propagation characteristics of lg across the tibetan plateau abstract we present the results of a study on the propagation of lg within the tibetan plateau we analyze over 1200 seismograms for lg propagation from 185 local and regional earthquakes recorded at distances from 150 to 2000 km 52 of which are located within the tibetan plateau although the propagation of lg has been observed across most of asia lg has not been observed for paths crossing the tibetan plateau we analyze paths that cross the plateau boundaries and paths contained entirely within the tibetan plateau lg is generated within the tibetan plateau and can propagate to epicentral distances of at least 600 km for events located outside of the tibetan plateau lg is either absent or severely diminished for paths that cross both the himalayan and kunlun ranges confirming that the margins of the plateau weaken lg transmission based on the observations from our qualitative analysis we invert lg amplitudes for event station paths that are confined to the tibetan plateau to estimate the quality factor q the inversion yields a frequency dependent q function q f 366 37 f 0 45 0 06 0 5 f 16 h z similar observations in other areas indicate that frequency dependent apparent q within the tibetan plateau is well below that expected for a typical continental interior instead it has a frequency dependence that is characteristic of a tectonically active region

coda of long range arrivals from nuclear explosions short period three component recordings from peaceful nuclear explosions pne of the profile quartz located in russia are used to constrain the nature of the coda of pne arrivals in particular we examine the unusually strong and extensive coda of the long range p n interpreted as a whispering gallery wg phase propagating to beyond 3000 km energy balance considerations in three dimensions show that such an extensive coda is inherent not only to wg but to all other p wave phases and can be explained by crustal scattering the long coda is a result of excitation of short period scattered waves pg sg lg rg within the crust by the waves incident from the mantle or conversely by generation of mantle phases from crustal guided waves within the source region the resulting estimates of coda q range between q 380 near 2 hz and q 430 near 5 hz and can be associated with crustal attenuation including the sediments our coda model also explains quantitatively the observed build up of the arrival amplitude with time and the apparent lack of a pronounced coda of the body wave arrivals from the mantle transition zone these effects result from adding up the energy of the later arrivals arriving during the codas of earlier arrivals we deconvolve the overlapping coda patterns and show that the true relative energies of the arrivals are significantly lower than the apparent energies measured from the raw records a whispering gallery interpretation of the long range p n and crustal scattering accounts for the entire range of observations of kinematic spectral and amplitude pattern of the pne wavefield and allows the derivation of constraints on attenuation

general features of the uppermost mantle stratification from long range seismic profiles abstract long range seismic studies made by russian institutions during the last two decades reached depths of 700 800 km on the continent peace nuclear explosions were used as a source and 100 km in the ocean ocean bottom stations recording 500 kg explosions in water comparison of the wave fields of these and other seismic profiles in russia western europe and the south atlantic shows that the classical lithosphere asthenosphere model is too simple to explain the observed data a stratified medium with alternating weak and rigid layers is a more realistic model of the upper mantle one of the layers is globally observed at a depth of 80 to 100 km it is located in the thermal lithosphere beneath old platforms at the bottom of the lithosphere under active tectonic areas and inside the asthenosphere below mid oceanic ridges relatively high velocities 8 4 to 8 5 km s are typical for this boundary both in the old platforms and in the high heat flow oceanic areas a change of structural pattern where the block structure of the uppermost mantle is transformed into a horizontally homogeneous one is typical at that boundary level such features suggest that the boundary separates the brittle and more ductile upper mantle layers and may be considered as the bottom of the global mechanical lithosphere

lg wave propagation in a laterally varying crust and the distribution of the apparent quality factor in central france the aim of this study is to evaluate the sensitix ity of lg waves to lateral changes of the earth s structure considering a simple model of uplift of the moho numerical simulations show that the geometrical attenuation of lg is not much affected by a smooth anomaly of the moho depth on the other hand the passing of the lg wave through the region of the moho uplift results in a clear deterioration of the wave shapes which confirms the occurrence of mode conversions the presence of an overlying sedimentary basin causes a local amplification of lg above the basin itself and the appearance behind the basin of a secondary surface wave guided in the sediments the effect of the basin on the lg wave is found to be reasonably taken into account by applying a local amplification function to the data we use a data set consisting of records of lg phases in france to test the conclusions of our numerical study the mapping of the apparent quality factor computed from lg at different frequencies confirms the interpretation of the strong attenuation of s waves around i hz in terms of scattering and shows the weak sensitivity of the amplitude of lg to smooth changes in the depth of the moho

