stuck in the mud earthquake nucleation and propagation through accretionary forearcs 1 subduction zone earthquakes can propagate to the surface causing large seafloor displacements resulting in tsunamis this requires the earthquake to rupture through clay rich sediments of the accretionary wedge which are largely aseismic as found previously the frictional properties of a range of wet clays at low slip velocity are velocity strengthening thus inhibiting earthquake nucleation however at high slip velocity the same materials weaken almost immediately resulting in a negligible critical slip weakening distance and fracture energy we interpret this behaviour as rapid thermal pressurization of the pore fluid within the clay gouge the lack of fracture energy can explain how a large rupture propagating from depth might not be arrested by clay rich velocity strengthening sediments as is commonly seen the results suggest that generally earthquakes may be difficult to nucleate on mature faults dominated by clay but the propagation of earthquakes through these zones is energetically very favourable

the heterogeneous upper mantle low velocity zone abstract the upper mantle low velocity zone lvz is a depth interval with slightly reduced seismic velocity compared to the surrounding depth intervals the zone is present below a relatively constant depth of 100 km in most continental parts of the world both in cratonic areas with high average velocity and tectonically active areas with low average velocity evidence for the low velocity zone arises from controlled and natural source seismology including studies of surface waves and of primary and multiple reflections of body waves from the bounding interfaces calculations of receiver functions and absolute velocity tomography the available data indicates a more pronounced reduction in seismic velocity and q value for s waves than p waves as well as high electrical conductivity in the lvz seismic waves are strongly scattered by the zone which demonstrates the existence of small scale heterogeneity the depth to the base of the lvz is systematically shallower in cold stable cratonic areas than in hot active regions of the world because of its global occurrence below a relative constant depth of 100 km the lvz cannot be explained by metamorphic or compositional variation and rheological changes calculated upper mantle temperatures indicate that the rocks are close to the solidus in an interval with variable thickness below 100 km depth provided that the rocks contain water and carbon dioxide the presence of even small amounts of such fluids in the mantle rocks will lower the solidus by several hundred degrees and introduce a characteristic kink on the solidus curve around 80 100 km depth the seismic velocities and q values are significantly reduced of rocks which are close to the solidus or contain small amounts of partial melt hence the lvz may be explained by upper mantle temperatures being close to the solidus in a depth interval below 100 km assuming that the rocks contain only limited amounts of fluids this mechanism may explain the low velocities q values and resistivity as well as the intrinsic scattering and the characteristic variation in thickness of the low velocity zone

deep structure of fennoscandia from fundamental and higher mode dispersion of rayleigh waves abstract surface wave dispersion for the baltic shield area has been investigated through analysis of phase velocities up to periods of about 250 s for the fundamental rayleigh mode and about 80 s for the first two higher modes this has enabled investigation of the lithosphere asthenosphere system and deeper regions down to about 400 km the shear wave velocitydepth relationship obtained from the inversion of dispersion data for the paths cop kev cop krk can be considered as representative of an average model for the baltic shield moreover the inversion of dispersion data supplemented by previous results from the scandinavian area suggest the presence of significant lateral heterogeneity down to depths of about 350 km moving from the older precambrian shield cop kev cop krk to the peripheral area nur cop models with small if any differences in average shear velocity are consistent with the data in the depth range 350 450 km for the regions studied

deep structure of the european mediterranean area from seismological data abstract over the past 20 years the study of p and s wave velocities in the upper mantle of the european mediterranean area has been the subject of intensive research work we present a summary of results based on inversion of available surface wave dispersion data and p wave travel time observations in the european mediterranean area the correlation between the lithosphere and upper mantle structure obtained from the aforementioned analysis with other geophysical data is discussed

area selection for diamond exploration using deep probing electromagnetic surveying abstract previously proposed methods of area selection for diamond prospective regions have predominantly relied on till geochemistry airborne geophysics and or an appraisal of tectonic setting herein we suggest that a novel deep probing geophysical technique electromagnetic studies using the natural source magnetotelluric mt method can contribute to such an activity essentially diamondiferous regions must have 1 old lithosphere 2 thick lithosphere and 3 lithosphere that contains high concentrations of carbon deep probing mt studies are able to address all three of these the second and the third of these can be accomplished independently using mt but for the first the geometries produced from modelling the mt observations must be interpreted with appropriate interaction with geologists geochemists and other geophysicists examples are given from the slave and superior cratons in north america with a brief mention of an area of the rae craton and general speculations about possible diamondiferous regions

