an automated time window selection algorithm for seismic tomography we present flexwin an open source algorithm for the automated selection of time windows on pairs of observed and synthetic seismograms the algorithm was designed specifically to accommodate synthetic seismograms produced from 3 d wavefield simulations which capture complex phases that do not necessarily exist in 1 d simulations or traditional traveltime curves relying on signal processing tools and several user tuned parameters the algorithm is able to include these new phases and to maximize the number of measurements made on each seismic record while avoiding seismic noise our motivation is to use the algorithm for iterative tomographic inversions in which the synthetic seismograms change from one iteration to the next hence automation is needed to handle the volume of measurements and to allow for an increasing number of windows at each model iteration the algorithm is sufficiently flexible to be adapted to many tomographic applications and seismological scenarios including those based on synthetics generated from 1 d models we illustrate the algorithm using data sets from three distinct regions the entire globe the japan subduction zone and southern california

imaging alpine crust using ambient noise wave equation tomography we present an improved crustal vs model and moho depth map using ambient noise wave equation tomography the so called ambient noise wave equation tomography is a method to invert seismic ambient noise phase dispersion data based on elastic waveform simulation which accounts for 3 d and finite frequency effects we use cross correlations of up to four years of continuous vertical component ambient seismic noise recordings from 304 high quality broadband stations in the alpine region we use model lsp eucrust1 0 obtained from traditional ambient noise tomography as initial model and we iteratively improve the initial model by minimizing frequency dependent phase traveltime differences between the observed and synthetic waveforms of rayleigh waves in the period range 10 50 s we obtain the final model after 15 iterations with 65 total misfit reduction compared to the initial model at crustal depth the final model significantly enhances the amplitudes and adjusts the shapes of velocity anomalies at moho and upper mantle depth the final model corrects an obvious systematic velocity shift of the initial model the resulting iso velocity moho map confirms a moho step along the external side of the external crystalline massifs of the northwestern alps and reveals underplated gabbroic plutons in the lower most crust of the central and eastern alps ambient noise wave equation tomography turns out to be a useful tool to refine shear wave velocity models obtained by traditional ambient noise tomography based on ray theory

s wave velocity images of the crust in the southeast margin of tibet revealed by receiver functions the southeast margin of tibet is the region in clockwise rotation around the eastern himalayan syntaxis due to the india eurasia collision and the resistance of the stable sichuan basin and south china block however the dynamic processes involved in the evolution and deformation of the region remain poorly understood due to a lack of reliable geophysical observations we collected abundant seismic data recorded by 108 permanent broadband stations deployed in the se margin of tibet since 2000 and obtained 4536 pairs of p wave receiver functions prfs with high signal to noise ratio in this study we have implemented a novel two step data inversion procedure that can reduce the dependence of the inversion results on the initial model we first use low frequency prfs obtained by iterative deconvolution in the time domain and then an initial model consisting of a series of 2 km thick isotropic layers to fit velocity models and thus determine an overall statistical solution by means of the bootstrap resampling technique this statistical solution is then regarded as a new initial model to adjust high frequency prfs hence the same resampling process is executed again to estimate the optimal s wave velocity structure below each station the results provide an accurate 3d image of the crust and uppermost mantle in the se margin of tibet we infer a wide intra crustal low velocity zone that varies laterally and in depth which is thinner or even absent in the most southern part of yunnan our hypothesis is that this low velocity zone is the result of the accumulation of lower crustal flow coming from central tibet furthermore we show that this lower crustal flow extends largely through the sichuan yunnan diamond shaped block and that there are significant variations in both crustal velocity structure and deformation mechanism across the great strike slip faults of the jinshajiang red river and xiaojiang fault systems

the amazon river plume during amasseds spatial characteristics and salinity variability the amazon river discharge forms a plume of low salinity water that extends offshore and northwestward over the north brazilian shelf observations acquired as part of a multidisciplinary amazon shelf sediment study amasseds are used to characterize the spatial structure and temporal variability of the amazon plume four shipboard conductivity temperature depth ctd surveys spanning the shelf from 1 s to 5 n during rising march 1990 maximum may 1990 falling august 1989 and minimum november 1991 discharge show the amazon plume is typically 3 to 10 m thick and 80 to over 200 km wide northwest of the river mouth the plume is often characterized by a wedge of low salinity water adjacent to the coast and a separate tongue of low salinity water extending offshore over the middle to outer shelf a bottom front separating the low salinity plume water from oceanic water is consistently located between the 10 and 20 m isobaths a moored array deployed about 300 km northwest of the river mouth from february to june 1990 included inner and midshelf moorings in 18 and 65 m of water on which temperature conductivity measurements were made the moored observations reveal salinity variations within the amazon plume of over 10 psu on timescales of days to weeks this variability includes intermittent events in which plume water pools up in the vicinity of the river mouth and the plume width can exceed 200 km these accumulation events are apparently due to wind events with a southeastward component which impede or block the normally northwestward freshwater transport the resulting bulges in the plume are then released northwestward when the wind reverses volume budgets indicate the amazon plume entrains roughly twice the river discharge between the river mouth at the equator and 3 n estimates of gradient richardson numbers from the moorings suggest entrainment due to the strong semidiurnal tidal currents occurs where the plume intersects the bottom and over the outer portion of the plume where salinities approach oceanic values

extracting time domain green s function estimates from ambient seismic noise 1 it has been demonstrated experimentally and theoretically that an estimate of the green s function between two seismic stations can be obtained from the time derivative of the long time average cross correlation of ambient noise between these two stations this tdgf estimate from just the noise field includes all tensor components of the green s function and these green s function estimates can be used to infer earth structure we have computed cross correlations using 1 to 30 continuous days of ambient noise recorded by over 150 broadband seismic stations located in southern california the data processing yielded thousands of cross correlation pairs for receiver separations from 4 500 km which clearly exhibit coherent broadband propagating dispersive wavetrains across frequency band 0 1 2 hz

observations of currents and water properties in the amazon frontal zone measurements of currents and water properties were obtained at various locations in the frontal zone of the amazon river outflow plume during four cruises in 1989 1991 as part of a multidisciplinary amazon shelf sediment study a salinity front resembling a salt wedge is found approximately 150 km seaward of the river mouth it continues northwestward more than 400 km along the shelf between the 10 and 20 m isobaths tidal currents which are oriented principally in the cross shelf direction reach 200 cm s 1 during spring tides and drop to less than 80 cm s 1 during neaps in the vicinity of the river mouth the nontidal flow is strongly sheared with near surface speeds of up to 100 cm s 1 and weak near bottom velocities the direction of the near surface flow is generally northwestward except near the river mouth where river discharge leads to a significant offshore component of flow the strong velocity shears are stabilized by strong stratification by salinity and by highly concentrated suspended sediment or fluid mud near the seabed variations in stratification and frontal position are due principally to spring neap variations in tidal mixing and seasonal variations in runoff

barotropic tides on the north carolina shelf observations from 18 near bottom pressure sensors and 8 current meter moorings provide a characterization of the barotropic tides over the north carolina continental shelf between chesapeake bay and cape hatteras the largest tidal constituents in this region are the m2 sea level amplitude 47 cm n2 11 cm and s2 10 cm semidiurnal tides and the k1 p1 7 cm and o1 5 cm diurnal tides the barotropic tidal currents are small less than 3 cm s21 except for the m2 current which reaches 10 cm s21 at mid shelf cross shelf currents increase linearly from approximately zero near the coast to a maximum over the mid and outer shelf alongshelf currents are nonzero near the coast and increase to roughly twice the coastal value over the mid and outer shelf while bottom friction is weak over most of the shelf in water depths of less than 10 m bottom friction results in a rapid phase decrease toward the coast in the semidiurnal alongshelf velocities this phase difference is not observed in the k1 p1 alongshelf flow possibly because diurnal wind forcing causes an opposing phase increase toward the coast alongshelf variations in tidal amplitudes and phases near the coast are much larger than expected based on variations along the shelf break inferred from basin scale altimeter estimates the shelf width in this region increases from 25 to 100 km over an alongshelf distance of about 150 km results from an analytic flat bottom two dimensional model indicate that widening of the shelf toward the north causes the observed alongshelf increase in the semidiurnal amplitude and phase but does not explain alongshelf variations in the weaker diurnal constituents

crustal deformation of the eastern tibetan plateau revealed by magnetotelluric imaging the ongoing collision of the indian and asian continents has created the himalaya and tibetan plateau through a range of deformation processes these include crustal thickening detachment of the lower lithosphere from the plate delamination and flow in a weakened lower crust 1 6 debate continues as to which of these processes are most significant 7 in eastern tibet large scale motion of the surface occurs but the nature of deformation at depth remains unresolved a large scale crustal flow channel has been proposed as an explanation for regional uplift in eastern tibet 6 8 9 but existing geophysical data 10 11 do not constrain the pattern of flow magnetotellurics uses naturally occurring electromagnetic waves to image the earth s subsurface here we present magnetotelluric data that image two major zones or channels of high electrical conductivity at a depth of 20 40 km the channels extend horizontally more than 800 km from the tibetan plateau into southwest china the electrical properties of the channels imply an elevated fluid content consistent with a weak crust 12 13 that permits flow on a geological timescale these findings support the hypothesis that crustal flow can occur in orogenic belts and contribute to uplift of plateaux our results reveal the previously unknown complexities of these patterns of crustal flow many previous studies of the indiaasia