studies of coda using array and three component processing the application of standard array processing techniques to the study of coda presents difficulties due to the design criteria of these techniques typically the techniques are designed to analyze isolated short arrivals with definite phase velocity and azimuth and have been useful in the frequency range around 1 hz coda is long in time and may contain waves of different types phase velocities and azimuths nonetheless it has proved possible to use or adapt array methods to answer two questions what types of waves are present in coda and where are they scattered most work has been carried out on teleseismicp coda work on local coda has lagged due to lack of suitable data and the difficulties of dealing with high frequencies the time domain methods of beamforming and vespagram analysis have shown that there is coherent energy with a high phase velocity comparable top orpp in teleseismicp coda these methods can detect this coherent coda because it has a fairly definite phase velocity and the same or close to azimuth as firstp orpp this component must consist ofp waves and is either scattered near the source or reflected in the mantle path as apdpp or precursorpp reflection the fourier transform method of the frequency wavenumber spectrum has been adapted by integrating around circles of constant phase velocity constant total wavenumber to produce the wavenumber spectrum which shows power as a function of wavenumber or phase velocity for teleseismicp coda wavenumber spectra demonstrate that there is a diffuse coda of shear lg or surface waves scattered from teleseismicp near the receiver wavenumber spectra also suggest that the coherent coda is produced by near source scattering in the crust not mantle reflection since it is absent or weak for deep focus events crustal earthquakes have a very strong coherent component of teleseismic coda suggesting scattering from shear to teleseismicp near the source three component analysis of single station data has shown the presence of off azimuth arrivals and may lead to the identification of waves scattered from a single scatterer

the seismic 8 discontinuity and partial melting in continental mantle strong scattered reflections beyond 8 degrees 8 offset are characteristic features of all high resolution seismic sections from the continents the reflections identify a low velocity zone below approximately 100 kilometers depth beneath generally stratified mantle this zone may be caused by partial melting globally initiated at equal depth in the continental mantle solid state is again attained at the lehmann discontinuity in cold stable areas whereas the zone extends to near the 400 kilometer discontinuity in hot tectonically active areas thus the depth to the lehmann discontinuity may be an indicator of the thermal state of the continental mantle

comparative analysis of teleseismic p coda and lg waves from underground nuclear explosions in eurasia this study has investigated the characteristics of p coda and lg waves recorded at the norsar and graefenberg arrays from presumed nuclear explosions in western russia lg waves were found to be more energetic relative to the preceding coda in the mid band frequency range 0 2 to 1 0 hz recorded on the broadband graefenberg instruments than in the high frequency band 0 6 to 3 0 hz at either array comparison of the log rms coda envelopes at the two arrays revealed that the early high frequency p coda at norsar is stronger relative to lg than at graefenberg also the amplitudes of p waves and early p coda waves within 55 sec after p recorded at the centers of the norsar subarrays are positively correlated indicating the effect of focusing defocusing on the p and coda waves however for subarrays which cluster spatially there is an inverse correlation which seems to be due to scattering attenuation suggesting that much of the early p coda is generated by local p wave scattering beneath the norsar array also the norsar coda envelopes flatten between about 219 and 352 sec after p whereas the graefenberg coda decays monitonically from the p wave out to the sn and lg arrival times the standard deviation across the norsar array of the log rms amplitudes of lg and s coda phases are higher by about 0 05 to 0 06 magnitude units than those of p coda phases these differences are probably related to differential site and propagation path effects on p s and lg waves in the p coda the flattening of the norsar coda envelopes appears to be a burst of energy not associated with any known regional phases the burst may be caused by forward scattering of lg to p waves along the path between the source and norsar based on a regional travel time curve for western russia the start and end time of the coda flattening is consistent with lg to p scattering in the distance range of 23 to 29 from norsar which brackets the ural mountains the lg propagation path from the source region to graefenberg does not appear to traverse the ural mountains which may explain why the coda flattening is not observed at graefenberg

