This paper presents a new traveltime inversion method based on the wave equation. In this method, designated as wave‐equation (WT), seismograms are computed by any full‐wave forward modeling (we use finite‐difference method). The velocity model is perturbed until traveltimes from synthetic best fitted to observed in least squares sense. A gradient optimization used and formula for Frechét derivative (perturbation of with respect velocity) derived directly No picking or ray tracing necessary,...

A least‐squares migration algorithm is presented that reduces the artifacts (i.e., recording footprint noise) arising from incomplete data. Instead of migrating data with adjoint forward modeling operator, normal equations are inverted by using a preconditioned linear conjugate gradient scheme employs regularization. The operator constructed an asymptotic acoustic integral equation, and its Kirchhoff operator. We tested performance on synthetic field in cases limited aperture, coarse...

Claerbout's daylight imaging concept is generalized to a theory of interferometric seismic (II). Interferometric defined be any algorithm that inverts correlated data for the reflectivity or source distribution. As examples, we show II can image distributions by migrating ghost reflections in passive and generalizes receiver-function method used seismologists. also migrate free-surface multiples common depth point (CDP) from data. Both synthetic field examples are illustrate different...

ABSTRACT Least‐squares migration has been shown to improve image quality compared the conventional method, but its computational cost is often too high be practical. In this paper, we develop two numerical schemes implement least‐squares with reverse time method and blended source processing technique increase computation efficiency. By iterative of supergathers, which consist in a sum many phase‐encoded shots, enhanced crosstalk noise associated encoded shots reduced. Numerical tests on 2D...

A plane-wave least-squares reverse-time migration (LSRTM) is formulated with a new parameterization, where the image of each shot gather updated separately and an ensemble prestack images produced along common gathers. The merits LSRTM are following: (1) can sometimes offer stable convergence even when velocity has bulk errors up to 5%; (2) significantly reduce computation cost, linear phase-shift encoding applied hundreds gathers produce dozens plane waves. Unlike random time shifts gather,...

Strong subsurface attenuation leads to distortion of amplitudes and phases seismic waves propagating inside the earth. Conventional acoustic reverse time migration (RTM) least-squares (LSRTM) do not account for this distortion, which can lead defocusing images in highly attenuative geologic environments. To correct we used a linearized inversion method, denoted as [Formula: see text]-LSRTM. During iterations, viscoacoustic modeling operator forward modeling. The adjoint equations were...

We show that a scheme to solve the 2-D eikonal equation by finite‐difference method can violate causality for moderate large velocity contrasts [Formula: see text]. As an alternative, we present in which solution region progresses outward from “expanding wavefront” rather than square,” and therefore honors causality. Our appears be stable reasonably accurate variety of models with contrasts. The penalty is increase computational cost programming effort.

We present a general formula for the back projection of traveltime residuals in tomography. For special choices an arbitrary weighting factor this reduces to asymptotic back‐projection term ray‐tracing tomography (RT), Woodward‐Rocca method, wavepath eikonal inversion (WET), and wave‐equation (WT). This unification provides understanding differences similarities among these methods. The case WET leads computationally efficient scheme space‐time domain that is, principle, almost as effective...

Least-squares migration (LSM) has been shown to be able produce high-quality images, but its computational cost is considered too high for practical imaging. We have developed a multisource least-squares algorithm (MLSM) increase the efficiency by using blended sources processing technique. To expedite convergence, deblurring filter used as preconditioner reduce data residual. This MLSM applicable with Kirchhoff migration, wave-equation or reverse time and gain in depends on choice of...

Prestack migration in the time and depth domains is premier tool for seismic imaging of complex structures. Unfortunately, an undersampled acquisition geometry, a limited recording aperture, strong velocity contrasts lead to uneven illumination subsurface. This results blurring migrated image, sometimes referred as footprint noise image. To remedy this partially, we introduce prestack deconvolution (MD). The MD filter layered-medium approximation inverse Hessian matrix that applied locally...

We develop a waveform-tomography method for estimating the velocity distribution that minimizes waveform misfit between predicted and observed early arrivals in space-time seismograms. By fitting waveforms of arrivals, arrival tomography (EWT) naturally takes into account more general wave-propagation effects compared to high-frequency traveltime tomography, meaning EWT can estimate wider range slowness wavenumbers. Another benefit is reliable convergence full-waveform because an...

