source model of the 2007 mw 8 0 pisco peru earthquake implications for seismogenic behavior of subduction megathrusts we use interferometric synthetic aperture radar teleseismic body waves tsunami waveforms recorded by tsunameters field observations of coastal uplift subsidence and runup to develop and test a refined model of the spatiotemporal history of slip during the mw 8 0 pisco earthquake of 15 august 2007 our preferred solution shows two distinct patches of high slip one patch is located near the epicenter while another larger patch ruptured 60 km further south at the latitude of the paracas peninsula slip on the second patch started 60 s after slip initiated on the first patch we observed a remarkable anticorrelation between the coseismic slip distribution and the aftershock distribution determined from the peruvian seismic network the proposed source model is compatible with regional runup measurements and open ocean tsunami records from the latter data set we identified the 12 min timing error of the tsunami forecast system as being due to a mislocation of the source caused by the use of only one tsunameter located in a nonoptimal azimuth the comparison of our source model with the tsunami observations validate that the rupture did not extend to the trench and confirms that the pisco event is not a tsunami earthquake despite its low apparent rupture velocity 1 5 km s we favor the interpretation that the earthquake consists of two subevents each with a conventional rupture velocity 2 4 km s the delay between the two subevents might reflect the time for the second shock to nucleate or alternatively the time it took for afterslip to increase the stress level on the second asperity to a level necessary for static triggering the source model predicts uplift offshore and subsidence on land with the pivot line following closely the coastline this pattern is consistent with our observation of very small vertical displacement along the shoreline when we visited the epicentral area in the days following the event this earthquake represents to our knowledge one of the best examples of a link between the geomorphology of the coastline and the pattern of surface deformation induced by large interplate ruptures

liquid water and active resurfacing on europa voyager images of the jovian moon europa show a bright icy surface transected by a complex pattern of long linear fracture like markings with a slightly lower albedo1 very few impact craters are observed with sizes generally hi the range 10 20 km indicators of surface composition and texture include deep ir h2o absorption features2 uv absorption features characteristic of sulphur in a water matrix on the trailing hemisphere3 and a photometric function indicating much more homogeneous scattering than areas of equal albedo on ganymede and callisto4 europe s mean density is 3 03 g cm 3 indicating a primarily silicate composition however if the density of the silicates is the same as for io the h2o mass fraction would be 6 enough to form an outer layer of h2o 100 km thick if completely differentiated several models have been suggested for the evolution and present state of europa5 8 we present here arguments for recent resurfacing by h2o from a liquid layer based on new interpretations of recent spacecraft and earth based observations and revised theoretical calculations

strength of the lithosphere of the galilean satellites abstract several approaches have been used to estimate the ice shell thickness on callisto ganymede and europa here we develop a method for placing a strict lower bound on the thickness of the strong part of the shell lithosphere using measurements of topography the minimal assumptions are that the strength of faults in the brittle lithosphere is controlled by lithostatic pressure according to byerlee s law and the shell has relatively uniform density and thickness under these conditions the topography of the ice provides a direct measure of the bending moment in the lithosphere this topographic bending moment must be less than the saturation bending moment of the yield strength envelope derived from byerlee s law the model predicts that the topographic amplitude spectrum decreases as the square of the topographic wavelength this explains why europa is rugged at shorter wavelengths 10 km but extremely smooth and perhaps conforming to an equipotential surface at longer wavelengths 100 km previously compiled data on impact crater depth and diameter schenk p m 2002 nature 417 419 421 on europa show good agreement with the spectral decrease predicted by the model and require a lithosphere thicker than 2 5 km a more realistic model including a ductile lower lithosphere requires a thickness greater than 3 5 km future measurements of topography in the 10 100 km wavelength band will provide tight constraints on lithospheric strength

estimates of europa s ice shell thickness from elastically supported topography 1 the thickness of europa s solid ice shell is uncertain and has important implications for europa s habitability and thermal history and the design of future spacecraft missions here we obtain an estimate of the ice shell thickness from observations of a plateau sw of cilix impact crater stereo topographic profiles suggest that the plateau is flexurally supported with an effective elastic thickness te of 6 2 5 km for a conductive temperature profile this te value implies a solid ice shell thickness of 15 9 20 km if the shell is convecting this estimate is a lower bound combined with independent estimates we infer a probable shell thickness of 25 km the shell thickness is likely to be uniform over the entire satellite

topographic variations in chaos on europa implications for diapiric formation 1 disrupted terrain or chaos on europa might have formed through melting of a floating ice shell from a subsurface ocean carr et al 1998 greenberg et al 1999 or breakup by diapirs rising from the warm lower portion of the ice shell head and pappalardo 1999 collins et al 2000 each model makes specific and testable predictions for topographic expression within chaos and relative to surrounding terrains on local and regional scales high resolution stereo controlled photoclinometric topography indicates that chaos topography including the archetypal conamara chaos region is uneven and commonly higher than surrounding plains by up to 250 m elevated and undulating topography is more consistent with diapiric uplift of deep material in a relatively thick ice shell rather than melt through and refreezing of regionally or globally thin ice by a subsurface ocean vertical and horizontal scales of topographic doming in conamara chaos are consistent with a total ice shell thickness 15 km contact between europa s ocean and surface may most likely be indirectly via diapirism or convection

tsunami modeling to validate slip models of the 2007 mw8 0 pisco earthquake central peru following the 2007 august 15th mw 8 0 pisco earthquake in central peru sladenet al j geophys res 115 b02405 2010 have derived several slip models of this event they inverted teleseismic data together with geodetic insar measurements to look for the co seismic slip distribution on the fault plane considering those data sets separately or jointly but how close to the real slip distribution are those inverted slip models to answer this crucial question the authors generated some tsunami records based on their slip models and compared them to dart buoys tsunami records and available runup data such an approach requires a robust and accurate tsunami model non linear dispersive accurate bathymetry and topography etc otherwise the differences between the data and the model may be attributed to the slip models themselves though they arise from an incomplete tsunami simulation the accuracy of a numerical tsunami simulation strongly depends among others on two important constraints i a fine computational grid and thus the bathymetry and topography data sets used which is not always available unfortunately and ii a realistic tsunami propagation model including dispersion here we extend sladen s work using newly available data namely a tide gauge record at callao lima harbor and the chilean dart buoy record while considering a complete set of runup data along with a more realistic tsunami numerical that accounts for dispersion and also considering a fine resolution computational grid which is essential through these accurate numerical simulations we infer that the insar based model is in better agreement with the tsunami data studying the case of the pisco earthquake indicating that geodetic data seems essential to recover the final co seismic slip distribution on the rupture plane slip models based on teleseismic data are unable to describe the observed tsunami suggesting that a significant amount of co seismic slip may have been aseismic finally we compute the runup distribution along the central part of the peruvian coast to better understand the wave amplification attenuation processes of the tsunami generated by the pisco earthquake

an integrated crustal velocity field for the central andes 1 we present an integrated velocity field for the central andes derived from gps observations collected between january 1993 and march 2001 that eliminates the velocity bias between the south america nazca plate project snapp and central andes gps project cap velocity fields published by norabuena et al 1998 and bevis et al 1999 the reference frame is realized by minimizing the motion of eight continuous gps stations and one rover gps station located in the stable core of the south american plate the rms horizontal motion of these stations is just 1 1 mm yr the amplitude of these residual motions is roughly compatible with expected levels of measurement error in our new solution five of the six snapp stations located just outside the orogenic belt are effectively stationary and the velocities for adjacent cap and snapp stations now agree at a level consistent with their formal uncertainties

