tomographic imaging by reflected and refracted arrivals at the north sea we discuss some processing steps of a marine 3 d data set from the oseberg field north sea we compare the prestack depth migrated images obtained by the velocity fields provided by different tools velocity spectra reflection tomography and joint tomographic inversion of reflected and refracted arrivals the last ones are definitely better we also produced a synthetic example by modeling the estimated earth structure and the actual recording geometry and we reached similar conclusions the correlation between reflected and refracted signals may be unclear for later arrivals because of their reciprocal interference and multiple reflections we adopt a technique based on a surgical mute in the p domain which allows coupling the signals coming from the same elastic interface

cenozoic deformation of the tarim plate and the implications for mountain building in the tibetan plateau and the tian shan 1 the tarim basin in nw china developed as a complex foreland basin in the cenozoic in association with mountain building in the tibetan plateau to the south and the tian shan orogen to the north we reconstructed the cenozoic deformation history of the tarim basement by backstripping the sedimentary rocks two dimensional and three dimensional finite element models are then used to simulate the flexural deformation of the tarim basement in response to the sedimentary loads and additional tectonic loads associated with overthrusting of the surrounding mountain belts the results suggest that uplift of both the western kunlun shan and the tian shan orogens started during or before oligocene since the miocene mountain building accelerated in the western kunlun shan but showed segmented development in the tian shan the results also indicate reduced tectonic load along the altyn tagh fault since late miocene consistent with geological and geophysical evidence of the fault cutting the entire lithosphere and migrating southward during its cause of the cenozoic evolution

did the growth of tibetan topography control the locus and evolution of tien shan mountain building the tien shan in central asia are the pre eminent example of intraplate mountain building and are typically considered an indirect result of the india eurasia collision via the northward indentation of the relatively strong precambrian lithosphere of the tarim plate into the relatively weak paleozoic lithosphere of the tien shan region this hypothesis fails to fully explain the concentration of tien shan mountain building along a tibet parallel axis located 500 700 km from tibet and also fails to explain the close synchronization of tien shan mountain building events with mountain building in tibet i suggest that bending stresses from lithospheric flexure in central asia exerted a critical influence on the locus and evolution of the tien shan models of paleogene to middle miocene flexure indicate that the growth of northeast tibet may have superimposed a strong bending stress field on the regional stress field the resultant stress field is characterized by strong topography normal tensile stress in the tarim basin and an 15 increase in compressive stress in the vicinity of the tien shan this stress field severely reduces the likelihood of mountain building south of the tien shan and increases the likelihood of mountain building within the tien shan this result suggests that the generation of bending stresses from lithospheric flexure is a viable and important mechanism for the propagation of stress and hence deformation into continental interiors

tomographic determination of velocity and depth in laterally varying media estimation of reflector depth and seismic velocity from seismic reflection data can be formulated as a general inverse problem the method used to solve this problem is similar to tomographic techniques in medical diagnosis and we refer to it as seismic reflection tomography seismic tomography is formulated as an iterative gauss newton algorithm that produces a velocity depth model which minimizes the difference between traveltimes generated by tracing rays through the model and traveltimes measured from the data the input to the process consists of traveltimes measured from selected events on unstacked seismic data and a first guess velocity depth model usually this first guess model has velocities which are laterally constant and is usually based on nearby well information and or an analysis of the stacked section the final model generated by the tomographic method yields traveltimes from ray tracing which differ from the measured values in recorded data by approximately 5 ms root mean square the i

effects of particle size of crushed gangue backfill materials on surface subsidence and its application under buildings in recent years solid waste backfill mining has developed rapidly and widely used to control surface subsidence and reduce accumulation of solid waste as crushed materials are used to backfill goafs the particle size of backfill materials becomes a key factor influencing the control of surface subsidence to analyse the influences of particle size of backfill materials on surface subsidence the compaction properties of crushed gangue backfill materials cgbm with different particle sizes were tested by using the yas5000 testing machine and a self made compacting device moreover based on the strain hardening behaviour of cgbm in the process of compaction a method of simulating cgbm using double yield model was put forward by employing this method in simulation the influence of particle size of cgbm on surface subsidence was studied the research results are demonstrated as follows with the increase in particle size of the backfill materials these maximum values such as the maximum surface subsidence horizontal movement inclination curvature and horizontal deformation increased gradually little difference was found in the surface subsidence and movement while using cgbm with particle sizes in the ranges of 2 5 16 and 2 5 50 mm with uniform gradation however both values were obviously smaller than those using cgbm with particle sizes of 20 31 5 and 31 5 50 mm in terms of samples with particle sizes of 2 5 50 mm the gradation of particles was uniform by using large particles to form frame structures and small particles to fill fractures such structures with strong anti deformation abilities produced a small amount of deformation under the load from overlying strata therefore this structure exerted a good controlling effect on surface deformation

depth image focusing in traveltime map based wide angle migration wide aperture prestack depth migration requires application of challenging and time consuming velocity analysis and depth focusing collectively referred to here as depth focusing we present an approach to depth focusing using 1 a detailed starting velocity model obtained by a 1 d transformation of the first arrival times followed iteratively by 2 interactive analysis of the common image gathers 3 computation of coherency attributes of the wavefield in the depth domain and 4 2 d traveltime tomography to update the background velocity model we employ two interactive method of migration velocities refinement in the first method similar to the common midpoint velocity spectrum approach residual velocity updates are picked directly from the common image gathers in another method analogous to the common velocity stacks we pick the velocity updates from the areas of maximum coherency in depth sections that are migrated using rescaled traveltime maps both types of migration velocity picks

fast salt boundary interpretation with optimal path picking salt boundary interpretation is a crucial step for velocity model building in seismic migration but remains a highly labor intensive task for manual interpretation and a big challenge for automatic methods we propose a semi automatic method to efficiently and accurately extract 2d and 3d complicated salt boundaries from a seismic attribute image that highlights salt boundaries in 2d salt boundary extraction we first pick a few points to interpolate an initial curve that is close to the true salt boundary these points are picked near the salt boundary but are not required to be exactly on the boundary which makes human interactions convenient and efficient we then resample the salt boundary attribute image in a band area centered at the initial curve to obtain a new image where the true salt boundary is an open curve extending laterally we then extract the salt boundary in the new image using an optimal path picking algorithm which is robust to track a highly discontinuous salt boundary following

dynamics of the india eurasia collision zone we present simple new dynamic calculations of a vertically averaged deviatoric stress field over a depth average of 100 km for asia from geodetic geologic topographic and seismic data a first estimate of the minimum absolute magnitudes and directions of vertically averaged deviatoric stress is obtained by solving force balance equations for deviatoric stresses associated with gravitational potential energy differences within the lithosphere plus a first order contribution of deviatoric stresses associated with stress boundary conditions this initial estimate of the vertically averaged deviatoric stress field is obtained independent of assumptions about the rheology of the lithosphere absolute magnitudes of vertically averaged deviatoric stresses vary between 5 and 40 mpa assuming bulk viscous behavior for the lithosphere the magnitudes of deviatoric stresses together with the magnitudes of strain rates inferred from quaternary fault slip rate and gps data yield vertically averaged effective viscosities for tibet of 0 5 5 1022 pa s compared with 1 2 5 1023 pa s in more rigid areas elsewhere in the region a forward modeling method that solves force balance equations using velocity boundary conditions allows us to refine our estimates of the vertically averaged effective viscosity distribution and deviatoric stress field the total vertically averaged deviatoric stress and effective viscosity field are consistent with a weak lower crust in tibet they are consistent with some eastward motion of tibet and south china lithosphere relative to eurasia and they confirm that gravitational potential energy differences have a profound effect on the spatially varying style and magnitude of strain rate around the tibetan plateau our results for the vertically averaged deviatoric stress argue for a large portion of the strength of the lithosphere to reside within the seismogenic upper crust to get deviatoric stress magnitudes there to be as high as 100 300 mpa in accord with laboratory and theoretical friction experiments indicating that stress drops in earthquakes are small fractions of the total deviatoric stress

advances in velocity model building technology for subsalt imaging seismic imaging of hydrocarbon accumulations below salt is a formidable challenge because complexly shaped salt bodies severely distort wavefronts or scatter seismic energy we have highlighted some recent advances in building a velocity model for subsalt imaging there are three main stages suprasalt velocity determination salt model definition and subsalt velocity update volumetric high resolution tomography that incorporates high velocity contrast boundaries is used to derive a good sediment velocity model before building a salt model to facilitate integration of interpretation and depth processing beam based interactive imaging is used to refine the salt geometry for subsalt velocity update either subsalt tomography or subsalt scan based techniques can be used depending on the quality of subsalt reflections there are concepts and techniques for attaining subsalt images suitable for hydrocarbon exploration beneath complexly shaped salt bodies

