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 anisotropy in the upper mantle inferred from the regionalization of phase velocities a data set of 2600 paths for rayleigh waves and 2170 paths for love waves was selected in order to resolve azimuthal anisotropy of surface waves in the period range 70 250 s the epicenters were chosen so that the paths provide uniform spatial and azimuthal coverage of earth a synthetic seismogram is computed for each path and compared to the observed seismogram in order to infer the phase velocity along each path to process such a large data set a new tomographic technique is designed a good correlation is found with surface tectonics in the whole period range for love waves and at shorter periods for rayleigh waves the directions of maximum velocities are also well correlated with plate tectonics motions for the 2 azimuthal term of rayleigh waves when the power spectrum of heterogeneities is computed it is found that for love waves the even orders are usually larger than the odd orders for rayleigh waves the degrees 2 and 6 dominate only at long periods suggesting a deep origin for these components

experimental study of extreme shear stress for shallow flow under simulated rainfall the raindrop impact and overland flow are two major factors causing soil detachment and particle transportation in this study the turbulent characteristics of the shallow rain impacted water flow were investigated using a 2 d fibre optic laser doppler velocimetry fldv and an artificial rainfall simulator the fluctuating turbulent shear stress was computed using digital data processing techniques the experimental data showed that the reynolds shear stress follows a probability distribution with heavy tails the tail probability increases with an increase of rainfall intensity or raindrop diameter and it decreases with an increase of reynolds number a modified empirical equation was derived using both the raindrop diameter and rainfall intensity as independent variables to provide a better prediction of the darcy weisbach friction coefficient f under rainfall conditions copyright 2009 john wiley sons ltd

lateral heterogeneity and azimuthal anisotropy of the upper mantle love and rayleigh waves 100 250 s the lateral heterogeneity and apparent anisotropy of the upper mantle are studied by measuring rayleigh and love wave phase velocities in the period range 100 250 s spherical harmonic descriptions of the lateral heterogeneity are obtained for order and degree up to 1 m 10 slow regions are evident at the east pacific rise northeast africa tibet tasman sea southwestern north america and triple junctions in the northern atlantic and indian oceans fast regions occur in australia western pacific and the southern atlantic these features are also found by a completely different analysis based on the backus gilbert method the backus gilbert method also shows that the obtained phase velocities are averaged values within an area of about 2000 km radius and the errors are about 1 of the phase velocity in the zeroth order spherically symmetric earth inversion for azimuthal dependence shows that for low angular order the fast phase velocity directions seem to correlate well with the plate motion vectors however resolution analysis by the backus gilbert method shows that the current data do not have enough resolution for everywhere on the globe only a few regions currently have adequate azimuthal coverage thus confirmation of the above correlation requires a more complete data set

long wavelength s wave velocity structure throughout the mantle summary long wavelength s wave velocity anomalies are obtained for the entire mantle by inverting 6ooo long period 40 100s sh body waves and lo00 long period 100 500 s love waves in the shallow mantle the patterns of fast and slow velocity anomalies correlate well with age and tectonics in the depth range of 400 1000 km we find two antipodal fast velocity anomalies one in the western pacific and the other in south america they form a fairly strong i 2 anomaly moreover the 1 2 anomaly is the largest spherical harmonic component throughout the entire mantle except for in the layer of 1000 1300 km depth a fast velocity anomaly near the caribbean previously reported by several other investigators is found between the depths of 1000 and 1300km with diminishing amplitudes it can be traced to canada and the aleutians and may be related to old subducted slabs in the same depth interval similar size anomalies can be found in the middle of the pacific and in the indian ocean these could be checked by more detailed studies to judge the reliability of this study heterogeneity power has a peak at the surface and a secondary peak at the bottom of the mantle d consistent with the existence of chemical and or thermal boundary layers at the base of the mantle we also find a fast velocity anomaly which surrounds the pacific ocean this feature has been found by other researchers previously but its interpretation is difficult due to the trade off between velocity anomaly and core mantle boundary deformation

the effect of post pangea subduction on global mantle tomography and convection there is an excellent correlation between tomographic patterns and global tectonics in the upper 200 km of the mantle below this depth there is little relationship with present tectonic provinces most of the power in the tomography is in the longest wavelengths l 1 3 with l 2 generally dominant this is quite different from expectations based on mantle convection models the question then arises what causes the long wavelength variations mapped by seismic techniques we investigate the hypotheses that past locations of supercontinents and subduction may control temperature variations in the mantle we look for correlations between pangea and post pangeatic subduction and seismic velocity variations at various depths the best correlations with time integrated slab locations occur near the base of the uppermantle suggesting that slabs bottom out in the mesosphere the pangea hemisphere has a colder than average uppermantle probably due to circum and intra pangea subduction hotspots and ridges avoid regions cooled by subduction over the past 180 ma the presence of large continents at the surface and large areas of cold slab at depth explain the dominance of long wavelengths in the mantle s thermal structure despite the high rayleigh number

p wave anisotropic tomography of the crust and upper mantle under hokkaido japan abstract we determined a 3 d anisotropic velocity structure beneath hokkaido in northern japan using a large number of first p wave arrival times the travel time inversion is parameterized with an isotropic component and two anisotropic parameters for each grid node by assuming p wave azimuthal anisotropy with hexagonal symmetry axis distributed horizontally the geometries of the conrad and moho discontinuities and the upper boundary of the subducting pacific plate are taken into account in the model our results show that low velocity zones exist beneath active arc volcanoes in the crust and in the central portion of mantle wedge above the high velocity pacific slab which are similar to the previous tomographic images p wave anisotropy is revealed in the crust mantle wedge and the subducting pacific slab in the upper crust the anisotropy is possibly caused by microcracks and cracks in the lower crust the anisotropic structure is different from that in the upper crust and it may be affected considerably by the plastic flow deformation in the mantle wedge the fast velocity direction fvd is generally trench normal in most of the study area while it becomes trench parallel in the pacific coast areas close to the trench which agrees with the shear wave splitting results beneath the volcanic front the fvd is also trench parallel which may suggest the existence of complex 3 d mantle flow in the mantle wedge the fvd in the subducting pacific slab is nearly north south which likely keeps the original fossil anisotropy of the pacific plate formed at the mid ocean ridge or is affected by the olivine fabric transition from a type to b type fabric due to the changes in water content stress and temperature

seismic structure of the upper mantle beneath the western philippine sea abstract we investigate the seismic structure of the western philippine sea using two sets of seismological observations scs reverberations which provide the layering framework for a regional upper mantle model and observations of frequency dependent phase delays for direct s waves surface reflected phases ss ss sss and surface waves r1 g1 which constrain the velocity and anisotropy structure within the layers the combined data set comprising 17 discontinuity amplitudes and layer travel times from the scs reverberation stack and more than 1000 frequency dependent phase delays was inverted for a path averaged radially anisotropic model mineralogical estimates of the bulk sound velocity and density are incorporated as complementary constraints the final model phb3 is characterized by a 11 5 km thick crust an anisotropic lid bounded by a sharp negative g discontinuity at 89 km an anisotropic low velocity layer extending to 166 km a subjacent high gradient region and transition zone discontinuities at depths of 408 km 520 km and 664 km the lid is slower than in a comparable model for the tonga hawaii corridor pa5 but also significantly thicker requiring a compositional variation between the two regions we explore the hypothesis that the thickness of the oceanic lid is controlled by the melting depth at the spreading centers during crust formation and that the thicker crust and lid in the philippine sea results from deeper melting owing to a higher potential temperature and perhaps a higher water content in the upper mantle

engineered damage zone sealing during a water injection test at the tournemire url low permeability clay formations provide good candidate host rocks for geological disposal of radioactive waste because there is expected to be limited movement of gas or water through the formation however when constructing tunnels the stress state in the formation around the tunnel will change which can lead to damage to the formation changing the bulk hydraulic properties of the formation close to the tunnel there is the potential for this damaged zone to act as a preferential pathway for fluid flow and radionuclide transport a water injection experiment is ongoing at the tournemire underground rock laboratory to investigate the hydraulic properties of the toarcian argillite in which the laboratory is constructed water is injected into the formation at the end of a sealed borehole and moves preferentially in the damaged zone along the borehole walls the rate of water injection into the rock changed over the first year of the experiment and the causes of this change are investigated in this paper by numerical modelling the study demonstrates that the change in water injection rate into the argillite can be explained by the evolving hydraulic properties of the damaged zone around the borehole the findings of the modelling study are discussed in the context of long term radioactive waste disposal

the geological origin of long wavelength lateral heterogeneity at depths of 300 400km on the basis of two three dimensional 3 d models of s wave velocity pumo hara et at 1993 and sh425 2 su and dziewonski 1991 we show that the deep roots of cratons and mid ocean ridges provide a satisfactory explanation of the pattern and amplitude of the earth s long wavelength lateral heterogeneity in the depth range from 300 to 400km

