resurfacing history of europa from pole to pole geological mapping abstract we produced geologic maps from two regional mosaics of galileo images across the leading and trailing hemispheres of europa in order to investigate the temporal distribution of units in the visible geologic record five principal terrain types were identified plains bands ridges chaos and crater materials which are interpreted to result from 1 tectonic fracturing and lineament building 2 cryovolcanic reworking of surface units with possible emplacement of sub surface materials and 3 impact cratering the geologic histories of both mapped areas are essentially similar and reflect some common trends tectonic resurfacing dominates the early geologic record with the formation of background plains by intricate superposition of lineaments the opening of wide bands with infilling of inter plate gaps and the buildup of ridges and ridge complexes along prominent fractures in the ice it also appears that lineaments are narrower and more widely spaced with time the lack of impact craters overprinted by lineaments indicate that the degree of tectonic resurfacing decreased rapidly after ridged plains formation in contrast the degree of cryovolcanic resurfacing appears to increase with time as chaos formation dominates the later parts of the geologic record these trends and the transition from tectonic to cryovolcanic dominated resurfacing could be attributed to the gradual thickening of europa s cryosphere during the visible geologic history that comprises the last 2 or 30 80 myr of europa s history an originally thin brittle ice shell could be pervasively fractured or melted through by tidal and endogenic processes the degree of fracturing and plate displacements decreased with time in a thickening shell and lineaments became narrower and more widely spaced formation of chaos regions could have occurred where the thickness threshold for solid state convection was exceeded and can be aided by preferential tidal heating of more ductile ice in a long term context it is not clear at this point whether this inferred thickening trend would reflect a drastic change in the thermal evolution of the satellite or cyclic or irregular episodes of tectonic and cryovolcanic activity

effects of drake passage on a strongly eddying global ocean the climate impact of ocean gateway openings during the eocene oligocene transition is still under debate previous model studies employed grid resolutions at which the impact of mesoscale eddies has to be parameterized we present results of a state of the art eddy resolving global ocean model with a closed drake passage and compare with results of the same model at noneddying resolution an analysis of the pathways of heat by decomposing the meridional heat transport into eddy horizontal and overturning circulation components indicates that the model behavior on the large scale is qualitatively similar at both resolutions closing drake passage induces i sea surface warming around antarctica due to equatorward expansion of the subpolar gyres ii the collapse of the overturning circulation related to north atlantic deep water formation leading to surface cooling in the north atlantic and iii significant equatorward eddy heat transport near antarctica however quantitative details significantly depend on the chosen resolution the warming around antarctica is substantially larger for the noneddying configuration 5 5 c than for the eddying configuration 2 5 c this is a consequence of the subpolar mean flow which partitions differently into gyres and circumpolar current at different resolutions we conclude that for a deciphering of the different mechanisms active in eocene oligocene climate change detailed analyses of the pathways of heat in the different climate subsystems are crucial in order to clearly identify the physical processes actually at work

recurring and triggered slow slip events near the trench at the nankai trough subduction megathrust the discovery of slow earthquakes has revolutionized the field of earthquake seismology defining the locations of these events and the conditions that favor their occurrence provides important insights into the slip behavior of tectonic faults we report on a family of recurring slow slip events sses on the plate interface immediately seaward of repeated historical moment magnitude mw 8 earthquake rupture areas offshore of japan the sses continue for days to several weeks include both spontaneous and triggered slip recur every 8 to 15 months and are accompanied by swarms of low frequency tremors we can explain the sses with 1 to 4 centimeters of slip along the megathrust centered 25 to 35 kilometers km from the trench 4 to 10 km depth the sses accommodate 30 to 55 of the plate motion indicating frequent release of accumulated strain near the trench

fluid volcanism on miranda and ariel flow morphology and composition several types of volcanic units have been recognized on the icy uranian satellites miranda and ariel on miranda ridges characterized by crest grooves are up to 10 km wide and 500 m high a continuous flat topped flow band also 10 km wide and 500 m high forms the outer southern margin of elsinore corona elsinore coronae at least appears to comprise coalesced flow bands and ridges on ariel in addition to at least one ridge unit similar to these on miranda flood plains material has covered the floors of deep chasmata grabens and an irregular depression flows on both satellites are characterized by linear vent geometries and distinct topographic margins which indicate extrusion of a relatively viscous material the topography of the flows can be used to estimate flow viscosity or yield strength using a bingham plastic model extrusion viscosity estimates incorporating plausible volcanologically based emplacement time scales and a rigid crust correction range from 107 to 109 p 1013 p in the unlikely absence of a chilled crust viscosity estimates are dependent on the assumed emplacement time scale however and could be as high as 1016 p if a solid stale based time scale is assumed bingham models indicate that it is yield strength that controls the final flow width and thickness that we see yield strength estimates are probably more reliable because of uncertainties in the viscous flow time scale yield strength estimates range from 10 1 to 10 2 bars consistent with yield strengths of partially crystallized silicate melts on other planets nevertheless both the viscosities and yield strengths are well within the range of and in some cases lower than silicate flows silicate compositions are not possible for these flows because of the ice rich composition of these satellites measured properties of ammonia water liquid crystal mixtures are consistent with the observed and estimated flow rheologic properties however and extrusion of such material s is a viable alternative to solid state extrusion for the origin of these flow features

