Estimation of Seismic Velocities from Deep Reflections in the τ-p Domain     

C. Bönnemann  B. Buttkus 《Pure and Applied Geophysics》1999,156(1-2):279-301

—In deep reflection seismics the estimation of seismic velocities is hampered in most cases due to the low signal level with respect to noise. In the τ-p domain, it is possible to perform the velocity analysis even under such unfavorable signal conditions. This is achieved by making use of special properties of the transform, which enhance the signal-to-noise ratio. Further noise suppression is realized by incorporating filter procedures into the transform algorithm. The velocity analysis itself is also done in the τ-p domain by calculating and evaluating constant velocity gathers. The results can be directly used in the time domain. A mute algorithm, implemented into the τ-p velocity analysis procedure, further reduces noise. This velocity estimation method is discussed with synthetic data and applied to DEKORP data.  相似文献   

τ-p SEISMIC DATA FOR VISCOELASTIC MEDIA - PART 2: LINEARIZED INVERSION1     

RUBEN D. MARTINEZ  GEORGE A. McMECHAN 《Geophysical Prospecting》1991,39(2):157-181

An approach to extraction of viscoelastic parameters from seismic data is implemented and succesfully tested. Viscoelastic inversion is performed using adaptive damping factors to control the sensitivity of the viscoelastic parameters in relation to the τ-p seismic data. A priori information is incorporated through the damping factors as standard deviations of the data and of the viscoelastic model parameters. The stability of the inversion process is controlled by the variation of the damping factors as a function of the residual errors and parameter updates at each iteration. Tests on synthetic and real data show that P- and S-wave quality factors, Q_p and Q_s, in addition to P- and S-wave velocities and density C_p, C_s and p, can be extracted from τ-p seismic information. Singular value decomposition analysis demonstrates that estimated Q_p and Q_s values are more affected by the presence of data inaccuracies and noise than are those of C_p and p. C_s and Q_s are not uniquely recovered due to the limited contribution of P-S converted waves. Knowledge of the viscoelastic parameters is of particular importance in accurately describing petrophysical properties of rocks and pore fluids existing in the subsurface; this is demonstrated with real data from the Gulf of Mexico.  相似文献   

VELOCITY ANALYSIS FOR WIDE APERTURE SEISMIC DATA*     

P. L. STOFFA  J. B. DIEBOLD  P. BUHL 《Geophysical Prospecting》1982,30(1):25-57

Common midpoint data are now being collected with ever increasing source-receiver offsets. For wide aperture seismic data classical methods of interpretation fail, since velocity analyses and signal-to-noise enhancement methods based on hyperbolic traveltime curves are no longer appropriate. Therefore, the goals of increased velocity resolution and signal enhancement, which motivate the increase in offset, are not achieved. Approximate methods, involving higher order traveltime curves or extrapolations, have been developed for velocity analysis but these are ineffective in the presence of refracted arrivals, and lack a physical basis. These problems can be minimized by transforming the observational data to the domain of intercept or vertical delay time τ and horizontal ray parameter p. In this domain headwave refractions are collapsed into points and both near vertical and wide angle reflections can be analyzed simultaneously to derive velocity-depth information, even in the presence of velocity gradients or low velocity zones.  相似文献   

LIMITS OF STRUCTURAL INVERSION OF SEISMIC HORIZONS*     

D. BILGERI  A. CARLINI 《Geophysical Prospecting》1984,32(4):581-607

Time horizons can be depth-migrated when interval velocities are known; on the other hand, the velocity distribution can be found when traveltimes and NMO velocities at zero offset are known (wavefront curvatures; Shah 1973). Using these concepts, exact recursive inversion formulae for the calculation of interval velocities are given. The assumption of rectilinear raypath propagation within each layer is made; interval velocities and curvatures of the interfaces between layers can be found if traveltimes together with their gradients and curvatures and very precise V_NMO velocities at zero offset are known. However, the available stacking velocity is a numerical quantity which has no direct physical significance; its deviation from zero offset NMO velocity is examined in terms of horizon curvatures, cable length and lateral velocity inhomogeneities. A method has been derived to estimate the geological depth model by searching, iteratively, for the best solution that minimizes the difference between stacking velocities from the real data and from the structural model. Results show the limits and capabilities of the approach; perhaps, owing to the low resolution of conventional velocity analyses, a simplified version of the given formulae would be more robust.  相似文献   

