deep structure of the bohemian massif from phase velocities of rayleigh and love waves phase velocities of rayleigh and love waves have been measured between the broadband seismic stations khc kasperske hory south bohemia and ksp ksi z lower silesia a profile that nearly coincides with the interactional dss profile vii the data for both wave types were separately inverted into models of shear wave velocity versus depth novotn s model khks 82 1 for the dss profile vii was used as a start model while the crustal section of novotn s model is compatible with both of our data sets our rayleigh wave data require smaller shear wave velocities on the average by 0 24 km s in the top 180 km of the mantle the average difference between novotn s model and our love wave model in that depth range is only 0 06 km s if our identification of the observed love waves as the fundamental mode is correct this result indicates the presence of polarization anisotropy in the uppermost mantle

an empirical model of tropical ocean dynamics to extend the linear stochastically forced paradigm of tropical sea surface temperature sst variability to the subsurface ocean a linear inverse model lim is constructed from the simultaneous and 3 month lag covariances of observed 3 month running mean anomalies of sst thermocline depth and zonal wind stress this lim is then used to identify the empirically determined linear dynamics with physical processes to gauge their relative importance to enso evolution optimal growth of sst anomalies over several months is triggered by both an initial sst anomaly and a central equatorial pacific thermocline anomaly that propagates slowly eastward while leading the amplifying sst anomaly the initial sst and thermocline anomalies each produce roughly half the sst amplification if interactions between the sea surface and the thermocline are removed in the linear dynamical operator the sst anomaly undergoes less optimal growth but is also more persistent and its location shifts from the eastern to central pacific optimal growth is also found to be essentially the result of two stable eigenmodes with similar structure but differing 2 and 4 year periods evolving from initial destructive to constructive interference variations among enso events could then be a consequence not of changing stability characteristics but of random excitation of these two eigenmodes which represent different balances between surface and subsurface coupled dynamics as found in previous studies the impact of the additional variables on lim sst forecasts is relatively small for short time scales over time intervals greater than about 9 months however the additional variables both significantly enhance forecast skill and predict lag covariances and associated power spectra whose closer agreement with observations enhances the validation of the linear model moreover a secondary type of optimal growth exists that is not present in a lim constructed from sst alone in which initial sst anomalies in the southwest tropical pacific and indian ocean play a larger role than on shorter time scales apparently driving sustained off equatorial wind stress anomalies in the eastern pacific that result in a more persistent equatorial thermocline anomaly and a more protracted and predictable enso event

segmentation of the nazca and south american plates along the ecuador subduction zone from wide angle seismic profiles we describe the deep structure of the south colombian northern ecuador convergent margin using travel time inversion of wide angle seismic data recently collected offshore the margin appears segmented into three contrasting zones in the north zone affected by four great subduction earthquakes during the 20th century normal oceanic crust subducts beneath the oceanic cretaceous substratum of the margin underlined by seismic velocities as high as 6 0 6 5 km s in the central zone the subducting oceanic crust is over thickened beneath the carnegie ridge a steeper slope and a well developed high velocity cretaceous oceanic basement characterizes the margin wedge this area coincides with a gap in significant subduction earthquake activity in the south zone the subducting oceanic crust is normal the fore arc is characterized by large sedimentary basins suggesting significant subsidence velocities in the margin wedge are significantly lower and denote a different nature or a higher degree of fracturing even if the distance between the three profiles exceeds 150 km the structural segmentation obtained along the ecuadorian margin correlates well with the distribution of seismic activity and the neotectonic zonation

seabeam and seismic reflection imaging of the tectonic regime of the andean continental margin off peru 4 s to 10 s abstract marine geophysical surveys employing seabeam multi and single channel seismic reflection gravity and magnetic instruments were conducted at two locations along the continental slope of the peru trench during the seaperc cruise of the r v jean charcot in july 1986 these areas are centered around 5 30 s and 9 30 s off the coastal towns of paita and chimbote respectively these data indicate that 1 the continental slope off peru consists of three distinct morpho structural domains from west to east are the lower middle and upper slopes instead of just two as previously reported 2 the middle slope has the characteristics of a zone of tectonic collapse at the front of a gently flexured upper slope 3 the upper half of the lower slope appears to represent the product of mass wasting 4 thrusting at the foot of the margin produces a continuous morphologic feature representing a deformation front where the products of mass wasting are overprinted by a compressional tectonic fabric 5 a change in the tectonic regime from tensional to compressional occurs at the mid slope lower slope boundary the accretionary prism being restricted to the very base of the lower slope in the paita area the andean margin off peru is an extensional active margin or a collapsing active margin developing a subordinated accretionary complex induced by massive collapse of the middle slope area

upper mantle structure under western europe from fundamental and higher mode surface waves using the nars array summary a generalized inversion of a new data set consisting of surface wave phase velocities and sn traveltimes has resulted in a new shear velocity and density model for the west european platform wepl 2 the surface wave phase velocity data set consists of fundamental and higher mode mode 1 6 measurements from 25 to 70mhz using the network of autonomously recording stations nars array which was specifically designed for higher mode surface wave measurements the sn traveltime data set consists of isc readings for selected european events major features of wepl 2 are a high velocity lid of 80 140 km depth underlain by a pronounced low velocity zone between 160 and 220 km depth the transition zone 400 650 km depth is characterized by high shear velocities with respect to prem the density shows a positive gradient from 60 to 140 km depth followed by an approximately constant value down to 400 km depth a model for the baltic shield scsh 2 is obtained by combination of nolet s 1977 higher mode phase velocity data set for western europe including the baltic shield and the present phase velocities for the platform this shield model shows an absence of the low velocity layer and low shear velocities in the top of the transition layer with respect to wepl 2 density although less well resolved shows lower values for the shield structure between 200 and 350 km depth

an asymptotic expansion for the recharge discharge model of enso abstractthe dynamics of el nino southern oscillation enso in the equatorial pacific ocean are largely associated with the slow thermocline adjustment at interannual and basin scales this adjustment involves among other things the fast propagation and reflection of equatorial waves by wind stress forcing a simple and straightforward asymptotic expansion of the long wave equations is proposed using the low frequency approximation the asymptotic expansion is performed in fourier space retaining only the gravest equatorial long waves and baroclinic modes with the largest scale and considering small dissipation by friction and boundary reflections this leads to an asymptotic model for the thermocline response to wind stress forcing which is in essence the ocean component of the recharge discharge model of enso the asymptotic model is nonheuristic and in broad agreement with some essential results scattered in previous studies thermocline variability is divided into a sloping tilt mode that adjus

development of the accretionary prism along peru and material flux after subduction of nazca ridge results from ocean drilling program leg 112 indicated tectonic erosion of the peruvian convergent margin during subduction of the nazca ridge followed by renewed accretion against the erosional scar seismic images and swath mapping morphology show a regional geology shaped as subduction of nazca ridge migrated 800 km along the peru trench the accretionary prism is imaged at two stages of development since upper miocene time with depth migrated seismic records in which the back stop is well defined from these data material flux can be quantified after the ridge crest subducted and accretion dominated over erosion the prism grew rapidly to 10 to 15 km width during rapid growth the margin taper was large and about 60 percent of the sediment supply accreted as the prism growth slowed only 30 percent accreted despite an increased trench sediment supply since the convergence rate changed little the inverse relation between sediment supply and prism growth rate suggests that other processes allow most of the sediment input to be subducted the decreased prism growth may be partially controlled by varying the structure of the back stop the force required to activate faults cutting across the back stop is probably greater than the force allowed by basal friction across the plate boundary thus the shear stress transmitted across the plate boundary is insufficient to drive out of sequence thrust faults that would thicken the back stop or raise it beyond a limited height a constant back stop height limits accretion and the subduction window appears to open and accommodate increased trench sediment beneath the back stop rather than inducing a transport of sediment over the top of the back stop nazca ridge subduction affected the convergent margin mass flux for about 8 ma mass balancing indicates an order of magnitude increase in the current sediment volume subducted in the north compared to that near the ridge crest when growth of the accretionary prism slowed a greater terrigenous input through the trench was accommodated by sediment subduction the resulting range of material flux is estimated to increase the sediment interlayer between the plates about 500 m which may affect coupling

seismic anisotropy of the pacific ocean inferred from long period surface waves dispersion abstract the dispersion of surface rayleigh and love waves in the period range 40 300 s along a large number of paths allows the estimation of both the azimuthal anisotropy and the shear wave polarization anisotropy the regional dispersion is determined taking into account simultaneously its dependence with age and an azimuthal factor the pacific ocean has been divided into 5 regions for rayleigh waves and into 3 regions for love waves this partition discriminates the regions of extreme age which show a fast variation of dispersion with age from the regions of intermediate age where the variation is weak a variation of 2 of rayleigh wave group velocity with the azimuth of the path measured with respect to the direction of spreading is displayed up to very long period on the contrary the azimuthal anisotropy for love waves is difficult to resolve for rayleigh waves the present day direction of plate motion seems to agree best with the direction of maximum velocity on the other hand the isotropic inversion of the regional dispersion curves indicates except for young regions a discrepancy between rayleigh wave and love wave models with this hypothesis sh velocities are higher than sv velocities for the regions older than 23 ma down to a depth of 300 km which is indicative of the presence of polarization anisotropy the latter very weak for the young part of the ocean increases with age and reaches 7 for the oldest region

density versus depth models from multimode surface waves multimode love and rayleigh wave data related to the pacific ocean and to north america are inverted using two sets of parameters 1 the isotropic p and s velocities plus the density and 2 five elastic parameters describing a transversely isotropic medium plus the density it is found that the assumption of isotropy leads to very unrealistic upper mantle models while much more realistic models are obtained under the assumption of transverse isotropy the lateral variations in density between the pacific ocean and north america are then less than 1 5 and in both regions a large density gradient is well resolved at a depth near 360 km

mapping the lithosphere asthenosphere boundary through changes in surface wave anisotropy abstract the alignment of olivine crystals is considered as the dominant source of seismic anisotropy in the subcrustal lithosphere and asthenosphere different components of large scale anisotropy can be traced in depth distributions of the radial and azimuthal anisotropy of surface waves we propose a global model of the lithosphere asthenosphere boundary lab as a transition between a frozen in anisotropy in the lithosphere to anisotropy in the sublithospheric mantle related to the present day flow due to different orientations of velocity maxima in the anisotropic subcrustal lithosphere and the asthenosphere the velocity contrast related to the lab can increase in particular directions because of their long wavelengths and horizontal propagation surface waves suffer from poor lateral resolution however surface waves with various wavelengths allow us to map gross features of the lab with a good vertical resolution we estimate depths to the lab to be between 200 and 250 km for the precambrian shields and platforms around 100 km for the phanerozoic continental regions and 40 70 km beneath oceans from the world wide depth distribution of the radial and azimuthal anisotropy of surface waves

