geophysical geological transect and tectonic evolution of the swiss italian alps a complete alpine cross section integrates numerous seismic reflection and refraction profiles across and along strike with published and new field data the deepest parts of the profile are constrained by geophysical data only while structural features at intermediate levels are largely depicted according to the results of three dimensional models making use of seismic and field geological data the geometry of the highest structural levels is constrained by classical along strike projections of field data parallel to the pronounced easterly axial dip of all tectonic units because the transect is placed close to the western erosional margin of the austroalpine nappes of the eastern alps it contains all the major tectonic units of the alps a model for the tectonic evolution along the transect is proposed in the form of scaled and area balanced profile sketches shortening within the austroalpine nappes is testimony of a separate cretaceous age orogenic event west directed thrusting in these units is related to westward propagation of a thrust wedge resulting from continental collision along the meliata hallstatt ocean further to the east considerable amounts of oceanic and continental crustal material were subducted during tertiary orogeny which involved some 500 km of n s convergence between europe and apulia consequently only a very small percentage of this crustal material is preserved within the nappes depicted in the transect postcollisional shortening is characterized by the simultaneous activity of gently dipping north directed detachments and steeply inclined south directed detachments both detachments nucleating at the interface between lower and upper crust large scale wedging of the adriatic or apulian lower crust into a gap opening between the subduced european lower crust and the pile of thin upper crustal flakes alpine nappes indicates a relatively strong lower crust and detachment between upper and lower crust

dating the evolution of c s microstructures a combined 40ar 39ar step heating and uv laserprobe analysis of the alpine roffna shear zone abstract a technique combining 40ar 39ar step heating analyses in situ uv laserprobe dating and electron microprobe chemical characterization has been developed to unravel the relationships between microstructures metamorphism and k ar systematics this technique has been applied to white micas of a discrete shear zone in the roffna metarhyolite in the suretta nappe se switzerland neoformed phengites from the roffna metarhyolite crystallised in shear zones during tertiary alpine deformation under blueschist and greenschist facies conditions in situ 40ar 39ar uv laser dating of white micas defining the schistosity and c planes yield systematically younger isotopic dates in the c planes which are also correlated with decreasing celadonite content i e si al ratio these results suggest that the timing of the high pressure deformation event is preserved in the schistosity high si micas appear to have lost no ar later deformation was localised preferentially in c planes giving younger 40ar 39ar dates probably related to a later period of phengite growth the age sequence is broadly consistent with the textural constraints and geological field relations

numerical modeling of frontal and basal accretion at collisional margins 1 we investigate the deformation of orogenic wedges that form in the early stages of continent continent collisions using a two dimensional numerical model limited to the upper lithosphere our models show that deformation at the plate margins is influenced by rheology surface processes and the balance between inward mass flux and outward subduction flux as controlled by the subduction load which represents the effects of slab pull and resistive forces and flexural downbending we find three characteristic deformation modes 1 near pure subduction with little or no accretion 2 frontal accretion with development of an accretionary wedge built up by offscraping of the sediment layer at shallow depth and 3 independent frontal and basal accretion where a retrothrust allows stacking of basement nappes at crustal to mantle depths near pure subduction is enabled for ordinary rheology materials characterized by brittle and viscous material behavior approximating a christmas tree type depth profile and almost zero friction along the subduction shear zone frontal accretion occurs when slightly increased friction along the subduction shear zone allows offscraping of the sediment layer from the subducting plate independent frontal and basal accretion develops in strong rheology models with an almost fully brittle material behavior major surface erosion or a reduction of the subduction load promote the development of large basement nappes frontal accretion is favored by major sedimentation during convergence a large backstop and in the case of a lateral transition from a strong rheology to an ordinary rheology subducting plate our numerical models develop first order characteristics as observed in natural orogenic wedges for example upper crustal nappe stacks frontal and basal accretion or extension in the core of an orogen frontal and basal accretion are interdependent and tend to stabilize the subduction system

the swiss alps and their peripheral foreland basin stratigraphic response to deep crustal processes 1 this paper gives a synoptic view of the cenozoic evolution of the swiss alps and their northern foreland basin in this orogen deep crustal processes subduction nappe stacking underplating and exhumation are intimately linked with surface processes surface uplift erosion basin formation and basin axis migration within the foreland basin the spatial pattern of subsidence and alluvial fan construction suggests that an increase in flexure of the foreland plate and the creation of relief in the orogen migrated from east to west in the course of collision in the orogen itself crustal thickening involved lower crust of the adriatic margin in the east and the european margin in the west exhumation of upper crustal units occurred earlier in the east as compared with the west an adriatic mantle wedge the ivrea body and its associated wedge of lower crustal material are identified as an extra lithospheric load which contributed to downward flexure of the european plate as a result of enhanced subsidence of the foreland plate relief was generated presumably in order to adjust to critical taper geometry it appears therefore that the westward motion of the adriatic wedge ultimately caused the contemporaneous westward propagation of the location of enhanced rates of alluvial fan construction coeval strike slip and n s convergence juxtaposed the adriatic wedge sequentially to different european upper crustal units which resulted in different styles of crustal structure and evolution along strike within the orogen

long lasting tectonic activities of the lepontine dome new evidence from low temperature thermochronology abstract to investigate the neogene exhumation history of the central european alps we apply low temperature thermochronology in combination with thermal history modelling fission track and u th sm he ages on apatites from the central lepontine dome ticino switzerland indicate higher exhumation rates in the centre of the dome and rather moderate exhumation at the northern and southern boundaries since neogene times we present a model for explaining the latest stage exhumation of the central lepontine dome and show that i both episodic and continuous exhumations are found on small scale throughout the neogene ii compressional tectonics control the exhumation until the late neogene iii the exhumation regime changes between 6 and 4 ma and iv increasing hinterland exhumation rates at the mio pliocene boundary cannot be related to tectonic structures of the dome and they are thus explained by climatic changes

the kinematic history of the pennine nappes east of the lepontine dome implications for the tectonic evolution of the central alps the pennine zone of the eastern central alps south middle and north pennine from top to bottom of sequence underwent a complex structural and strain history a first phase d1 is characterized by e w oriented stretching and is of cretaceous lower tertiary age d1 structures affected most but not all of the south and middle pennine units were probably obliterated in the north pennine adula nappe and are absent in the basement nappes underneath the adula nappe further deformation led to n nw directed nappe movement d2 followed by incipient strike slip motion along the periadriatic line late d2 subsequently large scale folding d3 affected mainly the nappe fronts in the adula nappe f3 folds verge towards the foreland whereas the overlying units were backfolded towards the hinterland the d2 d3 events were accompanied by a complex strain pattern that is best seen in the adula nappe and includes plane to prolate strains in the upper frontal part and oblate strains in both the lower frontal part and the interior of the nappe d3 backfolding was associated with the beginning of backthrusting at the periadriatic line and was accompanied and or followed by rapid uplift in the lepontine dome and subsequent unroofing of the latter which led to e ne directed extensional movements d4 in the eastern central alps the d1 event is related to the anticlockwise rotation of the adriatic plate relative to europe this caused dextral transpression between the adriatic and the european plates and partitioning of the deformation into convergence and strike slip it is suggested that the north pennine nappes below the adula nappe were situated along a major strike slip fault and escaped this event d2 resulted from continental collision between adria and europe d2 displacement directions are subperpendicular to the alpine arc and are best approximated by wnw nw oriented motion of adria the structures and the strain pattern of d3 are interpreted as the result of gravitational force late d2 strike slip deformation at the periadriatic line d3 backthrusting at the southern steep belt and the unroofing stage d4 are generally attributed to dextral transpression between adria and europe this approach implies that the alpine evolution of the central alps was largely governed by tangential convergence between the adriatic and the european plates

extension in compressional orogenic belts the eastern alps extension in the eastern alps encompasses the following 1 extension accompanying simple shear crustal stacking subhorizontal stretching occurs along flat lying foliations and regionally consistent stretching lineations with associated high strains on a local scale stretching results from extrusion of ductile sediments squeezed between rigid basement blocks basement blocks during thrust sheet imbrication the overall geometric effect is crustal thickening 2 classical extensional tectonics extension first occurs as a consequence of accretion and underthrusting of continental and oceanic material and represents gravitational adjustment of an unstable orogenic wedge extension then occurs as a consequence of terminal continental collision and is accommodated by lateral extrusion of crustal of crustal blocks the overall geometric effect is crustal thinning extension is generally oriented subparallel to the strike of the orogen

impact of high resolution fwi in the western black sea revealing overburden and reservoir complexity the western black sea wbs is now an area of active petroleum exploration and several seismic surveys have been acquired to support the ongoing activity seismic imaging in the wbs is challenging due to the presence of complex overburden such as canyons shallow gas channels and complex shallow stratigraphy such overburden complexities create amplitude dimming and wipeouts in the images and cause structural distortions of the reservoir units conventional velocity model building and seismic migration methods are not optimal for addressing such challenges full wavefield inversion fwi technology was applied to overcome the complex seismic imaging challenges in the wbs and to support the exploration and development program to date a suite of fwi products has been used to identify shallow hazards derisk prospects optimize well placement perform accurate resource estimation and support development planning unlike traditional seismic migration generated fwi products are not simply depictions of

