upper crustal seismic structure of the mazury complex and mazowsze massif within east european craton in ne poland the large scale seismic experiment polonaise 97 polish lithospheric onsets an international seismic experiment was carried out in may 1997 in poland lithuania and germany its main purpose was to investigate the structure of the crust and the uppermost mantle in the region of the trans european suture zone tesz that lies between the east european craton eec and the palaeozoic platform this paper covers the interpretation of seismic data along the nw se trending 180 km long profile p5 located on the eec the recordings were of a high quality with seismic energy clearly visible along the whole profile we have not found waves refracted below the upper crust in first arrivals in the nw part of the profile we have delineated a high velocity body with the p wave velocity in the range of 6 5 6 75 km s in the upper crust it corresponds to the ketrzyn anorthosite massif within the mazury complex the mazowsze massif is rather uniformly characterized by p wave velocities 5 9 6 05 and 6 2 6 35 km s in two layers respectively sufficient s wave data were available to estimate the vp vs ratio as well as the poisson ratio being 1 80 0 277 in the high velocity body and 1 67 0 220 in the upper crust apart from the 2 d model along the profile results of 3 d modelling in the area of the p5 profile are presented using off line recordings we got p wave velocity field up to 8 km s below the p5 profile at the depth of about 40 km as well as horizontal extent of the high velocity body

mass wasting triggered by the 5 march 1987 ecuador earthquakes on 5 march 1987 two earthquakes ms 6 1 and ms 6 9 occurred about 25 km north of reventador volcano along the eastern slopes of the andes mountains in northeastern ecuador although the shaking damaged structures in towns and villages near the epicentral area the economic and social losses directly due to earthquake shaking were small compared to the effects of catastrophic earthquake triggered mass wasting and flooding about 600 mm of rain fell in the region in the month preceding the earthquakes thus the surficial soils had high moisture contents slope failures commonly started as thin slides which rapidly turned into fluid debris avalanches and debris flows the surficial soils and thick vegetation covering them flowed down the slopes into minor tributaries and then were carried into major rivers rock and earth slides debris avalanches debris and mud flows and resulting floods destroyed about 40 km of the trans ecuadorian oil pipeline and the only highway from quito to ecuador s northeastern rain forests and oil fields estimates of total volume of earthquake induced mass wastage ranged from 75 110 million m3 economic losses were about us 1 billion nearly all of the approximately 1000 deaths from the earthquakes were a consequence of mass wasting and or flooding

the tectonic evolution of the fennoscandian border zone in denmark abstract the fennoscandian border zone is a complex tectonic zone defining the border between the stable fennoscandian baltic shield and the metastable danish basin and polish trough it forms the northwestern part of the tornquist teisseyre lineament one of the major european tectonic sutures intricate tectonic movements took place within the fennoscandian border zone from early paleozoic to recent time it is postulated that its evolution was dominated during the early palaeozoic by tensional tectonics and during the late paleozoic by dextral wrench movements the latter led to the development of curvilinear faults and the subsidence of pull apart basins transtensional stresses governing the triassic to early cretaceous evolution of the fennoscandian border zone induced the differential subsidence of rift basins during the late cretaceous and early cenozoic dextral transpressional stresses induced the partial inversion of mesozoic basins associated with the fennoscandian border zone this is reflected by the uplift of a major anticlinorium over which cretaceous strata became progressively truncated whilst adjacent areas developed into late cretaceous early tertiary depocentres basin inversion diminishes to the northwest along the fennoscandian border zone and disappears in the skagerrak area

synthetic seismograms for a complex crustal model the algorithm of the original reflectivity method has been vectorized and implemented on a cdc cyber 205 computer calculation times are shortened by a factor of 20 to 30 compared with a general purpose computer with a capacity of several million floating point operations per second mflop the rapid calculation of synthetic seismograms for complex models high frequency sources and all offset ranges is a provision for modeling not only particular phases but the whole observed wavefield as an example we model refraction data of the black forest southwest germany and are able to derive rather tight constraints on the physical properties of the lower crust

