seismic velocity and attenuation structures of the queen charlotte basin from full waveform tomography of seismic reflection data abstractwe applied viscoacoustic waveform tomography to four seismic reflection lines from the central and northern part of the queen charlotte sedimentary basin and using frequencies of 7 12 hz we estimated the compressional velocity and attenuation above a depth of approximately 1 2 km we refined our previously published inversion strategy by alternating between phase only and amplitude plus phase velocity inversion for the first two pairs of frequencies used and added a second step in which we inverted for attenuation from the lowest frequency using the final recovered velocity model and an initial homogeneous qp model our recovered velocity and attenuation models demonstrated an overall good correlation with the available sonic and gamma ray logs modeled seismic data matches the field data well and 1d velocity and attenuation profiles extracted at line intersections show a good correlation thus demonstrating the robust nature of the results recovered velocities aid in interpreting shallow str

evolution of the raman spectrum of carbonaceous material in low grade metasediments of the glarus alps switzerland terra nova 22 354 360 2010 abstract the raman spectrum of carbonaceous material cm from advanced diagenesis 200 c to low grade metamorphism 320 c is documented in the helvetic flysch of the glarus alps switzerland the spectrum is complex with several defect bands at 1200 d4 1350 d1 1500 d3 and 1620 d2 cm 1 we document the evolution of these bands relative to the graphite g band with increasing metamorphic grade and we show that this qualitative evolution may be used as a proxy for temperature in the glarus alps we develop a robust peak fitting method and propose quantitative parameters that may be used as proxies for thermal metamorphism in this region further work in other geological contexts is needed to assess whether the spectral evolution observed in the glarus alps may be generalized and to critically assess the potential for calibrating a general empirical and quantitative thermometer based on the raman spectrum of cm in low grade rocks

2d waveform tomography applied to long streamer mcs data from the scotian slope detailed velocity models of the earth s subsurface can be obtained through waveform tomography the accuracy of the long wavelength component of such velocity models which is the background velocity field is particularly sensitive to modeling low frequency refracted waves that have long paths through target structures thus field examples primarily have focused on the analysis of long offset wide angle data sets collected using autonomous receivers in which refractions arrive at significantly earlier times than reflections modern marine acquisition with long streamers now offers the ability to record refracted waves with high spatial density and uniform source both in shallow and deep water we used 2d multichannel seismic mcs data acquired with a 9 km long streamer over the scotian slope in water depths of 1600 m the refracted arrivals although mostly restricted to far offset receivers provided sufficient information to successfully invert for a high resolution background velocity field usin

reflection waveform inversion using local descent methods estimating attenuation and velocity over a gas sand deposit prestack seismic reflection data contain amplitudes traveltimes and moveout information waveform inversion of such data has the potential to estimate attenuation levels reflector depths and geometry and background velocities however when inverting reflection data strong nonlinearities can cause reflectors to be incorrectly imaged and can prevent background velocities from being updated to successfully recover background velocities previous authors have resorted to nonlinear global search inversion techniques we propose a two step inversion procedure using local descent methods in which we perform alternate inversions for the reflectors and the background velocities for our reflector inversion we exploit the efficiency of the back propagation method when inverting for a large parameter set for our background velocity inversion we use newton inverse methods during the background velocity inversions it is crucial to adaptively depth stretch the model to preserve the vertical traveltimes this reduces nonlinearity by largely decoupling the effects of the background velocities and reflectors on the data nonlinearity is further reduced by choosing to invert for slownesses and by inverting for a sparse parameter set which is partially defined using geological reflector picks applying our approach to shallow seismic data from the north sea collected over a gas sand deposit we demonstrate that the proposed method is able to estimate both the geometry and internal velocity of a significant velocity structure not present in the initial model over successive iterations the use of adaptive depth stretching corrects the pull down of the base of the gas sand vertical background velocity gradients are also resolved for an insignificant extra cost the acoustic attenuation parameter q is included in the inversion scheme the final attenuation tomogram contains realistic values of q for the expected lithologies and for the effect of partial fluid saturation associated with a shallow bright spot the attenuation image may also indicate the presence of fracturing

raman spectra of carbonaceous material in metasediments a new geothermometer metasedimentary rocks generally contain carbonaceous material cm deriving from the evolution of organic matter originally present in the host sedimentary rock during metamorphic processes this organic matter is progressively transformed into graphite s s and the degree of organisation of cm is known as a reliable indicator of metamorphic grade in this study the degree of organisation of cm was systematically characterised by raman microspectroscopy across several mesozoic and cenozoic reference metamorphic belts this degree of organisation including within sample heterogeneity was quantified by the relative area of the defect band r2 ratio the results from the schistes lustres western alps and sanbagawa japan cross sections show that 1 even through simple visual inspection changes in the cm raman spectrum appear sensitive to variations of metamorphic grade 2 there is an excellent agreement between the r2 values calculated for the two sections when considering samples with an equivalent metamorphic grade and 3 the evolution of the r2 ratio with metamorphic grade is controlled by temperature t along the tinos cross section greece which is characterised by a strong gradient of greenschist facies overprint on eclogite facies rocks the r2 ratio is nearly constant consequently the degree of organisation of cm is not affected by the retrogression and records peak metamorphic conditions more generally analysis of 54 samples representative of high temperature low pressure to high pressure low temperature metamorphic gradients shows that there is a linear correlation between the r2 ratio and the peak temperature t c 445 r2 641 whatever the metamorphic gradient and probably the organic precursor the raman spectrum of cm can therefore be used as a geothermometer of the maximum temperature conditions reached during regional metamorphism temperature can be estimated to 50 c in the range 330 650 c a few technical indications are given for optimal application