2 d image of seismic attenuation beneath the deep seismic sounding profile quartz russia we present a 2 d image of the upper mantle attenuation using nuclear explosion data from the ultra long refraction reflection profile quartz our analysis is based on a modified common spectrum technique followed by least squares inversion for q and iterative ray tracing in the velocity structure obtained earlier the resulting attenuation structure corroborates the earlier model for northern eurasia as well as our recent estimate based on the analysis of the long range p n phase and provides significantly more detail than the existing models the resulting upper mantle attenuation structure is characterised by q values ranging from 400 to 1800 down to the depths of 150 190 and probably 400 km the attenuation increases horizontally in se direction away from the baltic shield our model exhibits strong 2 d vertical and horizontal attenuation contrasts a high attenuation layer in the depth range of 120 150 to 160 180 km can apparently be associated with the presence of a partial melts within the base of the lithosphere

frequency dependence of q in the mantle underlying the shield areas of eurasia part iii the q model summary a large set of teleseismic body wave data covering a broad range in frequency was analysed to determine the frequency arid depth dependence of q for p and s waves under the northern shield areas of eurasia based on numerous f estimates for p and s waves covering the seismic band between 0 02 and 8 hz a q model of the eurasian shield was constructed the data require a model in which q increases with frequency and which is characterized by q values in the upper mantle that are generally higher than those of global average models the model with the best fit includes a minimum in q between about 100 and 200 km depth and high q values on the order of thousands throughout most of the deeper mantle these results are generally consistent with proposed models of attenuation as a thermally activated process which is influenced by the temperature and pressure in the earth preliminary results suggest that t under tectonic regions is higher than t under shield regions for all frequencies over the 0 02 to 8 hz frequency range suggesting that q varies regionally as well as with frequency and depth

on the nature of the teleseismic pn phase observed on the ultralong range profile quartz russia the most prominent secondary phase observed in the records from the ultralong profile quartz crossing northern eurasia is the high frequency long range teleseismic pn this phase propagating with the group velocity of about 8 1 to 8 2 km sec to over 3000 km distances dominates the records within the frequency range above about 5 hz within this teleseismic pn we distinguish onsets of several branches having higher apparent velocities between 8 5 and 8 6 km sec using travel time modeling techniques we associate the teleseismic pn with whispering gallery modes traveling within the top 160 km of the mantle the long incoherent coda of this phase results from scattering and from reverberations of seismic waves within the crust the contrast in frequency contents between the teleseismic pn and deeper refracted and reflected phases is explained by the increase of inelastic attenuation within the prominent low velocity zone lvz below the depth of about 150 km

p wave mantle velocity structure beneath northern eurasia from long range recordings along the profile quartz high resolution seismic sounding of the mantle using two peaceful nuclear explosions pnes along the 3950 km long quartz profile in northern eurasia reveal major unexpected vertical and lateral mantle inhomogeneities in contrast to standard seismological earth models such as prem and iasp91 three rather than two mantle discontinuities are found between 400 and 700 km depth they are located at about 420 550 and 670 km depth lateral variations in depths amount to 10 20 km and associated p wave velocities vary by 0 1 km s 1 in the upper mantle the uppermost layer through which pn propagates extends down to about 100 km depth the mantle below this depth but above the 410 km discontinuity is characterized by alternating high and low p wave velocities in the depth range between 100 and 200 km the velocity fluctuates between 8 3 and 8 7 km s 1 and shows variations from shotpoint to shotpoint average velocities are clearly higher than standard seismological reference models this part of the mantle overlies a low velocity zone between about 200 and 300 km depth this channel also displays substantial lateral variation in depth which could be interpreted as a laterally variable asthenosphere beneath the west siberian basin the asthenosphere seems to be well established whereas it is only poorly defined under the uralian belt and the tectonic units to the northwest with the addition of more data from this and other profiles future aims include two dimensional and three dimensional tomographic modelling as well as modelling of petrological composition of the mantle down to 850 km depth beneath northern eurasia