properties of the lower crust from modeling refraction and reflection data data of a refraction and a reflection seismic survey in the black forest of southwest germany are used for extensive one and two dimensional modeling the data are available along approximately the same line and therefore the same piece of crust is probed by two seismic methods we utilize this favorable circumstance for detailed model calculations concerning both data sets in this paper we focus on the lower crust its properties vary on the scale of a wavelength and thus full solutions of the elastic equations are required we use the reflectivity method for the evaluation of refraction seismograms and numerical solutions of the acoustic wave equation for the reflection response the lamellae of the lower crust appear as reflecting elements of several hundred meters length randomly distributed in space rocks with extremely low velocities 5 6 km s must be present indicating that anisotropy and or fluids play an important role in the lower crust ideas concerning lower crustal formation evolution and extinction of lamellaetion are developed

evolution of the petrological and seismic moho implications for the continental crust mantle boundary the chemical and petrological composition of mafic rocks from the lower continental crust are discussed by comparing mafic granulites and meta gabbroic rocks from the ivrea zone and the northern hessian depression nhd xenolith suite both regions contain contrasting types of meta mafic lithologies i former basaltic rocks with trace element patterns ranging from morb iike to subduction related or intra plate tholeutes and u ca and al enriched plagiodase dominated gabbroic rocks showing positive eu anomalies generated by complex deep crustal magmatic processes such as fractionation accumulation of plagiodase and pyroxene and crustal contamination the absence of typical garnet omphadte parageneses in these rocks indicates that the eclogite stability field was not reached during palaeozoic orogenic processes a compilation of experimentally determined p wave velocities and densities for mafic granulites gabbroic rocks eclogites and peridotites is used to evaluate key physical properties of lower crustal mafic rocks during crystal thickening caused by continent continent collision in a step by step scenario it is demonstrated that the position of the seismic moho defined as a first order velocity discontinuity and the petrological moho defined as the boundary between non peridotitic crustal rocks and olivine dominated rocks is not identical for the case that mafic rocks are transformed into edogites at the base of orogenically thickened crust p wave velocities of eclogites largely overlap with those of peridotites although their densities are significantly higher than common upper mantle rocks as a consequence refraction seismic field studies may not detect edogites as crustal rocks this means that the seismic moho detected by refraction seismic field studies appears at the upper boundary between edogites and overlying crustal units since edogites generally have higher densities than peridotites they might be recycled into the deeper lithosphere thereby transferring excess eu into the upper mantle this process could be a due for understanding the negative euanomaly in the upper continental crust which is apparently not balanced quantitatively by the abundance of common mafic crustal rocks

palaeozoic terranes and their lithospheric boundaries within the trans european suture zone tesz a review the trans european suture zone tesz is a broad and complex zone of terrane accretion separating ancient lithosphere of the baltic shield and east european craton eec from the younger lithosphere of western and southern europe there is debate about the number of terranes involved and their origins the most significant terrane boundaries originally oceanic sutures are poorly exposed and are defined using faunal provinciality prominent geophysical lineaments may represent sub terrane boundaries within composite terranes the avalonia composite terrane was amalgamated to baltica in latest ician time the provenance of the malopolska and moravo silesian terranes whose neoproterozoic basement is suspect with respect to baltica but with which they nonetheless share faunal affinities is still debated the extent of the variscide rhenohercynian zone defines the southern limit of the early palaeozoic accreted terranes terranes within the bohemian massif exhibit hp metamorphism recording subduction driven collision prior to incorporation in the tesz collage itself associated with a hp event in romania the saxothuringian zone and rheic suture are directly juxtaposed with the eec and the crustal structure of the tesz has been much modified by post palaeozoic tectonism deep seismic reflection data where available show that the oceanic sutures are frequently associated with inclined reflectivity zones irz in the lithospheric mantle here inferred to mark relict subduction zones interpreting the age of subduction is complicated by offset of originally coplanar mantle and crustal segments of the irz resulting from early orogenic lithospheric delamination at the moho interface and or post orogenic reordering processes the mantle irz appear to indicate a n directed polarity for early palaeozoic subduction apparently incompatible with the geological evidence which indicates subduction of the tornquist sea beneath avalonia and a large amount of underthrusting of avalonia by baltica possible explanations for these apparently incompatible observations are evaluated

crustal structure of the mid polish trough beneath the teisseyre tornquist zone seismic profile abstract a new seismic refraction and wide angle reflection experiment in the teisseyre tornquist zone ttz in poland was conducting during july 1993 as an international polish finnish german and swedish co operation the ttz profile running in an se nw direction was exactly located in the central part of the mid polish trough in the zone of maximum subsidence from upper permian to upper cretaceous 19 shot points were placed along the 450 km profile the interval between the shot points was about 25 km 31 explosions 90 to 1000 kg of dynamite were recorded in two deployments using 135 modern three component seismic stations with spacing of the recording sites of about 1 7 km in this area the depth of the consolidated basement with a velocity of about 5 7 5 8 km s is 5 to 12 km deep nevertheless the p wave velocity is very low vp