flooding the topography wave equation datuming of land data with rugged acquisition topography wave equation datuming overcomes some of the problems that seismic data recorded on rugged surface topography present in routine image processing the main problems are that 1 standard optimized migration and processing algorithms assume data are recorded on a flat surface and that 2 the static correction applied routinely to compensate for topography is inaccurate for waves that do not propagate vertically wave based processes such as stacking dip moveout correction normal moveout correction velocity analysis and migration after static shift can be severely affected by the nonhyperbolic character of the reflections to alleviate these problems i apply wave equation datuming early in the processing flow to upward continue the data to a flat datum above the highest topography this is what i refer to as flooding the topography this approach does not require detailed a priori knowledge of the near surface velocity and it streamlines subsequent processing because the data are regridded onto a regularly sampled datum wave equation datuming unravels the distortions caused by rugged topography and unlike the static shift method it does not adversely effect subsequent wave based processing the image obtained after wave equation datuming exhibits better reflector continuity and more accurately represents the true structural image than the image obtained after static shift

contemporaneous plutonism and strike slip faulting a case study from the tonale fault zone north of the adamello pluton italian alps 1 a field microstructural and geochronological study of contemporaneous plutonism and strike slip faulting along the eastern tonale fault zone provides new insights into the interrelationships between magmatic emplacement contact metamorphism and shearing and it places new time constraints for the periadriatic fault system although pluton emplacement and shearing were not caused by each other they mutually interacted during contact metamorphism the character of the composite tonale fault zone varies considerably with its proximity to the northern margin of the adamello pluton from a paired greenschist facies mylonite belt northern mylonite zone and cataclastic fault zone in the west to a fault zone consisting of northern mylonite zone cataclastic fault zone and a second mylonite belt southern mylonite zone formed by contemporaneous shearing and contact metamorphism in the east ongoing strike slip motion led to telescoping and advective cooling of the deforming contact aureole new u pb zircon ages for the northernmost adamello intrusions the avio at 34 6 1 0 ma and the presanella at 32 0 2 3 ma date the onset of contact metamorphism rb sr and k ar cooling ages and new zircon fission track ages provide evidence that postintrusive cooling to below 300 c was achieved rapidly i e approximately 30 myr ago being consistent with a shallow crustal emplacement at ambient temperatures of approximately 250 c cataclastic dextral strike slip faulting continued until about 20 ma when the tonale fault zone became offset by a number of minor sinistral shears and by the giudicarie fault hence dextral strike slip motion along the periadriatic fault system east of the bergell pluton lasted from approximately 35 20 myr ago

crustal structure of central sicily abstract we processed crustal seismic profile siripro acquired across central sicily to improve the seismic image we utilized the wave equation datuming technique a process of upward or downward continuation of the wave field between two arbitrarily shaped surfaces wave equation datuming was applied to move shots and receivers to a given datum plane removing time shifts related to topography and to near surface velocity variations the datuming procedure largely contributed to attenuate ground roll enhance higher frequencies increase resolution and improve the signal noise ratio processed data allow recognizing geometries of crust structures differentiating seismic facies and offering a direct image of ongoing tectonic setting within variable lithologies characterizing the crust of central sicily migrated sections underline distinctive features of hyblean plateau foreland and above all a crustal thinning towards the caltanissetta trough to the contact with a likely deep permo triassic rifted basin or rather a zone of a continent to oceanic transition inhomogeneity and fragmentation of sicily crust with a distinct separation of central sicily basin from western and eastern blocks appear to have guided the tectonic transport inside the caltanissetta crustal scale syncline and the accumulation of allochthonous terrains with south and north verging thrusts major tectonic stack operated on the construction of a wide anticline of the maghrebian chain in northern sicily sequential south verging imbrications of deep elements forming the anticline core denote a crust wedge indenting foreland structures deformation processes involved multiple detachment planes down to decoupling levels located near crust mantle transition supporting a presence of high density lenses beneath the chain interrelated to a southwards push of tyrrhenian mantle and asthenosphere

fast 3d target oriented reverse time datuming imaging of subsalt sediments is a challenge for traditional migration methods such as kirchhoff and one way waveequation migration consequently the more accurate twowaymethodofreverse timemigrationrtmispreferredfor subsalt imaging but its use can be limited by high computation cost to overcome this problem a 3d target oriented reverse time datuming rtd method is presented which can generate redatumed data economically in target areas beneath complex structures such as salt domes the redatumed datainthetargetareathencanbemigratedinexpensivelyusing a traditional migration method if the target area is much smaller than the acquisition area computation costs are reduced significantly by the use of a novel bottom up strategy to calculate the extrapolated green s functions target orientedrtdistestedon2dand3dseg eagesyntheticdata sets and a 3d field data set from the gulf of mexico results show that target oriented rtd combined with standard migration can image sediments beneath complex structures accurately with much less calculation effort than full volume rtm the requirement is that the area over the target zone is smallerthanthatoftheacquisitionsurvey

deformation mode switches in the penninic units of the urtier valley western alps evidence for a dynamic orogen abstract multiple deformation mode switches from shortening to extension have been detected in the penninic units of the urtier valley to the north of the gran paradiso massif an early shortening phase whose traces are poorly preserved led to the tectonic burial of rock units to high pressure conditions subsequent extensional shearing sz gr 1 led to the formation of mylonitic fabrics during this event the eclogitic piemonte unit was exhumed to greenschist facies conditions p 0 2 0 3 gpa in the footwall of the blueschist piemonte unit exotic slices of continental basement and mesozoic continental shelf carbonates are found along their contact implying the existence of older thrust stacks dissected by the younger extensional shear zones the extensional structures were later affected by upright folding fu indicating yet another deformation mode switch which led to re burial to p 0 6 0 8 gpa later multi stage deformation culminated in an episode of extensional shearing with top to the west kinematics sz gr 2 therefore at least two shortening extension cycles affected the piemonte units of the urtier valley existing geochronological data allow less than 20 myr for the complex deformation history discussed here shortening extension cycles can be inferred also from published studies from other sections of the western alps however while the first shortening extension cycle was widespread in the penninic units the lateral extent and relative timing of the second cycle in different areas are still unclear

prestack layer replacement we present a method of layer replacement based on the kirchhoff integral solution to the scalar wave equation the term layer replacement refers to replacing the overburden velocity with the velocity of the substratum thereby eliminating raypath bendings at the interface between the overburden and the substratum it is the raypath bendings that induce distortions and disruptions on reflections beneath a complex structure when implemented before stack layer replacement provides an opportunity to revise velocity estimates after correcting for the nonhyperbolic moveout on cmp data caused by a complex overburden as a result layer replacement also yields an improved unmigrated stack section imaging can then be completed by time migration after stack we demonstrate the layer replacement technique on field data with irregular water bottom topography

below surface ice melt on the coastal antarctic ice sheet in the jutulgryta area of dronning maud land antarctica subsurface melting of the ice sheet has been observed the melting takes place during the summer months in blue ice areas under conditions of below freezing air and surface temperatures adjacent snow covered regions having the same meteorological and climatic conditions experience little or no subsurface melting to help explain and understand the observed melt rate differences in the blue ice and snow covered areas a physically based numerical model of the coupled atmosphere radiation snow and blue ice system has been developed the model comprises a heat transfer equation which includes a spectrally dependent solar radiation source term the penetration of radiation into the snow and blue ice depends on the solar radiation spectrum the surface albedo and the snow and blue ice grain sizes and densities in addition the model uses a complete surface energy balance to define the surface boundary conditions it is run over the full annual cycle simulating temperature profiles and melting and freezing quantities throughout the summer and winter seasons the model is driven and validated using field observations collected during the norwegian antarctic research expedition nare 1996 97 the simulations suggest that the observed differences between subsurface snow and blue ice melting can be explained largely by radiative and heat transfer interactions resulting from differences in albedo grain size and density between the two mediums

combined high precision chronometry and geochemical tracing using accessory minerals applied to the central alpine bergell intrusion central europe abstract the behaviour of nd u th and pb isotopes in granitic rocks is usually controlled by accessory minerals in this study an approach is adopted which uses the initial 143 nd 144 nd as a geochemical tracer together with high precision u th pb geochronology for accessory phases and their respective whole rock this combination of techniques is applied to zircon allanite sphene apatite and thorite from both a tonalite and a granodiorite from the tertiary alpine bergell intrusion inherited isotopic signatures have been identified in bulk zircon fractions by inverse discordance in the u pb system in the case of the granodiorite the initial nd in the zircon is 1 77 units lower than the bulk rock this result indicates that nd isotopes in zircon may serve as a useful tool for tracing crustal precursors in silicic rocks all other accessories yield an initial nd equal to their respective whole rock and u th pb ages equal to or lower than the respective intrusion ages this indicates either the absence of inherited cores or that such cores have exchanged their nd and pb in the case of apatite also sr by diffusion where available experimental mineral melt equilibria and diffusion models are consistent with this behaviour u pb geochronology of carefully selected core free zircons yields a precise intrusion age of 31 88 0 09 ma for the tonalite in contrast granodioritic zircons are partially reset due to radiation damage caused by high u concentrations however an alternative means of dating young intrusions is to use 232th 208pb ages of allanite in the case of allanite the presence of a large excess of 206pb derived from 230th indicates that no total pb loss has occurred since crystallization and the nd isotopes indicate the absence of inheritance using both the allanite age and a 238u 206pb age for sphene an intrusion age of 30 13 0 17 ma is indicated for the granodiorite taken together with an allanite th pb age for the tonalite these results strongly support the high closure temperatures for the allanites studied here 700 800 c at high post magmatic cooling rates all other accessory mineral ages are reset to values similar to hornblende 39ar 40ar ages and reflect the effect of post magmatic cooling superimposed on post metamorphic cooling

