geographic and seasonal distributions of brunt vaisala frequency and rossby radii in the north pacific and north atlantic abstract long term mean temperature and salinity profiles computed from an edited set of historical hydrographic data have been used to calculate mean profiles of density and brunt vaisala seasonal variations in internal rossby radii are everywhere surprisingly small

assimilation of altimeter data into a quasigeostrophic model of the gulf stream system part ii assimilation results abstract the improvement in the climatological behavior of a numerical model as a consequence of the assimilation of surface data is investigated the model used for this study is a quasigeostrophic qg model of the gulf stream region the data that have been assimilated are maps of sea surface height that have been obtained as the superposition of sea surface height variability deduced from the geosat altimeter measurements and a mean field constructed from historical hydrographic data the method used for assimilating the data is the nudging technique nudging has been implemented in such a way as to achieve a high degree of convergence of the surface model fields toward the observations comparisons of the assimilation results with available in situ observations show a significant improvement in the degree of realism of the climatological model behavior with respect to the model in which no data are assimilated the remaining discrepancies in the model mean circulation seem to be mainly associated wi

a gulf stream model and an altimetry assimilation scheme a continuous data assimilation scheme and a multilayer primitive equation numerical model are described the model is an eddy resolving coastal ocean model that has been extended to include the gulf stream region it has complete thermohaline dynamics a bottom following sigma vertical coordinate system and a coastal following curvilinear orthogonal horizontal coordinate system calculated model fields are used to provide a model climatology and correlations between subsurface temperature and salinity anomalies and surface elevation anomalies an optimal interpolation method the surface to subsurface correlations and estimated model and data errors are the basis of the assimilation technique altimetry anomaly data extracted from the model calculations according to the geosat orbital schedule are used to test the assimilation scheme and to provide nowcasts and forecasts sensitivity studies are performed to test the effects of various parameters of the scheme it is found that the scheme is less efficient in the shallow continental shelf area than in the deeper regions of the model the results show significant nowcast skill with area averaged rms error for surface elevation and subsurface properties of about 40 50 of the corresponding error of the unassimilated case good forecast skill better than persistence is demonstrated for 10 20 days there is little skill after 30 40 days increasing the density of the satellite altimetry data especially by decreasing the separation distance between tracks should decrease the nowcast rms error to about 15 and improve the forecast

inversion of rayleigh wave phase and group velocities by simulated annealing abstract a joint inversion of regionalized phase and group velocities of fundamental mode rayleigh waves is performed by means of a simulated annealing scheme which makes use of some thermodynamic analogies based on the gibbs distribution the correlations and the uncertainties on shear wave velocities defining the elastic model are estimated by using a procedure based on the same thermodynamic analogies as a relevant feature the simulated annealing algorithm permits reducing the usual dependence of the solution on the sometimes arbitrary starting model a shortcoming linked to the use of this procedure for solving an inversion problem is the necessity of a previous empirical determination of some parameters controlling the annealing process with this aim a simulation of a joint inversion of synthetic surface wave dispersion data has been performed after that path averaged velocity dispersion curves corresponding to a hercynian area of the iberian peninsula have been inverted to derive two possible crust and upper mantle elastic structures whereas the first structure has been deduced by considering as unknown variables the shear velocities of the stratified earth model the second has been obtained also including the respective layer thicknesses both structures are compared with shear velocity and q models derived by the stochastic inversion procedure in previous studies and from the same rayleigh waves dataset finally advantages and shortcomings of the inversion of phase and group velocity data by means of simulated annealing are discussed

a direct method for assimilating sea surface height data into ocean models with adjustments to the deep circulation abstract there is as yet no consensus an the best method for inserting surface data into ocean models so that appropriate information is transmitted to the deeper layers in a rapid and efficient manner first we consider the correlation of sea surface pressure which is related to sea surface height as measured by altimeters and the surface and subsurface currents within the framework or a four layer quasi geostrophic model we begin by suggesting that the homogenization of potential vorticity q in the unforced layers discussed by rhines and young ensures that the potential vorticity anomalies in the deep ocean are weak it follows that instantaneous q information from thew deep layers may not need to be accurately known in order to reconstruct the deep eddy currents i e climatological q information may be sufficient taking the fields from the model we use the instantaneous surface streamfunction 1 data along with various approximate subsurface q climatologies and attempt to reconstruct the low

the control networks of the satellites of uranus abstract control networks of the five large satellites of uranus have been established photogrammetrically from pictures taken by the voyager 2 spacecraft the control networks cover the illuminated southern hemisphere of each satellite coordinates are listed for 103 points on miranda 52 points on ariel 43 points on umbriel 46 points on titania and 34 points on oberon some points are identified on the u s geological survey maps of these satellites miranda is ellipsoidal in shape with radii of 241 235 and 232 km mean radii are 579 km for ariel 586 km for umbriel 790 km for titania and 762 km for oberon

