a numerical method for determining the state of stress using focal mechanisms of earthquake populations application to tibetan teleseisms and microseismicity of southern peru the numerical method described in this paper enables the study in terms of stress of the kinematics of seismic faults provided by focal mechanisms this method assumes a mean state of stress in the source region and is based on the simple mechanical model used for fault population analysis which supposes slip in the direction of the resolved shear stress acting on the fault plane the proposed algorithm first defines compressional and tensional zones resulting from superimposition of the compressional and tensional quadrants limited by the nodal planes this enables one to test the data homogeneity furthermore this restricts the space where the principal stress axes have to be searched then for each principal stress reference whose location is constrained by above confined zones the r value chosen equal to 2 1 3 1 is computed which fits the slip vector on each nodal plane this permits one to select a set of preferred seismic fault planes from a set of auxiliary planes finally a state of stress is computed from the preferred seismic fault plane set using the non linear simplex method already applied to fault populations this algorithm is constructed so as to avoid two major difficulties misleading estimation of the deviatoric stress tensor which may result from excessive emphasis by minimizing the residuals by a least squares method if some of the data are wrong and a lengthy prospection of the stress references over all the space of directions this calculation does not take into account possible changes of the strike and dip of the nodal planes however we use rotations of nodal planes in agreement with the first arrival data to test the compatibility of these data with the computed state of stress tibetan teleseisms and southern peruvian microseisms are analyzed and results are compared with kinematics of superficial recent and active faults measured in field in the same regions this suggests that major seismic events may give a good evaluation of the regional mean state of stress focal mechanisms of the small events are also modelled by a mean stress deviator but this differs significantly from the regional state of stress in southern peru deduced from quaternary faulting this may be due to imprecise location of the small events however some movements are strongly different from those predicted by the computed mean stress deviator this suggests that small fault kinematics surely depend on the regional state of stress but that local effects may control the small deformations

high resolution reservoir characterization by an acoustic impedance inversion of a tertiary deltaic clinoform system in the north sea fluvio deltaic sedimentary systems are of great interest for explorationists because they can form prolific hydrocarbon plays however they are also among the most complex and heterogeneous ones encountered in the subsurface and potential reservoir units are often close to or below seismic resolution for seismic inversion it is therefore important to integrate the seismic data with higher resolution constraints obtained from well logs whereby not only the acoustic properties are used but also the detailed layering characteristics we have applied two inversion approaches for poststack time migrated seismic data to a clinoform sequence in the north sea both methods are recursive trace based techniques that use well data as a priori constraints but differ in the way they incorporate structural information one method uses a discrete layer model from the well that is propagated laterally along the clinoform layers which are modeled as sigmoids the second method uses a constant sampling rate from the well data and uses horizontal and vertical regularization parameters for lateral propagation the first method has a low level of parameterization embedded in a geologic framework and is computationally fast the second method has a much higher degree of parameterization but is flexible enough to detect deviations in the geologic settings of the reservoir however there is no explicit geologic significance and the method is computationally much less efficient forward seismic modeling of the two inversion results indicates a good match of both methods with the actual seismic data

reservoir characterization through target oriented ava petrophysical inversions with spatial constraints we apply three methods that use different regularization strategies to insert spatial constraints into the seismic petrophysical inversion the first method is what we call the structurally constrained inversion sci which directly uses the structural information brought by the seismic stack image to insert geological structural constraints into the inversion the second method is based on anisotropic markov random field amrf and uses the huber energy function to reasonably model the spatial heterogeneity of petrophysical reservoir properties finally the last method includes both geostatistical information describing the lateral variability of reservoir properties and hard data i e well log data constraints into the inversion kernel ghdc inversion for computationally feasibility we apply a target oriented inversion that uses the amplitude versus angle ava responses extracted along the top reservoir reflections to infer the petrophysical properties of interest i e porosity water saturation and shaliness for the target layer in particular an empirical linear rock physics model properly calibrated for the investigated area is used to rewrite the p wave reflectivity equation as a function of the petrophysical contrasts instead of the elastic constants this reformulation allows for a direct and a simultaneous estimation of petrophysical properties from ava data the implemented approaches are tested both on synthetic and field seismic data and compared against the standard method in which each ava response is inverted independently laterally unconstrained bayesian inversion lubi in the case of poor signal to noise ratio it turns out that the three considered spatially constrained methods achieve better delineations of reservoir bodies and provide more reliable results than the standard lubi approach more in detail the amrf recovers sharper geological boundaries than the sci and ghdc algorithms the sci algorithms is more sensitive to data noise whereas the key advantage of the ghdc consists in analytically providing posterior uncertainties for the model parameters finally for what concerns the computational cost the ghdc and the sci methods result the most and the least computationally demanding respectively