thermochronometry across the austroalpine pennine boundary central alps switzerland orogen perpendicular normal fault slip on a major overthrust and its implications for orogenesis fifty one new and 309 published thermochronometric ages nine systems with closure temperatures ranging from 450 to 70 c from the graubunden region of the central alps demonstrate that a pronounced thermal mismatch between the austroalpine allochthon alpine orogenic lid and the pennine zone persisted until at least 29 ma and allowably until circa 18 ma the observed mismatch supports previous suggestions that the famous overthrust between the austroalpine allochthon and the pennine zone historically regarded as primarily an eocene top north thrust fault is in fact primarily an oligocene miocene normal fault that has a minimum of 60 km of displacement with top south or top southeast sense of shear two hallmarks of alpine geology deposition of the foredeep molasse and emplacement of the helvetic nappes appear to be coeval peripheral manifestations of crustal thickening via the interposition of the pennine zone as a northward intruding wedge between the austroalpine lid and the european cratonic margin with the helvetic system european margin acting as the floor of the wedge we presume the penninic wedge is driven by the buoyant rise of subducted crust no longer able to remain attached to the descending slab if so emplacement of the pennine wedge could have occurred mainly after adria was juxtaposed against cratonic europe

upward continuation with topographic datuming operator the integrated wave equation datuming scheme revised the integrated wave equation datuming scheme is an integrated datuming method to implement the wave equation velocity replacement with a one way extrapolator for overthrust data the integrated wave equation datuming scheme is accomplished by downward continuing the data from the topography to a non planar base of the weathering layer followed by an upward continuation from the base of the weathering layer to a final planar datum both the downward and the upward continuation are accomplished by a one way extrapolator by a classical two step implementation the topographic datuming operator is a distinctive technique by which the shots and receivers are downward continued simultaneously although its inadaptability to non planar datum and the strong lateral variation of the near surface structure constrains its application to the downward continuation of the overthrust data we found that the one step feature of the topographic datuming operator is extremely suitable for the upward continuation in this paper the topographic datuming operator is incorporated into the integrated wave equation datuming scheme to perform upward continuation instead of a one way extrapolator thus a revised integrated wave equation datuming scheme is constructed compared with the previous scheme the computatiol cost of the revised integrated wave equation datuming scheme is greatly reduced thus the applicability of the integrated wave equation datuming scheme is further improved the synthetic and real data examples demonstrate its effectiveness and efficiency

interface scattering versus body scattering in subbasalt imaging and application of prestack wave equation datuming the presence of high velocity highly heterogeneous layers such as basalt have a detrimental effect on imaging below those structures internal characteristics of the basalt itself can also degrade the subbasalt image quality in many cases the boundary surfaces of a basalt sequence are not smooth but contain some roughness at a scale similar to the seismic wavelength interface scattering resulting from interface roughness can be a serious problem in this paper body and interface scattering problems are addressed through acoustic finite difference modeling interface scattering seems to have the most detrimental effect on imaging at depth a wave equation prestack datuming procedure is applied to synthetic acoustic data to remove the effects of rough interfaces this computational process transforms seismic data to a new datum plane in the subsurface eliminating propagation effects between the surface and the new datum plane the technique leads to a much improved image of below the basalt with the g

imaging low velocity anomalies with the aid of seismic tomography abstract theoretical considerations snell s law suggest that low velocity fanomalies are undersampled and therefore should be poorly resolved by inversion schemes based on ray tracing methods a synthetic study considering a 40 20 m low velocity anomaly 300 m s placed at the center of a 400 50 m block with gradient background velocity model from 3000 m s at the surface to 4000 m s at the base indicates that the low ray density in ray tracing coverage diagrams of tomographic inversion studies can be used as evidence for the existence of low velocity anomalies combined normal incidence seismic reflection images and the velocity models obtained by tomographic inversions of first arrival travel times form an efficient scheme to resolve low velocity anomalies such as fracture zones furthermore the velocity models derived from tomographic inversions are used in a wave equation datuming algorithm to account for statics caused by a strongly laterally variable shallow surface weathering layer and provide seismic reflection images of fracture zones low velocity anomaly within a granitic pluton

post collisional orogen parallel large scale extension in the eastern alps abstract large scale extension affected the eastern alps during post collisional lateral tectonic extrusion in early and middle miocene times the tauern window was mainly tectonically exhumed by the 160 km pullapart of the rigidly behaving austroalpine basement blocks forming the tectonic lid of the penninic contents of the window an evaluation of the syn extrusion fault pattern reveals displacements of several tens of kilometers along the low angle extensional shear zones at the western and eastern margins of the window and along the important strike slip fault zones north and south of the window large scale shear is reflected by discontinuities in mineral cooling patterns across important shear zones the cooling histories of the tectonic blocks show that the window boundaries during exhumation coincide only partly with the classical boundaries of the window defined by thrust units reconstruction of the exhumation history shows an asymmetric evolution of the tauern window we argue that the eastern and western low angle extensional shear zones formed in sequence which is reflected by different evolutions of the fragmentation and uplift history of the austraolpine tectonic blocks to the east and west of the window in the central and eastern alps three structural domes the lepontin dome in the central alps and the tauern and rechnitz domes in the eastern alps were formed by large scale extension in miocene times total e w stretch amounts to more than 300 km and results in 70 extension we propose that the central and eastern alps are part of an extensional province that also includes the pannonian basin and has a counterpart separated by the moesian indenter in the rhodope mountains the aegean sea and the menderes massif in asia minor in these regions a number of mainly tectonically exhumed domes or deep sedimentary basins formed by miocene large scale extension

rift related inheritance in orogens a case study from the austroalpine nappes in central alps se switzerland and n italy the austroalpine nappe systems in se switzerland and n italy preserve remnants of the adriatic rifted margin based on new maps and cross sections we suggest that the complex structure of the campo grosina languard and bernina nappes is inherited largely from jurassic rifting we propose a classification of the austroalpine domain into upper middle and lower austroalpine nappes that is new because it is based primarily on the rift related jurassic structure and paleogeography of these nappes based on the alpine structures and pre alpine rift related geometry of the lower bernina and middle campo grosina languard austroalpine nappes we restore these nappes to their original positions along the former margin as a means of understanding the formation and emplacement of the nappes during initial reactivation of the alpine tethyan margin the campo and grosina languard nappes can be interpreted as remnants of a former necking zone that comprised pre rift upper and middle crust these nappes were juxtaposed with the mesozoic cover of the bernina nappe during jurassic rifting we find evidence for low angle detachment faults and extensional allochthons in the bernina nappe similar to those previously described in the err nappe and explain their role during subsequent reactivation our observations reveal a strong control of rift related structures during the subsequent alpine reactivation on all scales of the former distal margin two zones of intense deformation referred to as the albula zebru and lunghin mortirolo movement zones have been reactivated during alpine deformation and cannot be described as simple monophase faults or shear zones we propose a tectonic model for the austroalpine nappe systems that link inherited rift related structures with present day alpine structures in conclusion we believe that apart from the direct regional implications the results of this paper are of general interest in understanding the control of rift structures during reactivation of distal rifted margins

strain accumulation during basal accretion in continental collision a case study from the suretta nappe eastern swiss alps abstract stacked crystalline basement nappes are a typical feature in the core of many orogens the suretta nappe exposed in eastern switzerland consists of briancon derived crustal slices which were assembled in a south dipping subduction zone during the alpine orogenic cycle the nappe contains post variscan rocks of the rofna porphyry complex rpc and permo mesozoic cover sequences which are ideal to study the strain evolution during alpine nappe formation we present new structural cross sections finite strain analyses and a retrodeformation for the frontal part of the suretta nappe the overall geometry of the suretta nappe is the result of two main deformation phases 1 eocene top to the nnw directed thrusting and folding ferrera phase which is overprinted by 2 backfolding and backshearing niemet beverin phase we suspect that this backshearing was caused by the buoyant rise of light continental crust beneath the suretta nappe and by frictional resistance at the top contact of the suretta nappe which had been accreted to the upper plate in the course of nappe stacking in the lower and interior parts of the suretta nappe weakly to undeformed boudins are generally surrounded by l tectonites indicating wsw ene stretching foliated equivalents reveal a plane strain deformation state the upper part of the suretta nappe which was strongly affected by backshearing shows flattening strain strain data were used to reconstruct the palinspastic evolution of the suretta nappe at two distinct time slots prior to niemet beverin backfolding the suretta nappe is characterized by thrust faults and large scale detachment folds before the onset of ferrera phase nappe stacking jurassic normal faults and the rpc intrusion shape trigger the localization of subsequent deformation our structural study confirms a complex polyphase evolution for the suretta nappe which might be characteristic for crystalline basement nappes in continental collision zones elsewhere

from source terrains of the eastern alps to the molasse basin detrital record of non steady state exhumation fission track cooling ages of detrital apatite aft in the east alpine molasse basin display age groups corresponding to geodynamic events in the orogen since jurassic times these age groups are typical of certain thermotectonic units which formed a patchwork in the swiss and eastern alps by a combination of petrographic and thermochronologic data progressive erosion of source terrains is monitored in different catchments since the oligocene the aft cooling ages show a decrease in lag time until when rapidly cooled debris derived from tectonically exhumed core complexes became exposed after termination of tectonic exhumation lag times of debris derived from the core complexes increased neither on the scale of the entire eastern alps or on the scale of individual catchments steady state exhumation is observed due to the highly dynamic changes of exhumation rates since late eocene collision d 2005 elsevier b v all rights reserved