relations among subduction parameters clues to the dynamics of the subduction process are found in the many measurable parameters of modern subduction zones based on a critical appraisal of the geophysical and geological literature 26 parameters are estimated for each of 39 modern subduction zones to isolate causal relationships among these parameters multivariate analysis is applied to this data set this analysis yields empirical quantitative relations that predict strain regime and strike slip faulting in the overriding plate maximum earthquake magnitude benioff zone length slab dip arc trench gap and maximum trench depth excellent correlation is found between length of the benioff zone and the product of convergence rate and age of the downgoing slab this relationship is consistent with the conductive heating model of molnar et al 1979 if the model is modified in one respect the rate of heating of the slab is not constant it is substantially slower during passage of the slab beneath the accretionary prism and overriding plate the structural style in the overriding plate is determined by its stress state though the stress state of overriding plates cannot be quantified one can classify each individual subduction zone into one of seven semiquantitative strain classes that form a continuum from strongly extensional class 1 back arc spreading to strongly compressional class 7 active folding and thrusting this analysis indicates that strain class is probably determined by a linear combination of convergence rate slab age and shallow slab dip interplate coupling controlled by convergence rate and slab age is an important control on strain regime and the primary control on earthquake magnitude arc parallel strike slip faulting is a common feature of convergent margins forming a forearc sliver between the strike slip fault and trench optimum conditions for the development of forearc slivers are oblique convergence a compressional environment and a continental overriding plate the primary factor controlling presence of strike slip faulting is coupling strongly oblique convergence is not required the rate of strike slip faulting is affected by both convergence obliquity and convergence rate maximum trench depth is a response to flexure of the underthrusting plate the amount of flexural deflection at the trench depends on the vertical component of slab pull force which is very sensitive to slab age and shallow slab dip shallow slab dip conforms to the cross sectional shape of the overriding plate which is controlled by width of the accretionary prism and duration of subduction deep slab dip is affected by the mantle trajectory established at shallow depth but may be modified by mantle flow much of the structural complexity of convergent margins is probably attributable to terrane juxtaposition associated with temporal changes in both forearc strike slip faulting and strain regime empirical equations relating subduction parameters can provide both a focus for future theoretical studies and a conceptual and kinematic link between plate tectonics and the geology of subduction zones

the continental rift system of the rhinegraben structure physical properties and dynamical processes abstract the geophysical investigation of the continental rift system of the rhinegraben by various methods has progressed to such a stage that details of structure physical properties and seismic activity and relations between these features can be recognised differences in the nature of the crust mantle boundary inside and outside the graben proper seem to be a typical property of continental rifts asymmetries of structure seismic activity temperature in the crust and physical properties in the lithosphere are an important clue to the understanding of rift dynamics these asymmetries indicate that the formation of the rift cannot be explained by the updoming of an asthenolith alone but that taphrogenesis took place in the foreland of the continent continent collision in the alpine mediterranean zone a number of future key experiments is proposed

polarization anisotropy and fine scale structure of the eurasian upper mantle we have observed shear wave splitting with tsh tsv tsv up to 1 5 on long period records of multiply reflected s waves bottoming in the upper mantle beneath the russian and siberian platforms the dispersion of love and rayleigh waves over these paths shows discrepancies of comparable or larger magnitude with respect to smooth isotropic si structures consistent with a model of the uppermost mantle having significant apparent vertical anisotropy although the splitting and dispersion data can be fit by smooth anisotropic sa models we have investigated the apparent anisotropy associated with fine scale rough structure beneath stable eurasia we fit the data with a rough isotropic ri model having an rms shear velocity fluctuation that varies from 14 in the uppermost mantle to zero at 400 km depth these fluctuations are larger than the variation in isotropically averaged parameters expected for even a diverse assemblage of upper mantle ultrabasic rocks which we take to be evidence for some sort of intrinsic local anisotropy

quaternary coastal uplift along the talara arc ecuador northern peru from new marine terrace data marine terrace sequences have been investigated along the talara arc a 1000 km long stretch of the coast of ecuador and northern peru characterized by subduction with a concave plan view seven areas were investigated evidencing flights of up to seven marine terraces with elevations reaching up to 360 in above mean sea level amsl dating of the terraces was made using the infra red stimulated luminescence irsl technique on sands as old as mis 9 similar to 330 ka c 14 and u series dates were obtained from fossil shells for geochronological cross control mean uplift rates along the talara arc range from about 0 10 up to 0 50 mm yr the strongest uplift is observed in the manta peninsula of ecuador in front of the subduction of the carnegie ridge the uplift rate tends to slow down towards the northern and southern ends of the talara arc and then the transition toward the stable or subsiding coasts of central peru and northern ecuador and colombia is sharp the uplift appears to be homogeneous and related to 1 the map view curvature of the are 2 the concave subduction pattern and 3 the carnegie ridge subduction c 2006 elsevier b v all rights reserved

isotropic and anisotropic pn velocity inversion of regional earthquake traveltimes underneath germany summary this paper investigates the uppermost mantle velocity beneath germany using regional earthquake traveltime data 2149 pn traveltimes corresponding to 220 events recorded at 70 stations covering the region of 47 n 52 n latitude 5 e 15 e longitude result in a satisfactory ray path distribution three methods with increasing degree of complexity are used to analyse the pn traveltime data a straight line fit the classical time term method and a modified time term method including azimuthal anisotropy first from the straight line fit to the data set an average pn velocity of 7 98 km s 1 is inferred second the classical time term method yields a mean uppermost mantle velocity of 7 99 km s 1 the most important feature in this analysis is the azimuth dependent pattern of the residuals indicating some evidence of velocity anisotropy in the upper mantle the time term method achieves about 55 per cent variance reduction relative to the straight line fit third two modified anisotropic time term methods provide an average pn velocity of 8 09 km s 1 with a further data variance reduction of 64 and 20 per cent relative to the straight line fit and the classical time term method respectively the estimated anisotropy level is about 3 5 4 per cent with maximum and minimum velocities of 8 24 8 27 km s 1 and 7 95 km s 1 our estimated maximum velocity direction of n25 e coincides with those of previous anisotropic studies on the uppermost mantle in this region based on seismic refraction data the results from the present study thus support the idea that pn wave anisotropy is a large scale lithospheric feature over much of central europe

azimuthally anisotropic model of the oceanic upper mantle abstract a mixed form of forward and backward modelings of azimuthally anisotropic oceanic upper mantle is attempted for a data set of surface wave velocities of periods 30 100 s one of the basic configurations of the anisotropy postulated in the lid and lvz is axial symmetry of elastic properties with a horizontal axis parallel to the spreading direction as found in ultramafic rocks from ophiolite complexes of the bay of islands and oman basic features of the resulting model are a thin lithosphere of 45 km a decrease of s wave velocities and an increase of p wave velocities and of partial melting dislocation relaxation with depth in the lvz this single model explains the overall features of anisotropy observations in the pacific ocean p n velocity anisotropy sh sv anisotropy and azimuthal anisotropy of surface waves and scs polarization anisotropy this fact leads us to a conclusion that the ultramafic rocks from the ophiolite complexes can explain the seismic properties of the oceanic lid and lvz

on the physical interpretation of the lead relation between warm water volume and the el nino southern oscillation the warm water volume wwv a proxy for the equatorial pacific heat content is the most widely used oceanic precursor of the el nino southern oscillation enso the standard interpretation of this lead relation in the context of the recharge oscillator theory is that anomalous easterlies during e g la nina favour a slow recharge of the equatorial band that will later favour a transition to el nino here we demonstrate that wwv only works as the best enso predictor during boreal spring i e during enso onset in both observations and cmip5 models at longer lead times the heat content in the western pacific wwvw is the best enso predictor as initially formulated in the recharge oscillator theory using idealised and realistic experiments with a linear continuously stratified ocean model and a comprehensive wave decomposition method we demonstrate that spring wwv mostly reflects the fast kelvin wave response to wind anomalies early in the year rather than the longer term influence of winds during the previous year wwv is hence not an adequate index of the slow recharge invoked in the recharge oscillator the wwvw evolution before spring is dominated by forced rossby waves with a smaller contribution from the western boundary reflection wwvw can be approximated from the integral of equatorial wind stress over the previous 10 months thus involving a longer term time scale than wwv main time scale 3 months we hence recommend using wwvw rather than wwv as an index for the slow recharge before the spring predictability barrier

wave theoretical inversion of teleseismic surface waves in a regional network phase velocity maps and a three dimensional upper mantle shear wave velocity model for southern germany summary using teleseimic surface wave data from 110 selected earthquakes recorded at 10broad band stations in southern germany we construct phase velocity maps of rayleigh waves for southern germany in a further step these maps are inverted for a three dimensional model of the sv velocity of the upper 200 km of the mantle we attempt to take into account the effect of heterogeneous structure outside the study region by jointly inverting the data for heterogeneous phase velocity inside the study region and the distortion of the incoming wavefields by the surrounding structure the total wavefield in the study region is computed with a scattering formalism which includes multiple forward scattering and single backscattering since in principle the data can be perfectly fit by the incoming wavefields without any heterogeneous structure inside the study area we impose additional constraints on the incoming wavefields to reduce the non uniqueness the most important constraint is an energy criterion which states that the energy of the modelled wavefield in the study area averaged over many events should be equal to the energy sampled by the stations we demonstrate that enforcing this criterion generates phase velocity maps with heterogeneous structure nevertheless we are able to satisfy the energy criterion without any heterogeneous structure at the price of an only slightly increased data misfit hence it must be concluded that a seismic network of size and station density such as the one used in this study is still insufficient to demonstrate convincingly the existence of heterogeneities in the network area using teleseismic surface waves any reasonable structure combined with the appropriate incoming wavefields would allow an acceptable fit of our data this frustrating conclusion of course applies to all other comparable studies which use teleseismic surface waves although we cannot convincingly show that any phase velocity map we find should be preferred over others we are able to obtain good reconstructions of test structures from realistic synthetic data with the same station and event distribution as the real data moreover we find that the geometric pattern of the phase velocity maps obtained from real data depends only weakly on the constraints applied in the inversion while the amplitude of the phase velocity perturbations is almost completely determined by the constraints for all periods considered the fit to the data is extremely good the reduction of the quadratic misfit relative to the case of plane incoming waves and no structure is dramatic for the shorter periods the 3 d model of vertical shear wave velocity down to a depth of 200 km exhibits a basic division into four quadrants separated by a vertical plane intersecting the surface along a nearly west east line and a horizontal plane at about 130 km depth the northern rants show high velocities in the top 120 km and low velocities below 140 km the opposite is the case for the southern quadrants an exception to this general feature is a pronounced low velocity zone in the northwestern corner of the region

interannual variability in a tropical atmosphere ocean model influence of the basic state ocean geometry and nonlinearity abstract the behavior of a tropical coupled atmosphere ocean model is analyzed for a range of different background states and ocean geometries the model is essentially that of cane and zebiak for the tropical pacific except only temporally constant background states are considered here for realistic background states and ocean geometry the model solutions feature oscillations of period of 3 5 yr by comparing the full model solution with a linearized version of the model it is shown that the basic mechanism of the oscillation is contained within linear theory a simple linear analog model is derived that describes the nature of the interannual variability in the coupled tropical atmosphere ocean system the analog model highlights the properties that produce coupled atmosphere ocean instability in the eastern ocean basin and the equatorial wave dynamics in the western ocean basin that are responsible for a delayed negative feedback into this instability growth the growth rate of the local instabil

