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

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

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

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

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

3 d crustal and uppermost mantle structure beneath ne china revealed by ambient noise adjoint tomography abstract we construct a new 3 d shear wave speed model of the crust and the uppermost mantle beneath northeast china using the ambient noise adjoint tomography method without intermediate steps of measuring phase dispersion the adjoint tomography inverts for shear wave speeds of the crust and uppermost mantle directly from 6 40 s waveforms of empirical green s functions egfs of rayleigh waves which are derived from interferometry of two years of ambient noise data recorded by the 127 northeast china extended seismic array stations with an initial 3 d model derived from traditional asymptotic surface wave tomography method adjoint tomography refines the 3 d model by iteratively minimizing the frequency dependent traveltime misfits between egfs and synthetic green s functions measured in four period bands 6 15 s 10 20 s 15 30 s and 20 40 s our new model shows shear wave speed anomalies that are spatially correlated with known tectonic units such as the great xing an range and the changbaishan mountain range the new model also reveals low wave speed conduits in the mid lower crust and the uppermost mantle with a wave speed reduction indicative of partial melting beneath the halaha xilinhot abaga and jingpohu volcanic complexes suggesting that the cenozoic volcanism in the area has a deep origin overall the adjoint tomographic images show more vertically continuous velocity anomalies with larger amplitudes due to the consideration of the finite frequency and 3 d effects

large scale experiments on the mechanics of pyroclastic flows design engineering and first results 1 a newly designed apparatus for experimental studies of pyroclastic flows consists of a cylindrical conduit that is filled with samples of natural volcanic products tephra blowing nozzles in the base plate of the conduit are connected to a volume of highly pressurized gas opening of fast solenoid valves results in impulse like coupling of the released gas to the sample the system was designed so that the range of mechanical energy transferred to the particle mass in the conduit reflects the mechanical energy observed and measured during fragmentation experiments with melts of similar composition depending on the specific mechanical energy sme of the system which results from pv m where p is gas overpressure i e pressure atmospheric v is gas volume and m is sample mass different behaviors are observed if sme 2 6 kj kg a dilute plume develops and particles are sedimented by fallout exclusively if sme 106 implying that flows are fully turbulent and that particle coupling to gas turbulence of natural pyroclastic flows is replicated by the experiments the measured shear current velocities are proportional to the impact mass flow rate i e the product of mixture density and impact velocity experimental data and grain size analysis of the produced particle deposits suggest that the scale of the experiment is large enough to reproduce the transport dynamics of natural pyroclastic flows

mobility of pyroclastic flows and surges at the soufriere hills volcano montserrat the soufriere hills volcano on montserrat has produced avalanche like pyroclastic flows formed by collapse of the unstable lava dome or explosive activity pyroclastic flows associated with dome collapse generate overlying dilute surges which detach from and travel beyond their parent flows the largest surges partially transform by rapid sedimentation into dense secondary pyroclastic flows that pose significant hazards to distal areas different kinds of pyroclastic density currents display contrasting mobilities indicated by ratios of total height of fall h run out distance l area inundated a and volume transported v dome collapse flow mobilities characterised by either l h or a v2 3 resemble those of terrestrial and extraterrestrial cold rockfalls dade and huppert 1998 in contrast fountain fed pumice flows and fine grained secondary pyroclastic flows travel slower but for comparable initial volumes and heights can inundate greater areas