application of multi source waveform inversion to marine streamer data using the global correlation norm conventional multi source waveform inversion using an objective function based on the least square misfit cannot be applied to marine streamer acquisition data because of inconsistent acquisition geometries between observed and modelled data to apply the multi source waveform inversion to marine streamer data we use the global correlation between observed and modelled data as an alternative objective function the new residual seismogram derived from the global correlation norm attenuates modelled data not supported by the configuration of observed data and thus can be applied to multi source waveform inversion of marine streamer data we also show that the global correlation norm is theoretically the same as the least square norm of the normalized wavefield to efficiently calculate the gradient our method employs a back propagation algorithm similar to reverse time migration based on the adjoint state of the wave equation in numerical examples the multi source waveform inversion using the global correlation norm results in better inversion results for marine streamer acquisition data than the conventional approach

extensional detachment faulting in the evolution of a tethys passive continental margin eastern alps switzerland the austroalpine nappes of switzerland represent an exhumed and tectonically imbricated segment of the passive continental margin of the jurassic tethys within one of these nappes err nappe part of an upper crustal extensional detachment is preserved indicating that the thinning of the crust was achieved by non uniform extension the mesozoic age of the detachment is shown by comparison between its associated cataclasites and identical cataclasites that are found as redeposited components in middle jurassic sedimentary breccias this low angle detachment within the basement was kinematically linked to synsedimentary high angle normal faults at the surface the area of the err nappe belongs in terms of jurassic paleogeography to the most distal part of the continental margin where both low and high angle normal faults dipped oceanward that is west to northwest in present day coordinates in the more proximal part of the margin however the high angle normal faults dipped eastward toward the continent ammonite stratigraphy within the sediment prisms adjacent to the faults gives evidence for an early jurassic age of the faulting in the proximal part of the margin whereas in the distal part faulting occurred during latest early to middle jurassic time we therefore propose that the jurassic extension of the crust which finally led to the opening of the piemont ligurian ocean was achieved by two fault systems which differ in geometry fault orientation and age these fault systems were composed of a basal low angle detachment with high angle normal faults above the orientation of the older eastward dipping detachment was prone for reactivation during early alpine crustal shortening the present day thrust contact between the two major tectonic units of the area the lower austroalpine and the central austroalpine nappe complex therefore might correspond to an eastward dipping jurassic low angle normal fault

late oligocene to early miocene lateral extrusion at the eastern border of the lepontine dome of the central alps bergell and insubric areas eastern central alps 1 how the internal domain of the central alps deformed during late stages of the continental collision remains poorly understood to fill this gap in knowledge we present new data constraining the late alpine brittle and brittle ductile tectonics in oligocene intrusions of the bergell alps eastern central alps syncollisional late normal faulting is widespread at all investigated scales but part of the deformation observed is also associated with oblique slip and transcurrent displacements the faults are explained by stress permutations in space and time implying the three principal stress axes and correspond to different homoaxial states of stress of one single transtensive tectonic event motion on these faults accommodated coeval orogen parallel extension and orogen perpendicular contraction during oblique indentation by the southern alpine crust extensional and transcurrent structures likely formed by lateral extrusion of the bergell alps via distributed eastward extrusion of imbricated wedge shaped crustal blocks during the late oligocene and lower miocene a first order wedge shaped crustal block in the bergell alps is represented by three coeval segments of the periadriatic fault system namely the tonale engadine and forcola faults the eastern central segment of the alpine belt appears to have deformed during the late oligocene and lower miocene in a similar way to its extremities where lateral escape tectonics occurred at least until the upper miocene according to free boundary availabilities

three dimensional geometry and tectonostratigraphy of the pennine zone central alps switzerland and northern italy abstract continental collision during alpine orogenesis entailed a polyphase deformation history d1 d5 in the pennine zone of the central alps the regional tectonostratigraphy was basically developed during d1 and d2 characterised by isoclinal typically north closing recumbent anticlines separated by pinched in synclines on the scale of tens of kilometres later deformation phases d3 and d4 warped the stack into wavy to open folds exhumation of this zone resulted locally in later vertical shortening and folding of already steep fabrics d5 three dimensional models of the nappe pile were constructed based on geostatistical assessment of the regional foliation field and considering the abundant structural field data these models indicate the existence of five principal tectonostratigraphic levels developed during d1 and thus equivalent to nappe units s str the gotthard the leventina antigorio the maggia simano and probably the monte leone as well as the composite lepontine series lebendun soja and adula cima lunga levels all these tectonic units formed part of the passive continental margin of europe prior to the onset of the alpine orogenesis individual isoclinal post nappe folds reflect relative displacements on the order of 40 km or more the most prominent d2 post nappe structure is the wandfluhhorn fold structurally equivalent to the northern closure of the leventina lucomagno antiform the lebendun and monte leone folds are of similar magnitudes and also affect the whole nappe pile whereas the smaller mogno and molare synforms only refold the maggia simano nappe internally principal d3 and d4 structures are the tight mergoscia synform directly north of the insubric fault between bellinzona and locarno southern steep belt the maggia steep zone forming the steep western limb of the campo tencia synform and subdividing the lepontine dome into the simplon and ticino subdomes the chiera synform steepening the dominant foliation in the north northern steep belt and the vanzone and claro antiforms steepening the dominant foliation in the south southern steep belt the current geometry of the northern and southern steep belts reflects an interplay between d4 and d3 involving both fold interference and reactivation tightening

miocene lateral extrusion in the inner western alps revealed by dynamic fault analysis 1 from early miocene to the present day the core parts of the western european alps experienced brittle extensional deformations mostly in a strike parallel direction here we present new data constraining the brittle deformation of the vanoise area french alps and a synthesis of 312 paleostress tensors in the whole arc of the internal western alps the data show a continuous change in the direction of extension from n065 simplon area to n s vanoise area and to nnw sse briancon area the abundance of orogen perpendicular 3 axes increases from the north to the south in the brianconnais area an extensional reactivation of the basal penninic thrust seems to be the origin of the e w to ne sw oriented 3 in light of these new data and the regional paleostress synthesis we propose a predominant orogen parallel extension in the internal zone as a whole this orogen parallel extension is related to the indentation rotation of the apulian microplate and to the opening of the ligurian sea during the lower middle miocene the locally observed orogen perpendicular extension is interpreted as an effect of the exhumation of the internal crystalline massifs the uplift of the external crystalline massifs and or the present day geodynamics postorogenic gravitational collapse some transcurrent tectonics older than the extension in the valais area and younger than the extension farther south is observed in the entire inner western alps strike slip movements are correlated with the apulian rotation and local permutation of stress axes

application of an integrated wave equation datuming scheme to overthrust data a case history from the chinese foothills an integrated wave equation datuming scheme improves the imaging quality of seismic data from overthrust areas it can be regarded as integrated because upward layer replacement is included in this scheme data are downward continued to a nonplanar datum such as the base of the weathering layer followed by upward continuation from the nonplanar datum to a final planar datum using a one way extrapolator when compared with a kirchhoff integral this method can deal better with the strong lateral velocity variation within the near surface after a test on synthetic data the scheme is applied successfully to real 2d overthrust data acquired in the qi lian foothills western china compared with results using static corrections integrated wave equation datuming results lead to better reconstruction of the diffractions and reflections more reliable migration velocity analyses and stronger stack and final depth images

kinematics of the alpine plate margin structural styles strain and motion along the penninic austroalpine boundary in the swiss austrian alps a structural and kinematic analysis of parts of the alpine suture zone i e the arosa zone and the edges of the overlying austroalpine and underlying penninic units is presented the arosa zone is interpreted as part of an accretionary wedge formed by the overriding of the austroalpine units the northern part of the adriatic plate over the penninic units structures strain and stretching trajectories indicate that two main deformation events followed each other discontinuously the earlier event was a wsw to nw directed thrusting under noncoaxial deformation and led to melange type structures the second event less penetrative in the arosa zone and with a downward increase in strain and noncoaxial flow formed n to ne verging folds and imbrication zones west directed displacement commenced in the early cretaceous and the motion changed to a prevailing northerly direction during the eocene as revealed by sediments involved in thrusting and by radiometric dating of the mylonites the kinematic history deduced from structural analysis agrees with the history obtained by recent work on plate margin sediments we correlate the anticlockwise rotation of the adriatic plate relative to europe between about 130 and 60 ma with the west directed motion in the arosa zone a change to relative n s motion during the lower tertiary led to the n to ne directed displacements a direct relationship thus exists between the motion of the adriatic plate and the resulting deformation along its northern margin during the early history of the eastern alps partitioning in brittle and ductile deformation and structural slicing under noncoaxial deformation is responsible for the melange type structures