is enso a cycle or a series of events 1 after early ideas that saw el ninos as isolated events the advent of coupled models brought the conception of enso as a cycle in which each phase led to the next in a self sustained oscillation twenty two years of observations that represent the el nino and la nina peaks east pacific sst and the memory of the system zonal mean warm water volume suggest a distinct break in the cycle in which the coupled system is able to remain in a weak la nina state for up to two years so that memory of previous influences would be lost similarly while the amplitude of anomalies persists from the onset of a warm event through its termination there is no such persistence across the la nina break these observations suggest that el ninos are in fact event like disturbances to a stable basic state requiring an initiating impulse not contained in the dynamics of the cycle itself

heartbeat of the southern oscillation explains enso climatic resonances the el ni no southern oscillation enso nonlinear oscillator phenomenon has a far reaching influence on the climate and human activities the up to 10 year quasi period cycle of the el ni no and subsequent la ni na is known to be dominated in the tropics by nonlinear physical interaction of wind with the equatorial waveguide in the pacific long term cyclic phenomena do not feature in the current theory of the enso process we update the theory by assessing low 10 years and high 10 years frequency coupling using evidence across tropical extratropical and pacific basin scales we analyze observations and model simulations with a highly accurate method called dominant frequency state analysis dfsa to provide evidence of stable enso features the observational data sets of the southern oscillation index soi north pacific index anomaly and enso sea surface temperature anomaly as well as a theoretical model all confirm the existence of long term and short term climatic cycles of the enso process with resonance frequencies of 2 5 3 8 5 12 14 61 75 180 years this fundamental result shows long term and short term signal coupling with mode locking across the dominant enso dynamics these dominant oscillation frequency dynamics defined as enso frequency states contain a stable attractor with three frequencies in resonance allowing us to coin the term heartbeat of the southern oscillation due to its characteristic shape we predict future enso states based on a stable hysteresis scenario of short term and long term enso oscillations over the next century

seismic structure of the upper mantle beneath the western philippine sea abstract we investigate the seismic structure of the western philippine sea using two sets of seismological observations scs reverberations which provide the layering framework for a regional upper mantle model and observations of frequency dependent phase delays for direct s waves surface reflected phases ss ss sss and surface waves r1 g1 which constrain the velocity and anisotropy structure within the layers the combined data set comprising 17 discontinuity amplitudes and layer travel times from the scs reverberation stack and more than 1000 frequency dependent phase delays was inverted for a path averaged radially anisotropic model mineralogical estimates of the bulk sound velocity and density are incorporated as complementary constraints the final model phb3 is characterized by a 11 5 km thick crust an anisotropic lid bounded by a sharp negative g discontinuity at 89 km an anisotropic low velocity layer extending to 166 km a subjacent high gradient region and transition zone discontinuities at depths of 408 km 520 km and 664 km the lid is slower than in a comparable model for the tonga hawaii corridor pa5 but also significantly thicker requiring a compositional variation between the two regions we explore the hypothesis that the thickness of the oceanic lid is controlled by the melting depth at the spreading centers during crust formation and that the thicker crust and lid in the philippine sea results from deeper melting owing to a higher potential temperature and perhaps a higher water content in the upper mantle

a new type of active margin the convergent extensional margin as exemplified by the middle america trench off guatemala the results of dsdp legs 67 and 84 during which a transect of holes was drilled across the middle america trench off guatemala show no accretion at the front of that subduction zone since early eocene time the tectonic evolution of the trench includes extensional structure on the landward as well as the seaward trench slopes the guatemalan margin is proposed as the model of a new type of active margin the convergent extensional active margin ce margin

andean forearc dynamics as recorded by detrital zircon from the eocene talara basin northwest peru abstract eocene strata of the talara forearc basin of northwest peru contain detrital zircon dz populations that when integrated with other provenance indicators record paleogeographic shifts in the andean forearc that can be linked to larger scale tectonic drivers such as subduction erosion plate convergence rate and regional accretion events because forearc basins along the western margin of south america are particularly difficult to preserve the new dz results provide rare insight into the trench arc dynamics associated with the andean orogenic cycle the talara basin tapped into both the andean volcanic arc and older basement and the dz populations subsequently reflect long lived plate interactions and progressive crustal growth along the northwestern edge of amazonia gondwana and south america dominant u pb zircon age populations include 36 110 ma andes convergence 215 285 ma western gondwana extension 460 625 ma rodinia extension and western gondwana convergence 950 1250 ma grenville orogeny and 1250 ma amazonia assembly the data corroborate previous geochronology on pre andean basement and support the existence of a famatinian arc 480 ma and carboniferous triassic magmatism along northwestern gondwana pre andean and amazonian dz likely was recycled from paleozoic metasedimentary rocks of the andean cordillera and amotape terrane although the data do not preclude delivery of amazonian detritus directly into the forearc via a large scale westward drainage the andean dz population constrains the timing of arc activity and quiescence with two peaks at 75 ma and 50 ma and a gap at 70 ma linked to accretion of the caribbean oceanic plateau against northwest south america arc volcanism was concurrent with eocene forearc deposition and syndepositional dz is used to revise maximum depositional age for the upper eocene helico member and verdun formation progressive subsidence and arc shut down in the late eocene coincide with arc collision to the north uplift of the amotape block subduction erosion and slab shallowing

lithospheric thickness and velocity anisotropy seismological and geothermal aspects abstract we compare inferences of regional variations in the lithospheric thickness in central europe based on three types of observations seismologically determined thicknesses derived from representative p wave residuals agree in most regions both with the magnetotelluric inferences of depths of the top of a layer of increased electrical conductivity and with the geothermally based calculations that allow inferences of the lithospheric thickness from surface heat flow data the seismological definition of the lithosphere as a high velocity layer overlying the low velocity zone in the upper mantle seems to be close to the geothermal concept in which the lithospheric base is defined by temperatures near partial melting decreasing the seismic velocities and increasing the electrical conductivity interpretations of seismic data used for constraining geothermal models of the deep lithosphere assume velocity variations to reflect mainly changes in the mineral composition however recent observations of large scale seismic anisotropy show clearly that in the subcrustal lithosphere velocity variations due to anisotropy caused by preferred orientations of olivine crystals can be much larger than the velocity variations caused by temperature or compositional changes

observations of warm water volume changes in the equatorial pacific and their relationship to el nino and la nina abstract this paper describes observed changes in surface winds sea surface temperature sst and the volume of water warmer than 20 c wwv in the equatorial pacific ocean for the period 1980 99 the purpose is to test recent hypotheses about the relationship between variations in wwv and the el nino southern oscillation enso cycle the results confirm inferences based on theory models and previous empirical analyses using proxy data namely sea level that enso involves a recharge and discharge of wwv along the equator and that the cyclic nature of enso results from a disequilibrium between zonal winds and zonal mean thermocline depth the authors also find that the magnitude of enso sst anomalies is directly related to the magnitude of zonal mean wwv anomalies furthermore for a given change in equatorial wwv the corresponding warm el nino sst anomalies are larger than the corresponding cold la nina anomalies this asymmetry between the warm and cold phases of the enso cycle implies differences

upper mantle seismic anisotropy and lithospheric decoupling the lithosphere underlying stable continental shield regions is thought to extend to a depth of 200 km compressional wave velocity models derived from a recent approximately ns refraction profile in northern australia include a pronounced high velocity zone at a depth of around 200 250 km conventional petrological interpretations in terms of mineralogical or compositional changes cannot readily explain this feature calculated velocities for the garnet pyrolite model using a derived geotherm fit the velocities above and below this high velocity zone but cannot account for the high velocity 8 6 km s 1 zone itself this feature is explained in terms of velocity anisotropy which might reflect mechanical decoupling of the continental lithosphere from the underlying mantle

recently formed elastic anisotropy and petrological models for the continental subcrustal lithosphere in southern germany this paper advances new evidence for elastic anisotropy in the continental subcrustal lithosphere in southern germany the range of petrological models compatible with the observed azimuthal variation of seismic p wave velocity is explored the azimuthal distribution of amplitudes of mantle phases and the observed increase of p velocity with depth both indicate a continuation of anisotropy with depth together with an increase of preferred orientation even depletion of the upper mantle in basaltic components as suggested by mantle xenoliths from various parts of germany cannot explain the velocity depth and azimuthal amplitude observations without an increase of anisotropy with depth preferred orientation of olivine is the most likely mechanism for the observed phenomena its fast a axis at the moho level is directed towards n22 5 e the b axis is also required to be horizontal i e the b plane one of the preferred glide planes of olivine is vertical with a strike of n22 5 e therefore this preferred glide plane of olivine practically coincides with the plane of maximum horizontal shear stress deduced from fault plane solutions of earthquakes in western germany this is a strong indication that the preferred orientation of olivine is formed in the recent west european crustal stress field leaking into the upper mantle the distribution of velocities to a depth of at least 50 km requires slight horizontal rotation of the a axis with depth by 10 towards n32 e and a change in the modal composition towards a depletion increasing with depth compatible with the composition of mantle xenoliths from western germany further experiments are needed to substantiate this suggestion which could lead to a better understanding of the interaction of crustal and upper mantle stress strain fields

numerical models of subduction and forearc deformation presence of a low strength megathrust and regional compression successful finite element models produce an outer arc at the top of the trench slope and forearc basin with geometry characteristic of natural analogues these structural features occur by upward inelastic bending of the lithospheric wedge overlying the megathrust this mechanically unstable behaviour may dissipate significant energy and cause the megathrust to migrate continuously by accretion tectonic erosion or abandonment and reinitiation farther offshore upward bending in the overriding plate is promoted by low megathrust dip low megathrust shear strength and high horizontal compression in the overriding plate

analysis of the non linearity in the pattern and time evolution of el nino southern oscillation in this study the observed non linearity in the spatial pattern and time evolution of el nino southern oscillation enso events is analyzed it is shown that enso skewness is not only a characteristic of the amplitude of events el ninos being stronger than la ninas but also of the spatial pattern and time evolution it is demonstrated that these non linearities can be related to the non linear response of the zonal winds to sea surface temperature sst anomalies it is shown in observations as well as in coupled model simulations that significant differences in the spatial pattern between positive el nino versus negative la nina and strong versus weak events exist which is mostly describing the difference between central and east pacific events central pacific events tend to be weak el nino or strong la nina events in turn east pacific events tend to be strong el nino or weak la nina events a rotation of the two leading empirical orthogonal function modes illustrates that for both el nino and la nina extreme events are more likely than expected from a normal distribution the bjerknes feedbacks and time evolution of strong enso events in observations as well as in coupled model simulations also show strong asymmetries with strong el ninos being forced more strongly by zonal wind than by thermocline depth anomalies and are followed by la nina events in turn strong la nina events are preceded by el nino events and are more strongly forced by thermocline depth anomalies than by wind anomalies further the zonal wind response to sea surface temperature anomalies during strong el nino events is stronger and shifted to the east relative to strong la nina events supporting the eastward shifted el nino pattern and the asymmetric time evolution based on the simplified hybrid coupled rechoz model of enso it can be shown that the non linear zonal wind response to sst anomalies causes the asymmetric forcings of enso events this also implies that strong el ninos are mostly wind driven and less predictable and strong la ninas are mostly thermocline depth driven and better predictable which is demonstrated by a set of 100 perfect model forecast ensembles