active normal faulting and crustal extension a world wide review of fault plane solutions and focal depths for large normal faulting earthquakes on the continents shows that the overwhelming majority of such earthquakes nucleate in the depth range 6 15 km on faults dipping between 30 and 60 in the few cases where levelling or seismic data are good enough these normal faults are shown to be approximately planar from the surface to their nucleation depth at the base of the brittle crust there is evidence that in some cases as a result of the enormous transitory increase in strain rate during large earthquakes rupture continues into the normally ductile lower crust on surfaces with substantially gentler dips these low angle surfaces may be analogous to some of the detachments seen in metamorphic core complexes of the western usa but the nature of the motion on them depends on strain rate as well as on rheological contrasts between the detachments and the blocks on either side such contrasts however are unlikely to introduce substantial curvature to an originally planar shear zone if the observed spread in active normal fault dips is caused by rotation of the faults and the blocks they bound during extension then a maximum value of 1 7 can be accommodated by seismic activity on a single generation of normal faults with continued extension either a new generation of steeper faults cutting the rotated first faults is likely to form or the deformation will continue aseismically on faults dipping at less than 30 large earthquakes have not been observed to nucleate on very low angle 20 normal faults within the continental crust anywhere in the world such faults can of course move aseismically but are unlikely to do so on a large scale within the upper crust in areas where steep normal faults are seismically active thus extensional models that require concentrated simple shear on large sub horizontal faults within the brittle upper crust will also require a spatial separation between aseismic very low angle faulting and seismic highangle faulting since seismogenic high angle faults dominate the topography of extending regions upper crustal very low angle faulting if it occurs on a large scale presumably does so in areas that are relatively fiat

active faulting in and along the qinling range china inferred from spot imagery analysis and extrusion tectonics of south china abstract since the beginning of the india asia collision about 2500 km of convergence has been accommodated by crustal thickening in and around the tibetan plateau and by extrusion of tibetan blocks and of the south china block the relative amounts of convergence accommodated by the two mechanisms are however still largely a matter of debate the main purpose of the present study is to determine the rate of left lateral movement between south china and north china during the late cenozoic this movement is accommodated by offsets along the more than 1000 km long e w trending qinling fault system which separates the south china block from the north china block and terminates to the east in the right lateral ndashs trending tanlu fault zone physiographic features typical of active faulting such as triangular facets along scarps and drainage deviations have been observed on spot images throughout the qinling fault system recent active faulting involves both left lateral strike slip and normal dip slip which are partitioned laterally east of the weihe graben two major faults the luonan and danfeng faults of the qinling fault system slip left laterally a cumulative slip rate of about 7 2 2 2 mm yr between the qinling shan south china and the hua shan north china has been estimated using quaternary morphological offsets in contrast the qinling frontal fault which bounds the cenozoic weihe graben to the south exhibits abundant evidence of normal faulting that accommodated large post early eocene vertical displacement in the graben crustal extension estimated from published seismic profiles and boreholes across the weihe graben contributes to a late cenozoic rate of left lateral movement of 2 0 5 mm yr in a n140 e direction between the hua shan and the ordos block combining these yields a rate of left lateral movement of 8 5 2 5 mm yr in a n100 e direction between south china and the ordos block is achieved additionally the ordos block rotates counterclockwise relative to gobi mongolia resulting in nw se crustal extension along the yinchuandashhetao grabens this is estimated from published seismic sections and adds a component of left lateral movement of 4 1 mm yr in a n125 e direction between south china and gobi mongolia the total rate of left lateral movement of south china with respect to gobi mongolia is 12 4 mm yr in a n110 e direction the eastward decrease of the left lateral strike slip on the active qinling fault system may be explained by the partitioning of left lateral movement on the faults bounding the dabie shan to the south and north and by a book shelf mechanism of counterclockwise rotating blocks separated by active ne sw right lateral faults in the dabie shan