solid state ice volcanism on the satellites of uranus voyager images of the uranian satellites ariel and miranda show flow features with morphologies indicating that ice has been extruded to the satellites9 surfaces in the solid state these images provide the first observational evidence for solid state ice volcanism in the solar system topographic profiles have been measured across a number of flow features on ariel with a simple model of extrusion spreading and cooling of a viscous flow the initial viscosity of the flow material is found to have been no more than about 10 16 poise far lower than expected for h 2 o ice at the ambient surface temperatures in the uranian system sharply reduced viscosities may have resulted from incorporation of ices like nh 3 or ch 4 in the uranian satellites

a slow thrust slip event following the two 1996 hyuganada earthquakes beneath the bungo channel southwest japan we report a slow thrust slip event that occurred beneath the bungo channel region southwestern japan on oct and dec 1996 two hyuganada earthquakes both mw 6 7 followed by afterslips occurred in addition a crustal movement characterized by an extremely slow rise was observed around the bungo channel about 200 km north from the epicenters and continued for about 300 days long assuming a slow slip on the plate boundary we estimate its duration and surface displacements from gps time series data by curve fitting and then determine the fault slip distribution we found that a slow slip without any earthquakes continued for nearly one year and released the seismic moment comparable to that of the hyuganada earthquakes occurrence of the slow thrust slip event suggests that this kind of event may be a characteristic mode of stress release at a transition region of interplate coupling

spatial and temporal evolution of stress and slip rate during the 2000 tokai slow earthquake 1 we investigate an ongoing silent thrust event in the tokai seismic gap along the suruga nankai trough central japan prior to the event continuous gps data from april 1996 to the end of 1999 show that this region displaced 2 cm yr to the northwest relative to the landward plate the gps time series show an abrupt change in rate in mid june 2000 that continues as of mid 2005 we model this transient deformation which we refer to as the tokai slow thrust slip event as caused by slip on the interface between the philippine sea and amurian plates the spatial and temporal distribution of slip rate is estimated with kalman filter based inversion methods our inversions reveal two slow subevents the first initiated in late june 2000 slightly before the miyake jima eruption the locus of slip then propagated southeast in the second half of 2000 with maximum slip rates of about 15 cm yr through 2001 a second locus of slip initiated to the northeast in early 2001 the depth of the slip zone is about 25 km which may correspond to the transition zone from a seismogenic to a freely sliding zone the cumulative moment magnitude of the slow slip event up to november 2002 is mw 6 8 we calculate shear stress changes on the plate interface from the slip histories stress change as a function of slip rate shows trajectories similar to that inferred for high speed ruptures however the maximum velocity is 8 orders of magnitude less than in normal earthquakes

offshore geodetic data conducive to the estimation of the afterslip distribution following the 2003 tokachi oki earthquake a cable based seafloor observatory located offshore of hokkaido japan provides the world s first direct observation of offshore post seismic displacement after removing thermal noise this data is used to constrain the distribution of offshore afterslip from a great interplate earthquake mw 8 0 that occurred during 2003 along the southern kuril trench a checkerboard resolution test showed a great contribution of the offshore data to improving the spatial resolution on the plate interface slip near the trench the 1 yr afterslip is distributed in a u shaped pattern encircling its co seismic slip area this result indicates that the stick slip frictional properties of the plate interface are distributed in a patch like pattern as opposed to a banding pattern as previously assumed in young subduction zones

drake passage and cenozoic climate an open and shut case drake passage opening has often been viewed as a single discrete event possibly associated with abrupt changes in global circulation and climate at or near the eocene oligocene boundary a new plate tectonic model based on recent reinterpretations of the opening history of basins in the scotia sea suggests that an effective ocean gateway may have developed even earlier during the middle eocene this is consistent with a growing body of evidence from sediment core proxy data for eocene changes in southern ocean circulation and biological productivity the period between earliest opening after 50 ma and the latest eocene was characterized by the evolution of various current pathways across the subsiding continental shelves and intervening deep basins this shallow opening may have caused important changes in southern ocean circulation contributing to eocene cooling and the growth of antarctic ice sheets

eocene circulation of the southern ocean was antarctica kept warm by subtropical waters 1 near the eocene s close 34 million years ago the climate system underwent one of the largest shifts in earth s history antarctic terrestrial ice sheets suddenly grew and ocean productivity patterns changed previous studies conjectured that poleward penetration of warm subtropical currents the east australian current eac in particular caused eocene antarctic warmth late eocene opening of an ocean gateway between australia and antarctica was conjectured to have disrupted the eac cooled antarctica and allowed ice sheets to develop here we reconstruct eocene paleoceanographic circulation in the tasmanian region using 1 biogeographical distributions of phytoplankton including data from recently drilled ocean drilling program leg 189 sites and 2 fully coupled climate model simulations we find that the eac did not penetrate to high latitudes and ocean heat transport in the region was not greater than modern our results do not support changes in thermal isolation as the primary driver of the eocene oligocene climatic transition

detection and monitoring of ongoing aseismic slip in the tokai region central japan analysis of global positioning system data shows that the rate of crustal deformations in the tokai region of japan a seismic gap area changed over the past 18 months kalman filtering analysis shows aseismic slip on the plate boundary in the western tokai region centered on lake hamana adjacent to the anticipated tokai earthquake source area the cumulative moment magnitude reaches 6 7 in june 2002 with a relative slip increase northeast of lake haman from january 2002 an existence of aseismic slip in the western tokai supports the hypothesis of a silent event as the cause of uplifting several days before the 1944 tonankai earthquake

