1. An Efficient Multiscale Method for Time-Domain Waveform Tomography C. Boonyasiriwat 1, P. Valasek 2, P. Routh 2, W. Cao 1, G.T. Schuster 1, and B. Macy 2 1 Department of Geology and Geophysics, University of Utah 2 Seismic Technology Development, ConocoPhillips

2. Outline 1 IntroductionIntroduction Efficient multiscale waveform tomographyEfficient multiscale waveform tomography Synthetic data resultsSynthetic data results 1D Model1D Model 2D Model2D Model Field data resultsField data results ConclusionsConclusions

3. Cons: Hamming window is a leaky, low-pass filter. Arbitrary frequency bands were used. 2 Introduction Pros and cons of the multiscale method proposed by Bunks et al. (1995): Pros: Partially overcome the local minima problem.

4. Outline 3 IntroductionIntroduction Efficient multiscale waveform tomographyEfficient multiscale waveform tomography Synthetic data resultsSynthetic data results 1D Model1D Model 2D Model2D Model Field data resultsField data results ConclusionsConclusions

5. 4 Efficient Multiscale Waveform Tomography We propose: more efficient low-pass filtersmore efficient low-pass filters a strategy for choosing optimal frequency bandsa strategy for choosing optimal frequency bands

6. Efficient Low-Pass Filters 5 Hamming Blackman-Harris Ricker Original

7. Strategy for Choosing Optimal Frequencies 11 Sirgue and Pratt (2004) proposed a formula for choosing frequencies: where f n is the current frequency, f n+1 is the next frequency to be chosen, and h = maximum half-offset z = maximum depth to be imaged

8. 12 At the current frequency f n, the updated vertical wavenumber range is determined by where c o is the homogeneous background velocity. Strategy for Choosing Optimal Frequencies

9. Gradient Vector Gradient vector Assumptions Amplitude effects may be ignored Reference medium is homogeneous We are in the far field 2

10. Wavenumber Illumination where 3

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13. 6 Strategy for Choosing Optimal Frequencies Image from Sirgue and Pratt (2004)

14. Strategy for Choosing Optimal Frequency Bands 7

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16. Outline 9 IntroductionIntroduction Efficient multiscale waveform tomographyEfficient multiscale waveform tomography Synthetic data resultsSynthetic data results 1D Model1D Model 2D Model2D Model Field data resultsField data results ConclusionsConclusions

17. 1D Model 10 Depth (km) Velocity (m/s)

18. 1D Model 11

19. 2D Model 12 3500 3000 2500

20. 2D Model 13

21. Outline 14 Goals of studyGoals of study Overview and introductionOverview and introduction Efficient multiscale waveform tomographyEfficient multiscale waveform tomography Synthetic data resultsSynthetic data results 1D Model1D Model 2D Model2D Model Field data resultsField data results ConclusionsConclusions

22. 515 Shots 480 Hydrophones 12.5 m dt = 2 ms T max = 10 s 15 Gulf of Mexico Data

23. Reconstructed Velocity 16

24. Kirchhoff Migration Images 17

25. Comparing CIGs 18

26. Outline 19 Goals of studyGoals of study Overview and introductionOverview and introduction Efficient multiscale waveform tomographyEfficient multiscale waveform tomography Synthetic data resultsSynthetic data results 1D Model1D Model 2D Model2D Model Field data resultsField data results ConclusionsConclusions

27. 20 Conclusions An efficient MWT method was developed.An efficient MWT method was developed. Increased efficiency is achieved by using efficient low-pass filters and optimal frequency bands.Increased efficiency is achieved by using efficient low-pass filters and optimal frequency bands. The strategy for choosing frequency bands was validated in both 1D and 2D synthetic model experiments.The strategy for choosing frequency bands was validated in both 1D and 2D synthetic model experiments. Marine data results are promising.Marine data results are promising.