imaging global body wave phases by stacking long period seismograms stacked record sections combining over 5 years of long period global digital seismograph network gdsn seismograms from shallow events show dozens of seismic body wave phases separate images are obtained for the vertical radial and transverse components using an automatic gain control algorithm which normalizes the amplitude of each trace prior to stacking these images provide an indication of the relative signal to noise characteristics of different parts of the gdsn data set core mantle boundary diffracted phases are particularly prominent in these stacks which show pdiff to 150 pkpdiff to 200 ppdiff to 230 sdiff to 160 and ssdiff to 220 high order s surface multiples can be seen extending through the surface wave train up to ranges of 540 two examples of possible upper mantle discontinuity reflected phases are visible one following ppp between about 95 and 125 the other following scs3 between about 210 and 240 an apparent offset between sh and sv arrivals is seen which becomes larger for the higher order s multiples sss ssss etc and appears consistent with models containing transverse isotropy in the upper mantle

mantle layering from scs reverberations 2 the transition zone this is the second paper in a four part sequence that examines the nature of mantle layering using the scsn phases and internal reflections observed within the reverberative interval of sh polarized seismograms mantle reflectivity profiles for 18 seismic corridors sampling portions of indonesia australia and the western and central pacific are constructed from low frequency 25 mhz scs reverberations i e scsn type phases reflected once from internal mantle discontinuities modeling the reflectivity profiles using synthetic seismograms yields precise path specific estimates of the travel times to the 410 km and 660 km discontinuities and their reflection coefficients the data are consistent with an olivine dominated model of the transition zone marked by two major phase transitions having average apparent depths of 414 2 km and 660 2 km and impedance contrasts of 0 046 0 010 and 0 072 0 010 respectively the interpath variations observed in the reverberation travel times imply that the topography on the two discontinuities is of the order of 20 km peak to peak and is negatively correlated consistent with an endothermic transition at 660 km whose clapeyron slope magnitude is comparable to that of the 410 km exothermic transition in the case of the 660 km discontinuity we have been able to supplement these long wavelength 1500 5000 km observations with an estimate of intrapath topography inferred from the frequency dependence of the 660 km reflection coefficient which gives peak to peak variations less than 40 km on scale lengths of 500 1500 km for the 660 km discontinuity the observed topography is significantly less than the dynamic topography expected for a simple compositional interface in regions of subduction however we do observed an intriguing negative correlation between the apparent depth and the reflection coefficient of the 660 km discontinuity which may involve small compositional variations plausible explanations for this correlation include heating of an initially cool chemical boundary layer gravitationally trapped above an endothermic phase transition loss of reflected energy due to local curvature or roughness of the reflector and or extreme topography occurring on a small compositional component to the discontinuity 40 of the total impedance contrast by stripping the 410 km and 660 km peaks from the composite path reflectivity profile we identify three minor reflectors at mean depths of 520 710 and 900 km the shallowest may mark the phase spinel phase transition the 710 km discontinuity can be attributed to the ilmenite gamet perovskite phase transition although changes in perovskite symmetry can potentially provide explanations for both the 710 km and 900 km features

seismic constraints on a model of partial melts under ridge axes in a recent global scale seismic study the correlation between s wave velocity under ridge axes and spreading rate was pointed out the correlation is strong for depths to about 70 km but it diminishes below this depth we present the correlation plots at four depths 38 66 90 and 110 km for which correlation is strong at 38 and 66 km but is weak at 90 km and is almost nonexistent at 110 km we present a model to explain this behavior which includes a thermal conduction model for the development of lithosphere and a simple melt percolation thermal effects on s wave velocity are assumed to be accounted for entirely by the plate cooling thermal conduction model we point out that the thermal model under this assumption predicts asymptotically no correlation between s wave velocity and spreading rate specifically for spreading rate larger than about 3 cm yr 1 this contradicts the correlation observed in the data at shallow depths the existence of partial melt is thus required to explain the observed behavior at 38 and 66 km depths we start from four basic equations that govern the distribution of partial melt and derive the relation between the amount of partial melt and the spreading rate we adopt a simple power law relation between permeability k and porosity by k k 0 n where k 0 and n are constants and assume that pores are filled with melt we then set up an integral relation between s wave velocity and spreading rate the final formula indicates that the gradient in the correlation plots is the inverse of the power 1 n in the permeability porosity relation thus enabling us to constrain n as well as k 0 from seismic data the data also have some sensitivity to the depth to solidus we show that 1 the depth to solidus is probably within the range 60 100 km and 2 if the power n is n 2 3 then k 0 10 8 10 10 m 2 these parameters predict that porosity and fluid velocity are 1 2 and about 0 5 m yr 1 respectively the depth to solidus is consistent with previous estimates by petrological data but is perhaps the first and direct seismological evidence of partial melt from surface wave data analytical forms for the dependence on depth and spreading rate of porosity fluid velocity within permeable rocks and ascent times of magma are also obtained

aspherical earth structure from fundamental spheroidal mode data free oscillation data reveal heterogeneity in the earth s mantle whose geographical pattern is dominated by spherical harmonics of angular degree two and correlates well with the hydrostatically referenced geoid the heterogeneity can be modelled as localized in the transition zone 420 670 km depth and may be related to a large scale component of mantle convection

upper mantle structure from long period differential traveltimes and free oscillation data summary we have performed an inversion to model upper mantle structure using ss s differential traveltime residuals in conjunction with previously reported structure coefficient estimates obtained from free oscillation frequency and attenuation measurements the model we obtain is consistent with both the differential traveltime and structure coefficient data sets and provides nearly the same level of fit as independent inversions of these data sets we find that a relatively simple model parametrization appears to be adequate for the data used upper mantle velocity perturbations and lateral variations in the radii of boundaries at 400 and 670 km depth are parametrized with spherical harmonic expansions up to degree and order 8 the expansions are fixed at specific depth knots separated by roughly 200 km spanning the range 20 670 km radial variations in velocity are obtained by linear interpolation between these depth knots smoothness constraints were applied as part of the inversion procedure as well as corrections for the thickness and velocity variations of the crust the smoothness constraints were adjusted to require a smoother structure in the bottom portion 400 to 670 km depth of the model where the structure coefficients have the greatest sensitivity the upper part of the model is primarily constrained by the differential traveltime data the resulting misfit of the final model shows that on average the individual structure coefficients and ss s measurements are fit to within approximately 1 5 standard deviations we suggest that some of the misfit is due to lower mantle structure which is not included in the modelling the power as a function of harmonic degree for the top portion of the model 20 to 220 km depth does not fall off significantly at the higher harmonic degrees suggesting that the differential traveltime data may require models which include structure for degrees greater than 8 boundary perturbations at depths of 400 and 670 km trade off strongly with the velocity variations allowing variations of the order of f10 km in the radii of the discontinuities at 400 and 670 km provides a slight improvement to the data fit comparisons of several depths of our upper mantle velocity model to the geoid show the strongest correlation at degree 2 for structure near 670 km depth the distribution of slab structures is highly correlated to the degree 2 components of the model for depths of 200 to 670 km examination of the model in the vicinity of hotspots shows no consistent hotspot related signal

degree one components of the earth s interior abstract the earth s geoid is a constraint for models of the composition of the earth s interior the long wavelength non hydrostatic portion of the geoid is assumed to be due to density contrasts associated with the convective forces which drive plate tectonics the longest wavelength component degree one can be set to an arbitrary value by appropriate choice of coordinate systems with negligible effect on other components the degree one component is usually set to zero internal models are unconstrained at degree one and results at degree one are not often analyzed theoretical considerations predict an internal degree one component with an effect at the surface even greater than those of the other nonhydrostatic components of the earth s geoid mantle convection theories relative sea level curves mantle viscosity measurements and geodynamo models may be affected

uppermantle anisotropy and the oceanic lithosphere rayleigh wave and love wave dispersion data for oceanic paths cannot be satisfied by an isotropic uppermantle and it is incorrect to invert these two datasets independently for separate isotropic structures available phase and group velocity data are inverted for oceanic structure as a function of age taking into account anelastic dispersion sphericity and anisotropy the resulting models are quite different from previous results which ignore the above effects and the extra parameters involved in proper anisotropic inversion the models have a high velocity nearly isotropic layer at the top of the mantle that thickens with age and an anisotropic low velocity zone with an age dependent anisotropy the lid or seismic lithosphere reaches a maximum thickness of 50 km which is about one half the thickness obtained in previous isotropic or pseudo isotropic inversions the seismic lithosphere therefore may be comparable in thickness to the elastic or flexural lithosphere raising the possibility that both are controlled by effects other than temperature stress and time such as mineralogy crystal orientation or partial melting the velocities in the low velocity zone are higher than inferred by previous surface wave studies

