new moho map for onshore southern norway a recent seismic refraction study across southern norway has revealed that the up to 2469 m high southern scandes mountains are not isostatically compensated by a thick crust rather the moho depths are close to average for continental crust with elevations of similar to 1 km evidence from new seismic data indicate that beneath the highest topography moho depths are around 38 40 km these measurements are similar to 2 km deeper than early estimates interpolated from coarsely spaced refraction profiles but up to 3 km shallower than receiver function estimates for the area moho depth variation beneath the mountains roughly correlates with changes in surface topography indicating that topography is at least to the first order controlled by crustal thickness however the highest mountains do not overlie the thickest crust and additional support for topography for example from flexural strength in the lithosphere low densities in the upper mantle or mantle dynamics is likely the relationship between topography and moho depth breaks down for the oslo graben and the fennoscandian shield to the east and north high density lower crustal rocks below oslo graben and increasing crust and lithospheric thicknesses below the fennoscandian shield may produce a negative correlation between topography and moho depth

anomalous surface waves from lop nor nuclear explosions observations and numerical modeling surface waves from the chinese test site of lop nor are analyzed using long period and broadband stations located at regional and teleseismic distances and at different azimuths for most azimuths strong love waves between 0 02 and 0 045 hz are observed with an amplitude of up to 10 times that of the rayleigh waves in addition an anomalous early rayleigh wave train is observed at some stations in western europe due to a particularly favorable station and source configuration it is possible to isolate the areas where the anomalies are created the high amplitude love waves must be attributed to either source effects or path effects immediately north of lop nor the early wave train is shown to be due to a partial energy conversion between love and rayleigh waves probably at the tornquist zone to estimate the possible contribution from surface wave conversions to the observed anomalies numerical simulations are carried out with the indirect boundary element method the simulations show that a relatively small variation of crustal thickness can induce rayleigh to love wave conversions between 0 02 and 0 1 hz frequency the calculated amplitudes of the love waves are significant up to 35 of the amplitude of the incoming rayleigh waves but they are too small to fit the observed amplitude anomaly the observed converted waves and the numerical results nevertheless indicate that surface wave conversions can be significant across strong lateral crustal heterogeneities in particular the conversions due to changes in crustal thickness are located in the period interval which is routinely used for estimation of ms

a proterozoic boundary in southern norway revealed by joint inversion of p receiver functions and surface waves abstract the seismic s wave velocity structure of the crust and uppermost mantle in southern norway and western sweden is estimated from joint inversion of teleseismic p receiver functions and rayleigh wave phase velocities the data comes from the temporary broad band seismological experiments magnus and danseis and from permanent stations in norway and sweden the s wave velocity profiles in western and central southern norway show a sharp and well defined moho discontinuity at depths between 29 and 42 km in contrast to the northeastern part of the study area where no sharp moho is found the crust mantle transition in this area is gradual and found at a depth from 40 to 50 km the gradual crust mantle transition could be caused by mafic underplates that are only partially eclogitized whereas the sharp and well defined moho discontinuity can be a consequence of extensional collapse of the sveconorwegian orogen the boundary between a sharp moho discontinuity and a gradual crust mantle transition has a northwest strike which is approximately perpendicular to the caledonides and suggests that the boundary survived the caledonian orogeny

wave theoretical inversion of teleseismic surface waves in a regional network phase velocity maps and a three dimensional upper mantle shear wave velocity model for southern germany summary using teleseimic surface wave data from 110 selected earthquakes recorded at 10broad band stations in southern germany we construct phase velocity maps of rayleigh waves for southern germany in a further step these maps are inverted for a three dimensional model of the sv velocity of the upper 200 km of the mantle we attempt to take into account the effect of heterogeneous structure outside the study region by jointly inverting the data for heterogeneous phase velocity inside the study region and the distortion of the incoming wavefields by the surrounding structure the total wavefield in the study region is computed with a scattering formalism which includes multiple forward scattering and single backscattering since in principle the data can be perfectly fit by the incoming wavefields without any heterogeneous structure inside the study area we impose additional constraints on the incoming wavefields to reduce the non uniqueness the most important constraint is an energy criterion which states that the energy of the modelled wavefield in the study area averaged over many events should be equal to the energy sampled by the stations we demonstrate that enforcing this criterion generates phase velocity maps with heterogeneous structure nevertheless we are able to satisfy the energy criterion without any heterogeneous structure at the price of an only slightly increased data misfit hence it must be concluded that a seismic network of size and station density such as the one used in this study is still insufficient to demonstrate convincingly the existence of heterogeneities in the network area using teleseismic surface waves any reasonable structure combined with the appropriate incoming wavefields would allow an acceptable fit of our data this frustrating conclusion of course applies to all other comparable studies which use teleseismic surface waves although we cannot convincingly show that any phase velocity map we find should be preferred over others we are able to obtain good reconstructions of test structures from realistic synthetic data with the same station and event distribution as the real data moreover we find that the geometric pattern of the phase velocity maps obtained from real data depends only weakly on the constraints applied in the inversion while the amplitude of the phase velocity perturbations is almost completely determined by the constraints for all periods considered the fit to the data is extremely good the reduction of the quadratic misfit relative to the case of plane incoming waves and no structure is dramatic for the shorter periods the 3 d model of vertical shear wave velocity down to a depth of 200 km exhibits a basic division into four quadrants separated by a vertical plane intersecting the surface along a nearly west east line and a horizontal plane at about 130 km depth the northern rants show high velocities in the top 120 km and low velocities below 140 km the opposite is the case for the southern quadrants an exception to this general feature is a pronounced low velocity zone in the northwestern corner of the region