short term slow slip and correlated tremor episodes in the tokai region central japan 1 we observe the related phenomenon of short term slow slip event sse and low frequency nonvolcanic tremor on the deeper extension of the 1944 tonankai and the anticipated tokai earthquake rupture areas central japan japan nation wide seismometer and tiltmeter array nied hi net has recorded these correlated episodes of sse and tremor known as episodic tremor and slip ets in 2004 and 2005 the events are located on two areas in the tokai region one is near the shima peninsula and the other is around the aichi area both episodes have a typical duration of 2 3 days and released seismic moment corresponding to mw 6 0 moreover these episodes repeatedly occur with a recurrence interval of about six months in both areas this evidence suggests that the coincidence between the sse and the tremor is a characteristic behavior in the whole tremor belt like zone in the nankai trough subduction zone

increased probability of large earthquakes near aftershock regions with relative quiescence it is shown that after a large earthquake of m6 class or over has taken place another event of similar size or larger is relatively more likely in the sense of rate per unit area to occur in the near field than in the far field in particular we show that the aftershock activity of the first event provides useful information for assessing the probability of a following large event in the neighborhood within a distance of a few degrees namely if the aftershock activity from the first event becomes relatively quiet compared to the normal decay the occurrence rate of larger events in the neighborhood is several times higher during the first decade after the main shock than would be the case for normal aftershock activity for measuring such phenomena precisely we need to model the normal aftershock activity in fact many aftershock sequences are more complex than the simple inverse power decay represented by the modified omori formula the epidemic type aftershock sequences etas model is a generalized version of the modified omori formula which fits well with various aftershock sequences including nonvolcanic type swarms using this model aftershock sequences are investigated for the 76 main shocks that occurred in and around japan during the last three quarters of a century the focus is placed on objective examination of whether or not in an aftershock sequence there exists a significant change point followed by relative quiescence that is a significant lowering of the seismicity from that predicted by the etas model relative quiescence can take place regardless of the seismicity level the extent of such quiescence if it exists is seen from the diagrams of cumulative numbers versus the transformed occurrence times based on the predicted occurrence rate by the estimated etas model it is thus demonstrated that relative quiescence can be a helpful factor in detecting anomalous aftershock activity this can then be used to forecast whether or not a large event is more likely to follow shortly within 6 years in the neighborhood within a distance of 3 of the initial event

detection of anomalous seismicity as a stress change sensor 1 anomalous seismicity such as quiescence and activation is defined by a systematic deviation of seismic activity from the predicted rate by the epidemic type aftershock sequence etas model that represents the normal occurrence rate of earthquakes in a region indicating the empirical triggering effect by the previous events the model is fitted to a data set of origin times and magnitudes of earthquakes or aftershocks during may august 2003 in and around northern japan the detected quiescence and activation relative to the predicted seismicity rate are consistent with the coseismic changes of coulomb failure stress cfs in the corresponding regions transferred from certain strong earthquakes few results in this paper agree with the claim that there should be a threshold value of cfs capable of affecting seismic changes thus we expect that significant deviation of actual activity from the predicted rates is sensitive enough to detect a slight stress change furthermore i offer a similar interpretation of the detected seismicity lowering relative to the modeled rates preceding the strong earthquakes assuming some aseismic slips

synchronous changes in the seismicity rate and ocean bottom hydrostatic pressures along the nankai trough a possible slow slip event detected by the dense oceanfloor network system for earthquakes and tsunamis donet abstract we detected long term hydrostatic pressure changes at ocean bottom stations of the dense oceanfloor network system for earthquakes and tsunamis donet along the nankai trough off southwestern japan we detected these changes after removing the contributions of ocean mass variations and sensor drift from the records in addition we detected a decrease in the background seismicity rate of a nearby earthquake cluster that was synchronous with the hydrostatic pressure changes we interpreted these observed hydrostatic pressure changes to reflect vertical deformation of the ocean floor of 3 8 cm and we consider the cause of the seafloor crustal deformation to be a slow slip event sse beneath the stations because the pressure changes were observed at stations with distances less than 20 km to each other we inferred that the sse occurred in the shallow part of the sedimentary wedge such as on a splay fault system the synchronous observation of an sse and a seismicity rate change suggests that both were triggered by a change in the regional stress that may be associated with stress accumulation and release processes occurring along the nankai trough these data show that continuous and careful monitoring of crustal activities by donet stations provides an effective way to detect seismic and geodetic signals related to the occurrence of megathrust or other types of large earthquakes

slow earthquakes and great earthquakes along the nankai trough abstract we have reexamined reports indicating that slow deformation occurred before the great japan earthquakes of 1944 tonankai and 1946 nankaido and find that the observations are well founded although no quantitative models have previously been proposed to explain all of the relevant data we show that they are satisfied by a simple model for both earthquakes the model based on known properties of subduction zones has slow slip on the subduction interface in an area deeper than the seismic rupture if this model is correct and a similar physical situation holds for an anticipated tokai earthquake existing instruments will be able to reveal the pre slip in real time while differences among the deformation time series at different sites will provide strong constraints on the slow rupture propagation these differences could result in delaying the recognition of a coherent event

