because these small elastic stress perturbations are relatively fast they give large strain rates that are detected by geodetic measurements the present nearly margin normal contraction in both places is due to the locking of the subduction fault and the consequent increase in elastic stress in the direction of plate convergence with the margin parallel compression being dominant the small increase in margin normal stress may change the forearc seismicity in cascadia from a mixture of thrust and strike slip types into mainly thrust before the next great subduction earthquake in nankai the change should be from strike slip to quiescence as observed in the nankai forearc prior to the 1944 1946 great subduction earthquakes

mechanics of low stress forearcs nankai and cascadia the nankai and cascadia subduction zones have low stress forearcs where the margin normal horizontal compressive stress is similar to or less than the vertical stress except in the accretionary prisms in the absence of active back arc spreading the forearc margin normal stress is controlled mainly by the total shear force along the subduction fault or the plate coupling force and the gravitational force the plate coupling force creates compression and the gravitational force in the presence of margin topography creates lateral tension we give a simple expression that relates the forearc stress to topography and average fault strength with the latter represented by an effective coefficient of friction we also use a finite element model of two converging plates in frictional contact to model the forearc stresses the analyses indicate that a low stress forearc requires not only the subduction fault to be very weak but also the mechanically coupled fault area to be narrow in the downdip direction and shallow in depth for nankai and cascadia where the coupled fault areas are narrow and shallow because of the young and hot subducting plates is about 0 05 or less and in any case less than 0 09 the low fault strength is probably not a unique property of low stress forearcs since the same low values combined with wider and deeper coupled areas can be shown to create large margin normal compression in addition there does not seem to be any relation between subduction earthquake magnitudes and plate coupling forces great earthquakes occur at subduction zones having low stress forearcs such as nankai and cascadia

on the application of simple rift basin models to the south polar region of enceladus 1 the south polar terrain spt of saturn s moon enceladus is a mysteriously active region that exhibits intriguing tectonic signatures and widespread fracturing the central region of the nearly circular spt is depressed into the surface by a few hundred meters and bounded by a ring of cliffs roughly 1 km high in this study we investigate whether this depression and surrounding mountainous uplift is consistent with the morphology of terrestrial rift basins and the possibility that the spt could have formed during a tectonic event analogous to those of such rift basins on earth using three mechanical models of basin formation we compare our predicted topography of the spt with observed topography of the region the first of three models we consider assumes crustal stretching by factor b and predicts a basin depth of roughly 600 m closely matching previously published estimates of the depth at the spt models of extension and compression assuming an elastic response in the ice crust predict best fit mountain uplift of roughly 1820 m and 1130 m respectively our preferred model suggests that the icy shell in the spt has been stretched but the extension is partially balanced by compression along the edges of the basin leading to the uplift of the mountains along the boundary thereby implying that the spt may have a tectonic origin analogous to that of a terrestrial basin

consequences of large impacts on enceladus core shape the intense activity on enceladus suggests a differentiated interior consisting of a rocky core an internal ocean and an icy mantle however topography and gravity data suggests large heterogeneity in the interior possibly including significant core topography in the present study we investigated the consequences of collisions with large impactors on the core shape we performed impact simulations using the code isale2d considering large differentiated impactors with radius ranging between 25 and 100 km and impact velocities ranging between 0 24 and 2 4 km s our simulations showed that the main controlling parameters for the post impact shape of enceladus rock core are the impactor radius and velocity and to a lesser extent the presence of an internal water ocean and the porosity and strength of the rock core for low energy impacts the impactors do not pass completely through the icy mantle subsequent sinking and spreading of the impactor rock core lead to a positive core topographic anomaly for moderately energetic impacts the impactors completely penetrate through the icy mantle inducing a negative core topography surrounded by a positive anomaly of smaller amplitude the depth and lateral extent of the excavated area is mostly determined by the impactor radius and velocity for highly energetic impacts the rocky core is strongly deformed and the full body is likely to be disrupted explaining the long wavelength irregular shape of enceladus core by impacts would imply multiple low velocity 2 4 km s collisions with deca kilometric differentiated impactors which is possible only after the lhb period

unstable extension of enceladus lithosphere abstract regions near enceladus equator sarandib and diyar planitia contain extensive sets of parallel ridges and troughs that may be diagnostic of the region s formation conditions we present photoclinometry profiles across these ridges and troughs which indicate that they are periodic low slope features with dominant wavelengths of 3 to 4 km and amplitudes between 100 and 400 m the morphology of these terrains is consistent with formation via unstable extension of the lithosphere our numerical modeling demonstrates that unstable extension can generate large scale topography under enceladus like conditions comparison of our photoclinometry profiles with the dominant wavelengths produced by our numerical model permits estimation of the background heat flow at the time the sarandib diyar province formed we estimate heat flows of 110 to 220 mw m 2 suggesting that resurfacing of the planitiae was accompanied by strong localized heating the extension necessary to produce the ridges and troughs may have been caused by now inactive diapirs internal phase changes or other mechanisms our heat flux estimates imply elastic thickness at the time of resurfacing of 0 4 to 1 4 km which are sufficient to have allowed satellite reorientation if the province was underlain by a low density region it is therefore plausible that enceladus has experienced multiple heating events each leading to localized resurfacing and global reorientation

solid tidal friction above a liquid water reservoir as the origin of the south pole hotspot on enceladus abstract earth jupiter s moon io and saturn s tiny moon enceladus are the only solid objects in the solar system to be sufficiently geologically active for their internal heat to be detected by remote sensing interestingly the endogenic activity on enceladus is only located on a specific region at the south pole from which jets of water vapor and ice particles have been observed spencer j r and 9 colleagues 2006 science 311 1401 1405 porco c c and 24 colleagues 2006 science 311 1393 1401 the current polar location of the thermal anomaly can possibly be explained by diapir induced reorientation of the satellite nimmo f pappalardo r t 2006 nature 441 614 616 but the thermal anomaly triggering and the heat power required to sustain it over geological timescales remain problematic using a three dimensional viscoelastic numerical model simulating the response of enceladus to tidal forcing we explore the effect of a low viscosity anomaly in the ice shell localized to the south polar region on the tidal dissipation patterns we demonstrate that only interior models with a liquid water layer at depth can explain the observed magnitude of dissipation rate and its particular location at the south pole moreover we show that tidally induced heat must be generated over a relatively broad region in the southern hemisphere and it is then transferred toward the south pole where it is episodically released during relatively short resurfacing events as large tidal dissipation and internal melting cannot be induced in the south polar region in the absence of a pre existing liquid decoupling layer we propose that liquid water must have been present in the interior for a very long period of time and possibly since the satellite formation owing to the orbital equilibrium requirement meyer j wisdom j 2007 icarus 188 535 539 sustaining some liquid water at depth is impossible if heat is continuously emitted at a rate of 4 8 gw at the south pole based on that requirement we propose that the current thermal emission is not in equilibrium with the heat production and that the thermal emission rate is abnormally high at present time alternatively continuous dissipation at a rate of 1 2 gw in the ice shell at the south pole should be sufficient to induce internal melting and it could sustain a layer of liquid water at depth over geologic timescales