gabor frame based gaussian packet migration we present a gaussian packet migration method based on gabor frame decomposition and asymptotic propagation of gaussian packets a gaussian packet has both gaussian shaped time frequency localization and space direction localization its evolution can be obtained by ray tracing and dynamic ray tracing in this paper we first briefly review the concept of gaussian packets after discussing how initial parameters affect the shape of a gaussian packet we then propose two gabor frame based gaussian packet decomposition methods that can sparsely and accurately represent seismic data one method is the dreamlet gaussian packet method dreamlets are physical wavelets defined on an observation plane and can represent seismic data efficiently in the local time frequency space wavenumber domain after decomposition dreamlet coefficients can be easily converted to the corresponding gaussian packet coefficients the other method is the gabor frame gaussian beam method in this method a local slant stack which is widely used in gaussian beam migration is combined with the gabor frame decomposition to obtain uniform sampled horizontal slowness for each local frequency based on these decomposition methods we derive a poststack depth migration method through the summation of the backpropagated gaussian packets and the application of the imaging condition to demonstrate the gaussian packet evolution and migration imaging in complex models we show several numerical examples we first use the evolution of a single gaussian packet in media with different complexities to show the accuracy of gaussian packet propagation then we test the point source responses in smoothed varying velocity models to show the accuracy of gaussian packet summation finally using poststack synthetic data sets of a four layer model and the two dimensional seg eage model we demonstrate the validity and accuracy of the migration method compared with the more accurate but more time consuming one way wave equation based migration such as beamlet migration the gaussian packet method proposed in this paper can correctly image the major structures of the complex model especially in subsalt areas with much higher efficiency this shows the application potential of gaussian packet migration in complicated areas

environmentally sustainable mining a case study of intermittent cut and fill mining under sand aquifers this paper presents an investigation on the effects of intermittent cut and fill mining on the overburden failure under sand aquifers in the intermittent cut and filling method the panel is divided into long pillars and then entries in every long pillar into a narrow strip every narrow strip is then cut and backfilled field measurements scale model tests and numerical simulations are used to compare overburden failure and subsidence due to three mining methods intermittent cut and fill mining longwall excavation and continuous filling these methods were applied in a case study of the taiping coal mine in shandong china the results of the numerical simulation and scale model testing reveal that the height of the maximum caving and water conducting fractured zones and the maximum subsidence due to intermittent cut and fill mining are much smaller than those with the use of longwall excavation and continuous filling and well verified by the field measurements additionally the numerical simulation results of the stress distribution and variation during intermittent cut and fill mining are in close agreement with those of the field measurements it has been proved that the intermittent cut and fill mining can successfully mitigate the overburden failure and subsidence which contribute to preventing water and sand inrush into coal mines under sand aquifers this provides a less costly and more effective approach to address surface subsidence and mine caving problems

geodynamics of the tarim basin and the tian shan in central asia the india asia collision has caused crustal thickening in tibet by at least a factor of 2 in the last 20 30 myr of this collision the tian shan mountain range has also been reactivated the tarim basin however shows little internal deformation we describe a series of numerical experiments which constrain the effective lithospheric strength parameters of the tarim basin and the tian shan in the context of a thin viscous sheet model we use a finite element representation of the thin viscous sheet model to approximate the deformation field in the india asia collision and compare model crustal thickness distributions with that inferred from a local isostatic model of topography the experiments show that a strong tarim basin while undergoing little internal deformation transfers strain to the tian shan producing significant crustal thickening in the tian shan region based only on diagnostic parameters such as the maximum thickening in the tian shan and the minimum in the tarim basin the principal features of the topography can be approximately reproduced using models in which either the tarim basin is strong or the tian shan is weak or both for a rheological model in which the stress versus strain rate exponent is n 3 the strength coefficient for the strong tarim basin model vtarim is between about 1 7 and 2 for the weak tian shan model the relative strength coefficient vtian is between about 0 65 and 0 75 if both strong tarim and weak tian shan are included there is a trade off between the required values of vtarim and vtian and the shape of the predicted crustal thickness profiles better matches the observed profiles the steep topographic slope on the southern margin of the tarim basin requires that it is anomalously strong while the rapid decrease of topographic height to the north of the tian shan requires that it is anomalously weak similar conclusions are obtained with a rheological model based on n 10 simplified rheological models of the lithosphere show that the variations in lithospheric strength may be explained by changes to the moho temperature of the order of 10 to 30 c

late cenozoic tectonic evolution of the southern chinese tian shan structural sedimentological magnetostratigraphic and 40ar 39ar thermochronological investigations were conducted in the southern chinese tian shan on the basis of our own mapping and earlier investigations in the area the late cenozoic southern tian shan thrust belt may be divided into four segments based on their style of deformation from west to east they are 1 kashi aksu imbricate thrust system 2 the baicheng kuche fold and thrust system 3 the korla right slip transfer system and 4 the lop nor thrust system the westernmost kashi aksu system is characterized by the occurrence of evenly spaced 12 15 km imbricate thrusts the baicheng kuche and korla systems are expressed by a major north dipping thrust the kuche thrust that changes its strike eastward to become a nw striking oblique thrust ramp the korla transfer zone the lop nor system in the eastern most part of the southern chinese tian shan consists of widely spaced thrusts all involved with basement rocks geologic mapping and cross section construction suggest that at least 20 40 km of crustal shortening with a horizontal shortening strain of 20 30 has occurred in the southern chinese tian shan during the late cenozoic these estimates are minimum because of both conservative extrapolation of the thrust geometries and partial coverage of the thrust belt by the cross sections the timing of initial thrusting is best constrained in the kuche basin where crustal shortening may have occurred at 21 24 ma the time of a major facies transition between lacustrine and braided fluvial sequences constrained in general by biostratigraphy and in detail by magnetostratigraphy this estimate represents only a minimum age as development of thrusts in the southern chinese tian shan may have propagated southward toward the foreland thus the sedimentary record only represents the southernmost and therefore youngest phase of thrusting if our estimate of timing for the thrust initiation 21 24 ma is correct using the estimated magnitude of shortening 20 40 km and shortening strain 20 30 the averaged rates of late cenozoic horizontal slip and shortening strain are 1 1 9 mm yr 1 and 2 9 4 5 10 16 s 1 respectively our reconnaissance 40ar 39ar thermochronological analysis in conjunction with earlier published results of apatite fission track analysis by other workers in the chinese tian shan suggests that the magnitude of cenozoic denudation is no more than 10 km most likely less than 5 km we demonstrate via a simple airy isostasy model that when the thermal effect on changes in surface elevation is negligible determination of the spatial distribution and temporal variation of both horizontal shortening strain and denudation becomes a key to reconstructing the elevation history of the tian shan using this simple model the loosely constrained magnitude of crustal shortening strain and denudation in the southern chinese tian shan implies that it may have been elevated 1 0 2 0 km since the onset of cenozoic thrusting

amplitude versus angle analysis of local angle domain common image gathers with prestack gaussian beam migration of seismic data the analysis of seismic reflection amplitude versus angle amplitude versus offset ava avo is an important tool for investigating the physical properties of subsurface rocks and or reservoirs we propose to generate local angle domain common image gathers adcigs from the surface recorded seismic data for ava analysis via gaussian beam migration gbm using a deconvolution imaging condition the traditional seismic reflection amplitude analysis is often based on the avo response from common middle point cmp gathers however the avo analysis based on the horizontally layered medium assumption can achieve success only in simple geological cases our approach provides an ava response during the migration process that reveals true local physical properties in the image domain even if the image point is at a tilted interface or has a complicated overburden geological structure we test our approach with a two layer velocity model with a tilted interface and with the benchmark marmousi2 model that has a complicated geological structure from these two numerical examples we demonstrate that our method faithfully provides the ava response that can be used to further interpret the rock reservoir physical properties

compressional velocity structure and poisson s ratio in marine sediments with gas hydrate and free gas by inversion of reflected and refracted seismic data south shetland islands antarctica abstract a bottom simulating reflector bsr on the south shetland margin antarctic peninsula was surveyed within the progetto nazionale di ricerche in antartide pnra high resolution multichannel mcs reflection profiles were acquired and a three component ocean bottom seismograph obs was deployed where the bsr was particularly strong the compressional velocity field associated to the bsr was determined by the inversion of travel times of reflected mcs data and refracted obs data events information on shear wave velocities was extracted from the horizontal components of the obs records the analysis indicates the presence of velocity anomalies both above and below the bsr that are not related to the lithologic characteristics of the sedimentary column but can be associated to gas hydrate and free gas presence in pore space amplitude versus offset avo analysis was performed on common depth point gathers which correspond to the obs position the study determined reflection coefficient trends that provided qualitative information about gas hydrate and free gas abundance a theoretical model for elastic porous media was applied to quantify amounts of gas hydrate and free gas the resulting theoretical velocity curves were compared to interval velocity obtained by seismic inversion a quantitative estimation of free gas and gas hydrates trapped in the sediment pore spaces was made by interpreting velocity anomalies with respect to reference velocity curves normally consolidated marine terrigenous sediments the comparison of the results obtained by these independent methods seismic inversion avo analysis and theoretical model gives consistent values of poisson s ratio and gas hydrate and free gas estimation