scales of structure in the lithosphere images of processes advances in deep seismic sounding observations of the lithosphere on continents allow to identify various scales of heterogeneities in the crust mantle transition in this paper a fresh look is taken at the dynamic properties of seismic waves propagating through this zone ranging from the lower crust well into the lithospheric mantle as observed in near vertical reflection and wide angle refraction experiments the abrupt termination of near vertical reflections at the moho and the coincident presence of a strong coda accompanying the supercritical pmp reflection phase in record sections of continental seismic wide angle refraction experiments reveal a new property of the crust mantle boundary the moho forms a sandwiched mix of crust mantle material between lower crust and topmost mantle in combination with a step in mean velocity a significant change in scale of the structural dimensions and of velocity variance this view is strongly supported by the recognition of the subcrustal lithosphere as a high frequency 5 10 hz scattering wave guide for long distance propagation of the pn phase over more than 3000 km detected during seismic experiments in russia using peaceful nuclear explosions evidence is brought forward that this high frequency wave guide is likely to be present also in the phanerozoic upper mantle of western europe it is furthermore hypothesized that the global propagation of teleseismic sn or corresponding pn waves observed on continents and oceans combined with the recording of strong pmp codas for wave paths on continents points to a world wide change of scale of structure and velocities near the moho a change in scale of heterogeneities under almost all physical and chemical conditions indicates possibly a differential horizontal movement or decoupling of crust and upper mantle at the level of the moho the global presence of the scattering pn wave guide with a preferred horizontal elongation is hypothetically described as a seismic image of processes in the lithospheric mantle locations of present day tectonic activity where horizontal decoupling between crust and mantle are likely to occur e g subduction at continent continent collision zones change of tectonic regimes and continental transform faults are discussed

the lithosphere asthenosphere boundary and cratonic lithospheric layering beneath australia from sp wave imaging sp and ps scattered wave receiver functions were calculated for nineteen stations across australia and the island of tasmania in order to image the lithosphere asthenosphere boundary and layering within the lithosphere within phanerozoic eastern australia and the eastern margin of the south australia craton prominent sp phases from a negative velocity contrast were found at depths of 61 11 km to 131 9 km consistent with the lithosphere asthenosphere boundary depth range from surface wave tomography these phases imply significant velocity drops over depth ranges of 30 40 km or less and thus cannot be explained by a lithosphere asthenosphere boundary that is controlled by temperature alone rather they imply that the asthenosphere is hydrated with respect to a drier depleted lithosphere or contains a small amount of partial melt the shallowest sp phases have the largest amplitudes and occur in regions with the most recent voluminous volcanism strengthening the link to partial melt at the base of the lithosphere in contrast no significant negative sp phases were found at the base of the thick cratonic lithosphere at the stations in central and western australia implying that the cratonic lithosphere asthenosphere velocity gradient is distributed over more than 50 70 km in depth this gradient may be purely thermal in origin although gradational changes in composition or melt content cannot be ruled out a negative sp phase was observed at depths of 69 8 km to 85 14 km at stations in central and western australia indicating the presence of a drop in velocity internal to the lithosphere this interface within the lithosphere may be a relic of cratonic mantle formation or the result of alteration by melt and metasomatism

variation with age of anisotropy under oceans from great circle surface waves global great circle measurements of regionalized mantle love wave phase velocities are interpreted in terms of regional models the same study had been made by j j leveque 1980 for rayleigh waves and the resulting models for the two oceanic regions of different ages are used as a basis for comparison the observed love wave dispersion cannot be explained with these models if isotropic the models obtained by inversion of love wave data are compared with the models mentioned the discrepancy appearing in the 250km depth range between the velocities h and v of respectively sh and sv waves is indicative of polarization anisotropy moreover we put forward a significant variation from young to old oceans the difference between h and v is of the order of 1 for the former compared to 3 for the latter this variation can bring information about the behaviour of upper mantle materials in connection with the motion of oceanic plates

testing for dynamical dependence application to the surface mass balance over antarctica dynamical dependence between key observables and the surface mass balance smb over antarctica is analyzed in two historical runs performed with the mpi esm p and the cesm1 cam5 climate models the approach used is a novel method allowing for evaluating the rate of information transfer between observables that goes beyond the classical correlation analysis and allows for directional characterization of dependence it reveals that a large proportion of significant correlations do not lead to dependence in addition three coherent results concerning the dependence of smb emerge from the analysis of both models i the smb over the antarctic plateau is mostly influenced by the surface temperature and sea ice concentration and not by large scale circulation changes ii the smb of the weddell sea and the dronning maud land coasts are not influenced significantly by the surface temperature and iii theweddell sea coast is not significantly influenced by the sea ice concentration

seismic observations of large scale deformation at the bottom of fast moving plates abstract we present a new tomographic model of azimuthal anisotropy in the upper mantle dr2012 and discuss in details the geodynamical causes of this anisotropy our model improves upon dkp2005 seismic model debayle et al 2005 through a larger dataset expanded by a factor 3 7 and a new approach which allows us to better extract fundamental and higher mode information our results confirm that on average azimuthal anisotropy is only significant in the uppermost 200 250 km of the upper mantle where it decreases regularly with depth we do not see a significant difference in the amplitude of anisotropy beneath fast oceanic plates slow oceanic plates or continents the anisotropy projected onto the direction of present plate motion shows a very specific relation with the plate velocity it peaks in the asthenosphere around 150 km depth it is very weak for plate velocities smaller than 3 cm yr 1 increases significantly between 3 and 5 cm yr 1 and saturates for plate velocities larger than 5 cm yr 1 plate scale present day deformation is remarkably well and uniformly recorded beneath the fastest moving plates india coco nazca australia philippine sea and pacific plates beneath slower plates plate motion parallel anisotropy is only observed locally which suggests that the mantle flow below these plates is not controlled by the lithospheric motion a minimum plate velocity of around 4 cm yr 1 is necessary for a plate to organize the flow in its underlying asthenosphere the correlation of oceanic anisotropy with the actual plate motion in the shallow lithosphere is very weak a better correlation is obtained with the fossil accretion velocity recorded by the gradient of local seafloor age the transition between frozen in and active anisotropy occurs across the typical age isotherm that defines the bottom of the thermal lithosphere around 1100 c under fast continents mostly under australia and india the present day velocity orients also the anisotropy in a depth range around 150 200 km depth which is not deeper than what is observed under oceans

seismic structure of the upper mantle in a central pacific corridor the seismic structure of the tonga hawaii corridor has been investigated by combining two data sets revenaugh and jordan s reflectivity profile from scs reverberations which provides travel times to and impedance contrasts across the major mantle discontinuities and 1500 new observations of frequency dependent phase delays for the three component s ss and sss body waves and the r1 and g1 surface waves which constrain the velocity structure within this layered framework the shear waves turning in the upper mantle showed significant splitting of the sh and sv components indicative of shallow polarization anisotropy the data set was inverted in conjunction with attenuation and mineralogical constraints to obtain a complete spherically symmetric radially anisotropic structure the final model pa5 is characterized by a high velocity anisotropic lid bounded at 68 km depth by a large negative g discontinuity a low velocity anisotropic layer below g extending to a small l discontinuity at 166 km an isotropic steep gradient region between 166 km and 415 km and transition zone discontinuities at 415 507 and 651 km the depth of the radial anisotropy in pa5 is shallower than in most previous studies based on surface waves and higher modes the average value of radial shear anisotropy in the lid 3 7 is consistent with the magnitude expected from the spreading controlled models of olivine orientation while anisotropy in the low velocity zone which is required by our data set could be induced either by paleostrains that took place near the ridge crest or by shearing in the asthenosphere as a result of present day plate motions on the basis of recent work by hirth and kohlstedt we suggest that the g discontinuity is caused by a rapid increase in the water content of mantle minerals with depth marking the fossilized lower boundary of the melt separation zone active during crust formation the high gradient zone between 200 and 400 km is a characteristic feature of convecting oceanic upper mantle and is probably controlled by a steady decrease in the homologous temperature over this depth interval the average shear velocity gradient in the transition zone is lower than in most previous seismic models in better agreement with the predictions for a pyrolitic composition

some aspects of the tectonics of subduction zones abstract the main structures of a subduction zone are as follows 1 1 on the outer wall faults formed either by reactivation of the structural grain of the oceanic plate when the latter is slightly oblique to the trench or by a new fault network parallel to the trench or both the width of the faulted zone is about 50 miles 2 2 on the inner wall either an accretionary prism or an extensional fault network or both collapsed structures and slumps are often associated sometimes creating confusion with the accretionary structures 3 3 the overall structure of the trench itself is determined by the shape of the edge of the continental crust or of the island arc its detailed structure however is related to the oceanic plate namely when the structural grain of the latter is slightly oblique to the trench which then takes an en echelon form collapsed units can fill up the trench which is in that case restricted to an irregular narrow depression the tectonic framework of the trench can be buried under a sedimentary blanket when the sedimentation rate is high and the trench bottom is a large flat area two extreme types of active margins can be distinguished convergent compressive margins when the accretionary mechanism is strongly active and convergent extensional margins where the accretionary mechanism is absent or only weakly active the status of a given margin between these two extreme types is related to the convergence rate of the plates the dip of the subduction zone the sedimentation activity and the presence of a continental obstacle because oceanic seamounts and aseismic ridges are easily subducted examples are taken from the barbados middle america peru kuril japan nankai marianna manila new hebredes and tonga trenches

inversion of multimode surface wave data evidence for sub lithospheric anisotropy summary multiparameter inversions of multimode dispersion data are performed for two large regions the pacific ocean and north america anisotropy is taken into account by considering transversely isotropic structures with a vertical axis of symmetry two fundamental questions are studied in detail 1 how to make the inverted models consistent when using different sets of parameters 2 what is the significance of transversely isotropic inversion for the actual earth s structure it is proved that full consistency of the inverted models can be achieved by properly taking into account some a priori informations on the model and it is shown that the use of transversely isotropic models with vertical axis of symmetry does not cause severe limitations when interpreting the data the models we have obtained are discussed in the light of these investigations considering an olivine rich upper mantle we make a tentative interpretation of these models in terms of preferred orientation of the a axis of the crystals in one fixed horizontal direction