cyclic crustal movement steady uplift of marine terraces and evolution of the island arc trench system in southwest japan summary in southwest japan where the philippine sea plate is descending beneath the eurasian plate at the nankai trough we can observe cyclic crustal movement related to the periodic occurrence of interplate earthquakes with the time interval of 102 yr steady uplift of the marine terraces formed by eustatic sea level changes for the last 105 yr and gradual evolution of the island arc trench system through the last 4 x 106 yr we demonstrate that these phenomena with very different characteristic time scales can be consistently explained by a single plate subduction model in our model the lithosphere asthenosphere system is represented by a stratified viscoelastic half space under gravity consisting of a high viscosity surface layer and a low viscosity substratum and interaction between oceanic and continental plates by steady slip motion over the whole plate boundary and its perturbation associated with the periodic occurrence of earthquakes the effects of accretion of oceanic sediments at plate boundaries erosion on land and sedimentation on inner trench walls are also considered in the model from comparison of theoretical results with observed data we obtained the following conclusions valid for young subduction zones observed deformation cycles cannot be explained by a simple rebound model in which the effect of steady plate subduction is ignored the steady plate subduction brings about steady uplift of marine terraces the present patterns of surface topography and gravity anomalies are held nearly stable by the balance of erosion sedimentation rates and substantial growth rates

mobile lid convection beneath enceladus south polar terrain 1 enceladus south polar region has a large heat flux 55 110 mw m 2 that is spatially associated with cryovolcanic and tectonic activity tidal dissipation and vigorous convection in the underlying ice shell are possible sources of heat however prior predictions of the heat flux carried by stagnant lid convection range from fconv 15 to 30 mw m 2 too low to explain the observed heat flux the high heat flux and increased cryovolcanic and tectonic activity suggest that near surface ice in the region has become rheologically and mechanically weakened enough to permit convective plumes to reach close to the surface if the yield strength of enceladus lithosphere is less than 1 10 kpa convection may instead occur in the mobile lid regime which is characterized by large heat fluxes and large horizontal velocities in the near surface ice i show that model ice shells with effective surface viscosities between 1016 and 1017 pa s and basal viscosities between 1013 and 1015 pa s have convective heat fluxes comparable to that observed by composite infrared spectrometer if this style of convection is occurring the south polar terrain should be spreading horizontally with v 1 10 mm a 1 where a is years and should be resurfaced in 0 1 10 ma on the basis of cassini imaging data the south polar terrain is 0 5 ma old consistent with the mobile lid hypothesis maxwell viscoelastic tidal dissipation in such ice shells is not capable of generating enough heat to balance convective heat transport however tidal heat may also be generated in the near surface along faults as suggested by nimmo et al 2007 and or viscous dissipation within the ice shell may occur by other processes not accounted for by the canonical maxwell dissipation model

shield volcano topography and the rheology of lava flows on io stereo and photoclinometry derived topography of shield like volcanoes on io indicate little relief 3 km and very low slopes 0 2 to 0 6 several shield volcanoes appear to be associated with broad rises of 1 to 3 km but only 5 shield volcanoes have been identified with steep flank slopes between 4 and 10 these steep slopes are restricted to within 20 30 km of the summit but where discernable most of the lava flows observed on these edifices occur on the outer flanks where slopes are less than a degree despite their abundance ionian shield volcanoes are among the flattest in the solar system the steepest volcanoes on io are most comparable to large venusian shield volcanoes using simplistic bingham rheologies we estimate the viscosity and yield strengths of ionian lavas yield strengths are estimated at 101 102 pa lower than most basaltic lavas viscosity estimates range from 103 to 105 pa s although these are probably upper limits actual values may have been as low as 100 pa s viscosity is sensitive to flow velocity which is poorly known on io the best constraint on flow velocity comes from observations of the 1997 pillan eruption which bracket the eruptive phase to 132 day maximum and more probably less than 50 days low slopes long run out distances and our estimated rheologic properties are consistent with but not proof of a low silica low viscosity high temperature composition for ionian lavas supporting arguments for low silica lava compositions such as basalt or komatiite we cannot eliminate sulfur on rheologic grounds however

cmt data inversion using a bayesian information criterion to estimate seismogenic stress fields summary we developed an inversion method to estimate the stress fields related to earthquake generation seismogenic stress fields from the centroid moment tensors cmt of seismic events by using akaike s bayesian information criterion abic on the idea that the occurrence of an earthquake releases some part of the seismogenic stress field around its hypocentre we define the cmt of a seismic event by a weighted volume integral of the true but unknown seismogenic stress field representing each component of the seismogenic stress field by the superposition of a finite number of 3 d basis functions tri cubic b splines we obtain a set of linear observation equations to be solved for the expansion coefficients model parameters we introduce prior constraint on the roughness of the seismogenic stress field and combine it with observed data to construct a bayesian model with hierarchic highly flexible structure controlled by hyper parameters the optimum values of the hyper parameters are objectively determined form observed data by using abic given the optimum values of the hyper parameters we can obtain the best estimates of model parameters by using a maximum likelihood algorithm we tested the validity of the inversion method through numerical experiments on two synthetic cmt data sets assuming the distribution of fault orientations to be aligned with the maximum shear stress plane in one case and to be random in the other case then we applied the inversion method to actual cmt data in northeast japan and obtained the pattern of the seismogenic stress field consistent with geophysical and geological observations

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

penitentes as the origin of the bladed terrain of tartarus dorsa on pluto simulations of pluto suggest that the sharp ridges in the tartarus dorsa region of pluto are penitentes that formed over the past tens of millions of years observations by the new horizons spacecraft have revealed a host of features on the surface of pluto among the most intriguing of these is an area of bladed terrain in the tartarus dorsa region of the dwarf planet several potential origins have been suggested on the basis of comparisons with similar structures found on earth such as the hard elongated snow formations known as nieves penitentes or simply penitentes which are found at high altitudes in the andes and other mountain regions john moores et al report simulations that reproduce the observed tri modal orientation and spacing of the tartarus dorsa features by deepening penitentes these penitentes deepen by about one centimetre per orbital cycle in the present era growing only during periods of high atmospheric pressure suggesting a formation timescale of several tens of millions of years penitentes are snow and ice features formed by erosion that on earth are characterized by bowl shaped depressions several tens of centimetres across whose edges grade into spires up to several metres tall1 2 3 penitentes have been suggested as an explanation for anomalous radar data on europa4 but until now no penitentes have been identified conclusively on planetary bodies other than earth regular ridges with spacings of 3 000 to 5 000 metres and depths of about 500 metres with morphologies that resemble penitentes have been observed by the new horizons spacecraft5 6 7 8 in the tartarus dorsa region of pluto 220 250 e 0 20 n here we report simulations based upon a recent model3 representing conditions on pluto7 9 in which deepening penitentes reproduce both the tri modal north south east west and northeast southwest orientation and the spacing of the ridges of this bladed terrain at present these penitentes deepen by approximately one centimetre per orbital cycle and grow only during periods of relatively high atmospheric pressure suggesting a formation timescale of several tens of millions of years consistent with crater ages this timescale implies that the penitentes formed from initial topographic variations of no more than a few tens of metres consistent with pluto s youngest terrains

