extension and partitioning in an oblique subduction zone new zealand constraints from three dimensional numerical modeling 1 contraction strike slip and extension displacements along the hikurangi margin northeast of the north island of new zealand coincide with large lateral gradients in material properties we use a finite difference code utilizing elastic and elastic plastic rheologies to build large scale three dimensional numerical models which investigate the influence of material properties on velocity partitioning within oblique subduction zones rheological variation in the oblique models is constrained by seismic velocity and attenuation information available for the hikurangi margin we compare the effect of weakly versus strongly coupled subduction interfaces on the development of extension and the partitioning of velocity components for orthogonal and oblique convergence and include the effect of ponded sediments beneath the raukumara peninsula extension and velocity partitioning occur if the subduction interface is weak but neither develops if the subduction interface is strong the simple mechanical model incorporating rheological variation based on seismic observations produces kinematics that closely match those published from the hikurangi margin these include extension within the taupo volcanic zone uplift over ponded sediments and dextral contraction to the south

empirical relationships among seismic velocity effective pressure porosity and clay content in sandstone we use a multivariate analysis to investigate the influence of effective pressure pe porosity and clay content c on the compressional velocity vp and shear velocity vs of sandstones laboratory measurements on water saturated samples of 64 different sandstones provide a large data set that was analyzed statistically for each sample relationships between effective pressure and vp and vs have been determined all samples were well fit by relationships that have an exponential increase in velocity at low pe tapering to a linear increase with pe for pe greater than 0 2 kbar there are differences in the pressure dependences of velocity for different rocks particularly at very low pressures however the differences cannot be attributed to or c for the combined set of measurements from all samples the best fitting formulations are vp 5 77 6 94 1 73c 0 446 pe e 16 7pe and vs 3 70 4 94 1 57c 0 361 pe e 16 7pe while this is admittedly a very simplified parameterization it is remarkable how well

three dimensional p and s velocity structure in the coalinga region california the coalinga earthquake sequence of 1983 provided a unique opportunity to perform a three dimensional velocity and hypocenter inversion in an area of complex three dimensional structure dominated by folding and blind thrusts additionally since other varied geological and geophysical studies have been completed in this area the three dimensional inversion solution could be compared to other interpretations inversion of 7696 p and 1511 s first arrivals from earthquakes and 696 p first arrivals from refraction shots produced a three dimensional velocity model with grid spacing of 1 2 km in the hypocentral area the overall shape and location of velocity features correspond well to the mapped surface geology the three dimensional inversion yields details of folds where the resolution is good and the general shape where resolution is lower the amounts of structural relief inferred for the local folds are similar to values inferred from geologic data the three dimensional velocity solution has several distinctive features there is a linear high velocity body 6 1 6 5 km s about 25 km long from 6 to 8 km depth that may represent a fragment of coast range ophiolite a shallow low velocity zone lvz which extends for 20 km along the fold axis at about 6 km depth and correlates with lvzs observed in both the refraction and the reflection data may indicate high pore pressure caused by lateral compressive strain deeper lvzs occur within inferred franciscan material and are characterized by horizontal or southwest dipping zones of varied thickness 4 8 km wide and 5 10 km long these lvzs may represent multiple thrust faults their locations and geometry are consistent with thrust faults inferred with seismic reflection data the three dimensional velocity solution compares well to prior two dimensional seismic reflection and refraction models and observed gravity the shape of the inferred sedimentary section agrees well with the reflections from the cenozoic strata compared to the refraction model the three dimensional solution has similar velocities and similar locations of velocity features but is more detailed in the hypocentral zone where it uses more data the gravity computed from the three dimensional velocities is similar to the observed gravity in both shape and amplitude both a simple one dimensional initial model and a complex initial model derived from the refraction interpretation were tried a simple starting model gave the best results the s velocity solution has different resolution than the p velocity solution because it uses a different set of stations and it has lower resolution because it uses fewer arrival times while the general patterns of velocity variation are similar for both vp and vs the vs solution tends to have more smearing of velocity features and can have somewhat different locations of velocity features

œdipus a new tool to study the dynamics of planetary interiors summary we present a new numerical method to describe the internal dynamics of planetary mantles through the coupling of a dynamic model with the prediction of geoid and surface topography our tool is based on the simulation of thermal convection with variable viscosity in a spherical shell with a finite volume formulation the grid mesh is based on the cubed sphere technique that divides the shell into six identical blocks an investigation of various numerical advection schemes is proposed we opted for a high resolution flux limiter method benchmarks of thermal convection are then presented on steady state tetrahedral and cubic solutions and time dependent cases with a good agreement with the few recent programs developed to solve this problem a dimensionless framework is proposed for the calculation of geoid and topography introducing two dimensionless numbers such a formulation provides a good basis for the systematic study of the geoid and surface dynamic topography associated to the convection calculations the evaluation of geoid and surface dynamic topography from the gridded data is performed in the spectral domain the flow solver is then tested extensively against a precise spectral program producing response functions for geoid as well as bottom and surface topographies for a grid mesh of a reasonable size 6 64 64 64 a very good agreement to within 1 per cent is found up to spherical harmonic degree 15

magma transport of heat on io a mechanism allowing a thick lithosphere models indicate that the high heat flow from io would result in a very thin approximately 5 km silicate lithosphere overlying a molten interior if all heat was transported through the lithosphere via conduction however the presence of mountains with relief in excess of 10 km would seem to demand a thick lithosphere at least locally a significant fraction of io s heat flow may be transported via advection through volcanoes advective heat transfer permits a thicker lithosphere than does pure conduction possibly reconciling io s high heat flow with the rugged topography

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

three dimensional attenuation tomography at loma prieta inversion of t for q three dimensional q 1 variations in the aftershock region of loma prieta are derived by tomographic inversion the data set consists of over 4000 aftershock recordings at 22 passcal program for array seismic studies of the continental lithosphere stations deployed after the loma prieta mainshock of 1989 estimates of attenuation are determined from nonlinear least squares best fits to the fourier amplitude spectrum of p and s wave arrivals the linear attenuation inversion is accomplished by using three dimensional velocity variations derived previously in nonlinear velocity inversions low q is observed near the surface and q generally increases with depth the southwest side of the san andreas fault exhibits lower q than does the northeast side and this feature apparently extends to approximately 7 km depth the fault zone as determined by the dipping plane of aftershock activity is characterized by slightly higher qp and lower qs compared to regions immediately adjacent to the fault these correlate with high velocity anomalies associated with seismicity at depth the results are in agreement with earlier observations regarding the association of high velocity anomalies seismicity and fault zone asperities

estimation of thermal structure in the mantle wedge of northeastern japan from seismic attenuation data 1 we estimated thermal structure in the mantle wedge of ne japan by applying the experimental results of olivine dominated rocks to seismic attenuation data obtained temperatures at a 40 km depth are 1000 1130 c and 960 1090 c beneath the volcanic front and the back arc side respectively we cannot obtain the areas with a temperature higher than 1400 c in the mantle wedge which have been inferred from petrological studies this is perhaps due to the localization of such anomalous areas the obtained temperature is higher than that of the wet solidus of peridotite in the greater part of the back arc side which suggests that the addition of aqueous fluids plays an important role in generating melts in the mantle wedge

seismotectonics of the loma prieta california region determined from three dimensional v p v p v s and seismicity three dimensional vp and vp vs velocity models for the loma prieta region were developed from the inversion of local travel time data 21 925 p arrivals and 1 116 s arrivals from earthquakes refraction shots and blasts recorded on 1700 stations from the northern california seismic network and numerous portable seismograph deployments the velocity and density models and microearthquake hypocenters reveal a complex structure that includes a san andreas fault extending to the base of the seismogenic layer a body with high vp extends the length of the rupture and fills the 5 km wide volume between the loma prieta mainshock rupture and the san andreas and sargent faults we suggest that this body controls both the pattern of background seismicity on the san andreas and sargent faults and the extent of rupture during the mainshock thus explaining how the background seismicity outlined the along strike and depth extent of the mainshock rupture on a different fault plane 5 km away new aftershock focal mechanisms based on three dimensional ray tracing through the velocity model support a heterogeneous postseismic stress field and can not resolve a uniform fault normal compression the subvertical or steeply dipping san andreas fault and the fault surfaces that ruptured in the 1989 loma prieta earthquake are both parts of the san andreas fault zone and this section of the fault zone does not have a single type of characteristic event

the percolation phase transition in sea ice sea ice exhibits a marked transition in its fluid transport properties at a critical brine volume fraction p c of about 5 percent or temperature t c of about 5 c for salinity of 5 parts per thousand for temperatures warmer than t c brine carrying heat and nutrients can move through the ice whereas for colder temperatures the ice is impermeable this transition plays a key role in the geophysics biology and remote sensing of sea ice percolation theory can be used to understand this critical behavior of transport in sea ice the similarity of sea ice microstructure to compressed powders is used to theoretically predict p c of about 5 percent

seismic wave attenuation determined from tectonic tremor in multiple subduction zones abstract tectonic tremor provides a new source of observations that can be used to constrain the seismic attenuation parameter for ground motion prediction and hazard mapping traditionally recorded earthquakes of magnitude 3 8 are used to develop ground motion prediction equations however typical earthquake records may be sparse in areas of high hazard in this study we constrain the distance decay of seismic waves using measurements of the amplitude decay of tectonic tremor which is plentiful in some regions tectonic tremor occurs in the frequency band of interest for ground motion prediction i e 2 8 hz and is located on the subducting plate interface at the lower boundary of where future large earthquakes are expected we empirically fit the distance decay of peak ground velocity from tremor to determine the attenuation parameter in four subduction zones nankai japan cascadia united states canada jalisco mexico and southern chile with the large amount of data available from tremor we show that in the upper plate the lower crust is less attenuating than the upper crust we apply the same analysis to intraslab events in nankai and show the possibility that waves traveling from deeper intraslab events experience more attenuation than those from the shallower tremor due to ray paths that pass through the subducting and highly attenuating oceanic crust this suggests that high pore fluid pressure is present in the tremor source region these differences imply that the attenuation parameter determined from intraslab earthquakes may underestimate ground motion for future large earthquakes on the plate interface

