Seismic Imaging: How we use waves to see the interior of the earth

1. Seismic Imaging: How we use waves to see the interior of the earth Apache Symposium on Imaging November 6, 2008 Y. C. Kim, TGS-NOPEC

2. Outline • Reflection of waves • Seismic imaging using wave equation • Challenges in seismic imaging • Summary

3. Reflection of Waves or

4. Seismic Data Acquisition Known: Unknown:

5. One-Way Wave Equation Wave equation: One-way wave equation: Downward continuation: Reflectivity using OWWE:

6. Reverse Time Migration Wave equation: Reflectivity:

7. Subsurface Image RTM

8. Parameter scan Challenges in Seismic Imaging • Compute resources • Compute cycle • Memory requirements (~10 GB) • Data storage (> 100 TB) • Earth model building • Velocities • Anisotropic parameters

9. Earth is Anisotropic! Isotropic Model Anisotropic Model

10. Parameter Scan • Velocity scan • Brute force method • Get what you see • Computationally high cost • Imaging condition scan • Scan for focusing • Get better focused image, but mispositioned • Computationally low cost

11. 4 Depth (km) 8 12 Image Before WEM Scan

12. 4 Depth (km) 8 12 Image After WEM Scan

13. Imaging Condition Scan By scanning either ∆x or ∆t, one can compensate for misfocusing due to velocity errors

14. 1 Depth (km) 6 11 Conventional WEM Image

15. 1 Depth (km) 6 11 WEM Image with Imaging Time Scan

16. Summary • Seismic imaging uses reflections for imaging the earth’s interior • Wavefields in the subsurface are computed using wave equation • Use scanning techniques to mitigate errors in model parameters