shear velocity structure radial anisotropy and dynamics of the tibetan crust geophysical and geological data suggest that tibetan middle crust is a partially molten mechanically weak layer but it is debated whether this low viscosity layer is present beneath the entire plateau what its properties are how it deforms and what role it has played in the plateau s evolution broad band seismic surface waves yield resolution in the entire depth range of the tibetan crust and can be used to constrain its shear wave velocity structure indicative of crustal composition temperature and partial melting and radial anisotropy indicative of the patterns of deformation we measured love and rayleigh wave phase velocity curves in broad period ranges up to 7 200 s for a few tens of pairs and groups of stations across tibet combining in each case hundreds of interstation measurements made with cross correlation and waveform inversion methods shear velocity profiles were then determined by extensive series of non linear inversions of the data designed to constrain the depth dependent ranges of isotropic average shear speeds and radial anisotropy shear wave speeds within the tibetan middle crust are anomalously low and also show strong lateral variations across the plateau the lowest mid crustal shear speeds are found in the north and west of the plateau 3 1 3 2 km s 1 within a pronounced low velocity zone in southeastern tibet crustal shear wave speeds increase gradually towards southeast whereas in the north the change across the kunlun fault is relatively sharp the lateral variations of shear speeds within the crust are indicative of those in temperature a mid crustal temperature of 800 c reported previously can account for the low shear velocities across lhasa in the north the temperature is higher and exceeds the solidus resulting in partial melting that we estimate at 3 6 per cent strong radial anisotropy is required by the data in western central tibet 5 per cent but not in northeastern tibet the amplitude of radial anisotropy in the crust does not correlate with isotropic average shear speed and by inference with crustal rock viscosity or with surface elevation instead radial anisotropy is related to the deformation pattern and is the strongest in regions experiencing extension crustal flattening as noted previously the growth of tibet by the addition of indian crustal rocks into its crust from the south is reflected in the higher crustal seismic velocities and thus lower temperatures in the southern compared to northern parts of the plateau more recently added rocks having had less time to undergo radioactive heating within the thickened tibetan crust gravity driven flattening the basic cause of extension and normal faulting in the southern western and central tibet is evidenced by pervasive radial anisotropy in the middle crust beneath the regions undergoing extension the overall eastward flow of the crust is directed by the boundaries and motions of the lithospheric blocks that surround tibet

seismic attenuation tomography in southwestern china insight into the evolution of crustal flow in the tibetan plateau abstract crustal flow in southwestern china is commonly attributed to the continental collision between the indian and the eurasian plates therefore studying crustal flow in this area can provide valuable insight into the collisional process the quality factor q is an indicator of seismic wave attenuation that provides constraints on lithology rheology and geodynamic processes which are vital for interpreting the nature of the crustal flow in a given region in this study we used local seismic waveforms to obtain regional attenuation models for p qp and s qs waves in the sichuan yunnan region syr the emeishan large igneous province elip is characterized by high qp and qs values in the middle yunnan block myb at depths greater than 5 km the qp and qs values in most of the fault zones surrounding the myb were lower than 300 indicating that the material within crustal faults causes high waveform attenuation our results suggest that the crustal flow was diverted into two channels in the northern myb due to resistance from the elip to illuminate the tectonic dynamics of the syr we propose a simple model that explains both the evolution of the crustal flow and the variation in the seismic wave attenuation

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

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

the interaction of ash flows with ridges using both laboratory experiments and theoretical models we examine the different flow regimes that may develop when an ash flow encounters a ridge for very small ridges all the flow may pass over the ridge for intermediate size ridges the flow may be partially blocked with a fraction of the flow reflected upstream as a travelling bore in this case the remainder of the flow which does pass over the ridge is hydraulically controlled at the ridge crest finally if the ridge is sufficiently high then the flow will be totally blocked new laboratory experiments show that the sedimentation patterns associated with these flow regimes may be very different most importantly flows that involve partial blocking and the formation of upstream propagating bores display enhanced sedimentation upstream of the ridge analogous to valley ponded and caldera fill deposits in contrast under some circumstances if the flow is able to scale a ridge the deposit may be relatively unaffected by the presence of the ridge the minimum ridge height that leads to total blocking of the flow increases with mass eruption rate and has a complex variation with distance from the source in a one dimensional channel the minimum ridge height that causes blocking increases with distance downstream this is because the flow becomes less dense through sedimentation of particles and entrainment of air and so requires less energy to scale a ridge of a particular height in axisymmetric flow the minimum ridge height initially decreases with distance downstream as the flow spreads radially but subsequently increases as the flow becomes less dense through sedimentation and entrainment a new quantitative model of dilute ash flows propagating over ridges indicates that flows with mass fluxes in excess of 108 109 kg s can partially scale barriers as high as 1000 m at distances of tens of kilometres from the source whereas smaller flows are likely to be totally blocked by such an obstacle our results shed new insight on the possible long range transport mechanism of several large flows including the ata fisher and aniakchak pyroclastic flows

