mapping upper mantle flow beneath french polynesia from broadband ocean bottom seismic observations upper mantle structures and flow related to the south pacific superswell and to the associated short lived hotspots are investigated using seismic stations deployed in french polynesia beside island stations broadband ocean bottom seismometers bbobs have been deployed between the various polynesian archipelagos to investigate the oceanic upper mantle unperturbed by thickened crust or hotspot activity we investigate seismic anisotropy measured at bbobs stations and found it rather similar to that from island stations this confirms the ability of obs to be used for anisotropy purposes and suggests some homogeneity in the upper mantle pervasive deformation the two obs installed on the head of the society hotspot provide different anisotropy signatures than most of the other french polynesian stations one is isotropic to sks waves and the other provides a fast split direction normal to the average value observed in this area suggesting a more complex mantle flow induced by the plume upwelling

sandwave migration in monterey submarine canyon central california abstract repeated high resolution multibeam bathymetric surveys from 2002 through 2006 at the head of the monterey submarine canyon reveal a sandwave field along the canyon axis between 20 and 250 m water depth these sandwaves range in wavelength from 20 to 70 m and 1 to 3 m in height a quantitative measure was devised to determine the direction of sandwave migration based on the asymmetry of their profiles despite appreciable spatial variation the sandwaves were found to migrate in a predominantly down canyon direction regardless of season and tidal phases a yearlong adcp measurement at 250 m water depth showed that intermittent internal tidal oscillations dominated the high speed canyon currents 50 80 cm s which are not correlated with the spring neap tidal cycle observed currents of 50 cm s or higher were predominantly down canyon applying a simple empirical model flows of such magnitudes were shown to be able to generate sandwaves of a size similar to the observed ones

run up of internal waves on a gentle slope in a two layered system this paper describes the dissipative phase of internal wave run up on uniform slopes of 0 030 and 0 054 rad as observed in a series of laboratory experiments the waves were generated continuously at the interface of two miscible layers of differing density as each wave in the perodic train propagated onto the slope it steepened and developed into a solitary like wave before finally overturning surrounding fluid was engulfed into the wave as it overturned and the resulting gravitational instability produced considerable turbulence and mixing the broken wave took the form of a discrete bolus of dense fluid which propagated for some distance up the slope bulk parameters which characterize the nature of the bolus were defined and the dependence of these on the incident wave parameters and their behaviour during the run up phase were examined

turbidity current sediment waves on the submarine slopes of the western canary islands two sediment wave fields have been identified on the flanks of the western canary islands of la palma and el hierro using a high quality 2 d and 3 d dataset that includes geosea and tobi imagery 3 5 khz profiles and short sediment cores the la palma sediment wave field covers some 20 000 km2 of the continental slope and rise and consists of sediment waves with wave heights of up to 70 m and wavelengths of up to 2 4 km the wave crestlines have a complex morphology with common bifurcation and a clear sinuosity waves have migrated upslope through time cores recovered from the wave field contain volcaniclastic turbidites interbedded with pelagic hemipelagic layers the wave field is interpreted as having formed beneath unconfined turbidity currents a simple previously published two layer model is applied to the waves revealing that they formed beneath turbidity currents flowing at 10 100 cm s 1 with a flow thickness of 60 400 m and a sediment concentration of 26 427 mg l the el julan sediment wave field lies within a turbidity current channel on the southwest flank of el hierro the sediment waves display wave heights of about 6 m and wavelengths of up to 1 2 km the waves are migrating upslope and migration is most rapid in the centre of the channel where the flow velocity is highest this wave field has been formed by channelised turbidity currents originating on the flanks of el hierro

extent of the south pacific superswell 1 the south pacific superswell is known as a broad area beneath french polynesia characterized by numerous volcanic chains and very shallow seafloor compared to the depth predicted for its age by classical seafloor subsidence models so far its exact extent has not yet been established thanks to better bathymetric coverage and a specially adapted filtering method we present here a new complete and precise mapping of the superswell we show that the superswell covers a region broader than previously expected it extends between latitudes 10 n and 30 s and longitudes 130 w and 160 w and has a maximum amplitude of 680 m it is composed of two branches that display different characteristics when compared to other geophysical observations under the southern branch a dip in the geoid is observed which could be linked to upwelling in a convective mantle where the low velocity zone is located immediately below the lithosphere as indicated by tomography models under the northern branch there is a 12 m high in the geoid surface anomaly that may be explained by isostatic compensation of a mass deficiency located in the mantle at 300 km depth the northern branch could also be related to another superplume that is now going down but which was rising up 30 90 m y ago when it initiated the secondary plumes which created the line islands

