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SUMMARY FullWaveform Inversion (FWI) methods use generally gradient based method, such as the nonlinear conjugate gradient method or more recently the l-BFGS quasi-Newton method. Several authors have already investigated the possibility of accounting more accurately for the inverse Hessian operator in the minimization scheme through Gauss-Newton or exact Newton algorithms. We propose a general framework for the implementation of these methods inside a truncated Newton procedure. We demonstrate that the exact Newton method can outperform the standard gradient-based methods in a near-surface application case for recovering high-velocity concrete structures. In this particular configuration, large amplitude multi-scattered waves are generated, which are better taken into account using the exact-Newton method.
NLRTM provides sub-images of the interactions of primaries/multiples and multiples/multiples from Nonlinear reverse-time migration is a modified reverse-time which one can build such gathers. Further information is extractable migration that accounts for the nonlinear relation between seismic from these NLRTM extended sub-images. Despite data and model in order to image multiply scattered waves the fact that each NLRTM sub-image uses different subsurface including multiples. The illumination of multiply scattered illumination (from primaries or multiples), these sub-images waves yields a representation of the Earth's subsurface that are still representations of the same subsurface. This consistency is more sensitive to model parameters, which allows for advanced between NLRTM sub-images is usable for MVA when seismic interpretation. The gain in sensitivity that multiply applying the semblance principle across sub-images.
- Geophysics > Seismic Surveying > Seismic Processing > Seismic Migration (1.00)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (1.00)
Summary Reverse time migration (RTM) is achieved by a forward and reverse time propagation of source and receiver wavefields respectively, followed by an imaging condition. The quality of the image from any RTM implementation depends directly on the method’s ability to separate the true reflection data from the backscattered correlation noise between the source and receiver wavefields. In this paper we demonstrate the application of an inverse scattering imaging condition that significantly reduces this backscattered correlation noise and results in a much higher quality subsurface image than is achieved by typical RTM imaging conditions.
SUMMARY This paper describes a higher-order method for gradient approximation in the solution of the eikonal equation on unstructured grids. At the element level, two approaches are discussed: a gradient approximation with quadratic shape functions for the entire element, and an application of local Fermat’s principle for each of the unknown nodes separately. The Fast Marching Dijkstra-type approach is used to propagate the solution on the unstructured grid. The error in the solution associated with the quality of the grid and error-reduction strategies for the problem related to the relative position of the normal of the wavefront and triangle orientation are discussed.
Summary The inversion of seismic reflection data is challenging due to the oscillatory nature of the seismic data, the nonlinear relation between the data and the Earth’s model parameters, and the relative sensitivity of the different subsets of the data to the model parameters. Full-waveform inversion solves this inverse problem in the data space but is known to have shortcomings, especially because of the multi-modality and the numerous locally optimal solutions that its objective function allows. Migration velocity analysis indirectly relates to the inversion of seismic reflection data. Used in velocity model building, the method yields a macro model of the Earth’s subsurface but constrains this model only to be kinematically correct. Migration velocity analysis has also its share of well-known pitfalls. Interestingly, the two methods have complementary characteristics which potentially mitigate the drawbacks of each technique. To take advantage of the capability of full-waveform inversion and migration velocity analysis, a bi-objective optimization strategy combines the two methods to solve the inversion of seismic reflection data. A numerical example illustrates the benefits of this new strategy.
SUMMARY Traveltime tomography with shot-based eikonal equation fixes shot positions then relies on inversion to resolve any contradicting information between independent shots and achieve a possible cost-function minimum. On the other hand, the double-square-root (DSR) eikonal equation that describes the whole survey, while providing the same first-arrival traveltimes, allows not only the receivers but also the shots to change position and therefore leads to faster convergence in tomographic inversion. The DSR eikonal equation can be solved by a version of the fast-marching method (FMM) with special treatment for its singularity at horizontally traveling waves. For inversion, we use an upwind finite-difference scheme and the adjoint-state method to avoid explicit calculation of Fréchet derivatives. The proposed method generalizes to the 3D case straightforwardly.