is there evidence for polar wander on europa abstract the orientations of the albedo lineaments bands and lineations on europa s surface have been compared in previous studies with the global stress fields set up by orbital eccentricity orbital recession and nonsynchronous rotation of these orbital and rotational effects nonsynchronous rotation combined with an offsetting of the tidal bulge comes closest to providing agreement between the stress field generated and the lineation orientations if the lineations trace tension or extension fractures mcewen 1986 nature321 49 51 however inferred minimum principal stress directions for a broad region of wedge shaped bands near the anti jove point cannot satisfactorily be accounted for by any of the stress fields above but are consistent with the stresses resulting from a rotation of europa s ice shell about an axis through the sub and anti jove points clockwise as seen from the anti jove hemisphere p m schenk and w b mckinnon 1989 icarus79 75 100 calculations by ojakangas and stevenson 1989 icarus81 220 241 of the thermal state of europa s ice shell indicate that spatial variations in the thickness of the shell may cause it to undergo such a reorientation we have investigated whether any reorientation of the shell about an axis through the sub and anti jove points produces a stress field consistent with the full global set of prominent lineations on europa s surface we find that no such reorientation provides a good fit between the lineations and plausible fracture orientations derived from the principal stress trajectories topographic ridges identified in a limited zone south of the anti jove point are roughly consistent with compression due to clockwise polar wander but the orientations of these ridges may be strongly biased by illumination direction within the limitations of the presently available imagery nonsynchronous rotation is still the most likely cause of the prominant fractures on europa s surface and the best specific albeit regionally limited tectonic evidence consistent with recent polar wander remains the wedge shaped bands

tidal heating in an internal ocean model of europa considerable evidence suggests that europe s internal structure might consist of a liquid water layer that decouples a thin 30 km overlying ice lithosphere from an underlying silicate core1 2 a lack of impact features extremely subdued topography and positive spectroscopic identification of h2o all imply recent resurfacing by water in addition curvilinear features resembling cracks are ubiquitous over the surface their orientations are broadly consistent with tidally controlled tectonic activity3 compositional models of europea indicate that the h2o layer could be over 100 km thick1 cassen et al 4 first showed how tidal heating if sufficiently intense might stabilize a thin 30 km ice lithosphere over the internal ocean and prevent the water from freezing other models of europa do not include an internal ocean and instead have an ice layer perhaps as thick as 100 km or as thin as a few kilometres resting directly on the silicate interior5 6 however based on studies of crater relaxation thomas and schubert7 have shown the version of this model with a thin ice layer to be unlikely the plausibility of the internal ocean model vis a vis the thick ice model depends critically on the level of tidal heating in europa here we present new calculations of tidal heating based on a more realistic three layer model of europa the tidal distortion of a decoupled ice lithosphere is only half that previously thought at the current value of orbital eccentricity tidal heating is only marginally able to prevent the internal ocean from freezing

furrow flexure and ancient heat flux on ganymede 0 5 km heat fluxes in the range 60 80 mw m 2 at the time of deformation and a brittle ductile transition depth of 2 3 km the elastic thicknesses are comparable to estimates for grooved terrain on ganymede and chaos regions on europa and may be characteristic of the point during cooling at which the available stresses can no longer cause significant ice shell deformation the furrowed dark terrain heat fluxes exceed likely chondritic values and are plausibly a result of early cooling of ganymede following accretion non synchronous rotation may have contributed to the 2 3 mpa stresses required to cause the observed deformation index terms 5418 planetology solid surface planets heat flow 5455 planetology solid surface planets origin and evolution 5475 planetology solid surface planets tectonics 8149 6218 planetology solar system objects jovian satellites 8149 tectonophysics planetary tectonics 5475 citation nimmo f and r t pappalardo 2004 furrow flexure and ancient heat flux on ganymede geophys res lett 31 l19701 doi 10 1029 2004gl020763

effective elastic thickness and heat flux estimates on ganymede 1 we identify sites of apparent flexural uplift at rift zone boundaries on ganymede using galileo stereo derived topography the estimated effective elastic thickness te is 0 9 1 7 km for a nominal young s modulus of 1 gpa using a viscoelastic model of the ice crust we find that the temperature defining the base of the elastic layer is 185 k for likely strain rates the inferred local heat flux during deformation is less than 245 mw m 2 and probably close to 100 mw m 2 the stresses required to cause fault motion are around 1 mpa both the high heat flux and the high stresses are consistent with estimates of these quantities during an episode of transient tidal heating in ganymede s past

friction of ice the frictional strength of ice seems to be well below that for all other rocks triaxial testing of cylinders of pure water ice containing a 45 inclined sawcut at temperatures of 77 t 115 k and confining pressures 0 1 p 250 mpa reveals the frictional laws 0 20 n 8 3 mpa for p 10 mpa and 0 55 n 1 0 mpa for p 5 mpa where and n are the shear and normal stresses on the sawcut surface friction is independent of t and over the one order of magnitude tested of average sliding velocity the sliding behavior is invariably stick slip examination of sliding surfaces shows only minor gouge development a curious arrangement of densely packed short vertical fractures occurs primarily in samples with anomalously low strength these results apply to models of near surface tectonic activity on jupiter s three large icy moons europa callisto and ganymede they indicate for example that a global expansion on ganymede of 3 linear percent will cause extensional movement on preexisting faults at depths to 7 3 km

seismic source of the earthquake of camana peru 2001 mw 8 2 from joint inversion of geodetic and tsunami data on june 23 2001 at 15 33 local time 20 33 utc a strong earthquake of magnitude mw 8 2 shook the southern region of peru causing considerable material damage and the loss of 74 human lives the epicenter was located in the sea near the city of atico arequipa as a coseismic effect a local tsunami was generated which after 15 min caused the flood and destruction of the beach resorts of camana and resulted in the death of 25 people and 62 missing persons another coseismic effect was the subsidence of the coastal zones in the source region evidenced by geodetic observations we have conducted a joint inversion of tsunami and geodetic data with a fault plane of variable dip to obtain the slip distribution the main asperity slip 12 6 m was located offshore camana this explains the great damage in this city the seismic moment was calculated in 2 72 times 10 21 nm and the corresponding moment magnitude was mw 8 2 the subfaults near the trench have a null slip therefore there is a high potential for the generation of a tsunamigenic earthquake in the updip of the fault plane near the trench

thickness constraints on the icy shells of the galilean satellites from a comparison of crater shapes a thin outer ice shell on jupiter s large moon europa would imply easy exchange between the surface and any organic or biotic material in its putative subsurface ocean1 2 3 4 the thickness of the outer ice shell is poorly constrained however with model dependent estimates ranging from a few kilometres5 6 to ten or more kilometres7 here i present measurements of depths of impact craters on europa ganymede and callisto that reveal two anomalous transitions in crater shape with diameter the first transition is probably related to temperature dependent ductility of the crust at shallow depths 7 8 km on europa the second transition is attributed to the influence of subsurface oceans on all three satellites3 8 9 which constrains europa s icy shell to be at least 19 km thick the icy lithospheres of ganymede and callisto are equally ice rich but europa s icy shell has a thermal structure about 0 25 0 5 times the thicknesses of ganymede s or callisto s shells depending on epoch the appearances of the craters on europa are inconsistent with thin ice shell models1 and indicate that exchange of oceanic and surface material could be difficult

the 2007 pisco peru earthquake m8 0 seismology and geodesy summary we investigate the 2007 pisco peru earthquake m8 0 using seismological and geodetic data analysis of teleseismic records indicates that the earthquake is characterized by a steadily increasing moment rate with the maximum occurring between about 55 and 70 s and the associated slip occurring about 40 km south of the epicentre we combine insar data from l band alos and c band envisat satellites to produce a 3 d image of the ground displacements caused by the earthquake distributed slip inversions of the interferograms identify a single large patch of slip in the location of the maximum moment rate identified by seismology despite a clear spatial coincidence between the location of the coseismic slip and the anomalously high topography of the paracas peninsula we find no evidence that the earthquake was directly responsible for motion on any upper plate faults

transient and steady state creep response of ice i and magnesium sulfate hydrate eutectic aggregates 1 using uniaxial compression creep experiments we characterized the transient and steady state deformation behaviors of eutectic aggregates of system ice i and mgso4 11h2o ms11 meridianiite which has significance because of its likely presence on moons of the outer solar system synthetic samples of eutectic liquid bulk composition which produce eutectic colonies containing 0 35 0 50 volume fraction ms11 were tested as functions of colony size and lamellar spacing temperature 230 250 k and confining pressure 0 1 and 50 mpa to strains 0 2 up to a differential stress of 6 mpa the ice i ms11 aggregates display an order of magnitude higher effective viscosity and higher stress sensitivity than do aggregates of pure polycrystalline ice at the same conditions the creep data and associated microstructural observations demonstrate however that the aggregates are additionally more brittle than pure ice approaching rate independent plasticity that includes rupture of the hydrate phase at 6 8 mpa depending on the scale of the microstructure microstructures of deformed samples reveal forms of semibrittle flow in which the hydrate phase fractures while the ice phase deforms plastically semibrittle flow in the icy shell of a planetary body would truncate the lithospheric strength envelope and thereby decrease the depth to the brittle ductile transition by 55 and reduce the failure limit for compressional surface features from 10 to 6 mpa a constitutive equation that includes eutectic colony boundary sliding and intracolony flow is used to describe the steady state rheology of the eutectic aggregates

