Subsalt event regularization with steering filters (ps.gz 3346K) (pdf 1178K) (src 16205K)
**Prucha M. L. and Biondi B. L.**

The difficulties of imaging beneath salt bodies where illumination is poor
are well known. In this paper, we present an angle-domain least-squares
inversion scheme that regularizes the seismic image, tending to smooth along
specified dips. This smoothing is accomplished using steering filters. We
show the results of using the regularized inversion with
smoothing along the angle axis and along both the angle and common
midpoint axes. Additionally, the ramifications of specifying incorrect dips
to smooth along will be examined. The results show that this regularized
least-squares inversion does produce a cleaner, more continuous result
under salt bodies. The inversion will reject incorrectly chosen dips
used for the regularization.

Shot-profile migration of multiple reflections (ps.gz 5225K) (pdf 1581K) (src 39949K)
**Guitton A.**

Least-squares joint imaging of primaries and multiples (ps.gz 1308K) (pdf 553K) (src 19415K)
**Brown M.**

Converted wave dip moveout (ps.gz 5271K) (pdf 1702K) (src 95510K)
**Rosales D.**

Converted wave azimuth moveout (ps.gz 371K) (pdf 187K) (src 3309K)
**Rosales D. and Biondi B.**

Accurate prestack partial migration operators are important
in seismic exploration. The development of different technologies, like
the use of PS converted wave data, suggests the extension of
applications of already successful operators and techniques
for PP data. Azimuth moveout (AMO) is a partial migration
operator that transforms prestack data into equivalent data with
arbitrary offset and azimuth. We introduce a new, more accurate
prestack partial migration operator for converted wave data.
This operator has promising future applications in the regularization of
ocean bottom seismic data.

Multidimensional imaging condition for shot profile migration (ps.gz 104K) (pdf 242K) (src 1563K)
**Valenciano A. A., Biondi B., and Guitton A.**

Wave-equation migration velocity analysis beyond the Born approximation (ps.gz 1404K) (pdf 1052K) (src 13693K)
**Sava P. and Fomel S.**

The Born approximation is based on the assumption of small
slowness perturbation.
We investigate the limits of the Born approximation when
applied to wave-equation migration velocity analysis and propose
two new schemes which allow for larger slowness anomalies,
while improving accuracy and increasing stability.
The new schemes are based on linearizations of
exponential functions using bilinear and implicit
approximations, rather than the (Born) explicit approximation.
We demonstrate the feasibility of our new
operators on a synthetic example with highly variable
background and strong slowness anomalies.

Matching dips in velocity estimation (ps.gz 3117K) (pdf 783K) (src 16226K)
**Clapp R. G.**

The proposed method for constraining reflector dip in tomography worked well
on the complex North Sea synthetic. The estimated velocity model was
more accurate with the dip constraint.
The migrated image showed
overall better image quality and the selected reflector was
more continuous and better positioned.
I would like to thank BP for the synthetic data
used in this paper.
...

Velocity estimation for seismic data exhibiting focusing-effect AVO (ps.gz 2351K) (pdf 928K) (src 20737K)
**Vlad I. and Biondi B.**

Transmission anomalies sometimes create AVO effects by focusing
the reflected seismic wavefields, which impedes AVO analysis. The AVO
anomalies caused by focusing are distinguishable by surface consistent
patterns. We analyze the previous efforts to define, describe and eliminate
spurious AVO anomalies. We also propose using wave equation
migration velocity analysis to build an accurate velocity
model. The transmission-related AVO can then be eliminated by downward
continuation through this velocity model.

Prestack imaging of overturned and prismatic reflections by reverse time migration (ps.gz 124K) (pdf 208K) (src 1346K)
**Biondi B.**

I present a simple method for computing angle-domain Common Image Gather
(CIG) using prestack reverse time migration.
The proposed method is an extension of the method
proposed by Rickett and Sava (2001) to compute CIGs
by downward-continuation shot-profile migration.
I demonstrate with a synthetic example the use
of the CIG gathers for migration velocity updating.
A challenge for imaging both overturned and prismatic reflections
is the discrimination of the reflection generated on
either side of interfaces.
I show how the propagation direction of the reflections
can be easily determined
by evaluating the crosscorrelation of the source wavefield
with the receiver wavefield at time lags different than zero.
Reflections can be easily separated once their
direction of propagation is determined.
I demonstrate the method by imaging overturned events generated
by a segment of dipping reflector immersed in a vertically
layered medium.
The example shows that for overturned reflections
velocity errors cause asymmetric residual moveouts.
This observation suggests that for updating
the velocity from overturned reflections,
the migrated CIGs should be scanned
using a different family of residual moveouts
than the standard parabolic moveouts used
for non-overturned events.
The migration of a synthetic example containing
prismatic reflection shows that the CIGs
computed using only horizontal subsurface offset
are not useful,
and that the vertical subsurface offset
should be also used.