FREQUENCY WAVENUMBER APPROACH OF THE τ-p TRANSFORM: SOME APPLICATIONS IN SEISMIC DATA PROCESSING*     

S.D. BENOLIEL  W.A. SCHNEIDER  R.N. SHURTLEFF 《Geophysical Prospecting》1987,35(5):517-538

The τ-p transform is an invertible transformation of seismic shot records expressed as a function of time and offset into the τ (intercept time) and p (ray parameter) domain. The τ-p transform is derived from the solution of the wave equation for a point source in a three-dimensional, vertically non-homogeneous medium and therefore is a true amplitude process for the assumed model. The main advantage of this transformation is to present a point source shot record as a series of plane wave experiments. The asymptotic expansion of this transformation is found to be useful in reflection seismic data processing. The τ-p and frequency-wavenumber (or f-k) processes are closely related. Indeed, the τ-p process embodies the frequency-wavenumber transformation, so the use of this technique suffers the same limitations as the f-k technique. In particular, the wavefield must be sampled with sufficient spatial density to avoid wavenumber aliasing. The computation of this transform and its inverse transform consists of a two-dimensional Fast Fourier Transform followed by an interpolation, then by an inverse-time Fast Fourier Transform. This technique is extended from a vertically inhomogeneous three-dimensional medium to a vertically and laterally inhomogeneous three-dimensional medium. The τ-p transform may create artifacts (truncation and aliasing effects) which can be reduced by a finer spatial density of geophone groups by a balancing of the seismic data and by a tapering of the extremities of the seismic data. The τ-p domain is used as a temporary domain where the attack of coherent noise is well addressed; this technique can be viewed as ‘time-variant f-k filtering’. In addition, the process of deconvolution and multiple suppression in the τ-p domain is at least as well addressed as in the time-offset domain.  相似文献   

Combined structure and velocity stacks via the tau–p transform     

G.D. Jones  P.J. Barton  S.C. Singh 《Geophysical Prospecting》2003,51(3):205-213

Reflection and refraction data are normally processed with tools designed to deal specifically with either near- or far-offset data. Furthermore, the refraction data normally require the picking of traveltimes prior to analysis. Here, an automatic processing algorithm has been developed to analyse wide-angle multichannel streamer data without resorting to manual picking or traveltime tomography. Time–offset gathers are transformed to the tau–p domain and the resulting wavefield is downward continued to the depth–p domain from which a velocity model and stacked section are obtained. The algorithm inputs common-depth-point (CDP) gathers and produces a depth-converted stacked section that includes velocity information. The inclusion of long-offset multichannel streamer data within the tau–p transformation enhances the signal from high-velocity refracted basalt arrivals. Downward continuation of the tau–p transformed wavefield to the depth–p domain allows the reflection and refraction components of the wavefield to be treated simultaneously. The high-slowness depth–p wavefield provides the velocity model and the low-slowness depth–p wavefield may be stacked to give structural information. The method is applied to data from the Faeroe Basin from which sub-basalt velocity images are obtained that correlate with an independently derived P-wave model from the line.  相似文献   

Seismic velocity estimation from post-critical wide-angle reflections in layered structures     

Mariusz Majdański  Maciej Trzeciak  Edward Gaczyński  Andrzej Maksym 《Studia Geophysica et Geodaetica》2016,60(3):565-582

The travel time inversion of wide-angle seismic data is a technique commonly used in the deep seismic sounding. We propose an application of this technique to a smaller scale of a sedimentary layer, where the characteristics of seismic observations changes significantly. Field observations confirmed by synthetic analysis recognize the dominant amplitudes of wide-angle post-critical reflections. A case study is presented in this paper, of a joint interpretation of conventional reflection seismic with reflection imaging, combined with the wide-angle travel time inversion of additional full-spread observations. A joint interpretation results in a precise recognition of the seismic velocity distribution, that is further used for the seismic depth conversion with the uncertainty analysis of the depth of the reflecting horizons. Despite the salt layer in the studied structure this method is able to precisely recognize the seismic velocities of the sub-salt structures.  相似文献   