anisotropy of the asthenosphere the higher mode data of the pacific revisited surface wave data previously used by the authors to constrain upper mantle anisotropy in the pacific ocean are re examined after an error was found in the calculations of the love wave phase velocities sub lithospheric anisotropy is still required by the corrected data but it extends to shallower depth than we originally proposed using different parameterizations of the upper mantle we present strong evidence that the bottom of the anisotropic layer has been reached around 250 km in the pacific beneath north america no revision of our data is required and anisotropy could extend to around 400 km depth our results are in agreement with an upper mantle anisotropy due to preferred orientation of olivine crystals in an overall horizontal shear strain parallel to the present day plate motion we suggest that this preferred orientation of the crystals mainly occurs within the upper mantle low velocity layer

the simplest enso recharge oscillator 1 eastern pacific sea surface temperature sst and mean equatorial pacific thermocline depth are key variables in el nino southern oscillation enso a linear fit to observations leads to a remarkably simple picture enso can be represented by a classical damped oscillator with sst and thermocline depth playing the roles of momentum and position respectively an independent fit of observed relationships between western and eastern thermocline depth central wind stress and eastern pacific sst yields the same picture and supports a recharge oscillator interpretation the oscillation arises from the interaction between the recharge time of the warm pool and the time delay between east and west pacific both finite kelvin wave speed and sst dynamics contribute to the time delay including seasonality in the description we find two periods of relative instability boreal spring with a large phase progression and autumn with nearly stationary phase

upper mantle structure beneath eastern siberia evidence from gravity modeling and mantle petrology 1 the spatial distribution of large scale lithospheric domains and the boundaries between them may control the emplacement of large ore bodies and as such regional mapping of the lithosphere is relevant to mineral exploration in this study we combine potential field geophysical data and mantle petrology to map major lithospheric structures on the eastern part of the siberian platform the platform consists of several archean and proterozoic terranes that have been mapped from regional magnetic data and basement exposures in the anabar shield we use garnet and chromite concentrates from a chain of paleozoic to mesozoic kimberlites across the platform to construct mantle sections which show significant lateral variation in rock type distribution within the lithospheric mantle these lateral variations correspond to the terranes mapped at the surface and indicate that the terrane boundaries are translithospheric archean terranes are underlain by depleted archean lithosphere more than 200 km thick while the proterozoic terranes are underlain by thinner and less depleted lithosphere geophysical data show more strongly negative bouguer anomalies and a more heterogeneous magnetic anomaly pattern over the archean terranes than on the proterozoic terranes the pattern of the gravity data reflects the lateral variation in mantle composition beneath the terranes as shown by mantle petrology studies we invert gravity and topography data to estimate the flexural strength or elastic thickness te of the lithosphere across the area although on a stable precambrian craton the te is relatively low 30 km across most of the area suggesting a relatively weak lithosphere comparable to that of tectonically much younger areas around the world a 150 km wide zone of very weak lithosphere te 10 km runs n s across the western part of the study area this weak zone coincides with a zone of thickened lower crust and abnormally high sub moho p wave velocities which suggest anisotropy in the upper mantle the kimberlite fields in the archean part of the platform are localized on the flanks of this zone of weak lithosphere we suggest that the low te zone may be a mantle shear zone which has been a preferred conduit for the emplacement of magmas into the lower crust and later has controlled the emplacement of kimberlites in the study area

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

enso dynamics and diversity resulting from the recharge oscillator interacting with the slab ocean el nino southern oscillation enso is the leading mode of interannual global climate variability which in its essence is often described by the equatorial dynamics of the recharge oscillator with a fixed pattern here we explore the idea that enso can be simulated in a model with a fixed pattern of sea surface temperature variability following the recharge oscillator mechanism which interacts with the thermodynamic red noise of a slab ocean this model is capable of simulating the leading modes of sea surface temperature variability in the tropical pacific in good agreement with the observations and most coupled general circulation models enso dynamics amplitude seasonality the structure of the leading patterns its meridional extension its variations in an eastern and central pacific pattern and associated positive feedbacks are all influenced and simulated well by including the interaction of recharge oscillator and the thermodynamic coupling to the slab ocean model we further point out that much of the enso diversity in the spatial structure is a reflection of this interaction however it also has to be noted that some equatorial dynamics are missing in this model and in coupled general circulation models that are important for the enso diversity

global tomography from rayleigh and love wave dispersion effect of ray path bending summary a large data set of fundamental mode rayleigh and love wave phases has been employed for global tomographic inversions these data represent observations of the first arriving surface waves r1 and l1 from approximately 850 seismic events with about 10 observations of dispersion per event the inversion for laterally varying depth dependent structure is performed in several steps at discrete periods from 111s 250s for love waves and from 111s 200s for rayleigh waves we first determine simultaneously the global distribution of phase velocity anomaly and the relocations of the seismic events each phase velocity distribution is then corrected for laterally varying moho depth and bathymetry followed by inversion for 3 d earth structure in the depth range 0 240 km in order to lie within the limits of ray theory we restrict all model perturbations to a degree 0 16 spherical harmonic expansion a second order scattering ray path correction is included in the inversions the phase velocity perturbations show a high correlation with surface tectonics at shorter periods comparison of inversions shows that those performed without the ray path correction exhibit a complicated pattern of fast and slow velocity bias the only common feature in the patterns of bias with respect to period or wave type is that fast velocity bias is concentrated in regions of large structural gradient the amplitude pattern of the depth dependent model has pronounced peaks in the intervals 0 70 km and 140 210 km the deeper peak is associated with lateral variations in asthenosphere structure we derive new estimates for the spherically averaged phase velocities of the fundamental mode rayleigh and love waves the spherically averaged phase velocities are decreased by about 0 1 per cent by including the ray path correction these phase velocity dispersions can be simultaneously fit well with an isotropic model either with or without the ray path correction but particularly well when the ray path correction is included in both cases a pronounced low velocity zone of the global extent is required in the depth range 120 190 km

neogene stratigraphy and andean geodynamics of southern ecuador abstract the present paper reviews tertiary volcanic and sedimentary formations in the inter andean region of southern ecuador between 2 s and 4 20 s in order to develop a geodynamic model of the region the formations occur in the southern shallow prolongation of the inter andean valley between the cordillera real to the east and the cordillera occidental and amotape tahuin provinces to the west one hundred fifty zircon fission track analyses has established a detailed chronostratigraphy for the sedimentary and volcanic formations and several small intrusions the paleogene to early miocene formations are dominated by intermediate and acidic volcanic and pyroclastic rocks in addition relics of eocene continental sedimentary series have been identified the neogene sedimentary series lie unconformably on deformed and eroded metamorphic sedimentary and volcanic formations they were deposited in two stages which are separated by a major unconformity dated at 10 9 ma 1 during the middle and early late miocene 15 10 ma marginal marine deltaic lagoonal lacustrine and fluvial environments prevailed which we group under the heading pacific coastal sequences they presumably covered a greater surface area in southern ecuador than their present occurrence in small topographic depressions we suggest that they were deposited in the shallow marine cuenca and loja embayments deposition in a marginal marine environment is also supported by the occurrence of brackish water ostracods and other fauna 2 above the regional angular unconformity the coastal facies are overlain by late miocene 9 5 ma continental alluvial fan and fluvial facies which are in turn covered by mainly airborne volcanic material they represent the intermontane sequences of the basins of cuenca giron santa isabel nabon loja and malacatos vilcabamba sedimentologic and stratigraphic results are used to discuss the tectonic setting of neogene sedimentation in the forearc and arc domain of the ecuadorian subduction system during the pacific coastal stage northward displacement of the coastal forearc block along the calacali pallatanga fault zone has driven crustal collapse in the inter andean region as a result extensional subsidence drove the eastward ingression of shallow seas into the cuenca and loja embayments from the manabi and progreso basins to the west tectonic inversion in the forearc area during the early late miocene at 9 5 ma reflects the initiation of w e oriented compression and uplift in the inter andean region and the establishment of smaller intermontane stage basins which host the continental sequences coeval topographic rise of the cordillera occidental is indicated by the onset of clastic input from the west the small intermontane basin of nabon 8 5 7 9 ma formed during the period of maximum compression the present data prove that the neogene andean forearc and arc area in southern ecuador was a site of important but variable tectonic activity which was presumably driven by the collision and coupling of the carnegie ridge with the ecuadorian margin since 15 9 ma

three dimensional seismic models of the earth s mantle accurate models of the distribution of elastic heterogeneity in the earth s mantle are important in many areas of geophysics the purpose of this paper is to characterize and compare quantitatively a set of recent three dimensional models of the elastic structure of the earth to assess their similarities and differences and to analyze their fit to one class of data in order to highlight fruitful directions for future research the aspherical models considered are the following m84c woodhouse and dziewonski 1984 lo2 56 dziewonski 1984 mdlsh tanimoto 1990a sh 10c 17 masters et al 1992 and s12 wm13 su et al 1994 through much of the discussion m84c and lo2 56 are combined into a single whole mantle model m84c lo2 56 the fit of each model to previously tabulated even degree normal mode structure coefficients taken from smith and masters 1989a and ritzwoller et al 1988 for multiplets along the normal mode fundamental and first second and fifth overtone branches is also presented rather than concentrating on detailed comparisons of specific features of the models analyses of these models are general and statistical in nature in particular we focus on a comparison of the amplitude and the radial and geographical distribution of heterogeneity in each model and how variations in each affect the fit to the normal mode observations in general the results of the comparisons between the models are encouraging especially with respect to the geographical distribution of heterogeneity and in the fit to the normal mode data sensitive to the upper mantle and lowermost lower mantle there remain however significant discrepancies in amplitude and in the radial distribution of heterogeneity especially near the top of the upper mantle and near the top of the lower mantle the confident use of these models to constrain compositional and dynamical information about the mantle will await the resolution of these discrepancies the factors that may be responsible for the differences in the models and or for the misfit between the observed and predicted normal mode data are divided into two types intrinsic or procedural and extrinsic or structural we discuss only three extrinsic factors at length here including errors in the reference crustal models unmodeled topography on discontinuities in the interior of the mantle and errors in the assumed relationships between shear s and compressional p heterogeneity

deciphering the late cretaceous cenozoic structural evolution of the north peruvian forearc system the link between plate tectonics and the evolution of active margins is still an ongoing task to challenge since the acceptance of plate tectonic paradigm this paper aims at deciphering the structural architecture and uplift history of the north peruvian forearc system to better understand the evolution and the mechanics that govern the late cretaceous cenozoic building of this active margin in this study we report surface structural geology data interpretation of seismic reflection profiles apatite fission track data and the construction of two offshore onshore crustal scale balanced cross sections the structure of the north peruvian forearc system is dominated by an accretionary style with northwestward propagation of thrust related structural highs involving continental oceanic basement rocks and off scrapped sediments the thrust systems bound thick thrust top forearc depocenters mainly deformed by crustal normal to strike slip faults and thin skinned gravitational instabilities the sequential restoration of the margin calibrated with apatite fission track data suggests a correlation between uplift shortening and plate convergence velocity during late cretaceous and miocene pliocene quaternary shortening and uplift of the coastal zone is rather related to the subduction of asperities during convergence rate decrease the development of crustal normal to strike slip faulting and subsidence zones might be the consequence of slab flexure local basal erosion along subduction fault and or oblique subduction associated with sediment loading control we conclude that the evolution of the north peruvian forearc system was controlled by subduction dynamics strong sediment accumulation and recent ridge subduction and it recorded the orogenic loading evolution of the andes over the cenozoic