isostatic and dynamic support of high topography on a north atlantic passive margin abstract substantial controversy surrounds the origin of high topography along passive continental margins here we focus on the well documented elevated passive margin in southwestern scandinavia and quantify the relative contributions of crustal isostasy and dynamic topography in controlling the present topography we find that majority of the topography is compensated by the crustal structure suggesting a topographic age that is in accord with the 400 myr old caledonian orogenesis in addition we propose that dynamic uplift of 300 m has rejuvenated existing topography locally in the coastal region over the last 10 myr such uplift combined with a general sea level fall can help explain a variety of observations that have traditionally been interpreted in favor of a peneplain uplift model we conclude that high topography along the scandinavian margin cannot represent remnants of a peneplain uplifted within the last 20 myr the topography must have been high since the caledonian orogeny

tomographic estimates of sub moho seismic velocities in fennoscandia and structural implications abstract pn and sn velocity estimates are derived for the sub moho structure beneath fennoscandia using a tomographic conjugate gradient scheme observational data stem from local earthquake recordings of crustal phases pg sg lg and the sub crustal phases pn and sn by the fennoscandian seismograph network unknowns are pn and sn velocities and event hypocenter parameters crustal thicknesses are assumed as known and are not estimated whereas velocities are allowed to vary the most prominent p and s velocity anomalies are found in the northwest inland lofoten and southwest more of norway and for shear waves also in central finland there is a good correlation between the velocity anomalies in norway and observed negative bouguer anomalies indicating the presence of low density sub moho material in these areas geologically the pn and sn velocity anomalies appear to be associated with geodynamic processes tied to the opening of the norwegian greenland sea

an upper mantle s wave velocity model for northern europe from love and rayleigh group velocities summary a model of upper mantle s wave velocity and transverse anisotropy beneath northwestern europe is presented based on regional surface wave observations group velocities for both love and rayleigh surface waves are measured on waveform data from international and regional data archives including temporary deployments and then inverted for group velocity maps using a method accounting for fresnel zone sensitivity the group velocity variations are larger than in global reference maps and we are able to resolve unprecedented details we then apply a linear inversion scheme to invert for local 1 d shear wave velocity profiles which are consequently assembled to a 3 d model by choosing conservative regularization parameters in the 2 d inversion we ensure the smoothness of the group velocity maps and hence of the resulting 3 d shear wave speed model to account for the different tectonic regimes in the study region and investigate the sensitivity of the 1 d inversions to inaccuracies in crustal parameters we analyse inversions with different reference models of increasing complexity pure 1 d 3 d crust 1 d mantle and pure 3 d we find that all inverted models are very consistent at depths below 70 km at shallower depths the constraints put by the reference models primarily moho depth which we do not invert for remain the main cause for uncertainty in our inversion the final 3 d model shows large variations in s wave velocity of up to 12 per cent we image an intriguing low velocity anomaly in the depth range 70 150 km that extends from the iceland plume beneath the north atlantic and in a more than 400 km wide channel under southern scandinavia beneath southern norway the negative perturbations are around 10 per cent with respect to ak135 and a shallowing of the anomaly is indicated which could be related to the sustained uplift of southern scandinavia in neogene times furthermore our upper mantle model reveals good alignment to ancient plate boundaries and first order crustal fronts around the triple junction of the baltica avalonia laurentia collision in the north sea

off great circle propagation of intermediate period surface waves observed on a dense array in the french alps array analysis is performed on surface waves recorded in the french alps using a small aperture 25 km temporary array of six broad band stations the analysis shows that both rayleigh and love waves deviate relative to the great circle path the deviations are particularly strong up to 30 between 20 and 40 s period to interpret these observations we first study the effect of large scale structures using ray tracing in a smooth laterally heterogeneous model of the earth second we evaluate the local effect by considering a model for the french alps including strong lateral heterogeneities around the array that were not taken into account in the ray tracing by combining these two possible causes of the observed deviations we propose an explanation for the general trend in the observed deviations finally we show that by taking into account azimuthal deviations phase velocities measured at a regional scale can be significantly improved

changes in the lithospheric structure across the sorgenfrei tornquist zone inferred from dispersion of rayleigh waves abstract surface wave analysis was used to study possible lateral changes in the lithospheric upper mantle structure across the sorgenfrei tornquist zone stz which is part of the transition zone between the ancient baltic shield and younger western europe records of long period surface waves from earthquakes at teleseismic distances were analysed the data originated from long period permanent stations in southeastern norway and from broadband nars stations installed in denmark between 1983 and 1986 this configuration made it possible to compare the lithospheric structure north and south of the stz by analysis of surface wave dispersion between pairs of closely spaced stations in the same tectonic unit phase velocities of fundamental mode rayleigh waves were determined by calculating cross spectra of pairs of records the phase velocity dispersion curves show significant differences between the two tectonic units north and south of stz linearized inversion of the observed dispersion curves to obtain models of shear wave velocity in the crust and upper mantle shows a low velocity zone lvz at a depth of about 110 km beneath the western part of denmark just south of the stz a similar lvz was not identified beneath southeastern norway north of the stz if a low velocity zone is present beneath the baltic shield in this area it must be very weak the lateral changes in lithospheric asthenospheric structures take place over a distance of less than 500 km our results therefore suggest that the stz coincides with a transition zone in the upper mantle