normal faulting in the upper continental crust observations from regions of active extension abstract observations of present day normal faulting in regions of active continental extension may be helpful when interpreting the geological record in older extensional basins the most obvious manifestation of active extension is normal faulting in earthquakes earthquake foci are mostly confined to the upper seismogenic continental crust whose thickness imposes a scale on the observed deformation large earthquakes move faults with lengths similar or large compared with the thickness of the seismogenic layer large seismogenic normal faults on the continents appear to be restricted to a dip range of around 30 60 dips significantly gentler than 20 have not been observed in fault plane solutions of large earthquakes large seismographic normal faults are approximately planar in cross section and cut through the base of the upper seismogenic layer rotating about a horizontal axis as they move a reasonable estimate of the regional extension can often be made from the dip of the large normal faults and the tilt of the blocks they bound the domino model such faults are rarely continuous for more than 15 20 km but commonly change strike or step in an en echelon fashion this segmentation may occur on a scale controlled by the thickness of the seismogenic layer and is an important influence on sedimentation and drainage these observations are common to large seismogenic normal faults from a variety of tectonic settings and suggest that the kinematics of normal faulting may not be strongly influenced by the forces responsible for the extension which can vary widely in nature and magnitude small earthquakes which move faults that are small compared with the seismogenic layer thickness show no simple pattern and often can be interpreted as internal deformation of blocks bounded by large faults in some places the seismogenic basement faults do not reach the surface but are decoupled from the sedimentary cover by layers of weak lithology faults in the sedimentary cover may be strongly curved in cross section requiring their hangingwalls to deform internally estimating extension from such faults is not straightforward and requires a knowledge of the hangingwall deformation estimates made in this way are often very non unique and prone to large errors we postulate that the thickness of the seismogenic upper crust controls both the maximum length of large normal fault segments along strike and the maximum size of blocks that can rotate coherently about a horizontal axis

intraplate seismotectonic features of north china abstract intraplate earthquakes in north china are characterized by shallow depth large magnitude and high frequency obviously the zonal distribution of earthquakes is closely related to recent active faults and cenozoic graben and rift systems the active faults are mainly oriented nne with right lateral movements and partially oriented nw with left lateral movements the hetao yinchuan graben fenhe weihe graben and north china plain rift systems often reflect crustal thinning and mantle uplift according to the data concerning crustal deformation particularly the movement patterns of faulting crustal taphrogenesis and earthquake surface rupture it is suggested that a shearing extension mechanism could be considered as a cause of the formation of seismotectonic structures in north china since the early cenozoic era graben and rift systems also developed in northeast and south china they formed earlier than the graben and rift systems in north china however and their activity has decreased during the quaternary period it is reasonable that the seismicity in northeast and south china is not as strong as that in north china

