effects of experimental leaching on rbsr and kar isotopic systems and ree contents of diagenetic illite leaching with 1 n hcl 1 n nh4cl acetone humic acid extracts cation exchange resin and nh4 edta have negligible effects on the rb sr and k ar systems of different size fractions 0 4 and 0 8 2 m of a 1m diagenetic illite none of these treatments including the 1 n hcl treatment induced preferential removal of radiogenic 87sr and 40ar from mineral structures however the 1 n hcl treatment removed significant amounts of sr and ree as compared to the treatments by nh4 edta and cation exchange resin however much of these hcl derived elements resided in non clay minerals such as carbonate and fe oxide phases the k ar and rb sr ages of the samples were not affected by the hcl treatment any more than by the nh4 edta or the cation exchange resin because of potential loss of solid material during elutriation of differentially treated samples the hcl treatment is preferred over other methods allowing sufficient controls on the isotopic and mass balances between the leachate and the corresponding residue of an untreated sample for rb sr isotopic dating purposes of clay minerals from sedimentary and metasedimentary rocks leaching experiments give information about the ambient environment of crystallization analysis of both the leachate and residue under carefully controlled conditions is recommended

the origin of teleseismic pn waves multiple crustal scattering of upper mantle whispering gallery phases 1 teleseismic pn arrivals with an extensive coda are observed to offsets beyond 3000 km along the peaceful nuclear explosion seismic profiles quartz and ruby which were recorded in the western part of the former soviet union we interpret these arrivals as multiply reflected sub moho refractions that travel over large distances due to a positive vertical upper mantle velocity gradient which is characteristic for the study area analysis of the observed data shows that the teleseismic pn and its coda contain significant amounts of energy at all frequencies between 0 and 10 hz our modeling results show that crustal scattering may fully explain the teleseismic pn coda contrary to another published model with upper mantle heterogeneity in the 35 130 km depth range these conclusions are based on two dimensional viscoelastic finite difference seismic wave field simulations in 2000 km long and 250 km deep models of the crust and upper mantle the computationally demanding calculations are facilitated by the use of supercomputer systems our preferred model of crustal scattering is consistent with the results of other high resolution wide angle and normal incidence seismic investigations of the crust and upper mantle they show pronounced reflectivity of the lower crust above an almost transparent uppermost mantle down to 80 100 km depth our model includes a high vertical velocity gradient in the upper mantle based on the results from seismic refraction studies we suggest that the teleseismic pn wave travels as an upper mantle whispering gallery phase and that the origin of its long coda is crustal scattering

teleseismic pn arrivals influence of mantle velocity gradient and crustal scattering teleseismic p n phases with a long high amplitude coda are observed to offsets 3000 km along the peaceful nuclear explosion seismic profiles quartz and ruby for the high frequency 5 hz part of the quartz data which is shown here coda lengths of more than 10 s can be visually observed in the seismic sections we interpret the teleseismic p n arrivals as multiple sub moho refractions whispering gallery phases which travel over large distances due to a positive upper mantle velocity gradient the coda of these arrivals is explained by lower crustal scattering of the whispering gallery phases from the mantle the modelling is based on calculation of reflectivity and 2 d visco elastic finite difference synthetic seismograms our models are in agreement with other deep seismic data from continental areas which typically show a reflective lower crust and an almost transparent uppermost mantle the lower crustal heterogeneity is described by von karman distribution with a standard deviation of 0 5 km s 1 for the p wave velocity and correlation lengths of 2 4 km horizontally and 0 6 km vertically the positive vertical upper mantle velocity gradient of 0 004 km s 1 km 1 which is characteristic for profile quartz forms a waveguide which gives rise to the teleseismic p n it is not necessary to include upper mantle heterogeneity in order to explain the characteristics of this arrival

the heterogeneous mantle rocks are composed of heterogeneous mixtures of minerals and assemblages of larger units and there is no reason to assume that the earth at large and intermediate scale should be homogeneous however the resolution of geophysical studies of the earth s mantle is limited there is a gap in resolution between studies of rock samples brought to the surface of the earth and seismological results which mainly show large scale structures there is also a gap between global tomographic models and the results of high resolution body wave and scattering techniques it is often assumed that the mantle is homogeneous at intermediate scales the standard model of geochemistry for example assumes that the upper mantle is homogenous

propagation of regional seismic phases in the indian shield constraints on crustal and upper mantle velocity models the regional seismic wave field in the central indian shield is studied including propagation characteristics of various prominent phases well recorded in the broadband seismograms of the 21 may 1997 jabalpur deep crustal focal depth 36 km earthquake m w 5 8 the seismograms covering a distance range out to about 1650 km although limited in number seem to well reveal the prominent phases including the p bar and lg as well as the high frequency pn and sn and their coda by detailed numerical simulations the generation and propagation characteristics of the p bar phase from earthquake sources at shallow and deep crustal depths are examined it is found that the p bar phase propagates efficiently at regional distances even for a deep crustal source depth the p bar phase is nevertheless very sensitive to the surface layer velocity structure extremely weak in the absence of a low velocity surface layer and also slightly weak in the presence of a relatively high velocity surface layer analyses of the jabalpur earthquake seismograms and the synthetics reveal that the p bar phase is well generated and propagates efficiently in the deccan traps v p 4 8 4 9 km sec covered regions i e even without a lower velocity surface layer surrounding the earthquake epicenter and the recording stations further the anatomy of the p bar phase is revealed by several computational models its time window composed of several multiple pmp reflections as well as pms conversions the principal boundaries being the moho and the free surface the first observations of high frequency pn and sn phases in the indian shield are recognized from the jabalpur earthquake seismograms by numerical simulations consistent with these observations including the coda a lamellae model with alternating high and low velocity layers for the structure of the indian continental uppermost mantle is inferred a complete synthesis of the regional seismograms is obtained based on the inferred models of the p and s wave velocity structure of the crust and upper mantle in the central indian shield comparison of the synthetics with the jabalpur earthquake seismograms reveals a consistent fit to various observations including the lg phase group velocity window 3 6 3 2 km sec the low pass filtered seismograms at the regional distances are further found to reveal coherent phases consistent with predicted reflection times from discontinuities in the upper mantle a plausible p velocity model inferred from these observations reveals velocity discontinuities at average depths of 230 320 430 and 680 km suggesting significant stratification of the upper mantle b region in the indian shield

