glacial rebound and plate spreading results from the first countrywide gps observations in iceland iceland is one of the few places on earth where a divergent plate boundary can be observed on land direct observations of crustal deformation for the whole country are available for the first t

transmission to reflection transformation of teleseismic wavefields 1 in this paper we review the transformation of p and sv transmission green s functions into the corresponding reflection quantities for one dimensional elastic media at precritical slownesses to obtain estimates of the transmission green s functions from observed data we apply a recently developed approach that exploits the minimum phase nature of the direct waves and employs autospectra and cross spectra of raw component seismograms representing multiple sources recorded at a single station to accomplish transformation to reflection green s functions we outline a practical recipe that involves amplitude balancing energy normalization cross correlation and removal of free surface effects we assess its performance through application to both synthetic seismograms and data from station hyderabad in all cases we are able to identify the first order scattering contributions from the continental moho the transmission to reflection transformation has potential applications for imaging hitherto elusive shallow mantle discontinuities since interfering forward and back scattering contributions are effectively separated by component in the resulting reflection green s functions

land uplift near vatnajokull iceland as observed by gps in 1992 1996 and 1999 summary war ming of the climate in the 20th century has been manifested by an ablation of europe s largest ice cap vatnajokull in iceland the thin elastic lithosphere and the low viscosity as thenosphere are responding to the reduction in mass by current land uplift in the vicinity of the ice cap suggested to be of the order of 5 10 mm yr 1 lithosphere thickness and asthenosphere viscosities compatible with these values have been inferred from our repeated gps epoch campaigns in 1992 1996 and 1999 uplift rates are estimated to be of the order of 5 19 mm yr 1 and the uplift rate is decreasing by 0 11 0 01 mm yr 1 km 1 with radial distance from the centre of the ice cap these results deviate from previous earth rheology models estimated for the region our data indicate that the lithosphere thickness might be of the order of 10 20 km and the asthenosphere viscosity may be as low as 5 10 17 pa s but these parameters need a careful fitting to the estimated uplift rates

lithospheric thickness beneath the dabie shan central eastern china from s receiver functions summary p and s receiver functions obtained from a portable array of 34 broad band stations in east central china provide a detailed image of the crust mantle and lithosphere asthenosphere boundaries lab in the dabie shan and its adjacent areas clear s to p converted waves produced at the lab show a thin lithosphere beneath the whole study area based on our results the thickest lithosphere of 72 km is observed beneath the southern part of the area within the yangtze craton whereas beneath the north china platform the lithosphere is only 60 km thick s receiver functions also reveal in good agreement with p receiver functions a maximum depth of the moho beneath the dabie shan orogen at approximately 40 km furthermore we interpret the structural difference at 32 latitude as the probable location of

interaction of deep and shallow convection is key to madden julian oscillation simulation 1 this study investigates the role of the interaction between deep and shallow convection in mjo simulation using the ncar cam3 two simulations were performed one using a revised zhang mcfarlane convection scheme for deep convection and the hack scheme for shallow convection and the other disallowing shallow convection below 700 mb in the tropical belt the two simulations produce dramatically different mjo characteristics while the control simulation produces realistic mjos the simulation without shallow convection has very weak mjo signals in the indian ocean and western pacific composite analysis finds that shallow convection serves to precondition the lower troposphere by moistening it ahead of deep convection it also produces enhanced low level mass convergence below 850 mb ahead of deep convection this work together with previous studies suggests that a correct simulation of the interaction between deep and shallow convection is key to mjo simulation in global climate models

geographic variability in the export of moist static energy and vertical motion profiles in the tropical pacific 1 column integrated moist static energy mse budgets were calculated using daily data from three reanalyses 1998 2001 and isccp radiative cooling the mse export by the circulation was separated into vertical and horizontal mse advection components in order to examine how observationally derived vertical motion profiles affect gross moist stability calculations in a 2000 km wide region in the central eastern pacific itcz vertical motions import mse implying a negative gross moist stability horizontal mse advection is negative and of similar magnitude to vertical mse advection in rainy regions geographic differences in export of mse by the vertical circulation are primarily due to differences in the shape of the vertical motion profile in the west pacific warm pool rainy regions mean horizontal convergence extends up to 300 mb while in parts of the pacific itcz where meridional sst gradients are strong the vertical motion profile is bottom heavy with convergence below 800 mb and divergence above on daily timescales the mode of vertical motion variability has little dependence on precipitation rate and is consistent with observed regional differences in the vertical structure of trmm pr reflectivities

an s receiver function analysis of the lithospheric structure in south america 1 we make use of s receiver function to investigate the structure and thickness of the crust and mantle lithosphere in the south american continent and adjacent areas the moho discontinuity has been detected at all stations and goes from 18 km beneath the coast of the continent to 80 km in the andean region the depth of the lithosphere asthenosphere boundary can be clearly detected below those stations that are located on stable areas from 50 km to 160 km the identification of this phase becomes more difficult when the stations are located near subduction zones we also observed the base of the subducted oceanic lithosphere down to depths of 220 km

the heterogeneous upper mantle low velocity zone abstract the upper mantle low velocity zone lvz is a depth interval with slightly reduced seismic velocity compared to the surrounding depth intervals the zone is present below a relatively constant depth of 100 km in most continental parts of the world both in cratonic areas with high average velocity and tectonically active areas with low average velocity evidence for the low velocity zone arises from controlled and natural source seismology including studies of surface waves and of primary and multiple reflections of body waves from the bounding interfaces calculations of receiver functions and absolute velocity tomography the available data indicates a more pronounced reduction in seismic velocity and q value for s waves than p waves as well as high electrical conductivity in the lvz seismic waves are strongly scattered by the zone which demonstrates the existence of small scale heterogeneity the depth to the base of the lvz is systematically shallower in cold stable cratonic areas than in hot active regions of the world because of its global occurrence below a relative constant depth of 100 km the lvz cannot be explained by metamorphic or compositional variation and rheological changes calculated upper mantle temperatures indicate that the rocks are close to the solidus in an interval with variable thickness below 100 km depth provided that the rocks contain water and carbon dioxide the presence of even small amounts of such fluids in the mantle rocks will lower the solidus by several hundred degrees and introduce a characteristic kink on the solidus curve around 80 100 km depth the seismic velocities and q values are significantly reduced of rocks which are close to the solidus or contain small amounts of partial melt hence the lvz may be explained by upper mantle temperatures being close to the solidus in a depth interval below 100 km assuming that the rocks contain only limited amounts of fluids this mechanism may explain the low velocities q values and resistivity as well as the intrinsic scattering and the characteristic variation in thickness of the low velocity zone

the relationship between crust lithosphere structures and seismicity on the southeastern edge of the tibetan plateau abstract the crust lithosphere structure especially the discontinuities such as moho and lithosphere asthenosphere boundary lab is important in the investigation of geodynamic process implications and tectonic evolution of the lithosphere and regional seismic activity we stacked the s receiver functions from 51 permanent broad band stations to investigate the crust lithosphere structures beneath the southeastern edge of the tibetan plateau and further discussed the mechanism of lower crust earthquakes the regional tectonics deformation characteristics and the relationship between the two discontinuities and seismicity in this region the results show that the moho depth increases from 40 to 52 km beneath the sichuan basin to 56 74 km on the both western side of the longmenshan lms fault and anninhe zemuhe fault the lab depth ranges from 130 to 170 km beneath the sichuan basin and a shallow belt ranges from 100 km to 130 km around the sichuan basin on the moho depth contour map 374 moderate earthquakes that accounted for 72 2 corresponding to the depth range of 44 52 km and 60 68 km on the both sides of a narrow strip longitude 102 104 on the lab depth contour map 321 earthquakes accounted for 62 15 in the depth range of 130 150 km the variation of lab corresponds to the increasing crustal thickness intensive lower crustal earthquakes hypocenters about 60 km and magnitude 4 0 ms 4 9 and surface abrupt elevations it implied that normal strong earthquakes generate the lower crustal earthquakes or aftershocks that resulted in the shear zones where fluid induced metamorphic transformations the eclogitization of dry granulite and further affect the crustal thickness and deformation to control the spatial distribution of deep faults and seismicity

zonal and vertical structure of the madden julian oscillation abstract a statistical study of the three dimensional structure of the madden julian oscillation mjo is carried out by projecting dynamical fields from reanalysis and radiosonde data onto space time filtered outgoing longwave radiation olr data mjo convection is generally preceded by low level convergence and upward motion in the lower troposphere while subsidence cooling and drying prevail aloft this leads to moistening of the boundary layer and the development of shallow convection followed by a gradual and then more rapid lofting of moisture into the middle troposphere at the onset of deep convection after the passage of the heaviest rainfall a westerly wind burst region is accompanied by stratiform precipitation where lower tropospheric subsidence and drying coincide with continuing upper tropospheric upward motion the evolution of the heating field leads to a temperature structure that favors the growth of the mjo the analysis also reveals distinct differences in the vertical structure