crustal seismic imaging from multifold ocean bottom seismometer data by frequency domain full waveform tomography application to the eastern nankai trough 1 in offshore surveys the deep crust is generally investigated by traveltime tomography applied to sparse ocean bottom seismometer data the inferred velocity models are of limited resolution precluding a quantitative analysis of deep tectonic discontinuities if dense arrays of ocean bottom seismometers can be deployed the resulting data sets become amenable to full waveform processing which should lead to a significant improvement in the resolution of structures such acquisition and processing were achieved on the eastern nankai subduction zone full waveform inversion is entirely implemented in the frequency domain enabling efficient finite difference wave modeling and allowing to limit the inversion to a few discrete frequencies of increasing value such a hierarchical procedure defines a multiresolution approach to seismic imaging the data set was recorded by 93 instruments deployed along a 105 km long profile thirteen frequencies ranging from 3 to 15 hz were inverted sequentially wavelengths imaged by the full waveform inversion typically range between 0 5 and 8 km full waveform tomography reveals an intense compression in the upper prism and underlying backstop as evidenced by several thrusts the frontal ones still active corresponding to negative velocity anomalies the subducting paleo zenisu ridge is also reconstructed above which stands the decollement velocities in the upper mantle beneath the ridge are rather low 7 5 km s 1 suggesting partially serpentinized mantle beneath the ridge this paper demonstrates the feasibility of full waveform tomography based on dense ocean bottom seismometer data sets and its ability to quantitatively image the entire crust with a significantly improved resolution compared to what is usually achieved through traveltime tomography

influence of thrust belt geometry and shortening rate on thermochronometer cooling ages insights from thermokinematic and erosion modeling of the bhutan himalaya advancements in thermochronology and numerical modeling offer the potential to associate the age of thermochronometric samples to both exhumational and deformational processes however understanding how these components are related in compressional systems requires linking the geometry and magnitude of fault slip to the distribution and amount of erosion to address this we apply a 2 d thermokinematic model to a forward modeled balanced cross section to quantify the cooling history in fold thrust belt settings the restored cross section provides a kinematic path of rocks and structures necessary to reproduce the surface geology by assigning ages to displacement amounts we produced a range of potential velocity vectors used to calculate heat transport erosion and rock cooling we test the predicted ages against a suite of previously published thermochronometric data from the bhutan himalaya to explore the utility of the data to constrain the timing rate and geometry of fault motion as well as variations in the exhumation rate we evaluate the cooling history associated with a constant rate of shortening of 18 mm yr rates that are 2 0 1 5 0 75 and 0 5 times the constant rate and rates that vary with time to determine which kinematic history best matches the measured cooling ages the combination of relatively old apatite fission track and zircon u th he measured ages and younger 15 9 ma 40ar 39ar ages from white mica is best matched with faster rates relative to constant rates between 11 5 and 8 ma and slower than constant rates from 17 to 11 5 ma and 8 ma to present

quantitative imaging of the permo mesozoic complex and its basement by frequency domain waveform tomography of wide aperture seismic data from the polish basin in this study we present the workflow and results of 2d frequency domain waveform tomography applied to the global offset seismic data acquired in central poland along a 50 km long profile during the grundy 2003 experiment the waveform tomography method allows full exploitation of the wide aperture content of these data and produces in a semi automatic way both the detailed p wave velocity model and the structural image i e perturbations in respect to the starting model thirteen frequencies ranging from 4 to 16 hz were inverted sequentially gradually introducing higher wavenumbers and more details into the velocity models although the data were characterised by relatively large shot spacings 1 5 km we obtained clear images both of the mesozoic and permian sedimentary cover velocity patterns indicated facies changes within the jurassic and zechstein strata a high velocity layer ca 5500 m s was found near the base of triassic scythian which made the imaging of a deeper layer difficult nevertheless we were able to delineate the base of the permian i e base of the rotliegend which was not possible to derive from conventional common depth point processing as well as some deeper events attributed to the carboniferous the sub permian events formed a syn form which favoured our previous interpretation of a depression filled with upper carboniferous molasse the validity of the waveform tomography derived model was confirmed by well log data forward ray tracing modelling and synthetic seismograms calculations provided another justification for the key structures present in the waveform tomography model

thermometry of quartz mylonites importance of dynamic recrystallization on ti in quartz reequilibration quartz mylonites from the tonale fault zone in the alps northern italy have been investigated by the ti in quartz geothermometer titaniq in order to test its applicability to measure deformation temperatures the eastern part of the tonale fault zone was contact metamorphosed by the synkinematic intrusion of the adamello pluton forming an 800 m wide mylonitic shear zone with a synkinematic temperature gradient from 280 c at the frictional viscous transition to 700 c at the pluton contact as derived from metamorphic mineral assemblages deformation microstructures from quartz mylonite samples systematically collected across the mylonitic shear zone display the entire range of dynamic recrystallization in quartz which comprise bulging recrystallization blg subgrain rotation recrystallization sgr and grain boundary migration recrystallization gbm titaniq geothermometry yields the near peak deformation temperature for quartz mylonites deformed at metamorphic temperatures above 540 c in the zone of gbm however for mylonites formed under lower temperatures in the zones of sgr and blg the preexisting ti concentrations were not reset it is suggested that this is due to the sluggish ti volume diffusion rates below 500 c and the short duration of contact metamorphism and deformation even in the higher temperature samples the reequilibration of ti in quartz content was achieved by grain boundary migration rather than by volume diffusion hence our results show that gbm is crucial for the reequilibration of ti in quartz while quartz mylonites deformed by either blg or sgr which predominate in natural shear zones at greenschist facies metamorphic conditions most likely yield inherited temperatures

characterization of a carbonate reservoir using elastic full waveform inversion of vertical seismic profile data abstract two dimensional elastic full waveform inversion was applied to two lines extracted from a spiral three dimensional vertical seismic profile data acquired in an oilfield offshore abu dhabi in the united arab emirates the lines were selected to be parallel and perpendicular to the plane defined by the deviated borehole the purpose of the inversion was to derive high resolution elastic properties of the subsurface after pre processing the data were band pass filtered with a minimum frequency of 3 5 hz and a maximum frequency of 30 hz a sequential inversion approach was used to mitigate non linearity the pre processing of the data consisted in the removal of bad traces followed by amplitude and phase corrections high resolution p and s wave velocity models that show good correlations with the available sonic logs were obtained the results of the inversion suggest that the oilfield consists of a stack of layers with varying lithology porosity and possibly fluid content