evidence for mechanically coupled lithosphere in central asia and resulting implications the recent dramatic increase in seismic anisotropy and surface global positioning system gps data for central asia permits a comprehensive examination of the mantle s role in mountain building a joint analysis of 178 shear wave splitting and 2000 gps observations using a new technique reveals that the crust and lithospheric mantle deform coherently arguing for crust mantle mechanical coupling during deformation the observed spatial variations in anisotropy refl ect the large scale pattern of lithospheric deformation as well as a change in deformational style from simple shear on the tibetan plateau transitioning to pure shear in surrounding regions

lagrangian flow observations of the amazon river discharge into the north atlantic nine satellite tracked drifters with near surface drogues were launched in or near the mouth of the amazon river on the north brazil shelf during 1989 1991 at four different stages of river discharge the drifters initially moved along shelf toward the northwest over the north brazil shelf with mean speeds varying from 41 to 128 cm s and a maximum along shelf velocity of 197 cm s many drifters experienced strong acceleration near 2 n between the 5 m and 20 m isobaths caused in part by the sharp reduction in cross shelf cross sectional area near the shore perpendicular cabo norte shoal the drifter trajectories showed strong cross shelf tidal variability in the flow field near the amazon river mouth and the largest low frequency along shelf variability was located over the open shelf just north of cabo norte good visual correlation between drifter along shelf velocity and along shelf wind stress supports the dynamical model of lentz this issue that subtidal fluctuations in near surface along shelf currents in the amazon river plume are strongly wind driven drifters left the north brazil shelf after about 5 to 30 days three drifters moved northwestward parallel to the northeast coast of south america crossed the shelf break near 8 n and moved into deeper north atlantic water where they began looping in anticyclonic eddies often called retroflection eddies or loopers with periods of approximately 11 days as they moved northwestward to the caribbean sea four drifters initially moved along shelf toward the northwest and then offshore between 3 n and 7 n where they followed the retroflection of the north brazil current only one drifter entered the zonal current system that characterizes the equatorial atlantic circulation

structure of the crust beneath the southeastern tibetan plateau from teleseismic receiver functions abstract southeastern tibet marks the site of presumed clockwise rotation of the crust due to the india eurasian collision and abutment against the stable sichuan basin and south china block knowing the structure of the crust is a key to better understanding of crustal deformation and seismicity in this region here we analyze recordings of teleseismic earthquakes from 25 temporary broadband seismic stations and one permanent station using the receiver function method we find that the crustal thickness decreases gradually from the tibetan plateau proper to the sichuan basin and yangtze platform but that significant intra crustal heterogeneity exists on shorter lateral scales 0 30 are detected beneath the southeastern margin of tibet but in the sichuan basin and southeastern yangtze platform the values are close to the global average combined with high regional heat flow and independent evidence for mid crustal layers of high electric conductivity the large intra crustal s wave velocity reduction 12 19 and the intermediate to high average crustal poisson s ratios are consistent with partial melt in the crust beneath parts of southeastern tibet these results could be used in support of deformation models involving intra crustal flow with the caveat that significant lateral variation in location and strength of this flow may occur

adjoint tomography of the southern california crust using an inversion strategy based on adjoint methods we developed a three dimensional seismological model of the southern california crust the resulting model involved 16 tomographic iterations which required 6800 wavefield simulations and a total of 0 8 million central processing unit hours the new crustal model reveals strong heterogeneity including local changes of 30 with respect to the initial three dimensional model provided by the southern california earthquake center the model illuminates shallow features such as sedimentary basins and compositional contrasts across faults it also reveals crustal features at depth that aid in the tectonic reconstruction of southern california such as subduction captured oceanic crustal fragments the new model enables more realistic and accurate assessments of seismic hazard

lithospheric structure of the southeastern margin of the tibetan plateau from rayleigh wave tomography lithospheric shear wave velocity beneath the southeastern margin of the tibetan plateau is obtained from rayleigh wave tomography using earthquake data recorded by the temporary chinarray and permanent china digital seismic array fundamental mode rayleigh wave phase velocities at periods of 20 100 s are determined and used to construct the 3 d shear wave velocity model low velocity anomalies appear along or close to the major faults in the middle crust and become a broad zone in the lower crust suggesting block extrusion in the shallow crust and diffuse deformation in the lower crust both of which play important roles in accommodating the collision between the indian and eurasian plates a vertical low velocity column beneath the tengchong volcano is observed which could be caused by upwelling of warm mantle due to the lithosphere extension in the thailand rift basin to the south or by fluid induced partial melting due to the subduction of the burma slab the western yangtze craton is characterized by low velocity in the crust and uppermost mantle above the fast mantle lithosphere indicating possible thermal erosion at the western craton edge resulted from the extrusion of the tibetan plateau a low velocity zone is imaged at the depths of 70 150 km beneath the eastern part of the yangtze craton which could be caused by small scale mantle convection associated with the subduction of the burma microplate and or the opening of the south china sea

two crustal low velocity channels beneath se tibet revealed by joint inversion of rayleigh wave dispersion and receiver functions abstract competing geodynamic models such as rigid block extrusion continuous deformation and the mid lower crustal flow have been proposed to describe the growth and expansion of eastern tibet however the dynamic processes responsible for plateau evolution and deformation remain poorly understood partly due to resolution limitations of previous models of lithospheric structure on the basis of joint inversion of rayleigh wave dispersion and receiver functions using data from a newly deployed seismic array we have obtained a high resolution 3d image that reveals the distribution of low velocity zones lvzs with unprecedented clarity the prominent feature of our model is two low velocity channels that bound major strike slip faults in se tibet and wrap around the eastern himalaya syntaxis consistent with the clockwise movement of crustal material in this region most large earthquakes in this region occurred in the boundaries of the lvzs we propose that ductile flow within these channels in addition to shear motion along strike slip faults played a significant role in accommodating intensive lithospheric deformation during the eastward expansion of tibet in the cenozoic

tidal computations for morecambe bay summary a numerical finite difference technique for computing tides in areas of shoaling water has been established and used to calculate the m2 tide in morecambe bay an essential feature of the method is the representation of drying banks which appear as the water level falls on the ebb and which are re submerged on the flood as the level rises again since the non linear advective acceleration should be important in shallow water schemes for incorporating these terms are examined and the influence of advection on the tide assessed in a series of tests the open sea tides applied to the outer boundary of the numerical bay model were taken first from existing tidal charts then from calculations with a larger scale encompassing model and finally from observations of current in each case the computed tidal elevations within the bay turned out to be in satisfactory agreement with those obtained from observations however it is significant that in the first case inaccuracy of the input tidal distribution deduced from charts gives rise to erroneous currents near the boundary

two crustal flowing channels and volcanic magma migration underneath the se margin of the tibetan plateau as revealed by surface wave tomography abstract the se margin of the tibetan plateau is an important area to develop a better understanding of the plateau uplift and the indian eurasian continental collision dynamics previous studies have reported widespread low velocity anomalies beneath this region particularly in the tengchong volcanic field tcvf however the spatial distribution and dynamic processes of these low velocity anomalies are not well constrained in this study a 3 d s wave velocity structure model of the crust and upper mantle 10 120 km in the region is constructed by the inversion of surface wave dispersion data a two step inversion procedure is adopted to generate the s wave velocity structure images the measured phase velocities and inverted s wave velocities jointly show a large scale low velocity anomaly distributed in the crust consistent with the view that the region is the passageway of the eastward migration of tibetan plateau material two crustal flowing channels are clearly observed at depths of 20 km and 30 km which connect and rotate clockwise around the eastern himalaya syntaxis beneath the tcvf there are two prominent low velocity anomaly zones at depths of 15 25 km and 50 80 km which indicate the existence of magma chambers one of the crustal flowing channels is connected with the magma chamber of the tcvf and the other has a short branch north of kunming toward the mile shizong fault at a depth of 20 km based on the distribution of the s wave velocities under the tcvf a dynamic model of the tengchong volcano magma system is proposed to explain the migration patterns of the volcanic material

modelling tidal energetics of the columbia river estuary abstract the columbia river estuary is shallow and has a mixed diurnal and semidiurnal tide strong riverflow broad tidal flats and variable channel cross section it is weakly non linear with respect to tidal forcing as measured by a ratio of tidal amplitude to depth these features common to many shallow estuaries were incorporated into a one dimensional harmonic transport model the harmonic method utilizes the fact that nearly all of the energy in the system is in a few fundamental tidal frequencies the first overtides thereof and the mean flow this allows the representation of the flow as a series of harmonic components whose spatial variability is determined by the model the model provides a qualitative explantation for and accurate quantitative predictions of along channel variations in tidal properties in terms of the momentum balance near the mouth of the estuary the boundary shear stress the pressure gradient and the acceleration terms are all important in the force balance and the tide behaves like a damped oscillator far upriver the pressure gradient is primarily balanced by friction at the bed and tidal wave propagation can be described as a diffusion process changes in the channel width in mid estuary cause partial reflection of the tidal wave and a maximum in tidal range this partial reflection decreases the tidal energy flux in the upstream direction the distribution of the time averaged energy fluxes was also determined from the model the analysis shows that there are two regions of high energy dissipation energy is supplied near the mouth of the estuary by the divergence of the landward flux of tidal potential energy and far upriver by the divergence of the seaward flux of fluvial potential energy these two regions of high dissipation are separated by a region of low dissipation the energy flux divergence minimum this spatial division of the estuary is mirrored in the system biology and geology it is likely that the energy flux divergence minimum is a common feature of shallow estuaries with strong riverflow