local earthquake tomography of the jalisco mexico region abstract the states of jalisco colima and michoacan in western mexico overlie the boundary of the subducting rivera and cocos plates presenting an ideal target for seismological inquiry to better understand the resulting mantle flow and regional volcanism the different dips between the two subducting plates are thought to provide a mantle conduit that has contributed to the colima volcanic complex cvc but there is considerable debate on the depth of the rivera plate and width of the resulting conduit with data from the mapping the rivera subduction zone mars and colima deep seismic experiment codex networks two temporary broadband arrays deployed in the region between 2006 and 2008 we inverted for three dimensional p and s wave velocity as well as vp vs structure of the upper 70 km of the crust and mantle in the jalisco region using a newly developed automatic p and s wave picker we increased p picks by 74 and s picks by more than a factor of four compared to a database of manual picks for the 803 earthquakes used in the inversion additional relocated earthquakes extending to the trench are consistent with previous interpretations of the rivera and cocos plate interfaces areas of high vp vs above both subducting slabs suggest the presence of fluids resulting from dehydration of subducted material extensive crustal seismicity occurs near these anomalies a zone of high vp vs is also present under the cvc we also compare the results of different methods for obtaining vp vs a direct inversion for vp vs from s minus p times versus simply dividing the vp model by the vs model we find direct inversions of s minus p times to be more reliable

seasonal changes in species composition numbers mass size and isotopic composition of planktonic foraminifera settling into the deep sargasso sea abstract planktonic foraminifera recovered from six successive sediment trap samples collected over fourteen months at a depth of 3200 m near bermuda show varied responses to seasonal changes in the near surface hydrography these include changes in species composition and within species changes in number of individuals collected per unit time average size and weight of individuals and in oxygen and carbon isotopic composition a total of seventeen species were identified and eleven were sufficiently abundant for isotopic analysis in at least some of the samples the accumulations on the sea floor of some of these species can be expected to contain a strong seasonal component in their oxygen isotopic composition which may be utilized in paleoclimatic and paleo oceanographic reconstructions best suited to this purpose are those species which form their tests in isotopic equilibrium with surface water and whose abundance is confined to a portion of the year only the best examples are pulleniatina o bliguiloculata globigerinoides conglobatus and neogloboquadrina dutertrei globigerinoides ruber is a good estimator of the average surface water temperature because it occurs in rather even abundance throughout the year hastigerina pelagica though very abundant in surface water is practically eliminated even before arrival on the sea floor by partial resorption and structural weakening of the tests during gametogenesis orbulina universa globorotalia truncaltulinoides and globorotalia hirsuta show morphological and istopic evidence for contibnued calcification in deeper water after initial test formation near ther surface globigerina bulloides represents the most striking example of oxygen isotopic disequilibrium with sea water

structure and seismogenic properties of the mentawai segment of the sumatra subduction zone revealed by local earthquake traveltime tomography 1 on 12 september 2007 an mw8 4 earthquake occurred within the southern section of the mentawai segment of the sumatra subduction zone where the subduction thrust had previously ruptured in 1833 and 1797 traveltime data obtained from a temporary local seismic network deployed between december 2007 and october 2008 to record the aftershocks of the 2007 event was used to determine two dimensional 2 d and three dimensional 3 d velocity models of the mentawai segment the seismicity distribution reveals significant activity along the subduction interface and within two clusters in the overriding plate either side of the forearc basin the downgoing slab is clearly distinguished by a dipping region of highvp 8 0 km s which can be a traced to 50 km depth with an increased vp vs ratio 1 75 to 1 90 beneath the islands and the western side of the forearc basin suggesting hydrated oceanic crust above the slab a shallow continental moho of less than 30 km depth can be inferred suggesting that the intersection of the continental mantle with the subducting slab is much shallower than the downdip limit of the seismogenic zone despite localized serpentinization being present at the toe of the mantle wedge the outer arc islands are characterized by low vp 4 5 5 8 km s and high vp vs greater than 2 0 suggesting that they consist of fluid saturated sediments the very low rigidity of the outer forearc contributed to the slow rupture of the mw 7 7 mentawai tsunami earthquake on 25 october 2010

ice melting and downward transport of meltwater by two phase flow in europa s ice shell with its young surface very few impact craters and the abundance of tectonic and cryovolcanic features europa has likely been subjected to relatively recent endogenic activity morphological analyses of chaos terrains and double ridges suggest the presence of liquid water within the ice shell a few kilometers below the surface which may result from enhanced tidal heating a major issue concerns the thermal gravitational stability of these water reservoirs here we investigate the conditions under which water can be generated and transported through europa s ice shell we address particularly the downward two phase flow by solving the equations for a two phase mixture of water ice and liquid water in one dimensional geometry in the case of purely temperate ice we show that water is transported downward very efficiently in the form of successive porosity waves the time needed to transport the water from the subsurface region to the underlying ocean varies between 1 and 100 kyr depending mostly on the ice permeability we further show that water produced in the head of tidally heated hot plumes never accumulates at shallow depths and is rapidly extracted from the ice shell within less than a few hundred kiloyears our calculations indicate that liquid water will be largely absent in the near subsurface with the possible exception of cold conductive regions subjected to strong tidal friction recently active double ridges subjected to large tidally driven strike slip motions are perhaps the most likely candidates for the detection of transient water lenses at shallow depths on europa

cooling patterns in rotating thin spherical shells application to titan s subsurface ocean abstract we use rotating convection simulations in a thin spherical shell to study fluid dynamics in subsurface oceans of icy moons we find two types of persistent results characterized by larger outer boundary heat flux either at polar regions or at the equatorial region simulations corresponding to larger rossby numbers result in polar cooling with moderate lateral heterogeneity in heat flux whereas lower rossby numbers give equatorial cooling with more pronounced heat flux heterogeneity the polar cooling scenario is in agreement with inferences for the heat flux at the top of titan s ocean which may provide a dynamical constraint for the vigor of convection in this layer our results may help unraveling the internal dynamics and the interactions among the different layers within the hydrosphere of titan possible implications for the deep interiors of other icy moons are envisaged

focal mechanisms of large earthquakes in the north island of new zealand slip partitioning at an oblique active margin we have used body wave modelling to determine the source parameters of 22 moderate to large earthquakes that have occurred along the hikurangi subduction margin and elsewhere in the north island of new zealand since 1964 we have also included events from the harvard cmt catalogue since 1977 as that catalogue contains smaller events than can be modelled with body waves we have found that shallow earthquakes occurring in the back arc taupo volcanic zone and its extension to the north show predominantly normal faulting with nodal planes parallel to the regional fabric and t axes indicating extension in a direction in agreement with geodetic measurements a normal faulting solution for the 1974 opunake earthquake is compatible with the mapping of active faults in the offshore taranaki region and the initiation depth of 17 km is close to the expected brittle ductile transition for that area earthquakes within the subducted plate at the southwestern end of the margin are dominated by down dip tension that is rotated towards the deepest part of the subducting plate further north the events in the upper part of the wadati benioff zone 200 km show pure down dip tension while this association is less obvious for the deeper events suggesting that the aseismic part of the subducting slab inferred from plate reconstructions has reached the 670 km discontinuity normal faulting earthquakes associated with plate bending below the region of interplate contact occur along the length of the margin while shallow normal faulting events also occur in the trench indicating that some slab pull propagates to that region we infer that large interplate earthquakes are not imminent because in other similar areas they are preceded by outer rise compressional events that have not been recorded in the region in historical times slip vectors of interplate thrust earthquakes indicate that the oblique plate motion across the margin is fully partitioned that is the plate interface accommodates very little transcurrent motion which is instead accommodated by faults in the overlying australian plate extensional geodetic strain has been measured across the margin in the northeast which has been regarded as unusual in view of the plate convergence we suggest that the topography at this part of the margin is too steep to be supported by the current horizontal forces due to friction on the plate interface this may have occurred due to a reduction in friction because of the subduction of seamounts and the subsequent entrapment of sediments this also being consistent with the idea of underplating at this part of the margin or due to the subduction of less buoyant crust other margins such as japan and mid america where there is known to be subduction of sediments also show extension in the forearc compressional strain observed across the margin in the southwest is more usual for a convergent margin but it does not show the partitioning we see in focal mechanisms these data might only agree after the long term compressional strain accumulation has been averaged over a complete seismic cycle large historical and palaeo earthquakes have occurred along the length of the margin associated with deformation in both the axial and the coastal ranges in addition along the length of the margin the rate of recent interplate thrust activity is low compared to margins that have a high proportion of aseismic slip these factors indicate that the entire length of this margin is capable of producing large earthquakes

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

validation of tectonic reconstructions by crustal volume balance new zealand through the cenozoic we describe a procedure that allows us to quantitatively test hypotheses about the tectonic evolution of a region including areas for which there is little or no geologic record and apply it to the pacific australian plate boundary in the new zealand region since 65 ma the derived models are a first attempt to quantify the effects of the development of the modern plate boundary on four major components of the tectonic evolution of new zealand i e sedimentation paleogeography growth of crustal root and nonrigid deformation the technique balances total rock volume through time using estimates of these factors although the solutions are non unique the uncertainties in each factor can be estimated and used to define the models the plate reconstructions we present are minor modifications of earlier work developed to test whether those proposed reconstructions are self consistent and consistent with present day crustal structure and sediment distribution they are digital and geographically referenced and they have the advantage that new data can be readily incorporated and new concepts tested against several criteria the model of the evolution of new zealand9s crustal root is new and incorporates a previously unpublished compilation the models show that rock redistribution is accounted for by erosion and sedimentation during the period 65 25 ma the pacific australian plate boundary began propagating through new zealand ca 45 ma in these models development of the boundary has no effect on nonrigid deformation until ca 25 ma that time marked the start of a significant increase in land area and of the nonrigid deformation of a large region in the center of the new zealand continent since ca 20 ma 575 000 km 3 of sediments were deposited in basins around new zealand and a crustal root with a volume of 2 200 000 km 3 is interpreted to have developed beneath the landmass a large area in the center of late cretaceous and tertiary reconstructions of the new zealand region inferred from outcrop well and seismic reflection data deformed eroded and was eventually amalgamated within the continental crust of new zealand a redistribution of 3 080 000 km 3 of rock at 0 porosity

the post glacial downcutting history in the waihuka tributary of waipaoa river gisborne district implications for tectonics and landscape evolution in the hikurangi subduction margin new zealand abstract determining the spatial and temporal deliveries of sediment from the waipaoa river catchment in the post glacial period is a major goal of integrated source to sink landscape evolution studies in the region in a 2 2 km long section of the waihuka tributary 217 km 2 of the waipaoa river 2150 km 2 in eastern north island new zealand a sequence of at least ten fluvial terraces and abandoned meanders up to 45 m above the present river records rates and times of post glacial downcutting dateable organic and tephra horizons in the terrace and meander infill stratigraphy indicate that downcutting at this location on the waihuka tributary was dominated by a short lived event in the early holocene from 10 8 ka bp when as much as half of the downcutting was accomplished in only 10 15 of post glacial time the large downcutting event is interpreted to record the passing of a succession of major knickpoints or a knickzone through this tributary the initiation of knickpoint retreat in the catchment was primarily a consequence of reduction in sediment supply at the end of mis 2 based on the timing of rapid downcutting in the waipaoa river mainstem we estimate that the rate of knickpoint retreat along the waihuka tributary was about 2 km kyr in the period before and after rapid downcutting in the waihuka tributary modest incision rates averaging 1 2 mm yr probably represent the regional tectonic uplift rate

