observations of the kuroshio s barotropic and baroclinic responses to basin wide wind forcing 1 observations show that the kuroshio in the east china sea ecs kuroshio responds to the large scale wind stress curl field at two time scales it is argued that these two responses are related to barotropic and baroclinic modes that reach the ecs via different waveguides variability in the ecs kuroshio is assessed by comparing satellite altimetry historical hydrography and the pacific decadal oscillation pdo index with the latter used as a proxy for the large scale wind stress curl forcing sea level difference across the ecs kuroshio is positively correlated with pdo at zero lag and negatively correlated at 7 year lag in contrast pycnocline steepness and pdo are uncorrelated at zero lag and negatively correlated at 7 year lag these signals in the ecs kuroshio considered together with wind stress curl anomalies in the open ocean are consistent with a barotropic response to the wind at zero lag the barotropic response is likely forced in the central north pacific by wind stress curl anomalies of opposite sign one of which is centered at ecs latitudes 27 n while the other sits further north this suggests that in general the absolute transport at a given latitude is not simply that predicted by the sverdrup balance along the latitude this is a consequence of waveguides that can steer the barotropic mode across latitude lines in contrast the signals that lag pdo by 7 years are consistent with a baroclinic mode which represents the ocean s time integrated response to the wind stress curl along a single latitude band between 24 n and 27 n

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

sensitivity studies of the red sea eddies using adjoint method the topography data is derived from general bathymetric chart of the oceans gebco https www gebco net the open boundary conditions are extracted from the estimating the circulation and climate of the ocean ecco product https ecco jpl nasa gov products the data supporting the analysis presented here can be found at figshare https figshare com articles data for 2018jc014531r 7243184 the research reported in this manuscript is supported by king abdullah university of science and technology kaust and made use of the resources of the supercomputing laboratory and computer clusters at kaust

complex upper mantle deformation beneath the north china craton implications for lithospheric thinning summary the mechanism of lithospheric thinning of the north china craton ncc remains controversial to constrain the mechanism this study investigated the upper mantle deformation pattern of the craton by measuring shear wave splitting at the cratonic edge the results derived from data recorded at 47 stations reveal a complex pattern of mantle deformation inside the eastern craton the majority of fast direction trends se nw parallel to the tectonic extension direction accompanying with the lithospheric thinning at the cratonic edge 15 stations with only null splitting results indicate undetectable anisotropy beneath the stations this may be due to upwelling or chaotic ascension of mantle flow to the north off the craton large delay times and variation of splitting parameter with backazimuth are generated by the combination of lithospheric and asthenospheric anisotropy based on comparison of the splitting results and the predicted ones by the compelling models it is likely that lithospheric delamination dominated the lithospheric thinning at the north edge of the ncc during the mesozoic to cenozoic

lithospheric structure of the central andes based on surface wave dispersion 1 shear wave velocity is very sensitive to temperature anomalies and partial melt and can provide important insights on the state of the lithosphere with that aim in mind phase velocities of rayleigh and love waves have been inverted for the regionalized shear wave velocity structure of the lithosphere across the central andes this inversion reveals strong lateral variations of vs both across the range and along strike in the altiplano crust in the upper crust the main features of our models are prominent low velocity anomalies probably related to partial melt below the los frailes ignimbrite complex and the southern altiplano at lower crustal level the altiplano is characterized by lower vs than the surrounding regions we find that the transition from the altiplano to the puna is associated with a 7 km thickening of the crust at mantle depths the nazca plate is found to be overlaid by a dipping low velocity zone with decreasing intensity with depth our results favor the idea of a cold mantle lid underlying the whole central andes

treating strong adjoint sensitivities in tropical eddy permitting variational data assimilation a variational data assimilation system has been implemented for the tropical pacific ocean using an eddy permitting regional implementation of the mitgcm the adjoint assimilation system was developed by the estimation of the circulation and the climate of the ocean consortium and has been extended to deal with open boundaries this system is used to adjust the model to match observations in the tropical pacific region using control parameters which include initial conditions open boundaries and time dependent surface fluxes this paper focuses on problems related to strong adjoint sensitivities that may impede the model fit to the observations a decomposition of the velocities at the open boundaries into barotropic and baroclinic modes is introduced to deal with very strong sensitivities of the model sea surface height to the barotropic component of the inflow increased viscosity and diffusivity terms are used in the adjoint model to reduce exponentially growing sensitivities in the backward run associated with nonlinearity of the forward model simplified experiments in which the model was constrained with levitus temperature and salinity data reynolds sea surface temperature data and topex poseidon altimeter data were performed to demonstrate the controllability of this assimilation system and to study its sensitivity to the starting guesses for forcing and initial conditions

mapping ocean observations in a dynamical framework a 2004 06 ocean atlas abstract this paper exploits a new observational atlas for the near global ocean for the best observed 3 yr period from december 2003 through november 2006 the atlas consists of mapped observations and derived quantities together they form a full representation of the ocean state and its seasonal cycle the mapped observations are primarily altimeter data satellite sst and argo profiles gcm interpolation is used to synthesize these datasets and the resulting atlas is a fairly close fit to each one of them for observed quantities especially the atlas is a practical means to evaluate free running gcm simulations and to put field experiments into a broader context the atlas derived quantities include the middepth dynamic topography as well as ocean fluxes of heat and salt freshwater the atlas is publicly available online www ecco group org this paper provides insight into two oceanographic problems that are the subject of vigorous ongoing research first regarding ocean circulation estimates

electrical resistivity structure of the upper mantle beneath northeastern china implications for rheology and the mechanism of craton destruction abstract the north china craton ncc and central asian orogen belt caob in northeastern china experienced a range of tectonic events during the phanerozoic dominated by lithospheric thinning of the eastern ncc in the late mesozoic and cenozoic in order to better understand the tectonic evolution of the ncc and the caob new broadband and long period magnetotelluric data were collected along a north west to south east trending profile that extended from the caob across the yanshan belt the tanlu fault zone to the liaodong peninsula a two dimensional 2 d resistivity model was derived from inversion of the transverse electric mode transverse magnetic mode and vertical magnetic field data in the crust of the caob the resistivity model shows a northwest dipping low resistivity zone beneath the solonker suture that is identified as the suture zone formed by the collision between the siberian and north china cratons the upper mantle of the caob is characterized by moderate resistivity values 300 1000 m that are best explained by the presence of hydrogen dissolved in olivine the water concentration of the caob mantle is comparable to values reported for the asthenosphere and cratons that have been significantly hydrated the ncc upper mantle is generally lower in resistivity than the caob upper mantle and a zone of lower resistivity is observed in the upper mantle at the southeast end of the profile beneath the ncc superimposed on this southeast decrease in upper mantle resistivity three low resistivity zones were imaged 1 below the xilamulun fault 2 close to the north south gravity lineament and 3 between the northern yanshan belt and tanlu fault zone the low resistivities can be explained as regions of partial melts or fluids perhaps caused by asthenospheric upwelling together with seismic imaging results and geochemical data the resistivity model shows that the modification of the lithosphere associated with craton destruction has occurred in a spatially non uniform manner in the region of the ncc investigated in this study

isostatic state and crustal structure of north china craton derived from goce gravity data abstract the crustal structure between different subregions of the north china craton ncc plays an important role in improving our understanding on the craton evolution here we present a flexural moho map and isostatic residual gravity field of the ncc derived from the go cons gcf 2 tim r3 model we first investigate the influence of additional sources on the forward flexure calculation especially the distinct thinning of the lithospheric thickness from west to east after removing the gravity effects of the lab undulations the flexural moho and isostatic residual gravity field of the ncc are calculated using the vening meinesz regional isostasy models there are high to medium positive residual anomalies beneath the eastern block and trans north china orogen while negative residual anomalies delineate the yinshan block ordos plateau and khondalite belt this obvious disparity is consistent well with the decreasing depth of the flexural moho from west to the east a profile across the eastern block trans north china orogen and the western block was employed to construct a density structure of the crust and uppermost mantle by comparing the surface topography bouguer gravity isostatic moho and seismological moho undulations we find that the flexural moho is much shallower than the seismic moho beneath the northern margin of the ordos block possibly indicating the over compensated isostatic state caused by the dominant nw se oriented compressional deformation in the lithospheric processes density modeling results further predicted that a high density body may exist in the lower crust beneath the northern margin of the ordos block which could be a westward dipping upper middle crust remnant stagnating in the lower crust beneath the western block medium to high pressure metamorphism of granulite facies or eclogite facies resulting from subsequent continental thickening during the continental collision may be responsible for modifying the remaining subduction remnant

