PS Reflection Research Articles

Application of multicomponent seismic data to tight gas reservoir characterization: A case study in the Sichuan Basin, China

Combining PP and PS waves from multicomponent data is an effective hydrocarbon characterization strategy because these two wave types are sensitive to different subsurface properties. We develop a case study using multicomponent data to characterize tight sandstone gas reservoirs in the Jurassic Shaximiao Formation, the western Sichuan Basin, China. In the study area, with PP data it is difficult to distinguish sandstones, mudstones, and gas sand, whereas recently acquired multicomponent data indicate potential for the joint characterization of lithology, porosity, and gas saturation from the combination of PP and PS reflections. Sandstones and mudstones have small P-wave velocity contrasts and large S-wave velocity contrasts. Thus, PS data provide a more accurate description of sandstones, as a substantial proportion of sandstones are undetectable from PP sections. P impedance is sensitive to sandstone porosity variation, and seismic-predicted porosities based on impedance inversion are in good agreement with log-interpreted porosities. The ratio of P-wave velocity to S-wave velocity is sensitive to gas accumulation, and the ratios derived from joint PP-PS prestack inversion are determined to be better than from PP prestack inversion in terms of their agreements with logs and distinct gas-sand boundaries.

Elastic Least-Squares Reverse Time Migration Using Decoupled P- and S-Wave Equations for PP and PS Reflectivity Imaging

Elastic Least-Squares Reverse Time Migration Using Decoupled P- and S-Wave Equations for PP and PS Reflectivity Imaging

Quasielastic least-squares reverse time migration of PS reflections

Conventional analysis of amplitude variation with offset for elastic PS reflections is based on analytical reflection coefficients in a layered medium, and wave-equation-based PS migration is mainly used to produce a structural image. To overcome this problem, we have developed a least-squares reverse time migration (LSRTM) method for elastic PS reflections based on a quasielastic wave equation. The quasielastic wave equation can accurately model PS reflections with elastic amplitudes under the first-order Born approximation. Our LSRTM method inverts for perturbations of the S-wave velocity and density by minimizing the [Formula: see text] norm of the difference between recorded and predicted PS reflections modeled using a quasielastic wave equation. We refer to our new method as quasielastic LSRTM of PS reflections. Numerical tests on synthetic and field data indicate that our method can properly handle the amplitudes of elastic PS reflections and provides an accurate estimate of the perturbations of S-wave velocity and density. Extending the method to the 3D case is not straightforward and might require incorporating certain PS data processing techniques into the inversion itself.

Investigating the PS seismic imaging of faults using seismic modelling and data from the Snøhvit field, Barents Sea

PS seismic data from the Snøhvit field are compared with seismic modelling to understand the effect of azimuthal separation and incidence angle on the imaging of faults and associated horizon discontinuities. In addition, the frequency content of seismic waves backscattered from faults is analysed. The study area consists of a horst structure delimited by a northern fault dipping NW and oblique to the east–west survey orientation, and a southern fault dipping SSW and subparallel to the survey. Due to the raypath asymmetry of PS reflections, the northern fault is imaged better by azimuthally partitioned W data that include receivers downdip of the fault, relative to the sources, than by E data where the receivers are updip from the sources. Partial stack data show a systematic increase in the PS fault-reflected amplitude and therefore quality of fault imaging with increasing incidence angle. Fault images are dominated by internal low-medium frequency shadows surrounded by medium-high frequencies haloes. Synthetic experiments suggest that this is due to the interaction of specular waves and diffractions, and the spectral contribution from the fault signal, which increases with fault zone complexity. These results highlight the impact of survey geometry and processing workflows on fault imaging. Supplementary material: model description, processed sections and videos are available at https://doi.org/10.6084/m9.figshare.c.5727552

High-yield thermalized positronium at room temperature emitted by morphologically tuned nanochanneled silicon targets

Nanochanneled silicon targets with high positron/positronium (Ps) conversion rate and efficient Ps cooling were produced. Morphological parameters of the nanochannels, such as their diameter and length, were adjusted to get a large fraction of thermalized Ps at room temperature being emitted into vacuum. Ps cooling measurements were conducted combining single-shot positron annihilation lifetime spectroscopy and Doppler spectroscopy of the 13S → 23P transition. 2γ–3γ annihilation ratio measurements were also performed to estimate the positron/Ps conversion efficiency. In a converter with nanochannel diameter of 7–10 nm and depth of 3.89 μm, ∼28% of implanted positrons with an energy of 3.3 keV was found to be emitted as Ps with a transverse kinetic energy of 11 ± 2 meV. The reduction of the nanochannels depth to 1.13 μm, without changing the nanochannel diameter, was found to result in a less efficient cooling, highlighting the presence of Ps reflection from the bottom end of nanochannels.