very large subaqueous sand dunes on the upper continental slope in the south china sea generated by episodic shoaling deep water internal solitary waves abstract very large subaqueous sand dunes were discovered on the upper continental slope of the northern south china sea the dunes were observed along a single 40 km long transect southeast of 21 93 n 117 53 e on the upper continental slope in water depths of 160 m to 600 m the sand dunes are composed of fine to medium sand with amplitudes exceeding 16 m and crest to crest wavelengths exceeding 350 m the dunes apparent formation mechanism is the world s largest observed internal solitary waves which generate from tidal forcing on the luzon ridge on the east side of the south china sea propagate west across the deep basin with amplitudes regularly exceeding 100 m and dissipate extremely large amounts of energy via turbulent interaction with the continental slope suspending and redistributing the bottom sediment while subaqueous dunes are found in many locations throughout the world s oceans and coastal zones these particular dunes appear to be unique for two principal reasons their location on the upper continental slope away from the influence of shallow water tidal forcing deep basin bottom currents and topographically amplified canyon flows and their distinctive formation mechanism approximately 60 episodic extremely energetic large amplitude events each lunar cycle

solibore induced sediment resuspension in the faeroe shetland channel 1 high resolution measurements of temperature and current velocity over the seabed in the faeroe shetland channel fsc reveal an intense internal wave train referred to as a solibore propagating up the continental slope in addition to enhancing turbulent mixing a rotor formed at the leading edge of the solibore generates sediment fluxes o 102 greater than background levels the interaction of solibores which appear to evolve from baroclinic bores with the seabed and the resulting rotor provides a dominant mechanism for the upward transport of sediment over continental slopes that may counteract downward avalanching of material by gravity

seismic azimuthal anisotropy in the oceanic lithosphere and asthenosphere from broadband surface wave analysis of obs array records at 60 ma seafloor we analyzed seismic ambient noise and teleseismic waveforms of nine broadband ocean bottom seismometers deployed at a 60 ma seafloor in the southeastward of tahiti island the south pacific by the tomographic investigation by seafloor array experiment for the society hotspot project we first obtained one dimensional shear wave velocity model beneath the array from average phase velocities of rayleigh waves at a broadband period range of 5 200 s the obtained model shows a large velocity reduction at depths between 40 and 80 km where the lithosphere asthenosphere boundary might exist we then estimated shear wave azimuthal anisotropy at depths of 20 100 km by measuring azimuthal dependence of phase velocities of rayleigh waves the obtained model shows peak to peak intensity of the azimuthal anisotropy of 2 4 with the fastest azimuth of nw se direction both in the lithosphere and asthenosphere this result suggests that the ancient flow frozen in the lithosphere is not perpendicular to the strike of the ancient mid ocean ridge but is roughly parallel to the ancient plate motion at depths of 20 60 km the fastest azimuths in the current asthenosphere are subparallel to current plate motion at depths of 60 100 km additional shear wave splitting analysis revealed possible perturbations of flow in the mantle by the hot spot activities and implied the presence of azimuthal anisotropy in the asthenosphere down to a depth of 190 210 km

mantle transition zone structure beneath the south pacific superswell and evidence for a mantle plume underlying the society hotspot abstract underside reflections of shear waves from the discontinuities at 410 and 660 km depth are used to map lateral variations in the thickness of the mantle transition zone beneath the south pacific superswell and surrounding regions differential travel times of reflected waves indicate that the transition zone is about 25 km thinner than normal and thus hotter than normal over an area 500 km or less in diameter beneath the society hotspot there is no general difference however in transition zone thickness between the superswell area and its surroundings our observations support the inference that the thermal flux from lower to upper mantle beneath the south pacific superswell occur on the lateral scale of a mantle plume several hundred kilometers rather than that of a superplume several thousand kilometers