lp norm deconvolution1 the purpose of deconvolution is to retrieve the reflectivity from seismic data to do this requires an estimate of the seismic wavelet which in some techniques is estimated simultaneously with the reflectivity and in others is assumed known the most popular deconvolution technique is inverse filtering it has the property that the deconvolved reflectivity is band limited band limitation implies that reflectors are not sharply resolved which can lead to serious interpretation problems in detailed delineation to overcome the adverse effects of band limitation various alternatives for inverse filtering have been proposed one class of alternatives is l p norm deconvolution l 1 norm deconvolution being the best known of this class we show that for an exact convolutional forward model and statistically independent reflectivity and additive noise the maximum likelihood estimate of the reflectivity can be obtained by l p norm deconvolution for a range of multivariate probability density functions of the reflectivity and the noise the l norm corresponds to a uniform distribution the l 2 norm to a gaussian distribution the l 1 norm to an exponential distribution and the l 0 norm to a variable that is sparsely distributed for instance if we assume sparse and spiky reflectivity and gaussian noise with zero mean the l p norm deconvolution problem is solved best by minimizing the l 0 norm of the reflectivity and the l 2 norm of the noise however the l 0 norm is difficult to implement in an algorithm from a practical point of view the frequency domain mixed norm method that minimizes the l 1 norm of the reflectivity and the l 2 norm of the noise is the best alternative l p norm deconvolution can be stated in both time and frequency domain we show that both approaches are only equivalent for the case when the noise is minimized with the l 2 norm finally some l p norm deconvolution methods are compared on synthetic and field data for the practical examples the wide range of possible l p norm deconvolution methods is narrowed down to three methods with p 1 and or 2 given the assumptions of sparsely distributed reflectivity and gaussian noise we conclude that the mixed l 1 norm reflectivity l 2 norm noise performs best however the problems inherent to single trace deconvolution techniques for example the problem of generating spurious events remain for practical application a greater problem is that only the main well separated events are properly resolved

high frequency sequence stratigraphy of upper cenozoic deposits in the central and southeastern north sea areas abstract during late cenozoic times southwestward prograding deposits filled in the central and southern part of the epicontinental north sea basin the ringkobing fyn high acted as a topographical high partly separating the central and southeastern north sea into two embayments which were connected towards the west by a deeper seaway located in the central graben area the stratal geometry deduced from seismic sections indicates different basin physiography subsidence rates and sediment influx between the two embayments eustatic sea level cycles of several frequencies interacted with low subsidence rates in the southern embayment to generate composite relative sea level cycles each composed of relative sea level cycles of higher frequencies forty five upper cenozoic sequences are identified in the southern embayment whereas only 21 sequences are recognized in the northern embayment major hiati and intervals of starved sedimentation may therefore be present in the northern embayment the sequences stack into nine composite sequences each reflecting a depositional cycle representing lowstand succeeded by transgressive highstand conditions in general a composite sequence is characterized by a period of increasing sediment accumulation rates

bayesian estimation in seismic inversion part i principles1 this paper gives a review of bayesian parameter estimation the bayesian approach is fundamental and applicable to all kinds of inverse problems its basic formulation is probabilistic information from data is combined with a priori information on model parameters the result is called the a posteriori probability density function and it is the solution to the inverse problem in practice an estimate of the parameters is obtained by taking its maximum well known estimation procedures like least squares inversion or l 1 norm inversion result depending on the type of noise and a priori information given due to the a priori information the maximum will be unique and the estimation procedures will be stable except in theory for the most pathological problems which are very unlikely to occur in practice the approach of tarantola and valette can be derived within classical probability theory the bayesian approach allows a full resolution and uncertainty analysis which is discussed in part ii of the paper