coincident seismic reflection refraction studies of the continental lithosphere a global review nearly 50 coincident seismic reflection refraction studies to depths of at least the moho provide an improved understanding of the continental lithosphere some conclusions include the following 1 a transparent upper crust a common observation on vertical reflection profiles cannot generally be correlated with velocity gradients or low velocity zones rather a commonly transparent upper crust may be explained by short wavelength steeply dipping features in the brittle upper crust and to a lesser degree by signal contamination from source generated noise 2 the reflective lower crust in extensional terranes appears to be characterized by a high average seismic velocity 6 6 7 3 km s and to consist of laminated high and low velocity layers with typical thicknesses of 100 200 m 3 landward dipping reflectors observed in the middle to lower crusts of convergent zones have been identified as paired high and low velocity slabs which represent oceanic crust and mantle accreted via underplating to the continental margin 4 the crust mantle boundary may differ sufficiently when imaged with vertical incidence and wide angle data to justify the retention for the present of the concept of separate reflection and refraction mohos while there is good evidence that these features are coincident within measurement uncertainties in most regions recently recorded data from the basin and range admit the possibility for noncoincidence in that area 5 upper mantle reflections which cannot be migrated into the lower crust remain rare despite isolated unequivocal examples thus the upper mantle appears to be relatively homogeneous at seismic reflection wavelengths and to lack the laminations inferred for the lower crust the wide angle method will likely provide the most reliable information on the velocity structure and physical state of this portion of the lithosphere for some years to come 6 there appear to be clear and consistent basic differences between convergent and extensional terranes which have been identified from coincident experiments these differences may be sufficiently universal to infer the tectonic history of poorly exposed terranes 7 no truly three dimensional coincident experiment i e including three dimensional migration has been conducted but some three dimensional data have been collected using both methods measurements of attenuation poisson s ratio and anisotropy within the crust using coincident data sets remain frontiers

geophysical characteristics of the tornquist fan area northwest trans european suture zone indication of late carboniferous to early permian dextral transtension

the reflectivity of magmatic underplating using the layered mafic intrusion analog abstract the reflection characteristics of layered mafic intrusions provide an analog for characterizing the reflectivity of magmatic underplates one dimensional seismic models of a variety of mafic intrusions with different parent magmas demonstrate that cumulate layering may typically be strongly reflective with reflection coefficients as high as 0 18 a seismic profile across the bjerkreim intrusion in southern norway shows that even a moderately reflective cumulate sequence with reflection coefficients on the order of 0 05 produces detectable reflections two dimensional models demonstrate that the subhorizontal cumulate layering in typical mid to upper crustal intrusions is conducive to seismic imaging but more complicated geometries such as concentric layering created during synmagmatic deformation complicate the seismic image reflection coefficients predicted for granulite facies mineral assemblages are similar to those predicted for the igneous assemblages reflection coefficients predicted for cumulates intruded or re equilibrated at eclogite facies conditions may be either decreased or enhanced with respect to the igneous assemblages depending on the abundance of plagioclase in the cumulate layers and the pressure results suggest that magmatic underplating should not be invoked as an explanation for non reflective crust except in cases where eclogitization has occurred

factors affecting seismic moment release rates in subduction zones the amount of shallow seismic activity in subduction zones varies greatly from region to region we quantify this seismicity by calculating seismic moment release rates and seismic slip rates for 24 subduction zones to calculate the moment release we sum the seismic moment for all interplate thrust type events with surface wave magnitude ms 7 0 occurring from 1904 to 1980 we present a time history plot of the seismic moment release for each subduction zone these exhibit the differences in the seismic release patterns for subduction zones where the time window of our study is not representative the total moment release is corrected using information on repeat times the moment release rates are compared with various subduction parameters in order to determine which factors influence the degree of coupling these parameters include the age of the subducting lithosphere absolute velocities of the upper and subducting plates convergence velocity and length maximum depth and dip of the wadati benioff zone the moment release rate decreases as the age of the subducting lithosphere increases when the zones belonging to a single subducting plate are considered this age versus moment release relation is consistent for the zones in which the pacific cocos philippine sea and indian plates are subducting the moment release rates for the subduction zones in which the pacific plate is subducting are much higher than for zones of other plates with similar age the age versus moment release relation holds among the zones which belong to one subducting plate however zones with similar ages but belonging to different plates do not have the same moment release rates this suggests that within a single plate the age is the dominating factor affecting the strength of seismic coupling but that each plate as a whole has a characteristic moment release budget zones with retreating upper plates tend to have lower moment release rates the moment release rate does not increase with convergence velocity no simple relationship was found between these two parameters the moment release rate depends most clearly on the age of the subducting lithosphere and the absolute velocity of the upper plate these are the two independent subduction zone parameters among the variables considered the other variables depend on these two parameters

