seismic tomography a window into deep earth abstract the goal of this paper is to provide an overview of the current state of the art in seismic tomography and trace its origins from pioneering work in the early 1970s to its present status as the pre eminent tool for imaging the earth s interior at a variety of scales due to length limitations we cannot hope to cover every aspect of this diverse topic or include mathematical derivations of the underlying principles rather we will provide a largely descriptive coverage of the methodology that is targeted at readers not intimately familiar with the topic the relative merits of local versus global parameterization ray tracing versus wavefront tracking backprojection versus gradient based inversion and synthetic testing versus model covariance are explored a variety of key application areas are also discussed including body wave traveltime tomography surface wave tomography attenuation tomography and ambient noise tomography established and emerging trends many of which are driven by the ongoing rapid increases in available computing power will also be examined including finite frequency tomography full waveform tomography and joint tomography using multiple datasets several practical applications of seismic tomography including body wave traveltime attenuation and surface waveform are presented in order to reinforce prior discussion of theory

global upper mantle structure from finite frequency surface wave tomography 1 we report global shear wave velocity structure and radial anisotropy in the upper mantle obtained using finite frequency surface wave tomography based upon complete three dimensional born sensitivity kernels because wavefront healing effects are properly taken into account finite frequency surface wave tomography improves the resolution of small scale mantle heterogeneities especially for deep anomalies that are constrained by the longest period surface waves in our finite frequency model ffsw1 the globally averaged radial anisotropy shows a transition from positive sh sv to negative anisotropy sv sh at about 220 km consistent with a change in the dominant mantle circulation pattern from predominantly horizontal flow at shallow depths to vertical flow at greater depths the radial anisotropy beneath cratons and the old pacific plate agrees well with previous studies however our model exhibits a strong negative radial anisotropy at depths greater than 120 km beneath mid ocean ridges a feature that is not present in previous upper mantle models more interestingly the depth extent of the ridge anomalies is distinctly different beneath fast and slow spreading centers anomalies beneath fast spreading centers are stronger but the strength decreases rapidly below 250 km in contrast beneath slow spreading centers such as the northern mid atlantic ridge and the red sea anomalies extend down at least to the top of the transition zone the different depth extent of the ridge anomalies suggests that the primary driving force of slow spreading seafloor may be different from that of fast spreading seafloor and that active upwelling beneath slow spreading ridges may play a major role in the opening of the seafloor

field determination of the three dimensional hydraulic conductivity tensor of anisotropic media 2 methodology and application to fractured rocks the analytical solutions developed in the first paper can be used to interpret the results of cross hole tests conducted in anisotropic porous or fractured media in the particular case where the injection and monitoring intervals are short relative to the distance between them the test results can be analyzed graphically from the transient variation of hydraulic head in a given monitoring interval one can determine the directional hydraulic diffusivity kd e ss and the quantity d ss by curve matching here kd e is directional hydraulic conductivity parallel to the unit vector e pointing from the injection to the monitoring interval ss is specific storage and d is the determinant of the hydraulic conductivity tensor k the principal values and directions of k together with ss can then be evaluated by fitting an ellipsoid to the square roots of the directional diffusivities ideally six directional measurements are required in practice a larger number of measurements is often necessary to enable fitting an ellipsoid to the data by least squares if the computed kd e ss values fluctuate so severely that a meaningful least squares fit is not possible one has a direct indication that the subsurface does not behave as a uniform anisotropic medium on the scale of the test test results from a granitic rock near oracle in southern arizona are presented to illustrate how the method works for fractured rocks at the site the oracle granite is shown to respond as a near uniform anisotropic medium the hydraulic conductivity of which is strongly controlled by the orientations of major fracture sets the cross hole test results are shown to be consistent with the results of more than 100 single hole packer tests conducted at the site

waveform inversions and the significance of surface wave mode coupling summary if body wave phases in laterally heterogeneous media are modelled by surface wave mode summation mode coupling is required to bring out the ray character of the body wave phases however it is frequently assumed that in laterally heterogeneous media surface wave modes propagate without interacting with other modes the effects of neglecting surface wave mode coupling on the results from waveform inversions including body wave arrivals have been studied by performing inversions with and without taking surface wave mode coupling into account the two inversion schemes are similar to the partitioned waveform inversion nolet 1990 but differ in the approximations used to compute the synthetics wkbj which neglects mode coupling or sea marquering snieder 1995 which does take mode coupling into account synthetic inversion experiments show that neglecting mode coupling can lead to biases in the deeper part of the model their most striking feature is that for real shallow lateral heterogeneities artificial anomalies with an opposite sign may show up in the deeper part of the model when mode coupling is taken into account as in the sea inversion scheme these biases do not occur we have also studied possible bias effects as the result of using wkbj in the eur s91 model of zielhuis nolet 1994 which is characterized by strong velocity anomalies extending as deep as the transition zone one of the most striking features in this model is the region of low velocities at larger depths beneath the fast russian platform on the eastern side of the tornquist teisseyre zone ttz nolet zielhuis 1994 suggested that these low velocities are an indication for injection of water in the mantle by an earlier subduction our results show that the neglect of mode coupling indeed does bias the model towards a larger reversal of velocities with depth and heterogeneities show up even where the s ray does not sample the mantle however low velocities deep below the eastern part of the ttz persist even when mode coupling is taken into account

global adjoint tomography first generation model we present the first generation global tomographic model constructed based on adjoint tomography an iterative full waveform inversion technique synthetic seismograms were calculated using gpu accelerated spectral element simulations of global seismic wave propagation accommodating effects due to 3d anelastic crust mantle structure topography bathymetry the ocean load ellipticity rotation and self gravitation frechet derivatives were calculated in 3d anelastic models based on an adjoint state method the simulations were performed on the cray xk7 named titan a computer with 18 688 gpu accelerators housed at oak ridge national laboratory the transversely isotropic global model is the result of 15 tomographic iterations which systematically reduced differences between observed and simulated three component seismograms our starting model combined 3d mantle model s362ani kustowski et al 2008 with 3d crustal model crust2 0 bassin et al 2000 we simultaneously inverted for structure in the crust and mantle thereby eliminating the need for widely used crustal corrections we used data from 253 earthquakes in the magnitude range 5 8 mw 7 0 for the first 12 iterations we combined 30 s body wave data with 60 s surface wave data the shortest period of the surface waves was gradually decreased and in the last three iterations we combined 17 s body waves with 45 s surface waves we started using 180 min long seismograms after the 12th iteration and assimilated minor and major arc body and surface waves the 15th iteration model features enhancements of well known slabs an enhanced image of the samoa tahiti plume as well as various other plumes and hotspots such as caroline galapagos yellowstone and erebus furthermore we see clear improvements in slab resolution along the hellenic and japan arcs as well as subduction along the east of scotia plate which does not exist in the starting model point spread function tests demonstrate that we are approaching the resolution of continental scale studies in some areas for example underneath yellowstone this is a consequence of our multi scale smoothing strategy in which we define our smoothing operator as a function of the approximate hessian kernel thereby smoothing gradients less wherever we have good ray coverage such as underneath north america

a dual porosity model for water level response to atmospheric loading in wells tapping fractured rock aquifers a fractured rock aquifer may be viewed as a permeable fracture network embedded within a less permeable porous matrix this permeability contrast gives rise to distinct pressure fields in the pore space and fractures and therefore to a response to atmospheric loading different from that of nonfractured porous media assuming that fracture sizes and orientations are uncorrelated and sufficiently random to ensure homogeneous and isotropic elastic behavior of the rock mass at the continuum scale an effective stress model proposed by tuncay and corapcioglu 1995 is used to develop a linear elastic stress strain relationship for dual porosity media elastic constants of the fractured rock mass required by the model are estimated using theoretical relations derived by budiansky and o connell 1976 the stress strain relationship and the coupled continuity equations for flow in deformable fractured media are combined to derive expressions for the undrained static confined barometric efficiency of a dual porosity medium two limiting cases are considered the initial instantaneous pressure response in the pore space and fractures due to a change of confining stress and the later stage of pressure equilibrium between the two phases the dual porosity response model developed here may be used to characterize hydraulic properties in fractured aquifers including low porosity and low permeability media the model is evaluated on water level hydrograph data from a borehole tapping fractured volcanic rocks water level and barometric data are supplemented by independent measurements of matrix porosities fracture spacing and rock elastic properties allowing an assessment of total porosity and specific storage at the site for the observed static confined barometric efficiency of 0 78 the instantaneous pressure response model yields plausible values for both parameters