This efficient multiscale method for time-domain waveform tomography incorporates filters that are more than Hamming-window filters. A strategy choosing optimal frequency bands is proposed to achieve computational efficiency in the time domain. staggered-grid, explicit finite-difference with fourth-order accuracy space and second-order used forward modeling adjoint calculation. The utilized inverting an computation of gradient directions. In approach, multifrequency data multiple grid sizes...

Formulas are derived that relate the strength of crosstalk noise in supergather migration images to variance time, amplitude and polarity shifts encoding functions. A image is computed by migrating an encoded supergather, where formed stacking a large number shot gathers. Analysis reveals for temporal source static each gather, exponentially reduced with increasing shift square frequency. This not too surprising because larger time lead less correlation between traces different gathers, so...

We use elastic least-squares reverse time migration (LSRTM) to invert for the reflectivity images of P- and S-wave impedances. Elastic LSRTM solves linearized elastic-wave equations forward modeling adjoint backpropagating residual wavefield at each iteration. Numerical tests on synthetic data field reveal advantages over (RTM) acoustic LSRTM. For our examples, have better resolution amplitude balancing, fewer artifacts, less crosstalk compared with RTM images. The are also focused reflector...

The theory of least-squares reverse time migration multiples (RTMM) is presented. In this method, least squares (LSM) used to image free-surface where the recorded traces are as histories virtual sources at hydrophones and surface-related observed data. For a single source, entire becomes an extended source downgoing more fully illuminate subsurface compared primaries. Since each trace treated history knowledge wavelet not required ringy series for automatically deconvolved. If can be...

We present the theory for wave-equation inversion of dispersion curves, where misfit function is sum squared differences between wavenumbers along predicted and observed curves. The curves are obtained from Rayleigh waves recorded by vertical-component geophones. Similar to traveltime tomography, complicated surface wave arrivals in traces skeletonized as simpler data, namely picked phase-velocity frequency domains. Solutions elastic equation an iterative optimization method then used invert...

A hybrid wave‐equation traveltime and waveform inversion method is presented that reconstructs the interwell velocity distribution from crosshole seismic data. This method, designated as WTW, retains advantages of both full wave inversion; i.e., it characterized by reasonably fast convergence which somewhat independent initial model, can resolve detailed features model. In principle, no picking required computational cost WTW about same for inversion. We apply to synthetic data field...

Reflectivity images of the earth are calculated by migrating discrete grids seismic traces. Typically, such traces spatially undersampled on a recording grid with limited aperture width and so give rise to migration noise sometimes referred as acquisition footprint. For poststack images, we show how partly deconvolve footprint applying deblurring filter section, where is approximate inverse Green’s function. Results synthetic field data that post‐stack deconvolution can noticeably improve...

We review the equations for correlation-based redatuming methods. A method uses natural-phase information in data to time shift weighted traces so they appear be generated by sources (or recorded geophones) shifted a new location. This compares model-based redatuming, which effectively shifts using traveltimes computed from prior velocity model. For wavefield daylight imaging, interferometric reverse-time acoustics (RTA), and virtual-source methods all require correlation of with one...

PreviousNext No AccessSEG Technical Program Expanded Abstracts 1993Least‐squares cross‐well migrationAuthors: Gerard T. SchusterGerard SchusterUniversity of Utahhttps://doi.org/10.1190/1.1822308 SectionsAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail Permalink: https://doi.org/10.1190/1.1822308FiguresReferencesRelatedDetailsCited ByReproduction wavefield reverse time migration22 March 2021 | Exploration Geophysics, Vol....

Least-squares migration (LSM) is a linearized waveform inversion for estimating subsurface reflectivity model that, relative to conventional migration, improves spatial resolution of images. The cost, however, high because LSM typically requires 10 or more iterations, which at least 20 times than the CPU cost migration. To alleviate this expense, we offer deblurring filter that can be used in regularization scheme preconditioning give acceptable images with less one-third standard method....

ABSTRACT Multiples contain valuable information about the subsurface, and if properly migrated can provide a wider illumination of subsurface compared to imaging with VSP primary reflections. In this paper we review three different methods for migrating multiples. The first method is model‐based, it more sensitive velocity errors than migration; second uses semi‐natural Green's function multiples, where part traveltimes are computed from model, (i.e., natural traveltimes) picked data...

We review five types of physics-informed machine-learning (PIML) algorithms for inversion and modeling geophysical data. Such use the combination a data-driven (ML) method equations physics to model or invert data (or both). By incorporating constraints physics, PIML can effectively reduce size solution space ML models, enabling them be trained on smaller sets. This is especially advantageous in scenarios which availability may limited expensive obtain. In this review, we restrict that from...