a multi sensor approach towards a global vegetation corrected srtm dem product abstract we develop the first global bare earth digital elevation model dem based on the shuttle radar topography mission srtm for all landmasses between 60n and 54s our new bare earth srtm dem combines multiple remote sensing datasets including point ground elevations from nasa s laser altimeter icesat a database of percentage of tree cover from the modis satellite as a proxy for penetration depth of srtm and a global vegetation height map in order to remove the vegetation artefacts present in the original srtm dem we test multiple methods of removing vegetation artefacts and investigate the use of regionalization our final bare earth srtm product shows global improvements greater than 10 m in the bias over the original srtm dem in vegetated areas compared with ground elevations determined from icesat data with a significant reduction in the root mean square error from over 14 m to 6 m globally therefore our dem will be valuable for any global applications such as large scale flood modelling requiring a bare earth dem

topographic gravity modeling for global bouguer maps to degree 2160 validation of spectral and spatial domain forward modeling techniques at the 10 microgal level over the past years spectral techniques have become a standard to model earth s global gravity field to 10 km scales with the egm2008 geopotential model being a prominent example for some geophysical applications of egm2008 particularly bouguer gravity computation with spectral techniques a topographic potential model of adequate resolution is required however current topographic potential models have not yet been successfully validated to degree 2160 and notable discrepancies between spectral modelling und newtonian numerical integration well beyond the 10 mgal level have been reported here we rigorously compute and validate gravity implied by a degree 2160 model of earth s topographic masses our experiments are based on two key strategies both of which require advanced computational resources first we construct a spectrally complete model of the gravity field which is generated by the degree 2160 earth topography model this involves expansion of the topographic potential to the 15th integer power of the topography and modelling of short scale gravity signals to ultra high degree of 21 600 translating into unprecedented fine scales of 1 km second we apply newtonian integration in the space domain with high spatial resolution to reduce discretisation errors our numerical study demonstrates excellent agreement 8 microgal rms between gravity from both forward modelling techniques and provides insight into the convergence process associated with spectral modelling of gravity signals at very short scales few km as key conclusion our work successfully validates the spectral domain forward modelling technique for degree 2160 topography and increases the confidence in new high resolution global bouguer gravity maps

a high accuracy map of global terrain elevations spaceborne digital elevation models dems are a fundamental input for many geoscience studies but they still include nonnegligible height errors here we introduce a high accuracy global dem at 3 resolution 90 m at the equator by eliminating major error components from existing dems we separated absolute bias stripe noise speckle noise and tree height bias using multiple satellite data sets and filtering techniques after the error removal land areas mapped with 2 m or better vertical accuracy were increased from 39 to 58 significant improvements were found in flat regions where height errors larger than topography variability and landscapes such as river networks and hill valley structures became clearly represented we found the topography slope of previous dems was largely distorted in most of world major floodplains e g ganges nile niger and mekong and swamp forests e g amazon congo and vasyugan the newly developed dem will enhance many geoscience applications which are terrain dependent

gravitational and topographic isotropy of the earth moon mars and venus the internal structures and surface shapes of the terrestrial planets are expected to be dominantiy isotropic we attempt to test this hypothesis by developing a criterion for recognizing statistical isotropy of spherical scalar fields and applying that test to the nonhydrostatic components of the gravitational and topographic fields of the earth moon mars and venus the criterion for topographic or geoidal surfaces is that the directional variance should be independent of azimuth that is the mean square east west slopes should be equal to the mean square north south slopes all four planets generally pass the criteria with a few minor exceptions most of the exceptions are likely to be artifacts of the current generation of planetary gravity and topography models rather than real features of the planets of the several broad band departures from isotropy which we found the only one likely to be real is the tendency for the earth s gravity and topography to have only 80 as much variance in a north south direction as in an east west direction

evidence for separation across a gray band on europa abstract thynia linea a gray band on europa is found to be a 25 km wide and 900 km long region of lithospheric separation which has been infilled by relatively dark material roughly a dozen older features and the cuspate segments that form its outline appear to have been displaced across its width displacement azimuths indicate a best fit pole of opening near 79 s 200 w however displacement magnitude decreases toward either end of the gray band indicating that it is more akin to a tear in a nonrigid europan lithosphere opening was in response to nw se directed tensile stress in accord with the stress predictions of nonsynchronous rotation observations of thynia linea are consistent with a laterally mobile brittle lithosphere decoupled from ductile or liquid material below as previously suggested to account for opening of wedge shaped bands in europa s antijovian region lithospheric separation and contemporaneous emplacement of new material offers a possible volcano tectonic scenario for resurfacing europa if this process is ongoing resurfacing can be accomplished on a time scale consistent with the satellite s surface age if one gray band or zone of wedge shaped bands forms every 10 3 10 4 yr and becomes unrecognizable with age this would imply that features on europa brighten with age as through continuous deposition of frost onto the surface

historical 1942 ecuador and 1942 peru subduction earthquakes and earthquake cycles along colombia ecuador and peru subduction segments two large shallow earthquakes occurred in 1942 along the south american subduction zone inclose proximity to subducting oceanic ridges the 14 may event occurred near the subducting carnegie ridge off the coast of ecuador and the 24 august event occurred off the coast of southwestern peru near the southern flank of the subducting nazca ridge source parameters for these for these two historic events have been determined using long periodp waveforms p wave first motions intensities and local tsunami data we have analyzed thep waves for these two earthquakes to constrain the focal mechanism depth source complexity and seismic moment modeling of thep waveform for both events yields a range of acceptable focal mechanisms and depths all of which are consistent with underthrusting of the nazca plate beneath the south american plate the source time function for the 1942 ecuador event has one simple pulse of moment release with a duration of 22 suconds suggesting that most of the moment release occurred near the epicenter the seismic moment determined from thep waves is 6 8 1020n m corresponding ot a moment magnitude of 7 8 7 9 the reported location of the maximum intensities ix for this event is south of the main shock epicenter the relocated aftershcks are in an area that is approximately 200 km by 90 km elongated parallel to the trench with the majority of aftershocks north of the epicenter in contrast the 1942 peru event has a much longer duration and higher degree of complexity than the ecuador earthquake suggesting a heterogeneous rupture seismic moment is released in three distinct pulses over approximately 74 seconds the largest moment release occurs 32 seconds after rupture initiation the seismic moment as determined from thep waves for the 1942 peru event is 10 25 1020n m corresponding to a moment magnitude of 7 9 8 2 aftershock locations reported by the iss occur over a broad area surrounding the main shock the reported locations of the maximum intensities ix are concentrated south of the epicenter suggesting that at least part of the rupture was to the south we have also examined great historic earthquakes along the colombia ecuador and peru segments of the south american subduction zone we find that the size and rupture length of the underthrusting earthquakes vary between successive earthquake cycles this suggests that the segmentation of the plate boundary as defined by earthquakes this century is not constant

