lithospheric and upper mantle structure of southern tibet from a seismological passive source experiment fifteen seismic stations were operated with about 20 km spacing in southern tibet across the zangbo suture the collision zone between india and asia between may and october 1994 as part of the international deep profiling of tibet and the himalaya project indepth ii for wide angle recording of the controlled source experiment and for passive earthquake recording in addition a dense deployment 4 km spacing of stations within the german depth profiling of tibet and the himalayas gedepth project also recorded a number of teleseismic earthquakes the third data source used in this study is the records of the permanent broadband station at lhasa teleseismic records have been obtained in sufficient quantity and quality to derive an image of the structure of the lithosphere and upper mantle from p to s converted phases important results are as follows the moho at 70 80 km and a second discontinuity at 50 60 km depth are observed over the entire profile south and north of the zangbo suture the data from the gedepth dense array enable the detection of inclined structures penetrating the crust at the zangbo suture a pronounced low velocity zone exists north of the zangbo suture at about 10 20 km depth the locations of the upper mantle discontinuities at 410 and 660 km depth are in agreement with the global reference model iasp91 kennett 1991 over a large region of the himalaya and southern tibet

continental crust composition constrained by measurements of crustal poisson s ratio deciphering the geological evolution of the earth s continental crust requires knowledge of its bulk composition and global variability the main uncertainties are associated with the composition of the lower crust seismic measurements probe the elastic properties of the crust at depth from which composition can be inferred of particular note is poisson s ratio this elastic parameter can be determined uniquely from the ratio of p to s wave seismic velocity and provides a better diagnostic of crustal composition than either p or s wave velocity alone1 previous attempts to measure have been limited by difficulties in obtaining coincident p and s wave data sampling the entire crust2 here we report 76 new estimates of crustal spanning all of the continents except antarctica we find that on average increases with the age of the crust our results strongly support the presence of a mafic lower crust beneath cratons and suggest either a uniformitarian craton formation process involving delamination of the lower crust during continental collisions followed by magmatic underplating or a model in which crust formation processes have changed since the precambrian era

three dimensional prestack plane wave migration of teleseismic p to s converted phases 1 theory 1 we present the theoretical foundations for a prestack migration technique to image teleseismic p to s converted phases the method builds on teleseismic p wave deconvolution pseudostation stacking neal and pavlis 1999 and on the idea of using a plane wave decomposition for imaging as introduced by treitel et al 1982 deconvolution operators are constructed by pseudostation stacking of the array aligned to the incident p wave arrival times to produce a space variable deconvolution operator the resulting data are then muted to remove the deconvolved direct p wave pulse and pseudostation stacked over a grid of feasible slowness vectors the pseudostation stack interpolates the wave field onto a regular grid along earth s surface producing a series one per slowness vector of uniformly sampled three dimensional data cubes two space variables and time the plane wave components can be propagated downward using a form of approximate ray tracing with a three dimensional earth model this yields a series of distorted cubes topologically equivalent to the original uniformly sampled data cubes these data volumes are summed as a weighted stack with the weights derived from an integration formula for inverse scattering based on the generalized radon transform this allows an image of the subsurface to be constructed on an event by event basis beneath the array we apply this technique to data from the lodore array that was deployed in northwestern colorado the results suggest the presence of a major lithospheric scale discontinuity defined by a south dipping boundary

interferometric seismic imaging of crustal structure using scattered teleseismic waves 1 the deployment of a dense seismic array of portable broadband stations has presented a number of imaging opportunities using scattered teleseismic waves interferometric seismic imaging isi of surface related multiple reflections extracted from cross correlations of teleseismic waves among pairs of receiver stations was investigated for possible applications and compared to receiver function rf method synthetic seismograms simulated by the elastic pseudospectral method for a simple 2 d crustal model demonstrate the potential imaging capabilities of isi for the moho structure with high spatial resolution isi has also been applied to teleseismic data from dense array experiments conducted at the northern fossa magna basin in central japan the results indicate that the moho phase with positive polarity at a depth of 38 40 km in the isi profile is consistent with the lower crustal structure estimated by rf imaging