sedimentological interpretation of the albian nahr umr formation in the united arab emirates abstract in the united arab emirates the nahr umr formation albian comprises a series of varicoloured shales siltstones and mudstones with increasing carbonate content toward the northern united arab emirates the percentage of clay minerals in the shale ranges from 62 to 73 while the non clay fraction 50 is dominated by calcite quartz and traces of dolomite feldspar pyrite glauconite and phosphate the formation ranges in thickness from 63 to 220 m 200 700 ft and forms an excellent cap rock to the major aptian 5030 reservoirs geochemical studies indicate that the shales have no oil or gas generating potential the total organic carbon content ranges from a low of 0 20 to a high of 0 50 these sediments were deposited in a shallow marine to distal offshore shelf setting

argon behaviour in an inverted barrovian sequence sikkim himalaya the consequences of temperature and timescale on 40ar 39ar mica geochronology abstract 40 ar 39 ar dating of metamorphic rocks sometimes yields complicated datasets which are difficult to interpret in terms of timescales of the metamorphic cycle single grain fusion and step heating data were obtained for rocks sampled through a major thrust sense shear zone the main central thrust and the associated inverted metamorphic zone in the sikkim region of the eastern himalaya this transect provides a natural laboratory to explore factors influencing apparent 40 ar 39 ar ages in similar lithologies at a variety of metamorphic pressure and temperature p t conditions the 40 ar 39 ar dataset records progressively younger apparent age populations and a decrease in within sample dispersion with increasing temperature through the sequence the white mica populations span 2 9 ma within each sample in the structurally lower levels garnet grade but only 0 3 ma at structurally higher levels kyanite sillimanite grade mean white mica single grain fusion population ages vary from 16 2 3 9 ma 2 to 13 2 1 3 ma 2 from lowest to highest levels white mica step heating data from the same samples yields plateau ages from 14 27 0 13 ma to 12 96 0 05 ma biotite yield older apparent age populations with mean single grain fusion dates varying from 74 7 11 8 ma 2 at the lowest structural levels to 18 6 4 7 ma 2 at the highest structural levels the step heating plateaux are commonly disturbed temperatures 600 c at pressures of 0 4 0 8 gpa sustained over 5 ma appear to be required for white mica and biotite ages to be consistent with diffusive open system cooling at lower temperatures and or over shorter metamorphic timescales more 40 ar is retained than results from simple diffusion models suggest diffusion modelling of ar in white mica from the highest structural levels suggests that the high temperature rocks cooled at a rate of 50 80 c ma 1 consistent with rapid thrusting extrusion and exhumation along the main central thrust during the mid miocene

new insight into the south tibetan detachment system not a single progressive deformation 1 low angle normal faults lanf typically regarded as accommodating crustal or lithospheric extension may also form during lithospheric shortening the best studied system of syn contractional lanfs is the south tibetan detachment system a network of low angle normal sense faults and shear zones that formed coevally with and parallel to south vergent thrusts during lithospheric shortening accompanying development of the himalayan orogen in the eastern himalaya there are several across strike exposures of the south tibetan detachment system we present new structural and thermometry data from the eastern himalaya that demonstrate that the south tibetan detachment system cannot have formed as a single progressive structure we characterize and distinguish two distinct structural and tectonic components within the currently recognized system 1 an extensive diffuse sheared layer that formed the boundary between strong upper crust and weak southward flowing middle crust and 2 a network of brittle ductile lanfs that locally exhume partly excise and overprint the earlier mylonite zone at the topographic break between the himalayan orogen and the tibetan plateau the sheared layer not a lanf formed the boundary between upper and middle crust during ductile flow of the middle crust and is extensively exposed in the himalaya at the base of klippen of upper crustal rocks preserved in bhutan along the crest of the himalaya where it has been excised and exhumed by the brittle ductile extrusion lanfs and bounding the cores of the north himalayan gneiss domes citation kellett d a and d grujic 2012 new insight into the south tibetan detachment system not a single progressive deformation tectonics 31 tc2007 doi 10 1029 2011tc002957

high resolution seismic attenuation imaging from wide aperture onshore data by visco acoustic frequency domain full waveform inversion summary here we assess the potential of the visco acoustic frequency domain full waveform inversion fwi to reconstruct p wave velocity vp and p wave attenuation factor q from surface onshore seismic data first we perform a sensitivity analysis of the fwi based upon a grid search analysis of the misfit function and several synthetic fwi examples using velocity and q models of increasing complexity subsequently we applied both the acoustic and viscoacousticfwitorealsurfacewide apertureonshoreseismicdatafromthepolishbasin wherea strongattenuationoftheseismicdataisobserved thesensitivityanalysisofthevisco acoustic fwi suggests that the fwi can jointly reconstruct the velocity and the attenuation factor if the signatureoftheattenuationissufficientlystronginthedata asyntheticexamplecorresponding to a homogeneous background model with an inclusion shows a reliable reconstruction of vp and q in the inclusion when q is as small as 90 and 50 in the background model and in the inclusion respectively a first application of acoustic fwi to real data shows that a heuristic normalization of the data with offset allows us to compensate for the effect of the attenuation in the data and reconstruct a reliable velocity model alternatively we show that visco acoustic fwi allows us to reconstruct jointly both a reliable velocity model and a q model from the true amplitude data we propose a pragmatical approach based upon seismic modelling and source wavelet estimation to infer the best starting homogeneous q model for visco acoustic fwi we find the source wavelet estimation quite sensitive to the quality of the velocity and attenuation models used for the estimation for example source to source wavelets are significantly more consistent when computed in the final fwi model than in the initial one a good kinematic and amplitude match between the early arriving phases of the real and time domain synthetic seismograms computed in the final fwi model provides an additional evidence of the reliability of the final fwi model we find the recovered velocity and attenuation models consistent with the expected lithology and stratigraphy in the study area we link high attenuation zones with the increased clay content and the presence of the mineralized fluids