anisotropic rayleigh wave phase velocity maps of the sunda plate abstract we explore the rayleigh wave phase velocity and shear velocity structures beneath sunda plate over a broad period range of 30 150 s and 5 100 km the two stations technique was used to measure dispersion curves from the waveforms of 19 233 teleseismic events 1998 2018 recorded worldwide by 75 broadband seismic stations spread around the sunda plate the interstation path specific dispersion curves are then inverted for high resolution isotropic and azimuthally anisotropic phase velocity maps in the frequency range 30 150 s as well as for shear velocity model between 5 and 100 km main findings include a strong dichotomy with fast velocities located beneath the south china sea and the sunda shelf compared with slow velocities found beneath the surrounding regions at short periods our model also exhibits very slow velocities beneath the hainan plume at lithospheric and asthenospheric depths the complex anisotropy in the region at shorter periods contrasts with the pattern observed at longer periods sampling the asthenosphere and is consistent with the absolute plate motions in the region

teleseismic p wave tomography and mantle dynamics beneath eastern tibet we determined a new 3 d p wave velocity model of the upper mantle beneath eastern tibet using 112 613 high quality arrival time data collected from teleseismic seismograms recorded by a new portable seismic array in yunnan and permanent networks in southwestern china our results provide new insights into the mantle structure and dynamics of eastern tibet high velocity high v anomalies are revealed down to 200 km depth under the sichuan basin and the ordos and alashan blocks low velocity low v anomalies are imaged in the upper mantle under the kunlun qilian and qinling fold zones and the songpan ganzi qiangtang lhasa and chuan dian diamond blocks suggesting that eastward moving low v materials are extruded to eastern china after the obstruction by the sichuan basin and the ordos and alashan blocks furthermore the extent and thickness of these low v anomalies are correlated with the surface topography suggesting that the uplift of eastern tibet could be partially related to these low v materials having a higher temperature and strong positive buoyancy in the mantle transition zone mtz broad high v anomalies are visible from the burma arc northward to the kunlun fault and eastward to the xiaojiang fault and they are connected upward with the wadati benioff seismic zone these results suggest that the subducted indian slab has traveled horizontally for a long distance after it descended into the mtz and return corner flow and deep slab dehydration have contributed to forming the low v anomalies in the big mantle wedge our results shed new light on the dynamics of the eastern tibetan plateau

seismic wavespeed images across the iapetus and tornquist suture zones 1 closures of the iapetus ocean and the tornquist sea lead to the collision of the paleocontinents of laurentia baltica and eastern avalonia during the caledonian orogeny it has been speculated that relicts of these two closures may be preserved within the crust or upper mantle over the past decades numerous wide angle seismic profiles were gathered in northwestern europe to search for related subsurface features although active source studies revealed detailed crustal structures across the iapetus and tornquist suture zones there are relatively few clear three dimensional upper mantle images beneath this region we use a new european crust and upper mantle model eu30 determined based on continental scale nonlinear adjoint tomography to explore upper mantle structures across these two suture zones model eu30 reveals two fast anomalies within the upper mantle one dips in a northwesterly direction down to approximately 400 km beneath the north sea and the other dips in a southwesterly direction down to nearly 250 km across the tornquist suture zone in addition we observe a gap between the lithospheres of laurentia and eastern avalonia across the iapetus suture zone beneath the central british isles these seismic images suggest that heterogeneity related to the closures of the iapetus ocean and the tornquist sea have been preserved within the upper mantle over hundreds of millions of years

determination of aquifer transmissivity from earth tide analysis the water level in an open well tapping an artesian aquifer responds to pressure head disturbance caused by earth tide dilatation of the aquifer because a finite amount of time is needed for water to flow into and out of the well there exists a phase shift or time lag between the tidal dilatation of the aquifer and the water level response in the well we derive an analytical solution that expresses the phase shift as a function of the aquifer transmissivity storage coefficient well radius and the period of the harmonic disturbance this solution is rather insensitive to the storage coefficient thus if the phase shift is known for a harmonic disturbance the transmissivity can be calculated given a rough estimate of the storage coefficient theoretical analysis shows that a significant phase shift may be present even if the disturbance is slowly varying as in the case of earth tides this opens the possibility of estimating aquifer transmissivity from water level records that show earth tide fluctuations a case study using data from a site near parkfield california is presented to illustrate application of the theory phase shifts of the o1 25 82 hour period and m2 12 42 hour period tidal constituents are chosen for analysis because they are free of systematic contamination by fluctuations in barometric pressure a brief error analysis suggests that the computed o1 phase shift is subject to large uncertainty while the computed m2 phase shift is substantially more accurate based on an assumed storage coefficient range of 10 4 to 10 6 the estimated transmissivity range is 8 10 6 to 2 10 5 m2 s while hydraulic tests have not been performed to validate these estimates the range is consistent with the transmissivity value determined by other investigators from analysis of the water level response to an earthquake

surface wave tomography of the gulf of california 1 we measured interstation fundamental mode rayleigh wave phase velocities using data from the nars baja seismic network located around the gulf of california a region average shear velocity model and a set of azimuthally anisotropic phase velocity maps are obtained from these data the average shear velocity structure shows a strong low velocity zone underlying a thin lid and the data are suggestive of low velocities down into the transition zone the phase velocity maps display signatures of sedimentary layers crustal thickness variations upwelling under the plate boundary and the presence of the subducted farallon microplate remnants beneath the gulf the upper mantle features inferred from this study provide new seismic evidence on the tectonic evolution of the region

complex deformation in the caucasus region revealed by ambient noise seismic tomography abstract cross correlation of 3years of ambient seismic noise recorded at 35 seismic stations deployed in caucasus region yields hundreds of short period surface wave phase speed dispersion curves on inter station paths we inverted these measurements using two techniques to construct tomographic images of the principal geological units of caucasus high resolution isotropic and azimuthally anisotropic phase velocity maps at periods between 5 and 20s and shear velocity tomographic maps between 5 and 30km are generated the resulting maps show a velocity dichotomy between the caucasus region and the surrounding that is interpreted in term of changes in crustal thickness there is also a strong dichotomy in the anisotropic pattern between the eastern part and the western part of the caucasus this difference in both amplitudes and directions of the 2 anisotropy is linked to the tectonic regime changes in the region these observations suggest a good correlation between the tomographic models and the geology of the region it was also possible to identify the early stage of the indentation of the arabian plate into the eurasian plate as well as to detect the possible magma chamber responsible for the javakheti highland

a multidisciplinary fractured rock characterization study at raymond field site raymond ca abstract a dedicated field site was developed and a suite of experiments were conducted in the sierra nevada foothills near the town of raymond ca to develop and test a multi disciplinary approach to the characterization of groundwater flow and transport in fractured rocks a wealth of geologic hydrologic and geophysical data was collected at the site using a variety of unique tools a cluster of nine approximately 90 m deep boreholes were drilled at the site in a v shaped pattern with an angle of 60 the boreholes are spaced 7 5 15 30 and 60 m from the central borehole various geophysical and hydrologic tests were conducted in and between these boreholes integration of cross hole radar and seismic tomography borehole flow surveys and images from a new digital borehole scanner indicated that groundwater flow is mainly confined to a few sub horizontal fracture zones a unique suite of hydraulic tests were conducted in which three to four intervals in each of the nine boreholes were isolated using pneumatic packers some 130 injection tests were conducted and more than 4100 cross hole transient pressure measurements were obtained a computer algorithm was developed to analyze such massive interference data systematically as a result of the analysis an image of the fracture connections emerged which is consistent with the geophysical data high precision tiltmeters were effective in remotely characterizing the preferential flow path several radial convergent tracer tests were conducted by injecting a mixture of several conservative tracers and one sorbing tracer deuterium fluorescein lithium bromide and polystyrene micro spheres some differences between the breakthrough curves are observed which may be due to possible differences among so called conservative tracers some characterization tools were found to be more effective than others in locating flowing fractures however no single tool was almighty characterization of fractured rock is extremely challenging and requires a stepwise and well thought approach which is basically a good old scientific approach prediction of transport based on the characterization results is even more challenging and one should always bear in mind that it is virtually impossible to uniquely characterize a fractured rock