imaging crust and upper mantle seismic structure in the southwestern united states using teleseismic receiver functions rio grande rift seismic transect ristra is designed to image and interpret crust and mantle structures beneath the southwestern united states including the nature of the colorado plateau and rio grande rift figure 1 key questions include the nature of crustal and mantle structures and thermal conditions beneath one of the more dramatic continental rifts on earth and clues to understanding the anomalously unextended colorado plateau which is currently surrounded by the predominantly extensional deformation of the western united states figure 1 regional tectonic map with ristra station locations stars indicate the 54 main transect stations the diamond locates global seismic network borehole station anmo stations tx01 tx06 lie in texas nm07 nm44 in new mexico az45 az50 in arizona and ut51 ut54 in utah the data collecting stage of ristra provided an exceptional 18 months 1999 2001 of broadband streckheisen sts 2 120 s seismometers teleseismic iris passcal data along a 950 km great circle transect of 54 sites with 18 3 6 km station spacing with endpoints near lake powell utah and pecos texas the northwest southeast trending transect was oriented parallel to the azimuth of the very active western pacific seismogenic zones analysis applied to this seismic data set includes surface wave dispersion inversion for crustal and mantle structure teleseismic body wave tomography and teleseismic mantle anisotropy here we discuss the use of ristra data to examine lithospheric structure using p to s mantle and crustal forward scattering observed in the s phases immediately following several tens of seconds the teleseismic p arrival figure 2 we migrate these signals to produce p to s converted mode images of the structure along the ristra array figure 2 global distribution of the 285 earthquakes red points with body wave magnitude 5 6 recorded during the ristra network deployment which have suitable offsets for calculating the 8361 receiver functions used in this study we use teleseisms from epicentral distances of

high resolution receiver function imaging reveals colorado plateau lithospheric architecture and mantle supported topography 1 after maintaining elevations near sea level for over 500 million years the colorado plateau cp has a present average elevation of 2 km we compute new receiver function images from the first dense seismic transect to cross the plateau that reveal a central cp crustal thickness of 42 50 km thinning to 30 35 km at the cp margins isostatic calculations show that only approximately 20 of central cp elevations can be explained by thickened crust alone with the cp edges requiring nearly total mantle compensation we calculate an uplift budget showing that cp buoyancy arises from a combination of crustal thickening heating and alteration of the lithospheric root dynamic support from mantle upwelling and significant buoyant edge effects produced by small scale convecting asthenosphere at its margins

seismic imaging of the crust and upper mantle using regularized joint receiver functions frequency wave number filtering and multimode kirchhoff migration 1 receiver functions provide an indispensable tool for producing discontinuity images of the crust and upper mantle from teleseismic earthquake arrivals however image quality can be significantly compromised by instabilities inherent in the deconvolution process and by irregularities in data coverage driven by source and or receiver geometries we present receiver function estimation and prestack migration techniques which both reduce receiver function deconvolution instability and produce regularized multimode receiver function images the receiver function estimation technique exploits frequency wave number filtering methods using frequency pseudowave number domain filtering of gathers to enhance arrivals with consistent moveout characteristics synthetic tests confirm robust recovery of features in the presence of high noise levels to process regularized receiver functions into accurate images of the subsurface seismic scattering potential we employ a regularized kirchhoff migration that migrates both direct and reverberated p to s converted modes to their correct subsurface locations the subsequent images can be stacked to mute mismigrated modes synthetic studies and model resolution tests demonstrate that this methodology is well suited to irregularly spaced stations and uneven data coverage and does not require the recording of a single earthquake at multiple stations