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

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

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

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

a diagnostic analysis of the presidents day storm of february 1979 abstract a diagnostic analysis of the presidents day storm of february 1979 is used to extend and quantify earlier findings of bosart the initial growth of cyclonic vorticity in the lower troposphere is driven primarily by convergence along the carolina coastal front rapid cyclone spinup accompanies the approach of a potent midtropospheric short wave trough from the ohio valley an analysis of the vorticity structure discloses that cyclone spinup is enhanced by the vertical advection of vorticity in the strongly cyclonic in situ vorticity environment along the coast as the upper level trough overspreads the region similarly a downward extension of high semige strophic potential vorticity air accompanies a tropopause fold to the west of thecyclone and prior to the rapid cyclogenesis stage confirming a result of uccellini and others semigeostrophic potential vorticity is poorly conserved however and there is evidence for a separate region of semigeostrophic potential vorticity growth below 800 mb n

crustal shear wave velocity and radial anisotropy in the xiaojiang fault zone system se tibet revealed by ambient noise interferometry abstract the xiaojiang fault zone system xjfs is located in the southeastern tibet with high seismicity in this study we invert rayleigh and love wave dispersion curves obtained from three dense seismic arrays jointly for high resolution 3 d crustal average shear wave velocity and radial anisotropy models simultaneously in xjfs our model reveals that the upper crust and mid lower crust generally exhibit negative and positive radial anisotropy respectively implying that the deformation pattern is depth dependent to the east of the lvzhijiang fault most of the low velocity zones in the mid crust correspond to the positive radial anisotropy vsh vsv the channelized weak zone seems to be continuous across the red river fault at depth of 20 km probably within a thin layer west of the lvzhijiang fault where it is inferred to be the inner zone of the permian emeishan large igneous province the high velocity zone and positive radial anisotropy in the mid lower crust can be attributed to the underplating and intruded magmatic rocks in the upper crust the high and low velocity zones are mostly belt shape and follow the north south direction parallel to the regional major faults the lateral variation of the radial anisotropy spatially corresponds to the activity of different segments of the xiaojiang fault zone our models depict detailed geometry of the channelized weak zone in the mid lower crust and provide new insight into the role of major faults in regional tectonics

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

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

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

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

complicated crustal deformation beneath the ne margin of the tibetan plateau and its adjacent areas revealed by multi station receiver function gathering abstract we use a multi station stacking method to analyze receiver function data recorded by a large scale dense seismic array covering the northeastern ne margin of the tibetan plateau and its adjacent regions to estimate crustal thickness h vp vs ratio and crustal anisotropy fast polarization direction and splitting time for each station of the array we gathered all the receiver functions recorded by the station and its nearby stations located inside a circle with a radius of 0 5 we applied the h stacking technique and the joint inversion scheme to a total of 654 station clusters to measure the h and respectively the measured moho depth varies from a peak value of 67 km beneath the northern central plateau to 39 45 km beneath the surrounding blocks in the northeast the front of the depressed moho beneath the plateau margin exhibits a complicated geometry which suggests that when the tibetan plateau encroached upon the surrounding terranes the front expanded unevenly depending on the strength of the encountering terranes the thickened crust beneath the margin also has a very low vp vs ratio indicating that the crust is composed largely of felsic minerals more than one third of the station clusters 221 have a splitting time significantly larger than 0 2 s the average splitting times of the 221 measurements is 0 68 s which is comparable to those measured from the sks skks xks phases 0 94 s the fast directions estimated from the moho ps and xks phases recorded by the station clusters within the margin are very similar and are also approximately parallel to the strikes of major faults sutures and thrust fronts in the area the low vp vs ratio together with the observed fast polarization directions from the moho ps and xks phases suggests that shortening of the entire lithosphere orthogonal to the compressional direction is likely the main cause for the observed crustal thickening occurring at the margin we also found that the moho ps and xks recorded by stations inside the western hetao basin and the yinchuan basin present very different anisotropy which may suggest that the crust and mantle beneath the two basins have very different deformation patterns