low wave speed zones in the crust beneath se tibet revealed by ambient noise adjoint tomography we present a refined 3d crustal model beneath se tibet from ambient noise adjoint tomography different from ray theory based tomography adjoint tomography in this study incorporates a spectral element method sem and takes empirical green s functions egfs of rayleigh waves from ambient noise interferometry as the direct observation the frequency dependent traveltime misfits between sem synthetic green s functions and egfs are minimized with a preconditioned conjugate gradient method meanwhile the 3d model gets improved iteratively utilizing 3d finite frequency kernels the new model shows 3 6 shear wave speed increasing beneath the western sichuan basin scb depth 15 km and the central chuan dian block cdb and 6 12 shear wave speed reduction in the mid lower crust beneath the northern and the southern cdb the inferred spatial pattern of low wave speed zones consistent with possible partial melt suggests more complex and disconnected geometry than the pervasive narrow zone from the channel flow models

radial anisotropy in the crust of se tibet and sw china from ambient noise interferometry 1 we use rayleigh and love wave green s functions estimated from ambient seismic noise to study crustal structure and radial anisotropy in the tectonically complex and seismically active region west of the sichuan basin and around the eastern himalaya syntaxis in agreement with previous studies low velocity zones are ubiquitous in the mid lower crust with substantial variations both laterally and vertically discrepancies between 3 ds hear velocity from either rayleigh vsv o r love vsh waves are examined both in view of non uniqueness of tomographic solutions and radial anisotropy low shear wave speed and radial anisotropy with vsh vsv are most prominent in mid lower crust in area northwest to the lijiang muli fault and around the red river and xiaojiang faults this anisotropy could be caused by sub horizontal mica fabric and its association with low velocity zones suggests mica alignment due to flow in deep crustal zones of relatively low mechanical strength citation huang h h yao andr d vanderhilst 2010 radialanisotropyinthecrust of se tibet and sw china from ambient noise interferometry geophys res lett 37 l21310 doi 10 1029 2010gl044981

partial melt in the upper middle crust of the northwest himalaya revealed by rayleigh wave dispersion article i nfo seismic shear wave velocities are sensitive to the partial melts that should be present in the himalayan orogen if low viscosity channel flow is active at the present day we analyzed regional earthquakes in the western himalaya and tibet recorded on 16 broadband seismometers deployed across the nw indian himalaya from the indian platform to the karakoram range we used a multiple filter technique to calculate the group velocity dispersion of fundamental mode rayleigh waves and then inverted the dispersion records to obtain separate one dimensional shear wave velocity models for five geologic provinces the tibetan plateau ladakh arc complex indus tsangpo suture zone tethyan himalaya and himalayan thrust belt our velocity models show a low velocity layer lvl with 7 17 velocity reduction centered at 30 km depth and apparently continuous from the tethyan himalaya to the tibetan plateau this lvl shows good spatial correspondence with observations of low resistivity from magnetotelluric studies along the same profile of the possible explanations for low velocity and low resistivity in the mid crust only the presence of melts or aqueous fluids or both satisfactorily explains both sets of observations elevated heat flow observed in the nw himalaya implies that if aqueous fluids are present in the mid crust then the mid crust is well above its solidus comparison of our results with laboratory measurements and theoretical models suggests 3 7 melt is present in a channel in the upper middle crust of the nw himalaya at the present day and the physical conditions to enable active channel flow may be present

simulations of ground motion in the los angeles basin based upon the spectral element method we use the spectral element method to simulate ground motion generated by two recent and well recorded small earthquakes in the los angeles basin simulations are performed using a new sedimentary basin model that is constrained by hundreds of petroleum industry well logs and more than 20 000 km of seismic reflection profiles the numerical simulations account for 3d variations of seismic wave speeds and density topography and bathymetry and attenuation simulations for the 9 september 2001 m w 4 2 hollywood earthquake and the 3 september 2002 m w 4 2 yorba linda earthquake demonstrate that the combination of a detailed sedimentary basin model and an accurate numerical technique facilitates the simulation of ground motion at periods of 2 sec and longer inside the basin model and 6 sec and longer in the regional model peak ground displacement velocity and acceleration maps illustrate that significant amplification occurs in the basin

bulk properties of intertidal sediments in a muddy macrotidal estuary abstract measurements are presented of the bulk and mineralogical properties of intertidal sediments along the axis of the tamar estuary southwest england bulk and dry density data indicate a significant increase in consolidation of the surface layer of the intertidal mudflats progressing down estuary from the turbidity maximum region to the mouth there are very significant trends of both density and estimated critical eroison shear stress with distance cross sectionally averaged bed shear stresses due to tidal currents are computed using a hydrodynamical model these tidal stresses generally increase along the axis of the estuary from mouth to head and reach a maximum in the upper reaches the increasing consolidation towards the mouth appears to result from the small bed shear stresses due to tidal currents in the lower reaches and the increasing proportion of coarse material there bed shear stresses are large in the upper reaches and regular intratidal resuspension and transport occur during spring tides with little time available for consolidation following deposition during slack water periods the silt and clay fraction of the intertidal sediments increases from the mouth to the turbidity maximum region near the head 60 to 99 dry weight the particulate organic carbon poc content assuming this to be approximated by loss on ignition similarly increases from about 2 of dry weight near the mouth to about 8 in the turbidity maximum region the poc content of a sample is largely dependent on the proportion of fine sediment within the sample regardless of its position the lower estuary is associated with intertidal sediments having relatively low silt and clay content and low associated organic material it appears to be a fairly stable zone between the marine and estuarine environments the upper estuary in the turbidity maximum region appears to be almost homogeneous in both poc 8 1 0 6 and silt content 95 5 during summer the central region is an area of great variability in the size fraction sediment type and poc content

separation of tidal and subtidal currents in ship mounted acoustic doppler current profiler observations a simple method is developed to analyze current measurements obtained from a moving platform the need for this is motivated by the now common use of the ship mounted acoustic doppler current profiler adcp to acquire absolute velocity data during an oceanographic survey of a given region the full potential of this new measurement technique is severely hindered when the presence of high frequency phenomena e g tidal or inertial motions prevents a clear visualization of the lower frequency current structure of interest our analysis method is based on a spatial interpolation scheme using arbitrary functions that allows for the tidal current time variability which then permits the tide induced motions to be subtracted from the adcp data to yield the subtidal current field the method also allows nearby moored and drifter current measurements if available to be combined with the shipboard adcp observations in a single analysis to obtain the best description of the tidal and subtidal currents to illustrate this method we present results from the analysis of adcp data taken during oceanographic surveys in two different continental shelf regions the east china sea and the amazon shelf a 5 day conductivity temperature depth ctd and adcp survey was made in the east china sea near the mouth of the yellow sea during january 1986 there the currents were essentially barotropic and dominated by the semidiurnal tide the adcp derived cotidal chart for the m2 12 42 hours component agrees well with existing charts derived empirically from sea level observations or from regional numerical models the adcp derived steady flow is also consistent with the observed density field and indicates little flow in or out of the yellow sea and a transport of about 1 sv toward the tsushima strait two ctd adcp surveys lasting 21 and 23 days were conducted over the amazon shelf during march and may 1990 simultaneously moored current observations were also obtained at three locations along a cross shelf array 200 km north of the amazon river mouth for a common period of at least 2 months february 12 to april 13 over the shelf tidal and subtidal currents were comparable in magnitude our analysis indicates that the tidal currents were essentially barotropic semidiurnal and polarized in the cross shelf direction increasing in magnitude toward the inner shelf where current values of more than 2 m s are common the adcp derived steady currents were aligned in the along shelf direction and strongly influenced by the north brazil current nbc during both adcp surveys the northwestward flowing nbc was transporting more than 2 sv over the shelf at depths shallower than 100 m

holocene palaeoenvironmental history of the amazonian mangrove belt abstract wetland dynamic in the northern brazilian amazon region during the holocene was reviewed using palynological carbon and nitrogen isotopes records and c n ratio previously published the integration of 72 radiocarbon dates recorded in 34 sediment cores sampled along the marine and fluvial littoral and mainly influenced by the amazon river reveals that marine influence and mangrove vegetation were wider than today on the mouth of amazon river between 8990 8690 and 2300 2230 cal yr bp forming a continuous mangrove belt along the northern brazilian amazon littoral the establishment of this mangrove strip is a direct consequence of the marine incursion caused by post glacial sea level rise possibly associated with tectonic subsidence during the early and middle holocene in the late holocene in areas influenced by the amazon river discharge the mangroves were replaced by freshwater vegetation and the coast morphology evolved from an estuarine dominated into a rectilinear coast due to coastal progradation nevertheless the marine influenced littoral which is currently dominated by mangroves and salt marsh vegetation has persistently had brackish water vegetation over tidal mud flats throughout the entire holocene likely the fragmentation of this continuous mangrove line during the late holocene was caused by the increase of river freshwater discharge associated to the change from dry into wet climates in the late holocene this caused a significant decrease of tidal water salinity in areas near the mouth of amazon river these changes in the amazon discharge are probably associated with dry and wet periods in the northern amazon region during the holocene

