the deep water fold and thrust belt offshore nw borneo gravity driven versus basement driven shortening the deep water region offshore nw borneo is an active fold and thrust belt that hosts a signifi cant number of proven hydrocarbon accumulations in the past two mechanisms have been discussed as primary control for neogene to holocene folding and thrusting in this deep water province 1 basement driven crustal shortening and 2 gravity related delta tectonics in this study new balanced interpretations of regional crustal scale depth migrated twodimensional 2 d multichannel seismicrefl ection profi les are presented that provide for the fi rst time quantitative data on tectonic shortening throughout the entire deep water fold and thrust belt of nw borneo we use our tectonic restorations to compare the amount of deep water shortening on the nw borneo slope to the amount of extension across the nw borneo shelf a key result of this balancing study is the observation that pliocene to holocene gravity driven shortening decreases from south to north while the total amount of shortening increases slightly to the north consequently the amount of purely basement driven compression along nw borneo is strongly inferred to increase toward the north because most of the shortening is late pliocene and younger we interpret the tectonic shortening to be ongoing

seismic anisotropy in the crystalline upper crust observations and modelling from the outokumpu scientific borehole finland summary seismic velocity anisotropy measurements are made of a fractured metamorphic formation from the 2 5 km deep international continental scientific drilling programme icdp borehole in outokumpu finland three component walk away vertical seismic profile vsp measurements are made along two source line azimuths at three receiver depths 1000 1750 and 2500 m and incidence angle dependent qp and qs wave velocities are extracted with a p method the highest qp wave anisotropy 13 6 per cent vfast 6160 m s 1 vslow 5370 m s 1 is measured between 1000 and 1750 m depth with anisotropy of up to 9 4 per cent vfast 6090 m s 1 vslow 5540 m s 1 measured between 1750 and 2500 m depth the top 1300 m of the region is composed of a homogeneous strongly intrinsically anisotropic biotite rich schist and is sampled by the shallowest walk away profile anisotropy of up to 11 1 per cent vfast 5950 m s 1 vslow 5320 m s 1 is measured by the walk away vsp between 50 and 1000 m depth along with shear wave splitting averaging 5 per cent 180 m s 1 laboratory derived intrinsic anisotropy of the schist cannot by itself explain the degree or orientation of the anisotropy measured in the walk away vsps however a model which modifies the intrinsic stiffnesses by the inclusion of a single set of dipping aligned cracks allows the observed in situ velocities to be reproduced forward modelling of the qp wave walk away vsp measurements from 50 to 1000 m depth is undertaken using an effective medium model to develop a 3 d velocity model of this region an orthorhombic medium is used to represent the intrinsic anisotropy of the biotite rich schist and a single set of aligned cracks is added to give a bulk elastic stiffness the resulting model predicts the schist to have an overall anisotropy of 16 8 per cent with qp wave velocities of up to 6315 m s 1 the accuracy of the model is assessed through its fit to the walk away vsp measurements as well as a comparison to known geology of the region

differential fault related early miocene sedimentation bayou hebert area southwestern louisiana well logs from the bayou hebert area in southwestern louisiana show that most of the differential sedimentation associated with one zone of contemporaneous faults cannot be attributed to simple expansion rather the lower miocene sequence on the downthrown side of the fault zone has grown principally by the episodic deposition of sedimentary units that have no correlative counterparts on the upthrown side such units range up to about 2 000 ft 600 m thick near faults and most are laterally discontinuous over distances of several kilometers the isolated downthrown intervals lie in different parts of the sequence at various places along the strike of the fault zone indicating lateral and temporal variation in subsidence rates in the downthrown block the intervals may represent times of erosion or sediment bypass updip of faults isolation of thick intervals on the downthrown block adds potential for unexpected reservoir units and may enhance the development of combination traps associated with contemporaneous faulting and deposition characteristic of growth faults overlapping of the tapered edges of multiple laterally adjacent intervals may also create potential for small flexural structures in the areas of overlap

stratigraphic development of synkinematic deposits in a large growth fault system onshore brunei darussalam kilometre scale synsedimentary faults associated with well preserved sedimentary successions on both hanging wall and footwall sides are rarely seen in outcrop however one such example is found in a middle miocene deltaic sand shale sequence exposed along the jerudong anticline in onshore brunei darussalam integration of detailed outcrop information with regional geophysical subsurface data documents that 1 initiation of the jalan tutong growth fault was related to delta front instability and failure 2 sediment loading under shallow marine conditions maintained syndepositional faulting 3 growth fault abandonment coincided with a significant basinward shift of deposition and subaerial exposure high resolution analysis of facies characteristics stratal expansion and throw development within the studied growth sequence indicates that differential fault movement strongly influenced facies composition sedimentary geometry and bedding characteristics sandstone poor shelf to lower shoreface successions developed during periods of rapidly increasing fault movement whereas sandstone rich amalgamated upper shoreface deposits preferentially formed during intervals of constant or decreasing throw development the data and interpretations presented may help to focus attention on the complex interplay between tectonics and sedimentation associated with the growth and decay of deltaic faults by providing for the first time an outcrop based view on a feature documented in similar scale only by geophysical subsurface data

3d seismic study of a shale expulsion syncline at the base of the champion delta offshore brunei and its implications for the early structural evolution of large delta systems an example of a late miocene expulsion rollover syncline related to mobile shale is described from 3d seismic data offshore brunei prodelta shales accumulated in the subsiding syncline were altered after deep burial by overpressure increase and hydraulic fracturing consequently seismic facies was modified from a continuous divergent reflection pattern to a low amplitude disrupted to chaotic seismic facies bounded by a high amplitude event that cross cuts original stratification without the resolution provided by 3d data the high amplitude event would be mistaken for early growth faults and the subdued country rock reflections for mobile shale typical features at the base of large deltas this study shows the existence of expulsion rollovers related to mobile shale which have not been described before and demonstrates that not all bright reflections at chaotic coherent facies boundaries are actually fault planes it also suggests that expulsion synclines even during early phases of delta development may be compaction related features rather than ones that drive the shale mass out of the area of progradation

anisotropy of schists contribution of crustal anisotropy to active source seismic experiments and shear wave splitting observations we have made sets of five independent compressional and shear wave velocity measurements which with density allow us to completely characterize the transverse isotropy of samples from five metamorphic belts the haast schist terrane south island new zealand poultney slate chugach phyllite coldfoot schist and pelona schist united states these velocity measurements include compressional wave velocities for propagation parallel perpendicular and at 45 to the symmetry axis shear wave velocity for propagation and particle motion perpendicular to the symmetry axis and shear wave velocity for propagation parallel to the symmetry axis velocity measurements were made up to pressures of 1 gpa 35 km depth where microcracks are closed and anisotropy is due to preferred mineral orientation our samples exhibit compressional wave anisotropy of 9 20 as well as significant shear wave splitting metamorphic terranes that are anisotropic to ultrasonic waves may also be anisotropic at the scale of active and passive seismic experiments our data suggest that a significant thickness 10 20 km of appropriately oriented steeply dipping foliation schist in the crust could contribute as much as 45 of observed shear wave splitting our data set can also be used to model the effects of crustal anisotropy for active source seismic experiments in order to determine if the anisotropy of the terrane is significant and needs to be taken into account during processing and modeling of the data

shear wave splitting and subcontinental mantle deformation splitting observations are interpreted in terms of the strain induced lattice preferred orientation of mantle minerals especially olivine we consider three hypotheses concerning the origin of the continental anlsotropy 1 strain associated with absolute plate motion as in the oceanic upper mantle 2 crustal stress and 3 the past and present internal deformation of the subcontinental upper mantle by tectonic episodes it is found that the last hypothesis is the most successful namely that the most recent significant episode of internal deformation appears to be the best predictor of q for stable continental regions this is interpreted as fossil anisotropy whereas for presently active regions such as alaska the anisotropy reflects present day tectonic activity in the stable portion of north america there is a good correlation between delay time and lithospheric thickness this is consistent with the anisotropy being localized in the subcontinental lithosphere and suggests that intrinsic anisotropy is approximately constant the acceptance of this hypothesis has several implications for subcontinental mantle deformation first it argues for coherent deformation of the continental lithosphere crust and mantle during orogenies this implies that the anisotropic portion of the lithosphere was present since the deformational episode and rules out the addition of undeformed material to this layer by subsequent underplating or conductive growth of the thermal boundary layer one of the most important issues in the study of orogenies is the need to reconcile the formation of thickened lithosphere with the paradoxically high mantle temperatures often associated with orogenic episodes most efforts to date have focussed on modes of deformation whereby the cold lithospheric mantle is removed by convective instability or delamination and replaced by warm asthenosphere these models however are incompatible with the evidence for preserved coherent lithospheric deformation rather the deformed mantle appears to have been heated in place we suggest that the elevated mantle temperatures may be due to the strain heating accompanying the deformation

a simple method of determining sand shale ratios from seismic analysis of growth faults an example from upper oligocene to lower miocene niger delta deposits a plot of fault throw vs depth is a simple geometric tool that graphically represents strata thickness variations in growth fault and growth fold settings and has previously been used to infer fault kinematics in this paper we use it as a prediction tool for lithological change employing only seismic data if growth faulting is a continuous process intervals of shale deposition are recorded by unthickened units while intervals of sand fill in topographic lows the throw vs depth plot easily allows depiction of unthickened and thickened sedimentary intervals from even rough seismic records and can therefore be used to predict sand shale ratios the method is here applied to a growth fault in the niger delta that affects oligocene to lower miocene deltaic deposits most shale intervals are identified and the sand shale ratios are predicted we suggest that the method can be a valuable tool in oil exploration