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

dynamic transfer of simulated altimeter data into subsurface information by a numerical ocean model a global eddy resolving capability to predict the ocean circulation is technologically feasible within the next decade for this purpose the satellite altimeter is the most promising operational source of oceanic data with global coverage but only at the surface a comparable source of subsurface data is not on the horizon this investigation demonstrates the ability of a numerical ocean model to dynamically transfer simulated altimeter data into subsurface information this was done for a variety of dynamical regimes with 1 barotropic baroclinic mixed and episodic instabilities 2 flat bottoms or large amplitude topography 3 relatively vigorous or gentle exchange of energy between the layers and 4 major time scales that are short 60 days long 1 year or both in all cases the pattern of the deep pressure field is much different from the one for the current related variations in the sea surface elevation and sometimes not obviously related to it the model was able to reconstruct the deep pressure field even in situations with energetic shallow and deep circulations baroclinic instability and a vigorous vertical exchange of energy however in such experiments the frequency of updating for the free surface elevation was critical in this study the maximum update interval that allowed successful dynamic surface to subsurface transfer was about half the shortest major time scale smts e g 50 60 days in the experiments with baroclinic instability without knowledge of the deep pressure field numerical predictions of the surface pressure field and the depth of the pycnocline typically were better than climatology for 1 4 to 1 2 the smts but with successful dynamic surface to subsurface transfer forecasts without updating were better than climatology for the smts or more the time scale for predictive skill can be substantially longer than the maximum update interval permitted because the update interval must be short enough to allow decreasing error in the deep pressure field from one free surface update to the next until the error asymptotes at some acceptable level approximately 30 50 in these results forecasts of nondispersive isolated eddies with beta rossby number o 1 demonstrated predictive skill for 3 months or more even when the subsurface initial state was unknown a serendipitous result of the study is some progress in understanding the generation of cyclonic eddies associated with the loop current in the eastern gulf of mexico section 5 5

observational evidence of salt lens formation in the iberian basin the quasi synoptic picture of the mesoscale eddy field off portugal is presented on the basis of recent hydrographic measurements the dynamic topography and the salinity field at middepths 900 1300 m is shown to be dominated by several isolated meddy structures superimposed on a general east west gradient deduced from the actual dynamical situation there is evidence for meddy generation in this region numerical process studies demonstrate the possibility of vortex formation by baroclinic instability of a northward middepth jet of mediterranean water and by fragmentation of larger scale mediterranean water blobs

variational assimilation of geosat data into an eddy resolving model of the gulf stream extension area abstract a variational inverse technique is applied to assimilate sea surface height ssh measurements into a simple eddy resolving quasigeostrophic ocean model the data used were measured by geosat in the spring of 1987 in an area in the gulf stream extension the assimilation technique minimizes the weighted least squares difference between model and observations while the dynamical model equations are satisfied exactly fitting the model to data by applying the adjoint technique allows us not only to solve for the best model trajectory in phase space but also the wind forcing and internal model parameters describing for example diffusion or stratification the method is first tested systematically by performing a number of identical twin experiments with model produced observations a hierarchy of ocean models is then applied to test their performance in assimilating two repeat cycles of geosat sea surface height ssh measurements the most successful model is nonlinear and baroclinic it can f

imaging of shear wave velocity structure beneath iberia summary a detailed dispersion analysis of rayleigh waves propagating across the iberian peninsula is carried out the starting data are high quality long period data recorded at the broad band nars stations installed in the iberian peninsula during the iliha project we apply methods to obtain a correct selection of data and subsequent twostation surface wave velocity measurements a total of 64 teleseismic events recorded by the nars array and 143 seismic paths have been studied several techniques which provide a significant improvement in the signal to noise ratio are employed to remove higher mode interference efficiently and improve the isolation of the fundamental mode rayleigh wave from the seismograms thereafter the interstation rayleigh wave phase and group velocities are determined we perform simultaneous inversion of phase and group velocity dispersion data by means of the stochastic inverse operator and test the reliability of the results by computing resolving kernels and also by forward modelling a regionalization procedure based on the backus gilbert approach for linear inversion of traveltime data is applied both the inversion results and the contoured shear wave velocity panoramas display the main features of the deep structure of iberia we find a subcrustal low velocity channel which extends over practically the whole peninsular area and spans a depth interval of approximately 40 50 km it exhibits velocities of between 4 30 and 4 50 km s at depths of 66 81 km we find the highest velocities in the lithosphere which reach values of 4 85 km s in many cases the low velocity channel of the asthenosphere spans a large depth interval of approximately 80 180 km it shows the lowest velocity values computed by us we find velocities decreasing with depth which are of the order of 4 25 4 36 km spl for the first 40 km and of the order of 4 00 4 25 km s for the rest the upper mantle under the asthenosphere exhibits high velocities which range between 4 62 and 4 82 km sc1 in most cases the shear wave velocity structure of the iberian subcrustal lithosphere and asthenosphere is mapped at 11 depth intervals from 24 to 201 km at the top of the mantle relatively low velocities span the ebro valley and also the southern third of the peninsula low velocities appear in the south southwest quadrant and high velocities occur over the hercynian basement at greater lithospheric depths very low velocities extending over the whole peninsula suggest a low velocity channel of non uniform lateral structure where a reduced zone to the west of the iberian plateau shows relatively high velocities at the greatest lithospheric depths the whole iberian block is fairly homogeneous laterally the asthenosphere shows a notable lateral heterogeneity as well we distinguish two parts the upper asthenosphere a 40 km thick layer with predominant velocity values of 4 25 km spl or more and the lower asthenosphere a 60 km thick layer with velocity values generally below 4 25 km sf the upper asthenosphere seems to be less laterally heterogeneous than the lower asthenosphere the lower asthenosphere exhibits a more pronounced negative velocity gradient than the upper asthenosphere

radii shapes and topography of the satellites of uranus from limb coordinates abstract limb coordinates are used to find the radii shapes and local topography of the five large satellites of uranus the technique provides a direct measure of ellipsoidal shapes of satellites and fixes radii to subpixel accuracy umbriel titania and oberon are best fit by spheres miranda and ariel are ellipsoids whose equatorial bulges are consistent with published mean densities limb topography on miranda shows substantial deformation of both old cratered terrain and the younger coronae and complex faulting and uplift at the margins of the coronae the maximum deformation is about 10 km umbriel s limb shows a basin of undetermined origin about 500 km across and 6 km deep