geodetic data inversion based on bayesian formulation with direct and indirect prior information summary mechanical interaction between adjacent plates which causes crustal deformation in plate boundary zones is rationally represented by tangential displacement discontinuity fault slip at plate interfaces given fault slip distribution we can compute surface displacements on the basis of elastic dislocation theory thus we can determine the functional form of a stochastic model to extract information about unknown fault slip distribution from observed surface displacement data in addition to observed data we usually have prior information for example plate tectonics postulates that primary fault slip is parallel to relative plate motion this is direct prior information that bounds the values of model parameters within certain ranges from physical consideration we may impose prior constraint on the roughness of fault slip distribution this is indirect prior information that regulates the structure of stochastic models by combining the direct and indirect prior information with observed data in a proper way we constructed a bayesian model for geodetic data inversion which has a hierarchic flexible structure controlled by hyper parameters the optimum values of hyper parameters are objectively determined from observed data by using akaike s bayesian information criterion abic the inversion formula derived from the bayesian model unifies the jackson matsu ura formula with direct prior information and the yabuki matsu ura formula with indirect prior information in a rational way we demonstrated the effectiveness of the unified inversion formula through the analysis of the surface displacement data associated with the 1923 kanto earthquake in the analysis with direct and indirect prior information we obtained the bimodal distribution of fault slip almost parallel to plate convergence on the north american philippine sea plate interface if we ignore the direct prior information in the analysis additional significant distribution of fault slip perpendicular to plate convergence appears to the east which is incomprehensible from plate tectonics

enceladus s ice shell structure as a window on internal heat production abstract its extraordinary level of geologic activity its potential for habitability and the prospects of returning samples from its plume of erupting water ice make saturn s small 500 km diameter moon enceladus a high priority target for future exploration and a key to our developing understanding of icy ocean worlds the structure of its outer ice shell is particularly important as it relates to the global heat budget the global scale response to tidal forces and the nature of the ongoing eruptions it is also diagnostic of how and where heat is dissipated internally here using the most recent shape model and a new approach to modeling isostasy we obtain a shell structure that simultaneously accommodates the shape gravity and libration observations and suggests that tidal dissipation near the base of the ice shell is likely an important mode of internal heating the implied conductive heat loss is greater than the heat loss associated with the eruptions but is nevertheless compatible with the condition of steady state

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

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

a kinematic model for evolution of island arc trench systems summary plate subduction zones are typically characterized by the patterns of surface topography and gravity anomalies consisting of island arc high trench low and outer rise gentle high these patterns are stable on the time scale of 106 107 yr at some subduction zones regardless of its age steady uplift of marine terraces formed by eustatic sea level changes during the last lo5 yr can be also observed the stable patterns of topography and gravity anomalies and the steady uplift of marine terraces seem to contradict each other we constructed a kinematic model which could explain the evolution process of island arc trench systems and demonstrated that this puzzle could be solved by considering the effect of accretion at plate boundaries in our model the lithosphere asthenosphere system is represented by a stratified visco elastic half space under gravity which consists of a high viscosity surface layer and a low viscosity substratum the rheological properties of both layers are assumed to be a maxwell fluid in shear and an elastic solid in bulk interaction between oceanic and continental plates is represented by the steady increase of discontinuity in tangential displacement across the plate boundary the other essential factors considered in our model are accretion of oceanic sediments at plate boundaries erosion on land and sedimentation on inner trench wall we computed the evolution process of island arc trench systems by using the kinematic model and obtained the following results the island arc trench systems grow at nearly constant rates in the early stage of plate subduction therefore at young subduction zones we can generally expect the steady uplift of marine terraces the stable patterns of topography and gravity anomalies are formed within several million years after the initiation of plate subduction when the accretion process continuously proceeds at plate boundaries these stable patterns gradually migrate seaward as a whole in such a case we can expect the steady uplift of marine terraces even at old subduction zones we demonstrate that our model can consistently explain the observed surface topography gravity anomalies and uplift rates of marine terraces at subduction zones

subduction of asian lithospheric mantle beneath tibet inferred from models of continental collision the relative northward motion of the indian subcontinent that followed the onset of continental collision with asia has produced extensive deformation of the earth s crust giving rise to the world s highest mountains in the himalayan chain and the world s largest high elevation region the tibetan plateau the formation of the broad mountain belt implies that contrary to the original tenets of plate tectonics the lithospheric plates have experienced widespread deformation far from the plate boundary1 several models have been proposed2 6 to explain the manner in which this post collisional deformation is distributed within the continental lithosphere of the indian and asian plates here we propose an alternative model in which subduction of the asian lithospheric mantle develops following the collision of india our model is supported by numerical calculations of crustal deformation and thickening and is consistent with available geological and geophysical data7 9 this picture suggests that lithospheric mantle is not deformed along with the crust and would imply that continental collision zones are more analogous to oceanic subduction zones than was previously believed

stress data inversion to estimate collision rate distribution and its application to the izu peninsula japan abstract in convergent plate boundary zones convergent motion between adjacent plates is accommodated by fault slip along the plate interface subduction combined with the compressional deformation of the plates collision the collision rate is defined as the ratio of the long term increase rate of the irrecoverable slip deficit at the plate interface to the full plate convergence rate in order to quantitatively represent this mechanical aspect the distribution of the collision rate on the plate interface is a major active source that generates a tectonic stress field in the plate interior we developed a new inversion method based on these concepts to estimate the collision rate distribution from the patterns of the intraplate tectonic stress fields in the inversion the analytically obtained tectonic stress data were used and a bayesian approach was considered the application of the inversion method to the izu collision zone in central japan revealed that a broad belt of high collision rates surrounded the base of the izu peninsula the collision belt was divided into three parts 1 a central strong collision zone spreading landwards at the base of the izu peninsula where the value of the collision rate becomes a maximum 2 an eastern moderate collision zone widely covering the philippine sea north american plate boundary along the sagami trough and 3 a western moderate collision zone concentrated in a shallower part of the philippine sea eurasian plate boundary along the suruga trough the central collision zone coincided with the colliding front of the izu ogasawara bonin island arc which indicated that the estimated collision rate distribution described the actual arc collision process the eastern and western collision zones might imply a higher absolute strength of their corresponding large interplate seismogenic zones

one hundred km scale basins on enceladus evidence for an active ice shell 1 stereo derived topographic mapping of 50 of enceladus reveals at least 6 large scale ovoid depressions basins 90 175 km across and 800 to 1500 m deep and uncorrelated with geologic boundaries in contrast the south polar depression is larger and apparently shallower and correlates with active resurfacing the shape and scale of the basins is inconsistent with impact geoid surface deflections or with dynamically supported topography isostatic thinning of enceladus ice shell associated with upwellings and tidally driven ice melting can plausibly account for these basins thinning implies upwarping of the base of the shell of 10 20 km beneath the depressions depending on total shell thickness loss of near surface porosity due to enhanced heat flow may also contribute to basin lows alternatively the basins may overly cold inactive and hence denser ice but thermal isostasy alone requires thermal expansion more consistent with clathrate hydrate than water ice

a clathrate reservoir hypothesis for enceladus south polar plume we hypothesize that active tectonic processes in the south polar terrain of enceladus the 500 kilometer diameter moon of saturn are creating fractures that cause degassing of a clathrate reservoir to produce the plume documented by the instruments on the cassini spacecraft advection of gas and ice transports energy supplied at depth as latent heat of clathrate decomposition to shallower levels where it reappears as latent heat of condensation of ice the plume itself which has a discharge rate comparable to old faithful geyser in yellowstone national park probably represents small leaks from this massive advective system