3d seismic analysis of gravity driven and basement influenced normal fault growth in the deepwater otway basin australia abstract we use three dimensional 3d seismic reflection data to analyse the structural style and growth of a normal fault array located at the present day shelf edge break and into the deepwater province of the otway basin southern australia the otway basin is a late jurassic to cenozoic rift to passive margin basin the seismic reflection data images a nw se 128 308 striking normal fault array located within upper cretaceous clastic sediments and which consists of ten fault segments the fault array contains two hard linked fault assemblages separated by only 2 km in the dip direction the gravity driven down dip fault assemblage is entirely contained within the 3d seismic survey is located over a basement plateau and displays growth commencing and terminating during the campanian maastrichtian with up to 1 45 km of accumulated throw vertical displacement the up dip normal fault assemblage penetrates deeper than the base of the seismic survey but is interpreted to be partially linked along strike at depth to major basement involved normal faults that can be observed on regional 2d seismic lines this fault assemblage displays growth initiating in the turonian santonian and has accumulated up to 1 74 km of throw our detailed analysis of the 3d seismic data constraints post cenomanian fault growth of both fault assemblages into four evolutionary stages 1 turonian santonian basement reactivation during crustal extension between australia and antarctica this either caused the upward propagation of basement involved normal faults or the nucleation of a vertically isolated normal fault array in shallow cover sediments directly above the reactivated basement involved faults 2 continued campanian maastrichtian crustal extension and sediment loading eventually created gravitational instability on the basement plateau nucleating a second vertically isolated normal fault array in the cover sediments 3 eventual hard linkage of fault segments in both fault arrays to form two along strike nw se striking fault assemblages and 4 termination of fault growth in the latest maastrichtian we document high variability of throw along strike and down dip for both fault assemblages thereby providing evidence for lateral and vertical segment linkage our results highlight the complexities involved in the growth of both gravity driven normal fault arrays such as those present in the niger delta and gulf of mexico and basement linked normal fault arrays such as those present in the north sea and suez rift with the interaction of an underlying and reactivating basement framework this study provides an excellent example of spatial variability in growth of two normal fault assemblages over relatively short spatial scales 2 km separation down dip

anisotropic reflection and transmission calculations with application to a crustal seismic survey from the east greenland shelf a three component refraction data set recorded over the east greenland shelf contained two anomalous shear wave arrivals the direct s phase emerged at the receiver as an apparent sh wave even though the airgun source was purely compressional we have concluded that this arrival is the result of anisotropy in the upper crust by employing a number of fairly simple techniques we were able to highlight a second delayed quasi shear arrival and interpret shear wave splitting modeling of the polarization amplitude and delay time of direct s suggested that the anisotropy is due to aligned subvertical fractures perpendicular to the local seafloor spreading direction the second shear arrival of interest is a p to s conversion from the moho pms the relative strength of this arrival suggests that the moho is a sharp transition in this region pms also contained a significant transverse component but attempts to identify shear wave splitting were inconclusive however modeling revealed that the transverse pms displacement may be due to anisotropy in the upper mantle alignment of olivine crystals with the spreading direction which causes the converted s reflection to have a significant sh transverse component an understanding of and ability to model anisotropic reflection and transmission effects are essential to these interpretations therefore we also outline an efficient method to obtain all of the reflection and transmission coefficients at boundaries between anisotropic media this has been incorporated into a new ray tracing package a trak based on asymptotic ray theory capable of modeling three dimensional inhomogeneous media separated by curved interfaces

tectonic evolution of the sanga sanga block mahakam delta kalimantan indonesia the sanga sanga block contains four large to giant hydrocarbon fields in mid to upper miocene deltaic sandstones of the mahakam delta eastern kalimantan indonesia these fields occur in the northeast trending mahakam fold belt which is characterized by long tight fault bounded anticlines and broad synclines and cored by overpressured shales onshore sections of the fold belt are strongly deformed uplifted and eroded whereas the eastern offshore sections are little deformed and buried by the progradational delta wedge section balancing of depth converted seismic lines together with scaled analog modeling was used to develop a new tectonic model of inverted delta growth faults for the evolution of the mahakam fold belt section balancing shows that the fault bounded anticlines of the sanga sanga block are formed by contractional reactivation of early delta top extensional growth faults the change from gravity driven extension to regional contraction occurred at around 14 ma anticlinal folds controlled local sedimentation patterns and influenced the distribution of the reservoir channel sands in the main hydrocarbon fields scaled analog models of progradational loading above a ductile substrate produced delta top extensional growth faults and depobelts together with delta toe fold thrust contraction inverted the extensional growth faults and depobelts producing tight fault bounded anticlines the results support the model of delta inversion and thus the most viable explanation for the geometric kinematic and mechanical evolution of the structures in the sanga sanga block the inverted delta model has applications to other hydrocarbon bearing deltas around borneo and in other contracted delta systems

thin skinned extensional tectonics on a salt detachment northern kwanza basin angola abstract thin skinned extension on a salt detachment of a style known as raft tectonics characterizes deformation of the late aptian to recent section in the northern kwanza basin angola large rafts and intervening grabens are interpreted to have developed as a result of gravity gliding increased dip and gravity spreading asymmetrical loading of a sedimentary wedge major raft movement occurred primarily from the middle tertiary but some deformation appears to have started as early as late cenomanian or early turonian times individual grabens measure up to 70 km in length 15 km in width and nearly 3 km in depth and show switching polarities in the sense of thickening of the tertiary sedimentary infill graben geometries were controlled by syndepositional extension and the local availability of salt from the data examined which includes both seismic and well data the grabens appear to become younger from east to west reflecting basinward progression of the deformation as the age relationships could be related to insufficient sampling of strata deposited in complex sedimentation patterns they may have no relevance to the timing of the deformation the diachronous deformation is therefore speculative extension in the northern kwanza basin is estimated at 60 the outermost raft is translated 55 km westwards in addition to the extensional structures compressional folds thrust faults and salt structures mark the toe of the gravity gliding and spreading system all of the rafts lie within the african portion of the aptian salt basin on rifted continental crust and they are generally unrelated to structures below the salt biostratigraphy and lithostratigraphy indicate that the grabens formed on the shelf and upper slope from the middle eocene associated compressional features developed near the slope rise the unusual expression of raft tectonics is attributed to a combination of 1 the presence of a salt layer 2 a stable basement configuration that allowed quiescent accumulation of the raft sequence and 3 an increase in basin dip and sediment supply

pore pressure stress coupling in brunei darussalam implications for shale injection shale dykes diapirs and mud volcanoes are common in the onshore and offshore regions of brunei darussalam outcrop examples show that shale has intruded along both faults and tensile fractures conventional models of over pressure induced brittle failure assume that pore pressure and total stresses are independent of one another however data worldwide and from brunei show that changes in pore pressure are coupled with changes in total minimum horizontal stress the pore pressure stress coupling ratio describes the rate of change of minimum horizontal stress magnitude with changing pore pressure minimum horizontal stress measurements for a major offshore field where undepleted pore pressures range from normal to highly overpressured show a pore pressure stress coupling ratio of 0 59 as a consequence of pore pressure stress coupling rocks can sustain a greater increase in pore pressure prior to failure than predicted by the prevailing values of pore pressure and stress pore pressure stress coupling may favour the formation of tensile fractures with increasing pore pressure rather than reactivation of pre existing faults anthropogenically induced tensile fracturing in offshore brunei supports this hypothesis

the influence of pre existing structure on the growth of syn sedimentary normal faults in a deltaic setting niger delta abstract three dimensional seismic reflection data from the western niger delta were used to investigate the segmentation and linkage of a syn sedimentary normal fault array and to estimate the influence of a pre existing normal fault on the geometry and growth of younger faults the nucleation growth and linkage of a regional seaward dipping deltaic fault system were analyzed on reflectivity time horizon slices and vertical seismic sections in the deep subsurface a master fault that consists of two segments northwestern nw and southeastern se grew through time into a single fault by lateral tip propagation reaching a final length of about 15 km after attaining this length displacement along the fault system developed non uniformly through time the analysis of the hanging wall sediments of the deep seated master fault shows two different processes of vertical linkage above the nw and se segment the se segment links vertically to several younger faults contemporaneously with displacement accumulation on the master fault in contrast fault linkage above the nw segment occurred only after an interval of master fault inactivity connecting the deep seated structure upwards to a single syn sedimentary normal fault the observed differences in fault development suggest that although multi segment deltaic faults form single fault systems after segment linkage individual pre linkage characteristics can be preserved supporting a possibly diverse upward growth and connection to younger faults in the overburden the geological interpretations presented highlight the influence of large deep rooted structures on the development location and geometry of shallow deltaic faults documenting the influence of an older structural grain on delta tectonics

estimation of elastic stiffness coefficients of an orthorhombic physical model using group velocity analysis on transmission data abstractwe acquired 3c ultrasonic transmission seismograms measured group velocities associated with the three quasi body wave types and determined density normalized stiffness coefficients aij cij over an orthorhombic physical laboratory model the estimation of aij is based on an approximate relationship between the nine orthorhombic aij and group velocities estimation of the anisotropic aij is usually done using phase velocities with well known formulas expressing their theoretical dependence on aij however on time domain seismograms arrivals are observed traveling with group velocities group velocity measurements are found to be straightforward reasonably accurate and independent of the size of the transducers used in contrast the accuracy of phase velocities derived from the p transform analysis was found to be very sensitive to small differences in picked arrival times and to transducer size theoretical phase and group velocities calculated in a forward manner from the aij est

characteristics of repeated detached miocene pliocene tectonic inversion events in a large delta province on an active margin brunei darussalam borneo abstract the baram delta province evolved during the middle miocene to present day from a foreland basin to a shelf margin episodic folding events affected the region causing uplift of the hinterland delta progradation and inversion of gravity related faults existing models place the n s and ne sw trending folds in a strike slip transpressional setting new geological mapping and re interpretation of existing data suggest the region is better understood as the development of a west verging thrust belt in a middle miocene foreland basin filled by sandstones and shales of the belait and setap formations with key major folds jerudong and belait anticlines belait syncline forming during the middle miocene as fault bend and fault propagation folds the deformation style is complicated by the predominantly shaley middle miocene pliocene setap formation becoming thicker and more overpressured from south to north onshore where the setap formation is thin or absent the belait formation is attached to the underlying lower miocene and older sequences offshore and in a narrow onshore strip the overpressured setap formation causes deformation in the beltait formation to be detached from the underlying cretaceous tertiary accretionary prism basement the detached style exhibits considerable structural complexity including lift off folds growth faults shale diapirs and pipes onshore thrust and inversion features are dominantly n s trending and began activity in the middle miocene deformation is probably associated with an e w maximum horizontal stress direction in the late miocene around 7 5 ma watters et al 1999 ne sw striking inversion folds developed located mostly over early counter regional faults and associated reactive diapirs folds verge towards the nw when underlain by counter regional faults and towards the s or se when underlain by regional faults folds and diapirs along n s trends were also reactivated continuation of this deformation into the pliocene is largely confined to the offshore area onshore the n s structures no detachment were not reactivated during the pliocene