separating intrinsic and apparent anisotropy abstract seismic anisotropy plays a key role in studies of the earth s rheology and deformation because of its relation to flow induced lattice preferred orientation lpo of intrinsically anisotropic minerals in addition to lpo small scale heterogeneity produces apparent anisotropy that need not be related to deformation in the same way as intrinsic anisotropy quantitative interpretations of observed anisotropy therefore require the separation of its intrinsic and apparent components we analyse the possibility to separate intrinsic and apparent anisotropy in media with hexagonal symmetry typically used in surface wave tomography and sks splitting studies our analysis is on the level of the wave equation which makes it general and independent of specific data types or tomographic techniques we find that observed anisotropy can be explained by isotropic heterogeneity when elastic parameters take specific combinations of values in practice the uncertainties of inferred anisotropy are large enough to ensure that such a combination is always within the error bars it follows that commonly observed anisotropy can always be explained completely by a purely isotropic laminated medium unless all anisotropic parameters are known with unrealistic accuracy most importantly minute changes in the poorly constrained p wave anisotropy and the parameter can switch between the possible or impossible existence of an isotropic equivalent important implications of our study include 1 intrinsic anisotropy over tomographically resolved length scales is never strictly required when reasonable error bars for anisotropic parameters are taken into account 2 currently available seismic observables provide weak constraints on the relative contributions of intrinsic and apparent anisotropy 3 therefore seismic observables alone are not sufficient to constrain the magnitude of mantle flow 4 quantitative interpretations of anisotropy in terms of mantle flow require combined seismic geodynamic inversions as well as the incorporation of additional data such as topography gravity and scattered waves

seismic imaging of the waltham canyon fault california comparison of ray theoretical and fresnel volume prestack depth migration abstract near vertical faults can be imaged using reflected refractions identified in controlled source seismic data often theses phases are observed on a few neighboring shot or receiver gathers resulting in a low fold data set imaging can be carried out with kirchhoff prestack depth migration in which migration noise is suppressed by constructive stacking of large amounts of multifold data fresnel volume migration can be used for low fold data without severe migration noise as the smearing along isochrones is limited to the first fresnel zone around the reflection point we developed a modified fresnel volume migration technique to enhance imaging of steep faults and to suppress noise and undesired coherent phases the modifications include target oriented filters to separate reflected refractions from steep dipping faults and reflections with hyperbolic moveout undesired phases like multiple reflections mode conversions direct p and s waves and surface waves are suppressed by these filters as an alternative approach we developed a new prestack line drawing migration method which can be considered as a proxy to an infinite frequency approximation of the fresnel volume migration the line drawing migration is not considering waveform information but requires significantly shorter computational time target oriented filters were extended by dip filters in the line drawing migration method the migration methods were tested with synthetic data and applied to real data from the waltham canyon fault california the two techniques are applied best in combination to design filters and to generate complementary images of steep faults

87sr 86sr ratios in hydrothermal waters and deposits from the east pacific rise at 21 n abstract 87 sr 86 sr ratios of three hydrothermal waters collected on the east pacific rise at 21 n define a mixing line between seawater and a hydrothermal end member at 0 7030 which is derived by seawater basalt interaction at ca 350 c and water rock ratio of about 1 5 sr concentrations are not affected in the process while mg uptake from seawater is almost complete up to2 3 of this hydrothermal component is involved in anhydrite precipitation while the sr isotopic ratio in sulfides chalcopyrite sphalerite cannot be distinguished from that of sulfate it is estimated that ca 1 10 10 moles of strontium are yearly cycled in the hydrothermal systems of mid oceanic ridges thereby affecting the 87 sr 86 sr budget of seawater mass balance between river runoff limestone precipitation and ridge basalt alteration suggests that the 87 sr 86 sr ratios of the river runoff are in the range 0 7097 0 7113 and are largely dominated by limestone alteration

87sr 86sr and 18o 16o ratios of clays from a hydrothermal area near the galapagos rift as records of origin crystallization temperature and fluid composition abstract strontium and o isotope compositions of green clay minerals from sediment cores of three boreholes drilled into sites 424a and 509b and close to a hydrothermal mound site 424b near the galapagos spreading center dsdp legs 54 and 70 were determined the green clays consist mostly of a transition from fe smectite nontronite to glauconite 87sr 86sr ratios were measured on clay size fractions after gentle acid leaching and on the recovered leachates from different samples the 87sr 86sr ratios of the clay residues from both the 424a and b sites are well below the modern seawater value which points consistently to precipitation from hydrothermal fluids that contained variable amounts of seawater even away from mound however most of the clay residues from mound site 509b have 87sr 86sr ratios significantly above the seawater value suggesting the occurrence of a detrital component together with the new authigenic particles the clay minerals of the hydrothermal mound are mixed with detrital components and that of the sample taken outside but near the mound as a reference for the surrounding oceanic environment yields a hydrothermal signature crystallization temperatures of the clays range from 32 to 63 c assuming a 18o value of 2 2 for the mineralizing fluids hydrothermal fluids generated in the underlying oceanic crust mixed in varied proportions with ambient seawater and migrated into beds of the mound in a sequence of recurrent processes that ultimately resulted in the formation of the observed clay minerals no significant temperature differences were detected for crystallization of the k rich glauconite and k depleted nontronite the 87sr 86sr ratios of the sr leached off the clay particles are near the value of modern seawater inferring a progressive replacement of the hydrothermal fluids by seawater in the pore space of the mound sediments

sr and ar isotope studies of detrital smectites from the atlantic ocean d s d p legs 43 48 and 50 mineralogical morphological and isotopic rb sr and k ar determinations were made on some detrital smectites of palaeocene and cenomanian ages from d s d p drillings in the atlantic ocean these minerals are not inert in their depositional environment authigenic laths grow on detrital sheets with sharp borders this authigenesis could occur slightly after deposition in a closed system for some of these smectites it has been tentatively quantified by the rb sr and k ar isotopic methods which seem also well suited to evaluate the chemical extent of this authigenesis at least no preferential loss of 40ar vs 87sr could be detected in the minerals even in those which are smaller than 0 2 m

on the nature of p n pn phases are observed along many refraction seismic profiles and are common in earthquake records their velocities usually range from 7 8 to 8 2 km s 1 classical ray theory used to interpret these observations implies a positive upper mantle velocity gradient however a wide spread positive velocity gradient in the lithospheric mantle is not expected from petrological and petrophysical data laboratory velocity measurements at elevated temparatures and pressures suggest positive velocity gradients only for very low heat flow values 40 mw m 2 higher heat flow causes negative gradients consequently petrological models of the upper mantle would restrict pn observations to precambrian shields and old platforms contrary to observations we overcome this contradiction by considering media that contain random velocity fluctuations superimposed on positive or negative velocity gradients in both cases these structures generate pn phases by wide angle scattered waves short wavelength random velocity fluctuations of only 0 5 1 superimposed on negative velocity gradients are sufficient for generating pn phases consequently this implies that an observed pn wave does not necessitate a positive upper mantle velocity gradient for a peridotitic upper mantle fluctuations of this size can be explained by slightly varying the relative proportions of its mineralogical constituents anisotropy is likely to contribute to the inferred fluctuations

