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70th EAGE Conference and Exhibition - Workshops and Fieldtrips
- Conference date: 09 Jun 2008 - 12 Jun 2008
- Location: Rome, Italy
- ISBN: 978-94-6282-104-0
- Published: 09 June 2008
81 - 91 of 91 results
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Waveform inversion by one-way wavefield extrapolation
By J. ShraggeOne-way Riemannian wavefield extrapolation (RWE) on computational
meshes conforming to the direction of turning-wave
propagation is presented as an alternative forward modeling
procedure for waveform inversion. Forward modeling tests
demonstrate that the RWE approach may be a sufficiently accurate
approximation for calculating the wavefield phases important
for early-arrival waveform inversion. Initial results indicate
that RWE waveforms are well matched at wide offsets to
finite-difference data, and can be used in a waveform inversion
scheme to invert synthetic data for 1D velocity perturbations.
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Sources Near The Free-Surface Boundary: Pitfalls for Elastic Finite-Difference Seismic Simulation And Multi-Grid Waveform Inversion
Authors J. E. Anderson, J. R. Krebs and D. HinkleyElastic full-waveform inversion requires the capability to efficiently do accurate forward seismic
simulations based upon an earth model. The rotated staggered grid (Saenger, 2000) has been
a great advance for accurate elastic wave simulation in isotropic and anisotropic media but has
requirements that complicate source insertion too close to a free surface boundary. Coarse-grid
simulations limited to lower-frequency components in the data are frequently used to accelerate
early stages of waveform inversion both for computational efficiency and to better condition the
inversion (Bunks et al., 1995). This works better for acoustic waveform inversion than in the
elastic case. In the elastic case, the free-surface boundary requires a fine spatial grid both for
accurate computation of surface waves and for accurate source insertion. These requirements
offset part of the multi-grid advantage, especially for typical seismic acquisition geometries with
sources and receivers located somewhere near the surface of the earth.
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3D Pre-Stack Plane Wave Full Waveform Inversion
Authors D. Vigh and E. W. StarrPSDM has been in place for decades with numerous tools to derive velocity fields in depth,
particularly in mature areas such as the Gulf of Mexico. The existing methods have reached
their limits to further define and/or fine-tune the velocity models. With the new wide azimuth
acquisitions where better illumination is foreseeable, velocities can be more accurately
determined. One of the most advanced tools is to use full waveform inversion. Pre-stack
seismic full waveform inversion is a highly challenging task due to non-linearity and nonuniqueness.
Combined with compute intensive forward modeling and residual wavefield back
propagation, the method makes the technique computer intensive, especially for 3D projects.
For PSDM, forward modeling and reverse time migration are widely used in the industry.
Even in the 3D sense the focus has become what sort of methods could be used to achieve
higher resolution velocity models. The answer is full waveform inversion. Here we examine
the time domain plane wave implementation of 3D waveform inversion supported with
synthetic and field data examples.
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3D acoustic frequency-domain full waveform tomography (FWT): application to the SEG/EAGE Overthrust model
Authors H. Ben-Hadj-Ali, S. Operto, J. Virieux and F. SourbierWe present a massively parallel frequency-domain full-waveform tomography (FWT) algorithm for imaging
3D acoustic media. FWT refers to imaging method based on the complete solution of the two-way
wave equation for the forward problem and on inverse problem theory for the imaging problem (Tarantola,
1987). A model is built by minimization of the misfit between the recorded data and that computed
in a starting model. The frequency-domain (FD) formulation of FWT was originally developed
for 2D cross-hole acquisition surveys which involve wide-aperture propagations (Pratt and Worthington,
1990). Only few discrete frequencies are required to develop a reliable image of the medium thanks to
the wavenumber redundancy provided by multifold wide-aperture geometries. Full wave propagation
modeling is a critical issue in FWT methods since it is the most computationally expensive task in the
processing flow. In the frequency domain, the forward problem reduces to the resolution of a large sparse
system of linear equations for each frequency to be considered. Therefore, a 3D optimal finite-difference
stencil was designed by Operto et al. (2007) that leads to 4 grid points per wavelength. Aim of this work
is to provide some insights on the feasibility and relevance of 3D frequency-domain FWT for building
high-resolution velocity models of isotropic acoustic media. Indeed, we present application of FWT to
two targets of the SEG/EAGE Overthrust model.
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Practical 3D wavefield tomography on field datasets
More LessWaveform tomography has been used for a number of years in 2D on synthetics and field data
and recently in 3D (Stekl et al 2007, Ben Hadj Ali et al 2007, Sirgue et al 2007) but only on
synthetics data sets. 3D waveform inversion is still computationally expensive procedure but
recent developments on computing power have enabled application of the procedure on the
production scale data. We are going to show results obtained by 3D waveform inversion
method developed by Stekl, Warner, Umpleby 2007 on a field data set over a shallow
channel.
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Multiscale Waveform Tomography with an Adaptive Early-Arrival Muting Window
Authors C. Boonyasiriwat, W. Cao, G. T. Schuster, P. Valasek, P. Routh and B. MacyWe propose a time-domain multiscale waveform tomography method by combining earlyarrival
waveform tomography and time-domain multiscale waveform tomography. A Wiener
filter is used for data processing and a multiscale V-cycle with an adaptive early-arrival
muting window for the inversion. The proposed method is very robust and can reconstruct an
accurate velocity structure from marine seismic data.
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Viscoelastic Modeling and Full Waveform Inversion in Attenuating Media
Authors G. T. Royle and S. C. SinghSince the 1980’s a significant amount of research in the field of full waveform has been conducted,
and we are now at the stage where more accurate descriptions of the subsurface are
being sought in addition to the elastic parameters. Elasticity accounts for materials that have a
capacity to store mechanical energy with no dissipation of energy. A more accurate description
of real earth media takes into account the time-dependent nature of previous stress states. In
other words, the material possess a characteristic referred to as a memory effect (Robertsson
et al. 1994).