evidence for a weakly stratified europan ocean sustained by seafloor heat flux we interpret chaos type features on the surface of europa as melt through structures formed by rotationally confined steady and or episodic oceanic plumes that rise to the base of the ice shell from magmatically heated regions of the seafloor smaller lenticular features in the vicinity of chaos type regions might be formed by baroclinically unstable vortices that spin off the main convective plume or by persistent heating from localized hydrothermal venting sites the ocean is assumed to be weakly stratified because of turbulent convection generated by heating from below and cooling from above seafloor heating maintained by tidal dissipation in the rocky interior generates an estimated global heat flux of 8 7 1012 w and limits the mean ice thickness to 2 5 km for seafloor heat sources with radii r that are less than the ocean s deformation radius rd nd n is the brunt vaisala frequency d is the water depth and is the coriolis parameter the diameters of chaos type regions are expected to diminish from o 100 km within equatorial regions to o 10 km at high latitudes assuming spatially uniform water depth and density structure where r rd the scale of the source region determines the scale of the melt through features provided there is sufficient time before refreezing ice rafts in large melt through regions are imbedded in episodes of preferentially anticyclonic circulation corresponding to clockwise counterclockwise motions in the northern southern hemisphere we calculate that 1021 j were required to melt the ice in the 100 km diameter conamara chaos region and that for a steady localized heat flux f 1011 w 1 of the global heat flux it took 1000 years for the initial melt through to occur assuming that ice raft displacements in conamara chaos occurred during a major melt through event maximum current speeds in the region were o 10 cm s 1 and refreezing occurred within 20 hours a lack of well defined ice drift in other major melt through regions suggests that these regions formed through episodes of melting and refreezing that modified the existing structure but left little time for the establishment of organized advective motion

assessment of the size of large and great historical earthquakes in peru a critical reappraisal of great historical earthquakes in peru is made in order to obtain quantitative estimates of rupture length seismic moment tsunami magnitude mt and moment magnitude mw newly collected information concerning several historical earthquakes permits the evaluation of macroseismic zones and from the size of these zones the estimation of length of rupture seismic moment and magnitude mw it is found that local tsunami data provide good quantitative estimates of mt and therefore an independent way of verifying macroseismic estimates of rupture length and seismic moment a space time diagram of great historical earthquakes shows the existence of three zones roughly corresponding to the segmentation of the nazca plate hasegawa and sacks 1981 subducting under peru the northern zone looks aseismic the central one is very complex it breaks either completely or in smaller segments and it may go through long quiescence periods the recurrence time for the southern segment the more regular one is of the order of one century

near global validation of the srtm dem using satellite radar altimetry abstract this paper reports the results of a near global validation of the srtm dem dataset using a unique database of completely independent height measurements derived from satellite altimeter echoes primarily gathered by ers 1 these heights are obtained using a rule based expert system which identifies each echo as 1 of 11 different characteristic shapes and selects the optimal retracking algorithm to obtain best range to surface the results of this comparison which includes over 54 million altimeter derived heights show generally very good agreement with the srtm data with global statistics for mean difference of 3 m and a standard deviation of 16 m quantitative validation results are given for each continent and are summarised here mean difference m standard deviation of differences m africa 1 86 15 62 australia 1 09 11 49 eurasia 2 54 16 09 north america 3 15 15 18 south america 12 22 18 51 global 3 60 16 16 a range of examples are included to illustrate key findings of this work and to indicate synergistic applications of these two datasets currently being studied including the potential for forest canopy measurement

thermal constraints on the frictional conditions of the nucleation and rupture area of the 1992 nicaragua tsunami earthquake summary the 1992 nicaragua earthquake was a tsunami earthquake which generated tsunamis disproportionately large for its surface wave magnitude ms 7 2 seismological studies and tsunami simulation indicated that the event was a slow earthquake which occurred on the plate boundary between the subducting cocos plate and the overriding caribbean plate we present a finite element model that enables us to estimate for the first time the temperature and inferred frictional conditions in the rupture area of a tsunami earthquake direct and indirect observations are used to constrain all model parameters and surface heat flux measurements provide independent information to verify the model results furthermore we used a genetic algorithm to perform a sensitivity analysis of all model parameters and to define the spatial range of thermally defined updip limit of the seismogenic zone the earthquake nucleated in the seismogenic zone at temperatures of 150 c and propagated updip towards the trench axis the centroid or centre of mass of moment release was located in a region characterized by temperatures of 50 c thus the rupture propagated through a region where plate motion is normally accommodated by aseismic creep our observations support a model in which tsunami earthquakes nucleate in the seismogenic zone near its updip limit however in such an environment coupled asperities are perhaps too small to cause large earthquakes seamounts however are abundant on the incoming cocos plate therefore in addition to temperature dependent metamorphic induration of sediments increased normal stress by seamount subduction may contribute to accumulate stress sufficiently large to release enough energy near the updip limit of the seismogenic zone to promote dynamic slip along a

great earthquakes and subduction along the peru trench subduction along the peru trench between 9 and 15 s involves both large interplate underthrusting earthquakes and intraplate normal fault earthquakes the four largest earthquakes along the peru trench are from north to south the 1970 m 7 9 intraplate normal fault earthquake and the interplate underthrusting earthquakes in 1966 m 8 0 1940 m 8 and 1974 m 8 0 we have studied the rupture process of these earthquakes and can locate spatial concentrations of moment release through directivity analysis of source time functions deconvolved from long period p wave seismograms the 1966 earthquake has a source duration of 45 s with most of the moment release concentrated near the epicenter two intraplate normal fault events occurred in 1963 m 6 7 and 7 0 at the down dip edge of the 1966 dominant asperity the 1940 earthquake is an underthrusting event with a simple source time function of 30 s duration that represents the rupture of a single asperity near the epicenter the 1974 earthquake has a source duration of 45 50s and two pulses of moment release this earthquake has a bilateral rupture with the first pulse of moment release located northwest of the epicenter and the second pulse of moment release located southeast of the epicenter both pulses of moment release occur on the northern half of the aftershock area the 1970 earthquake is one of the largest intraplate normal fault earthquakes to occur in a subduction zone and has a moment release comparable with many large underthrusting events the aftershocks for the 1970 earthquake form two distinct clusters the smaller cluster near the epicenter has focal mechanisms characterized by down dip tension but the second aftershock cluster located 80 km southeast of the epicenter has focal mechanisms characterized by down dip compression the p waves for the main shock can be modeled as two sources with different focal mechanisms and depths similar to the two clusters of aftershocks the first event has a down dip tensional focal mechanism and is followed 40 s later by a distinct second event located 80 km southeast of the epicenter with a down dip compressional focal mechanism and a somewhat shallower depth than the first event the observable directivity indicates that the second source is located at the second cluster of aftershocks that have down dip compressional focal mechanisms the occurrence of both down dip tensional and compressional focal mechanisms may be explained by extreme unbending stresses associated with the anomalous slab geometry the unusually large size of the 1970 earthquake may also be related to the subduction of the mendana fracture zone the historic earthquake record along the peru trench indicates that the previous event in 1746 was much larger than any of the three underthrusting earthquakes this century the 1746 earthquake may have ruptured the entire segment in a multiple asperity earthquake thus the mode of rupture along the peru coast has changed between successive earthquake cycles

new ultrahigh resolution picture of earth s gravity field 9 10 abstract 11 we provide an unprecedented ultra high resolution picture of earth s gravity over all continents 12 and numerous islands within 60 degree latitude this is achieved through augmentation of new 13 satellite and terrestrial gravity with topography data and use of massive parallel computation 14 techniques delivering local detail at 200 m spatial resolution as such our work is the first of 15 its kind to model gravity at unprecedented fine scales yet with near global coverage the new 16 picture of earth s gravity encompasses a suite of gridded estimates of gravity accelerations 17 radial and horizontal field components and quasigeoid heights at over 3 billion points covering 18 80 of earth s land masses we identify new candidate locations of extreme gravity signals 19 suggesting that the codata standard for peak to peak variations in free fall gravity is too low 20 by about 40 the new models are beneficial for a wide range of scientific and engineering 21 applications and freely available to the public 22 23 keywords 24

geophysical implications of the long wavelength topography of rhea 1 we use limb profiles to investigate the long wavelength topography and topographic variance spectrum of rhea one dimensional variance spectra show a break in slope at a wavelength of 300 km a similar effect is seen on the moon and may be a signature of an elastic lithosphere having a thickness te 10 km the implied heat flux is 15 mw m 2 much higher than can be explained by radiogenic heating we use the 1 d spectral behavior to constrain our solution for the long wavelength global topography of rhea the degree 3 topography is large enough if uncompensated to contaminate estimates of the degree 2 gravity using existing flyby data current models of rhea internal structures which rely on these degree 2 estimates may thus be inaccurate illustrating the need to acquire further rhea gravity data