on the role and importance of orogen parallel and perpendicular extension transcurrent shearing and backthrusting in the monte rosa nappe and the southern steep belt of the alps penninic zone switzerland and italy during europe adria collision in tertiary times the monte rosa nappe was penetratively deformed in several stages after an eclogite facies pressure peak 1 top to the nw thrust shearing mattmark phase after 40 ma 2 orogen parallel top to the sw extensional shear ing and folding malfatta phase 3 orogen perpendicular top to the se extensional shearing and folding mischabel phase before 30 ma and 4 large scale upright se vergent folding vanzone phase c 29 28 ma structural analysis and neutron texture goniometry of quartz mylonites show that the stellihorn shear zone in the monte rosa nappe accommodated a complex and multidirec tional sequence of shearing movements during the mattmark malfatta and mischabel phases and was folded in the vanzone phase in the tail shaped eastward prolongation of the monte rosa nappe in the southern steep belt of the alps both dextral and sinistral mylonites olino phase were formed during and after the formation of the vanzone fold reflecting renewed orogen parallel sw ne extension contemporaneous with nw se shortening from c 29 ma onward a similar sequence of deformation stages was identified in the adula nappe at the eastern border of the lepon tine metamorphic dome important consequences arise for the insubric fault at the southern border of the lepontine dome 1 the nw to n dipping orientation of the insubric fault is not a primary feature but resulted from rotation of an originally se dipping shear zone after c 30 ma and 2 the strong contrast in metamorphic grade across this fault upper amphibolite facies to the north versus anchizone to the south results from north side up faulting coupled with orogen parallel extension of the northern block lepontine dome while no such extension occurred in the southern block southern alps extension in the northern block started in the malfatta phase and continued in the mischabel phase when the foliation in the area which later became the southern steep belt still dipped towards south during vanzone olino deformation further unroofing and uplift of the lepontine dome relative to the south alpine block took place while the southern steep belt was progressively rotated into its present overturned pos ition changing its character from a normal fault into a backthrust complex deformation paths in the southern steep belt resulted from the combination of extension of the northern block with strike slip motion along the insubric fault

solar heating rates and temperature profiles in antarctic snow and ice observations of temperature maxima at about 10 cm depth in cold antarctic snow during summer have previously been explained by proposing that solar heating is distributed with depth whereas thermal infrared cooling is localized at the surface the solid state greenhouse an increase in temperature from the surface to 10 cm depth t 4 k found by rusin 1961 on the antarctic plateau was successfully reproduced by schlatter 1972 in a combined radiative transfer and heat transfer model

an integrated method for resolving the seismic complex near surface problem we describe an integrated method for solving the complex near surface problem in land seismic imaging this solution is based on an imaging approach and is obtained without deriving a complex near surface velocity model we start by obtaining from the data the kinematics of the one way focusing operators i e time reversed green s functions that describe propagation between the acquisition surface and a chosen datum reflector using the common focus point technology the conventional statics solutions obtained from prior information about the near surface are integrated in the initial estimates of the focusing operators the focusing operators are updated iteratively until the imaging principle of equal traveltime is fulfilled for each subsurface gridpoint of the datum reflector therefore the seismic data is left intact without any application of time shifts which makes this method an uncommitted statics solution the focusing operators can be used directly for wave equation redatuming to the respective reflector or for prestack imaging if determined for multiple reflecting boundaries the underlying velocity model is determined by tomographic inversion of the focusing operators while also integrating any hard prior information e g well information this velocity model can be used to perform prestack depth imaging or to calculate the depth of the new datum level we demonstrate this approach on 2d seismic data acquired in saudi arabia in an area characterized by rugged topography and complex near surface geology

the building of the central swiss alps an experimental approach abstract a kinematic model explaining the building of the central swiss alps is proposed from a review of various kind of data including structural geophysical petrological and geochronological data the eo alpine event is taken into account in order to determine the thermo mechanical evolution from the cretaceous to the late tertiary the stacking process of crustal wedges which took place during cretaceous time has led to the formation of a thickened crust with a very low geothermal gradient high pressure low temperature metamorphism this period was followed by a lull in tectonic activity during which thermal relaxation took place the major tertiary deformation is thought to result from horizontal compression of a thickened crust having a geothermal gradient higher than the average horizontal surface forces are due to the adriatic sub plate acting as a rigid indenter the model explaining the present day structure of the swiss alps emphasizes vertical extrusion and horizontal intrusion of the deepest highly ductile basement units several scale model experiments have been carried out in order to test this basic kinematic idea they display quite similar structures to those identified for the swiss alps striking features of the swiss alps such as their metamorphic and uplift history are discussed and compared with the timing of the tectonic evolution we conclude that the general process of vertical extrusion and horizontal intrusion can possibly explain the overall structure of the central swiss alps external crystalline massifs and the penninic zone

the issues of prestack reverse time migration and solutions with graphic processing unit implementation prestack reverse time migration rtm is a very useful tool for seismic imaging but has mainly three bottlenecks highly intensive computation cost low frequency band imaging noise and massive memory demand traditionally pc clusters with thousands of computation nodes are used to perform rtm but it is too expensive for small companies and oilfields in this article we use graphic processing unit gpu architecture which is cheaper and faster to implement rtm and we obtain an order of magnitude higher speedup ratio to solve the problem of intensive computation cost aiming at the massive memory demand we adopt the pseudo random boundary condition that sacrifices the computation cost but reduces the memory demand for rugged topography rtm it is difficult to deal with the rugged free boundary condition with the finite difference method we employ a simplified boundary condition that avoids the abundant logical judgment to make the gpu implementation possible and does not induce any sacrifice on efficiency besides we have also done some tests on multi gpu implementation for wide azimuth geometries using the latest gpu cards and drivers finally we discuss the challenges of anisotropy rtm and gpu solutions all the jobs stated above are based on gpu and the synthetic data examples will show the efficiency of the algorithm and solutions

formation of recumbent folds during synorogenic crustal extension austroalpine nappes switzerland in sedimentary rocks of the austroalpine nappes in eastern switzerland several generations of alpine cretaceous tertiary folds can be distinguished by overprinting relations the second generation d 2 probably late cretaceous in age includes spectacular kilometre scale folds refolding the earlier formed nappe pile d 2 folds are interpreted here as resulting from east southeast directed crustal extension rather than as previously assumed from north south crustal shortening for the following reasons 1 d 2 folds are restricted to a predominantly ductile layer underlying the brittlely extended orogenic lid and 2 d 2 folds are associated with structures indicating extension in a direction parallel to the extension direction of the brittle layer before the east southeast extension started the layering of the rocks was already steeply inclined owing to earlier d 1 folding the deformation producing the second phase folds probably had a noncoaxial component with a top to the east southeast shear sense and a component of coaxial deformation leading to shortening in the vertical direction and stretching in an east southeast horizontal direction the folds developed with axes oblique to parallel to the direction of bulk stretching i suggest that folding of initially nonhorizontal layers by ductile crustal extension is an important deformation mechanism in the austroalpine and possibly also in other parts of the alps initially steep orientations of layers resulted from transpressive deformation in the obliquely convergent alpine belt and crustal extension parallel to the chain resulted from gravitational spreading i propose that this process can lead to the often encountered phenomenon of stretching parallel to the axes of folds

angle domain common image gathers for migration velocity analysis by wavefield continuation imaging we analyze the kinematic properties of offset domain common image gathers cigs and angle domain cigs adcigs computed by wavefield continuation migration our results are valid regardless of whether the cigs were obtained by using the correct migration velocity they thus can be used as a theoretical basis for developing migration velocity analysis mva methods that exploit the velocity information contained in adcigs we demonstrate that in an adcig cube the image point lies on the normal to the apparent reflector dip that passes through the point where the source ray intersects the receiver ray the image point position on the normal depends on the velocity error when the velocity is correct the image point coincides with the point where the source ray intersects the receiver ray starting from this geometric result we derive an analytical expression for the expected movements of the image points in adcigs as functions of the traveltime perturbation caused by velocity errors by applying this ana

comparison between interferometric migration and reduced time migration of common depth point data one of the difficulties in seeing beneath salt is that the migration velocity in the salt and above it is not well known this can lead to defocusing of migration images beneath the salt in this paper we show that reduced time migration rtm and interferometric migration im can partly mitigate this problem rtm time shifts the traces with the time difference between the calculated arrival time sg ref and the natural arrival time sg ref of a reference reflection where s and g denote the source and receiver locations on the surface respectively we use the terms natural and calculated to represent respectively the arrival times that are velocity independent traveltimes directly extracted from the data without knowledge of the velocity model and velocity dependent traveltimes calculated by ray tracing through a given velocity model the benefit of rtm is a significant reduction of defocusing errors caused by errors in the migration velocity im on the other hand requires extrapolation of

brittle deformation in the inner nw alps from early orogen parallel extrusion to late orogen perpendicular collapse internal parts of the alps have undergone widespread extensional deformation in the course of their neogene exhumation history palaeostress inversion methods are used to map the prevailing stress fields and their evolution through time here we present new data from 100 sites with a total of about 2000 faults striae couples covering a large portion of the inner north western alps palaeostress tensors are mostly extensional although one third of them are transcurrent the dominant direction of minimum horizontal stress axes 3 is in an orogen parallel n30 to n70 orientation around the bend of the north west alpine arc a comparison between this older neogene post metamorphic stress field with the current stress and strain field determined from seismotectonics and geodesy indicates a change in deformation mode from early orogen parallel extrusion to a late and ongoing orogen perpendicular spreading

the tectonometamorphic history of the peridotitic chiavenna unit from mesozoic to tertiary tectonics a restoration controlled by melt polarity indicators eastern swiss alps abstract occurrences of mantle and lower crustal rocks are often preserved in mountain ranges when they occur in the internal part of collision belts their initial geometry and palaeogeography are sources of debate the mafic ultramafic chiavenna unit is one example in the pennine units located in the eastern swiss alps because of strong deformation and metamorphism during tertiary collision tectonics the pre collision geometry of this unit can only be restored using a qualitative geometrical analysis of the successive ductile deformation phases d1 d4 in situ melting and melt migration during the main alpine deformation phase d2 is a way up indicator and is of special importance to this restoration the restored prealpine geometry of the chiavenna unit indicates that a sub continental mantle close to a thinned continental margin becomes denuded during the mesozoic extension and subsequently covered by carbonate sediments taking into account the position of the chiavenna unit in the nappe pile and its pt path a northern brianconnais situation during mesozoic time becomes most probable