mjo signals in latent heating results from trmm retrievals abstract four tropical rainfall measuring mission trmm datasets of latent heating were diagnosed for signals in the madden julian oscillation mjo in all four datasets vertical structures of latent heating are dominated by two components one deep with its peak above the melting level and one shallow with its peak below profiles of the two components are nearly ubiquitous in longitude allowing a separation of the vertical and zonal temporal variations when the latitudinal dependence is not considered all four datasets exhibit robust mjo spectral signals in the deep component as eastward propagating spectral peaks centered at a period of 50 days and zonal wavenumber 1 well distinguished from lower and higher frequency power and much stronger than the corresponding westward power the shallow component shows similar but slightly less robust mjo spectral peaks mjo signals were further extracted from a combination of bandpass 30 90 day filtered deep and shallow components largest amplitudes of bo

crustal structure of iceland and greenland from receiver function studies 1 we used data from both permanent and temporary seismic networks on iceland and greenland to investigate the crustal thickness by partly reinterpreting earlier data p receiver functions and adding s receiver functions to better constrain the results we obtained good conversions from the moho and also crustal multiples in both iceland and greenland the central ice covered part of greenland has an average crustal thickness of 40 km typical for a craton at the edges of greenland the crustal thickness decreases to 30 40 km on the east coast of greenland where the track of the iceland plume is thought to have affected the lithosphere the crustal thickness is only 24 26 km in contrast to previous studies we find that the crustal thickness in the east and the northwest coastal regions of iceland is more than 40 km similar to beneath the active volcanic region in the southwest region of iceland and along the mid ocean ridge the crustal thickness is only 25 km or less also in contrast to earlier receiver function interpretations which deduced a broad crust mantle transition zone for iceland we find indications for a normal sharper moho beneath a number of sites

an assessment of crustal and upper mantle velocity structure by removing the effect of an ice layer on the p wave response an application to antarctic seismic studies standard p wave receiver function analyses in polar environments can be difficult because reverberations in thick ice coverage often mask important p to s conversions from deeper subsurface structure and increase ambient noise levels thereby significantly decreasing the signal to noise ratio of the data in this study we present an alternative approach to image the subsurface structure beneath ice sheets we utilize downward continuation and wavefield decomposition of the p wave response to obtain the up and downgoing p and s wavefield potentials which removes the effects of the ice sheet the upgoing p wavefield computed from decomposition of the waveform at a reference depth is capable of indicating ice layer thickness this simple step removes the necessity of modeling ice layer effects during iterative inversions and hastens the overall velocity analysis needed for downward continuation the upgoing s wave is employed and modeled using standard inversion techniques as is done with receiver functions at the free surface using a least squares approximation to illustrate our proof of concept data from several antarctic networks are examined and our results are compared with those from previous investigations using p and s wave receiver functions as well as body and surface wave tomographic analyses we demonstrate how our approach satisfactorily removes the ice layer thus creating a dataset that can be modeled for crustal and upper mantle structure solution models indicate crustal thicknesses as well as average crustal and upper mantle shear wave velocities electronic supplement 1 figure of measured data the vertical component stack used in deconvolution and the resultant vertical radial and tangential transfer functions 1 http www bssaonline org lookup suppl doi 10 1785 0120160262 dc1

melting at the base of the greenland ice sheet explained by iceland hotspot history basal melting is widespread in the north central greenland ice sheet geophysical data and numerical modelling suggest a geothermal anomaly in this region resulting from the earlier passage of greenland over the iceland mantle plume

lithospheric structure and crust mantle decoupling in the southeast edge of the tibetan plateau abstract convergence between the indian plate and the eurasian plate has resulted in the uplift of the tibetan plateau and understanding the associated dynamical processes requires investigation of the structures of the crust and the lithosphere of the tibetan plateau yunnan is located in the southwest edge of the plateau and adjacent to myanmar to the west previous observations have confirmed that there is a sharp transition in mantle anisotropy in this area as well as clockwise rotations of the surface velocity surface strain and fault orientation we use s receiver functions from 54 permanent broad band stations to investigate the structures of the crust and the lithosphere beneath yunnan the depth of the moho is found to range from 36 to 40 km beneath southern yunnan and from 55 to 60 km beneath northwestern yunnan with a dramatic variation across latitude 25 26 n the depth of the lithosphere asthenosphere boundary lab ranges from 180 km to less than 70 km also varying abruptly across latitude 25 26 n which is consistent with the sudden change of the fast s wave direction from nw se to e w across 26 28 n in the north of the transition belt the lithosphere is driven by asthenospheric flow from tibet and the crust and the upper mantle are mechanically coupled and moving southward because the northeastward movement of the crust in the burma micro plate is absorbed by the right lateral sagaing fault the crust in yunnan keeps the original southward movement however in the south of the transition belt the northeastward mantle flow from myanmar and the southward mantle flow from tibet interact and evolve into an eastward flow by momentum conservation as shown by the structure of the lab this resulting mantle flow has a direction different from that of the crustal movement it is concluded that the sagaing fault causes the west boundary condition of the crust to be different from that of the lithospheric mantle thus leading to crust mantle decoupling in yunnan

viscosity structure beneath northeast iceland the dynamics of crustal rifting in iceland depend strongly on the lower crustal rheology which controls the intensity of upper crustal stress concentration and scale time of heat diffusion from the underlying mantle plume while magnetotelluric surveys suggest the presence of a pervasive hot and highly ductile lowermost crust with possibly high fraction of partial melt observations of low seismic attenuation and strong shear wave transmission suggest a much cooler lower crust and upper mantle since viscosity is also sensitive to the degree of partial melt present viscosity estimates for these regions could shed light on the factors responsible for these observations in this study we utilize horizontal and vertical displacement vectors determined in gps campaigns in northeast iceland since 1986 these are modeled in terms of steady state tectonic loading plus postseismic postdiking relaxation following the 1975 1984 krafla rifting episode as first proposed by foulger and others with the elastic part of the model fixed by external constraints these data have a high sensitivity to the viscosity structure beneath iceland lower crust and upper mantle viscosities of about 3 1019 pa s and 3 1018 pa s respectively yield the closest agreement with the data our lower crustal viscosity estimate is consistent with the low attenuation and low subsolidus temperature for the lower crust inferred in recent studies inversions for fissure opening during the krafla rifting episode yield about 7 m of opening centered on the krafla rift as is observed allowing for contemporaneous deep rifting on vertical faults along the askja segment partially accounts for the observed increase in separation across the rift during 1987 1992 but does not account for large displacements in the southeastern part of the network or the large relative subsidence around the askja rift during 1987 1990 recent deep normal faulting beneath the askja rift and further south might explain all of these remaining features

the lithosphere asthenosphere boundary in the north west atlantic region abstract a detailed knowledge of the thickness of the lithosphere in the north atlantic is an important parameter for understanding plate tectonics in that region we achieve this goal with as yet unprecedented detail using the seismic technique of s receiver functions clear positive signals from the crust mantle boundary and negative signals from a mantle discontinuity beneath greenland iceland and jan mayen are observed according to seismological practice we call the negative phase the lithosphere asthenosphere boundary lab the seismic lithosphere under most of the iceland and large parts of central greenland is about 80 km thick this depth in iceland is in disagreement with estimates of the thickness of the elastic lithosphere 10 20 km found from postglacial rebound data in the region of flood basalts in eastern greenland which overlies the proposed iceland plume track the lithosphere is only 70 km thick about 10 km less than in iceland which is located directly above the proposed plume at the western greenland coast the lithosphere thickens to 100 120 km with no indication of the iceland plume track identified below jan mayen the lithospheric thickness varies between 40 and 60 km

crustal thickness estimation beneath the southern central andes at 30 s and 36 s from s wave receiver function analysis summary we have used the s wave receiver function srf technique to investigate the crustal thickness beneath two seismic profiles from the charge project in the southern central andes a previous study employing the p wave receiver function method has observed the moho interface beneath much of the profiles they found however that the amplitude of the p to s conversion was diminished in the western part of the profiles and have attributed it to a reduction of the impedance contrast at the moho due to lower crustal ecologitization with srf we have successfully detected s to p converted waves from the moho as well as possible conversions from other lithospheric boundaries the continental south american crust reaches its maximum thickness of 70 km along 30 s between 70 w and 68 5 w beneath the principal cordillera and the famatina system and becomes thinner towards the sierras pampeanas with a thickness of 40 km negative phases possibly related to the base of the continental and oceanic lithosphere can be recognized in the summation traces at different depths by comparing our results with data obtained from previous investigations we are able to further constrain the thickness of the crust and lithosphere beneath the central andes