seismic velocity anisotropy of phyllosilicate rich rocks characteristics inferred from experimental and crack model studies of biotite rich schist summary seismic velocity anisotropy of biotite schist 30 per cent mode biotite was measured under confining pressures up to 150 mpa the rock shows weak orthotropy which was altered from transverse isotropy ti generated by biotite preferred orientation the orthotropy was caused by microfolding in the rock the velocity increase under confining pressure indicates that most crack planes are aligned parallel to the cleavage planes silicate sheet of the oriented biotite minerals the anisotropy of the rock is basically ti due to both the aligned biotite minerals and cracks which have a common symmetry axis we found that other sheet silicate rich rocks have a similar anisotropy with the biotite schist in which the ti type anisotropy is characterized by the slow p and s wave velocities along the symmetry axis this is caused by the preferred orientation of sheet silicate minerals and the extremely slow p and s wave velocities along the axis perpendicular to the silicate sheet compared to the directions along the silicate sheet when rock contains a large percentage of highly oriented sheet silicates the fast and slow shear waves exchange their polarities at some off symmetry axis directions indicating that the qswave quasi s wave velocity exceeds the sh wave velocity the phase velocity distribution of qs wave shows an asymmetry with respect to the angle from the symmetry axis which is characterized by a bulge in this distribution located near the symmetric axis this is inherent to most sheet silicate minerals when crack density of aligned cracks increases the p wave velocity along the symmetry axis decreases considerably the qs wave phase velocity in the off axis directions also decreases in accordance with the decrease of the p velocity along the symmetry axis the asymmetry of the qs wave phase velocity distribution increases as the p wave velocity decreases along the symmetry axis this relationship can be well understood by means of berryman s extended thomsen approach

shear wave velocity structure beneath europe the northeastern atlantic and western asia from waveform inversions including surface wave mode coupling summary waveforms of 449 seismograms have been inverted for s wave velocity structures beneath europe the northeastern atlantic and western asia down to a depth of 670 km recorded waveforms were used in the time window starting at the s wave arrival and ending after the fundamental mode rayleigh wave arrival the inversion method is based on the partitioned waveform inversion nolet 1990 with the difference that synthetic seismograms are calculated taking surface wave mode coupling into account in order to model body waves in laterally heterogeneous media more accurately the partitioning of the inversion procedure makes non linear optimization feasible even for inversions including surface wave mode coupling the non linear inversion of the waveforms resulted in linear constraints on the 3 d velocity structure in a second step these constraints were used in a linear inversion for the 3 d shear wave velocity model beneath europe the northeastern atlantic and western asia the eur sc 95 model is presented which is characterized by a wide range of length scales of the velocity structures in central europe where the ray density is highest small scale structures are recovered such as the presence of high velocities associated with the hellenic subduction zone on the edges of the inversion model where the ray density and therefore also the resolution is poorer we find larger scale features such as the relatively laterally homogeneous high velocity structure beneath the russian platform to a depth of 300 km in this paper we discuss the inversion method data processing parametrization difficulties due to the introduction of surface wave mode coupling spatial resolution of the model and structures in the eur sc 95 model

upper mantle s velocity structure of central and western south america we have used broadband seismograms recorded at portable and permanent seismic stations in south america to image the three dimensional s velocity structure beneath central and western south america we have interactively fitted the waveforms of s and surface wave trains in 500 seismograms from 90 earthquakes and 60 different stations the constraints on upper mantle s velocity structure provided by the waveform fits have been combined with independent estimates of depth to the mohorovicic discontinuity yielding model sa99 the s velocity structure of sa99 reveals a highly heterogeneous upper mantle with a maximum peak to peak difference of 1 km s above 100 km the heterogeneity seems to be correlated with tectonic and geologic domains sa99 shows high lithospheric s velocities for the precambrian cratons the amazon basin is also underlain by high s velocities while three other intraplatform basins are underlain by low s velocities at various depths sa99 shows extremely low velocities in the mantle wedge beneath the volcanically active andes we explain these low s velocities as originating from realistic amounts of volatiles released by the subducting nazca crust and resulting amounts of partial melt within the peridotitic mantle wedge without requiring elevated temperatures while sa99 could be consistent with diffuse influx for corner flow in the mantle wedge it does not support models that require influx of subcontinental upper mantle into the mantle wedge through a laterally uniform low viscosity channel

reflection transmission coefficients and azimuthal anisotropy in marine seismic studies summary introduce two methods for inferring the direction of vertical fractures from marine seismic data first we derive the necessary reflection and transmission coefficients for an interface between a liquid and an azimuthally anisotropic solid next we show that multicomponent ocean bottom seismometer data from surface airgun sources along two perpendicular shot lines can be rotated into the principal directions of azimuthal anisotropy to determine the orientation of vertical fractures finally we show that p wave amplitude versus offset avo depends on the orientation of the shot line with respect to the vertical fractures thus p wave avo can also be used to determine fracture orientation

relay ramp forms and normal fault linkages canyonlands national park utah fieldwork within a series of mesoscale grabens in southeast utah has revealed a particularly well exposed system of interlinked extensional faults a series of down faulted grabens are developed within a 460 m thick brittle layer of upper paleozoic sandstone and shale which overlies a ductile layer with a high gypsum content all the major grabens consist of two or more overlapping elements which are composed of fault segments these segments may be hard linked fault surfaces are joined or soft linked fault surfaces are isolated but linked by ductile strain of the rock volume between them in map view relay structures are defined as zones connecting the footwalls and hanging walls of overlapping fault segments representing soft linkage of fault segments in the canyonlands grabens the transfer of displacement between soft linked fault segments is characterized by well de fined dipping relay ramps commonly rotated and extended to accommodate the ductile strain between the overlapping fault segments relay ramps develop as ephemeral structures eventually becoming breached by hard linkage of the fault segments breakdown of ramps by breaching is part of the process of fault growth by segment linkage within the canyonlands graben system four orders of segmentation are present this may be a consequence of different scales of mechanical heterogeneity but evidence from the canyonlands grabens and elsewhere points to a fundamental process of discontinuous fault growth by segment linkage

global crustal thickness from neural network inversion of surface wave data summary we present a neural network approach to invert surface wave data for a global model of crustal thickness with corresponding uncertainties we model the a posteriori probability distribution of moho depth as a mixture of gaussians and let the various parameters of the mixture model be given by the outputs of a conventional neural network we show how such a network can be trained on a set of random samples to give a continuous approximation to the inverse relation in a compact and computationally efficient form the trained networks are applied to real data consisting of fundamental mode love and rayleigh phase and group velocity maps for each inversion performed on a 2 2 grid globally we obtain the a posteriori probability distribution of moho depth from this distribution any desired statistic such as mean and variance can be computed the obtained results are compared with current knowledge of crustal structure generally our results are in good agreement with other crustal models however in certain regions such as central africa and the backarc of the rocky mountains we observe a thinner crust than the other models propose we also see evidence for thickening of oceanic crust with increasing age in applications characterized by repeated inversion of similar data the neural network approach proves to be very efficient in particular the speed of the individual inversions and the possibility of modelling the whole a posteriori probability distribution of the model parameters make neural networks a promising tool in seismic tomography

estimation of fracture parameters from reflection seismic data part iii fractured models with monoclinic symmetry existing geophysical and geological data indicate that orthorhombic media with a horizontal symmetry plane should be rather common for naturally fractured reservoirs here we consider two orthorhombic models one that contains parallel vertical fractures embedded in a transversely isotropic background with a vertical symmetry axis vti medium and the other formed by two orthogonal sets of rotationally invariant vertical fractures in a purely isotropic host rock using the linear slip theory we obtain simple analytic expressions for the anisotropic coefficients of effective orthorhombic media under the assumptions of weak anisotropy of the background medium for the first model and small compliances of the fractures all effective anisotropic parameters reduce to the sum of the background values and the parameters associated with each fracture set for the model with a single fracture system this result allows us to eliminate the influence of the vti background by evaluating the differences between t

microcrack induced elastic wave anisotropy of brittle rocks the failure of brittle rocks during compression is preceded by the formation growth and coalescence of microcracks elastic wave velocities are reduced in the presence of open microcracks and fractures and may therefore be used to monitor the progressive damage of the rock in general these microcracks are not randomly oriented and the rock displays an elastic anisotropy the elastic anisotropy due to cracks can be expressed in terms of a second rank and fourth rank crack density tensor for open cracks the contribution of the fourth rank crack density tensor to the elastic wave velocities is small these results are compared with recent measurements of the ultrasonic compressional and shear wave velocities for propagation parallel and perpendicular to an increasing axial stress applied at constant confining stress to berea sandstone inversion of the velocity measurements indicates that the microcracks propagate parallel to the maximum compressive stress in agreement with current rock mechanics theory a reasonable fit to the data is obtained using only the second rank crack density tensor even though at high confining stress the cracks are expected to be in partial contact along their length this is consistent with the model of elastic wave propagation in a medium containing partially contacting fractures published by white however measurements of off axis wave velocities are required to fully quantify the contribution of the fourth rank crack density tensor

