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Thesis

Multiscale Seismology: the future of inversion W. MENKE Lamont-Doherty Earth Observatory Columbia University E. CHESNOKOV and R.L. BROWN Institute for Theoretical Geophysics University of Oklahoma. Thesis

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Thesis

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  1. Multiscale Seismology:the future of inversionW. MENKELamont-Doherty Earth Observatory Columbia UniversityE. CHESNOKOV and R.L. BROWNInstitute for Theoretical Geophysics University of Oklahoma

  2. Thesis The past 15 years has seen a tremendous improvement in the fidelity of many types of seismic images. This improvement was driven by, more and higher quality seismometers, faster computers, better data archiving and processing methodologies. But our ability to integrate knowledge from multiple data types hasn’t kept up. Often different data types are telling us seemingly-contradictory things.

  3. Example: Surface Wave Tomography e.g. of North America

  4. Woodward and Snieder, 1993 275 seismograms

  5. Zhang & Tanimoto, 1993 18,000 seismograms globally, about 324 prorated for area

  6. 685 seismograms

  7. 400,000 seismograms globally, about 7,200 prorated for areanote inversion includes transverse anisotropy

  8. “Exponential” growth of data ! Images better & better in evolutionary way

  9. But how do these impressive imagesconnect withother things we know about the earth?

  10. Connection 1Continental Scale Body Wave Traveltimes

  11. Surface wave models have big asthenospheric LVZ’s that imply very large shadow zones Are such shadows actually observed in continental-scale P or S waves?

  12. Connection 2SKS Shear Wave Splitting

  13. North America has large amount of transverse anisotropy From Gaherty

  14. Correctly predicts large Love-Rayleigh discrepancy along paths parallel to MOMA Array Predicts

  15. But inconsistent with SKS splitting results along MOMA array Fouch’s splitting data as plotted by Gaherty No plausible anisotropic material can have fast-axis parallel to array and have large Love-Rayleigh discrepancy parallel to the array, too

  16. More overlap in parameters than length scale !

  17. Hypothesis: differentlength scalesstrongly influence interpretation

  18. Length scale of Length scale of EARTH OBSERVATION (seismic waves) Strong Spooky Interactions Length scale of INVERSION

  19. we understand this interactionpretty well(but only in very idealized media) Length scale of Length scale of OBSERVATION EARTH (seismic waves) strong spooky interactions

  20. WHAT IS THE STRUCURE OF THIS MEDIUM ? bulk modulus 1 shear modulus 1, density 1 thickness 1 bulk modulus 2 shear modulus 2 density 2 thickness 2

  21. WHAT IS THE STRUCTURE OF THIS MEDIUM ? Inhomogenous with various properties of isotropic layers? YES ! when l<<thickness

  22. WHAT IS THE STRUCTURE OF THIS MEDIUM ? Strongly Scattering? YES ! when l~thickness

  23. WHAT IS THE STRUCURE OF THIS MEDIUM ? Effectively homogeneous and anisotropic? YES ! when l>>thickness

  24. Theory for understanding this effect in 3-D media with random heterogeneities is well developed … Elasticity and density written in terms of average and deviation from average

  25. 1. elasticity and density are frequency-dependent 2. integrals embody interaction of wavefield with scale length of heterogeneities … • Chesnokov et al. 2000 3. … through correlation functions weird! effective density is a tensor ..

  26. “UPSCALING” ExampleReconciling Sonic Log with VSP Collect Sonic Logs (500 Hz) of Vp, Vs1, Vs2, density Infer all components of Cijkl(f=500 Hz) Compute Correlation Functions Is this Inversion? Not quite … Predict Cijkl(f=50 Hz) Compare with VSP (50 Hz) experiment

  27. Result for C55 Sonic Log VSP Predicted VSP

  28. theorycan beextendedto includemore complicated micro-physicse.g.fluid/rockinteractions

  29. Length scale of There’s been some interesting efforts on this side of the triangle, too OBSERVATION strong spooky interactions Length scale of INVERSION

  30. Results of Slip Inversions Highly Dependent on Scale of Model Representation True Slip on Hypothetical Fault Three Inversions That Fit the Data Equally Well Courtesy of Morgan Page

  31. A Challenge of the Future Create Earth knowledge that practitioners using different techniques AGREE UPON !

  32. Length scale of OBSERVATION (seismic waves) Length scale of EARTH Joint Inversions that handle multiple scales in a Physics-Based way Length scale of INVERSION

  33. Business as Usual The Future ? Scale1 Data Scale1 Data Scale2 Data Scale2 Data physics-based parameterization 1 Ad-hoc parameterization 1 Ad-hoc parameterization 2 feedback Speculative attempts to integrate and reconcile results Assessment of underlying physics Improved knowledge of earth confusion ?!

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