- Geophysics > Seismic Surveying > Seismic Processing (1.00)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (0.47)
SUMMARY Seismic full-waveform inversion (FWI) (Tarantola, 1984) has gained much interest because of its ability to produce high-resolution earth models (Vigh and Starr, 2008; Virieux and Operto, 2009). However, the task of accurately recovering the geometry of salt bodies, typically found in geologically complex marine environments like the Gulf of Mexico, still presents a great challenge to FWI. Therefore, the salt geometry often must be manually picked by seismic interpreters, which is not only subjective but also a time-consuming and costly process. Better definition of the salt geometry has been shown to greatly improve imaging in the subsalt sedimentary regions, as shown by Vigh et al. (2010). In this paper, we present an approach to directly invert the geometry of the salt bodies, using FWI, by partitioning the inversion domain into salt and sediment regions and using a level set representation to parameterize the salt geometry.
- North America > United States (0.36)
- North America > Mexico (0.25)
Summary We introduce 3D Cauchy-type integrals that extend the classic theory of Cauchy integrals to 3D potential fields. In particular, we show how we are able to evaluate the gravity and gravity gradiometry responses of 3D bodies as surface integrals over arbitrary volumes that may have spatially variable densities. This entirely new method of 3D spatial-domain modeling is particularly suited to the terrain correction of airborne gravity gradiometry (AGG) data. The surface integrals are evaluated numerically on a topographically conforming grid with a resolution equal to the digital elevation model (DEM). Thus, our method directly avoids issues related to prismatic discretization of the digital elevation model, and their associated volume integration. We demonstrate this with a model study for AGG data simulated for a 1 Eö/vHz system over the Kauring test site in Western Australia.
- Information Technology > Software (0.48)
- Information Technology > Software Engineering (0.34)
Summary In this abstract, we describe how to improve time domain full waveform inversion using source wavelet convolution, windowed back propagation and source side illumination. Instead of estimating the source wavelet from field data, a user defined source wavelet can be convolved to field data. This convolution makes waveform matching between modeled and field data easier. Increasing time window applied to residual enables top down velocity update and reduces the possibility of being stuck at a local minimum. The balance of gradient value can be improved by the illumination compensation using the square of source side wavefield. Well balanced gradient helps FWI restore the absolute value of velocity. We apply this method to estimate migration velocities using 2D and 3D synthetic and real data examples.
- Geophysics > Seismic Surveying > Seismic Processing (1.00)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling > Seismic Inversion (0.68)
SUMMARY We present integrated geophysical data to characterize a geothermal system at Neal Hot Springs in eastern Oregon. This system is currently being developed for geothermal energy production. The hot springs are in a region of complex and intersecting fault trends associated with two major extensional events, the Oregon-Idaho Graben and the Western Snake River Plain. The intersection of these two fault systems, coupled with high geothermal gradients from thin continental crust produces pathways for surface water and deep geothermal water interactions at Neal Hot Springs. New geologic mapping, geochemistry and several boreholes in the area suggest a steeply dipping 60° normal fault dips to the southwest to form a half-graben basin. This basin-bounding fault serves as the primary conduit for deep water circulation. Potential field, electrical, and seismic data characterize this major fault along with other smaller scale structures in the area. A self-potential survey indicates that water is upwelling in the fault plane, and suggests that the fault does provide the means for heated water to migrate to the surface. Electrical and magnetic surveys offer methods to locate hydrothermal waters near the surface by identifying areas affected by hydrothermal waters.
- North America > United States > Idaho (0.74)
- North America > United States > Oregon (0.59)
- Geology > Structural Geology > Fault > Dip-Slip Fault > Normal Fault (1.00)
- Geology > Geological Subdiscipline (1.00)
- Geology > Structural Geology > Tectonics > Extensional Tectonics (0.92)
- Geophysics > Seismic Surveying (1.00)
- Geophysics > Magnetic Surveying (1.00)
- Geophysics > Gravity Surveying (1.00)