three layered models of ganymede and callisto compositions structures and aspects of evolution abstract three layered structural models are determined for ganymede and callisto each consists of a rock core a mixed ice rock lower mantle and a pure ice upper mantle this structure results from differentiation subsequent to accretional melting attention is given to evaluating various candidates for the rock component and three alternatives representing various degrees of silicate hydration and oxidation are modeled and incorporated structures are calculated on the basis of a 250 k isotherm which is a reasonablev approximation to the gentle adiabats expected to occur in icy satellites differentiation of an ice rock satellite generally involves an increase in radius and the three layered approach allows this process to be examined in some detail it is determined that satellite expansion is most significant early in the process and much less so as differentiation proceeds to completion if tectonics are due to global expansion distinguishing on this basis between a completely differentiated satellite and one that is only partially differentiated is difficult the postaccretional global expansion of ganymede which may have left a tectonic record was probably limited to 1 in radius in agreement with observed limits useful quantities such as silicate mass and volume fraction uncompressed density j2 c22 binding energy and surface heat flow are also determined nonhydrostatic contributions to j2 and c22 are estimated and shown to be nonnegligible encounters with jupiter orbiting spacecraft are unlikely to determine callisto s degree of central condensation we conclude by calculating the relative likelihood of postaccretional melting caused by radiogenic heating three layered satellites have generally hotter interiors because additional thermal boundary layers divide the separately convecting upper and lower mantles inhibiting heat transport ganymedes and callistos that are less than about 1 3 differentiated by mass should experience a second episode of melting as these boundary layers are either above the level of the water ice minimum melting temperature or intersect the melting curve at deeper levels runaway differentiation to at least a depth corresponding to a pressure in the ice v stability field is likely the main point here is that if satellite tectonics are tied to differentiation by melting or its aftermath as in the instability following ocean closure of kirk and stevenson moderate or small amounts of accretional differentiation are unlikely to explain an absence of tectonics as in callisto because extensive differentiation ultimately occurs

gravity induced deformation on the north flank and floor of the sporadhes basin of the north aegean sea trough pdr and continuous seismic profiling surveys in the sporadhes basin the western part of the north aegean sea trough reveal active gravity induced deformation of the postorogenic sedimentary sequence different deformational patterns in the uppermost sedimentary layers of the flanks and floor of the basin suggest that the layers are deformed by several gravity induced processes including slumping sliding and creep contemporaneous with sediment deposition antithetic faulting on the northern flank of the basin the thermaicos slope results from downslope creep of surface layers over deeper tilted bedding planes this process is a consequence of progressive slope development associated with the evolution of the sporadhes basin the morphology of the sea floor and the deformation of the upper layers clearly reflect synsedimentary tectonics in a subsiding basin environment

depositional models for fine grained sediment in the western hellenic trench eastern mediterranean sediment in tectonically active topographically restricted settings of the western hellenic arc eastern mediterranean consists primarily of clayey silt and silty clay failure of metastable sediment temporarily stored on relatively steep slopes is triggered by earthquake tremors and eustatic oscillations redeposition of these materials by gravitative transport has resulted in markedly different lithofacies from site to site most piston cores include three late quaternary stratigraphic units that can be correlated with sections in other parts of the eastern mediterranean numerous radiocarbon age determinations enhance the correlation seven fine grained sediment types are identified in cores from eight distinct depositional environments some muds are closely related to specific environments slump and debris flow deposits on slope and high relief environments or to time well laminated mud during the latest pleistocene mid holocene or to both uniform and faintly laminated muds restricted to trench basins turbiditic and hemipelagic muds are common throughout the study area mud distribution patterns correlate closely with calculated sedimentation rates we propose two depositional models for these sediments the first emphasizes downslope transformations resulting in progressively reduced flow concentration during transport from slump and debris flow turbidity current low density turbidity current or turbid layer mechanisms the distal end member deposits settling from low concentration flows are thick rapidly emplaced fine grained uniform muds closely associated with faintly laminated muds these were ponded in flat trench basin plains planktonic and terrigenous fractions in the turbiditic finely laminated and uniform muds record mixing of materials of gravitative and suspension origin during redeposition this sequence prevails under conditions of minimal stratification of water masses as characterized by the present mediterranean in the second model developed for conditions of well developed water mass stratification well laminated rather than uniform mud prevails as the end product of low concentration flows these very finely laminated and graded muds record particle by particle settling from detached turbid layers concentrated along density interfaces they include material from turbid layers complemented by the normal rain of pelagic material stratification barriers resulted in region wide distribution of such deposits in both slope and trench environments

thermal convection heated both volumetrically and from below implications for predictions of planetary evolution abstract solid state thermal convection as a model for the internal dynamics of planetary mantles is generated both by volumetric heating and heating from below a series of 2d and 3d numerical experiments is described where a bottom heat flux is prescribed as well as a constant fraction of volumetric heating with either free slip or no slip conditions for the two horizontal boundaries the assumption that hot plumes rising in the interior of the layer act as a volumetric heat source leads to a first order scaling of thermal boundary layers cases with a no slip boundary agree well with this scaling while cases with free slip systematically deviate a decrease of 20 30 is observed for the temperature difference across the boundary layer when the fraction of heating from below is increased from 0 to 1 these differences are attributable to a velocity structure near the boundary varying with the fraction of volumetric heating the main planetary implications are that i the average thermal structure of the bulk mantle and lithosphere are not good indicators of the distribution of heat sources between the interior e g radioactive heating secular cooling and the lower interface e g core cooling ii in contrast the nature of volcanism whether it is localized hot spot like or widespread reflect this distribution and should thus help to constrain the global thermal structure as well as the existence of a magnetic dynamo

modern sedimentation in the n w aegean sea abstract the area under investigation is located within 22 45 to 23 45 e and from 39 15 to 40 15 n sedimentological bathymetric and shallow geophysical data were collected from here during the 7 78 cruise of r r s shackleton twenty seven sea bed surface samples were collected using a day grab from different environments these were analysed for grain size distribution carbonate content and clay mineralogy on the basis of the bathymetric and shallow geophysical data the area has been classified into five major physiographic environments according to their bathymetry and topography 1 shelf thermaicon plateau 2 slope 3 marginal plateau 4 the canyon system and valleys and 5 sporades basin based on the sedimentological analyses the surface sediments have been classified into four major provinces as follows 1 province 1 shelf muds 2 province 2 muddy sands 3 province 3 outer margin muds and 4 province 4 outer shelf shelf break it is concluded that modern sedimentation in the n w aegean sea is dominated by the terrigenous river inputs and by the circulation of both high and low salinity masses

p wave attenuation structure in the fault area of the 1995 kobe earthquake the three dimensional 3 d p wave attenuation structure in the kobe epicentral area is determined using aftershock records from the 1995 kobe hyogo ken nanbu earthquake waveform data from both permanent seismic networks and portable stations set up following the kobe mainshock were used the observed p wave amplitude spectra were inverted for the spectral plateau value the source corner frequency and a frequency independent t operator assuming an 2 type source model the calculated t operators were subsequently used for the computation of the 3 d absorption structure using a 3 d velocity model only high quality amplitude spectra were used for the estimation of reliable attenuation parameters resulting in a final data set of 4100 t operators two regions of high absorption were found in the upper part of the crust one is below the northern part of awaji island and reaches down to a depth of 5 km the other region northeast of kobe city is along the arima takatsuki tectonic line and extends along the rokko kashiodani and yamada faults it extends northward to the hokusetsu sanchi area in both regions a high density of fault lineations is mapped and high poisson ratios are known this suggests that partially saturated cracks cause the observed high attenuation

a three dimensional image of shallow subduction crustal structure of the raukumara peninsula new zealand summary earthquake arrival time data from a 36 station deployment of portable seismographs on the raukumara peninsula have been used to determine the 3 d vp and vp vs structure of this region of shallow subduction a series of inversions have been performed starting with an inversion for 1 d structure then 2 d and finally 3 d this procedure ensures a smooth regional model in places of low resolution the subducted plate is imaged as a northwest dipping feature with vp consistently greater than 8 5 km s 1 in the uppermost mantle of the plate structure in the overlying plate changes significantly along strike in the northeast there is an extensive low velocity zone in the lower crust underlying the most rapidly rising part of the raukumara range it is bounded on its arcward side by an upwarp of high velocity a viable explanation for the low velocity zone is that it represents an accumulation of underplated subducted sediment while serpentinization of the uppermost mantle may be responsible for the adjacent high velocity region the low velocity zone decreases and the adjacent high velocity region is less extensive in the southwest this change is interpreted to be related to a change in the thickness of the crust of the overlying plate in the northeast the crust is thinner and subducted sediment ponds against relatively strong uppermost mantle while in the southwest the crust is thicker and the relatively weak lower crust allows sediment subduction to greater depths a narrow zone of high vp vs parallels the shallow part of the plate interface this suggests elevated fluid pressures with the distribution of earthquakes about this zone further suggesting that these pressures may be close to lithostatic the plate interface at 20 km depth beneath the raukumara peninsula may thus be a closed system for fluid flow similar to that

crustal heterogeneity and subduction processes 3 d vp vp vs and q in the southern north island new zealand summary along the southern hikurangi subduction zone in the southern north island new zealand the subduction zone changes from volcanic with moderately weak interseismic coupling to non volcanic with strong coupling in wellington to investigate how material heterogeneity relates to subduction processes we compute 3 d seismic properties using 342 earthquakes and 2 shots recorded by a 165 station seismic array the time base for some telemetered temporary stations was not stable which required revising the inversion code to allow an additional origin time related to the telemetered stations progressive inversions from 2 d to fine 3 d were carried out for vp vp vs and qp combined interpretation of these three seismic properties highlights features of the subduction zone the subducted slab is imaged as a high velocity high q feature in the overlying crust from southeast to northwest there is low velocity in the accretionary wedge high velocity in the axial ranges and low velocity in the wanganui basin high vp vs and low qp characterize the crust east of the north island dextral fault belt high vp vs is imaged above the subducted slab to 40 km depth in the northern half of the study area low qp is also prominent above the slab particularly trenchwards of the volcanic region in marked contrast to the high vp vs the low qp above the slab extends as a continuous feature up to the low qp in the shallow crust underlying the volcanic region the low qp and high vp vs are correlated with the region of weaker coupling and are consistent with significant subducted sediments with associated fluid release vp vs is particularly sensitive to overpressured fluid in the compressional forearc whereas qp also images the hydrostatically pressured fluid transport in the more permeable extensional volcanic region the rheology of the lower crust of the overlying plate is a factor in large scale subduction coupling as evidenced by the terrane boundaries and haast schist in the section near wellington the changing rheology of the lower crust of the overlying plate in the southern north island also provides a possible explanation for the southward cessation of volcanism