reflection seismic constraints on paleozoic crustal structure and moho beneath the ne german basin abstract a 330 km long ne sw trending seismic transect across the ne german basin combined with a 75 km long perpendicular cross line in the basin centre reveals the structure of this intracontinental basin between the stable precambrian baltic shield and the weaker mid european variscides the combination of high fold vibroseis and low fold explosive seismic profiling images both upper and lower crustal structures in detail distinct faults related to a rift stage are not observed below the permian sedimentary basin but there is evidence of lower crustal thinning a moho pattern less reflective below the basin centre than at the margins may be related to magmatic underplating the rather flat lying moho dips slightly towards the basin margins structures further north suggest a southern extent of baltica below the ne german basin the caledonian accretionary wedge may be outlined by sw dipping mid crustal reflectors beneath the basin

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

deep seismic structure of the earth s crust along the baltic sea profile abstract in summer of 1989 the institute of oceanology of the russian academy of sciences moscow for the first time used a new large volume airgun for deep seismic sounding dss in the baltic sea the experiment was carried out during the 23 rd cruise of r v professor shtockman the wave field analysis showed clear p and s wave arrivals including moho reflections the moho reflections were distinctly observed at distances exceeding 100 km the p waves can be followed to a maximum distance of 368 km two dimensional raytracing modelling of the data revealed a pronounced topography of the moho along the baltic sea profile a depression in the middle of the profile at a depth of 45 km is bounded by 2 3 km steps and uplifts on both sides reflections off a sub moho boundary at a depth of 60 km have also been recorded the upper mantle velocities vary between 7 8 km s under the depression to 8 1 km s to the side of it the crustal p waves velocities define three layers 5 8 6 3 6 3 6 7 and 6 9 7 1 km s all crustal velocity boundaries bend over the moho depression and reach their deepest points in the central part of the profile the velocities in the crust also change laterally reaching their minimum within the central depression the crustal thickness along the profile varies notably between 38 and 45 km a comparison with the fennolora and the babel b profiles indicates that the moho depression found along the baltic sea profile correlates with similar depressions on the other profiles

crustal structure along the central segment of the egt from seismic refraction studies abstract the seismic refraction line between the gulf of genova and the baltic sea was carried out in 1986 as part of the european geotraverse egt 86 the central segment of the egt also known as eugemi european geotraverse middle part has a total length of 825 km and runs from the northern margin of the alps to the baltic sea traversing mainly the variscan mountain area of western germany the p wave data of nine shotpoints were interpreted in detail and a two dimensional p velocity model of the crust was developed between the molasse basin and the southern end of the north german basin for the north german basin the data quality justifies only the construction of a simplified model the internal crustal structure is quite complex in the upper crust of the moldanubian and saxothuringian zones of the variscan orogen the velocities are lower than in the rhenohercynian area the velocity of 6 0 km s representing consolidated seismic basement is reached at depths of as much as 10 12 km northern margin of alps and north german basin and of only 3 km under the mid german crystalline rise mid crustal velocities range from 5 8 to 6 1 km s forming weak velocity reversals in some parts in the lower crust velocities as low as 6 2 km s are seen near the alps in contrast to velocities between 6 8 and 7 2 km s in the exposed variscan orogen north of shotpoint e between hannover and the river elbe the velocity of the lower crust is about 6 4 km s north of the elbe line it increases abruptly to 6 9 km s the crust mantle boundary rises from 34 km depth under the northern margin of the alps to 29 km under the swabian jura under the variscan orogen to the north the crustal thickness varies only slightly around an average depth of about 29 1 k but drops to about 30 km under the north german basin between the elbe line and the ringkobing fyn high the moho rises to a depth of about 26 km and the data indicate at least one fault like step of 1 km before the crust thickens toward the basement high the velocities in the uppermost mantle show considerable variation the highest velocity of 8 4 km s is observed beneath the saxothuringian zone and the lowest values of 7 8 7 9 km s are recorded under the hessen depression