broadband seismic background noise at temporary seismic stations observed on a regional scale in the southwestern united states background noise power spectral density psd estimates for 54 pass cal colorado plateau rio grande rift great plains seismic transect la ristra stations were computed using data from 1999 to 2000 at long periods 0 01 0 1 hz typical vertical noise levels are approximately 12 db higher than the nearby global seismic network gsn borehole station anmo but horizontal power spec tral density psd noise levels are approximately 30 db higher long period noise levels exhibit essentially no spatial correlation along the la ristra transect indi cating that local thermal or atmosphere driven local slab tilt is the dominant source of noise in this band between 0 1 and 0 3 hz typical noise levels are dominated by naturally occurring microseismic noise and are essentially identical to those observed at anmo at short periods 0 3 8 hz typical noise levels along the network exceed anmo levels by approximately 15 db with the highest levels corresponding to proximity to cultural noise sources no significant day night variations were observed in the microseismic band however both low and high frequency noise levels show an increase of up to 8 db in median midday versus midnight noise levels we find that the major shortcomings of these shallow passcal style temporary vaults rela tive to a gsn style borehole installation are increased susceptibility to long period horizontal 20 sec noise and to surface noise sources above approximately 2 hz although the high frequency near surface noise field is unavoidable in shallow vaults we suggest that increased understanding and mitigation of local tilt effects in shallow vaults offers the possibility of significantly improving the long period noise environment

mantle discontinuity structure beneath the colorado rocky mountains and high plains analysis of mantle discontinuity structure using converted p to s pas phases beneath colorado from the program for array seismic studies of the continental lithosphere passcal rocky mountain front rmf experiment reveals significant topography at the 410 and 660 km depth discontinuities and corresponding transition zone thickness variations a stack of all radial receiver functions resolves the 410 and 660 km discontinuities at average depths of 419 and 677 km respectively imaging of lateral variations in mantle discontinuity structure is accomplished by geographically binning the pds conversion points and then stacking the receiver functions in each bin to form spatial images analogous to common depth point stacking corrections for lateral velocity heterogeneity are calculated using the local s wave tomographic model of lee and grand 1996 and a constant lnvs lnvp scaling of 1 3 this scaling value is determined from the relative scaling between teleseismic p and s wave travel time residuals measured from the rocky mountain front deployment mantle discontinuity images using 150 km square bins show 20 km of 410 km discontinuity topography 30 km of 660 km discontinuity topography and up to 40 km of transition zone thickness variation features of the discontinuity structure include a 20 km depression of the 660 km discontinuity beneath western colorado and a gradual 10 km dip of the 410 km discontinuity beneath the high plains the thickening of the transition zone beneath southwest colorado is consistent with the presence of the subducted farallon slab in this region as imaged by van der lee and nolet 1997 in general our results show that the transition zone discontinuity structure is more complex than that predicted by the simple model of olivine phase boundaries modulated by vertically coherent thermal anomalies

seismic migration processing of p sv converted phases for mantle discontinuity structure beneath the snake river plain western united states we experiment with backprojection migration processing of teleseismic receiver functions from the snake river plain srp broadband seismic experiment previous analyses of data from this experiment have used a common midpoint cmp stacking approach a method widely applied for analysis of p sv converted phases receiver functions to obtain high resolution imaging of upper mantle discontinuities the cmp technique assumes that all p sv conversions are produced by flat lying structures and may not properly image dipping curved or laterally discontinuous interfaces in this paper we adopt a backprojection migration scheme to solve for an array of point scatterers that best produces the large suite of observed receiver functions we first perform synthetic experiments that illustrate the potential improvement of migration processing over cmp stacks application of the migration processing to the srp data set shows most of the major features as in the original cmp work but with a weaker 410 km discontinuity and a more intermittent discontinuity at 250 km apparent depth random resampling tests are also performed to assess the robustness of subtle features in our discontinuity images these tests show that a 20 km elevation of the 660 km discontinuity directly beneath the snake river plain is robust but that the variations in 410 km discontinuity topography that we observe are not stable upon resampling bright spots near 250 km apparent depth are robust upon resampling but interpretation of these features is complicated by possible sidelobe artifacts from topside moho reverberations

array measurements of phases used in receiver function calculations importance of scattering receiver function methods utilize three component teleseismic p coda to determine structure beneath seismographs most methods treat coda complexity as mode conversions and reflections off subhorizontal interfaces beneath the station such as the moho this assumption is evaluated beneath a broadband array in the kopet dagh foothills at geyokcha turkmenistan by applying array processing techniques to p coda waves at frequencies near 1 hz beneath the geyokcha array horizontal components show signals that deviate significantly in slowness and bearing from predictions of a plane layered earth large phases arrive at the same time as the predicted ps conversion from the moho yet systematically come from a single azimuth from nne and travel at phase velocities of 3 to 5 km sec the coda waves appear to be p to s converted waves from a near surface scatterer an inversion for scatterer location is developed and applied to 29 events most coda energy comes from a scatterer 16 km nne of the array this location is coincident with the range bounding faults that separate kopet dagh mountains from adjacent basins thus array analysis shows that signals potentially interpreted as moho conversions are instead scattered from a near surface structure although these results suggest caution is necessary in interpreting single station receiver functions particularly at high frequencies they also demonstrate the power of array sampling in resolving lateral structure variations

