kinematics of active deformation in the sulaiman lobe and range pakistan the western margin of the indian plate is highly oblique to the direction of convergence between india and asia and represents an excellent example of large scale oblique continent continent collision determining the strain field in western pakistan and how it relates to the plate motion and plate margin geometry affords an exceptional opportunity for understanding oblique margin processes in general through the inversion of regional and teleseismic body waves we have determined the source parameters of 10 moderate sized earthquakes that occurred between 1964 and 1985 in and around the sulaiman range pakistan the earthquakes are dominantly thrust events with slip vectors that are approximately perpendicular to the lobate sulaiman mountain front slip vector orientations rotate 60 70 from a n s to a wnw ese direction of compression consistent with the geometries of the complex festoon shaped mountain belts of this margin we have estimated the spatial variation of the horizontal strain rate and velocity fields within sulaiman using vertically averaged models that accommodate plate motion constraints within a deforming layer the most important factors determining the style of strain rotation in the sulaiman lobe and range are the presence of pure strike slip motion along the chaman fault and the relatively rigid and undeformed katawaz basin that is therefore allowed to translate obliquely relative to india this same conclusion is obtained using either a three dimensional frictional analogue model with significant basal tractions or a thin sheet viscous numerical model without basal tractions thrusting in a predominantly nw se direction in the sulaiman range accommodates 5 14 mm yr of n s motion between india eurasia and 3 6 mm yr of e w shortening seismic moment release this century within the india eurasia plate boundary zone west of the western himalayan syntaxis constitutes roughly 40 of the expected total seismic moment release for this time period particularly significant moment rate deficits exist within the sulaiman range and along the chaman fault

shallow virtual source redatuming by multi dimensional deconvolution recently new on shore acquisition designs have been presented with multicomponent sensors deployed in the shallow sub surface 20 m 60 m virtual source redatuming has been proposed for these data to compensate for surface statics and to enhance survey repeatability in this paper we investigate the feasibility of replacing the correlation based formalism that undergirds virtual source redatuming with multi dimensional deconvolution offering various advantages such as the elimination of free surface multiples and the potential to improve virtual source repeatability to allow for data driven calibration of the sensors and to improve robustness in cases with poor sensor spacing in the shallow sub surface resulting in a relatively high wavenumber content we propose a new workflow for this configuration we assume a dense source sampling and target signals that arrive at near vertical propagation angles first the data are preconditioned by applying synthetic aperture source filters in the common receiver domain virtual source redatuming is carried out for the multi component recordings individually followed by an intermediate deconvolution step after this specific pre processing we show that the downgoing and upgoing constituents of the wavefields can be separated without knowledge of the medium parameters the source wavelet or sensor characteristics as a final step free surface multiples can be eliminated by multi dimensional deconvolution of the upgoing fields with the downgoing fields

partitioning of india eurasia convergence in the pamir hindu kush from gps measurements 1 convergence of 29 1 mm yr between the nw corner of the indian plate and asia is accommodated by a combination of thrust and strike slip faulting on prominent faults and apparent distributed deformation within the hindu kush pamir south tien shan and kohistan ranges an upper bound to the slip rate of known faults is obtained by ignoring distributed strain and rotation convergence occurs on thrust faults north of the peshawar basin 13 1 mm yr and in the alai south tien shan 12 2 mm yr and shear on the northeast trending northern chaman gardiz konar system 18 1mm yr and the darvaz karakul fault zone 11 2 mm yr slip rates on the herat and talas ferghana faults are small 2 mm yr shortening not attributable to known active faults occurs within the hindu kush and central pamir 16 2 mm yr with concomitant east west extension in the latter of 9 2 mm yr this diversity of strain styles confirms the importance of mechanical heterogeneity to continental tectonics and shows that the pamir although less than half the size behaves more like tibet than like a linear belt of localized deformation