the lithosphere asthenosphere boundary in the tien shan karakoram region from s receiver functions evidence for continental subduction 1 significant s to p converted wave energy from the crust mantle and lithosphere asthenosphere boundaries the moho and the lab respectively has been observed in the tien shan and karakoram orogenic belts and used for the determination of the thickness of the crust and the mantle lithosphere the moho lies at depths of 45 65 km in the tien shan and adjacent regions and deepens to 70 km depth in pamir and karakoram the thickness of the lithosphere varies between 90 and 120 km underneath the tien shan and increases to a value of 160 km beneath the tarim basin to the south of the tarim basin the lower boundary of the asian lithosphere can be clearly followed to a depth of 270 km beneath central pamir and karakoram while the indian lithosphere is observed beneath the karakoram dipping from 130 km to 170 km towards the north the observations indicate a scenario of continental collision and subduction consistent with seismicity and the surface wave tomography results

an upper mantle seismic discontinuity beneath the galapagos archipelago and its implications for studies of the lithosphere asthenosphere boundary an upper mantle seismic discontinuity the gutenberg or g discontinuity at which shear wave velocity decreases with depth has been mapped from s to p conversions in radial receiver functions recorded across the galapagos archipelago the mean depth of the discontinuity is 91 8 km beneath the southeastern archipelago and 72 5 km beneath surrounding regions the discontinuity appears deeper beneath the portion of the nazca plate that we infer passed over the galapagos mantle plume than elsewhere in the region we equate the depth of the g discontinuity to the maximum depth extent of anhydrous melting which forms an overlying layer of dehydrated and depleted mantle we attribute areas of shallow discontinuity depth to the formation of the dehydrated layer near the galapagos spreading center and areas of greater discontinuity depth to its modification over a mantle plume with an excess temperature of 115 30 c the g discontinuity lies within a high seismic velocity anomaly that we conclude forms by partial dehydration and a gradual but steady increase in seismic velocity with decreasing depth after upwelling mantle first encounters the solidus for volatile bearing mantle material at the depth of the solidus for anhydrous mantle material removal of remaining water creates a sharp decrease in velocity with depth this discontinuity may also mark a site of melt accumulation results from seismic imaging the compositions of galapagos lavas and rare earth element concentrations across the archipelago require that mantle upwelling and partial melting occur over a broad region within the dehydrated and depleted layer we conclude that the g discontinuity beneath the archipelago does not mark the boundary between rigid lithosphere and convecting asthenosphere

structure of the jan mayen microcontinent and implications for its evolution an extensive seismic survey using ocean bottom seismographs obs was performed in the area across the jan mayen basin north atlantic from the jan mayen ridge to the iceland plateau the jan mayen ridge and surrounding area are considered to be a fragment of a continent which was separated from greenland just prior to magnetic anomaly 6 this study presents the crustal structure of the jan mayen microcontinent and the ocean continent transition to the west of the jan mayen ridge the crustal structures from the centre of the jan mayen ridge to the jan mayen basin are characterized by a deep sedimentary basin a thin basaltic layer within the sedimentary section and extreme thinning of the continental crust towards the iceland plateau the obs data indicate that a continental upper crust v p 5 8 6 1 km s 1 and lower crust v p 6 7 6 8 km s 1 underlie the deep sedimentary basin the thickness of the continental lower crust varies significantly from 12 km beneath the jan mayen ridge to almost zero thickness beneath the northwestern part of the jan mayen basin an ocean continent transition zone is found at the western edge of the jan mayen basin within the 10 km wide transition zone crustal velocities increase towards the iceland plateau and approach the velocities of the oceanic crust obtained at the iceland plateau that is 3 8 5 1 km s 1 oceanic layer 2a 5 9 6 5 km s 1 oceanic layer 2b and 6 8 7 3 km s 1 oceanic layer 3 the crustal model indicates very thin oceanic crust 5 km immediately oceanwards of the ocean continent transition zone beneath the iceland plateau the oceanic crust is thicker 9 km than the typical thickness of normal oceanic crust this might imply that the oceanic crust at the iceland plateau has been generated by asthenospheric material slightly hotter than normal from the crustal structure obtained by the present study it is proposed that the western part of the jan mayen ridge may be referred to as a non volcanic continental margin generated by a long duration of rifting even if the asthenospheric material upwelling along the margin were hotter than normal only small amounts of magmatic intrusions and extrusions would have been generated because of significant conductive cooling under the long duration of rifting

formation of cratonic mantle keels by arc accretion evidence from s receiver functions 1 delineating mantle interfaces can provide important clues for understanding the formation of continents we use s wave receiver functions to investigate lithospheric structure along a transect extending from vancouver island to baffin island observed sp converted waves allow for interpretation of boundaries in the depth range expected for tectonic plates receiver functions show a distinct negative amplitude feature interpreted as the lithosphere astbenosphere boundary at shallow depths beneath british columbia 85km deepening abruptly at the eastern edge of the cordillera to 260km beneath the canadian shield dipping mid lithospheric discontinuities extend beneath several giant ca 1 8 ga epicontinental magmatic arcs consistent with formation of cratonic lithosphere by arc accretion this model provides a plausible explanation for global mid lithospheric discontinuities within cratons and aids in understanding their formation

the seismic 8 discontinuity and partial melting in continental mantle strong scattered reflections beyond 8 degrees 8 offset are characteristic features of all high resolution seismic sections from the continents the reflections identify a low velocity zone below approximately 100 kilometers depth beneath generally stratified mantle this zone may be caused by partial melting globally initiated at equal depth in the continental mantle solid state is again attained at the lehmann discontinuity in cold stable areas whereas the zone extends to near the 400 kilometer discontinuity in hot tectonically active areas thus the depth to the lehmann discontinuity may be an indicator of the thermal state of the continental mantle

the influence of decadal to millennial scale ice mass changes on present day vertical land motion in greenland implications for the interpretation of gps observations 1 we show predictions of present day vertical land motion in greenland using a recently developed glacial isostatic adjustment gia model calibrated using both relative sea level rsl observations and geomorphological constraints on ice extent predictions from our gia model are in agreement with the relatively small number of gps measurements of absolute vertical motion from south and southwest greenland this suggests that our model of ice sheet evolution over the holocene period is reasonably accurate the uplift predictions are highly sensitive to variations of upper mantle viscosity thus depending on the earth model adopted different periods of ice loading change dominate the present day response in particular regions of greenland we also consider the possible influence of more recent changes in the ice sheet by applying a second ice model specifically a surface mass balance smb model which covers the period 1866 to 2005 predictions from this model suggest that decadal scale smb changes over the past 140 years play only a small role in determining the present day viscous response at the sub mm yr level in most locations for a range of earth model parameters high rates of peripheral thinning from 1995 to 2005 predicted using the smb model produce large elastic uplift rates 6 mm yr in west and southwest greenland this suggests that in some areas close to the ice margin modern surface mass balance changes have a dominant control on present day vertical land motion

seismic anisotropy a key to resolve fabrics of mantle lithosphere of fennoscandia abstract by merging different regional sets of body wave data we compile a relief of the lithosphere asthenosphere boundary in one of the oldest continental regions on the planet the fennoscandian shield a maximum lithospheric thickness of 200 220 km is observed in the central part of the shield and a significant thinning at its margins particularly in the southwest at the trans european suture zone fabric of the mantle lithosphere is modelled from independent sets of anisotropic parameters relative p residual spheres and shear wave splitting the mantle lithosphere of fennoscandia consists of several domains consistent olivine fabrics of dipping foliations in 3d anisotropic models of the proterozoic lithosphere or predominantly dipping lineations in models of the archean lithosphere the strength of seismic anisotropy agrees with findings from mantle xenoliths we interpret the anisotropic domains as fragments of mantle lithosphere retaining an old fossil olivine fabric which was created before these micro continents assembled we envisage an early form of plate tectonic processes such as successive subduction episodes stacking of oceanic plates and accretion of magmatic arcs such processes could create the generally observed fossil dipping fabrics of the thick precambrian mantle lithosphere starting as early as the archean