the relationships between the velocities attenuations and petrophysical properties of reservoir sedimentary rocks1 the authors have measured the velocities and attenuations of compressional and shear waves in 29 water saturated samples of sandstones and shales at a confining pressure of 60 mpa and at frequencies of about 0 85 mhz the measurements were made using a pulse echo method in which the samples diameter 5 cm length 1 5 cm to 2 5 cm were placed between perspex buffer rods inside a high pressure cell the velocity of each seismic wave was determined from the travel time difference of equivalent phase points corrected for diffraction effects of the signals reflected from the top and from the base of each samples attenuation was determined in a similar way by comparison of the diffraction corrected amplitudes of the signals the attenuation data are presented as quality factors q sub p and q sub s for compressional and shear waves respectively and shear waves respectively the results show that qs is strongly correlated with v sub s that q sub p is weakly correlated with v sub p and that q sub p is strongly correlated with q sub s center dot q sub p is strongly dependent on the volume percentage of the assemblage of intra pore minerals whether they are clays or carbonates it is concluded that themore attenuation mechanism is due to the local fluid flow arising from the differential dilation of the solid rock frame and the intra pore mineral assemblage which is a results of their very different elastic moduli less

anisotropic elastic full waveform inversion of walkaway vertical seismic profiling data from the arabian gulf abstract borehole seismic addresses the need for high resolution images and elastic parameters of the subsurface full waveform inversion of vertical seismic profile data is a promising technology with the potential to recover quantitative information about elastic properties of the medium full waveform inversion has the capability to process the entire wavefield and to address the wave propagation effects contained in the borehole data multi component measurements anisotropic effects compressional and shear waves and transmitted converted and reflected waves and multiples full waveform inversion therefore has the potential to provide a more accurate result compared with conventional processing methods we present a feasibility study with results of the application of high frequency up to 60 hz anisotropic elastic full waveform inversion to a walkaway vertical seismic profile data from the arabian gulf full waveform inversion has reproduced the majority of the wave events and recovered a geologically plausible layered model with physically meaningful values of the medium

application of waveform tomography to marine seismic reflection data from the queen charlotte basin of western canada to obtain a higher resolution quantitative p wave velocity model 2d waveform tomography was applied to seismic reflection data from the queen charlotte sedimentary basin off the west coast of canada the forward modeling and inversion were implemented in the frequency domain using the visco acoustic wave equation field data preconditioning consisted of f k filtering 2d amplitude scaling shot to shot amplitude balancing and time windowing the field data were inverted between 7 and 13 66 hz with attenuation introduced for frequencies 10 5 hz to improve the final velocity model two different approaches to sampling the frequencies were evaluated the limited maximum offset of the marine data 3770 m and the relatively high starting frequency 7 hz were the main challenges encountered during the inversion an inversion strategy that successively recovered shallow to deep structures was designed to mitigate these issues the inclusion of later arrivals in the waveform tomography resulted in a veloci

the south tibetan detachment system facilitates ultra rapid cooling of granulite facies rocks in sikkim himalaya 1 the eastern himalaya is characterized by a region of granulites and local granulitized eclogites that have been exhumed via isothermal decompression from lower crustal depths during the india asia collision spatially most of these regions are proximal to the south tibetan detachment system an orogen parallel normal sense detachment system that operated during the miocene suggesting that it played a role in their exhumation here we use geo and thermochronological methods to study the deformation and cooling history of footwall rocks of the south tibetan detachment system in northern sikkim india these data demonstrate that the south tibetan detachment system was active in sikkim between 23 6 and 13 ma and that footwall rocks cooled rapidly from 700 to 120 c between 15 13 ma while active the south tibetan detachment system exhumed rocks from mid crustal depths but an additional heat source such as strain heating advected melt and or crustal thinning is required to explain the observed isothermal decompression cessation of movement on the south tibetan detachment system produced rapid cooling of the footwall as isotherms relaxed a regional comparison of temperature time data for the eastern south tibetan detachment system indicates a lack of synchronicity between the sa er sikkim yadong section and the nw bhutan section to accommodate this requires either strike slip tear faulting or local out of sequence thrusting in the younger segment of the orogen

multiscale imaging of complex structures from multifold wide aperture seismic data by frequency domain full waveform tomography application to a thrust belt summary an application of full waveform tomography to dense onshore wide aperture seismic data recorded in a complex geological setting thrust belt is presented the waveform modelling and tomography are implemented in the frequency domain the modelling part is solved with a finite difference method applied to the visco acoustic wave equation the inversion is based on a local gradient method only the p wave velocity is involved in the inversion the inversion is applied iteratively to discrete frequency components by proceeding from low to high frequencies this defines a multiscale imaging in the sense that high wavenumbers are progressively incorporated in images the linearized waveform tomography requires an accurate starting velocity model that has been developed by first arrival traveltime tomography after specific pre processing of the data 16 frequency components ranging between 5 4 and 20 hz were inverted ten iterations were computed per frequency component leading to 160 tomographic models the waveform tomography has successfully imaged southwest dipping structures previously identified from other geophysical data as being associated with high resistivity bodies the relevance of the tomographic images is locally demonstrated by comparison of a velocity depth function extracted from the waveform tomography models with a coincident vertical seismic profiling vsp log available on the profile moreover comparison between observed and synthetic seismograms computed in the starting traveltime and waveform tomography models demonstrates unambiguously that the waveform tomography successfully predicts for wide angle reflections from southwest dipping geological structures this study demonstrates that the combination of first arrival traveltime and frequency domain full waveform tomographies applied to dense wide aperture seismic data is a promising approach to quantitative imaging of complex geological structures indeed wide aperture acquisition geometries offer the opportunity to develop an accurate background velocity model for the subsequent waveform tomography this is critical because the building of the macromodel remains an open question when only near vertical reflection data are considered