observational and theoretical constraints on crustal and upper mantle heterogeneity abstract the effects of crustal and mantle heterogeneity are reflected in the relative complexity of short period seismograms at regional to teleseismic distances observations of events at regional ranges from indonesia and new guinea at the warramunga array in northern australia allow a separation of the propagation through the mantle by concentrating on the coherent signal across the medium aperture array most of the incoherent features on the seismograms arise from signal generated noise in the general vicinity of the array with scale lengths of the order of 1 2 km or smaller partially coherent phases with relatively rapid changes in waveform across the array are to be associated with organised heterogeneity this is most likely to arise from features in the crust or at the crust mantle boundary near the receiver but could in some cases be due to structural effects near the source the coherent signals show considerable complexity for phases travelling large portions of their path above 80 km as the depth of sources increases this coherent portion of the seismic field tends to become simpler which suggests that the scale length of heterogeneity is larger at depth the use of horizontally stratified models has provided a convenient framework for the understanding of many seismic wave phenomena via the calculation of synthetic seismograms however further development is needed for calculating the response of the laterally heterogeneous earth the convenience of physical interpretation provided by working with the reflection and transmission properties of the medium can be retained if the structure can be split into a stratified reference model with superimposed heterogeneity with a plane wave decomposition of the wavefield the effect of lateral variations can be introduced by forcing mixing of wavenumber components a wide variety of phenomena can be simulated by varying the statistical description of the heterogeneity field in the wavenumber domain this varies the cross coupling between wavenumber components and so changes the nature of the resulting theoretical seismograms such an approach allows a quantitative study of the degradation of the major seismic phases compared to the predictions for stratified models and also the characterisation of the codas of these phases

high frequency wave propagation in the uppermost mantle short period three component recordings of the seismic wave field of peaceful nuclear explosions recorded on deep seismic sounding profiles quartz and ruby i collected in 1984 and 1988 respectively in northern russia are used to constrain the nature of the high frequency teleseismic p n phase which can be observed for receiver distances of 3000 km we suggest that this phase is caused by velocity fluctuations in the upper mantle acting as scatterers to test this hypothesis and to determine the properties of the upper mantle scatterers the elastic reflectivity method one dimensional isotropic models was used to model the coda of the high frequency teleseismic p n phase both the observed data and the synthetic record sections were analyzed by examining the coda decay rates of the teleseismic p n phase at 5 hz synthetic seismograms are computed for different models based on the global model iasp91 with an added zone of randomly distributed velocity fluctuations lamellae just below the crust mantle boundary these models may be characterized by the thickness of the scattering layer l the vertical heterogeneity correlation length a and the heterogeneity standard deviation the numerical simulation of the wave propagation in these models generated a high frequency teleseismic p n phase with a well pronounced long coda a comparison of the modeling results with the observations shows clearly that a velocity model containing fluctuations in the upper mantle can easily explain the presence of a high frequency teleseismic p n comparing the coda decay rates of synthetic seismograms with the observation we tried to constrain the properties of the velocity fluctuations in the upper mantle l a and in the distance range of the uninterfered high frequency teleseismic p n phase beyond 1300 km the coda decay rates for our best fitting model are similar to the observed ones this model has a 75 km thick zone of scatterers below the moho containing lamellae with an average thickness of 2 km and a rms velocity perturbation of 5 the modeling results show also that two other possible models the whispering gallery phase along the crust mantle boundary and scattering in the lower crust taken alone are not able to explain the coda properties of the high frequency teleseismic p n phase

propagation and attenuation characteristics of the crustal phase lg thelg wave consists of the superposition ofs waves supercritically reflected and thus trapped in the crust this mode of propagation explains the strong amplitude of this phase and the large distance range in which it is observed the numerical simulation leads to successful comparison between observed seismograms in stable continental areas and synthetics computed for simple standard crustal models in regions with strong lateral variations the influence of large scale heterogeneities on thelg amplitude is not yet clearly established in terms of the geometrical characteristics of the crustal structure