extension in the graben systems around the ordos china and its contribution to the extrusion tectonics of south china with respect to gobi mongolia the graben basins around the ordos block are major tectonic features of late cenozoic extension in north china this paper gives a synthetic view of the basic characteristics of the graben basins and of the kinematics of the graben bounding faults this view is based on the available geological data spot imagery analysis field observations and focal mechanisms of earthquakes from this region these graben basins have been grouped into two major systems the yinchuan hetao graben system along the northern and northwestern margins of the ordos and the weihe shanxi graben system along the southern and eastern margins of the ordos crustal deformation along these graben systems involves normal slip on ne sw striking graben bounding faults normal right lateral and normal left lateral slip on nne ssw and wnw ese striking faults respectively this fault pattern is consistent with nw se trending extension the amount and rate of deformation resulting from this extension have been estimated from geological data using a cross sectional area balance and the extensional factor method deduced from the tilt of faulted blocks the results of these estimates show that the uppermost pliocene quaternary extension rate in a nw se direction is in the order of 1 6 mm yr 1 across the weihe graben 0 5 mm yr 1 across the central shanxi graben on the southeastern margin of the ordos block and 3 1 mm yr 1 across the linhe graben on the northwestern margin of the ordos block the extension across these graben systems is accompanied with counterclockwise rotation of continental blocks in north china ordos taihang shan north china plain a kinematic model is proposed in which the late cenozoic extension and block rotation in north china are interpreted as the effect of the eastward termination of the left lateral slip haiyuan fault and kunlun taibai fault system the ordos block rotates counterclockwise as a result of the push of tibet through the left lateral strike slip haiyuan fault and the liupan shan thrust and fold belt the extension along the weihe shanxi graben system may represent the effect of the left lateral slip on the kunlun taibai qinling fault system the rough estimates of the extensional deformation around the ordos block indicate that this contributes to about 5 2 mm yr 1 of left lateral movement in a n125 e direction between south china and gobi mongolia this motion adds to the left lateral slip on the qinling fault zone about 7 2 mm yr 1 in a n90 e direction between the qinling shan and the hua shan north china thus the eastward motion of south china with respect to gobi mongolia is partitioned between normal faulting around the ordos and strike slip faulting in the qinling shan it is estimated to be in the order of 12 4 mm yr 1 in a n105 e direction during the quaternary

neotectonic activity along the shanxi rift system china abstract the shanxi rift system is one of the most outstanding pliocene quaternary continental rift systems and strong earthquake belts in china it extends as a series of en echelon left stepping asymmetrical half graben basins on the shanxi highlands over a distance of more than 1200 km it describes a sinous s shaped curve with a nne trending transtensional segment in the middle and ne ene trending extensional domains on both terminal segments the latter are characterized by apparently synchronous high angle normal faulting accommodating large vertical and relatively smaller lateral strains 3 5 8 5 which produces the modern basin and range structure the rift system has been intermittently active since the pliocene geomorphological neotectonic and seismic studies indicate that the rift system is at present still developing as demonstrated by the occurrence of strong destructive historical earthquakes of magnitudes 7 8 and the large slip rates on the nne trending transtensional faults in the middle segment the slip rates of these faults reached 4 9 6 4 mm per year during the holocene geophysical studies show that the rifting occurred in a thickened crust and no compelling evidence exists for the major thermal event in the mantle uniquely associated with the rifting the development of the shanxi rift system is consistent with the regional brittle strain pattern of a right lateral shear belt and a regional stress field of ene wsw compression and nnw sse extension of the north china subplate this structural setting corroborates the hypothesis that the deformation is in response to the escape tectonics caused by the himalayan indenter from the southwest and at the same time by the counter clockwise rotation of the intervening crustal blocks this provides the mode of formation of the shanxi rift system

petrophysical seismic inversion conditioned to well log data methods and application to a gas reservoir hydrocarbon reservoirs are characterized by seismic welllog and petrophysical information which is dissimilar in spatial distribution scale and relationship to reservoir properties we combine this diverse information in a unified inverse problem formulation using a multiproperty multiscale model linking properties statistically by petrophysical relationships and conditioningthemtowell logdata twoapproacheshelpus 1markov chainmontecarlosampling whichgeneratesmanyreservoir realizationsforestimatingmediumpropertiesandposteriormarginalprobabilities and2optimizationwithaleast squaresiterativetechniquetoobtainthemostprobablemodelconfiguration our petrophysical model applied to near vertical anglestacked seismicdataandwell logdatafromagasreservoir includesadeterministic component based on a combination of wyllie and wood relationships calibrated with the well log data and a random component based on the statistical characterization of the deviations of well log data from the petrophysical transform at the petrophysical level the effects of porosity and saturation on acoustic impedance are coupled conditioning the inversion to well log data helps resolve this ambiguity the combination of well logs petrophysics and seismic inversion builds on the correspondingstrengthsofeachtypeofinformation jointlyimproving 1 cross resolution of reservoir properties 2 vertical resolution of property fields 3 compliance to the smooth trend of property fields and 4 agreement with well log data at well positions