pyrite alteration and neoformed magnetic minerals in the fault zone of the chi chi earthquake mw7 6 1999 evidence for frictional heating and co seismic fluids 1 during an earthquake physical and chemical transformations lead to alteration and formation of minerals in the gouge layer altered and neoformed minerals can be used as tracers of some earthquake processes in this study we investigate pyrite and magnetic minerals within the host chinshui siltstone and the 16 cm thick gouge this gouge hosts the principal slip zone of chi chi earthquake mw7 6 1999 in the chinshui siltstone pyrite framboids of various sizes and euhedral pyrite are observed the magnetic mineral assemblage comprises stoichiometric magnetite greigite and fine grained pyrrhotite the pyrite content is generally reduced in the gouge compared to the wall rock the magnetic mineral assemblage in the gouge consists of goethite pyrrhotite and partially oxidized magnetite the pyrrhotite goethite and some magnetite are neoformed pyrrhotite likely formed from high temperature decomposition of pyrite 500 c generated during co seismic slip of repeated earthquakes goethite is inferred to have formed from hot aqueous co seismic fluid 350 c in association with the 1999 chi chi event elevated fluid temperatures can also explain the partial alteration of magnetite and the retrograde alteration of some pyrrhotite to pyrite we suggest that characterization of neoformed magnetic minerals can provide important information for studying earthquake slip zones in sediment derived fault gouge

high resolution body wave tomography beneath the svekalapko array ii anomalous upper mantle structure beneath the central baltic shield high resolution body wave tomography beneath the svekalapko array ii anomalous upper mantle structure beneath the central baltic shield

complex lithospheric structure under the central baltic shield from surface wave tomography complex lithospheric structure under the central baltic shield from surface wave tomography

trace element anomaly in fault rock induced by coseismic hydrothermal reactions reproduced in laboratory friction experiments friction experiments at high velocities 0 1 to 0 4 m s at room temperature under high pore fluid pressures 2 or 5 mpa and trace element analyses of the run products were carried out on simulated fault gouge derived from the chelungpu fault taiwan the friction coefficient decreased to 0 1 during sliding and the slip surface temperature reached 300 c by 6 m of slip displacement the slip caused a small but distinct decrease of li in the deformed gouge when the slip surface temperature exceeded 300 c the observed li depletion agreed with calculated results indicating that it resulted from a hydrothermal reaction at a high temperature produced by short duration up to 40 s frictional heating the geochemical data suggest a small fluid rock ratio and low reaction temperature in the simulated fault which is explained by higher normal stress or repeated earthquakes which elevated fluid rock ratios in the natural fault

seismic anisotropy a key to resolve fabrics of mantle lithosphere of fennoscandia abstract by merging different regional sets of body wave data we compile a relief of the lithosphere asthenosphere boundary in one of the oldest continental regions on the planet the fennoscandian shield a maximum lithospheric thickness of 200 220 km is observed in the central part of the shield and a significant thinning at its margins particularly in the southwest at the trans european suture zone fabric of the mantle lithosphere is modelled from independent sets of anisotropic parameters relative p residual spheres and shear wave splitting the mantle lithosphere of fennoscandia consists of several domains consistent olivine fabrics of dipping foliations in 3d anisotropic models of the proterozoic lithosphere or predominantly dipping lineations in models of the archean lithosphere the strength of seismic anisotropy agrees with findings from mantle xenoliths we interpret the anisotropic domains as fragments of mantle lithosphere retaining an old fossil olivine fabric which was created before these micro continents assembled we envisage an early form of plate tectonic processes such as successive subduction episodes stacking of oceanic plates and accretion of magmatic arcs such processes could create the generally observed fossil dipping fabrics of the thick precambrian mantle lithosphere starting as early as the archean