contrasts of seismic velocity density and strength across the moho abstract we provide an overview of contrast of elastomechanical parameters across the moho basically contrasts in seismic wave velocities density and yield strength these can be regarded as dynamic and quasi static endmembers of elastomechanical parameters of the crust mantle transition with respect to practical applications they are closely related because seismic investigations play the role of exploring the earth structure and physical state forming the boundary conditions for determining density and rheological models we address both average global moho models and petrophysical and structural factors that cause deviations from the global averages such as variations in moho depth temperature and rock composition fabric anisotropy and macro scale heterogeneity besides principle considerations these factors are put in a regional context in order to demonstrate how they are related to past and present tectonic processes seismic velocity and density contrasts are found between 0 and 25 whereas strength or viscosity contrasts may be orders of magnitude higher but may vanish as well or show a discontinuity of higher order only especially oceanic and old cratonic crust and near moho mantle may appear as a rheological unit although they are seismically well distinguishable in terms of seismic velocities the moho may vanish mainly under the influence of serpentinization or eclogitization originally defined as a first order discontinuity in seismic velocity the moho has turned out to be an interface across which other seismic properties such as seismic velocity gradients anisotropy and heterogeneity scale parameters can change strongly too however knowledge of these parameters as well as their relation to the rheology of the crust mantle transition is still restricted to local or regional examples so no global conclusions can be drawn

the mohorovicic discontinuity beneath the continental crust an overview of seismic constraints abstract the seismic signature of the moho from which geologic and tectonic evolution hypotheses are derived is to a large degree a result of the seismic methodology which has been used to obtain the image seismic data of different types passive source earthquake broad band recordings and controlled source seismic refraction densely recorded wide angle deep seismic reflection and normal incidence reflection using vibroseistm explosives or airguns have contributed to the description of the moho as a relatively complex transition zone of critical importance for the quality and resolution of the seismic image are the acquisition parameters used in the imaging experiments a variety of signatures have been obtained for the moho at different scales generally dependent upon bandwidth of the seismic source this variety prevents the development of a single universally applicable interpretation in this way source frequency content and source and sensor spacing determine the vertical and lateral resolution of the images respectively in most cases the different seismic probes provide complementary data that gives a fuller picture of the physical structure of the moho and its relationship to a petrologic crust mantle transition in regional seismic studies carried out using passive source recordings the moho is a relatively well defined structure with marked lateral continuity the characteristics of this boundary change depending on the geology and tectonic evolution of the targeted area refraction and wide angle studies suggest the moho to be often a relatively sharp velocity contrast whereas the moho in coincident high quality seismic reflection images is often seen as the abrupt downward decrease in seismic reflectivity the origin of the moho and its relation to the crust mantle boundary is probably better constrained by careful analysis of its internal details which can be complex and geographically varied unlike the oceanic moho which is formed in a relatively simple well understood process the continental moho can be subject to an extensive variety of tectonic processes making overarching conclusions about the continental moho difficult speaking very broadly 1 in orogenic belts still undergoing compression and active continental volcanic arcs the moho evolves with the mountain belt 2 in collapsed phanerozoic orogenic belts the moho under the collapse structure was formed during the collapse often by a combination of processes 3 in regions having experienced widespread basaltic volcanism the moho can result from underplated basalt and basaltic residuum in precambrian terranes the moho may be as ancient as the formation of the crust in others precambrian tectonic and magmatic processes have reset it we note that seismic reflection data in phanerosoic orogens as well as from precambrian cratonic terranes often show thrust type structures extending as deep as the moho and suggest that even where crust and mantle xenoliths provide similar age of formation dates the crust may be semi allochothonous

seismic images of eclogites crustal scale extension and moho relief in the eastern grenville province quebec seismic images from a 250 km lithoprobe reflection profile in the interior of the eastern grenville province provide important new constraints on the crustal architecture of this part of the orogen prominent upper crustal reflections can be correlated with exposures of high pressure metamorphic rocks in the manicouagan shear belt providing the first direct evidence for eclogite reflectivity in the grenville province the eclogites are cut by major late grenvillian normal faults that penetrate the deep crust and preserve evidence of extensional collapse of the overthickened orogen north to south crustal thinning indicated by a change in moho reflection time from 16 to 13 s correlates well with regional bouguer gravity trends and is accompanied by a dramatic increase in the reflectivity of the lower crust these features underscore the significance of recently recognized along strike variations in tectonic style within the grenville province and point to the internal complexity that characterizes the root zones of collisional orogens

constraints on reflective bodies below the 8 discontinuity from reflectivity modelling summary delayed first arrivals followed by a long wave train of scattered phases of up to 8 s duration are observed in the 800 1400 km offset range of the four peaceful nuclear explosion pne seismic sections of the 3500 km long profile kraton in siberia the scattered phases are consistent with energy reflected from bodies embedded in a y75 km thick low velocity zone below the 8u discontinuity at y100 km depth inhomogeneities in the crust or uppermost mantle are not likely to cause the observed scattered phases reflectivity modelling of inhomogeneous media shows that p wave velocity fluctuations of about t1 5 per cent of the background velocity in the 100 175 km depth range can produce sufficiently strong arrivals to explain the observations from stochastic modelling we conclude that the thickness of the reflecting bodies is 4 7 km since the reflectivity modelling approach assumes 1 d models it cannot resolve the lateral extent of the bodies a high density seismic record section acquired by airgun shooting during the babel experiment indicates that the lateral extent of reflecting bodies below 100 km depth is less than 20 km in the baltic shield at the average receiver spacing of y15 km of pne profile kraton traditional phase correlation is not possible for the strong arrivals from the reflecting bodies below 100 km depth which suggests that the scattering bodies have limited horizontal extent in areas where the temperature distribution with depth is described by a generalized shield geotherm the temperature is likely to be higher than or close to the solidus temperature for peridotite with small amounts of c h o below y100 km depth the p wave velocity of mantle peridotite decreases significantly as the temperature approaches that of the solidus therefore we interpret the reflecting bodies in the 100 175 km depth interval of the upper mantle as local accumulations of rocks which are in a state close to or slightly above the melting point the melt accumulations cannot rise above y100 km depth because the melts are bound to solidify during upward migration due to the higher melting point at shallower levels