constraints on the velocity structure beneath the tornquist teisseyre zone from beam forming analysis summary the primary indicators of lateral heterogeneity in the earth are the slowness and azimuth of incoming seismic signals on a regional scale surface waves in the upper mantle and crust are often scattered and or refracted which results in deviations from the great circle azimuth the slowness and direction of propagation of an arriving wave packet provides information about the lateral heterogeneity and can be measured by performing beam forming on the recordings across an array of stations the azimuthal deviation gives a constraint on the transverse velocity gradient along the path in addition its frequency dependence gives information on the depth dependence of the heterogeneity we have performed beam forming of fundamental mode rayleigh waves in the period range of 20 to 100 s travelling from the south east of europe to the nars nl array in the netherlands the purpose of this study is to obtain new information about the velocity structure beneath the tornquist teisseyre zone ttz the ttz is known to be a transition between the higher seismic velocities in the thicker and older precambrian crust of the east european platform eep and the lower velocities in the thinner and younger palaeozioc crust of central and western europe tectonic europe te however the lateral velocity gradient and the depth extent of this transition are not very well constrained we have used events located at both sides of the ttz and both the direct rayleigh wave and its coda have been analysed on the one hand the deviation of the wave propagation paths relative to the great circle observed in the direct wave for the events on the eastern side of the ttz confirms earlier results i e it gives independent evidence for a thicker crust and up to 10 per cent higher velocities in the first 150 km of the upper mantle beneath the eep than beneath the te such a contrast also explains observed surface head waves refracted along the ttz on the other hand no energy reflected at the ttz is detected in the coda for the events on the western side from synthetic experiments based on a linearized theory we conclude that from this absence of reflections no lower bound can be imposed on the width of the transition zone across the ttz at different depths source mechanisms other than the ones for the events used are needed to observe these reflections at different depths for both a sharp and a smooth transition

deblurring of frequency wavenumber images from small scale seismic arrays summary temporary arrays installed in urban areas for investigating the upper most geological structure typically comprised of a limited number of stations and are arranged in geometries constrained by environmental boundaries therefore it is expected that the frequency wavenumber images are significantly blurred by the array transfer function and are corrupted by noise in this paper the effect of the richardson lucy regularization method applied to the problem of deblurring frequency wavenumber images is investigated the images are computed by analysing data from two small aperture 2 d arrays installed with different configurations in a test site within the town of potenza southern italy for near surface investigations we show that removing the effects of the array response from the frequency wavenumber images improve the phase velocity estimation reducing the relevant level of uncertainty furthermore the richardson lucy regularization method is effective in reducing the level of noise related to spatial aliasing by eliminating spurious peaks allowing the maxima related to different seismic sources to be better discriminated

the deep structure of the scandes and its relation to tectonic history and present day topography abstract we review the results of the toposcandiadeep project a component of the topoeurope project in which we have studied the crustal and upper mantle structures of southern norway in relation to its high topography the scandinavian mountain chain the scandes is an intracontinental mountain chain at the western edge of the baltic shield and has its southern part located in southern norway the timing as well as the processes causing the formation of the scandes are disputed we bring new geophysical constraints to this issue by providing crustal and mantle seismic models for the area and by integrated modeling of the lithosphere and its potential deformation new maps of moho depth and crustal seismic velocities have been compiled using data from refraction lines p receiver functions and noise cross correlation these results show a thickening of the crust from southwest to northeast and a small crustal root not directly located below the topographic high p s and surface wave tomography infer seismic mantle velocities lower than in normal shield structure with a possible sharp boundary close to the oslo graben these low velocities are imaged in the lithosphere and in the underlying mantle down to the 410 km discontinuity integrated modeling of seismic models and gravity data shows that the low velocities below southern norway are compatible with a change in lithosphere thickness from c 100 km under southern norway to nearly 200 km under southern sweden with possible additional differences in composition the study also indicates that the topography can be isostatically sustained by the density distribution in the crust and lithospheric mantle we argue that the lithospheric lateral variation has been present for at least 300 my and has had a significant influence on the localization of the topography independently of the mechanism for uplift

teleseismic surface wave study for s wave velocity structure under an array southern california summary teleseismic surface wave data from the dense seismographic network in southern california cisn california integrated seismic network are used to construct s wave velocity maps for the region surface wave phase velocity measurements are achieved by way of a waveform matching spectral domain technique that was developed for use within the cisn array a two station phase velocity measurement technique was developed which takes advantage of the fact that for surface wave arrivals from any azimuth there are multiple pairs of cisn stations which are almost exactly on the same great circle paths to ensure the validity of this assumption particle motions were analysed for measured pairs within the network showing that the deviation between expected backazimuth from ray theory and observed backazimuths are small enough to be analysed by a simple distance correction this method was applied to 114 large earthquakes for time periods between 1999 and 2002 and led to the retrieval of phase velocity maps for rayleigh waves between 20 and 55 mhz and for love waves between 25 and 45 mhz finite frequency effect for propagating surface waves was approximately taken into consideration using a geometrical technique an ellipse determined by wavelength and great circle distance between the source and receiver can describe an influence zone for the finite frequency effect phase velocity map reconstructions using a method which incorporates this effect show minimal changes in phase velocity maps for our region but do extend solvable velocity regions inversion for s wave velocity distribution with depth shows that deep structural contrast across the san andreas extends into the upper mantle a slow velocity anomaly is evident under the southern sierras and the salton sea the latter region indicating the northward extension of tectonic activity in the gulf of california fast velocity roots that reach 60 km are found under the western part of transverse ranges and the northern peninsular ranges reconstruction of past location of the western transverse range microplate implies that these two ranges may have been adjacent to one another historically both the western transverse range fast velocity root and the peninsular range fast velocity root may be a remnant of old oceanic plate