shear velocity structure beneath the iberian massif from broadband rayleigh wave data abstract up to a few years ago dispersion analyses of surface waves across the iberian peninsula and adjacent zones were based on analog data recorded at the long period iberian stations the installation of the nars array on iberian territory for a period of one year has provided a greater station density than was previously available with the very few permanent long period seismological stations installed on the peninsula the nars array also provided quality digital records and increased the path coverage for two station surface wave velocity measurements fundamental mode rayleigh waves recorded at broadband stations belonging to this array have been analyzed to produce phase and group velocity dispersion curves for the period range 10 90 s with the dataset now available the elastic structure beneath the iberian massif has been investigated in terms of the shear velocity distribution as a function of depth time variable filtering is employed to remove higher mode interference efficiently and to improve isolation of the fundamental mode rayleigh wave from the seismograms multiple filtering is then used to compute group velocities at each station the interstation rayleigh wave group velocity can thus be easily calculated frequency domain wiener deconvolution is used to determine the interstation phase velocity we perform inversion of velocity dispersion data containing both rayleigh wave phase velocities and group velocities according to the generalized inversion theory by means of the stochastic inverse operator the theoretical models for the lower crust and uppermost mantle beneath the iberian massif obtained by joint inversion show a continental lithosphere with a thickness of 81 km the crustal and subcrustal velocities are greater than in other areas of the iberian peninsula the asthenosphere appears as a layer 100 km thick defined by very low velocities when compared with the rest of the peninsular area both the lithosphere and the asthenosphere exhibit a low velocity channel in the lithosphere a subcrustal low velocity channel has velocity constrained between 4 33 and 4 62 km s 1 in the asthenosphere the low velocity channel is constrained between 4 13 and 4 36 km s 1

processing and inversion of long period surface wave data collected in the iberian peninsula summary several filtering techniques have been used to remove the effects of multipathing and modal contamination and to isolate the fundamental mode from rayleigh wavetrains group velocity data are obtained by means of the multiple filter technique a time variable filter has allowed the influence of noise as well as the interference produced by higher modes to be removed multiple filtering is then used again to compute group velocities at each station the interstation group velocity for the fundamental mode rayleigh wave is estimated according to the velocities at two stations frequency domain wiener deconvolution is used to compute the phase velocity between two stations the well known three station method is applied to correct the distances travelled by the waves across the array and therefore to determine interstation phase and group velocities in a more accurate manner on the other hand lateral refraction at the atlantic continental edge of the peninsula is also studied phase velocities are corrected for the anelastic effect inversion of the interstation rayleigh wave phase velocities is then made in accordance with generalized inversion theory to obtain theoretical 2 d layered earth models in this paper these methods are applied to rayleigh waves generated by teleseismic events propagating across the iberian peninsula and recorded at wwssn stations as a consequence new and principal features for the iberian lithosphere asthenosphere system are obtained a very interesting feature of the the iberian lithosphere was found a low velocity layer directly under the moho between 39 and 64 km depth with shear velocities ranging from 4 12 to 4 37 km s 1 the iberian asthenosphere which lies between 100 and 180km depth is not an homogeneous layer and shows a negative velocity gradient from top to bottom together with a sudden increase in shear velocity beneath the low velocity zone

crustal parameters in the iberian peninsula abstract the structure of the crust in the iberian peninsula has been investigated for the last 15 years by spanish and portuguese groups in close collaboration with other european institutions the first experiments were carried out in portugal mueller et al 1973 with the aim of investigating the crustal structure of the hercynian belt in the southwest corner of the iberian peninsula other experiments have been subsequently realized to study different aspects of the crust in various regions of portugal in spain the main effort has been focused in alpine areas with the first experiments in the alboran sea and the betic cordilleras working group for deep seismic sounding in spain 1974 1975 1977 working group for deep seismic sounding in the alboran sea 1974 1975 1978 follow up experiments until 1981 completed the work in the betic cordillera extensive experiments were carried out in the pyrenees in 1978 further surveys covered the balearic islands in 1976 the valencia trough in 1976 and 1983 and the celtiberian chain or iberic system in 1981 the hercynian belt has only been studied in detail in the northwest corner of spain in 1982 with smaller studies in the central iberian massif in 1976 and 1986 mostaanpour 1984 has compiled some crustal parameters crustal thickness average crustal velocity and pn velocity for western europe meanwhile more complete data are available for the iberian peninsula the results presented here were derived from a large number of seismic refraction experiments which have been carried out mostly along or close to coastal areas of the iberian peninsula offshore explosions of various sizes were used as the energy source in most cases in addition to some quarry blasts unfortunately this leaves most of the inner part of the iberian peninsula unsurveyed our purpose is to summarize some of the crustal parameters obtained so far and to detail the appropriate literature for the interested reader