the cenozoic tectonic evolution of the great north china two types of rifting and crustal necking in the great north china and their tectonic implications abstract the great north china underwent widespread continental rifting during cenozoic time that caused extension and necking of the crust in this area and formed four major rift systems in this paper we provide geological and geophysical evidence that rifting and extension in the western part of the great north china differs from that in its eastern part in age and nature the space time relationships show that the origins of the western rift group of the great north china are probably related to the tibet plateau tectonics whereas those of the eastern rift group are related to the subduction events in the western margin of the pacific plate furthermore the quaternary tectonic regime in the eastern part of the great north china differs from the neogene tectonic pattern and shows relations with western rifts we speculate that during the quaternary the processes that caused rifting in the west have spread further east and now affect the eastern part of the great north china

balanced cross section construction from seismic sections in areas of extensional tectonics abstract the application of the technique of balanced section construction initially developed for areas of compressional folding and faulting is reviewed with reference to extensional tectonics a number of examples are discussed where these techniques have been successfully applied in the north sea the interpretation of geoseismic sections is considered to be greatly assisted by careful application of geometrical balance and a consideration of strain even in areas of low crustal extensions the nature of seismic sections however places limitations on the validity of balancing which must be borne in mind with such interpretations and wherever possible the balancing of a geoseismic section should be confirmed by complete depth conversion the rapid testing of the integrity of the geoseismic section by attempting to balance the section at the interpretational phase can eliminate many problems as well as allowing the fullest use to be made of the geophysical information

automatic 1 d waveform inversion of marine seismic refraction data summary full waveform synthetic seismograms are now used as standard in the interpretation of marine refraction data but only with a laborious trial and error fitting procedure we show how the matching of observed waveforms with wkbj synthetic seismograms can be efficiently and automatically performed for 1 d earth models automation of the inversion is difficult because of the multi modal irregular form of the misfit of data and synthetics a sequence of three steps is required for a complete inversion location of the deepest valley of the misfit function descent to the global minimum and description of the neighbourhood of the minimum for error analysis the first step is accomplished with a monte carlo search through a very large model space defined by poor prior knowledge of velocities and gradients of the solution weak traveltime constraints are used to eliminate poorly fitting models from waveform calculations a comparison of the traveltime and waveform misfits of the monte carlo models clearly illustrates that waveforms are providing more information than traveltimes alone bayesian statistics are used to construct marginal probability distributions and the covariance matrix which give a rough preliminary error analysis in the second step damped least squares linearized inversion makes small adjustments to the best fitting monte carlo model as it descends to the global minimum finally the immediate neighbourhood of the global minimum is explored with constrained least squares inversion realistic error bounds on each parameter are defined from the resulting slices through the misfit function these bounds are much narrower than traveltime inversion provides correlations between parameters are obtained from the covariance matrix constructed from models examined during this error analysis the inversion methods are illustrated on the ff2 refraction data set of the scripps institution of oceanography the monte carlo search successfully locates the valley of the global minimum as well as a nearby secondary minimum the error analysis puts realistic error bounds on the detailed inversion of this data set by spudich orcutt

seismogenic strike slip faulting and the development of the north china basin the actively subsiding north china sedimentary basin is associated with an unusually high level of seismic activity this oil and gas producing basin has been the site of nine large m 7 destructive earthquakes since 1600 a d an analysis of faulting during the tangshan earthquake sequence which includes some of the largest shocks that have occurred in this basin during the past 400 years showed that the dominant pattern of deformation during this sequence was associated with displacement on right stepping right lateral strike slip faults a large amount of subsidence 1 0 1 5 m occurred in pull apart regions between steps of the north northeast nne trending strike slip faults the directivity of the p wave radiation pattern and the distribution of aftershocks of the bohai gulf earthquake of july 18 1969 also indicate strike slip faulting on planes of similar nne trend together with the four largest shocks of the hsingtai sequence in 1966 earthquakes with right lateral slip on nne trending faults account for about two thirds of the seismic moment released in this region for the past 100 years the average regional strain due to seismic slip has a dominant component of dextral simple shear on nne striking planes that is approximately twice as large as north south extension or east west shortening based on a combination of published field and borehole data the dominance of horizontal dextral simple shear over subsidence seems to have begun no later than the mid pliocene and the total amount of extension over the entire basin is only about 20 30 this pattern of deformation the spatially variable heat flow values the scattered locations of rapid deposition of quaternary sediments and the fluctuating rate of sedimentation in space and time during the neogene in this basin are difficult to explain by pure extension and thermal subsidence we propose that these observations and the shape of the whole north china basin that of a lazy z are a consequence of pulling apart associated with right lateral movement on the nne trending strike slip fault systems and that the basin as a whole has formed and evolved as a composite pull apart basin due to right lateral slip on numerous right stepping faults since the eocene