Statistical stability and time-reversal imaging in random media (ps.gz 495K) (pdf 237K) (src 4700K)
**Berryman J. G., Borcea L., Papanicolaou G. C., and Tsogka C.**

Localization of targets imbedded in a heterogeneous background medium
is a common problem in seismic, ultrasonic, and electromagnetic
imaging problems. The best imaging techniques make direct use of
the eigenfunctions and eigenvalues of the array response matrix,
as recent work on time-reversal acoustics has shown. Of the various
imaging functionals studied, one that is representative of a preferred
class is a time-domain generalization of MUSIC (MUltiple SIgnal
Classification), which is a well-known linear subspace method normally applied only in the frequency domain.
Since statistical stability is not characteristic of the frequency domain,
a transform back to the time domain after first
diagonalizing the array data in the frequency domain takes optimum
advantage of both the time-domain stability and the frequency-domain
orthogonality of the relevant eigenfunctions.

Reverse time migration in midpoint-offset coordinates (ps.gz 74K) (pdf 81K) (src 152633K)
**Biondi B.**

Reverse-time migration
Baysal et al. (1984)
has some potential advantages with respect
to downward-continuation migration.
It can migrate overturned and prismatic reflections
even in the presence of strong lateral velocity
variations Biondi (2002).
It also models the amplitude
...

Adaptive subtraction of multiples with the -norm (ps.gz 1219K) (pdf 454K) (src 19263K)
**Guitton A. and Verschuur E.**

The estimation of shaping filters with the -norm
as opposed to the -norm leads to a proper attenuation
of multiples when significant amplitude discrepancies exist between multiples
and primaries. The actual method implemented is the fairly standard
iteratively re-weighted least-squares method which is an excellent
approximation to . Synthetic and field data results illustrate the
advantages of the -norm.

A hybrid adaptive subtraction method (ps.gz 1345K) (pdf 603K) (src 14657K)
**Guitton A.**

A hybrid adaptive subtraction scheme is proposed. This hybrid
scheme uses prediction-error filters as covariance operators within
the filter-estimation step. This methods proves to be the most
efficient when the noise and signal interfere. Although
prediction-error filters are utilized, this technique is not
a pattern-recognition technique: it simply
tries to remove the correlated signal information to unbias
the estimation of the matched-filters. Tests on synthetic and real
data for a multiple attenuation problem
illustrate the efficiency of the proposed scheme.

Removal of coherent noise from electroseismic data (ps.gz 1092K) (pdf 634K) (src 46345K)
**Haines S. and Guitton A.**

Theoretical aspects of noise attenuation (ps.gz 20K) (pdf 25K) (src 4K)
**Guitton A.**

In Guitton (2001) I presented
an efficient algorithm that attenuates coherent noise based on the
spatial predictability of noise and signal. I called this algorithm the
subtraction method. In this paper I show that
the subtraction approach is closely related to another described
method, the filtering method
Brown and Clapp (2000); Clapp and Brown (2000); Soubaras (1994); Spitz (1999) if I use a preconditioning strategy Claerbout and Fomel (2001).
...

Removing velocity stack artifacts (ps.gz 850K) (pdf 405K) (src 6645K)
**Karpushin A.**

The Prediction Error Filter (PEF) is a widely used tool in various
geophysical applications such as signal-noise separation and
interpolation of missing data.
Over the years, SEP has developed tools to estimate
non-stationary Prediction Error
Filters. Non-stationary PEFs are successfully used for multiple
removal, ground-roll
attenuation, and in other geophysical problems.
I apply a non-stationary PEF to a
velocity stack
to remove artifacts caused by a limited offset of the data. My first goal is to
create
an artifact-free model in which individual reflections are easier to
identify.
To do this I create a simple model of the artifacts in the space.
This ``noise'' model is data-independent and relies only on the
geometry
of the data acquisition and parameters of the velocity stack. Then I
estimate a non-stationary PEF on this ``noise'' model and use it to improve
the
velocity stack.
In the second part of the paper, I test the
possibility of using the described PEF as a preconditioner for a velocity
stack least-squares inversion.