voyager 2 in the uranian system imaging science results voyager 2 images of the southern hemisphere of uranus indicate that submicrometersize haze particles and particles of a methane condensation cloud produce faint patterns in the atmosphere the alignment of the cloud bands is similar to that of bands on jupiter and saturn but the zonal winds are nearly opposite at mid latitudes 70 degrees to 27 degrees where winds were measured the atmosphere rotates faster than the magnetic field however the rotation rate of the atmosphere decreases toward the equator so that the two probably corotate at about 20 degrees voyager images confirm the extremely low albedo of the ring particles high phase angle images reveal on the order of 10 2 new ringlike features of very low optical depth and relatively high dust abundance interspersed within the main rings as well as a broad diffuse low optical depth ring just inside the main rings system nine of the newly discovered small satellites 40 to 165 kilometers in diameter orbit between the rings and miranda the tenth is within the ring system two of these small objects may gravitationally confine the e ring oberon and umbriel have heavily cratered surfaces resembling the ancient cratered highlands of earth s moon although umbriel is almost completely covered with uniform dark material which perhaps indicates some ongoing process titania and ariel show crater populations different from those on oberon and umbriel these were probably generated by collisions with debris confined to their orbits titania and ariel also show many extensional fault systems ariel shows strong evidence for the presence of extrusive material about halfof miranda s surface is relatively bland old cratered terrain the remainder comprises three large regions of younger terrain each rectangular to ovoid in plan that display complex sets of parallel and intersecting scarps and ridges as well as numerous outcrops of bright and dark materials perhaps suggesting some exotic composition

extensional tilt blocks on miranda evidence for an upwelling origin of arden corona subparallel ridges and troughs in the outer belt of arden corona on the uranian satellite miranda are interpreted as tilt blocks formed by extension and normal faulting fault scarps generally face outward from the corona exposing dark material in the subsurface reconstruction of faults along a deep rift zone bounding the corona suggests initial dips of 50 local extension reaches 70 extremely high in comparison to previous estimates of strain on icy satellites a rise adjacent to the rift zone is modeled as flexural and indicates an effective elastic lithospheric thickness of 2 km at the time of flexure the assumption that faulting has significantly weakened the lithosphere suggests a mechanical lithosphere thickness of 5 to 10 km corresponding thermal gradients in a frictionally controlled ice lithosphere are 8 to 20 k km 1 and lithospheric tensional strength is 0 4 to 1 8 mpa normal faulting in arden corona indicates that internal upwelling likely formed the corona and the outward facing direction of faults is consistent with such a model an upwelling origin of miranda s coronae eliminates the need to invoke catastrophic breakup and reaccretion of the satellite as an explanation for its surface geology

dynamic deformation of the accretionary prism excites very low frequency earthquakes 1 we have detected anomalous very low frequency earthquakes within the accretionary prism along the nankai trough southwestern japan centroid moment tensor inversion analysis reveals that the earthquake hypocenters are distributed at 10 km depth above the upper surface of the subducting philippine sea plate and within 50 70 km landward of the trough axis the focal mechanisms indicate reverse faulting their hypocenters are distributed beneath a deformation zone of an accretionary prism in sea floor topography these observations suggest that the occurrence of very low frequency earthquakes is related to numerous reverse fault systems within the accretionary prism and that the earthquakes reflect the dynamics of deformation within this accretionary prism

cryomagmatic mechanisms for the formation of rhadamanthys linea triple band margins and other low albedo features on europa we investigate cryomagmatic mechanisms for the formation of the diffuse low albedo margins of triple bands and haloes associated with elliptical lenticulae on europa one mechanism involves explosive venting of a gas particle spray derived from a subsurface body of volatile bearing water assuming the dark features represent cryoclastic deposits erupted from a medial or central vent modeling the dynamics of the eruptive plumes indicates that eruption velocities of 30 to 250 m s 1 and volatile contents of 0 1 to 20 wt are required to produce deposits having the observed dimensions calculated heights for ballistic plumes range from 1 to 25 km as an alternative mechanism we consider conductive heating of lithospheric ice by a subsurface heat source e g a warm ice diapir or cryomagmatic intrusion which promotes enhanced sublimation of surface ice producing local enrichment of nonice material an analytical model describing a constant temperature infinite heat source places lower bounds on the time scales required to produce a detectable feature a numerical treatment of more realistic geometries and boundary conditions allows cooling of the heat source to be modeled we find that the thermal model satisfactorily explains features with the dimensions of minor lineaments and lenticulae haloes a few kilometers over time intervals of 104 to 105 years the formation of a sublimation lag deposit proceeds rapidly once the ice temperature exceeds a threshold of 130 k however for triple bands measuring up to 25 km in width additional heat sources such as repeated or multiple intrusions are necessary to reproduce the observed dimensions this is consistent with the observation that well developed triple bands typically have multiple medial ridge sets each of which may represent a discrete tabular heat source although neither the volcanic nor intrusive thermal model can be ruled out at this stage the latter is a more satisfactory explanation for some characteristics of the low albedo features analyzed in this study

seismic activity changes progressing simultaneously with slow slip in the tokai area abstract anomalous movements were detected simultaneously in both the seismic and the gps observations in the tokai area the central part of the japanese islands from the late 1990s to 2000 the anomalies are of great concern since the pending risk of a large megathrust earthquake in this area has been predicted for more than 20 years the gps data revealed that a slow slip on the plate interface had commenced beneath lake hamana the center of which is positioned around the edge of the assumed focal zone on the other hand the seismic data indicated that a delicate but clear quiescence appeared over a wide area that spreads into the main focal zone analyses of the seismicity changes in space and time confirmed that the contrast in the seismicity rate is distinct inside the focal zone while the integrated seismicity indicated quiescence some locations were distinguished as activated zones possibly indicating the appearance of asperities the rise of the seismicity rate in a quasi stationary manner suggests an increase in the stress rate at that location the following hypothesis is proposed based on the simultaneously detected evidences the slow slip progressing beneath lake hamana will induce a stress shift that invades the interior of the main locked zone which will increase the contrast of the seismicity rate possibly reflecting inhomogeneity in the locking strength even in this stage the activated zones still maintain a locked state to prevent overall breakage investigations of the b value changes and of tidal dependence in seismicity that reveal the stress concentrated state also support the hypothesis if this is the case the observed change in seismicity would indicate the process of stress redistribution in the locking state which represents the preparatory process toward final breakage tracking such seismicity changes would yield valid information for predictions of the next tokai earthquake