Weak faults at megathrust plate boundary respond to tidal stress

Lateral spatial variations of weak portions at the plate boundary in subduction zones have been estimated primarily by the distribution of slow earthquakes mainly occurring around seismogenic zones. However, the detailed depth profile of weak faults remains elusive. Here, we deployed six ocean bottom seismometers in the Nankai subduction zone, Japan, to observe reflections originated from drilling vessel Chikyu ship noise (hydroacoustic P wave) that was persistently radiated from a fixed position at the sea surface, and retrieved P-to-s (Ps) reflections from multiple dipping faults near the plate boundary. The Ps amplitudes were stacked and compared according to the degrees of tidal stresses, and high amplitudes were observed at high tide (compression). A migration technique shows that the locations where velocity contrasts fluctuate were estimated at both the megasplay fault and another fault between the megasplay fault and the top of the oceanic crust. This indicates that the physical properties of these faults are altered by tidal stress. The physical-property changes are attributed to fluid connections and isolations within the faults due to tidal stress fluctuations, inducing the variation of seismic anisotropy. Such a variation was confirmed by a three-dimensional numerical simulation for wave propagation with anisotropic medium. Our observation suggests that multiple weak faults are present around the plate boundary, and the obtained changes of fault physical properties may have implications for in-depth understanding of tidal triggering of earthquakes.

Rock Physics Model and Seismic Dispersion and Attenuation in Gas Hydrate-Bearing Sediments

A rock physics model was established to calculate the P-wave velocity dispersion and attenuation caused by the squirt flow of fluids in gas hydrate-bearing sediments. The critical hydrate saturation parameter was introduced to describe different ways of hydrate concentration, including the mode of pore filling and the co-existence mode of pore filling and particle cementation. Rock physical modeling results indicate that the P-wave velocity is insensitive to the increase in gas hydrate saturation for the mode of pore filling, while it increases rapidly with increasing gas hydrate saturation for the co-existence mode of pore filling and particle cementation. Meanwhile, seismic modeling results show that both the PP and mode-converted PS reflections are insensitive to the gas hydrate saturation that is lower than the critical value, while they tend to change obviously for the hydrate saturation that is higher than the critical value. These can be interpreted that only when gas hydrate begins to be part of solid matrix at high gas hydrate saturation, it represents observable impact on elastic properties of the gas hydrate-bearing sediments. Synthetic seismograms are calculated for a 2D heterogeneous model where the gas hydrate saturation varies vertically and layer thickness of the gas hydrate-bearing sediment varies laterally. Modeling results show that larger thickness of the gas hydrate-bearing layer generally corresponds to stronger reflection amplitudes from the bottom simulating reflector.

Polarity-reversal correction for vector-based elastic reverse time migration

Polarity reversal is a well-known problem in elastic reverse time migration, and it is closely related to the imaging conditions. The dot product of source and receiver wavefields is a stable and efficient way to construct scalar imaging conditions for decomposed elastic vector wavefields. However, for PP images, the dot product introduces an angle-dependent factor that will change the polarity of image amplitudes at large opening angles, and it is also contaminated by low-wavenumber artifacts when sharp contrasts exist in the velocity model. Those two problems can be suppressed by muting the reflections with large opening angles at the expense of losing useful information. We have developed an elastic inverse-scattering imaging condition that can retain the initial polarity of the image amplitude and significantly reduce the low-wavenumber noise. For PS images, much attention is paid to the polarity-reversal problem at the normal incidence, and the dot-product-based imaging condition successfully avoids this kind of polarity reversal. There is another polarity-reversal problem arising from the sign change of the PS reflection coefficient at the Brewster angle. However, this sign change is often neglected in the construction of a stacked PS image, which will lead to reversed or distorted phases after stacking. We suggested using the S-wave impedance kernel used in elastic full-waveform inversion but only in the PS mode as an alternative to the dot-product imaging condition to alleviate this kind of polarity-reversal problem. In addition to dot-product-based imaging conditions, we analytically compare divergence- and curl-based imaging conditions and the elastic energy norm-based imaging condition with the presented imaging conditions to identify their advantages and weaknesses. Two numerical examples on a two-layer model and the SEAM 2D model are used to illustrate the effectiveness and advantages of the presented imaging conditions in suppressing low-wavenumber noise and correcting the polarity-reversal problem.

