Processing and Binning Overview

1. Processing and Binning Overview From chapter 14 “Elements of 3D Seismology” by Chris Liner

2. Outline • Justification for Processing • Processing Flow • Bins

3. Justification Field data representation of the data is distant from a distance-depth representation of data.

5. Categories of Processing • Adjustments to wavelets, or short-pulse adjustments e.g., • frequency filtering • phase shifts (rotation) • vibroseis correlation • Traveltime Corrections (fig. 14.1) : • Statics • Normal Moveout • Dip Moveout • Migration

6. Categories of Processing • Amplitude Corrections • Geometric spreading • Automatic Gain Control • Noise Reduction • Vertical stack • Muting • CMP stack • filtering (f, f-k, tau-p (or radon) • multiple suppression

7. An example of analysis for near-surface seismic structure Xia et al., 2004

8. Seismic data “Multiple universes for seismic data” • Shotpoint gathers (distance versus time) • CMP gathers (distance versus time) • Tau-p (horizontal slowness versus intercept time) • f-k (frequency versus wavenumber)

9. Distance between shot and the receiver (m) Two-way traveltime (s)

10. Velocity (m/s) Distance between shot and the receiver (m) Two-way traveltime (s) T0 dT/dx = 1/V (s/m) T2 = T02 + x2/ V2

11. Velocity (m/s) Distance between shot and the receiver (m) Two-way traveltime (s) T0 dT/dx = 1/V (s/m) T2 = T02 + x2/ V2

12. x V dT/dx = 1/V (s/m) 1/V = 0 ( s/m) 1/V = p (ray parameter)

13. Velocity (m/s) Distance between shot and the receiver (m) Two-way traveltime (s) T0 dT/dx = 1/V (s/m) T2 = T02 + x2/ V2

14. x V angle dT/dx = 1/Vh (s/m) 1/Vh = 1/[V/ sin(angle) ] ( s/m) 1/Vh = p (ray parameter)

15. Velocity (m/s) Distance between shot and the receiver (m) Two-way traveltime (s) T0 dT/dx = 1/V (s/m) T2 = T02 + x2/ V2

16. x angle V 1/Vh = 1/[V/sin(angle) ]( s/m) 1/Vh = p (ray parameter)

17. p (s/m) x (m) Two-way traveltime (s) tau (intercept time) s p=0 T0 Add amplitude

18. p (s/m) x (m) Two-way traveltime (s) tau (intercept time) s p=0 T0 Add amplitude

19. f (1/s) x (m) Two-way traveltime (s) k (wavenumber - 1/m) p=0 1000m/s V=f/k (m/s) 1/10 m 100 Hz

20. f (1/s) x (m) Two-way traveltime (s) k (wavenumber - 1/m) p=0 1000m/s V=f/k (m/s) 1/10 m 100 Hz

21. f (1/s) x (m) Two-way traveltime (s) k (wavenumber - 1/m) Vh=1000 (m/s) Vh=inf (m/s) Vh=1000 (m/s) Vh=inf (m/s)

22. Sz Sx P-wave & Sv -wave

23. Vh ~= 90% shear wave velocity “skin depth” = 1/2 longest wavelength

24. Dispersion t1 t2 t0 t1 t2 Dispersion

25. Xia et al., 2004

26. f (1/s) x (m) Two-way traveltime (s) k (wavenumber - 1/m) p=0 1000m/s V=f/k (m/s) 100 Hz

27. Outline Bins Calculated common midpoints “CMP bin center” Length and width of bin <= spatial aliasing dimensions

28. To prevent aliasing: max dimension = V/4fmax For GOM: V = V0 + 0.4 x depth Rule of Thumb: 12.5m by 12.5 m for > 2000 m IDEAL BIN SIZE: 5m by 5m for seafloor and deeper

29. The “best” bin: • SMALL • ALL OFFSETS • ALL AZIMUTHS • LARGE FOLD

30. Outline • Justification for Processing • Processing Flow • Bins