elastic anelastic regional structures for the iberian peninsula obtained from a rayleigh wave tomography and a causal uncoupled inversion the elastic and anelastic structure of the lithosphere and asthenosphere of the iberian peninsula is derived by means of tomographic techniques applied to local phase and group velocities and local attenuation coefficients of rayleigh wave fundamental mode the database consists of surface wavetrains recorded at the broadband stations located in the iberian peninsula on the occasion of the iliha project path averaged phase and group velocities and attenuation coefficients were previously obtained by standard filtering techniques of surface wavetrains and subsequently local dispersion curves were computed according to the yanovskaya ditmar formulation first a principal component analysis pca and the average linkage al clustering algorithm are applied to these local values in order to classify the iberian peninsula in several rather homogeneous domains from the viewpoint of the similarity of the corresponding local dispersion curves without previous seismotectonic constraints second averaged phase and group velocities and attenuation coefficients representing each homogeneous region are used to derive the respective elastic and anelastic models of the lithosphere and asthenosphere this purpose is achieved by using the uncoupled causal inversion of phase and group velocities and attenuation coefficients the main features of the homogeneous regions are discussed by taking as reference the hercynic alpine and neogene domains of the iberian peninsula and two questions affecting the reliability of the elastic anelastic models are revised first the coherence of the shear velocity and q 1 models obtained by causal uncoupled inversion for each region is analysed second the influence of the causal phase and group velocities on the shear velocity models is evaluated by comparing elastic and anelastic models derived from causal uncoupled inversion with those deduced from non causal inversion

shear wave velocity tomography of the lithosphere asthenosphere system beneath the mediterranean area abstract the purpose of this study is deriving a 3d tomographic image of the shear wave velocity structure of the lithosphere asthenosphere system of the mediterranean region from rayleigh wave fundamental mode dispersion data the database consists of almost 200 wavetrains corresponding to regional events recorded at the mednet very broad band stations placed in the mediterranean area on the basis of the path averaged group velocities derived for each epicentre station trajectory local group velocities over the area covered by the seismic paths have been obtained for the 10 90 s period range by means of yanovskaya s formulation for laterally heterogeneous media according to the resolution of these local velocities a grid of 1 of latitude per 1 of longitude has been defined over the mediterranean area and a local group velocity dispersion curve has been then assigned to each gridpoint the stochastic inversion of almost 450 local dispersion curves permits deriving the respective 1d shear velocity structures from which the elaboration of a 3d tomographic image of the lithosphere asthenosphere system of the mediterranean region is straightforward as expected taking into account the complexity of this area the shear velocity model reveals significant lateral changes in the crust and uppermost mantle elastic structure as a main feature low shear velocities are deduced for most part of the central and eastern mediterranean basin at shallow depths down to 35 40 km whereas significantly higher velocities are obtained for the basins of the western mediterranean at this depth range this velocity pattern suggests a thicker crust in the centraleastern part with a greater thickness of sedimentary layers on account of the lower velocities deduced for the uppermost levels on the contrary for depths 80 km low shear velocities are obtained towards the west while the highest shear velocities are derived for the eastern mediterranean sea the aegean sea greece the centre and the south of the italian peninsula and the adriatic sea sicily and tunisia the velocity pattern at this depth range suggests a deeper beginning of the asthenosphere varying between 100 and 150 km under these areas while a shallower top around 70 km depth is found beneath the western mediterranean sea the areas where a thicker lithosphere has been deduced depict the main contact between the eurasian and african plates this feature being related to the collision and subduction processes linked to the convergence of both lithospheric plates

crust and upper mantle structure of the central iberian meseta spain summary quarry blasts recorded along three lines on the central iberian meseta are used in an attempt to interpret the crustal structure the results of the interpretation of the data together with published surface wave and earthquake data suggest a layered structure of the crust having the following features the basement in some areas covered by up to 4 km of sediments has a p velocity of 6 1 km s 1 a low velocity layer between 7 and 11 km depth seems to exist on the basis of both p and s interpretation of seismic data a thick middle crust of 12 km has a p velocity of 6 4 km s 1 and overlies a lower crust with a mean p velocity of 6 9 km s 1 and a possible slight negative gradient the mean vp vs ratio for the crust is about 1 75 the moho is reached at about 31 km depth and consists of a transition zone at least 1 5 km thick the p velocity of the upper mantle is close to 8 1 km s 1 and the s velocity about 4 5 km s 1 which gives a vp vs ratio of 1 8 for the uppermost mantle a tentative petrological interpretation of the velocities and composition of the layers is given

assimilation of altimeter data into an ocean circulation model space versus time resolution studies abstract one of the most important forthcoming synoptic datasets for ocean circulation studies will he the sea surface height data provided by the topex poseidon satellite the topex poseidon project is in the planning stage and must still decide upon the particular characteristics of the satellite track the repeat period will be between 10 and 20 days for a variety of technical and strategic reasons these choices win give a global coverage with spatial resolution east west or north south separation of crossover points in midlatitudes of roughly 2 8 of latitude and longitude for a 10 day repeat orbit and 1 4 of latitude and longitude for a 20 day repeat orbit thus the crucial question we address in the present study is what is the effect of changing space or time resolution or both upon the success of a numerical model in reconstructing a four dimensional picture a the ocean circulation through the assimilation of altimetric data to answer this question we carry out a series of numerical experi

deep structure of the iberian peninsula determined by rayleigh wave velocity inversion summary a rigorous study of velocity dispersion of surface waves generated by teleseismic events propagating across the iberian peninsula and traversing main geological units has been carried out from a set of selected analogue data as digital records have only become available recently dispersed seismic signals have been obtained over a period of 16 years between 1967 and 1982 at the five iberian stations having long period instruments in our study we have considered many earthquakes thus obtaining a fairly good path coverage of most of the peninsula for two station rayleigh wave velocity measurements in all cases the approach azimuths of the wavefronts were carefully checked several digital filtering techniques have been employed to remove the effects of multipathing and modal contamination and to isolate the fundamental mode from rayleigh wavetrains thus we have obtained good estimates for both phase and group velocities a time variable filter has reduced the influence of noise and removed higher mode interference multiple filtering is then used to compute group velocity frequency domain wiener deconvolution is used to compute the interstation phase velocity the determined average rayleigh wave velocities reveal differences in the propagation conditions of the seismic energy across the peninsula a mapping of velocities for various periods of reference together with a mapping of errors in velocity are the basis for obtaining the rayleigh wave velocity distribution in the peninsula theoretical 2 d layered earth models are obtained by joint inversion of phase and group velocity dispersion curves using the stochastic inverse operator in our inversion scheme we use velocities corrected for anelastic effects finally a 3 d mapping of s velocity is performed this study shows important regional features of the deep structure of iberia we see small lateral inhomogeneities and also two low velocity layers one with shear velocities usually ranging from 4 23 to 4 31 km s 1 directly under the moho and another the asthenosphere with a negative velocity gradient for depths between 81 and 181 km terminated at the bottom by a sharp discontinuity