travel times and station corrections for p waves at teleseismic distances approximately 3300 shallow focus earthquakes and 1000 seismic stations have been used in a study of p wave travel times and station residuals including azimuthal effects the events were selected from a catalog containing 160 000 earthquakes and those having uniform distance and azimuthal coverage were systematically relocated and used to refine p wave travel times and station corrections station corrections are provided for 994 seismic stations the station corrections involve three terms the static effect and two cosine terms with appropriate phase shifts they exhibit general consistency over broad geographic areas and where coverage is dense often show abrupt changes from one geological province to another the cos 2 terms appear to be due to upper mantle anisotropy and they correlate with the stress direction in the crust

measurement of mantle wave velocities and inversion for lateral heterogeneity and anisotropy 1 analysis of great circle phase velocities long period 100 330 s fundamental mode love and rayleigh waves have been processed to measure the great circle phase velocities for about 200 and 250 paths respectively the observations are inverted for regionalized phase velocities and for an even order harmonic expansion of the lateral velocity heterogeneity the regionalized inversions achieve a maximum variance reduction of about 65 and 85 for the love and the rayleigh wave data respectively the l max 2 inversions give a maximum variance reduction of about 60 and 90 for love and rayleigh waves respectively the l max 8 inversion does not make a large improvement in the fit the love wave phase velocities have more power in l 4 and 6 relative to l 2 than the rayleigh waves for both love and rayleigh wave data the sectoral component dominates the l 2 harmonics and this component is stable if we increase l max from 2 to 6 heat flow also has strong sectoral components lm 22 which are approximately in phase with those of the phase velocities the l 2 harmonics of the nonhydrostatic geoid are dominated by large zonal lm 20 and moderate sectoral components the sectoral components are in phase with those of the phase velocities the sectoral pattern of heat flow and phase velocity is controlled by high heat flow low velocity of the east pacific rise and western north america which is reinforced by low velocities in the antipodal region red sea gulf of aden east african rift by contrast the geoid l 2 pattern is dominated by geoid highs over the western pacific subduction zones a spherical harmonic expansion of regionalized phase velocities shows that they have l 2 variations similar to those of the l max 2 nonregionalized inversions this means that the regionalization approach is appropriate as a first step for studying lateral heterogeneity of the earth however the great circle phase velocities are not sufficient by themselves to uniquely locate the lateral heterogeneity the same is true for free oscillation data regions of convergence have the interesting property of being slow for short period waves and fast faster than shields for long period waves

simultaneous inversion for 3 d variations in shear and bulk velocity in the mantle until recently most of the seismic tomographic modeling has been addressing the question of lateral heterogeneity either in p or s wave velocities the s wave velocity variations are larger and hence provide stronger signal on long period waveforms the direct p travel times being the first arrivals on the other hand are most frequently reported in the international seismological centre isc bulletins in mineral physics experiments the variation in bulk velocity is more often measured to better understand the differences between vp and vp patterns and better link the results from mineral physics to those of seismic tomography we formulate the inverse problem in terms of relative perturbations in the shear velocity vs 12 and bulk sound velocity v k 12 we use a large data set which consists of waveforms waveform derived travel times and travel times from the isc bulletins the earthquakes are relocated using corrections for lateral heterogeneity the events which cannot be reliably determined are discarded the model is defined as spherical harmonics to degree 12 horizontally and as chebyshev polynomials to order 13 radially for both shear and bulk sound velocity the inversion is performed under smoothness constraint the resolution tests and bootstrapping analysis indicate that the model is well recovered particularly at long wavelength the results indicate a much larger variability of shear than bulk sound velocity the model explains observations well the most intriguing result obtained in this study is that the variations in shear velocity and bulk sound velocity are negatively correlated in the lowermost mantle the explanation is not very clear from the mineral physics point of view it is not unlikely that this could be explained in terms of thermal variation even though we are unwilling to rule out the possibility of large wavelength compositional variations

toroidal poloidal partitioning of global post seismic deformation an earth model subject to dislocations is studied in order to investigate the toroidal poloidal content of global post seismic deformation differently from previous analyses our approach allows us to deal with some of the main complexities of the real earth such as sphericity self gravitation and rheological stratification the time dependent ratio between toroidal and poloidal displacements is evaluated in the near and far field of both strike and dip slip lithospheric sources characterized by a finite length our findings show that post seismic deformation changes its nature from poloidal to toroidal and viceversa on time scales of several decades and over distances comparable with the dimensions of the lithospheric plates the effects on horizontal velocities in north america of both poloidal and toroidal components induced by the alaska 1964 earthquake is comparable with the signatures due to postglacial rebound these two geodynamical phenomena are currently detectable by variations along baselines connecting vlbi stations

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

regional 3 d heterogeneities by waveform inversion application to the atlantic area the waveform inversion method described in woodhouse dziewonski 1984 was modified to retrieve regional scale 3 d heterogeneities by using the minor arc part of seismograms the lateral heterogeneities are expanded horizontally into blocks 10 10 and radially into legendre polynomials up to order 3 0 670 km and thus the results show much fine details of lateral variation than previous global scale studies we assumed that the heterogeneities produce the perturbation of eigenfrequencies which are the minor arc average of local eigenfrequency shift we applied the method to the upper mantle beneath the atlantic ocean and its environments care was taken about the weighting of the data set we found that the fit of each seismogram became better when the weighting of each seismogram is proportional to the inverse of initial data residuals resolution is good in the triangular region surrounded by south america europe and north america resolution is not good in the south atlantic because of the poor path coverage depth resolution is not clear because of the use of legendre polynomials though the results suggest a broad half width of the order of 200 km or more we found some similarities between previous global studies and our results for example low velocities beneath the east pacific rise chile rise and azores triple junction and a high velocity canadian shield are obtained however there are also differences the high velocity zone beneath the brazilian shield at shallow depth is not a prominent feature in this study instead we found a somewhat unexpected feature near the romanche and vema fracture zones where shallow positive anomalies exist smoothed results calculated by the spherical harmonic expansion are also shown for the purpose of comparison with global studies

the 3 d shear wave structure in the mantle by overtone waveform inversion ii inversion of x waves r waves and g waves summary the 3 d upper mantle structure from the surface of the earth to a depth of about 1000 km is obtained by inverting waveforms of fundamental and higher mode surface waves minor and major arc waves of r waves g waves and x waves higher mode wave packets are used as basic data two features of the solution seem fairly robust one is the shallow structure in the upper few hundred kilometres which is strongly correlated with the age of the crust the second feature is the deep fast velocity anomaly near the western pacific indonesia philippines and mariana region and its antipodal region of south america both of which are subduction zones which forms a strong l 2 pattern simple slab models with 100 km thicknesses of 10 per cent faster velocity material do not explain such large scale fast velocity anomalies this may indicate large scale deformation of the 670 km discontinuity piling up of slabs in the upper mantle or thickening lithosphere in the lower mantle or large horizontal motions of subducted material these results are stable whether an earth model 1066a or prem is used as a starting model

the zh ratio method for long period seismic data sensitivity kernels and observational techniques summary amplitude ratio between vertical and horizontal components of rayleigh waves is controlled by structure beneath a seismic station this ratio measured as a function of frequency has been extensively analysed for shallow crustal structure study in earthquake engineering and applied seismology this quantity termed the zh ratio in this paper may be useful for deep earth structure study and its feasibility for the frequency range between 0 004 and 0 05 hz period 20 250 s is explored in this paper for depth sensitivity kernels we demonstrate that a numerical approach is practical and provides sufficient accuracy for structural inversion depth extent of sensitivity kernels are about half of depth extent in phase velocity kernels indicating that the zh ratio is useful for studying the lithospheric structure two observational approaches for measurement of the zh ratio are presented the first approach uses simple envelope amplitude ratio and the second approach uses waveform correlation technique between vertical and horizontal components the zh ratio data alone only constrains structure beneath seismic stations but recent densification of seismic networks may make it possible to extend the analysis to regional scale structure a greater opportunity may exist in combination of the zh ratio method and the phase and group velocity measurements