crustal structure along the egt profile across the tornquist fan interpreted from seismic gravity and magnetic data abstract the tornquist fan is a northwestward widening splay of late carboniferous to early permian fault zones in the danish area which emanates from the teisseyre tornquist zone in the baltic sea it is located over an area of deep sedimentary basins around denmark in the southwestern corner of the former baltica plate this paper presents an integrated model of seismic velocity density and magnetic properties along the egt profile across the tornquist fan between southern sweden and northern germany the model shows distinct features that may be related to the main tectonic events in the area the caledonian crustal suture between baltica and eastern avalonia is interpreted from changes in physical parameters at all crustal levels most noticeable as an abrupt lateral change in seismic velocity in the lowest crust at moho level from 6 9 km s in baltica to only 6 4 km s in eastern avalonia thick sedimentary successions beneath the mesozoic sequence are interpreted as palaeozoic sedimentary rocks which may have been deposited on the southern margin of the baltica plate in a deep caledonian foreland basin and in late carboniferous early permian rifts and extensional basins rift related magmatism is indicated by the presence of zones of high velocity density and magnetic susceptibility as well as strong remanent magnetization thermal subsidence following the emplacement of these bodies may be the origin of regional subsidence of the danish and north german basins of late paleozoic and mesozoic age late cretaceous to early cenozoic inversion of basin structures is detected at the sorgenfrei tornquist zone stz in the transition between shield and basin areas the stz coincides with a pronounced change in crustal thickness and the southwestern edge of a major magmatic intra crustal body significant abrupt changes in moho depth exist along the profile 26 30 km beneath the deep basins ca 35 km beneath the ringkobing fyn basement high and 48 km beneath the baltic shield around the sorgenfrei tornquist inversion zone the basement in the tornquist fan area is of proterozoic age the moho topography indicates strong thinning of the crust during its phanerozoic evolution the model supports the hypothesis that existing tectonic structures and weakness zones are continuously being reactivated during subsequent tectonic activity

moho topography and lower crustal wide angle reflectivity around the tesz in southern scandinavia and northeastern europe abstract the moho topography is strongly undulating in southern scandinavia and northeastern europe a map of the depth to moho shows similarities between the areas of the teisseyre tornquist zone ttz in poland and the fennoscandian border zone fbz which is partly coinciding with the sorgenfrei tornquist zone stz in denmark the moho is steeply dipping at these zones from a crustal thickness of approximately 32 km in the young palaeozoic platform and basin areas to approximately 45 km in the old precambrian platform and baltic shield the moho reflectivity pmp waveform in the polonaise 97 refraction wide angle seismic data from poland and lithuania is variable ranging from sharp to strongly reverberating signals of up to 2 s duration there is little or no lower crustal wide angle reflectivity in the thick precambrian platform whereas lower crustal reflectivity in the thin palaeozoic platform is strongly reverberating suggesting that the reflective lower crust and upper mantle is a young phenomena from stochastic reflectivity modelling we conclude that alternating high and low velocity layers with average thicknesses of 50 300 m and p wave velocity variations of 3 4 of the background velocity can explain the lower crustal reflectivity sedimentary layering affects the reflectivity of deeper layers significantly and must be considered in reflectivity studies although the reverberations from the deeper crust cannot be explained by the sedimentary layering only the reflective lower crust and upper mantle may correspond to a zone that has been intruded by mafic melts from the mantle during crustal extension and volcanism

seismic structure of the palaeozoic platform along polonaise 97 profile p1 in northwestern poland abstract the deep seismic profile p1 was conducted in northwestern poland as part of the polonaise 97 project data acquisition involved 100 mobile seismographs which recorded seismic waves from 11 dispersed chemical controlled explosions along this 300 km long profile a variety of seismic modelling techniques were employed to derive a velocity model along the profile this model indicates that the mesozoic and palaeozoic sediments are 6 km thick in the northwest and 3 km thick in the southeast with the main thickness variation taking place in the palaeozoic succession an undulating basement surface indicates tectonic activity during deposition of the lower palaeozoic sequence the crust is 30 33 km thick along the profile thickening gradually to the southeast the p wave seismic velocities are low 1 down to a depth of 20 km along the whole profile which we interpret as evidence for their being of sedimentary or volcanic origin the lower crust has a high p wave velocity 6 7 7 5 km s 1 high vertical velocity gradient and strong ringing reflectivity the velocity of the sub moho mantle p n is high 8 2 km s 1 features similar to the ones below this profile have been interpreted for the area south of the caledonian deformation front in northern germany and southern denmark these similarities indicate that the crust between the southeastern north sea and poland has a common origin we therefore suggest that the deep crust beneath the profile is not of variscan origin despite its location south of the variscan deformation front we propose that variscan tectonism in the area was thin skinned while the deeper crust may originate from the caledonian microcontinent east avalonia or possibly from baltica