crustal and uppermost mantle structure of southern norway results from surface wave analysis of ambient seismic noise and earthquake data summary we use ambient seismic noise and earthquake recordings on a temporary regional network in southern norway to produce rayleigh and love wave phase velocity maps from 3 to 67 s period local dispersion curves are then jointly inverted for a 3 d shear wave velocity model of the region we perform a two step inversion approach first a direct search monte carlo algorithm is applied to find best fitting isotropic velocity depth profiles those profiles are then used as initial models for a linearised inversion which takes into account radial anisotropy in the shear wave structure results reveal crustal as well as uppermost mantle structures in the studied region velocity anomalies in the upper crust are rather small in amplitude and can in most parts be related to surface geology in terms of rock densities old tectonic units like the oslo graben 300 240 ma and the caledonian nappes 440 410 ma are clearly imaged furthermore we find clear indications for localized crustal anisotropy of about 3 per cent despite generally poor resolution of interface depths in surface wave inversion we find lateral variation of crustal thickness in agreement with previous studies we are able to confirm and locate the transition from a slow lithospheric upper mantle underneath southern norway to a fast shield like mantle towards sweden

the northern and southern scandes structural differences revealed by an analysis of gravity anomalies the geoid and regional isostasy abstract we investigate the scandes mountain range by analysing the gravity field the geoid heights and the degree of isostatic compensation of the lithosphere topographically the scandes mountain range can be divided in the northern and southern scandes comparisons between the present topographic expression and the gravity field and the geoid show that the axis of highest elevation in the northern scandes is shifted eastwards compared to the minimum of the bouguer anomaly while the two coincide perfectly in the southern scandes geoid heights reduced by the effect of topographic masses show a large scale minimum in the northern scandes but no anomaly in the southern scandes regional flexural isostatic calculations yield a flexural rigidity of d 1023 nm for the lithosphere of the southern scandes and the isostatic gravity and geoid residuals point to additional isostatic support by low density rocks below the moho on the other side for the lithosphere in the northern scandes no significant flexural rigidity can be resolved here the bouguer anomaly is best modelled with a small flexural rigidity indicating nearly airy isostatic behaviour local subsurface loading and horizontal tectonic forces overprint the isostatic compensations and increase the tectonic complexity of the northern scandes these distinctive features of the scandes cannot be explained by currently existing models of the present and neogene uplift and the isostatic mechanism of the scandes

contrasts in lithospheric structure within the australian craton insights from surface wave tomography abstract contrasts in the seismic structure of the lithosphere within and between elements of the australian craton are imaged using surface wave tomography new data from the wacraton and tigger experiments are integrated with re processed data from previous temporary deployments of broad band seismometers and permanent seismic stations the much improved path coverage in critical regions allows an interpretation of structures in the west of australia and a detailed comparison between different cratonic regions improvements to the waveform inversion procedure and a new multi scale tomographic method increase the reliability of the tomographic images in the shallowest part of the model 75 km a region of lowered velocity is imaged beneath central australia and confirmed by the delayed arrival times of body waves for short paths within the cratonic lithosphere there is clearly structure at scale lengths of a few hundred kilometres resolution tests indicate that path coverage within the continent is sufficient to reveal features of this size in the upper part of our model in western australia differences are seen beneath and within the archaean cratons at depths greater than 150 km faster velocities are imaged beneath the yilgarn craton than beneath the pilbara craton in the complex north australian craton a fast wavespeed anomaly continuing to at least 250 km is observed below parts of the craton suggesting the possibility of archaean lithosphere underlying areas of dominantly proterozoic surface geology

integrated geophysical modelling of a lateral transition zone in the lithospheric mantle under norway and sweden summary the scandinavian mountain chain the scandes exhibits characteristics that are unusual for an old palaeozoic mountain belt these include renewed neogene uplift in a passive margin setting and the lack of a pronounced crustal root we investigate the influence of present day thermal compositional and geometric structures in the crust and mantle on the topography of the southern scandes and the resulting implications for the tectonic history of fennoscandia a self consistent 3 d subsurface model of southern norway and sweden is constructed from recent geophysical data sets that constrain the crustal architecture lithosphere geometry density distributions and thermal properties recent seismological studies show evidence for a relatively abrupt transition from seismically slower lithospheric mantle underneath southern norway to seismically faster lithospheric mantle underneath southern sweden we find that a transition from thin subcontinental lithospheric mantle sclm underneath southern norway to a significantly thicker sclm beneath southern sweden can explain this velocitytrend adifferenceincompositionbetweenthetwosclmdomains owingtodifferent depletion refertilization is required to satisfy the gravity field and isostatically compensated topography but contributes only slightly to the observed velocity contrast such a lateral transition zone constituting a major change in the lithospheric structure in southwestern fennoscandia can be related to several major proterozoic and phanerozoic tectonic events such as the sveconorwegian orogeny the permian oslo rift and perhaps even the opening of the atlantic