imaging the continental upper mantle using electromagnetic methods abstract the internal structure of the continental lithosphere holds the key to its creation and development and this internal structure can be determined using appropriate seismic and electromagnetic methods these two are complementary in that the seismic parameters usually represent bulk properties of the rock whereas electrical conductivity is primarily a function of the connectivity of a minor constituent of the rock matrix such as the presence of a conducting mineral phase e g carbon in graphite form or of a fluid phase e g partial melt or volatiles in particular conductivity is especially sensitive to the top of the asthenosphere generally considered to be a region of interconnected partial melt knowledge of the geometry of the lithosphere asthenosphere boundary is important as this boundary partially controls the geodynamic processes that create modify and destroy the lithosphere accordingly collocated seismic and electromagnetic experiments result in superior knowledge than would be obtained from using each on its own this paper describes the state of knowledge of the continental upper mantle obtained primarily from the natural source magnetotelluric technique and outlines how hypotheses and models regarding the development of cratonic lithosphere can be tested using deep probing electromagnetic surveying the resolution properties of the method show the difficulties that can be encountered if there is conducting material in the crust examples of data and interpretations from various regions around the globe are discussed to demonstrate the correlation of electromagnetic and seismic observations of the lithosphere asthenosphere boundary also the observations from laboratory measurements on candidate mineralogies representative of the mantle such as olivine are presented

heat flow and thermal structure of the lithosphere across the baltic shield and northern tornquist zone abstract terrestrial heat flow data from archean and proterozoic provinces of the baltic shield its southwestern margin and the tectonic transition to the younger tectonic units of central europe northern segment of the european geotraverse are compiled and examined for local and regional variations a 2 d numerical lithospheric temperature and heat flux model is presented covering 1800 km of the deep seismic fennolora profile across the baltic shield and 500 km of eugeno s northern eugemi seismic lines across the northern tornquist zone and the danish and north german basins thermal lithosphere defined as the outer layer with relatively low temperatures t c in which heat transfer is dominantly by conduction is found to vary markedly in thickness from 85 110 km beneath basins and tornquist zone to about 150 km in central shield areas and 200 250 km in areas of low heat flow along the northern shield profile these results are in very good agreement with seismological information from surface wave dispersion analysis and the refraction wide angle seismic interpretation of fennolora data the combined thermal and seismologic evidence indicates that the uppermost mantle region stratified in seismic velocity is restricted to the upper relatively cold thermal layer which is interpreted to constitute shield lithosphere local and to some extent regional variations in surface heat flow are found to be closely related to variations in near surface radiogenic heat production for the southern baltic shield a heat flow heat production relationship of q 0 32 8 7 6 h 0 is derived regional increase in heat flow from northern and central shield provinces to the shield margin and the tornquist zone is interpreted to be related partly to differences in upper crustal heat generation partly and in southernmost areas mainly to an increased heat flux from the upper mantle upper mantle heat flux is estimated at 20 25 mw m 2 along the northern and central shield transect increasing to 30 40 mw m 2 beneath the shield margin basins and tornquist zone lithospheric thickness variations in this region of northern europe are found to be closely associated with variations in heat flux from the uppermost mantle and perhaps to a large extent controlled by geodynamically determined lateral differences in upper mantle heat flux earthquake focal depth data and information on crustal strength show baltic shield seismicity to be limited generally to the upper 20 25 km brittle part of the crust at temperatures less than 300 400 c maximum source depth of magnetic anomalies at temperatures near 600 c is in the deepest part of the crust near the crust mantle boundary in the southern region about 25 km depth along the tornquist zone and about 35 40 km in southern shield areas and in the uppermost mantle 60 70 km depth in the northern shield areas some petrologic implications are discussed the present deep crust is supposed to be at lower temperature pressure conditions than at early stages of formation however also the present deepest parts of the shield crust 35 40 km are within the stability field of eclogites the general absence of significant gravity anomalies in areas of marked crustal thickness variations indicate high density eclogites to be present in significant amounts in the deep shield crust

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

analysis of waves converted from s to p in the upper mantle beneath the baltic shield teleseismic data recorded by broadband stations of the swedish national seismic network have been used in a study of waves converted from s to p in the uppermost mantle s to p converted waves are recorded as precursors to the direct s arrival this enables us to study seismic discontinuities at depths of 100 300 km where the traditional receiver function technique based on p to s conversion fails due to disturbances from crustal reverberations clear signals of s to p conversion are seen for several horizons in the 50 200 km depth range this is interpreted as a layered lithosphere with alternating high and low velocity bodies a sharp contrast is imaged at depths around 160 km and continuous for almost 1000 km in the southern part of the profile this structure coincides with the velocity contrast interpreted by several authors as the lower limit of a prominent low velocity zone in the 95 to 160 km depth range a feature which we identify as the lithosphere asthenosphere boundary is clearly imaged at depths around 200 km