structure of the crust and uppermost mantle of the yanshan belt and adjacent regions at the northeastern boundary of the north china craton from rayleigh wave dispersion analysis abstract we have used rayleigh wave dispersion analysis and inversion to produce a high resolution s wave velocity imaging profile of the crust and uppermost mantle structure beneath the northeastern boundary regions of the north china craton ncc using waveform data from 45 broadband ncisp stations rayleigh wave phase velocities were measured at periods from 10 to 48 s and utilized in subsequent inversions to solve for the s wave velocity structure from 15 km down to 120 km depth the inverted lower crust and uppermost mantle velocities about 3 75 km s and 4 3 km s on average are low compared with the global average the moho was constrained in the depth range of 30 40 km indicating a typical crustal thickness along the profile however a thin lithosphere of no more than 100 km was imaged under a large part of the profile decreasing to only 60 km under the inner mongolian axis ima where an abnormally slow anomaly was observed below 60 km depth the overall structural features of the study region resemble those of typical continental rift zones and are probably associated with the lithospheric reactivation and tectonic extension widespread in the eastern ncc during mesozoic cenozoic time distinctly high velocities up to 4 6 km s were found immediately to the south of the ima beneath the northern yanshan belt ysb extending down to 100 km depth the anomalous velocities are interpreted as the cratonic lithospheric lid of the region which may have not been affected by the mesozoic cenozoic deformation process as strongly as other regions in the eastern ncc based on our s wave velocity structural image and other geophysical observations we propose a possible lithosphere asthenosphere interaction scenario at the northeastern boundary of the ncc we speculate that significant undulations of the base of the lithosphere which might have resulted from the uneven mesozoic cenozoic lithospheric thinning may induce mantle flows concentrating beneath the weak ima zone the relatively thick lithospheric lid in the northern ysb may serve as a tectonic barrier separating the on craton and off craton regions into different upper mantle convection systems at the present time

constraints on absolute s velocities beneath the aegean sea from surface wave analysis summary the 3 d structure of the lithosphere beneath the aegean sea is investigated through surface wave dispersion analysis rayleigh and love waves recorded by 12 broad band stations installed for a duration of 6 months in the aegean region are processed through array analysis and wiener filtering data from three geofon stations in the area of crete were also used the resulting two station phase velocities are used to determine lateral variations of rayleigh wave phase velocities between periods of 20 and 100 s by a 2 d ray tomography method the obtained phase velocities are inverted to calculate variation of s wave velocity with depth using a combination of linearized inversion and a monte carlo based non linear inversion the absolute s wave velocity is resolved to a depth of approximately 200 km a highvelocity anomaly of 3 per cent is observed in the southern aegean attributed to the hellenic subduction in the northern part of the aegean in the prolongation of the north anatolian fault which is influenced by strong extensional movements we found low absolute s wave velocities at 50 100 km depth this supports a model of a distributed deformation of the upper mantle in the area separate rayleigh and love wave phase velocity inversions along common profiles reveal a strong love rayleigh discrepancy in the northern aegean down to at least 150 km depth i e most probably including the top of the asthenosphere

measuring surface wave phase velocities beneath small broad band arrays tests of an improved algorithm and application to the french alps the local measurement of dispersion curves of intermediate period surface waves is particularly difficult because of the long wavelengths involved we suggest an improved procedure for measuring dispersion curves using small aperture broad band arrays the method is based on the hypotheses of plane incoming waves and that averaging over a set of events with a good backazimuth distribution will suppress the effects of diffraction outside the array none of the elements of the processing are new in themselves but each step is optimized so we can obtain a reliable dispersion curve with a well defined uncertainty the method is based on the inversion for the slowness vector at each event and frequency using time delays between pairs of stations where the time delays deltat are obtained by frequency domain wiener filtering the interstation distance projected on to the slowness vector d is then calculated the final dispersion curve is found by at each frequency calculating the inverse of the slope of the best fitting line of all d deltat points to test the algorithm it is applied to synthetic seismograms of fundamental mode rayleigh waves in different configurations 1 the sum of several incident waves 2 an array located next to or above a crustal thickening and 3 added white noise using regular and irregular backazimuth distributions in each case a circular array of 23 km diameter and composed of six stations is used the algorithm is stable over a large range of wavelengths between half and a tenth of the array size depending on the configuration the situations of several simultaneously incoming waves or neighbouring heterogeneities are well handled and the inferred dispersion curve corresponds to that of the underlying medium above a strong lateral heterogeneity the inferred dispersion curve corresponds to that of the underlying medium up to wavelengths of eight times the array size in the configuration considered but further work is needed to better understand the limits under which the obtained dispersion curve is not biased in the case of 5 per cent spectral amplitude white noise the dispersion curve is also stable for wavelengths up to approximately eight times the array size but this limit depends of course strongly on the noise level the method is finally applied to data from two arrays in the french alps located 50 km apart it is possible to measure the dispersion curves up to wavelengths approximately ten times bigger than the array diameter the difference in the dispersion curves is compatible with a crustal and lithospheric thickening under the alps however the observed errors are large which result in severe limits on the interpretation in terms of lithospheric structure longer recording periods may help to reduce the errors otherwise the algorithm is likely to be of use mainly in areas where the lateral variations outside the array are smaller than those of the french alps

measurements of rayleigh wave phase velocities in nevada implications for explosion sources and the massachusetts mountain earthquake single station measurements of rayleigh wave phase velocity are obtained for paths between the nevada test site and the livermore broadband regional stations nuclear underground explosions detonated in yucca valley were the sources of the rayleigh waves the source phase phi sup s required by the single station method is calculated for an explosion source by assuming a spherically symmetric point source with step function time dependence the phase velocities are used to analyze the rayleigh waves of the massachusetts mountain earthquake of 5 august 1971 measured values of source phase for this earthquake are consistent with the focal mechanism determined from p wave first motion data a moment tensor inversion of the rayleigh wave spectra for a 3 km deep source gives a horizontal least compressive stress axis oriented n63 sup 0 w and a seismic moment of 5 5 x 10 sup 22 dyne cm the general agreement between this work and the work of others on p waves supports the measurements of phase velocities and in turn the explosion source model used to calculate phi sup s 20 references 15 figures

slip distribution of the 2015 lefkada earthquake and its implications for fault segmentation this work was partially supported by the uk natural environmental research council nerc through ne k011006 1 ne p008828 1 and the centre for the observation and modelling of earthquakes volcanoes and tectonics comet ga 13 m 031 http comet nerc ac uk

sensitivity of western boundary transport at the mean north equatorial current bifurcation latitude to wind forcing abstractthe bifurcation of the north equatorial current nec plays an important role in the heat and water mass exchanges between the tropical and subtropical gyres in the pacific ocean the variability of western boundary transport wbt east of the philippine coast at the mean nec bifurcation latitude 12 n is examined here a tropical pacific regional model is set up based on the massachusetts institute of technology general circulation model and its adjoint which calculates the sensitivities of a defined meridional transport to atmospheric forcing fields and ocean state going backward in time the adjoint derived sensitivity of the wbt at the mean nec bifurcation latitude to surface wind stress is dominated by curl like patterns that are located farther eastward and southward with increasing time lag the temporal evolution of the adjoint sensitivity of the wbt to wind stress resembles wind forced rossby wave dynamics but propagating with speeds determined by the background stratification and curre

rayleigh wave tomography of china and adjacent regions 1 this paper presents a tomographic study on the s wave velocity structure of china and adjacent regions group velocity dispersions of fundamental rayleigh waves along more than 4000 paths were determined with frequency time analysis the study region was divided into a 1 1 grid and velocities in between grid nodes were calculated by bilinear interpolation the occam s inversion scheme was adopted to invert for group velocity distributions this method is robust and allows us to use a fine grid in model parameterization and thus helps to restore a more realistic velocity pattern checkerboard tests were carried out and the lateral resolution was estimated to be 4 6 in china and its eastern continental shelves the resulting group velocity maps from 10 to 184 s showed good correlation with known geological and tectonic features the pure path dispersion curves at each node were inverted for shear wave velocity structures the three dimensional velocity model indicates thick lithospheres in the yangtze and tarim platforms and hot upper mantles in baikal and western mongolia coastal area and continental shelves of eastern china and indochina and south china sea regions the tibetan plateau has a very thick crust with a low velocity zone in its middle beneath the crust a north dipping high velocity zone mimicking a subducting plate reaches to 200 km in depth and reaches to the kunlun mountains northward in northern tibet a low velocity zone immediately below the moho extends eastward then turns southward along the eastern edge of the plateau until it connects to the vast low velocity area in indochina and the south china sea