surface wave array tomography in se tibet from ambient seismic noise and two station analysis i phase velocity maps summary empirical green s functions egfs between pairs of seismographs can be estimated from the time derivative of the long time cross correlation of ambient seismic noise these egfs reveal velocity dispersion at relatively short periods which can be used to resolve structures in the crust and uppermost mantle better than with traditional surface wave tomography we combine rayleigh wave dispersion estimates from egfs and from traditional two station ts analysis into a new approach to surface wave array tomography with data from dense receiver arrays we illustrate the methodology with continuous broad band recordings from a temporary seismographic network on the southeastern part of the tibetan plateau in sichuan and yunnan provinces sw china the egfs are robust under temporal changes in regional seismicity and the use of either ambient noise approximated by records without signal from events with magnitude mb 5 or 4 or surface wave coda produces similar results the egfs do not strongly depend on the presence of large earthquakes but they are not reciprocal for stations aligned in the n s direction this directionality reflects the paucity of seismicity to the north of the array using a far field representation of the surface wave green s function and an image transformation technique we infer from the egfs the rayleigh wave phase velocity dispersion in the period band from 10 30 s a classical ts approach is used to determine rayleigh wave phase velocity dispersion between 20 120 s together they constrain phase velocity variations for t 10 120 s which can be used to study the structure from the crust to the upper mantle beneath se tibet short and intermediate period 10 80 s phase velocities are prominently low suggesting that the crust and upper mantle beneath se tibet is characterized by slow shear wave propagation

tidal and subtidal flow patterns on a tropical continental shelf semi insulated by coral reefs 1 the present study sets out to describe the tidal and subtidal water motion at the berau coastal shelf which represents a tropical continental shelf area of variable width hosting a complex of barrier reefs along its oceanic edge moored and shipboard measurements on currents and turbulence were made as part of the multidisciplinary east kalimantan research program these results and collected data on sea levels meteorology and bathymetry were used to setup and calibrate a three dimensional barotropic hydrodynamic model in the ecomsed environment which is derived from the princeton ocean model concurrent profile measurements of flow velocity and reynolds stress with an acoustic doppler current profiler were used to infer values of the drag coefficient on locations on the shelf and within the barrier reef environment the drag coefficients determined from shelf measurements differed less than 20 from optimal model settings diurnal and semidiurnal tides have the same character propagating across the isobaths with amplitudes that increase toward the coast the tidal amplification is captured in a one dimensional model revealing an analogy with the amazon shelf regarding the subtidal depth mean flow tidal eulerian residual currents dominate over monsoon driven currents lagrangian mean flows reveal freshwater pathways from the coast to the coral reef environment at a regional scale the reef complex is established to be semitransparent to tides the barrier reef influences the tidal phases rather than the amplitudes especially in the shelf region that is fringed by the reefs this may explain why tidal phases predicted from hydrodynamic models of tropical continental shelves often feature substantial discrepancies from observations

morphodynamics of a high discharge tropical delta san juan river pacific coast of colombia abstract the san juan river has one of the most extensive and best developed deltas on the pacific coast of south america measuring 800 km 2 the river drainage basin measures 16 465 km 2 and is located in one of the areas with the highest precipitation in the western hemisphere the annual rainfall varies from 7000 to 11 000 mm and as a result the san juan river has the highest water discharge 2550 m 3 s 1 sediment load 16 10 6 t yr 1 and basin wide sediment yield 1150 t km 2 yr 1 on the west coast of south america the san juan delta growth began approximately 5000 years bp the structure of the delta is determined by the interactions between fluvial deposition and the effect of 1 7 m significant swells mostly from the sw and strong tidal currents analysis of delta progradation indicates that during 1848 1992 the morphology of the delta was characterized by beach ridge accretion spit growth narrowing of inlets and a general advance of the delta shoreline during the past decade processes such as rapid erosion of the delta shore narrowing of barrier islands and breaching of a new inlet are the result of a long term relative sea level rise of 2 6 mm yr 1 due to tectonically induced subsidence coupled with a eustatic rise of sea level the delta also experiences strong oceanographic manifestations associated with the el nino la nina cycle causing regional sea level elevation of 20 30 cm during el nino years recent coastal subsidence in the delta is evidenced by 1 increased occurrence of non storm washover events 2 increased erosion of barrier islands with average loss of 11 m yr 1 during 1993 1997 and 3 a relative sea level rise of 3 4 mm yr 1 during 1991 1999 the morphology and recent evolution of the san juan delta are unique when compared to other deltas of south america because of the singular combination of extreme climatic geologic and oceanographic conditions under which the delta has formed and the absence of human induced impact in the drainage basin

lowermost amazon river morphology and shallow seismic characteristics abstract the riverbed morphology of the lowermost amazon river was characterized by high resolution acoustic profiling in 21 areas this technique has been used for the first time in this area and allowed the discovery of a variety of reflectors which delineate areas either of sediment transport or of deposition on an older river bottom records obtained with the pinger system made it possible to distinguish three main kinds of reflectors both surface and sub bottom 1 flat 2 wavy and 3 irregular reflection patterns which can be interpreted as strata deposited in a variable mostly high energy setting or reworked structures of initially flat or wavy strata that have been changed mapping of these different reflectors shows that they are not randomly distributed the constant association of a given reflector with a particular morphological setting is indicative of its lithological significance supported by riverbed sampling and erosional depositional processes depositional areas are characterized by transparent units consisting of soft silt overlying a highly reflective sub bottom related to old substrates alter do chao or barreiras formation this may result from inundation and incision caused by quaternary sea level changes previously eroded areas are covered by a wavy layer consisting of very fine to fine sand unit fs which can change locally to medium coarse sand unit ms reflectors are more abundant downstream a minimum of 3 units were indicated by seismic records and could be related to sea level fluctuations and changes in the river discharge moreover the detection of fault scarps interpreted to result from neotectonic activity shows that neotectonic features can be important locally and should not be ignored as a possible reason for modern river instability the dynamic setting of the lowermost amazon area results in patterns of deposition and erosion probably controlled by complex interactions of fluvial and oceanic processes the effect of the gurupa arch may result in a zone of sediment bypass in the central part and a zone of increased deposition in the distal downstream part

relative sea level and climatic changes in the amazon littoral during the last 500 years abstract an integrated approach focused on sedimentology geochemistry palynology c and n isotopes and radiocarbon dating of a sediment core from an herbaceous plain not flooded by tides of the amapa littoral near the amazon river mouth allowed identification of two phases with marine and terrestrial influences mangroves occurred over tidal mud flats with marine influence between 5610 5470 and 470 310 cal yr bp the absence of mangrove vegetation since 470 310 cal yr was followed by the transition of brackish water organic matter to terrestrial c3 plants also the geochemical data indicate a decrease in sea water influence during this last time interval likely the displacement of mangrove forest to lower surfaces was caused by a relative sea level fall that may be associated with drier conditions with less rainfall during the second part of the last millennium as suggested by this work slight relative sea level fluctuations caused by regional or global climatic change may affect significantly the current mangrove area

kinematics and dynamics of the southeastern margin of the tibetan plateau summary on the southeastern margin of the tibetan plateau lies a large region which seismicity and gps data show to be actively deforming this paper describes the active faulting in the region and how it relates to the velocity field observed with gps in places the velocity field is accommodated by rotations about vertical axes and most or all of the strain at the surface in the region appears to be released seismically gps velocities are then compared to velocities calculated using a model for deformation driven by gravitational driving forces using rheologies estimated from experimentally derived mineral flow laws the model provides velocities that are in good agreement with observed gps velocities it is not possible to uniquely determine the rheology or flow velocity at depth and there are two forms of model solution which match the observed horizontal surface velocities in one of these vertical planes deform by pure shear and in the other vertical gradients of horizontal velocity are present within the crust two distinct regions of normal faulting earthquakes are present in the region and have mechanisms which are most easily explained by gravity driven deformation

origin of amazon mudbanks along the northeastern coast of south america abstract seismic profiles sediment cores and water column measurements were collected along the northeastern coast of brazil to examine the origin of mudbanks in the amazon coastal mud belt these 10 60 km long shore attached features previously had been observed to migrate along the 1200 km coast of the guianas in response to wave forcing chirp 3 5 khz seismic profiles of the shoreface and inner shelf located two mudbanks updrift of the previous eastern limit in french guiana 210 pb geochronology shows that these two banks are migrating to the northwest over a relict mud surface in 5 20 m water depth the mudbanks are 3 4 m thick and are translating over a modern shoreface mud wedge deposited by previous mudbank passage in

an introduction to the geological significance of sediment transport and accumulation on the amazon continental shelf in order to understand the formative processes and resulting stratigraphy on the amazon shelf and adjacent shoreline of amapa geological investigations were undertaken as part of a multidisciplinary amazon shelf sediment study amasseds the design of the study provided results of a multifaceted nature integrated with observations in other disciplines focused on sedimentary processes representative of fluctuating conditions on several time scales and broadly distributed on the shelf including regions not investigated in the past on short time scales most muddy sediment is transported northwest of the river mouth from there it moves seaward as fluid mud to cause rapid accumulation of foreset beds and moves northwestward to prograde the northernmost amapa shoreline and to supply sediment to the guianas fluid muds cover the shelf as far northward as 3 5 n and allow strong tides to propagate to shore where tidal currents cause most of the amapa shoreline to undergo erosion today averaged over decades and centuries about half of the amazon sediment discharge accumulates on the adjacent shelf and another significant fraction one sixth leads to accretion of the northernmost amapa shoreline and northwestward bypassing of sediment the remaining sediment is hypothesized to be trapped in deltaplain deposits of the lower amazon river system the foreset region and shoreline represent the two common loci of sediment accumulation that alternate their predominance on time scales of millennia and lead to a two stage progradation of coastal plain and subaqueous deltaic deposits this muddy regressive sedimentation during high sea level is replaced by formation of erosional sand layers during low sea level and transgressive conditions future research in the study area should address important considerations that were delineated by the present study including mechanisms of shoreline accretion the holocene history recorded in topset and coastal plain strata the role in local sedimentation played by the large shoal extending from cabo norte and the entrapment of amazon sediment by the delta plain