DECOMPOSITION AND INVERSION OF SEISMIC DATA–AN INSTANTANEOUS SLOWNESS APPROACH*     

B. MILKEREIT 《Geophysical Prospecting》1987,35(8):875-894

Interpretation techniques are presented that aim at the estimation of seismic velocities. The application of localized slant stacks, weighted by coherency, produces a decomposition of multichannel seismic data into single trace instantaneous slowness p(x, t) components. Colour displays support the interpretation of seismic data relevant to the near surface velocity structure. Since p(x, t) is directly related to stacking velocities and the depth of reflection, or bottoming points, in the subsurface, this data transformation provides a powerful tool for the inversion of reflection and refraction data.  相似文献   

Strong variation in weathering of layered rock maintains hillslope‐scale strength under high precipitation          下载免费PDF全文

Jennifer Von Voigtlander  Marin K. Clark  Dimitrios Zekkos  William W. Greenwood  Suzanne P. Anderson  Robert S. Anderson  Jonathan W. Godt 《地球表面变化过程与地形》2018,43(6):1183-1194

The evolution of volcanic landscapes and their landslide potential are both dependent upon the weathering of layered volcanic rock sequences. We characterize critical zone structure using shallow seismic V_p and V_s profiles and vertical exposures of rock across a basaltic climosequence on Kohala peninsula, Hawai’i, and exploit the dramatic gradient in mean annual precipitation (MAP) across the peninsula as a proxy for weathering intensity. Seismic velocity increases rapidly with depth and the velocity–depth gradient is uniform across three sites with 500–600 mm/yr MAP, where the transition to unaltered bedrock occurs at a depth of 4 to 10 m. In contrast, velocity increases with depth less rapidly at wetter sites, but this gradient remains constant across increasing MAP from 1000 to 3000 mm/yr and the transition to unaltered bedrock is near the maximum depth of investigation (15–25 m). In detail, the profiles of seismic velocity and of weathering at wet sites are nowhere monotonic functions of depth. The uniform average velocity gradient and the greater depths of low velocities may be explained by the averaging of velocities over intercalated highly weathered sites with less weathered layers at sites where MAP > 1000 mm/yr. Hence, the main effect of climate is not the progressive deepening of a near‐surface altered layer, but rather the rapid weathering of high permeability zones within rock subjected to precipitation greater than ~1000 mm/yr. Although weathering suggests mechanical weakening, the nearly horizontal orientation of alternating weathered and unweathered horizons with respect to topography also plays a role in the slope stability of these heterogeneous rock masses. We speculate that where steep, rapidly evolving hillslopes exist, the sub‐horizontal orientation of weak/strong horizons allows such sites to remain nearly as strong as their less weathered counterparts at drier sites, as is exemplified by the 50°–60° slopes maintained in the amphitheater canyons on the northwest flank of the island. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

INVERSION METHOD IN THE SLANT STACK DOMAIN USING AMPLITUDES OF REFLECTION ARRIVALS*     

Ph.M. CARRION  J. T. KUO  P. L. STOFFA 《Geophysical Prospecting》1984,32(3):375-391

Almost all ray-tracing methods ignore the analysis of the amplitudes of seismic arrivals and therefore utilize only half of the available information. We propose a method which is a combination of ray-tracing imaging and transformation of the amplitudes of wide-aperture data. Seismic data in the conventional X-T domain are first transformed to the domain of intercept time τ and ray parameter p to recover the plane wave response. The next step is the derivation of a series of plane wave reflection coefficients, which are mapped as a function of τ and p. The reflection coefficients R(τ, p) for two arbitrarily chosen traces can then be used in our inversion method to derive a slowness-depth and a density-depth profile. It is shown that the inclusion of amplitudes of seismic arrivals (in this method, we consider the acoustic case) makes the inverse method highly stable and accurate. In a horizontally stratified medium one can recover separate profiles of velocity and density. Since this method utilizes large-offset data, it can be used for separate recovery of velocity and density to a greater depth.  相似文献   