mechanics of fold and thrust belts and accretionary wedges cohesive coulomb theory a critically tapered fold and thrust belt or submarine accretionary wedge is one that is on the verge of coulomb failure everywhere including its base where frictional sliding along a decollement is assumed to be occurring cohesion within a wedge can add significantly to the overall strength near the toe the effect of this is to decrease the near toe taper leading to a critical topographic profile that is concave upward if the decollement is planar we obtain an approximate self consistent solution for the state of stress within a thin skinned cohesive critical coulomb wedge and determine the relationship between the wedge taper and its strength and basal friction the theory is then applied to the presently deforming fold and thrust belt of western taiwan fitting of theoretical critical wedge shapes to topographic profiles and measurements of the step up angles of thrust faults from the basal decollement are used to constrain the taiwan wedge strength parameters an attractive assertion fully consistent with all the observations is that the mechanics of fold and thrust belts and accretionary wedges is governed by normal frictional and fracture strengths of rocks measured in the laboratory in particular if byerlee s law b 0 85 is adopted as the coefficient of sliding friction on the base we find a coefficient of internal friction 0 9 1 0 in the wedge and a wedge cohesion so 5 20 mpa other solutions having strengths and ambient stresses up to 4 times lower than this can also however satisfy the data

adaptive decomposition of multicomponent ocean bottom seismic data into downgoing and upgoing p and s waves with wavefield decomposition the recorded wavefield at a certain depth level can be separated into upgoing and downgoing wavefields as well as into p and s waves the medium parameters at the considered depth level e g just below the ocean bottom need to be known in order to be able to do a decomposition in general these parameters are unknown and in addition measurement related issues such as geophone coupling and crosstalk between the different components need to be dealt with in order to apply decomposition to field data an adaptive five stage decomposition scheme was developed in which these issues are addressed in this study the adaptive decomposition scheme is tested on a data example with a relatively shallow water depth 120 m consisting recordings from of a full line of ocean bottom receivers although some of the individual stages in the decomposition scheme are more difficult to apply because of stronger interference between events compared to data acquired over deeper water

virtual source method applied to crosswell and horizontal well geometries the virtual source method is a useful tool for redatuming a seismic survey below complicated overburden by creating virtual sources at downhole receiver locations hence generating data independent of the overburden and the time lapse changes therein in this article we first apply this technique to crosswell geometries whereby a virtual crosswell survey is simulated by shooting a line of surface shots passing through two boreholes instrumented with downhole sensors using this acquisition geometry receivers in one of the two wells are turned into virtual sources by correlating the wavefield recorded by those receivers with the recording at receivers in the other well and summing the correlated data over the surface shots

target oriented interferometric tomography for gpr data an interferometric form of fermat s principle and traveltime tomography is used to invert ground penetrating radar gpr data for the subsurface velocity distribution the input data consist of gpr traveltimes of reflections from two buried interfaces a reference and b target where the data are excited and recorded by gpr antennas at the surface fermat s interferometric principle is then used to redatum the surface transmitters and receivers to interface a so the associated reflection traveltimes correspond to localized transit times between interfaces a and b the overburden velocity model above interface a is not required the result after tomographic inversion is a high resolution estimate of the velocity between interfaces a and b that does not depend on the velocity model above interface a a motivation for introducing interferometric traveltime tomography is that typical layer stripping approaches will see the slowness error increase with depth as the layers are inverted this suggests that

crosswell monitoring using virtual sources and horizontal wells time lapse crosswell seismic provides an efficient way to monitor the migration of a c o2 plume or its leakage after c o2 injection into a geologic formation recently crosswell seismic has become a powerful tool for monitoring underground variations using the concept of a virtual source with virtual sources positioned at the receivers installed in the well and thus the positions of sources and receivers can be invariant during monitoring however time lapse crosswell seismic using vertical wells and virtual sources has difficulty in describing the front of a c o2 plume which usually is parallel to the vertical wells and in obtaining sufficient ray coverage for the first arrival tomography these problems arise because of the theoretical downward illumination directivity limitation of the virtual source we have developed an effective monitoring method that uses virtual sources and two horizontal wells one above and one below the c o2 sequestration reservoir in our method we redatum the traces th