surface wave tomography for southeastern asia using iris farm and jisnet data abstract previous seismic studies for southeastern asia around indonesia have used global seismic data and thus included few regional broadband seismic stations to better understand seismic structure of this area we temporarily deployed japan indonesia seismic network jisnet which was composed of 23 broadband seismic stations in central to western indonesia since 1998 under the super plume project of japan in this study we analyse regional jisnet data and global incorporated research institute of seismology iris fast archive recovery method farm data in order to obtain detailed images of 3d s wave velocity vs of this area we use vertical component lp seismograms of farm data recorded from 1989 to 1993 13471 seismograms and vertical component of broadband jisnet data recorded from 1998 to 2000 1782 seismograms we select seismic events with body wave magnitudes greater than 5 5 and take hypocenters and centroid moment tensor solutions from the harvard cmt catalogue phase velocity anomalies of fundamental mode rayleigh waves period from 34 to 197 s relative to preliminary reference earth model prem are determined by measuring phase differences between the synthetic waveforms and the observations global distribution of rayleigh wave phase velocities are determined by block inversions using damped least squares with a finer block size of 5 5 for the indonesia region than the surrounding area firstly we compare the results obtained from the inversion using the farm data alone called farm inversion and those from the inversion using both the farm and the jisnet data called jisnet farm inversion for the fundamental rayleigh waves of short periods phase velocities obtained from the jisnet farm inversion show greater degrees of negative anomaly throughout indonesia than those from the farm inversion the clearest difference is seen for the region around kalimantan and java slower phase velocities of less than 1 relative to prem at periods of about 70 s are obtained by the farm inversion whereas including jisnet data requires lower phase velocity anomalies of 2 5 secondly we compare the resolution kernels of both data set around java sumatra kalimantan and sulawesi the resolution of the jisnet farm inversion is substantially better than that of the farm data alone with the peaks of resolution kernels up to five times as high as those for the farm inversion the best resolution improvement is obtained for west kalimantan to java sea thirdly we invert the phase velocity perturbations for the modes to obtain the upper mantle 3d s wave velocity vs structure of the study area the jisnet farm inversion tends to give larger up to four times negative vs anomalies when compared with the farm inversion the vs heterogeneities concentrate in the uppermost mantle shallower than 200 km throughout indonesia beneath sumatra java and kalimantan the uppermost 100 km of the mantle is slower than prem by about 2 3 a prominent high vs anomaly 2 4 around the depths from 100 to 200 km extends from northern australia through the banda sea to east sulawesi and halmahera the subducted indian plate is visible as a nearly 1 high vs anomaly

stacking investigations of the dispersion of higher order mantle rayleigh waves and normal modes abstract using a number of stacking techniques including non linear stacking we have systematically investigated both in the travelling wave and normal mode formalisms the dispersion of the third fourth and fifth branches of rayleigh overtones which travel with identical group velocities at similar frequencies and are a prominent part of the horizontal away from the source components of long period seismograms from major earthquakes using data from six major events recorded on the global digital seismological network we have extracted more than 100 normal modes from these three branches in the period range 82 160 s our results are generally in excellent agreement with values computed from available models of the earth and also with previously published values for a well separated part of the third branch

turbulence intensities of shallow rain impacted flow over rough bed a thorough understanding of the effect of raindrop impacts on the characteristics of a shallow flow is very helpful to properly predict and control water erosion the turbulence properties of a shallow rain impacted flow over a rough bed were studied using a two dimensional fiber optic laser doppler velocimeter and an oscillating type raindrop generator it was found that the value of momentum correction factor for a rough boundary was much smaller than that for a smooth boundary at a given value of reynolds number because of the vertical mixing effect of the boundary roughness for the condition without rainfall the vertical distribution of the longitudinal turbulence intensity became more uniform as the boundary roughness increased for the fully rough condition with rainfall and constant roughness size the effect of roughness on the distributions of turbulence intensities was small similar to the condition with smooth boundary the rainfall generated turbulence was greatest near the water surface and decreased downward at an exponential rate for the flow over rough bed two types of statistical correlations were developed to predict the distributions of both the longitudinal and the vertical turbulence intensities depending on whether the flow is completely penetrated by the raindrops

lithospheric thickness and thermal anomalies in the upper mantle inferred from the love wave data the study of global earth structure by surface waves can now resolve wavelengths of about 1000 km phase velocity maps are detailed enough to test some plate tectonic models our results for love waves indicate l continuous thickening and or velocity increase with age of oceanic plates older than 100 million years 2 failure of boundary layer scaling laws seen in the rate of thickening of oceanic lithosphere and 3 asymmetric thickening of plates about ridges the latter two points suggest that there is a wide variety of differences in the thermal states of oceanic lithosphere thermal anomalies possibly caused by hotspots are identified in residual maps

mantle layering from scs reverberations 1 waveform inversion of zeroth order reverberations this is the first paper in a four part sequence that examines the nature of mantle layering required by the multiple scs phases and internal reflections observed within the reverberative interval of sh polarized seismograms here we present path averaged estimates of the two way travel times through the crust mantle scs and crust alone m the whole mantle quality factor qscs and the reflection coefficient at the m discontinuity r0 zm obtained by iterative waveform inversion of scs reverberations we show that qscs estimates derived from direct waveform inversion can be biased significantly if reverberations originating within the crust are ignored especially in continental regions where the crust is thick applying our technique which explicitly models crustal reverberations we substantially expand the geographical coverage of scs and qscs measurements available from previous studies the scs data correlate well with whole mantle travel times predicted by the harvard tomographic models both the scs data and the qscs data support the hypothesis that variations in velocity and attenuation structure between old continents and oceans persist to depths of several hundred kilometers in particular the value of qscs derived for paths crossing stable continent is very high 280 30 at 30 mhz compared with that for mature ocean basin 189 16 consistent with the thick plate model of cratons requiring that differences in thermal structure extend to several hundred kilometers the crustal thicknesses implied by the observations of path averaged m are consistent with those inferred from short range refraction data gravity measurements and surface topography the path averaged reflectivity of the m discontinuity is also tectonically correlated becoming brighter as the percentage of continental crust encountered along the path increases this result implies that on average the impedance at the base of the continental crust is significantly lower than at the base of the oceanic crust

geohydromechanical processes in the excavation damaged zone in crystalline rock rock salt and indurated and plastic clays in the context of radioactive waste disposal abstract the creation of an excavation disturbed zone edz or excavation damaged zone edz is expected around all man made openings in geologic formations macro and micro fracturing and in general a redistribution of in situ stresses and rearrangement of rock structures will occur in this zone resulting in drastic changes of permeability to flow mainly through the fractures and cracks induced by excavation the edz may have significant implications for the operation and long term performance of an underground nuclear waste repository various issues of concern need to be evaluated such as processes creating fractures in the edz the degree of permeability increase and the potential for sealing or healing with permeability reduction in the zone in recent years efforts along these lines have been made for a potential repository in four rock types crystalline rock salt indurated clay and plastic clay and these efforts have involved field laboratory and theoretical studies the present work involves a synthesis of the ideas and issues that emerged from presentations and discussions on edz in these four rock types at a cluster conference and workshop held in luxembourg in november 2003 first definitions of excavation disturbed and edzs that may be applicable to all four rock types are proposed then an approach is suggested for the synthesis and intercomparison of geohydromechanical processes in the edz for crystalline rock salt indurated clay and plastic clay comparison tables of relevant processes associated factors and modelling and testing techniques are developed a discussion of the general state of the art and outstanding issues is also presented a substantial bibliography of relevant papers on the subject is supplied at the end of the paper

source mechanisms of twenty six large shallow earthquake ms 6 5 during 1980 from p wave first motion and long period rayleigh wave data source mechanisms of 26 large shallow earthquakes are determined in terms of a double couple point source with a correction for the nondirectional part of source finiteness by using p wave first motions and long period rayleigh wave spectra recorded on wwssn ida and gdsn networks the combined use of both data sets allows us to determine the double couple mechanism uniquely in most cases constrained linear moment tensor inversion m xz m yz 0 correctly determines the strike of the fault but fails to estimate the dip and underestimates the scalar moment all thrust events along the deep sea trenches analyzed in this study show nodal planes which dip perpendicular to the trench axis at an angle shallower than 45 the fit to data of the double couple inversion is comparable to that of the constrained moment tensor inversion using the phase spectra of surface waves we can detect a slow source process with an accuracy of about 10 to 20 sec

finite element modelling of surface wave transmission across regions of subduction summary propagation of rayleigh waves across the regions of subduction of japan and of the north island of new zealand is examined in the frequency domain by the finite element method study of the japan region of subduction ese of the island of honshu has shown that for perfectly elastic 2d models although love waves decrease in velocity across the region rayleigh waves of periods of 35 60s increase slightly in velocity the material properties of the predominantly crustal material being subducted appear to slow the love waves whereas the rayleigh waves of periods of from 35 to 60 s tend to retain their oceanic velocities which are higher than the velocities of rayleigh waves of those periods for the island of honshu amplitude calculations have shown that at periods of 60 s down to 10 s love waves are increasingly forward scattered into higher love modes whereas at a period of 20s 98 per cent of the energy of rayleigh waves is transmitted as the rayleigh fundamental mode this result together with that of drake for the continental margin at berkeley california confirms the practice of using rayleigh waves at a period of approximately 20 s measured at seismographic stations near continental margins and near regions of subduction to estimate the magnitude of teleseisms study of the new zealand region of subduction se of lake taupo on the north island of new zealand has shown similar results to those for the japan region of subduction although love waves decrease in velocity across the region rayleigh waves of periods of 60 s down to 20 s increase slightly in velocity amplitude calculations have shown that at periods of 60 s down to 15 s love waves are increasingly forward scattered into higher love modes on the other hand at a period of 20 s 96 per cent of the energy of rayleigh waves is transmitted as the rayleigh fundamental mode at a period of 10 s in contrast to the results for the japan region of subduction and for the continental margin at berkeley 73 per cent of the energy of love waves is transmitted as the love fundamental mode and 97 per cent of the energy of rayleigh waves is transmitted as the rayleigh fundamental mode amplitude and phase changes of love and rayleigh waves at continental margins and in regions of subduction need to be allowed for when waveform inversions of waves which have traversed these regions are made