correlation between the shear speed structure and thickness of the mantle transition zone the 410 and 660 km seismic discontinuities that bound the mantle transition zone tz are attributed to phase transformations in olivine structure this implies that variations in tz thickness htz should correlate with those in tz temperature pertinent seismic evidence has so far been ambiguous however we measure converted wave p ds differential times tdiff tp 660s tp 410s in se asia and australia and compare them with s velocity tz estimates from regional tomographic models both tdiff and tz vary on a scale of a few hundred kilometers inferred variations in htz are up to 30 km over length scales larger than 500 km implying 200 k thermal heterogeneity if the effect of composition can be neglected tdiff and tz correlate strongly the linear dependence of htz on the average temperature within the tz is consistent with olivine clapeyron slopes we also show that this relationship holds on a global scale as well provided that the scalelengths and uncertainties of the variations in tdiff and tz are taken into account these results confirm that the transformations in olivine structure give rise to the 410 and 660 km discontinuities globally 2003 elsevier science b v all rights reserved

the response of water level in a well to a time series of atmospheric loading under confined conditions the water level in a well that penetrates a confined aquifer can fluctuate in response to changes in atmospheric pressure the response varies with the well casing and screen dimensions the transmissivity and compressibility of the aquifer and to a small extent its storativity recently this loading response problem has been solved in terms of a frequency response function that characterizes how attenuation and phase shifts in the response signal vary with frequency the counterpart of this solution in the time domain is an impulse response function this solution has the immediate appeal that it can be used directly to filter raw loading and water level records via serial convolution where the response at any time is a weighted aggregate of the previous loading signal the impulse response function derives from well known solutions to the slug test problem when based on the cooper bredehoeft papadopulos solution the response function is precise but computationally intensive based on the hvorslev solution the response function is computationally simple but applicable only to aquifers with small storativity simulations and a field example clearly illustrate the dominating influence of transmissivity in dampening and lagging the response of a confined aquifer to a loading signal and how both effects increase with higher frequency the results also illustrate the weak influence of storativity in modulating the response signal

fate of mantle plume material trapped within a lithospheric catchment with reference to brazil 1 local regions of thin lithosphere act as catchments of hot buoyant plume material unless replenished the trapped plume material cools by convection to the mantle adiabat by several tens of million years in particular currently hot material from the 130 ma parana starting plume head is unlikely to supply 85 ma to recent volcanism on the mainland of brazil and the martin vaz and fernando hot spots rather a plume tail may now underlie southern brazil where tomographic studies detect conduit shaped velocity anomaly through the upper mantle if the tomographic study in fact found a plume tail the track crossed the amazon rift at 85 ma and since then lateral flow along thin regions of the lithosphere from the tail fed widespread feeble volcanism including the flow line hot spots of martin vaz and fernando

seismic evidence for stratification in composition and anisotropic fabric within the thick lithosphere of kalahari craton 1 based on joint consideration of s receiver functions and surface wave anisotropy we present evidence for the existence of a thick and layered lithosphere beneath the kalahari craton our results show that frozen in anisotropy and compositional changes can generate sharp mid lithospheric discontinuities mld at depths of 85 and 150 200 km respectively we found that a 50 km thick anisotropic layer containing 3 s wave anisotropy and with a fast velocity axis different from that in the layer beneath can account for the first mld at about 85 km depth significant correlation between the depths of an apparent boundary separating the depleted and metasomatised lithosphere as inferred from chemical tomography and those of our second mld led us to characterize it as a compositional boundary most likely due to the modification of the cratonic mantle lithosphere by magma infiltration the deepening of this boundary from 150 to 200 km is spatially correlated with the surficial expression of the thabazimbi murchison lineament tml implying that the tml isolates the lithosphere of the limpopo terrane from that of the ancient kaapvaal terrane the largest velocity contrast 3 6 4 7 is observed at a boundary located at depths of 260 280 km beneath the archean domains and the older proterozoic belt this boundary most likely represents the lithosphere asthenosphere boundary which shallows to about 200 km beneath the younger proterozoic belt thus the kalahari lithosphere may have survived multiple episodes of intense magmatism and collisional rifting during the billions of years of its history which left their imprint in its internal layering

general solution for tidal behavior in confined and semiconfined aquifers considering skin and wellbore storage effects tidal analysis provides a cost effective way of estimating aquifer properties tidal response models that link aquifer properties with tidal signal characteristics such as phase and amplitude hav

partitioned waveform inversion and two dimensional structure under the network of autonomously recording seismographs nonlinear optimization methods are very effective in finding models that predict optimal waveform fits to observed seismograms provided the number of model parameters is small to reduce the size of the large scale two or three dimensional seismic modelling problem path integrals over seismic velocities may be defined as model parameters instead of the seismic velocities themselves this partitions the large scale optimization problem into a number of independent small scale problems and reduces the computational effort by several orders of magnitude the path integral parameters are transformed such that their correlation matrix becomes diagonal a linear inversion performs the mapping from the space of path integral parameters into the model space of seismic velocities and makes backus gilbert resolution analysis possible the method has been applied to body wave and surface wave data from the broadband portable network of autonomously recording seismographs nars in western europe using a surface wave ray approximation to generate synthetics by mode summation waveforms were fitted for frequencies as high as 50 mhz variations in s velocity as large as 6 1 have been established with a vertical resolution of 100 150 km and a horizontal resolution as small as 400 km in parts of the model although a low velocity layer is present under the southern part of the nars array such layer is very weak or absent north of the paris basin horizontal velocity gradients are well resolved down to 400 km depth

application of surface wave tomography to mineral exploration a case study from siilinjarvi finland abstract in order to assess the feasibility and validity of surface wave tomography as a tool for mineral exploration we present an active seismic three dimensional case study from the siilinjarvi mine in eastern finland the aim of the survey is to identify the formation carrying the mineralization in an area south of the main pit which will be mined in the future before acquiring the data we performed an accurate survey design to maximize data coverage and minimize the time for deployment and recollection of the equipment we extract path averaged rayleigh wave phase velocity dispersion curves by means of a two station method we invert them using a computationally efficient tomographic code which does not require the computation of phase velocity maps and inverts directly for one dimensional s wave velocity models the retrieved velocities are in good agreement with the data from a borehole in the vicinity and the pseudo three dimensional s wave velocity volume allows us to identify the geological contact between the formation hosting most of the mineralization and the surrounding rock we conclude that the proposed method is a valid tool given the small amount of equipment used and the acceptable amount of time required to process the data

a new scheme for joint surface wave and earthquake travel time inversion and resulting 3 d velocity model for the western north island new zealand abstract we have developed a joint inversion of surface wave group velocity u and local earthquake travel time let data and applied it to the north island new zealand to improve the existing new zealand wide 3 d seismic velocity model this approach takes full advantage of the differing sensitivities of surface and body waves the data are complementary particularly at shallow depths where let tomography suffers from vertical smearing and surface wave tomography is susceptible to horizontal smearing the employed u observations are 2 d models at discrete periods which were developed for rayleigh wave dispersion curves measured from the 1744 interstation green s functions obtained by stacked cross correlations of broadband ambient noise data in the volume surrounding each u observation we distribute numerous points for relating the u observation to the gridded 3 d tomography model analogous to points along a raypath the partial derivatives at the points are computed using the u sensitivity kernels for vp and vs with vs related to vp and vp vs perturbations thus the u observations are included along with the travel time observations in a joint inversion to best fit the data and the existing tomography model the resulting model favors the u where there is little travel time resolution the combined inversion used 2949 u observations at 6 16 s period and let from 1509 earthquakes that extend to 370 km depth and improved the model fit by reducing the u residual data variance by 62 and the let by 9 the resulting model generally has better constrained depth of shallow anomalies with decreased velocity in the upper 2 km in the western north island and slight focusing of crustal high velocity features at 8 km depth significantly the increased resolution in the shallowest 5 km of the model improves the utility of the 3 d model for use in seismic hazard assessment wave propagation studies and studies comparing seismic velocities to geological mapping