extraction of moho generated phases from vertical and radial receiver functions of a seismic array abstract receiver function analysis is an effective tool for investigating crustal seismological structure here we present the extraction of the moho reflected pppp that emerges in teleseismic p coda via a deconvolution process using nonlinear waveform analysis an approach using simulated annealing technique we estimate the source wavelet of a teleseismic p wave from records of the vertical component observed at an array of seismometers pppp recorded on the vertical component can be extracted by deconvolving individual vertical components by the resulting source wavelet by employing this technique in a case study in southwestern japan seismic images from pppp as well as from ps and ppps successfully image the continental moho the oceanic moho and the top surface of the philippine sea slab in addition we found that the amplitude of pppp is useful in precisely determining crustal properties such as vertically averaged v p v s and the crustal thickness by grid search techniques it is also important to take into account the variations of the conversion reflection coefficients for decreasing errors of the parameters in the grid search technique moreover we demonstrate that improved seismic images of horizontal discontinuities can be obtained by using a stacking technique

p and s wave receiver function imaging of subduction with scattering kernels a method for scattered wave imaging in 3d with both teleseismic p and s wave receiver function data is introduced the approach relies on body wave scattering kernels that are derived from the adjoint data sensitivity kernels which are typically used for full waveform tomography the forward problem is approximated using ray theory yielding a computationally efficient imaging algorithm that can resolve dipping and discontinuous interfaces using both p and s wave receiver functions travel time fields for the incident teleseismic arrivals and the receiver point sources are obtained by solving the eikonal equation using a fast marching code which can handle a 3d reference velocity model an energy stable finite difference method is used to simulate elastic wave propagation in a 2d hypothetical subduction zone model the resulting synthetic p and s wave receiver function datasets are used to validate the imaging method the kernel images are compared with those generated by the generalized radon transform and common conversion point stacking methods these results demonstrate the potential of the kernel imaging approach for constraining lithospheric structure in complex geologic environments with sufficiently dense recordings of teleseismic data potential imaging targets include short wavelength compositional variations in the mantle wedge and the slab s lithosphere asthenosphere boundary

high resolution 3 d crustal structure beneath ne china from joint inversion of ambient noise and receiver functions using necessarray data abstract we used ambient noise data recorded by the necessarray a portable seismic array deployed in northeast china to construct rayleigh wave phase velocity dispersion curves and obtain phase velocity maps for periods from 6 to 40 s s wave velocity structure beneath ne china is obtained by joint inversion of the phase velocities and receiver functions our results show good correlation between crustal velocity structure and geological features at shallow depths the songliao basin is separated into two small sub basins by a fast velocity anomaly corresponding to a southwest uplifted horst and the southern sub basin is associated with the kailu depression a low velocity anomaly extending from the lower crust to uppermost mantle beneath the changbaishan mountain range is consistent with p and s wave tomography models the mantle low velocity has been interpreted as a local mantle upwelling attributed to the subducting pacific slab induced return flow finally the s wave velocity in the mid and lower crust is lower beneath the xing an mongolia orogenic belt xmob than beneath the changbaishan mountain range this was not expected since the changbaishan mountain range has experienced more extensive volcanic activity in the cenozoic including the currently active changbaishan and jingpohu volcanoes than the xmob we infer that the mid and lower crust of the xmob is mainly felsic in composition and propose that the low shear wave velocity of the mid and lower crust beneath the xmob could be the consequence of removal of deep mafic crust through a continental accretion and subsequent delamination event in the paleozoic or via convection removal induced by the rollback of the flat subducted paleo pacific slab during the middle mesozoic