scales of heterogeneities in the continental crust and upper mantle a seismological characterization of crust and upper mantle can refer to large scale averages of seismic velocities or to fluctuations of elastic parameters large is understood here relative to the wavelength used to probe the earth in this paper we try to characterize crust and upper mantle by the fluctuations in media properties rather than by their average velocities as such it becomes evident that different scales of heterogeneities prevail in different layers of crust and mantle although we cannot provide final models and an explanation of why these different scales exist we believe that scales of inhomogeneities carry significant information regarding the tectonic processes that have affected the lower crust the lithospheric and the sublithospheric upper mantle we focus on four different types of small scale inhomogeneities 1 the characteristics of the lower crust 2 velocity fluctuations in the uppermost mantle 3 scattering in the lowermost lithosphere and on 4 heterogeneities in the mantle transition zone

lower lithospheric structure beneath the trans european suture zone from polonaise 97 seismic profiles abstract the large scale polonaise 97 seismic experiment investigated the velocity structure of the lithosphere in the trans european suture zone tesz region between the precambrian east european craton eec and palaeozoic platform pp in the area of the polish basin the p wave velocity is very low vp 8 25 km s in the palaeozoic platform and 8 1 km s in the precambrian platform good quality record sections were obtained to the longest offsets of about 600 km from the shot points with clear first arrivals and later phases of waves reflected refracted in the lower lithosphere two dimensional interpretation of the reversed system of travel times constrains a series of reflectors in the depth range of 50 90 km a seismic reflector appears as a general feature at around 10 km depth below moho in the area independent of the actual depth to the moho and sub moho seismic velocity ringing reflections are explained by relatively small scale heterogeneities beneath the depth interval from 90 to 110 km qualitative interpretation of the observed wave field shows a differentiation of the reflectivity in the lower lithosphere the seismic reflectivity of the uppermost mantle is stronger beneath the palaeozoic platform and tesz than the east european platform the deepest interpreted seismic reflector with zone of high reflectivity may mark a change in upper mantle structure from an upper zone characterised by seismic scatterers of small vertical dimension to a lower zone with vertically larger seismic scatterers possible caused by inclusions of partial melt

topo europe studying continental topography and deep earth surface processes in 4d abstract topo europe is a multidisciplinary international research program that addresses the interaction of processes inherent to the deep earth lithosphere mantle with surface processes erosion climate sea level which together shaped the topography of europe the objective of this programme is to assess neotectonic deformation rates and to quantify related geo risks such as earthquakes flooding landslides rock falls and volcanism research incorporating data interactive modeling focuses on the lithosphere memory and neotectonics with special attention on the thermo mechanical structure of the lithosphere mechanisms controlling large scale plate boundary and intraplate deformations anomalous subsidence and uplift and links with surface processes and topography evolution the topo europe natural laboratories in which these processes are analyzed cover a wide range of geodynamic settings these include the post collisional alpine carpathian pannonian basin system the very active aegean anatolian and apennines tyrrhenian orogens and back arc basins the caucasus levant area in the arabia europe collision zone the iberian peninsula caught up between alpine orogens the meta stable west and central european platform the stable east european platform and the seismically active and elevated scandinavian continental margin the topo europe project is a component of the international lithosphere program a european science foundation eurocores project provides funding for part of the research for a total amount of 13 5 m euro creating new research positions for 60 young researchers

an olivine fabric database an overview of upper mantle fabrics and seismic anisotropy we present a unique database of 110 olivine petrofabrics and their calculated seismic properties the samples come from a variety of the upper mantle geodynamic environments ophiolites subduction zones and kimberlites with a wide range of micro structures a phenomenological relationship is established between p and s wave seismic anisotropy and the degree of crystal alignment fabric strength seismic anisotropy increases rapidly at low fabric strength before reaching a near saturation level of 15 to 20 for p waves and 10 to 15 for s waves despite a large variation in the symmetry of fabric patterns the average seismic properties of the different fabric micro structural and geodynamic settings have similar anisotropies in both magnitude and symmetry hence it would seem possible to determine some measure of fabric strength from seismic anisotropy if the dimensions of the anisotropic region are known but not geodynamic environment or details of the petrofabric pattern a simple pattern of seismic anisotropy characterises the average sample of the database which has the following features the polarisation plane of the fastest s wave is parallel or sub parallel to the foliation plane the maximum shear wave splitting is parallel to the y structural direction in foliation plane and normal to the lineation the maximum of the p wave velocity is parallel to the high concentration of 100 axes which is sub parallel to the lineation the 100 orientation distribution has the greatest influence on the p wave seismic anisotropy the 100 and 001 orientation distributions have the greatest influence on the symmetry of s wave anisotropy although the magnitude of anisotropy is influenced by the distribution of all three principal axes although the database only contains olivine petrofabrics this statistical study clearly shows that seismic anisotropy can be used to deduce the orientation of the structural frame in the upper mantle 1998 elsevier science b v all rights reserved

rb sr systematics of vendian cambrian claystones from the east european platform implications for a multi stage illite evolution a combined mineralogical chemical morphological and rb sr isotopic study of blue clays from the lower cambrian lontova unit shows that these minerals contain three generations ofillite the oldest detrital 2m illite particles are typicauy round with sharp borders sometimes rolled up and have a minimum isotopic age of 722 13 ma this generation of illite is mainly concentrated in the 0 6 2 zm size fractions of the samples the second generation of illite is represented by well crystallized lath type particles of 0 1 zm size with an age of 533 8 ma considered to be the sedimentation age faulting and or regional emergence during the ordovician to early silurian time probably induced extensive circulations of subsurface waters which precipitated an additional 0 1 gm generation of low temperature lath type illite particles at 430 480 ma ago the precambrian cambrian boundary may be set at 530 10 ma based on the data presented here leaching of different clay subfractions by ammonium acetate shows that illite particles of different generations crystallizcd in environments with different svsr z6sr ratios the varied environmental sr isotopic ratios were at least in part due to local interactions between the interstitial waters and the sedimentary mass additionally the initial stsr s6sr ratios of the clay particles from argillaceous sedimentary rocks were mostly higher than that of marine st