2D and 3D amplitude‐preserving elastic reverse time migration based on the vector‐decomposed P‐ and S‐wave records

ABSTRACTThe elastic reverse time migration approach based on the vector‐wavefield decomposition generally uses the scalar product imaging condition to image the multicomponent seismic data. However, the resulting images contain the crosstalk artefacts and the polarity reversal problems, which are caused by the nonphysical wave modes and the angle‐dependent reduction of image amplitudes, respectively. To overcome these two problems, we develop an amplitude‐preserving elastic reverse time migration approach based on the vector‐decomposed P‐ and S‐wave seismic records. This approach includes two key points. The first is that we employ the vector‐decomposed P‐ and S‐wave multicomponent records to independently reconstruct the PP and PS reflection images to mitigate the crosstalk artefacts. The second is that we propose two schemes in addressing the issue of polarity reversal problem in the conventional PP image. One solution is to adopt the angle‐dependent equation. Another one is to reconstruct an amplitude‐preserving PP image with a separated scalar P‐wave particle velocity, which has a clear physical meaning. Numerical examples using two‐dimensional and three‐dimensional models demonstrate that the proposed elastic reverse time migration approach can provide the images with better amplitude‐preserving performance and fewer crosstalk artefacts, compared with the conventional elastic reverse time migration approach based on the scalar product imaging condition.

Separation of PP‐ and PS‐wave reflected seismic data using two‐dimensional finite offset common‐reflection‐surface traveltime approximation

ABSTRACTRecently, the interest in PS‐converted waves has increased for several applications, such as sub‐basalt layer imaging, impedance estimates and amplitude‐versus‐offset analysis. In this study, we consider the problem of separation of PP‐ and PS‐waves from pre‐stacked multicomponent seismic data in two‐dimensional isotropic medium. We aim to demonstrate that the finite‐offset common‐reflection‐surface traveltime approximation is a good alternative for separating PP‐ and PS‐converted waves in common‐offset and common shot configurations by considering a two‐dimensional isotropic medium. The five parameters of the finite‐offset common‐reflection‐surface are firstly estimated through the inversion methodology called very fast simulated annealing, which estimates all parameters simultaneously. Next, the emergence angle, one of the inverted parameters, is used to build an analytical separation function of PP and PS reflection separation based on the wave polarization equations. Once the PP‐ and PS‐converted waves were separated, the sections are stacked to increase the signal‐to‐noise ratio using the special curves derived from finite‐offset common‐reflection‐surface approximation. We applied this methodology to a synthetic dataset from simple‐layered to complex‐structured media. The numerical results showed that the inverted parameters of the finite offset common‐reflection‐surface and the separation function yield good results for separating PP‐ and PS‐converted waves in noisy common‐offset and common shot gathers.

Frequency‐dependent PP and PS reflection coefficients in fractured media

ABSTRACTWhen a porous layer is permeated by mesoscale fractures, wave‐induced fluid flow between pores and fractures can cause significant attenuation and dispersion of velocities and anisotropy parameters in the seismic frequency band. This intrinsic dispersion due to fracturing can create frequency‐dependent reflection coefficients in the layered medium. In this study, we derive the frequency‐dependent PP and PS reflection coefficients versus incidence angle in the fractured medium. We consider a two‐layer vertical transverse isotropy model constituted by an elastic shale layer and an anelastic sand layer. Using Chapman's theory, we introduce the intrinsic dispersion due to fracturing in the sand layer. Based on the series coefficients that control the behaviour of velocity and anisotropy parameters in the fractured medium at low frequencies, we extend the conventional amplitude‐versus‐offset equations into frequency domain and derive frequency‐dependent amplitude‐versus‐offset equations at the elastic–anelastic surface. Increase in fracture length or fracture density can enlarge the frequency dependence of amplitude‐versus‐offset attributes of PP and PS waves. Also, the frequency dependence of magnitude and phase angle of PP and PS reflection coefficients increases as fracture length or fracture density increases. Amplitude‐versus‐offset type of PP and PS reflection varies with fracture parameters and frequency. What is more, fracture length shows little impact on the frequency‐dependent critical phase angle, while the frequency dependence of the critical phase angle increases with fracture density.