crustal and upper mantle structure of the southeastern tibetan plateau from joint analysis of surface wave dispersion and receiver functions abstract researches on the southeastern tibetan plateau provide important insights into the tectonic evolution of the tibetan plateau in this study we have constructed a high resolution 3d shear wave velocity model through joint inversion of receiver functions and surface wave dispersion data the crustal thickness and poisson s ratio models are first determined by h k stacking of receiver functions the crustal thickness changes from 30 km in the south to 62 km in the north presenting strong lateral variations the fundamental mode of rayleigh wave dispersion data spanning periods from 8 to 65 s were then jointly used to constraint the absolute shear wave velocity the shear wave velocity structure shows lateral variations there are low velocity zones distributed in the crust and upper mantle two continuously distributed low velocity zones are clearly presented in the middle to lower crust which extend from north toward southeast and southwest respectively joining together in southern yunnan in this study we deduced the migration model of soft materials in middle to lower crust in southeastern tibetan plateau which explains that the resistance from sichuan basin separates the flowing materials from tibetan plateau into southeast and northwest branches they flow along the west margin of sichuan basin and then extrude out from northeastern and southeastern tibetan plateau respectively the southeast branch is blocked and cannot flow in the entire crust it is limited in a certain range of depths and channels the two low velocity zones in this study possibly present two flow channels of the middle to lower crustal materials extruded from the tibetan plateau

flow of variably fluidized granular masses across three dimensional terrain 1 coulomb mixture theory rock avalanches debris flows and related phenomena consist of grain fluid mixtures that move across three dimensional terrain in all these phenomena the same basic forces govern motion but differing mixture compositions initial conditions and boundary conditions yield varied dynamics and deposits to predict motion of diverse grain fluid masses from initiation to deposition we develop a depth averaged three dimensional mathematical model that accounts explicitly for solid and fluid phase forces and interactions model input consists of initial conditions path topography basal and internal friction angles of solid grains viscosity of pore fluid mixture density and a mixture diffusivity that controls pore pressure dissipation because these properties are constrained by independent measurements the model requires little or no calibration and yields readily testable predictions in the limit of vanishing coulomb friction due to persistent high fluid pressure the model equations describe motion of viscous floods and in the limit of vanishing fluid stress they describe one phase granular avalanches analysis of intermediate phenomena such as debris flows and pyroclastic flows requires use of the full mixture equations which can simulate interaction of high friction surge fronts with more fluid debris that follows special numerical methods described in the companion paper are necessary to solve the full equations but exact analytical solutions of simplified equations provide critical insight an analytical solution for translational motion of a coulomb mixture accelerating from rest and descending a uniform slope demonstrates that steady flow can occur only asymptotically a solution for the asymptotic limit of steady flow in a rectangular channel explains why shear may be concentrated in narrow marginal bands that border a plug of translating debris solutions for static equilibrium of source areas describe conditions of incipient slope instability and other static solutions show that nonuniform distributions of pore fluid pressure produce bluntly tapered vertical profiles at the margins of deposits simplified equations and solutions may apply in additional situations identified by a scaling analysis assessment of dimensionless scaling parameters also reveals that miniature laboratory experiments poorly simulate the dynamics of full scale flows in which fluid effects are significant therefore large geophysical flows can exhibit dynamics not evident at laboratory scales

hydraulics of the august 7 1980 pyroclastic flow at mount st helens washington open channel hydraulic theory for flow of an inviscid fluid down a channel of changing slope and width yields a longitudinal velocity profile that matches measured velocities of the august 7 1980 pyroclastic flow at mount st helens the model is useful for prediction of zones of erosion deposition and hazards it requires only topographic data estimates of volumetric flow rate and a manning coefficient appropriate for the channel

low velocity crustal flow and crust mantle coupling mechanism in yunnan se tibet revealed by 3d s wave velocity and azimuthal anisotropy abstract we used teleseismic data recorded by a permanent seismic network in yunnan se tibet and measured the interstation rayleigh wave phase velocity between 10 and 60 s a two step inversion scheme was used to invert for the 3d s wave velocity and azimuthal anisotropy structure of 10 110 km the results show that there are two low velocity channels between depths of 20 30 km in yunnan and that the fast axes are sub parallel to the strikes of the low velocity channels which supports the crustal flow model the azimuthal anisotropy pattern is quite complicated and reveals a complex crust mantle coupling mechanism in yunnan the n s trending luzhijiang fault separates the dianzhong block into two parts in the western dianzhong block the fast axis of the s wave changes with depth which indicates that the crust and the lithospheric mantle are decoupled in the eastern dianzhong block and the western yangtze craton the crust and the lithospheric mantle may be decoupled because of crustal flow despite a coherent s wave fast axis at depths of 10 110 km in addition the difference between the s wave fast axis in the lithosphere and the sks splitting measurement suggests that the lithosphere and the upper mantle are decoupled there in the baoshan block the stratified anisotropic pattern suggests that the crust and the upper mantle are decoupled

