Elastic Green's theorem preprocessing for on-shore internal multiple attenuation: theory and initial synthetic data tests Jing Wu* and Arthur B. Weglein May 28th, 2014 Austin, TX 1 1
( Bahareh Boustani et al. 2013 ) Problem ( Bahareh Boustani et al. 2013 ) Ground Roll (Rayleigh Wave)
( Bahareh Boustani et al. 2013 ) Problem Reference wave Green’s theorem Ground Roll (Rayleigh Wave) ( Bahareh Boustani et al. 2013 )
( Bahareh Boustani et al. 2013 ) Problem Elastic Green’s theorem Reference wave Ground Roll (Rayleigh Wave) ( Bahareh Boustani et al. 2013 )
Elastic Green’s theorem reference wave prediction Theory of Elastic Green’s theorem reference wave prediction
Actual medium Experiment Reference medium Perturbation Active source ( “Passive source” ) “Source”
Off-shore: reference medium Air Water ( Acoustic ) F. S.
Off-shore: reference medium M. S. F. S. Air Water ( Acoustic )
Off-shore: reference medium + “source” Earth M. S. F. S. Air Water ( Acoustic )
Off-shore: reference wave M. S. F. S. Earth Air Water ( Acoustic ) ( Weglein and Secrest 90; Weglein 02; J. Zhang 05, 06, 07; Mayhan 12, 13; L. Tang 13 )
Off-shore: reference wave M. S. F. S. Earth Air Water ( Acoustic ) ( Weglein and Secrest 90; Weglein 02; J. Zhang 05, 06, 07; Mayhan 12, 13; L. Tang 13 )
On-shore: reference medium Elastic F. S. Air
On-shore: reference medium M. S. F. S. Elastic Air
On-shore: reference medium + “source” Elastic M. S. F. S. Air Earth
On-shore: reference wave M. S. F. S. Elastic Air Earth
On-shore: reference wave M. S. F. S. Elastic Air Earth
On-shore: reference wave M. S. F. S. Elastic Air Earth
On-shore: reference wave prediction in (x,)
On-shore: reference wave prediction in (x,) ( Stolt & Weglein 1992, 2012 )
On-shore: reference wave prediction in (x,) ( Stolt & Weglein 1992, 2012 )
M. S. F. S. Elastic Air
F. S. Elastic Air M. S.
F. S. Elastic Air M. S.
F. S. Elastic Air M. S.
F. S. Elastic Air M. S.
F. S. Elastic Air M. S.
F. S. Elastic Air M. S.
On-shore: reference wave prediction in (kx,) Assuming M.S. is horizontal
On-shore: reference wave prediction in (kx,) M. S. F. S. Elastic Air Earth
Wavelet Estimation or
Numerical Evaluation
Water (acoustic) /elastic model --- OBC Zs = -10 m O. B. 0m M.S. 1 m Elastic Water Layer P Velocity (m/s) S Velocity (m/s) Density (kg/m3) 1 1500 1000 2 1700 700 2000
Water (acoustic) /elastic model --- OBC Zs = -10 m O. B. 0m M.S. 1 m Elastic Water Layer P Velocity (m/s) S Velocity (m/s) Density (kg/m3) 1 1500 1000 2 1700 700 2000
Reference wave prediction in water/earth: P wave component Scholte wave Input data P Predicted Reference wave P0 P-P0
Actual wavelet
Estimated wavelet from P0
Reference wave prediction in water/earth: S wave component Input data S Predicted Reference wave S0 S-S0 Scholte wave
Actual wavelet
Estimated wavelet from S0
Air/elastic model --- On shore Zs = 0 m F. S. 0m M.S. 1 m Elastic Layer P Velocity (m/s) S Velocity (m/s) Density (kg/m3) 1 340 3 2 2200 1200 2000
Reference wave prediction in air/earth: P wave component Input data P Predicted Reference wave P0 P-P0 Rayleigh wave
Reference wave prediction in air/earth: S wave component Input data S Predicted Reference wave S0 S-S0 Rayleigh wave
The elastic Green’s theorem method Summary The elastic Green’s theorem method Predicts reference wave Estimates the wavelet Removes the ground roll without damaging the reflection data
Discussion & Future research Data requirements ( Weglein & Secrest 1990; Weglein, Keho & Secrest 1990; Corrigan, Weglein & Thompson 1991 )
Discussion & Future research Back out near surface properties (L. Tang et al.)
Discussion & Future research Extend to near surface with lateral variance
Thank you Comments/Questions?
Appendix
For isotropic homogeneous medium
(ux,uz) space to (P,S) space For isotropic homogenous medium (Weglein and Stolt 1992, Zhang 2006)
For actual medium (inhomogeneous)
For actual medium (inhomogeneous)
Green’s Function Reference medium Air Boundary Elastic
Air Boundary Elastic P S
P Air Boundary Elastic S
Elastic Air Boundary S P
Boundary condition At two sides of the boundary (z=0) (Aki & Richards, 2002) Air Boundary Elastic
The constitutive relation
The constitutive relation
The constitutive relation
Air Boundary at depth 0 Elastic P S
When z0, by using the boundary condition, The coefficients can be confirmed. air elastic
Air Boundary at depth 0 Elastic P S
With boundary condition at z=0 air elastic
Air Boundary at depth 0 Elastic S P
With boundary condition at z=0 air elastic
If both source and receiver are below the boundary
Green’s theorem reference wavefield prediction derivation
Air Earth m.s. v e.s.
Green’s Second Identity
Green’s Second Identity
Reference wave prediction in (x, )
Reference wave prediction in (kx, )
Reference wave prediction in (kx, )
Reciprocity of Green’s function
Even, only real part left
Odd, only image part left
Appendix
Boundary condition (acoustic/elastic) Displacement X: viscid is low along the boundary, can be discontinuous; Z: no cavitation in the earth along the boundary, continuous. Traction Same magnitudes and opposite directions;
At two side of the boundary (z=0) Boundary condition Air Boundary Elastic At two side of the boundary (z=0)