a new model of upper mantle p wave velocity below the baltic shield indication of partial melt in the 95 to 160 km depth range abstract the subcrustal mantle to about a depth of 160 km below the baltic shield can be divided seismically into two main intervals the upper interval between ca 45 and 100 km is characterized by refracted waves with velocities between 8 0 and 8 6 km s interpreted as a sandwich layered model of intermixed high and low velocity layers the lower interval is a ca 40 km thick zone of relatively low average velocity at a depth increasing from 95 km in the southern part to 120 km in the northern part of the shield seismic sections show that isolated bodies in this interval generate scattered reflections with substantial amplitude variation over short distance the maximum velocity difference at the reflectors is 1 0 km s which is larger than in the upper main interval our model is based on a general gap in correlation of seismic arrivals at offsets between 800 and 1100 km at larger offsets we observe continuous linear first arrivals indicating a relatively homogenous layer of high 8 6 km s velocity below a depth of 160 km petrologically the lower reflective interval is explained by partially melted small bodies with patches of carbonatitic or kimberlitic magma of horizontal extent less than 20 km this new model of the upper mantle is based on seismic data from the baltic shield and there is clear indication that it is equally valid for other shield and platform areas

high velocity frictional properties of clay rich fault gouge in a megasplay fault zone nankai subduction zone 1 we conducted high velocity friction experiments on clay rich fault gouge taken from the megasplay fault zone in the nankai subduction zone under dry and wet conditions in the dry tests dehydration of clay minerals occurred by frictional heating and slip weakening is related to thermal pressurization associated with water vaporization resulting in a random distribution of clay clast aggregates in the gouge matrix in the wet tests slip weakening is caused by pore fluid pressurization via shear enhanced compaction and frictional heating and there is a very weak dependence of the steady state shear stress on the normal stress the resulting microstructure reflects the grain size segregation in a granular fluid shear flow at high shear rates these results suggest that earthquake rupture propagates easily through clay rich fault gouge by high velocity weakening potentially leaving the microstructures resulting from the frictional heating or the flow sorting at high slip rates

mantle structure and composition to 800 km depth beneath southern africa and surrounding oceans from broadband body waves abstract average one dimensional p and s wavespeed models from the surface to depths of 800 km were derived for the southern african region using travel times and waveforms from earthquakes recorded at stations of the kaapvaal and south african seismic networks the herglotz wiechert method combined with ray tracing was used to derive a preliminary p wavespeed model followed by refinements using phase weighted stacking and synthetic seismograms to yield the final model travel times combined with ray tracing were used to derive the s wavespeed model which was also refined using phase weighted stacking and synthetic seismograms the presence of a high wavespeed upper mantle lid in the s model overlying a low wavespeed zone lwz around 210 to 345 km depth that is not observed in the p wavespeed model was inferred the 410 km discontinuity shows similar characteristics to that in other continental regions but occurs slightly deeper at 420 km depletion of iron and or enrichment in aluminium relative to other regions are the preferred explanation since the p wavespeeds throughout the transition zone are slightly higher than average the average s wavespeed structure beneath southern africa within and below the transition zone is similar to that of the iasp91 model there is no evidence for discontinuity at 520 km depth the 660 km discontinuity also appears to be slightly deeper than average 668 km although the estimated thickness of the transition zone is 248 km similar to the global average of 241 km the small size of the 660 km discontinuity for p waves compared with many other regions suggests that interpretation of the discontinuity as the transformation of spinel to perovskite and magnesiowustite may require modification alternative explanations include the presence of garnetite rich material or ilmenite forming phase transformations above the 660 km discontinuity and the garnet perovskite transformation as the discontinuity

average lithospheric structure of southern africa summary we present a new 1 d earth model for the crust and upper mantle beneath the archaean core of southern africa the crustal structure is constrained by published seismic refraction reflection data and by the modelling of teleseismic receiver function data the mantle structure is constrained by traveltime measurements for p and s waves by waveform inversion of multimode surface waves and by forward modelling of p waveforms for regional earthquakes the 42 km thick crust of southern africa consists of four layers a 2 km thick 5 05 km s surface layer a 5 km thick 6 08 km s upper crust a 20 km thick 6 30 km s l mid crust and a 15 km thick 6 73 km s lower crust below the crust there is an 80 km thick upper mantle lid v and v are 8 09 and 4 62 km s l respectively at the top of the lid and the compressional and shearvelocity gradients through the lid are 0 0008 s l and 0 0013 s respectively below the lid there is a substantial shear wave lvz with the shear wave velocity dropping from 4 72 km s l in the lower part of the lid to 4 32 km s at 250 km depth the shear wave lvz is required to fit both the v measurements and the regional surface waveforms forward modelling of p suggests that no upper mantle p wave lvz exists there is an increase in the p wave velocity gradient at 125 km depth to 0 0015 s and a second increase at 250 km depth to 0 0035 s velocities and densities in the seismic model of the lid agree closely with velocity and density estimates from the geochemical analysis of garnet periodotite nodules from kimberlites of the kaapvaal craton implying that the estimates from kirnberlites are representative of a wider region of the archaean core of southern africa not just of the restricted region beneath which the kimberlites are found a comparison of the southern african seismic model with seismic models for other shield regions where nodule data are not available shows that the nodule results may also be representative of the upper mantle in those regions