the foreslope hills large scale fine grained sediment waves in the strait of georgia british columbia abstract the foreslope hills are a set of 20 m high 5 km long ridges at 230 350 m water depth in the south central strait of georgia occupying a 60 km 2 area at the base of the fraser river delta foreslope they are composed of clay silt and fine sand previous authors have interpreted them as 1 a single mass slide deposit 2 mud diapirs 3 in situ rotational failures and 4 creep deformation features but collaborative evidence for these interpretations is lacking seafloor surface morphological renders derived from recent multibeam sonar bathymetry data show linear evenly spaced symmetrical ridges with ridge bifurcation resembling wave ripples but on a much larger scale detailed multichannel and single channel seismic reflection data show sinusoidal internal reflections suggesting upslope migration the ridges occur within the uppermost portion of the holocene section in a very high sedimentation rate environment consequently they are probably less than 3000 years old moored current meter records for the region show reversing currents largely oriented normal to the ridge crests averaging 10 cm s with a maximum of 50 cm s this evidence combined with increasing documentation of large scale sedimentary bedforms in slope and rise environments suggests that the foreslope hills should be re interpreted as sediment waves upslope migration is typical of many large scale fine grained sediment waves the preferred physical interpretation for the creation and maintenance of the foreslope hills as sediment waves is the lee wave model requiring a phase shift in density stratified flow as it passes over the wavy topography maximum measured bottom currents are easily strong enough to entrain silt and clay delivered to the site by turbidity currents or by sediment plume fallout from fraser river outflow either strong flood tides or severe biannual density intrusions due to their intense stratification may be susceptible to lee wave formation and the creation of sediment waves leading to the observed pattern of upslope migration

shear wave speed structure beneath the south pacific superswell using broadband data from ocean floor and islands 1 we determined three dimensional shear wave speed structure beneath the south pacific superswell down to a depth of 200 km by analyzing rayleigh wave records from broadband ocean bottom seismograph stations and island stations in the pacific ocean the ocean bottom stations were deployed from 2003 to 2005 on the seafloor in the french polynesian region which enabled us to study the upper mantle structure beneath the superswell with unprecedentedly high resolution we measured the dispersions of fundamental mode rayleigh waves at periods between 40 and 140 seconds by the two station method we found pronounced slow anomalies near the hot spots and in the lau basin the slow anomalies beneath the hot spots have deeper rooted than those associated with the lau basin the slow anomalies near the society macdonald marquesas and pitcairn hot spots continue down to at least 200 km depth

radially anisotropic 3 d shear wave structure of the australian lithosphere and asthenosphere from multi mode surface waves abstract a new radially anisotropic shear wave speed model for the australasian region is constructed from multi mode phase dispersion of love and rayleigh waves an automated waveform fitting technique based on a global optimization with the neighbourhood algorithm allows the exploitation of large numbers of three component broad band seismograms to extract path specific dispersion curves covering the entire continent a 3 d shear wave model is constructed including radial anisotropy from a set of multi mode phase speed maps for both love and rayleigh waves these maps are derived from an iterative inversion scheme incorporating the effects of ray path bending due to lateral heterogeneity as well as the finite frequency of the surface waves for each mode the new s wave speed model exhibits major tectonic features of this region that are in good agreement with earlier shear wave models derived primarily from rayleigh waves the lateral variations of depth and thickness of the lithosphere asthenosphere transition lat are estimated from the isotropic voigt average s wave speed model and its vertical gradient which reveals correlations between the lateral variations of the lat and radial anisotropy the thickness of the lat is very large beneath the archean cratons in western australia whereas that in south australia is thinner the radial anisotropy model shows faster sh wave speed than sv beneath eastern australia and the coral sea at the lithospheric depth the faster sh anomaly in the lithosphere is also seen in the suture zone between the three cratonic blocks of australia one of the most conspicuous features of fast sh anisotropy is found in the asthenosphere beneath the central australia suggesting anisotropy induced by shear flow in the asthenosphere beneath the fast drifting australian continent