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

origin of upper mantle seismic scattering evidence from russian peaceful nuclear explosion data summary detailed interpretation of upper mantle scattered waves recorded in the 800 1400 km offset range of four reversed peaceful nuclear explosion seismic sections along the 3500 km long profile kraton in russia has revealed an 85 km thick seismically inhomogeneous low velocity zone below the 8 discontinuity at 100 km depth the scattered waves make up a wave train of high amplitude that decreases in duration from 8 s at 800 km offset to 4 s at 1400 km offset 2 d elastic finite difference modelling of the seismic wavefield has previously shown that the inhomogeneous zone from 100 to 185 km depth may be described by continuous random velocity fluctuations represented by an exponential medium with a horizontal correlation length of 5 10 km a vertical correlation length of 5 km and a standard deviation of 2 per cent of the average background velocity value here we demonstrate that other proposed velocity fluctuations in the lower crust and in the uppermost mantle from the moho to 100 km depth cannot explain the observed scattered phases our study shows that upper mantle velocity fluctuations below the 8 discontinuity at 100 km depth are needed in order to explain the observed seismic wavefield and that they lead to scattering that is significantly different from the scattering caused by the fluctuations at shallower levels

geochemical evolution of the central pacific ocean over the past 56 myr 1 we measured the elemental concentrations of 69 sediment samples collected at ocean drilling program site 1215 and employed a suite of statistical methods and elemental ratios to quantify the lithogenic biogenic and authigenic hydrogenous hydrothermal ahh components we show that the changes in their abundance record 1 northwestward migration of the pacific plate 2 changes in climatic and oceanographic processes associated with the transition from the eocene greenhouse into the oligocene icehouse and 3 changes in pacific spreading rates and plate reorganization the distributions of three separate lithogenic end members depend on the latitudinal positioning of the site underneath the different wind belts locations north of 22 n received material from asia which was transported to the central pacific via the westerlies locations between 20 and 22 n display a silicic volcanic composition and may reflect the boundary between westerlies and northeast trade winds locations south of 20 n are geochemically e g cr ta sc th etc distinct from locations north of 22 n and suggest a north american origin rb sc significantly increases from values of 2 8 g g 1 at 20 22 ma to 5 7 g g 1 in the modern recording the development of the east asian monsoon and formation of asian loess during the early to mid eocene 53 54 ma when site 1215 was located at 11 13 n and was above the carbonate compensation depth export production increased by 40 55 and was 25 greater than the modern value at 9 n the ahh component dominated from late eocene to the late miocene and during the late eocene may have been driven by elevated hydrothermal activity during increased seafloor spreading

strontium isotopes of tertiary phillipsites from the southern pacific timing of the geochemical evolution abstract the rb sr system of phillipsites from an indurated volcano sedimentary mass sampled in the southern pacific ocean became closed long after the deposition of the host rock middle miocene 14 7 3 3 ma and middle eocene respectively this isotopic age of about 15 ma probably represents the end of an induration phenomenon which stopped the chemical exchanges between the zeolites and their environment these minerals inherited sr primarily from volcanic material as demonstrated by their initial 87sr 86sr ratio at 0 70441 0 00036 2 which plots within the values of the known 87sr 86sr ratios of the nearby basalts the leaching technique with diluted acid was checked by recalculation of the rb and sr contents of the leachates and residues according to their percentage in the untreated sample and comparison with their amounts in the corresponding untreated sample any discrepancy is in most cases smaller than 3 5 percent for both rb and sr amounts this technique may therefore be used to obtain a correct amount of the distribution of these elements among the soluble and insoluble fractions the examination of the leachates also showed that the volcano sedimentary material forming the cores of nodules from the water sediment interface experienced a more complex history than the underlying analogous volcano sedimentary level

the rbsr isotope system as an index of origin and diagenetic evolution of southern pacific red clays abstract morphological mineralogical chemical and rb sr isotopic studies have been made on fesmectites nontronites from southern pacific red clays cored near the marquisas islands these minerals have at the top of the core an 87 sr 86 sr ratio of 0 70917 0 00007 which indicates an authigenic origin in isotopic equilibrium with seawater weak leaching experiments with 1n hcl show that the nontronites also contain a volcanic component with a lower 87 sr 86 sr ratio which combined with the morphology of the particles suggests a transportation by bottom currents of clay formed elsewhere during burial the nontronites experience diagenetic modifications resulting in an increase in fe k and rb contents a concomitant decrease of mg ca ti na and sr and a preferential migration of radiogenic 87sr from the clays into the surrounding pore waters the 87 sr 86 sr ratio of the sr adsorbed on the outermost surfaces of the nontronites does not change with depth in the core and is therefore independent of diagenetic influence which is rather characterized by the 87 sr 86 sr ratios of the interstitial waters the isotopic composition of both the adsorbed sr and that of the pore fluids may yield useful information on the crystallization environment and subsequent history of deep sea red clays

velocity shift in heterogeneous media with anisotropic spatial correlation summary converted waves analysis is used to map the anisotropy as a function of depth in the upper mantle stacking of sv a ndt component records of several seismic events well distributed in azimuth helps to detect these converted waves weighting coe cients are used to extract the anisotropic signal in the records synthetic examples show that a harmonic analysis helps to separate azimuthal anisotropy eiects from the eiects of lateral heterogeneity such as those resultingfrom dipping structures a good azimuthal coverage of the data set is important in order to separate the diierent eiects in the stack sections obtained for diierent azimuthal orders the procedure is applied to data observed at geoscope station can and gives a model with two anisotropic layers in the upper mantle the upper layer located between the crust and a depth of140 km has its fast axis in an east west direction the lower layer 40 km thick has its fast axis in a north south direction the fast axis directions are in agreement with results obtained from surface wave analysis and tectonic information

some attributes of wavefields scattered from ivrea type lower crust abstract the ivrea zone in northern italy is a well studied sliver of extended lower continental crust which was brought to the surface in the course of alpine lithospheric shortening based on two 1 25 000 geological maps from the central ivrea zone and petrophysical parameters of the corresponding lithologies we have constructed geologically constrained stochastic seismic models of ivrea type lower crust a stochastic rather than a deterministic approach is applied due to the limited availability of detailed geological maps and the high degree of small scale structural and petrophysical complexity of the ivrea zone the primary characteristic of the resulting model is its layered self affine or fractal structure and its bimodal velocity distribution while we are not suggesting that ivrea type structure is universal for extended lower continental crust synthetic seismograms may help to constrain some pertinent quantitative aspects observed in deep seismic reflection data 1 1 ivrea type lower crust can explain the igh observed reflection coefficients and bright reflectivity in the lower crust 2 2 observed lower crustal q factors can be largely explained by scattering losses and intrinsic q factors of reflective lower crust are likely to be larger than 1000 which is incompatible with the presence of free volatiles 3 3 in agreement with recent broad band studies of the lower crust ivrea type lower crust does not create any tuning effects and 4 4 for ivrea type heterogeneity the lateral correlation of the reflected signal is largely independent of the lateral characteristic scale of the scattering structures which suggests that multiple scattering may be important in the reflective lower crust