interpretation in statu nascendi of seismic wide angle reflections based on eugeno s data abstract in a new interpretation approach seismic wide angle data are analysed in statu nascendi i e in the state where the interpretational characteristics of the signals are born the approach is complementary to other interpretation methods such as kinematic interpretation of velocity models seismogram sections are qualitatively compared and classified in order to perform the analysis as close as possible to the seismic wavefield correlation of seismic phases and selection of representative reflection characteristics of the phases are required for the analysis the approach has been tested on the methodologically homogeneous eugeno s data set from the danish and surrounding areas together with other data the classifications of intra crustal and pmp reflections show clear regionalizations which correlate with the main geological tectonic and orogenic units the reflection characteristics of the thin crust below the deep basins in denmark the tornquist fan are different from the thick crust of the baltic shield and the ringkobing fyn high the character of moho reflections is ringing in the basin area as opposed to sharp in the latter areas and intra crustal reflections are stronger and more consistent in the basin area than in the latter areas

effects of the shallow subsurface on upper crustal seismic reflection images abstract seismic imaging of the upper crust is strongly affected by the interactions of the seismic wavefield with the shallow subsurface in order to better understand these effects we have evaluated the seismic responses of a suite of canonical models of the upper crystalline crust and the near surface region our modelling is restricted to two dimensions but otherwise includes the full seismic wavefield notably the effects of attenuation and topographic variations along the free surface we find that s wave scattering is important in the upper crust and contributes significantly to the vertical component of the seismic reflection response the backscattered wavefield undergoes mode conversions when it interacts with the free surface even moderate topographic variations or velocity variations in the near surface region enhance these mode conversions and cause additional scattering much of the earth s surface is covered by thin layers of unconsolidated material or weathered bedrock with high attenuation and high velocity contrasts at the layer boundaries scattered and mode converted seismic energy gets trapped in these layers and thus interacts repeatedly with the free surface and its topography in analogy to large scale seismic resonance effects of sedimentary valley fills the level and duration of source generated noise depends heavily on the degree of attenuation in the shallow layers low attenuation causes high noise levels and vice versa in contrast the level of source generated noise is less sensitive to near surface layer thicknesses and velocity contrasts

the crust as a heterogeneous optical medium or crocodiles in the mist abstract based on petrophysical data geologic maps and a well log we present statistical descriptions of likely upper middle and lower crustal rocks to characterize the fine scale heterogeneity observed in crustal exposures and inferred from deep crustal seismic data the statistical models developed for granitic and metamorphic upper crust and for an extended metamorphic lower crust are used to construct whole crustal models of seismic velocity heterogenity we present finite difference synthetic cmp data from several models which compare favorably with field data the statistical models also permit classification of the seismic reflection experiment and the crustal heterogeneity according to scattering regime the optical or scattering properties of importance for classification are the velocity fluctuation intensity the horizontal and vertical correlation lengths of the medium the correlation function of the medium and the velocity population function for the crustal properties we measured the bandwidth of a typical deep crustal experiment overlaps from the weak to the strong scattering regime with implications for crustal seismic data processing and imaging notably deep crustal signals are likely to have experienced multiple scattering making common seismic imaging techniques of questionable value moreover the details of the unmigrated cmp stacked section bears little resemblance to the underlying medium

geophysical evidence for early permian igneous activity in a transtensional environment denmark abstract integrated interpretation of gravity magnetic and seismic data in the area of the strong silkeborg gravity high in central denmark has led to a structural geological model involving a transtensional rift feature which probably formed in connection with permo carboniferous wrench faulting and the development of the oslo horn graben system reinterpretation of the deep seismic data from profile 2 of the eugeno s project in the area of the silkeborg gravity high detected a new thin high velocity layer 6 25 km s at about 7 km deep within the palaeozoic sedimentary sequence in the crystalline basement a separate body of high velocity 6 9 7 0 km s was found at 11 km deep beneath this body the moho reaches its shallowest position in the area the seismic results compare well with an interpretation based on magnetism of a shallow volcanic or subvolcanic layer at a depth of 6 8 km this layer shows strong remanent and induced magnetization with a southward inclination of about 10 gravity reinterpretation of the area allows the separation of an upper body of density contrast 0 1 g cm3 from a lower body of density contrast 0 2 g cm3 the upper body roughly coincides with the magnetic body the lower body the major one coincides with the deep seismic body and it is responsible for the main gravity anomaly in the area