2 d wavepath migration prestack kirchhoff migration km is computationally intensive for iterative velocity analysis this is partly because each time sample in a trace must be smeared along a quasi ellipsoid in the model as a less costly alternative we use the stationary phase approximation to the km integral so that the time sample is smeared along a small fresnel zone portion of the quasi ellipsoid this is equivalent to smearing the time samples in a trace over a 1 5 d fat ray i e wavepath so we call this wavepath migration wm this compares to standard km which smears the energy in a trace along a 3 d volume of quasi concentric ellipsoids in principle single trace migration with wm has a computational count of o n1 5 compared to km which has a computational count of o n3 where n is the number of grid points along one side of a cubic velocity model our results with poststack data show that wm produces an image that in some places contains fewer migration artifacts and is about as well resolved as the km

3 d prestack kirchhoff beam migration for depth imaging a beam implementation is presented for efficient full volume 3 d prestack kirchhoff depth migration of seismic data unlike conventional kirchhoff migration in which the input seismic traces in time are migrated one trace at a time into the 3 d image volume for the earth s subsurface the beam migration processes a group of input traces a supergather together the requirement for a supergather is that the source and receiver coordinates of the traces fall into two small surface patches the patches are small enough that a single set of time maps pertaining to the centers of the patches can be used to migrate all the traces within the supergather by taylor expansion or interpolation the migration of a supergather consists of two major steps stacking the traces into a p beam volume and mapping the beams into the image volume since the beam volume is much smaller than the image volume the beam migration cost is roughly proportional to the number of input supergathers the computational speedup of be

3d wavepath migration 3d kirchhoff migration km smears a trace s time sample along a quasi ellipsoid in the model space this is a costly and sometimes noisy process as reflection energy is smeared far away from the actual reflector position introducing far field migration artefacts as a reduced form of 3d km 3d wavepath migration wm smears a picked reflection arrival to a small fresnel zone portion centred about the specular reflection point leading to fewer migration artefacts and reduced computation time both the traveltime and the angle of incidence are required by wm for locating the specular reflection point our results with 3d prestack synthetic data show that wm generates fewer migration artefacts and can sometimes define complex structure better than km our results with 3d prestack field data show that wm can mostly suppress migration artefacts and can sometimes resolve reflection interfaces better than km the cpu comparison shows that for both the synthetic and field data examples wm can be more than an order of magnitude faster than km the limitation with 3d wm is that the angle of incidence calculation is sensitive to the recording geometry and the signal to noise s n ratio which can lead to blurred images

cenozoic tectonic and geodynamic evolution of the kyrgyz tien shan mountains a review of geological thermochronological and geophysical data abstract the complex crustal structure of the tien shan has a strong impact on the distribution of strain induced by the india eurasia collision with intracontinental deformation in eurasia s interior as a distant effect the northward propagation of the india eurasia deformation front is suggested by the rejuvenation of mountain ranges and intermittent intramontane basins the tien shan basement is formed by the rigid heterogeneous precambrian blocks microcontinents of tarim issyk kul or central tien shan and aktyuz boordin surrounded by a soft matrix of paleozoic accretion collision belts the kyrgyz tien shan mountains are situated between the active structures of the tarim plate and the pamir indenter south and the stable kazakhstan shield north underplating by the tarim plate and thrusting by the pamirs are responsible for the building of the cenozoic tien shan the reactivation of its inherited structural fabric and the tectonic layering of the upper lithosphere underlying the area large earthquakes m 6 delineate the northern and southern margins of the issyk kul microcontinent indicating that crustal heterogeneity influenced the location of active structures in the northern kyrgyz tien shan

lithospheric deformation beneath the altyn tagh and west kunlun faults from recent gravity surveys 1 new gravity and topographic elevation data crossing the altyn tagh and west kunlun faults in northern tibet are used to test key features of a recently proposed tectonic model for the northern boundary of the tibetan plateau the observations collected in 1997 and 1998 at 468 stations along three profiles were converted to bouguer gravity anomalies to constrain flexural models for isostatic compensation of the large relief associated with these faults initially we failed to reproduce the main features of the gravity anomalies with any isostatic model that assumes that the main contribution to the observed gravity anomalies is from the flexure of the moho by integrating sedimentary information derived from exploration seismology in the tarim and qaidam basins we obtained satisfactory fits to the data using simple models of isostasy no elastic strength across the altyn tagh is required to fit the gravity data suggesting that the fault breaks the entire lithosphere beneath it and has negligible thrust component currently or in the past this result is consistent with tectonic models that create the thickened crust of northern tibet through thick skinned thrust sheets progressively overriding asia to the northeast as the altyn tagh behaving as a classic transform fault propagates in that direction farther west the gravity observations across the west kunlun are best explained by significant underthrusting of the high topography by an elastic plate with effective thickness between 30 and 40 km in agreement with geologic interpretation and modeling of earlier but very sparse gravity observations

environmentally sustainable mining a case study on surface subsidence control of grouting into overburden this paper presents an investigation on the effect of grouting into multi bed separation to control mining induced surface subsidence in the overburden without obvious thick and hard strata for generating large scale bed separation overburden grouting is carried out by increasing the number of boreholes and grouting strata the scale model test numerical simulation and field measurements are used to study distribution and process of bed separation and to compare the overburden failure with surface subsidence due to pre and post overburden grouting with a case study of the qi nan coal mine anhui province china the scale model test and numerical simulation results of the overburden grouting process are in close agreement with those obtained from the field measurements filling masses with different diffusion radii are commonly formed in the different bed separation which are overlaid to control the surface subsidence it is proven that overburden grouting can successfully mitigate overburden failure and subsidence without obvious hard strata and bed separations this provides an effective and cost efficient approach for addressing the surface subsidence and overburden deformation problems due to mining

introduction to this special section low frequency seismic geophysicists in the seismic exploration industry have long recognized the potential benefits of extending the bandwidth of seismic measurements to well below 10 hz low frequencies generated by a seismic shot travel much farther through the subsurface than do higher frequencies just as the low frequencies in thunder travel farther in the atmosphere thus the amount of power available in the low end of the seismic spectrum is especially important for deep exploration targets such as subsalt and sub basalt plays and for deep crustal studies in many areas of the world higher frequencies are often too attenuated scattered and dispersed to provide useful signal for probing such objectives also low frequencies play a critical role in the inversion process by which seismic data are converted into acoustic impedance sections and ultimately into reservoir properties surface seismic data usually lack low frequencies necessary for accurate inversion so they are commonly augmented by data from well log me

enhanced prestack depth imaging of wide azimuth data from the gulf of mexico a case history we present a case study of enhanced imaging of wide azimuth data from the gulf of mexico utilizing recent technologies and we discuss the resulting improvements in image quality especially in subsalt areas relative to previous results the input seismic data sets are taken from many large scale wide azimuth surveys and conventional narrow azimuth surveys located in the mississippi canyon and atwater valley areas in the course of developing the enhanced wide azimuth processing flow the following three key steps are found to have the most impact on improving subsalt imaging 1 3d true azimuth surface related multiple elimination srme to remove multiple energy in particular complex multiples beneath salt 2 reverse time migration rtm based delayed imaging time dit scans to update the complex subsalt velocity model and 3 tilted transverse isotropic tti rtm to improve image quality our research focuses on the depth imaging aspects of the project with particular emphasis on the applicati