sequence stratigraphy and syndepositional deformation of the agbada formation robertkiri field niger delta nigeria the agbada formation in robertkiri field is a 2 7 km 9000 ft thick succession of miocene shallow marine and nonmarine deposits formed as the continental margin of the niger delta structurally collapsed under accumulating sediments a high resolution sequence stratigraphic framework for these strata was constructed by combining data from 20 well logs and a 1400 km2 550 mi2 seismic volume syndepositional structural collapse occurred along a succession of major cuspate offshore dipping normal faults and associated antithetic faults and rollover anticlines within downdropped blocks six fourth order sequences each hundreds of meters thick formed during episodic progradation and retrogradation of deltaic shorelines their development was complicated by the thickening of deposits across major growth faults and away from the crests of adjacent rollover anticlines successively younger sequences became thinner more laterally uniform in thickness and less structurally deformed and contain less growth strata above downdropped fault blocks erosion along successively younger sequence boundaries became shallower and broader as accommodation declined and more sediment was bypassed basinward areas of deepest sequence boundary incision and most rapid structural deformation shifted basinward over time with regional delta progradation stratigraphic patterns across successive downdropped fault blocks suggest that collapse of this continental margin occurred under prograding deltaic deposits on the shelf instead of within lowstand intraslope basins differences in the development of successive sequences reflect gradually slowing rates of structural collapse as underlying mobile shale is depleted allowing deltaic deposition to shift farther basinward

growth faults at the prodelta to delta front transition cretaceous ferron sandstone utah cliff exposures of synsedimentary growth faults at the base of the cretaceous ferron sandstone in central utah represent outcrop analogs to subsurface growth faults delta front sands prograded over and deformed less dense prodelta muds of the underlying tununk shale detailed fault patterns and associated facies changes demonstrate a complex fault history and style for growth fault development rather than a simple progressive development of faults in a basinward position the most proximal and most distal fault sets were the earliest active faults growth faulting was initiated by deposition of cross bedded distributary channel and mouth bar sandstones that reach 9 m thick in the hangingwalls of the faults curvature of the beds in the hangingwall of the faults nucleates smaller conjugate fault sets cross bed sets in the hangingwalls of faults decrease from meter to decimeter scale away from the faults suggesting decreasing flow velocity or decreased preservation of cross sets as a result of decreasing accommodation in distal hangingwalls shifts in depositional loci including upstream and downstream accretion of mouth bar sands contribute to the complex faults history and internal heterogeneity and development of potentially isolated sandy reservoir compartments

acoustic reflectivity from variously oriented orthorhombic media analogies to seismic responses from a fractured anisotropic crust the variations in the strength of seismic reflections with both angles of incidence and azimuth are being used to constrain the orientations and degrees of mechanical anisotropy of geological formations this information is often used in turn to infer the directions of fracturing and stress usually assuming simplified geological structures that in many cases are not realistic in order to further understand this problem the reflectivities from a set of variously titled samples cut from a single block of a common anisotropic composite material are measured with both angles of incidence and azimuth in the laboratory each sample is analogous to a formation in which the fracture sets increasingly dip the observed responses differ from plane wave theory due to the finite nature of the experiment however the deviations are well accounted for by modeling the acoustic reflectivity using its bounded pulse as expected the reflectivities vary with the sample tilt the angle of incidence and the azimuth at which the measurements are made however some of these responses such as the pre critical reflectivities do not appear to strongly vary with azimuth for a given sample critical angle phenomena too must be used cautiously as the observed reflectivity peaks do not lie at the exact critical angle these results suggest that reflectivities could be an important source of information with regards to the spatial orientation of anisotropic layer

temporal and lateral variation in the development of growth faults and growth strata in western niger delta nigeria this study examines eight syndepositional faults and syntectonic sediments in five major fault blocks in western niger delta offshore nigeria on three dimensional seismic data the initiation lateral growth and retreat periods of activity and quiescence and decay of faulting around these blocks can be ascertained by analyzing a series of time structure and isopach maps the study area can be subdivided into three structural zones the first structural zone is a northwestern zone characterized by a major counterregional growth fault in the deep subsurface this deep seated structure is superposed by an array of younger regional growth faults displacing a kilometer thick sedimentary overburden that accumulated on the former footwall the second structural zone is a central to eastern zone that seems mostly unaffected by young deltaic faulting this zone is characterized by the thinnest sedimentary record of the study area the third structural zone is a southeastern zone that is dominated by a large listric backstepping master fault zone associated with a kilometer scale rollover system regional structural and stratigraphic analyses document an apparently strong relationship between syntectonic sedimentation and syndepositional fault activity in that phases of significant fault activity lateral fault growth and fault migration concur with major depositional phases in turn areas and intervals characterized by the least sediment accumulation also record the lowest fault activity however one particularity of the studied system is that it underwent at least one period of seaward fault progression that coincided with a backstepping of faulting on the landward side although the forward stepping of faulting near the delta front can be interpreted as the consequence of the progressive loading during delta progradation the contemporaneous backstepping of faulting further inboard likely reflects the sustained lateral growth of mature deltaic faults into previously undeformed proximal parts of the depocenter the results of this study thus document that although an apparent correlation with the superimposed depositional system exists on a regional scale inboard deltaic faults may persist to grow irrespective of sedimentary loading the recognition of such fault trends is particularly important for estimating the influence of late stage fault movement on hydrocarbon migration or the discovery of subtle fault controlled hanging wall reservoirs

multiparameter tti tomography of p wave reflection and vsp data abstracttransversely isotropic models with a tilted symmetry axis tti media are widely used in depth imaging of complex geologic structures here we present a modification of a previously developed 2d p wave tomographic algorithm for estimating heterogeneous tti velocity fields and apply it to synthetic and field data the symmetry direction velocity vp0 anisotropy parameters e and and symmetry axis tilt are defined on a rectangular grid to ensure stable reconstruction of the tti parameters reflection data are combined with walkaway vertical seismic profiling vsp traveltimes in joint tomographic inversion to improve the convergence of the algorithm we develop a three stage model updating procedure that gradually relaxes the constraints on the spatial variations of the anisotropy parameters while the symmetry axis is kept orthogonal to the reflectors only at the final stage of the inversion are the parameters vp0 e and updated on the same grid we also incorporate geologic constraints

structural evolution of shale diapirs from reactive rise to mud volcanism 3d seismic data from the baram delta offshore brunei darussalam two areas of shale diapirism in a deltaic setting were examined using 3d seismic data from offshore brunei to determine the origin evolution and geometry of shale diapirs the study areas cover parts of the egret and ampa fields within the baram delta province the ampa diapir consists of a small bulge of the mobile setap shale around which lies a zone of chaotically disrupted country rock reflections at the crest of this chaotic zone vertical cylindrical shale pipes arise that end in a wider head the diapir heads wear halos of high amplitude reflections probably due to the presence of methane gas the egret data show the same features except that the bulge of the source layer is not detected due to low reflectivity and chaotic reflections at the base of the overburden the bulging of the setap shale on the ampa data is interpreted as modified reactive diapirism in response to differential loading the initial reactive diapir shape was modified by lateral or oblique upward migration of fluidized shales into the hanging wall of the fault controlling the reactive diapir this probably occurred as a network of dykes and sills the presence of some preserved bedding is indicated by weak but coherent reflectivity from the area initially defined as chaotic shale the spreading of overpressure and the injection of shale into the overburden is thought to be a late phenomenon possibly late pliocene or early pleistocene and the mobility of the shale is attributed to overpressure increase due to gas generation within the setap shale and maybe the lower part of the overburden gas migration perhaps ahead of the diapir intrusion probably facilitated the mud injection the ampa and egret diapirs formed in two diapiric phases an early reactive diapirism and a later active diapirism but the phases have little in common they are seperated by about 9 million years of inactivity and differ in process and probably differ in degree of overpressure in overpressure generating mechanism and in properties of the diapiric mud

approximations to seismic ava responses validity and potential in glaciological applications amplitude variation with angle ava methods establish the seismic properties of material either side of a reflective interface and their use is growing in glaciology the ava response of an interface is defined by the complex knott zoeppritz k z equations numerous approximations to which we typically assume weak interface contrasts and isotropic propagation inconsistent with the strong contrasts at glacier beds and the vertically transverse isotropic vti fabrics were associated with englacial reflectivity we considered the validity of a suite of approximate k z equations for the exact p wave reflectivity rp of ice overlying bedrock sediment and water and englacial interfaces between isotropic and vti ice we found that the approximations of aki richards shuey and fatti match exact glacier bed reflectivity to within rp 0 05 smaller than the uncertainty in typical glaciological ava analyses but only for maximum incident angle i limited to 30 a stricter limit of i 20 o ffered comparable accuracy to a hydrocarbon benchmark case of shale overlying gas chargedsand the vti compliant rugerapproximation accurately described englacial reflectivity to within rp 0 01 and it can be modified to give a quadratic expression in sin 2 i suitable for curve matching operations having shown the circumstances under which ava approximations were valid for glaciological applications we have suggested that their interpretative advantages can be exploited in the future ava interpretations

structural styles in the deep water fold and thrust belts of the niger delta the deep water niger delta includes two large fold and thrust belts products of contraction caused by gravity driven extension on the shelf that exhibit complex styles of thrusting these contractional structures formed above multiple detachment levels in the overpressured shales of the akata formation using the patterns of growth sedimentation fold shapes fault plane seismic reflections and combined conventional and shear fault bend folding theories we describe and model the structural styles and kinematics of the fault related folds and imbricate thrust systems that compose these belts individual fault related folds involving both forethrusts and backthrusts are characterized by long planar backlimbs that dip less than the associated fault ramps with upward shallowing of dips in growth strata above the backlimbs suggesting components of progressive limb rotation forelimbs are short compared to backlimbs but growth strata show more consistent dips that suggest a component of folding by kink band migration thus we employ a combination of classic and shear fault bend fold theories to describe these structures including the influence of a weak basal detachment zone in the overpressured shales we expand upon these theories to model the kinematics of imbricate thrust systems which display a complex history of thrusting related to spatial and temporal variations in deposition across the delta regional patterns of folded growth strata are used to define break forward break backward and coeval thrusting involving single and multiple detachment levels we define two main types of imbricate thrust systems type i system with a single basal detachment level and type ii imbricate system with multiple basal detachment levels which cause massive structural thickening of the akata formation and refolding of shallow thrust sheets through the sequential restoration of two regional cross sections across these systems we resolve the structural styles the timing and sequences of thrusting as well as the regional amounts of shortening all of which have important implications for hydrocarbon maturation and charge in the deep water niger delta