3d shear velocity structure beneath the gulf of california from rayleigh wave dispersion active extension in the gulf of california is characterized by the transition from continental rifting to seafloor spreading puzzling variations in the patterns of both tectonics and magmatism are observed along the length of the gulf and are likely to be related to mantle heterogeneity regional scale mantle structure however has been difficult to constrain due to the lack of broadband seismic stations in the region in this study we utilized new data from the deployment of the nars baja array and other networks and computed a three dimensional shear speed model of the upper mantle beneath the region applying a combination of cross correlation analysis and multimode waveform inversion we measured interstation rayleigh wave dispersion for 450 pairs of stations in a broad period range of 9 250 s we computed phase velocity maps and then inverted the phase velocity data for shear speed structure our results suggest that the location of the transition from seafloor spreading south to continental rifting north in the gulf of california as well as differences in volcanism across baja california and the gulf can be explained by heterogeneity in the upper mantle in particular by the presence of a slab remnant beneath the south central part and an absence of such a slab remnant beneath the northern part of the gulf

mapping the upper mantle three dimensional modeling of earth structure by inversion of seismic waveforms a method is presented for the inversion of waveform data for the three dimensional distribution of seismic wave velocities the method is applied to data from the global digital networks international deployment of accelerometers global digital seismograph network the selected data set consists of some 2000 seismograms corresponding to 53 events and 870 paths the moment tensors of the earthquakes are determined through an iterative procedure which minimizes the corrupting influence of lateral heterogeneity a global model is constructed for shear wave velocity expanded up to degree and order 8 in spherical harmonics and described by a cubic polynomial in depth for the upper 670 km of the earth s mantle although no a priori information is incorporated the model predictions reproduce much of what is known about the dispersion of mantle waves for example high phase velocities for shields low velocities at ridges and a strong degree 2 pattern for rayleigh waves since the method makes use of complete waveforms overtone data are also included it is shown that the model is reproducible in that substantially the same model can be constructed from each half of the total data set considered independently the model shows that shields and ridges are major features in the depth interval 25 250 km the ridges of the southern pacific and the larger shields persist to 350 km but the southeast indian rise is underlain by a high velocity anomaly at this depth as is much of the mid atlantic ridge at 450 650 km the major features are a broad region of high velocities incorporating south america much of the south atlantic and parts of west africa a broad region of low velocities in the central and eastern pacific high velocities in the western pacific and a low velocity anomaly beneath the red sea and the gulf of aden in the absence of a crustal correction degrees 2 and 3 show a high positive correlation with the geoid paradoxically this is largely destroyed when the distribution in crustal thickness is taken into account spherical harmonic degrees 4 7 show a significant negative correlation

depth discrete specific storage in fractured sedimentary rock using steady state and transient single hole hydraulic tests abstract a method is presented for obtaining depth discrete values of specific storage ss from single hole hydraulic tests in fractured rock boreholes using straddle packers 1 5 17 m test intervals low flow constant head ch step tests analyzed using the thiem method provide transmissivity t values free from non darcian error short term constant rate pumping tests 0 5 2 h analyzed using the cooper jacob approximation of the theis method provide s from the hydraulic diffusivity using the darcian t value from the ch step test this synergistic use of two types of hydraulic tests avoids the common source of error when pumping tests injection or withdrawal are conducted at higher flow rates and thereby induce non darcian flow resulting in the underestimation of t other errors such as well bore storage and leakage can also substantially influence s by causing a shift in the time axis of the cooper jacob semi log plot in this approach the darcian t values from the ch step tests are used in the analysis of the transient pumping test data for calculating s throughout the pumping test using the cooper jacob approximation to minimize all of the aforementioned errors resulting in more representative s values the effect of these non idealities on the measured drawdown is illustrated using the theis equation with the darcian t and s values to calculate drawdown for comparison to measured data the ss values for tests in sandstone obtained from this approach are more consistent with confined aquifer conditions than values derived from the traditional cooper jacob method and are within the range of field and lab values presented from a compilation of literature values for fractured sandstone 10 7 10 5 m 1 this method for obtaining ss values from short interval straddle packer tests improves the estimation of both k and ss and provides opportunity to study their spatial distribution in fractured rock

response of well aquifer systems to earth tides problem revisited two recent works cause us to reexamine bredehoeft s 1967 analysis of earthtide response of water wells narasimhan et al 1984 raise several questions regarding bredehoeft s 1967 analysis and suggest that the analysis is internally inconsistent they argue that one cannot directly estimate the specific storage which characterizes the drained behavior of a porous medium from earth tide response which is an undrained phenomenon we resolve the questions raised by narasimhan et al 1984 and show that bredehoeft s analysis is internally consistent in addition we show that it is possible to determine the specific storage from undrained loading while bredehoeft s analysis is somewhat heuristic and neglects grain compressibility van der kamp and gale 1983 present a more rigorous analysis that is based on biot s 1941 constitutive relationships and accounts for grain compressibility however their results reduce to bredehoeft s results when grains are assumed incompressible this suggests that bredehoeft s analysis has incorporated all the essential features of biot s relationships except for grain compressibility upon reexamining bredehoeft s analysis we find that this is indeed the case

depth constraints on azimuthal anisotropy in the great basin from rayleigh wave phase velocity maps abstract we present fundamental mode rayleigh wave azimuthally anisotropic phase velocity maps obtained for the great basin region at periods between 16 s and 102 s these maps offer the first depth constraints on the origin of the semi circular shear wave splitting pattern observed in central nevada around a weak azimuthal anisotropy zone a variety of explanations have been proposed to explain this signal including an upwelling toroidal mantle flow around a slab lithospheric drip and a megadetachment but no consensus has been reached our phase velocity study helps constrain the three dimensional anisotropic structure of the upper mantle in this region and contributes to a better understanding of the deformation mechanisms taking place beneath the western united states the dispersion measurements were made using data from the usarray transportable array at periods of 16 s and 18 s which mostly sample the crust we find a region of low anisotropy in central nevada coinciding with locally reduced phase velocities and surrounded by a semi circular pattern of fast seismic directions away from central nevada the fast directions are n s in the eastern great basin nw se in the walker lane region and they transition from e w to n s in the northwestern great basin our short period phase velocity maps combined with recent crustal receiver function results are consistent with the presence of a semi circular anisotropy signal in the lithosphere in the vicinity of a locally thick crust at longer periods 28 102 s which sample the uppermost mantle isotropic phase velocities are significantly reduced across the study region and fast directions are more uniform with an e w fast axis the transition in phase velocities and anisotropy can be attributed to the lithosphere asthenosphere boundary at depths of 60 km we interpret the fast seismic directions observed at longer periods in terms of present day asthenospheric flow driven deformation possibly related to a combination of juan de fuca slab rollback and eastward driven mantle flow from the pacific asthenosphere our results also provide context to regional sks splitting observations we find that our short period phase velocity anisotropy can only explain 30 of the sks splitting times despite similar patterns in fast directions this implies that the origin of the regional shear wave splitting signal is complex and must also have a significant sublithospheric component

layered anisotropy within the crust and lithospheric mantle beneath the sea of japan abstract continental rifting during the oligocene to mid miocene caused the opening of the sea of japan and the separation between the japanese islands and the eurasian plate the tectonic evolution in the sea of japan is important for understanding the evolution of back arc regions in active convergent margins here we use data from the seismic stations surrounding the sea of japan to map the rayleigh wave azimuthal anisotropy in the crust and lithospheric mantle beneath the sea of japan we explore the variations of rayleigh wave phase velocity beneath the sea of japan in a broad period range 30 80 s rayleigh wave dispersion curves are measured by the two station technique for a total of 231 interstation paths using vertical component broad band waveforms at 22 seismic stations around the sea of japan from 1411 global earthquakes the resulting maps of rayleigh wave phase velocity and azimuthal anisotropy allow the examination of azimuthal anisotropy at specific periods they exhibit several regions with different isotropic and anisotropic patterns the japan basin displays fast velocities at shorter periods 30 and 40 s with nne ssw anisotropy whereas at 60 s and longer the velocities become slow even if the anisotropy remains ne sw the east china sea shows fast velocities at all periods 30 80 s with constant nw se anisotropy trench normal anisotropy beneath the japanese islands is found at short periods 30 40 s and become trench parallel at periods of 60 s and longer overall our model resolves two layers of anisotropy the shallowest and deepest layers being potentially related to frozen deformation due to recent geodynamic events and asthenospheric flow respectively

subduction of the indian lithosphere beneath the tibetan plateau and burma abstract subduction of the indian lithosphere under eurasia plays an important role in the tectonic evolution of the tibetan plateau and surrounding regions to improve our knowledge of pertinent mantle structures through tomographic imaging we combine p wave arrival time data from temporary arrays in tibet and stations of the chinese seismograph network with reprocessed data from the international seismological centre the new images reveal considerable spatial variations in mantle structure along the collision zone and the horizontal distance over which presumed continental indian lithosphere slides northward beneath the plateau decreases from west where it underlies the himalayas and the entire plateau to east where no indication is found for present day underthrusting beyond the himalayan block and indus tsangpo suture p wavespeed appears low in the shallow mantle beneath much of central and eastern tibet these observations suggest that indian lithosphere underlies only the southwestern part of the plateau and that the central and northeastern part is underlain by lithosphere of asian origin the continental parts of the indian plate that currently underthrust or subduct below the plateau appear generally detached from the oceanic slab fragments that subducted longer ago and that have been detected deeper in the mantle except perhaps in the central part of the collision zone 80 90 e this suggests that ongoing india eurasia collision must increasingly be driven by other forces such as subduction of the indian plate further west and east e g beneath indochina our images reveal structures associated with eastward subduction along the burmese arc southeast of the eastern himalayan syntaxis the tengchong volcanic complex in southwest china is marked by slow wave propagation to 150 km depth suggesting a causal link to subduction along the burmese arc the low velocities beneath the red river fault region extend to greater depth and may be related to upper mantle processes further southeast