identification of crustal and upper mantle heterogeneity by modelling of controlled source seismic data abstract high frequency controlled source seismic sections with dense spatial sampling show the existence of heterogeneity at different depth levels of the continental crust and upper mantle our sources of information are the peaceful nuclear explosion pne seismic data sets recorded to large offsets in the former soviet union supplemented by recordings from the north american early rise deep seismic experiment and normal incidence reflection seismic sections collected in northwest europe heterogeneity in the crust and upper mantle can be uniquely identified in reversed high frequency 2 10 hz pne seismic sections collected with dense spatial sampling nominal receiver spacing of 10 15 km out to 4000 km offset we document pronounced seismic scattering from three heterogeneous zones the lower crust from 20 km to 40 km depth an 80 km thick low velocity zone below 100 km depth and the 320 460 km depth interval around the top of the mantle transition zone we calculate the full seismic wavefield in heterogeneous crust mantle models with a two dimensional finite difference algorithm we represent the heterogeneous layers by random fluctuations of the elastic parameters and q values the spatial horizontal and vertical correlation lengths and the standard deviation of the scattering media are constrained by comparison of observed and calculated seismic sections the lower crustal heterogeneity causes a coda to the upper mantle arrivals at all recorded frequencies this coda is a prominent feature for whispering gallery phases teleseismic pn which travel as multiply reflected refractions below the moho to more than 3000 km offset from the pne sources the heterogeneous mantle low velocity zone causes a scattered coda trailing the first arrivals in the 800 1400 km offset range the best fit to the observations along profile kraton in siberia is obtained by an 80 km thick heterogeneous low velocity zone below 100 km depth represented by fluctuations described by a von karman distribution function with a hurst number of 0 5 and spatial correlation lengths of 5 10 km horizontally and 3 5 km vertically scattered arrivals which trail the reflection from the 410 discontinuity and a reflection from a shallower depth of 320 km constrain heterogeneity around the top of the transition zone this heterogeneity is modelled by fluctuations in the 320 460 km depth interval with correlation lengths on the order of 20 40 km by 5 10 km scattering from the two shallower heterogeneous zones improves the description of the phases from around the transition zone

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

po so synthetics for a variety of oceanic models and their implications for the structure of the oceanic lithosphere summary polso synthetic seismograms were computed for a variety of oceanic structures in order to model data from an t zb 5 7 earthquake recorded during the oss iv seismic experiment satisfactory modelling of polso waveshapes and frequency content was achieved with no lateral heterogeneity but with a small random vertical heterogeneity in the mantle superimposed on a mean velocity structure which is consistent with seismic refraction data the random heterogeneity in the p and s velocities appears to be about 2 per cent with a scale length of 5 km this kind of heterogeneity is easily achieved by varying slightly the major mineral components in either the peridotite or eclogite mantle mineralogy and can be another cause of observed upper mantle anisotropy using a step function source time behaviour our numerical modelling also indicates that in the upper mantle qp is roughly proportional to rising from about 450 at f 1 hz to about 800 at f 15 hz and that q is roughly proportional to rising from about 900 at f 1hz to about 1800 at f 15hz a slight decrease in q from these values in any small zone of the upper mantle reduces so amplitudes drastically and we believe this is why so is sometimes missing from observed seismograms the computed synthetic record sections were also used to examine the relation between intrinsic q and the apparent q inferred from data in earlier studies apparent q was found to be lower than intrinsic q below about 5hz and higher than intrinsic q above 5 hz when these differences are accounted for the mantle q s of this study agree with the mantle q s of butler et al 1987 to within 10 per cent there can no longer be any doubt that oceanic upper mantle q s are very large above 5 hz and that q is about twice as large as qp

delineating tectonic units beneath the donbas fold belt using scale lengths estimated from dobre 2000 2001 deep reflection data 1 a novel statistical analysis which augments conventional interpretation of deep seismic reflection refraction data is applied to the dobre 2000 2001 reflection profile the goal is to improve delineation of the lithosphere in terms of lithotectonic units and to compare these to existing interpretations after a successful validation of the method using synthetic data stochastic parameters estimated from windowed average lateral autocorrelations in the dobre data are compiled in a two dimensional profile of von karman type causative reflectivity these estimates in terms of lateral correlation lengths and power law exponents are accompanied by associated uncertainties given its low uncertainties the lateral correlation length ax turns out to be a robust delineator the profile of ax reveals systematic spatial variations in the lithospheric fabric below the donbas fold belt as in earlier interpretations based upon conventional processing of reflection refraction data both the sedimentary basin and moho discontinuity stand out clearly as well as a region indicating massive vertical intrusion in the crust from upper mantle sills and ultramafic underplating of the lower crust notable differences with conventional interpretations include the number and extent of supra moho rift pillow structures the lack of imaging a crust cutting dislocation feature and a laterally disturbed uppermost mantle von karman lateral correlation length provides new independent information at a scale between velocity models from wide angle reflection refraction data and line drawings from near vertical reflections and provides new insights and understanding of lithospheric evolution

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

imaging crustal structure along refraction profiles using multicomponent recordings of first arrival coda in a way similar to receiver function imaging coda of the first arrivals can be used to constrain crustal structure along controlled source refraction profiles with multicomponent recording stacked cross correlations of the radial and vertical components of recordings from three peaceful nuclear explosions of the 3850 km long profile quartz russia exhibit good correlation with the depth to the basement and provide a horizontal resolution level close to recording station spacing 10 15 km the results also suggest high 0 35 0 4 average poisson s ratios within the sediments when applied to other multicomponent long range refraction profiles this approach could provide a simple and inexpensive way to constrain the structure of the upper crust that is required for interpretation of the deeper structures and that cannot be constrained by other means most importantly reverberations within the sedimentary column appear to account for much of the observed complexity of the first arrival waveforms and therefore such reverberations should be taken into account in the interpretations of seismic scattering from within the mantle manuscript received 24 january 2002

pb and sr isotopic systematics of some basalts and sulfides from the east pacific rise at 21 n project rita abstract tholeiitic basalts and sulfide deposits from the cyana and alvin diving programs rita project on the east pacific rise were analyzed for pb and sr isotopes the basalt data plot within the field defined previously by other east pacific rise basalts 206 pb 204 pb 18 35 18 58 207 pb 204 pb 15 48 15 53 208 pb 204 pb 37 8 38 1 87 sr 86 sr 0 7022 0 7025 pb u and sr contents 0 5 0 05 and 110 ppm respectively and values 6 are typical of morb whereas th u ratios 3 5 are significantly higher the pb isotopic ratios of the sulfide samples are very homogeneous 206 pb 204 pb 18 47 207 pb 204 pb 15 49 208 pb 204 pb 37 90 and plot in the middle of the basalt field this indicates that 1 the sulfide pb was derived from the basaltic crust without any significant contribution from either seawater or hemipelagic sediments and 2 the solutions from which the sulfides were deposited had uniform pb isotopic composition the pb contents of three sulfide samples is relatively high 170 1310 ppm the sr contents of five sulfide samples are widely scattered from 12 to 210 ppm with 87 sr 86 sr ratios intermediate between basaltic and seawater values 0 70554 0 00005 to0 70795 0 00011 leaching experiments show that both basalt derived sr and seawater sr were present in the solutions which deposited the sulfides in some cases sr was also adsorbed from seawater onto the sulfides following their deposition basalt derived sr and seawater sr are also present in associated non sulfide phases