3 d modelling of plate interfaces and numerical simulation of long term crustal deformation in and around japan we developed a 3 d simulation model for long term crustal deformation due to steady plate subduction in and around japan by incorporating viscoelastic slip response functions into a realistic 3 d plate interface model constructed on the basis of the topography of ocean floors and hypocenter distributions of earthquakes the lithosphere asthenosphere system is modelled by an elastic surface layer overlying a maxwellian viscoelastic half space kinematic interaction at plate interfaces is rationally represented by the increase of tangential displacement discontinuity fault slip across the interfaces with this model giving the steady slip rates at plate interfaces calculated from nuvel 1a we simulated long term crustal deformation due to steady plate subduction in and around japan the simulated crustal deformation pattern is characterized by steep uplift at island arcs sharp subsidence at ocean trenches and gentle uplift at outer rises the numerical results show the strong dependence of the deformation pattern on the 3 d geometry of plate interfaces

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 an active ice world in the saturn system enceladus one of the mid sized icy moons of saturn has an importance to planetary science far greater than its modest 504 km diameter would suggest intensive exploration of enceladus by the cassini saturn orbiter has revealed that it is the only known icy world in the solar system with ongoing deep seated geological activity active tectonic fractures at enceladus s south pole dubbed tiger stripes warmed by internal tidally generated heat spew supersonic jets of water vapor other gases and ice particles into circum saturnian space a subsurface saltwater sea probably exists under the south pole between the ice shell and the silicate core because of evidence that liquid water is probably present at the jet sources enceladus is also of great astrobiological interest as a potential habitat for life

simulation of tectonic evolution of the kanto basin of japan since 1 ma due to subduction of the pacific and philippine sea plates and the collision of the izu bonin arc abstract the kanto basin the largest lowland in japan developed by flexure as a result of 1 the subduction of the philippine sea phs and the pacific pac plates and 2 the repeated collision of the izu bonin arc fragments with the japanese island arc geomorphological geological and thermochronological data on vertical movements over the last 1 my suggest that subsidence initially affected the entire basin after which the area of subsidence gradually narrowed until finally the basin began to experience uplift in this study we modeled the tectonic evolution of the kanto basin following the method of matsu ura and sato 1989 for a kinematic subduction model with dislocations in order to quantitatively assess the effects of phs and pac subduction we include the steady slip rate deficit permanent locking rate at the plate interface in our model to account for collision process we explore how the latest collision of the izu peninsula block has been affected by a westerly shift in the phs plate motion vector with respect to the eurasian plate thought to have occurred between 1 0 0 5 ma using long term vertical deformation data to constrain extent of the locked zone on the plate interface we evaluated the change in vertical deformation rate for two scenarios 1 a synchronous shift in the orientation of the locked zone as phs plate motion shifts and 2 a delayed shift in the orientation of the locked zone following the shift in plate motion observed changes in the uplift subsidence pattern are better explained by scenario 2 suggesting that recent

a dislocation model for the earthquake cycle at convergent plate boundaries summary a kinematic model for the earthquake cycle at convergent plate boundaries has been constructed on the basis of dislocation theory we model the lithosphere asthenosphere system by a stratified semi infinite medium under gravity consisting of an elastic surface layer an intervening layer with maxwell viscoelasticity and an elastic substratum the steady motion of plate convergence is naturally represented by uniform slip at a constant rate on the upper boundary of the descending oceanic plate the occurrence of interplate earthquakes is regarded as a perturbation of the steady state plate motion and represented by a periodic sequence of step slips on a finite seismic zone of the plate interface based on dislocation theory we can show that the steady slip on the interface deeper than the lithosphereasthenosphere boundary does not contribute to surface deformation in the steady state accordingly the surface deformation associated with the earthquake cycle is given by the superposition of viscoelastic responses to the steady slip on the interface shallower than the lithosphere asthenosphere boundary the steady backslip on the seismic zone and the periodic sequence of seismic slips we have computed cyclic patterns of vertical displacements at the free surface for two representative cases taking account of gravity effects the patterns of vertical displacements differ notably in the latter stage of the cycle depending on whether or not the seismic zone extends through the entire thickness of the lithosphere after the completion of one earthquake cycle our model yields a certain amount of permanent deformation resulting from the steady plate convergence the pattern of the permanent deformation that is characterized by steep uplift on the continental side sharp subsidence at the plate boundary and gentle uplift on the oceanic side is irrespective of the cyclic process of stress accumulation and release repeated on the seismic zone the earthquake cycle model developed here provides a possible explanation for the formation of earthquake origin marine terraces

basins fractures and volcanoes global cartography and topography of pluto from new horizons abstract the 2015 new horizons flyby has produced the first high resolution maps of morphology and topography of pluto and charon the most distant objects so mapped global integrated mosaics of pluto were produced using both lorri framing camera and mvic line scan camera data showing the best resolution data obtained for all areas of the illuminated surface 78 of the body a unique feature of the pluto imaging data set is the observation of terrains illuminated only by light scattered from atmospheric haze allowing us to map terrains in the southern hemisphere that would otherwise have been in darkness mvic 4 color data were combined with the panchromatic map to produce full color global maps digital elevation models dems over 42 of pluto were produced using combinations of mvic hemispheric scans and lorri mosaics from which slopes at scales of 1 km can be determined pluto can be divided into regions each with distinct topographic signatures corresponding with major physiographic terrain types large areas of pluto are comprised of low relief moderately cratered plains units deeply pitted and glaciated plains east of sputnik planitia are elevated 0 7 km the most dominant topographic feature on pluto is the 1200 by 2000 km wide depression enclosing the bright sputnik planitia ice sheet the surface of which is 2 5 to 3 5 km deep relative to the rim and 2 km deep relative to the mean radius the partial ring of steep sided massifs several of which are more than 5 km high along the western margins of sputnik planitia produce some of the locally highest and steepest relief on pluto with slopes of 40 50 the second major topographic feature is a complex eroded ridge trough system 300 400 km wide and at least 3200 km long extending north to south along the 155 meridian this enormous structure has several kilometers of relief it may predate the large impact event forming the basin though some post sputnik planitia deformation is evident the large depressed partially walled plain hyecho palus lies due southwest of sputnik planitia near the center of hyecho palus lie the circular constructional edifices wright and piccard montes wright mons rises 4 5 km above these plains with a central depression 4 5 km deep whereas piccard mons best observed in haze light rises 5 5 km above the plains but has a bowl shaped central depression 5 5 km below the plains for a total relief of up to 11 km the greatest observed on pluto both of these features are interpreted as constructional volcanic in nature additional prominent topographic features include a 2 3 km high and 600 km wide dome centered on the illuminated iau pole and the amoeboidal plateaus of bladed terrains in the equatorial region which rise 2 5 km above local terrains and are the highest standing geologic units on the encounter hemisphere the mean elevations in the integrated dem for the two radio occultation areas are consistent with the 5 6 km difference in elevation as determined independently by the radio experiment and a limb profile near the egress point confirms the presence of elevated bladed terrains in that area local relief of 3 5 km at massifs troughs and pits supports conclusions that the icy shell of pluto is relatively rigid numerous examples of topographic control of ice or frost deposition occur across pluto including the distinct coloration of the polar dome the elevated terrains of eastern tombaugh regio and along the ridge trough system where ridge tops and fossae rims are covered in different ices than at lower elevations the topographic hypsogram of pluto s encounter hemisphere is strongly bimodal due to the large sputnik planitia depression otherwise the topographic signature of pluto is controlled by deviations from the otherwise dominant low plains including elevated bladed terrain plateaus and the depressed volcanic province including wright and piccard montes