probing the depths of the india asia collision u th pb monazite chronology of granulites from nw bhutan 1 rocks metamorphosed to high temperatures and or high pressures are rare across the himalayan orogen where peak metamorphic conditions recorded in the exposed metamorphic core the greater himalayan sequence ghs are generally at middle to upper amphibolite facies however mafic garnet clinopyroxene assemblages exposed at the highest structural levels in bhutan eastern himalaya preserve patchy textural evidence for early eclogite facies conditions overprinted by granulite facies conditions monazite hosted within the leucosome of neighboring granulite facies orthopyroxene bearing felsic gneiss yields la mc icp ms u th pb ages of 13 9 0 3 ma monazite associated with sillimanite grade metamorphism in granulite hosting migmatitic gneisses yields u th pb rim ages between 15 4 0 8 ma and 13 4 0 5 ma monazite associated with sillimanite grade metamorphism in gneiss at structurally lower levels yields u pb rim ages of 21 17 ma these data are consistent with miocene exhumation of ghs material from a variety of crustal depths at different times along the himalayan orogen we propose that these granulitized eclogites represent lower crustal material exhumed by tectonic forcing over an incoming indian crustal ramp and that they formed in a different tectonic regime to the ultrahigh pressure eclogites in the western himalaya their formation and exhumation in the miocene therefore do not require diachroneity in the timing of the initial india asia collision

exhumation of the main central thrust from lower crustal depths eastern bhutan himalaya geothermometry and mineral assemblages show an increase of temperature structurally upwards across the main central thrust mct however peak metamorphic pressures are similar across the boundary and correspond to depths of 35 45 km garnet bearing samples from the uppermost lesser himalayan sequence lhs yield metamorphic conditions of 650 675 c and 9 13 kbar staurolite kyanite schists about 30 m above the mct yield p t conditions near 650 c 8 10 kbar kyanite bearing migmatites from the greater himalayan sequence ghs yield pressures of 10 14 kbar at 750 800 c top to the south shearing is synchronous with and postdates peak metamorphic mineral growth metamorphic monazite from a deformed and metamorphosed proterozoic gneiss within the upper lhs yield u pb ages of 20 18 ma staurolite kyanite schists within the ghs a few metres above the mct yield monazite ages of c 22 1 ma we interpret these ages to reflect that prograde meta morphism and deformation within the main central thrust zone mctz was underway by c 23 ma u pb crystallization ages of monazite and xenotime in a deformed kyanite bearing leucogranite and kyanite garnet migmatites about 2 km above the mct suggest crystallization of partial melts at 18 16 ma higher in the hanging wall south verging shear bands filled with leucogranite and pegmatite yield u pb crystallization ages for monazite and xenotime of 14 15 ma and a 1 2 km thick leuco granite sill is 13 4 0 2 ma thus metamorphism plutonism and deformation within the ghs con tinued until at least 13 ma p t conditions at this time are estimated to be 500 600 c and near 5 kbar from these data we infer that the exhumation of the mct zone from 35 to 45 km to around 18 km occurred from 18 to 16 to c 13 ma yielding an average exhumation rate of 3 9 mm year 1 this process of exhumation may reflect the ductile extrusion by channel flow of the mctz from between the overlying tibetan plateau and the underthrusting indian plate coupled with rapid erosion

a short duration pulse of ductile normal shear on the outer south tibetan detachment in bhutan alternating channel flow and critical taper mechanics of the eastern himalaya in easternmost bhutan the south tibetan detachment std is a ductile shear zone that juxtaposes the radi or sakteng klippe of the tethyan sedimentary series from underlying high grade greater himalayan rocks in situ la icpms u th pb analysis of metamorphic monazite from the immediate footwall and hanging wall of the std within the shear zone at the base of the klippe constrains north vergent normal shear to between 25 and 20 ma coeval thrusting on the main central thrust during this time supports a phase of channel flow viscous wedge model activity lasting only ca 3 ma geochronologic data from the eastern himalaya indicate alternating mechanisms for extrusion of the metamorphic core of the orogen from the late oligocene through to the late miocene switching from channel flow viscous wedge behavior to critical taper frictional wedge behavior each phase lasting approximately only 2 to 5 ma the tectonic evolution of the eastern himalaya is comparable to central and western himalayan tectonics during the early miocene but during the middle miocene metamorphism and magmatism in the eastern himalaya migrated towards the orogenic hinterland a process not widely documented elsewhere in the himalaya thus highlighting the need for an orogenic model in three spatial dimensions

earth model building from shallow to deep with full waveform inversion full waveform inversion fwi is a high resolution model building technique that uses the entire recorded seismic data content to build the earth model conventional fwi usually utilizes diving and refracted waves to update the low wavenumber background components of the model however the update is often depth limited due to the limited offset range acquired to extend conventional fwi beyond the limits of the transmitted energy we must use reflection data synthetic and field data examples demonstrate that even in a complex subsalt gulf of mexico setting the background velocity model can be updated from shallow to deep water using conventional fwi followed by reflection based fwi a future refinement of the technique shows that after updating the sediment model the salt boundaries can be further updated by level set technology

seismic attenuation tomography using the frequency shift method we present a method for estimating seismic attenuation based on frequency shift data in most natural materials seismic attenuation increases with frequency the high frequency components of the seismic signal are attenuated more rapidly than the low frequency components as waves propagate as a result the centroid of the signal s spectrum experiences a downshift during propagation under the assumption of a frequency independent q model this downshift is proportional to a path integral through the attenuation distribution and can be used as observed data to reconstruct the attenuation distribution tomographically the frequency shift method is applicable in any seismic survey geometry where the signal bandwidth is broad enough and the attenuation is high enough to cause noticeable losses of high frequencies during propagation in comparison to some other methods of estimating attenuation our frequency shift method is relatively insensitive to geometric spreading reflection and transmission effects source and receiver coupling and radiation patterns and instrument responses tests of crosswell attenuation tomography on 1 d and 2 d geological structures are presented