Reference velocity selection by a generalized Lloyd method (ps.gz 1661K) (pdf 630K) (src 29538K)
**Clapp R. G.**

Selecting reference velocities can be thought of as a non-linear
problem.
Choosing a reference velocity to use at a given location is a function
of which reference velocity is actually closest to the given velocity,
which makes posing the problem in a traditional linear framework
difficult.
When compressing signals, electrical engineers face a similar problem.
They try to describe a signal with as few bytes as possible.
To do this they develop a codebook. Each member of the codebook
represents a region described by a single value.
...

One-way wave equation absorbing boundary condition (ps.gz 81K) (pdf 71K) (src 557K)
**Shan G.**

In modeling and migration based on wave equation,
the wavefield has to be extrapolated in a finite domain
due to the limitations of our survey and computers.
Absorbing boundary conditions must be introduced, otherwise
some reflections will occur at the artificial grid boundary.
In this paper, I will introduce an absorbing boundary condition based on the
one-way wave equation, with some numerical examples.

Speeding up wave equation migration (ps.gz 481K) (pdf 345K) (src 10317K)
**Clapp R. G.**

When doing downward continuation in the offset domain,
we begin by organizing our data cube as a function
of midpoint *x*, offset *h*, and frequency *f*. We then apply
the double square root (DSR) equation to move the wavefield
down one depth step Claerbout (1995).
We apply an imaging condition,
...

Finite-difference -x migration of unregularized seismic data (ps.gz 185K) (pdf 152K) (src 792K)
**Vlad I.**

Wavefield downward continuation does not need to be done on a
structured spatial mesh. Semistructured meshes have advantages (no need
for regularization before migration) but they sometimes produce
artifacts. There are at least two acquisition settings which will not
result in artifacts. The implementation is simple. I present a 2D zero-offset -x
semistructured mesh migration (SMM) of a synthetic dataset. Its
outputs are compared with those of -x migration on a regular
grid, with zero traces inserted in the place of missing data. There
are several potential ways of removing the artifacts. Extension to 3D
is also possible.

Effect of velocity uncertainty on amplitude information (ps.gz 4788K) (pdf 1206K) (src 20881K)
**Clapp R. G.**

An extension of poroelastic analysis to double-porosity materials: (ps.gz 64K) (pdf 91K) (src 131K)
**Berryman J. G.**

Double-porosity materials were introduced as models for oil and
gas reservoirs having both storage and transport porosities, and were
at first usually treated as static mechanical systems in order
to study the flow patterns of fluids during reservoir pump-down. Because fluid
withdrawal normally increases the effective stress acting on the
reservoir, it also turns out to be important to study the geomechanics
of the reservoir and how changing fluid pressure affects the solid
compaction and fluid permeability of these systems. At the
microscale, the mechanical properties of the solid constituents and
their distribution in space determine the overall macromechanics of
the reservoir system. For systems containing two porosities and two
types of solid constituents, exact results for all but one (which may
be taken as the overall drained bulk modulus of the system) of the
mechanical constants can be derived when the constituents' properties
are known using methods developed in this paper. For multi-porosity
systems, closure of the system of equations remains an open question,
although it is clear that the system can always be closed by the
addition of further macroscale measurements.

Amplitude inversion for three reflectivities (ps.gz 26K) (pdf 46K) (src 112K)
**Prucha M. L. and Herkenhoff E. F.**

Seismic amplitudes can provide information about rock properties
if the amplitudes can be properly processed Backus (1983); Castagna and Backus (1993).
This is very difficult
to do given the nonlinearity of the Zoeppritz equation. The linearized
Bortfeld approximation Bortfeld (1961) allows us to invert the data to
obtain the reflectivities of events. Unfortunately, most
...

Fault contours from seismic (ps.gz 490K) (pdf 331K) (src 3367K)
**Lomask J.**

Fault contours are created by mapping the slip distribution along a
fault surface.
Fault contours have many useful applications in geophysics and geology
including rock stress analysis, interpretation, and processing.
Therefore, automatic calculation of fault contours from 3D data would be
very valuable.
As the first step in that direction, displacement is calculated from
a simple 2D model of faulted seismic data.
Making a stationary assumption, the displacement is calculated by
fitting a smooth line to a cross-correlagram.
The cross-correlagram is created by windowed cross-correlation
across the fault.
To fit this line, I use a non-linear optimization method that has
similarities to Simulated Annealing.
This removes most of the displacement which will later allow other
methods to solve the non-stationary problem.

