Post-critical Reflections Research Articles

Searching the e-dessert: a post-critical reflection on e-textbooks for early childhood education

The title phrase “e-desert” is a metaphor that emphasizes the comparison of e-textbooks to a desert, i.e., a place which may initially seem difficult to access and unfriendly, but at the same time, which can be full of potentiality. E-textbooks, a relatively new teaching tool supporting early childhood education, symbolize a new educational space that may be unfamiliar and require an adaptation. The task set for this article is to analyze their potential from a post-critical perspective. The considerations will aim to identify the potential of e-textbooks for early school education posted on the zpe.gov.pl platform.

Aesthetics and Cartography: Post-Critical Reflections on Deviance in and of Representations

Cartographic representations are subject to sensory perception and rely on the translation of sensory perceptions into cartographic symbols. In this respect, cartography is closely related to aesthetics, as it represents an academic discipline of sensory perceptions. The scholarly concern with cartographic aesthetics, by today, has strongly been focused on the aesthetic impact of cartographic representations. The consideration of the philosophical sub-discipline of aesthetics however is rather restrained. This is also true for the connection between sociological questions and the social construction of aesthetic judgments. We address both topics in this article. We refer to post-critical cartographic theory. It accepts the socially constructed nature and power-bound nature of maps but does not reject “traditional” and widely established positivist cartography. Drawing on the theory of deviant cartographies related to this, we understand cartography designed according to aesthetic criteria as meta-deviant, as it makes the contingency of world interpretations clear. Especially augmented and virtual environments show a great potential to generate aesthetically constructed cartographic representations. Participatory cartography enables many people to reflect on the contingency of their spatial experiences and spatial abstractions without expert-like special knowledge. A prerequisite, however, is the greatest possible openness to topics and representations. This is not subject to a moral restriction.

Post-drill geophysical characterization of two deep-water wells of Cauvery Basin, East Coast of India

The depth of the reservoir causes an increase in the degree of uncertainty in the prediction of reservoir quality. High frequency is suppressed with depth because Earth functions as a low-pass filter. The seismic amplitudes observed at various interfaces are influenced by spherical divergence, transmission losses, mode conversions, and inter-bed multiples. Seismic data have numerous essential components that must be thoroughly examined during hydrocarbon prospect identification and maturation, including post-critical reflections, events coherency (in near and far offsets), mode conversion, and interbed multiples. Seismic amplitudes are typically derived from 2D/3D seismic data and utilized directly or indirectly for reservoir interpretation and better prediction of subtle geological and geophysical information. To accurately depict subsurface geological features, stratigraphic architecture, and reservoir facies, it should be used in conjunction with the existing paleoenvironment data. When employed alone, the subsurface geophysical data may lead to erroneous interpretation of subsurface lithologies and inaccurate reservoir property predictions. Understanding these factors could help interpreters make better use of seismic data while maturing and de-risking the prospectivity. This study examines the post-drill geophysical characterization of two exploratory wells that were drilled in the deep-water area of the Cauvery Basin, East Coast of India. Analysis and correlation with a discovery well is done to understand the sediment depositional heterogeneity and corresponding seismic amplitude response, primarily for the cemented reservoir (dry well). To discover prospects and subsequently de-risk the existing prospect inventory, a dashboard checklist for in-depth study of seismic and well data has been developed. The top-down geophysical analytical approach that has been presented will aid in defining reservoir characteristics generally, estimating deliverability, and subsequently raising the geological probabilities and chance of success (COS) of any exploration project. The findings of this study allow critical analysis of seismic data to distinguish between softer/slower/possibly better reservoir rocks and hard/fast/tight rocks.