early transient cooling of mars previous evolution models for one plate planets have commonly assumed steady state cooling beneath a rigid lid recent 3d numerical models indicate however that conductive lid cooling exhibits early transient stages where the quasi static assumption is not valid we apply scaling laws for these transient stages to mars a wide range of initial conditions for the martian mantle reflects the possible consequence of the early differentiation of the planet our results display large variations for the timing of early transient cooling from several 100 ma up to a few ga indicating that classical quasi static models cannot describe a significant part of the planet s evolution this suggests new scenarios for mars early history with initial heat fluxes in good agreement with values inferred from both gravity and topography data from the mgs mission

late quaternary sedimentation on the north aegean continental margin greece the late quaternary seismic stratigraphy of the north aegean continental shelf and adjacent basins has been interpreted from boomer and 3 5 khz seismic profiles ages derived from shallow cores and offshore wells and relative offsets on small synsedimentary faults provide chronological control sea level history inferred from seismic stratigraphy correlates with the global eustatic sea level record based on oxygen isotopic curves outer shelf progradation correlates with lowstands of sea level in isotopic stages 2 3 and 6 whereas shelf wide transgression surfaces correspond to the stage 6 5 and 2 1 transitions when rapid deglaciation occurred the present depth of the delta plain formed on the outer shelf during the late stage 6 lowstand provides a dated and originally horizontal marker for estimating rates of tectonic subsidence gross distribution of sediment facies is similar in both tectonically stable and active areas the shelf break formed by delta progradation but is marked by faults in most places because of the accommodation provided by graben subsidence rates of 0 3 1 5 mm yr standard sequence stratigraphic analysis can be applied to these sediments deposited during high amplitude quaternary sea level oscillations high rates of subsidence result in the preservation of an unusually complete record of sea level change major lowstand progradation is dependent on the duration rather than the magnitude of sea level lowstand the long glaciations in isotopic stages 6 12 16 and 22 resulted in the most prominent seaward progradation on the margin sandy lowstand turbidite deposits formed only when there was rapid fall in sea level otherwise sand was trapped on delta tops and silty muds were deposited in deep water

plate interface properties in the northeast hikurangi subduction zone new zealand from converted seismic waves arrival time inversion of local earthquakes in the northeast hikurangi subduction zone has indicated high vp vs at the plate interface but the thickness of the anomalous zone is poorly constrained by the p and s travel times we investigate this plate interface zone further by modeling s to p converted phases using synthetic seismograms for upgoing rays of earthquakes in the subducting plate mantle the modeling indicates a low velocity layer at the plate interface which is generally 1 2 km thick and has vp of 5 0 5 35 km s and vp vs of 2 this is consistent with a subducting sediment channel with near lithostatic fluid the low rigidity indicates a weak zone which will have a strong influence on the distribution of deformation the modeling approach shows promise in defining rheological parameters at the plate interface and mapping their variation across the seismogenic zone of the subduction thrust

seismicity structure and tectonics of the wellington region new zealand summary the wellington region lies on the border between the pacific and australian plates the former being subducted the plate interface lies at shallow depth under the region 10 60 km so that detailed and long term monitoring of the seismicity of the zone where large thrust earthquakes are expected to occur is possible hypocentres for events recorded by a 12 station seismic network for the period 1978 1982 7231 events have been refined by the use of a threedimensional velocity model derived from a simultaneous inversion of arrival time data from 129 local events for both hypocentres and velocity the hypocentres show that the subducting pacific plate is defined by a nw dipping zone of relatively intense activity the plate interface as given by the upper envelope of this activity is offset vertically by 7 km on average along a nw se line through cook strait parallel to the direction of absolute motion of the pacific plate rather than to the direction of convergence the strike of the interface at deeper levels also changes across this line this distortion may partly reflect effects of the transition to continent continent type convergence further south within the subducting pacific plate the seismic activity defines two parallel zones separated by about 20 km the lower zone being much less active and perhaps merging with the upper zone at a depth of 80 90 km composite focal mechanisms of events in the upper zone imply predominantly down dip tension with a compression axis perpendicular to the plate interface the mechanism in the lower zone also implies down dip tension but the compression axis has rotated to be horizontal and along strike indicating a component of lateral shearing within the plate these two types of mechanism correlate well with those found previously for events at depths of 150 km or more thus it seems that the large negative buoyancy of the subducted lithosphere dominates the internal stress field throughout the length of the seismically active region the lithosphere acting as a stress guide there is no evidence for a significant number of events with mechanisms indicating thrusting along the plate interface the seismic velocity in the region corresponding to the upper seismic band is close to that typical for oceanic crust which here is probably considerably thicker than normal there is no evidence for a substantial increase in velocity down

temporal variations in sedimentation patterns nw aegean sea abstract cores are examined from the northern continental slope environment of the sporadhes basin the western part of the north aegean sea trough three distinct lithofacies have been identified which correspond with similar environments identified elsewhere in the western and southeastern mediterranean these layers turbiditic mud hemipelagic mud calcareous ooze represent late quaternary climatic and eustatic sea level changes and tectonic activity based on benthic foraminiferal evidence from the eastern part of the north aegean sea trough it is suggested that contemporary sediment supply and physical oceanographic conditions in the area under investigation might be conducive to sapropel formation also that the depositional sequence in the cores represents a gradual recovery in the mediterranean sea since its last stagnation and sapropel formation some 8000 years ago

structures and fabrics in glacial ice a review abstract glaciers ice sheets and ice caps represent tectonic systems driven by gravity their movement can be studied in real time and the rheological properties and strength of ice determined from laboratory experiments and field measurements all glacial ice has primary stratification exhibited by variations in grain size bubble content and debris content as it deforms with deformation dominated by plastic flow and recrystallization accompanied locally by fracture under tension a suite of structures develops that reflects the primary fabric of the ice and the anisotropy that develops as a result of cumulative deformation initial variations in solid impurity content and strain dependent anisotropy as a result of a crystallographic fabric give rise to effective viscosity increases or decreases compared to isotropic polycrystalline ice of about a factor of ten foliation develops from inherited mostly stratification or introduced mostly ice veins or fracture traces fabric elements and from dynamic recrystallization it is largely dependent on the accumulated strain which is highest at the base and near the margins of glaciers ice sheets and ice streams folds develop largely passively due to initial amplification of irregularities in the primary stratification to variations in flow with time or to inhomogeneous flow associated with shear zones and ductile accommodation around open fractures buckle folds and boudinage mostly on a small scale occur where viscosity contrast is large mostly in basal ice thrusting and wrench faulting are documented in surging glaciers but theoretically most unlikely and rare or absent elsewhere many structures interpreted as faults are not due to shear failure but rather result from shear displacements during opening and closing of tensile fractures

europa s crust and ocean origin composition and the prospects for life abstract we have considered a wide array of scenarios for europa s chemical evolution in an attempt to explain the presence of ice and hydrated materials on its surface and to understand the physical and chemical nature of any ocean that may lie below we postulate that following formation of the jovian system the europan evolutionary sequence has as its major links a initial carbonaceous chondrite rock b global primordial aqueous differentiation and formation of an impure primordial hydrous crust c brine evolution and intracrustal differentiation d degassing of europa s mantle and gas venting e hydrothermal processes and f chemical surface alteration our models were developed in the context of constraints provided by galileo imaging near infrared reflectance spectroscopy and gravity and magnetometer data low temperature aqueous differentiation from a carbonaceous ci or cm chondrite precursor without further chemical processing would result in a crust ocean enriched in magnesium sulfate and sodium sulfate consistent with galileo spectroscopy within the bounds of this simple model a wide range of possible layered structures may result the final state depends on the details of intracrustal differentiation devolatilization of the rocky mantle and hydrothermal brine reactions could have produced very different ocean crust compositions e g an ocean crust of sodium carbonate or sulfuric acid or a crust containing abundant clathrate hydrates realistic chemical physical evolution scenarios differ greatly in detailed predictions but they generally call for a highly impure and chemically layered crust some of these models could lead also to lateral chemical heterogeneities by diapiric upwellings and or cryovolcanism we describe some plausible geological consequences of the physical chemical structures predicted from these scenarios these predicted consequences and observed aspects of europa s geology may serve as a basis for further analys is and discrimination among several alternative scenarios most chemical pathways could support viable ecosystems based on analogy with the metabolic and physiological versatility of terrestrial microorganisms

estimating slab earthquake response spectra from a 3d q model the problem of estimating response spectra for a heterogeneous lithosphere can be addressed by directly computing attenuation from physical models in a subduction zone slab earthquakes will have different attenuation through the mantle wedge than the slab this article is primarily concerned with very high loss paths through the attenuating mantle underlying the volcanic zone of the north island new zealand where low q requires modification of the standard new zealand engineering response spectrum model a lack of strong motion data prevents a standard regression analysis for paths from deep slab earthquakes through the highly attenuating mantle zone instead modifications have been derived using a 3d frequency independent q model that has been developed for the north island subduction zone from 2 20 hz local earthquake t data by calibrating the t crustal results to the standard new zealand model amplitudes can be compared between the standard model and the 3d q model additional path averaged attenuation rate coefficients cq for each source and station pair are determined this results in simple expressions for cq as a function of centroid depth for modifying the standard model this modification reduces the model spectra by a factor of approximately 2 4 for mantle wedge paths below the volcanic region this reduction is similar to the observed variation in response spectra at periods below 0 4 sec for a 160 km deep m w 6 0 earthquake for shallow earthquakes propagating through the shallow volcanic region the new model gives results that are similar to a volcanic path attenuation term derived by regression analysis manuscript received 24 february 2003

observations of very high p velocities in the subducted slab new zealand and their relation with the slab geometry summary a set of high quality aftershock data recorded on a closely spaced network of seismographs at wellington new zealand has enabled the determination of apparent wavefront speeds and azimuths controlled by the subducting pacific plate the former were very high 8 7 f 0 2 km s and the latter were shifted by as much as 10 eastward of the source receiver line which made an angle of about 12 downdip with the strike of the subducted slab beneath the north island the wavefront characteristics are modelled in terms of head wave propagation along a curved refractor with a cylindrical geometry using both a simple geometrical approach as well as a 3 d ray tracing program with this structure it is not possible to explain both the high apparent velocity as well as the large azimuthal anomaly without the presence of an unusually high p wave velocity of around 9 0 km s within the upper mantle of the subducted pacific plate such high velocities although reported previously in the north island are very hard to reconcile with known upper mantle rock velocities other alternatives were sought to explain the apparent slowness in particular modifications in the slab curvature along strike according to proposed models were found to contribute to the high wavefront speeds but very high intrinsic p velocities 8 8 km s l are still required from slowness vector data it is not possible to constrain the depth at which such velocities have to exist however traveltime considerations limit them to depths between the base of the subducted oceanic crust to about 12 km deeper