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

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

high resolution crustal model of se tibet from joint inversion of seismic p wave travel times and bouguer gravity anomalies and its implication for the crustal channel flow abstract we present a high resolution 3 d crustal model of southeastern tibetan plateau se tibet by joint inversion of local earthquake p wave travel times and bouguer gravity anomalies the joint inversion improves the resolution compared with travel time only tomography and more clearly depicts the spatial distribution of low velocity zones in the crust our joint inversion model finds no evidence for crustal channel flow in this part of se tibet however our velocity model shows three distinct low velocity zones in the mid crust which are generally associated with the major fault systems that control the deformation of se tibet in the cenozoic the thick mafic ultramafic underplating beneath the emeishan large igneous province effectively blocks the crustal flow from tibetan plateau and the crustal low velocity zone beneath the luzhijiang fault and xiaojiang fault is more likely due to localized asthenospheric upwelling at the southern end of nujiang fault the joint inversion model reveals the magmatic system beneath the tengchong volcano that facilitates melt migration from uppermost mantle to the magma chambers in the upper to mid crust

3d shear wave velocity structure beneath the southeastern tibetan plateau from ambient noise we perform high resolution 3d shear wave structures of the crust and upper mantle using continuous wave data recorded at 170 stations from national and regional networks in the southeastern tibetan plateau first empirical green s functions are obtained between all the possible station pairs then rayleigh wave group velocity and phase velocity dispersion curves are retrieved using the frequency time analysis method the rayleigh wave group velocity images at periods from 8 to 50 s and phase velocity images at periods from 8 to 40 s are inverted on a 1 1 grid finally the 1d shear wave structure beneath each grid and the 3d shear wave velocity structure are acquired by linear interpolation our results indicate that low velocity layers lvls are ubiquitous in the middle lower crust beneath the southeastern tibetan plateau but vary in depth 20 35 km thickness 5 20 km and strength 5 4 10 8 velocity reduction in different blocks the 3d geometry of the lvls is complex and cannot be interpreted as a model with a uniform flow channel the shear velocity in the chuandian block is unevenly distributed indicating that the block is inhomogeneous the 12 may 2008 wenchuan and 20 april 2013 lushan earthquake sequences m s 3 0 all occurred in the crustal layers in which lvls are inhibited by the strong sichuan basin and in which the topography and crustal thickness vary sharply this formed the earthquake preparation environment of the two earthquakes the ningnan qiaojia pull apart region is characterized by low shear wave velocity in the shallow crust which agrees well with the sedimentary features of the upper crust a relatively high velocity is observed in the central part of the low velocity sichuan basin in the shallow layers indicating the basement beneath the sichuan basin may be uplifted around the central part of the basin