Diving Wave Tomography: Velocity Modelling Using First Arrival Traveltime

In hydrocarbon exploration, information carried by diving waves and post-critical reflections that are used to reconstruct the long-to-intermediate wavelength of the subsurface is an integral part of successful velocity model building. Diving wave tomography (DWT) is one of the tools for shallow velocity assessment particularly when seismic data has poor signal-to-noise ratio (SNR) with complex geologic settings where no clear reflector is present. Considering the relationship between velocity with time and space, the output from tomography plays a crucial role to align data between time and depth domain and produce a reliable image of the deeper structure where hydrocarbon reservoir is typically located. In geophysics, tomography is primarily used to correct seismic trace alignment to produce a reliable stack section. In advanced imaging it is used as an initial model for waveform inversion in an integrated workflow. In the post-processing stage, it is used to correct the misfit between well logs and seismic data and is crucial for the quantitative analysis of rock physics. In this paper, we focus on tomography and its working principle on near-surface velocity modelling. We restricted our workflow to 2D synthetic data simulating the shallow gas occurrence that is prominent in the offshore Malay Basin to demonstrate how tomography works in velocity reconstruction. Results from synthetic and real data example shows that DWT can recover local large-scale structure and improved stacked data, considering no other seismic data and constraint from well data is included in the iterative process.

Three-Dimensional Seismic-Wave Propagation Simulations in the Southern Korean Peninsula Using Pseudodynamic Rupture Models

ABSTRACTAccurate and practical ground-motion predictions for potential large earthquakes are crucial for seismic hazard analysis of areas with insufficient instrumental data. Studies on historical earthquake records of the Korean Peninsula suggest that damaging earthquakes are possible in the southeastern region. Yet classical ground-motion prediction methods are limited in considering the physical rupture process and its effects on ground motion in complex velocity structures. In this study, we performed ground-motion simulations based on rigorous physics through pseudodynamic source modeling and wave propagation simulations in a 3D seismic velocity model. Ensembles of earthquake scenarios were generated by emulating the one- and two-point statistics of earthquake source parameters derived from a series of dynamic rupture models. The synthetic seismograms and the distributions of simulated peak ground velocities (PGVs) were compared with the observations of the 2016 Mw 5.4 Gyeongju earthquake in the Korean Peninsula. The effects of surface-wave radiation, rupture directivity, and both local and regional amplifications from the 3D wave propagation were reproduced accurately in the spatial distribution of simulated PGVs, in agreement with the observations from dense seismic networks by mean log residuals of −0.28 and standard deviations of 0.78. Amplifications in ground motions were found in regions having low crustal velocities and in regions of constructive interference from the crustal shear-wave phases associated with postcritical reflections from the Moho discontinuity. We extended the established approach to earthquake scenarios of Mw 6.0, 6.5, and 7.0, at the same location, to provide the distribution of ground motions from potential large earthquakes in the area. Although we demonstrate the value of these simulations, improvements in the accuracy of the 3D seismic velocity model and the scaling relationship of the source models would be necessary for a more accurate estimation of near-source ground motions.

Prediction of Elastic Properties Within CO2 Plume at Sleipner Field Using AVS Inversion Modified for Thin‐Layer Reflections Guided by Uncertainty Estimation

AbstractExisting amplitude variation with offset (AVO) and slowness (AVS) theories fail to interpret observed amplitudes in terms of actual elastic properties of the media for a reflection event resulting from a stack of thin layers. We propose a method to replace the stack of thin layers with an equivalent medium of elastic properties using the Backus averaging theory. Numerical examples show considerable deviation in intercept calculated from the modified AVO and AVS theories from the conventional methods. AVS theory is preferred as it can be applied irrespective of impedance contrast in both precritical and postcritical reflections, and no spherical divergence correction is required. P and S wave velocities, density, and thickness of thin layers are determined using the inversion scheme of very fast simulated annealing (VFSA). Uncertainty in prediction is evaluated using an approximate marginal posterior probability density function and a parameter correlation matrix. We demonstrate our methodology on synthetic and real seismic data from the Sleipner field, which is a good example of enhanced seismic amplitudes due to interference among reflections from thin layers. We select 11 common depth point (CDP) gathers for amplitude analysis of four identified reflectors along a line of 3‐D seismic data acquired in 2008. Predicted mean models of CO2‐saturated sand layers at all locations show that the thickness, density, and P and S wave velocities vary from 5–7 m, 1.8–2.0 g/cm3, and 1,460–1,490 and 630–650 m/s, respectively. Our analysis suggests that the model parameters are well constrained and independent except at a few locations.