mass transfer between eastern tien shan and adjacent basins central asia constraints on regional tectonics and topography summary using depths and ages derived from isopachs drill holes or cross sections it is possible to reconstruct the space time depositional history of a sedimentary basin drill holes and cross sections give the local sedimentation history while isopachs allow the definition of the spatial distribution of the sediments assuming several simple hypotheses such as similarity of the strata and regional applicability of results derived from local analyses one can reconstruct balanced maps of the solid or grain volumes and hence the mass of sediments deposited during several time intervals since the palaeogene applying this method to the tarim and dzungar basins nw china we estimate the total cenozoic solid phase volume and mass of sediments stored to be 1358 f 520 x lo3 km3 36 7 f 14 x 1017 kg and 172 f 56 x lo3 km3 4 6 f 1 5 x 1017 kg respectively the reconstruction also enables us to detect two main pulses in the sedimentation the first around 17 ma affected only the northern part of the tarim basin also known as the kucha or kuche depression at the foot of the tien shan mountains and supports the idea that the presently active shortening regime in that range started at that time the second 5 to 6 ma affected most of the depositional areas of the region and may have an even greater geographical extent assuming local isostasy we estimate the volume of shortening induced by the rotation of the tarim block relative to siberia and stored in the range and adjacent basins to be between 1 15 x lo6 and 4 23 x lo6 km3 this correspbnds to a clockwise rotation of between 2 5 and 8 7 we use these results in two simple models of self similar growth of pyramidal topographies that approximately fit the eastern tien shan

origin and deformation of intra salt sulphate layers an example from the dutch zechstein late permian from salt mine galleries and well data it is known that thick rock salt layers can contain anhydrite and carbonate layers with thicknesses on the millimetre to tens of metre scale the relatively thick zechstein 3 anhydrite carbonate layer in the northern netherlands has been studied previously using 3 d seismic data observations from geophysical well logs in this study reveal the presence of thin sulphate layers on the sub seismic scale imbedded in the zechstein 2 z2 salt core samples thin sections seismic data and geochemical measurements were used to determine the mineralogy and origin of one of these z2 sulphate layers bromine analyses show that they mark a freshening event in the z2 salt which can be correlated over large distances in the northern netherlands their core calibrated log signature indicates that the z2 sulphate layers consist either of pure anhydrite or of anhydrite and polyhalite the mineralogy and thickness of the sulphate layers are interpreted to vary between synsedimentary morphologic lows thin anhydrite polyhalite couplets and highs thicker anhydrite layers such a combination of core observations and well log analysis is a powerful tool to detect lateral trends in evaporite mineralogy and to reconstruct the environmental setting of their formation salt internal geometries can further be used to distinguish between different deformation mechanisms in our study area the distribution of sulphate layers within the z2 salt indicates that subjacent salt dissolution was not the dominant process leading to salt related deformation

flexure of the continental lithosphere with multilayered rheology summary in this paper a model of flexure of the continental lithosphere is derived taking into account crustal and mantle rheologies bending of the continental lithosphere is modelled with a double yield stress envelope three layers brittle elastic and ductile for the crust and three analogous layers for the mantle portion the deformation of the layers is controlled by the rheological properties of quartz rich crustal rocks and olivine rich mantle rocks the influence of various factors such as the depth of moho strain rates thermal structure of the lithosphere boundary conditions and topographic load is examined results show that the mechanical strength of the continental lithosphere in the horizontal and vertical directions is primarily controlled by the present thermal structure of the plate boundary forces and moments and the applied topographic load this explains why mountainous regions may be more locally compensated than adjacent regions we also thus are able to explain why many continental plates have apparent effective rigidities much smaller than those predicted on the basis of their geological ages the model is then applied to the tien shan tarim area central asia and original topography and gravity data are used to constrain parameters of the model we found that the model satisfactorily matches the data and is also able to predict the thermal state of the plate and the location of the deep seismicity

exhumation of basement cored uplifts example of the kyrgyz range quantified with apatite fission track thermochronology 1 the kyrgyz range the northernmost portion of the kyrgyzstan tien shan displays topographic evidence for lateral propagation of surface uplift and exhumation the highest most deeply dissected segment lies in the center of the range to the east topography and relief decrease and preserved remnants of a cretaceous regional erosion surface imply minimal amounts of bedrock exhumation the timing of exhumation of range segments defines the lateral propagation rate of the range bounding reverse fault and quantifies the time and erosion depth needed to transform a mountain range from a juvenile to a mature morphology new multicompositional apatite fission track aft data from three transects from the eastern kyrgyz range combined with published aft data demonstrate that the range has propagated over 110 km eastward over the last 7 11 myr on the basis of the thermal and topographic evolutionary history we present a model for a time varying exhumation rate driven by rock uplift and changes in erodability and the timescale of geomorphic adjustment to surface uplift easily eroded cenozoic sedimentary rocks overlying resistant basement control early rapid exhumation and exhibit slow surface uplift rates as increasing amounts of resistant basement are exposed exhumation rates decrease while surface uplift rates are sustained or increase thereby growing topography as the range becomes high enough to cause ice accumulation and to develop steep river valleys fluvial and glacial erosion becomes more powerful and exhumation rates once again increase independently determined range normal shortening rates also varied over time suggesting a feedback between erosional efficiency and shortening rate

3d common reflection point based seismic migration velocity analysis three dimensional prestack depth migration and depth residual picking in common image gathers cigs are the most time consuming parts of 3d migration velocity analysis most migration based velocity analysis algorithms need spatial coordinates of reflection points and cig depth residuals at different offsets or angles to provide updated velocity information we propose a new algorithm that can analyze 3d velocity quickly and accurately spatial coordinates and orientations of reflection points are provided by a 3d prestack parsimonious depth migration the migration involves only the time samples picked from the salient reflection events on one 3d common offset volume ray tracing from the reflection points to the surface provides a common reflection point crp gather for each reflection point predicted nonhyperbolic moveouts for local velocity perturbations based on maximizing the stacked amplitude give the estimated velocity updates for each crp gather then the velocity update for each voxel in the velocity model is obtained by averaging over all predicted velocity updates for that voxel prior model constraints may be used to stabilize velocity updating compared with other migration velocity analyses the traveltime picking is limited to only one common offset volume and needs to be done only once there is no need for intensive 3d prestack depth migration hence the computation time is orders of magnitude less than other migration based velocity analyses a 3d synthetic data test shows the algorithm works effectively and efficiently

common reflection surface stack image and attributes the common reflection surface stack provides a zero offset simulation from seismic multicoverage reflection data whereas conventional reflection imaging methods e g the nmo dip moveout stack or prestack migration require a sufficiently accurate macrovelocity model to yield appropriate results the common reflection surface crs stack does not depend on a macrovelocity model we apply the crs stack to a 2 d synthetic seismic multicoverage dataset we show that it not only provides a high quality simulated zero offset section but also three important kinematic wavefield attribute sections which can be used to derive the 2 d macrovelocity model we compare the multicoverage data derived attributes with the model derived attributes computed by forward modeling we thus confirm the validity of the theory and of the data derived attributes for 2 d acquisition the crs stack leads to a stacking surface depending on three search parameters the optimum stacking surface needs to be determined for each point

gaussian beam migration just as synthetic seismic data can be created by expressing the wave field radiating from a seismic source as a set of gaussian beams recorded data can be downward continued by expressing the recorded wave field as a set of gaussian beams emerging at the earth s surface in both cases the gaussian beam description of the seismic wave propagation can be advantageous when there are lateral variations in the seismic velocities gaussian beam downward continuation enables wave equation calculation of seismic propagation while it retains the interpretive raypath description of this propagation this paper describes a zero offset depth migration method that employs gaussian beam downward continuation of the recorded wave field the gaussian beam migration method has advantages for imaging complex structures like finite difference migration it is especially compatible with lateral variations in velocity but gaussian beam migration can image steeply dipping reflectors and will not produce unwanted reflectio

crp based seismic migration velocity analysis a new migration velocity analysis is developed by combining the speed of parsimonious prestack depth migration with velocity adjustments estimated within and across common reflection point crp gathers the proposed approach is much more efficient than conventional tomographic velocity analysis because only the traces that contribute to a series of crp gathers are depth migrated at each iteration the local interval velocity adjustments for each crp are obtained by maximizing the stack amplitude over the predicted nonhyperbolic moveout in each crp gather this does not involve retracing rays at every iteration the velocity in each pixel is updated by averaging over all the predicted velocity updates finally crp positions and orientations are updated by parsimonious migration and rays are retraced to define new crp gathers for the next iteration this ensures internal consistency between the updated velocity model and the crp gather because the algorithm has a gridded model parameterization no explicit representation or fitting of reflectors is involved strong lateral velocity variations such as those found at salt flanks can be handled application to synthetic and field data sets show that the proposed algorithm works effectively and efficiently