hanging wall fault kinematics and footwall collapse in listric growth fault systems we describe the structure of a listric growth fault system from se asia using high resolution 3 d seismic data the fault system shows systematic changes in geometry and kinematics that are sympathetic with along strike changes in the structure of the bounding fault where the position of the bounding fault remained fixed there is an overall landward decrease in the age of the hanging wall growth faults along strike three phases of footwall collapse caused by the active bounding fault stepping back into the footwall block were responsible for the punctuated stepwise landward migration of the rollover hinge and associated hanging wall growth faults during extension the migration of these hanging wall structures is similar to that predicted by simple analogue models with fixed detachment surfaces care should therefore be taken in defining kinematic models in areas where the geometry of the bounding fault is either poorly defined or unknown

the influence of differential sedimentary loading and compaction on the development of a deltaic rollover abstract three dimensional seismic data and wireline logs from the western niger delta were analyzed to reveal the sedimentary and tectonic history of a major deltaic growth fault depocenter comprising a kilometer scale rollover anticline the seismic units of the rollover show a non uniform thickness distribution with their respective maximum near the main bounding growth fault on the landward side of the system this wedge shaped sediment storage architecture ultimately reflects the non uniform creation of accommodation space in the study area that was controlled by 1 the differential compaction of the hanging wall and footwall strata 2 the lateral variation of fault induced tectonic subsidence above the listric master fault and possibly 3 local subsidence related to the subsurface movement of mobile shale reacting to loading and buoyancy a sequential three dimensional decompaction of the interpreted deltaic rollover units allowed to reconstruct and measure the compaction development of the rollover succession through time documenting that sediment compaction contributed per depositional interval to between 25 and 35 of the generation of depositional space subsequently filled by deltaic sediments the incremental decompaction of sedimentary units was further used to quantify the cumulative amount of accommodation space at and around the studied rollover that was created by fault movement shale withdrawal regional tectonic subsidence isostasy and changes in sea level if data on the regional subsidence and eustasy are available the contribution of these basinwide controls to the generation of depositional space can be subtracted from the cumulative accommodation balance which ultimately quantifies the amount of space for sediments to accumulate created by fault movement or shale withdrawal this observation is important in that it implies that background knowledge on subsidence stratigraphic age and sea level changes allows to reconstruct and quantify fault movement in syn tectonic deltaic growth successions and this solely based on hanging wall isopach trends independent of footwall information

elastic properties of anisotropic synthetic calcite muscovite aggregates 1 a set of synthetic aggregates containing mixtures of calcite and muscovite were compacted with varying uniaxial loads ranging from 20 mpa up to 400 mpa their elastic properties have been measured using compressional and shear waves in confining hydrostatic pressures up to 475 mpa measured seismic velocities are shown to depend on 1 the ratio of calcite to muscovite 2 the uniaxial load used during sample manufacturing and 3 the porosity amount prior to velocity measurements the matrix framework may also affect the seismic velocities but this effect is not easily quantifiable in general measured seismic velocities decrease with increasing muscovite content and porosity elastic properties have been calculated based on texture measurements which were obtained by neutron diffraction the calculated velocities are based on the calcite and muscovite single crystal elastic tensors their orientation distribution functions and their modal fractions a large discrepancy is apparent between calculated and measured velocities where the former always overestimate the actual velocities shear waves display less of a difference between calculated and measured values than do compressional waves indicating that waves propagating by shearing are less affected by sample porosity and matrix framework a better agreement between measured and calculated seismic velocities arises when the initial porosity is taken into account using a differential effective medium model seismic anisotropy is evident from both measured and calculated velocities and is low for samples containing pure calcite but becomes prominent as the muscovite concentration increases the intensity of anisotropy further depends on the uniaxial load used during sample compaction and the initial porosity

partitioned waveform inversion and two dimensional structure under the network of autonomously recording seismographs nonlinear optimization methods are very effective in finding models that predict optimal waveform fits to observed seismograms provided the number of model parameters is small to reduce the size of the large scale two or three dimensional seismic modelling problem path integrals over seismic velocities may be defined as model parameters instead of the seismic velocities themselves this partitions the large scale optimization problem into a number of independent small scale problems and reduces the computational effort by several orders of magnitude the path integral parameters are transformed such that their correlation matrix becomes diagonal a linear inversion performs the mapping from the space of path integral parameters into the model space of seismic velocities and makes backus gilbert resolution analysis possible the method has been applied to body wave and surface wave data from the broadband portable network of autonomously recording seismographs nars in western europe using a surface wave ray approximation to generate synthetics by mode summation waveforms were fitted for frequencies as high as 50 mhz variations in s velocity as large as 6 1 have been established with a vertical resolution of 100 150 km and a horizontal resolution as small as 400 km in parts of the model although a low velocity layer is present under the southern part of the nars array such layer is very weak or absent north of the paris basin horizontal velocity gradients are well resolved down to 400 km depth

mapping the moho with seismic surface waves a review resolution analysis and recommended inversion strategies abstract the strong sensitivity of seismic surface waves to the moho is evident from a mere visual inspection of their dispersion curves or waveforms rayleigh and love waves have been used to study the earth s crust since the early days of modern seismology yet strong trade offs between the moho depth and crustal and mantle structure in surface wave inversions prompted doubts regarding their capacity to resolve the moho here we review surface wave studies of the moho with a focus on early work and then use model space mapping to establish the waves sensitivity to the moho depth and the resolution of their inversion for it if seismic wavespeeds within the crust and upper mantle are known then moho depth variations of a few kilometres produce large 1 perturbations in phase velocities however in inversions of surface wave data with no a priori information wavespeeds not known strong moho depth shear speed trade offs will mask 90 of the moho depth signal with remaining phase velocity perturbations 0 1 only in order to resolve the moho with surface waves alone errors in the data must thus be small up to 0 2 for resolving continental moho with larger errors moho depth resolution is not warranted and depends on error distribution with period an effective strategy for the inversion of surface wave data alone for the moho depth is to first constrain the crustal and upper mantle structure by inversion in a broad period range and then determine the moho depth in inversion in a narrow period range most sensitive to it with the first step results used as reference prior information on crustal and mantle structure reduces the trade offs and thus enables resolving the moho depth with noisier data such information should be used whenever available joint analysis or inversion of surface wave and other data receiver functions topography gravity can reduce uncertainties further and facilitate moho mapping

p wave attenuation anisotropy in fractured media a seismic physical modelling study we used a laboratory scale model to study the effects aligned fractures might have on seismic wave propagation at a larger scale in real earth imaging our main objective was to investigate the effect of aligned fractures on seismic p wave amplitude through the estimation of the induced attenuation the physical model was constructed from a mixture of epoxy resin and silicon rubber with inclusions designed to simulate two sets of inclined fractures at an angle of 29 2 with each other two dimensional reflection data were acquired using the pulse and transmission method in three principal directions relative to the fracture strike azimuth with the model submerged in a water tank we used the quality versus offset qvo method an extension of the classical spectral ratio method for determining attenuation to estimate the induced attenuation inverse of the seismic quality factor from the common mid point cmp pre processed gathers the results of our analysis show that the induced p wave attenuation is anisotropic with elliptical cos2 variations with respect to the survey azimuth angle the minor axis of the q ellipse corresponds to the fracture normal in this direction i e across the material grain the attenuation is a maximum the major axis corresponds to the fracture strike direction parallel to the material grain where minimum attenuation occurs these attenuation results show consistency with the azimuthal anisotropy observed in the stacking velocities in the fractured layer and are all consistent with the physical model and thus provide a physical basis for using attenuation anisotropy to derive fracture properties from seismic data

crustal thickness estimation using high frequency rayleigh waves the method of nonlinear waveform fitting was extended to include changes in the depth of the moho studies performed on synthetic data at 10 epicentral distance showed that it is theoretically possible to determine moho depth with an accuracy of less than a kilometer if the frequency range extends to 0 12 hz we applied this method on several broadband records from two earthquakes in western united states to invert for crustal thickness waveform fitting of rayleigh waves for epicentral distances between 3 and 10 for individual paths in this region show that the average moho depth can be resolved to 1 2 km it was possible to obtain good waveform fits for frequencies between 0 02 0 08 hz we conclude that broadband seismic data from local events allow us to determine moho depth independently from crustal shear wave velocity

a multioffset vertical seismic profiling experiment for anisotropy analysis and depth imaging a multioffset vertical seismic profile vsp was carried out in the rocky mountain foothills of southern alberta canada the purpose of this experiment was to investigate whether the dipping shale strata exhibit p wave velocity anisotropy and if so to calculate the thomsen anisotropy parameters for use in anisotropic depth migration traveltime inversion of first arrival data from the multioffset vsp revealed that the dipping mesozoic clastics in the area exhibit seismic velocity anisotropy of about 10 the anisotropy parameters derived from this experiment were then used in anisotropic prestack depth migration of data from a surface seismic line close to the vsp well comparison of the anisotropic migration with the corresponding isotropic prestack depth migration showed that the target was imaged incorrectly in the isotropic case a lateral shift of 180 m in the updip direction of the overlying beds was observed the image obtained with an anisotropic velocity model was also better focused than that obtained assuming isotropic velocities

determination of the principal directions of azimuthal anisotropy from p wave seismic data in an azimuthally anisotropic medium the principal directions of azimuthal anisotropy are the directions along which the quasi p and the quasi s waves propagate as pure p and s modes when azimuthal anisotropy is induced by oriented vertical fractures imposed on an azimuthally isotropic background two of these principal directions correspond to the directions parallel and perpendicular to the fractures s waves propagating through an azimuthally anisotropic medium are sensitive to the direction of their propagation with respect to the principal directions as a result primary or mode converted multicomponent s wave data are used to obtain the principal directions apart from high acquisition cost processing and interpretation of multicomponent data require a technology that the seismic industry has not fully developed anisotropy detection from conventional p wave data on the other hand has been limited to a few qualitative studies of the amplitude variation with offset avo for different azimutha