source receiver interferometric redatuming using sparse buried receivers to address complex near surface environments a case study of seismic imaging quality and time lapse repeatability

anomalous ocean load tide signal observed in lake level variations in tierra del fuego 1 we demonstrate the application of a 100 km long lake as a sensor for studying the tidal effects on tierra del fuego main island the lake level variations observed in lago fagnano reflect both the direct response to the tidal potential and the indirect effect of the ocean tidal loading modeling both contributions explains the observed tidal signal in the lake to about 70 underestimated model load tide amplitudes are found to be probably responsible for the remaining difference we interpret this discrepancy as a hint for regional elastic lithosphere properties differing substantially from those represented by currently available global models

geology and vein tin mineralization in the dadoushan deposit gejiu district sw china vein type tin mineralization in the dadoushan deposit laochang ore field gejiu district sw china is predominantly hosted in triassic carbonate rocks gejiu formation over cupolas of the unexposed laochang equi granular granite intrusion the most common vein mineral is tourmaline accompanied by skarn minerals garnet di opside epidote phlogopite and beryl the main ore mineral is cassiterite accompanied by minor chalcopyrite pyrrho tite and pyrite as well as scheelite the tin ore grade varies with depth with the highest grades 1 2 sn prevalent in the lower part of the vein zone muscovite 40 ar 39 ar dating yielded a plateau age of 82 7 0 7 ma which defines the age of the vein type mineralization measured sulfur isotope compositions 34 s0 4 1 to 3 9 of the sulfides arseno pyrite chalcopyrite pyrite and pyrrhotite indicate that the sulfur in veins is mainly derived from a magmatic source the sulfur isotope values of the ores are consistent with those from the underlying granite laochang equigranular granite 3 7 to 0 1 but are different from the carbonate wall rocks of the gejiu formation 7 1 to 11 1 the calculated and measured oxygen and hydrogen isotope com positions of the ore forming fluids 18 oh2o0 2 4 to 5 5 d0 86 to 77 suggest an initially magmatic fluid which gradually evolved towards meteoric water dur ing tin mineralization

data driven adaptive decomposition of multicomponent seabed recordings dual sensor hydrophone and three component geophone data recorded on the seafloor allow the elastic wavefield to be decomposed into its upgoing and downgoing p and s wave components most decomposition algorithms require accurate knowledge of the elastic properties of the seafloor in the vicinity of the receivers and properly calibrated sensors in order for the data to be a faithful vector representation of the ground motion we present a multistep adaptive decomposition scheme that provides the necessary information directly from the data by imposing constraints on intermediate decomposition results the proposed scheme requires no a priori information and only a minimal amount of user defined input thus allowing multicomponent data to be decomposed in an automated data driven fashion the performance of the technique is illustrated using seabed data acquired in the north sea with prototype single sensors multicomponent geophones individually sampled realistic seafloor properties and sensor calibration operators are obtained and elastic decomposition of the calibrated data generally yields good results dominant water layer reverberations are successfully attenuated and primary reflections are substantially enhanced in the computed upgoing p wave potential just below the seafloor in contrast the result for the upgoing s wave potential is somewhat less convincing although the energy of water layer multiples is substantially reduced notable amounts of undesired multiple energy remain in this section after decomposition particularly at high offsets these imperfections may point to inaccuracies in the parametrization of the seafloor or remaining inaccuracies in the vector fidelity of the horizontal geophone recordings nevertheless the results obtained with the extended data driven decomposition scheme are at least comparable to previously published results