thickness of a europan ice shell from impact crater simulations several impact craters on jupiter s satellite europa exhibit central peaks on the terrestrial planets central peaks consist of fractured but competent rock uplifted during cratering therefore the observation of central peaks on europa indicates that an ice layer must be sufficiently thick that the impact events did not completely penetrate it we conducted numerical simulations of vapor and melt production during cratering of water ice layers overlying liquid water to estimate the thickness of europa s icy crust because impacts disrupt material well beyond the zone of partial melting our simulations put a lower limit on ice thickness at the locations and times of impact we conclude that the ice must be more than 3 to 4 kilometers thick

constraints on yield strength in the oceanic lithosphere derived from observations of flexure summary the wavelength and amplitude of outer rises seaward of sub duction zones and arches surrounding islands and seamounts are used to parameterize flexure profiles in terms of the moment and curvature at the first zero crossing the data show the clear age dependence in the mechanical thickness of the lithosphere up to 60 100myr saturation of moment at large curvature is interpreted in terms of a depth dependent yield strength for the lithosphere using relations adopted from laboratory experiments of rock deformation a comparison of theoretical curves with observed moments indicates that old oceanic lithosphere has no long term strength below about 40 km depth with no difference between 100 and 165 myr old crust moderate axial loading forces 200 mpa can explain most variations in the moment curvature observations except in the case of the kuril trench which appears anomalous given the age of the crust regional tension causes greater variability in moment as compared to regional compression because of the greater slope in the brittle failure envelope under tension the observations point to a lithosphere weaker than the prediction from experimental deformation of rocks of the possible weakening mechanisms elevated pore fluid pressure on faults does not predict the correct age dependence and is incompatible with earthquake focal mechanisms our favoured explanation is that the activation energy q appropriate for ductile flow at geological strain rates is lower than the values derived from laboratory extrapolations of dry olivine data taken at high temperatures if recent oceanic geotherms are reliable q in the lower lithosphere must be lower than 100kcal mol 1 the method used here is most appropriate for trench profiles with curvatures greater than 10 7m 1 for lower curvatures such as along seamount profiles small errors in the curvature estimate cause large changes in rheological parameters

tectonic segmentation of the north andean margin impact of the carnegie ridge collision the north andean convergent margin is a region of intense crustal deformation with six great subduction earthquakes mw 7 8 this century the regional pattern of seismicity and volcanism shows a high degree of segmentation along strike of the andes segments of steep slab subduction alternate with aseismic regions and segments of flat slab subduction this segmentation is related to heterogeneity on the subducting nazca plate in particular the influence of the carnegie ridge collision is investigated four distinct seismotectonic regions can be distinguished region 1 from 6on to 2 5on with steep ese dipping subduction and a narrow volcanic arc region 2 from 2 5on to 1os showing an intermediate depth seismic gap and a broad volcanic arc region 3 from 1os to 2os with steep ne dipping subduction and a narrow volcanic arc region 4 south of 2os with flat subduction and no modern volcanic arc the carnegie ridge has been colliding with the margin since at least 2 ma based on examination of the basement uplift signal along trench parallel transects the subducted prolongation of carnegie ridge may extend up to 500 km from the trench as suggested by the seismic gap and the perturbed broad volcanic arc these findings conflict with previous tectonic models suggesting that the carnegie ridge entered the trench at 1 ma furthermore the anomalous geochemical adakitic signature of the volcanoes in the broad ecuador volcanic arc and the seismicity pattern are proposed to be caused by lithospheric tears separating the buoyant shallowly subducting carnegie ridge from segments of steep subduction in regions 1 and 3 it is further suggested that carnegie ridge supports a local flat slab segment similar to that observed in peru the impact of the carnegie ridge collision on the upper plate causes transpressional deformation extending inboard to beyond the volcanic arc with a modern level of seismicity comparable to the san andreas fault system the pattern of instrumental and historical seismicity indicates 1 great earthquakes on the northern and southern flanks of the colliding ridge 2 a slight reduction in observed seismicity at the trench ridge intersection 3 increased stress far into the continent and 4 a nne displacement of the n andes block to be further effects of the collision 1999 elsevier science b v all rights reserved

geology and origin of europa s mitten feature murias chaos 1 the mitten provisionally named murias chaos by the international astronomical union is a region of elevated chaos like terrain in the leading hemisphere of europa its origin had been explained under the currently debated theories of melting through a thin lithosphere or convection within a thick one galileo observations reveal several characteristics that suggest that the mitten is distinct from typical chaos terrain and point to a different formational process photoclinometric elevation estimates suggest that the mitten is slightly elevated with respect to the surrounding terrain geologic relations indicate that it must have raised significantly from the plains in its past resembling disrupted domes on europa s trailing hemisphere moreover the mitten material appears to have extruded onto the plains and flowed for tens of kilometers the area subsequently subsided as a result of isostatic adjustment viscous relaxation and or plains loading using plate flexure models we estimated the elastic lithosphere in the area to be several kilometers thick we propose that the mitten originated by the ascent and extrusion of a large thermal diapir thermal mechanical modeling shows that a mitten sized plume would remain sufficiently warm and buoyant to pierce through the crust and flow unconfined on the surface such a diapir probably had an initial radius between 5 and 8 km and an initial depth of 20 40 km consistent with a thick lithosphere model in this scenario the mitten appears to represent the surface expression of the rare ascent of a large diapir in contrast to lenticulae and chaos terrain which may form by isolated and clustered small diapirs respectively

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

variations in the mode of great earthquake rupture along the central peru subduction zone the historic record for the central peru subduction zone suggests significant variations in the earthquake size during the last 400 years during this century there have been four great underthrusting earthquakes along the central peru seismic zone from north to south these are the 17 october 1966 mw 8 1 24 may 1940 m 8 3 october 1974 mw 8 1 and 24 august 1942 m 8 2 earthquakes modified mercalli intensity data and tsunami observations for the earthquakes in this century are compared with the 29 october 1746 and 20 october 1687 earthquakes the 1746 earthquake had maximum intensity values between 9 and 13 s while the 1687 event had maximum values between 12 and 14 s suggesting that the two events failed different segments of the subduction zone we find that the 1746 event occurred along the segiment that includes both 1940 and 1966 earthquakes the size of the 1746 event is estimated to be mw 8 8 based on the ratio of near field tsunami heights for the 1746 and 1966 earthquakes the 1687 earthquake probably raptured the 1974 segment as well as the adjacent segment to the south where there is at present a gap between the 1942 and 1974 rupture zones the size of the 1687 event is estimated to be mw 8 7 based on both far field and near field tsunami height ratios of the 1687 and 1974 events both 1746 and 1687 earthquakes appear to be much larger than the events of this century in contrast to the simple single asperity nature of the 20th century earthquakes these older and larger events may represent multiple asperity ruptures along the peru subduction zone hence variations in the mode of earthquake rupture from cycle to cycle along the central peru seismic zone may explain the significant difference in earthquake size during die last 400 years

convective instability in europa s floating ice shell models of the tidally heated floating ice shell proposed for the jovian satellite europa generally find shell thicknesses less than 30 km past parameterized convection models indicated that such shells are stable against convective overturn which otherwise ostensibly leads to freezing of the ocean underneath here i apply the temperature dependent viscosity convection scaling developed by solomatov and coworkers to the europan ice shell the temperature dependent properties of ice are linearized about 260 k as any convective interior should be close to this temperature with the colder ice forming an essentially passive stagnant lid ice shells 10 km thick are found to be unstable to convection at their base for melting point viscosities of 1013 pa s as linearized by tidal stresses if the ice deforms by superplastic creep but such low viscosities require small grain sizes 1 mm this requirement may be met if grain sizes observed in terrestrial polar glaciers can be strain rate scaled to europa regardless convection at the base of the ice shell if initiated may not freeze the ocean because of tidal heating a stagnant lid regime ice shell is much more dissipative than a conductive shell of the same thickness such a shell should thin not thicken and the potential exists for further thermal instabilities and runaways