evolution of titan s rocky core constrained by cassini observations 1 we model the thermal evolution of titan s core and search for solutions that are consistent with the mean moment of inertia yielded by the cassini huygens mission like previous studies we assume that titan s core is enriched in hydrated silicates however our modeling accounts for the possible dehydration of these minerals the resulting models are consistent with titan s moment of inertia if the inner dry silicate core remains smaller than 1300 km in radius this constraint is met if at least 30 of potassium was leached from the silicate during the hydration event i e the core is depleted in one of its major heat source in this scenario the core is currently undergoing dehydration

on convection in ice i shells of outer solar system bodies with detailed application to callisto it has been argued that the dominant non newtonian creep mechanisms of water ice make the ice shell above callisto s ocean and by inference all radiogenically heated ice i shells in the outer solar system stable against solid state convective overturn conductive heat transport and internal melting oceans are therefore predicted to be or have been widespread among midsize and larger icy satellites and kuiper belt objects alternatively at low stresses where non newtonian viscosities can be arbitrarily large convective instabilities may arise in the diffusional creep regime for arbitrarily small temperature perturbations for callisto ice viscosities are low enough that convection is expected over most of geologic time above the internal liquid layer for plausible ice grain sizes a few mm the alternative for early callisto a conducting shell over a very deep ocean 450 km is not compatible with callisto s present partially differentiated state moreover if convection is occurring today the stagnant lid would be quite thick 100 km and compatible with the lack of active geology nevertheless callisto s steady state heat flow may have fallen below the convective minimum for its ice i shell late in solar system history in this case convection ends the ice shell melts back at its base and the internal ocean widens considerably the presence of such an ocean of order 200 km thick is compatible with callisto s moment of inertia but its formation would have caused an 0 25 radial expansion the tectonic effects of such a late slow expansion are not observed so convection likely persists in callisto possibly subcritically ganymede due to its greater size rock fraction and full differentiation has a substantially higher heat flow than callisto and has not reached this tectonic end state titan if differentiated and triton should be more similar to ganymede in this regard pluto like callisto may be near the tipping point for convective shutdown but uncertainties in its size and rock fraction prevent a more definitive assessment

evolution of the taupo hikurangi subduction system abstract the present day taupo hikurangi subduction system is a southward extension of the tonga kermadec arc system into a sediment rich continental margin environment it consists of a shallow structural trench the hikurangi trough a 150 km wide imbricate thrust controlled accretionary borderland the continental slope shelf and coastal hills of eastern north island a frontal ridge the main greywacke ranges of north island and a volcanic arc and marginal basin the taupo volcanic zone structural elements become progressively more elevated and subduction more oblique towards the south the whole nne trending system is truncated at a largely strike slip transform boundary that extends along the southwestern part of the hikurangi trough and the hope fault of south island to the main alpine fault the volcanic arc is 200 270 km from the structural trench and comprises a nne trending chain of andesite dacite volcanoes extending along the eastern side of the taupo volcanic zone most of the andesites are olivine bearing and have been erupted within the last 50 000 years it is suggested the taupo hikurangi margin has evolved by rotation of accretionary elements from an original nw trending subduction system north of new zealand the older elements of the prism were associated with subduction of a re entrant of the pacific plate and perhaps the south fiji basin in mid tertiary times they subsequently became separated from their nw trending volcanic arc by dextral strike slip movement along curved faults east of the main greywacke ranges during the plio pleistocene oblique subduction and accretion intensified as the taupo hikurangi margin rotated into line with the nne trending kermadec system and a marginal basin was developed along a similar trend to form the taupo volcanic zone within the last 50 000 years olivine bearing andesite volcanism has commenced along the eastern side of the taupo volcanic zone

heat transport in the high pressure ice mantle of large icy moons abstract while the existence of a buried ocean sandwiched between surface ice and high pressure hp polymorphs of ice emerges as the most plausible structure for the hundreds of kilometers thick hydrospheres within large icy moons of the solar system ganymede callisto titan little is known about the thermal structure of the deep hp ice mantle and its dynamics possibly involving melt production and extraction this has major implications for the thermal history of these objects as well as on the habitability of their ocean as the hp ice mantle is presumed to limit chemical transport from the rock component to the ocean here we describe 3d spherical simulations of subsolidus thermal convection tailored to the specific structure of the hp ice mantle of large icy moons melt production is monitored and melt transport is simplified by assuming instantaneous extraction to the ocean above the two controlling parameters for these models are the rheology of ice vi and the heat flux from the rock core reasonable end members are considered for both parameters as disagreement remains on the former especially the pressure effect on viscosity and as the latter is expected to vary significantly during the moon s history we show that the heat power produced by radioactive decay within the rock core is mainly transported through the hp ice mantle by melt extraction to the ocean with most of the melt produced directly above the rock water interface while the average temperature in the bulk of the hp ice mantle is always relatively cool when compared to the value at the interface with the rock core 5 k above the value at the surface of the hp ice mantle maximum temperatures at all depths are close to the melting point often leading to the interconnection of a melt path via hot convective plume conduits throughout the hp ice mantle overall we predict long periods of time during these moons history where water generated in contact with the rock core is transported to the above ocean

is io s mantle really molten abstract the tremendous heating dissipated by jovian tides in io s interior is essentially evacuated by an intense volcanic activity so that the heat is removed from the interior to the surface much more by advection than by conduction through the lithosphere the efficiency of this heat pipe cooling process is investigated through numerical models of convection performed in spherical geometry with a permeable top boundary this new heat transfer model provides a cooling twice as efficient as that obtained with an impermeable condition traditionally used in mantle convection modeling the globally averaged temperature varies as ra 1 2 where ra is the rayleigh number whereas the power law exponent is classically 1 4 so that the expected ra would not be in excess of 10 7 if the whole mantle of io is involved in the convection process the major portion could remain solid while a possible molten zone could be confined to a 100 km thick layer between the solid part and the core this model predicts the existence of a strong lithosphere which is required to support the observed topographic amplitude of the io s relief

deep seismic structure of the atacama basin northern chile 1 the atacama basin is a prominent morphological anomaly in the central andean forearc 3d seismic structure beneath the depression and its surroundings has been determined from local earthquake tomography depth maps of p wave velocity and attenuation 1 qp through the lithosphere reveal a rheologically strong high qp and vp lithospheric block beneath the basin surrounded by weak regions low qp and vp beneath pre and western cordilleras the anomalous lithospheric structure appears to bar hot asthenospheric mantle from penetrating trenchward and hence causes the volcanic front to be deflected by the salar de atacama basin the cold block may also influence the thermal structure of the subducted slab causing reduced benioff seismicity and less hydration of mantle rocks evident from reduced vp vs ratios seismic data are hard to reconcile with extension and lithospheric thinning as a mechanism for subsidence of the basin instead high strength of the atacama lithospheric block may contribute to basin formation by focussing deformation and uplift along the block s weak edges

fluid budgets along the northern hikurangi subduction margin new zealand the effect of a subducting seamount on fluid pressure we estimate fluid sources around a subducted seamount along the northern hikurangi subduction margin of new zealand using thermomechanical numerical modelling informed by wedge structure and porosities from multichannel seismic data calculated fluid sources are input into an independent fluid flow model to explore the key controls on overpressure generation to depths of 12 km in the thermomechanical models sediment transport through and beneath the wedge is calculated assuming a pressure sensitive frictional rheology the change in porosity pressure and temperature with calculated rock advection is used to compute fluid release from compaction and dehydration our calculations yield more precise information about source locations in time and space than previous averaged estimates for the hikurangi margin the volume of fluid release in the wedge is smaller than previously estimated from margin averaged calculations 14 m3 yr 1 m 1 and is exceeded by fluid release from underlying subducting sediment 16 m3 yr 1 m 1 clay dehydration contributes only a small quantity of fluid by volume 2 m3 yr 1 m 1 from subducted sediment but the integrated effect is still significant landward of the seamount fluid source terms are used to estimate fluid pressures around a subducting seamount in the fluid flow models using subducted sediment permeability derived from porosity and testing two end members for decollement permeability models in which the decollement acts as a fluid conduit predict only moderate fluid overpressure in the wedge and subducting sediment however if the subduction interface becomes impermeable with depth significant fluid overpressure develops in subducting sediment landward of the seamount the location of predicted fluid overpressure and associated dehydration reactions is consistent with the idea that short duration shallow slow slip events sses landward of the seamount are caused by anomalous fluid pressures alternatively it may result from frictional effects of changing clay content along the subduction interface

reconstructions of the new zealand region for the neogene abstract the major structural elements of the present day plate boundary zone through new zealand are a subduction zone under the northern half of the country linked by a wide transform zone to the southward extension of the plate boundary through fiordland and the macquarie ridge using finite rotations of the pacific australian plate pair a sequence of reconstructions of the relative positions of the plates is presented reconstructions of the plate boundary zone based on paleomagnetic data involve essentially the same structural elements as today but with large clockwise changes in their trend with time

anatomy of a megathrust the 2010 m8 8 maule chile earthquake rupture zone imaged using seismic tomography abstract knowledge of seismic velocities in the seismogenic part of subduction zones can reveal how material properties may influence large ruptures observations of aftershocks that followed the 2010 m w 8 8 maule chile earthquake provide an exceptional dataset to examine the physical properties of a megathrust rupture zone we manually analysed aftershocks from onshore seismic stations and ocean bottom seismometers to derive a 3 d velocity model of the rupture zone using local earthquake tomography from the trench to the magmatic arc our velocity model illuminates the main features within the subduction zone we interpret an east dipping high p wave velocity anomaly 6 9 km s as the subducting oceanic crust and a low p wave velocity we assess the role played by physical heterogeneity in governing megathrust behaviour greatest slip during the maule earthquake occurred in areas of moderate p wave velocity 6 5 7 5 km s where the interface is structurally more uniform at shallow depths high fluid pressure likely influenced the up dip limit of seismic activity the high velocity bodies lie above portions of the plate interface where there was reduced coseismic slip and minimal postseismic activity the northern velocity anomaly may have acted as a structural discontinuity within the forearc influencing the pronounced crustal seismicity in the pichilemu region our work provides evidence for how the ancient geological structure of the forearc may influence the seismic behaviour of subduction megathrusts