Toward subsurface illumination-based seismic survey design (ps.gz 686K) (pdf 456K) (src 27673K)
**Alvarez G.**

Non-stationary, multi-scale prediction-error filters and irregularly sampled data (ps.gz 844K) (pdf 415K) (src 5530K)
**Curry W.**

Madagascar satellite data: an inversion test case (ps.gz 1426K) (pdf 814K) (src 30858K)
**Lomask J.**

The Madagascar satellite data set provides images of a spreading ridge off the coast of Madagascar. This data set has two regions: the southern half is densely sampled and the northern half is sparsely sampled. This data set is an excellent test case for inversion methods. It presents several challenges that geophysicists face in generating seismic maps in general. The data is acquired in swaths that follow irregular paths(tracks), similar in some respects to irregular 3D acquisition geometries. Inversion allows us to combine these different data paths into one image. Shifts between tracks are removed by taking the derivative along the tracks in the inversion fitting goals. By looking at the residual in data-space, we were able to see errors in the weighting operator. The sparsely sampled region presents a missing data problem. In the future, we intend to estimate 2D prediction error filters (PEFs) on these sparse tracks and use them to fill in the missing data. I have tested one method on a simple 1D model, in which I estimate a PEF and missing data simultaneously while throwing out fitting equations where the leading 1 coefficient of the PEF lands on unknown data. Thus, this data will give us an opportunity to test different methods of estimating PEFs on sparse and irregular data. Also, preconditioning on the helix greatly speeds convergence.

Implementing non-stationary filtering in time and in (ps.gz 685K) (pdf 2019K) (src 20772K)
**Alvarez G.**

Non-stationary filtering of seismic data can be accomplished in
time or in Fourier domain by the theory of non-stationary convolution
Margrave (1998). Here I show the results of implementing this theory
for time-variant filtering of seismic data with an arbitrary number of
filters and for forward and inverse NMO correction in the
frequency domain. In the first case I show that the filters may be made to
change sample-by-sample down the trace without artifacts being introduced
and in the second case that the
accuracy of the implied fractional sample interpolation can be controlled
as an input parameter.

A return to passive seismic imaging (ps.gz 54K) (pdf 90K) (src 301K)
**Artman B.**

Rekindling the passive seismic imaging effort at Stanford,
I have acquired grants with Simon Klemperer of
the Stanford Crustal Research Group from both the
Petroleum Research Fund and the National Science Foundation to pursue
two- and three-dimensional imaging efforts of the subsurface in a
passive listening methodology. Utilizing the outstanding SEP hardware and
software infrastructure and expertise, I have begun to build the
resources necessary to manipulate the massive datasets toward
producing an image. Efforts to acquire several existing datasets that seem to fit the
requirements of this method are presently underway, while 180 Gbytes
of the Santa Clara Valley Seismic Experiment from 1998 arrived in
house on the first of March.

Is 2D possible? (ps.gz 1831K) (pdf 434K) (src 9453K)
**Artman B.**

Coherent noise in the passive imaging experiment (ps.gz 20K) (pdf 23K) (src 40K)
**Artman B.**

Inherent in the passive seismic imaging experiment is the troublesome
coexistence of the direct source phase and its excited ghost
reflections that image the subsurface. Akin to the multiple problem
in conventional seismic, I propose to attack the direct waves as noise
in the framework outlined by Guitton et al. (2001).
Whereas his methodology is effective at separation of signal and noise
models, building an
appropriate noise model is often the most limiting aspect of the technique.
I propose a method to reconstruct the parameters of the
...

WEI: Wave-Equation Imaging Library (ps.gz 313K) (pdf 190K) (src 2589K)
**Sava P. and Clapp R. G.**

This paper introduces `WEI`, a new library in the SEP library
of programs (`SEPlib`). The `WEI` library implements
a `Fortran90` imaging engine for mixed-domain
downward-continuation operators.
The main imaging operators are broken into functional operators
which can be modified by the user without explicit contact with
I/O, parallelization etc. The code is parallelized using a combination
of the Open MP and MPI standards, and can run on both shared-memory
and cluster computers.

Displaying seismic data with VTK (ps.gz 3273K) (pdf 1030K) (src 8616K)
**Arroyo E. R. and Clapp R. G.**

Cluster building and running at SEP (ps.gz 3164K) (pdf 467K) (src 7198K)
**Clapp R. G. and Sava P.**

When we first decided that we wanted to buy a new cluster we got
quotes from several different vendors. These quotes varied up to 50%
for the same configuration based upon the add-on features that
each company provided. However, even the lowest figure was
30% more than what we calculated if we built the cluster ourselves.
Once we decided that the 30% cost differential was significant enough
to make building it ourselves worthwhile, we had to determine
what exactly we wanted to build.

...

6/8/2002