reducing numerical diffusion effects with pycnocline filter numerical or artificial diffusion is the unintentional smoothing of gradients associated with the discretization of the transport equations in lakes and reservoirs where through flow is small the effects of numerical diffusion of mass are cumulative leading to a progressive weakening of vertical density stratification this density field misrepresentation precludes accurate long term three dimensional 3d hydrodynamic simulations on fixed grids in closed basins with an active thermocline an ad hoc technique to limit the destratifying effects of numerical diffusion of mass is presented and tested for a 3d hydrostatic z coordinate numerical model the technique quantifies the domain integrated numerical diffusion by assessing the change in the background potential energy eb at each time step the change in eb associated with numerical diffusion is calculated then removed using a sharpening filter applied to each water column in idealized test cases the filtering technique is effective in maintaining density stratification over one year while undergoing periodic large amplitude forcing by internal waves forty day simulations of lake kinneret compared to field measurements demonstrate improved representation of density stratification using the filtering technique

observation of high frequency teleseismic p n on the long range quartz profile across northern eurasia short period three component recordings of the seismic wave field of peaceful nuclear explosions pnes on long range profiles are used to determine the fine structure of the mantle lithosphere by analyzing the frequency content of the recorded phases and applying different band pass filters to the data it is possible to divide the wave field into two distinctly different constituents low frequency body waves traveling along fermat paths first arrivals and the high frequency teleseismic or long range pn phase traveling with a group velocity of 8 1 km s and accompanied by a long incoherent coda this high frequency teleseismic pn phase is observable from about 750 km where it separates from the faster first arrival to the maximum recording distance of 3145 km it is recorded from shots at different locations and appears to be almost unaffected by the major tectonic feature along the profile the urals the frequency spectrum of this pn phase contains more high frequency energy up to 12 hz than first arrivals that penetrate deeper into the upper mantle the teleseismic high frequency pn arrival has a remarkable coda which is incoherent between closely spaced stations the coda duration is dependent on the component of motion being shortest on the vertical and longest on the transverse component we propose a velocity model that is characterized by a zone extending from the crust mantle boundary to a depth of about 100 km this zone has randomly distributed spatially anisotropic velocity fluctuations we propose that these velocity heterogeneities are stretched in the horizontal direction this zone forms a scattering waveguide that confines the high frequency teleseismic pn there are indications that below this pn waveguide either the scale of the velocity fluctuations or the q factor changes this is expressed in a separation of the teleseismic pn phase from the phase diving deeper into the mantle lithosphere

heterogeneity of the uppermost mantle beneath russian eurasia from the ultra long range profile quartz the 3850 km long deep seismic sounding profile quartz crosses six major geologic provinces in eurasia and is sourced by 3 nuclear and 48 chemical explosions we present the first interpretation of the entire data set using two dimensional 2 d ray tracing and inversion resolution analysis and 1 d amplitude modeling our interpretation shows a 42 km thick high velocity crust under the baltic shield a 29 km thick crust and high velocity upper mantle under the mezenskaya depression 52 km thick crust with high velocity lower crust and uppermost mantle under the urals and 40 km thick crust under the west siberian basin deepening to 45 km under the altay sayan fold belt high velocity 8 4 km s uppermost mantle is found under the mezenskaya depression and under the east flank of the urals one almost continuous upper mantle boundary occurs at 65 to 80 km depth and another with an approximately 40 km thick lvz occurs at 120 to 140 km depth the shallow upper mantle blocks and the two extensive interfaces indicate strong upper mantle heterogeneity resolution analysis based on direct multivariate model perturbations artificial neural network and principal component analysis indicate the depth uncertainty of the 410 km discontinuity within 6 km and also its trade off with dip and velocities above and below the discontinuity decreased near critical amplitudes of reflections from the 410 km and 660 km discontinuities indicate that these boundaries are most likely represented by gradient zones about 15 20 km thick lithosphere thins asthenospheric velocity decreases and the 410 km discontinuity dips to the se approaching the himalayan orogenic belt