paraxial ray kirchhoff migration a rapid nonrecursive prestack kirchhoff migration is implemented for 2 d or 2 5 d media by computing the green s functions both traveltimes and amplitudes in variable velocity media with the paraxial ray method since the paraxial ray method allows the green s functions to be determined at points which do not lie on the ray two point ray tracing is not required the green s functions between a source or receiver location and a dense grid of thousands of image points can be estimated to a desired accuracy by shooting a sufficiently dense fan of rays for a given grid of image points the paraxial ray method reduces computation time by one order of magnitude compared with interpolation schemes the method is illustrated using synthetic data generated by acoustic ray tracing application to vsp data collected in a borehole adjacent to a reef in michigan produces an image that clearly shows the location of the reef

building the northern tien shan integrated thermal structural and topographic constraints abstract paired apatite fission track and u th he dates provide the first late cenozoic cooling ages for the northern tien shan these data clearly argue for pulsed deformation since the late miocene with early 10 11 ma and late 0 3 ma intervals of rapid exhumation separated by an extended interval of much slower rates by integrating these bedrock cooling rates with shortening estimates derived from a balanced section detrital cooling ages and geomorphological estimates of conditions before deformation we reconstruct a four stage history of range growth and exhumation following 100 m yr of tectonic quiescence abruptly accelerated rock uplift exhumation and cooling in the kyrgyz range commenced at 11 ma with rates exceeding 1 km m yr during the subsequent 7 m yr deformation and cooling rates decreased three to sixfold before accelerating by comparable amounts during the past 3 m yr since mid miocene times the surface elevation of the kyrgyz range has increased 2 km consistent with

tomographic evidence for localized lithospheric shear along the altyn tagh fault seismic tomography across the altyn tagh fault at the north edge of the tibetan plateau reveals a low p wave velocity anomaly below the fault down to 140 kilometers this anomaly probably reflects strike slip shear in the lithosphere slip partitioning may also induce a wedge of crust from the tarim basin to plunge into the mantle

polarization based wave equation migration velocity analysis in acoustic media abstractthe source extrapolation step in wave equation prestack reverse time migration gives wavefield polarization information which can be used to generate angle domain common image gathers adcigs from seismic reflection data from acoustic media concatenation of p wave polarization segments gives wavefield propagation paths wavepaths which are similar to the raypaths in ray based velocity tomography the adcigs provide residual depth moveout rmo information from which a system of linear equations is constructed for tomography to solve for the velocity ratio used for velocity updating an empirical relation between the rmo data and the velocity ratio updates reduces the amount of computation and is stabilized by the feedback provided by the iterative loop through prestack migration to rmo to velocity update to prestack migration correcting the rmos to flatten the adgigs is the convergence condition synthetic data for a layered model with a fault successfully illustrates the method

tectonostratigraphic history of the southern tian shan western china from seismic reflection profiling abstract the modern tian shan formed due to the india eurasia collision uplift of the tian shan is recorded notably by the sedimentary sequences and subsidence history of the coupling foreland basins we analyzed a 353 km long seismic profile and logging data of four wells in the southern tian shan foreland area to decipher its tectonic stratigraphic and subsidence history the sedimentary sequences comprise the cambrian silurian devonian permian triassic jurassic cretaceous and paleogene tectonostratigraphic units overlain by the late oligocene quaternary foreland basin unit the jidike formation is the oldest sedimentary sequence of the foreland succession deposited at 26 ma based on magnetostratigraphic constraints indicating that uplift of the southern tian shan was initiated by at least 26 ma in addition the tectonic subsidence rate of the southern tian shan foreland basin increased significantly since 26 ma due to lithospheric flexure caused by building of the topography of the southern tian shan the envelope line of the forelandward onlaping points within the foreland unit indicates that the forebulge of the southern tian shan foreland basin migrated southwards at 1 6 0 1 mm yr between 26 ma and 12 ma and at 14 6 0 1 mm yr after 12 ma the increase of migration rate at 12 ma suggests an accelerated convergence between the tarim basin and the tian shan

staining algorithm for seismic modeling and migration abstractin seismic migration some structures such as those in subsalt shadow zones are not imaged well the signal in these areas may be even weaker than the artifacts elsewhere we evaluated a method to significantly improve the signal to noise ratio s n in poorly illuminated areas of the model we constructed a phantom wavefield an extension of the wavefield to the complex domain the imaginary wavefield was synchronized with the real wavefield but it contained only the events relevant to a target region of the model which was specified using a staining algorithm the real wavefield interacted with the entire model however all structures except for the target were transparent to the imaginary wavefield which is excited only when the real wavefront arrives at the target structure the real and the imaginary source wavefields were crosscorrelated with the regular receiver wavefield the results were revealed in two images the conventional reverse time migration image and an image of the target

evolution of the cenozoic tarim basin by flexural subsidence and sediment ponding insights from quantitative basin modelling abstract the tarim basin became a closed continental sedimentary basin in the cenozoic due to uplift of the western kunlun tian shan and the altyn tagh ranges in the context of the indian asia collision a north northeast trending seismic profile across the basin reveals that cenozoic strata comprise a wedge of sediments in the southern and northern regions generated by flexural subsidence overlain by a more uniform regional sediment drape we obtain the subsidence profiles across the basin at 26 ma 13 ma 5 ma and the present day using backstripping based on the sedimentary architecture shown in the seismic profile we use a numerical finite elastic plate to model these subsidence profiles our modelling indicates that the southern and northern flexural depressions started to interfere to form a single flexural bulge within the basin since late paleogene times the flexural bulge migrated 52 km toward the western kunlun range since 26 ma reflecting a decrease in the ratio of loads of the western kunlun range versus the tian shan we separate the sediment drape from the flexural subsidence according to the preceding modelling results our separating demonstrates that the thickness of the drape increased from 230 30 m at 26 ma to 1910 200 m at present occupying 30 of cenozoic strata in the profile the rise in the base level since the paleogene is estimated as 356 80 m by correcting for sediment loading of the drape we adopt a decreasing basin width to model the evolution of the flexural subsidence suggesting significant uplifting of the western kunlun range and the tian shan from 26 ma to 13 ma relative stable elevations in these ranges from 13 ma to 5 ma and their rapid uplifts since 5 ma

prestack 2d parsimonious kirchhoff depth migration of elastic seismic data we have extended prestack parsimonious kirchhoff depth migration for 2d two component reflected elastic seismic data for a p wave source recorded at the earth s surface first we separated the p to p reflected pp waves and p to s converted ps waves in an elastic common source gather into p wave and s wave seismograms next we estimated source ray parameters source p values and receiver ray parameters receiver p values for the peaks and troughs above a threshold amplitude in separated p and s wavefields for each pp and ps reflection we traced 1 a source ray in the p velocity model in the direction of the emitted ray angle determined by the source p value and 2 a receiver ray in the p or s velocity model back in the direction of the emergent pp or ps wave ray angle determined by the pp or ps wave receiver p value respectively the image point position was adjusted from the intersection of the source and receiver rays to the point where the sum of the source time and receiver ray

tomographic velocity estimation with plane wave synthesis in areas with structurally complex geology tomographic velocity analysis is often required to estimate velocities in this paper i describe an algorithm for tomographic velocity estimation that uses plane wave synthesis imaging as a prestack migration the classical iterative two step process measures the traveltime errors with the current velocity model and then update the velocity model is performed as follows the events are picked in the image space after prestack migration with surface oriented plane wave synthesis imaging the traveltime deviations are measured through residual moveout rmo velocity analysis in common surface location csl gathers obtained by reflector oriented plane wave synthesis imaging and the velocity update is calculated by inverting the traveltime deviations through a conjugate gradient the results from synthetic data indicate that the tomographic method successfully estimates interval velocity models that lead to depth migrated images with no residual moveout