Amplitude variation with offset inversion using acoustic-elastic local solver

Conventional amplitude variation with offset (AVO) inversion analysis uses the Zoeppritz equations, which are based on a plane-wave approximation. However, because real seismic data are created by point sources, wave reflections are better modeled by spherical waves than by plane waves. Indeed, spherical reflection coefficients deviate from planar reflection coefficients near the critical and postcritical angles, which implies that the Zoeppritz equations are not applicable for angles close to critical reflection in AVO analysis. Elastic finite-difference simulations provide a solution to the limitations of the Zoeppritz approximation because they can handle near- and postcritical reflections. We have used a coupled acoustic-elastic local solver that approximates the wavefield with high accuracy within a locally perturbed elastic subdomain of the acoustic full domain. Using this acoustic-elastic local solver, the local wavefield generation and inversion are much faster than performing a full-domain elastic inversion. We use this technique to model wavefields and to demonstrate that the amplitude from within the local domain can be used as a constraint in the inversion to recover elastic material properties. Then, we focus on understanding how much the amplitude and phase contribute to the reconstruction accuracy of the elastic material parameters ([Formula: see text], [Formula: see text], and [Formula: see text]). Our results suggest that the combination of amplitude and phase in the inversion helps with the convergence. Finally, we analyze elastic parameter trade-offs in AVO inversion, from which we find that to recover accurate P-wave velocities we should invert for [Formula: see text] and [Formula: see text] simultaneously with fixed density.

Anomalous SmKS induced by postcritical reflection and refraction at the core-mantle boundary

Earth’s outer core is generally thought to be a well-mixed liquid consisting mostly of iron and a small amount of lighter elements. Recent seismic studies using SmKS waves show that the top a few hundred kilometers of the outer core possess a P-wave velocity slightly lower than the PREM model, which cannot be explained by self-compression of a chemically homogeneous outer core. We investigated the SmKS waveforms of a deep earthquake occurring beneath South America recorded by a large and dense seismic array in China, and measured the differential arrival times of the SmKS pairs. We found significant waveform distortion of the SmKS caused by postcritical refraction and reflection at the core-mantle boundary. This waveform distortion can introduce significant bias to the measured differential times, leading to incorrect estimate of P-wave velocity of the outer core. Whether stable stratification is occurring in outer core or not requires further seismic investigations.

Post-critical SsPmp and its applications to Virtual Deep Seismic Sounding (VDSS) – 2: 1-D imaging of the crust/mantle and joint constraints with receiver functions

SUMMARY Virtual Deep Seismic Sounding (VDSS) has emerged as a novel method to image the crust–mantle boundary (CMB) and potentially other lithospheric boundaries. In Part 1, we showed that the arrival time and waveform of post-critical SsPmp, the post-critical reflection phase at the CMB used in VDSS, is sensitive to several different attributes of the crust and upper mantle. Here, we synthesize our methodology of deriving Moho depth, average crustal Vp and uppermost-mantle Vp from single-station observations of post-critical SsPmp under a 1-D assumption. We first verify our method with synthetics and then substantiate it with a case study using the Yellowknife and POLARIS arrays in the Slave Craton, Canada. We show good agreement of crustal and upper-mantle properties derived with VDSS with those given by previous active-source experiments and our own P receiver functions (PRF) in our study area. Finally, we propose a PRF-VDSS joint analysis method to constrain average crustal Vp/Vs ratio and composition. Our PRF-VDSS joint analysis shows that the southwest Slave Craton has an intermediate crustal composition, most consistent with a Mesoarchean age.

Post-critical SsPmp and its applications to Virtual Deep Seismic Sounding (VDSS)—1: sensitivity to lithospheric 1-D and 2-D structure