shear wave velocity variations in the upper mantle beneath central europe summary a new model eur s91 of shear wave velocity variations in the upper mantle beneath central europe and surrounding regions down to a depth of 670km is presented the model is derived from the inversion of the waveforms of 217 seismograms using the partitioned waveform inversion method for the seismogram in the time window from the s wave arrival to the fundamental mode of the rayleigh wave the seismograms were mostly assembled from digitally recording long period and broad band stations in europe the resulting 3 d model accurately predicts most of the observed waveforms in a wide band of frequencies body waves were fit for frequencies up to 60mhz the fundamental rayleigh mode which at high frequencies is more prone to scattering and multipathing was generally low passed at 25 mhz the resolving power of the data set depends strongly on the density of available wave paths and varies as a function of geographical position small scale heterogeneities like the subducted lithosphere in the hellenic collision zone were imaged in the region with the highest density of wave paths which indicates an optimum resolution of better than 200 km the main new results of this study pertain to the transition between east and central europe we present new information about the structure below the tornquist teisseyre zone ttz the ttz is generally regarded as the boundary between the precambrian crust of the baltic shield russian platform and the younger crust of central europe our 3 d s velocity model reveals that below this line a sharp lateral boundary extends down to at least 140 km depth with high velocities beneath the baltic shield and russian platform contrasting to the low velocities beneath the younger regions of europe the observed velocity contrast across the ttz is largest between the pannonian basin and the russian platform where it is equal to 12 per cent at 80 km depth at depths of 300 400 km the ttz is underlain by a zone of low s velocity which indicates a local thinning of the deeply rooted high velocity structure or tectosphere that underlies most of eastern europe in addition to these new results on the transition region between east and central europe a number of features that are present in other tomographic results have been confirmed the precambrian provinces of europe are characterized by high s velocities low velocities are found beneath the pannonian basin the western mediterranean northern aegean sea turkey and a small region south west of the massif central the lithosphere beneath the paris basin has a positive s velocity anomaly the resolution of all these anomalies has been established with sensitivity tests

crustal structure across the yanshan belt at the northern margin of the north china craton abstract we applied an integrated receiver function imaging technique to the teleseismic data from 54 ncisp iii broadband seismic stations to study the fine scale crustal structure beneath the eastern yanshan belt ysb and adjacent areas at the northern margin of the north china craton ncc the robustness and reliability of the resultant crustal image were noticeably improved by achieving imaging consistency between common conversion point stacking and waveform inversion of the receiver functions our imaging result revealed substantial lateral heterogeneities in the crust of the study region as displayed by the undulating intra crustal interfaces highly varying upper middle and lower crust thicknesses and interlayers of low and high velocities the crustal structure of the ysb is characterized by significant structural variations together with a sharp moho a thin to normal crust and a lower crust with lower velocity and normal thickness it differs markedly from the bohai bay basin and the taihang mountains within the interior of the ncc the distinct features and structural complexity of the ysb might be attributed to the complex tectonic history of the region especially the multiple phases of contraction and possible occurrence of crustal delamination which is in large contrast to other subregions of the ncc where tectonic extension likely dominated the crustal deformation since the late mesozoic

the enigmatic yinshan fold and thrust belt of northern china new views on its intraplate contractional styles the east to east northeast trending yinshan belt lies within north china extending westward at least 1100 km from china s eastern coast to inner mongolia this intraplate jurassic cretaceous belt underwent contractional and normal faulting folding and contemporaneous terrestrial sedimentation and magmatism current views on its contractional deformational style favor relatively limited thick skinned faulting of archean basement and cover units these views are challenged however by recent discoveries in the eastern part of the belt of south directed ductile nappe formation and large displacement 40 45 km thin skinned northward thrust faulting both involving archean and younger rock units collision of the siberian and north china plates upon closure of a jurassic and early cretaceous mongolo okhotsk ocean more than 800 1100 km to the north may have been responsible for yinshan north south contraction some patterns of contraction e g jurassic cretaceous ductile nappe formation appear to have been influenced by a superposed magmatic regime related to westward subduction of a pacific basin plate beneath the north china plate

dynamic cause of marginal lithospheric thinning and implications for craton destruction a comparison of the north china superior and yilgarn cratons we present a comparative tectonic analysis of the north china craton ncc which has lost parts of its root with the yilgarn and superior cratons which preserve their roots we compare the geophysical structure and tectonic histories of these cratons to search for reasons why some cratons lose their roots while others retain them based on the comparison and analysis of geological geophysical and geochemical data it is clear that the lithospheric thinning beneath craton margins is a common phenomenon which may be caused by convergence between plates however craton destruction is not always accompanied by lithospheric thinning except for cratons that suffered subduction and collision from multiple sides the western block also known as the ordos block of the ncc yilgarn and superior cratons have not experienced craton destruction the common ground among them is that they are surrounded by weak zones e g mobile belts or orogens that sheltered the cratons from deformation which contribute

constraints on the timing of uplift of the yanshan fold and thrust belt north china this paper reports in situ u pb ages and hf isotopic data on detrital zircons from paleozoic to late mesozoic strata in the xishan area near beijing that provide important constraints on the evolution and paleogeography of the northern part of the north china craton ncc zircons from carboniferous to late mesozoic sandstones are characterized by three major groups of u pb ages 2 5 2 3 ga 1 9 1 7 ga and late phanerozoic ages the neoarchean and paleoproterozoic zircons and some phanerozoic zircons have negative ehf t values similar to igneous zircons from intrusive rocks known from the ncc indicating that the source of the sandstones was locally derived however late triassic to late jurassic 205 158 ma sandstones contain a group of phanerozoic zircons with positive ehf t values distinct from known igneous zircons in the ncc suggesting an exotic source the nearest potential source is the xing meng orogenic belt xmob to the north of the ncc where considerable amounts of juvenile crustal materials exist it is concluded that there are two sudden shifts in source provenances of the xishan sediments from the ncc before the late triassic to a mixed source from the ncc and xmob during the late triassic to late jurassic and then from the ncc again during the late jurassic 158 ma the first shift in source resulted from the exhumation and denudation of rocks due to uplift of the xmob which coincided with post collisional extension in the late triassic and intraplate extension of the ncc in the middle to late jurassic the second source shift resulted from the uplift of the yanshan fold and thrust belt thus constraining the timing of this to the late jurassic

lithospheric structure beneath the central and western north china craton and the adjacent qilian orogenic belt from rayleigh wave dispersion analysis abstract we used surface wave tomography to image the lithospheric s wave velocity structure along a linear seismic array across the central and western north china craton ncc and the adjacent qilian orogenic belt qb using waveform data from 8 earthquakes collected at 60 broadband stations rayleigh wave phase velocities were measured at periods of 20 120 s and subsequently inverted for reliable s wave velocities from 60 to 200 km depth distinct lithospheric structures and marked lateral variations were revealed beneath the study region correlating well with regional geological and tectonic features the average s wave velocity from 60 to 200 km depth beneath the array is 4 45 km s 1 lower than that in model ak135 high velocities of 4 45 km s are most pronounced beneath the stable ordos block western ncc however the depth to which the observed high velocity body extends varies significantly laterally it is deepest 200 km under eastern ordos and becomes shallower on both sides along the array the maximum depth of the high velocity body gradually shallows westward and reaches 110 km near the western edge of ordos this depth variation suggests a coexistence of both preserved and modified lithosphere in ordos the depth of high velocities decreases rapidly eastward by 80 km over a lateral distance of

lithospheric thickness of the chinese continent abstract we invert for the upper mantle temperatures of the chinese continent in the depth range of 70 240 km from a recent s velocity model the depth where temperatures intersect a mantle adiabat with a potential temperature of 1300 c is in close correspondence with the top of the seismic low velocity zone for most regions this correspondence implies that seismic lithosphere estimated from short time scale seismic information may be equivalent to the long time scale geodynamical lithosphere defining the 1300 c adiabat as coinciding with the lithospheric base we estimate the seismic thermal lithosphere thickness the estimated thickness shows obvious dependence on the tectonic settings beneath eastern china which mainly belongs to the circum pacific tectonic domain it has a thickness of 100 km and beneath the qinghai tibet plateau and south to the tarim craton which belong to the tethyan tectonic domain it has a thickness of 160 220 km the lithospheric thicknesses of the three large para platforms cratons range from 170 km for the western yangtze 140 km for tarim and 100 km for sino korean the three cratons may have been reshaped by phanerozoic tectonic activities and are thinner than most cratons in other continents