acoustic nonlinear full waveform inversion on an outcrop based detailed geological and petrophysical model book cliffs utah analog outcrops are commonly used to develop predictive reservoir models and provide quantitative parameters that describe the architecture and facies distribution of sedimentary deposits at a subseismic scale all of which aids exploration and production strategies the focus of this study is to create a detailed geological model that contains realistic reservoir parameters and to apply nonlinear acoustic full waveform prestack seismic inversion to this model to investigate whether this information can be recovered and to examine which geological features can be resolved by this process outcrop data from the fluviodeltaic sequence of the book cliffs utah are used for the geological and petrophysical two dimensional model eight depositional environments are populated with average petrophysical reservoir properties adopted from a north sea field these units are termed lithotypes here synthetic acoustic prestack seismic data are then generated with the help of an algorithm that includes all internal multiples and transmission effects a nonlinear acoustic full waveform inversion is then applied to the synthetic data and two media parameters compressibility inversely related to the square of the compressional wave velocity vp and bulk density are recovered at a resolution higher than the shortest wavelength in the data this is possible because the inversion exploits the nonlinear nature of the relationship between the recorded data and the medium contrast properties in conventional linear inversion these details remain masked by the noise caused by the nonlinear effects in the data random noise added to the data is rejected by the nonlinear inversion contributing to improved spatial resolution the results show that the eight lithotypes can be successfully recovered at a subseismic scale and with a low degree of processing artifacts this technique can provide a useful basis for more accurate reservoir modeling and field development planning allowing targeting of smaller reservoir units such as distributary channels and lower shoreface sands

bounds on the holocene slip rate of the haiyuan fault north central china abstract we measured the offsets of six stream valleys of 30 to 90 m along the northwest southeast trending left lateral haiyuan strike slip fault in north central china minimum ages of these offsets were determined to estimate lower bounds for the holocene slip rate the most reliable bounds are 7 6 1 0 and 6 7 1 0 mm yr with three others that are smaller 3 4 0 7 3 5 0 9 and 4 1 0 4 mm yr and one large value 16 4 5 9 mm yr that we doubt thus the average holocene slip rate of the haiyuan fault is larger than 6 mm yr and probably exceeds 7 mm yr if the average slip rate of 5 to 10 mm yr for the quaternary period is applicable to the holocene epoch the average rate is 8 2 mm yr

faulting associated with large earthquakes and the average rate of deformation in central and eastern asia we determine approximate average rates of deformation in portions of eastern and central asia for the last 80 years these rates are based on estimates of source dimensions average displacements seismic moments and orientations of faults of all large earthquakes m 7 5 and as many other major earthquakes m 7 0 as possible in asia since 1900 a major part of this study is the compilation of these data for separate parts of asia we combine seismic moment tensors to estimate the average rotational strain or deformation tensors for these regions for the last 80 years we estimate that shortening across the tien shan has occurred at 11 mm yr between 5 and 19 mm yr left lateral shear on easterly trending planes in mongolia in northwestern tibet gansu and ningxia and on the xianshuihe fault in western sichuan has been very rapid more than 10 mm yr in each region and apparently as rapid as 40 mm yr in northwestern tibet gansu and ningxia slower rates of a few to 10 mm yr appear to characterize east west extension and conjugate north south shortening of tibet the earthquake history of the himalaya is consistent with rates of underthrusting of more than 10 mm yr but is probably less than the convergence rate of india with eurasia of about 50 mm yr the overall strain field is consistent with a large part of india s penetration into eurasia being absorbed by the extrusion of material out of india s way as a result southeast china moved at about 21 mm yr east southeast with respect to eurasia in the last 80 years with an uncertainty of about a factor of 2 in this estimated rate