the intraplate character of supercontinent tectonics abstract for several decades geoscientists have recognised intraplate tectonic activity far from plate margins both from modern and ancient examples this apparent disconnect with the drivers of plate tectonics does not necessarily imply unconnected processes but rather an uncertainty in understanding exactly how these systems operate are the driving forces derived locally or do they propagate from plate margins how do these forces interact with a complex tectonic inheritance to generate the observed tectonism furthermore what novel approaches have been applied to understand these processes here we review the general literature and the contents of this special issue to develop some partial answers to these questions key observations include the critical importance of local lithospheric heterogeneities as a control on the mode of orogenesis and also the role of locally derived forces from mantle upwelling or from depositing thick piles of magmatic or sedimentary rocks these processes happen within the overarching tectonic setting provided by far field plate margins which show intimate links in both time and observed processes with many intraplate regions these insights would not be possible without a growing arsenal of geological geophysical and numerical methods that can be applied to intraplate regions and this is reflected in the varied approaches within the issue we envisage that this special issue will provide a stimulus for further progress in understanding intraplate tectonics

time migration velocity analysis by image wave propagation of common image gathers image wave propagation or velocity continuation describes the variation of the migrated position of a seismic event as a function of migration velocity image wave propagation in the common image gather cig domain can be combined with residual moveout analysis for iterative migration velocity analysis mva velocity continuation of cigs leads to a detection of those velocities in which events flatten although image wave continuation is based on the assumption of a constant migration velocity the procedure can be applied in inhomogeneous media for this purpose cigs obtained by migration with an inhomogeneous macrovelocity model are continued starting from a constant reference velocity the interpretation of continued cigs as if they were obtained from residual migrations leads to a correction formula that translates residual flattening velocities into absolute time migration velocities in this way the migration velocity model can be improved iteratively until a satisfactory result is reached wi

seismic characterization of fractured reservoirs by focusing gaussian beams abstractnaturally fractured reservoirs occur worldwide and they account for the bulk of global oil production the most important impact of fractures is their influence on fluid flow to maximize oil production the characterization of a fractured reservoir at the scale of an oil field is very important for fluid transport the critical parameters are connectivity and transmittivity plus orientation these can be related to fracture spacing compliance and orientation which are the critical seismic parameters of rock physics models we discovered a new seismic technique that can invert for the spatially dependent fracture orientation spacing and compliance using surface seismic data unlike most seismic methods that rely on using singly scattered diffracted waves whose signal to noise ratios are usually very low we found that waves multiply scattered by fractures can be energetic the direction information of the fracture multiply scattered waves contains fracture orientation and spacing informati

introduction to this special section subsalt exploration salt basins occur worldwide figure 1 and large hydrocarbon deposits are often associated with the presence of salt structures due to favorable conditions for accumulation and trapping of oil and gas because of the cost and difficulty of drilling subsalt it is important to be able to image subsalt prospects correctly however the large velocity contrast between the salt and sediments and the complexity of many salt bodies make subsalt imaging a difficult task a step change in technology is therefore required and two recent workshops have been held to address the issues the workshop on subsalt imaging problems practical problems seeking solutions was held at the colorado school of mines in 2005 during which presenters from oil and service companies focused on the difficulties of subsalt imaging leveille et al tle 2005 the 2006 seg eage summer research workshop on subsalt exploration and development imaging interpretation and drilling what have we learned covered a wide range of sal

generalized staining algorithm for seismic modeling and migration abstractthe staining algorithm is introduced to improve the signal to noise ratio s n of poorly illuminated subsurface structures in seismic imaging however the amplitudes of the original and the stained wavefield i e the real and the imaginary wavefields differ by several orders of magnitude and the waveform of the stained wavefield may be greatly distorted we have developed a generalized staining algorithm gsa to achieve amplitude preservation in the stained wavefield the real wavefield and the stained wavefield propagate in the same velocity model a source wavelet is used as the source of the real wavefield however the real wavefield is extracted from the stained area as the source of the stained wavefield the gsa maintains some properties of the original staining algorithm the stained wavefield is synchronized with the real wavefield and it contains only information relevant to the target region by imaging with the stained wavefield we obtain higher s ns in images of target struct

efficient velocity model building for prestack depth migration prestack depth migration is capable of imaging subsurface reflectors in the presence of severe lateral velocity gradients however to produce accurate images of such structures using prestack depth migration it is critical to build an accurate velocity model the velocity model building should be data driven and based upon offset consistency that is images from different offsets must be identical to one another if the velocity model is correct velocity model building is typically iterative and requires many runs of computationally intensive prestack depth migration

a 3d subsalt tomography based on wave equation migration perturbation scans we have developed a simple but practical methodology for updating subsalt velocities using wave equation migration perturbation scans for the sake of economy and scalability with respect to full source receiver migration and accuracy with respect to common azimuth migration we use shot profile wave equation migration as input for subsalt velocity analysis we provide wave equation migration scans with velocity scanning limited to the subsalt sediments throughout the migration scan sections we look for the best focusing or structural positioning of characteristic seismic events the picking on the migration stacks selects the value of the best perturbation attribute alpha scaling factor along with the corresponding position and local dip for the chosen seismic events the associated locally coherent events are then demigrated to the base of the salt horizon our key observation is that this process is theoretically equivalent to performing a datuming to a base of salt followed by subsalt migr

geologically constrained seismic imaging workflow we present the geologically constrained workflow for velocity model building as a case study from offshore brazil the workflow involves basin reconstruction gravity modeling and seismic interpretation in addition to standard prestack depth migration psdm model building tools building a salt model based on seismic evidence can be highly nonunique in a geologically constrained seismic processing workflow the main aim is to use geologic understanding with geophysical models and datasets to improve an input velocity realization for the psdm loop thereby improving image quality all of these methods are inherently uncertain and a final model is based on a range of subjective choices thus a final result that agrees with all sciences still can be completely wrong however an understanding of these choices enables a unique way of testing and constraining the number of antimodels velocity models that fit the observations but are different from the final result this can reduce time spent and uncertainty in geologic evaluation

magnetostratigraphy of the yaha section tarim basin china 11 ma acceleration in erosion and uplift of the tian shan mountains we report a magnetostratigraphic and rock magnetic study of the yaha section located on the southern flank of the central tian shan mountains asia our results show a two fold increase in sedimentation rate as well as marked changes in rock magnetic characteristics ca 11 ma after 11 ma sedimentation rate remained remarkably constant until at least 5 2 ma these findings are consistent with sedimentary records from other sections surrounding the tian shan we conclude that uplift and erosion of the tian shan accelerated ca 11 ma long after the onset of the collision between india and asia and that the range rapidly evolved toward a steady state geometry via a balance between tectonic and erosion processes

stable isotopic constraints on the tectonic topographic and climatic evolution of the northern margin of the tibetan plateau abstract this study presents oxygen and carbon isotopic records from lacustrine paleosol alluvial and fluvial carbonate sampled in thirteen cenozoic sedimentary sections that span the northern margin of the tibetan plateau isotopic analyses of 1475 carbonate samples yield 18 o values that range from 13 1 to 38 9 smow and 13 c values range from 11 5 to 3 7 pdb based on these analyses we see two isotopic trends regionally we interpret a paleogene decrease in average oxygen isotope values to result from an increase in the mean elevation of the study region s drainages as they tapped waters from a growing tibetan plateau to the south of the study area we interpret a neogene increase in both carbon and oxygen isotope values to result from the initiation of local mountain building in the study area and the withdrawal of marine waters which increased basin isolation aridity and temperatures the timing of inferred initiation of uplift in this region is consistent with structural thermochronological and sedimentological evidence for a tectonic transition in the early and middle miocene from accommodation of india eurasia convergence through extrusion along the altyn tagh fault to accommodation of convergence through active shortening and mountain building in this region this study also supports tectonic models for the differential uplift of the tibetan plateau in that mountain building in this study region significantly postdates estimates for the attainment of high elevation from isotopic studies of the central tibetan plateau

cenozoic depositional sequences in the piedmont of the west kunlun and their paleogeographic and tectonic implications abstract the west kunlun forms the northwestern margin of the qinghai tibet plateau well developed cenozoic depositional sequences in the piedmont along the margins of the tarim basin record changes in sedimentary environment and the uplift of the west kunlun during the cenozoic during latest cretaceous to oligocene deposition in the west kunlun occurred in a marine environment the tarim bay during the paleogene gypsum beds bivalve shell limestones and variegated clastics were deposited rapid sedimentation during the late miocene resulted in the deposition of molasse sediments 2000 3000 m thick indicating a relatively high depositional rate the upper miocene sequences show a coarsening up tendency indicating a rapid and accelerated uplift of the west kunlun from late miocene to early pleistocene times molasse deposition was interrupted in the early pleistocene by a tectonic pulse which resulted in tilting of the molasse and underlying sediments at high angle towards the tarim basin undeformed middle to late pleistocene coarse fluvial and pluvial deposits overlie the steeply dipping molasse and older rocks unconformably and represent the resumption of rapid deposition a continual high rate of uplift during the holocene is presumed on the basis of an incised drainage system that flows from west kunlun into the tarim basin and cuts middle to late pleistocene gravels and older sediments to a depth from 50 m to more than 100 m although climatic changes may also have played a part