imaging high resolution seismic velocity from walkaway vertical seismic profile data in a carbonate reservoir using acoustic waveform tomography abstracthigh resolution seismic velocity was obtained using acoustic full waveform tomography of walkaway vertical seismic profile vsp data from an oil field dominated by carbonate rocks offshore abu dhabi in the united arab emirates the data were collected in a deviated borehole with receivers located from 521 to 2742 m depth the inversion was performed in the frequency domain the success of the inversion was determined by three important factors the starting model the preconditioning of the input data and the inversion strategy which included an appropriate selection of a damping term in the laplace fourier transformation the inversion was performed between the frequencies of 4 and 50 hz and a logarithmic data residual was used the extracted 1d velocity profiles from the final high resolution velocity model correlate well with the sonic log and estimated vertical incidence vsp velocities the predicted data obtained by the final velocity model indicate a generally good fit with the field

three dimensional seismic refraction tomography a comparison of two methods applied to data from the faeroe basin this paper presents a comparison of two tomographic methods for determining three dimensional 3 d velocity structure from first arrival travel time data the first method is backprojection in which travel time residuals are distributed along their ray paths independently of all other rays the second method is regularized inversion in which a combination of data misfit and model roughness is minimized to provide the smoothest model appropriate for the data errors both methods are nonlinear in that a starting model is required and new ray paths are calculated at each iteration travel times are calculated using an efficient implementation of an existing method for solving the eikonal equation by finite differencing both inverse methods are applied to 3 d ocean bottom seismometer obs data collected in 1993 over the faeroe basin consisting of 53 479 travel times recorded at 29 obss this is one of the most densely spaced large scale 3 d seismic refraction experiments to date different starting models and values for the free parameters of each tomographic method are tested a new form of backprojection that converges more rapidly than similar methods compares favorably with regularized inversion but the latter method provides a simpler model for little additional computational expense when applied to the faeroe basin data bounds on two model features are assessed using regularized inversion with combined smoothness and flatness constraints an inversion of synthetic data corresponding to 100 data recovery from the real experiment shows a marked improvement in lateral resolution at deeper depths and demonstrates the potential of currently feasible 3 d refraction experiments to provide well resolved long wavelength velocity models the similarity of the final models derived from the two tomographic methods suggests that the results from the new form of backprojection can be relied on when limited computational resources rule out regularized inversion

comparison of waveform inversion part 1 conventional wavefield vs logarithmic wavefield this is the first in a series of three papers focused on using variants of a logarithmic objective function approach to full waveform inversion in this article we investigate waveform inversion using full logarithmic principles and compare the results with the conventional least squares approach we demonstrate theoretically that logarithmic inversion is computational similar to the conventional method in the sense that it uses exactly the same back propagation technology as used in least squares inversion in the sense that it produces better results for each of three numerical examples we conclude that logarithmic inversion is also more robust we argue that a major reason for the inherent robustness is the fact that the logarithmic approach produces a natural scaling of the amplitude of the residual wavefield by the amplitude of the modelled wavefield that tends to stabilize the computations and consequently improve the final result we claim that any superiority of the logarithmic inversion is based on the fact that it tends to be tomographic in the early stage of the inversion and more dependent on amplitude differences in the latter stages

geneses and evolutions of iron bearing minerals in banded iron formations of 3760 to ca 2200 million year old constraints from electron microscopic x ray diffraction and mossbauer spectroscopic investigations abstract minerals preserved in banded iron formations bifs are diagenetic and or metamorphic rather than primary knowing their geneses and evolutions are essential for understanding the interactions between the atmosphere ocean and biosphere in the first two billion years of life history on earth here we use high resolution electron microscopy x ray diffraction and mossbauer spectroscopy to investigate the mineralogy of six bifs aged from 3760 ma to ca 2200 ma with a variety of genetic conditions the results reveal that each major iron mineral magnetite hematite carbonate and silicate has a range of structural and morphological features that represent different geneses and evolutionary histories euhedral magnetite crystals with homogeneous internal structures and compositions 3 5 nm hematite particles aggregated in iron rich bands and submicrometer sized euhedral hematite in chert matrix of fe si transitional bands are identified to have transformed from precursors directly precipitated from seawaters these minerals retain some primary environmental information when bifs are deposited the other mineral phases display features of alteration due to multi redox reactions hydrothermal or supergene processes such as crosscutting mineral replacement or overgrowth deformation fracture and porous structures that have overprinted the primary signatures such minerals include 1 massive magnetite with fragmentation structures 2 partly to completely oxidized magnetite crystals 3 acicular fibrous hematite in fractures or iron and silica layering 4 microplaty hematite 5 hematite oxidized from other fe ii bearing minerals e g magnetite and stilpnomelane 6 carbonates with heterogeneous chemical compositions 7 carbonates replacing other minerals e g siderite thin film coating the euhedral magnetite crystals 8 irregular carbonate cementing other minerals e g magnetite 9 preferentially orientated fibrous spindle like silicates cutting iron and silica rich bands and 10 massive silicate pieces this study provides detailed mineralogical and petrologic characterizations of bif minerals that can serve as a reference for future in situ geochemical measurements by recent developed techniques

waveform tomography at a groundwater contamination site surface reflection data wehaveappliedacoustic waveformtomographyto452d seismic profiles to image the 3d geometry of a buried paleochannel at a groundwater contamination site at hill air force base in utah the paleochannel which is incised into an alluvium covered clay aquitard acts as a trap for dense nonaqueous phase liquids dnapls that contaminate the shallowest groundwater system in the study area the 2d profiles were extracted from a 3d surface reflection data set first arrival traveltime tomography provided initial velocity models for the waveform tomography we inverted for six frequency components in the band 30 90 hz of the direct and refracted waves to produce 45 2d velocity models the flanks and bottom of a channel with a maximum depth of about 15 m were well modeled in most of the 45 parallel 2d slices whichallowedustoconstructa3dimageofthechannel by combining and interpolating between the 45 image slices the 3d model of the channel will be useful for siting extraction wells within the site remediation program the alluvium that fills the channel showed marked vertical and lateral velocity heterogeneity traveltime tomography and waveform tomography can be complementary approaches used together they can provide high resolution images of complicatedshallowstructures