lithospheric bending at subduction zones based on depth soundings and satellite gravity a global study of trench flexure was performed by simultaneously modeling 117 bathymetric profiles original depth soundings and satellite derived gravity profiles a thin elastic plate flexure model was fit to each bathymetry gravity profile by minimization of the l norm the six model parameters were regional depth regional gravity trench axis location flexural wavelength flexural amplitude and lithospheric density a regional tilt parameter was not required after correcting for age related trend using a new high resolution age map estimates of the density parameter confirm that most outer rises are uncompensated we find that flexural wavelength is not an accurate estimate of plate thickness because of the high curvatures observed at a majority of trenches as in previous studies we find that the gravity data favor a longer wavelength flexure than the bathymetry data a joint topography gravity modeling scheme and fit criteria are used to limit acceptable parameter values to models for which topography and gravity yield consistent results even after the elastic thicknesses are converted to mechanical thicknesses using the yield strength envelope model residual scatter obscures the systematic increase of mechanical thickness with age perhaps this reflects the combination of uncertainties inherent in estimating flexural wavelength such as extreme inelastic bending and accumulated thermoelastic stress the bending moment needed to support the trench and outer rise topography increases by a factor of 10 as lithospheric age increases from 20 to 150 ma this reflects the increase in saturation bending moment that the lithosphere can maintain using a stiff dry olivine rheology we find that the lithosphere of the gdh1 thermal model stein and stein 1992 is too hot and thin to maintain the observed bending moments moreover the regional depth seaward of the oldest trenches 150 ma exceeds the gdh1 model depths by about 400 m

on the origins of band topography europa we use stereo derived topography of extensional bands on europa to show that these features can be elevated by 100 150 m with respect to the surroundings and that the positive topography sometimes extends beyond the band margins lateral variations in shell thickness cannot maintain the observed topography for timescales greater than 0 1 myr lateral density variations can maintain the observed topography indefinitely mean density contrasts of 5 and 50 kg m 3 are required for shell thicknesses of 20 and 2 km respectively density variations caused by temperature contrasts require either present day heating or that bands are young features 1 myr old stratigraphic analyses suggest that these mechanisms are unlikely the observation that bands form from ridges may be explained by an episode of shear heating on ridges weakening the ridge area and leading to strain localization during extension fracture porosity is likely to persist over myr timescales in the top one third to one quarter of the conductive part of the ice shell lateral variations in this porosity of order 20 are the most likely mechanism for producing band topography if the ice shell is thin 2 km porosity variations of 2 or less are required if the shell is thicker 20 km if the ice shell is thick lateral variations in salt content are a more likely mechanism warm ice will tend to lose dense low melting temperature phases and be buoyant relative to colder salt rich ice thus lateral density variations will arise naturally if bands have been the sites of either localized heating or upwelling of warm ice during extension

europa stratigraphy and geological history of the anti jovian region from galileo e14 solid state imaging data a tidal bulge and associated deformation are predicted to occur in europa s anti jovian region voyager data showed polygonal low albedo bands in this region it was demonstrated that when the low albedo material comprising these bands was removed the margins could be reconstructed suggesting that fracturing and lateral separation has occurred higher resolution galileo images of a 300 000 km2 portion of the anti jovian region permit recognition and mapping of a variety of features and documentation of the geological history we identify background ridged plains several distinctive types of bands and ridges lenticulae and regions of chaotic terrain these images are at relatively low incidence angles thus albedo variations predominate over topography this presents a challenge to morphologically based mapping but does not preclude development of a regional stratigraphy stratigraphic relationships show that dark bands crosscut the bright ridged plains and are themselves disrupted by lenticulae and chaos suggesting a geological history beginning with background ridged plains followed by a period dominated by band formation with the most recent history predominantly characterized by formation of lenticulae and chaos the paucity of impact craters in this region indicates that the entire sequence of units is geologically recent

role of fluids in the tectonic evolution of titan abstract detailed analyses of slopes and arcuate planform morphologies of titan s equatorial mountain ridge belts are consistent with formation by contractional tectonism however contractional structures in ice require large stresses 4 10 mpa the sources of which are not likely to exist on titan cassini spacecraft imagery reveals a methane based hydrological cycle on titan that likely includes movement of fluids through the subsurface these crustal liquids may enable contractional tectonic features to form as groundwater has for thrust belts on earth in this study we show that liquid hydrocarbons in titan s near subsurface can lead to fluid overpressures that facilitate contractional deformation at smaller stresses

postseismic relocking of the subduction megathrust following the 2007 pisco peru earthquake characterizing the time evolution of slip over different phases of the seismic cycle is crucial to a better understanding of the factors controlling the occurrence of large earthquakes in this study we take advantage of interferometric synthetic aperture radar data and 3 5 years of continuous global positioning system gps measurements to determine interseismic coseismic and postseismic slip distributions in the region of the 2007 mw 8 0 pisco earthquake peru using the same fault geometry and inversion method our interseismic model based on pre 2007 campaign gps data suggests that the 2007 pisco seismic slip occurred in a region strongly coupled before the earthquake while afterslip occurred in low coupled regions large afterslip occurred in the peripheral area of coseismic rupture in agreement with the notion that afterslip is mainly induced by coseismic stress changes the temporal evolution of the region of maximum afterslip characterized by a relaxation time of about 2 3 years is located in the region where the nazca ridge is subducting consistent with rate strengthening friction promoting aseismic slip we estimate a return period for the pisco earthquake of about 230 years with an estimated aseismic slip that might account for about 50 of the slip budget in this region over the 0 50 km seismogenic depth range a major result of this study is that the main asperity that ruptured during the 2007 pisco earthquake relocked soon after this event

evaluation of high degree series expansions of the topographic potential to higher order powers 1 mass associated with surface topography makes a significant contribution to the earth s gravitational potential at all spectral scales accurate computation in spherical harmonics to high degree requires calculations of multiple integer powers of the global topography the purpose of this paper is to analyze the contributions of earth s topography to its potential to the tenth power of the topography and quantify truncation errors resulting from neglecting higher order powers to account for the effect of gravity attenuation with height we use series expansions for gravity upward continuation to the earth s surface with degree 2160 expansions limitation to the first three powers of the topography as often done in practice may give rise to maximum truncation errors exceeding 100 mgal at a reference sphere and 25 mgal at the topography aiming for a maximum truncation error of 1 mgal we found that higher order terms to the seventh power are required over the himalaya mountains as example of earth s most rugged land region upward continuation of topographic gravity effects with mgal precision from the sphere to the earth s surface is accomplished with a series expansion of fifth order as a key finding the accurate conversion of topography to gravity effects at the earth s surface is governed by two similar yet not identical series expansions for degree 2160 expansions we recommend that the powers of earth s topography be used up to seventh order to accurately evaluate the topographic potential to the mgal level as required e g for the construction of high resolution bouguer gravity anomaly maps in spherical harmonics

three dimensional tsunami generation simulation due to sea bottom deformation and its interpretation based on the linear theory summary the present study investigates the tsunami generation process by using 3 d numerical simulations and the linear potential theory first we evaluate the relation between sea bottom elevation and sea surface elevation as function of source size l sea depth h and source duration t based on 3 d numerical simulations the surface elevation decreases with increasing sea depth and source duration the difference between the sea bottom and the sea surface elevation appears when the source size is smaller than approximately 10 times the sea depth for a short source duration the linear potential theory can precisely predict the numerical simulation results based on the theory we can consider the tsunami generation as two spatial lowpass filter processes in which the cut off wavenumbers are given by the sea depth and the source duration the criteria for small source size and short source duration are given as l 13h and t l 8c respectively where c is the phase velocity of the tsunami we then simulate the tsunami generation of the 1896 sanriku tsunami earthquake japan the simulated sea surface elevation is significantly different from the sea bottom elevation which suggests the need for correction of the sea depth and source duration for the precise evaluation of the initial water height distribution to include these effects in 2 d simulations we can use the impulse response function and add the fractional sea surface uplift within the time step to the sea surface for each time step

exogenic and endogenic albedo and color patterns on europa new global and high resolution multispectral mosaics of europa have been produced from the voyager imaging data photometric normalizations are based on multiple image techniques that explicitly account for intrinsic albedo variations through pixel by pixel solutions the exogenic color and albedo pattern on europa is described by a second order function of the cosine of the angular distance from the apex of orbital motion on the basis of this second order function and of color trends that are different on the leading and trailing hemispheres the exogenic pattern is interpreted as being due to equilibrium between two dominant processes 1 impact gardening and 2 magnetospheric interactions including sulfur ion implantation and sputtering redistribution removal of the model exogenic pattern in the mosaics reveals the endogenic variations consisting of only two major units darker redder and bright materials therefore europa s visual spectral reflectivity is simple having one continuous exogenic pattern and two discrete endogenic units