fracture characterization using earth tide analysis summary wells tapping confined aquifer systems are known to commonly produce water level fluctuations caused by strain induced earth tides in this investigation a straightforward methodology is presented for quantifying the specific storage and secondary porosity of a fractured fault zone aquifer system using earth tides water level and barometric pressure head data are smoothed and then filtered to remove low frequency responses the resulting tidal signals are used in the program baytap g to yield amplitude and phase shifts of all the major tidal groups the resulting tidal parameters can be used to compute the time dependent volumetric strain caused by the m 2 and o 1 tides stress strain hysteresis loops are produced when the reduced water levels are compared to the volumetric strain induced by these tides for amplification factors near unity representing the ratio of pressure response to tidal loading in the fracture to water level response in the well the slopes of the loops represent the specific storage of the fracture the barometric efficiency and specific storage can then be used to estimate a secondary porosity and other parameters of the aquifer system this analysis was carried out at the fractured rock research site frs in the blue ridge physiographic province in floyd county virginia

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

geomechanics field characterization of woodford shale and barnett shale with advanced logging tools and nano indentation on drill cuttings the woodford shale and barnett shale have emerged as prolific gas plays in the us midcontinent however the intrinsically low permeability of these gas shales hinders profitable pro duction unless horizontal well drilling and multistage hydraulic fracturing are employed the success of these operations depends on accurate de terminations of the anisotropic elastic and poroelastic properties of these shale formations

seismic evidence for olivine phase changes at the 410 and 660 kilometer discontinuities the view that the seismic discontinuities bounding the mantle transition zone at 410 and 660 kilometer depths are caused by isochemical phase transformations of the olivine structure is debated combining converted wave measurements in east asia and australia with seismic velocities from regional tomography studies we observe a correlation of the thickness of and wavespeed variations within the transition zone that is consistent with olivine structural transformations moreover the seismologically inferred clapeyron slopes are in agreement with the mineralogical clapeyron slopes of the mg fe 2sio4 spinel and postspinel transformations

on the trade off between seismic anisotropy and heterogeneity numerical simulations and application to northeast japan p wave tomography has been recently used to study 3 d azimuthal and radial anisotropy of subduction zones and continental regions however the fundamental issue about the trade off between the isotropic and anisotropic structures is still unclear in this study we investigate this issue systematically with comprehensive synthetic tests our results indicate that good ray coverage in the azimuth for azimuthal anisotropy and incidence for radial anisotropy is required for determining reliable anisotropic models the isotropic and anisotropic structures are strongly coupled and smearing effects are significant when the rays used in the inversion are limited in a small range of azimuth or incidence we therefore plot ray azimuth and ray incidence ellipses at every grid nodes and propose to use the normalized length of the short axis i e the ratio of the short axis and long axis lengths for estimating the ray coverage quantitatively applying our novel approach to a large number of high quality arrival time data of local shallow and intermediate depth earthquakes we obtained new tomographic images of 3 d p wave azimuthal and radial anisotropy in northeast japan both the azimuthal and radial anisotropy results are determined reliably for the shallow parts of the study region whereas the smearing effects are significant in the deeper part of the mantle wedge and the subducting slab our results show dominant trench normal and vertical fast anisotropy in the mantle wedge while trench parallel and horizontal fast anisotropy in the subducting slab which indicates different dynamics in different domains of the subduction zone

closing the gap between regional and global travel time tomography recent global travel time tomography studies by zhou 1996 and van der hilst et al 1997 have been performed with cell parameterizations of the order of those frequently used in regional tomography studies i e with cell sizes of 1 2 these new global models constitute a considerable improvement over previous results that were obtained with rather coarse parameterizations 5 cells the inferred structures are however of larger scale than is usually obtained in regional models and it is not clear where and if individual cells are actually resolved this study aims at resolving lateral heterogeneity on scales as small as 0 6 in the upper mantle and 1 2 3 in the lower mantle this allows for the adequate mapping of expected small scale structures induced by for example lithosphere subduction deep mantle upwellings and mid ocean ridges there are three major contributions that allow for this advancement first we employ an irregular grid of nonoverlapping cells adapted to the heterogeneous sampling of the earth s mantle by seismic waves spakman and bijwaard 1998 second we exploit the global data set of engdahl et al 1998 which is a reprocessed version of the global data set of the international seismological centre their reprocessing included hypocenter redetermination and phase reidentification finally we combine all data used p pp and pwp phases into nearly 5 million ray bundles with a limited spatial extent such that averaging over large mantle volumes is prevented while the signal to noise ratio is improved in the approximate solution of the huge inverse problem we obtain a variance reduction of 57 1 synthetic sensitivity tests indicate horizontal resolution on the scale of the smallest cells 0 6 or 1 2 in the shallow parts of subduction zones decreasing to approximately 2 3 resolution in well sampled regions in the lower mantle vertical resolution can be worse up to several hundreds of kilometers in subduction zones with rays predominantly pointing along dip important features of the solution are as follows 100 200 km thick high velocity slabs beneath all major subduction zones sometimes flattening in the transition zone and sometimes directly penetrating into the lower mantle large high velocity anomalies in the lower mantle that have been attributed to subduction of the tethys ocean and the farallon plate and low velocity anomalies continuing across the 660 km discontinuity to hotspots at the surface under iceland east africa the canary islands yellowstone and the society islands our findings corroborate that the 660 km boundary may resist but not prevent present day large scale mass transfer from upper to lower mantle or vice versa this observation confirms the results of previous global mantle studies that employed coarser parameterizations

bedrock fracture parameters from the interpretation of well tides this paper presents a theory to account for the main features of the tidal response of an isolated plane fracture as revealed by the water level in an intersecting open borehole according to the theory the diurnal and semidiurnal tidal constituents both amplitude and phase of water level variations depend on the fracture aperture the orientation dip and strike and the radial extent of the fracture and the compressibility of the asperites the theory is applied to water level observations made in six open boreholes located in crystalline rock at a test site at the chalk river nuclear laboratories atomic energy of canada limited in chalk river ontario canada the boreholes were uncased and intersected many open fractures so that a definitive test of the theory could not be made however in four cases a fracture model could be found which fitted the observations within the experimental error

upper mantle beneath southeast asia from s velocity tomography 1 we present a three dimensional s velocity model of the se asian western pacific upper mantle with 400 km lateral resolution using the novel automated multimode inversion technique we processed 4038 vertical component seismograms and extracted 22 708 linear equations with uncorrelated uncertainties that constrain upper mantle structure we used time frequency windows to select signal with negligible proportion of scattered energy the windows included the fundamental rayleigh mode and s and multiple s waves the observed range of s velocity variations is the widest 17 18 in the upper 150 km of the mantle high velocity continental roots can reach beyond the present extent of the overlying archean proterozoic crust by 500 km beneath some precambrian units the roots are absent which can be attributed to deformation and gradual destruction of the ancient lithosphere at 120 150 km s velocity beneath some cratons reaches 4 8 km s this can be accounted for by thermal and compositional effects beneath the hainan island area a low velocity anomaly is observed from near the surface to the bottom of our model the hot spot type volcanism here may be caused by the deep mantle hainan plume a low velocity mantle domain underlies the south central sea of japan surrounded on the surface by intraplate volcanoes a deep seismicity gap is present near 40 n in the pacific slab subducting below and may result from a plume slab interaction a high velocity anomaly is present in the transition zone beneath the northern boundary of the yangtze craton we propose that the anomaly corresponds to subducted continental lithosphere stagnant atop the 660 km discontinuity