crustal structure of the eastern qinling orogenic belt and implication for reactivation since the cretaceous a high resolution crustal model of the eastern qinling belt and central north china craton central ncc is obtained along a n s trending profile corridor by joint inversion of surface wave and receiver function the ncc is one of the oldest cratons on earth and the qinling belt is the suture zone between the ncc and south china block scb the qinling belt is characterized by low crustal velocity 1 8 the forward gravity modeling supports the presence of a high density layer 3 05 g cm3 at the base of the crust beneath the central ncc we propose that the high velocity in the lowermost crust beneath the central ncc is most likely due to the repeated mafic underplating which also results in high crustal vp vs ratio and is responsible for the rapid crustal uplift during the late mesozoic

seismic waves converted from velocity gradient anomalies in the earth s upper mantle summary modelling of elastic wave propagation in 1 d structures is frequently performed using reflectivity techniques in which the earth s velocity profile is approximated by stacks of homogeneous layers the complete reflection transmission r t response of a zone with arbitrary 1 d depth variation including both gradients and discontinuities in material properties can however be calculated using invariant embedding techniques results from earlier studies are here extended to derive exact expressions for r t matrices in arbitrary 1 d anisotropic media using a form of born approxi mation valid for thin scatterers and which does not assume small perturbations in material properties the r t matrices are solutions to a system of non linear ordinary differential equations of ricatti type and may be manipulated using standard r t matrix algebra in an equivalent description the wavefield within the heterogeneous zone is considered in terms of depth dependent contributions from up and downgoing waves propagating within the embedding reference medium this leads to efficient calculation of the internal wavefield using r t matrices of the heterogeneous stratification and portions thereof at minor additional expense mode conversion of teleseismic p and s phases from velocity gradients is examined by way of examples and comparison with three component data from broad band stations of the yellowknife seismic array the frequency dependence of such wave interactions depends on the differences in vertical slowness between incident and scattered modes it is shown that significant energy is converted from transition zones with extent l p 2 a broader interval than will generally produce intramode reflections a layer structure identified from ps conversions near 75 km depth below the slave craton is shown to be compatible with a 10 km thick gradient zone in which anisotropy increases from ambient levels to vp 5 per cent vs 2 5 per cent at a discontinuous upper boundary this characterization supports a previous interpretation as the upper strata of a former oceanic plate juxtaposed against overriding lithosphere during an ancient episode of shallow subduction

rocky mountain evolution tying continental dynamics of the rocky mountains and deep probe seismic experiments with receiver functions 1 in this study we have determined the crustal structure using three different receiver function methods using data collected from the northern transect of the continental dynamics of the rocky mountains cd rom experiment the resulting migrated image and crustal thickness determinations confirm and refine prior crustal thickness measurements based on the cd rom and deep probe experiment data sets the new results show a very distinct and thick lower crustal layer beneath the archean wyoming province in addition we are able to show its termination at 42n latitude which provides a seismic tie between the cd rom and deep probe seismic experiments and thus completes a continuous north south transect extending from new mexico into alberta canada this new tie is particularly important because it occurs close to a major tectonic boundary the cheyenne belt between an archean craton and a proterozoic terrane we used two different stacking techniques based on a similar concept but using two different ways to estimate uncertainties furthermore we used receiver function migration and common conversion point ccp stacking techniques the combined interpretation of all our results shows 1 crustal thinning in southern wyoming 2 strong northward crustal thickening beginning in central wyoming 3 the presence of an unusually thick and high velocity lower crust beneath the wyoming province and 4 the abrupt termination of this lower crustal layer north of the cheyenne belt at 42n latitude

a survey of seismic activity near wairakei geothermal field new zealand a five week survey showed that seismic activity within 20 km of wairakei geothermal field took place mainly at shallow depths 2 km in or close to the taupo fault belt and occurred in swarms twenty eight earthquakes with magnitudes m between 1 3 and 2 8 were located 43 other earthquakes with m 0 2 were recorded but could not be located the distribution of located earthquakes did not correlate with known areas of surface geothermal activity no located earthquake occurred beneath the main production borefield or an area of ground subsidence adjacent to the borefield a value for b of 0 7 0 2 was obtained for events with 0 8 m 1 25 within 6 5 km of the borefield no earthquakes were sufficiently clearly recorded to demonstrate attenuation of s phases within the borefield area seismic activity in and near the field is similar to that reported in neighbouring parts of the region operation of the field therefore does not appear to have caused any large increase or decrease of seismic activity in the taupo fault belt within or near the field