origin of mountains on io by thrust faulting and large scale mass movements voyager stereoimages of euboea montes io indicate that this mountain formed when a large crustal block was uplifted 10 5 kilometers and tilted by approximately 6 degrees uplift triggered a massive slope failure on the northwest flank forming one of the largest debris aprons in the solar system this slope failure probably involved relatively unconsolidated layers totaling approximately 2 kilometers in thickness overlying a rigid crust or lithosphere at least 11 kilometers thick mountain formation on io may involve localized deep rooted thrust faulting and block rotation due to compression at depth induced during vertical recycling of io s crust

seismic and aseismic slip on the central peru megathrust slip on a subduction megathrust can be seismic or aseismic with the two modes of slip complementing each other in time and space to accommodate the long term plate motions although slip is almost purely aseismic at depths greater than about 40 km heterogeneous surface strain suggests that both modes of slip occur at shallower depths with aseismic slip resulting from steady or transient creep in the interseismic and postseismic periods thus active faults seem to comprise areas that slip mostly during earthquakes and areas that mostly slip aseismically the size location and frequency of earthquakes that a megathrust can generate thus depend on where and when aseismic creep is taking place and what fraction of the long term slip rate it accounts for here we address this issue by focusing on the central peru megathrust we show that the pisco earthquake with moment magnitude m w 8 0 ruptured two asperities within a patch that had remained locked in the interseismic period and triggered aseismic frictional afterslip on two adjacent patches the most prominent patch of afterslip coincides with the subducting nazca ridge an area also characterized by low interseismic coupling which seems to have repeatedly acted as a barrier to seismic rupture propagation in the past the seismogenic portion of the megathrust thus appears to be composed of interfingering rate weakening and rate strengthening patches the rate strengthening patches contribute to a high proportion of aseismic slip and determine the extent and frequency of large interplate earthquakes aseismic slip accounts for as much as 50 70 of the slip budget on the seismogenic portion of the megathrust in central peru and the return period of earthquakes with m w 8 0 in the pisco area is estimated to be 250 years

hydrocode simulation of ganymede and europa cratering trends how thick is europa s crust abstract one of the continuing debates of outer solar system research centers on the thickness of europa s ice crust as it affects both the habitability and accessibility of its sub surface ocean here we use hydrocode modeling of the impact process in layered ice and water targets and comparison to europan cratering trends and galileo derived topographic profiles to investigate the crustal thickness full or partial penetration of the ice crust by an impactor occurred in simulations in which the ice thickness was less than 14 times the projectile radius craters produced in these thin shell simulations were consistently smaller than for larger ice thicknesses which will complicate inference of large impactor population sizes simulations in which the resultant crater was 3 times the ice layer thickness resulted in summit pit morphology this work supports that summit pit craters noted on both rocky and icy bodies can be created by the presence of a weaker layer at depth we suggest that floor pits seen only on ice rich bodies require a different formation mechanism to summit pits pristine craters formed in a target with high heat flow were shallower than for the same impact into a target of lesser heat flow suggesting that the starting crater morphology for viscous relaxation isostatic readjustments and erosion rate studies is different for craters formed in times of different heat flow we find that the crater depth diameter trend of europa can only be recreated when simulating impact into an upper brittle ice layer of 7 km depth with a corresponding geothermal gradient of 0 025 k m as this ice thickness estimate is below 10 km results from this work suggest that convective overturn of the surface ice may occur or have occurred on europa making the development of indigenous life a possibility

eruption of lava flows on europa theory and application to thrace macula europa on the basis of its spectral characteristics and its apparently young surface age is likely to be at least partially resurfaced by liquid water volcanic processes however convincing evidence for lava flow morphology in voyager data has not previously been found and the lower density of liquid water relative to an overlying solid water ice crust suggests that extrusive volcanism could be uncommon we examine a candidate lava flow like feature thrace macula and compare its characteristics with theoretical predictions for the ascent and eruption of water magma on europa outlining a range of conditions under which water ice magma could plausibly be erupted to the surface thrace macula 45 s 171 w is a dark lobate feature extending nnw to sse its northern part is centered in a 140 km diameter arcuate to circular lineament and within this zone are radial and concentric lineaments and three dark lobes similar in appearance to flow lobes extending away from a central region for distances of 40 50 and 160 km the 160 km lobe appears to follow local topographic features producing lobate margins at subdued structures broadening locally parallel to structural trends and terminating against a gray band models for the present structure and state of the predominantly h2o exterior of europa range from solid water ice to a thin ice layer overlying a liquid water layer and these conditions may even vary as a function of space and time ascent and eruption of h2o magma through a less dense water ice crust means that sustained effusive eruptions are very difficult to produce if a globally continuous liquid water or salt water layer exists e g crawford and stevenson 1988 kargel 1991 for flows as extensive as the thrace macula feature we thus require magma source regions sufficiently localized that excess pressure can be built up in the source region given the elastic properties of ice at these source depths the most likely scenario is intrusion of silicate magma into the base of an ice crust and melting and mobilization of water magma with this range of magma source settings we model plausible surface vent geometries for a water lava flow interpretation of thrace macula modeling calculations show that flow lobes with the above geometries and thicknesses on the order of 10 m could be formed in water eruptions on europa involving discharge rates of 2 105 m3 s through dikes with widths in the range 5 10 m these discharge rates about 3 times larger than those of terrestrial flood basalts should not be unusual for water eruptions on europa under these conditions and suggest that water volcanic resurfacing could be common on the satellite if source regions meeting these criteria were readily available the lack of abundant similar dark flows could be due to brightening with time or might imply that conditions for their formation grounded or nearly solid ice crust only evolved in the latter part of europan history

tidal tectonic processes and their implications for the character of europa s icy crust 1 jupiter s satellite europa is covered by an icy crust likely overlying a deep global liquid water ocean the mutually dependent relationship between the orbit and tidal processes controls europa s rotation heating and stress observations of the surface and investigation of tidal tectonic processes indicate that the dominant types of surface terrain have been created by frequent repeated exposure of an underlying ocean to the surface surface lineaments including ubiquitous cycloidal chains of arcs features are correlated with tidal stress patterns demonstrating that they form by crustal cracking but only if a substantial ocean is present to give adequate tidal amplitude stratigraphy of tectonic features combined with models of how and where they formed demonstrates a moderate rate of nonsynchronous rotation tidal driving of strike slip displacement in which surface areas shear passed one another by daily 85 hours on europa tidal stresses suggests that cracks penetrate to a liquid layer the characteristic ridge sets that cover tectonic terrain may be built by tidal pumping of fluid and slush to the surface on a daily basis widespread tectonic dilation creates new surface as material rises from below in addition to those tectonic terrains nearly half of the surface is chaotic terrain with morphology and other characteristics indicative of melt through from below consistent with the tectonic indications of thin ice and plausible tidal heating rates formation of both chaotic and tectonic terrains has continually resurfaced the satellite while connecting the ocean to the surface surface colorants correlate with locations where ocean water reached the surface such as along large scale ridge systems and around chaotic terrain as a result of tides liquid water may have bathed crustal cracks and surfaces with heat transporting and mixing substances vertically such daily transported materials would include substances from the oceanic reservoir oxidants and fuels created at the surface as well as any organisms and their chemical products thus a variety of habitable environments likely exist in the crust deactivation of individual cracks after thousands of years due to the tidally driven nonsynchronous rotation constrains processes like ridge building and strike slip displacement and would require any living organisms to adapt to such change