surface water dynamics in the amazon basin application of satellite radar altimetry 1 satellite radar altimetry has the ability to monitor variations in surface water height stage for large wetlands rivers and associated floodplains a clear advantage is the provision of data where traditional gauges are absent as part of an international program a complete altimetric analysis of the amazon basin is being undertaken here an updated and more rigorous evaluation of the topex poseidon t p data set is presented for the first 7 5 years of the mission with an initial study group of 230 targets height variability at many ungauged locations can be observed for 30 50 the range reflecting the clarity of the variations in lieu of instrument limitations an assessment of the instrument performance confirms that the minimum river width attainable is 1 km in the presence of some inundated floodplain this constraint does allow observation of the main stem solimoes amazon and the larger tributaries but rugged terrain in the vicinity of the target additionally places severe limitations on data retrieval first order validation exercises with the deduced 1992 1999 time series of stage fluctuations reveal accuracies ranging from tens of centimeters to several meters mean 1 1 m rms altimetric water levels in the solimoes and amazon are particularly well defined with amplitudes 13 m and variations in peak level timing from may to july the water surface gradient of the main stem is found to vary both spatially and temporally with values ranging from 1 5 cm km downstream to 4 0 cm km for more upstream reaches in agreement with ground based estimates the seasonal variability of the gradients reveals that the hysteresis characteristic of the flood wave varies along the main stem and the derived altimetric velocity of this flood wave is estimated to be 0 35 m s overall the altimetric results demonstrate that the t p mission is successfully monitoring the transient flood waves of this continental scale river basin

measurements in the bottom boundary layer on the amazon subaqueous delta abstract an instrumented bottom tripod geoprobe recorded flow and suspended sediment data in the bottom boundary layer above the lower foresets of the amazon subaqueous delta in 65 m mean water depth in february 1990 after about two weeks of operation the apparent seafloor at the tripod site rapidly elevated over a 14 hour period by about 44 cm this sudden change which was detected by an acoustic altimeter and which caused the loss of signals from the lowermost geoprobe current and optical sensors is thought to have been caused by the incursion of a dense bottom layer of fluid mud that migrated downslope from shallower sections of the foresets the fluid mud migration across the outer part of the foresets if a repetitive and occasional process in this region could be a major mechanism for episodic seaward growth of the delta current velocity profiles are used to estimate shear velocities u and roughness lengths zo during the first two weeks of measurements the extremely energetic semi diurnal tidal motion required correction of the estimates of u and zo for acceleration average values of u and zo for the two week period were 1 7 cm s and 0 3 cm respectively the effects of strong stratification due to flocculated near bottom suspended sediment on the estimates of u are significant for the lower values of u u

distribution of fluid muds on the amazon continental shelf abstract a comprehensive study of suspended sediment transport on the amazon shelf was conducted as part of the amasseds project a multidisciplinary amazon shelf sediment study to understand the link between physical processes and the fate of amazon river sediment a small instrumented tripod was used to measure the fluid flow and suspended sediment characteristics throughout the water column on varying time scales e g semidiurnal fortnightly seasonal dense nearbed suspensions or fluid muds suspended sediment concentration 10 g l on the order of a few meters in thickness were found on the inner and middle shelf covering an area ranging from 5 700 km2 during falling and low river discharge to 10 000 km2 during rising and high discharge fluid muds generally observed in the region of bottom salinity fronts extend across the topset beds to the foreset beds during rising and high discharge salinity and temperature anomalies frequently observed in fluid muds imply that often the muds do not result from erosion and resuspension from the seabed but from trapping processes at the bottom salinity front and transport across the shelf the vertical structure of fluid mud varies in space and tune variability close to the river mouth is predominantly fortnightly related to the location and structure of the bottom salinity front on the open shelf the variability appears to be related to seasonal differences in river and sediment discharge and the location of the bottom salinity front the total suspended sediment inventory on the shelf during the season of high discharge is approximately equal to the annual sediment discharge from the river 1 2 109 tons yr and 90 of that inventory is within fluid mud suspended sediment transport on the shelf is dominated by fluid mud

tide induced mixing in the amazon frontal zone the freshwater discharge from the amazon river produces a bottom salinity front on the amazon shelf that extends many hundreds of kilometers along the shelf between the 10 and 20 m isobaths strong cross shelf tidal currents cause advective excursions of the front of more than 20 km and supply the major source of kinetic energy for mixing on the shelf this mixing is manifested in spring neap variations in the frontal structure and position with weaker stratification and seaward migration of the front during periods of strong tidal currents and stronger stratification and landward migration during neap tides mixing appears to be driven by shear instability based on local estimates of gradient richardson number and bulk estimates of the water column stability maximum mixing occurs during ebb when vertical shear is greatest suspended sediment reaches such high concentrations in the frontal zone that it makes a significant contribution to the stratification thus increasing the stability of the flow and reducing the effectiveness of tide induced mixing

origin transport and deposition of leaf wax biomarkers in the amazon basin and the adjacent atlantic paleoenvironmental studies based on terrigenous biomarker proxies from sediment cores collected close to the mouth of large river systems rely on a proper understanding of the processes controlling origin transport and deposition of biomarkers here we contribute to the understanding of these processes by analyzing long chain n alkanes from the amazon river system we use the dd composition of long chain n alkanes from river bed sediments from the amazon river and its major tributaries as well as marine core top samples collected off northeastern south america as tracers for different source areas the d13c composition of the same compounds is used to differentiate between long chain n alkanes from modern forest vegetation and petrogenic organic matter our d13c results show depleted d13c values 33 to 36 in most samples indicating a modern forest source for most of the samples enriched values 31 to 33 are only found in a few samples poor in organic carbon indicating minor contributions from a fossil petrogenic source long chain n alkane dd analyses show more depleted values for the western tributaries the madeira and solimoes rivers 152 to 168 while n alkanes from the lowland tributaries the negro xingu and tocantins rivers 142 to 154 yield more enriched values the n alkane dd values thus reflect the mean annual isotopic composition of precipitation which is most deuterium depleted in the western amazon basin and more enriched in the eastern sector of the basin samples from the amazon estuary show a mixed long chain n alkane dd signal from both eastern lowland and western tributaries marine core top samples underlying the amazon freshwater plume yield dd values similar to those from the amazon estuary while core top samples from outside the plume showed more enriched values although the variability in the river bed data precludes quantitative assessment of relative contributions our results indicate that long chain n alkanes from the amazon estuary and plume represent an integrated signal of different regions of the onshore basin our results also imply that n alkanes are not extensively remineralized during transport and that the signal at the amazon estuary and plume includes refractory compounds derived from the western sector of the basin these findings will aid in the interpretation of plant wax based records of marine sediment cores collected from the adjacent ocean

stratigraphic evidence of changes in amazon shelf sedimentation during the late holocene abstract late holocene sedimentation on the amazon shelf was investigated using a combination of seismic sedimentological and geochronological methods piston cores collected in the subaqueous delta region during a multidisciplinary amazon shelf sediment study amasseds penetrated a regionally traceable 1 25 10 4 km 2 seismic discontinuity which corresponds to a dense relict mud reflector overlain by acoustically transparent sediment distinct offsets in profiles of wet bulk density p wave velocity and 210 pb activity are noted in cores at the reflector horizon unconformity signifying a past change in sedimentation conditions on the shelf bulk sediment 14 c dating indicates net depositional conditions for the subaqueous delta from 1800 yr b p to 700 yr b p and a net erosional phase from about 700 yr b p to 100 yr ago sedimentological evidence of the erosional phase includes lag deposits and burrows present at the unconformity surface in piston cores the deposits above and below the unconformity are similar with respect to grain size parameters and sedimentary structures suggesting that environmental conditions during the two depositional periods were similar according to 14 c dates of coastal deposits the shoreline of amapa state brazil served as a major depocenter of amazon mud during the erosional phase on the shelf 210 pb geochronology indicates that the most recent phase of sediment accumulation in the study area commenced about 100 yr ago resulting in rapid progradation of topset deposits and burial of relict strata in the present environment oceanographic and meteorologic processes cause along shelf variations in sediment dispersal and depositional patterns and about 1400 km 2 of the erosional relict deposits are still exposed at the seabed the short time scales over which amazon shelf strata respond to changes in the physical environment preclude the influence of relative sea level cyclicity on recent sedimentation patterns during the late holocene sedimentation and strata formation on the amazon shelf are linked to fluvial oceanographic and meteorologic processes that affect sediment supply deposition and erosion

surface wave array tomography in se tibet from ambient seismic noise and two station analysis ii crustal and upper mantle structure summary we determine the 3 d shear wave speed variations in the crust and upper mantle in the southeastern borderland of the tibetan plateau sw china with data from 25 temporary broad band stations and one permanent station interstation rayleigh wave phase velocity dispersion curves were obtained at periods from 10 to 50 s from empirical green s function egf derived from ambient noise interferometry and from 20 to 150 s from traditional two station ts analysis here we use these measurements to construct phase velocity maps from 10 to 150 s using the average interstation dispersion from the egf and ts methods between 20 and 50 s and estimate from them with the neighbourhood algorithm the 3 d wave speed variations and their uncertainty the crust structure parametrized in three layers can be well resolved with a horizontal resolution about of 100 km or less because of the possible effect of mechanically weak layers on regional deformation of particular interest is the existence and geometry of low shear velocity layers lvls in some regions prominent lvls occur in the middle crust in others they may appear in the lower crust in some cases the lateral transition of shear wave speed coincides with major fault zones the spatial variation in strength and depth of crustal lvls suggests that the 3 d geometry of weak layers is complex and that unhindered crustal flow over large regions may not occur consideration of such complexity may be the key to a better understanding of relative block motion and patterns of seismicity

