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Slope tomography based on eikonal solvers and the adjoint-state method
- Source :
- Geophysical Journal International, Geophysical Journal International, Oxford University Press (OUP), 2017, 209 (3), pp.1629-1647. ⟨10.1093/gji/ggx111⟩, Geophysical Journal International, 2017, 209 (3), pp.1629-1647. ⟨10.1093/gji/ggx111⟩
- Publication Year :
- 2017
- Publisher :
- HAL CCSD, 2017.
-
Abstract
- International audience; Velocity macromodel building is a crucial step in the seismic imaging workflow as it provides the necessary background model for migration or full waveform inversion. In this study, we present a new formulation of stereotomography that can handle more efficiently long-offset acquisition, complex geological structures and large-scale data sets. Stereotomography is a slope tomographic method based upon a semi-automatic picking of local coherent events. Each local coherent event, characterized by its two-way traveltime and two slopes in common-shot and common-receiver gathers, is tied to a scatterer or a reflector segment in the subsurface. Ray tracing provides a natural forward engine to compute traveltime and slopes but can suffer from non-uniform ray sampling in presence of complex media and long-offset acquisitions. Moreover, most implementations of stereotomography explicitly build a sensitivity matrix, leading to the resolution of large systems of linear equations, which can be cumbersome when large-scale data sets are considered. Overcoming these issues comes with a new matrix-free formulation of stereotomography: a factored eikonal solver based on the fast sweeping method to compute first-arrival traveltimes and an adjoint-state formulation to compute the gradient of the misfit function. By solving eikonal equation from sources and receivers, we make the computational cost proportional to the number of sources and receivers while it is independent of picked events density in each shot and receiver gather. The model space involves the subsurface velocities and the scatterer coordinates, while the dips of the reflector segments are implicitly represented by the spatial support of the adjoint sources and are updated through the joint localization of nearby scatterers. We present an application on the complex Marmousi model for a towed-streamer acquisition and a realistic distribution of local events. We show that the estimated model, built without any prior knowledge of the velocities, provides a reliable initial model for frequency-domain FWI of long-offset data for a starting frequency of 4 Hz, although some artefacts at the reservoir level result from a deficit of illumination. This formulation of slope tomography provides a computationally efficient alternative to waveform inversion method such as reflection waveform inversion or differential-semblance optimization to build an initial model for pre-stack depth migration and conventional FWI.
- Subjects :
- Mathematical optimization
Seismic tomography
010504 meteorology & atmospheric sciences
Computer science
Geophysical imaging
Eikonal equation
[SDU.STU]Sciences of the Universe [physics]/Earth Sciences
Inversion (meteorology)
Solver
010502 geochemistry & geophysics
System of linear equations
01 natural sciences
Geophysics
Numerical modelling
Geochemistry and Petrology
Adjoint state method
Tomography
Inverse theory
Algorithm
0105 earth and related environmental sciences
Subjects
Details
- Language :
- English
- ISSN :
- 0956540X and 1365246X
- Database :
- OpenAIRE
- Journal :
- Geophysical Journal International, Geophysical Journal International, Oxford University Press (OUP), 2017, 209 (3), pp.1629-1647. ⟨10.1093/gji/ggx111⟩, Geophysical Journal International, 2017, 209 (3), pp.1629-1647. ⟨10.1093/gji/ggx111⟩
- Accession number :
- edsair.doi.dedup.....3883cb9d81ae1009ae567b2660c46cad
- Full Text :
- https://doi.org/10.1093/gji/ggx111⟩