structure and dynamics of earth s inner core abstract the seismological exploration of the earth s inner core has revealed unexpected and puzzling structural complexities its elastic anisotropy is now well established and has been shown to vary spatially there is a well defined hemispherical dichotomy in anisotropy and attenuation and significant variations in the radial direction with weaker anisotropy in the uppermost regions and possibly different properties in an innermost inner core of radius 300 600 km perhaps even more puzzling is the observation of a stably stratified layer at the base of the outer core which has recently been proposed to result from melting of inner core material if confirmed the presence of this layer has major implications for our understanding of convection in the outer core inner core differential rotation with respect to the mantle remains controversial we will review here recent progress in understanding the dynamics of the inner core a number of different models have been proposed for the development of the inner core s structure and formation of the stable layer at the base of the outer core and particular care will be taken to clarify under which conditions the proposed mechanisms can be active

on factors controlling the depth of interseismic coupling on the hikurangi subduction interface new zealand abstract we apply a finite difference numerical thermal model to the shallow region of the hikurangi subduction margin north island new zealand this subduction zone is characterised by subduction of thick and buoyant crust of the hikurangi plateau and along strike variations in subduction obliquity onshore surface heat flow low in the south high in the north inferred pore fluid pressure and seismic style locked in the south aseismic in the north the model reproduces low onshore surface heat flow observed in the southern hikurangi margin we propose that greater surface heat flow in the north is caused by shear heating and convective heat flow by fluids escaping from the interface the model predicts that the hikurangi megathrust is comparatively cold so that if the lower limit of the interface seismogenic zone is thermally controlled it should occur near the intersection with the hangingwall moho this agrees with observation in the southern locked segment but thermal control alone cannot explain the shallow interseismic locking depth in the central and northern margin in crustal strength curves changing fluid pressure is capable of moving the brittle viscous transition vertically by tens of kilometres we propose that subduction zone seismic style depends on the fluid pressure regime both in the hangingwall and along the interface and define four end member types of megathrust fault segments contrary to many previous studies we suggest that the high fluid pressure low shear strength end member is fully coupled with potential for large interplate earthquakes in the hydrostatic case the fault is stronger but the brittle viscous transition occurs significantly shallower than in the near lithostatic case inferred to promote aseismic creep at relatively shallow levels along strike variation in seismic style on the hikurangi megathrust can therefore be explained by variation in fluid pressure state along the margin

late pleistocene holocene sedimentation in the nw aegean sea a palaeoclimatic palaeoceanographic reconstruction sedimentological particle size organic carbon calcium carbonate clay mineralogy and radiocarbon dating and micropalaeontological investigation of 9 cores from the nw aegean sea eastern mediterranean have enabled five main lithological units to be identified the units cover a period from the late pleistocene to the present day on the basis of these results and reference to other studies a palaeo reconstruction is presented for the area the reconstruction takes into account the increase in sea level during the period the decrease in fluvial inputs issuing to the area from the north mediterranean coastline and the possible influence of water issuing from the black sea it is concluded that the sedimentological and oceanographic regimes of the area were strongly influenced by a fluvial component during the late pleistocene and early holocene whereas today the sedimentary record is more indicative of an open oceanic environment

a heat pipe mechanism for volcanism and tectonics on venus a heat pipe mechanism is proposed for the transport of heat through the lithosphere on venus this mechanism allows the crust and lithosphere on venus to be greater than 150 km thick a thick crust and thick lithosphere can explain the high observed topography and large associated gravity anomalies for a 150 km thick lithosphere the required volcanic flux on venus is 200 km sup 3 yr this is compared with a flux of 17 km sup 3 yr associated with the formation of the oceanic crust on earth a thick basaltic crust on venus is expected to transform to eclogite at a depth of 60 to 80 km the dense eclogite would contribute the lithospheric delamination that returns the crust to the interior of the planet completing the heat pipe cycle topography and the associated gravity anomalies can be explained by airy compensation of the thick crust the principal observation that is contrary to this hypothesis is the mean age of the surface that is inferred from crater statistics the minimum mean age is about 130 ma and this implies an upper limit of 2 km sup 3 yr for the surface volcanic flux if the heat pipe mechanism was applicable on earth in the archean itmore would provide the thick lithosphere implied by isotopic data from diamonds less

tidal resonance in icy satellites with subsurface oceans tidal dissipation is a major heat source for the icy satellites of the giant planets several icy satellites likely possess a subsurface ocean underneath an ice shell previous studies of tidal dissipation on icy satellites however have either assumed a static ocean or ignored the effect of the ice lid on subsurface ocean dynamics in this study we examine inertial effects on tidal deformation of satellites with a dynamic ocean overlain by an ice lid based on viscoelasto gravitational theory although ocean dynamics is treated in a simplified fashion we find a resonant configuration when the phase velocity of ocean gravity waves is similar to that of the tidal bulge this condition is achieved when a subsurface ocean is thin 1 km the enhanced deformation increased h2 and k2 love numbers near the resonant configuration would lead to enhanced tidal heating in the solid lid a static ocean formulation gives an accurate result only if the ocean thickness is much larger than the resonant thickness the resonant configuration strongly depends on the properties of the shell demonstrating the importance of the presence of a shell on tidal dissipation

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

crustal heterogeneity highlighted by spatial b value map in the wellington region of new zealand summary we map the b value in the subduction zone of the wellington region new zealand using a high quality earthquake catalogue relocated with a 3 d seismic velocity model consisting of 50 314 events that occurred between 1990 and 2005 in order to investigate heterogeneity in the crust of the overlying plate and in the upper plane of the wadati benioff zone wbz we analyse a series of cross sections perpendicular to the strike of the subduction zone we calculate the b values selecting events with magnitude of completeness 2 4 and depth 65 km and projecting the seismicity within 20 km on each side of the cross sectional planes we observe areas of high b value 1 7 near the plate interface and regions of low b value anomalies are detected both in the wbz in the northwest region below 40 km depth and in the overlying plate in the northern south island at 10 km depth the anomalies are statistically significant based on utsu s p test and the bootstrap method and are not data processing method or parameter dependent we compare the b value distribution with previously determined 3 d distributions of vp vp vs and qp from seismic tomography this comparison suggests that material inhomogeneity caused by fluid filled cracks resulting from dehydration of the subducted slab and subducted sediments is the predominant cause of b value variation in the shallow part of this subduction zone our observations are consistent with a previously proposed conceptual model that fluid distribution in the shallow part of this subduction zone is controlled by the permeability of geological terranes in the overlying plate

slow wavespeeds and fluid overpressure in a region of shallow geodetic locking and slow slip hikurangi subduction margin new zealand abstract travel times recorded onshore from active source marine seismic surveys were used to determine hikurangi forearc wavespeeds ray path midpoints sample forearc crust above the shallow v p from the seabed to 4 km depth consistent with rapidly deposited clastic sediments and near constant v p 5 0 0 2 km s at depths of 4 10 km within the forearc the northern region has slow slip events at shallow depths of c 5 15 km beneath the volume sampled by our analysis average travel times at offsets of 20 80 km are 1 s more than at equivalent offsets in the south and v p increases with depth within the forearc from 3 5 0 1 km s at 4 km depth to 4 5 0 2 km s at 10 km depth we interpret the low wavespeeds in terms of compaction disequilibrium and compare seismic inferences of anomalously high porosity 10 with hydrostatic reference compaction models to show effective stress is low in both the north 27 10 mpa and south 36 14 mpa in the south pore space and conduits have a high chance of being localized on faults or sand layers the wedge is clearly compressionally critical and we suggest the higher seismic velocities recorded primarily reflect higher effective stress levels transmitted through the rock framework the observed wedge geometry and our estimate of fluid pressure within the wedge 0 87 0 05 suggest a weak overpressured subduction thrust in the north we suggest high fluid pressure is maintained by a large fluid inventory from subducting sediment a pore space geometry characterized by pervasively fractured rock and mudstone and a lower mean stress due to its stable and non critical wedge geometry we consider both end member assumptions of convergent and tensile failure the latter of which reveals the possibility of near lithostatic fluid pressure on the north hikurangi subduction interface although this remains unproven our observations are consistent with high fluid pressures encountered in petroleum wells at depths

three dimensional attenuation model of the shallow hikurangi subduction zone in the raukumara peninsula new zealand 1 the material properties of the shallow subduction zone are imaged with data from a passive seismic deployment in the raukumara peninsula attenuation images are obtained using t values measured from 2848 spectra of p wave arrivals the t values are inverted for frequency independent three dimensional 3 d qp using a 3 d velocity model linked nodes in a preliminary 2 d inversion are used to obtain the most reliable initial model for 3 d inversions the results show the benefits of obtaining 3 d q in addition to 3 d vp and vp vs q is related to localized permeability and heterogeneity and thus 3 d q is an important tool for interpreting active tectonic regions qp in the shallow overlying plate generally corresponds to the mapped geology two high qp features 600 represent subducted seamounts or cretaceous volcanics within the overlying plate the gradient above the subducting plate is the strongest feature in the qp model with the slab having high qp 600 900 below 20 km depth and above the plate interface there is a zone of 50 decrease in qp and high vp vs about 10 km thick which represents actively subducting sediment and has distributed microearthquake activity associated with active underplating

gravity anomalies crustal structure and seismicity at subduction zones 2 interrelationships between fore arc structure and seismogenic behavior an ensemble averaging technique is used to remove the long wavelength topography and gravity field associated with subduction zones short wavelength residual anomalies are attributed to the tectonic structure of subducting and overthrusting plates a paired positive negative fore arc anomaly is observed consisting of a long 1000 km linear trench parallel ridge landward of the deep sea terrace basin ridges have amplitudes of 1500 3000 m and 160 240 mgal wavelengths of 150 200 km and high gravity anomaly to topography ratios 50 75 mgal km 1 the ridge crests correlate with the downdip limit of coseismic slip and strong interplate coupling and in cascadia the updip limit of tremor epicenters the ridge crest may be interpreted as defining the boundary between the velocity weakening and seismogenic region of the subduction interface and the downdip frictional transition zone in tonga kermadec the kuril islands and chile landward ridges are associated with extinct volcanic arcs paired anomalies are attributed to the preferential subduction erosion of the outer fore arc and a spatially varying combination of a lower crustal underplating beneath the inner fore arc b the transformation of interseismic strain into permanent geologic strain via faulting folding or buckling of the inner fore arc and c the relative trenchward migration of extinct volcanic arcs in regions operating with a net crustal deficit along strike transitions in fore arc morphology and seismogenic behavior are related to preexisting crustal structure of subducting and overthrusting plates fore arcs have the added potential of recording the time integrated response of the upper plate to subduction processes and fore arc structure should be considered in tandem with seismological observations