first two station rayleigh wave velocity measurements for the northern iberian region abstract up to now dispersion analysis of surface waves across the iberian peninsula and adjacent zones has been based on analog data recorded at the long period iberian stations also the northern region of the peninsula has never been investigated due to the lack of seismological stations with the iliha data set now available it is possible to investigate the northern part of iberia from quality digital records to efficiently remove higher mode interference and to improve isolation of the fundamental mode rayleigh wave from the seismograms time variable filtering is employed once the signal is filtered multiple filtering is then used to compute group velocities at each station the interstation rayleigh wave group velocity can thus be easily calculated frequency domain wiener deconvolution is used to determine the interstation phase velocity we carried out inversion of velocity dispersion data containing both rayleigh wave phase velocities and group velocities according to the generalized inversion theory by means of the stochastic inverse operator the theoretical 2 d earth models determined by joint inversion allow us to obtain for the first time the distribution of the shear wave velocity both laterally and with depth for the northern iberian region and to emphasize the main features of the crust mantle structure of this area

2 5 dimensional tomography of uppermost mantle beneath sichuan yunnan and surrounding regions abstract we examine the pn and sn travel time data with long and short epicentral distance ranges separately and obtain 2 5 dimensional tomographic models for the uppermost mantle velocity and the vp vs ratio beneath the sichuan yunnan and adjacent regions the tomographic models show that the average vp and vs of the upper layer are approximately 8 10 km s and 4 60 km s and those of the deeper layer are 8 19 km s and 4 65 km s respectively the average velocity ratio is 1 76 under the study area a comparison of the pn and sn velocity distribution reveals that the high and low velocity anomalies are consistent high velocity and low vp vs ratios exist in the sichuan basin and low velocity and high ratios distribute in the myanmar yunnan songpan ganzi and hainan regions respectively our models provide more evidence for the subduction of the indian plate beneath the myanmar yunnan region and the existence of the hot material upwelling beneath the hainan region in our velocity model there is a significant difference between the southern and the northern parts of the yunnan region i e north and south of 26 n we infer that these regions are controlled by different dynamic processes the velocity distributions at different depths are mainly similar in most of the regions of the study area and the differences between the upper layer and the deeper layer beneath the yunnan region indicate that the heat flow from the upper mantle has complex characteristics

upper mantle anelasticity and tectonic evolution of the western united states from surface wave attenuation rayleigh wave phase and group velocities and attenuation coefficients in the period range 18 to 120 s have been determined for three regions along nine paths across the western united states using a two station technique the attenuation coefficients were found to increase from east to west between the rocky mountains and the pacific coast rayleigh wave group and phase velocities were inverted using a differential procedure to obtain shear wave velocity models for three regions these velocity models were then used in an inversion process where q 1 as a function of depth was obtained from observations of rayleigh wave attenuation the inversion results show that q values in the upper mantle of the western united states are lowest for the coastal regions and westernmost basin and range and highest for the rocky mountains and western great plains intermediate q values appear to occur in the upper mantle beneath the basin and range province and the columbia and colorado plateaus although uncertainties in the data prevent a clear separation between that region and coastal regions low values of q occur in the upper crust higher values in the lower crust and highest values in the uppermost 20 km of the mantle of all these regions these overlie an upper mantle low q zone in which q values decrease from east to west lowest values 15 20 being similar to those observed above descending slabs in the western pacific the regional pattern of upper mantle shear wave q values is similar to that observed for upper crustal shear wave q values inferred from surface wave studies and for lg coda q values the patterns of upper crustal and upper mantle q variations correlate with the temporal sequence of tectonic and magmatic activity in the western united states lowest q values in both depth ranges occurring where tectonic activity has been most recent partial melting and or enhanced dislocation motion in the mantle and variations in the volume of interstitial hydrothermal fluids in cracks in the upper crust may both be ultimately due to processes which occurred during plate consumption and interaction near the western margin of the united states

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

a quasi synoptic survey of the thermocline circulation and water mass distribution within the canary basin shipboard hydrographic measurements and moored current meters are used to infer both the large scale and mesoscale water mass distribution and features of the general circulation in the canary basin we found a convoluted current system dominated by the time dependent meandering of the eastward flowing azores current and the formation of mesoscale eddies at middepths several distinctly different water masses are identified subpolar mode and labrador sea water are centered in the northwest subantarctic intermediate water is centered in the southeast and the saltier warmer mediterranean tongue lies between them mesoscale structures of these water masses suggest the presence of middepth meanders and detached eddies which may be caused by fluctuations of the azores current