changes in morphometric meander parameters identified on the karoon river iran using remote sensing data abstract river meander dynamics and mobility are important indicators of environmental change related to climate changes and anthropogenic activities at local and river basin scales the aim of the present study is to identify morphological changes of the karoon river in iran using high accuracy maps and landsat satellite images by analyses during the time period 1989 2008 in this study 20 meandering reaches were analyzed over a 128 km long river reach located in the middle part of the karoon river iran morphometric indicators such as river width w meander neck length l axis length a radius of curvature r water flow length s and sinuosity of meander c were extracted for the identified meanders the results of a paired t test showed that river width w and meander neck length l have significantly changed during the study period 1989 2008 with an increase of 3 5 m for w and a decrease of 274 m for l spearman correlation analysis has shown that meander parameter changes are highly correlated to each other the parameters that do not have significant correlation together are c with w and l w and l and l with s and a during the period of the study the flow length and river sinuosity decreased for the whole river reach by 4 77 km and 0 11 respectively analysis of land use land cover categories 1989 and 2008 using the support vector machine svm and kernel function method served as one of the tools for interpretation of the meander parameter changes these changes can be attributed not only to lu lc riparian vegetation to agriculture area ratio but also to dam construction in the upstream part of the river that leads to major hydrological regime and sediment transfer alteration sediment extraction may also be an important factor

energy of nonlinear internal waves in the south china sea 1 four sets of adcp measurements were taken in the south china sea scs these results were combined with previous satellite observations and internal tide numerical model results analysis suggests that strong internal tides are generated in luzon strait propagate as a narrow tidal beam into the scs are amplified by the shoaling continental slope near tungsha island become nonlinear and evolve into high frequency nonlinear internal waves niw internal waves in the scs have geographically distinct characteristics 1 west of luzon strait the total internal wave energy eiw is 10 that predicted by garrett munk spectra egm levine 2002 there is no sign of niw 2 near tungsha island eiw 13 egm strong nonlinear and high harmonic tides are present repetitive trains of large amplitude niw appear primarily at a semidiurnal periodicity with their amplitudes modulated at a fortnightly tidal cycle the rms vertical velocity of niw shows a clear spring neap tidal cycle and is linearly proportional to the barotropic tidal height in luzon strait with a 1 85 day time lag consistent with the travel time of internal tides from luzon strait to tungsha island 3 at the northern scs shelfbreak eiw 4 egm single depression waves are found but no multiple waves packets are evident 4 on the continental shelf eiw 2 egm both depression and elevation niw exist

broadband ocean bottom seismology broadband ocean bottom seismographs bbobss were first developed in the 1980s and have since been used to explore the structure of earth s interior beneath oceanic regions for example mid oceanic ridges subduction zones hot spots and the oceanic lithosphere asthenosphere boundary the best approach for broadband seismic observations in oceanic regions is that of a borehole seismic observatory attached to the ocean floor cable which is realized in several near coast networks considering the high cost of such networks there is still a need to develop autonomous bbobss with a better signal to noise ratio for temporary observations of focused scientific targets far from the coast

on the vertical extent of the large low shear velocity province beneath the south pacific superswell the three dimensional s wave velocity structure beneath the south pacific superswell is obtained from joint broadband seismic experiments on the ocean floor and islands we collected only approximately 800 relative times of long period teleseismic sh waves by using a waveform cross correlation from 76 events occurring from january 2003 to may 2005 we conducted relative time tomography to obtain a 3d structure to depths of 1600 km in the resultant image we find a characteristic distribution of low velocity regions the most prominent features are a large doughnut shaped low velocity region at 800 km depth and an elongated large low velocity region beneath the society to pitcairn hotspots at 1200 km depth our model suggests that a large low shear velocity province rooted in the d00 extends upwards and culminates near the top of the lower mantle beneath the central part of the south pacific superswell although its perfect continuity is not still confirmed

internal solitary waves in the coastal mixing and optics 1996 experiment multimodal structure and resuspension 1 observations of internal solitary waves isws and of their role in sediment resuspension during the coastal mixing and optics 1996 cmo 96 experiment are reported the largest resuspension events observed in the experiment can be related to retarded flow under the wave footprint two distinctly different periods of resuspension events could be distinguished based on the prevailing atmospheric conditions a calm period which we consider characteristic of nominal conditions and an energetic period during which two major storms occurred isws arrived at the mooring site from a variety of sources though a common intermodal dynamics seemed to occur repeatedly both mode 1 and mode 2 isws have been observed the present analysis of the month long portion of the cmo 96 data set constitutes the first reported observations insofar as we are aware of mode 2 waves on the continental shelf both mode 1 and mode 2 isws were found to stimulate resuspension the mode 2 waves seem to be generated locally by resonant or topographic interactions with mode 1 isws internal wave fields of the type described here are expected to exist in a variety of other shallow seas as well