insights into the october november 2010 gunung merapi eruption central java indonesia from the stratigraphy volume and characteristics of its pyroclastic deposits abstract the 2010 eruption of merapi was the second most deadly in the historic record of this volcano claiming over 380 lives by relating the observations of this eruption with detailed examination of deposit distribution stratigraphy and sedimentology a reconstruction of the properties of the pyroclastic density currents pdcs is presented including the valley controlled block and ash flows bafs and widespread energetic pyroclastic surges the distribution volume and mobility characteristics of all types of pdc during the eruption sequence show evidence for levels of intensity unseen since the large scale 1872 and 1930 eruption phases especially during the climactic events of october 26 and november 5 many tephra falls interbedded with pdc units show that most dome collapse events occurred along with and between explosive vulcanian eruptions the 2010 eruption produced very long runout bafs reaching 16 1 km in the kali gendol on november 5 this runout could be explained by its large volume 20 million m 3 around 10 times that of previous merapi bafs during the last 130 years major avulsion of these dense bafs to form overbank deposits became more common through the eruptive sequence as the valley was progressively filled with successive pdc deposits spreading avulsed bafs were a particular hazard downstream of 10 km where the landscape is less dissected less clear however is why pyroclastic surges extended up to 10 km from the vent on november 5 and 6 4 km on october 26 these expanded much farther from baf margins 2 km than ever seen before at merapi in one location they were decoupled from valley centered bafs with high momentum traveling initially laterally across steep valley systems before draining downslope at this site on the western side of the upper gendol at around 3 km from source surge decoupling was apparently exacerbated by upstream collision and deflection of high flux hot and gas rich bafs against the cliffs of gunung kendil the 1 4 km long cliff face was impacted directly for the first time in 2010 events and may have been responsible for the formation of larger than normal turbulent ash rich clouds above bafs these results imply that future eruption events under the present summit and upper flow path configuration are also highly likely to generate wide dispersal pyroclastic surges and extreme hazard especially now that dense forest has been destroyed on the upper southern slopes of the volcano

the 1982 eruptions of el chichon volcano mexico 3 physical properties of pyroclastic surges two major pyroclastic surges generated during the 4 april 1982 eruption of el chichon devastated an area of 153 km2 with a quasi radial distribution around the volcano the hot surge clouds carbonized wood throughout their extent and were too hot to allow accretionary lapilli formation by vapor condensation field evidence indicates voidage fraction of 0 99 in the surge cloud with extensive entrainment of air thermal calculations indicate that heat content of pyroclasts can heat entrained air and maintain high temperatures in the surge cloud the dominant bed form of the surge deposits are sand waves shaped in dune forms with vertical form index of 10 20 characterized by stoss side erosion and lee side deposition of 1 10 cm reversely graded laminae a systematic decrease in maximum lithic diameter with distance from source is accompanied by decrease in wavelength and amplitude modal analysis indicates fractionation of glass and pumice from the surge cloud relative to crystals resulting in loss of at least 10 25 of the cloud mass due to winnowing out of fines during surge emplacement greatest fractionation from the 1 0 0 0 grain sizes reflects relatively lower pumice particle density in this range and segregation in the formative stages of the surge cloud extensive pumice rounding indicates abrasion during bed load transport flow of pyroclastic debris in the turbulent surge cloud was by combination of bed load and suspended load transport the surges are viewed as expanding pyroclastic gravity flows which entrain and mix with air during transport the balance between sedimentation at the base of the surge cloud and expansion due to entrainment of air contributed to low cloud density and internal turbulence which persisted to the distal edge of the surge zone

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

analogue study of particle segregation in pyroclastic density currents with implications for the emplacement mechanisms of large ignimbrites analogue flume experiments were conducted to investigate the transport and sedimentation behaviour of turbulent pyroclastic density currents the experimental currents were scaled approximately to the natural environment in three ways 1 they were fully turbulent 2 they had a very wide range of particle sizes and associated rouse numbers the ratio of particle settling velocity to effective turbulent eddy velocity in the current and 3 they contained particles of two different densities two sets of surge type experiments were conducted in a 5 m long water filled lock exchange flume at five different volumetric particle concentrations from 0 6 to 23 in one set one component experiments the currents contained just dense particles in the other set two component experiments they contained both light and dense particles in equal volume proportions in both sets of experiments the population of each component had a log normal size distribution in the two component experiments the size range of the light particle population was selected in order to be in hydrodynamic equivalence with that of the dense particles dense particles were normally graded both vertically and downstream in the deposits from both sets of experiments the mass loading normalized to the initial mass of the suspension and grain size of the dense component in the deposits decreased with distance from the reservoir and were insensitive to initial total particle concentration in the currents on the other hand in the two component experiments the light particles were extremely sensitive to concentration they were deposited in hydrodynamic equivalence with the dense particles from dilute currents but were segregated efficiently at concentrations higher than a few per cent with increasing particle concentration the large light particles were carried progressively further down the flume because of buoyancy effects deposits from the high concentration currents exhibited reverse vertical grading of the large light particles efficient segregation of the light component was observed even if the bulk density of the current was less than that of the light particles in both sets of experiments marked inflexions in the rate of downstream decline in mass loading and maximum grain size of the dense component can be attributed to the presence of two different particle settling regimes in the flow 1 particles with rouse numbers 2 5 which did not respond to the turbulence and settled rapidly and 2 particles with rouse numbers 2 5 which followed the turbulent eddies and settled slowly the results are applied to the transport and sedimentation dynamics of pyroclastic density currents that generate large widespread ignimbrites field data fail to reveal significant departures from aerodynamic equivalence between pumice and lithic clasts in three such ignimbrites the particulate loads of some large ignimbrites are transported principally in turbulent suspensions of low concentration in some ignimbrites the well developed inflexions in curves of maximum lithic ml size vs distance can be attributed to the existence of distinct high and low rouse number particle settling regimes that mark the transition from an overcharged state to one in which the residual particulate load is transported more effectively by turbulence