seismic imaging of the western iberian crust using ambient noise boundaries and internal structure of the iberian massif abstract we present new rayleigh wave dispersion maps of the western iberian peninsula for periods between 8 and 30 s obtained from correlations of seismic ambient noise following the recent increase in seismic broadband network density in portugal and spain group velocities have been computed for each station pair using the empirical green s functions generated by cross correlating one day length seismic ambient noise records the resulting high path density allows us to obtain lateral variations of the group velocities as a function of period in cells of 0 5 0 5 with an unprecedented resolution as a result we were able to address some of the unknowns regarding the lithospheric structure beneath sw iberia the dispersion maps allow the imaging of the major structural units namely the iberian massif and the lusitanian and algarve meso cenozoic basins the cadiz gulf gibraltar strait area corresponds to a strong low velocity anomaly which can be followed to the largest period inverted although slightly shifted to the east at longer periods within the iberian massif second order perturbations in the group velocities are consistent with the transitions between tectonic units composing the massif

efficient representation of the north atlantic hydrographic and chemical distributions abstract the large scale temperature salinity oxygen and nutrient distributions of the north atlantic ocean are explored with the aim of identifying the minimum data set necessary to describe the general circulation and to identify the dominant physical characteristics a form of empirical onthogonal function principal component analysis based upon the singular value decomposition is used six modes are capable of describing 92 of the variance of the full hydrographic fields a second singular value decomposition applied to the horizontal property modes shows that there are only two independent tracers among the six used the modal reconstruction satisfactorily reproduces the large scale transport properties of the original data a clear physical interpretation of the modes has not been found but they are obviously connected to the large scale water mass characteristics of the ocean much remains to be learned about how to use such descriptions

a test of the great circle approximation in the analysis of surface waves a new way of reconstructing wave fronts is de veloped for testing the validity of the great circle approxima tion in dispersion analysis of surface waves phase and time delays between pairs of stations of an array are used to re construct the wave fronts or surfaces of equal phase this techque is applied to fundamental mode rayleigh waves recorded at the nars stations dudlag the iliha iberian lithosphere heterogeneity and anisotropy project the re sulting wave fronts are compared with the theoretical ones i e calculated assuming that the waves have traveled along the great circle path with a constant phase velocity and the angle between both fronts is calculated waves traveling mosfiy through a laterally homogeneous oceanic path before arriving to the iberian peninsula are analyzed for the fre quency range of 10 to 60 mhz these show angles up to 8 degrees between the theoretical wave fronts and the wave fronts reconstructed using the delay data this implies that we make a relative error less than 1 when calculating path averaged phase velocities ignoring the deviation of the ar rival of the wave from the great circle direction

can meddies be detected by satellite altimetry geosat exact repeat mission altimeter data have been used to estimate the sea surface height anomaly relative to a 2 year mean reference surface in the eastern north atlantic ocean horizontal maps of the sea surface height anomaly for various periods were constructed by means of an objective analysis procedure the mean sea level was approximated by the dynamic topography from climatological hydrographic data results were compared to the dynamic topography calculated from hydrographic ground truth data sampled during march 1988 on an eddy resolving station network in the iberian basin despite the low signal to noise ratio of the altimeter data in this part of the ocean the agreement of the altimeter signal with hydrographic measurements is found to be significant individual cyclonic and anticyclonic eddies in the mediterranean outflow are identified in the altimetric maps the information visible in the sea surface height is significantly correlated with the dynamic topography of the layer 500 3000 dbar containing the core of the mediterranean outflow and maximum velocities of the baroclinic eddies the successive development of the identified eddies as studied from a sequence of sea surface height maps indicates a slight westward drift of the most pronounced feature with approximately 1 9 cm s propagation velocity the inferred path of that feature is consistent with additional information from moored current meter data

shear wave velocity structure below the iberian peninsula as obtained by a detailed analysis of surface waves abstract a tentative tomography of iberia based on broadband surface wave data is performed for the first time in this paper we have complemented a previous study of the northern half of the iberian peninsula with a study of the southern half of the peninsula based on a detailed analysis of rayleigh wave dispersion now we present the first shear velocity contour maps at different subcrustal depths quality digital records provided by the nars array have been used standard techniques as multiple filtering and time variable filtering are employed to efficiently remove higher mode interference and improve isolation of the fundamental mode rayleigh wave from the seismograms and thus to calculate the interstation rayleigh wave group velocity frequency domain wiener deconvolution is used to determine the interstation phase velocity we perform simultaneous inversion of phase and group velocity dispersion data by means of the stochastic inverse operator the inversion results previously reported for the northern iberian region together with the results obtained here are used for 3 d mapping of shear wave velocity over the iberian peninsula lateral variation in velocity at five depth intervals chosen in agreement with the theoretical earth models determined by joint inversion is displayed for the lithosphere and asthenosphere of iberia

coordinates of features on the galilean satellites control nets of the four galilean satellites have been established photogrammetrically from pictures taken by the two voyager spacecraft during their flybys of jupiter in 1979 coordinates of 504 points on io 112 points on europa 1547 points on ganymede and 439 points on callisto are listed selected points are identified on u s geological survey maps of the satellites measurements of these points were made on 234 pictures of io 115 pictures of europa 282 pictures of ganymede and 200 pictures of callisto the systems of longitude were defined by craters on europa ganymede and callisto preliminary solutions have been found for the directions of the axes of rotation of the galilean satellites new mean radii have been determined as 1815 5 km for io 1569 10 km for europa 2631 10 km for ganymede and 2400 10 km for callisto

geosat data assimilation with application to the eastern north atlantic abstract an attempt is made to determine the three dimensional ocean circulation from satellite altimeter measurements by assimilating geosat sea surface height data into an eddy resolving quasigeostrophic qg model of the eastern north atlantic ocean results are tested against independent information from hydrographic field observations and moored current meter data collected during the geosat erm the comparison supports the concept of inferring aspects of the three dimensional flow field from sea surface height observations by combining altimetric measurements with the dynamics of ocean circulation models a holland type qg model with open boundaries is set up on a 2000 km 2000 km domain of the eastern north atlantic between 25 and 45 n 32 and 8 w by using a simple nudging technique about two years of geosat altimeter data are assimilated into the model every five days as space time objective analyses on the model grid the error information resulting from the analysis is used during the assim