a test of the great circle approximation in the analysis of surface waves a new way of reconstructing wave fronts is de veloped for testing the validity of the great circle approxima tion in dispersion analysis of surface waves phase and time delays between pairs of stations of an array are used to re construct the wave fronts or surfaces of equal phase this techque is applied to fundamental mode rayleigh waves recorded at the nars stations dudlag the iliha iberian lithosphere heterogeneity and anisotropy project the re sulting wave fronts are compared with the theoretical ones i e calculated assuming that the waves have traveled along the great circle path with a constant phase velocity and the angle between both fronts is calculated waves traveling mosfiy through a laterally homogeneous oceanic path before arriving to the iberian peninsula are analyzed for the fre quency range of 10 to 60 mhz these show angles up to 8 degrees between the theoretical wave fronts and the wave fronts reconstructed using the delay data this implies that we make a relative error less than 1 when calculating path averaged phase velocities ignoring the deviation of the ar rival of the wave from the great circle direction

remarks on the stability of temporary cuts a re analysis of the observations and data related to the stability of excavations in clays gives a new insight into the problem it is shown that for clays with a liquidity index greater than 0 4

upper mantle structure in southern norway from beamforming of rayleigh wave data presenting multipathing summary a model for the upper mantle sv wave velocity under southern norway is obtained by depth inversion of the average phase velocity of the rayleigh wave fundamental mode in the area the average dispersion curve is obtained in the period range 22 200 s by beamforming of 190 rayleigh waves recorded by the magnus network a temporary regional network of 41 broad band stations resolution of the beamforming procedure is increased by deconvolving the original beams from the array response function using the lucy richardson algorithm in addition to an average phase velocity beamforming gives us some information concerning the nature of the incoming wavefield we detect deviations of the wave propagation direction from the great circle paths which commonly reach 10 at a period of 25 s for the teleseismic events the amplitude of the deviations decreases with increasing period and with decreasing epicentral distance as expected the phase velocity measured by beamforming does not show any correlation with the deviation from great circle path suggesting that deviation does not bias phase velocity measurements we detect also significant multipathing with characteristics that vary rapidly with frequency the obtained sv wave velocity profile clearly shows that southern norway is underlain by a low velocity zone in the upper mantle and does not have shield like characteristics despite its location in the baltic shield these findings support the hypothesis that the high topography of southern norway is sustained by anomalous upper mantle material

upper mantle s wave speed heterogeneity and anisotropy beneath the north atlantic from regional surface wave tomography the iceland and azores plumes summary we present a high resolution sv wave velocity and azimuthal anisotropy model for the upper mantle beneath the north atlantic and surrounding region derived from the analysis of over 3000 fundamental and higher mode rayleigh waveforms much of the data set comes from global and national digital seismic networks but to improve the path coverage we have also deployed a number of instruments at coastal sites in northwest europe iceland and eastern greenland the dense path coverage wide azimuthal distribution substantial higher mode content and the relatively short path lengths in the data set have enabled us to build an upper mantle model for the region with a horizontal resolution of a few hundred kilometres extending to 400 km depth three major hotspots iceland azores and eifel exist within the region of the model and slow upper mantle velocities are associated with each of these areas the best depth resolution in our model occurs in nw europe and in this area low sv velocities in the vicinity of the eifel hotspot extend to approximately 400 km depth major negative velocity anomalies exist in the north atlantic upper mantle beneath both iceland and the azores hotspots both anomalies are above 200 km depth 5 7 per cent slow with respect to prem and are elongated along the mid atlantic ridge low velocities extend to the south of iceland beneath the reykjanes ridge where other geophysical and geochemical observations have indicated the presence of hot plume material a similar but somewhat weaker feature exists beneath the kolbeinsey ridge north of iceland where there is also supporting evidence for the presence of hot plume material this observation might also be associated with a plume beneath jan mayen the low velocity structure beneath the azores hotspot is also elongated along the mid atlantic ridge the fast propagation direction of horizontally propagating sv waves in the atlantic south of iceland correlates well with the east west ridge spreading direction at all depths and changes to a direction close to ns in the vicinity of iceland

love rayleigh wave incompatibility and possible deep upper mantle anisotropy in the iberian peninsula love and rayleigh wave phase velocities are analyzed with the goal of retrieving information about the anisotropic structure of the iberian lithosphere the cross correlation method is used to measure the interstation phase velocities between diverse stations of the iliha network at periods between 20 and 120 s despite the 2 d structure of the network the love wave data are too few to enable an analysis of phase velocity azimuthal variations azimuthal averages of love and rayleigh wave phase velocities are calculated and inverted both in terms of isotropic and anisotropic structures realistic isotropic models explain the rayleigh wave and short period love wave phase velocities therefore no significant anisotropy needs to be introduced in the crust and down to 100 km depth in the upper mantle to explain our data a discrepancy is observed only at long periods where the data are less reliable love wave data at periods between 80 and 120 s remain 0 15 km s faster than predicted by isotropic models explaining the long period rayleigh wave data possibilities of biases in the measurements due to interferences with higher modes are examined but seem unlikely a transversely isotropic model with 8 of s wave velocity anisotropy in the upper mantle at depths larger than 100 km can explain the whole set of data in terms of a classical model of mantle anisotropy this corresponds to 100 of the crystals perfectly oriented in the horizontal plane in a pyrolitic mantle this is a rather extreme model which predicts at time delay between 0 and 2 seconds for split sks