model based radiation pattern correction for interferometric redatuming in 4d seismic interferometric virtual source vs redatuming converts surface triggered source records into the equivalent records as if they originated from buried receiver locations by crosscorrelating downgoing waves with the corresponding upgoing waves theory suggests that when the receivers are surrounded by an enclosing boundary of sources then the vs has an isotropic radiation pattern and yield accurate response the resultant records should show improving the seismic repeatability and image quality comparing with non vs however in the presence of complex near surface intricate shallow structure and highly variable weathering layers can severely distort the ray path such that it produces the uneven angle coverage to the buried vs additionally near surface reverberations surface multiples and other mode converted waves may leak into the time gated early arrivals and further corrupt the direct wavefields abovementioned issues can result in distorted radiation patterns and contaminated responses of the v

dual sensor obc technology before the invention and successful implementation of the towed streamer in the late 1940s the ocean bottom cable obc method and variations thereof represented our only means for acquiring seismic data in marine areas the marine streamer facilitated more rapid acquisition of 2 d data its widespread adoption relegated obc to shallow waters where streamers could not be towed

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

modal expansion of one way operators in laterally varying media one of the main benefits of prestack depth migration in seismic processing is its ability to handle complicated medium configurations when considerable lateral variations in the acoustic parameters are present in the subsurface prestack depth migration is necessary for optimal lateral resolution however most migration algorithms still deal with lateral variations in an approximate manner because these variations are in many cases moderate compared to the profound variations in the depth direction from other areas of science e g optics oceanography and seismology it is known that lateral variations can be dealt with by a decomposition of the wavefield into wave modes in this paper we explore the possibility of applying this concept to the construction of one way wavefield operators for depth migration we expand the helmholtz operator on an orthogonal basis of wave modes and obtain one way wavefield operators that are unconditionally stable and significantly increase the lateral resolution of the result

on the use of multicomponent streamer recordings for reconstruction of pressure wavefields in the crossline direction three component measurements of particle motion would bring significant benefits to towed marine seismic data if processed in conjunction with the pressure data we show that particle velocity measurements can increase the effective nyquist wavenumber by a factor of two or three depending on how they are used a true multicomponent streamer would enable accurate data reconstruction in the crossline direction with cable separations for which pressure only data would be irrecoverably aliased we also show that conventional workflows aimed at reducing these aliasing effects such as moveout correction applied before interpolation are compatible with multicomponent measurements some benefits of velocity measurements for deghosting data are well known we outline how the new measurements might be used to address some long standing deghosting challenges of particular interest specifically we propose methods for recovering de ghosted data between streamers and for 3d deghosting of seismic data at the stream

target enclosed seismic imaging seismic reflection data can be redatumed to a specified boundary in the subsurface by solving an inverse or multidimensional deconvolution problem the redatumed data can be interpreted as an extended image of the subsurface at the redatuming boundary depending on the subsurface offset and time we retrieve targetenclosed extended images by using two redatuming boundaries which are selected above and below a specified target volume as input we require the upgoing and downgoing wavefields at both redatuming boundaries due to impulsive sources at the earth s surface these wavefields can be obtained from actual measurements in the subsurface they can be numerically modeled or they can be retrieved by solving a multidimensional marchenko equation as output we retrieved virtual reflection and transmission responses as if sources and receivers were located at the two target enclosing boundaries these data contain all orders of reflections inside the target volume but exclude all interactions with the part of the medium outside this volume the retrieved reflection responses can be used to image the target volume from above or from below we found that the images from above and below are similar given that the marchenko equation is used for wavefield retrieval if a model with sharp boundaries in the target volume is available the redatumed data can also be used for two sided imaging where the retrieved reflection and transmission responses are exploited because multiple reflections are used by this strategy seismic resolution can be improved significantly because target enclosed extended images are independent on the part of the medium outside the target volume our methodology is also beneficial to reduce the computational burden of localized inversion which can now be applied inside the target volume only without suffering from interactions with other parts of the medium