persistent sea surface temperature and declined sea surface salinity in the northwestern tropical pacific over the past 7500 years abstract to understand holocene climate evolutions in low latitude region of the western pacific paired 18o and mg ca records of planktonic foraminifer globigerinoides ruber 250 300 m sensu stricto s s from a marine core ori715 21 121 5 e 22 7 n water depth 760 m underneath the kuroshio current kc off eastern taiwan were analyzed over the past 7500 years the geochemical proxy inferred sea surface temperature sst hovered around 27 28 c and seawater 18o 18ow slowly decreased 0 2 0 4 for two kc sites at 22 7 and 25 3 n comparison with a published high sst and high salinity equatorial tropical pacific record md98 2181 located at the mindanao current mc at 6 3 n reveals an anomalous time interval at 3 5 1 5 kyr ago before 1950 ad sst gradient between the mc site and two kc site decrease from 1 5 2 0 c to only 0 1 c and 18ow from 0 1 0 3 to 0 for this 2 kyr time window the high sst and low gradient could result from a northward shift of the north equatorial current which implies a weakened kc the long term descending 18ow and increasing precipitation in the entire low latitude western pacific and the gradually decreasing east asian summer monsoonal rainfall during middle to late holocene is likely caused by different land and ocean responses to solar insolation and or enhanced moisture transportation from the atlantic to pacific associated with the southward movement of itcz

interannual to decadal variations of tropical subtropical exchange in the pacific ocean boundary versus interior pycnocline transports abstract interannual to decadal variations of tropical subtropical mass exchange in the pacific ocean are investigated using a near global ocean general circulation model along with satellite observations of sea level and wind and a data assimilation product the analysis focuses on the variability of pycnocline transports through the western boundary and interior near 10 n and 10 s in contrast to time mean exchange where boundary and interior pycnocline transports are both equatorward the variations of boundary and interior pycnocline transports are found to be generally anticorrelated to each other moreover the variation of the boundary pycnocline transport is smaller than that of the interior again different from time mean exchange where the boundary transport at 10 n is substantially larger than that through the interior interannual variations of the boundary and interior transports are consistent with near surface geostrophic flow inferred from sea level data interior pycnocline flow into th

construction of the adjoint mit ocean general circulation model and application to atlantic heat transport sensitivity we first describe the principles and practical considerations behind the computer generation of the adjoint to the massachusetts institute of technology ocean general circulation model gcm using r giering s software tool tangent linear and adjoint model compiler tamc the tamc s recipe for fortran line by line generation of adjoint code is explained by interpreting an adjoint model strictly as the operator that gives the sensitivity of the output of a model to its input then the sensitivity of 1993 annual mean heat transport across 29on in the atlantic to the hydrography on january 1 1993 is calculated from a global solution of the gcm the kinematic sensitivity to initial temperature variations is isolated showing how the latter would influence heat transport if they did not affect the density and hence the flow over 1 year the heat transport at 29on is influenced kinematically from regions up to 20 o upstream in the western boundary current and up to 5 o upstream in the interior in contrast the dynamical influences of initial temperature and salinity perturbations spread from as far as the rim of the labrador sea to the 29on section along the western boundary the sensitivities calculated with the adjoint compare excellently to those from a perturbation calculation with the dynamical model perturbations in initial interior salinity influence meridional overturning and heat transport when they have propagated to the western boundary and can thus influence the integrated east west density difference our results support the notion that boundary monitoring of meridional mass and heat transports is feasible

multiparameter monitoring of fogo island cape verde for volcanic risk mitigation fogo island in the cape verde archipelago north atlantic is a stratovolcano of nearly conical shape that rises 2829 m above sea level and v6000 m above the surrounding seafloor with a population of 40 000 the island has known intense historical volcanic activity since ad 1500 with an average interval between eruptions of the order of 20 years twentieth century rates were more subdued with only two flank eruptions in 1951 and 1995 following the 1995 eruption increased awareness of the volcanic hazard affecting the population of the island led to the deployment of the permanent vigil network seismographic stations both broadband and short period tiltmeters and a co2 sensor where installed in fogo together with a telemetry infrastructure to allow remote real time monitoring a broadband seismographic station was installed in neighbour brava island the operation of the network was complemented by the introduction of routine geodetic and microgravity surveying and the operation of an automatic meteorological station in this paper we describe the methodology adopted to monitor the volcanic activity combining real time data analysis volcanotectonic and volcanic earthquakes volcanic tremor and tilt with repeated surveying at intervals of several months gps microgravity examples of data from the first years of operation are presented in particular the data pertaining to a period of anomalous activity in september october 2000 are discussed in the context of the risk mitigation strategy currently being developed

the nascent kuroshio of lamon bay a northward flowing current emanating from the north equatorial current nec bifurcation at the philippine margin enters lamon bay along luzon s eastern coast there the nec tropical water masses merge with subtropical water of the western north pacific to form the kuroshio a northward flowing western boundary current is first observed near 16 5 n marking the initiation of the kuroshio the current feeding into the nascent kuroshio of lamon bay is bracketed by an anticyclonic dipole to its northeast and a cyclonic dipole to its southwest ship based observational programs in the spring seasons of 2011 and 2012 detect a shift of the lamon bay thermohaline stratification with marked enrichment of nec tropical thermocline water in 2012 relative to a dominant western north pacific subtropical stratification of 2011 temperature salinity time series from moorings spanning the two ship based observations identify the timing of the transition as december 2011 the nec bifurcation was further south in may 2012 than in may 2011 we suggest that the more southern bifurcation in may 2012 induced increased nec thermocline water injection into lamon bay and nascent kuroshio increasing the linkage of the western north pacific subtropical and tropical thermoclines this connection was reduced in may 2011 as the nec bifurcation shifted into a more northerly position and western north pacific subtropical thermocline dominated lamon bay stratification

long term observations of tropical instability waves abstract reynolds sea surface temperature sst data showing tropical instability waves tiws in the tropical pacific are analyzed along with current measurements from the tropical atmosphere ocean tao buoy array and wind speeds from the european remote sensing satellite ers 1 and 2 scatterometers tiws are visible as undulations in the sst cold fronts that delineate the northern and southern boundaries of the cold tongue in the equatorial pacific the sst pattern results from advection of the sst front by instabilities in the near surface equatorial currents although the waves are seen on both sides of the pacific cold tongue and north of the equator in the atlantic they are most intense and thereby most observable in the north equatorial pacific the combination of data used in this analysis provides information about these waves the factors controlling them and their coupling to the atmosphere on annual and interannual timescales on annual timescales the tiws generally establish a strong

seismic anisotropy beneath stable continental interiors a robust knowledge of seismic anisotropy beneath the continents is essential to our understanding of plate tectonic theory as anisotropy provides a unique constraint on the character of past and present deformation in the lithosphere and sublithospheric mantle this review paper summarizes the range of techniques currently available to image seismic anisotropy with passive source seismic data and addresses current issues surrounding the observation and interpretation of continental seismic anisotropy to this end we present case studies for four regions where seismic anisotropy has been extensively investigated in recent years eastern north america the canadian shield australia and southern africa based on this full suite of results we infer that stable continental regions generally contain seismic anisotropy that is clearly located within both the lithosphere and the sublithospheric mantle usually to depths of at least 200 km and perhaps more an implication of these results is that tectonic plates are at most only partially coupled to the underlying mantle the results from these case studies also demonstrate that while remarkable progress in seismic anisotropy imaging has been achieved in recent years it is clear that much more work will be required to adequately understand the origin of continental seismic anisotropy we suggest that a more robust characterization of anisotropic parameters can only be achieved by integrating complementary seismic datasets and by incorporating constraints from key related datasets from mineral physics magnetotellurics gravity and geodesy