oceanic lithospheric s wave velocities from the analysis of p wave polarization at the ocean floor our knowledge of the absolute s wave velocities of the oceanic lithosphere is mainly based on global surface wave tomography local active seismic or compliance measurements using oceanic infragravity waves the results of tomography give a rather smooth picture of the actual s wave velocity structure and local measurements have limitations regarding the range of elastic parameters or the geometry of the measurement here we use the p wave polarization apparent p wave incidence angle of teleseismic events to investigate the s wave velocity structure of the oceanic crust and the upper tens of kilometres of the mantle beneath single stations in this study we present an up to our knowledge new relation of the apparent p wave incidence angle at the ocean bottom dependent on the half space s wave velocity we analyse the angle in different period ranges at ocean bottom stations obs to derive apparent s wave velocity profiles these profiles are dependent on the s wave velocity as well as on the thickness of the layers in the subsurface consequently their interpretation results in a set of equally valid models we analyse the apparent p wave incidence angles of an obs data set which was collected in the eastern mid atlantic we are able to determine reasonable s wave velocity depth models by a three step quantitative modelling after a manual data quality control although layer resonance sometimes influences the estimated apparent s wave velocities the apparent s wave velocity profiles are well explained by an oceanic prem model in which the upper part is replaced by four layers consisting of a water column a sediment a crust and a layer representing the uppermost mantle the obtained sediment has a thickness between 0 3 km and 0 9 km with s wave velocities between 0 7 km s 1 and 1 4 km s 1 the estimated total crustal thickness varies between 4 km and 10 km with s wave velocities between 3 5 km s 1 and 4 3 km s 1 we find a slight increase of the total crustal thickness from 5 km to 8 km towards the south in the direction of a major plate boundary the gloria fault the observed crustal thickening can be related with the known dominant compression in the vicinity of the fault furthermore the resulting mantle s wave velocities decrease from values around 5 5 km s 1 to 4 5 km s 1 towards the fault this decrease is probably caused by serpentinization and indicates that the oceanic transform fault affects a broad region in the uppermost mantle conclusively the presented method is useful for the estimation of the local s wave velocity structure beneath ocean bottom seismic stations it is easy to implement and consists of two main steps 1 measurement of apparent p wave incidence angles in different period ranges for real and synthetic data and 2 comparison of the determined apparent s wave velocities for real and synthetic data to estimate s wave velocity depth models

long term creep rates on the hayward fault evidence for controls on the size and frequency of large earthquakes the hayward fault hf in california exhibits large m w 6 5 7 1 earthquakes with short recurrence times 161 65 yr probably kept short by a 26 78 aseismic release rate including postseismic its interseismic release rate varies locally over time as we infer from many decades of surface creep data earliest estimates of creep rate primarily from infrequent surveys of offset cultural features revealed distinct spatial variation in rates along the fault but no detectable temporal variation since the 1989 m w 6 9 loma prieta earthquake lpe monitoring on 32 alinement arrays and 5 creepmeters has greatly improved the spatial and temporal resolution of creep rate we now identify significant temporal variations mostly associated with local and regional earthquakes the largest rate change was a 6 yr cessation of creep along a 5 km length near the south end of the hf attributed to a regional stress drop from the lpe ending in 1996 with a 2 cm creep event north of there near union city starting in 1991 rates apparently increased by 25 above pre lpe levels on a 16 km long reach of the fault near oakland in 2007 an m w 4 2 earthquake initiated a 1 2 cm creep event extending 10 15 km along the fault using new better constrained long term creep rates we updated earlier estimates of depth to locking along the hf the locking depths outline a single 50 km long locked or retarded patch with the potential for an m w 6 8 event equaling the 1868 hf earthquake we propose that this inferred patch regulates the size and frequency of large earthquakes on hf online material 2007 event creep models plots of creepmeter data maps and cross sections of relocated microearthquakes and active fault traces and iterative solutions for depth of creep

strong lateral variations of lithospheric mantle beneath cratons example from the baltic shield abstract understanding mechanisms for creation and evolution of precambrian continental lithosphere requires to go beyond the large scale seismic imaging in which shields often appear as laterally homogeneous with a thick and fast lithosphere we here present new results from a seismic experiment polenet lapnet in the northern part of the baltic shield where we identify very high seismic velocities vs 4 7 km s in the upper part of the mantle lithosphere and a velocity decrease of 0 2 km s at approximately 150 km depth we interpret this velocity decrease as refertilisation of the lower part of the lithosphere this result is in contrast to the lithospheric structure immediately south of the study area where the seismic velocities within the lithosphere are fast down to 250 km depth as well as to that of southern norway where there is no indication of very high velocities in the lithospheric mantle vs of 4 4 km s while the relatively low velocities beneath southern norway can tentatively be attributed to the opening of the atlantic ocean the velocity decrease beneath northern finland is not easily explained with present knowledge of surface tectonics our results show that shield areas may be laterally heterogeneous even over relatively short distances such variability may in many cases be related to lithosphere erosion and or refertilisation at the edge of cratons which may therefore be particularly interesting targets for seismic imaging

