Velocity-stack inversion using L norms (ps.gz 1498K) (pdf 1277K) (src 4011K)
**Nichols D.**

Velocity-stack inversion is the process of creating a model in
velocity space that can correctly reconstruct the measured data.
This is usually implemented by minimizing the *L _{2}* norm of the data
misfit and the

Velocity analysis of the Mobil AVO dataset (ps.gz 2633K) (pdf 2291K) (src 29261K)

This document was generated using the

Amplitude-preserved multiple suppression (ps.gz 31K) (pdf 52K) (src 7086K)

Water-bottom and pegleg multiples can contaminate primary reflections and distort AVO amplitude information. We develop an inversion method for suppressing multiple reflections while simultaneously preserving amplitudes along primary reflections. An iterative time-domain conjugate gradient scheme is used to find a velocity scan which ``fits'' its associated CMP gather to within a few percent misfit energy, when a hyperbolic forward modeling operator is applied to that inverted velocity scan. This ensures that most amplitude and AVO information is preserved in the transform pair. A primary velocity trend is then automatically picked in the scan by a Monte Carlo method, and a mask is designed on this basis to isolate multiple energy in velocity space. An estimate of the multiple reflection energy is generated by forward modeling the masked velocity scan. An amplitude-preserved multiple-suppressed CMP gather is then obtained by subtracting the estimated multiples from the input CMP gather. Current test results with the Mobil AVO dataset are very encouraging.

AVO estimation using surface-related multiple prediction (ps.gz 331K) (pdf 269K) (src 1332K)

In this work I explore the use of surface multiple prediction in enhancing AVO estimation. Multiple reflections from a proposed reflection event are predicted using surface-related multiple prediction () and compared to the actual data to identify anomalous amplitude behavior.

Estimating a pseudounitary operator for velocity-stack inversion (ps.gz 26K) (pdf 42K) (src 3289K)

I estimate a pseudounitary operator for enhancing an iterative conjugate-gradient (CG) inversion of CMP data to derive a best-fitting model in velocity-stack space. The amplitude balance of the operator is approximated with a simple time- and offset-variant operator weighting function. The spectral balance of the operator is tuned with a finite-aperture finite-fold approximation to the continuous integral rho filter. Convergence of the CG inversion and separation of multiple and primary velocity-stack energy is improved by application of the pseudounitary operator weights. Application of the rho filter improves the first few CG iterations, but counterintuitively slows or reverses convergence in subsequent iterations.

Prestack migration velocity analysis using wavefront synthesis (ps.gz 433K) (pdf 384K) (src 2511K)

Common-reflection-point (CRP) gathers provide important clues in various migration velocity analysis schemes (Al-Yahya, 1987; Etgen, 1990). Conventionally, CRP gathers are obtained by prestack migration of shot records or constant-offset sections. This paper introduces a way to generate a CRP gather for residual velocity analysis using wavefront synthesis imaging. Compared to CRP gathers obtained by other prestack migrations, those obtained by wavefront synthesis imaging provide a better resolution residual velocity panel. As a result, we can easily determine and get more reliable residual velocity, which is very important in inverting it into the true interval velocity of a medium.

The quest for anisotropic moveout (ps.gz 62K) (pdf 60K) (src 4414K)

This document was generated using the

AVS as a 3-D seismic data visualizing platform (ps.gz 23K) (pdf 32K) (src 637K)
**Clapp R. G., Biondi B., and Karrenbach M.**

In an effort to increase SEP's ability to work with 3-D prestack data sets
we have continued the development of our integrated 3-D seismic visualizer
using Advanced Visual Systems (AVS) as our integrating platform.
To the capacity of displaying SEP data sets,
we have added the ability to simultaneously display non-seismic 3-D
geophysical and geological data.
The main thrust of our work has been the integration
of GOCAD model building tool into AVS.
To achieve this goal we have developed a few AVS modules to
convert GOCAD surface into AVS geometry objects.
In addition, we have begun integrating SEP batch programs into
our AVS environment. Specifically, we have added an interactive wave modeler,
which can be viewed simultaneously.

Depth migration of complex surfaces with GOCAD: Study of the curvature of a triangulated surface (ps.gz 19K) (pdf 27K) (src 814K)
**Berlioux A.**

The depth migration of time-migrated surfaces by demigration with
GOCAD is inaccurate in the case of complex surfaces, such as folded
horizons, in areas where the curvature of the surface reverses its
sign. I believe this problem can be avoided by cutting the original
complex surface into pieces for which the depth migration is accurate.
To do so, I propose an algorithm to study the sign of the curvature
of the GOCAD surface in order to divide it up properly before
performing the depth migration. Putting the depth-migrated pieces
back together, I should then obtain a depth-migrated surface more
representative of the true geology than the direct depth-migrated
surface.

Coherent partial stacking by offset continuation of 2-D prestack data (ps.gz 1092K) (pdf 995K) (src 14552K)
**Chemingui N. and Biondi B.**

Previously, we introduced a new
partial-migration operator named
Azimuth Moveout (AMO), that rotates the azimuth and shifts the offset
of 3-D prestack data. The restriction of this operator to the 2-D case
defines a new operator for offset-continuation that has many
applications on its own. We apply the 2-D AMO on the
synthetic Marmousi data set
to reduce its size by coherent partial stacking prior to prestack migration.
We show that AMO transformation eliminates the dip filtering action of
CMP stacking and preserves the complex geology of the model.
We derive a time-space formulation
of the 2-D AMO by stationary phase
approximation to its Fourier
domain definition.
The expression for the traveltime curve is used for a Kirchhoff-style
implementation, with care taken to avoid aliasing.