Elastic least-squares reverse time migration in vertical transverse isotropic media

Using adjoint-based elastic reverse time migration, it is difficult to produce high-quality reflectivity images due to the limited acquisition apertures, band-limited source time function, and irregular subsurface illumination. Through iteratively computing the Hessian inverse, least-squares migration enables us to reduce the point-spread-function effects and improve the image resolution and amplitude fidelity. By incorporating anisotropy in the 2D elastic wave equation, we have developed an elastic least-squares reverse time migration (LSRTM) method for multicomponent data from the vertically transversely isotropic (VTI) media. Using the perturbed stiffness parameters [Formula: see text] and [Formula: see text] as PP and PS reflectivities, we linearize the elastic VTI wave equation and obtain a Born modeling (demigration) operator. Then, we use the Lagrange multiplier method to derive the corresponding adjoint wave equation and reflectivity kernels. With linearized forward modeling and adjoint migration operators, we solve a linear inverse problem to estimate the subsurface reflectivity models for [Formula: see text] and [Formula: see text]. To reduce the artifacts caused by data over-fitting, we introduce total-variation regularization into the reflectivity inversion, which promotes a sparse solution in terms of the model derivatives. To accelerate the convergence of LSRTM, we use source illumination to approximate the diagonal Hessian and use it as a preconditioner for the misfit gradient. Numerical examples help us determine that our elastic VTI LSRTM method can improve the spatial resolution and amplitude fidelity in comparison to adjoint migration.

True-amplitude linearized waveform inversion with the quasi-elastic wave equation

We present a quasi-elastic wave equation as a function of the pressure variable, which can accurately model PP reflections with elastic amplitude variation with offset effects under the first-order Born approximation. The kinematic part of the quasi-elastic wave equation accurately models the propagation of P waves, whereas the virtual-source part, which models the amplitudes of reflections, is a function of the perturbations of density and Lamé parameters [Formula: see text] and [Formula: see text]. The quasi-elastic wave equation generates a scattering radiation pattern that is exactly the same as that for the elastic wave equation, and only requires the solution of two acoustic wave equations for each shot gather. This means that the quasi-elastic wave equation can be used for true-amplitude linearized waveform inversion (also known as least-squares reverse time migration) of elastic PP reflections, in which the corresponding misfit gradients are with respect to the perturbations of density and the P- and S-wave impedances. The perturbations of elastic parameters are iteratively updated by minimizing the [Formula: see text]-norm of the difference between the recorded PP reflections and the predicted pressure data modeled from the quasi-elastic wave equation. Numerical tests on synthetic and field data indicate that true-amplitude linearized waveform inversion using the quasi-elastic wave equation can account for the elastic PP amplitudes and provide a robust estimate of the perturbations of P- and S-wave impedances and, in some cases, the density. In addition, true-amplitude linearized waveform inversion provides images with a wider bandwidth and fewer artifacts because the PP amplitudes are accurately explained. We also determine the 2D scalar quasi-elastic wave equation for P-SV reflections and the 3D vector equation for PS reflections.

Full Waveform Modelling for Subsurface Characterization with Converted-Wave Seismic Reflection: Residual PP Removal on PS Component Using F-K Filter

The application of converted-wave seismic method in hydrocarbon exploration has increased significantly. Since the conventional seismic ceases to provide an adequate image in complex geology area and it often provides an ambiguous bright spot response. The main principle is that an incident P-wave produces reflected and converted P and SV wave on an interface. Converted-wave seismic uses the multicomponent receiver that records both of vertical component and horizontal component. The vertical component is assumed to correspond to the compressional PP wave and the horizontal correspond to the PS converted-wave. In this and previous research (Viony and Triyoso, 2018), a synthetic seismic data with the shallow gas and the salt dome model are constructed by the full-waveform modelling. The purpose of this study is to improve the imaging quality on the PS section and the PS AVO curve due to the existence of the residual PP events on the horizontal data in the previous study (Viony and Triyoso, 2018). The PS gather has been NMO corrected by the PP velocity. Therefore, the residual PP reflections are well-corrected and the PS reflections are under-corrected. To obtain the more reliable PS data, the residual PP reflections have been removed by rejecting the well-corrected data in f-k filtering process. The results of this study present that the imaging quality and the AVO of the filtered PS is better and more reliable than the un-filtered PS in the previous study (Viony and Triyoso, 2018).