continental subduction and three dimensional crustal structure the northern south island new zealand the three dimensional vp and vp vs structure of a region where subduction transitions to oblique transform faulting has been determined using arrival times from 579 local earthquakes recorded during a temporary deployment and 3146 earthquakes have been relocated between 40 km and 100 km depth the subducted plate is imaged as a relatively low velocity feature in the uppermost mantle reflecting the continental nature of the subducted crust in this region an increase in amplitude of this low velocity feature from northeast to southwest can be related to an increase in the thickness of the crust of the subducted plate in this direction velocity variations within the subducted and overlying plates show some spatial correlation this suggests an interaction between the plates which extends well beyond the plate interface and is consistent with other geophysical and geological evidence that the plate interface beneath marlborough is currently not accommodating much active subduction in the overlying plate the awatere fault is a major structural feature associated with a low velocity zone extending to 23 km depth there is a marked change in structure near this fault with seismic velocities being lower to the southeast a relatively high level of seismicity occurs in this region of lower seismic velocities suggesting a relationship between the two a possible explanation for this is elevated pore pressures caused by fluids derived from dehydration of the continental subducted crust the low velocity region in the overlying plate coincides with the region of most intense active deformation suggesting it is relatively weak

fault spacing in continental strike slip shear zones abstract strike slip shear zones with sub parallel arrays of evenly spaced faults are widely observed in nature but the controls on the spacing between major faults are unclear we analyze a 2 d model and develop a scaling law relating the fault spacing to structural and rheological parameters in the continental crust we find that fault spacing positively correlates with brittle layer thickness viscous lower crust thickness and strength contrast between active faults and surrounding intact blocks and is inversely correlative with lower crust viscosity this is corroborated for either a zero shear traction decoupled or a prescribed velocity coupled basal boundary condition in the 2 d analytical solution the zero shear traction boundary condition represents low viscosities in the lowermost crust or the topmost mantle that may decouple deformations from mantle flow the prescribed velocity boundary condition emphasizes basal drag tractional forces imparted on the lower crust by a strong mantle for a viscous layer that is thicker than half of its average fault spacing models with either of the boundary conditions produce the same results otherwise a thinner viscous layer with a linear velocity condition tends to produce smaller fault spacings than a no shear model all else being equal these theoretical models are comparted to data from shear zones in california the marlborough fault zone in new zealand and central tibet modeling indicates that the effective viscosity of the viscous layer underlying the brittle layer in all of the selected areas is 2 10 20 to 4 10 21 pa s the subducted oceanic plate attached to the lower crust of the eastern marlborough fault zone also appears to influence fault spacing in the overriding plate

new constraints on seismicity in the wellington region of new zealand from relocated earthquake hypocentres summary the wellington region of new zealand overlies a strongly coupled portion of the shallow subduction interface between the pacific and australian plates to better understand the active deformation in the area we perform a double difference dd relocation of 6825 local earthquakes that occurred between 1990 and 2001 using both cross correlation cc and bispectrum bs methods we calculate high quality waveform based differential times wbdts for event pairs we manage to more than triple the s wave differential time measurements after reasonably estimating many of the unpicked s arrivals after relocation the image of the double seismic zone beneath this region is greatly sharpened we find several northeast striking linear seismic features near lake wairarapa on the north island which may result from slip along normal faults within the subducting pacific plate we further search for repeating events that might define creeping patches along the interplate thrust using a 20 s data window for cc we find 287 event clusters with very high waveform similarities most of these clusters contain just a doublet that occurred within a short time period the failure to find repeating earthquakes along the plate boundary in this 12 yr time period is consistent with the hypothesized strong coupling between the pacific and australian plates under the wellington region

three dimensional velocity structure in northern california coast ranges from inversion of local earthquake arrival times abstract the three dimensional p wave velocity structure in the upper crust in the northern california coast ranges from santa rosa to ukiah is obtained by simultaneous inversion of local earthquake and refraction travel time data for velocity and hypocentral parameters in this region where there are lateral heterogeneities the three dimensional inversion provides important results not found in two dimensional refraction studies the medium is parameterized with velocities at the intersections gridpoints of a nonuniform three dimensional grid travel times are calculated with approximate ray tracing along arcuate paths which are reasonable for lateral distances less than 45 km inversions with 5 to 10 and 2 to 3 km gridspacing achieved 80 per cent decreases in data variance the inversion with 2 to 3 km gridspacing reduced the rms residual level to approximately the level of timing error anomalously low velocities to at least 6 km depth are found along the maacama and healdsburg rodgers creek hrc fault zones the low velocity region is widest at the en echelon junction of the maacama and hrc fault zones low velocities are associated with the clear lake basin where there is a thick sequence of volcanics interbedded with sedimentary deposits there is a high velocity body located southeast of the geysers between the maacama and collayomi fault zones which may be associated with igneous intrusives or high grade metamorphism related to an underlying inferred partial melt body modeled in previous teleseismic travel time studies there is some indication in the vapor dominated geothermal reservoir of lower velocities relative to surrounding water saturated rock as has been shown in some laboratory experiments hypocenter locations obtained in the inversion show little variation from hypocenters obtained through inversion for one dimensional velocity model and station corrections for the inversion with 2 to 3 km gridspacing however some groups of events become more tightly clustered

evidence from gps measurements for contemporary interplate coupling on the southern hikurangi subduction thrust and for partitioning of strain in the upper plate the spatial extent and strength of contemporary coupling between the pacific and australian plates on the hikurangi subduction interface beneath the wellington region of new zealand are not well known consequently the potential for the plate interface to produce great thrust earthquakes or to load the major wellington and wairarapa faults in the overlying plate is also unknown to address these issues a gps network across the southern north island has been partially or wholly surveyed six times between 1992 and 1999 and yields well determined relative velocities between 82 points the relative velocity of the east coast with respect to the west coast across the 80 km width of the southern end of the north island is 14 mm yr 1 at an azimuth of 258 this is about one third of and closely parallel to the nuvel 1a relative velocity of the pacific with respect to the australian plate 39 4 mm yr 1 at 261 strain rate solutions indicate partitioning of contemporary strain with a 35 change in principal axis orientations across the network using elastic dislocation theory an inversion of the observed point velocities and their full variance covariance matrix determines the variation with depth of contemporary coupling at the subduction interface if uniform coupling is assumed then 100 coupling occurs from very shallow depths down to 29 1 km however if variable coupling is assumed it reaches 100 at depths between 16 and 24 km at greater depths there is a transition zone at least 20 km wide down to a depth of at least 40 km over which contemporary coupling diminishes to zero these depth ranges correlate moderately well with low angle thrust focal mechanisms recently obtained by other workers and indicate that the downdip width of the interface over which a great thrust earthquake could occur exceeds 100 km elastic dislocation models also explain the observed partitioning of strain with coulomb stress calculations indicating that the wairarapa fault is being loaded at seismogenic depths

geophysical investigations of habitability in ice covered ocean worlds geophysical measurements can reveal the structures and thermal states of icy ocean worlds the interior density temperature sound speed and electrical conductivity thus characterize their habitability we explore the variability and correlation of these parameters using 1 d internal structure models we invoke thermodynamic consistency using available thermodynamics of aqueous mgso 4 nacl as seawater and nh 3 pure water ice phases i ii iii v and vi silicates and any metallic core that may be present model results suggest for europa that combinations of geophysical parameters might be used to distinguish an oxidized ocean dominated by mgso 4 from a more reduced ocean dominated by nacl in contrast with jupiter s icy ocean moons titan and enceladus have low density rocky interiors with minimal or no metallic core the low density rocky core of enceladus may comprise hydrated minerals or anhydrous minerals with high porosity cassini gravity data for titan indicate a high tidal potential love number k 2 0 6 which requires a dense internal ocean ocean 1 200 kg m 3 and icy lithosphere thinner than 100 km in that case titan may have little or no high pressure ice or a surprisingly deep water rock interface more than 500 km below the surface covered only by ice vi ganymede s water rock interface is the deepest among known ocean worlds at around 800 km its ocean may contain multiple phases of high pressure ice which will become buoyant if the ocean is sufficiently salty callisto s interior structure may be intermediate to those of titan and europa with a water rock interface 250 km below the surface covered by ice v but not ice vi

sedimentation in the zakynthos channel a conduit link to the hellenic trench eastern mediterranean abstract sedimentological oceanographic and geophysical data sets are used to examine contemporary and past transport processes in a tectonically active submarine valley canyon which acts as a feeder area to a trench system around 4000 m in depth provinces are identified together with the major redistribution processes active over the area the conclusions are that 1 the zakynthos channel is a major proximal source for a transport system which has its distal end in the north matapan trench basin 2 tectonically induced movement is the major mechanism triggering down slope mass gravity flow 3 the holocene late pleistocene facies associated with the upper reaches of the valley canyon system are dominated by local terrigenous sources and 4 sedimentation rates vary from being moderately high in the shallow water continental shelf feeder provinces low along the conduit axis high in the perched basin and extremely high at the distal end

tidally heated convection constraints on europa s ice shell thickness 1 the thickness of europa s ice shell is constrained with numerical experiments of thermal convection including heterogeneous tidal heating thermal convection occurs in the stagnant lid regime with most of the tidal heating located in the bottom half of the layer the addition of tidal heating mainly results in the increase of the temperature of the well mixed interior and in the decrease of the heat flux at the base of the ice layer in many simulations the ice in hot plumes is heated up to its melting point this induces episodic upwellings 0 5 ma of partially molten ice up to the base of the conductive lid with possible implications for the formation of lenticulae and chaos regions the thickness of the convective ice shell in equilibrium with the heat flow from the silicate core is estimated to be about 20 25 km tidal dissipation and surface temperature variations create lateral variations of the ice shell thickness of about 5 km with maxima near the equator at the jovian and anti jovian points and minima at midlatitudes surface heat flux is about 35 40 mw m 2 it is almost constant all over europa s surface even though the tidal dissipation rate is four times larger at the poles than at the equator