the lithosphere of north china craton from surface wave tomography abstract fundamental mode rayleigh wave group velocity dispersion data were used in a tomographic study to reconstruct the crust and upper mantle shear velocity structure in east asia this article expounds the features of lithosphere structure in different sub regions of north china and discusses their implications for the tectonic evolution and present tectonics of north china craton ncc the study revealed that strong earthquakes took place in the low velocity zones and along the boundaries between high and low velocities in the middle and lower crust the active nw trending zhangjiakou bohai seismic belt corresponds to a prominent low velocity zone in the crust and upper mantle lid in addition to the well known structural difference between western and eastern ncc we are able to resolve clearly the lithospheric features of sub regions in eastern ncc the southern north china basin and north yellow sea are characterized by a high velocity crust and upper mantle lid down to 70 80 km depth while the northern north china basin has a low velocity crust and the velocity below moho to about 130 km is rather uniform and low there is also a general trend of velocity decrease in the upper mantle from west to east the velocity images bear the imprints of subduction and collision that took place in the periphery of ncc since mesozoic and shed some light on the mechanism of mesozoic lithospheric thinning of eastern ncc

crust and upper mantle heterogeneities in the southwest pacific from surface wave phase velocity analysis abstract direct earthquake to station rayleigh and love wave data observed on high gain broadband records are analyzed in order to improve the lateral resolution of the uppermost mantle in the southwest pacific region we used data of nine permanent geoscope and iris stations located in the southern hemisphere and nine other stations as part of two temporary networks the first one installed in new caledonia and vanuatu hereafter named cavascope network by orstom and the eost from louis pasteur university in strasbourg france and the second one installed in the fiji tonga and niue islands hereafter named spase network by washington university in st louis usa in order to collect more significant details on the surficial structures we included the analysis of short period waves down to 8 s a multiple frequency filtering technique has been used to recover phase velocities of rayleigh and love waves for selected earthquakes with magnitude greater than 5 5 and with known centroid moment tensor cmt about 1100 well distributed seismograms have been processed in the period range 8 100 s and corrections for topography and water depth have been applied to the observed phase velocities the geographical distribution of phase velocity anomalies have then been computed using the tomographic method developed by montagner montagner j p 1986a regional three dimensional structures using long period surface waves ann geophys 4 b3 283 294 due to a poor knowledge of dense well distributed crustal thickness values and corresponding velocity models we did not perform or speculate on the construction of an s wave 3d velocity model therefore we limited this study to the interpretation of the phase velocity distribution the location of phase velocity anomalies are well determined and the deviations are discussed within the framework of the geological context and compared with other tomographic models at long periods from 40 s to 100 s our results agree well with most of previous studies the tomographic imaging shows a large contrast between low and high phase velocities along the solomon new hebrides and fiji tonga trenches the lowest phase velocity anomalies are distributed beneath northern and southern fiji basins and the lau basin corresponding to the volume situated just above the dipping slabs whereas the highest values are displayed beneath the pacific plate and the eastern part of indian plate downgoing under the north fiji basin at shorter periods our results show that the phase velocity distributions are well correlated with the large structural crustal domains the use of local temporary broadband stations in the central part of the studied area gives us the opportunity to observe surface waves showing well dispersed trains allowing extended velocity measurements down to 8 s although aliasing due to multipaths become important the continental regions eastern australia new guinea fiji islands and new zealand show low velocities which are likely due to thick continental crust whereas the tasmanian d entrecasteaux and the northern and southern fiji basins are characterized by higher velocities suggesting thinner oceanic crust additional analysis including the anisotropic case and s wave velocity inversion with depth is in progress

importance of horizontal seafloor motion on tsunami height for the 2011 mw 9 0 tohoku oki earthquake abstract it is now clear that the 2011 tohoku oki earthquake ruptured the subduction interface all the way to the japan trench however there is significant disagreement about just how much slip occurred at the trench with most geodetic studies locating only a small fraction of the maximum slip there whereas broadband seismic studies put the majority of the slip near the trench measurements of seafloor displacement near the trench also imply more slip there than is estimated by the geodetic studies here by means of a joint inversion of displacement measurements and seafloor pressure data we show that it is possible to reconcile geodetic and seismic studies and that a considerable amount of slip indeed occurred at the trench with slip magnitudes reaching 57 74 of the maximum slip the seafloor displacement predicted by our model agrees very well with independent measurements made close to the trench we also find good agreement between our tsunami model and independent measurements of tsunami height in the ocean and on land re running of the inversion without the near field pressure gauge data however leads to underprediction of the flooding on land even when the seafloor geodetic data are still included thus even if the seafloor geodetic measurements had been available in real time they would still not have allowed reliable prediction of near field tsunami inundation close to the trench the dip of the plate interface is shallow which serves to decrease the vertical motion of the sea floor for any given slip however the horizontal motion is conversely larger because the ocean floor slopes steeply near the trench it acted like a giant wedge converting the horizontal motion of the ground into an uplift of the water column and causing the peak initial tsunami wave height to be twice as high as it would have been from vertical displacement alone

evidence for a wind driven intensification of the kuroshio current extension from the 1970s to the 1980s the spatial and temporal characteristics of oceanic thermal variations in the mixed layer and main thermocline of the midlatitude north pacific are distinctive suggesting different physical origins within the main thermocline 400 m depth the variability is dominated by a westward intensified pattern of decadal scale indicative of enhanced eastward geostrophic flow along the southern flank of the kuroshio current extension during the 1980s relative to the 1970s the authors argue that the decadal scale change in the strength of the kuroshio extension was a result of the dynamical adjustment of the oceanic circulation to a decadal variation in wind stress curl according to sverdrup theory four times daily wind stress fields from the national center for atmospheric research national centers for environmental prediction reanalysis project are used to compute the decadal change in sverdrup transport associated with the 1976 77 climate transition it is shown that the decadal changes in sverdrup transport inferred from the wind stress curl field and in observed geostrophic flow inferred from the upper ocean thermal field are consistent both in terms of spatial pattern and magnitude the decadal change in depth averaged geostrophic transport along the kuroshio extension referenced to 1 km is 11 6 sv similar to the sverdrup transport change 11 5 13 9 sv the decadal scale thermocline variation along the western boundary between 308 and 408n exhibits a lag of approximately 4 5 yr relative to the decadal variation in the basin wide wind stress curl pattern this delay may be indicative of the transient adjustment of the gyre scale circulation to a change in wind stress curl via long baroclinic rossby waves

a past giant lateral collapse and present day flank instability of fogo cape verde islands fogo island is a large and extremely steepsided oceanic island volcano in the cape verde archipelago it has a large ca 9 km across east facing summit collapse structure the monte amarelo collapse with a probable volume of at least 150 200 km3 for most of its history the monte amarelo volcano had a small but productive central vent complex and radial rift zones fed by laterally propagating dykes shortly before the collapse the latter were replaced by north south trending arrays of en echelon vertically propagating dykes since the monte amarelo collapse the scar has partly filled with a new volcano the cha das caldeiras volcano the summit cone of this volcano the pico do fogo is a very young feature but has been abandoned in the most recent phase of activity from the 18th century onwards the same period has also seen the abandonment of earlier radial rift zones with laterally propagating dykes and their replacement with en echelon arrays of vents fed by vertically propagating dykes these form an n s trending array within the older collapse structure and are associated with seaward displacement of the eastern flank of the volcano within the old collapse structure the most recent eruptions those of 1951 and 1995 appear to be associated with episodes of flank instability manifested in n s surface fissuring and east facing normal faults these recent structural changes in the volcano parallel those which took place in the monte amarelo volcano prior to its collapse

archean blocks and their boundaries in the north china craton lithological geochemical structural and p t path constraints and tectonic evolution an examination of lithological geochemical geochronological structural and metamorphic p t path data suggests that the basement of the north china craton can be divided into eastern and western blocks separated by major crustal boundaries that roughly correspond with the limits of a 300 km wide zone called the trans north china orogen the eastern block consists predominantly of late archean domiform tonalitic trondhjemitic granodioritic ttg batholiths surrounded by anastomosing networks and linear belts of open to tight synforms of minor volcanic and sedimentary rocks metamorphosed from greenschist to granulite facies at 2 5 ga with anticlockwise p t paths some early to middle archean rocks are locally present in the eastern block but their tectonic history is unclear due to reworking by the 2 5 ga tectonothermal event the western block has a late archean assemblage structural style and metamorphic history similar to that of the eastern block but it differs in the absence of early to middle archean assemblages and in being overlain by and interleaved with paleoproterozoic khondalites which were affected by a 1 8 ga metamorphic event involving clockwise p t paths a mantle plume model is proposed for the formation and evolution of late archean basement rocks in the eastern and western blocks based on a combination of extensive exposure of ttg gneisses affinities of mafic rocks to continental tholeiitic basalts presence of voluminous komatiitic rocks dominant diaprism related domiform structures anticlockwise p t paths and a short time span from the primary emplacement of ttg and ultramafic to mafic rocks until the onset of regional metamorphism between the two blocks is the trans north china orogen which is bounded by two major fault systems and is composed of late archean to paleoproterozoic ttg gneisses and granitoids interleaved with abundant sedimentary and volcanic rocks that are geochemically interpreted as having developed in magmatic arc and intra arc basin environments these rocks underwent multiple phases of compressional deformation and peak high pressure metamorphism followed by rapid exhumation during the late paleoproterozoic at 1 8 ga as a result of collision between the eastern and western blocks resulting in the amalgamation of the north china craton