Separation of P- and S-wavefields from wide-angle multicomponent OBC data for a basalt model     

Yanbin Wang  Satish C. Singh 《Geophysical Prospecting》2003,51(3):233-245

Wide-angle multicomponent ocean-bottom cable (OBC) data should further enhance sub-basalt imaging by using both compressional and converted shear wavefields. The first step in analysing multicomponent OBC data is to decompose the recorded wavefields into pure P- and pure S-wavefields, and extract the upgoing P- and S-waves. This paper presents a new scheme to separate P- and S-wavefields from wide-angle multicomponent OBC data in the τ–p domain. By considering plane-wave components with a known horizontal slowness, the P- and S-wavefields are separated into the directions of observed P- and S-wave oscillations using the horizontal and vertical components of the data. The upgoing P- and S-waves are then extracted from the separated P- and S-wavefields. The parameters used in the separation are the seismic wave velocities and the density at the receiver location, which can be estimated from the first reflection phase observed on the horizontal and vertical components. Numerical tests on synthetic data for a plane-layered model show good performance and demonstrate the accuracy of the scheme. Separation of wavefields from a basalt model is performed using synthetic wide-angle multicomponent OBC data. The results show that both near-offset and wide-angle reflections and conversions from within and below basalt layers are enhanced and clearly identified on the separated wavefields.  相似文献   

DETERMINATION OF LATERAL INHOMOGENEITIES IN REFLECTION SEISMICS BY INVERSION OF TRAVELTIME RESIDUALS*     

G. NEUMANN 《Geophysical Prospecting》1981,29(2):161-177

Lateral inhomogeneities generate fluctuations in the traveltime of seismic waves. By evaluation of these traveltime fluctuations from different source and receiver positions, lateral inhomogeneities can be located using a pseudo inverse matrix method (Aki, Christoffersson and Husebye 1977). The formulation of the problem is possible for transmitted waves as well as for reflected and refracted waves. In reflection seismics this method is of importance, if no reflections from the inhomogeneities themselves, but only reflections from lower boundaries can be observed. The basic assumptions for the mathematical formulation are (1) the average velocities and depths of the reflecting horizons are known already from standard processing methods, and (2) the traveltime residuals are due to lateral velocity changes between different reflectors or between reflectors and the surface. The area of the earth to be considered is divided into layers and the layers into rectangular blocks. The parallel displacement of a ray after passing a disturbed block is neglected, only the traveltime residual is taken into account. In this paper the method and its application to data obtained with two-dimensional models are described.  相似文献   

COMMON REFLECTION POINT DATA-STACKING TECHNIQUE FOR CONVERTED WAVES1     

G. TESSMER  A. BEHLE 《Geophysical Prospecting》1988,36(7):671-688

For converted waves stacking requires a true common reflection point gather which, in this case, is also a common conversion point (CCP) gather. We consider converted waves of the PS- and SP-type in a stack of horizontal layers. The coordinates of the conversion points for waves of PS- or SP-type, respectively, in a single homogeneous layer are calculated as a function of the offset, the reflector depth and the velocity ratio v_p/v_s. Knowledge of the conversion points enables us to gather the seismic traces in a common conversion point (CCP) record. Numerical tests show that the CCP coordinates in a multilayered medium can be approximated by the equations given for a single layer. In practical applications, an a priori estimate of v_p/v_s is required to obtain the CCP for a given reflector depth. A series expansion for the traveltime of converted waves as a function of the offset is presented. Numerical examples have been calculated for several truncations. For small offsets, a hyperbolic approximation can be used. For this, the rms velocity of converted waves is defined. A Dix-type formula, relating the product of the interval velocities of compressional and shear waves to the rms velocity of the converted waves, is presented.  相似文献   