cause of low velocity anomaly along the south atlantic hotspots a recent upper mantle seismic velocity model shows a narrow strip of asthenospheric low velocity anomaly in the south atlantic that connects four hotspots tristan da cunha st helena ascension and cape verde this deep strip of slow velocity anomaly runs approximately along the seam where africa and south america broke up according to available plate reconstruction models there is thus a possibility that the deep slow velocity strip is preserving the shape of the boundary along which the break up occurred if this is the case it will be a useful constraint in the reconstruction of plates a question arises however as to why there is a line of low velocity anomaly rather than localized low velocity anomalies near hotspots we propose three possible causes for this observation which are 1 upwelling along this line 2 lithosphere controlled passive breakup and 3 plume controlled breakup with lateral channeled flow from plumes to the seam of breakup when rifts were created between adjacent hotspots we favor the last hypothesis since it naturally explains the local velocity minimums near hotspots as well as the connected low velocity anomaly and furthermore the same mechanism seems to be working under the red sea in the present earth

worldwide distribution of group velocity of mantle rayleigh waves as determined by spherical harmonic inversion we have determined the worldwide distribution of group velocity of mantle rayleigh waves for periods between 100 and 300 sec without assuming any regionalization group slowness 1 u is expressed by spherical harmonics and the coefficients up to angular order 7 have been determined from travel times of rayleigh waves by a least squares method from these u has been synthesized since we cannot obtain information about the odd terms of the expansion from one circuit measurements around the world we have used group velocities of mainly r 2 and r 3 the overall pattern of u for periods between 100 and 200 sec is consistent with results of previous pure path and regional studies group velocities for tectonically active regions are low and those of the shields and the northwestern pacific are high

global tomography from rayleigh and love wave dispersion effect of ray path bending summary a large data set of fundamental mode rayleigh and love wave phases has been employed for global tomographic inversions these data represent observations of the first arriving surface waves r1 and l1 from approximately 850 seismic events with about 10 observations of dispersion per event the inversion for laterally varying depth dependent structure is performed in several steps at discrete periods from 111s 250s for love waves and from 111s 200s for rayleigh waves we first determine simultaneously the global distribution of phase velocity anomaly and the relocations of the seismic events each phase velocity distribution is then corrected for laterally varying moho depth and bathymetry followed by inversion for 3 d earth structure in the depth range 0 240 km in order to lie within the limits of ray theory we restrict all model perturbations to a degree 0 16 spherical harmonic expansion a second order scattering ray path correction is included in the inversions the phase velocity perturbations show a high correlation with surface tectonics at shorter periods comparison of inversions shows that those performed without the ray path correction exhibit a complicated pattern of fast and slow velocity bias the only common feature in the patterns of bias with respect to period or wave type is that fast velocity bias is concentrated in regions of large structural gradient the amplitude pattern of the depth dependent model has pronounced peaks in the intervals 0 70 km and 140 210 km the deeper peak is associated with lateral variations in asthenosphere structure we derive new estimates for the spherically averaged phase velocities of the fundamental mode rayleigh and love waves the spherically averaged phase velocities are decreased by about 0 1 per cent by including the ray path correction these phase velocity dispersions can be simultaneously fit well with an isotropic model either with or without the ray path correction but particularly well when the ray path correction is included in both cases a pronounced low velocity zone of the global extent is required in the depth range 120 190 km

whole earth structure estimated from seismic arrival times the arrival times of 10 compressional and shear phases p s pp pcp ss scs pk pab pk pbc pk pdf sk sac and two sets of differential times ss s410s and ss s660s are used to infer the earth s three dimensional structure with the exception of ss sds the raw data are composed of arrival times from the international seismological centre isc catalogue the isc events have been relocated using p and s phases and the ak135 radial earth model a total of 818 655 summary arrival times constrain lateral velocity variations in the crust mantle and core we also determine relocation parameters for all events stations corrections for each phase boundary topography 410 km 660 km core mantle boundary inner core boundary and inner core anisotropy variations our model of p and s velocity variations in the crust and mantle contains the general features observed in other body wave inversions a low velocity ring around the pacific ocean basin in the depth range 35 400 km high velocity anomalies associated with subducting slabs most prominent in the depth range 660 1070 km and high velocity anomalies surrounding the pacific basin just above the core mantle boundary in the outer core there is evidence of a latitudinal variation in velocity approaching 0 6 in magnitude with lower p velocities at the poles and higher velocities near the equator this pattern is observed throughout the outer core but is most prominent in the depth range 3671 4071 km and near the inner core boundary synthetic tests indicate that outer core features are moderately resolvable and inversions of random arrival times indicates that the anomalies are a factor of 2 above the estimated parameter noise level lateral heterogeneity in the inner core trades off with anisotropy resulting in poor resolution of isotropic velocity variations anisotropy in the inner core is predominantly subparallel to the earth s axis and of the order of 3 but this value can decrease if more inner core isotropic lateral heterogeneity is allowed a comparison of structure above and below the core mantle boundary cmb indicates that velocity heterogeneity is uncorrelated across the cmb but there is a moderate correlation between cmb topograpy and outer core heterogeneity an inversion in which the pk pdf residuals were absent indicates that the latitudinal pattern of outer core velocity variations is not due to the influence of inner core velocity structure

modelling curved surface wave paths membrane surface wave synthetics summary earth s heterogeneity near the surface is so severe that surface waves with period 20 s exhibit complicated propagation effects such as curved paths and multiple rays in order to take account of these effects a new method to analyse surface waves is developed the method which we call the membrane surface wave method is an approximation to the green s function method in a 3 d medium and is valid for a laterally smoothly varying media we also present the formulae to invert the seismograms as an example we apply the method to a preliminary california model use of the method for the forward calculation shows that heterogeneity in the model is so severe that the wavefront due to the whittier narrows earthquake is split in two by the time it reaches the san francisco bay area the kernels in the inverse formula to the six berkeley stations show curved paths multipathings and finite wavelength effects and visually demonstrate how waves sample the medium the method is attractive in that these complications cause no problems in its application

analysis of flow path around the sealing section hg a experiment in the mont terri rock laboratory as part of the hg a experiment in the mont terri rock laboratory large scale in situ water gas injection experiments was conducted in a microtunnel this research work focuses on the numerical analysis of the experimental data and the in situ observations concerning a temporary change of the hydromechanical properties of opalinus clay during experimental operations three phases were numerically interpreted these included the generation of excavation damaged zone during tunnel excavation in which highly permeable flow paths around the tunnel have been formed the self sealing effect during water tests and the pressure evolution during a long term gas injection test a coupled two phase flow and mechanics model taking into account the strong anisotropic properties of opalinus clay was developed to interpret the measured data the hydraulic anisotropy was described by a transversely isotropic permeability tensor an elasto plastic model was established to consider both stiffness anisotropy and strength anisotropy anisotropic plasticity was studied using the microstructure tensor method

measurements of mantle wave velocities and inversion for lateral heterogeneities and anisotropy 3 inversion lateral heterogeneity in the earth s upper mantle is investigated by inverting dispersion curves of long period surface waves 100 330 s models for seven different tectonic regions are derived by inversion of regionalized great circle phase velocity measurements from our previous studies we also obtain a representation of upper mantle heterogeneities with no a priori regionalization from the inversion of the degree 6 spherical harmonic expansion of phase and group velocities the data are from the observation of about 200 paths for love waves and 250 paths for rayleigh waves for both the regionalized and the spherical harmonic inversions corrections are applied to take into account lateral variations in crustal thickness and other shallow parameters these corrections are found to be important especially at low spherical harmonic order the trench region and fast velocities down to 250 km under shields below 200 km under the oceans both s velocity and s anisotropy support a model of small scale convection in which cold blobs detach from the bottom of the lithosphere when its age is large enough the spherical harmonic models clearly demonstrate a posteriori the relation between surface tectonics and s velocity heterogeneities in the first 250 km all shields are fast most ridges are slow below 300 km a belt of fast mantle follows the pacific subduction zones however at greater depths large scale heterogeneities that seem to bear no relationship to surface tectonics are observed the most prominent feature at 450 km is a fast velocity region under the south atlantic ocean smaller scale heterogeneities that are not related to surface tectonics are also mapped at shallower depths an anomalously slow region centered in the south central pacific is possibly linked to intense hot spot activity a very fast region southeast of south america may be related to subduction of old pacific plate between 200 and 400 km a belt of sv sh anisotropy follows part of the ridge and subduction systems indicating vertical mantle flow in these regions the spherical harmonic results open new horizons for the understanding of convection in the mantle perspectives for the improvement of the models presented are discussed