numerical investigation of solitary internal wave induced global instability in shallow water benthic boundary layers abstract the time dependent boundary layer induced by a weakly nonlinear solitary internal wave in shallow water is examined through direct numerical simulation waves of depression and elevation are both considered the mean density field corresponds to that typical of the coastal ocean and lakes where the lower fraction of the water column is subject to the stabilizing effect of a diffuse stratification sufficient resolution of the inviscid dynamics of the boundary layer is ensured through use of a legendre spectral multidomain discretization scheme in the vertical direction at higher reynolds numbers where the simulations become underresolved because of restrictions in available computational resources spectral accuracy and numerical stability at the scales of physical interest are preserved through use of a penalty scheme in the vertical and explicit spectral filtering thus a highly accurate description of the qualitative dynamics of the wave induced global instability is possible and finesca

measurements of mantle wave velocities and inversion for lateral heterogeneities and anisotropy 3 inversion lateral heterogeneity in the earth s upper mantle is investigated by inverting dispersion curves of long period surface waves 100 330 s models for seven different tectonic regions are derived by inversion of regionalized great circle phase velocity measurements from our previous studies we also obtain a representation of upper mantle heterogeneities with no a priori regionalization from the inversion of the degree 6 spherical harmonic expansion of phase and group velocities the data are from the observation of about 200 paths for love waves and 250 paths for rayleigh waves for both the regionalized and the spherical harmonic inversions corrections are applied to take into account lateral variations in crustal thickness and other shallow parameters these corrections are found to be important especially at low spherical harmonic order the trench region and fast velocities down to 250 km under shields below 200 km under the oceans both s velocity and s anisotropy support a model of small scale convection in which cold blobs detach from the bottom of the lithosphere when its age is large enough the spherical harmonic models clearly demonstrate a posteriori the relation between surface tectonics and s velocity heterogeneities in the first 250 km all shields are fast most ridges are slow below 300 km a belt of fast mantle follows the pacific subduction zones however at greater depths large scale heterogeneities that seem to bear no relationship to surface tectonics are observed the most prominent feature at 450 km is a fast velocity region under the south atlantic ocean smaller scale heterogeneities that are not related to surface tectonics are also mapped at shallower depths an anomalously slow region centered in the south central pacific is possibly linked to intense hot spot activity a very fast region southeast of south america may be related to subduction of old pacific plate between 200 and 400 km a belt of sv sh anisotropy follows part of the ridge and subduction systems indicating vertical mantle flow in these regions the spherical harmonic results open new horizons for the understanding of convection in the mantle perspectives for the improvement of the models presented are discussed

three dimensional shear wave structure beneath the philippine sea from land and ocean bottom broadband seismograms 1 we obtained three dimensional 3 d shear wave speed structure beneath the philippine sea and the surrounding region from seismograms recorded by land based and long term broadband ocean bottom seismographic stations the ocean bottom data gave us a better station coverage to obtain a higher spatial resolution about 300 400 km in the philippine sea than in previous studies we employed a new technique of surface wave tomography in which multimode phase speeds are measured and inverted for a 3 d shear wave speed structure by incorporating the effects of finite frequency and ray bending there is a sharp speed contrast along the izu bonin mariana trench across which the philippine sea side has a significantly slower upper mantle than the pacific ocean side in the upper 120 km the shear wave speed structure is well correlated with the age of the provinces at depths greater than 160 km the pattern is dominated by fast anomalies of the subducted slabs of the pacific plate and two slow anomalies to the south of the daito ridge and in the southernmost part of the philippine sea