a contribution of slab melts to the formation of high mg andesite magmas hf isotopic evidence from sw japan 1 hf isotope ratios were measured for high mg andesites hma and basalts from the setouchi volcanic belt southwest japan in order to examine whether fluid or melt from subducted slabs act as metasomatic agents for hma magma genesis since hf is one of the incompatible elements that may not be readily transported by aqueous fluids hf isotopes should provide strong constraints on the origin of such slab derived components setouchi hmas and basalts are distinct in their lower 176hf 177hf ehf 13 suggesting significant contribution of subducted sediments to setouchi magma genesis it should be further stressed that hf isotopes are well correlated with sr nd isotopes and la nb ratios among the setouchi magmas geochemical modeling suggests that such characteristics can be best explained by addition of slab derived components with sediment melts rather than aqueous fluids to the hma source

a dynamical model for generating sharp seismic velocity contrasts underneath continents application to the sorgenfrei tornquist zone new seismic velocity models based on teleseismic traveltime tomography show a sharp lithospheric boundary at the sorgenfrei tornquist zone stz between 100 and 250 km depth with p waves about 4 faster and s waves 6 faster within the cratonic lithosphere to the north experiments and thermodynamic calculations indicate that seismic velocity differences in the shallow mantle down to the transition zone must be mostly of thermal origin as typical mantle rocks are characterized by similar velocities based on composition alone we propose a dynamical model of convection in the upper mantle that is consistent with rheological data and that satisfies the seismic observations by maintaining an abrupt lateral temperature contrast over hundreds of myrs a step like increase in lithospheric thickness from 100 to 250 km is assumed to have formed in a triassic rifting event at the stz around 220 ma and is subsequently exposed to active convection below a lithosphere that is distinct from the mantle in terms of temperature and composition remains stable against convective erosion heat advection to different depth beneath the thin and the thick lithosphere leads to a maximum horizontal contrast of 500 c at 150 km depth over a lateral transition distance of 100 km sufficient to generate 5 and 8 in maximum p and s wave velocity perturbation respectively a purely conductive model under the same conditions yields only vp 1 and vs 2 while a lithospheric evolution simulation without a compositional effect on the rheology leads to significant thermo mechanical erosion of the lithosphere giving vp 2 and vs 4

mantle structure from inter station rayleigh wave dispersion and its tectonic implication in western china and neighboring regions abstract we processed more than 3000 inter station great circle paths to determine the phase velocity for the fundamental mode of rayleigh wave and finally arrived at 110 paths of high quality dispersion data which show good spatial coverage in western china and neighboring regions rayleigh wave phase velocity dispersion model wchina1d was obtained and compared with previous global and regional models phase velocity maps from 15 to 120 s were inverted and the maps of 20 40 80 and 120 s are presented in this paper checkerboard tests show the average lateral resolution in our area of interest is about 7 our tomographic results corroborate a prominent low velocity anomaly lying mainly in the lower crust and uppermost mantle in the chang thang terrane the apparent low velocity anomaly also appears in the wide area of northeastern tibet in the crust and upper mantle the low velocity area around southeastern tibet may be created by the southeastern migration of the low velocity mass of the tibetan plateau the eastern tarim shows structure with higher velocities relative to that of central tarim a large scale low velocity anomaly is clearly seen in central and western mongolia our high quality measurements were also used to evaluate the cub global shear velocity model shapiro n ritzwoller m 2002 monte carlo inversion for a global shear velocity model of the crust and upper mantle geophys j int 151 88 105 of the crust and upper mantle the 40 s rayleigh phase velocity map predicted from cub model shows an apparent discrepancy with our measurements in western china and western mongolia which implies a higher estimated about 1 2 phase velocity model in these regions probably due to the gaussian smoothing condition in their tomography inversion