past present and future of geophysical inversion a new millennium analysis geophysicists have been working on solutions to the inverse problem since the dawn of our profession an interpreter infers subsurface properties on the basis of observed data sets such as seismograms or potential field recordings a rough model of the process that produces the recorded data resides within the interpreter s brain the interpreter then uses this rough mental model to reconstruct subsurface properties from the observed data in modern parlance the inference of subsurface properties from observed data is identified with the solution of a so called inverse problem in contrast the forward problem consists of the determination of the data that would be recorded for a given subsurface configuration and under the assumption that given laws of physics hold until the early 1960s geophysical inversion was carried out almost exclusively within the geophysicist s brain since then we have learned to make the geophysical inversion process much more quantitative and versatile by recourse to a

right lateral shear and rotation as the explanation for strike slip faulting in eastern tibet the convergence of two continents can be accommodated by crustal thickening and by lateral transport of crust out of the path of the converging continents1 3 the principal features suggesting that lateral transport is important are major strike slip faults striking roughly orthogonally to the orientation of convergence between the continents displacement on such faults is imagined to allow lateral transport of material with respect to the converging continents possibly accounting for a large fraction of the convergence between the two continents the most spectacular example of such strike slip faulting is in the eastern part of the tibetan plateau where three major left lateral faults with slip rates of 10 mm yr 1 and several smaller roughly parallel faults dominate the regional strain field2 3 cobbold and davy4 suggested that these faults may be rotating in a clockwise fashion here we put bounds on that rate of rotation and conclude that the image of lateral transport on such faults2 known also as continental escape extrusion or expulsion is an illusion and that instead the left lateral slip on east striking planes in eastern tibet is a manifestation of north striking right lateral simple shear if this conclusion is correct the east striking left lateral faults and the crustal blocks between them are rotating clockwise at 1 2 myr 1 the east west dimension of eastern tibet is shortening at 10 20 mm yr 1 and little material is moving eastward out of india s path into eurasia by left lateral simple shear

neogene and quaternary faulting in and along the qinling shan the structure of the qinling shan mountain range shaanxi china involves major east south east strike slip faults field observations made during two expeditions in 1983 and 1984 show that the faults are active and may have undergone several tens of kilometres of post eocene left lateral displacement the faults cut the morphology sharply and offset left laterally small channels their trace is marked by cataclastic to mylonitic non coaxial deformation zones at least 50 100 m wide the qinling faults allow the eastward extrusion of south china and may be considered the easternmost continuation of the altyn tagh fault system they link extensional tectonics in northeastern china to the himalayan collision

hydraulic properties of a major alluvial aquifer an isotropic inhomogeneous system abstract field observations pump test analyses and three dimensional digital simulations of a portion of the missouri river valley floodplain provided insights about the hydraulic properties of this alluvial aquifer three distinct facies can be recognized in the alluvial sediments a lower cobble facies a middle gravel sand facies and an upper sand silt clay facies type curve solutions and two dimensional finite difference models must be used with caution for such strongly inhomogeneous aquifers three dimensional digital model analyses suggest the alluvium is best simulated as an isotropic but inhomogeneous system ratios of vertical to horizontal hydraulic conductivity obtained from analyses such as delayed yield theory are created by aquifer inhomogeneity and not anisotropy per se empirical power relations showing an increase of hydraulic conductivity with depth provide valid estimates in the absence of field data however these relations do not hold for the beds and banks of the major rivers or their tributaries finally riverstage and observation well data show that groundwater levels are controlled primarily by river stage fluctuations and pumping recharge from precipitation seepage into and out of smaller streams and probably bedrock recharge are all minor influences