sodium chloride as a geophysical probe of a subsurface ocean on enceladus 1 recent data from the cassini spacecraft suggest that an ocean exists inside saturn s satellite enceladus here we show that the size of an ocean can be estimated if the nacl concentration of the ocean is known we find that concentrations of aqueous nacl reported by postberg et al 2009 imply a relatively large ocean comprising at least 17 by mass of volatiles on enceladus structural calculations indicate that this ocean would underlie more of enceladus surface than just the geologically active south polar region consistent with modeling of localized tidal dissipation conduction calculations suggest that a half global ocean can be maintained by steady state tidal heating provided that clathrate hydrate dominates enceladus ice shell we also find that rapid freezing of oceanic water could release large fluxes of stored tidal heat perhaps partly explaining the anomalous energy output of enceladus an alternative saltier ocean model is also examined

mechanics of evenly spaced strike slip faults and its implications for the formation of tiger stripe fractures on saturn s moon enceladus abstract we present the first mechanical analysis based on realistic rheology and boundary conditions on the formation of evenly spaced strike slip faults two quantitative models employing the stress shadow concept widely used for explaining extensional joint spacing are proposed in this study 1 an empirically based stress rise function model that simulates the brittle deformation process during the formation of evenly spaced parallel strike slip faults and 2 an elastic plate model that relates fault spacing to the thickness of the fault hosting elastic medium when applying the models for the initiation and development of the tiger stripe fractures tsf in the south polar terrain spt of enceladus the mutually consistent solutions of the two models as constrained by the mean spacing of the tsf at 35 km requires that the brittle ice shell thickness be 30 km the elastic thickness be 0 7 km and the cohesive strength of the spt ice shell be 30 kpa however if the brittle and elastic models are decoupled and if the ice shell cohesive strength is on the order of 1 mpa the brittle ice shell would be on the order of 10 km

3 d simulation of tectonic loading at convergent plate boundary zones internal stress fields in northeast japan the evidence of east west compression in northeast japan has been reported by many investigators on the basis of geodetic geologic and geomorphic data but its origin still remains far from understood in the present study we have proposed a mechanical model of tectonic loading at convergent plate boundary zones and demonstrated its validity through the numerical simulation of internal stress fields in northeast japan with realistic 3 d geometry of plate interfaces at convergent plate boundary zones in general a part of plate convergence is consumed by steady slip along plate interfaces and the remaining part by inelastic deformation seismic faulting aseismic faulting and active folding of overriding plates such a plate boundary process to be called partial collision can be quantitatively described by introducing a collision rate defined as c 1 steady slip rate at plate interfaces plate convergence rate by this definition we can simply represent the mechanical process of partial collision which includes total subduction c 0 and total collision c 1 as two extreme cases in terms of steady slip rates at plate interfaces on the basis of elastic dislocation theory first we numerically computed the internal stress fields in northeast japan produced by the total subduction of the pacific plate beneath the north american plate however the computed stress pattern was opposite in sense to observations then we computed the internal stress fields by taking c 0 1 on average and succeeded in reproducing the observed east west compression in northeast japan this indicates that the concept of partial collision is essential to understand the mechanism of intraplate tectonic loading

shapes of the saturnian icy satellites and their significance the sizes and shapes of six icy saturnian satellites have been measured from cassini imaging science subsystem iss data employing limb coordinates and stereogrammetric control points mimas enceladus tethys dione and rhea are well described by triaxial ellipsoids iapetus is best represented by an oblate spheroid all satellites appear to have approached relaxed equilibrium shapes at some point in their evolution but all support at least 300 m of global wavelength topography the shape of enceladus is most consistent with a homogeneous interior if enceladus is differentiated its shape and apparent relaxation require either lateral inhomogeneities in an icy mantle and or an irregularly shaped core iapetus supports a fossil bulge of over 30 km and provides a benchmark for impact modification of shapes after global relaxation satellites such as mimas that have smoother limbs than iapetus and are expected to have higher impact rates must have relaxed after the shape of iapetus was frozen

mechanical model for the tectonics of doubly vergent compressional orogens a mechanical model of crustal shortening and deformation driven by the relative convergence of rigid underlying mantle plates explains many features of convergent orogens results based on numerical models and supported by sandbox models show that a coulomb crustal layer subject to basal velocity boundary conditions corresponding to asymmetric detachment and subduction of the underlying mantle passes through three stages of orogenic growth 1 block uplift bounded by step up shear zones 2 development of a low taper wedge over the underthrusting mantle plate and 3 development of a low taperwedge overlying the overthrusting mantle plate and verging in the opposite direction when modified by isostasy basal viscous flow surface erosion and denudation and sedimentation the resultant model orogens exhibit a variety of styles with characteristics in common with small rapidly denuded orogens large orogens with plateaus and extensional characteristics and active subduction margins with doubly vergent accretionary wedges and deformed fore arc basins

the 3 d tectonic stress fields in and around japan inverted from centroid moment tensor data of seismic events 1 we can regard the occurrence of earthquakes as the partial release of tectonic stress by sudden brittle rupture in the framework of linear elasticity any indigenous source including earthquake rupture is represented by a moment tensor the moment tensor is mathematically equivalent to the volume integral of stress release over the whole elastic region surrounding the source and so we can quantitatively relate the centroid moment tensor cmt of seismic events with an unknown tectonic stress field on the basis of such an idea and bayesian statistical inference theory we developed an inversion method to estimate the 3 d pattern of tectonic stress from cmt data applying the cmt data inversion method to 12 500 seismic events in and around japan we obtained precise 3 d tectonic stress patterns that illuminate the present day quaternary complex tectonic motion of japanese islands the stress pattern of the kuril japan nankai arc is basically e w compression but the direction of intermediate principal stress changes from n s reverse faulting type in northeast japan to vertical strike slip faulting type in southwest japan on the other hand the stress pattern of the ryukyu and izu bonin back arc regions is basically trench perpendicular tension normal faulting type in addition to these basic stress patterns governed by mechanical interaction between the eurasian north american pacific and philippine sea plates we can recognize several characteristic local stress patterns corresponding to the horizontal motion of the kuril fore arc sliver the collision of the izu peninsula with the mainland of japan and the opening of the beppu shimabara rift zone

an oceanic composition on early and today s enceladus 1 the oceanic composition on saturn s moon enceladus is evaluated through calculations of thermochemical equilibria at hydrothermal and freezing settings conditions of rock alteration are constrained from assumptions and models for the moon s interior composition and thermal evolution and from the composition of enceladus plume results show that an early ocean was an alkaline na cl hco3 solution underlying altered rocks consisted of mg phyllosilicates magnetite fe and ni sulfides and carbonates subsequent freezing of oceanic water caused the deposition of a nacl hydrate na k and ca carbonates and the formation of a salt free ice shell if an aqueous phase exists on today s enceladus it could consist of eutectic na cl hco3 brine that at least locally decouples the ice shell and facilitates tidal heating a lack of firm detection of na and cl at enceladus is consistent with the accumulation of salts at the ice rock boundary and implies the plume formation via sublimation in the ice shell

tidally induced melting events as the origin of south pole activity on enceladus abstract the intense activity at the south pole of enceladus hints at an internal water reservoir however there is no direct evidence of liquid water at present and its long term stability in the interior remains problematic by modeling heat production and transfer in the ice shell in a spherical geometry we show that tidal heating naturally leads to a concentration of convective hot upwellings in the south polar region favoring the preservation of liquid water at depth we show that large volumes of water are produced within the ice shell at the south pole during periods of elevated orbital eccentricity 3 5 times the present day value strong lateral variations in the melt production and crystallization rates result in stress concentration in the south polar region thus providing an explanation for the tectonic activity observed today we predict that an internal ocean may be sustained over the long term as the consequence of repeated periods with elevated orbital eccentricity leading to episodic melting and resurfacing events