Virtual Deep Seismic Sounding (VDSS) has recently emerged as a novel method to image the Moho and potentially other lithospheric boundaries. The behaviour of SsPmp, the post-critical reflection phase at the Moho that is utilized in VDSS, is rich with complexities not yet widely considered. Here, motivated by observations from the Ordos Plateau in North China, we use synthetic seismograms computed with a broad range of 1-D models to evaluate how different parts of the lithosphere along the ray path of SsPmp affect its phase, amplitude and arrival time. Our findings include: (1) When the crust–mantle boundary is a sharp discontinuity, the SsPmp phase shift relative to the direct S wave is controlled by lower-crustal V_p, upper-mantle V_p and ray parameter. This property indicates the possibility of using SsPmp to constrain V_p in the lower crust and uppermost mantle. (2) When the crust–mantle boundary is a velocity-gradient zone, SsPmp arrival times vary as different functions of ray parameter from cases with a sharp crust–mantle boundary, because different rays turn at different depths. This feature allows measurement of the vertical velocity gradient in the crust–mantle transition zone with SsPmp. (3) When the virtual source (location of S-to-P conversion at the free surface) is in a sedimentary basin, SsPmp amplitude can be significantly reduced due to low S-to-P reflected energy at the virtual source. This may cause the absence of SsPmp despite appropriate source–receiver geometry. In addition to 1-D models, we further conduct 2-D waveform modelling and find that the SsPmp arrival time relative to direct S is not only controlled by crustal thickness at the reflection point but also by lateral variation of V_s beneath the virtual source and receiver. Therefore, in areas with significant lateral heterogeneity in the lithosphere the accuracy of crustal-thickness measurements from SsPmp arrival times depends on our knowledge of the variability of lithospheric structure across a broad region.

A Local Magnitude Relation for Earthquakes in the Western Canada Sedimentary Basin

A local magnitude ( M L) relation for the western Canada sedimentary basin (WCSB) is developed using a rich ground‐motion dataset compiled from local and regional networks in the area. The assessment of amplitude decay with distance suggests that joining direct waves with postcritical reflections from Moho discontinuity modifies the attenuation pattern in the 100–200 km distance range. The M L distance correction is parameterized using a trilinear function that accounts for the observed attenuation attributes. Regression of ground‐motion amplitudes results in the following distance correction model (−log A ) for earthquakes in WCSB: ![Graphic][1] in which R is the hypocentral distance (km). The standard M L relations fail to capture the rates and shape of amplitude attenuation in the region, resulting in overestimated magnitudes by 0.3–0.6 units. The overestimation is larger for local networks due to the increased discrepancy between standard M L relations and actual attenuation properties at close distances. The derived relationship results in unbiased M L magnitude estimates in WCSB over a wide distance range (2–600 km), which ensures consistent magnitude estimates from local and regional networks. [1]: /embed/inline-graphic-1.gif

Survey design for coal-scale 3D-PS seismic reflection

Survey design for converted-wave (PS) reflection is more complicated than for standard P-wave surveys, due to raypath asymmetry and increased possibility of phase distortion. Coal-scale PS surveys (depth [Formula: see text]) require particular consideration, partly due to the particular physical properties of the target (low density and low velocity). Finite-difference modeling provides a pragmatic evaluation of the likely distortion due to inclusion of postcritical reflections. If the offset range is carefully chosen, then it may be possible to incorporate high-amplitude postcritical reflections without seriously degrading the resolution in the stack. Offsets of up to three times target depth may in some cases be usable, with appropriate quality control at the data-processing stage. This means that the PS survey design may need to handle raypaths that are highly asymmetrical and that are very sensitive to assumed velocities. A 3D-PS design was used for a particular coal survey with the target in the depth range of 85–140 m. The objectives were acceptable fold balance between bins and relatively smooth distribution of offset and azimuth within bins. These parameters are relatively robust for the P-wave design, but much more sensitive for the case of PS. Reduction of the source density is more acceptable than reduction of the receiver density, particularly in terms of the offset-azimuth distribution. This is a fortuitous observation in that it improves the economics of a dynamite source, which is desirable for high-resolution coal-mine planning. The final-survey design necessarily allows for logistical and economic considerations, which implies some technical compromise. However, good fold, offset, and azimuth distributions are achieved across the survey area, yielding a data set suitable for meaningful analysis of P and S azimuthal anisotropy.

Simultaneous Determination of Crustal Thickness andPWavespeed by Virtual Deep Seismic Sounding (VDSS)

The method of virtual deep seismic sounding (VDSS) uses the large amplitude, postcritical reflection off the Moho, the SsPmp phase, to probe the Moho. In this study, we augment VDSS using the change in differential travel times between phases SsPmp and Ss ( T ) as a function of distance (moveout) to determine simultaneously both the thickness ( H ) and overall P wavespeed ( V P ) of the crust. Tests using synthetic data show that for typical uncertainties in measuring T (1 standard deviation of ±0.2 s), a minimum uncertainty of ∼±1.1 km and ±0.06 km/s can be reached for nominal values of H and V P , respectively. We then demonstrate its utility with field data recorded by two permanent stations in Australia.