an integrated global model of present day plate motions and plate boundary deformation summary in this paper we present a global model gsrm 1 of both horizontal velocities on the earth s surface and horizontal strain rates for almost all deforming plate boundary zones a model strain rate field is obtained jointly with a global velocity field in the process of solving for a global velocity gradient tensor field in our model we perform a least squares fit between model velocities and observed geodetic velocities as well as between model strain rates and observed geological strain rates model velocities and strain rates are interpolated over a spherical earth using bi cubic bessel splines we include 3000 geodetic velocities from 50 different mostly published studies geological strain rates are obtained for central asia only and they are inferred from quaternary fault slip rates for all areas where no geological information is included a priori constraints are placed on the style and direction but not magnitude of the model strain rate field these constraints are taken from a seismic strain rate field inferred from normalized focal mechanisms of shallow earthquakes we present a global solution of the second invariant of the model strain rate field as well as strain rate solutions for a few selected plate boundary zones generally the strain rate tensor field is consistent with geological and seismological data with the assumption of plate rigidity for all areas other than the plate boundary zones we also present relative angular velocities for most plate pairs we find that in general there is a good agreement between the present day plate motions we obtain and longterm plate motions but a few significant differences exist the rotation rates for the indian arabian and nubian plates relative to eurasia are 30 13 and 50 per cent slower than the nuvel1a estimate respectively and the rotation rate for the nazca plate relative to south america is 17 per cent slower on the other hand caribbean north america motion is 76 per cent faster than the nuvel 1a estimate while crustal blocks in the india eurasia collision zone move significantly and self consistently with respect to bounding plates only a very small motion is predicted between the nubian and somalian plates by integrating plate boundary zone deformation with the traditional modelling of angular velocities of rigid plates we have obtained a model that has already been proven valuable in for instance redefining a no net rotation model of surface motions and by confirming a global correlation between seismicity rates and tectonic moment rates along subduction zones and within zones of continental deformation

viscosity of rock ice mixtures and applications to the evolution of icy satellites theory and experiments are used to establish lower and upper bounds on the ratio of actual viscosity to pure ice viscosity for a suspension of rock particles in a water ice matrix for typical conditions encountered in icy satellites this ratio is of order ten or possibly larger depending on unknown factors such as the particle size distribution it is shown that even this modest increase in viscosity may be enough to have caused a failure of solid state convective self regulation early in the evolution of a homogeneous rock water ice satellite provided the satellite is large enough and sufficiently silicate rich the criteria for this failure are satisfied by ganymede and are marginal for callisto if the silicates are hydrated failure of self regulation means that the viscosity is too high for the interior to remain completely solid and eliminate the heat production of long lived radioisotopes by solid state convection partial melting of the ice then occurs it is further shown that satellites of this size may then undergo runaway differentiation into a rock core and almost pure ice mantle because the gravitational energy release is sufficient to melt nearly all the ice and the rayleigh taylor instability time scale is short although the high pressure phases of ice melt the resulting water quickly refreezes at a higher level it is conjectured that these results explain the striking surface dissimilarity of ganymede and callisto if these satellites accreted cold and undifferentiated ganymede may have gone supercritical melted and differentiated because of a failure of self regulation whereas callisto remained undifferentiated to the present day like all proposed explanations for the ganymede callisto dichotomy this conjecture cannot be quantified with confidence because of inadequate or incomplete observations theory and experimental data

slow earthquakes linked along dip in the nankai subduction zone we identified a strong temporal correlation between three distinct types of slow earthquakes distributed over 100 kilometers along the dip of the subducting oceanic plate at the western margin of the nankai megathrust rupture zone southwest japan in 2003 and 2010 shallow very low frequency earthquakes near the nankai trough as well as nonvolcanic tremor at depths of 30 to 40 kilometers were triggered by the acceleration of a long term slow slip event in between this correlation suggests that the slow slip might extend along dip between the source areas of deeper and shallower slow earthquakes and thus could modulate the stress buildup on the adjacent megathrust rupture zone

mobilization of cryogenic ice in outer solar system satellites voyager images of the uranian satellites show a diversity of geological features including clear evidence for the softening and mobilization of ice on miranda and ariel some of these features are similar to those seen on jovian and saturnian satellites where the mobile material is believed to be water or a water ammonia mixture however the extremely low temperatures and probable unavailability of large energy sources within the uranian satellites lead us to consider flow mechanisms that operate at very low temperature t 100 k we propose here a form of pressure solution creep in which very fine grained water ice or clathrate hydrate is mobilized by a small amount of intergranular cryogenic fluid ch 4 co or n 2 viscosities as low as 10 12 p are possible for a limited time sufficient to allow flooding of rift valleys and perhaps even substantial lateral flows glaciers