the m2 tide on the amazon shelf as part of a multidisciplinary amazon shelf sediment study amasseds moored and shipboard current measurements made over the amazon shelf during 1990 1991 have been analyzed to determine the dominant semidiurnal tidal constituent the m2 these results have been combined with coastal sea level data from within the amazon and para rivers the adjacent shelf and with satellite derived tidal elevation data from off the shelf to provide a more complete description of the m2 tide in this complex river shelf system near the amazon river mouth the m2 tide propagates across the shelf and through the mouth as a damped progressive wave with its amplitude decreasing and phase increasing upriver over the adjacent shelf north of cabo norte the m2 tide approaches a damped standing wave with large amplitudes greater than 1 5 m near the coast due to near resonance within the coastal embayment formed by the cabo norte shoal to the south and cabo cassipore to the north the observed m2 tidal currents are nearly rectilinear and oriented primarily across the local isobaths comparisons between tidal observations in both the north channel and the cabo norte cabo cassipore embayment and a simple variable width channel tidal model indicate that 1 most of the m2 tidal energy dissipation occurs over the mid and inner shelf in water depths less than 20 m and 2 fluid muds found there cause a significant reduction of order 50 in the effective bottom friction felt by the m2 tide the approximate resonant period of the cabo norte cabo cassipore embayment is 11 9 hours and at resonance the average energy dissipation per forcing period is roughly 2 2 times the average mechanical energy in the embayment this damping rate is large enough that the tidal amplification is rather insensitive to forcing frequency so that the response of the embayment to forcing over the semidiurnal band should be essentially the same the vertical structure of the m2 tidal current is examined at one outer shelf site located in 65 m water depth the observed semimajor axis increases logarithmically with height above bottom within the lowest 1 2 m and reaches a maximum in excess of 0 5 m s at approximately 11 m above bottom the mean ellipticity is small less than 0 1 and positive indicating clockwise rotation of a nearly rectilinear current and the semimajor axis is oriented within 10 of the local cross isobath direction the m2 phase increases with height above bottom with flood at the bottom leading flood at the surface by about 1 hour a simple local homogeneous tidal model with time and space dependent eddy viscosity simulates the observed near bottom velocity reasonably well however the model suggests that stratification above the lowest few meters may significantly affect the tidal boundary layer structure at this site the m2 energy flux onto the amazon shelf and into the amazon and para rivers has been estimated using current and surface elevation data and the best fit variable width channel model results the net m2 energy flux into the mouths of the amazon and para rivers is 0 47 1010w and 0 19 1010w respectively a net m2 energy flux of about 3 3 1010w occurs onto the shelf between the north channel of the amazon river and cabo cassipore this stretch of the amazon shelf accounts for about 1 3 of the global dissipation of the m2 tide

structure and dynamics of fluid muds on the amazon continental shelf thick layers of fluid mud occur in strong tidal flows over the inner portion of the amazon continental shelf in regions of strong salinity fronts associated with the plume discharged from the amazon river detailed shipboard profile measurements obtained in this region during a multidisciplinary amazon shelf sediment study amasseds provide an unprecedented opportunity to examine the structure and dynamics of fluid muds under natural conditions the analysis focuses on flows in which the motion is fully turbulent and suspended sediment dominates the stratification under these conditions a comparison of measurements and one dimensional model calculations indicates that vertical transport is controlled by suppression of turbulent mixing at gradient richardson numbers near 1 4 this constraint produces a distinctive vertical structure and leads to an upper bound on the total amount of suspended sediment that may be carried in a turbulent suspension by a tidal flow

seasonal variations in the horizontal structure of the amazon plume inferred from historical hydrographic data near surface salinity observations from the national oceanographic data center hydrographic data archive for the region 4 s 10 n 60 40 w show that the amazon river discharge forms a plume of low salinity water that extends northwestward into the western tropical north atlantic the average near surface salinity within the plume increases away from the amazon river mouth consistent with an average entrainment of oceanic water of 2 105 m3 s every 1 of latitude there are two notable seasonal variations in the vicinity of the amazon river mouth 0 2 n the plume extends about 200 300 km eastward from june through december however from march to may the plume was often much wider 400 500 km in the vicinity of the river mouth possibly due to the combination of near maximum river discharge and winds with a southeastward component north of 5 n the amazon plume fans out over a broad region of the western tropical north atlantic during january through june low salinity amazon plume water north of 5 n is primarily found west of 52 w spreading northwestward toward the caribbean beginning typically in may some of the amazon plume water is deflected eastward in the north brazil current nbc retroflection from august through october surface salinities suggest 70 of the amazon plume water is carried eastward in the nbc retroflection while the remaining 30 flows northwestward toward the caribbean

the geological evolution of the tibetan plateau the geological evolution of the tibetan plateau is best viewed in a context broader than the india eurasia collision zone after collision about 50 million years ago crust was shortened in western and central tibet while large fragments of lithosphere moved from the collision zone toward areas of trench rollback in the western pacific and indonesia cessation of rapid pacific trench migration 15 to 20 million years ago coincided with a slowing of fragment extrusion beyond the plateau and probably contributed to the onset of rapid surface uplift and crustal thickening in eastern tibet the latter appear to result from rapid eastward flow of the deep crust probably within crustal channels imaged seismically beneath eastern tibet these events mark a transition to the modern structural system that currently accommodates deformation within tibet

heterogeneity and anisotropy of the lithosphere of se tibet from surface wave array tomography 1 understanding the geotectonic evolution of the southeastern tibetan plateau requires knowledge about the structure of the lithosphere using data from 77 broadband stations in sw china we invert rayleigh wave phase velocity dispersion curves from ambient noise interferometry t 1 0 40 s and teleseismic surface waves t 2 0 150 s for 3 d heterogeneity and azimuthal anisotropy in the lithosphere to 150 km depth our surface wave array tomography reveals 1 deep crustal zones of anomalously low shear wave speed and 2 substantial variations with depth of the pattern of azimuthal anisotropy upper crustal azimuthal anisotropy reveals a curvilinear pattern around the eastern himalayan syntaxis with fast directions generally parallel to the main strike slip faults the mantle pattern of azimuthal anisotropy is different from that in the crust and varies from north to south the tomographically inferred 3 d variation in azimuthal anisotropy helps constrain the source region of shear wave splitting south of 26 n off the high plateau most of the observed splitting can be accounted for by upper mantle anisotropy but for stations on the plateau proper with thick crust crustal anisotropy cannot be ignored on long wavelengths the pattern of azimuthal anisotropy in the crust differs from that in the mantle this is easiest explained if deformation varies with depth the deep crustal zones of low shear wave speed and presumably mechanical strength may represent loci of ductile deformation but their lateral variation suggests that in se tibet localized crustal channel flow and motion along the major strike slip faults are both important

sh wave structure of the crust and upper mantle in southeastern margin of the tibetan plateau from teleseismic love wave tomography abstract the deep structure of southeastern tibet is important for determining lateral plateau expansion mechanisms such as movement of rigid crustal blocks along large strike slip faults continuous deformation or the eastward crustal channel flow we invert for 3 d isotropic sh wave velocity model of the crust and upper mantle to the depth of 110 km from love wave phase velocity data using a best fitting average model as the starting model the 3 d sh velocity model presented here is the first sh wave velocity structure in the study area in the model the tibetan plateau is characterized by prominent slow sh wave velocity with channel like geometry along strike slip faults in the upper crust and as broad zones in the lower crust indicating block like and distributed deformation at different depth positive radial anisotropy vsh vsv is suggested by a high sh wave and low sv wave anomaly at the depths of 70 110 km beneath the northern indochina block this positive radial anisotropy could result from the horizontal alignment of anisotropic minerals caused by lithospheric extensional deformation due to the slab rollback of the australian plate beneath the sumatra trench

currents on the shelf of north eastern south america from the continental shelf region extending 400 km north of the mouth of the amazon river current meter data data on salinity temperature and suspended material were analyzed to study mean and tidal currents based on a grid point system the mean circulation patterns along the shelf are shown and the temporal variations in the tidal currents are depicted for the region at 2 h intervals maximum and minimum current speeds were studied for information on the spatial structure of the flow and on the along shelf and across shelf components

modelling the mean barotropic circulation in the bay of fundy and gulf of maine abstract two dimensional nonlinear numerical models are used to study the residual barotropic circulation generated by tides and steady winds in the bay of fundy and gulf of maine the first a multi grid model is used to examine the bay of fundy with a coarse look at the gulf of maine the circulation in the upper bay of fundy is predominantly tidally driven the model clearly reproduces the major gyres observed at the head of the bay steady wind stresses have some effect on the strength of these currents but little cited on the pattern the counterclockwise gyre observed in the body of the bay of fundy is not reproduced in the model the second model covers the lower bay of fundy and the gulf of maine with a single fine grid and is used to look at details in the gulf of maine a clockwise circulation around georges bank and nantucket shoals is clearly indicated from tidal forcing alone as is a gyre over the shallow part of browns bnak different steady wind stress fields give rise to variations in