solution of the bearing capacity problem by the slip line method the authors have derived the bearing capacity factor nq on sloping ground based on the slip line method and have verified it using finite difference analysis the bearing capacity factor n on sloping ground is obtained by an iterative finite difference solution of the slip line equations and the results are close to those from laboratory testing design figures for n on sloping ground are prepared for rapid engineering use for earthquake loading the authors have applied the concept of equivalent horizontal acceleration and have derived nq and n based on slip line analysis key words bearing capacity slip line finite difference sloping ground earthquake

glacio isostatic crustal movements caused by historical volume change of the vatnajokull ice cap iceland measurements of the lake level of lake langisjor at the sw edge of the vatnajokull ice cap indicate a tilt of 0 26 0 06 rad year away from the ice cap in the years 1959 1991 the tilt is too large to be explained as an elastic earth response to ice retreat this century or to be caused by change in the gravitational pull of the ice cap but it can be explained by sub lithospheric viscous adjustment regional subsidence in historical times in se iceland can similarly be attributed to viscous adjustment resulting from the increased load of vatnajokull during the little ice age the inferred sub lithospheric viscosity is 1 1018 5 1019 pa s

moho depth and crustal composition in southern africa abstract we present new results on structure thickness and composition of the crust in southern africa based on 6300 seismic receiver functions at 85 stations application of hk stacking to the entire sase dataset and use of multi frequency bands improve resolution substantially we observe a highly heterogeneous crustal structure with short wavelength variations in thickness h vp vs ratio composition and moho sharpness which defines 20 blocks that do not everywhere coincide with surface tectonic features in the zimbabwe craton the tokwe block has h 35 38 km and vp vs 1 74 1 79 whereas the thicker crust in the tati block h 47 51 km may be related to deformation of the archean crust along the cratonic margin two distinct crustal blocks with similar crustal thickness 42 46 km but significantly different vp vs ratios are recognized in the limpopo belt extreme values of 1 90 1 94 at the dyke swarms in eastern limpopo and 1 84 at the olifants river dyke swarm and easternmost bushveld intrusion complex bic indicate voluminous magmatic intrusions in the whole crust we find no evidence for magmatic intrusions in the central inferred part of bic where the crust is thick 45 50 km and vp vs is low 1 68 1 70 this thick crustal root may have deflected rising magmas to form the two bic lobes most of central kaapvaal has thin 35 40 km crust and vp vs 1 74 these characteristics are similar to the tokwe block in zimbabwe craton and may indicate delamination of pre existing lower crust which is further supported by a very sharp moho transition the exposed cross section in the vredefort impact crater is non representative of cratonic crust due to shallow moho 34 km and high vp vs 1 80 attributed to shock metamorphism high vp vs 1 76 is typical of the witwatersrand basin and anomalously low vp vs 1 66 1 67 marks the kaapvaal kheis namaqua transition highly heterogeneous crust both in thickness and vp vs ratio is typical of the namaqua natal and cape fold belts

an idealized semi empirical framework for modeling the madden julian oscillation abstractthe authors present a simple semi empirical model to explore the hypothesis that the madden julian oscillation can be represented as a moisture mode destabilized by surface flux and cloud radiative feedbacks the model is one dimensional in longitude the vertical and meridional structure is entirely implicit the only prognostic variable is column water vapor w the zonal wind field is an instantaneous diagnostic function of the precipitation field the linearized version of the model has only westward propagating relative to the mean flow unstable modes because wind induced surface latent heat flux anomalies occur to the west of precipitation anomalies the maximum growth rate occurs at the wavelength at which the correlation between precipitation and surface latent heat flux is maximized this wavelength lies in the synoptic to planetary scale range and is proportional to the horizontal scale associated with the assumed diagnostic wind response to precipitation anomalies the nonlinear version

scattered wave imaging of the lithosphere asthenosphere boundary several recent studies have imaged discontinuities interpreted as the lithosphere asthenosphere boundary using receiver function methods these are exciting results since this boundary is fundamental and yet relatively elusive its location is not well imaged nor are its properties well understood the receiver function method provides high depth resolution and the multitude of studies using this method have increased lateral resolution a better global understanding of the location and nature of the boundary is developing which ultimately will have implications for mantle dynamics and planetary evolution however these new results do not all form a clear and consistent picture and in some cases introduce new complexities and questions some apparent contradictions may represent unmodeled earth structure overall interpretation and synthesis requires careful consideration of the approaches and sensitivities of individual studies

a review on the analysis of the crustal and upper mantle structure using receiver functions abstract the discontinuities in the earth such as moho lithosphere asthenosphere boundary lab 410 and 660 km discontinuities are characterized with an abrupt jump in velocities of p and s waves the depths of these discontinuities are an important parameter to investigate tectonic evolution in the lithosphere receiver functions technique with teleseismic events is very suitable for studying the crust and upper mantle structure beneath stations thus becoming one of the standard tools for such study the principle of receiver functions is to separate the converted ps or sp phases generated at the discontinuities beneath stations in the case that the direct p or s is a delta function in this paper the methods of receiver function analysis are collected from literatures we introduce the coordinate transform technique for the separation of ps or sp waves the deconvolution algorithm to extract p and s receiver functions the waveform fitting method to invert for s wave velocity structure the stacking technique to improve signals and the migration from time series to depth domain with some illustrative examples the care that should be taken in study of the crustal and upper mantle structure using receiver functions are summarized

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

low frequency modes in an equatorial shallow water model with moisture gradients motivated by observations of the mean state of tropical precipitable water pw a moist first baroclinic mode shallow water system on an equatorial plane with a background saturation profile that depends on latitude and longitude is studied in the presence of a latitudinal moisture gradient linear analysis of the non rotating problem reveals large scale symmetric eastward and westward propagating unstable modes the introduction of a zonal moisture gradient breaks the east west symmetry of the unstable modes the effects of rotation are then included by numerically solving the resulting eigenvalue problem on an equatorial plane with a purely meridional moisture gradient the system supports large scale low frequency eastward and westward moving neutral modes some of the similarities and some of the discrepancies of these modes with intraseasonal tropical waves are pointed out finally a zonal moisture gradient in the presence of rotation renders some of the aforementioned neutral modes unstable in particular according to observations of large scale low frequency tropical variability it is seen that regions where the background saturation profile increases decreases to the east favour eastward westward moving moist modes

a new mechanism of the slow eastward propagation of unstable disturbances with convection in the tropics implications for the mjo abstractto understand the slow eastward propagation of the madden julian oscillation mjo the authors propose a new mechanism of slow eastward propagation of an unstable disturbance slow eastward propagating disturbance sed in the tropics assuming a simplified instability source two conditions are necessary over the convective region associated with the sed for this mechanism i moderately negative gross moist stability gms and ii strong stretching in the lower layer the instability due to i needs to be moderate for causing a propagating convective disturbance under the structure of twin cyclonic vortices to the west and convection to the east stretching of planetary vorticity associated with the convection produces cyclonic vorticity which results in eastward propagation of the vortices equatorial plane dynamics explain the positional relation between the twin vortices and convection coherently strong equatorial low level westerly winds accompanying the vortices induce convergence

modeling tropical convergence based on the moist static energy budget abstract the vertically integrated moist static energy equation provides a convenient starting point for the construction of simple models of the time mean low level convergence in the tropics a vertically integrated measure of the moist static stability the gross moist stability proves to be of central importance minima in this quantity mark the positions of the tropical convergence zones we argue that the positions of these minima are determined by the time mean moisture field which is in turn closely tied to the time mean surface temperature

propagating versus nonpropagating madden julian oscillation events abstractbasinwide convective anomalies over the indian ocean io associated with the madden julian oscillation mjo sometimes propagate eastward and reach the west pacific wp but sometimes do not long term observations and reanalysis products are used to investigate the difference between the propagating and nonpropagating mjo events io convection onset events associated with the mjo are grouped into three categories based on the strengths of the simultaneous dry anomalies over the eastern maritime continent and wp the io convection anomaly preferentially makes eastward propagation and reaches the wp when the dry anomaly is stronger analysis of the column integrated moist static energy mse budget shows that horizontal advection moistens the atmosphere to the east of the positive mse anomaly associated with the active convection over the io and is of sufficient magnitude to explain the eastward propagation of the positive mse anomaly interpretation is complicated however by lack of closure in

successive mjo propagation in merra 2 reanalysis composite circumnavigating madden julian oscillation mjo events in version 2 of the nasa modern era reanalysis for research and applications merra 2 reanalysis propagate as convectively coupled kelvin waves over the western hemisphere and moisture waves like that described by adames and kim 2016 over the warm pool estimated zonally variable phase speeds of coupled kelvin waves in the tropics are calculated by determining the effective static stability experienced by the wave the wave is structured similarly to a classically derived deep tropospheric kelvin wave and its phase speed is up to 33 m s 1 or 40 m s 1 over the central eastern pacific or atlantic equatorial africa respectively during boreal winter theoretically estimated phase speeds of convectively coupled kelvin waves over the tropical warm pool are greater than 15 m s 1 much faster than the propagation of the reanalyzed mjo a complete theory for mjo propagation around the globe must allow both coupled kelvin waves and moisture waves