SLANT STACKING AND ITS SIGNIFICANCE FOR ANISOTROPY*     

H. HAKE 《Geophysical Prospecting》1986,34(4):595-608

Slant stacking transforms seismic data, recorded as a function of source-receiver offset and traveltime, into the domain of intercept time τ and ray parameter p. The shape of the τ-p-curves thus obtained is closely related to the slowness surfaces of the layers. A layer-stripping operation in the τ-p-domain removes all effects of the layers above the target layer. The resulting curve is equal to the slowness surface of the layer except for a scaling factor containing the thickness and dip of the layer. The slowness surface is a characteristic surface for anisotropic media. This makes the τ-p-domain very suitable for detecting and describing anisotropic layers. The relationship between the shape of τ-p-curves, the slowness surfaces, and the geometry of the layers is derived. Synthetic τ-p-curves calculated with the reflectivity method show some difficulties that can arise in determining the shape of the curves and in applying the stripping operation. It is shown that the effects of vertical inhomogeneity on the interpretation of τ-p-curves in terms of anisotropy are small.  相似文献   

Piecewise‐continuous velocity inversion          下载免费PDF全文

Igor Ravve 《Geophysical Prospecting》2016,64(3):517-542

We suggest a new method to determine the piecewise‐continuous vertical distribution of instantaneous velocities within sediment layers, using different order time‐domain effective velocities on their top and bottom points. We demonstrate our method using a synthetic model that consists of different compacted sediment layers characterized by monotonously increasing velocity, combined with hard rock layers, such as salt or basalt, characterized by constant fast velocities, and low velocity layers, such as gas pockets. We first show that, by using only the root‐mean‐square velocities and the corresponding vertical travel times (computed from the original instantaneous velocity in depth) as input for a Dix‐type inversion, many different vertical distributions of the instantaneous velocities can be obtained (inverted). Some geological constraints, such as limiting the values of the inverted vertical velocity gradients, should be applied in order to obtain more geologically plausible velocity profiles. In order to limit the non‐uniqueness of the inverted velocities, additional information should be added. We have derived three different inversion solutions that yield the correct instantaneous velocity, avoiding any a priori geological constraints. The additional data at the interface points contain either the average velocities (or depths) or the fourth‐order average velocities, or both. Practically, average velocities can be obtained from nearby wells, whereas the fourth‐order average velocity can be estimated from the quartic moveout term during velocity analysis. Along with the three different types of input, we consider two types of vertical velocity models within each interval: distribution with a constant velocity gradient and an exponential asymptotically bounded velocity model, which is in particular important for modelling thick layers. It has been shown that, in the case of thin intervals, both models lead to similar results. The method allows us to establish the instantaneous velocities at the top and bottom interfaces, where the velocity profile inside the intervals is given by either the linear or the exponential asymptotically bounded velocity models. Since the velocity parameters of each interval are independently inverted, discontinuities of the instantaneous velocity at the interfaces occur naturally. The improved accuracy of the inverted instantaneous velocities is particularly important for accurate time‐to‐depth conversion.  相似文献   

A direct method of calculating interval velocities and layer thicknesses from wide-angle seismic reflection times     

Kalachand Sain  K. L. Kaila 《Pure and Applied Geophysics》1996,146(2):343-363

Wide-angle reflections are now routinely recorded in high resolution explosion seismics to study the crustal structure. Use of Dix's hyperbolic approximation to the nonhyperbolic wide-angle reflection travel times causes major errors in the determination of interval velocities and layer thicknesses of a stack of horizontal velocity layers. Here we propose a layer stripping method to directly calculate the interval velocities and layer thicknesses in a vertically heterogeneous earth from the strong and reliable wide-angle reflected events. Synthetic reflection travel times, at wide-angle range, for a given velocity model, contaminated by some random errors, have been used to demonstrate the reliability of the algorithms to determine the interval velocities and thicknesses of various layers. The method has also been tested on two field examples along two deep seismic sounding (DSS) profiles with well identified wide-angle reflection travel times, which illustrates the practical feasibility of the proposed method.  相似文献   