3d upper mantle structure beneath japan and its surrounding region from inter station dispersion measurements of surface waves abstract three dimensional shear wave speed structure of the upper mantle beneath the japanese islands and the surrounding regions is constructed from the measurements of inter station phase speeds of surface waves we employ the dense broad band seismic network f net deployed throughout japan as well as permanent stations of global seismic network in east asia a temporary broad band seismic network in far east russia which has been constructed as a part of the stagnant slab project since 2004 is also used in combination with the permanent stations using seismic events from 2005 to 2007 with moment magnitude greater than 6 0 and depth shallower than 100 km we measure the phase speeds of the fundamental mode rayleigh and love waves working with the conventional two station technique phase speed maps of the japanese islands and the sea of japan are obtained from the inversions of inter station phase speeds that are measured for a large number of station pairs we have collected over 5300 paths for rayleigh waves and 3800 paths for love waves the phase speed maps of rayleigh waves in the period range from 25 to 140 s are inverted to obtain an isotropic 3d shear wave speed model in the depth range from 40 to 200 km the isotropic s wave model represents prominent fast wave speed anomalies in northeastern japan associated with the subducting pacific plate fast anomalies of the lithosphere beneath the sea of japan are also imaged implying that the average thickness of lithosphere beneath the yamato rise and japan basin is about 60 10 km immediately below this oceanic lithosphere slow anomalies are found in the asthenosphere beneath the entire region of the sea of japan in the depth down to about 200 km in southwestern japan the low angle subduction of the philippine sea plate is mapped clearly indicating that the northern end of the plate extends beyond the northern coast of the chugoku region reaching beneath the oki islands in the sea of japan a strong low velocity anomaly off the west coast of kyushu is found in the depth down to about 130 km which supports the existence of an upwelling flow beneath this area we also invert the phase speed maps of rayleigh and love waves in the period range from 30 to 80 s simultaneously to construct the radially anisotropic shear wave speed model a remarkable anisotropy with sh sv is found in the mantle wedge beneath northeastern japan while only weak anisotropy is seen beneath the sea of japan such anisotropic properties which cannot readily be obtained from body wave studies only will be an important key to understanding the dynamic processes in this tectonically actively region

topography of the mantle discontinuities beneath the south pacific superswell as inferred from broadband waveforms on seafloor we analyzed seismic waveforms recorded by the broadband ocean bottom seismographs deployed in the south pacific superswell to determine the depths of the mantle discontinuities using a receiver function method we estimated the thickness of the mantle transition zone mtz to be 245 km on average beneath the superswell region which is close to the global average the mtz is found to be thinned locally beneath the society hot spot by 30 km temperature anomalies computed from the thinned transition zone and the clapeyron slope of the olivine phase transformations are 150 200 k beneath the society hot spot previous studies using land based data suggested the presence of a hot mtz beneath the pitcairn hot spot the locally hot transition zone beneath the hot spots is attributed to narrow mantle plumes probably rising from the lower mantle the normal average thickness obtained from the present study indicates that there is no broad upwelling across the transition zone beneath the entire superswell region at present

bedforms of the canadian eastern seaboard a comparison with global occurrences this paper presents a compilation of sedimentary bedforms identified from acoustic and seismic records collected over the southeastern canadian continental shelf in order to make the compilation it was found necessary to firstly review and synthesise the various terminologies used to describe the bedforms found and thereafter to relate the subsequent terminology to any diagnostic generic characteristic identifiable from the records sand waves are considered to be those forms that are composite in nature and are generated solely by the action of superimposed megaripples these latter features are identifiable adopting the classification of dalrymple et al 1978 which proves adequate for the acoustic differentiation of 2 d and 3 d types though we observed a greater coherence in bedform spacing of the 2 d types than reported hitherto sand ridges were adequately defined and recognised using the description of swift et al 1978 with respect to storm generated ridges and that of off 1963 and others with respect to tidal current ridges such ridges appear not to be uniquely described by ratios of their metrics the bedforms on the southeastern canadian continental shelf are abundant and wide spread virtually all types of bedforms recognisable on the u s shelf are present to the north the majority of these bedforms appear to be storm generated and are considered intermittently active many of the sand waves s s have no measureable relief though retaining their distinctive spatial geometry both active and moribund sand ridges were found of these ridges both tidal and storm generated types were identified the storm generated ridges were further broken down into shoreface connected ridges and offshore ridges a metrical analysis of the various bedforms show that a differentiation into stable bed phases can be made using height length ratios provided the bedforms are active and fully developed there is some overlap between megaripples and small sand waves and indeed between 2 d and 3 d megaripples yet the distinction is good between sand waves and sand ridges even moribund types sand ribbons in general can be confused with moribund sand waves and megaripples a detailed morphological examination is required to distinguish each feature data from sand ridges of the eastern canadian shelf combined with data from similar features found globally shows that ridge heights tend to cluster into three distinctive modes these modes are at heights of 7 13 and 27 m the first mode is correlated with storm generated ridges the second with tidal current ridges and the third possibly with submerged barrier islands