millimeter level ultra long period multiple earth circling surface waves retrieved from dense high rate gps network abstract high rate gps networks have proven to be capable of continuously recording strong ground motion which is valuable for studying earthquake rupture processes and seismic hazard mitigation previous studies of high rate gps usually resolved dynamic ground displacements of some major seismic phases stronger than a few millimeters in this study we explore the feasibility of retrieving much weaker ground motions sub millimeter in long duration records by stacking high rate gps network we processed data of the 2011 tohoku oki earthquake recorded by more than 600 high rate gps stations of the plate boundary observatory pbo and analyzed kinematic displacement results with seismic array methods from these high rate gps seismograms we identified abundant seismic phases not only including clear body waves such as multiple s waves s ss sss ssss traveling along minor major great circle arc and ssssss beyond 360 degrees but also the r1 r5 rayleigh waves and g1 g6 love waves some of which travel around the earth multiple times many of these seismic phases have not been reported by previous high rate gps studies the group velocity dispersion curves extracted from multiple earth circling love waves of high rate gps are consistent with those of broadband seismic records in the period from 150 to 600 s which can sample the mantle structure down to top of the lower mantle thus important for understanding interaction between upper mantle and lower mantle so the dense high rate gps networks should be useful for deep mantle research as an additional valuable dataset with the development of multi system gnss and the more precise modeling of error sources high rate gnss data should have great potential for accurately detecting more geodynamic processes with much wider bandwidth in geoscience studies

magmatism on rift flanks insights from ambient noise phase velocity in afar region during the breakup of continents in magmatic settings the extension of the rift valley is commonly assumed to initially occur by border faulting and progressively migrate in space and time toward the spreading axis magmatic processes near the rift flanks are commonly ignored we present phase velocity maps of the crust and uppermost mantle of the conjugate margins of the southern red sea afar and yemen using ambient noise tomography to constrain crustal modification during breakup our images show that the low seismic velocities characterize not only the upper crust beneath the axial volcanic systems but also both upper and lower crust beneath the rift flanks where ongoing volcanism and hydrothermal activity occur at the surface magmatic modification of the crust beneath rift flanks likely occurs for a protracted period of time during the breakup process and may persist through to early seafloor spreading

global azimuthal seismic anisotropy and the unique plate motion deformation of australia differences in the thickness of the high velocity lid underlying continents as imaged by seismic tomography have fuelled a long debate on the origin of the roots of continents1 2 3 4 5 some of these differences may be reconciled by observations of radial anisotropy between 250 and 300 km depth with horizontally polarized shear waves travelling faster than vertically polarized ones2 this azimuthally averaged anisotropy could arise from present day deformation at the base of the plate as has been found for shallower depths beneath ocean basins6 such deformation would also produce significant azimuthal variation owing to the preferred alignment of highly anisotropic minerals7 here we report global observations of surface wave azimuthal anisotropy which indicate that only the continental portion of the australian plate displays significant azimuthal anisotropy and strong correlation with present day plate motion in the depth range 175 300 km beneath other continents azimuthal anisotropy is only weakly correlated with plate motion and its depth location is similar to that found beneath oceans we infer that the fast moving australian plate contains the only continental region with a sufficiently large deformation at its base to be transformed into azimuthal anisotropy simple shear leading to anisotropy with a plunging axis of symmetry may explain the smaller azimuthal anisotropy beneath other continents

a sporadic low velocity layer atop the 410 km discontinuity beneath the pacific ocean waveforms of ss precursors recorded by global stations are analyzed to investigate lateral heterogeneities of upper mantle discontinuities on a global scale a sporadic low velocity layer immediately above the 410 km discontinuity lvl 410 is observed worldwide including east asia western north america eastern south america the pacific ocean and possibly the indian ocean our best data coverage is for the pacific ocean where the lvl 410 covers 33 50 of the resolved region lateral variations of our lvl 410 observations show no geographical correlation with 410 km discontinuity topography or tomographic models of seismic velocity suggesting that the lvl 410 is not caused by regional thermal anomalies we interpret the lvl 410 as partial melting due to dehydration of ascending mantle across the 410 km discontinuity which is predicted by the transition zone water filter hypothesis given the low vertical resolution of ss precursors it is possible that the regions without a clear lvl 410 detection also have a thin layer therefore the strong lateral heterogeneity of the lvl 410 in our observations suggests partial melting with varying intensities across the pacific and further provides indirect evidence of a hydrous mantle transition zone with laterally varying water content

determination of fluid flow properties from the response of water levels in wells to atmospheric loading the water level in a well that taps a partially confined aquifer is often sensitive to atmospheric loading the magnitude and character of this response is partly governed by the well radius the lateral hydraulic diffusivity of the aquifer the thickness and vertical pneumatic diffusivity of the unsaturated zone and the thickness and vertical hydraulic diffusivity of the saturated zone overlying the aquifer these key elements can be combined into five dimensionless parameters that partly govern the phase and attenuation of the response in many cases the response of a well to atmospheric loading can be broken up into a high intermediate and low frequency response the high frequency response is governed largely by the well radius and lateral diffusivity of the aquifer the intermediate frequency response is governed by the loading efficiency of the aquifer the low frequency response is governed by the vertical pneumatic diffusivity and thickness of the unsaturated zone and the vertical hydraulic diffusivity and thickness of the saturated material above the aquifer cross spectral estimation is used to fit the response to atmospheric loading of three water wells to the theoretical curves in order to yield estimates of three of the key dimensionless parameters these estimates then are used to make estimates or place bounds on the vertical pneumatic diffusivity of the unsaturated zone the lateral permeability of the aquifer and the composite vertical hydraulic diffusivity of the overlying saturated materials

determination of fracture inflow parameters with a borehole fluid conductivity logging method there is much current interest in determining the flow characteristics of fractures intersecting a well bore in order to provide data for use in estimating the hydrologic behavior of fractured rocks inflow rates from these fractures into the well bore are usually very low moreover in most cases only a few percent of the fractures identified by core inspection and geophysical logging actually conduct water the rest being closed clogged or isolated from the water flow system a new procedure is proposed and a corresponding method of analysis developed to locate water conducting fractures and obtain fracture inflow rates by means of a time sequence of electric conductivity logs of the borehole fluid the physical basis of the analysis method is discussed and the procedure is applied to an existing set of data which shows initiation and growth of nine conductivity peaks in a 900 m section of a 1690 m borehole corresponding to nine water conducting fractures intersecting the borehole by applying our analysis to these nine peaks the flow rates and the salinity of the water from these fractures are determined these results are used with other information to obtain transmissivities of the nine fractures which are validated against independent hydraulic measurements by packer tests the salinities measured in fluids from the fractures are also validated against salinity values obtained by chemical sampling of fluids from different depths of the borehole the applicability of this technique is discussed in the context of a borehole testing program

multimode rayleigh wave inversion for heterogeneity and azimuthal anisotropy of the australian upper mantle summary we present an azimuthally anisotropic 3 d shear wave speed model of the australian upper mantle obtained from the dispersion of fundamental and higher modes of rayleigh waves we compare two tomographic techniques to map path average earth models into a 3 d model for heterogeneity and azimuthal anisotropy method i uses a rectangular surface cell parametrization and depth basis functions that represent independently constrained estimates of radial earth structure it performs an iterative inversion with norm damping and gradient regularization method ii uses a direct inversion of individual depth layers constrained by bayesian assumptions about the model covariance we recall that bayesian inversions and discrete regularization approaches are theoretically equivalent and with a synthetic example we show that they can give similar results the model we present here uses the discrete regularized inversion of independent path constraints of method i on an equal area grid with the exception of westernmost australia we can retrieve structure on length scales of about 250 km laterally and 50 km in the radial direction to within 0 8 per cent for the velocity 20 per cent for the anisotropic magnitude and 20 for its direction on length scales of 1000 km and longer down to about 200 km there is a good correlation between velocity heterogeneity and geologic age at shorter length scales and at depths below 200 km however this relationship breaks down the observed magnitude and direction of maximum anisotropy do not in general appear to be correlated to surface geology the pattern of anisotropy appears to be rather complex in the upper 150 km whereas a smoother pattern of fast axes is obtained at larger depth if some of the deeper directions of anisotropy are aligned with the approximately n s direction of absolute plate motion this correspondence is not everywhere obvious despite the fast 7 cm yr 1 northward motion of the australian plate more research is needed to interpret our observations in terms of continental deformation predictions of sks splitting times and directions an integrated measure of anisotropy are poorly matched by observations of shear wave birefringence