fabric related velocity anisotropy and shear wave splitting in rocks from the santa rosa mylonite zone california the directional dependence of p and s wave velocities have been measured at pressures up to 600 mpa and temperatures up to 700 c in rocks from the santa rosa mylonite zone southern california during tectonism these were progressively deformed from granodiorite protolith to mylonite and ultimately phyllonite the mineralogical and chemical composition of protolith and mylonite is nearly identical thus these rocks provide excellent material for documenting the effect of microstructural and textural changes on rock anisotropy velocity anisotropy increases significantly with the degree of deformation whereas average velocities and densities do not change at low pressure 50 mpa the velocity anisotropy ranges from 1 7 in granodiorite up to 19 in phyllonite and is due to both oriented microfractures and crystallographic preferred orientation at high pressure 600 mpa the residual anisotropy up to 12 is mainly due to preferred mineral orientation in particular of biotite significant shear wave splitting is measured parallel to the foliation plane and shows a good correlation with the biotite texture these observations confirm that oriented microcracks and preferred orientation of minerals should be taken into account in the interpretation of seismic reflection and refraction data in terranes with deformed rocks

when do fractured media become seismically anisotropic some implications on quantifying fracture properties fractures are pervasive features within the earth s crust and they have a significant influence on the multi physical response of the subsurface the presence of coherent fracture sets often leads to observable seismic anisotropy enabling seismic techniques to remotely locate and characterise fracture systems in this study we confirm the general scale dependence of seismic anisotropy and provide new results specific to shear wave splitting sws we find that sws develops under conditions when the ratio of wavelength to fracture size s d is greater than 3 where rayleigh scattering from coherent fractures leads to an effective anisotropy such that effective medium model emm theory is qualitatively valid when 1 s d 3 there is a transition from rayleigh to mie scattering where no effective anisotropy develops and hence the sws measurements are unstable when s d 1 we observe geometric scattering and begin to see behaviour similar to transverse isotropy we find that seismic anisotropy is more sensitive to fracture density than fracture compliance ratio more importantly we observe that the transition from scattering to an effective anisotropic regime occurs over a propagation distance between 1 and 2 wavelengths depending on the fracture density and compliance ratio the existence of a transition zone means that inversion of seismic anisotropy parameters based on emm will be fundamentally biased more importantly we observe that linear slip emm commonly used in inverting fracture properties is inconsistent with our results and leads to errors of approximately 400 in fracture spacing equivalent to fracture density and 60 in fracture compliance although emm representations can yield reliable estimates of fracture orientation and spatial location our results show that emm representations will systematically fail in providing quantitatively accurate estimates of other physical fracture properties such as fracture density and compliance thus more robust and accurate quantitative estimates of in situ fracture properties will require improvements to effective medium models as well as the incorporation of full waveform inversion techniques

crustal model in eastern qinghai tibet plateau and western yangtze craton based on conditional variational autoencoder abstract eastern margin of the qinghai tibet plateau and western margin of the yangtze craton has a complex crust mantle structure and is an important region for studying the crust mantle deformation mechanism because the rayleigh surface wave group velocity has a strong constraint on the structure of the crust and upper mantle a lot of researches have used the rayleigh surface wave group velocity to invert the crust mantle structure in this region but the layered multi parameter joint inversion and the uncertainty of the inversion result evaluation is still a research hotspot motived by conditional variational autoencoder cvae which is composed of a decoding and encoding process that uses a deep neural network to predict the variational distribution of parameters we propose a crustal model by cvae to attain the forward and inversion relationship between the group velocity of rayleigh wave and the crustal model in which the cvae decoding corresponds to the forward process and the encoding corresponds to the inverse process moreover the inversion results of this method are constrained from three aspects as follows the network inputs and outputs have the same group velocities the decoded outputs are normal distribution of hidden variables representing the crustal model the mean values of the decoded output during cvae training are the sampled crustal models the proposed method can invert multi parameters and evaluate uncertainty of the inversion efficiently based on the latest group velocity model we invert for mean and variance of thickness in the upper middle and lower sedimentary cover and of thickness p wave velocity s wave velocity and density in the upper middle and lower crystalline crust for eastern qinghai tibet plateau and western yangtze craton compared with the existing crustal models obtained by different methods the results of this study are in good agreement we conclude that cvae based group velocity inversion of the crustal model is a feasible and reliable method

new constraints on upper mantle s velocity structure and crustal thickness of the iranian plateau using partitioned waveform inversion summary the continental collision between the african and eurasian plates resulted in a tectonically young and complex deformation in the iranian plateau the present day iranian plateau is characterized by diverse tectonic domains including the continental collisions e g zagros and alborz and the oceanic plate subduction e g makran partitioned waveform inversion method is used here to image the s velocity structure of the upper mantle and moho depth variations in the iranian plateau of nearly 3000 waveforms originally selected for the analysis we have fitted 974 waveforms from 101 events and 39 stations which result in 11 688 linear constraints on the upper mantle s velocity structure and moho depth for the region our new seismic images show seismically faster upper mantle beneath the zagros and the arabian plate compared to the central iran and alborz this high velocity anomaly has descended beneath the central iran along the main zagros thrust across the zagros collision zone the tomographic images show a slab stagnation in the transition zone at about 410 km depth in the form of a horizontal high velocity zone which does not penetrate the deeper parts of the mantle the lowest s velocities are concentrated beneath the central iran and alborz according to our velocity models a strong high velocity anomaly is resolved beneath the trapped south caspian basin with clear indication of westward underthrusting beneath the talesh and western alborz in makran southeast iran there is a clear evidence of subduction of oceanic crust of the arabian plate beneath the makran belt which is correlated with seismicity pattern across the makran zone also the inverted moho map using a priori information of crustal thickness constraints shows the large crustal thickness beneath the zagros suture zone in some places to a maximum depth of 65 km which indicates the influence of crustal thickening and shortening beneath arabian eurasian plate boundary a significantly crustal thinning is observable across the south caspian basin compared to its margins

fracture characterization at valhall application of p wave amplitude variation with offset and azimuth avoa analysis to a 3d ocean bottom data set the delineation and characterization of fracturing is important in the successful exploitation of many hydrocarbon reservoirs such fracturing often occurs in preferentially aligned sets if the fractures are of subseismic scale this may result in seismic anisotropy thus measurements of anisotropy from seismic data may be used to delineate fracture patterns and investigate their properties here fracture induced anisotropy is investigated in the valhall field which lies in the norwegian sector of the north sea this field is a chalk reservoir with good porosity but variable permeability where fractures may significantly impact production e g during waterflooding to investigate the nature of fracturing in this reservoir p wave amplitude variation with offset and azimuth avoa is analyzed in a 3d ocean bottom cable obc data set in general 3d ocean bottom seismic obs acquisition leads to patchy coverage in offset and azimuth and this must be addressed when considering such data to overcome this challenge and others associated with 3d obs acquisition a new method for processing and analysis is presented for example a surface fitting approach which involves analyzing azimuthal variations in avo gradients is used to estimate the orientation and magnitude of the fracture induced anisotropy this approach is also more widely applicable to offset azimuth analysis of other attributes e g traveltimes and any data set where there has been true 3d data acquisition land or marine using this new methodology we derive high resolution maps of p wave anisotropy from the avoa analysis for the top chalk reflection at valhall these anisotropy maps show coherent but laterally varying trends synthetic avoa modeling using effective medium models indicates that if this anisotropy is from aligned fracturing the fractures are likely liquid filled with small aspect ratios and the fracture density must be high furthermore we show that the fracture normal direction is parallel to the direction of most positive avo gradient in other situations the reverse can be true i e the fracture normal direction can be parallel to the direction of the most negative avo gradient effective medium modeling or comparisons with anisotropy estimates from other approaches e g azimuthal variations in velocity must therefore be used to resolve this ambiguity the inferred fracture orientations and anisotropy magnitudes show a degree of correlation with the positions and alignments of larger scale faults which are estimated from 3d coherency analysis overall this work demonstrates that significant insight may be gained into the alignment and character of fracturing and the stress field variations throughout a field using this high resolution avoa method

joint inversion of local regional and teleseismic data for crustal thickness in the eurasia africa plate boundary region summary a new map for the moho discontinuity eam02 in the eurasia africa plate boundary region is presented reliable results have also been obtained for the southern and eastern mediterranean basin the northern african coasts and the eastern atlantic ocean regions only occasionally considered in studies on the mediterranean region the moho topography model is derived from two independent sets of constraints information contained in the fundamental and highermode rayleigh waves obtained from waveform modelling is used to constrain the moho depth between estimates of crustal thickness taken from published reflection and refraction surveys gravity studies and receiver function analysis strong lateral variations in the moho topography have been observed in the mediterranean sea confirming the complex evolution of this plate boundary region in the west the moho discontinuity has been found at 15 20 km depth suggesting extended and at least in some locations oceanic crust while in the east the crust is on average 25 30 km thick there it is interpreted either as mesozoic oceanic or thinned precambrian continental crust covered by thick sedimentary deposits standard continental crust 30 35 km is observed along the eastern part of the northern african coast while to the west a rapid change from a relatively deep moho down to 42 km below the atlas mountain range to the thin crust of the southwestern mediterranean sea has been found the crust beneath the eastern north atlantic ocean can be up to 5 km thicker compared with standard oceanic crust 6 km the crust has been interpreted to be heterogeneous as a consequence of irregular magma supply at the mid atlantic ridge in addition serpentinization of the submoho mantle could contribute to the imaging of apparently anomalous thick oceanic crust in europe the presence of crustal roots 45 km beneath the major mountain belts has been confirmed while thin crust 25 km has been found beneath extensional basins comparing the obtained moho topography and moho depth computed assuming isostatic compensation at 60 km depth shows that most of the mediterranean and eastern atlantic region appears to be in isostatic equilibrium the large positive residuals observed for the eastern mediterranean are likely to be due to overestimating crustal thickness owing to the thick sediment deposits present