combination of surface and borehole seismic data for robust target oriented imaging a novel application of seismic interferometry si and marchenko imaging using both surface and borehole data is presented a series of redatuming schemes is proposed to combine both data sets for robust deep local imaging in the presence of velocity uncertainties the redatuming schemes create a virtual acquisition geometry where both sources and receivers lie at the horizontal borehole level thus only a local velocity model near the borehole is needed for imaging and erroneous velocities in the shallow area have no effect on imaging around the borehole level by joining the advantages of si and marchenko imaging a macrovelocity model is no longer required and the proposed schemes use only single component data furthermore the schemes result in a set of virtual data that have fewer spurious events and internal multiples than previous virtual source redatuming methods two numerical examples are shown to illustrate the workflow and to demonstrate the benefits of the method one is a synthetic model and the other is a realistic model of a field in the north sea in both tests improved local images near the boreholes are obtained using the redatumed data without accurate velocities because the redatumed data are close to the target

virtual source applications to imaging and reservoir monitoring the virtual source method is a breakthrough that allows us to image and monitor the subsurface in cases where surface seismic or vsp fail to deliver in settings where the overburden is complex or changing traditional time lapse signals are weak or nonrepeatable leading to ineffective seismic input to reservoir modeling and little of value generated by repeated seismic surveys on the other hand the virtual source method allows us to image under complex overburden yields repeatable data for reservoir monitoring enables shear seismic and may help us look ahead as we drill

strengthening the virtual source method for time lapse monitoring time lapse monitoring is a powerful tool for tracking subsurface changes resulting from fluid migration conventional time lapse monitoring can be done by observing differences between two seismic surveys over the surveillance period along with the changes in the subsurface differences in the two seismic surveys are also caused by variations in the near surface overburden and acquisition discrepancies the virtual source method monitors below the time varying near surface by redatuming the data down to the subsurface receiver locations it crosscorrelates the signal that results from surface shooting recorded by subsurface receivers placed below the near surface for the mars field data redatuming the recorded response down to the permanently placed ocean bottom cable obc receivers using the virtual source method allows one to reconstruct a survey as if virtualsources were buried at the obc receiver locations and the medium above them were a homogeneous half space separating the recorded wavefields

synthetic aperture controlled source electromagnetics controlled source electromagnetics csem has been used as a de risking tool in the hydrocarbon exploration industry although there have been successful applications of csem this technique is still not widely used in the industry because the limited types of hydrocarbon reservoirs csem can detect in this paper we apply the concept of synthetic aperture to csem data synthetic aperture allows us to design sources with specific radiation patterns for different purposes the ability to detect reservoirs is dramatically increased after forming an appropriate synthetic aperture antenna consequently the types of hydrocarbon reservoirs that csem can detect are significantly extended because synthetic apertures are constructed as a data processing step there is no additional cost for the csem acquisition synthetic aperture has potential for simplifying and reducing the cost of csem acquisition we show a data example that illustrates the increased sensitivity obtained by applying synthetic aperture csem source

wavelet crosscorrelation based interferometric redatuming in 4d seismic interferometric virtual source redatuming crosscorrelates downgoing waves with the corresponding upgoing waves to convert records from surface source gathers to virtual gathers at the buried receiver locations the assumption is that the virtual source records show reduced effects of overburden complexity and therefore provide improved seismic repeatability and image quality in practice however the repeatability and quality of the redatumed data can be degraded by one sided illumination and inadequate preprocessing in the presence of complex near surface structure for land redatuming intricate shallow structure and highly variable weathering layers introduce surface multiples ground roll scattering noise interferences among different wave modes which additionally contaminate both down and upgoing wavefields to address these issues we propose a new interferometric redatuming method based on crosscorrelation in the wavelet domain specifically by transforming time offset data into local time sca