COMPARISON OF GLOBAL SEARCH OPTIMIZATION ALGORITHMS TO PERFORM THE VELOCITY ANALYSIS WITH A CONVERTED WAVE MOVEOUT EQUATION

Even with previous works having studied about the accuracy and objective function of several nonhyperbolic multiparametric travel-time approximations for velocity analysis, they lack tests concerning different optimization algorithms and how they influence the accuracy and processing time. Once many approximations were tested and found the multimodal one which presented the best accuracy results, it is possible to perform a velocity analysis with different global search optimization algorithms. The minimization of the curve calculated with the converted wave moveout equation to the observed curve can be done for each optimization algorithm selected in this work. The travel-time curves tested here are the PP and PS reflection events coming from the interface of the top of an offshore ultra-deep reservoir. After the inversion routine have been performed, it is possible to define the processing time and the accuracy of each optimization algorithm for this kind of problem.

Optimum source-receiver orientations to capture PP, PS, SP, and SS reflected wave modes

We conducted a field experiment at the geotechnical research soil site #1 in Ottawa, Ontario, Canada, and recorded 9-C seismic data along a short line traverse 90 m in length using a multicomponent vibrator source named Microvibe and a landstreamer receiver array with 48 3-C 28-Hz geophones at 0.75-m intervals. The receiver spread length is 35.25 m, and the near-offset is 1.50 m. We used three source and three receiver orientations — vertical (V), inline-horizontal (H1), and transverse-horizontal (H2). We identified several reflection wave modes in the field records — PP, PS, SP, and SS, in addition to refracted waves, and Rayleigh-mode and Love-mode surface waves. We computed the semblance spectra of the selected shot records and ascertained the wave modes based on the semblance peaks. We then performed CMP stacking of each of the 9-C data sets using the PP, PS/SP, and SS stacking velocities. This field test convincingly demonstrates that there is no pure P- or S-wave land seismic source — any source type can generate any combination of wave modes — PP, PS, SP, and SS, and partitioning of the source energy depends on the source orientation and VP/VS ratio. All three receiver orientations will capture all reflected wave modes — PP, PS, SP, and SS — but with varying strength. The magnitude of the reflection amplitude captured by one of the three receiver orientations will depend on the reflector depth, source-receiver offset, and the near-surface P- and S-wave velocities in the vicinity of the receiver location. The most prominent PP reflection energy is recorded by the VV source-receiver orientation, whereas the most prominent SS reflection energy is recorded by the H2H2 source-receiver orientation. Additionally, the optimum source-receiver orientation for PS reflection mode is VH1, and the optimum source-receiver orientation for SP reflection mode is H1V.

Elastic model low- to intermediate-wavenumber inversion using reflection traveltime and waveform of multicomponent seismic data

Low-, intermediate-, and high-wavenumber components of P- and S-wave velocities jointly influence the elastic wave propagation and scattering in an isotropic medium. By taking advantage of all information in the data, elastic full-waveform inversion (E-FWI) has the potential to recover these model components. However, if the transmitted wave data are insufficient to illuminate the deeper part of the subsurface, we should rely on the solutions using reflection data. To reduce the nonlinearity of waveform inversion, we choose to decouple the effects of the model background and perturbation on the reflected waves within a linearized inversion framework. This resorts to three stages aiming to gradually fit the traveltimes and waveforms of the reflected PP and PS waves based on data or gradient preconditioning through P/S mode decomposition. For the first two stages, once the multicomponent seismograms have been separated into PP and PS reflection recordings, reflection traveltime inversion using an acoustic wave propagator (A-RTI) can successively recover the low-wavenumber components of P- and S-wave velocities. In the last stage, starting from the models having reliable low-wavenumber components, elastic reflection waveform inversion (E-RWI) can easily get out of the local minima and continue to retrieve the increasing wavenumber features sensitive to the waveform and amplitude variations. This is supported by gradient preconditioning through P/S mode decomposition of the extrapolated normal and adjoint wavefields, and alternately updating model background and high-wavenumber components in terms of linearized least-squares inversion. Numerical examples have demonstrated the performance of our E-RWI approach and the validity of the three-stage inversion workflow.