upper mantle seismic velocities and anisotropy in china determined through pn and sn tomography 1 we have obtained velocity images of the uppermost mantle beneath china by performing tomographic inversion of both pn and sn traveltimes from the annual bulletin of chinese earthquakes 99 139 pn arrivals and 43 646 sn arrivals were selected pn anisotropy was also obtained simultaneously with pn velocity average pn and sn velocities are 8 05 and 4 55 km s respectively and maximum velocity perturbations are about 3 4 the pn and sn velocities are low in eastern china and high in western china particularly high velocities are associated with old basins for example tarim junggar turpan hami qaidam and sichuan and stable craton for example ordos low sn velocities are found mainly throughout north china in addition velocities are relatively low beneath the central tibetan plateau and the north south seismic zone along 103 e in tarim and central china where we observe strong anisotropy the fast pn velocity directions are consistent with the directions of maximum principal compressive stress as well as directions of crustal movement determined from global positioning system beneath the india eurasia collision zone the pn anisotropy direction is parallel to the collision arc and nearly perpendicular to both the direction of maximum compression and crustal movement resulting from pure shear deformation both the velocity variations and anisotropy indicate that the tibetan plateau was extruded and the mantle material beneath the plateau has flowed around the east himalaya syntax while the remaining material has diverted northwestward beneath the tarim basin

lithospheric thickness beneath the pitcairn hot spot trail as inferred from rayleigh wave dispersion abstract we have determined the s velocity model beneath the pitcairn hot spot trail from rayleigh wave phase velocities in order to examine the plate reheating model in which the lithosphere is expected to be thinned by reheating due to a hot spot the rayleigh wave dispersion for the pitcairn hotspot trail was measured by the two station method the phase velocity dispersion obtained for the pitcairn hot spot trail is consistent with oceanic upper mantle models with lithospheric ages corresponding to the pitcairn hot spot trail the dispersion data were inverted for s velocity structure using a hybrid method combining a grid search method and a non linear inversion method the lithospheric thickness was constrained to be from 50 to 80 km which is consistent to the thickness of the corresponding age indicating that the oceanic lithosphere is not anomalously thinned beneath the studied region

carboniferous granitic plutons from the northern margin of the north china block implications for a late palaeozoic active continental margin we report four late palaeozoic zircon sensitive high resolution ion microprobe shrimp u pb ages for granitic plutons from the inner mongolia palaeo uplift on the northern margin of the north china block these cast a new light on the poorly understood tectonic history of the northern margin of the north china block and the central asian orogenic belt during the late palaeozoic the plutons have for a long time been considered to belong to the early precambrian basement of the north china block our new shrimp u pb zircon dating of four plutons at longhua daguangding boluonuo and hushiha has yielded intrusive ages of 311 2 ma 324 6 ma 302 4 ma and 310 5 ma respectively geochemical data suggest that these granitoids have a calc alkaline subduction related i type signature indicating the existence of an andean style continental arc along the northern margin of the north china block during the late palaeozoic our results also indicate that the palaeo asian ocean still existed during latest carboniferous earliest permian time and that the final collision between the southern mongolia composite terranes and the north china block occurred later than c 290 ma we suggest that the northern margin of the north china block was an active continental margin and the inner mongolia palaeo uplift is a deeply exhumed mid crustal root of a late palaeozoic andean style continental arc

adjoint sensitivity of the nino 3 surface temperature to wind forcing theevolutionof sea surface temperature sst overthe easternequatorialpacific playsa significant rolein the intense tropicalair sea interaction there and is of central importance to the el nino southern oscillation enso phenomenon effects of atmospheric fields especially wind stress and ocean state on the eastern equatorial pacific sst variations are investigated using the massachusetts institute of technology general circulation model mitgcm and its adjoint model which can calculate the sensitivities of a cost function in this case the averaged 0 30 m temperature in the nino 3 region during an enso event peak to previous atmospheric forcing fields and ocean state going backward in time the sensitivity of the nino 3 surface temperature to monthly zonal wind stress in preceding months can be understood by invoking mixed layer heat balance ocean dynamics and especially linear equatorial wave dynamics the maximum positive sen sitivity of the nino 3 surface temperature to local wind forcing usually happens 1 2 months before the peak of the enso event and is hypothesized to be associated with the ekman pumping mechanism in model experiments itsmagnitudeiscloselyrelatedtothesubsurfaceverticaltemperaturegradient exhibitingstrong event to eventdifferenceswithstrong weak positivesensitivityduringla nina strongelnino events the adjoint sensitivity to remote wind forcing in the central and western equatorial pacific is consistent with the standardhypothesisthattheremotewindforcingaffectsthenino 3surfacetemperature indirectlybyexciting equatorial kelvin and rossby waves and modulating thermocline depth in the nino 3 region the current adjoint sensitivity study is consistent with a previous regression based sensitivity study derived from per turbation experiments finally implication for enso monitoring and prediction is also discussed

what drove late mesozoic extension of the northern china mongolia tract the northern china mongolia tract exhibited a tectonic transition from contractional to extensional deformation in late mesozoic time late middle to early late jurassic crustal shortening is widely thought to have resulted from collision of an amalgamated north china mongolia block and the siberian plate but widespread late late jurassic early cretaceous extension has not been satisfactorily explained by existing models some prominent features of the extensional tectonics of the northern china mongolia tract are 1 late jurassic voluminous volcanism prior to early cretaceous large magnitude rapid extension 2 overlapping in time of contractional deformation in the yinshan yanshan belt with development of extensionrelated basins in the interior of the northern china mongolia tract and 3 widespread occurrence of alkali granitic plutonism extensional basins and metamorphic core complexes in the early cretaceous a new explanation is advanced in this study for this sequence of events the collision of amalgamated north china mongolia with siberia led to crustal overthickening of the northern china mongolia tract and formation of a high standing plateau subsequent breakoff at depth of the north dipping mongol okhotsk oceanic slab is suggested as the main trigger for late mesozoic lithospheric extension of that tract slab breakoff resulted in mantle lithospheric stretching of the adjacent northern china mongolia tract with subsequent ascent of hot asthenosphere and magmatic underplating at the base of the crust collectively these phenomena triggered gravitational collapse of the previously thickened crust leading to late late jurassic early cretaceous crustal extension and importantly coeval contraction along the southern margin of the plateau in the yinshan yanshan belt the proposed model provides a framework for interpreting the spatial and temporal relationships of distinct processes and reconciling some seemingly contradictory phenomena such as the synchronous extension of northerly terranes during major contraction in the neighboring yanshan yinshan belt d 2003 elsevier b v all rights reserved

crust and uppermost mantle beneath the north china craton northeastern china and the sea of japan from ambient noise tomography 1 a 3 d shear velocity model of the crust and uppermost mantle to a depth of 100 km is presented beneath the north china craton ncc northeastern china the korean peninsula and the sea of japan ambient noise rayleigh wave tomography is applied to data from more than 300 broadband seismic stations from chinese provincial networks cearray the japanese f net and the iris global seismic network continuous data from 2007 to 2009 are used to produce group and phase velocity maps from 8 s to 45 s periods the model is motivated to constrain the distributed intraplate volcanism crustal extension cratonic rejuvenation and lithospheric thinning that are hypothesized for the study region numerous robust features are observed that impose new constraints on the geometry of these processes but discussion concentrates only on four 1 the north south gravity lineament follows the 40 km contour in crustal thickness and crustal thickness is anticorrelated with water depth beneath the sea of japan consistent with crustal isostasy for a crust with laterally variable composition 2 the lithosphere is thin 70 km beneath the songliao bohai graben but seismically fast 3 even thinner more attenuated lithosphere bounds three sides of the eastern ncc in a horseshoe shape identifying a region of particularly intense tectonothermal modification where lithospheric rejuvenation may have reached nearly to the base of the crust 4 low velocity anomalies reach upward in a y shape in the mantle beneath the eastern and western borders of the sea of japan extending well into continental east asia in the west and are separated by a 60 km thick lithosphere beneath the central sea of japan this anomaly may reflect relatively shallow slab dehydration in the east and in the west may reflect deeper dehydration and convective circulation in the mantle wedge overlying the stagnant slab