evidence from core reflected shear waves for anisotropy in the earth s mantle seismologists have begun to recognize that the upper mantle at depth is anisotropic and that seismological data are not fully explicable if anisotropy is ignored1 5 on entering an anisotropic zone a plane shear wave splits into two orthogonally polarized phases6 an effect observed by several researchers7 notably by ando et al 5 8 9 the near vertical scs wave an s wave reflected once at the core mantle boundary is one of the most suitable phases to study the phenomenon of shear wave birefringence because it is isolated from other phases and because its particle motion is nearly horizontal and thus free from s to p conversion the split scs shear waves travel with different velocities in the anisotropic zone and consequently there is a time delay between their arrival at stations my aim was to determine this time delay and the azimuth of polarization using the scs records of two horizontal components from the japanese islands for a deep shock beneath the sea of okhotsk from the total of 41 stations 34 show a polarization of the maximum velocity phase in the nnw sse direction with an average time advance of 0 8s from the minimum velocity phase the relevant anisotropic zone seems to be deep seated

upper mantle cross section from tonga to newfoundland a record section of long period u s and canadian observations of multibounce sh waves from a tonga event is used to study lateral variation in the upper mantle source to receiver distances range from 81 to 131 with triplication patterns apparent in s4 for the western north america stations and s5 for the more distant stations a corresponding synthetic section explaining the timing separation and waveform distortions for the various multiple s phases was derived by forward modeling initial trial models consisted of connecting existing pure path models assuming atl old atlantic as an analog for the old pacific tna for the western portion of the united states and sna for the shield portion of north america isovelocity depth contours were constructed to connect these models and corresponding synthetics were computed following a modified wkbj method lateral heterogeneity is found to exist in the upper 350 km of the pacific ocean region and can be modeled reasonably well with a high velocity lid vs 4 7 km s which thickens with increasing oceanic crustal age at the expense of the underlying low velocity zone velocities in the upper 200 km of the older southwest pacific are found to be up to 6 faster than those at comparable depths in the younger tectonic region near western north america the best fitting model indicates that the upper mantle structure of the old pacific is similar to that of the old atlantic although perhaps slightly slower

development of the gulf of guayaquil ecuador during the quaternary as an effect of the north andean block tectonic escape 1 interpretation of industrial multichannel seismic profiles and well data are used to identify the main tectonic features of the gulf of guayaquil gg area these include two e w trending major detachments the posorja and the jambeli detachment systems which represent half grabens with oppositely dipping detachments to the south and to the north respectively the ne sw trending puna santa clara fault system developed as a transfer fault system between the posorja and the jambeli detachments the esperanza and the jambeli basins exhibit 3 4 km of sediment that accumulated during the past 1 6 1 8 myr the puna santa clara fault system bounds the esperanza and the jambeli basins evidencing that the evolution of these basins is tightly controlled by the two detachments at depth to the west the n s trending domito fault system bounding the posorja detachment system and the esperanza basin to the west acted as a transfer zone between the shelf area and the continental slope the pliocene series show no significant variations in thickness throughout the gulf of guayaquil area suggesting that no important tectonic deformation occurred from 5 2 to 1 8 1 6 ma the major period of tectonic deformation in the gulf of guayaquil area occurred during the pleistocene times three main tectonic steps are identified from early pleistocene to 180 ka major subsidence occurred along the esperanza and jambeli basins from 180 to 140 ka most of the gulf of guayaquil area was above sea level during the isotope substage 6 low stand from 140 ka to present tectonic activity is restricted along the normal faults bounding the esperanza basin the tenguel fault and the puna santa clara and domito fault systems a n s trending tensional stress regime characterizes the pleistocene times throughout the northward drifting of the north andean block is proposed to control the tectonic evolution and associated subsidence of the gulf of guayaquil area it is also accepted that the collision of the carnegie ridge with the trench axis has to play a major role in controlling the north andean block northward drift because the carnegie ridge subduction is possibly an ongoing process which began prior to the pliocene we postulate the along strike morphology of the ridge at the origin of interplate coupling variations the subduction of an along strike positive relief of the ridge is proposed at the origin of the major tectonic reorganization of the gg area occurring at 1 8 1 6 ma

forearc basin formation in the tectonic wake of a collision driven coastwise migrating crustal block the example of the north andean block and the extensional gulf of guayaquil tumbes basin ecuador peru border area trench parallel extensional strain resulting from the northward drift of the north andean block has controlled the tectonic evolution of the gulf of guayaquil tumbes basin at least for the past 1 8 1 6 ma industrial multichannel seismic and well data document that e w to ene low angle detachment normal faults the posorja and jambeli detachment systems to the north and the tumbes detachment system to the south accommodated the main subsidence step along the shelf area during late pliocene quaternary times 1 8 1 6 ma to present two tectonic regimes showing different styles and ages controlled the evolution of the southern ecuador and northern peru continental margin and shelf the n s extensional regime along the shelf area is related to north andean block drift whereas the e w extensional regime along the continental margin results from tectonic erosion at depth strain rotation takes place along a major n s trending transfer system formed by the inner domito fault and the inner banco peru fault which bound the detachment systems to the west the strike slip component along this transfer system roughly located at the continental margin shelf break evolved as a response to slip along the detachment systems bounding the basin to the north and to the south the tumbes detachment system is the master fault controlling basin evolution through time and it may represent the shallower expression of a reactivated obduction megathrust it connects landward with the continental structures assumed to be part of the eastern frontier of the north andean block for the past 2 ma the total lengthening calculated along a complete n s transect of the gulf of guayaquil tumbes basin ranges between 13 5 and 20 km this lengthening is compatible with the documented drift of the north andean block for the same period of time the gulf of guayaquil tumbes basin is not a classical pull apart basin it exemplifies a particular type of pull apart basin basically controlled by 1 detachments extending downward across the brittle crust and 2 plate coupling along the subduction decollement which controls the inward segmentation of deformation

a three dimensional crustal model of southwest germany derived from seismic refraction data abstract from densely covered seismic refraction data obtained in 1978 urach experiment and 1984 schwarzer zollern wald experiment and from seismic reflection data and results from previous refraction investigations a three dimensional crustal model of southwest germany was derived travel time and amplitude information of seismic refraction data were interpreted with two dimensional forward modeling ray tracing to calculate two crustal cross sections in southwest germany these results fill a gap in the existing data and enabled the construction of a detailed three dimensional crustal model while seismically the upper crust is laterally homogeneous 5 9 6 0 km s throughout the area the middle and lower crust show pronounced lateral variations in thickness velocity and reflectivity the moho is a flat surface at a relatively shallow depth 25 26 km we classify the middle and lower crust of southwest germany into two characteristic crustal types type i consists of a mid crustal low velocity zone 5 4 5 8 km s overlying a thick 10 km high velocity 6 6 6 8 km s lower crust type ii has no prominent mid crustal low velocity zone and a thin

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

sediment subduction subduction erosion and strain regime in the northern south sandwich forearc 1 the first swath bathymetry and side scan sonar imagery from the south sandwich forearc reveals detailed seafloor morphology tectonic fabric and sedimentary features in an area where plate convergence is approximately normal to the trench simultaneously collected seismic reflection gravity and magnetic data provide information about the structure and composition of the forearc crust interpretation of these data together with the marine magnetic record of seafloor spreading in the east scotia sea back arc basin since 15 ma has enabled quantitative estimation of sediment subduction and subduction erosion rates any accretionary prism present is constrained to be very small extending 6 km or less from the trench the contrast between this result and a time integrated estimate of potential accretionary prism volume suggests that 95 of the sediment which has entered the trench since 15 ma has been subducted the position of the south sandwich island arc in relation to back arc magnetic lineations implies that the arc has migrated 70 km westward relative to the sandwich plate since 15 ma taking account of published observations concerning the typical geometric evolution of arc trench systems the average rate of forearc slope retreat during this interval is inferred to be 3 1 4 7 km myr 1 gravity modeling suggests that the forearc crust averages 10 km in thickness within 110 km of the trench for 10 km thick forearc crust the rate of slope retreat implies an average rate of subduction erosion of forearc crust of 31 47 km3 km 1 myr 1 at the present convergence rate of 74 km myr 1 this erosion rate requires a 420 635 m thick layer of subducting material derived from the forearc crust a time integrated estimate of the potential volume of forearc derived trench fill sediments subducted since 15 ma implies that frontal erosion can only account for 40 of total subduction erosion therefore basal erosion must significantly exceed frontal erosion the new data also provide insights concerning forearc strain regime and forearc basin evolution in the area studied extensional faulting near the trench slope break is probably caused by gravitational instability of the steep lower forearc slope a lack of extensional strain indicators in the upper forearc and arc may be a consequence of the fact that the east scotia sea is a mature back arc basin contributing significant ridge push in the vicinity of the arc the data reveal no evidence of arc parallel extension or of large serpentinite seamounts as found in the mariana forearc and a causal link between these two observations is proposed seismic profiles across the forearc basin suggest that the balance between sediment accumulation and erosion is sensitive to changes in the elevation of the trench slope break it is hypothesized that the basin is a dynamic feature which goes through repeated cycles of growth and destruction controlled by cyclic uplift and collapse of the trench slope break

analysis of the slab ocean el nino atmospheric feedbacks in observed and simulated enso dynamics in a recent study it was illustrated that the el nino southern oscillation enso mode can exist in the absence of any ocean dynamics this oscillating mode exists just due to the interaction between atmospheric heat fluxes and ocean heat capacity the primary purpose of this study is to further explore these atmospheric slab ocean enso dynamics and therefore the role of positive atmospheric feedbacks in model simulations and observations the positive solar radiation feedback to sea surface temperature sst due to reduced cloud cover for anomalous warm ssts is the main positive feedback in the slab ocean el nino dynamics the strength of this positive cloud feedback is strongly related to the strength of the equatorial cold tongue the combination of positive latent and sensible heat fluxes to the west and negative ones to the east of positive anomalies leads to the westward propagation of the sst anomalies which allows for oscillating behavior with a preferred period of 6 7 years several indications are found that parts of these dynamics are indeed observed and simulated in other atmospheric or coupled general circulation models agcms or cgcms the cmip3 agcm slab ensemble of 13 different agcm simulations shows unstable ocean atmosphere interactions along the equatorial pacific related to stronger cold tongues in observations and in the cmip3 and cmip5 cgcm model ensemble the strength and sign of the cloud feedback is a function of the strength of the cold tongue in summary this indicates that the slab ocean el nino dynamics are indeed a characteristic of the equatorial pacific climate that is only dominant or significantly contributing to the enso dynamics if the sst cold tongue is sufficiently strong in the observations this is only the case during strong la nina conditions the presence of the slab ocean enso atmospheric feedbacks in observations and cgcm model simulations implies that the family of physical enso modes does have another member which is entirely driven by atmospheric processes and does not need to have the same spatial pattern nor the same time scales as the main enso dynamics