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

large scale subduction of continental crust implied by india asia mass balance calculation continental crust is buoyant compared with its oceanic counterpart and resists subduction into the mantle when two continents collide the mass balance for the continental crust is therefore assumed to be maintained here we use estimates of pre collisional crustal thickness and convergence history derived from plate kinematic models to calculate the crustal mass balance in the india asia collisional system using the current best estimates for the timing of the diachronous onset of collision between india and eurasia we find that about 50 of the pre collisional continental crustal mass cannot be accounted for in the crustal reservoir preserved at earth s surface today represented by the mass preserved in the thickened crust that makes up the himalaya tibet and much of adjacent asia as well as southeast asian tectonic escape and exported eroded sediments this implies large scale subduction of continental crust during the collision with a mass equivalent to about 15 of the total oceanic crustal subduction flux since 56 million years ago we suggest that similar contamination of the mantle by direct input of radiogenic continental crustal materials during past continent continent collisions is reflected in some ocean crust and ocean island basalt geochemistry the subduction of continental crust may therefore contribute significantly to the evolution of mantle geochemistry buoyant continental crust is thought to resist subduction calculation of the crustal mass balance during the collision between india and eurasia indicates that about 50 of pre collisional continental crust has been subducted into the mantle

cassini observes the active south pole of enceladus cassini has identified a geologically active province at the south pole of saturn s moon enceladus in images acquired by the imaging science subsystem iss this region is circumscribed by a chain of folded ridges and troughs at 55 s latitude the terrain southward of this boundary is distinguished by its albedo and color contrasts elevated temperatures extreme geologic youth and narrow tectonic rifts that exhibit coarse grained ice and coincide with the hottest temperatures measured in the region jets of fine icy particles that supply saturn s e ring emanate from this province carried aloft by water vapor probably venting from subsurface reservoirs of liquid water the shape of enceladus suggests a possible intense heating epoch in the past by capture into a 1 4 secondary spin orbit resonance

the impact of a pressurized regional sea or global ocean on stresses on enceladus liquid water is likely present in the interior of enceladus but it is still debated whether this water forms a global ocean or a regional sea and whether the present day situation is stable as the heat flux of enceladus exceeds most heat source estimates the liquid water is likely cooling and crystallizing which results in expansion and pressurization of the sea or ocean we determine using an axisymmetric finite element model the tectonic patterns that pressurization of a regional sea or global ocean might produce at the surface of enceladus tension is always predicted above where the ice is thinnest and generates cracks that might be at the origin of the tiger stripes tectonic activity is also expected in an annulus around the sea if the ice shell is in contact with but slips freely along the rocky core of the satellite cracks at the north pole are expected if the shell slips along the core or if there is a global ocean with thin ice at the pole water is likely injected along the base of the ice when the shell is grounded which may lead to cycles of tectonic activity with the shell alternating between floating and grounded states and mid latitude faulting occurring at the transition from grounded to floating states

self consistent generation of single plume state for enceladus using non newtonian rheology the thermal dichotomy of enceladus suggests an asymmetrical structure in its global heat transfer so far most of the models proposed that obtained such a distribution have prescribed an a priori asymmetry i e some anomaly in or below the south polar ice shell we present here the first set of numerical models of convection that yield a stable single plume state for enceladus without prescribed mechanical asymmetry using the convection code stagyy in a 2 d spherical annulus geometry we show that a non newtonian ice rheology is sufficient to create a localized single hot plume surrounded by a conductive ice mantle we obtain a self sustained state in which a region of small angular extent has a sufficiently low viscosity to allow subcritical to weak convection to occur due to the stress dependent part of the rheological law we find that the single plume state is very unlikely to remain stable if the rheology is newtonian confirming what has been found by previous studies in a second set of numerical simulations we also investigate the first order effect of tidal heating on the stability of the single plume state tidal heating reinforces the stability of the single plume state if it is generated in the plume itself lastly we show that the likelihood of a stable single plume state does not depend on the thickness of the ice shell

a unified interpretation of vertical movement in himalaya and horizontal deformation in tibet on the basis of elastic and viscoelastic dislocation theory abstract the present day convergence rate between the indian and the eurasian plates has been estimated to be about 50 mm year at the collision boundary extending along the himalayas about 40 of the total convergence is consumed by the subduction of the indian plate beneath the eurasian plate the rest of about 60 is consumed by the internal deformation of the eurasian plate the present crustal movement in this region is characterized by rapid uplift along the high himalayas and large scale horizontal deformation in and around tibet the fundamental causes of these two different types of crustal movement are the same interaction between the indian and the eurasian plates in this study we represent the plate interaction by steady increase in tangential displacement discontinuity dislocation across the interface that divides a surface layer overlying a viscoelastic half space into the indian and the eurasian plates first given a steady slip of 20 mm year at the plate interface with a ramp shaped undulation below the high himalayas we computed the profile of surface uplift rates along a line perpendicular to the himalayan arc the result accords with observed free air gravity anomalies and the intermediate and short term uplift rates estimated respectively from the present heights of river terraces and levelling data this means that the rapid uplift of the high himalayas is due to the steady slip along the ramp shaped plate interface below it second given the steady slips of 20 mm year along the 2000 km long collision boundary and 50 mm year along the remaining portions of the india eurasia plate boundary we computed the increase rates of horizontal deformation in and around tibet the result accords with the observed strikes and slip rates of major quaternary active faults this means that the horizontal deformation in and around tibet is due to the slip deficits of 30 mm year at the collision boundary from these two results we can conclude that the present rapid uplift of the high himalayas and large scale horizontal deformation in and around tibet are consistently explained by a single plate interaction model based on elastic and viscoelastic dislocation theory this study sheds new light on the driving mechanism of the crustal deformation in the india eurasia collision zone as follows the plate interaction on single plate interface consists of coexisting two different physical mechanisms 1 slip along the ramp undulation spatial changes in slip direction 2 slip deficit at the collision boundary spatial changes in slip rates as a consequence the two different types of crustal deformation in the india eurasia collision zone are driven by these two different physical mechanisms