geological and hydrogeological environment in shanghai with geohazards to construction and maintenance of infrastructures shanghai administrative region sar is located on the deltaic deposit of the yangtze river the bed rock under sar is generally buried in the depth of 200 m to 300 m except for several massifs where the bed rock is exposed to the ground surface the quaternary deposit in shanghai is soft sediment the variation of palaeoclimate influenced the sea level and resulted in a very complicated sedimentary environment the quaternary deposit in sar is composed of an alternated multi aquifer aquitard system maas the groundwater system is composed of one artesian aquifer and five confined aquifer layers with very high groundwater pressure head the maas was formed mainly within the warm geological era updated to 2 6 million years ago between two aquifers there is an aquitard which is composed of soft clayey soil formed mainly within the cold era the aquitards are composed of very soft clayey silt with very high compressibility and humus content the humus material was transformed into methane gas under a long term geological process with the development of economy the infrastructures were or are being constructed in the top shallow soft clayey deposit aquifer i and aquifer ii in sar the following geohazards occurred or possibly occur during the construction and maintenance of infrastructures i quicksand and piping hazards ii pumping induced hazards and recharge cutoff hazards iii long term settlement due to the seasonal fluctuation of groundwater level and iv geohazards of methane gas

receiver function arrays a reflection seismic approach summary the receiver function method rfm is a commonly used technique to study the crustal and upper mantle velocity structure early receiver function rf investigations were performed mostly at individual permanent stations they were focused on crustal structures and later on upper mantle velocity discontinuities 410 km and 660 km discontinuities only recently has research been directed towards the study of the lateral 2 and 3 d variability of major velocity boundaries in the crust and upper mantle by receiver function arrays using temporary and permanent three component short period and broad band seismic stations to improve the signal to noise ratio receiver functions are calculated for individual earthquakes and are then binned moveout corrected and stacked we show that this processing sequence is similar to that applied routinely in exploration seismology therefore existing tools from the near vertical data processing can be adopted for receiver functions velocity analysis tools solutions for static and residual static problems coherence enhancement of seismic phases migration etc the high spatial density of seismic stations of recent and future receiver function experiments provides the opportunity and obligation to use the more sophisticated migration methods full wavefield migration commonly and successfully used in exploration seismics parasynthetics calculated by the finite difference method for simple 2 d crustal models are employed here to test our processing approach and to show the potentials and limitations of stacking and migrating rf data we show that binning normal move out nmo corrections stacking and post stack migration of the synthetic data can reconstruct the models reliably with a high spatial resolution

3 d structure of the rio grande rift from 1 d constrained joint inversion of receiver functions and surface wave dispersion the southern terminus of the rio grande rift region has been poorly defined in the geologic record with few seismic studies that provide information on the deeper rift structure in consequence important questions related to tectonic and lithospheric activity of the rio grande rift remain unresolved to address some of these geological questions we collect and analyze seismic data from 147 earthscope transportable array usarray and other seismic stations in the region to develop a 3 d crust and upper mantle velocity model we apply a constrained optimization approach for joint inversion of surface wave and receiver functions using seismic s wave velocities as a model parameter in particular we compute receiver functions stacks based on ray parameter and invert them jointly with collected surface wave group velocity dispersion observations the inversions estimate 1 d seismic s wave velocity profiles to 300 km depth which are then interpolated to a 3 d velocity model using a bayesian kriging scheme our 3 d models show a thin lower velocity crust anomaly along the southeastern rio grande rift a persistent low velocity anomaly underneath the colorado plateau and basin and range province and another one at depth beneath the jemez lineament and the southern rgr