formation of fractured zones in overburden due to longwall mining the fractured zones caused by mining were studied in the overburden of the torezko snezhnyanskaya area ukraine through the change in natural gas emission from these zones during longwall coal excavation zones of interconnected fractures and separate horizontal fractures were studied with vertical wells drilled from the ground surface down to active underground workings the maximum heights of the zone of interconnected fractures and separate horizontal fractures may reach 19 41 and 53 92 times the thickness of the coal seam respectively it was found that the ratio between the maximum height of the zone of interconnected fractures and the thickness of the extracted coal seam increases with the increasing number of rock layer interfaces and decreases with the increasing stiffness of immediate roof it is shown that the growth of the zone of interconnected fractures occurred during 17 39 days at an average rate of 0 94 1 97 m day 1 and it was accompanied by increasing methane emission from overburden observation shows that the formation of separate horizontal fractures began only 11 49 5 days after the height of the zone of interconnected fractures reached its maximum value formation of separate horizontal fractures in overburden over the longwall excavation occurred as a stepped process from lower to upper sandstone sandy shale layer interfaces in the direction of the ground surface

slowing extrusion tectonics lowered estimate of post early miocene slip rate for the altyn tagh fault abstract determination of long term slip rate for the altyn tagh fault is essential for testing whether asian tectonics is dominated by lateral extrusion or distributed crustal shortening previous slip history studies focused on either quaternary slip rate measurements or pre early miocene total offset estimates and do not allow a clear distinction between rates based on the two the magmatic and metamorphic history revealed by shrimp zircon dating of clasts from miocene conglomerate in the xorkol basin north of the altyn tagh fault strikingly matches that of basement in the southern qilian shan and northern qaidam regions south of the fault this match requires that the post early miocene long term slip rate along the altyn tagh fault cannot exceed 10 mm year supporting the hypothesis of distributed crustal thickening for post early miocene times this low long term slip rate and recently documented large pre early miocene cumulative offset across the fault support a two stage evolution wherein asian tectonics was dominated by lateral extrusion before the end of early miocene and since then has been dominated by distributed crustal thickening and rapid plateau uplift

ray equation migration of wide angle reflections from southern alaska a kirchhoff style prestack depth migration algorithm is implemented for wide angle reflections in two dimensional variable velocity acoustic media extrapolation of both source and recorder wavefields is performed by ray tracing the imaging condition at each point in the image space is the total source to recorder travel time since the migration algorithm is based on ray tracing migration can be performed for any medium through which rays can be traced there is no inherent limitation on the size of the region to be imaged regions up to 3 6 103 km2 are utilized in this study the algorithm is illustrated by migration of two synthetic and three real data sets from the u s geological survey s trans alaska crustal transect program images are produced of inferred subduction assemblages in southern alaska emphasis in this paper is on obtaining reflector positions and shapes rather than detailed structural interpretations

surface subsidence characteristics of grout injection into overburden case study of yuandian no 2 coalmine china a study on the surface subsidence characteristics is essential for evaluating the effects of subsidence control technologies and improving such technologies one such technology is grout injection into overburden gio which is used in coal mining areas in the past the subsidence reduction ratio a single index was often used to evaluate the final amount of subsidence control achieved by gio however little research has been conducted on the dynamic process of surface subsidence in this study the surface subsidence characteristics of gio on the side of a stopping line ssl of a longwall were examined through in situ monitoring and the characteristics of areas with grouting were compared with those without the final maximum subsidence horizontal displacement and subsidence rate decreased considerably 70 2 80 4 and 77 5 respectively with the use of gio however 4 6 of the mining height subsided at a certain surface point on the ssl before gio controlled subsidence at that point compared with the duration of the active period without grouting that with grouting and the corresponding subsidence decreased considerably 44 2 and 87 1 respectively generally it is quite difficult to control the surface subsidence when gio is implemented on the ssl of a longwall because the surface and subsurface are already affected by the coal extraction without grouting on the side of the open off cut thus the success of gio technology in the case study described in this paper demonstrates its effectiveness in controlling the surface subsidence in coal mining areas

from sea level to high elevation in 15 million years uplift history of the northern tibetan plateau margin in the altun shan approximately 1300 in of oligocene miocene clastic strata are exposed along the miran river in the southeastern tarim basin where the adjacent altun shan form the topographic escarpment of the northern tibetan plateau the sedimentary section is faulted against proterozoic rocks of the altun shan in the footwall of the south dipping oblique reverse northern altyn tagh fault oligocene lower miocene strata consist of fine grained rocks that record low gradient depositional systems mid miocene and younger rocks consist of coarse conglomerate derived from the altun shan and deposited by high gradient depositional systems the change to coarse high gradient depositional systems with detrital source areas coincident with the modern miran river drainage is interpreted to mark the onset of uplift of the altun shan on the northern altyn tagh fault and its erosional exhumation the age of the change from pre orogenic to synorogenic sedimentation is constrained by a foraminifera assemblage at the base of the conglomeratic section that includes early middle miocene planktonic foraminifera this interpretation is also supported by apatite fission track and u th he ages and thermal models that indicate rapid miocene cooling and hence rapid exhumation of the altun shan in addition to defining the age of the synorogenic section the foraminifera assemblage contains planktonic taxa indicating a connection to open marine waters and benthic assemblages typical of brackish to near sea level paleobathymetry thus micropaleontologic evidence demonstrates that the miran river locality now at 1400 in elevation was at sea level approximately 15 million years ago thus in addition to constraining the age of surface uplift and exhumation of the altun shan the principal mountain range of the tibetan plateau in this region as 15 to 16 ma the foraminifera assemblage indicates that the se tarim basin off the northern edge of the plateau had an average surface uplift rate of nearly 100 m m y for the past 15 million years these results suggest that shortening in the altun shan and uplift of the range significantly post dated the initiation of large scale strike slip on the altyn tagh fault and that regional surface uplift mechanisms operated in the tarim basin beyond the margins of the tibetan plateau

spatial variations of flexure parameters over the tibet quinghai plateau we investigate the tibet quinghai plateau and the tarim basin in terms of spatial variations of the elastic thickness te in the frame of the thin plate flexure model the method of investigation makes use of a convolutive method which allows high spatial resolution of the flexure properties and overcomes some of the problems tied to the spectral admittance coherence methodologies we study the relation between the topographic and subsurface loads and the observed crust mantle interface cmi undulations the latter having been obtained from gravity inversion the gravity data used for the inversion are a unique set of high quality data available over the chinese part of the plateau and constitute the highest resolution grid today available in this impervious area the gravity inversion is constrained by results from the study of the propagation of seismic waves the two extensive sedimentary basins the tarim and the qaidam basins are modeled by forward gravity modeling the oscillations of the cmi obtained from the gravity inversion agree well with those expected by loading the thin plate model of spatially variably elastic thickness with the surface and subsurface loads it is found that the modeling of the sedimentary basins is essential in the flexure analysis the spatial variations of elastic thickness correlate with the extensions of the different terrains that constitute the plateau most of the tibet plateau has low te varying in the bounds 10 30 km with lower values in the qiangtang terrain where the te reaches 8 km the tarim and the qaidam basins precambrian platforms overlain by sediments are rigid and have a te of up to 110 km and 70 km respectively the flexural analysis distinctly discerns the tibet plateau with thick crust part of which is molten from the cratonic areas the tarim and qaidam basins which though of thinner crust act as undeformable rigid blocks

gaussian beam migration of common shot records gaussian beam migration is a depth migration method whose accuracy rivals that of migration by wavefield extrapolation so called wave equation migration and whose efficiency rivals that of kirchhoff migration this migration method can image complicated geologic structures including very steep dips in areas where the seismic velocity varies rapidly however applications of prestack gaussian beam migration either have been limited to common offset common azimuth data volumes and thus are inflexible or suffer from multiarrival inaccuracies in a common shot implementation in order to optimize both the flexibility and accuracy of gaussian beam migration i present a common shot implementation that handles multipathing in a natural way this allows the migration of data sets that can include a variety of azimuths and it allows a simplified treatment of near surface issues application of this method to model data typical of canadian foothills structures and to model data that includes a complicate