attenuation of high frequency shear waves in the crust measurements from new york state south africa and southern california we compare the attenuation of high frequency 3 30 hz shear waves for crustal paths in new york state south africa and southern california over source receiver distances of about 10 400 km the data consist of digital recordings of s waves 5 100 km and lg waves 100 400 km produced by earthquakes we use a coda normalization method to remove the effects of site amplification and source excitation from the amplitudes of the s and lg waves over the entire distance range studied 10 400 km the amplitude decay of 3 hz shear wave energy is considerably less for the tectonicaily stable areas of new york and south africa than for the tectonicaily active region of southern california high frequency 30 hz s wave attenuation is significantly less for new york and south africa than for southern california for distances between 15 and 90 km we parameterize the decay with distance r of coda normalized shear wave amplitudes with a frequency independent q and geometrical spreading exponent where geometrical spreading is proportional to r for new york state the s wave amplitude decay 3 30 hz is well described by a frequency independent q of 2100 330 490 and of 1 3 0 1 the decay of lg wave amplitudes from 3 to 15 hz in the new york state region is fit with a frequency independent q of 1600 280 330 of 0 70 0 2 the s wave amplitudes 3 30hz in south africa yield a q of 1500 190 380 and of 1 3 0 1 fixing the geometrical spreading at r 0 5 produces an lg wave q estimate at 3 hz in south africa of 360 50 80 this lg wave q is low considering that south africa is a cratonic tectonicaily stable area the s wave amplitudes from southern california are described with a frequency independent q of 800 150 240 and a large geometrical spreading exponent of of 1 9 0 2 we find an lg wave q at 3 hz of 260 30 for southern california after constraining the geometrical spreading at r 0 5

regionalization of crustal coda q in the continental united states a contour map of crustal q sub 0 values for the entire united states is presented based on a scattering model to explain the coda waves of local and near regional earthquakes these coda q sub 0 values are in good agreement with q of lg waves data are obtained from over 250 local earthquakes with most magnitudes between 3 0 and 5 0 recorded by 25 wwssn and 27 lrsm stations throughout the continental united states these two sets of data provide a range of frequencies from 0 5 to 3 5 hz a frequency dependence of q is observed in the range of frequencies considered a power law dependence of the form q q sub 0 f f sub 0 sup eta is assumed the value of frequency dependence eta is found to be maximum in the tectonically active western united states and least in the stable regions of the central and south central united states the lowest q sub 0 values are obtained in the western united states with values ranging from 140 to 200 in the coastal plains average crustal q sub 0 values for the basin and range province vary from 200 to 300 increasing gradually to 400 in the colorado plateau region q sub 0 valuesmore in the columbia plateau vary from 200 to 400 q sub 0 values increase very rapidly along the central and southern rocky mountains from 400 to 800 east of the rocky mountains q sub 0 values increase gradually in the interior plains to a maximum value of around 1300 in the mississippi embayment region farther east q sub 0 values decrease gradually to an almost constant value of 1000 along the appalachian mountains coastal regions of eastern and northeastern united states have a crustal q sub 0 value between 900 to 700 regions of north central and gulf coastal plains show low q sub 0 values ranging from 600 to 400 and less the source factor b f sub p a measure of the intensity of scattering was obtained for several different regions of the continental united states regions of high q sub 0 values exhibit low intensity of scattering less

bsr occurrence along the sunda margin evidence from seismic data the occurrence of bottom simulating reflections bsrs along the sunda margin off indonesia is investigated for the first time using seismic reflection data from three surveys conducted across the subduction zone and the forearc domain off southern sumatra to central java bsrs commonly concur with the base of the thermodynamically stable hydrate zone and are thus an important indicator for gas hydrates along the sunda arc bsr occurrence is restricted to the forearc domain in regions likely to represent a focussing of fluid flow such as the forearc basin slopes or anticline structures dissociation of gas hydrates due to uplift along anticline structures may be an important secondary cause of bsr formation the absence of bsrs in the forearc basin center despite continuous sedimentation to ensure carbon supply may be related to the very high sedimentation rate 0 4 km ma which causes unused carbon to pass through the stability zone even for a high rate constant of methanogenesis in addition the interbedding of low and high permeability layers renders fluid flow across layering ineffective no bsr phases could be detected along the accretionary prism or the outer high although the p t regime would allow a potential bsr to lie within the accretionary sedimentary column