shear wave splitting as a diagnostic of variable anisotropic structure of the upper mantle beneath central fennoscandia abstract we analyze splitting of shear waves recorded during the svekalapko passive seismic experiment in south central finland to study fabrics of the mantle lithosphere of the precambrian region and thus to bring information into a debate on existence of plate tectonics or its forms in the early stage of continent formation geographical variations of the splitting parameters and their distinct dependence on direction of wave propagation through the upper mantle allow us to identify six domains of the central fennoscandian mantle lithosphere including the proterozoic archean transition and to model their fabrics by joint inversion of body wave anisotropic parameters fabrics of the archean mantle lithosphere can be approximated by a peridotite aggregate with lineation a dipping to the ne on the other hand anisotropy of the proterozoic mantle lithosphere is weaker and we model its fabric by the a c foliations dipping to the se we present a 3d self consistent anisotropic model of the proterozoic and archean upper mantle along the sw ne profile in the south central finland boundaries of inter growing wedges of the proterozoic and archean mantle lithospheres explain the longitudinal and shear wave propagation and polarization mantle xenolith ages surface wave tomography and location of the upper mantle reflectors we interpret the six anisotropic domains as fragments of mantle lithosphere retaining an old fossil olivine fabric which was created before these micro continents assembled

eurid a regionalized 3 d seismological model of europe abstract this paper presents a 3 d regionalized model of the european crust and mantle velocity structure down to depths of approximately 300 km the model is entirely based upon the existing geological and geophysical literature and it incorporates topographic and bathymetric features the resulting model which we call eurid european i data set consists of approximately 6400 1 d vertical structures having an average separation of about 100 km eurid is compared quantitatively with eur s91 a recent s wave velocity tomographic model obtained from body and surface wave waveform inversion zielhuis a nolet g 1994 shear wave velocity variations in the upper mantle beneath central europe geophys j int 117 695 715 it is found that the s wave velocities in eurid and in eur s91 zielhuis and nolet 1994 do not differ by more than about 4 over most of the area to validate eurid surface wave dispersion analysis is performed along some selected paths the fundamental mode group velocity curves obtained using 1 d average models derived from eurid are found in good agreement with those determined from observations broadband waveform synthetics are also calculated along the same paths and compared with the observed time series overall we believe that eurid is representative of our current knowledge of the crust upper mantle structure beneath europe and it can be used to model realistically ground motion for periods above 10 s within structurally homogeneous regions the first digital version of this structure database is available for public use

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

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

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

geochemical signals for determining the slip weakening mechanism of an ancient megasplay fault in the shimanto accretionary complex 1 to investigate the slip behavior of a megasplay fault branching from a subduction boundary megathrust we investigated the geochemistry of an out of sequence thrust that formed at 2 5 5 5 km depth rocks from the slip zone show major element and fluid immobile trace element compositions that are consistent with disequilibrium flash melting distinct depletions of li rb and cs in the slip zone rocks indicate fluid rock interactions at high temperatures 350 c these findings suggest a slip process in which high temperature pore fluids were generated by frictional slip but the thermally enhanced pressure might not have reached a sufficient level to cause thermal pressurization and the temperature continued to increase to attain melting of mica minerals comparison with slip zone that formed at a shallower depth 1 2 km where only thermal pressurization occurred suggests a transition from melt lubrication at depth to thermal pressurization at shallower depths along a megasplay faults

upper mantle structure of the baltic shield below the swedish national seismological network snsn resolved by teleseismic tomography summary upper mantle structure under the baltic shield is studied using non linear high resolution teleseismic p phase tomography observed relative arrival time residuals from 52 teleseismic earthquakes recorded by the swedish national seismological network snsn are inverted to delineate the structure of the upper mantle the network consists of 47 currently working three component broad band stations located in an area about 450 km wide and 1450 km long in order to reduce complications due to possible significant three dimensionality of earth structure events chosen for this study lay close to in line with the long axis of the array 30 results indicate p wave velocity perturbations of 3 per cent down to at least 470 km below the network the size of the array allows inversion for structures even at greater depths and lateral variations of velocity at depths of up to 680 km appear to be resolved below the central part of the array 60 64 n where ray coverage is best the data reveals a large region of relatively low velocity at depths of over about 300 km at depths less than about 250 300 km the models include a number of features including an apparent slab like structure dipping gently towards the north