roughness of the mantle transition zone discontinuities revealed by high resolution wavefield imaging we processed two independent data sets 2 458 973 three component seismograms from all earthscope transportable array usarray stations and 141 080 pairs of high quality receiver functions from the earthscope automated receiver survey using the generalized iterative deconvolution method and shaped the output with a 0 1 hz ricker wavelet we used these data as input to our 3 d plane wave migration method to produce an image volume of p to s scattering surfaces under all of the lower 48 states model simulations show that compared to the widely used common conversion point stacking method our method is capable of resolving not only dipping discontinuities but also subtler details of amplitude and topography variations at scales near the diffraction limit maps of attributes derived from these discontinuities reveal several previously unobserved features of the 410 and 660 discontinuities d410 and d660 topography with many tens of kilometers is resolved at a range of scales additionally we observed large variations of amplitude on the radial component and in the radial to transverse amplitude ratio that correlate with inferred variations in discontinuity topography we argue that this combination of observations can be explained by roughness at a range of scales the structural fabric we imaged is preferentially aligned orthogonal to the farallon north american relative motion two regions we infer to have exceptional roughness show spatial correlation with locations where tomography models indicate that the subducted slab is passing through the transition zone we suggest that these rough regions are indicators of vertical mantle flows through the transition zone

a first detailed look at the greenland lithosphere and upper mantle using rayleigh wave tomography we present the results of a surface wave study carried out across greenland as part of the glatis greenland lithosphere analysed teleseismically on the ice sheet project rayleigh wave phase velocity dispersion curves were estimated for 45 two station paths across greenland using data from large teleseismic earthquakes the individual dispersion curves show characteristics broadly consistent with those of continental shields worldwide but with significant differences across the greenland landmass reliable phase velocity measurements were made over a period range of 25 160 s providing constraint on mantle structure to a depth of 300 km an isotropic tomographic inversion was used to combine the phase velocity information from the dispersion curves in order to calculate phase velocity maps for greenland at several different periods the greatest lateral variation in phase velocity is observed at intermediate periods 50 80 s where a high velocity anomaly is resolved beneath central southwestern greenland and a low velocity anomaly is resolved beneath southeastern greenland the results of the phase velocity inversion were used to construct localized dispersion curves for node points along two parallel north south profiles in southern greenland these curves were inverted to obtain models of shear wave velocity structure as a function of depth again with the assumption of isotropic structure a similar inversion was carried out for two two station dispersion curves in northern greenland where the resolution of the phase velocity maps is relatively low the models show a high velocity lid structure overlying a zone of lower velocity beneath which the velocity gradually increases with depth the lid structure is interpreted as the continental lithosphere within the lithosphere the shear wave velocity is 4 12 per cent above global reference models with the highest velocities beneath central southwestern greenland however the assumption of isotropic structure means that the maximum velocity perturbation may be overestimated by a few per cent the lithospheric thickness varies from 100 km close to the southeast coast of greenland to 180 km beneath central southern greenland

imaging the colliding indian and asian lithospheric plates beneath tibet 1 a high resolution image of the base of the lithosphere from s to p converted seismic waves revealed the collision architecture of the indian and asian continental plates beneath the tibetan plateau the base of the indian lithosphere dips northward from a depth of 160 km beneath the himalayas to a depth of 220 km just south of the bangong suture the base of the asian lithosphere is nearly horizontal at the depth of 160 180 km from central to northern tibet there is a vertical gap of about 50 km between indian and asian lithospheres our observation of a well defined thick lithosphere throughout the entire plateau is not consistent with models of wholesale convective instability of a thickened mantle lithosphere which would predict a very thin asian lithosphere the hypothesized sequential southward subduction of tibetan and asian continental lithospheres leading to the growth of the tibetan plateau if correct cannot be occurring below 180 km depth our results along with available geological and geophysical data strongly support that the plateau is predominantly formed by a relatively coherent north dipping subducted indian continental lithosphere in the south which presently can be traced to the middle of the plateau and a south dipping subducted asian lithosphere in the north at a shallower depth

contrasting characteristics between the northward and eastward propagation of the intraseasonal oscillation during the boreal summer abstract this study investigates the structural and evolutionary characteristics of the eastward and northward propagating intraseasonal oscillation iso in the indian ocean and western pacific during the boreal summer along the equator the near surface moisture convergence located to the east of the deep convection region appears to result in the eastward propagation of the iso consistent with the frictional wave cisk conditional instability of the second kind mechanism proposed in previous studies the eastward propagation is characterized by sequentially downstream development of deep convection occuring mainly in certain regions such as 60 95 120 and 145 e and the date line the northward propagation of deep convection can be attributed to the low level moisture convergence located to the north this convergence is a deep structure extending from the surface to the middle troposphere near surface convergence appears only after the systems approach the landmass in the north it is sugges

conductivity structure of the lithosphere asthenosphere boundary beneath the eastern north american margin tectonic plate motion and mantle dynamics processes are heavily influenced by the characteristics of the lithosphere asthenosphere boundary lab yet this boundary remains enigmatic regarding its properties and geometry the processes involved in rifting at passive margins result in substantial alteration of the lithosphere through the transition from continental to oceanic lithologies here we employ marine magnetotelluric mt data acquired along a 135 km long profile offshore martha s vineyard new england usa to image the electrical conductivity structure beneath the new england continental margin for the first time we invert the data using two different mt 2 d inversion algorithms and present a series of models that are obtained using three different parameterizations fully unconstrained unconstrained with an imposed lab discontinuity and a priori constrained lithosphere resistivity this suite of models infers variability in the depth of the lab with an average depth of 115 km at the eastern north america passive margin models robustly detect a 350 m lithospheric anomalous conductivity zone lacz that extends vertically through the entire lithosphere our preferred conductivity model is consistent with regional p to s receiver function data shear wave velocity gravity anomalies and prominent geological features we propose that the lacz is indicative of paleo lithospheric thinning either resulting from kimberlite intrusions associated with rifting and the new england great meteor hotspot track or from shear driven localized deformation related to rifting

glacial isostatic adjustment and the viscosity structure underlying the vatnajokull ice cap iceland we examine the dependence of glacial isostatic adjustment gia due to changes in the vatnajokull ice cap iceland on the underlying viscosity structure iceland offers a unique case study for gia research with a thinner elastic lithosphere underlain by a low viscosity zone or asthenosphere as opposed to regions such as fennoscandia or north america described by a thicker lithosphere while not necessarily featuring an asthenosphere

the s receiver functions synthetics and data example summary recently the s receiver function method has been successfully developed to identify upper mantle interfaces s receiver functions have the advantage of being free of s wave multiple reflections and can be more suitable than p receiver functions for studying mantle lithosphere however because of specific ray geometry and interference of diverse phases the s receiver function method has some technical difficulties and limitations we use synthetic seismograms to demonstrate the feasibility and limitations of s receiver functions for studying mantle structures full wavefield seismograms were calculated using the reflectivity method and processed to generate synthetic s receiver functions for s sks and scs waves results show that s receiver functions can be obtained from waveforms of s sks and scs waves the synthetic s receiver functions for these incident waves show s to p converted phases at all discontinuities in the crust and upper mantle useful ranges of epicentral distances for calculation of s receiver functions are 55 85 for s 85 for sks and 50 75 for scs waves we apply both the s and p receiver function methods to data recorded at broadband station ykw3 in northwest canada the study shows that there is significant agreement among different receiver function methods and demonstrates the usefulness of s receiver functions for imaging the mantle lithosphere

the lithosphere asthenosphere boundary beneath the western united states summary s receiver functions from 67 broad band seismic stations in the western united states clearly reveal the existence of a mantle discontinuity with velocity reduction downward which we interpret as the lithosphere asthenosphere boundary lab the average depth of the lab is 70 km the boundary is relatively sharp with an overall sharpness of less than 20 km the boundary is more prominent south of the mendocino triple junction where the farallon plate has completely subducted this may indicate partial melts at the base of the lithosphere caused by the upwelling of the asthenospheric flow through the slab window a double low velocity zone is observed at base of the lithosphere beneath southern sierra nevada implying a second melting zone at a depth of 100 km well correlated with previous studies of lithospheric delamination in the area