aseismic slip and low frequency earthquakes in the bungo channel southwestern japan 1 analysis of global positioning system gps data has shown transient crustal deformation in the bungo channel in southwestern japan since late august 2003 six years after a similar event in 1996 1997 considering the southeastward motion at many of the gps sites and the similarity between the 1996 1997 and 2003 events it is highly likely that the transients were caused by aseismic interplate slip between the philippine sea plate and the amurian plate the 2003 aseismic slip is estimated beneath the bungo channel and the relative slip increased with time on the west side with a moment magnitude mw amounting to 7 0 in contrast to the gradual subsidence of low frequency earthquakes which began and ended in coincidence with the 2003 event the 2003 transient crustal deformation proceeded at a roughly constant rate until the end of november 2003 the bungo channel area may release energy accumulated from the subduction of the philippine sea plate by aseismic slip

episodic slow slip events in the japan subduction zone before the 2011 tohoku oki earthquake abstract we describe two transient slow slip events that occurred before the 2011 tohoku oki earthquake the first transient crustal deformation which occurred over a period of a week in november 2008 was recorded simultaneously using ocean bottom pressure gauges and an on shore volumetric strainmeter this deformation has been interpreted as being an m6 8 episodic slow slip event the second had a duration exceeding 1 month and was observed in february 2011 just before the 2011 tohoku oki earthquake the moment magnitude of this event reached 7 0 the two events preceded interplate earthquakes of magnitudes m6 1 december 2008 and m7 3 march 9 2011 respectively the latter is the largest foreshock of the 2011 tohoku oki earthquake our findings indicate that these slow slip events induced increases in shear stress which in turn triggered the interplate earthquakes the slow slip event source area on the fault is also located within the downdip portion of the huge coseismic slip area of the 2011 earthquake this demonstrates episodic slow slip and seismic behavior occurring on the same portions of the megathrust fault suggesting that the faults undergo slip in slow slip events can also rupture seismically

precursory seismic quiescence before the mw 8 3 tokachi oki japan earthquake on 26 september 2003 revealed by a re examined earthquake catalog 1 the 2003 tokachi oki earthquake mw 8 3 occurred on 26 september 2003 off the pacific coast of hokkaido japan in the present study an earthquake catalog is used that lists 2 000 earthquakes with m 3 3 all of the earthquake waveforms were recorded by the institute of seismology and volcanology hokkaido university in the present study these waveforms are manually re examined and hypocenters and magnitudes are re calculated a detailed analysis of the re determined earthquake catalog between 1994 and 2003 using a gridding technique zmap shows that the 2003 tokachi oki earthquake is preceded by two neighboring seismic quiescence anomalies that start around the beginning of 1999 and last about 5 years until the main shock occurs these quiescence anomalies are located around the asperity ruptured by the main shock and the z values are 3 9 and 4 0 for a time window of tw 4 years using a sample size of n 100 earthquakes the detected seismic quiescences can be interpreted as being caused by a decrease of 50 in the stressing rate based on dieterich s theory it is proposed that a quasi static pre slip occurs at the northeastern edge of the asperity ruptured by the main shock and lasts for five years until the main shock occurs by calculating the change in the coulomb failure stress cfs it is found that negative cfs areas are consistent with the two quiescence anomalies and a positive cfs area corresponds to the hypocenter of the main shock indicating that the quasi static pre slip model is a plausible one

tsunami scenarios based on interseismic models along the nankai trough japan from seafloor and onshore geodesy the recent availability of global positioning system acoustic seafloor geodetic observations enables us to resolve the spatial distribution of the slip deficit rate near the nankai trough southwestern japan considering a tectonic block model and the transient deformation due to the major earthquakes in this area the slip deficit rate between the two relevant blocks can be estimated in this study we remove the time dependent postseismic deformation of the 2004 southeastern off the kii peninsula earthquakes mjma 7 1 7 4 which had led to the underestimation of the slip deficit rate in earlier studies we model the postearthquake viscoelastic relaxation using the 3d finite element model with bi viscous burgers rheology as well as the afterslip on the finite faults the corrected global positioning system acoustic and land based global navigation satellite systems data are aligned to the existing tectonic model and used to estimate the slip deficit rate on the plate boundary we then calculate the coseismic displacements and tsunami wave propagation with the simple assumption that a hundred years of constant slip deficit accumulation was released instantaneously to evaluate the influence of uncertainties in the plate interface geometry on a tsunami model for the nankai trough we investigated two different geometries and performed checkerboard inversion simulations although the two models indicate roughly similar results the peak height of the tsunami wave and its arrival time at several points are significantly different in terms of the expected hazard

statistical model for standard seismicity and detection of anomalies by residual analysis abstract a statistical point process model is derived to describe the standard activity of earthquake occurrences by assuming that general seismicity is given by the superposition of aftershock sequences the parameters are estimated ty the maximum likelihood method using the estimated model the residual point process of the data is defined and used to find the anomalies which are included in the data set but not captured in the considered model for the standard seismicity for instance seismic quiescences can be measured quantitatively by using the residual process some examples are provided to illustrate such analyses furthermore a time series of the magnitudes on the residual point process is considered to investigate its dependence either on the time or on the history of the seismicity by assuming the exponential distribution at each time and modelling of the b value we can examine such dependences and estimate them two practical examples are shown