three dimensional velocity structure and resolution of the core mantle boundary region from whole mantle inversions of body waves the nature of the core mantle boundary cmb has important implications for deep earth processes particularly those which have their origin in the lower mantle or outer core the possibility of the existence of lateral p wave velocity variations in the outermost core is explored here by obtaining models of three dimensional cmb region velocity structure using an inversion of waveform data the numerical inversions involve determination of the three dimensional structure of the earth s outermost core and lower mantle using over 5000 long period seismic waveforms collected from global digital seismic networks spheroidal modes with periods between 33 and 100 s were selected to model the body wave portion of seismograms recorded from global earthquakes first order perturbations in s wave velocities in 11 mantle layers 200 350 km thick and p wave velocities in one outermost core layer comprise the least squares solutions to the inverse problem although the statistical f test supports the additional layer in the inversions this layer is not required by the f ratio to occur in the outermost core pattern retrieval resolution tests in which synthetic data constructed from an initial synthetic earth model are inverted for model parameters are used to compare parameters for one region to those of another in which some coefficient power smearing is suspected depth resolution tests indicate that the best radial resolution at the cmb is 500 km thus this method does not produce the resolution required for outermost core lateral velocity variation analysis an examination of the limitations of this approach demonstrates the need for waveform inversion techniques which more accurately predict raypaths in the deep mantle improvements in radial resolution are needed before whole mantle velocity models can begin to distinguish whether significant heterogeneity related to core mantle interactions occurs in the cmb region

global postseismic rebound of a viscoelastic earth theory for finite faults and application to the 1964 alaska earthquake a spherically symmetric earth model with viscoelastic rheology is used to study the postseismic rebound associated with finite lithospheric dislocations we perform a systematic study of surface deformations due to sources characterized by two and three dimensional faults modeled by a linear and planar distribution of point sources our approach is based on the normal mode technique for a layered earth with linear viscoelastic rheology and allows for a self consistent description of the time evolution of postseismic displacements due to strike and dip slip faults as a case study we compare the predicted horizontal displacements due to the 1964 alaska earthquake with very long baseline interferometry vlbi baselines changes observed in this region in the period 1984 1989 although subduction and postglacial isostatic adjustment are expected to contribute significantly to present day velocities our results show that the postseismic rebound due to the 1964 alaska earthquake plays a relevant role in the changes of several vlbi baselines the last section is devoted to the analysis of the evolution of other north american baselines as suggested by recent investigations based on forward approaches isostatic readjustment of the earth s crust in response to the melting of the last pleistocene ice sheets is a major contributor to baseline variations in this area our results indicate that a correct interpretation of vlbi baseline changes in north america should account also for the effects of postseismic deformation

spectra of mantle shear wave velocity structure summary we applied the stochastic method of gudmundsson davies clayton 1990 which was applied to isc p wave data to teleseismic isc s wave data to obtain an independent estimate of mantle structure we inverted the variance of s wave traveltime residuals of bundles of rays to obtain a description of the spectrum of lateral heterogeneity as a function of depth through the mantle the technique yields robust estimates of the traveltime scattering power the product of a characteristic scalelength of heterogeneity and the mean square of slowness perturbations we can estimate the characteristic scalelength half width from the autocovariance which can be reconstructed from the spectra hence by division we can estimate the root mean square slowness by extrapolating the variance of bundles of rays to bundles of zero cross sectional area we can also estimate the scale incoherent signal which is a plausible estimate of the noise in the data which is removed from the data we find that most of the structure generating shear wave traveltime residuals is located in the uppermost mantle about half of the structure is short scale harmonic degree 1 50 the large scale structure 1 50 has a half width of about 500 km in the upper half of the mantle this s wave half width is consistent with the p wave half widths determined by gudmundsson et al 1990 the s wave half width in the lower half of the mantle is poorly constrained it varies from 500 to 3000km which spans the better constrained value of 1200 km found by gudmundsson et al 1990 for p waves the incoherent scatter suggests that the signal to noise ratio of the s wave data set is around 1 5 assuming that the compressional and shear wave velocity variations are correlated then the signal weighted value of the ratio d in y ld in y is 2 as also found in normal mode studies this is much larger than the value of 0 8 1 4 suggested by laboratory experiments undertaken at atmospheric pressure there is no evidence of periodicity in the traveltime autocovariance this suggests little or no periodicity in the underlying convection the short half width through most of the mantle suggests high rayleigh number convection with its attendant small scale structures the power decreases by an order of magnitude or more in going from the upper mantle to the lower mantle the same as found by gudmundsson et al 1990 for p waves this large difference suggests either a change in convective regime and or a difference in the temperature sensitivity of elastic constants in both layers the increased short scale structure at the top of the mantle suggests that a large part of the seismic signature at this boundary is compositional since one would expect a red spectrum for a thermal boundary layer the derived spectra between 1 10 and i 50 are similar in shape to spectra from the mantle convection simulations of glatzmaier 1988 with a rayleigh number of 106 107 which would suggest layered convection if the comparison is valid

a 2 d synthetic study of global traveltime tomography a 2 d synthetic test study of global traveltime inversion for deep seated earth structure has been undertaken this was done by generating traveltime residual data using reasonable models for earth structure the data were then inverted by similar methods to those applied in global studies of earth structure our results indicate that models of the aspherical structure in the lower mantle based on traveltime data are only partially successful and only at the largest scales harmonic degree 3 and that maps of the core mantle boundary based on traveltimes are unsuccessful

lateral variations in mantle velocity structure and discontinuities determined from p pp s ss and ss sds travel time residuals on the basis of p pp s ss arrival times and ss s410s ss s660s differential times we construct models of mantle p and s velocity structure and boundary topography of the 410 km and 660 km discontinuities events from the catalog of the international seismological centre isc are relocated relative to the international association of seismology and physics of the earth s interior 1991 iasp91 velocity model using both p and s arrival times the arrival times are corrected for ellipticity and the pp and ss residuals are corrected for the topography at the bounce point the cap averaged pp p and ss s differential time residuals plotted at the pp and ss surface reflection points form broad coherent patterns the geographic distribution of the cap averaged residuals agrees quite well with pp p and ss s differential time residuals derived from long period global digital seismograph network gdsn data a robust lp inversion scheme is used to infer global mantle structure synthetic tests indicate that for regions well sampled by ss s410s and ss s660s differential times the velocity estimates are not seriously contaminated by the topography of the 410 and 660 km discontinuities however estimates of boundary deflections may be influenced by extensive p and s velocity variations of 3 or greater we find the 410 km discontinuity to be depressed by as much as 24 km beneath north america conversely the discontinuity is deflected upward underneath eurasia in some regions the topography of the 660 km discontinuity is quite distinct from that of the 410 km discontinuity but the two appear to be positively correlated a series of depressions are found at several intersections of the 660 km discontinuity with known subduction zones the elevated topography in the 410 km discontinuity beneath europe is underlain by a trough in the 660 km discontinuity a number of subduction zones are characterized by a thinning of the transition zone negative p and s velocity anomalies underlying back arc basins and tectonically active continental regions encircle the pacific where they are resolved the stable continental cratons are systematically positive velocity features that extend below 200 km with the inclusion of pp and ss travel time residuals we are better able to constrain midmantle structure most notably in the depth range 35 660 km beneath the northwest pacific we observe high p velocity where they are resolved mid ocean ridges are most clearly imaged as low velocity features in the s model the northern portion of the mid atlantic ridge is underlain by negative s velocity anomalies in the pacific the east pacific rise is an extensive low s velocity anomaly

waveform inversion for three dimensional density and s wave structure long period seismic data longer than about 100 s are sensitive to density as well as p wave and s wave structure in the earth seismograms containing overtone and fundamental mode signals are inverted directly for density and s wave velocity structure a simple relation between p wave and s wave velocity perturbations is assumed in order to reduce the number of unknowns a model is parameterized by spherical harmonics up to degree and order 8 and by five knots in depth at 30 220 450 670 and 882 km with linear interpolation between adjacent knots density resolution is good only at shallow depths in fact only the average in the upper 200 km is marginally resolved s wave resolution is generally good throughout the depth range s wave results show good correlation to surface geological features and are similar to previous studies density results show quite different patterns from s wave maps high density regions appear along the subduction zones surrounding the pacific ocean and low density regions appear in most major continents most continents have low density and high s wave velocity which suggests that continental mantle consists of compositionally different materials since thermal effects can never produce such perturbations high s wave velocity also suggests a relatively cold geotherm for continents and thus continents should consist of significantly low density material such as depleted mantle rocks as proposed by many researchers before the density map also correlates well with a geoid map for spherical harmonic components l 4 6 but not for l 2 3 it suggests that sources for these geoid undulations l 4 6 are in the upper mantle probably in the upper 300 400 km but those for l 2 3 are in deeper regions