variable shortening rates in the eastern himalayan thrust belt bhutan insights from multiple thermochronologic and geochronologic data sets tied to kinematic reconstructions 1 we present data on the burial displacement and exhumation history of the himalayan fold thrust belt in eastern bhutan these data document the magnitude and timing of displacement of large discrete structures and highlight temporal variability in shortening rates eight new40ar 39ar ages from white mica 32 new zircon u th he ages 7 new apatite fission track ages and 1 new u pb zircon la mc icp ms metamorphic rim growth age are combined with published cooling ages and deformation temperatures and incremental shortening magnitudes from restorations of two published balanced cross sections to illustrate the kinematic and temporal development of the bhutan thrust belt integrating these data from 23 ma to the present illustrates rapid horizontal shortening rates 28 35 mm yr between 23 20 ma and 15 10 ma separated by more moderate rates 10 23 mm yr shortening rates decrease significantly to 7 10 mm yr and possibly as low as 3 4 mm yr from 10 to 0 ma this decrease is interpreted to represent the onset of strain partitioning in the eastern part of the himalayan tibetan orogenic system between shortening in the bhutan thrust belt uplift of the shillong plateau and deformation and outward growth of the northern and eastern tibetan plateau within estimated error horizontal shortening rates during emplacement of the main central thrust sheet and during construction of the upper lesser himalayan duplex approached india asia tectonic velocities thus for periods of time between 23 20 ma and 15 10 ma the bhutan thrust belt may have absorbed nearly all india asian convergence at this longitude

extrusion vs duplexing models of himalayan mountain building 1 discovery of the pabbar thrust confirms duplex dominated growth of the northwestern indian himalaya since mid miocene ongoing himalayan growth is generally thought to be dominated by duplexing and or extrusion processes these models may be tested by reconstructing himalayan fold thrust belt growth since the middle miocene however our knowledge of basic structural geometry remains too fragmentary to resolve the issue even in areas with rich stratigraphic diversity such as the northwestern indian himalaya in this region a primary outstanding question involves the uncertain relationship of the berinag thrust and the tons thrust structures with displacements of 80 km and 40 km respectively the uncertain geometry and kinematics allow for the complete range of duplexing or extrusion processes for the integrated kinematic history since the middle miocene to address this issue field mapping and kinematic analysis were performed to reconstruct the deformation of the lesser himalayan sequence in the northwest indian himalaya our results reveal a new discovery a 450 m thick top to southwest shear zone termed the pabbar thrust the pabbar thrust placed the outer lesser himalayan sequence the tons thrust hanging wall directly on the berinag group the berinag thrust hanging wall this discovery requires that the berinag thrust and tons thrust are in fact the same structure and discrete duplexing processes dominated growth of the northwest indian himalaya for the past 10 15 million years along strike extension of these kinematics and corresponding geometries is consistent with the observed orogenic framework and resolves a stratigraphic continuity problem across the india west nepal border where prior work suggests that structures are continuous but stratigraphy does not match

misfit functionals in laplace fourier domain waveform inversion with application to wide angle ocean bottom seismograph data in seismic waveform inversion non linearity and non uniqueness require appropriate strategies we formulate four types of l2 normed misfit functionals for laplace fourier domain waveform inversion i subtraction of complex valued observed data from complex valued predicted data the conventional phase amplitude residual ii a conventional phase only residual in which amplitude variations are normalized iii a logarithmic phase amplitude residual and finally iv a logarithmic phase only residual in which the only imaginary part of the logarithmic residual is used we evaluate these misfit functionals by using a wide angle field ocean bottom seismograph obs data set with a maximum offset of 55 km the conventional phase amplitude approach is restricted in illumination and delineates only shallow velocity structures in contrast the other three misfit functionals retrieve detailed velocity structures with clear lithological boundaries down to the deeper part of the model we also test the performance of additional phase amplitude inversions starting from the logarithmic phase only inversion result the resulting velocity updates are prominent only in the high wavenumber components sharpening the lithological boundaries we argue that the discrepancies in the behaviours of the misfit functionals are primarily caused by the sensitivities of the model gradient to strong amplitude variations in the data as the observed data amplitudes are dominated by the near offset traces the conventional phase amplitude inversion primarily updates the shallow structures as a result in contrast the other three misfit functionals eliminate the strong dependence on amplitude variation naturally and enhance the depth of illumination we further suggest that the phase only inversions are sufficient to obtain robust and reliable velocity structures and the amplitude information is of secondary importance in constraining subsurface velocity models

relationships among compressional wave attenuation porosity clay content and permeability in sandstones anelastic attenuation is the process by which rocks convert compressional waves into heat and thereby modify the amplitude and phase of the waves understanding the causes of compressional wave attenuation is important in the acquisition processing and interpretation of high resolution seismic data and in deducing the physical properties of rocks from seismic data we have measured the attenuation coefficients of compressional waves in 42 sandstones at a confining pressure of 40 mpa equivalent to a depth of burial of about 1 5 km in a frequency range from 0 5 to 1 5 mhz the compressional wave measurements were made using a pulse echo method in which the sample 5 cm diameter 1 8 cm to 3 5 cm long was sandwiched between perspex lucite buffer rods inside the high pressure rig the attenuation of the sample was estimated from the logarithmic spectral ratio of the signals corrected for beam spreading reflected from the top and base of the sample the results show that for these samples compressio