the role of ocean gateways in the dynamics and sensitivity to wind stress of the early antarctic circumpolar current the date of inception of the antarctic circumpolar current is debated due to uncertainty in the relative opening times of drake passage and the tasman seaway using an idealized eddy resolving numerical ocean model we investigate whether both ocean gateways have to be open to allow for a substantial circumpolar current we find that overlapping continental barriers do not impede a circumpolar transport in excess of 50sv as long as a circumpolar path can be traced around the barriers however the presence of overlapping barriers does lead to an increased sensitivity of the current s volume transport to changes in wind stress this change in sensitivity is interpreted in terms of the role of pressure drops across continental barriers and submerged bathymetry in balancing the momentum input by the surface wind stress specifically when the pressure drop across continents is the main balancing sink of momentum the zonal volume transport is sensitive to changes in wind stress changes in zonal volume transport take place via altering the depth independent part of the circumpolar transport rather than that arising from thermal wind shear in such a scenario isopycnals continue to slope steeply across the model southern ocean implying a strong connection between the deep and surface oceans this may have consequences for the meridional overturning circulation and its sensitivity to wind stress

tsunamigenic potential of the shallow subduction plate boundary inferred from slow seismic slip at subduction zones slip along the shallowest parts of the plate boundary is generally thought to be aseismic observations of very low frequency earthquakes occurring at shallow levels on the plate boundary of the nankai trough subduction zone imply that slow but seismic slip can occur there and could potentially generate tsunamigenic earthquakes

detailed structural image around splay fault branching in the nankai subduction seismogenic zone results from a high density ocean bottom seismic survey 1 to investigate megathrust earthquake and tsunami generation in a subduction seismogenic zone it is important to know the detailed structure around the plate boundary and active splay fault system the nankai trough southwestern japan is among the best studied subduction zones with splay faults in the world this paper presents a detailed structural image around the splay fault in the coseismic rupture zone of the 1944 tonankai earthquake in the central nankai trough based on results from a wide angle high density ocean bottom seismograph obs survey our seismic image clearly shows for the first time the subduction structure along with the splay fault reflections imaged on a previously obtained seismic reflection profile the correspondence between the splay fault reflections imaged on the seismic reflection profile and our reflectivity image was confirmed by converting the time migrated section to a depth section by using a velocity model estimated from the wide angle obs data in this study the high resolution seismic image obtained by the high density obs survey demonstrates a zone of low velocity gradient just above and along the splay fault we focused specifically on the detailed structure around the splay fault a simple amplitude analysis of the wide angle reflections showed that it is likely that a thin low velocity layer with velocities 0 5 1 5 km s slower than those in the surrounding rock exists above the splay fault the presence of this layer suggests elevated fluid pressure in the fault zone which cut through the relatively homogeneous rock of the accretionary prism and generated past megathrust earthquakes

sea ice feedback and cenozoic evolution of antarctic climate and ice sheets 1 the extent and thickness of antarctic sea ice have important climatic effects on radiation balance energy transfer between the atmosphere and ocean and moisture availability this paper explores the role of sea ice and related feedbacks in the cenozoic evolution of antarctic climate and ice sheets using a numerical climate model with explicit dynamical representations of sea ice and continental ice sheets in a scenario of decreasing cenozoic greenhouse gas concentrations our model initiates continental glaciation before any significant sea ice forms around the continent once variable ice sheets are established seasonal sea ice distribution is highly sensitive to orbital forcing and ice sheet geometry via the ice sheet s control on regional temperature and low level winds although the expansion of sea ice has significant climatic effects near the coast it has only minimal effects in the continental interior and on the size of the ice sheet therefore the cenozoic appearance of antarctic sea ice was primarily a response to the growth of grounded ice sheets and was not a critical factor in episodes of paleogene and neogene glaciation the influence of the east antarctic ice sheet on sea ice southern ocean surface temperatures and winds has important implications for ocean circulation the marine carbon cycle and the development of the west antarctic ice sheet the sensitivity of sea ice to grounded ice sheets implies reconstructions of sea ice based on marine diatoms are good indicators of glacial conditions in the continental interior and may provide insight into the long term stability of antarctic ice sheets

crustal velocity field of southwest japan subduction and arc arc collision we investigate crustal deformation in southwest japan over a 3 year period revealed by a permanent dense global positioning system gps array southwest japan is a part of the amurian plate a microplate moving about 10 mm yr toward the east with respect to the eurasian plate it overrides the philippine sea plate at the nankai trough and collides with the northeast japan arc in the central part of japan in this paper we first derive gps site velocities relative to the stable part of the amurian plate in order to isolate signals of crustal deformation caused by the subduction and or the collision the velocity field has a conspicuous feature indicating the interseismic elastic loading by the philippine sea plate slab at the nankai trough characterized by the northwestward movements of points throughout the studied area their amplitudes are the largest at the pacific coast and decay toward the japan sea coast with a subtle systematic shift of azimuths a model assuming an elastic half space the convergence rate at the nankai trough based on a refined euler vector and the strength of the coupling inferred from a thermal model could explain the velocity field in the western part of the studied area to a large extent those in the eastern part systematically deviate from them and the residual components there show east west shortening and north south extension this may represent crustal thickening and trenchward extrusion of crustal blocks caused by the collision between southwest and northeast japan this suggests that the collision between southwest and northeast japan gives rise to not only crustal thickening but also trenchward extrusion of crustal block a velocity contrast was found across the median tectonic line the largest inland active fault in japan but the current permanent gps network is not dense enough for us to discuss its coupling depth