amplitude effects due to multiscale impedance contrasts and multiple scattering implications for ivrea type continental lower crust summary studying seismic wave propagation in non deterministic media is interesting as some parts of the earth e g in the continental lower crust may be amenable to a stochastic description in this paper we study the acoustic response of a 1 d binary stochastic fractal medium and separate the single from the multiple scattered wavefield we show that for our models with scales that partly overlap the seismic bandwidth amplitude changes occur due to both the presence of multiple scattering and the multiscale nature of the impedance contrasts we study these changes as functions of sc a measure of the nominal bimodal reflection coefficient ka a measure of the relative length scales of the medium compared to the wavelength of the probing waves and c the scatterer density as our models are binary two lithologies the results should be interpreted as an upper bound for the general class of acoustic 1 d stochastic fractal model responses we present a measure to quantify the interference of single and multiple scattered wavefields and use this measure to study the importance of the three aforementioned dependences since stochastic fractal media have been proposed for ivrea type lower crust we relate our results to such a model and find that amplitudes may increase by up to 45t15 per cent the contribution of multiple scattering to this increase ranges from 1t 1t o 20t15 per cent the main contribution being due to the multiscale nature of the impedance contrasts we claim that the parameters used to model ivrea type lower crust sc 5 per cent c 5r10 x2 1 jkaj24 and m 9 6r10 x1 are robust although we recognize that the scatterer density c is determined by the vertical sampling dz in our models the heuristic argument that extra geometrical spreading in two three dimensions will further diminish the importance of multiple scattering effects combined with our results makes it tempting to claim that multiple scattering is not important for 2 3 d generalizations of our 1 d models however in the light of indirect evidence for the importance of multiple scattering in ivrea type lower crust reported by other authors we argue that elasticity p s conversions may be important therefore we believe that it is necessary to study the 2 d case with a similar direct approach to that presented in this paper before a satisfactory conclusion can be drawn about the validity of the standard processing of deep seismic reflection data and the importance of multiple scattering

stochastic waveguide in the lithosphere indonesian subduction zone to australian craton summary earthquakes occurring in the indonesian subduction zone recorded in the cratonic regions of northern australia have long high frequency coda associated with both p and s waves similar behaviour is seen for earthquakes within australia on paths within the cratonic regions the complex character of the coda and its rapid spatial variation indicate that the high frequency waves have travelled within a zone of strong multiple scattering with very high intrinsic q there are subtle variations in the nature of the coda that can be described through a coda q the variations in coda are associated with the position along the arc and the nature of the transition from the subduction zone to the continental lithosphere the character of the coda observations can be captured with numerical simulations in models derived from seismic tomography for northern australia and the neighbouring subduction zone incorporating lower crustal and mantle heterogeneity with much longer horizontal than vertical correlation length high frequency calculations to high frequency 16 hz for long propagation distances up to 1500 km have been carried out using finite difference modelling on the earth simulator the variations in coda properties can be associated with the way in which the seismic energy gets ducted into the stochastic waveguide associated with the lithosphere the most efficient transfer occurs where continental lithospheric material is adjacent to the earthquake zone

subduction zone guided waves and the heterogeneity structure of the subducted plate intensity anomalies in northern japan 1 the subducting pacific plate acts an efficient waveguide for high frequency signals and often produces anomalously large intensity on the eastern seaboard of northern japan during deep earthquakes the waveform records in the region of high intensity show a low frequency f 2 hz later arrivals with a long coda this behavior is not explained by a simple subduction zone model comprising a high velocity plate with low attenuation from the analysis of observed broadband waveforms and numerical simulation of seismic wave propagation in the pacific subduction zone we demonstrate that the high frequency guided waves traveling in the subducting plate arise from the scattering of seismic waves by heterogeneity in plate structure our preferred model of the heterogeneity has elongated scatterers parallel to the plate margin described by a von karmann function with a downdip correlation length of about 10 km and much shorter correlation length of about 0 5 km in thickness the standard deviation of wave speed fluctuations from the averaged background model is about 2 this new heterogeneous plate model generates significant scattering of seismic waves with wavelengths shorter than correlation distance in thickness but low frequency waves with long wavelengths can easy tunnel through such lamina structure the result is frequency selective propagation characteristics with a faster low frequency phase followed by large and high frequency signals with very long coda a low wave speed channel effect from the former oceanic crust at the top of the subducting slab is not necessary to explain the observed dispersed signals and the very long high frequency coda three dimensional simulations using the earth simulator supercomputer for modeling of high frequency seismic wave propagation in the pacific subduction zone including plate heterogeneity clearly demonstrate the scattering waveguide effects for high frequency seismic waves traveling in the plate the region of large intensity for the heterogeneous model migrates away from the hypocenter into northern japan with an elongated zone along the pacific coast almost comparable to the observations from deep events in the pacific plate

finite difference modelling of p wave scattering in the upper mantle summary scattering within the upper mantle is prominently documented in the so called high frequency teleseismic pn phase generated by velocity fluctuations in the upper mantle this phase is seen in many data sets from active and passive seismology whenever the source generated frequencies are high enough 5 10 hz to allow their observation at large distances 2000 km this phase appears in the recordings of the russian pne programme in other long range refraction experiments and in numerous recordings of earthquakes using a 2 d finite difference scheme we calculate complete synthetic seismograms in order to relate the scales of the fluctuation of the elastic parameters to wavefield properties we discuss the influence of critical parameters on the scattering properties of the upper mantle and on the propagation mechanism of the teleseismic pn variations in vertical and horizontal correlation lengths rms velocity fluctuations thickness of the heterogeneous layer and cross correlation of p and s wave velocities a teleseismic pn phase arises only if the velocity fluctuations are strong enough to cause multiple scattering and if the horizontal correlation length exceeds the vertical by an order of magnitude our favourite model for the russian pne profiles includes a 100 150 km thick zone of scatterers below the moho containing heterogeneities with a horizontal correlation length of 20 km a vertical correlation length of 0 5 km and an rms velocity perturbation of 2 per cent while keeping the p and s wave velocities correlated as the teleseismic pn is often observed this scale of velocity fluctuations seems to be characteristic of the uppermost mantle anisotropy is likely to contribute to the inferred velocity fluctuations