upper mantle beneath southeast asia from s velocity tomography 1 we present a three dimensional s velocity model of the se asian western pacific upper mantle with 400 km lateral resolution using the novel automated multimode inversion technique we processed 4038 vertical component seismograms and extracted 22 708 linear equations with uncorrelated uncertainties that constrain upper mantle structure we used time frequency windows to select signal with negligible proportion of scattered energy the windows included the fundamental rayleigh mode and s and multiple s waves the observed range of s velocity variations is the widest 17 18 in the upper 150 km of the mantle high velocity continental roots can reach beyond the present extent of the overlying archean proterozoic crust by 500 km beneath some precambrian units the roots are absent which can be attributed to deformation and gradual destruction of the ancient lithosphere at 120 150 km s velocity beneath some cratons reaches 4 8 km s this can be accounted for by thermal and compositional effects beneath the hainan island area a low velocity anomaly is observed from near the surface to the bottom of our model the hot spot type volcanism here may be caused by the deep mantle hainan plume a low velocity mantle domain underlies the south central sea of japan surrounded on the surface by intraplate volcanoes a deep seismicity gap is present near 40 n in the pacific slab subducting below and may result from a plume slab interaction a high velocity anomaly is present in the transition zone beneath the northern boundary of the yangtze craton we propose that the anomaly corresponds to subducted continental lithosphere stagnant atop the 660 km discontinuity

azimuthal offset dependent attributes applied to fracture detection in a carbonate reservoir offset dependent attributes amplitude versus offset avo and frequency versus offset are extracted from 2 d p wave seismic data using the multiple signal classification technique these attributes are used to detect fracture orientation in a carbonate reservoir located in the maporal field in the barinas basin of southwestern venezuela in the fracture normal direction p wave reflectivity is characterized by a large increase of amplitude with offset large positive avo gradient and a large decrease of frequency with offset large negative frequency versus offset gradient in the fracture strike direction p wave reflectivity shows a scattered variation in avo but a small variation in frequency with offset our results also show that the reservoir heterogeneity can lead to large variations of avo signatures and that using azimuthal offset dependent frequency attributes can help lessen the ambiguity when detecting fracture orientation

characterization of dipping fractures in a transverselyisotropic background although it is believed that natural fracture sets predominantly have near vertical orientation oblique stresses and some other mechanisms may tilt fractures away from the vertical here we examine an effective medium produced by a single system of obliquely dipping rotationally invariant fractures embedded in a transversely isotropic with a vertical symmetry axis vti background rock this model is monoclinic with a vertical symmetry plane that coincides with the dip plane of the fractures multicomponent seismic data acquired over such a medium possess several distinct features that make it possible to estimate the fracture orientation for example the vertically propagating fast shear wave and the fast converted ps wave is typically polarized in the direction of the fracture strike the normal moveout nmo ellipses of horizontal reflection events are co orientated with the dip and strike directions of the fractures which provides an independent estimate of the fracture azimuth however the polarization vector of the slow shear wave at vertical incidence does not lie in the horizontal plane an unusual phenomenon that can be used to evaluate fracture dip also for oblique fractures the shear wave splitting coefficient at vertical incidence becomes dependent on fracture infill saturation a complete medium characterization procedure includes estimating the fracture compliances and orientation dip and azimuth as well as the thomsen parameters of the vti background we demonstrate that both the fracture and background parameters can be obtained from multicomponent wide azimuth data using the vertical velocities and nmo ellipses of pp waves and two split ss waves or the traveltimes of ps waves reflected from horizontal interfaces numerical tests corroborate the accuracy and stability of the inversion algorithm based on the exact expressions for the vertical and nmo velocities

a new calibration of seismic velocities anisotropy fabrics and elastic moduli of amphibole rich rocks 1 a large portion of the middle to lower crust beneath the continents and oceanic island arcs consists of amphibolites dominated by hornblende and plagioclase we have measured p and s wave velocities vp and vs and anisotropy of 17 amphibole rich rock samples containing 34 80 vol amphibole at hydrostatic pressures p up to 650 mpa combined petrophysical and geochemical analyses provide a new calibration for mean density average major element contents mean vp p and vs p coefficients intrinsic vp and vs anisotropy poisson s ratios the logarithmic ratio rs p and elastic moduli of amphibole rich rocks the vp values decrease with increasing sio2 and na2o k2o contents but increase with increasing mgo and cao contents the maximum 0 38 0 40 km s and minimum s wave birefringence values occur generally in the propagation direction parallel to y and normal to foliation respectively amphibole plays a critical role in the formation of seismic anisotropy whereas the presence of plagioclase quartz pyroxene and garnet diminishes the anisotropy induced by amphibole crystallographic preferred orientations cpos the cpo variations cause different anisotropy patterns illustrated in the flinn diagram of vp x vp y vp y vp z plots the results make it possible to distinguish in terms of seismic properties the amphibolites from other categories of lithology such as granite granodiorite diorite gabbro diabase felsic gneiss mafic gneiss eclogite and peridotite within the earth s crust hence amphibole aligned by dislocation creep anisotropic growth or rigid body rotation is the most important contributor to the seismic anisotropy of the deep crust beneath the continents and oceanic island arcs which contains rather little phyllosilicates such as mica or chlorite

upper mantle s velocity structure of north america we have inverted fundamental and higher mode rayleigh waveforms from 685 vertical component broadband seismograms with wave paths over north america to obtain an image of the upper mantle s velocity structure down to 660 km among the well resolved features of the new model are 1 a high velocity root beneath the north american craton which extends no deeper than 250 km except near the archean core of the craton where depths of 350 km are reached 2 a weak band of low velocity along the eastern margin of the north american craton which reaches into the transition zone 3 a low velocity slab window beneath the western united states down to a depth of 300 km 4 areas of low uppermost mantle velocity beneath the cascade volcanoes the yellowstone hotspot track the colorado plateau the sierra madre occidental and the grabens bordering the jalisco block and 5 a pronounced band of high velocities in the transition zone coinciding with the expected location of the subducted trailing fragments of the farallon plate we introduce several improvements to the method of partitioned waveform inversion which was used to compute the new model rather than to correct for an estimated depth to the mohorovicic discontinuity we leave the crustal thickness as a free though yet poorly resolved parameter in the inversion we also improve the windowing and filtering operator used to select uncontaminated waveforms

three dimensional s velocity of the mantle in the africa eurasia plate boundary region from phase arrival times and regional waveforms 1 a new model of the three dimensional shear velocity structure of the africa eurasia plate boundary is presented the new model is derived by jointly inverting different types of seismic data the two main sources of information are regional waveforms and teleseismic s wave arrival times we show that it is possible to find a model that fit the different data types nearly as well as when inverting solely one type of data the main improvement in resolving power is achieved between depths of 300 and 700 km though the improvements are not limited to this depth range our model reflects the complicated evolution of this plate boundary area the transition zone is dominated by high velocity anomalies which we infer to represent a mix of lithosphere that subducted relatively recently or is not sufficiently cold and dense to traverse the 660 km discontinuity the only low velocity zone in the transition zone is beneath the ionian sea the high velocity hellenic slab is continuous throughout the upper mantle and into the lower mantle to about 1200 km most likely representing subducted neo tethys lithosphere the uppermost mantle is dominated by low velocities consistent with the high level of tectonic activity low velocity regions are relatively strong beneath the mid atlantic ridge turkey and the dead sea region the region s current lithosphere is relatively thin except beneath the adriatic and ionian seas and the easternmost atlantic ocean

temporal and spatial development of a gravity driven normal fault array middle upper jurassic south viking graben northern north sea abstract three dimensional seismic and well data from the south viking graben northern north sea basin is used to investigate the temporal and spatial development of a gravity driven normal fault array above an evaporite rich detachment two moderate throw 500 900 m middle to upper jurassic normal faults the gudrun and brynhild faults are developed within the study area both faults die out laterally and tip out upwards at different structural levels within the syn rift succession both faults terminate downwards into late permian evaporites zechstein group and do not offset pre evaporite basement units this thin skinned fault array developed in response to westwards tilting of the hangingwall of the south viking graben during late jurassic rifting and consequent westward gliding and extensional break up of units above the mechanically weak evaporite horizon isochron mapping and well based correlation of middle to upper jurassic syn rift units allow constraints to be placed on the temporal evolution of the fault array several stages of structural development are observed which document i a period of relatively minor early i e pre rift halokinesis ii variable spatial activity on individual faults within the array and iii the progressive upslope migration of active faulting within the array as a whole the progressive upslope migration of fault activity is interpreted to reflect progressive unbuttressing and extensional faulting of upslope post evaporite units the overall structural style and kinematic evolution identified here shares many characteristics with both rift raft tectonics documented in other rifts developed above an evaporitic sub stratum and raft tectonics described from passive margin basins containing thick mobile salt or shale intervals this style of fault array evolution differs from that observed in rifts lacking mobile layers at depth and highlights the importance of these units in the structural development of rifts

outcrop examples of soft sediment deformation associated with normal fault terminations in deepwater eocene turbidites a previously undescribed conjugate fault termination style abstract a set of small scale layer bound faults developed in a package of three eocene turbidite sandstone beds in a wave cut platform thandwe beach myanmar display unusual downward terminations between converging conjugate faults the faults were initially triggered by loading during deposition of the uppermost turbidite sandstone in the fault affected stratigraphic package the growth of a small gravity driven anticline and subsequent loading by a post deformation turbidite modified the initial fault geometry and re mobilized part of the layer bound sequence causing thinning of the sequence to zero in the vicinity of the fold crest typically conjugate faults display an x shaped pattern of intersection while the observed faults before reaching the point of intersection die out in a drastically thinned basal sandstone located in a keystone block which requires either an underlying detachment or that a volume of sand and fluid was lost from the basal layer probably a combination of gravity driven detachment primary movement and volume loss secondary permitted development of the faults the structures described represent yet another aspect of the wide variety of gravity driven features that form in the deepwater turbidite fan settings it is thought that such features have not been previously described in the literature and represent a new style variant within the general theme of conjugate fault development