recognizing episodic lithospheric thinning along a convergent plate margin the example of the early oligocene alps large scale tectonic mode switches from lithospheric shortening to lithospheric extension may play a fundamental role in the tectonometamorphic evolution of orogens located along convergent plate margins short lived episodes of lithospheric extension can be inferred from the concomitant occurrence of bimodal magmatism rapid exhumation of rock units activity of extensional shear zones steep geothermal gradients and possibly topographic collapse of the orogenic belt here we provide a synthesis of existing data from the european alps supporting the hypothesis on tectonic mode switches data are interpreted to suggest that at ca 38 34 ma a period of n s orogen perpendicular shortening led to the formation of medium to ultra high pressure mineral assemblages by lithosphere scale thrust imbrication a tectonic mode switch took place at ca 34 ma marked by the onset of e w extension during this extensional event internal units of the western and central alps were rapidly exhumed to mid crustal level in the footwall of regional scale extensional shear zones tectonic thinning was also accomplished through pervasive e w stretching of the nappe pile lithospheric stretching resulted in the onset of an anomalous thermal regime which was responsible for the overprint of the older medium to ultra high pressure mineral assemblages by barrovian type mineral assemblages and by migmatization at the same time attenuation of the isotherms led to partial melting of mantle lithosphere and to bimodal magmatism contemporaneous topographic collapse of the orogen is suggested by the deposition in the foreland of flysch units rich in minerals that were probably derived from erosion of the early oligocene calc alkaline volcanics erupted in the hinterland this short lived episode of lithospheric stretching took place in no more than 4 myr from ca 34 ma to ca 32 30 ma renewed lithospheric thickening which is observed in seismic tomography studies resulted in large scale folding of the extensional structures and the in rapid generation of topographic relief feeding abundant clastic sedimentation in the peripheral basins

exhumation of high and ultrahigh pressure metamorphic rocks by slab extraction exhumation of high and ultrahigh pressure metamorphic rocks in collisional orogens may be explained by upward extrusion of these rocks erosion of their overburden or extensional thinning of the overburden some high pressure terranes such as the adula nappe in the central alps fit none of these scenarios we propose an additional way in which part of the overburden may be removed it may sink off into the deeper mantle slab extraction structural and metamorphic relationships in and around the adula nappe indicate that the emplacement of this alpine high to ultrahigh pressure nappe to 3 2 gpa in a pile of lower pressure nappes resulted from the interaction of two subduction zones that accommodated the closure of two ocean basins ultimately leading to the extraction of the intervening slab in terms of mechanics the cause of the exhumation is in this case not the buoyancy of the high pressure rocks but the negative buoyancy of the extracted slab

reduced time migration of transmitted ps waves we develop the novel theory of transmitted ps migration and show that ps transmitted arrivals in a gulf of mexico vertical seismic profile vsp data set can be migrated to accurately image a salt sheet even though the receiver array is below the transmitting boundary we also show that migrating transmitted arrivals is effective in illuminating the base of an orebody invisible to pp reflections in general interfaces that bisect wavepath propagation i e the source and receiver are on opposite sides of the interface and therefore invisible to pp reflections can be imaged by migration of ps transmitted waves these results suggest that migration of ps transmitted waves opens new opportunities in imaging nearly vertical impedance boundaries that are typically invisible to conventional reflection imaging of crosswell and vsp data we also present a new interferometric method denoted as reduced time migration which uses the arrival time difference between the direct p wave and subsequent events to incre

collision tectonics in the swiss alps insight from geodynamic modeling this paper compares results from two dimensional finite element dynamic modeling with the kinematic evolution of the swiss alps during the collision phase in particular we investigate the role of inherited lateral strength heterogeneities on orogenesis a number of first order characteristics are directly comparable at crustal scales in the models the entry of continental crust into the convergent margin marks the end of near perfect subduction accretion of material of the subducting plate to the upper plate creates an orogenic wedge on the incoming pro side and initiates a retroshear zone or model backthrust the addition of material to the upper plate builds a bivergent orogen heterogeneities in the pro crust focus shear and lead to the development of nappe structures the combined action of pro shear nappe stacking and retroshear backthrusting uplifts a plug between the two shear zones subsequent focusing of shear along the retroshear zone results in rotation of the plug and overlying units leading to crustal scale backfolds as observed in the swiss alps the model experiments predict features relevant to alpine dynamics including 1 similar crustal thicknesses and exhumation patterns to those observed in the swiss alps today for erosion rates comparable to natural ones 1 mm yr 1 2 continued accretion and subduction of upper crustal fragments allowing high pressure metamorphic conditions 3 tilting and exhumation of lower crust when a midcrustal weak zone is present and 4 shunting of material across the strong lower crustal wedge of the upper plate

common shot fresnel beam migration based on wave field approximation in effective vicinity under complex topographic conditions gaussian beam migration is a versatile imaging method for geologically complex land areas which overcomes the limitation of kirchhoff migration in imaging multiple arrivals and has no steep dip limits of one way wave equation migration however its imaging accuracy depends on the geometry of gaussian beam that is determined by the initial parameter of dynamic ray tracing as a result its applications in exploration areaswith strong variations in topography and near surface velocity are limited combined with the concept of fresnel zone and the theory of wave field approximation in effective vicinity we present a more robust common shot fresnel beam imaging method for complex topographic land areas in this paper compared with the conventional gaussian beam migration for irregular topography our method improves the beam geometry by limiting its effective half width with fresnel zone radius moreover through a quadratic travel time correction and an amplitude correction that is based on the wave field approximation in effective vicinity it gives an accurate method for plane wave decomposition at complex topography which produces good imaging results in both shallow and deep zones trials of two typical models and its application in field data demonstrated the validity and robustness of our method

wave equation datuming for improving deep crustal seismic images abstract reflection quality in deep crustal seismic sections is often poor due to surface waves irregularities in the surface layer and variations in topography in an effort to remove the effects of the variable near surface layer and topography we have used wave equation datuming to downward continue shot gathers to the base of the surface layer and then redatumed upward to a flat surface using the basement velocity as the replacement velocity we discuss briefly the theory behind the method present a simple synthetic example of a datumed shot gather and conclude with an example of a datumed shot gather from the risc crustal seismic experiment in southeastern california

metamorphic core complexes windows into the mechanics and rheology of the crust metamorphic core complexes are products of normal fault displacements sufficient to exhume rocks from below the brittle ductile transition these faults detachments may initiate within the brittle crust at steep angles but they sole into the ductile middle crust and during displacement rotate to gentler dips due to hanging wall extension the exhumed footwall commonly adopts an arched or domed geometry owing to flexural isostatic readjustment and may be overlain by strongly extended upper crustal rocks that slipped on gently dipping low friction shallow segments of the detachment metamorphic rocks exhumed beneath the detachment record progressively increasing flow stress strain localization and strain rate with decreasing temperature providing a window into physical conditions and deformational processes in the mid crust the metamorphic and deformational history of the footwall rocks may reflect tectonic processes that predate formation of the detachment fault in addition to those accompanying exhumation these processes may include diapiric emplacement of gneiss domes or exhumation in a subduction channel and may not be directly related to formation of the core complex factors favouring core complex formation are high gravitational potential energy of the extending crust weak rheology and a change in the tectonic boundary conditions such as a cessation or slowing of plate convergence

correlation of very low grade data to calibrate a thermal maturity model in a nappe tectonic setting a case study from the alps abstract vitrinite and bituminite reflectance data xrd studies on clay minerals radiometric data and geochemical data have been used to investigate metamorphism of very low and low grade sediments from the lower austroalpine and south penninic nappes in the oberhalbstein valley central alps numerical maturity modelling methods are calibrated with petrological structural and new geochronological data to reconstruct temperature histories even in nappe tectonic settings the combination of low grade data and maturity modelling shows that the duration of peak temperature metamorphism plays an important role in the alteration of organic matter vitrinite reflectance vr often does not correlate with other low grade parameters but in the oberhalbstein equilibrium between the different parameters is evident because heating near the peak conditions for more than 20 ma took place it is proposed to use the comparison to evaluate equilibrium conditions for the temperature parameters in general in addition from petrological work and vr modelling the pressure conditions are estimated the results yield an eroded overburden of 6 1 km and a temperature gradient of 30 2 c km 1 at the base of the nappe stack pressure conditions of 4 1 kbar are determined and therefore no evidences for a high pressure event the main heating is dated between 90 and 70 5 ma and is attributed to nappe stacking in the upper crust

tomostatics turning ray tomography static corrections applications of tomographic velocities to static corrections have drawn much attention recently in computing field statics with the help of seismic tomography geophysical prospecting 1987 w n de amorin et al showed that the waves refracted at the base of a low velocity layer can be used successfully for computing and refining field static corrections in tomographic inversion for velocity plus statics seg expanded abstracts 1991 livia squires et al pointed out that velocity variations and static shifts caused by near surface effects and positional uncertainties can be solved simultaneously using constraint tomography

plate interactions at the southern end of the rhine graben abstract the southern end of the rhine graben in the basel area originated in the early tertiary as an extensional structure it is the site of a transfer zone that connected the rhine graben with the bresse rhone grabens this transfer zone is located in an area into which a late paleozic trough projects which apparently was reactivated from the beginning of miocene to recent times three distinct phases of slight compression were superimposed on the southern end of the rhine graben the first one in the aquitanian early burdigalian is coeval with the development of the helvetic nappes and the insubric fault zone in the alps the second one in the langhian tortonian interval occurred when the external massifs and an important part of the lombardic fold thrust belt in the southern alps developed and the third pliocene to recent one is contemporaneous with the inactivation of this belt and its incorporation into the foredeep of the northern apennines in the aquitanian the forebulge of the alpine orogen is recognizable as a system of flexures that developed preferably on the margin of the late paleozoic trough the middle late miocene one gave rise to uplift of the black forest vosges domain and a river system flowing from this high to the south in the pliocene to recent one alpine rivers made their appearance flowing first to the west into the rhone system and then as the rhine to the north the pliocene to recent phase seems to be decoupled from the body of the central and southern alps