tibetan and indian lithospheres in the upper mantle beneath tibet evidence from broadband surface wave dispersion broadband seismic experiments over the last two decades have produced dense data coverage across tibet yet the mechanism of the india asia lithospheric convergence beneath it remains a puzzle with even its basic features debated and with very different end member models advocated today we measured highly accurate rayleigh and love wave phase velocity curves in broad period ranges up to 5 200 s for a few tens of pairs and groups of stations across tibet combining in each case hundreds to thousands of interstation measurements made with cross correlation and waveform inversion methods robust shear velocity profiles were then determined by extensive series of nonlinear inversions of the data designed to constrain the depth dependent ranges of isotropic average shear speeds and radial anisotropy temperature anomalies in the upper mantle were estimated from shear velocities using accurate petrophysical relationships our results reveal strong heterogeneity in the upper mantle beneath tibet very large high velocity anomalies in the upper mantle are consistent with the presence of underthrust beneath southwestern tibet and subducted beneath central and eastern tibet indian lithosphere the corresponding thermal anomalies match those estimated for subducted indian lithosphere in contrast to the indian lithosphere tibetan lithosphere and asthenosphere display low to normal shear speeds tibetan lithosphere is thus warm and thin radial anisotropy in the upper mantle is weak in central and strong in northeastern tibet possibly reflecting asthenospheric flow above the subducting indian lithospheric slab

finite frequency effects in global surface wave tomography summary we compare traditional ray theoretical surface wave tomography with finite frequency tomography using 3 d born sensitivity kernels for long period fundamental mode dispersion measurements the 3 d kernels preserve sidelobes beyond the first fresnel zone and fully account for the directional dependence of surface wave scattering and the effects of timedomain tapering and seismic source radiation tomographic inversions of love and rayleigh phase delay measurements and synthetic checkerboard tests show that 1 small scale s wave velocity anomalies are better resolved using finite frequency sensitivity kernels especially in the lowermost upper mantle 2 the resulting upper mantle heterogeneities are generally stronger in amplitude than those recovered using ray theory and 3 finite frequency tomographic models fit long period dispersion data better than ray theoretical models of comparable roughness we also examine the reliability of 2 d phase velocity sensitivity kernels in global surface wave tomography and show that phase velocity kernels based upon a forwardscattering approximation or previously adopted geometrical simplifications do not reliably account for finite frequency wave propagation effects 3 d sensitivity kernels with full consideration of directional dependent seismic scattering are the preferred method of inverting long period dispersion data finally we derive 2 d boundary sensitivity kernels for lateral variations in crustal thickness and show that finite frequency crustal effects are not negligible in long period surface wave dispersion studies especially for paths along continent ocean boundaries unfortunately we also show that in global studies linear perturbation theory is not sufficiently accurate to make reliable crustal corrections due to the large difference in thickness between oceanic and continental crust

mantle dynamics and seismic anisotropy abstract observations of seismic anisotropy yield some of the most direct constraints available on both past and present day deformation in the earth s mantle insight into the character of mantle flow can also be gained from the geodynamical modeling of mantle processes on both global and regional scales we highlight recent progress toward understanding mantle flow from both observations and modeling and discuss outstanding problems and avenues for progress particularly in the integration of seismological and geodynamical constraints to understand seismic anisotropy and the deformation that produces it to first order the predictions of upper mantle anisotropy made by global mantle circulation models match seismological observations well beneath the ocean basins but the fit is poorer in regions of greater tectonic complexity such as beneath continental interiors and within subduction systems in many regions of the upper mantle models of anisotropy derived from surface waves are seemingly inconsistent with shear wave splitting observations which suggests that our understanding of complex anisotropic regions remains incomplete observations of anisotropy in the d layer hold promise for improving our understanding of dynamic processes in the deep earth but much progress remains to be made in characterizing anisotropic structure and relating it to the geometry of flow geochemical heterogeneity or phase transitions major outstanding problems related to understanding mantle anisotropy remain particularly regarding the deformation and evolution of continents the nature of the asthenosphere subduction zone geodynamics and the thermo chemical state of the lowermost mantle however we expect that new seismological deployments and closer integration of observations with geodynamical models will yield rapid progress in these areas

quantifying fractured crystalline rock properties using well tests earth tides and barometric effects summary characterization of fractured rock aquifers often requires the acquisition and analysis of diverse datasets obtained from various instrumentation configurations in this investigation at the fractured rock research site in floyd county virginia a high precision borehole extensometer and tiltmeter were used during pumping to monitor deformation in the vicinity of fractures identified from borehole logging strain data obtained from earth tide analyses were used with the extensometer and tiltmeter data to quantify hydromechanical properties including fracture volumetric specific storage porosity poisson s ratio the drained formation elastic modulus and the effective dip direction of the fracture borehole tiltmeter data were used to estimate deformation caused by an aquifer test consisting of three pumping and recovery periods performed in well ex 1 during each period of the aquifer test the extensometer located in w 03 and 27 7 m from the pumping well was anchored over 2 m long sections of 1 a fracture in hydraulic communication with ex 1 2 a fracture that is not hydraulically connected with ex 1 and 3 an unfractured portion of bedrock directly above the hydraulically connected fracture results from the pumping tests yielded compressibilities of 1 3 10 11 pa 1 and 1 7 10 11 pa 1 for the lower and upper fractures respectively when coupled with areal strain calculated from earth tide analyses the volumetric specific storage values are 3 2 10 11 pa 1 and 2 8 10 11 pa 1 and the poisson s ratios are 0 26 and 0 31 respectively using this with a calculated barometric efficiency of 0 45 allows for porosity calculations of 0 02 and 0 03 respectively for the vicinity of fractures in well w 03

asthenospheric flow and origin of volcanism in the baikal rift area the origin of low volume hotspot like volcanism often observed in continental rift areas is debated as is the nature of the flow in the mantle beneath in this paper we assemble seismic constraints on the mantle flow below the baikal rift zone we combine new evidence from upper mantle tomography and from a radially anisotropic shear velocity profile measured beneath and se of the rift with published shear wave splitting constraints on azimuthal anisotropy fast directions of azimuthal anisotropy are perpendicular to the rift on both of its sides stable siberian platform lithosphere on the northern side extends down to 200 km on the southern side the lithosphere is only 60 70 km thick this asymmetry with the thick cratonic root forming a barrier to convective flow inhibits a mid ocean ridge like flow pattern the radially anisotropic profile yields evidence for horizontal flow in the upper asthenosphere 60 100 km se of the rift but no evidence for vertical flow these results are consistent with horizontal asthenospheric flow nw to se perpendicular to the rift from beneath the thick siberian towards the thin baikal mongolian lithosphere when asthenosphere ascends from the 200 km depth beneath the craton to shallower depths beneath the rift decompression melting of embedded veins of enriched rock can produce the hotspot like basaltic volcanism observed the occurrence of such veins of enriched mantle in sub cratonic asthenosphere has been predicted by geochemical mantle models we propose that sub horizontal asthenospheric flow from beneath cratons is a common cause for hotspot like volcanism in continental rift zones

global upper mantle tomography with the automated multimode inversion of surface and s wave forms summary we apply the automated multimode inversion of surface and s wave forms to a large global data set verify the accuracy of the method and assumptions behind it and compute an s vvelocity model of the upper mantle crust 660 km the model is constrained with 51 000 seismograms recorded at 368 permanent and temporary broadband seismic stations structure of the mantle and crust is constrained by waveform information both from the fundamentalmode rayleigh waves periods from 20 to 400 s and from s and multiple s waves higher modes in order to enhance the validity of the path average approximation we implement the automated inversion of surface and s wave forms with a three dimensional 3 d reference model linear equations obtained from the processing of all the seismograms of the data set are inverted for seismic velocity variations also relative to a 3 d reference in this study composed of a 3 d model of the crust and a one dimensional 1 d global average depth profile in the mantle below waveform information is related to shear and compressional velocity structure within approximate waveform sensitivity areas we use two global triangular grids of knots with approximately equal interknot spacing within each a finely spaced grid for integration over sensitivity areas and a rougher spaced one for the model parametrization for the tomographic inversion we use lsqr with horizontal and vertical smoothing and norm damping we invert for isotropic variations in s and p wave velocities but also allow for s wave azimuthal anisotropy in order to minimize errors due to possible mapping of anisotropy into isotropic heterogeneity the lateral resolution of the resulting isotropic upper mantle images is a few hundred kilometres varying with data sampling we validate the imaging technique with a spectral element resolution test inverting a published global synthetic data set computed with the spectral element method using a laterally heterogeneous mantle model we are able to reconstruct the synthetic model accurately this test confirms both the accuracy of the implementation of the method and the validity of the jwkb and path average approximations as applied in it reviewing the tomographic model we observe that low s v velocity anomalies beneath mid ocean ridges and backarc basins extend down to 100 km depth only shallower than according to some previous tomographic models this presents a close match to published estimates of primary melt production depth ranges there in the seismic lithosphere beneath cratons unambiguous high velocity anomalies extend to 200 km pronounced low velocity zones beneath cratonic lithosphere are rare where present south america tanzania they are neighboured by volcanic areas near cratonic boundaries the images of these low velocity zones may indicate hot material possibly of mantle plume origin trapped or spreading beneath the thick cratonic lithosphere