rayleigh wave phase velocity measurements across the philippine sea from a broad band obs array summary we obtained phase velocities of fundamental rayleigh waves in the northwestern pacific ocean and the northern philippine sea from seismograms retrieved from a long term broad band ocean bottom seismometer lt obs array deployed in 1999 2000 and from those recorded in japan guam and ponape islands this array observation was one of the first attempts to record continuous seismograms on the seafloor using broad band seismographs on a long term basis the geographical distribution of the lt obs stations and the surrounding land stations enabled us to determine pure path phase velocities in a frequency range from 0 01 to 0 05 hz across the mariana trough the parece vela basin the shikoku basin and the minami daito basin which were found to be systematically lower than those of the pacific seafloor at comparable ages this result along with other geophysical and geological observations in the philippine sea may be explained by an uppermost mantle that is relatively fe rich

three dimensional s wave structure of the upper mantle beneath turkey from surface wave tomography summary a 3 d upper mantle structure beneath turkey is investigated using phase speeds of fundamental mode rayleigh waves employing a conventional two station method with high density seismic networks in turkey we analyse 289 seismic events with moment magnitude 5 5 and greater and with focal depth shallower than 100 km between 2006 and 2008 waveform data are derived from 164 three component broad band seismic stations operated by two national seismic networks at first rayleigh wave phase speed maps are obtained from the inversion of two station phase speeds using about 1000 3000 paths depending on the period of rayleigh waves the three dimensional s wave model is then obtained in the depth range from 40 to 180 km using the phase speed maps in the period range from 25 to 120 s our model reveals the fast anomalies in the north of cyprus associated with the subducted portion of the african oceanic lithosphere from the cyprus trench we identify a vertical discontinuity of the fast anomaly associated with the cyprus slab starting at 60 80 km depth which may represent a minor tear of the cyprus slab we observed that the western part of the cyprus slab is getting closer to the edge of the hellenic slab beneath the isparta angle ia and antalya basin our model also indicates a slow wave speed anomaly beneath the ia and antalya basin probably due to hot materials of asthenosphere rising from a tear of the subducted african oceanic lithosphere that is a slab tear between the cyprus and the hellenic subductions in the eastern part of turkey a widespread slow anomaly appears in the model that corresponds to the eastern anatolian accretionary complex eaac our model shows a fast anomaly beneath the eaac that can be interpreted as the detached portion of the subducted arabian lithosphere

thickness of the mantle transition zone beneath the south pacific as inferred from analyses of scs reverberated and ps converted waves abstract we study the thickness of the mantle transition zone beneath the south pacific in order to determine temperature anomalies associated with presumed hot plumes in the south pacific superswell the scs reverberation method is used to determine the average thickness between an event station pair and the velocity spectrum stacking vss method is used to determine the thickness near each station the thickness obtained by the scs reverberation method shows that the average thickness beneath the superswell is less than the globally averaged thickness by 6 km while the average thickness beneath the tonga fiji subduction is greater than the global average by 10 km the vss method shows nearly normal thickness beneath stations used in the superswell region we conclude that substantial thinning of the transition zone associated with presumed hot plumes occurs locally beneath the society hot spot as revealed by our previous ss precursor study and is not widespread beneath the whole area of the superswell

south pacific hotspot swells dynamically supported by mantle flows the dynamics of mantle plumes and the origin of their associated swells remain some of the most controversial topics in geodynamics here we construct a numerical model of the mantle flow beneath the french polynesia region our study is based on a new regional seismic tomography model which high resolution allows obtaining information at the scale of plumes we find excellent correlations between the observed and the modeled dynamic swells between the modeled flow pattern and the active volcanism and between the buoyancy fluxes obtained from our numerical model and the ones deduced from the swells morphology these outstanding fits reveal for the first time that a direct link exists between the surface observations and mantle flows