Interferometric Extraction of SSP from Passive Seismic Data

1. Interferometric Extraction of SSP from Passive Seismic Data Yanwei Xue Feb. 7, 2008

2. OUTLINE • Motivation • Theory • Field data test • Conclusions and the way ahead

3. Motivation Why? • No individual experiment required • Can get Green’s function between two randomly selected receivers How? • Interferometric Transform

4. OUTLINE • Motivation • Theory • Field data test • Conclusions and the way ahead

5. S 0 . . A B P(B) =∫ G(B|x)N(x)d x 2 S src Im[G(A|B)] = k<p(A)*p(B)> = k∫ G(B|x)G(A|x)*d x x 2 S src z x’ S src Random Sources <N(x)*N(x’)> =δ(x-x’)S(ω)

6. Random Scatterers

7. Input data d Truncate d in time into several data panels Crosscorrelate each trace with a given trace at x Output Sum and average the crosscorrelation panels Workflow

8. OUTLINE • Motivation • Theory • Field data test • Conclusion and the way ahead

9. Data Introduction Receiver position 8 receiver lines 779 receivers Receiver interval: 27 - 30 m 6100 3 4 2 Y (m) 5 1 6 8 7 0 0 6100 X (m)

10. Trace Example Amplitude 0 Time (s) 960

11. 0.0 Time (s) 2.4 X (m) 2500 0 Virtual Shot Gather Receiver line 6 90 receivers Frequency used to do the interferometry is 1 - 11.5 Hz Event velocity 1450 m/s

12. 0.0 Time (s) 2.4 X (m) 2500 0 Virtual Shot Gather Receiver line 6 90 receivers Frequency used: 1 – 9 Hz Event velocity 1450 m/s

13. 0.0 Time (s) 2.4 X (m) 2500 0 Virtual Shot Gather Receiver line 8 95 receivers Frequency used: 1 - 9 Hz Event velocity 1455 m/s

14. 0.0 Time (s) 2.4 X (m) 2500 0 Virtual Shot Gather Receiver line 2 90 receivers Frequency used: 1 - 5 Hz

15. 0.0 Time (s) 2.4 X (m) 2500 0 Virtual Shot Gather Receiver line 2 90 receivers Frequency used: 1 - 44 Hz Left-going events removed

16. OUTLINE • Introduction • Theory • Field data test • Conclusions and the way ahead

17. Conclusions • Field data test gives continuous events • Low frequency results have a velocity of 1450 m/s • High frequency (1 - 44 Hz) results look like reflections • We need records with longer time to get better results

18. Road Ahead • Test the data with longer time records • Velocity analysis of the virtual gathers • Migrate the virtual data

19. Thanks!