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

the horizontal propagation of p waves through scattering media analog model studies relevant to long range pn propagation the authors compare seismograms produced through the use of analog models of scattering and nonscattering earth structure to access the effect of lateral heterogeneities on the horizontal propagation of p waves the results are applicable to propagation out to 16 sup 0 and to periods as short as 5 sec it was found that layers of scatterers within the mantle near the turning points of p waves can cause these phases to have long coda similar in certain respects to the coda observed in long range p sub n the overall appearance of this coda is similar to that produced in laterally homogeneous models that include low velocity crustal material near their surfaces scatterers at shallower depths in the mantle or crust have a different effect those in very uppermost mantle seem to suppress the horizontal propagation of p waves while those in the crust have very little overall effect at least at the perod range studied it was also found that the scatterers have an amplifying effect on the horizontal propagation of the very longest periods 20 sec an effect that may be related to the scattering controlled boundary waves discovered by biot 1968

synthetic tsunami mareograms for realistic oceanic models summary we study how the tsunami mode is generated by a scaled double couple seismic source and how it propagates in realistic oceanic models the method developed and used is the direct extension to tsunami waves propagating in multilayered oceanic media of the well known haskell method the most intensive tsunamis may be expected from sources located within the crust in the deep water parts of the ocean the extension to laterally heterogeneous structures shows that if the thickness of the ocean liquid layer diminishes the maximum amplitude of the tsunami wave train increases

on the nature of mantle heterogeneities and discontinuities evidence from a very dense wide angle shot record abstract a seismic survey with a receiver spacing of 50 m provided one of the most densely sampled wide angle seismic reflection images of the lithosphere this unique data set recorded by an 18 km long spread reveals that at wide angles the shallow subcrustal mantle features high amplitude reflectivity which contrasts with a lack of reflectivity at latter travel times this change in the seismic signature is located at approximately 120 150 km depth which correlates with the depth estimates of the lithosphere asthenosphere boundary lab of previous dss studies this seismic signature can be simulated by two layer mantle model both layers with similar average velocities differ in their degree of heterogeneity the shallow heterogeneous layer and the deeper and more homogeneous one correlate with the lithosphere and the asthenosphere respectively studies involving surface outcrops of ultramafic massifs and mantle xenoliths infer that the upper mantle is a heterogeneous mixture of ultramafic rocks lherzolites harzburgites pyroxenites peridotites dunites and small amounts of eclogites laboratory measurements of physical properties of these mantle rocks indicate that compositional variations alone can account for the wide angle reflectivity a temperature increase would homogenize the mixture decreasing the seismic reflection properties due to melting processes it is proposed that this would take place below 120 150 km 1200 c the lab

implications of seismic scattering below the 8 discontinuity along pne profile kraton abstract strong scattered arrivals are observed in the 800 1400 km offset range of the four peaceful nuclear explosion pne seismic sections along the 3500 km long e w trending russian profile kraton they give evidence of an 85 km thick inhomogeneous scattering layer in the upper mantle which has a slightly reduced 1 average p wave velocity compared to the layers above and below the top of the anomalous zone is the 8 discontinuity at 100 km depth which is constrained by a clear travel time delay of up to 2 s consistently observed at 900 1000 km 8 offset in the four pne seismic sections we model the inhomogeneous zone below the 8 discontinuity by random velocity fluctuations the full waveform seismic response of a suite of stochastic velocity models is calculated using a two dimensional finite difference scheme the calculated seismic sections resemble the pne data for models where the random fluctuations have a horizontal correlation length of 5 10 km a vertical correlation length not greater than 5 km and a standard deviation of about 2 of the average background velocity fluctuations with significantly larger correlation lengths give rise to coherent scattered arrivals and considerably shorter correlation lengths lead to significantly weaker scattering none of which resemble the observed data the preferred seismic velocity model is in agreement with an upper mantle model in which the low velocity zone below the 8 discontinuity may contain small amounts of partially molten material alternatively the combined effects of rheological weakening and small scale anisotropy may also account for the low velocity scattering layer

measurements of coda buildup and decay rates of western pacific p po and so phases and their relevance to lithospheric scattering we use empirical functions to characterize the shape of band passed p po and so coda envelopes of 93 earthquakes the data sets consist of earthquake data from the western and northwestern pacific recorded by arrays of several stations and include both hydrophone and geophone recordings on analog and digital instruments each earthquake was band passed into six octave wide frequency bands between 0 8 and 50 hz the empirical function a poisson function pn t a n 1 tn e t n has parameters a a measure of energy falloff rate and nc time of the maximum the study showed that these parameters varied in systematic ways po so area a ratios were found to be considerably higher for hydrophone data in the 20 35 range than for geophone and hydrophone data in the 8 20 range the difference was significantly larger than between vertical and hydrophone data in the same range in some instances a strong frequency dependence or reverse dispersion of the time of maximum amplitude n was observed with the lower 1 2 hz frequencies arriving up to 25s later than the higher 10 20 hz frequencies p po and so average falloff rates a vary systematically with frequency where the lowest frequencies most commonly have the minimum falloff rates and the middle frequencies have the maximum falloff rates the variation in falloff between earthquakes is large with the trends only becoming apparent upon averaging many measurements a strong increase in falloff rates at about 3 hz may be associated with a decrease in the amount of scatterers with scale lengths of about one half the wavelength of a 3 hz compressional wave which is about 1 3 km falloff rates were seen to decrease with epicentral range reflecting an increased scattering with length of propagation path the scattering that produces the coda is thus not concentrated in the source region but distributed along the propagation path falloff rates were seen to decrease with increasing age of crust the difference may be due to the different average age of the lithosphere in these two geographical areas earthquakes at a depth of 100 300 km have systematically lower po falloff values than shallower events this effect is clearly seen in trench earthquakes and indicates that significant scattering occurs within or near the deeper buried part of the subducting plate the so po falloff ratio is a factor of 2 lower for the hydrophone data than for the geophone measurements this difference is most likely due to conversion of shear waves at or below the seafloor if we assume that the coda decay is controlled by intrinsic attenuation then measurements of coda decay can be converted into estimates of the quality factor q at 10 hz our falloff rates give qpo 1250 which is a reasonable number for a compressional wave quality factor in the uppermost mantle and qso qpo 2 the low snear wave q is in disagreement with inferences made by other observers however the fact that the falloff rates are fairly constant in the frequency range 5 30 hz but vary with propagation distance suggests that attenuation cannot be the only phenomenon determining the decay of the coda other factors such as reverberations in the water column may play an important part in the coda formation as well and may bias these estimates q