are the alps collapsing abstract orogenic collapse is a process that transfers gravitational potential energy from regions of high potential energy to regions of lower potential energy this transfer is classically considered to be accomplished by extension in the orogenic core and by synchronous shortening in foreland regions of the orogen not all extensional features in collisional mountain belts need however reflect orogenic collapse normal faulting thrust faulting and strike slip faulting are all active in different parts of the alps today and reflect complex local responses to ongoing europe adria convergence the western alps is the only area today where extension and shortening radial to orogen trend occur synchronously and where orogenic collapse may be an important process elsewhere in the alps normal faults are oriented at a high angle to orogen trend and were primarily active in oligocene and miocene time most present day activity in the central and eastern alps is on strike slip faults that are accommodati

velocity independent redatuming a new approach to the near surface problem in land seismic data processing it is well known that a complex near surface encountered in areas such as desert mountainous and glacial till environments can significantly distort primary reflections from deeper horizons of interest this has been and remains a major problem in seismic data processing

full waveform inversion of diving reflected waves for velocity model building with impedance inversion based on scale separation full waveform inversion fwi aims to reconstruct high resolution subsurface models from the full wavefield which includes diving waves post critical reflections and short spread reflections most successful applications of fwi are driven by the information carried by diving waves and post critical reflections to build the long to intermediate wavelengths of the velocity structure alternative approaches referred to as reflection waveform inversion rwi have been recently revisited to retrieve these long to intermediate wavelengths from short spread reflections by using some prior knowledge of the reflectivity and a scale separation between the velocity macromodel and the reflectivity this study presents a unified formalism of fwi named as joint fwi whose aim is to efficiently combine the diving and reflected waves for velocity model building the two key ingredients of joint fwi are on the data side the explicit separation between the short spread reflections and the wide angle arrivals and on the model side the scale separation between the velocity macromodel and the short scale impedance model the velocity model and the impedance model are updated in an alternate way by joint fwi and waveform inversion of the reflection data least squares migration respectively starting from a crude velocity model joint fwi is applied to the streamer seismic data computed in the synthetic valhall model while the conventional fwi is stuck into a local minimum due to cycle skipping joint fwi succeeds in building a reliable velocity macromodel compared with rwi the use of diving waves in joint fwi improves the reconstruction of shallow velocities which translates into an improved imaging at deeper depths the smooth velocity model built by joint fwi can be subsequently used as a reliable initial model for conventional fwi to increase the high wavenumber content of the velocity model

forethrusting backfolding and lateral gravitational escape in the northern part of the western alps monte rosa region a penetrative composite foliation and stretching lineation in the ophiolite of the zermatt saas vanzone region developed under eclogite facies conditions in mid cretaceous time eclogite facies mineral parageneses in this foliation were progressively replaced by blueschist facies and greenschist to amphibolite facies mineral assemblages during late cretaceous and mid tertiary time and were subsequently completely retrogressed kinematic indicators associated with the various stretching lineations of the different metamorphic facies reveal that shearing was initially approximately top to west high p phase and changed during the greenschist amphibolite facies stage into a top to west northwest orientation forethrusting was followed by low angle normal shearing during the final retrograde phase this sense of shear was upper block to southwest west southwest unambiguous structural relics of the high pressure event were not recognized in the gneiss of the monte rosa nappe but the close similarity of the metamorphic evolution of the zermatt saas and monte rosa units including the high p event makes a common tectonic history probable in late oligocene and miocene time the zermatt saas vanzone region was affected by an initial phase of backfolding mischabel phase predating top southwest west southwest directed low angle normal shearing toward the south southeast followed by a second backfolding event vanzone phase the main geometrical and structural features suggest that the mischabel phase resulted from vertical extrusion and horizontal intrusion of the ductile basement monte rosa into shallower units antrona and zermatt seas ophiolites and is in accord with a recently proposed kinematic model for the central alps no clear cut relations between the second phase of backfolding and the retrograde phase were observed this suggests that both events took place largely simultaneously backfolding northeast of the simplon line postdated retrograde normal shearing and is of late miocene age it is concluded that backfolding in the zermatt saas vanzone region cannot be causally linked with backfolding northeast of the simplon line

kinematic evolution of the tethys belt from the atlantic ocean to the pamirs since the triassic abstract we present an updated series of kinematic reconstructions of the major plates around the tethys from the atlantic ocean to the pamirs between the early jurassic and the present this set is used elsewhere as a basis for paleogeographic maps of the entire region the problems related to the positions of the continents in the lower triassic are also discussed no direct analyses of magnetic anomalies and fracture zones in the atlantic have been made rather all available poles and rotations have been tested in order to eliminate or minimize possible kinematic errors the reconstructions are shown for nine key geological periods which correspond to well recognized magnetic anomalies except for the jurassic cretaceous boundary and the cretaceous tertiary boundary which correspond to interpolated positions paleolatitudes have been drawn using the study of westphal et al 1986 an attempt has been made to take into account the displacements caused by formation of the continental margins and basins by stretching the resulting relative vector of motions along the northern boundary of the tethys shows a significant change 80 m y ago left lateral motion with compression dominates before whereas right lateral motion with compression dominates after to the east rates of motion vary by a factor of three with time and four maxima can be clearly related to tectonic events in the late jurassic late cretaceous eocene and post middle miocene to the west north of apulia on the contrary the motion rate has not changed significantly since the early cretaceous and is close to 1 cm yr as an average these rather complex adjustments in rates and directions of relative motion are produced in great part through a complex migration of the africa eurasia pole of rotation and seem to be mostly governed by the tectonics of the tethys plate boundary

linking danube river activity to alpine ice sheet fluctuations during the last glacial ca 33 17 ka bp insights into the continental signature of heinrich stadials abstract offshore archives retrieved from marine lacustrine environments receiving sediment from large river systems are valuable quaternary continental records in the present study we reconstruct the danube river activity at the end of the last glacial period based on sedimentological mineralogical and geochemical analyses performed on long piston cores from the north west black sea margin our data suggest that the danube river produced hyperpycnal floods throughout the ca 33 17 ka period four main periods of enhanced danube flood frequency each of 1 5 3 kyr duration are recorded at ca 32 5 30 5 ka equivalent to the first part of heinrich stadial hs 3 at ca 29 27 5 ka equivalent to greenland stadial 4 at ca 25 3 23 8 ka equivalent to hs 2 and at ca 22 3 19 ka based on mineralogical and geochemical data we relate these events to enhanced surface melting of the alpine ice sheet ais that covered 50 000 km2 of the danube watershed at the last glacial maximum lgm our results suggest that i the ais growth from the inner alps to its lgm position in the northern alpine foreland started from ca 30 5 ka ended no later than ca 25 3 ka and was interrupted by a melting episode ca 29 27 5 ka ii the ais volume drastically decreased from ca 22 3 to 19 ka as soon as summer insolation energy at the ais latitude increased and iii hss strongly impacted the ais mass balance through enhanced summer surface melt this together with evidence of severely cool winters and the rapid expansion of sea ice in the north atlantic implies strong seasonality in continental europe during stadials

evidence for east west crustal extension in the eastern alps implications for the unroofing history of the tauern window the contact between the western border of the tauern window and the overlying austroalpine nappes austria and italy is marked by a structural petrologic and geochronologic discontinuity that developed in the early stages of unroofing of the window within the window pressure temperature time paths j selverstone 1985 indicate that significant ductile thinning occurred shortly after the cessation of thrusting paleocene eocene sense of shear indicators rotated porphyroblasts asymmetric augen and pressure shadows s c fabrics associated with a west plunging stretching lineation indicate that this thinning occurred in response to top to the west low angle normal shear during metamorphism the same sense of normal shear is present in the mesozoic members of the austroalpine sequence west of the window in these rocks however west directed shear occurred at low temperatures 300 c after the thermal peak of metamorphism structural data and the regional geometry imply that the western end of the tauern window is a low angle normal fault brenner line that juxtaposed brittlely deformed rocks of the austroalpine nappes against more ductilely deformed rocks from the window biotite k ar and rb sr data suggest a miocene age for final movement on the brenner line these data indicate a prolonged history of east west extension in the eastern alps that affected all crustal levels early ductile thinning of lower crust followed by mid to upper crustal low angle normal faulting a model is presented that relates the young east west extension to displacement transfer from dextral movement on the periadriatic lineament in this model the brenner line and by analogy the simplon line can be thought of as detachment faults that tectonically unroofed the tauern window and lepontine thermal highs respectively