geodynamics of the southeastern tibetan plateau from seismic anisotropy and geodesy ongoing plate convergence between india and eurasia provides a natural laboratory for studying the dynamics of continental collision a fi rst order process in the evolution of continents regional climate and natural hazards in southeastern tibet the fast directions of seismic anisotropy determined using shear wave splitting analysis correlate with the surfi cial geology including major sutures and shear zones and with the surface strain derived from the global positioning system velocity fi eld these observations are consistent with a clockwise rotation of material around the eastern himalayan syntaxis and suggest coherent distributed lithospheric deformation beneath much of southeastern tibet at the southeastern edge of the tibetan plateau we observe a sharp transition in mantle anisotropy with a change in fast directions to a consistent e w direction and a clockwise rotation of the surface velocity surface strain fi eld and fault network toward burma around the eastern himalayan syntaxis the coincidence between structural crustal features surface strain and mantle anisotropy suggests that the deformation in the lithosphere is mechanically coupled across the crust mantle interface and that the lower crust is suffi ciently strong to transmit stress at the southeastern margin of the plateau in yunnan province a change in orientation between mantle anisotropy and surface strain suggests a change in the relationship between crustal and mantle deformation lateral variations in boundary conditions and rheological properties of the lithosphere play an important role in the geodynamic evolution of the himalayan orogen and tibetan plateau and require the development of three dimensional models that incorporate lateral heterogeneity

numerical treatment of cross shelf open boundaries in a barotropic coastal ocean model abstract using a barotropic coastal ocean model with a straight coastline and uniform cross shelf bottom slope seven different cross shelf open boundary conditions four of which are applied in either implicit or explicit form are compared in three numerical experiments 1 a mound of water is allowed to collapse and radiate waves toward the open boundaries 2 a uniform alongshelf wind stress is applied at zero time over the entire shelf and held constant for the duration of the experiment 3 a uniform cross shelf wind stress is applied at zero time over the entire shelf and held constant for the duration of the experiment the boundary condition which is most transparent to waves consists of a sponge at the outer edge of the model domain with an orlanski radiation condition at the outer edge of the sponge several open boundary conditions perform adequately in the wind stress experiments but the orlanski radiation condition alone without a sponge appears to give the best total performance of thes

paleogeothermal influence on organic metamorphism in the neotectonics of the japanese islands abstract the paleogeothermal influence on the lowest grade metamorphic and diagenetic alteration of young sediments is discussed with special reference to the present conditions of the island arc system around japan vitrinite reflectance r 0 is adopted to detect the thermal influence the regional variation of r 0 in certain horizons the stratigraphic variation in steeply dipping successions and the depth variation in boreholes are investigated in cenozoic sediments of specific tectonic situations of fore arc and back arc depressions in the northeastern and the southwestern japan arcs the results have revealed a zonal distribution of a contrasting pattern of organic metamorphism that underwent either lower temperature and or higher pressure conditions or higher temperature and or lower pressure conditions the distribution of organic metamorphism seems to correspond to the present heat flow distribution i e the former low temperature high pressure corresponds to the present low heat flow region and the latter high temperature low pressure to the present high heat flow region

normal modes of the world ocean part iv synthesis of diurnal and semidiurnal tides abstract diurnal and semidiurnal tides of second and third degree are synthesized from 60 normal modes with period in the range 8 to 96 h diurnal tides especially those of second degree can be represented by remarkably few modes the principal lunar diurnal constituent for example consists almost entirely of a single forced mode excited mainly in the pacific and indian oceans semidiurnals are spectrally more heterogeneous and more resonant than diurnals but some specific features can be attributed to individual modes several of the most energetic modes in the principal lunar semidiurnal constituent are prominent in the atlantic ocean together with the fact that diurnally excited modes are relatively weak in that region this presumably accounts for the observed tendency for the total tide to be predominantly semidiurnal in the atlantic but mixed diurnal and semidiurnal in many parts of the pacific and indian oceans

normal modes of the world ocean part ii description of modes in the period range 8 to 80 hours abstract we have calculated normal modes with period between 8 and 80 h for a domain consisting of the arctic atlantic indian and pacific oceans in this period range the numerical model has 56 modes of which 13 are topographic vorticity waves all slower than 30 h the trapping sites for these modes are the siberian shelf the icelandic plateau the grand banks the falkland plateau and patagonian shelf the kerguelen plateau the new zealand and fiji plateaus and the hawaiian ridge predominantly planetary vorticity waves do not appear in the model at periods less than 80 h the 41 modes found between 30 and 8 h include basin modes in the north atlantic indian and equatorial pacific quarter wave resonances in the arabian sea bay of bengal and gulf of guinea and kelvin waves on the antarctic coast the pacific north american coast and the new zealand coast several vorticity and gravity modes exhibit an eastward circumglobal flow of energy that is confined to equatorial latitudes except where defl

introduction to special section on physical oceanography of the amazon shelf the amazon shelf is an unusual oceanographic environment in addition to the large input of fresh water from the amazon river unusually large tidal currents vigorous wind driven currents and an impinging western boundary current contribute to one of the most energetic continental shelf environments in the world much of the shelf is very shallow the 20 m isobath extends as far as 200 km from the river mouth the proximity of the amazon shelf to the equator means that rotational effects are much weaker than at midlatitudes

rates and mechanisms of shoreface progradation and retreat downdrift of the amazon river mouth field surveys of the 350 km shoreline adjacent to the amazon river mouth reveal three distinct types erosional mud accretionary sand and accretionary mud formation of these zones is controlled by the delivery of amazon suspended sediment mediated by the hydrodynamic regime erosional mud shorelines extend from rio araguari near the amazon river mouth northwestward 280 km to 3 5 n near cabo cassipore shoreface 5 m water depth retreat annually yields 1 4 106 tons of fine grained sediment deposited during an earlier phase of shoreface progradation sandbodies up to 5 m thick overlie erosional mud shorefaces for 10 30 km downdrift of small rivers the sand is supplied from these rivers and released by shoreline retreat of the river mouth areas amazon river sand is restricted in the coastal zone from its mouth north to the cabo norte shoal area where it mixes with sand carried by rio araguari from the guiana highlands north of 3 5 n mud aggradation and progradation is taking place on underconsolidated low gradient tidal flats backed by mangrove swamps 210pb and 14c geochronology of vibracores from the mudflats indicate that sediment accumulation is rapid 0 24 2 0 cm yr landward of the 2 m isobath supplied from a thick 50 150 cm seasonal surface layer shoreface progradation is episodic separated by decadal hiatuses fine grained suspended sediment flux from the amazon and minor amounts of sand and mud from the local rivers supply sediment to the mudflats shore normal tidal currents and solitary waves rework the surface mud layer preferentially transporting available sand landward into the mangrove fringe and producing very fine grained accumulation on the tidal flat 10 12 mean grain size lateral accretion of features 10 100 km long termed mudcapes produces tens of kilometers of seaward coastal plain addition along the northern coast similar features are identified downdrift along the guianas coast as far as the orinoco river 1600 km the northern amapa shoreface deposits are a locus of modern sediment accumulation which progrades over subaqueous deltaic strata

the amazon river plume during amasseds subtidal current variability and the importance of wind forcing current variability over the north brazilian shelf particularly within the amazon plume is characterized using observations from a moored array deployed about 300 km north of the amazon river mouth from february to june 1990 as part of a multidisciplinary amazon shelf sediment study amasseds the moored array consisted of a transect perpendicular to the coast with inner shelf 18 m depth and midshelf 65 m moorings and a third mooring near the shelf break in 100 m of water to our knowledge the amasseds moored array includes the first long term 2 months moored observations made within the amazon plume the current variability is dominated by two components semidiurnal cross shelf currents with peak velocities of 50 to 200 cm s and vertically sheared subtidal timescales days to weeks along shelf currents this study focuses on the subtidal flow within the amazon plume which is strong and variable with along shelf currents ranging from 50 cm s to over 150 cm s the variability in the along shelf current within the plume is wind driven the relatively weak 0 5 dyn cm2 along shelf wind stresses in this region drive strong along shelf current variability because the amazon plume is thin and the interfacial drag is weak however in the absence of an along shelf wind stress the plume flow is northwestward at 40 to 80 cm s indicating that direct wind forcing does not account for the mean northwestward flow of the amazon plume in the cross plume direction there is a tendency for the onshore wind stress due to the persistent trade winds to balance the typically offshore buoyancy force and the coriolis force associated with the wind driven along shelf flow thus the wind stress is a key factor influencing variability in both the flow and cross shelf structure of the amazon plume in the vicinity of the moored array

varied thermo rheological structure mechanical anisotropy and lithospheric deformation of the southeastern tibetan plateau abstract to investigate the lithospheric structure and deformation of the tibetan plateau we present thermo rheological models for two transects across the southeastern tibetan plateau se tibet showing strong lateral heterogeneity the geodynamic implications are also investigated in relation to gps motions seismic anisotropy seismicity distribution and crustal isostatic state the unmatched pattern between pms and sks splittings which even intersect at right angles to the south of 26 n suggests the crust mantle decoupling constrained by a brittle load bearing layer at the uppermost mantle beneath the indochina block the decoupling may occur below the uppermost mantle the strong crust beneath the south china plate and indochina block implied by the seismicity distribution has two thick brittle load bearing layers indicating a coupled system the crust beneath the emeishan large igneous province elip also has two brittle load bearing layers but the brittle deformation is restricted to the topmost 10 km of the upper and lower crust only one brittle load bearing layer resides in the upper crust in the other part of the chuandian block combining with gps and pms splitting we can infer that the weak crust with seismicity restricted into the depth of

tidal energy loss in coastal embayments the tidal energy balance for an embayment over the spring neap cycle is used to obtain a relationship between the phase of the m 2 and s 2 tidal flow at the entrance using solely tidal elevation harmonic constants as inputs for possible values of the phase of the flow the calculated frictional drag coefficient k or comparison with observation of the variation of the phase of the flow through the spring neap cycle may be used to allow the frictional energy dissipation to be estimated application to the bristol channel for values of k which are consistent with the generally accepted range of values used in two dimensional numerical models give estimates of the phase of the flow within the range of those observed and of the tidal energy dissipation consistent with previous estimates the method should allow estimates of the energy dissipation per unit mass to be made in embayments where tidal elevation harmonic constants alone are available and thus provide an insight into the potential mixing