lithospheric structure of the aegean obtained from p and s receiver functions combined p and s receiver functions from seismograms of teleseismic events recorded at 65 temporary and permanent stations in the aegean region are used to map the geometry of the subducted african and the overriding aegean plates we image the moho of the subducting african plate at depths ranging from 40 km beneath southern crete and the western peloponnesus to 160 km beneath the volcanic arc and 220 km beneath northern greece however the dip of the moho of the subducting african plate is shallower beneath the peloponnesus than beneath crete and rhodes and flattens out beneath the northern aegean observed p to s conversions at stations located in the forearc indicate a reversed velocity contrast at the moho boundary of the aegean plate whereas this boundary is observed as a normal velocity contrast by the s to p conversions our modeling suggests that the presence of a large amount of serpentinite more than 30 in the forearc mantle wedge which generally occurs in the subduction zones may be the reason for the reverse sign of the p to s conversion coefficient moho depths for the aegean plate show that the southern part of the aegean crustal thickness of 20 22 km has been strongly influenced by extension while the northern aegean sea which at present undergoes the highest crustal deformation shows a relatively thicker crust 25 28 km this may imply a recent initiation of the present kinematics in the aegean western greece crustal thickness of 32 40 km is unaffected by the recent extension but underwent crustal thickening during the hellenides mountains building event the depths of the aegean moho beneath the margin of the peloponnesus and crete 25 28 and 25 33 km respectively show that these areas are also likely to be affected by the aegean extension even though the cyclades crustal thickness of 26 30 km were not significantly involved in this episode the aegean lithosphere asthenosphere boundary lab mapped with s receiver functions is about 150 km deep beneath mainland greece whereas the lab of the subducted african plate dips from 100 km beneath crete and the southern aegean sea to about 225 km under the volcanic arc this implies a thickness of 60 65 km for the subducted african lithosphere suggesting that the aegean lithosphere was not significantly affected by the extensional process associated with the exhumation of metamorphic core complexes in the cyclades

crustal and uppermost mantle structure in the middle east assessing constraints provided by jointly modelling ps and sp receiver functions and rayleigh wave group velocity dispersion curves

imaging the lithosphere asthenosphere boundary of the indian plate using converted wave techniques 1 the lithospheric structure of the indian plate has been investigated using converted wave techniques p and s receiver functions and a novel stacking analysis technique without using deconvolution applied to a large seismological data set from permanent and temporary broadband seismic stations we observe coherent energy from at least two seismic discontinuities i e the crust mantle moho and lithosphere asthenosphere boundary lab in the uppermost mantle here we provide a novel seismic image of the indian lithosphere showing definitive evidence of its flexure which is interpreted to be primarily caused by the hard collision at 55 myr resulting in the world s highest mountain chain the himalayas and the tibetan plateau results from geoidal and gravity studies do suggest postcollisional flexuring of the indian plate however the flexure lacks observational constraints the observed wavelength of the flex is 1000 km with the thickness of the indian shield lithosphere varying from 70 km to 140 km such a low value for a continent implies that the indian plate has been reworked in the past the plate deepens in the himalayan region to a depth of 170 km further the converted phases are interpreted to be resulting from the bottom of the lithosphere we clearly demonstrate that these are distinct and different from the midlithospheric discontinuity for a large number of stations the midlithospheric discontinuity and lab are clearly separated in depth our observations suggest that the archaean lithosphere is no longer intact and is prone to deformation

seismic evidence for significant lateral variations in lithospheric thickness beneath the central and western north china craton abstract we have migrated teleseismic s receiver functions to construct detailed lithospheric structure images that cover the three constituent parts of the north china craton ncc our images show that in contrast to the eastern ncc where significantly thinned lithosphere 60 100 km is widespread the central and western ncc are characterized by the coexistence of both preserved thick and dramatically thinned lithosphere the thick lithosphere 200 km is present beneath the stable ordos plateau and the thinned lithosphere up to 80 km is found in the late cenozoic yinchuan hetao and shaanxi shanxi rift areas with sharp changes occurring over a lateral distance of

simulation of the madden julian oscillation in the ncar ccm3 using a revised zhang mcfarlane convection parameterization scheme abstract this study presents the simulation of the madden julian oscillation mjo in the ncar ccm3 using a modified zhang mcfarlane convection parameterization scheme it is shown that with the modified scheme the intraseasonal 20 80 day variability in precipitation zonal wind and outgoing longwave radiation olr is enhanced substantially compared to the standard ccm3 simulation using a composite technique based on the empirical orthogonal function eof analysis the paper demonstrates that the simulated mjos are in better agreement with the observations than the standard model in many important aspects the amplitudes of the mjos in 850 mb zonal wind precipitation and olr are comparable to those of the observations and the mjos show clearly eastward propagation from the indian ocean to the pacific in contrast the simulated mjos in the standard ccm3 simulation are weak and have a tendency to propagate westward in the indian ocean nevertheless there remain several deficiencies that are yet

imaging the seismic lithosphere asthenosphere boundary of the oceanic plate 1 the seismic lithosphere asthenosphere boundary lab or g discontinuity a seismologically characterized abrupt drop in wave speed in the uppermost mantle is one of the key issues in current geodynamics although plate tectonics started as a theory for the ocean reports on lab for normal oceanic regions are scarce due to paucity of seismic data and whether or not the oceanic lab grows with age is the key issue to be resolved we conduct a systematic survey for the oceanic lab using s to p converted seismic waves along three margins of oceanic plates whose crustal age ranges from 10 myr to 130 myr and we observe laterally continuous oceanic lab images the thickness of the oceanic plate estimated from labs increases with the plate age though scattered suggesting that the evolution of oceanic lithosphere is predominantly governed by temperature and that the oceanic seismic lab represents a boundary that grows with age

development characteristics and dynamic structure of tropical intraseasonal convection anomalies abstract the development and dynamical structure of intraseasonal low frequency convection anomalies in the equatorial region are investigated using 10 years 1975 85 of outgoing longwave radiation olr and 7 years 1979 85 of 200 and 850 mb wind data the composite olr anomalies for 36 cases show a four stage development process initiation over equatorial africa rapid intensification when passing through the indian ocean mature evolution characterized by a weakening in the maritime continent and redevelopment over the western pacific and dissipation near the date line in moderate events or emanation from the equator toward north america and southeastern pacific in strong events a noticeable feature in vertical structure is that the 850 mb convergence leads convection and midtropospheric upward motion by about 30 degrees longitude in both developing and mature phases equatorial upper lower level easterly westerly anomalies and associated twin anomalous anticyclonic cyclonic circulation an

s wave velocity structure of the upper mantle beneath the arctic region from rayleigh wave dispersion data abstract a new model of the upper mantle structure of the arctic region based on a representative dataset of rayleigh wave group velocity dispersion curves from 10 to 250 s period is presented a surface wave tomography procedure is used to image the group velocity distributions local dispersion curves are constructed and inverted to vertical s wave velocity sections up to the depth of 500 km results are presented in two forms as horizontal slices of s wave velocity variations relative to the average velocities at several mantle depths and as 2d velocity sections along three profiles crossing different tectonic units the model shows lateral and vertical velocity variations over the whole depth range within the study area the most prominent velocity heterogeneities are localized in the uppermost mantle up to the 200 km depth in this depth range the velocity anomalies are strongly correlated with the main tectonic structures the calculated s wave velocity distribution demonstrates that the upper mantle of the continental shields is characterized by high s wave velocities and contains regional velocity anomalies associated with small scale blocks low mantle velocities are attributed to the areas with high level of tectonic and seismic activity significant difference in deep velocity structure of the marginal seas and deep water oceanic basins of various ages is revealed the obtained model suggests some insights into the geodynamical evolution of the lithosphere of the arctic region

frictional moisture convergence in a composite life cycle of the madden julian oscillation abstract a composite life cycle of the madden julian oscillation mjo is constructed using an index based on the first two eofs of the bandpass filtered 20 80 days 850 mb zonal wind averaged from 5 n to 5 s every 2 5 around the equator precipitation 1000 mb convergence 850 mb wind and 200 mb wind are composited for the period 1979 95 water vapor integrated from the surface to 300 mb is composited for the period 1988 92 frictional moisture convergence at the equator is shown to play an important role in the life cycle of the madden julian oscillation mjo regions of boundary layer convergence foster growth of positive water vapor anomalies to the east of convection this convergence coincides with 850 mb easterly wind anomalies as is consistent with kelvin wave dynamics drying of the atmosphere occurs rapidly after the passage of convection with the onset of 850 mb westerly perturbations possible mechanisms for this drying include boundary layer divergence and subsidence or horizontal advect