wave equation velocity replacement of the low velocity layer for overthrust belt data seismic land data are commonly plagued by nonhyperbolic distortions induced by a variable near surface low velocity layer lvl first arrival refraction analysis is conventionally employed to estimate the lvl geometry and velocities then vertical static time shifts are used to replace the lvl velocities with the more uniform faster velocities that characterize the underlying refracting layer this methodology has earned a good reputation as a geophysical data processing tool however velocity replacement with static shifts assumes that no ray bending occurred at the lvl base and that waves propagated vertically through the lvl even though conventional refraction analysis methods which are used to derive lvl models from seismic data are less restrictive these assumptions often are inadequate in thick complex lvl situations where resulting errors may considerably hamper a statics based velocity replacement procedure wave equation datuming may be used to perform lvl velocity replacement when statics are inadequate this method extrapolates the seismic data from the surface to the lvl base with the lvl velocities then it extrapolates the data from the lvl base to an arbitrary datum with the replacement velocity field the marine analog of such a procedure has been well documented in the geophysical literature where the object is to remove distortions caused by an irregular water layer application of wave equation datuming to land data is more difficult because of certain common characteristics of land data irregular shooting large data gaps and crooked line geometry combined with lower signal noise and because the lvl estimation procedure is considerably more difficult we demonstrate wave equation velocity replacement on land data from a western u s overthrust belt the lvl in this region was particularly thick and complicated and ideal for a wave theoretical velocity replacement procedure standard refraction analysis techniques were employed to estimate the lvl then wave equation datuming was used to perform the velocity replacement our derived lvl model was not perfect so some imaging errors were expected because wave equation datuming is highly dependent upon the lvl model nevertheless our results show that wave equation datuming generally allowed better shallow reflector imaging than could be achieved with conventional statics processing

the transition from passive to active margin tectonics a case study from the zone of samedan eastern switzerland the zone of samedan is part of a fossil early mesozoic rift system originally situated in the distal lower austro alpine domain of the adriatic passive continental margin an early mesozoic configuration of asymmetrical rift basins bounded by relative structural highs compartmentalized late cretaceous active margin tectonics jurassic half grabens were folded into arcuate synclines whereas relative structural highs engendered thin imbricated thrust sheets west directed thrusting and folding initiated at the surface and continued to depths favoring mylonitization under lower greenschist facies conditions at this time liguria piemontese ophiolites were accreted to lower austro alpine units directly underlying the zone of samedan late cretaceous orogenic collapse of the adriatic active margin involved the reactivation of west directed thrusts as low angle top to the east normal faults these faults accommodated extensional uplift of liguria piemontese ophiolites and lower austro alpine units beneath and within the zone of samedan during paleogene collision some late cretaceous faults in the zone of samedan were reactivated under lower anchizonal conditions as north directed thrusts the latter stages of this early tertiary thickening were transitional to brittle high angle normal faulting associated with top to the east extension and spreading above the warm uplifting lepontine dome

jura alps and the boundary of the adria subplate abstract the thin skinned jura fold thrust belt is the frontal part of a thick skinned late miocene alpine nappe important late miocene structures in the alps that help define this nappe are the external massifs in the north the orobic thrusts and the piemontese southern alps in the south the giudicarie brenner line in the east and more vaguely the south end of the belledonne massif in the west a bottom boundary compatible with the data is the brittle ductile transition bdt this jura nappe is separated from the latest oligocene early miocene helvetic nappe system most obviously by the late miocene orobic giudicarie brenner fault complex in contrast the distinctive boundary of the early miocene thick skinned helvetic nappe was the iorio tonale line it in the south merging into the piemontese southern alps at what may be termed the locarno singularity the point of minimum width of the thick skinned alps the northern boundary passed through the gotthard and montblanc massifs motion along the southern boundary was dextrally transpressive associated with complex strain partitioning patterns one part of these patterns is the confusing entity comprising the piemontese southern alps and the lepontine dome the slivers composing the piemontese southern alps are dragged dextrally by the iorio tonale strike slip at the locarno singularity and thereby exhibit an important characteristic trait of exotic terranes crustal slivers dragged along strike slip faults the lepontine dome around the locarno singularity on the north side of the iorio tonale line displays the characteristics of a backstop in thrust systems as modeled in sandbox experiments the special boundary functioning as a backstop compatible with the transpressive kinematics was the ivrea body a strong mafic ultramafic granulitic complex which in the early miocene migrated dextrally along the iorio tonale line forcing detachment to descend into the hot middle crust and producing an upsurge of the hot masses in the late miocene jura phase this particular impediment had moved to the west enabling decollement at the brittle ductile transition to propagate across the insubric line into the lombardic domain large scale strain partitioning manifestations resemble those of the equally dextrally transpressive southern boundary of the caribbean plate in spite of a difference in scales the foremost of these manifestations are regional right slip faults slicing through a broad band of contraction accompanied by collapse basins

a purely structural restoration of the nfp20 east cross section and potential tectonic overpressure in the adula nappe central alps common extrusion type models for the high to ultrahigh pressure adula nappe require a major normal fault along the top of this unit which is not conveyed in the structural record this implies that such a normal fault existed but was completely erased during later deformational stages however there is evidence that decompression occurred during top to the foreland thrusting we performed a new purely structural kinematic restoration of the central part of the nfp20 east cross section in order to estimate the burial depths of individual units without converting petrological pressure data into depth under the assumption that pressures were lithostatic the results show that pressures within most of the units were close to but somewhat higher than lithostatic for several stages of the tectono metamorphic history only for the maximum burial stage of the adula nappe we estimate local tectonic overpressures of 40 to 80 of the lithostatic pressures accepting such an amount of overpressure which is moderate compared to values theoretically possible the adula nappe was probably not subducted to subcrustal depth we propose that the structural record of the penninic nappe stack is quite complete and suggest that the decay of tectonic overpressure is a feasible explanation for decompression from eclogite to amphibolite facies conditions during thrusting consequently exhumation and convergence rates of the eocene to oligocene alps may be smaller than previously assumed

physical and optical properties of snow covering arctic tundra on svalbard snow thickness duration of snow coverage and amount of ice covering the soil are crucial for the development of biota in the arctic tundra environment the snow thickness and optical properties control the amount of photosynthetically active radiation par that is available for vegetation a late snow cover may prevent birds from nesting on the ground furthermore ice at the snow soil interface can be an obstacle for grazing of svalbard reindeer and affect the microfauna population snow and ice thickness and the physical and optical properties of snow covering arctic tundra were measured on the broggerhalvoya peninsula on western svalbard in spring of 1997 additionally thicknesses of ground covering ice were measured in spring of 1998 the initial maximum thickness of snow in the observed areas varied from 0 4 to 0 9 m the snow around ny alesund began to disappear by the beginning of june with the entire snow pack disappearing within 2 3 weeks at the bottom of the snow pack there was a soil covering ice layer between 0 05 and 0 1 m thick we obtained radiation and reflectance parameters spectral albedo attenuation of par and global radiation as well as physical properties of snow e g temperature and density over six weeks from early may to late june electrolytic conductivity of melted snow samples from snow pits shows clearly different conductivity for different stratigraphic sections within the snow pack in early june later on these contrasts disappeared as internal ice layers melted and the snow pack underwent percolation the albedo maximum before melt onset exceeded 0 9 whereas in the later phase of melting snow surfaces exhibited significantly lower albedo due to metamorphosis thinning and blackening by soil particle contamination however even an apparently clean snow surface had about 30 lower albedo in mid june than in mid may observations from under snow par measurements are verified using a physically based radiative transfer model this comparison indicates that scattering features that are smaller than the bulk grain size may contribute significantly to the interaction between radiation and snowpack

3d prestack plane wave full waveform inversion prestack depth migration has been used for decades to derive velocity distributions in depth numerous tools and methodologies have been developed to reach this goal exploration in geologically more complex areas exceeds the abilities of existing methods new data acquisition and data processing methods are required to answer these new challenges effectively the recently introduced wide azimuth data acquisition method offers better illumination and noise attenuation as well as an opportunity to more accurately determine velocities for imaging one of the most advanced tools for depth imaging is full waveform inversion prestack seismic full waveform inversion is very challenging because of the nonlinearity and nonuniqueness of the solution combined with multiple iterations of forward modeling and residual wavefield back propagation the method is computer intensive especially for 3d projects we studied a time domain plane wave implementation of 3d waveform inversion we found that plane wave gathers

mitigation of defocusing by statics and near surface velocity errors by interferometric least squares migration with a reference datum abstractimaging seismic data with an erroneous migration velocity can lead to defocused migration images to mitigate this problem we first choose a reference reflector whose topography is well known from the well logs for example reflections from this reference layer are correlated with the traces associated with reflections from deeper interfaces to get crosscorrelograms interferometric least squares migration ilsm is then used to get the migration image that maximizes the crosscorrelation between the observed and the predicted crosscorrelograms deeper reference reflectors are used to image deeper parts of the subsurface with a greater accuracy results on synthetic and field data show that defocusing caused by velocity errors is largely suppressed by ilsm we have also determined that ilsm can be used for 4d surveys in which environmental conditions and acquisition parameters are significantly different from one survey to the next the limitations of ilsm are that it requires prior knowledge of

light reflection and transmission by a temperate snow cover an understanding of the reflection and transmission of light by snow is important for snow thermodynamics hydrology ecology and remote sensing snow has an intricate microstructure replete with ice air interfaces that scatter light spectral observations of light reflection and transmission from 400 to 1000 nm were made in temperate snowpacks under cold and under melting conditions the optical observations were made using a dual detector spectroradiometer one detector was placed above the snow surface to monitor the incident and reflected solar irradiance and the second detector was placed at the base of snow cover to measure downwelling irradiance the optical measurements were supplemented by a physical characterization of the snow including depth density and an estimate of grain size in general transmitted light levels were low and showed a strong spectral dependence with maximum values between 450 and 550 nm for example a 10 cm thick snow layer reduced visible transmission 500 nm to about 5 of the incident irradiance and infrared transmission 800 nm to less than 1 extinction coefficients were in the range 3 30 m 1 and tended to decrease slightly as the snow aged and increase as snow density increased