polonaise 97 an international seismic experiment between precambrian and variscan europe in poland abstract the trans european suture zone tesz comprises a series of sutures that developed by palaeozoic amalgamation of the phanerozoic central europe onto the proterozoic baltica and east european plate during the formation of pangea within tesz the permian basin in poland forms the easternmost part of the permian central european basin which is bordered on the east by the east european craton eec and on the southwest by the bohemian massif the axis of the basin the mid polish trough parallels the edge of the eec the teisseyre tornquist zone ttz is a geological inversion zone in the polish trough a large seismic experiment the polonaise 97 project was conducted in poland during may of 1997 and targeted the deep structure of the tesz and the complex series of upper crustal features associated with it it included contributions from the geophysical communities in poland denmark the usa lithuania germany finland sweden and canada this large lithospheric seismic experiment deployed 613 instruments to record 64 shots along five profiles with a total length of about 2000 km moreover five multichannel seismic reflection stations 90 and 120 channels recorded all signals from shots two dimensional velocity models were derived by p wave tomographic inversion these models provide an initial interpretation of this massive data set and allow us to present a few significant seismic and tectonic observations one of the most important is a very distinct asymmetry between the maximum thickness of the sedimentary cover in the polish trough 16 20 km and the crustal root 50 km associated with tesz ttz

shear wave evidence for an anisotropic lower crust beneath the black forest southwest germany abstract controlled shear wave sources a horizontal vibrator and dynamite were used in near vertical reflection studies to explore the nature of the reflective laminated lower crust in southwest germany the data reveal strong s wave reflections from the lower crust these lower crustal s reflections were not observed by previous wide angle surveys in the same region a laminated crustal model with isotropic layers and changing poisson s ratio cannot explain the differing near and far offset s response by introducing alternating anisotropic and isotropic lamellae this discrepancy may be resolved this seismic model is consistent with a petrological model of deformed amphibolites containing 10 30 of preferentially orientated hornblende observed amplitude differences in p and s wave reflections from the same depth in the lower crust suggest regions with a changing poisson s ratio

deep seismic reflection characteristics of the continental crust four types of seismic reflection fabrics appear to characterize the continental crust 1 a cratonic fabric dominated by diffractions and dipping reflections but lacking a pronounced reflection moho 2 regions of thin skinned foreland deformation with abundant shallow but sparse deep reflections 3 a unidirectional fabric that dips toward the hinterland and may represent a crustal scale ramp zone and 4 zones of highly layered lower crust and high amplitude reflection moho the first three types are commonly observed in transects across single mountain belts but the fourth appears to correspond to regions of elevated lower crustal temperatures such as those encountered in rift provinces and perhaps elsewhere

a stochastic view of lower crustal fabric based on evidence from the ivrea zone despite its complicated history the ivrea zone is considered to be a representative surface exposure of extended continental crust we have digitized two standard 1 25 000 geological maps from this area and evaluated their structural statistics because of the subvertical orientation of the ivrea zone these maps can be considered as small scale cross sections through the lower continental crust the autocorrelation functions of the digitized lithologies measured from these maps show a clear self similar or fractal rather than a gaussian or deterministic trend we found that an anisotropic von karman correlation function with an aspect ratio around 4 and a hurst number of 0 3 corresponding to a fractal dimension of 2 7 matches the observed data our results represent an explicit confirmation of previous indirect evidence for the fractal nature of lithospheric heterogeneities and provide the means to construct realistic crustal scale seismic models of ivrea type lower continental crust