imaging the indian lithosphere beneath the eastern himalayan region summary lithospheric thickness is an important parameter to understand the nature of collision and subduction between the indian and asian tectonic plates in this study we apply the s receiver function technique to data from a network of broad band stations in the northeast india and eastern himalayan regions and image the geometry of indian plate collision this analysis reveals clear s to p conversions from the moho and lithosphere asthenosphere boundary lab in the various tectonic units of the study region the indian lithosphere is found to be only 90 km thick beneath the shillong plateau deepening to 135 km on either side suggestive of a lithospheric upwarp related to the plateau uplift the lithosphere thickens northward with values reaching 180 km beneath the eastern himalaya the trend of the lab north of the foredeep region indicates that the indian plate plunges beneath the eastern himalaya the consistent northward dipping character of the indian plate suggests that the indian plate is traceable until it gets subducted beneath tibet just south of bangong suture zone the deepening of the lab and its correlation with the topographic elevation is in agreement with homogeneous thickening of the lithosphere in response to compressive forces due to the continental collision of india with asia

seismic upper mantle discontinuities beneath southeast tibet and geodynamic implications abstract in this study a total of 13 080 p receiver functions and 2800 s receiver functions recorded by 116 stations in southeast tibet are used to determine the depths of the moho the lithosphere asthenosphere boundary lab and the 410 km and 660 km discontinuities the results show that the lab depth increases from 80 100 km beneath southern yunnan to 140 180 km beneath sichuan most of the 410 km discontinuity is flat and at 410 km depth with a slight depression of 10 20 km beneath the longmenshan lms fault the central sichuan yunnan sy diamond shaped block and southeastern yunnan for the 660 km discontinuity the greatest depth occurs beneath the lms and southern yunnan reaching 670 680 km the deepening of 660 km discontinuity is attributed to compositional heterogeneity within the mtz or dynamic pressure on the discontinuity additionally the velocity of movement in the crust and upper mantle beneath sy is different in yunnan crustal movement is southeastward whereas across the red river fault part of the crustal motion is redirected southwest by the westward rollback of the mantle beneath myanmar the interaction between the asthenosphere moving northeastward from myanmar and southeastward from tibet near latitude 26 n causes the crust and lithospheric mantle beneath southern yunnan to have different movement directions

post rifting stress relaxation at the divergent plate boundary in northeast iceland interaction of the elastic lithosphere with the underlying anelastic asthenosphere causes strain to propagate along the earth s surface in a diffusion like manner following tectonism at plate boundaries this process transfers stress between adjacent tectonic segments and influences the temporal tectonic pattern along a plate boundary observations of such strain transients have been rare and have hitherto been confined to strike slip and underthrusting plate boundaries1 here we report the observation of a strain transient at the divergent spreading plate boundary in iceland a global positioning system survey undertaken a decade after an episode of dyke intrusion accompanying several metres of crustal spreading reveals a spatially varying strain field with the expected diffusion pulse shape and an amplitude three times greater than the 5 7 cm that would be expected from the average spreading rate2 a simple one dimensional model with a thin elastic layer overlying a viscous layer fits the data well and yields a stress diffusivity of 1 1 a 0 3 m2s 1 combined with struc tural information from magnetotelluric measurements this implies a viscosity of 0 3 2 1019 pa s a value comparable to that derived for iceland from post glacial rebound23 but low compared with estimates for mantle viscosity obtained elsewhere3

rayleigh wave group velocity of the icelandic crust from correlation of ambient seismic noise 1 by cross correlating 2 years of ambient seismic noise from 31 broadband stations distributed across iceland we have been able to measure rayleigh wave group velocity in three discrete frequency bands centered on 4 7 and 17 s sensitive to approximately the top 6 10 and 25 km of the crust for 289 420 and 139 station to station paths respectively these are inverted to yield tomographic group velocity maps of the icelandic crust the results correlate with the major tectonic features on iceland and agree well with earlier seismic studies based on traditional methods active source and earthquake specifically we obtain low velocities in the central parts of iceland coinciding with the rift zones and young crust in contrast the parts of iceland covered with older tertiary volcanics reveal relatively higher velocities at the shorter periods 4 and 7 s this correlation reflects porosity degree of fracturing and alteration at the longest period 17 s i e at greater depth this correlation may reflect the thermal state of the crust with warm and seismically slow material near the rifts and cooler and seismically faster material beneath the tertiary formations to the east and west

crustal and lithospheric structure of northeast china from s wave receiver functions abstract lithospheric thickness is closely associated with lithospheric response to tectonic forces or thermal processes analysis of s wave receiver functions srfs from a dense seismic array has revealed lithospheric thickness variations along a 1200 km long profile that spans all major geological terranes of northeast china the srf images identify the shallowest moho and lithosphere asthenosphere boundary lab depths beneath the rifted songliao basin thus spatially correlating well with the thick sediment accumulation these features can be explained by a pure shear regime operating in the lower crust and upper mantle suggesting the predominance of roughly symmetric lithosphere stretching from continental rifting in contrast thicker lithosphere in western and eastern terranes of ne china indicates the lithosphere in these regions was not strongly affected by the extensional processes during the late mesozoic flat lab structure beneath the erguna and xing an terranes along with the overlying relatively deeper moho beneath the great xing an range suggests the north south gravity lineament may not be a trans lithospheric structure

calibrating a glaciological model of the greenland ice sheet from the last glacial maximum to present day using field observations of relative sea level and ice extent we constrain a three dimensional thermomechanical model of greenland ice sheet gris evolution from the last glacial maximum lgm 21 ka bp to the present day using primarily observations of relative sea level rsl as well as field data on past ice extent our new model huy2 fits a majority of the observations and is characterised by a number of key features i the ice sheet had an excess volume relative to present of 4 1 m ice equivalent sea level at the lgm which increased to reach a maximum value of 4 6 m at 16 5 ka bp ii retreat from the continental shelf was not continuous around the entire margin as there was a younger dryas readvance in some areas the final episode of marine retreat was rapid and relatively late c 12 ka bp leaving the ice sheet land based by 10 ka bp iii in response to the holocene thermal maximum htm the ice margin retreated behind its present day position by up to 80 km in the southwest 20 km in the south and 80 km in a small area of the northeast as a result of this retreat the modelled ice sheet reaches a minimum extent between 5 and 4 ka bp which corresponds to a deficit volume relative to present of 0 17 m ice equivalent sea level our results suggest that remaining discrepancies between the model and the observations are likely associated with non greenland ice load differences between modelled and observed present day ice elevation around the margin lateral variations in earth structure and or the pattern of ice margin retreat

imaging ruptured lithosphere beneath the red sea and arabian peninsula abstract the red sea rift an archetype of a newly formed ocean basin is an ideal environment in which to study the controversial processes associated with continental rifting different models have been proposed to explain how rifting in the red sea evolved however accurate constraints on lithospheric structure have not been available to discriminate rifting models we use the s wave receiver function technique to produce the first images of the lithosphere asthenosphere boundary lab structure along the red sea and throughout the arabian peninsula lithospheric thickness varies considerably with thin lithosphere centered on the rift axis thickening toward the arabian interior gravity data are well fit by our structural model and indicate that high surface topography along the rift flank is not in isostatic equilibrium requiring dynamic compensation for its support while our derived structure is consistent with active rifting processes previous studies demonstrated that the red sea initiated as a passive rift therefore our results suggest a two stage rifting history where extension and erosion by flow in the underlying asthenosphere are responsible for variations in lab depth lab topography guides asthenospheric flow beneath western arabia and the red sea demonstrating the important role lithospheric variations play in the thermal modification of tectonic environments

evidence for a missing crustal root and a thin lithosphere beneath the central alborz by receiver function studies summary the alborz mountains build the northern part of the alpine himalayan orogen in western asia they are located south of the caspian sea and form an east west range across the north of iran this region is one of the most active tectonic areas as it undergoes extensive crustal deformation and shortening in the present work we used data from 11 permanent stations of the tehran telemetry seismic network to estimate the thickness of the crust and mantle lithosphere beneath the central alborz region by p and s receiver function methods results of both p and s receiver functions revealed a relatively large crustal thickness beneath this region 51 54 km which can be associated with the shortening process related to the orogenic belt no remarkable crustal thickening has been detected below the high topography of central alborz a thick crust 67 5 km is observed locally in the region beneath the damavand volcano which is possibly related to the magmatic addition at the base of the crust beneath the volcanic region the s receiver functions exhibit the existence of a seismic discontinuity in the upper mantle at a depth of 90 km which we interpreted as the base of the lithosphere the missing crustal root and the relatively thin lithosphere beneath the alborz may imply that sublithospheric mantle could be responsible for and support the elevation of the alborz