azimuthal anisotropy in the earth from observations of sks at geoscope and nars broadband stations abstract we have analyzed observations of low frequency sks waves recorded on horizontal components at several broadband stations of the geoscope and nars arrays splitting of sks is consistently observed and in good agreement with a hypothesis of azimuthal anisotropy due to transverse anisotropy with a horizontal axis in the upper mantle beneath the receivers we have designed an inversion method which takes advantage of observations made simultaneously at different azimuths and which permits us to obtain estimates of the direction of fast axis of anisotropy as well as the time delay between the orthogonal quasi shear waves in general the directions of fast velocity obtained both for stations around the atlantic and around the pacific appear to be related to directions of past and present plate motions

regional dispersion of first order overtone rayleigh waves summary records of the first rayleigh overtone in the 70 110s period range following deep subduction zone events are analysed through standard surface wave techniques to retrieve dispersion characteristics in the oceanic environment our data are in general agreement with published models obtained from regionalization of fundamental rayleigh wave paths a general increase in phase velocity with age is observed with a somewhat smaller effect on group velocities continental and trench area data are processed through a regionalization scheme indicating that the difference between average continental and oceanic velocities both phase and group is about 0 2 km s l at periods of the order of 95 s an investigation of a set of simple models allowing structural heterogeneities between oceans and continents down to variable depth suggests that they probably do not extend past the bottom of the asthenosphere 250 km

inverse relationship between the equatorial eastern pacific annual cycle and enso amplitudes in a coupled general circulation model we propose a dynamical interpretation of the inverse relationship between the tropical eastern pacific annual cycle ac amplitude and the el nino southern oscillation enso amplitude based on a pre industrial simulation of geophysical fluid dynamics laboratory couple climate model 2 0 with a fixed concentration of greenhouse gases spanning approximately 500 years the slowly varying background conditions over more than a decade alternately provided favorable conditions for two opposite regimes namely the strong ac weak enso regime and the weak ac strong enso regime for the weak ac strong enso regime the tropical eastern pacific shows meridional asymmetric surface warming with an emphasis on the southern part leading to weakening of both the zonal trade wind and the cross equatorial southerly wind as well as deepening of both the thermocline and mixed layer the deeper mixed layer weaker southerly wind and reduced zonal gradient of the mean sea surface temperature due to tropical eastern pacific warming all acts to reduce the ac conversely the enso was intensified by the deeper mixed layer and deeper thermocline depth thermocline feedback but suppressed by the deeper thermocline depth ekman feedback and the reduced zonal temperature gradient we also computed the coupling strengths of the enso and ac defined as the linear regression coefficients of the zonal and meridional wind stresses against the eastern pacific sst respectively the coupling strengths of both the ac and enso are larger when they are intensified and vice versa all processes for the weak ac strong enso regime operate in the opposite manner for the strong ac weak enso regime

long period love wave overtone data in north america and the pacific ocean new evidence for upper mantle anisotropy abstract two tonga trench earthquakes recorded in north america on wwssn long period instruments have been processed by making use of spatial analysis techniques to retrieve the phase velocities of love wave modes dispersion data up to the third overtone at periods longer than 30 s have been obtained for two broad areas the pacific ocean and north america it is found that the observed love wave phase velocities are not in agreement with the values predicted from the previously published models inferred from rayleigh wave data phase velocity discrepancies as large as 3 4 in the pacific ocean and 2 in north america are observed up to the second overtone preliminary direct computations which have been performed in the framework of transversely isotropic models with the axis of symmetry oriented vertically suggest that the cause for this departure from isotropy probably extends to depths 200 km

slope instabilities at an active continental margin large scale polyphase submarine slides along the northern peruvian margin between 5 s and 6 s a mega submarine slide was evidenced along the peruvian margin during a seabeam survey of the r v charcot bourgois et al 1986 the debris slide was initially interpreted as the result of the slope failure occurring along a seaward curved scarp and extending from east to west along the line of maximum slope complementary bathymetrie data obtained from the r v sonne survey conducted to the north and to the south of the previous surveyed area has resulted in the identification of large scale polyphase submarine slides involving a total surface of about 1000 km2 between latitudes 5 15 s and 6 05 s using seabeam and hydrosweep multibeam echosounder data in combination with deep sea submersible observations three distinct slope failure types related to three main stages have been revealed the three sliding phases occurred roughly along the same trend orientated n230 and are therefore mainly controlled by the n80 orientation of the subducting nazca plate 1 the first phase of slope failure is documented by a debris avalanche deposit which extends from the lower slope down to 5 km within the trench floor the deposit originates from the northern wall of a wide valley located along the upper slope 2 the second phase of slope failure is characterized by a debris avalanche with a crescent shaped scar located along the middle slope and a hummocky deposit covering the lower slope and extending up to 10 km across the trench the volume of rock involved in this event is estimated to some 250 km3 the slope failure is assumed to be related to an oversteepening of the middle slope induced by a rollover deformation 3 the third phase of slope failure corresponds to a translational sliding block and a toppling block with volumes of 6 km3 and 13 km3 respectively the seismic energy produced during the seismic cycle has greatly increased facturation and fluids buildup along the area previously weakened by a rollover fold a restricted n s folding is observed in the vicinity of the trench to the north of the two debris avalanche deposits it may have formed in relation to the local compression limited to the subduction of the nazca plate sliding and folding thus document the paradox between the compressive regime in the lower plate and the extensional regime in the upper part of the upper plate

improving el nino prediction using a space time integration of indo pacific winds and equatorial pacific upper ocean heat content 1 equatorial westerly easterly wind anomalies phase locked to the seasonal cycle typically propagate from the eastern equatorial indian ocean and into the western pacific immediately before an el nino la nina a space time integration of this indo pacific signal yields an index that for 11 out of 12 months of the calendar year leads the el nino index nino3 4 with a correlation of 0 5 or greater for at least some lead in the range 10 15 months cross validated hindcasts suggest that a linear combination of this atmospheric index and the ocean indices nino3 4 and t the anomalous equatorial pacific upper ocean heat content is an excellent predictor of el nino it can predict across the nearest spring persistence barrier but not the one after that the present el nino should die over the spring leaving near neutral conditions for the rest of 2003

three dimensional radial anisotropic structure of the north american upper mantle from inversion of surface waveform data summary seismic anisotropy provides insight into palaeo and recent deformation processes and there fore mantle dynamics in a first step towards a model for the north american upper mantle with anisotropy characterized by a symmetry axis of arbitrary orientation aimed at filling the gap between global tomography and sks splitting studies we inverted long period waveform data simultaneously for perturbations in the isotropic s velocity structure and the anisotropic parameter v 2 sh v2 in the framework of normal mode asymptotic coupling theory nact the resulting 2 d broad band sensitivity kernels allow us to exploit the information contained in long period seismograms for fundamental and higher mode surface waves at the same time to ensure high quality of the retrieved regional upper mantle structure accurate crustal cor rections are essential here we follow an approach which goes beyond the linear perturbation approximation and split the correction into a linear and non linear part the inverted data set consists of more than 40 000 high quality three component fundamental and overtone sur face waveforms recorded at broad band seismic stations in north america from teleseismic events and provides a fairly homogeneous path and azimuthal coverage the isotropic part of our tomographic model shares the large scale features of previous regional studies for north america we confirm the pronounced difference in the isotropic velocity structure between the western active tectonic region and the central eastern stable shield as well as the presence of subducted material juan de fuca and farallon plate at transition zone depths the new regional 3 d radial anisotropic model indicates the presence of two distinct anisotropic layers beneath the cratonic part of the north american continent a deep asthenospheric layer con sistent with present day mantle flow and a shallower lithospheric layer possibly a record of ancient tectonic events

the nature and cause of polarization anomalies of surface waves crossing northern and central eurasia summary results of a pilot experiment preliminary to a systematic study of surface wave polarization across eurasia are presented long period fundamental rayleigh and love waves recorded by the broad band seismic stations kiv kislovodsk and obn obninsk of the iris ida network deployed in the former soviet union fsu were analysed from 14 events to the north east east and south east of these stations in search of particle motion anomalies using a technique called frequency time polarization analysis ftpan all anomalies indicate deviations of wave propagation paths to the north relative to the great circle paths polarization anomalies at obn are uniformly small 5 significant frequency dependent polarization anomalies 5 20 are found for rayleigh and love waves arriving at kiv from teleseismic events at a wide range of backazimuths 26 103 polarization measurements are repeatable both for a number of nearly degenerate events and for reciprocal paths and vary smoothly and continuously as epicentral location is moved consequently such measurements are robust and can provide useful structural information the systematics of the frequency dependence of the polarization anomalies as epicentral position is moved from north to south display sensitivity to structures at a number of length scales results from synthetic experiments using coupled normal mode and gaussian beam synthetics reveal that 1 recently constructed long wavelength aspherical models produce polarization anomalies that are significantly smaller 5 at kiv but of the same sign negative as the observed anomalies and 2 the frequency dependence of the observed anomalies must result from a combination of structures of differing wavelengths with scale lengths ranging from regional to global thus polarization measurements provide new information about currently unmodelled structures a model that fits the polarization anomalies observed at kiv includes a regional scale low velocity feature near to kiv in order to fit the large magnitude short period polarization anomalies and a smaller magnitude continent scale increase in upper mantle velocities and or the reduction of crustal thickness from south to north in central eurasia in order to fit the broad band longer period anomalies the small scale low velocity feature is a model of the sedimentary basin of the sub caspian depression we conclude that measurements of polarization anomalies can be obtained accurately that they are reproducible that they contain currently unmodelled information and that they should prove to be useful in combination with velocity and amplitude information in future tomographic inversions especially to help focus global scale models to regional wavelengths

seismic structure and evidence for eclogitization during the himalayan convergence abstract reflections on the deep moho of the tethyan himalayas have been obtained from vertical seismics at the time predicted by wide angle reflection interpretations supporting the previous inference of a low average crustal velocity a mostly felsic composition is then required through the 70 km of the thickened crust the moho appears as a heterogenous transition layer more than 10 km thick the high velocity measured beneath the moho from pn refractions cannot be attributed any more to e w oriented olivine since sks observations do not confirm such an anisotropy instead eclogite just under the seismic moho could account for the observations these three results from independent parts of the seismic data set support a model of the himalayan convergence in which the indian crust has undergone phase transformation in the granulite eclogite system upon burial the intermediate and basic composition rocks of the middle and lower layers of an initial crust of average platform type can be transformed to such high velocities that they are lost across the himalayas into the level of the moho or just under the moho defined by seismic velocity mostly upper crustal type material then remains to form the thickened crust above consistent with the observed low velocity the variation in moho depth across the himalayas as suggested from wide angle seismics accounts for the first order variation in teleseismic transit times variations in the velocity depth structure of the mantle hence do not dominate but a change in the orientation of sks splitting anisotropy would suggest deformation within the lithosphere to change across the high himalayas and the indus tsangpo suture