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

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.

Full waveform inversion of diving & reflected waves for velocity model building with impedance inversion based on scale separation

Full waveform inversion (FWI) aims to reconstruct high-resolution subsurface models from the full wavefield, which includes diving waves, post-critical reflections and short-spread reflections. Most successful applications of FWI are driven by the information carried by diving waves and post-critical reflections to build the long-to-intermediate wavelengths of the velocity structure. Alternative approaches, referred to as reflection waveform inversion (RWI), have been recently revisited to retrieve these long-to-intermediate wavelengths from short-spread reflections by using some prior knowledge of the reflectivity and a scale separation between the velocity macromodel and the reflectivity. This study presents a unified formalism of FWI, named as Joint FWI, whose aim is to efficiently combine the diving and reflected waves for velocity model building. The two key ingredients of Joint FWI are, on the data side, the explicit separation between the short-spread reflections and the wide-angle arrivals and, on the model side, the scale separation between the velocity macromodel and the short-scale impedance model. The velocity model and the impedance model are updated in an alternate way by Joint FWI and waveform inversion of the reflection data (least-squares migration), respectively. Starting from a crude velocity model, Joint FWI is applied to the streamer seismic data computed in the synthetic Valhall model. While the conventional FWI is stuck into a local minimum due to cycle skipping, Joint FWI succeeds in building a reliable velocity macromodel. Compared with RWI, the use of diving waves in Joint FWI improves the reconstruction of shallow velocities, which translates into an improved imaging at deeper depths. The smooth velocity model built by Joint FWI can be subsequently used as a reliable initial model for conventional FWI to increase the high-wavenumber content of the velocity model.

Numerical modeling of seismic waves for estimating the influence of the Greenland ice sheet on observed seismograms

We calculate regional synthetic seismograms for a realistic structure model beneath Greenland, including surface topography and ice sheet thickness, for observations of the multinational GreenLand Ice Sheet monitoring Network (GLISN). The thick and heterogeneous Greenland ice sheet can cause distortion of the seismic waveforms observed at the GLISN stations on ice. We developed a numerical technique that calculates accurate regional seismic wavefields with low computational requirements. Here, we calculate the elastic wave propagation up to 2 Hz for four structural models of the Greenland ice sheet from a seismic source at various depths and with different mechanisms. Our computations for a realistic ice sheet model, the near-surface seismic source produced a very characteristic wave train with a group velocity smaller than the S-wavespeed in the ice, considered to be an ice-sheet guided S wave, developed by the superposition of post-critical reflections between the free surface and the ice bed. We named this wave “Le”, analogous to the Lg wave, a crustally guided S wave. Furthermore, computation for a deeper seismic source resulted in reinforcement of the crustal Sg-coda wave with a group velocity range of ∼3.1–2.6 km/s, which agrees with the characteristic waveform observed on the Greenland ice sheet.

Removing source-side scattering for virtual deep seismic sounding (VDSS)

We present a method that extends both the applicability and the quality of virtual deep seismic sounding (VDSS)—a technique for estimating crustal thickness that is robust even if the crust–mantle transition is complex or the crustal thickness is large. The results are important for studies of crustal contributions to isostasy and for understanding dynamic topography due to mantle convection. VDSS uses S-to-P conversions beneath seismic stations as virtual sources for large, post-critical reflections off the Moho, that is, the seismic phase SsPmp. Original applications of VDSS rely on deep earthquakes as sources of illumination to circumvent strong, near-source scattering (e.g. depth phases) and are, therefore, limited by the uneven distribution of deep seismicity. The method presented here effectively removes effects of the earthquake source wavelet (SW, including complexities arising from long, complicated source time functions and near-source scattering) and can be applied to signal from shallow and deep earthquakes. It involves two steps. First, based on analyses of particle motion, we separate ‘pseudo-P’ and ‘pseudo-S’ wave trains from the vertical and the radial component of ground motion. The latter is then used as the appropriate reference time-series for the deconvolution of the vertical and the radial component of ground motion. Since the reference time-series contains both the SW and S-type signals due to scattering near the receiver, the deconvolution also effectively removes S-type multiples, such as the phase SsPms and related reverberations. Applying this method to synthetic seismograms verifies that it is robust in removing complex SWs, even in the presence of random or signal-generated noise. The method is further validated using data recorded by the Hi-CLIMB array from both deep and shallow earthquakes. Impulsive signals are now routinely achieved, significantly improving both the quality and quantity of results from VDSS.