a deforming block model for the present day tectonics of tibet 1 we use gps data from 45 sites across the tibetan plateau surveyed between 1991 and 2001 to study the distribution of strain in that part of the india eurasia collision zone the plateau is cut by a few major rapidly slipping strike slip fault zones with broadly distributed strain between those zones the gps velocities can be fit well by a simple deforming block model that combines uniform strain with the motion of blocks separated by the major known fault zones within the plateau the boundaries of the four blocks in this model correspond to the major rapidly slipping faults a rigid block model with a smaller number of blocks fits the data poorly and can be rejected we estimate that 5 9 0 7 mm yr of extension in the n69 w direction occurs on the yadong gulu rift south of the plateau localized extension may extend as far north as the nyainqentanglha range we find 7 4 0 7 mm yr of right lateral slip on the karakorum jiali fault zone significantly slower than that previously estimated from offset geologic features our deforming block model and a two dimensional single fault screw dislocation model give lower and upper bounds of 4 4 1 1 and 10 3 0 4 mm yr on the slip rate on the kunlun fault respectively comparable in its highest to the long term slip rate observed geologically the distributed deformation is surprisingly uniform over the tibetan plateau qaidam basin and qilian shan and approximates a combination of pure shear and uniaxial contraction with the same axes of maximum contraction n32 e this strain field is a combination of shortening and extension that produces little net dilatation 1 area loss per million years at present the broadly distributed strain most likely represents slip on many faults each with a relatively low slip rate distributed conjugate strike slip faulting is the most plausible mechanism to produce the observed strains as supported by the record of medium to large earthquakes within the plateau the distributed deformation is just as important in the accommodation of the total india eurasia convergence as is slip on the major faults the eastward motion of central tibet is as large as 50 of the convergence rate between india and eurasia however this eastward motion is not motion of a relatively undeforming block bounded by rapidly moving strike slip faults as suggested by past extrusion models instead much of this eastward extrusion is driven by the internal extension of the plateau our inference is in agreement with the model of f shen et al 2001 that suggested east west extension north south contraction and eastward plateau growth dominate the present tectonics of the tibetan plateau

insar observations of low slip rates on the major faults of western tibet two contrasting views of the active deformation of asia dominate the debate about how continents deform i the deformation is primarily localized on major faults separating crustal blocks or ii deformation is distributed throughout the continental lithosphere in the first model western tibet is being extruded eastward between the major faults bounding the region surface displacement measurements across the western tibetan plateau using satellite radar interferometry insar indicate that slip rates on the karakoram and altyn tagh faults are lower than would be expected for the extrusion model and suggest a significant amount of internal deformation in tibet

late quaternary and present day rates of slip along the altyn tagh fault northern margin of the tibetan plateau 1 both global positioning system gps measurements and studies of late quaternary faulting are consistent with a slip rate of 10 mm yr along the central segment of the altyn tagh fault and a systematic decrease in that rate toward the eastern end of the fault dates of terraces above and below laterally offset terrace risers yield bounds on quaternary slip rates that range from those that agree with gps measurements to values as much as three times faster we argue that offset terrace risers that are protected by topography upstream of them are more closely dated by the age of the upper terrace than by that of the lower terrace in some cases valleys upstream of the fault have been incised into bedrock and few if any terrace risers can be seen within the valleys such streams debouch onto alluviated floodplains or fans that become incised presumably during climate changes to create terrace risers the terrace risers are then displaced so that they lie downslope from bedrock ridges on the upstream side of the fault and thus the risers become protected from further incision in such cases dates of upper terraces should more closely approximate the ages of the risers than those of lower terraces such dates yield slip rates of 10 mm yr in the central segment of the fault and decreasing rates eastward although we cannot with certainty rule out the higher slip rates along the altyn tagh fault our analysis does show that viable interpretations consistent with gps measurements are more likely at least along some segments of the fault not only do these rates support the view that the tibetan plateau deforms internally by slip on a distributed network of faults in the shallow brittle crust and hence behaves as a continuum at depth but the gradual decrease toward the east also shows that the altyn tagh fault does not separate two effectively rigid lithospheric plates correspondingly the relatively low slip rate and the eastward decrease in slip rate suggest that the altyn tagh fault does not transfer a significant portion of the convergence between india and asia into northeastward extrusion of the tibetan plateau thus large scale extrusion of crustal material in india s path into eurasia seems to be limited largely to the confines of the tibetan plateau