an experiment in systematic study of global seismicity centroid moment tensor solutions for 201 moderate and large earthquakes of 1981 data from the global digital seismograph network were used to obtain centroid moment tensor solutions using the method of dziewonski et al 1981 results were obtained for 201 earthquakes ranging in seismic moment from 7 1023 to 3 1027 dyne cm the wide dynamic range of the sro asro stations allows us to investigate using the same algorithm series of events among which the smallest and the largest may differ in moment by a factor as large as 1000 among the events studied is a particularly interesting series in january 1981 off the island of honshu the main shock was preceded by three foreshocks and followed by four aftershocks all falling within the range of our analysis there is an indication that the source mechanism changes with the size of the event statistical analysis of the results for all earthquakes reveals that the half duration of shallow and intermediate events is approximated by 1 6 10 8 m01 3 the shifts in origin time for deep focus earthquakes are indicative of the general complexity of these events which depends only weakly on the seismic moment the extreme departures from a double couple mechanism seem to depend both on the moment and on the focal depth while for shallow earthquakes these departures decrease from a maximum at about 1025 dyne cm with increasing moment the reverse appears to be true with respect to deep focus earthquakes shallow earthquakes north of new guinea and along the solomon islands show systematic and substantial departures from the double couple mechanism

inversion for laterally heterogeneous upper mantle s wave velocity structure using iterative waveform inversion summary in contrast to previous work which treats the earth s lateral heterogeneity as an infinitesimal perturbation to a spherically symmetrical starting model we conduct iterative linearized waveform inversion for the earth s laterally heterogeneous structure we use the direct solution method dsm geller et al 1990a to calculate synthetic seismograms and their partial derivatives for a laterally heterogeneous earth model we invert surface wave data from the ida and geoscope networks we expand the lateral heterogeneity of rigidity in spherical harmonics up to angular order number 8 and use three parameters to specify the depth dependence of each harmonic giving us a total of 240 unknowns the shortwavelength lateral heterogeneity s 4 6 and 8 in the deeper part of the upper mantle obtained by this study differs significantly from m84a the relative improvement in the variance reduction as compared with model m84a is about 20 per cent for the ida data and more than 100 per cent for the geoscope data

inversion for laterally heterogeneous earth structure using a laterally heterogeneous starting model preliminary results summary we present a method for inverting for laterally heterogeneous earth structure with respect to a laterally heterogeneous starting model our method makes it possible to perform iterative linearized inversion of seismic waveform data in contrast previous methods have been limited to a single iteration in which the entire laterally heterogeneous part of the model is treated as a perturbation we demonstrate the feasibility of our approach by inverting for low angular order s 1 to s 4 laterally heterogeneous upper mantle structure with respect to a laterally heterogeneous starting model using data from the ida network

the effect of regional variation of lattice preferred orientation on surface waveforms summary we investigate the effect of the lateral variation of seismic anisotropy on long period surface waves calculating synthetic seismograms for earth models with azimuthal anisotropy whose hexagonal symmetry axes are horizontally oriented in the depth range between the moho discontinuity and 420 km depth the following anisotropic earth models are examined in the first model the hexagonal symmetry axes are uniformly oriented in the second model the azimuth of the symmetry axis changes according to n where n and are a positive integer and the colatitude respectively in the third model the seismic anisotropy is the same as that of the first model but the anisotropic region is restricted in a given range of colatitude for all anisotropic earth models a quasi love wave commonly appears as a wave packet prior to the rayleigh wave arrival on the vertical and radial component seismograms in the first earth model the quasi love wave is strongly excited when the ray path of the surface wave obliquely crosses the symmetry axes an anomalously large spectral amplitude which is caused by toroidal spheroidal coupling associated with the azimuthal anisotropy is found at frequencies lower than 4 mhz the second earth model shows that as the lateral variation of axis orientation becomes rougher the spectral amplitude anomaly is seen at higher frequencies and thus the quasi love waveform becomes high frequency the surface wave synthetics calculated for azimuthal anisotropy whose axis orientation varies laterally with very short wavelength exhibit a transversely isotropic characteristic in the third earth model if the surface wave arrives at a station after travelling into an anisotropic region then the quasi love wave is observed irrespective of whether the observation station is located in an anisotropic or an isotropic region the quasi love wave is effectively generated by love to rayleigh conversion in the vicinity of the boundary between isotropic and anisotropic regions

rifting of africa and pattern of mantle convection beneath the african plate abstract the mesozoic and cenozoic tectonic setting of the african continent is characterized by an extensional stress regime as is evident from the evolution of the west central and east african rift systems the opening of the indian and atlantic oceans and the development of tethys domain as well as from the results of geophysical investigations the most prominent feature of the bouguer gravity anomaly map of africa is a great belt of negative bouguer anomalies which extends across the entire african continent from ethiopia in the east to benguela in the west in conjunction with the red sea spreading zone this belt appears to encircle a centre in cameroon it probably corresponds to a distinct zone of lithospheric thinning and extension the entire african continent is characterized by higher than normal elevations it is located inside the african residual geoid high earthquake fault plane solutions confirm the extensional character of the present tectonic regime of eastern and southern africa where normal faulting predominates the average orientation of t axes is n s in south africa nw se in zambia mozambique and madagascar e w in kenya and ethiopia and ne sw in the red sea region from north to south the orientation of t axes rotates systematically in a clockwise sense by 130 and describes a radial pattern centred on equatorial west africa this indicates that the african lithosphere has been subject to continent wide radial extension around a hypothetical west african spreading centre referred to as the african spreading centre a asc a which coincides with the geographical centre of the african plate shear traction exerted by the convecting mantle on the base of the lithosphere is considered to be a major driving force of plate movements in the case of africa the continent wide regularities in the pattern of lithospheric extension the elevated position of the continent as well as the evolution of the mid oceanic ridge system surrounding africa provide distinct boundary conditions for the pattern of large scale mantle flow beneath the african plate it is proposed that relatively warm and less dense mantle material rises below africa forming a single mega plume or a number of plumes at the base of the african lithosphere the ascending material diverges and flows radially away from the centre of ascent corresponding to the asc a this ascending flow forms part of a very large mantle convection cell which occupies the eurafrican hemisphere the descending branch of this convection cell is located at a distance of 80 90 from the asc a the mid oceanic ridges surrounding the african continent are located between the upwelling and the downwelling branches of this convection cell at a distance of 50 60 from the asc a upper mantle flow below the sea floor spreading axes is uni directional and horizontal and is directed away from the asc a

scs wave splitting of deep earthquakes around japan summary scs wave splitting of five deep earthquakes in subduction zones near japan is investigated using horizontal seismograms recorded al jma stations for each earthquake we clearly observe uniform scs wave splitting in all stations over japan especially for the events located south of honshu in 1982 1984 and 1993 however the directions of fast polarized waves of these events differed by a maximum of about 50 from one another the orientation of fast polarized waves in the 1982 event was nnw sse those in the two later events wnw ese we also recognize this discrepancy in the results of the analysis of the 1971 sea of okhotsk event reported by fukao 1984 the sakhalin islands event in 1990 reveals a linear particle motion without such a change in direction of the second arrivals implying no anisotropy these observations are interpreted as indicating an anisotropic region within the slab near the earthquake sources but not beneath the receivers since the orientations of fast polarized waves recorded at each station are not common to all the earthquakes furthermore we consider that anisotropy exists non uniformly within the slab the event in 1982 which occurred in almost the same area as those in 1984 and 1993 showed a fast direction different from the events in 1984 and 1993 the 1982 event was 179 km deep but the two later events were at 398 km and 360 km respectively the fast direction observed from the 1982 event is parallel to the fossil plate motion whereas those from the events in 1984 and 1993 are parallel to the compression axis within the subducting slab the depth of 400 km is a phase boundary where olivine changes to spinel we consider that the most likely cause of the change in anisotropy direction is the re orientation of crystals associated with the phase change of olivine to spinel due to subduction of the slab