shear wave velocities in the upper mantle of the western alps new constraints using array analysis of seismic surface waves it remains challenging to obtain absolute shear wave velocities of heterogeneities of small lateral extension in the uppermost mantle this study presents a cross section of vs across the strongly heterogeneous 3 d structure of the western european alps based on array analysis of data from 92 broad band seismic stations from the cifalps experiment and from permanent networks in france and italy half of the stations were located along a dense sublinear array using a combination of these stations and off profile stations fundamental mode rayleigh wave dispersion curves were calculated using a combined frequency time beamforming approach we calculated dispersion curves for seven arrays of approximately 100 km aperture and 14 arrays of approximately 50 km aperture the latter with the aim of obtaining a 2 d vertical cross section of vs beneath the western alps the dispersion curves were inverted for vs z with crustal interfaces imposed from a previous receiver function study the array approach proved feasible as vs z from independent arrays vary smoothly across the profile length results from the seven large arrays show that the shear velocity of the upper mantle beneath the european plate is overall low compared to ak135 with the lowest velocities in the internal part of the western alps and higher velocities east of the alps beneath the po plain the 2 d vs model is coherent with i a 100 km thick eastward dipping european lithosphere west of the alps ii very high velocities beneath the po plain coherent with the presence of the alpine european slab and iii a narrow low velocity anomaly beneath the core of the western alps from the brianconnais to the dora maira massif and approximately colocated with a similar anomaly observed in a recent teleseismic p wave tomography this intriguing anomaly is also supported by traveltime variations of subvertically propagating body waves from two teleseismic events that are approximately located on the profile great circle

distinct lateral variation of lithospheric thickness in the northeastern north china craton abstract a detailed knowledge of the thickness of the lithosphere in the northeastern north china craton ncc is important for understanding the significant tectonic reactivation of the craton in the mesozoic and cenozoic time we achieve this goal by applying the newly proposed wave equation based migration technique to the s receiver functions recently collected in the region distinct negative signals are identified below the moho in all the s receiver function migrated images and stacks which we interpret as representing the s to p conversions from the lithosphere asthenosphere boundary lab the imaged lab is as shallow as 60 70 km in the southeast basin and coastal areas and deepens to no more than 140 km in the northwest mountain ranges and continental interior these observations indicate widespread lithospheric thinning in the study region in comparison with the 180 km lithospheric thicknesses typical of most cratonic regions the revealed topography of the lab generally agrees with the lateral variation in upper mantle seismic anisotropy previously measured through sks splitting analysis in particular a sharp lab step of 40 km is detected at the triple junction of the basin and mountains at almost the same place where an abrupt change from nw se to ne sw in fast polarization direction of shear waves was found these findings suggest a close correlation between the seismic anisotropy and hence deformation of the upper mantle the lithospheric thickness and the surface tectonics of the northeastern ncc while the thinned lithosphere and the nw se fast shear wave polarizations in the east areas probably are related to the dominant nw se tectonic extension in the late mesozoic cenozoic time the thicker lithosphere and the ne sw fast polarization direction in the west mountain ranges may reflect earlier contractional deformations of the region synthetic tests indicate that the lab beneath the northeastern ncc is a well defined zone 10 20 km thick combined with seismic tomography results and geochemical and petrological data this suggests that complex modification of the lithosphere probably accompanied significant lithospheric thinning during the tectonic reactivation of the old craton

interannual to decadal variability in the bifurcation of the north equatorial current off the philippines satellite altimeter sea surface height ssh data from the past 17 yr are used to investigate the interannualto decadal changes in the bifurcation of the north equatorial current nec along the philippine coast the nec bifurcation latitude migrated quasi decadally between 108 and 158n with northerly bifurcations observed in late 1992 1997 98 and 2003 04 and southerly bifurcations in 1999 2000 and 2008 09 the observed necbifurcationlatitudecanbeapproximatedwellbythesshanomaliesinthe128 148nand1278 1308ebox east of the mean nec bifurcation point using a 1 layer reduced gravity model forced by the ecmwf reanalysis wind stress data the authors find that the ssh anomalies in this box can be simulated favorably to serve as a proxy for the observed nec bifurcation with the availability of the long term reanalysis wind stress data this helps to lengthen the nec bifurcation time series back to 1962 although quasi decadal variability was prominent in the last two decades the nec bifurcation was dominated by changes with a 3 5 yr period during the 1980s and had low variance prior to the 1970s these interdecadalmodulationsin the characteristics of the nec bifurcation reflect similar interdecadal modulations in the wind forcing field over the western tropical north pacific ocean although the nec bifurcation on interannual and longer time

crust mantle structure difference across the gravity gradient zone in north china craton seismic image of the thinned continental crust the archean north china craton ncc has been tectonically modified and lost its thick lithospheric keel during the mesozoic and cenozoic the processes and mechanisms of the lithospheric modification and its appearance in and the relation between different subregions of the ncc are still poorly understood seismic data from 45 stations along a 470 km long profile cross the bohai bay basin bbb and the taihangshan mountain range tmr in the ncc were employed to construct a coherent structural image of the crust and uppermost mantle an integrated receiver function imaging technique combining the common conversion point stacking approach with waveform inversion and forward modeling was proposed to extract the structural information beneath the study region modeling of bouguer gravity anomalies was also applied to constrain the density distribution the imaging result reveals distinct structural features between the mountain range and the basin area and presents a picture of uneven crust thinning within the study region in the east bbb the crust is significantly thinned due mainly to the reduction in the thickness of the lower crust including the crust mantle transition zone by up to 12 km the west tmr in contrast is characterized by a relatively thick lower crust of 20 km the teleseismic waveform data and the gravity observation suggest a thicker crust and a buoyant mantle lithosphere beneath the tmr compared with the bbb the contrasting crustal structural features appear coupled with the lithospheric processes and possibly reflect that different tectonic mechanisms and deformation regimes dominated the evolution of the two regions the north south gravity lineament lying between the tmr and bbb might represent a deep intra continental boundary separating the ncc into topographically and tectonically different regions

the 2014 2015 eruption of fogo volcano geodetic modeling of sentinel 1 tops interferometry after 20 years of quiescence fogo volcano erupted in november 2014 the eruption produced fast moving lava flows that traveled for several kilometers and destroyed two villages this event represents the first episode of significant surface deformation imaged by the new european space agency s sentinel 1 satellite in its standard acquisition mode terrain observation by progressive scans tops which differs from that of previous synthetic aperture radar sar missions we perform a bayesian inversion of sentinel 1 tops sar interferograms spanning the eruption and accurately account for variations in the tops line of sight vector when modeling displacements our results show that magma ascended beneath the pico do fogo cone and then moved laterally toward its southwestern flank where the eruptive fissure opened this study provides important insights into the inner workings of fogo volcano and shows the potential of sentinel 1 tops interferometry for geophysical e g volcano monitoring applications

moho depth variations from receiver function imaging in the northeastern north china craton and its tectonic implications a detailed knowledge of the crustal thickness in the northeastern north china craton ncc is important for understanding the unusual phanerozoic destruction of the craton we achieve this goal by employing a 2 d wave equation based migration method to p receiver functions from 198 broadband seismic stations using ps conversions and surface reflected multiples by combining receiver function images along 19 profiles we constructed a high resolution moho depth model for the northeastern ncc the results present dominant e w moho depth variations similar to previous observations and new regional n s variations beneath both sides of the north south gravity lineament to the west while a deeper moho approximate to 42km appears in the interior of the trans north china orogen a relatively shallow moho approximate to 38km exists in the northern margin of the trans north china orogen to western ncc to the east the crust beneath the yan mountains in the marginal area is thicker approximate to 32 40km than that approximate to 26 32km beneath the bohai bay basin in the craton interior and the moho further shallows from ne approximate to 32km to sw approximate to 26km within the basin along with other observations we conclude that the dominant e w difference may have been associated with the paleo pacific plate subduction under eastern asia since the mesozoic the newly observed complex n s variations may have reflected the structural heterogeneity of the cratonic lithosphere inherited since the formation of the ncc in the paleoproterozoic or spatially uneven effects on the cratonic lithosphere of subsequent thermotectonic events during the long term evolution of the craton or both