anelastic structure of the iberian peninsula obtained from an automated regionalization algorithm and stochastic inversion abstract an automated regionalization of a reduced domain of the earth s surface without a priori seismotectonic information and the corresponding anelastic structures are achieved by means of a sequential application of a principal component analysis a clustering procedure and the stochastic inversion algorithm to anelastic attenuation coefficients of rayleigh waves our database is formed by path averaged attenuation coefficients derived from fundamental mode rayleigh waves crossing the iberian peninsula the wavetrains were recorded at the broad band stations installed some years ago in the iberian peninsula for the iliha project before the sequential application of the algorithms the area covered by the seismic paths was characterized by 22 maps of local attenuation coefficients corresponding to the 10 120 s period range all these maps were obtained by applying yanovskaya s formulation for laterally heterogeneous media to the set of path averaged attenuation coefficients mentioned above after that we divided the iberian peninsula into six homogeneous regions in terms of the local attenuation coefficients for 22 different periods and by means of the principal component analysis and the clustering algorithm we then obtained by stochastic inversion the respective anelastic structure down to a depth of 225 km for the six homogeneous regions the coefficients vary from 1 0 to 2 0 10 3 km 1 and the q 1 structures ranging from 110 10 3 to 40 10 3 suggest for five of the regions an asthenosphere with its upper and lower boundaries close to 80 and 180 km depth respectively a shallow beginning of the asthenosphere is detected for the sixth homogeneous region this range is very similar to the depths deduced from previous tomographic studies of the iberian peninsula based on rayleigh wave phase and group velocities finally correlations obtained between the regions and some seismotectonic characteristics of the peninsula are discussed it is noteworthy that we cannot associate each of the six homogeneous regions with a single hercynian alpine or neogene domain

oberon color photometry from voyager and its geological implications abstract three primary terrains are exposed at the surface of oberon average cratered terrain bright crater rays and prominent dark deposits often seen on but not restricted to crater floors we have applied hapke s 1986 icarus 67 264 280 photometric model to voyager imaging and earth based observations to determine photometric properties and colors of oberon s terrains and compare the results with those for the other uranian satellites all terrains on oberon exhibit photometric roughnesses 21 that are lunar like and similar to average global photometric roughnesses of titania and umbriel the asymmetry factors are backscattering for all terrains 0 35 g 0 20 and fall within the observed range for other uranian satellites at visual wavelengths g becomes more backscattering with decreasing single scattering albedo 0 25 0 0 61 the brightest materials on oberon are relatively neutral in color typical of materials covering other uranian satellites but the violet clear and green clear albedo ratios for the darkest terrains on oberon are atypically large for uranian satellites the variation can be modeled in terms of a binary mixture of low albedo and high albedo materials having slightly different colors oberon s leading hemisphere is dominantly covered with dark surface materials identical in color to dark deposits on crater floors while materials on the trailing hemisphere are richer in a spectrally neutral icy component with dark materials occurring in small irregular patches bright ray craters appear to have excavated into a relatively cleaner spectrally neutral icy crust dark materials at the surface may be effusive flood deposits a dark layer below the icy crust which is more exposed on the leading hemisphere due to preferential erosion by impacts or possibly exogenic in origin

improvements in the knowledge of the anelastic structure of the iberian peninsula from seismic data of the iliha project summary attenuation coefficients of rayleigh waves propagating across the iberian peninsula and quality factor models were obtained for different two station great circle paths the data used were long period wave trains contained in the seismograms provided by the iliha array installed in the peninsula in the 1980s more than 300 seismograms were analysed to obtain 14 sets of similar paths consisting of either paths totally included in one of the four pure tectonic regions or mixed paths crossing several regions we used the two station method to determine attenuation parameters r and then an inversion method to derive q 1 models the attenuation coefficients of seismic energy in the 10 120 s range are in the range 2 8 10 3 0 1 10 3 km 1 and correlate well with both previous results obtained from analogue wwssn and most seismogeotectonic characteristics of iberia the q models obtained also agree with a few models for iberia determined earlier and they show significant variations from one region to another as a general feature the values are higher in the active seismotectonic regions typical maximum of 2 6 10 3 km 1 than in the more stable ones typical maximum of 1 4 10 3 moreover the maximum of q 1 in the active regions 145 10 3 120 10 3 is higher than in the stable ones 40 10 3 100 10 3 in general both the regionalized attenuation coefficients of rayleigh waves and the quality factor models exhibit a good agreement with previously published lg wave attenuation and coda q distribution patterns in iberia

verification of geosat sea surface topography in the gulf stream extension with surface drifting buoys and hydrographic measurements altimeter data from geosat have been analyzed in the gulf stream extension area horizontal maps of the sea surface height anomaly relative to an annual mean for various 17 day intervals were constructed using an objective mapping procedure the mean sea level was approximated by the dynamic topography from climatological hydrographic data geostrophic surface velocities derived from the composite maps mean plus anomaly are significantly correlated with surface drifter velocities observed during an oceanographie experiment in the spring of 1987 the drifter velocities contain much energy on scales less than 100 km which are not resolved in the altimetric maps it is shown that the composite sea surface height also agrees well with ground verification from hydrographic data along sections in a triangle between the azores newfoundland and bermuda except in regions of high mean gradients