MAPPING NON-REFLECTING VELOCITY INTERFACES BY NORMAL MOVEOUT VELOCITIES OF UNDERLYING HORIZONS*     

TH. KREY 《Geophysical Prospecting》1980,28(3):359-371

The normal moveout velocity of a reflecting bed is a function of the dips and curvatures of all overlying velocity interfaces. Now let the (N– 1)th velocity interface be a non- (or badly) reflecting bed, whereas the other interfaces, including the base of the Nth layer, reflect satisfactorily, and let the velocities U_{N– 1} and U_N of the (N– 1)th and Nth layer, respectively, be known. Then the normal moveout velocity for the base of the Nth layer, if known in one direction at a certain part of the surface of the earth, provides a second order differential equation in the horizontal coordinates x and y for the depth Z_{N – 1}(x, y) of the unknown interface. The mathematics becomes rather simple in the case of two-dimensional geological structures. For this case and N= 2 the differential equation mentioned can be solved by stepwise integration or by iteration. One of the many possible applications of the new concept is the determination of the structure of the base of an overthrusting sheet.  相似文献   

A LAYER-STRIPPING TECHNIQUE FOR THE SUPPRESSION OF WATER-BOTTOM MULTIPLE REFLECTIONS*     

Ph.M. CARRION 《Geophysical Prospecting》1986,34(3):330-342

A new method to suppress water-bottom multiples (water-bottom reverberations) uses the fact that in the domain of intercept time and ray parameter (τ–p domain) the water-bottom reverberations are strictly periodical for a horizontal flat sea bottom. Using this property a comb filter can be designed. The window of the filter should be approximately equal to the duration of a source pulse. The algorithm finds the maximum of the periodical energy throughout the τ–p domain and then designs the comb filter which eliminates the water bottom reverberations from each trace in the τ– p domain. This process can be repeated for higher order reverberations. Finally the τ–p domain with attenuated multiples is transformed back to the conventional x -- t space. The method is illustrated on a variety of synthetic data and on a set of real marine CMP data acquired in the North Sea near the Norwegian shore.  相似文献   

Crustal structure of Gondwana- and Yangtze-typed blocks: An example by wide-angle seismic profile from Menglian to Malong in western Yunnan   总被引：10，自引：0，他引：10  

ZHANG Zhongjie  BAI Zhiming  WANG Chunyong  TENG Jiwen  Lü Qingtian  LI Jiliang  SUN Shanxue & WANG Xinzheng . Institute of Geology  Geophysics  Chinese Academy of Sciences  Beijing  China  . Institute of Geophysics  Chinese Seismological Bureau  Beijing  China  . Institute of Deposition Resource  Chinese Academy of Geological Sciences  Beijing  China 《中国科学D辑(英文版)》2005,48(11):1828-1836

Ancient Tethyan vestige extends from Alps, Kaebaiqn Mountain and eastward through Turkey, IranAfghanistan, and the middle and north of Tibetan Plateau, then turns to western Yunnan and Sichuan, andfinally ends at Zhongnan Peninsula. The PaleoTethyan is supposed as one eastward opened Oceanand superposed by tectonic deformation in the latestage of the late Mesozoic to Paleocene of Cenozoicand covered by Mesozoic and Cenozoic deposits. The Sanjiang region in southwestern China is in the…  相似文献   

Multiparametric Traveltime Inversion     

Biloti  Ricardo  Santos  Lúcio T.  Tygel  Martin 《Studia Geophysica et Geodaetica》2002,46(2):177-192

In conventional seismic processing, the classical algorithm of Hubral and Krey is routinely applied to extract an initial macrovelocity model that consists of a stack of homogeneous layers bounded by curved interfaces. Input for the algorithm are identified primary reflections together with normal moveout (NMO) velocities, as derived from a previous velocity analysis conducted on common midpoint (CMP) data. This work presents a modified version of the Hubral and Krey algorithm that is designed to extend the original version in two ways, namely (a) it makes an advantageous use of previously obtained common-reflection-surface (CRS) attributes as its input and (b) it also allows for gradient layer velocities in depth. A new strategy to recover interfaces as optimized cubic splines is also proposed. Some synthetic examples are provided to illustrate and explain the implementation of the method.  相似文献