modeling the morphological diversity of impact craters on icy satellites abstract impact craters on icy satellites display a wide range of morphologies some of which have no counterpart on rocky bodies numerical simulation studies have struggled to reproduce the diversity of features such as central pits and transitions in crater depth with increasing diameter observed on the icy galilean satellites the transitions in crater depth at diameters of about 26 and 150 km on ganymede and callisto have been interpreted as reflecting subsurface structure using the cth shock physics code we model the formation of craters with diameters between 400 m and about 200 km on ganymede using different subsurface temperature profiles our calculations include recent improvements in the model equation of state for h 2 o and quasi static strength parameters for ice we find that the shock induced formation of dense high pressure polymorphs ices vi and vii creates a gap in the crater excavation flow which we call discontinuous excavation for craters larger than about 20 km discontinuous excavation concentrates a hot plug of material 270 k and mostly on the melting curve in the center of the crater floor the size and occurrence of the hot plug are in good agreement with the observed characteristics of central pit craters and we propose that a genetic link exists between them we also derive depth versus diameter curves for different internal temperature profiles in a 120 k isothermal crust calculated craters larger than about 30 km diameter are deeper than observed and do not reproduce the transition at about 26 km diameter calculated crater depths are shallower and in good agreement with observations between about 30 and 150 km diameter using a warm thermal gradient representing a convective interior hence the depth to diameter transition at about 26 km reflects thermal weakening of ice finally simulation results generally support the hypothesis that the anomalous interior morphologies for craters larger than 100 km are related to the presence of a subsurface ocean

a melt through model for chaos formation on europa the character of chaotic terrain on europa is consistent with its formation by the melting of a thin conducting ice shell from below tidal dissipation can provide adequate energy for such a process for example only a few percent of europa s predicted tidal heat spread over a region 200 km in diameter can lead to large melt regions within a few tens of thousands of years stronger more localized concentrations result in melt through in significantly shorter times i e a few hundred years the time scale for melt through is shorter than the time scale for the solid state viscous inflow of ice by several orders of magnitude in general modest concentrations of tidal heat can melt ice away faster than viscous inflow leading to melt through a mechanism to transmit these heat concentrations through the ocean is required for this model such heat transport could be the result of convective plumes in the ocean driven by seafloor volcanism or by the destabilization of a stratified ocean

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

galileo magnetometer measurements a stronger case for a subsurface ocean at europa on 3 january 2000 the galileo spacecraft passed close to europa when it was located far south of jupiter s magnetic equator in a region where the radial component of the magnetospheric magnetic field points inward toward jupiter this pass with a previously unexamined orientation of the external forcing field distinguished between an induced and a permanent magnetic dipole moment model of europa s internal field the galileo magnetometer measured changes in the magnetic field predicted if a current carrying outer shell such as a planet scale liquid ocean is present beneath the icy surface the evidence that europa s field varies temporally strengthens the argument that a liquid ocean exists beneath the present day surface

verification of the vertical error in c band srtm dem using icesat and landsat 7 otter tail county mn the shuttle radar topography mission srtm provided scientists with digital elevation data on a nearly global scale and with highly consistent accuracy this paper compares elevation values of the c band srtm 30 m digital elevation model dem with pointwise elevations from the ice cloud and land elevation satellite icesat laser altimetry for otter tail county minnesota the accuracy of srtm dem is measured as a function of land covers and geomorphologic characteristics the typical mean vertical difference between the srtm dem and icesat elevations in this paper was determined in each classified land use type and is approximately 1 5 m over bare ground with the srtm measuring lower elevations significant changes in the srtm dem uncertainties have been identified over different surface types classified from landsat 7 imagery e g bare ground urban and forested areas based on this result the difference of the srtm 30 m dem and icesat elevations has been removed from the dem and made available for improved hydrological applications

does europa have a subsurface ocean evaluation of the geological evidence it has been proposed that jupiter s satellite europa currently possesses a global subsurface ocean of liquid water galileo gravity data verify that the satellite is differentiated into an outer h2o layer about 100 km thick but cannot determine the current physical state of this layer liquid or solid here we summarize the geological evidence regarding an extant subsurface ocean concentrating on galileo imaging data we describe and assess nine pertinent lines of geological evidence impact morphologies lenticulae cryovolcanic features pull apart bands chaos ridges surface frosts topography and global tectonics an internal ocean would be a simple and comprehensive explanation for a broad range of observations however we cannot rule out the possibility that all of the surface morphologies could be due to processes in warm soft ice with only localized or partial melting two different models of impact flux imply very different surface ages for europa the model favored here indicates an average age of 50 myr searches for evidence of current geological activity on europa such as plumes or surface changes have yielded negative results to date the current existence of a global subsurface ocean while attractive in explaining the observations remains inconclusive future geophysical measurements are essential to determine conclusively whether or not there is a liquid water ocean within europa today

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

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

the use of height data in gravity field approximation by collocation the accuracy of a gravity field model depends on the amount of available data and on the variation of the gravity field when topographic height data are available for example in the form of a digital terrain model it is possible to smooth the gravity field on a local scale by removing the gravitational effects calculated from models of the topographic masses in this way significant improvements of the prediction results are obtained in mountainous areas in this paper we describe methods for the calculation of such gravitational terrain effects applicable in collocation approximation of the gravity field the terrain effects on gravity field quantities such as gravity anomalies deflections of the vertical and geoid undulations are calculated using a system of rectangular prisms representing either a quasi traditional model of the topography and the isostatic compensation or a residual terrain model where only the deviation of the topography from a mean elevation surface is considered to test the terrain reduction methods numerical prediction experiments have been conducted in the mountainous white sands area new mexico from gravity anomalies spaced approximately 6 arc min apart other known gravity anomalies and deflections of the vertical were predicted using collocation when using terrain effects calculated on the basis of 0 5 0 5 arc min point heights the rms errors decreased by a factor of nearly 3 to 1 arc sec for the deflections and 3 4 mgal for the gravity anomalies quite insensitive to the actual type of terrain reduction used the feasibility of using topographic reductions in collocation is thus effectively demonstrated

europa s differentiated internal structure inferences from four galileo encounters radio doppler data from four encounters of the galileo spacecraft with the jovian moon europa have been used to refine models of europa s interior europa is most likely differentiated into a metallic core surrounded by a rock mantle and a water ice liquid outer shell but the data cannot eliminate the possibility of a uniform mixture of dense silicate and metal beneath the water ice liquid shell the size of a metallic core is uncertain because of its unknown composition but it could be as large as about 50 percent of europa s radius the thickness of europa s outer shell of water ice liquid must lie in the range of about 80 to 170 kilometers

estimates of ice thickness in the conamara chaos region of europa europa the second galilean moon outward from jupiter is similar in size to earth s moon but has an outer water ice layer on the order of 100 km thick images acquired by the galileo spacecraft reveal domical features and iceberg like blocks in some areas that suggest the ice was regionally thin at the time the features formed this paper applies buoyancy and flexural models to some of the features to estimate ice thickness assuming that the ice blocks were floating in a liquid sublayer the buoyancy model suggests an ice layer 0 2 3 0 km thick also the flexural models suggest that only the upper 0 1 0 5 km of that ice layer responded elastically to stresses acting as an elastic lithosphere

light at deep sea hydrothermal vents ambient light spectral data were acquired at two deep sea hydrothermal vents with a temperature of 350 c the hole to hell site on the east pacific rise at 9 n and the snake pit site on the mid atlantic ridge measurements were made with a simple multi channel photometer which simultaneously detected light in four 100 nm wide bands over the wavelength range of 650 1050 nm most of the light detected is near infrared 750 1050 nm but there is a 19x greater photon flux than expected from thermal radiation alone at shorter wavelengths 650 750 nm at the hole to hell vent at snake pit more light in the 750 850 nm band was observed 10 cm above the orifice where the temperature was 50 100 c than at the 351 c vent opening these data suggest the presence of non thermal light sources in the vent environment some possible non thermal mechanisms are identified but further data will be required to resolve them

temperatures on europa from galileo photopolarimeter radiometer nighttime thermal anomalies galileo observations of europa s thermal emission show low latitude diurnal brightness temperatures in the range of 86 to 132 kelvin nighttime temperatures form an unexpected pattern with high temperatures on the bright ejecta blanket of the crater pwyll and an equatorial minimum in temperatures after sunset uncorrelated with surface albedo or geology the nighttime anomalies may be due to regional thermal inertia variations of an unknown origin which are equivalent to a two to threefold variation in thermal conductivity or to endogenic heat fluxes locally reaching 1 watt per square meter endogenic heat flow at this high level although consistent with some geological evidence is theoretically unlikely