crustal radial anisotropy across eastern tibet and the western yangtze craton 1 phase velocities across eastern tibet and surrounding regions are mapped using rayleigh 8 65 s and love 8 44 s wave ambient noise tomography based on data from more than 400 program for array seismic studies of the continental lithosphere and chinese earthquake array stations a bayesian monte carlo inversion method is applied to generate 3 d distributions of vsh and vsv in the crust and uppermost mantle from which radial anisotropy and isotropic vs are estimated each distribution is summarized with a mean and standard deviation but is also used to identify highly probable structural attributes which include 1 positive midcrustal radial anisotropy vsh vsv across eastern tibet spatial average 4 8 1 4 that terminates abruptly near the border of the high plateau 2 weaker 1 0 1 4 negative radial anisotropy vsh vsv in the shallow crust mostly in the songpan ganzi terrane 3 negative midcrustal anisotropy 2 8 0 9 in the longmenshan region 4 positive midcrustal radial anisotropy 5 4 1 4 beneath the sichuan basin and 5 low vs in the middle crust 3 427 0 050 km s of eastern tibet midcrustal vs 3 4 km s perhaps consistent with partial melt is highly probable only for three distinct regions the northern songpan ganzi the northern chuandian and part of the qiangtang terranes midcrustal anisotropy provides evidence for sheet silicates micas aligned by deformation with a shallowly dipping foliation plane beneath tibet and the sichuan basin and a steeply dipping or subvertical foliation plane in the longmenshan region near vertical cracks or faults are believed to cause the negative anisotropy in the shallow crust underlying tibet

connection between macrotidal estuaries along the southeastern amazon coast and its role in coastal progradation abstract sediment transport in the southeastern amazon coastal zone sacz is substantially affected by tidal asymmetry seasonal variation of the wind and wave regime and especially rainfall i e river discharge the regional climate and geological configuration have resulted in numerous estuaries and large mangrove covered coastal plains that partially divide the estuarine basins which are connected by tidal channels based on the investigation of the furo grande tidal channel we assess the relevance of connectivity on the sediment transport and evolution of the 8000 km2 sacz mangrove belt extensive sedimentologic and bathymetric surveys as well as hydrodynamic measurements including water level water and sediment flow and physical chemical characteristics of the water were undertaken at different seasonal periods water level variation along the channel shows that sediment transport convergence stc tends to be formed within the connecting channel as the tide propagates from both ends morphologic and sedimentologic results show the accumulation trend of fine sediments within the stc zone and this is relevant for mud retention and further delivery to the mangrove plains which may eventually lead to channel connection closure despite the stc results also show that there is an important net flux of suspended sediments between estuaries through the studied channel however the connected estuaries of taperacu and caete have substantial differences regarding riverine discharge and thus estuarine processes tidal propagation and sediment transport bottom sediments and morphology reflect long term trends and show stc migration towards the taperacu as a result of substantially smaller fluvial discharge in that estuary and therefore higher sediment accumulation rates compared to the caete estuary the migration of the stc prevents the closure of the connection and its maintenance preserves these channels as sediment flow conduits between estuaries the connectivity is a key process to redistribute mainly muddy sediments along this coastal sector which helps to explain the evolution and maintenance of the relatively homogeneous and widespread progradation of mangroves along the sacz with uneven mud supply

internal tides as a major process in amazon continental shelf fine sediment transport abstract the description of hydrodynamics associated with the extensive reef system on the shelf break adjacent to the amazon river is still a challenge for ocean sciences despite the discharge of more than one billion tons of cohesive sediment per year the outer continental shelf of the world s largest river presents very low concentrations of suspended sediment near the bottom and an absence of modern fine sediment deposits nearly one hundred kilometers before the shelf break the offshore limit of the subaqueous delta consists of a sigmoidal clinoform standing between 40 and 70 m in depth a depositional feature that cannot be explained solely by estuarine like gravitational circulation this paper aims to test the hypothesis that internal tides have a major role in the control of offshore fine sediment transport for that we implement a set of tridimensional non hydrostatic and high resolution up to 2 m vertical and 2 km horizontal delft3d models the experiments showed that even disregarding river plume buoyancy wind drag superficial waves and ocean currents the exclusive interaction between barotropic tidal currents bathymetry and the stratification structure of the ocean is capable of generating asymmetrical current patterns compatible with modern deposition the maximum shelf slope and the relative depth between the outer shelf and the pycnocline represent the main factors influencing the generation and shoreward propagation of internal tides over time spring neap cycles are eventually capable of reverting cross shore subtidal transport tendencies while seasonal variability in ocean stratification modulates the intensity of baroclinic processes

some field measurements concerned with the behaviour of resistance coefficients in a tidal channel measurements of the individual terms in the one dimensional unsteady flow momentum equation in a 1 2 km tidal reach of the conwy estuary n wales have yielded values for the resistance coefficients commonly adopted in open channel flow hydraulics the results indicate clearly that manning s n or darcy weisbach s f vary significantly with stage and to a lesser extent with flow direction the relative importance of the various terms in the one dimensional momentum equation are illustrated and the techniques employed in measuring them indicated values of nikuradse s roughness parameter k s have also been computed and are shown to vary significantly with water level mean bed shear stresses have been evaluated and the variation in bed shear velocity throughout different tidal cycles determined the results indicate the inadvisability of selecting a single roughness parameter to represent the hydraulic characteristics of any individual element in a numerical tidal model

variations of sediment texture on the amazon continental shelf abstract grain size distribution on the continental shelf adjacent to the amazon river reveals three detrital sedimentary deposits an outer shelf sand deposit 1 5 3 0 well sorted negatively skewed an inner shelf mud deposit 6 9 poorly sorted positively skewed and a corridor extending from the river mouth across the inner shelf in which mud is interbedded with sand modern mud covers most of the inner shelf and surface sediment does not reveal along shelf or across shelf sorting of discrete particles size sorting of particle aggregates floccules fecal pellets may occur at the time of deposition but is difficult to evaluate a lack of shoreward fining reverse grading c ntradicts the sedimentation model of gibbs 1976 the model most consistent with textural observations is that of a modern subaqueous delta prograding over a relict basal sand the outer shelf sand modern sand in surface sediment is restricted to the corridor extending from the river mouth across the inner shelf ambient physical processes are not competent to transport this sand along shelf subsurface sand layers within the inner shelf mud deposit i e outside the corridor are similar in texture to surficial sand in the corridor of interbedded mud and sand these observations may suggest that the location and or size of the corridor has changed with time

structure of the upper mantle and transition zone beneath southeast asia from traveltime tomography 1 tomographic images of the mantle beneath east asia were obtained from the inversion of traveltime data from global and regional seismograph networks and from temporary arrays on and around the tibetan plateau our results are consistent with previous studies but the unprecedented resolution of mantle heterogeneity provides new insight into the large scale tectonic framework of the continental india asia collision in the western part of the study region and subduction of the oceanic lithosphere in the east in the realm of continental collision west of 100 e a relatively slow p wave speed characterizes the upper mantle beneath much of the tibetan plateau but the wave speed is high beneath cratonic india the southern and western part of the tibetan plateau hindu kush and the tian shan in the subduction realm east of 110 e the main structures are i pronounced low wave speed anomalies at a depth of between 100 and 400 km beneath asia s southeastern seaboard and the back arc regions of ongoing subduction ii narrow fast anomalies in the upper mantle beneath major subduction zones and iii widespread fast anomalies at a depth of 500 700 km beneath the sea of japan the northern part of the philippine sea plate and southeastern china if the latter anomalies represent stagnant slabs their fragmented nature and large lateral extent suggest that they are produced by different episodes of subduction beneath western pacific island arcs along the old se margin of asia or during the mesozoic collision of cratonic units in southeast asia attribution to ancient subduction systems implies that slab fragments can reside in the transition zone for at least several tens of millions of years shallow slow anomalies beneath the red river fault region connect to deep anomalies beneath the south china fold belt and south china sea suggesting a causal relationship between the evolution of the continental lithosphere of sw china and deeper mantle processes between the collision and the subduction realms tomography reveals high wave speed continental roots beneath the western part of the north china craton ordos block and the south china or yangtze craton sichuan basin to a depth of 300 km

a synoptic view of the distribution and connectivity of the mid crustal low velocity zone beneath tibet 1 based on 1 2 years of continuous observations of seismic ambient noise data obtained at more than 600 stations in and around tibet rayleigh wave phase velocity maps are constructed from 10 s to 60 s period a 3 d vsv model of the crust and uppermost mantle is derived from these maps the 3 d model exhibits significant apparently inter connected low shear velocity features across most of the tibetan middle crust at depths between 20 and 40 km these low velocity zones lvzs do not conform to surface faults and significantly are most prominent near the periphery of tibet the observations support the internal deformation model in which strain is dispersed in the deeper crust into broad ductile shear zones rather than being localized horizontally near the edges of rigid blocks the prominent lvzs are coincident with strong mid crustal radial anisotropy in western and central tibet and probably result at least partially from anisotropic minerals aligned by deformation which mitigates the need to invoke partial melt to explain the observations irrespective of their cause in partial melt or mineral alignment mid crustal lvzs reflect deformation and their amplification near the periphery of tibet provides new information about the mode of deformation across tibet