geophysical constraints on the crustal structure of the southern rio grande rift abstract evidence of geologic activity still occurring in the rio grande rift rgr includes quaternary faulting seismicity and widening at a small rate we map the crustal thickness and seismic velocity ratio to generate constrained crustal model cross sections that highlight the regional extension of the southern rgr srgr specifically we computed receiver functions and receiver function stacks for 147 stations from earthscope usarray transportable array and previously collected data in the southwestern united states and interpolated the crustal and velocity results using a kriging interpolation scheme we include a new optimized gravity inversion approach using the receiver function results as a constraint for inverted density profiles we produce constrained crustal models that characterize the srgr as showing a shallower moho 30 km in the region of the srgr which is thicker than previously suggested the crust appears to be delaminated west of the rgr in the basin and range province and thicker east of the rgr toward the great plains with a denser lower crustal layer we also find that the delaware basin shows a significant geophysical anomaly likely due to thick saturated sediments given that there is no deep mantle anomaly determined from other studies in this region we suggest that rifting could be the result of small scale convection of the uppermost mantle and we conclude that the rgr is at a minimum the boundary between the basin and range province and the great plains perhaps reflecting the terminus of flat slab subduction

kirchhoff modeling inversion for reflectivity and subsurface illumination because of its computational efficiency prestack kirchhoff depth migration is currently one of the most popular algorithms used in 2 d and 3 d subsurface depth imaging nevertheless kirchhoff algorithms in their typical implementation produce less than ideal results in complex terranes where multipathing from the surface to a given image point may occur and beneath fast carbonates salt or volcanics through which ray theoretical energy cannot penetrate to illuminate underlying slower velocity sediments to evaluate the likely effectiveness of a proposed seismic acquisition program we could perform a forward modeling study but this can be expensive we show how kirchhoff modeling can be defined as the mathematical transpose of kirchhoff migration the resulting kirchhoff modeling algorithm has the same low computational cost as kirchhoff migration and unlike expensive full acoustic or elastic wave equation methods only models the events that kirchhoff migration can image kirchhoff modeling is also

crustal structures across the western weihe graben north china implications for extrusion tectonics at the northeast margin of tibetan plateau the stable ordos plateau extensional weihe graben and qinling orogenic belt are located at the northeast margin of the tibetan plateau they have been thought to play different roles in the eastward expanding of the tibetan plateau peking university deployed a linear seismic array across the western end of the weihe graben to investigate the crustal structures of the tectonic provinces of this structure receiver function analyses revealed low to moderate poisson s ratios and anticorrelations between poisson s ratios and topography beneath the qinling orogen these features may indicate a tectonic thickening of the felsic upper crust by folding and thrusting within the qinling orogen we observed a strong horizontal negative signal at the midcrust beneath the ordos plateau which may indicate a low velocity zone this observation would suggest the stable cratonic ordos plateau had been modified due to the compression between the tibetan plateau and the ordos plateau we also observed an abrupt 4 km moho offset across the weihe fault changing from 44 km beneath the ordos plateau to 40 km beneath the qinling orogen we conclude that the weihe fault is a lithosphere scale fault shear zone which extends into the upper mantle beneath the weihe graben it acts as the major boundary separating the stable ordos plateau and the active qinling orogen

thick crust beneath the ordos plateau implications for instability of the north china craton abstract surrounded by seismicity and other manifestations of active deformation the ordos plateau or the western portion of the north china craton ncc is a uniquely stable terrane in asia results from virtual deep seismic sounding and crustal receiver functions suggests that the crust under the eastern ordos is thicker at least 60 km than expected from previous studies and from its modest elevation 1500 m above sea level receiver functions also reveal a pronounced elastic impedance contrast within the crust at 40 km depth which we interpret as the conrad discontinuity the presence of a 20 km thick layer of mafic lower crust between the conrad and moho discontinuities would maintain crustal isostasy the 1000 km long seismic profile from the ordos plateau in the west to the north china basin in the east reveals that crustal thickness changes by almost a factor of two across the active shanxi rift in central ncc over a distance of only about 100 km insofar the current configuration of the lithosphere under the ordos plateau might serve as a proxy for the initial condition prior to reactivation of the eastern part of ncc where a cratonic keel no longer seems to exist our results support the hypothesis that lower crust foundering was due to transformation of a thick mafic lower crust to a garnet rich assemblage possibly caused by hydration associated with subduction during and or before mid mesozoic times