An analysis of AVO inversion for postcritical offsets in HTI media

Azimuthal variations of wavefield characteristics, such as traveltime or reflection amplitude, play an important role in the identification of fractured media. A transversely isotropic medium with a horizontal symmetry axis (HTI medium) is the simplest azimuthally anisotropic model typically used to describe one set of vertical fractures. There exist many techniques in industry to recover anisotropic parameters based on moveout equations and linearized reflection coefficients using such a model. However, most of the methods have limitations in defining properties of the fractures due to linearizations and physical approximations used in their development. Thus, azimuthal analysis of traveltimes based on normal moveout ellipses recovers a maximum of three medium parameters instead of the required five. Linearizations made in plane-wave reflection coefficients (PWRCs) limit the amplitude-versus-offset (AVO) analysis to small incident angles and weak-contrast interfaces. Inversion based on azimuthal AVO for small offsets encounters nonuniqueness in the resolving power of the anisotropy parameters. Extending the AVO analysis and inversion to and beyond the critical reflection angle increases the amount of information recovered from the medium. However, well-accepted PWRCs are not valid in the vicinity of the critical angle and beyond it, due to frequency and spherical wave effects. Recently derived spherical and effective reflection coefficient (ERC) methods overcome this problem. We extended the ERCs approach to HTI media to analyze the potential of near- and postcritical reflections in azimuthal AVO analysis. From the sensitivity analysis, we found that ERCs are sensitive to different sets of parameters prior to and beyond the critical angle, which is useful in enhancing our resolution of the anisotropy parameters. Additionally, the resolution of the parameters depends on a sufficient azimuthal coverage in the acquisition setup. The most stable AVO results for the azimuthal acquisition setup with minimum number of lines (three) are achieved when the azimuthal angle between lines is greater than 45°.

Finite-difference modelling for the optimisation of coherent-noise suppression in very shallow seismic reflection

Seismic reflection surveys with targets at depths of 0-100m have been widely reported in the published literature. There are many case studies and theoretical discussions of methodology and technique. However, there exist no significant modelling studies of shallow seismic methodology. In this study we have used viscoelastic finite-difference modelling to generate shot records that can be processed using a real world sequence. This approach has allowed investigation of a range of problematic issues relating to very-shallow reflection. Perhaps the most fundamental shallow-reflection problem relates to the extraction of signal from beneath coherent noise. Our modelling provides a clear demonstration of the stringent acquisition parameters that are needed if this noise is to be removed using conventional f-k domain processing tools. Concepts investigated in the modelling are further explored via an engineering scale hammer seismic survey, which successfully images reflectors in the range 0-50m, using both pre-critical and post-critical reflections.

Elastic inversion of near- and postcritical reflections using phase variation with angle

Near- and postcritical (wide-angle) reflections provide the potential for velocity and density inversion because of their large amplitudes and phase-shifted waveforms. We tested using phase variation with angle (PVA) data in addition to, or instead of, amplitude variation with angle (AVA) data for elastic inversion. Accurate PVA test data were generated using the reflectivity method. Two other forward modeling methods were also investigated, including plane-wave and spherical-wave reflection coefficients. For a two half-space model, linearized least squares was used to invert PVA and AVA data for the P-wave velocity, S-wave velocity, and the density of the lower space and the S-wave velocity of the upper space. Inversion tests showed the feasibility and robustness of PVA inversion. A reverse-time migration test demonstrated better preservation of PVA information than AVA information during wavefield propagation through a layered overburden. Phases of deeper reflections were less affected than amplitudes by the transmission losses, which makes the results of PVA inversion more accurate than AVA inversion in multilayered media. PVA brings useful information to the elastic inversion of wide-angle reflections.