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Advanced Seismic Imaging GG 6770

Advanced Seismic Imaging GG 6770. Variance Analysis of Seismic Refraction Tomography Data. By Travis Crosby. Outline. Description of field experiment Description of refraction tomography processing and inversion Description of variance analysis Results of tomography experiment

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Advanced Seismic Imaging GG 6770

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  1. Advanced Seismic ImagingGG 6770 Variance Analysis of Seismic Refraction Tomography Data By Travis Crosby

  2. Outline • Description of field experiment • Description of refraction tomography processing and inversion • Description of variance analysis • Results of tomography experiment • Results of variance analysis

  3. Site Location Map

  4. Site Location Map SITE

  5. Line Location Map

  6. Seismic Data Acquisition Parameters Geophones - 120 40-Hz vertical component at 5 meter intervals. Source - Elastic Weight Drop with 550 pound hammer activated at 20 meter intervals (every 4th geophone). 31 total shot points per line. Five impacts summed per shot point. Recording - 0.5 ms sample rate, 2000 samples per trace, 1 second listening time.

  7. Seismic Refraction Data Common Shot Gather West East Created with Vista

  8. Seismic Data Processing Parameters - 3188 traveltimes picked (out of 3720 total) - 0.6 meter grid size - One dynamic smoothing schedule 21x11 30 iterations - 3.9 times more knowns (traveltimes) than unknowns (smoothing schedule) - Final residual 3.9 ms Residual vs Iteration

  9. Description of Variance Analysis - Velocity data was obtained from 30 inversions where first-arrival time was randomly altered up to ± 4 ms ( ¼ period of average first arrival). - The sample variance of each slowness cell over the 30 samples was determined. - The variance provides an idea of how widely spread the values of each slowness cell are likely to be. - The larger the variance, the more scattered the velocities are. It may be inferred that there is more uncertainty in these parts of the model. - Sample variance: S² = Σ (xi – xave)² / n-1

  10. Tomography Results – Original Data VelocityProfile Ray Density Plot

  11. with color thresholding Variance Results Variance Ray Density Plot

  12. without color thresholding Variance Results Variance Ray Density Plot

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