development of shape and lattice preferred orientations application to the seismic anisotropy of the lower crust abstract we review the physical basis of the development of fabrics in plastic and viscous flow and illustrate the typical fabrics formed by these processes in the main rock forming silicates of the lower crust feldspar quartz pyroxene and amphibole the orientation process in plastic deformation where a single slip is dominant is recalled and the role of the constraint of neighbouring grains is emphasized the fabric development of anisometric crystals in viscous flow is discussed as a function of the main controlling parameters shear strain aspect ratio and interference between crystals the same sense of fabric asymmetry is introduced by plastic and viscous flow between the flow plane and the shape preferred orientation and hence coherent kinematic analysis can be undertaken in both modes of flow in order to assess the role of such fabrics in the seismic laminations of the lower continental crust we have calculated the seismic p wave properties of typical fabrics for hypothetical monomineralic and polymineralic rocks the calculations show that the strongest anisotropies develop in monomineralic rock with values between 5 and 16 compared with 5 and 8 for typical rock compositions the strongest anisotropies for layered monomineralic rocks generated by fabrics is only 6 compared to the 14 suggested by model studies of the observed seismic laminations we suggest that other effects such as compositional layering and or constructive interference of seismic waves are responsible for augmenting the apparent anisotropy

sequence stratigraphic responses to shoreline perpendicular growth faulting in shallow marine reservoirs of the champion field offshore brunei darussalam south china sea the champion field offshore brunei darussalam comprises a thick middle upper miocene succession of shallow marine sediments associated with major growth fault systems and deposited as part of the paleo baram delta the structural evolution of the champion field has resulted in an unusual situation where growth faults strike perpendicular to the paleoshoreline orientation shoreface parasequences and tidal estuarine complexes are mapped directly from three dimensional 3 d seismic data calibrated from wells the seismic interpretations provide chronostratigraphic correlations that are more robust than some well based markers because the seismic interpretations have better spatial coverage depositional responses to growth faulting are defined by two end member models 1 layer thickening and 2 addition of layers in the hanging wall layer addition makes correlation across faults problematical growth may be accommodated by either or a combination of these processes and areas of layer addition are related to transgressive events in the hanging wall topographic changes thought to be associated with fault movements may fundamentally change shoreline type sand body orientations and petrophysical properties for discrete periods of time these stratigraphic complexities are linked spatiotemporally to accommodation history but cannot be adequately predicted from well data alone

the crustal structure from teleseismic p wave coda i method summary the crustal structure beneath a broad band station has a strong influence on the recorded body wave coda conversely it is evident that crustal receiver effects can be employed to obtain information about the crustal structure at the receiver site in this paper we present a method to estimate the crustal receiver response and we invert the response to obtain a model of the most distinct features of the crustal structure beneath the station the crustal receiver response of a station is determined from the p wave coda of deep teleseisnic events by deconvolution with an empirically determined source wavelet this source wavelet is assumed to incorporate source attenutation and instrument effects responses obtained from clusters of events are stacked to enhance the signal to noise ratio of the data and to obtain an estimate of the variance of the data the crustal p and s velocity structure at the station is determined by non linear waveform inversion of its crustal responses an inversion strategy was developed to search efficiently for the global minimum in the misfit between data and synthetics the inversion appears to be most sensitive to large velocity constrasts in the velocity structure which give rise to high amplitude reflected and converted phases the method is illustrated by the inversion of the crustal responses of nars station ne05 it is shown that a thin layer 1 2 km of unconsolidated sediments and a strong mid crustal discontinuity at 11 km depth constitute the most prominent features of the crustal structure at this station they cause an apparent delay of the first arrival on the radial component of the seismograms and produce high amplitude sv multiples in the p wave coda

seismic fracture anisotropy in the earth s crust an overview fluid filled fractures and microcracks are the most stress sensitive component of crustal rock and often determine the pathways and volume of crustal fluid movement if we are to comprehend the role of fractures and fluids in tectonic processes to formulate an accurate hypothesis for phenomena precursory to catastrophic seismic failure or to monitor hydrocarbon and geothermal reservoirs for the presence or absence of major fluid pathways we must understand how seismic waves interact with the fracture crack and microcrack structures within the rock mass a salient feature of fracture related rock structure is the effective seismic anisotropy of aligned fractures and microcracks with the advent of large volume digital seismic data sets it is feasible to use polarized shear waves to explore the anisotropic fracture properties of the crust crustal fracture structures which may be monitored by polarized shear waves range in dimensions from the 10 100 km scale of crustal stress orientation and preseismic stress buildup through the 100 1000 m scale of fluid reservoir structure and characterization and the 1 10 scale of mining and geoengineering rock strain monitoring to millimeter and micrometer or possibly smaller fluid filled inclusions determining the elastic response of the intact rock mass to focus developments in seismic anisotropic studies of crustal fracture phenomena the american geophysical union and the society of exploration geophysicists sponsored a chapman conference on seismic anisotropy in the earth s crust held may 31 to june 4 1988 at the lawrence berkeley laboratory of the university of california this was the third international workshop on seismic anisotropy 3iwsa nineteen conference papers are presented in this special section of the journal of geophysical research

growth faults above shale seismic scale outcrop analogues from the makran foreland sw pakistan abstract the southern makran fold thrust belt pakistan displays unique outcrop examples of well exposed kilometre scale listric growth faults that displace miocene age deltaic growth strata by several hundreds of metres to kilometers the largest growth faults are counter regional landward dipping bounding major clastic depocentres exposed over areas 1000 km 2 stratal offset along these faults can exceed 1 5 km fault zone thicknesses range between ca 100 and 400 m and average fault thickness displacement ratios are around 1 10 high resolution satellite data show in unprecedented detail the faults and the stratigraphic architecture of associated growth sequences which comprise kilometre scale progradational clinoforms thick mudstone units and basinwards wedging sandstone shale deposits the true vertical thickness of the syn kinematic record is in places up to 8 km making the outcrop examples equivalent to major growth faulted successions known from seismic data of large deltas and at least an order of magnitude larger than other outcrop examples a comparison of the makran outcrops with seismic reflection examples offshore nw borneo reveals distinct similarities in the gross depocentre geometries and internal architecture the key control for growth faulting is interpreted to result from sedimentary loading with rapid sedimentary progradation causing the development of rollover synclines by differential compaction and fluid expulsion and counter regional growth faults preferentially forming on the basinward side of these synclines the data and interpretations presented can be used to assess the key parameters that contribute to the development of growth faults and growth successions above shale reinforcing structural and stratigraphic observations from seismic interpretation and modelling studies in demonstrating their occurrence in exposure

crustal thickness map of the western united states by partitioned waveform inversion the partitioned waveform inversion method nolet 1990 was used to obtain a new crustal thickness map of the western united states we fitted 200 seismograms containing higher and fundamental mode rayleigh waves for events and stations in the western united states which provided average crustal thickness constraints between each source receiver pair all these constraints were combined in a linear inversion to obtain a crustal thickness map local crustal thickness estimates from published seismic reflection refraction work were used as additional constraints to overcome deficiencies of path coverage in some areas the resulting crustal thickness map shows thicker 45 km crust beneath the cascades thick 40 km crust beneath the sierra nevada thin 30 km crust beneath the basin and range and thick greater than 45 km crust beneath the colorado plateau the boundary between the colorado plateau and the southern leg of the basin and range is a prominent feature of the model thick crust is seen at the bend of the san andreas fault near los angeles our model is broadly consistent with the crustal thickness map of mooney and weaver 1989 a quantitative comparison with the crustal thickness model 3smac nataf and ricard 1996 was performed by inverting for a model that deviates least from it results show that we are able to retain most of the features of that model while maintaining a good fit to the surface wave and point constraint data

an analysis of avo inversion for postcritical offsets in hti media abstractazimuthal variations of wavefield characteristics such as traveltime or reflection amplitude play an important role in the identification of fractured media a transversely isotropic medium with a horizontal symmetry axis hti medium is the simplest azimuthally anisotropic model typically used to describe one set of vertical fractures there exist many techniques in industry to recover anisotropic parameters based on moveout equations and linearized reflection coefficients using such a model however most of the methods have limitations in defining properties of the fractures due to linearizations and physical approximations used in their development thus azimuthal analysis of traveltimes based on normal moveout ellipses recovers a maximum of three medium parameters instead of the required five linearizations made in plane wave reflection coefficients pwrcs limit the amplitude versus offset avo analysis to small incident angles and weak contrast interfaces inversion based on azimuthal

seismic characterization of naturally fractured reservoirs using amplitude versus offset and azimuth analysis p wave seismic reflection data with variable offset and azimuth acquired over a fractured reservoir can theoretically be inverted for the effective compliance of the fractures the total effective compliance of a fractured rock which is described using second and fourth rank fracture tensors can be represented as background compliance plus additional compliance due to fractures assuming monoclinic or orthotropic symmetry which take into account layering and multiple fracture sets the components of the effective second and fourth rank fracture compliance tensors can be used as attributes related to the characteristics of the fractured medium synthetic tests indicate that using a priori knowledge of the properties of the unfractured medium the inversion can be effective on noisy data with s n on the order of 2 monte carlo simulation was used to test the effect of uncertainties in the a priori information about elastic properties of unfractured rock two cases were considered with wide azimuth waz and narrow azimuth naz reflection data and assuming that the fractures have rotationally invariant shear compliance the relative errors in determination of the components of the fourth rank tensor are substantially larger compared to the second rank tensor under the same assumptions elastic properties of background media consisting in horizontal layers without fractures do not cause azimuthal changes in the reflection coefficient variation with offset thus due to the different nature of these properties compared to fracture tensor components which cause azimuthal anomalies simultaneous inversion for background isotropic properties and fracture tensor components requires additional constraints singular value decomposition svd and resolution matrix analysis can be used to predict fracture inversion efficacy before acquiring data therefore they can be used to determine the optimal seismic survey design for inversion of fracture parameters however results of synthetic inversion in some cases are not consistent with resolution matrix results and resolution matrix results are reliable only after one can see a consistent and robust behaviour in inversion of synthetics with different noise levels