mechanisms of seismic attenuation in the crust scattering and anelasticity in new york state south africa and southern california the envelopes of high frequency seismograms from earthquakes in new york state south africa and southern california are analyzed to determine how much of the observed attenuation of shear waves in the crust is caused by anelasticity and how much is produced by scattering from small scale heterogeneities for seismograms from new york and south africa there is a systematic enrichment of high frequency energy that develops in the coda relative to the direct s or l sub g waves the author uses the growth with source receiver distance of the high frequency energy in the coda relative to the direct wave to estimate the scattering attenuation of the crust and the relative time decay of high frequency energy in the coda to determine the anelastic attenuation using the estimate of l sub g wave q as a constraint he finds that the scattering q in the crust of new york is either independent of frequency or increases with frequency f slower than f sup 0 3 a similar analysis for south africa indicates that scattering is the major cause of the observed s wave attenuation of high frequency energy 30 hz at local distances 100 km for southern california the extent of the scattering attenuation is unclear from the data more although the relatively steep coda decay of southern california implies that anelastic attenuation is stronger there than in new york or south africa for southern california and new york state the 3 hz coda q taken from the late coda 50 110 s is comparable to the l sub g wave q however the 3 hz coda q for south africa over these lapse times is about 5 times the estimated l sub g wave q for all three areas the frequency dependence of the coda q does not match the frequency dependence of the s wave q and for new york and south africa it changes with lapse time less

the role of fluids in lower crustal earthquakes near continental rifts earthquakes in the lower continental crust of the earth are rare as the lower crust is thought to be too hot to allow brittle failure so it is surprising that they occasionally occur where continental crust is rifting apart a study of three dimensional crustal structure and seismicity in the taupo volcanic zone an active continental rift in new zealand has now provided insight into how these earthquakes arise the crustal earthquakes form a continuous band along the rift and often occur in swarms suggesting fluid movement in critically loaded fault zones seismic velocities within the band are consistent with the presence of fluids and the linking of upper and lower crust seismicity to crustal structure point to a common explanation for all of the seismicity probably the weakening of faults on the periphery of an otherwise dry crust by hot fluids a report on three dimensional tomographic imaging of seismic velocities and attenuation in the taupo volcanic zone an active continental rift where earthquakes are known to occur in the lower crust finds that crustal earthquakes form a continuous band along the rift and often occur in swarms suggesting fluid movement in critically loaded fault zones the occurrence of earthquakes in the lower crust near continental rifts has long been puzzling as the lower crust is generally thought to be too hot for brittle failure to occur1 2 such anomalous events have usually been explained in terms of the lower crust being cooler than normal3 4 but if the lower crust is indeed cold enough to produce earthquakes then the uppermost mantle beneath it should also be cold enough2 and yet uppermost mantle earthquakes are not observed5 numerous lower crustal earthquakes occur near the southwestern termination of the taupo volcanic zone tvz an active continental rift in new zealand6 here we present three dimensional tomographic imaging of seismic velocities and seismic attenuation in this region using data from a dense seismograph deployment7 we find that crustal earthquakes accurately relocated with our three dimensional seismic velocity model form a continuous band along the rift deepening from mostly less than 10 km in the central tvz to depths of 30 40 km in the lower crust 30 km southwest of the termination of the volcanic zone these earthquakes often occur in swarms suggesting fluid movement in critically loaded fault zones8 seismic velocities within the band are also consistent with the presence of fluids and the deepening seismicity parallels the boundary between high seismic attenuation interpreted as partial melt within the central tvz and low seismic attenuation in the crust to the southwest this linking of upper and lower crustal seismicity and crustal structure allows us to propose a common explanation for all the seismicity involving the weakening of faults on the periphery of an otherwise dry mafic crust by hot fluids including those exsolved from underlying melt such fluids may generally be an important driver of lower crustal seismicity near continental rifts

grain size sensitive seismic wave attenuation in polycrystalline olivine 1 in order to investigate the processes responsible for the attenuation of seismic shear waves in the earth s upper mantle four olivine polycrystals ranging in mean grain size d from 3 to 23 m have been fabricated characterized and mechanically tested in torsion at high temperatures and seismic frequencies both the shear modulus which governs the shear wave speed vs and the dissipation of shear strain energy q 1 have been measured as functions of oscillation period to temperature t and for the first time grain size at sufficiently high t all four specimens display similar absorption band viscoelastic behavior adequately represented for 1000 t 1200 or 1300 c and 1 to 100 s by the expression q 1 a tod 1 exp e rt with a 7 5 102 s m 0 26 and e 424 kj mol 1 this mildly grain size sensitive viscoelastic behavior of melt free polycrystalline olivine is attributed to a combination of elastically and diffusionally accommodated grain boundary sliding the latter becoming progressively more important with increasing t and or to extrapolation to the larger mm cm grain sizes expected in the earth s upper mantle yields levels of dissipation comparable with those observed seismologically implying that the same grain size sensitive processes might be responsible for much of the observed seismic wave attenuation the temperature sensitivity of vs is increased substantially by the viscoelastic relaxation allowing the lateral variability of wave speeds to be associated with relatively small temperature perturbations

sedimentation and accumulation of organic carbon in the angola basin and on walvis ridge preliminary results of deep sea drilling project leg 75 leg 75 investigated two periods of accumulation of sediments rich in organic matter in the upper cretaceous section more than 200 beds of gray or black shale and mudstone rich in organic carbon as much as 18 are intercalated within a sequence of red and green mudstones that contain less than 1 organic carbon the black shale beds are 1 to 62 cm thick and constitute less than 10 of the section in the 20 cores in which they were recovered both turbiditic and pelagic processes were involved in the deposition of these black shale beds a combination of factors including increased productivity and warm saline bottom waters probably resulted in a delicate balance between oxic and anoxic conditions that periodically favored the accumulation and preservation of organic matter in the basinal sediments the pliocene pleistocene sediments are thoroughly bioturbated and there is no evidence of persisting anoxia in the overlying water in spite of the high organic carbon content of the sediments these two different periods of accumulation of organic matter both resulted in significant concentration of organic carbon 2 maximum 18 but the pliocene pleistocene sediments contain the greater mass of organic carbon per unit volume of the solid sediment

crustal shear wave tomography of the taupo volcanic zone new zealand via ambient noise correlation between multiple three component networks the central north island of new zealand is characterized by extension high heat flow and active volcanism caused by the pacific plate subducting beneath the australian plate off the east coast of the north island the taupo volcanic zone tvz is the current locus of rifting and active volcanism the shear velocity structure derived here from short period surface wave analysis fills a gap in the geophysical information obtained in previous active and passive source studies using ambient noise correlation techniques we reprocess data from four three component temporary seismic arrays that were deployed between 2001 and 2005 in the central north island and data from permanent seismic stations operational at the same time special attention has been paid to the correction of timing errors and incomplete instrument response information low shear velocities in the top 15 20 km of the crust inferred from rayleigh wave dispersion analysis coincide with the presumed source regions of rhyolitic magma in the tvz and are correlated with conductive bodies inferred from a 3 d magnetotelluric survey based on the observed changes in shear velocity we use empirical relations to infer an average percentage of partial melt in the upper crust of 4 comparison of our shear velocity model with compressional wave cross sections from active and passive source studies and shear velocities derived from previous 3 d vp and vp vs models reveals several consistent features especially in the lower crust the greater sensitivity of shear velocity than compressional velocity to the presence of melt and other fluids aids in linking seismic and electromagnetic observations and provides additional constraints on the distribution of magmatic structures in active continental rifting environments

earthquake locations and three dimensional crustal structure in the coyote lake area central california previous work on the simultaneous inversion method has been improved and extended to incorporate iterative solution for earthquake locations and laterally heterogeneous structure approximate ray tracing and parameter separation are important elements of the improved method application of the method to p wave arrival time data recorded by stations of the u s geological survey central california network yields a three dimensional model for the velocity structure of the upper crust in an area encompassing the rupture zone of the coyote lake earthquake of august 1979 very strong correlations between the velocity model and the geology and gravity and magnetic anomalies are observed improved estimates of the locations of earthquakes in the study area are also determined the relocation of explosions indicates epicentral accuracies of the order of a kilometer or better based on the revised hypocentral locations it is concluded that the san andreas fault is vertical in this area with no actual offset between the epicenters and the fault trace in contrast the calaveras has two or more active fault surfaces one nearly vertical and another dipping 75 to the northeast

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

seismological studies at parkfield i simultaneous inversion for velocity structure and hypocenters using cubic b splines parameterization a model for the 3d p and s wave velocity structure at parkfield has been developed by the systematic inversion of arrival times for microearthquakes and surface vibroseis sources recorded by nearby calnet stations and by the local borehole installed 10 station high resolution seismic network there a modification of the linear b splines model parameterization method of thurber 1983 to a cubic b splines formulation through tests inverting synthetic data sets for the parkfield configuration is found to produce smooth velocity distributions that still retain some small scale features application of the method to 953 p wave and 288 s wave arrivals from 111 microearthquakes and 8 vibroseis locations throughout the study area yields a velocity structure having variable resolution a low velocity zone appears to coincide with the creeping segment of the san andreas fault zone northwest of the 1966 parkfield earthquake epicenter an increase of about 15 per cent in seismic velocities is seen from the northeast to southwest across this segment of the fault zone the higher velocities to the southwest apparently correspond to the granitic basement the contrast across the fault is subdued to the southeast along the 1966 rupture zone a high vp vs ratio of 1 9 is seen in a 2 km wide volume near the location of the 1966 main shock hypocenter presumably the nucleation zone for the expected m 6 parkfield earthquake

multiple resolution seismic attenuation imaging at mt vesuvius abstract a three dimensional s wave attenuation tomography of mt vesuvius has been obtained with multiple measurements of coda normalized s wave spectra of local small magnitude earthquakes we used 6609 waveforms relative to 826 volcano tectonic earthquakes located close to the crater axis in a depth range between 1 and 4 km below the sea level recorded at seven 3 component digital seismic stations we adopted a two point ray tracing rays were traced in an high resolution 3 d velocity model the spatial resolution achieved in the attenuation tomography is comparable with that of the velocity tomography we resolve 300 m side cubic cells we statistically tested that the results are almost independent from the radiation pattern we also applied an improvement of the ordinary spectral slope method to both p and s waves assuming that the differences between the theoretical and the experimental high frequency spectral slope are only due to the attenuation effects consequently we could check the coda normalization method also comparing the s attenuation image with the p attenuation image the images were obtained inverting the spectral data with a multiple resolution approach results have shown the general coincidence of low attenuation with high velocity zones the joint interpretation of velocity and attenuation images allows us to interpret the low attenuation zone intruding toward the surface until a depth of 500 m below the sea level as related to the residual part of solidified magma from the last eruption in the depth range between 700 and 2300 images are consistent with the presence of multiple acquifer layers no evidence of magma patches greater than the minimum cell dimension 300 m has been found a shallow p wave attenuation anomaly beneath the southern flank of the volcano is consitent with the presence of gas saturated rocks the zone characterized by the maximum seismic energy release cohincides with a high attenuation and low velocity volume interpreted as a cracked medium