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The campanian active volcanoes: Somma-Vesuvius and Campi Flegrei
Authors D. M. Palladino, S. Simei and R. TrigilaSomma-Vesuvius and Campi Flegrei are two of the most risky active volcanoes on earth, being
located in a three million people inhabited area. Although contiguous and coeval, the two volcanoes
do not share any important classificative patterns in the overall morphology, structure or magma
composition.
Several pieces of evidence on the relationships between the volcanic catastrophic events, the natural
environment and the population density, make the Campanian region a point of reference for the
volcanological research in the world.
In the last few years, specific studies, focused on stratigraphy, eruptive mechanisms and volcanotectonic
events, contributed to expand our knowledge on this area (see Mastrolorenzo et al., 2004
for a comprehensive review). At the present time, a still increasing amount of geo-archaeological
information allows us to understand better the effects of natural events which were acting on the
territory with different intensities and at different time scales. In this relatively small area, which
includes the Campanian Plain with its coasts and reliefs, few key sites, with well exposed sections,
will allow us to summarize its volcanological history by a through field-trip lasting two days.
Here, we find Somma-Vesuvius and Campi Flegrei, two of the most important districts of the
Quaternary volcanism of the Tyrrhenian margin. They have grown mostly on alluvial and marine
sediments filling up the graben formed during the Pliocene and Pleistocene by the subsidence of
Mesozoic carbonate platforms that make up the substrate of the Campanian plain; this platform now
lies about 2 km below the volcano (Scandone et al., 1991).
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The Laga Basin: stratigraphic and structural setting
Authors S. Bigi, M. Moscatelli and S. MilliMost of the ancient turbidite systems are known being deposited in foredeep basins
at the front of active thrust belt. Differently from fluvio-deltaic systems generally
lacated in the more internal portion of these basins, the turbidite systems occur at
different depth in the more deeper portions of these basins (foredeep turbidite systems)
or in the relatively shallower tectonically confined depressions occurring on top of the
thrust belt (wedge-top turbidite systems) (see discussion in Mutti et al. 2002, 2003).
Foredeep turbidite systems represent the classical sedimentation in a broad and flat
basin plain, showing thick to thin parallel and continuous sandstone beds with the
Bouma-type depositional division. Wedge-top turbidite systems are directly fed by
fluvio-deltaic systems and more clearly record both climate changes affecting the source
areas and tectonic activity of the orogenic wedge.
Messinian turbidite deposits of the northern and central Apennines show many
characters indicating sedimentation in confined basins, formed since the upper
Tortonian in relation to the segmentation of the Langhian-lower Tortonian Marnoso-
Arenacea foredeep basin (inner stage of the Marnoso-Arenacea, Ricci Lucchi, 1986). In
these last years, detailed facies and physical stratigraphic analyses as a well as structural
and thermal analyses, conducted on the Laga and Argilloso-Arenacea Fms (central
Apennines), demonstrate as these basins were located at the hinge between foredeep and
wedge-top depozones of the Messinian Apennine thrust belt (Milli and Moscatelli,
2000, 2001; Bigi et al., 2003; Moscatelli, 2003; Milli et al., 2004; Falcini et al., 2006;
Stanzione et al., 2006; Casero and Bigi, 2006; Aldega et al., 2006; Critelli et al., 2007;
Milli et al., 2007). Anisotropy of the subducted plate and thrust propagation rate deeply
controlled the onset of complex basins at the top of the orogenic wedge (Casero and
Bigi 2006; Bigi et al., 2006). The resulting topography of these basins and the
concomitant climate changes exerted a strong control on turbidite sedimentation and on
the stratigraphic organization of these deposits.
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Walking through downtown Rome. A discovery tour on the key role of geology in the history and urban development of the city
Authors R. Funiciello, G. Giordano, B. Adanti, C. Giampaolo and M. ParottoMany characteristics of the natural environment where Rome has developed for the last 3000 years have played a major positive role in promoting the excellence of Rome as a political, economic and administrative power, the so-called Caput Mundi of the ancient world. Aside from anthropological and ethnological factors, the positive geological and geomorphological setting of the future site of Rome favoured the settlement of several archaic villages along the left bank of the Tiber River since the beginning of the third millennium B.P. The sites were strategically located, being characterized by proximity to the river, over isolated tufaceous cliffs dominating the alluvial plain, the abundance of spring water and the wide availability of stones and natural building material that promoted a quick technological development of building and infrastuctural services to the growing town. The main natural factors playing a strategic role in the development of the long-lived city of Rome have been:
- The geomorphology of the distal volcanic plateau
- Tiber river network and the related alluvial deposits
- The surface geology and its natural materials
- The hydrogeology and microclimatic constraints
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Mathematics of Modeling, Migration and Inversion with Gaussian Beams
By N. BleisteinGaussian beams are extensions of asymptotic ray theory to waves with complex traveltime. These waves have Gaussian decay orthogonal to a central ray. Solutions of wave problems are represented by integrals (sums) over a suite of Gaussian beams. This tends to produce representations that are smoother than those produced by symptotic ray theory, facilitating smoother modeling, migration and inversion output than what is produced by classical asymptotic ray theory.
Asymptotic ray theory is reviewed in the hierarchy of Cartesian coordinates, ray-centered coordinates, ray-centered coordinates with complex traveltimes (Gaussian beams!). Green’s functions and plane-wave modeling are described in each case, with the last requiring integrals over suites of Gaussian beams. Examples of Kirchhoff migration/inversion using Gaussian beam representations of Green’s functions are presented.
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