least squares migration of incomplete reflection data a least squares migration algorithm is presented that reduces the migration artifacts i e recording footprint noise arising from incomplete data instead of migrating data with the adjoint of the forward modeling operator the normal equations are inverted by using a preconditioned linear conjugate gradient scheme that employs regularization the modeling operator is constructed from an asymptotic acoustic integral equation and its adjoint is the kirchhoff migration operator we tested the performance of the least squares migration on synthetic and field data in the cases of limited recording aperture coarse sampling and acquisition gaps in the data numerical results show that the least squares migrated sections are typically more focused than are the corresponding kirchhoff migrated sections and their reflectivity frequency distributions are closer to those of the true model frequency distribution regularization helps attenuate migration artifacts and provides a sharper better frequency distribution of estimated reflectivity the least squares migrated sections can be used to predict the missing data traces and interpolate and extrapolate them according to the governing modeling equations several field data examples are presented a ground penetrating radar data example demonstrates the suppression of the recording footprint noise due to a limited aperture a large gap and an undersampled receiver line in addition better fault resolution was achieved after applying least squares migration to a poststack marine data set and a reverse vertical seismic profiling example shows that the recording footprint noise due to a coarse receiver interval can be suppressed by least squares migration

multimode 3 d kirchhoff migration of receiver functions at continental scale in geology and in particular in geophysics direct and indirect observations of processes occurring both at the surface of the earth and at depth are used to understand the structure and dynamics of the earth for instance seismic waves generated by large earthquakes can be used to study the structure of heterogeneities in the first few hundred kilometers inside the earth in this work we use the scattered wavefield which corresponds to energy arriving after the incident wavefield to image the earth by nature the scattered waves are linked to the scattering heterogeneities encountered along their propagation path i e the fine scale structure of the earth hence the scattered wavefield has the ability to highlight structures where rapid velocity variations would otherwise be smoothed out by tomographic regularization such as the structure of subducting slabs to extract the information from the scattered wavefield we resort to receiver function rf analysis and pre stack depth migration standard migration procedures either rely on the assumption that underlying discontinuities are horizontal such as in common conversion point stacking ccp or are computationally expensive and usually limited to 2d geometries such as in reverse time migration rtm or generalized radon transform grt here we develop a kirchhoff type teleseismic imaging method that uses fast 3d travel time calculations with minimal assumptions about the underlying structure this provides high computational efficiency without limiting the problem to 1d or 2d geometries in our method we apply elastic kirchhoff migration to transmitted and reflected teleseismic waves i e rf the approach expands on the work of cheng et al 2016 the 3d elastic kirchhoff migration is adapted to the passive seismology scattering geometry and to account for free surface multiples we use an eikonal solver based on the fast marching method fmm to compute travel times for all scattered phases 3d scattering patterns are computed to correct the amplitudes and polarities of the three component input signals we consider three different stacking methods linear phase weighted and 2 nd root to enhance the structures that are most coherent across scattering modes to showcase the efficiency and accuracy of our migration procedure we test it by conducting a series of synthetic tests in both artificially challenging and realistic scenarios results from synthetic tests show that our imaging principle can recover scattering structures accurately with minimal artifacts we show that integrating the three components of the rf into the imaging principle allows to coherently retrieve the scattering potential for arbitrarily dipping discontinuities from all back azimuths and are able to retrieve a typical 2 5d subduction zone structure we apply this novel 3d multi mode kirchhoff migration method to two different subduction zones in western greece and southern alaska

usarray design implications for wavefield imaging in the lithosphere and upper mantle although seismic tomography is currently the mainstay of global seismic imaging the large scale deployment of portable instruments to be conducted as the usarray component of earthscope over the next decade will allow much higher resolution imaging of the solid earth using migration inversion methods similar to those used in petroleum exploration direct wavefield imaging in solid earth structural seismology has been uncommon in comparison to practices in exploration seismology generally due to the large separation between seismic stations with the development of portable observatory quality broadband 0 01 20 hz seismographs and acquisition of modest numbers of them for the passcal instrument pool over the past decade a number of academic field programs have had receiver spacing dense enough for wavefield back projection and imaging recordings from these experiments have been used in several different imaging schemes all of which are outgrowths of and bear resemblance to either post or prestack d