Lithospheric discontinuities in Central Australia

Lithospheric discontinuities are elusive, with properties that are strongly frequency dependent. Results from a temporary deployment of broadband stations along a north-south transect through Central Australia, and the permanent arrays ASAR and WRA, are used to evaluate the spatial coherence of lithospheric features, particularly mid-lithospheric discontinuities. We exploit stacked station autocorrelograms that provide an estimate of P-wave reflectivity beneath stations, with imaging methods exploiting teleseismic arrivals. We use both common conversion point (CCP) stacking from Ps receiver functions and reflection point imaging using the autocorrelation of the P wavetrain. The results tie well for the Moho and have a good general correspondence for deeper levels. Although indications of mid-lithospheric discontinuities from changes in the frequency of reflectivity occur at similar depths, the spatial continuity of specific features at high frequency (around 2 Hz) is of the order of 10–15 km. Broader trends can be tracked across the profile, but no strong lithospheric interfaces can be mapped, except for a south dipping feature traversing the lithosphere on the southern part of the profile that is likely to be a former mantle detachment zone.

Full waveform seismic AVAZ signatures of anisotropic shales by integrated rock physics and the reflectivity method

A set of parallel vertical fractures embedded in a vertically transverse isotropy (VTI) background leads to orthorhombic anisotropy and corresponding azimuthal seismic responses. We conducted seismic modeling of full waveform amplitude variations versus azimuth (AVAZ) responses of anisotropic shale by integrating a rock physics model and a reflectivity method. The results indicate that the azimuthal variation of P-wave velocity tends to be more complicated for orthorhombic medium compared to the horizontally transverse isotropy (HTI) case, especially at high polar angles. Correspondingly, for the HTI layer in the theoretical model, the short axis of the azimuthal PP amplitudes at the top interface is parallel to the fracture strike, while the long axis at the bottom reflection directs the fracture strike. In contrast, the orthorhombic layer in the theoretical model shows distinct AVAZ responses in terms of PP reflections. Nevertheless, the azimuthal signatures of the R- and T-components of the mode-converted PS reflections show similar AVAZ features for the HTI and orthorhombic layers, which may imply that the PS responses are dominated by fractures. For the application to real data, a seismic-well tie based on upscaled data and a reflectivity method illustrate good agreement between the reference layers and the corresponding reflected events. Finally, the full waveform seismic AVAZ responses of the Longmaxi shale formation are computed for the cases of HTI and orthorhombic anisotropy for comparison. For the two cases, the azimuthal features represent differences mainly in amplitudes, while slightly in the phases of the reflected waveforms. Azimuth variations in the PP reflections from the reference layers show distinct behaviors for the HTI and orthorhombic cases, while the mode-converted PS reflections in terms of the R- and T-components show little differences in azimuthal features. It may suggest that the behaviors of the PS waves are dominated by vertically aligned fractures. This work provides further insight into the azimuthal seismic response of orthorhombic shales. The proposed method may help to improve the seismic-well tie, seismic interpretation, and inversion results using an azimuth anisotropy dataset.

ELASTIC REVERSE TIME MIGRATION BASED ON WAVEFIELD SEPARATION

AbstractCompared with other imaging algorithms (e.g., ray‐based, one‐way wave equation), reverse time migration (RTM) based on the two‐way wave equation exhibits greater superiority, especially in handling steeply dipping structures. However, imaging with conventional single‐component seismic data is unsuited for some complicated structures (e.g., gas clouds). Elastic RTM, which is based on the elastodynamic equation and uses multi‐component seismic data to extract PP and PS reflectivity and subsurface information, can more consistently reproduce the characteristics of elastic wave propagation in real Earth media, resulting in seismic images that more accurately characterize the subsurface. To begin with, we exploit the first order stress‐velocity equations to extrapolate the elastic vector wavefield, then the P‐ and S‐wavefields are separated by computing the divergence and curl operator of the extrapolated particle‐velocity wavefield. Then, imaging profiles with pure wave modes are computed by applying the source normalized cross‐correlation imaging condition, thus avoiding crosstalk between unseparated wave modes. To address the polarity reversal problem of the converted image, we propose an alternative method in the common‐shot domain. We also develop an efficient method that reconstructs the source wavefield in the reverse time direction to save storage in the GPU and to avoid large input/output in the elastic reverse time migration. During the forward modeling, the method only saves the particle‐velocity wavefield of all time intervals within an efficient absorbing boundary and the total wavefields in the final time interval. When we extrapolate the receiver wavefield in the reverse time direction, we simultaneously reconstruct the total source wavefields via the saved wavefields. Numerical examples performed with the graben and Marmousi2 models have shown that the polarity reversal correction method works, and elastic reverse time migration can accurately characterize complicated structures.