Berryhill's ``pure migration'' = Gardner's PSI (ps.gz 25K) (pdf 36K) (src 821K)
**Popovici A. M.**

Kinematically, Berryhill's ``pure migration'' or nonimaging
shot-record migration is equivalent to dip moveout (DMO)
before normal moveout (NMO) followed
by Gardner's Prestack Imaging (PSI). The two
processes have the same effect on a point diffractor
in midpoint, offset, and time coordinates, compressing the
Cheops pyramid surface to the same curve.
The two methods produce the same kinematic result, although
from a computational point of view, Berryhill's method
is much faster.

Shortest-path calculation of first arrival traveltimes by expanding wavefronts (ps.gz 37K) (pdf 74K) (src 2216K)
**Urdaneta H. and Biondi B.**

A new approach to computing traveltimes and ray paths by solving the shortest
path problem is presented. The technique is based on a partitioning
of the shortest path optimization problem into smaller problems.
We recursively evaluate the solution on expanding wavefronts instead of finding the
global shortest paths from the source. To solve the local minimization, we apply
a modified version of the Bellman-Ford optimization algorithm because of its
suitability for a parallel implementation in three dimensions.

Datuming velocity from traveltime tomography (ps.gz 852K) (pdf 1011K) (src 22716K)
**Bevc D.**

Near-surface velocity anomalies cause kinematic and focusing
effects which can be ameliorated by wave-equation datuming and layer
replacement. The trick is to find the correct datuming velocity.
When the anomalies are shorter in lateral extent than the cable length,
residual times picked from deep non-hyperbolic events can
be used for traveltime tomography.
The optimal reconstruction is obtained by constraining the
model to the near surface and by estimating the inverse covariance matrix
with a prediction error filter.
Downward continuation with the traveltimes from this model, followed
by upward continuation with a replacement velocity, removes
most of the unwanted distortions.

Computing tomographic resolution matrices using Arnoldi's iterative inversion algorithm (ps.gz 41K) (pdf 59K) (src 26K)
**Berryman J. G.**

Resolution matrices are useful in seismic tomography because they
allow us to evaluate the information content of reconstructed images.
Techniques based on the multiplicity of equivalent exact formulas that
may be used to define the resolution matrices have been used previously
by the author to design algorithms that avoid the need for any singular
value decomposition of the ray-path matrix.
An explicit procedure is presented for computing both model and data
resolution matrices using Arnoldi's algorithm for iterative inversion
in seismic tomography. Arnoldi's method differs from the Lanczos scheme
by including explicit reorthogonalization of basis vectors. Some convenient
notation is introduced to permit ready comparison of Arnoldi's method
with the Lanczos approach. Arnoldi's method requires greater storage of
basis vectors but completely overcomes the lack of basis vector
orthogonality, which is the major practical limitation of the Lanczos method.

A simple example of a null space and how to modify it (ps.gz 21K) (pdf 28K) (src 7K)
**Nichols D.**

This document was generated using the
**LaTeX**2`HTML` translator Version 97.1 (release) (July 13th, 1997)
Copyright © 1993, 1994, 1995, 1996, 1997,
Nikos Drakos,
Computer Based Learning Unit, University of Leeds.
The command line arguments were:

**latex2html** `-dir /net/sepwww/public/docs/sep82/dave1/paper_html index.ltx`.
...

Spectral preconditioning (ps.gz 19K) (pdf 23K) (src 4K)
**Claerbout J. and Nichols D.**

This document was generated using the
**LaTeX**2`HTML` translator Version 97.1 (release) (July 13th, 1997)
Copyright © 1993, 1994, 1995, 1996, 1997,
Nikos Drakos,
Computer Based Learning Unit, University of Leeds.
The command line arguments were:

**latex2html** `-dir /net/sepwww/public/docs/sep82/jon2/paper_html index.ltx`.
...

Preconditioning the wave equation (ps.gz 24K) (pdf 32K) (src 8K)
**Karrenbach M.**

The solution of systems of equations can employ preconditioning of
the involved operators. This preconditioning process aims at accelerating
convergence and
requires some estimate of the solution or of the operator behavior.
I outline a preconditioning operation for use with
wave equations having the aim of increasing the region of
stability of the evolution equation.

Birth of a C++ Project (ps.gz 17K) (pdf 21K) (src 6K)
**Schwab M.**

This document was generated using the
**LaTeX**2`HTML` translator Version 97.1 (release) (July 13th, 1997)
Copyright © 1993, 1994, 1995, 1996, 1997,
Nikos Drakos,
Computer Based Learning Unit, University of Leeds.
The command line arguments were:

**latex2html** `-dir /net/sepwww/public/docs/sep82/matt1/paper_html index.ltx`.
...

What's new in SEPLIB? (ps.gz 15K) (pdf 21K) (src 6K)
**Nichols D., Karrenbach M., and Urdaneta H.**

The CD-ROM version of this report is distributed with a new
version of the SEP software ``SEPLIB'' on it. The new version has a more
robust Input/Ouput (I/O) system that is extendible to support
new types of I/O. It also unifies the behavior of all input and output files.
The distribution contains experimental support for a geometry database
to permit the use of non-uniformly sampled data.

SEP goes World Wide Web (ps.gz 11K) (pdf 11K) (src 253K)
**Karrenbach M., Claerbout J., and Berlioux A.**

User friendly navigation software (*MOSAIC*) for the Internet,
the World Wide Web (*WWW*),
recently became publically available.
This software understands the standardized mark-up language
for electronic online documents (*HTML*).
This presents a unique opportunity for increasing SEP's
visibility in the scientific community and will also give sponsors easy access
to research results. We see it as a unique complement to our past electronic
publishing efforts, which have been restricted to CDROM, and we hope that
this makes it easier to disseminate our research results and views
on electronic publishing.

5/11/2001