deformation of an island arc rates of moment release and crustal shortening in intraplate japan determined from seismicity and quaternary fault data the historical record of large m 6 9 earthquakes and geologically determined rates of slip on quaternary faults in intraplate japan honshu and shikoku are used to estimate the average rate of seismic moment release m for the last 400 years and during the late quaternary respectively values of m estimated from the two data sets are similar in regions where seismic activity is concentrated on land we interpret this observation to suggest that m in intraplate japan has been constant during the late quaternary and is relatively free from secular variation when averaged over periods of several hundreds of years m in shikoku may be attributed almost solely to right lateral slip of the median tectonic line mtl the easterly strike of the mtl is consistent with a compressive stress field that trends northwest crustal shortening of the izu peninsula taken up on a set of strike slip faults that show north by northwest compression is 1 mm yr northeast honshu is characterized by a set of reverse type faults that trend northerly conversion of m in northeast japan to strain rates suggests that about 5 of the relative plate motion between japan and the pacific plate 9 7 cm yr is accommodated as a permanent east west shortening 5 mm yr of northeast honshu the predominant deformation in central and western honshu takes place as slip on a conjugate system of strike slip faults that strike northeast and southeast and show right lateral and left lateral motion respectively crustal shortening resulting from slip on faults in central and western honshu is 5 and 0 5 mm yr respectively in an easterly direction central and western honshu are in closest proximity to the nankai trough and hence the stress field in these regions cannot simply be attributed to the accommodation of the relative northwesterly convergence of the philippine sea plate the northward impingement of the izu peninsula into honshu may influence stresses in central and western japan but a conclusive explanation of the stress field in central and western honshu remains an enigma

pit chains on enceladus signal the recent tectonic dissection of the ancient cratered terrains abstract enceladus is the first outer solar system body on which pit chains have been positively identified we map the global distribution of pit chains and show that pit chains are among the youngest tectonic features on enceladus s surface concentrated in the cratered plains centered on enceladus s saturnian and anti saturnian hemispheres pit chains on enceladus are interpreted as the surface expressions of subsurface dilational fractures underlying a cover of unconsolidated material which we infer to be a geologically young cover of loose regolith that mantles the surface of enceladus a widespread layer of regolith may act to insulate the surface which has implications for the thermal state of enceladus s ice shell the widespread distribution of pit chains across the cratered plains indicates that this ancient surface has recently been tectonically active

interplate coupling in the tokai district central japan deduced from continuous gps data i invert gps displacement rates in the tokai district to investigate strain accumulation associated with the anticipated tokai earthquake i apply a representation of interseismic strain accumulation at subduction zones by savage 1983 and estimate a distribution of virtual normal fault slip back slip on the plate boundary surface estimated back slip takes its maximum value of 30 40mm year under the sea of enshu this value is nearly equal to the relative plate motion there implying almost complete coupling back slip is smaller under suruga bay and its direction is different from the relative motion between the eurasian and the philippine sea plates localized deformation at the northern tip of the philippine sea plate may be responsible for this discrepancy partitioning tectonic strain due to the plate convergence into faults on both sides of the izu peninsula and also distributed strain inside the peninsula

convection driven compaction as a possible origin of enceladus s long wavelength topography 1 the long wavelength surface topography of enceladus shows depressions about 1 km in depth and 102 km wide one possible cause of this topography is spatially variable amounts of compaction of an initially porous ice shell driven by spatial variations in heat flux here we show that the heat flux variations associated with convection in the shell can quantitatively match the observed features we develop a simple model of viscous compaction that includes the effect of porosity on thermal conductivity and find that an initial shell porosity of at least 20 25 is required to develop the observed topography over 1 ga this mechanism produces topographic depressions not rises above convective upwellings and does not generate detectable gravity anomalies unlike transient dynamic topography it can potentially leave a permanent record of ancient convective processes in the shallow lithospheres of icy satellites

enceladus an estimate of heat flux and lithospheric thickness from flexurally supported topography fluxes of 200 270 mw m 2 at the time of formation the heat fluxes are comparable to average heat flux values measured in enceladus active south polar region and they are consistent with estimates derived via models of unstable extension of the lithosphere at this location surface porosity can reduce the obtained heat fluxes to an estimated minimum of 45 60 mw m 2 c rater size frequency counts fix the time of formation from presentday of the rift zone at either 3 5 0 4 0 1 ga assuming an

true polar wander of enceladus from topographic data many objects in the solar system are suspected to have experienced reorientation of their spin axes as their rotation rates are slow and their shapes are nearly spherical the formation of mass anomalies by either endogenic or exogenic processes can change objects moments of inertia therefore the objects reorient to align their largest moment of inertia with their spin axis such a phenomenon is called true polar wander tpw here we report the discovery of a global series of topographic lows on saturn s satellite enceladus that we interpret to show that this synchronously locked moon has undergone tpw by 55 about the tidal axis we use improved topographic data from the spherical harmonic expansion of cassini limb and stereogrammetric measurements to characterize regional topography over the surface of enceladus we identify a group of nearly antipodal basins orthogonal to a basin chain tracing a non equatorial circumglobal belt across enceladus surface we argue that the belt and the antipodal regions are fossil remnants of earlier equator and poles respectively we argue that these lows arise from isostasic compensation and that their pattern reflects spatial variations in internal dynamics of the ice shell our hypothesis is consistent with a variety of geological features visible in cassini images

breaking up is hard to do global cartography and topography of pluto s mid sized icy moon charon from new horizons abstract the 2015 new horizons flyby through the pluto system produced the first high resolution topographic maps of pluto and charon the most distant objects so mapped global integrated mosaics of the illuminated surface of pluto s large icy moon charon have been produced using both framing camera and line scan camera data including four color images at up to 1 47 km pixel scales showing the best resolution data at all areas of the surface digital elevation models dems with vertical precisions of up to 0 1 km were constructed for 40 of charon using stereo imagery local radii estimates for the surface were also determined from the cartographic control network solution for the lorri framing camera data which validate the stereo solutions charon is moderately cratered the largest of which is 250 km across and 6 km deep charon has a topographic range over the observed hemisphere from lowest to highest of 19 km the largest topographic amplitude of any mid sized icy body including ceres other than iapetus unlike saturn s icy moons whose topographic signature is dominated by global relaxation of topography and subsequent impact cratering large scale tectonics and regional resurfacing dominate charon s topography most of charon s encounter hemisphere north of the equator oz terra is broken into large polygonal blocks by a network of wide troughs with typically 3 6 km relief the deepest of these occur near the illuminated pole and are up to 13 km deep with respect to the global mean radius the deepest known surfaces on charon the edge of this terrain is defined by large tilted blocks sloping 5 or so the crests of which rise to 5 or 6 km above charon mean the highest known points on charon the southern resurfaced plains vulcan planitia consist of rolling plains locally fractured and pitted that are depressed 1 km below the mean elevation of the disrupted northern terrains of oz terra that comprise much of the northern hemisphere but 2 2 5 km below the surfaces of the blocks themselves these plains roll downward gently to the south with a topographic range of 5 km the outer margins of vulcan planitia along the boundary with oz terra form a 2 3 km deep trough suggesting viscous flow along the outer margins isolated massifs 2 4 km high also flanked by annular moats lie within the planitia itself the plains may be formed from volcanic resurfacing of cryogenic fluids but the tilted blocks along the outer margins and the isolated and tilted massifs within vulcan planitia also suggest that much of charon has been broken into large blocks some of which have been rotated and some of which have foundered into charon s upper mantle now exposed as vulcan planitia a history that may be most similar to the disrupted terrains of ariel