shear wave velocities in the upper mantle of the western alps new constraints using array analysis of seismic surface waves it remains challenging to obtain absolute shear wave velocities of heterogeneities of small lateral extension in the uppermost mantle this study presents a cross section of vs across the strongly heterogeneous 3 d structure of the western european alps based on array analysis of data from 92 broad band seismic stations from the cifalps experiment and from permanent networks in france and italy half of the stations were located along a dense sublinear array using a combination of these stations and off profile stations fundamental mode rayleigh wave dispersion curves were calculated using a combined frequency time beamforming approach we calculated dispersion curves for seven arrays of approximately 100 km aperture and 14 arrays of approximately 50 km aperture the latter with the aim of obtaining a 2 d vertical cross section of vs beneath the western alps the dispersion curves were inverted for vs z with crustal interfaces imposed from a previous receiver function study the array approach proved feasible as vs z from independent arrays vary smoothly across the profile length results from the seven large arrays show that the shear velocity of the upper mantle beneath the european plate is overall low compared to ak135 with the lowest velocities in the internal part of the western alps and higher velocities east of the alps beneath the po plain the 2 d vs model is coherent with i a 100 km thick eastward dipping european lithosphere west of the alps ii very high velocities beneath the po plain coherent with the presence of the alpine european slab and iii a narrow low velocity anomaly beneath the core of the western alps from the brianconnais to the dora maira massif and approximately colocated with a similar anomaly observed in a recent teleseismic p wave tomography this intriguing anomaly is also supported by traveltime variations of subvertically propagating body waves from two teleseismic events that are approximately located on the profile great circle

the shear wave velocity structure in the upper mantle beneath eurasia summary we develop an approach that allows us to invert for the mantle velocity structure within a finely parametrized region as a perturbation with respect to a low resolution global tomographic model we implement this technique to investigate the upper mantle structure beneath eurasia and present a new model of shear wave velocity parametrized laterally using spherical splines with 2 9 spacing in eurasia and 11 5 spacing elsewhere the model is obtained from a combined data set of surface wave phase velocities long period waveforms and body wave traveltimes we identify many features as narrow as few hundred kilometres in diameter such as subducting slabs in eastern eurasia and slow velocity anomalies beneath tectonically active regions in contrast to regional studies in which these features have been identified our model encompasses the structure of the entire eurasian continent furthermore including mantleand body wave waveforms helped us constrain structures at depths larger than 250 km which are poorly resolved in earlier models we find that up to 9 per cent faster than average anomalies within the uppermost 200 km of the mantle beneath cratons and some orogenic regions are separated by a sharp gradient zone from deeper 1t o 2 per cent anomalies we speculate that this gradient zone may represent a boundary separating the lithosphere from the continental root which might be compositionally distinct from the overlying lithosphere and remain stable either due to its compositional buoyancy or due to higher viscosity compared with the suboceanic mantle our regional model of anisotropy is not significantly different from the global one

sharp contrast in lithospheric structure across the sorgenfrei tornquist zone as inferred by rayleigh wave analysis of tor1 project data abstract this work is a part of the tor1 project 1996 1997 and is devoted to determining the lithospheric structure across the sorgenfrei tornquist zone in northern europe for the first time in europe a very dense seismic broadband array has offered the possibility of determining very sharp lateral variations in the structure of the lithosphere at small scales using surface wave analysis we measure phase velocities for rayleigh waves with periods ranging between 10 and 100 s both within arrays with apertures of 40 50 km small compared to the wavelength and along long profiles of at least 100 km dispersion curves are then inverted and shear wave velocity models down to the depth of 200 km are proposed we show that the sorgenfrei tornquist zone is a major tectonic feature within the whole lithosphere north east of this feature in sweden beneath the baltic shield no lithosphere asthenosphere boundary is observed to exist to depths of 200 km south west of the sorgenfrei tornquist zone beneath denmark we find a lithospheric thickness of 120 20 km the transition across the sorgenfrei tornquist zone is sharp and determined to be very steeply dipping to the south west we also demonstrate the existence of a sharp discontinuity between the lithospheres beneath denmark 120 20 km thick and beneath germany characterized by thicknesses of 50 10 km in the northernmost part and 100 20 km in the southwest this discontinuity is most likely related to the trans european fault at the surface

the lithosphere asthenosphere system in fennoscandia abstract we present a summary of the available information on rayleigh wave dispersion data for the fennoscandian region the observations have been combined to produce regional dispersion relations which have then been subjected to the hedgehog inversion procedure the results are presented on a map outlining the thickness of the lid and the shear velocities in both the lid and the asthenosphere channel lid thickness up to around 135 km is found in the bothnia north central finland area with if any weak shear velocity contrast to the underlying layer the surrounding areas are characterized by lid thickness up to around 75 km a stronger low velocity zone to lid contrast may be found in the caledonian and baltic sea area 0 25 0 45 km s taking into account moho depth data and the aforementioned results a map of the lithosphere asthenosphere system was derived