localization of mining induced horizontal fractures along rock layer interfaces in overburden field measurements and prediction the locations of mining induced horizontal fractures along rock interfaces in the overburden of donetsk coal basin were identified using an original experimental device the device traps methane from horizontal fracture zone 100 fold coal seam thickness over an active longwall mining excavation presence or absence of horizontal fractures along rock layer interfaces is correlated with physical characteristics of the overburden such as thickness uniaxial compressive strength of overburden rock layers location of rock layer interfaces and thickness of extracted coal seams as a result a combined criterion based on these physical characteristics is proposed to predict the presence of overburden horizontal fracturing in coal mine operations

mining subsidence and its effect on the environment some differing examples the impact of mining subsidence on the environment can occasionally be very catastrophic destroying property and even leading to the loss of life usually however such subsidence gives rise to varying degrees of structural damage that can range from slight to very severe different types of mineral deposits have been mined in different ways and this determines the nature of the associated subsidence some mining methods result in contemporaneous subsidence whereas with others subsidence may occur long after the mine workings have been abandoned in the latter instance it is more or less impossible to predict the effects or timing of subsidence a number of different mineral deposits have been chosen to illustrate the different types of associated subsidence that result and the problems that arise the examples provided are gold mining in the johannesburg area bord and pillar mining of coal in the witbank coalfield south africa longwall mining of coal in the ruhr district mining of chalk and limestone in suffolk and the west midlands respectively and solution mining of salt in cheshire these mineral deposits have often been worked for more than 100 years and therefore a major problem results from abandoned mines especially those at shallow depth the presence of which is unrecorded abandoned mines at shallow depth can represent a serious problem in areas that are being developed or redeveloped abstraction of natural brine has given rise to subsidence with its own particular problems and cannot be predicted although such abstraction is now inconsequential in cheshire dereliction associated with past subsidence still remains

what information on the earth model do reflection travel times provide inversion of reflection travel times or reflection tomography or tomographic inversion allows determination of the structure of the subsurface from arrival times of reflected waves because the solution of a tomographic inversion is often underdetermined it is essential to carry out an uncertainty analysis on the solution which is classically done by linearizing the problem at the vicinity of the computed solution earlier uncertainty analyses gave results which strongly depend on the chosen discretization interval they have no physical meaning our goal is to compute numerical uncertainties that approximate the physical uncertainties limiting our study to hilbertian model spaces we theoretically derive a necessary and sufficient condition which yields the desired result the norm chosen in model space has to bind the frechet derivative of the forward map physically this requires the velocity distribution and the reflectors to be smooth functions an assumption which is quite compatible with the smoothness imposed to make use of ray theory the required degree of smoothness depends on the space dimension two or three dimensional this theoretical study yields a new method which allows in the classical framework of a linearization calculation of uncertainties that are almost independent of the chosen model discretization interval they are thus intrinsically related to travel time information hence we can predict how travel times determine the slowness distribution and the reflector geometries our method is validated for a simple example as a result a very fine parameterization of the model is needed for an accurate estimate of the uncertainties on the solution

redatuming through a salt canopy and target oriented salt flank imaging we describe a new shortcut strategy for imaging the sediments and salt edge around a salt flank through an overburden salt canopy we tested its performance and capabilities on 2d synthetic acoustic seismic data from a gulf of mexico style model we first redatumed surface shots using seismic interferometry from a walkaway vertical seismic profile survey as if the source and receiver pairs had been located in the borehole at the positions of the receivers this process creates effective downhole shot gathers by completely moving surface shots through the salt canopy without any knowledge of overburden velocity structure after redatuming we can apply multiple passes of prestack migration from the reference datum of the bore hole in our example first pass migration using only a simple vertical velocity gradient model reveals the outline of the salt edge a second pass of reverse time prestack depth migration using full two way wave equation was performed with an updated velocity model that consisted of the velocity gradient and salt dome the second pass migration brings out dipping sediments abutting the salt flank because these reflectors were illuminated by energy that bounced off the salt flank forming prismatic reflections in this target oriented strategy the computationally fast redatuming process eliminates the need for the traditional complex process of velocity estimation model building and iterative depth migration to remove effects of the salt canopy and surrounding overburden this might allow this strategy to be used in the field in near real time

relatively recent construction of the tien shan inferred from gps measurements of present day crustal deformation rates the tien shan a high seismically active intracontinental mountain belt 1 000 2 000 km north of the himalaya has grown as a result of india s collision with asia1 the crustal shortening 200 50 km refs 2 3 and thickening that gave rise to the tien shan accommodates only a small fraction of india s total penetration into asia 2 000 3 000km and the temporal relationship of deformation in this belt to the india asia collision remains unclear here we report geodetic measurements of the tien shan using the global positioning system gps that indicate that the current crustal shortening rate is nearly half of india s convergence rate with eurasia in this area4 we infer a total shortening rate for the tien shan of 20 mm yr 1 which is approximately twice that inferred previously from the extrapolation of slip rates in the holocene3 and earthquake induced displacements during this century5 suggesting that the rate of mountain building in this region has accelerated several fold since the onset of collision 50 55 myr ago6 7 if as we argue the current shortening rate can be extrapolated to geological timescales then our results suggest that most of the tien shan has been constructed during the past 10 myr perhaps in response to an increased horizontal force following an abrupt rise of the tibetan plateau8 9

magnetostratigraphy of the dahonggou section northern qaidam basin and its bearing on cenozoic tectonic evolution of the qilian shan and altyn tagh fault article i nfo the timing of uplift of the tibet plateau has a central role in the development of tectonic models for the tibet plateau and cenozoic global climate change a detailed magnetostratigraphic study of the dahonggou section northern qaidam basin reveal that the section spans from 34 to 8 5 ma and the ages of the shang ganchaigou xia youshashan and shang youshashan formations are from 34 to 22 20 ma 22 20 to 13 ma and 13 to 8 5 ma respectively variations in lithofacies sedimentation rate and magnetic susceptibility k suggest that the southern qilian shan was tectonically inactive and didn t respond to the rapid slip on the altyn tagh fault at 30 ma in contrast the similar sedimentary records in the dahonggou section the xishuigou section along the altyn tagh fault and even more localities along much of the qilian range front imply that the qilian shan and the altyn tagh fault were synchronously tectonically active at about 12 ma the lower k between 12 ma and 8 5 ma in the sediments of the dahonggou section is interpreted to be due to long distanced oxidation and sorting which cause not only that magnetite was oxidated to hematite but also that magnetic minerals are enriched in fine grained sediments and coarse grained sediments bear few magnetic mineral

gravity anomalies and the structure of western tibet and the southern tarim basin gravity anomalies across the western part of the tarim basin and the kunlun mountain belt show that this area is not in local isostatic equilibrium these data can be explained if a strong plate underlying the tarim basin extends southwestward beneath the belt at least 80 km and supports part of the topography of northwest tibet this corroborates norin s inference that late tertiary crustal shortening has occurred in this area by southward underthrusting of the tarim basin beneath the kunlun this study places a lower bound on the amount of underthrusting

dynamic disaster control under a massive igneous sill by grouting from surface boreholes abstract an overlying 140 m thick massive igneous sill has adversely affected mining activities considerably in the haizi coal mine china a coal and gas outburst disaster occurred during the drivage for a subsequent longwall after the extraction of two faces in the ii102 mining area the massive sill was determined to be primarily responsible for this outburst owing to the bed separation that occurred below the sill due to the sill s large span this is because such separation meant the massive sill was not supported by the gob as in a general case but it was supported by the solid coal instead resulting in a long load transfer distance that caused the drivage gate to collapse unexpectedly into the abutment thus it was determined that the high abutment pressure primarily triggered the outburst such disaster risk would have remained had the drivage in the gate continued and a wide area and sudden roof fall could have occurred during the extraction of the next longwall had the igneous sill broken suddenly as the critical span was reached with these risks in mind a field trial of a method of grouting into the overburden of the abandoned faces from surface boreholes was conducted for dynamic disaster control this technique alleviates the abutment pressures and restrains the igneous sill deflection by eliminating fractures and voids in the overburden using grouting the adoption of this grouting method led to the subsequent drivage and mining of a further 510 m without occurrence of any further dynamic disasters