the nature and cause of polarization anomalies of surface waves crossing northern and central eurasia summary results of a pilot experiment preliminary to a systematic study of surface wave polarization across eurasia are presented long period fundamental rayleigh and love waves recorded by the broad band seismic stations kiv kislovodsk and obn obninsk of the iris ida network deployed in the former soviet union fsu were analysed from 14 events to the north east east and south east of these stations in search of particle motion anomalies using a technique called frequency time polarization analysis ftpan all anomalies indicate deviations of wave propagation paths to the north relative to the great circle paths polarization anomalies at obn are uniformly small 5 significant frequency dependent polarization anomalies 5 20 are found for rayleigh and love waves arriving at kiv from teleseismic events at a wide range of backazimuths 26 103 polarization measurements are repeatable both for a number of nearly degenerate events and for reciprocal paths and vary smoothly and continuously as epicentral location is moved consequently such measurements are robust and can provide useful structural information the systematics of the frequency dependence of the polarization anomalies as epicentral position is moved from north to south display sensitivity to structures at a number of length scales results from synthetic experiments using coupled normal mode and gaussian beam synthetics reveal that 1 recently constructed long wavelength aspherical models produce polarization anomalies that are significantly smaller 5 at kiv but of the same sign negative as the observed anomalies and 2 the frequency dependence of the observed anomalies must result from a combination of structures of differing wavelengths with scale lengths ranging from regional to global thus polarization measurements provide new information about currently unmodelled structures a model that fits the polarization anomalies observed at kiv includes a regional scale low velocity feature near to kiv in order to fit the large magnitude short period polarization anomalies and a smaller magnitude continent scale increase in upper mantle velocities and or the reduction of crustal thickness from south to north in central eurasia in order to fit the broad band longer period anomalies the small scale low velocity feature is a model of the sedimentary basin of the sub caspian depression we conclude that measurements of polarization anomalies can be obtained accurately that they are reproducible that they contain currently unmodelled information and that they should prove to be useful in combination with velocity and amplitude information in future tomographic inversions especially to help focus global scale models to regional wavelengths

three dimensional modelling of upper mantle structure under the pacific ocean and surrounding area summary long period 75 250 s fundamental mode love and rayleigh waves are inverted for the seismic velocity variations in the upper mantle under the pacific ocean and surrounding area the data are inverted to map the regional variation of phase velocity and then the velocity structure of the upper mantle no a priori regionalization is used in this study and the lateral heterogeneity is expanded horizontally into blocks lo x 10 to estimate the reliability of the velocity distribution we have calculated the resolving kernels in the central nw ne and sw regions the resolving kernels have fairly sharp peaks in the se region however resolution is not so good the results show good correlation with surface tectonics in the velocity map shields and ridges are the major features in the depth interval 50 100km anomalies associated with the east pacific rise and the shields persist to 300 km at 400 and 500 km high velocity anomalies appear under the eastern and southern pacific ridges and a low velocity anomaly appears beneath australia the present study provides better resolution than previous studies because of the better path coverage for example a large low velocity anomaly emerges under hawaii down to the depth of 200 km for sh velocity the horizontal extent of this anomaly is comparable to the sue of the hawaiian swell this feature supports that the hawaii hotspot is an isolated truly anomalous feature in the pacific ocean

global postseismic gravity changes of a viscoelastic earth a spherically symmetric earth model with a viscoelastic mantle and an inviscid core is used to study the gravitational perturbation due to a lithospheric shear dislocation in the coseismic and postseismic regime our approach is based on a quasi static solution of the equilibrium equations taking advantage of the normal mode technique for a layered incompressible earth with linear viscoelastic rheology we perform a systematic study of space and time evolution of gravity changes associated with a wide selection of seismic sources investigating the effects of several different mantle viscosity profiles our results show that the gravitational signal is sensitive not only to the viscosity of the asthenosphere but also to that of the mantle including the portion below the 670 km discontinuity as a case study we compute the coseismic and postseismic gravity perturbation due to the 1964 alaska earthquake the last section is devoted to the analysis of the postseismic relaxation rates of the gravitational perturbation following that earthquake for several different viscosity profiles of the mantle our results show that experimental attempts to obtain reliable detection of static and quasi static gravitational perturbation associated with seismic events would be of great importance in understanding the dynamic and viscosity profile of both upper and lower mantle

the three dimensional shear wave structure in the mantle by overtone waveform inversion i radial seismogram inversion summary the three dimensional 3 d shear wave structure of the mantle down to the depth of about 900 km is obtained by inverting waveforms of radial component seismograms radial component seismograms contain large amplitude overtone signals which circle the earth as wave packets and are sometimes called x1 x2 x3 we use data which contain r1 x1 and x2 and filtered between 2 and 10mhz it is shown that unless each seismogram is weighted all seismograms are not fitted uniformly only data from large earthquakes are fitted and the final velocity anomalies are biased by the small number of large earthquake data resolution is good at shallow depths becomes worse in the intermediate depth range between about 400 and 500 km and then becomes better at greater depth ranges 600 900km even though we use only spheroidal mode data velocity anomalies in the shallow structure show excellent correlation with the age of the surface rocks of the earth in the deeper regions between about 600 and 900km south america shows a fast velocity anomaly which may indicate the slab penetration beyond 700 km there another region which shows a fast velocity anomaly is the mariana trench but other subduction regions do not show such features

the effect of deformation history on the evolution of olivine cpo abstract olivine crystallographic preferred orientation cpo is the primary cause of seismic anisotropy in the upper mantle in tectonic environments with complex flow patterns for example corner flow near mid ocean ridges or subducting slabs the interpretation of seismic anisotropy may be complicated by evolving thermochemical deformation conditions and the integrated deformation history to understand how deformation history influences cpo evolution deformation experiments were conducted on samples of aheim dunite which has a strong pre existing texture experiments were performed in a triaxial geometry using a griggs apparatus at p 1 gpa t 1473 k up to a maximum strain of 0 7 to simulate different deformation histories samples were deformed in three different configurations with the pre existing foliation perpendicular oblique and parallel to the shortening axis of deformation distinct patterns of cpo development are observed for each experimental configuration likewise texture strength symmetry and orientation evolved differently in each set of experiments these data are interpreted as evidence that cpo did not reach steady state and that achieving steady state texture requires larger strains than previously thought it is concluded that the integrated deformation history plays a significant role in cpo evolution and the consequent interpretation of seismic anisotropy in earth s mantle

effect of sharp lateral heterogeneity on the earth s normal modes when inverting normal mode data for global large scale heterogeneity possible biases due to small scale structure are commonly ignored the authors conducted two experiments in the first one they calculated with a recently developed first order scattering formalism the effect of a simplified subduction zone model on the eigenfrequencies of the fundamental spheroidal mode branch the frequency shifts induced by this single subduction zone appear to be smaller by only a factor of 3 to 4 than shifts observed on long period seismograms or than shifts induced by existing models of global upper mantle inhomogeneity the second experiment involved a model of a hot spot plume on the core mantle boundary solving the variational problem with many coupling terms included the authors calculated the effect of such a plume on the amplitude of some low angular order modes the results suggest an effect at least as large as that due to available large scale mantle modes it thus appears that relatively small scale sharp lateral structure in different depth ranges of the earth may have an important effect on normal mode observations and that these effects may not be ignored in inversions of normal mode data

higher order moments of velocity fluctuations in an open channel flow with large bottom roughness the present study was undertaken to examine the effect of surface roughness on the higher order velocity moments in a turbulent open channel flow the wall roughness is large and the ratio of the roughness size to the depth of flow ranges from 0 1 to 0 15 flow over two types of roughness conditions ribs and dunes are examined and compared with that over a smooth open channel in the case of the rib roughness three different spacings are used p k 4 5 9 and 18 here p distance between the leading edges of two consecutive ribs and k height of a rib with square cross section the shape of the smooth wall dunes was geometrically similar to that commonly used in previous studies in an effort to understand the influence of local wall roughness rough wall dunes are also used in the present study the variables of interest include higher order moments conditional statistics based on a quadrant analysis relationship of higher order moments to the reynolds stress and energy production although there

tomographical mapping of the lithosphere and asthenosphere beneath southern scandinavia and adjacent areas abstract in this paper we report on a seismic tomographical survey of the lithosphere asthenosphere beneath southern scandinavia and adjacent areas the ach inversion technique has been used and the observational data in the form of p wave travel time residuals have been obtained from seismogram records from networks in denmark southern norway and southern sweden the volume under investigation subdivided into four levels layers of 7 7 knots blocks each for estimation of velocity perturbations covers the area 54 62 n and 7 20 e and depth range 0 600 km major findings are as follows level 1 0 100 km pronounced velocity lows beneath southern jutland zealand the variscan foredeep and the sveco norwegian province of southeastern norway 1500 ma old the svecofennides of southeastern sweden exhibit relatively high velocities while the sveco norwegian province of southwestern sweden 1700 ma old is characterized by moderately high velocities the transition between velocity highs and lows coincides with the tornquist teisseyre line ttl or fennoscundian border zone level 2 100 300 km velocity anomalies are less pronounced at this level although velocity lows are found beneath the northern jutland zealand area and slightly northwestwards of the oslo rift the only velocity high is found beneath the southeasternmost part of sweden the ttl does not appear to have a clear counterpart in the velocity anomaly pattern in this depth range although a clearly unambiguous answer here would require far more extensive observational data a research goal of the future level 3 300 500 km and level 4 500 600 km velocity anomalies are weak which is not unexpected for the upper mantle beneath shield areas