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

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

synthesizing large scale pyroclastic flows experimental design scaling and first results from pele pyroclastic flow eruption large scale experiment pele is a large scale facility for experimental studies of pyroclastic density currents pdcs it is used to generate high energy currents involving 500 6500 m3 natural volcanic material and air that achieve velocities of 7 30 m s 1 flow thicknesses of 2 4 5 m and runouts of 35 m the experimental pdcs are synthesized by a controlled eruption column collapse of ash lapilli suspensions onto an instrumented channel the first set of experiments are documented here and used to elucidate the main flow regimes that influence pdc dynamic structure four phases are identified 1 mixture acceleration during eruption column collapse 2 column slope impact 3 pdc generation and 4 ash cloud diffusion the currents produced are fully turbulent flows and scale well to natural pdcs including small to large scales of turbulent transport pele is capable of generating short pulsed and sustained currents over periods of several tens of seconds and dilute surge like pdcs through to highly concentrated pyroclastic flow like currents the surge like variants develop a basal 0 05 m thick regime of saltating rolling particles and shifting sand waves capped by a 2 5 4 5 m thick turbulent suspension that grades upward to lower particle concentrations resulting deposits include stratified dunes wavy and planar laminated beds and thin ash cloud fall layers concentrated currents segregate into a dense basal underflow of 0 6 m thickness that remains aerated this is capped by an upper ash cloud surge 1 5 3 m thick with 100 to 10 4 vol particles their deposits include stratified massive normally and reversely graded beds lobate fronts and laterally extensive veneer facies beyond channel margins

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

methods of computation of suspended load from bed materials and flow parameters computation of the grain size distribution of the suspended load above a sand bed must take into consideration 1 sorting processes from the bed to the bed layer and 2 sorting between the bed layer and suspension grain size distributions of the bed layers above sand beds of three different types have been computed in this work both by the einstein and the gessler methods using these as references suspended load distributions have been obtained in each case by the rouse suspension equation a new formula has also been developed in partial modification of hunt s method for direct computation of bed load and suspended load from a bed s grain size distribution and flow parameters comparison of the computed data with actual observations in laboratory flumes show that no one method is particularly superior to the others but the present method is advantageous because it affords direct computation of the suspended load from a bed s grain size distribution without going through an intermediate stage bed load the possible sources of error in each of the methods have been discussed

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

surface wave tomography of eastern and central tibet from two plane wave inversion rayleigh wave and love wave phase velocity mapssurface wave tomography of eastern and central tibet from two plane wave inversion rayleigh wave and love wave phase velocity maps

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

transdimensional bayesian seismic ambient noise tomography across se tibet abstract we analyze seismic ambient noise data recorded at a set of permanent and temporary stations across southeastern tibet to image crustal structure high resolution phase velocity maps are presented based on transdimensional bayesian seismic ambient noise tomography seismic images exhibit more apparent horizontal heterogeneities and show more detailed information compared to previous studies based on traditional ambient noise tomography as noted from the phase velocity image at 25 s the rigid high velocity anomalies beneath the sichuan basin and the south china fold system act as a blockage to crustal material expansion and the distribution of velocity anomalies contributes to the interpretation of a surface clockwise rotation pattern our results imply a more complex distributed low velocity zone rather than two isolated channels beneath se tibet