wave propagation in a multiple scattering upper mantle observations and modelling summary a striking feature of russian long range seismic refraction data from peaceful nuclear explosions is the observation of a high frequency teleseismic p phase which travels with a group velocity of 8 0 km s l out to distances of several thousands of kilometres modelling using the reflectivity method shows that this phase can be understood as the response of an upper mantle that contains random rms velocity fluctuations of about 44 per cent superimposed on a positive velocity gradient this class of model explains the existence of the teleseismic p its high frequency content and its coda length a teleseismic p can only be generated if velocity fluctuations are strong enough to cause multiple scattering and occur on a subwavelength scale cross correlation properties of p and s wave velocity fluctuations exert a substantial influence on the wavefield a completely unexpected phase can be observed if the fluctuations are imposed on a negative gradient

scales of structure in the lithosphere images of processes advances in deep seismic sounding observations of the lithosphere on continents allow to identify various scales of heterogeneities in the crust mantle transition in this paper a fresh look is taken at the dynamic properties of seismic waves propagating through this zone ranging from the lower crust well into the lithospheric mantle as observed in near vertical reflection and wide angle refraction experiments the abrupt termination of near vertical reflections at the moho and the coincident presence of a strong coda accompanying the supercritical pmp reflection phase in record sections of continental seismic wide angle refraction experiments reveal a new property of the crust mantle boundary the moho forms a sandwiched mix of crust mantle material between lower crust and topmost mantle in combination with a step in mean velocity a significant change in scale of the structural dimensions and of velocity variance this view is strongly supported by the recognition of the subcrustal lithosphere as a high frequency 5 10 hz scattering wave guide for long distance propagation of the pn phase over more than 3000 km detected during seismic experiments in russia using peaceful nuclear explosions evidence is brought forward that this high frequency wave guide is likely to be present also in the phanerozoic upper mantle of western europe it is furthermore hypothesized that the global propagation of teleseismic sn or corresponding pn waves observed on continents and oceans combined with the recording of strong pmp codas for wave paths on continents points to a world wide change of scale of structure and velocities near the moho a change in scale of heterogeneities under almost all physical and chemical conditions indicates possibly a differential horizontal movement or decoupling of crust and upper mantle at the level of the moho the global presence of the scattering pn wave guide with a preferred horizontal elongation is hypothetically described as a seismic image of processes in the lithospheric mantle locations of present day tectonic activity where horizontal decoupling between crust and mantle are likely to occur e g subduction at continent continent collision zones change of tectonic regimes and continental transform faults are discussed

resolution of prominent crustal scatterers near the noress small aperture array summary our goal is to identify prominent scatterers near seismic arrays so that the secondary phases they generate can be anticipated and recognized as being of local not teleseismic origin toward this end we have developed a technique to scan seismic coda recorded by arrays for phases generated locally by scattering of teleseismic energy from large topographical and crustal heterogeneities in this paper we test the technique by using the noress small aperture array in southern norway to image free surface secondary r sources excited by incoming teleseismic p waves in essence our technique suppresses the teleseismic energy and migrates the residual array records to image coherent local sources to assess the azimuthal and radial resolution that the noress array provides we have analysed point source synthetics a preliminary analysis of recorded data provides an initial view of the scatterers in the vicinity of noress and identifies limitations of imaging using the full coda of individual events single events can be used to image scatterers but more robust images with higher azimuthal resolution can be obtained by using a broadly distributed suite of events radial resolution of scatterers can be enhanced by deconvolution a composite image generated by simultaneously considering a suite of 31 deconvolved teleseisms indicates that two secondary r sources are present at or near the free surface near noress one 27 km to the south west of the array appears to be related to dramatic topographic relief at the south west edge of lake mjosa another roughly 10 km to the east of the array is judged by a bootstrapresampling analysis to be only marginally significant this apparent source does not coincide with obvious topography and is likely buried although the time delay that separates the scattered and parent phases depends somewhat on the angle of approach of the incoming waves in general these secondary sources are contributing wave trains to the seismic coda that begin 4 and 11 s respectively after the primary onset