terrane accumulation and collapse in central europe seismic and rheological constraints abstract an attempt is made to compare the tectonic units and their evolution in central europe with the deep seismic velocity structure and patterns of reflectivity caledonian and variscan terrane accretion and orogenic collapse dominate the tectonic development in central and western europe and have left their marks in a distinct velocity structure and crustal thickness as well as in the various reflectivity patterns whereas the memory of old collisional structures is still preserved in the rigid upper crust collapse processes have formed and modified the lower crust they have generally created rejuvenated thin crusts with shallow mohos in the variscan internides the center of collision and post orogenic heat pulses the lower crust developed strong and thick seismic lamellae the cooler externides show a thrust and shear pattern in the whole crust and the north german basin experienced large mafic intrusions in the lower crust and developed a high velocity structure with only very thin lamellae on top of the moho the various kinds of reflectivity patterns in the lithosphere can be explained by a thermo rheological model from terrane collision with crustal thickening to collapse in a hot post orogenic setting

a comparison of the moho interpreted from gravity data and from deep seismic reflection data in the northern north sea summary we present the results of gravity modelling of the nsdp 84 deep seismic reflection profiles in the northern north sea the moho depths inferred from forward modelling of marine bouguer gravity anomalies from independent inversion of free air gravity anomalies derived from satellite altimetry and from deep seismic reflection profiling are in good mutual agreement this agreement suggests that the moho discontinuity interpreted from seismic reflection data corresponds to a major jump in density and therefore is likely to represent not only the geophysical but also the petrological boundary between the continental crust and the upper mantle in spite of the significant lateral heterogeneity of the crystalline basement below the northern north sea area as documented by seismic reflection profiling the average density contrast between the basement and the upper mantle is interpreted to show rather little variation this is not true for the deepest part of the viking graben where the nature of the lower crust and upper mantle may have been changed by magmatic processes accompanying the graben formation a relationship between the degree of crustal extension and the volume of magmatic intrusion into the lower crust is tentatively supported by our results

deep structure of the earth s crust in the contact zone of the palaeozoic and precambrian platforms in poland tornquist teisseyre zone abstract one of the major tectonic problems in europe concerns the southwest margin of the east european platform in the region of the so called polish danish trough in general this margin is assumed to be the tornquist teisseyre t t line running approximately from northwest to southeast in this part of europe determination of deep crustal structure of the contact zone between the precambrian platform and the palaeozoic platform was the main aim of the deep seismic sounding dss programme in poland in 1965 1982 deep seismic soundings of the earth s crust have been made in the t t line zone along nine profiles with a total length of about 2600 km the results of deep seismic soundings have shown that the crust in the marginal zone of the east european platform has highly anomalous properties the width of this zone ranges from 50 km in northwest poland to about 90 km in southeast poland the crustal thickness of the palaeozoic platform in poland is 30 35 km and of the precambrian platform 42 47 km while in the t t tectonic zone it varies from 50 to 55 km above the moho boundary in the t t zone at a depth of 40 45 km there is a seismic discontinuity with p wave velocities of 7 5 7 7 km s boundary velocities mean velocities and stratification of the earth s crust vary distinctly along the t t zone there are also observed high gravimetric and magnetic anomalies in the t t zone the t t tectonic zone determined in this manner is a deep tectonic trough with rift properties the deep fractures delineating the t t tectonic zone are of fundamental importance for the localization of the plate edge of the precambrian platform of eastern europe in the light of dss results the northeastern margin of the t t tectonic zone is a former plate boundary of the east european platform

a seismic velocity model for the sw baltic sea derived from basin 96 refraction seismic data abstract within the basin 96 project basin analysis and seismic investigation in north germany 1996 a marine survey gathered seismic data in the southwest baltic sea to study the caledonian collisional zone between baltica to the north and avalonia to the south additionally the airgun pulses have been observed by several land stations special attention was paid to record good quality data on rugen island aiming at linking offshore and land seismic wide angle observations therefore a complex geophone array the star of rugen was designed to enhance the signal quality the star of rugen data and other onshore observations in ne germany and on bornholm an island in the baltic sea have been used for p wave velocity modelling important structures of the transition zone from palaeozoic western europe to the precambrian baltic shield are imaged in the resulting three dimensional velocity model a pronounced basement high north of rugen island indicates the location of the caledonian deformation front cdf velocities also reflect other prominent features such as the ronne graben a pull apart structure of the tornquist zone and the basement outcrops around bornholm island in the investigated area the moho depth varies between 27 and 33 km a high velocity layer in the lower crust below the ne german mainland may indicate genetic relations to baltica the structural continuity however is disturbed by a velocity decrease in an area north of the cdf sporadic but strong reflections from the upper mantle below the cdf seem to be consistent with the reflection seismic data dekorp basin research group 1999 geology 27 1 55 58