non linear surface wave phase velocity inversion based on ray theory summary the development of temporary and permanent broad band seismic arrays reinforces the need for advanced interpretation techniques in surface wave analysis we present a new method based on 2 d paraxial ray theory of inverting teleseismic surface wave phase information and constructing phase velocity maps on a regional scale measurements of local phase velocities and propagation directions of rayleigh waves taken from full waveform synthetic seismograms are used to validate the ray theory for smooth structures on a regional scale curved wavefronts created by heterogeneous structure outside the study area are taken into account through joint inversion for the phase velocity field and the shape of the incoming wavefronts in the forward ray tracing procedure the curved wavefronts are introduced through the boundary conditions by equating the slowness vector of the ray at the edge of the study region with the known gradient of the arrival time of the wave to make the inverse problem non singular we constrain the parameters in the inversion primarily by applying a smoothness criteria on the velocity field and on the incoming wave field inversions of synthetic data sets computed by direct ray tracing and by full waveform modelling show that for 100 km spacing between stations the minimum size of structure that we can image is approximately 150 km heterogeneities with a size approximately equal to the wavelength are reconstructed by the ray based inversion even though velocity variations are underestimated due to the wave field smoothing of the structures a minimum signal to noise ratio of 3 5 is necessary in order to correctly retrieve the phase velocity field inversion of a subset of the svekalapko data for 60 s period demonstrates the applicability of the method on real data

waveform inversion of surface wave data test of a new tool for systematic investigation of upper mantle structures summary in most tomographic inversion of surface wave data the long period seismograms are first interpreted in terms of dispersion and or attenuation curves before performing an inversion in terms of laterally and depth varying properties an alternative to this approach is to perform a direct waveform inversion or as in cara lev que 1987 to use another set of secondary observables built up from the seismograms in this paper we systematically test with actual rayleigh wave records this latter technique by considering laterally homogeneous models we use for this purpose a set of recent long period digital records from the geoscope station dumont d urville antarctica for surficial events in the south indian ocean and the southeast pacific ocean and for intermediate depth events in the vanuatu and kermadec trenches in addition to the obvious advantages of being able to deal with situations where overtones are present in the seismogram it is found that the waveform inversion procedure allows us to reach a better depth resolution than in classical inversion of dispersion curves even when only the fundamental mode is present in the seismogram quite good resolution is obtained to depth as large as 300km for s velocity when using surficial events located at a few thousand kilometres from the station while classical surface wave studies do not allow us to resolve s velocity at depth larger than 150 km for these events when intermediate depth events are used at distances of about 5000 km the presence of overtones in the signal allows us to get resolution to depth as large as 600 km for s velocity poorer resolution is obtained in both situations for the attenuation factor s velocity appears furthermore to be more robust than attenuation at depth where good resolution is achieved due to the great sensitivity of surface wave amplitude to departure from the assumption of lateral homogeneity more sophisticated direct modelling would be required to get more confidence in the inverted attenuation models

structure of the scandes lithosphere from surface to depth abstract in this review we give an overview of geophysical data and models available for the scandinavian mountains and adjacent areas as they are of relevance to the debate about the existence and cause of neogene uplift emphasis is given to potential field and petrophysical data of which the earth science communities of norway and sweden have a long tradition of acquisition and interpretation this is reflected in the wealth and dense coverage of data available the topography of the scandes mountain chain correlates to a large degree with a bouguer gravity low which suggests isostatic compensation but comparison with magnetic and petrophysical data shows that the gravity low is partly influenced by the trans scandinavian igneous belt signals due to the effects of surface geology can be further eliminated by considering the near surface density distribution as provided by petrophysical sampling to illuminate the entire lithospheric structure active and passive seismic and magnetotelluric data can be used recent and ongoing experiments are aimed at improving the existing models of the lithosphere integration of these different geophysical data sets allows the structure of the lithosphere of the scandes and its surroundings to be addressed seismic models show no pronounced crustal root below the scandes which could provide isostatic compensation but instead an increase of crustal thickness towards the central fennoscandian shield from the integrated model isostatic compensation is inferred to be largely controlled by the density distribution of the crust and that a high density lower crust to the east of the scandes is necessary to achieve isostatic equilibrium on a regional scale we demonstrate the typical crustal structure with profiles crossing from the scandes into the shield and a combined onshore offshore basement map

lithospheric and sublithospheric anisotropy beneath the baltic shield from surface wave array analysis abstract we report measurements of radial and azimuthal anisotropy in the upper mantle beneath southern and central finland which we obtained by array analysis of fundamental mode rayleigh and love waves azimuthally averaged phase velocities were analysed in the period range 15 to 190 s for rayleigh waves and 15 to 100 s for love waves the azimuthal variation of the rayleigh wave phase velocities was obtained in the period range 20 to 100 s the limited depth resolution of fundamental mode surface waves necessitated strong damping constraints in the inversion for anisotropic parameters we investigated the effects of non unicity on the final model by experimenting with varying model geometries the radial anisotropy beneath finland can be explained by a lithosphere at least 200 km thick predominantly 50 by volume composed of olivine crystals having their a axes randomly distributed in the horizontal plane on the contrary the measured lithospheric azimuthal anisotropy is small this can be reconciled with body wave observations made in the area that indicate a complex pattern of rapidly varying anisotropy below 200 250 km depth that is below the petrologic lithosphere as revealed by xenolith analyses conducted in the area the magnitude of the azimuthal anisotropy increases and would be compatible with a mantle containing 15 20 by volume of olivine crystals whose a axes are coherently aligned in the n ne direction the alignment of the a axes is off the direction of present day absolute plate motion in either the no net rotation or hot spot reference frame currently n55 n60 we interpret this mismatch as evidence for a complex convective flow pattern of the mantle beneath the shield which by inference is decoupled from the overlying lithosphere

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