seismological structure of the upper mantle a regional comparison of seismic layering abstract we investigate seismic layering i e discontinuities regions of anomalous velocity gradients and anisotropy and its lateral variability in the upper mantle by comparing seismic models from three tectonic regions old 100 ma pacific plate younger 40 ma philippine sea plate and precambrian western australia these models were constructed by combining two data sets scs reflectivity profiles which provide travel times and impedance contrasts across mantle discontinuities and observations of frequency dependent travel times of three component turning s ss ss sss sss sa and surface r1 g1 waves which constrain the anisotropic velocity structure between discontinuities the models provide a better fit to observed seismograms from these regions than the current generation of global tomographic models the australian model is characterized by high shear velocities throughout the upper 350 km of the mantle with no low velocity zone lvz in the isotropically averaged shear velocities in contrast the oceanic models are characterized by a thin high velocity seismic lid underlain by a distinct lvz with a sharp boundary the g discontinuity separating them the g is significantly deeper beneath the western philippine sea plate than beneath the older pacific 89 and 68 km respectively implying that thermal cooling alone does not control the thickness of the lid we interpret this discontinuity as a compositional boundary marking the fossilized base of the melt separation zone msz active during sea floor spreading no discontinuity is detected at the base of the lvz in the oceanic models the s velocity gradient between 200 and 410 km depth is much steeper in the oceans than beneath australia this high oceanic gradient is probably controlled by a decrease in the homologous temperature over this depth interval the relative depths of the transition zone tz discontinuities are consistent with clapeyron slopes expected for an olivine dominated mineralogy the 660 km discontinuity displays variability in its amplitude that appears to correlate with its depth shallow and bright beneath the pacific deep and dim beneath australia and the philippine sea such behavior is possibly caused by the juxtaposition of the olivine and garnet components of the phase transition radial anisotropy extends through the upper 250 km of the mantle in the australia model and through the upper 160 km of the two oceanic models the magnitude of anisotropy is consistent with that expected for models of horizontally oriented olivine and the localization of anisotropy in the shallowest upper mantle implies that it reflects strain associated with past or present tectonic events

along strike variations in the thermal and tectonic response of the continental ecuadorian andes to the collision with heterogeneous oceanic crust oblique to strike geological segmentation in the andean chain has been previously recognised at various scales and is commonly attributed to changes in the convergence vectors of the oceanic and continental plates as well as the upperplate expressions of differing along strike subducted slab age strength and composition we present new white mica and biotite 40 ar 39 ar and zircon and apatite fission track data from several traverses across the cordillera real of ecuador in the northern andes that reveal distinct along strike differences in the timing of accelerated crustal cooling during the cenozoic the data record elevated cooling rates from temperatures of v380 c during v65 55 and v43 30 ma from all sampled regions of the cordillera real and at v15 ma and since v9 ma in the northern cordillera real each cooling period was probably driven by exhumation in response to the accretion and subduction of heterogeneous oceanic crust elevated cooling rates of up to v30 20 c myr were initiated during the palaeocene and eocene early oligocene along the entire contemporaneous margin of ecuador and were driven by the accretion of the oceanic pallatanga terrane and pin on macuchi block respectively onto northwestern south america both of these geological provinces originated at the southern parts of the leading and trailing boundaries of the caribbean plateau and accreted onto the margin during the approximately northeastward migration of the plateau into its current position within ecuador the development of higher topography and elevated cooling rates of up to 50 c myr at v15 ma and since v9 ma are restricted to the region north of 1 30ps and is situated above the postulated subducted flatslab section of the aseismic carnegie ridge plate convergence rate calculations suggest the carnegie ridge collided with the ecuador trench at v15 ma which caused the pre existing coastal provinces to displace to the northeast subsequently driving extension and marine ingressions in southern ecuador and compression and uplift in northern ecuador fl 2001 elsevier science b v all rights reserved

tectonic record of strain buildup and abrupt coseismic stress release across the northwestern peru coastal plain shelf and continental slope during the past 200 kyr 200 kyr both segments uplifted at high rates of 10 to 20 mm yr 1 through tectonic pulses coeval with the eustatic deglacial sea level rises of isotope stage 1 and warm isotope substage 5e respectively the uplift and related extensive emersion of the coastal plain require high coupling along the subduction zone and or underplating at depth offshore industry acquired reflection seismic lines combined with em12 bathymetric data allow us to investigate the tectonic regime and deformation of the continental margin and shelf major dipping seaward detachments control the long term subsidence of this area these main tectonic features define a tectonic segmentation the talara paita and sechura segments are identified from north to south no clear tectonic correlation in time exists between the onshore and the continental margin segmentations or in space either the longterm subsidence of the offshore indicative of subduction erosion working at depth requires low coupling along the subduction channel at depth the distribution of permanent deformation along the northern peru forearc area includes long term uplift along the coastal plain and long term subsidence along the continental margin the neutral line being located within the 10 km seaward from the present coastline an extensive sequence of raised marine cliffs and associated notches evidences that the most recent uplift step 20 23 ka to present along the cabo blanco segment is related to a sequence of major earthquakes we infer that eustacy exerts important feedback coupling to the seismogenic behavior of the north peru subduction zone we speculate that during sea level fall pore fluid pressure diminishes along the subduction channel inducing a possible seaward migration of the locked zone i e migration of the updip limit reaching a maximum by the end of the eustatic low stand during eustatic sea level rise pore fluid pressure increases along the subduction channel this in turn is capable of weakening the previously locked zone along the plate interface beginning an earthquake sequence earth s orbital variations are a potential external cause that may control the physical processes at work along plate interface

comment on tectonic record of strain buildup and abrupt coseismic stress release across the northwestern peru coastal plain shelf and continental slope during the past 200 kyr by jacques bourgois et al citation pedoja k l ortlieb t j devries j machare l audin and v regard 2011 comment on tectonic record ofstrain buildup and abrupt coseismic stress release across the northwestern peru coastal plain shelf and continental slope duringthe past 200 kyr by jacques bourgois et al j geophys res 116 b09401 doi 10 1029 2011jb008321

anisotropic gradients in the upper mantle pn amplitudes in some widely spaced sets of orthogonal marine refraction lines on young oceanic crust are greater in the fast direction than in the slow direction this is inconsistent with the predicted amplitude behavior for simple head waves but can be explained by an increase in anisotropy with depth it appears that these gradients are due to increasing olivine crystal orientation although changes in the relative abundance of two anisotropic minerals without variable tectonization could also account for the observations depth variation of tectonization most probably indicates very high temperature gradients at the moho this would imply a substantial amount of convective heat transport in the whole oceanic crust near mid ocean rises

cenozoic marine sedimentation in the sechura and pisco basins peru abstract the central and northern peruvian margin consists of a series of 8 paired forearc basins which may be separated into an inner set of shelf basins and a seaward set of slope basins we have examined the cenozoic stratigraphy of the onshore portions of the sechura basin 5 7 s and pisco basin 13 16 s two shelf basins which have accumulated marine sediment discontinuously since the mid to late eocene cenozoic sediments in the pisco basin were deposited during at least three major transgressive cycles each sequence is preserved as a similar vertical progression of facies including coarse nearshore bioclastic conglomerates and sandstones grading upwards into sandy siltstones and mudstones and capped by biogenic deposits including diatomites diatomaceous mudstones dolomitic horizons and phosphate deposits stratigraphic nomenclature for the pisco basin has recently evolved a stratigraphy presented here includes the eocene caballas fm upper eocene los choros fm upper eocene to lowermost oligocene yumaque fm uppermost oligocene to middle miocene chilcatay fm and upper miocene to pliocene pisco fm major hiatuses in the pisco basin span the late cretaceous to middle eocene early to late oligocene middle miocene and late pliocene pleistocene to recent cenozoic sediments of the sechura basin were deposited within at least 4 major transgressive cycles with hiatuses during the paleocene to middle eocene oligocene early to middle miocene and late miocene based on recent biostratigraphic studies sediments enriched in biogenic components accumulated between about 40 36 ma 24 16 ma and 11 3 ma in the pisco basin and between 40 37 ma and 8 5 4 5 ma in the sechura basin in both basins the most diatomaceous sediments are restricted to the late eocene and late miocene through pliocene the temporal distribution of biogenic sediments suggests that high productivity conditions linked to coastal upwelling have occurred episodically since at least the late eocene the occurrence of diatomites and phosphorites is diachronous between the pisco and sechura basins and between the peruvian forearc and other circum pacific monterey formation analogs a reflection of the strong influence of local tectonism on sedimentation patterns the volume of neogene sediments along the peruvian forearc is nearly twice that of the monterey fm despite basin to basin facies diachroneity these deposits very likely contributed to fluctuations of the late miocene carbon co 2 system by acting as large carbon sinks

implications of seismic scattering below the 8 discontinuity along pne profile kraton abstract strong scattered arrivals are observed in the 800 1400 km offset range of the four peaceful nuclear explosion pne seismic sections along the 3500 km long e w trending russian profile kraton they give evidence of an 85 km thick inhomogeneous scattering layer in the upper mantle which has a slightly reduced 1 average p wave velocity compared to the layers above and below the top of the anomalous zone is the 8 discontinuity at 100 km depth which is constrained by a clear travel time delay of up to 2 s consistently observed at 900 1000 km 8 offset in the four pne seismic sections we model the inhomogeneous zone below the 8 discontinuity by random velocity fluctuations the full waveform seismic response of a suite of stochastic velocity models is calculated using a two dimensional finite difference scheme the calculated seismic sections resemble the pne data for models where the random fluctuations have a horizontal correlation length of 5 10 km a vertical correlation length not greater than 5 km and a standard deviation of about 2 of the average background velocity fluctuations with significantly larger correlation lengths give rise to coherent scattered arrivals and considerably shorter correlation lengths lead to significantly weaker scattering none of which resemble the observed data the preferred seismic velocity model is in agreement with an upper mantle model in which the low velocity zone below the 8 discontinuity may contain small amounts of partially molten material alternatively the combined effects of rheological weakening and small scale anisotropy may also account for the low velocity scattering layer

seismic anisotropy within the uppermost mantle of southern germany summary this paper presents an updated interpretation of seismic anisotropy within the uppermost mantle of southern germany the dense network of reversed and crossing refraction profiles in this area made it possible to observe almost 900 traveltimes of the p phase that could be effectively used in a time term analysis to determine horizontal velocity distribution immediately below the moho for 12 crossing profiles amplitude ratios of the p phase compared to the dominant crustal phase were utilized to resolve azimuthally dependent velocity gradients with depth a p wave anisotropy of 3 4 per cent in a horizontal plane immediately below the moho at a depth of 30 km increasing to 11 per cent at a depth of 40 km was determined for the axis of the highest velocity of about 8 03 kms at a depth of 30 km a direction of n31 e was obtained the azimuthal dependence of the observed p amplitude is explained by an azimuth dependent sub moho velocity gradient decreasing from 0 06 s in the fast direction to 0 s in the slow direction of horizontal p wave velocity from the seismic results in this study a petrological model suggesting a change of modal composition and percentage of oriented olivine with depth was derived