effective resolution and drift of paroscientific pressure sensors derived from long term seafloor measurements 1 starting with the installation of the noaa tsunami early warning system dart in 1983 the paroscientific digiquarz broadband depth sensor has been deployed for long term ocean bottom pressure measurements in numerous marine investigations the sensor turned out to be very reliable with a good signal repeatability within a broad measuring range and high resolution however up to now its long term drift noise level and effective resolution under in situ conditions at the seafloor are only known from a few published studies and for a few sensors in this study we analyze 118 long term seafloor pressure time series longer than 2 months and up to a maximum time period of 9 years to investigate effective resolution and long term drift under in situ conditions the data are from dart ifm geomar lolem and cork stations the noise level of the data and therefore the mean sensor resolution are lower than an upper threshold of 20 7 pa corresponding to 2 07 mm equivalent water level for stations installed directly on the seafloor the noise level of cork sensors is much larger with a median value of 127 pa long term sensor drift is assumed to be composed of an initial exponential part and a subsequent linear drift in situ mean drift is 0 88 0 73 kpa a determined from all available data with a slight increase of drift with deployment depth for the first time we are able to quantify effective pressure resolution and drift of the widely used paroscientific pressure gauges under in situ conditions our results provide important constrains for the interpretation of seafloor pressure records however in situ self calibration procedures for the paroscientific sensors are still needed in order to benefit from high effective resolution and long term stability and also to increase accuracy especially for the monitoring of geodynamic processes at the seafloor

effect of the deepening of the tasman gateway on the global ocean 1 we examine the effect of the deepening of the tasman seaway at the end of the eocene in a climate model with realistic late eocene bathymetry and winds for this we have constructed an eocene numerical model based on the university of victoria climate model with wind forcing derived from a fully coupled eocene simulation the model climate state is characterized by an oceanic meridional overturning circulation moc involving southern hemisphere sinking and a northward atmospheric moisture transport across the equator the deepening of the tasman seaway in the presence of an open drake passage and the associated establishment of the antarctic circumpolar current acc have a limited climatic impact on antarctica nonetheless the antarctic deep sinking regions cool sufficiently to lead to a global deep ocean cooling of 3 c no initiation of northern component water is found indicating that this may require the development of a more mature acc previous studies suggest that the ross sea gyre cools the east coast of australia and expected the deepening of the tasman seaway to lead to a warming east of australia due to the introduction of warmer water from the australo antarctic gulf we here find that this warming is limited to close to the australian coast and that widespread cooling prevails further off shore

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

on the driving processes of the atlantic meridional overturning circulation because of its relevance for the global climate the atlantic meridional overturning circulation amoc has been a major research focus for many years yet the question of which physical mechanisms ultimately drive the amoc in the sense of providing its energy supply remains a matter of controversy here we review both observational data and model results concerning the two main candidates vertical mixing processes in the ocean s interior and wind induced ekman upwelling in the southern ocean in distinction to the energy source we also discuss the role of surface heat and freshwater fluxes which influence the volume transport of the meridional overturning circulation and shape its spatial circulation pattern without actually supplying energy to the overturning itself in steady state we conclude that both wind driven upwelling and vertical mixing are likely contributing to driving the observed circulation to quantify their respective contributions future research needs to address some open questions which we outline

timing and climatic consequences of the opening of drake passage age estimates for the opening of drake passage range from 49 to 17 million years ago ma complicating interpretations of the relationship between ocean circulation and global cooling secular variations of neodymium isotope ratios at agulhas ridge southern ocean atlantic sector suggest an influx of shallow pacific seawater approximately 41 ma the timing of this connection and the subsequent deepening of the passage coincide with increased biological productivity and abrupt climate reversals circulation productivity linkages are proposed as a mechanism for declining atmospheric carbon dioxide these results also indicate that drake passage opened before the tasmanian gateway implying the late eocene establishment of a complete circum antarctic pathway

deciphering the role of southern gateways and carbon dioxide on the onset of the antarctic circumpolar current 1 growth of antarctic ice sheet during the cenozoic 34 million years ago appears as a potential tipping point in the long term cooling trend that began 50 ma ago for decades the onset of the antarctic circumpolar current acc following the opening of the drake passage and of the tasman seaway has been suggested as the main driver of the continental scale antarctic glaciation however recent modeling works emphasized that the eocene oligocene atmospheric carbon dioxide co2 lowering could be the primary forcing of the antarctic glaciation questioning the acc theory here we investigate the response of the acc to changes in co2concentrations occurring from the late eocene to the late oligocene we used a fully coupled atmosphere ocean model foam with a mid oligocene geography we find that the opening of southern oceanic gateways does not trigger the onset of the acc for co2typical of the late eocene 840 ppm a cooler background climatic state such as the one prevalent at the end of the oligocene is required to simulate a well developed acc in this cold configuration the intensified sea ice development around antarctica and the resulting brine formation lead to a strong latitudinal density gradient in the southern ocean favoring the compensation of the ekman transport and consequently the acc our results imply that the acc has acted as a feedback rather than as a driver of the global cooling

synchronous seismicity changes in and around the northern japan preceding the 2003 tokachi oki earthquake of m8 0 1 the epidemic type aftershock sequence etas model predicts the normal seismic rate that superposes the empirical laws of decreasing aftershock activity anomalies lowering and enhancement of the seismic rate from the rate predicted by the etas model are found to have occurred concurrently during 1996 in three interplate aftershock sequences and in inland intraplate seismicity in and around northern japan each anomaly is explained by change in coulomb failure stress caused by aseismic slip that is assumed to have occurred on the plate interface of the 2003 tokachi oki rupture of m8 0 the slip is also supported by a significant change in the distribution of fault mechanisms of moderate earthquakes before and after 1996 in northern japan using the occurrence data of strong earthquakes of m5 0 or larger for the long period 1926 2003 a similar relative quiescence lasting about 10 years is indicated not only preceding the recent 2003 earthquake but also preceding the 1952 and 1968 great tokachi oki earthquakes