investigating collapse structures in oceanic islands using magnetotelluric surveys the case of fogo island in cape verde abstract one of the most remarkable natural events on earth are the large lateral flank collapses of oceanic volcanoes involving volumes of rock exceeding tens of km3 these collapses are relatively frequent in recent geological times as supported by evidence found in the geomorphology of volcanic island edifices and associated debris flows deposited on the proximal ocean floor the island of fogo in the cape verde archipelago is one of the most active and prominent oceanic volcanoes on earth the island has an average diameter of 25 km and reaches a maximum elevation of 2829 m above sea level m a s l at pico do fogo a young stratovolcano located within a summit depression open eastward due to a large lateral flank collapse the sudden collapse of the eastern flank of fogo island produced a megatsunami 73 ky ago the limits of the flank collapse were deduced as well from geomorphologic markers within the island the headwall of the collapse scar is interpreted as either being located beneath the post collapse volcanic infill of the summit depression or located further west corresponding to the bordeira wall that partially surrounds it the magnetotelluric mt method provides a depth distribution of the ground resistivity obtained by the simultaneous measurement of the natural variations of the electric and magnetic field of the earth two n s magnetotelluric profiles were acquired across the collapsed area to determine its geometry and boundaries the acquired mt data allowed the determination of the limits of the collapsed area more accurately as well as its morphology at depth and thickness of the post collapse infill according to the newly obtained mt data and the bathymetry of the eastern submarine flank of fogo the volume involved in the flank collapse is estimated in 110 km3 this volume the first calculated onshore stands between the previously published more conservative and excessive calculations offshore that were exclusively based in geomorphic evidence the model for the summit depression proposing two caldera collapses preceding the collapse of the eastern flank of fogo is supported by the mt data

lithospheric structure variations between the eastern and central north china craton from s and p receiver function migration abstract i imaged the lithospheric structure beneath the bohai bay basin bbb in the eastern north china craton ncc and the taihang mountains tm and areas further to the west in the central ncc by applying the wave equation migration technique to both the s and p receiver functions rfs collected in this region the data images and synthetic modeling results indicate that s rf imaging is more appropriate than p rf imaging for mapping lithospheric discontinuities especially the lithosphere asthenosphere boundary lab in various types of regions even directly applicable to basin areas that are covered by thick sediments the constructed s rf images show that the lithospheric thickness of the study region is highly variable the imaged lab is on average 80 km beneath the bbb and displays obvious undulations from 120 km under the tm to 40 km under the mountain areas in the central ncc consistent with previous p rf imaging results the observed structural differences between the eastern and central ncc are likely associated with different lithospheric tectonics in these two regions while widespread lithosphere reactivation and extension in the eastern ncc during the late mesozoic time was plausibly responsible for both the thinned crust and lithosphere in the bbb lithospheric thinning in the central ncc may be equally heterogeneous but less significant and probably occurred mainly in cenozoic such a process may have given rise to the highly variable present day lithospheric thickness in this region however it probably did not noticeably affect the overlying crust that was reported to have thickened in response to the early magmatic underplating in the mesozoic time the different tectonic processes in the eastern and central ncc may have induced the formation of the nsgl which likely serves as a major tectonic boundary separating the two regions of contrasting lithospheric structures at present

a network based enhanced spectral diversity approach for tops time series analysis for multitemporal analysis of synthetic aperture radar sar images acquired with a terrain observation by progressive scan tops mode all acquisitions from a given satellite track must be coregistered to a reference coordinate system with accuracies better than 0 001 of a pixel assuming full sar resolution in the azimuth direction such a high accuracy can be achieved through geometric coregistration using precise satellite orbits and a digital elevation model followed by a refinement step using a time series analysis of coregistration errors these errors represent the misregistration between all tops acquisitions relative to the reference coordinate system we develop a workflow to estimate the time series of azimuth misregistration using a network based enhanced spectral diversity nesd approach in order to reduce the impact of temporal decorrelation on coregistration example time series of misregistration inferred for five tracks of sentinel 1 tops acquisitions indicates a maximum relative azimuth misregistration of less than 0 01 of the full azimuth resolution between the tops acquisitions in the studied areas standard deviation of the estimated misregistration time series for different stacks varies from 1 1e 3 to 2e 3 of the azimuth resolution equivalent to 1 6 2 8 cm orbital uncertainty in the azimuth direction these values fall within the 1 sigma orbital uncertainty of the sentinel 1 orbits and imply that orbital uncertainty is most likely the main source of the constant azimuth misregistration between different tops acquisitions we propagate the uncertainty of individual misregistration estimated with esd to the misregistration time series estimated with nesd and investigate the different challenges for operationalizing nesd

insar observations of the 1995 fogo cape verde eruption implications for the effects of collapse events upon island volcanoes 1 fogo volcano cape verde islands erupted in april 1995 after 43 years of dormancy about 46 106 m3 of lava erupted during 7 5 weeks from vents on the sw flank of pico do fogo into cha das caldeiras interferograms obtained from 1993 1998 ers sar data show ground deformation due to the feeder dike but lack evidence for any volcano wide deformation related to volume changes of a shallow magma reservoir this suggests that fogo is fed from a relatively deep mantle lithospheric source 16 5 km depth consistent with petrological data this supports the concept that cha das caldeiras is the fill of a collapse scar created by a giant landslide and not a collapse caldera overlying a central shallow magma chamber the disturbance of the magmatic system by giant landslides may explain why some oceanic island volcanoes with high magma supply rates currently lack well developed shallow reservoirs

remote forcing of tasman sea marine heatwaves recent marine heatwave mhw events in the tasman sea have had dramatic impacts on the ecosystems fisheries and aquaculture off tasmania s east coast however our understanding of the large scale drivers forcing and potential predictability of mhw events in this region off southeast australia is still in its infancy here we investigate the role of oceanic rossby waves forced in the interior south pacific on observed mhw occurrences off southeast australia from 1994 to 2016 including the extreme 2015 16 mhw event first we used an upper ocean heat budget analysis to show that 51 of these historical tasman sea mhws were primarily due to increased east australian current eac extension poleward transports through the region second we used lagged correlation analysis to empirically connect the eac extension intensification to incoming westward propagating sea surface height ssh anomalies from the interior south pacific third we dynamically analyzed these ssh anomalies using simple process based baroclinic and barotropic rossby wave models forced by wind stress curl changes across the south pacific finally we show that associated monthly ssh changes around new zealand may be a useful index of western tasman sea mhw predictability with a lead time of 2 3 years in conclusion our findings demonstrate that there is potential predictability of advection dominated mhw event likelihoods in the eac extension region up to several years in advance due to the deterministic contribution from baroclinic and barotropic rossby waves in modulating the eac extension transports

a near uniform fluctuation of ocean bottom pressure and sea level across the deep ocean basins of the arctic ocean and the nordic seas across the arctic ocean and the nordic seas a basin wide mode of ocean bottom pressure and sea level fluctuation is identified using satellite and in situ observations in conjunction with a global ocean circulation model and its adjoint the variation extends across the interconnected deep ocean basins of these semi enclosed arctic seas collectively called the arctic mediterranean with spatially near uniform amplitude and phase the basin wide fluctuation is barotropic and dominates the region s large scale variability from sub monthly to interannual timescales the fluctuation results from bifurcating coastally trapped waves generated by winds along the continental slopes of the arctic mediterranean and its neighboring seas including the north atlantic ocean the winds drive ekman transport across the large bathymetric gradients forcing mass divergence between the shallow coastal area and the deep ocean basins and creating ocean bottom pressure anomalies of opposite signs in the two regions the anomalies rapidly propagate away as barotropic coastally trapped waves with the coast and continental slope as respective boundaries the waves subsequently bifurcate at the shallow straits connecting the arctic mediterranean with the rest of the globe the straits transmit the shallow anomalies but not the deep variations thereby inhibiting the anomalies mutual cancelation by geographically separating the two anomalies that enter the deep arctic basins equilibrate uniformly across the domain characterized by a homogeneous depth integrated planetary potential vorticity distribution the potential vorticity s steep gradient that borders the basins shields the region from neighboring shallow variations giving rise to the observed spatially confined fluctuation compensating anomalies outside the arctic adjust similarly across the rest of the globe but are comparatively negligible in amplitude because of the global ocean s larger area relative to that of the deep arctic mediterranean the study from a technical perspective illustrates the utility of a model s adjoint in identifying causal mechanisms underlying a complex system