the mediterranean water tongue and its chlorofluoromethane signal in the iberian basin in early summer 1989 hydrographic observations from the iberian basin demonstrate the variability of water masses in upper and intermediate layers the surveyed area embraces the internal front between water masses from higher latitudes and the mediterranean outflow exhibits several isolated mediterranean eddy meddy structures at middepth and displays the virtual source region for the mediterranean water mw tongue off the portuguese continental slope the description is enhanced by additional chlorofluoromethane measurements which show anomalously high concentrations at middepth due to mixing of mw with the overlying atlantic waters in the gulf of cadiz the geostrophic stream function shows several meddylike features that not only are remarkably extended in the depth range of the mw but are also correlated with surface height anomalies

crater formation and modification on the icy satellites of uranus and saturn depth diameter and central peak occurrence depth diameters d d for fresh craters on the intermediate sized icy satellites of uranus and saturn have been determined using photoclinometry and shadow lengths and are compared with similar measurements on the terrestrial planets simple bowl shaped craters on icy satellites including those on miranda for which the highest resolution data are available are systematically 20 40 shallower than on the terrestrial planets this pronounced difference between crater depths on icy and rocky surfaces indicates that differences in impact velocity or surface gravity are not as important as the differences in mechanical properties between ice and rock in controlling simple crater morphology experimental impact studies indicate that differences in material properties such as angle of internal friction can control crater depth alternatively breccia lenses may be thicker in icy satellite simple craters complex craters on the icy satellites become significantly deeper with increasing crater diameters unlike complex craters on terrestrial planets which are nearly constant in depth central peaks and hence floor rebound are also volumetrically and morphologically more prominent than wall slumping rim collapse on the icy satellites the magnitude of viscous relaxation of very large craters e g herschel and odysseus on the icy satellites can be estimated from extrapolation of the d d fits at smaller crater diameters the transition diameter from simple to complex morphology is inversely correlated with gravity as it is on the terrestrial planets but at significantly smaller diameters than would be expected from a simple extrapolation of the terrestrial trend thus crater modification especially floor rebound is easier to initiate on icy satellites estimated effective cohesions for shocked icy material are lower by a factor of 10 20 relative to rock although estimated effective viscosities are similar the distinct systematic differences between crater morphology on icy and rocky worlds indicate that gross material property differences between rock and ices play a key role in crater formation and modification but gravity is still the primary driving force

dynamical interpolation of mesoscale flows in the topex poseidon diamond surrounding the u s joint global ocean flux study bermuda atlantic time series study site an open boundary ocean model is configured in a domain bounded by the four topex poseidon t p ground tracks surrounding the u s joint global ocean flux study bermuda atlantic time series study bats site this implementation facilitates prescription of model boundary conditions directly from altimetric measurements both t p and ers 2 the expected error characteristics for a domain of this size with periodically updated boundary conditions are established with idealized numerical experiments using simulated data a hindcast simulation is then constructed using actual altimetric observations during the period october 1992 through september 1998 quantitative evaluation of the simulation suggests significant skill the correlation coefficient between predicted sea level anomaly and ers observations in the model interior is 0 89 that for predicted versus observed dynamic height anomaly based on hydrography at the bats site is 0 73 comparison with the idealized experiments suggests that the main source of error in the hindcast is temporal undersampling of the boundary conditions the hindcast simulation described herein provides a basis for retrospective analysis of bats observations in the context of the mesoscale eddy field

crustal shear wave velocity models retrieved from rayleigh wave dispersion data in northern canada baffin island is one of the several seismically active regions in the far north of canada in 1933 a strong earthquake with m w 7 3 occurred in the region on 7 july 2009 a relatively strong earthquake with m w 6 0 occurred in the same area this earthquake was very well recorded by many modern seismic stations we systematically organized the rayleigh wave displacement records measured rayleigh wave dispersion data at 28 stations surrounding the epicenter and retrieved the s wave velocity models we used a previous model for the western quebec seismic zone as the initial model in our analyses and found that the velocities of all models at the shallow depths 15 km were obviously slower than those of the initial model in the middle crust the velocities in most models were close to those of the initial model in the directions of azimuths 171 218 and 241 the velocities in the middle crust were faster than those of the initial model in the directions of 263 279 the velocities in the middle crust were slower than those of the initial model the slowest s wave velocities in the top layers occurred in the directions of azimuths 90 and 218 these findings indicate differences in the existing crustal structures

the receiver structure beneath the ebro basin iberian peninsula abstract a model of the lithospheric structure of the eastern sector of the ebro basin has been obtained by means of an inversion of the receiver functions from teleseismic events recorded by one of the institut d9estudis catalans stations located at the northeastern iberian peninsula the technique consists of the isolation and modeling of the amplitude and travel time of the direct p teleseismic wave reverberations in a local structure and has been used for events recorded at poblet station pob placed in the southeast margin of the basin from 1994 to 1997 the analysis of pob records shows the influence of large scale heterogeneities in the wave pulses coming from azimuths crossing the catalan coastal ranges whereas a simple medium response is obtained when teleseismic waves only sample the basin the inversion of such simple receiver functions in terms of a flat layered media 2 to 3 km layer thicknesses along with a comparison of the results with previous and independent works enables us to obtain a crustal and upper mantle velocity structure for the ebro basin the preferred solution models show a strong near surface velocity gradient a nearly constant p velocity upper crust of about 5 9 km sec and a sharp velocity contrast at the crust mantle boundary located at 32 km depth overlayed by a lower crust consisting of a significant positive velocity gradient the upper mantle shows an average p velocity of about 8 0 km sec