Elastic imaging and time-lapse migration based on adjoint methods

Geophysics ◽  
2009 ◽  
Vol 74 (6) ◽  
pp. WCA167-WCA177 ◽  
Author(s):  
Hejun Zhu ◽  
Yang Luo ◽  
Tarje Nissen-Meyer ◽  
Christina Morency ◽  
Jeroen Tromp
Keyword(s):  
Wave Speed ◽  
Time Lapse ◽  
Compressional Wave ◽  
Finite Frequency ◽  
Adjoint Methods ◽  
Transmission Tomography ◽  
Efficient Simulation ◽  
Sensitivity Kernel ◽  
Adjoint Tomography ◽  
Exploration Seismology

We have drawn connections between imaging in exploration seismology, adjoint methods, and emerging finite-frequency tomography. All of these techniques rely on spatial and temporal constructive interference between observed and simulated waveforms to map locations of structural anomalies. Modern numerical methods and computers have facilitated the accurate and efficient simulation of 3D acoustic, (an)elastic, and poroelastic wave propagation. Using a 2D cross section of the SEG/EAGE salt model, we have determined how such waveform simulations might be harnessed to improve onshore and offshore seismic imaging strategies and capabilities. We have found that the density sensitivity kernel in adjoint tomography is related closely to the imaging principle in exploration seismology, and that in elastic modeling the impedance kernel actually is a better diagnostic tool for reflector identification. The shear- and compressional-wave speed sensitivity kernels in adjoint tomography are related closely to finite-frequency banana-doughnut kernels, and these kernels are well suited for mapping larger-scale structure, i.e., for transmission tomography. These ideas have been substantiated by addressing problems in subsalt time-lapse migration.

Targeted stacking of weak seismic phases for improving mantle discontinuity imaging using full-waveform inversion

2021 ◽  
Author(s):  
Maria Koroni ◽  
Andreas Fichtner
Keyword(s):  
Seismic Waves ◽  
Waveform Inversion ◽  
Real Data ◽  
Full Waveform Inversion ◽  
Finite Frequency ◽  
Adjoint Methods ◽  
Frequency Sensitivity ◽  
Full Waveform ◽  
Discontinuity Structure ◽  
Mantle Discontinuity

<p>This study is a continuation of our efforts to connect adjoint methods and full-waveform inversion to common beamforming techniques, widely used and developed for signal enhancement. Our approach is focusing on seismic waves traveling in the Earth's mantle, which are phases commonly used to image internal boundaries, being however quite difficult to observe in real data. The main goal is to accentuate precursor waves arriving in well-known times before some major phase. These waves generate from interactions with global discontinuities in the mantle, thus being the most sensitive seismic phases and therefore most suitable for better understanding of discontinuity seismic structure. </p><p>Our work is based on spectral-element wave propagation which allows us to compute exact synthetic waveforms and adjoint methods for the calculation of sensitivity kernels. These tools are the core of full-waveform inversion and by our efforts we aim to incorporate more parts of the waveform in such inversion schemes. We have shown that targeted stacking of good quality waveforms arriving from various directions highlights the weak precursor waves. It additionally makes their traveltime finite frequency sensitivity prominent. This shows that we can benefit from using these techniques and exploit rather difficult parts of the seismogram.  It was also shown that wave interference is not easily avoided, but coherent phases arriving before the main phase also stack well and show on the sensitivity kernels. This does not hamper the evaluation of waveforms, as in a misfit measurement process one can exploit more phases on the body wave parts of seismograms.</p><p>In this study, we go a step forward and present recent developments of the approach relating to the effects of noise and a real data experiment. Realistic noise is added to synthetic waveforms in order to assess the methodology in a more pragmatic scenario. The addition of noise shows that stacking of coherent seismic phases is still possible and the sensitivity kernels of their traveltimes are not largely distorted, the precursor waves contribute sufficiently to their traveltime finite-frequency sensitivity kernels.<br>Using a well-located seismic array, we apply the method to real data and try to examine the possibilities of using non-ideal waveforms to perform imaging of the mantle discontinuity structure on the specific areas. In order to make the most out of the dense array configuration, we try subgroups of receivers for the targeted stacking and by moving along the array we aim at creating a cluster of stacks. The main idea is to use the subgroups as single receivers and create an evaluation of seismic discontinuity structure using information from each stack belonging to a subgroup. <br>Ideally, we aim at improving the tomographic images of discontinuities of selected regions by exploiting weaker seismic waves, which are nonetheless very informative.</p>

scholarly journals A New Compressional Wave Speed Inversion Method Based on Granularity Parameters

IEEE Access ◽  
2019 ◽  
Vol 7 ◽  
pp. 185849-185856 ◽  
Author(s):  
Jingqiang Wang ◽  
Zhengyu Hou ◽  
Guanbao Li ◽  
Guangming Kan ◽  
Xiangmei Meng ◽  
...  
Keyword(s):  
Wave Speed ◽  
Compressional Wave ◽  
Inversion Method

Finite-frequency traveltime tomography using the Generalized Rytov approximation

2020 ◽  
Vol 221 (2) ◽  
pp. 1412-1426 ◽  
Author(s):  
B Feng ◽  
W Xu ◽  
R S Wu ◽  
X B Xie ◽  
H Wang
Keyword(s):  
Convergence Rate ◽  
Large Scale ◽  
Frequency Theory ◽  
Seismic Exploration ◽  
Finite Frequency ◽  
Traveltime Tomography ◽  
Sensitivity Kernel ◽  
Rytov Approximation ◽  
Weak Scattering ◽  
Small Phase

SUMMARY Wave-equation-based traveltime tomography has been extensively applied in both global tomography and seismic exploration. Typically, the traveltime Fréchet derivative is obtained using the first-order Born approximation, which is only satisfied for weak velocity perturbations and small phase shifts (i.e. the weak-scattering assumption). Although the small phase-shift restriction can be handled with the Rytov approximation, the weak velocity-perturbation assumption is still a major limitation. The recently developed generalized Rytov approximation (GRA) method can achieve an improved phase accuracy of the forward-scattered wavefield, in the presence of large-scale and strong velocity perturbations. In this paper, we combine GRA with the classical finite-frequency theory and propose a GRA-based traveltime sensitivity kernel (GRA-TSK), which overcomes the weak-scattering limitation of the conventional finite-frequency methods. Numerical examples demonstrate that the accumulated time delay of forward-scattered waves caused by large-scale smooth perturbations can be correctly handled by the GRA-TSK, regardless of the magnitude of the velocity perturbations. Then, we apply the new sensitivity kernel to solve the traveltime inverse problem, and we propose a matrix-free Gauss–Newton method that has a faster convergence rate compared with the gradient-based method. Numerical tests show that, compared with the conventional adjoint traveltime tomography, the proposed GRA-based traveltime tomography can obtain a more accurate model with a faster convergence rate, making it more suited for recovering the large-intermediate scale of the velocity model, even for strong-perturbation and complex subsurface structures.

scholarly journals Finite-frequency sensitivity of surface waves to anisotropy based upon adjoint methods

2007 ◽  
Vol 168 (3) ◽  
pp. 1153-1174 ◽  
Author(s):  
Anne Sieminski ◽  
Qinya Liu ◽  
Jeannot Trampert ◽  
Jeroen Tromp
Keyword(s):  
Surface Waves ◽  
Finite Frequency ◽  
Adjoint Methods ◽  
Frequency Sensitivity
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