europe from the bottom up a statistical examination of the central and northern european lithosphere asthenosphere boundary from comparing seismological and electromagnetic observations abstract the lithosphere asthenosphere boundary lab is a fundamental boundary in the plate tectonic paradigm it is the most pervasive on the planet yet comparatively it is one we know little about defined initially on the basis of the mechanical response of the earth to loading its usage has become ubiquitous across the geosciences but the natural differences in its definition due to differences in thermal physical and chemical parameters cause confusion to advance this debate comparisons are made both qualitatively and quantitatively between the delineation of the lab for europe based on seismological and electromagnetic observations we examine statistically using robust methods the labs derived from independent datasets and methods essentially all definitions of the lab as an impedance contrast from receiver functions slabrf a seismic anisotropy change slaba and an increase in conductivity from magnetotellurics elab are consistent with a deeper lab beneath precambrian europe and a shallower lab beneath phanerozoic europe with some exceptionally deep regions in phanerozoic europe such as the alps all three labs increase in depth significantly and rapidly at a location consistent with the surface expression of the trans european suture zone tesz which separates precambrian europe to the north and east from phanerozoic europe in the centre two of the definitions slabrf and elab are consistent for phanerozoic europe with mean values of 90 100 km compared to an average slabrf of 135 km a different two slaba and slabrf are consistent for precambrian europe with mean values of 170 180 km compared to an elab mean of 250 km the deeper elab depths for precambrian europe are more consistent with body wave and surface wave tomography models than are the slaba and slabrf ones suggesting that the lower lithosphere beneath precambrian europe between 170 to 250 km is responding to shearing on the base of the lithosphere from plate driving forces taken together the definitions provide strong constraints on the nature of the lab for example the electrical elab beneath the tesz is anomalously thick to possibly the transition zone whereas slaba and slabrf seismological definitions would place it at far shallower depths given the sensitivity of electrical conductivity to partial melt and water content the thick elab beneath the tesz excludes interpretation of the seismic lab in that location in terms of a thermal structure that would induce partial melting or of hydration

essential ingredients to the dynamics of westerly wind bursts abstractwesterly wind bursts wwbs are brief anomalously westerly winds in the tropical pacific that play a role in the dynamics of enso through their forcing of ocean kelvin waves they have bee

proto iceland plume caused thinning of irish lithosphere abstract the lithosphere asthenosphere boundary lab separates the rigid lithospheric plates from the hot convective mantle in the region of the north atlantic this boundary is widely influenced by the spreading head of the proto iceland plume p kumar et al the lithosphere asthenosphere boundary in the north west atlantic region earth planet sci lett 236 2005 249 257 that also caused the evolution of the british tertiary volcanic province btvp with the giant s causeway basalts as famous landmark using teleseismic shear wave receiver functions we map the lab underneath ireland and find a distinctive lithospheric thinning of about 30 km towards the northern part of the island as this region is part of the btvp we explain the lithospheric thinning in agreement with geochemical results by thermal erosion originating from the head of the proto iceland plume

seismic receiver functions and the lithosphere asthenosphere boundary abstract the lower boundary of the lithospheric plates has remained as an enigmatic boundary for seismologists since it is relatively poorly observed by seismic means there is traditionally a broad consensus that the asthenosphere is observable as a low velocity zone by seismic surface waves seismic techniques which use shorter period p to s or s to p converted body waves are now far enough developed to be successful in observing such a low velocity zone with a higher resolution the principle of this technique the so called receiver function technique is that a strong teleseismic mother phase e g p s pp or sks incident from below on any seismic discontinuity beneath a station produces a converted phase ps or sp which indicates its depth and properties we discuss details of this technique a sufficient number of such observations exist already to indicate that the top of the low velocity zone is a globally observable discontinuity and it is sharper than previously thought an intriguing observation is that in some cratons the new seismic data indicate that the low velocity zone exists already at shallower depths than obtained from surface waves this confirms earlier results from controlled source observations thybo and perchuc 1997 we discuss possible interpretations of this shallow low velocity zone in cratonic regions

post glacial rebound and asthenosphere viscosity in iceland during the weichselian glaciation iceland was covered with an ice cap which caused downward flexure of the earth s surface the post glacial rebound in iceland was very rapid being completed in about 1 000 years the length of this time interval constrains the maximum value of asthenosphere viscosity in iceland to be 1 times 10 sup 19 pa s or less further clarification of the ice retreat and uplift history may reveal lower viscosity current changes in the mass balance of icelandic glaciers must lead to measurable elevation changes considering this low viscosity expected current elevation changes around the vatnajoekull ice cap are of the order of 1 cm per year due to mass balance change in this century

seismic imaging of thickened lithosphere resulting from plume pulsing beneath iceland ocean plates conductively cool and subside with seafloor age plate thickening with age is also predicted and hot spots may cause thinning however both are debated and depend on the way the plate is defined determining the thickness of the plates along with the process that governs it has proven challenging we use s to p sp receiver functions to image a strong persistent lab beneath iceland where the mid atlantic ridge interacts with a plume with hypothesized pulsating thermal anomaly the plate is thickest up to 84 6 km beneath lithosphere formed during times of hypothesized hotter plume temperatures and as thin as 61 6 km beneath regions formed during colder intervals we performed geodynamic modeling to show that these plate thicknesses are inconsistent with a thermal lithosphere instead periods of increased plume temperatures likely increased the melting depth causing deeper depletion and dehydration and creating a thicker plate this suggests plate thickness is dictated by the conditions of plate formation

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

lithospheric thickness estimation beneath northwestern south america from an s wave receiver function analysis we make use of the s to p receiver function technique beneath colombia and neighboring regions to make a first order approximation of the depth of the lithosphere asthenosphere boundary lab and therefore of lithospheric thickness a deconvolution technique was used to calculate the receiver functions and after a moveout correction and a time depth conversion lab depths for different tectonic regions of northwestern south america were obtained results are typically between 65 and 110 km consistent with previous estimates around the world and other regions in south america lithospheric thickness beneath an oceanic island in the caribbean is 80 km whereas for the ecuador colombia trench it is 65 km and around 100 km for the panama arc the transition to the continent is associated with an increase in lab depth where it can reach 110 km with no significant differences among terranes and or tectonic blocks

clouds associated with the madden julian oscillation a new perspective from cloudsat abstractthe evolution of total cloud cover and cloud types is composited across the madden julian oscillation mjo using cloudsat data for june 2006 may 2010 two approaches are used to define mjo phases 1 the local phase is determined at each longitude and time from filtered outgoing longwave radiation and 2 the global phase is defined using a popular real time multivariate mjo rmm index which assigns the tropics to an mjo phase each day in terms of local phase cloudsat results show a familiar evolution of cloud type predominance in the growing stages shallow clouds coexist with deep intense but narrow convective systems widespread cloud coverage and rainfall appear during the active phases becoming more anvil dominated with time and finally suppressed conditions return results are compared to the convectively coupled kelvin wave which has a similar life cycle to the mjo convection in the mjo tends to be modulated more by moisture variations compared to the kelvin wave in terms of globa

upper mantle stratification by p and s receiver functions summary seismic stratification of the upper mantle is investigated by applying two complementary techniques to the records of the graefenberg array in southern germany the anisotropic p receiver function technique kosarev et al 1984 vinnik montagner 1996 is modified by using summary seismic events instead of individual events and different weighting functions instead of the same function for the harmonic angular analysis of the sv and t components of the pds phases the summary events provide better separation of the second azimuthal harmonic than the individual events the parameters of the second harmonics of sv and t thus evaluated should be similar if they reflect the effects of azimuthal anisotropy this can be used as a criterion to identify the anisotropy to detect the sdp phases and their azimuthal variations caused by azimuthal anisotropy we have developed a stacking technique which can be termed the s receiver function technique it includes axis rotation to separate interfering p and s arrivals determination of the principal m component of the s wave motion deconvolution of the p components of many recordings by their respective m components and stacking of the deconvolved p components with weights depending on the level of noise and the angle between the m direction and the backazimuth of the event both techniques yield consistent results for the graefenberg array as indicated by the p receiver functions the upper layer of the mantle between the moho and 80 km depth is anisotropic with dvs vs around 0 03 and the fast direction close to 20 clockwise from north the fast direction of anisotropy below this layer is around 110 the boundary between the upper and the lower anisotropic layers is manifested by the detectable pds and sdp converted phases shear wave splitting in sks is strongly dominated by azimuthal anisotropy in the lower layer asthenosphere