waveform inversion using secondary observables a new method is proposed for inverting single station surface wave seismograms instead of inverting directly the time signal use is made of secondary observables built up from a set of time frequency images this allows us to enhance the signal to noise ratio and to make more linear the relationship between the model parameters and the inverted observables the feasibility of the method is checked on multimode synthetics prior to present the inversion of a long period multimode seismogram related to the pacific ocean

refraction of fault zone guided seismic waves abstract finite difference synthetic seismograms were computed for a surface source and a surface receiver array along and within a low velocity fault damage zone this survey geometry is analogous to a body wave refraction survey along the fault trace the synthetic data demonstrate that dispersive fault zone guided waves are refracted by an increase in both fault zone and crustal velocity with depth refraction of the guided waves allows the surface source and surface array to record waves that sample the deep fault zone at each frequency the observed group arrival times can be inverted for a 1d or 2d model of group velocity within the fault plane the synthetic seismograms were successfully used to derive the fault zone properties in the subsurface using multiple sources and receivers this method can be used to derive 3d fault zone structure to seismogenic depths mapping variations both along strike and in depth

temporal changes of hydraulic properties of overburden aquifer induced by longwall mining in ningtiaota coalfield northwest china abstract characterizing the mining induced temporal changes of hydraulic properties of the overburden aquifer is significant for groundwater resource protection conventional hydrogeological methods e g hydraulic test physical model test and numerical simulation of determining hydraulic properties of the overburden aquifer cannot quantitatively analyze the temporal changes of the hydraulic properties induced by mining disturbances this paper demonstrates a quantitative determination for the temporal changes of parameters compressibility porosity and specific storage in the overburden aquifer influenced by the mining processes based on in situ continuous measurements of groundwater level that was affected by earth tide atmospheric loading and mining disturbances the results showed that when working face reached a certain distance 127 m from borehole j6 in this study those parameters compressibility porosity and specific storage of overburden aquifer began to show gradual decrease with approximately up to two order of magnitudes after the working face passed by the observation borehole j6 those properties of overburden aquifer recovered in about 80 days which might reflect the characteristic of elastic deformation of the aquifer those findings of the mining induced parameters temporal changes could improve our understanding of the mining effects on aquifer system and could be meaningful in groundwater resource protection

mantle structure and dynamic topography in the mediterranean basin 1 we study the contribution of mantle flow to surface deformation within the mediterranean basin flow is modeled numerically based on lateral changes in mantle temperature estimated from tomography models we find that modeling results are significantly affected by the properties of the selected tomography models shear velocity models based on surface wave observations achieve the highest resolution of upper mantle structure and as a result are most successful in predicting microplate motion and dynamic topography

the fate of the indian lithosphere beneath western tibet upper mantle elastic wave speed structure from a joint teleseismic and regional body wave tomographic study abstract we investigate the fate of the indian lithosphere following its descent beneath western tibet by means of tomographic imaging based on arrival times of body waves from regional and teleseismic sources recorded by a portable network deployed in the region from 2007 to 2011 we use a non linear iterative algorithm that simultaneously models absolute regional and relative teleseismic arrival times to obtain a 3 d velocity structure in a spherical segment that extends from 26 n to 37 n from 76 e to 89 e and from the surface to 430 km depth we find that variations in p and s wave speeds in the upper mantle are similar and identify a number of prominent fast anomalies beneath western tibet and the adjacent himalayas we associate these fast anomalies with the mantle lithosphere of india that is likely colder and hence faster than the ambient mantle resolution tests confirm the ability of our dataset to resolve their shapes in the upper 300 km and the lack of significant downward smearing of these features we interpret the presence of faster material below 300 km as being consistent with former indian lithosphere having reached these depths there are two main fast anomalies in our model one resembles a 100 km wide sub vertical column located directly beneath the india asia plate boundary the other anomaly is thinner and has the shape of a dipping slab that spans the north south width of the lhasa block it dips towards the ne starting near the indus yarlung suture and ending north of the bangong nujiang suture at depths in excess of 300 km another finding of our study is the absence of major fast anomalies west of 80 e which our resolution tests show to be significant our results do not support the notion of a continuous body of formerly indian lithosphere being presently underthrust northward and extending all the way to the northern boundary of the plateau rather shapes of fast anomalies in western tibet suggest colder material beneath the northernmost himalaya and the southernmost part of the plateau the presence of multiple relatively small scale anomalies rather than a single large fast body aligned with the india asia boundary rules out subduction of the intact indian lithosphere our preferred scenario for the process that currently removes the mantle lithosphere of india from the collision zone envisages viscous behavior with gravity driven instabilities leading to the formation of multiple drips of different size to reconcile our findings with evidence of past underthrusting of indian lithosphere beneath tibet we postulate a geologically recent change in the mode of lithosphere removal our scenario includes initial underthrusting subsequent gravitational destabilization and removal of the mantle lithosphere of indian plate at present the mantle lithosphere of india that continues to underthrust southern tibet develops a drip like instability that is seen as a fast columnar feature in our model

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

flow modeling and permeability estimation using borehole flow logs in heterogeneous fractured formations a numerical model of flow in the vicinity of a borehole is used to analyze flowmeter data obtained with high resolution flowmeters the model is designed to 1 precisely compute flow in a borehole 2 approximate the effects of flow in surrounding aquifers on the measured borehole flow 3 allow for an arbitrary number n of entry exit points connected to m n far field aquifers and 4 be consistent with the practical limitations of flowmeter measurements such as limits of resolution typical measurement error and finite measurement periods the model is used in three modes 1 a quasi steady pumping mode where there is no ambient flow 2 a steady flow mode where ambient differences in far field water levels drive flow between fracture zones in the borehole and 3 a cross borehole test mode where pumping in an adjacent borehole drives flow in the observation borehole the model gives estimates of transmissivity for any number of fractures in steady or quasi steady flow experiments that agree with straddle packer test data field examples show how these cross borehole type curves can be used to estimate the storage coefficient of fractures and bedding planes and to determine whether fractures intersecting a borehole at different locations are hydraulically connected in the surrounding rock mass

using flowmeter pulse tests to define hydraulic connections in the subsurface a fractured shale example cross borehole flowmeter pulse tests define subsurface connections between discrete fractures using short stress periods to monitor the propagation of the pulse through the flow system this technique is an improvement over other cross borehole techniques because measurements can be made in open boreholes without packers or previous identification of water producing intervals the method is based on the concept of monitoring the propagation of pulses rather than steady flow through the fracture network in this method a hydraulic stress is applied to a borehole connected to a single permeable fracture and the distribution of flow induced by that stress monitored in adjacent boreholes the transient flow responses are compared to type curves computed for several different types of fracture connections the shape of the transient flow response indicates the type of fracture connection and the fit of the data to the type curve yields an estimate of its transmissivity and storage coefficient the flowmeter pulse test technique was applied in fractured shale at a volatile organic contaminant plume in watervliet new york flowmeter and other geophysical logs were used to identify permeable fractures in eight boreholes in and near the contaminant plume using single borehole flow measurements flowmeter cross hole pulse tests were used to identify connections between fractures detected in the boreholes the results indicated a permeable fracture network connecting many of the individual boreholes and demonstrated the presence of an ambient upward hydraulic head gradient throughout the site

new images of the earth s upper mantle from measurements of surface wave phase velocity anomalies 1 the sensitivity of a surface wave to the lateral structure of the earth s mantle depends on the local structure and thickness of the crust particularly at short periods the strong lateral heterogeneity of the crust has a significant nonlinear effect on the surface wave sensitivity functions thus far this effect has not been quantified and tomographic studies of the upper mantle based on surface wave observations have not taken it into account on the basis of a jeffreys wentzel kramers brillouin jwkb description of surface wave propagation we find and discuss the lateral variations of the sensitivity of love and rayleigh waves to mantle seismic anomalies associated with a realistic model of the crust mooney et al 1998 we then use the resulting laterally varying sensitivity kernels to determine a new tomographic image of horizontally and vertically polarized shear velocity in the upper mantle from love and rayleigh wave phase velocity measurements periods from 35 to 300 s in terms of large scale patterns of high and low velocity our model is similar to previously published ones confirming among other features the anomalous anisotropy underlying the central pacific ekstrom and dziewonski 1998 we find however that the lateral dependence of the surface wave sensitivity kernels has a significant effect on the absolute amplitude of the anomalies which should not be neglected as we attempt to obtain higher resolution images of the upper mantle