structure and evolution of the lunar procellarum region as revealed by grail gravity data gravity data show a rectangular pattern of narrow linear anomalies bordering the lunar procellarum region that are interpreted to be the frozen remnants of lava filled rifts and underlying feeder dykes the procellarum region is a broad area on the nearside of the moon characterized by low elevations and thin crust and largely covered by dark basalts that can be seen from earth with the unaided eye this structure has been interpreted as an ancient impact basin jeffrey andrews hanna et al use data from nasa s gravity recovery and interior laboratory grail mission to examine the subsurface structure of the procellarum they find that a pattern of narrow linear anomalies border the region interpreted to be the frozen remnants of lava filled rifts and underlying feeder dikes the discontinuous surface structures that were earlier interpreted as remnants of an impact basin rim are a part of this continuous set of quasi rectangular border structures with angular intersections the authors conclude that the procellarum was formed in response to thermal stresses produced by the differential cooling of the province relative to its surroundings coupled with magmatic activity driven by elevated heat flux the procellarum region is a broad area on the nearside of the moon that is characterized by low elevations1 thin crust2 and high surface concentrations of the heat producing elements uranium thorium and potassium3 4 the region has been interpreted as an ancient impact basin approximately 3 200 kilometres in diameter5 6 7 although supporting evidence at the surface would have been largely obscured as a result of the great antiquity and poor preservation of any diagnostic features here we use data from the gravity recovery and interior laboratory grail mission8 to examine the subsurface structure of procellarum the bouguer gravity anomalies and gravity gradients reveal a pattern of narrow linear anomalies that border procellarum and are interpreted to be the frozen remnants of lava filled rifts and the underlying feeder dykes that served as the magma plumbing system for much of the nearside mare volcanism the discontinuous surface structures that were earlier interpreted as remnants of an impact basin rim are shown in grail data to be a part of this continuous set of border structures in a quasi rectangular pattern with angular intersections contrary to the expected circular or elliptical shape of an impact basin9 the spatial pattern of magmatic tectonic structures bounding procellarum is consistent with their formation in response to thermal stresses produced by the differential cooling of the province relative to its surroundings coupled with magmatic activity driven by the greater than average heat flux in the region

3 d simulation of steady plate subduction with tectonic erosion current crustal uplift and free air gravity anomaly in northeast japan free air gravity anomaly in plate subduction zones characterized by island arc high trench low and outer rise gentle high reflects the cumulative effects of long term crustal uplift and subsidence in northeast japan the island arc high of observed free air gravity anomaly takes its maximum about the eastern coastline on the other hand the current vertical crustal motion estimated from geological and geomorphological observations shows a gentle uplift in the land area and steep subsidence in the sea area with the neutral point near the eastern coastline such a discrepancy in spatial patterns between the free air gravity anomaly and current vertical crustal motion can be ascribed to a change in the mode of crustal uplift and subsidence associated with the initiation of tectonic erosion at the north american pacific plate interface we developed a realistic 3 d simulation model of steady plate subduction with tectonic erosion in northeast japan on the basis of elastic viscoelastic dislocation theory through numerical simulations with this model we found that simple steady plate subduction brings about the crustal uplift characterized by island arc high with its maximum about the eastern coastline while steady plate subduction with tectonic erosion which is represented by the landward retreat of the plate interface brings about gentle uplift in the land area and steep subsidence in the sea area with the neutral point near the eastern coastline therefore if we suppose that tectonic erosion started 3 4 million years ago after the long duration of simple steady plate subduction we can consistently explain both patterns of free air gravity anomaly and current crustal uplift in northeast japan

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

enceladus south polar sea recent observations of the south pole of saturn s moon enceladus by the cassini spacecraft have revealed an active world powered by internal heat in this paper we propose that localized subsurface melting on enceladus has produced an internal south polar sea evidence for this localized sea comes from the shape of enceladus which does not match a differentiated body at its current orbital position we show that melting induced by the observed heat flow at the south pole produces a large enough pit to match the shape of enceladus with a differentiated rock and ice interior numerical modeling of melting and ice flow shows that the sea produced beneath the south pole is stable against inflow of ductile ice from its surroundings for the duration of the heating the shape modification due to melting also produces a negative degree two gravity anomaly which can reorient the spin axis of enceladus in order to place the sea at the pole

geodetic data inversion using a bayesian information criterion for spatial distribution of fault slip summary we developed a new inversion method to reconstruct static images of seismic sources from geodetic data using akaike s bayesian information criterion abic coseismic surface displacements are generally related with a slip distribution on a fault surface by linear integral equations parametric expansion of the fault slip distribution by a finite number of known basis functions yields a set of observation equations expressed in a simple vector form incorporating prior constraints on the smoothness of slip distribution with the observation equations we construct a bayesian model with unknown hyperparameters the optimal values of the hyperparameters which control the structure of the bayesian model are objectively determined from observed data by using abic once the values of hyperparameters are determined we can use the maximum likelihood method to find the optimal distribution of fault slip we examined the validity of this method through a numerical experiment using theoretical data with random noise we analysed geodetic data associated with the 1946 nankaido earthquake ms 8 2 by using this method the result shows that the fault slip distribution of this earthquake has two main peaks of 4 and 6 m located off kii peninsula and muroto promontory these two high slip areas are clearly separated by a low slip zone extending along kii strait such a slip distribution corresponds with the fact that the rupture process of this earthquake in the western part is notably different from that in the eastern part

effect of enceladus s rapid synchronous spin on interpretation of cassini gravity enceladus s degree 2 gravity determined by cassini is nominally nonhydrostatic to 3 j2 c22 3 38 3 63 as opposed to 10 3 iess et al 2014 interpret this in terms of a hydrostatic interior core and isostatic not hydrostatic floating ice shell enceladus s rapid 1 37 d synchronous spin and tide distorts its shape substantially though enough that the predicted hydrostatic j2 c22 is not 10 3 but closer to 3 25 this leads to the following revision to the internal picture of enceladus compared with iess et al 1 the satellite s core is somewhat smaller and slightly denser 190 km radius and 2450 kg m3 2 the compensation depth shell thickness of the global degree 2 ice shell is 50 km rather close to the base of the modeled ice water layer and 3 the compensation depth shell thickness beneath the south polar terrain from j3 remains shallower thinner at 30 km independent of but influenced by the degree 2 solution

crater modification and geologic activity in enceladus heavily cratered plains evidence from the impact crater distribution abstract although we can observe current activity on saturn s satellite enceladus with cassini insight into past activity is best achieved for now through studying the impact crater distributions furthermore approximation of terrain ages can only be attained through calculations using crater densities and estimations of impact rates in the saturnian system here we focus on what the impact crater distribution in enceladus heavily cratered plains can tell us about enceladus geologic history we use cassini iss images to count craters in the heavily cratered plains on enceladus along with rhea dione tethys and mimas as references to develop and compare their size frequency distributions comparisons of our counts show that enceladus cratered plains distribution is unique in that it appears to have a relative deficiency of craters for diameters 2 km and 6 km compared to the other satellites heavily cratered plains our data also indicates that the impact crater density within the cratered plains changes with latitude specifically both the north and south mid latitude regions have approximately three times higher density than the equatorial region we hypothesize that the missing small and large craters in enceladus cratered plains is due to a combination of viscous relaxation of the larger craters and burial of the relaxed large craters and small craters by south polar plume and possibly e ring material we also conclude that the spatial density distribution is not consistent with recent polar wander

evidence for subduction in the ice shell of europa despite widespread evidence for extension there have been few signs of contraction on the icy surface of jupiter s europa evidence for a subduction like convergent boundary suggests that europa may have active plate tectonics