full waveform tomography for lithospheric imaging results from a blind test in a realistic crustal model summary a comprehensive validation of 2 d frequency domain acoustic wave equation tomography was undertaken in a blind test using third party realistic elastic wave equation data the synthetic 2 d wide angle seismic data were provided prior to a recent workshop on the methods of controlled source seismology the true model was not revealed to the authors until after the presentation of our waveform tomography results the original model was specified on a detailed grid with variable p wave velocity s wave velocity density and viscoelastic q factor structure designed to simulate a section of continental crust 250 km long and 40 km deep synthetic vertical and horizontal component data were available for 51 shot locations spaced every 5 km recorded at 2779 receivers spaced every 90 m evenly spread along the surface of the model the data contained energy from 0 2 to 15 hz waveform tomography a combination of traveltime tomography and 2 d waveform inversion of the early arrivals of the seismic waveforms was used to recover crustal p velocity structure from the vertical component data using data from 51 sources 1390 receivers and frequencies between 0 8 and 7 0 hz the waveform tomography result contained apparent structure at wavelength scale resolution that was not evident on the traveltime tomography result the predicted acoustic waveforms in the final result matched the original elastic data to a high degree of accuracy during the workshop the exact model was revealed over much of the model the waveform tomography results provided a good correspondence with the true model from large to intermediate wavelength scales with a resolution limit on the order of 1 km a significant near surface low velocity zone invisible to traveltime methods was correctly recovered the results also provided a high resolution image of the complex structure of the entire crust and the depth and nature of the crust mantle transition some inaccuracies were observed near the edges of the images due to the limited ray coverage inherent to the footprint of the survey geometry several aspects of the waveform tomography strategy were critical to the success of the acoustic method with realistic synthetic viscoelastic data i the accuracy of the starting model from traveltime tomography ii implementation in the frequency domain iii the use of complex valued frequencies to effect time damping of the data residuals iv the selection of a suitable subset of data and data frequencies v progressive inversion of low to high frequency components of the data vi initial pre inversion matching of the amplitudes between observed and modelled data and vii sufficient preconditioning of both the data and the update images combined these strategies were effectively equivalent to a multiscale approach that mitigated the non linearity of the seismic inverse problem during the inversion we carried out repeated forward modelling to ensure our modelled waveforms matched the observed data as closely as possible in both frequency and time domains the synthetic data set used in this paper provides a benchmark for future testing of modelling inversion and imaging algorithms for wide angle lithospheric imaging

on acoustic waveform tomography of wide angle obs data strategies for pre conditioning and inversion we successfully apply the acoustic laplace fourier waveform tomography method to delineate p wave velocity structures of the mega splay fault system in the central part of the seismogenic nankai subduction zone offshore japan using densely sampled wide angle ocean bottom seismograph obs data originally acquired in 2004 our success is due to new and carefully designed data preconditioning and inversion strategies to mitigate i the well known non linearity of waveform inversion ii the challenges arising from crustal scale survey designs e g undersampling of the obss and iii modelling errors due to the use of the acoustic assumption we identify a sixfold set of key components that together lead to the success of the high resolution waveform tomography image i availability of low frequency components starting at 2 25 hz reducing the non linearity and access to large offset data up to 55 km increasing the depth of illumination and the recovery of low wavenumber components ii a highly accurate traveltime tomography result with an rms error of approximately 60 ms that further mitigates the non linearity iii a hierarchical inversion approach in which phase spectra are inverted first to reduce artefacts from the acoustic assumption and amplitude information is only incorporated in the final stages iv a laplace fourier domain approach that facilitates a multiscale approach to mitigate non linearity by restricting the inversion to the low frequency components and early arrivals first and sequentially including higher frequencies and later arrivals v a pre conditioning strategy for eliminating undesirable high wavenumber components from the the gradient vi a strategy for source estimation that reduce the influence of the instrumental design in the obs case study used for illustration purposes laplace fourier waveform tomography retrieves velocity anomalies as small as 700 m horizontally and 350 m vertically above the top of the philippine sea plate the resulting velocity structures include low velocity zones and thrust structures which have not been previously identified clearly the velocity models are validated by scrutiny of synthetic and observed waveforms by evaluating the coherency of source estimates and by comparison with 3 d pre stack migrated presdm images chequerboard tests and point scatter tests demonstrate both the reliability and the limitations of the acoustic implementation

crosshole seismic waveform tomography i strategy for real data application summary the frequency domain version of waveform tomography enables the use of distinct frequency components to adequately reconstruct the subsurface velocity field and thereby dramatically reduces the input data quantity required for the inversion process it makes waveform tomography a computationally tractable problem for production uses but its applicability to real seismic data particularly in the petroleum exploration and development scale needs to be examined as real data are often band limited with missing low frequencies a good starting model is necessary for waveform tomography to fill in the gap of low frequencies before the inversion of available frequencies in the inversion stage a group of frequencies should be used simultaneously at each iteration to suppress the effect of data noise in the frequency domain meanwhile a smoothness constraint on the model must be used in the inversion to cope the effect of data noise the effect of non linearity of the problem and the effect of strong sensitivities of short wavelength model variations in this paper we use frequency domain waveform tomography to provide quantitative velocity images of a crosshole target between boreholes 300 m apart due to the complexity of the local geology the velocity variations were extreme between 3000 and 5500 m s 1 making the inversion problem highly non linear nevertheless the waveform tomography results correlate well with borehole logs and provide realistic geological information that can be tracked between the boreholes with confidence

reflection seismic waveform tomography 1 in seismic waveform tomography if using reflection data with limited source receiver offsets it is difficult to reconstruct the deep part of the subsurface velocity model we present two approaches to tackle this problem layer stripping and weighted updating in a layer stripping procedure we replace the top portion of seismic data with synthetics generated from the previous layer inversion and make the current inversion focus on the minimization of the data misfit corresponding to the deep part of the model to improve efficiency we use only sparsely sampled frequency data in the deeper layer inversions unlike the first layer inversion where we use densely sampled frequency data as usual the sparsely sampled frequencies together have the full wave number coverage for effective imaging combined use of dense and sparse sampling in frequency is a compromise between resolution and efficiency as it reduces the number of iterations needed in layer stripping inversion while still producing a good image in the second scheme we apply depth dependent weights to model updates in order to improve the convergence in an iterative solution the weighting is inversely proportional to the ray density variation along the depth and is mathematically equivalent to the application of an inverse hessian matrix which sharpens the gradient vector for model updating for real seismic data we transfer point source shot records to line source records by partial amplitude compensation and phase adjusting before inputting it to the waveform tomography we perform traveltime inversion to generate a reliable layered velocity model and then waveform tomography to produce a high resolution image of the subsurface model through frequency domain iteration