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Determination of anisotropic ice fabric using seismic data

Determination of anisotropic ice fabric using seismic data. Anja Diez, Olaf Eisen, Coen Hofstede, Ilka Weikusat , Ulrich Polom , Thomas Bohlen, Astrid Lambrecht , Christoph Mayer, Heinrich Miller . Overview. Crystal orientation fabric (COF) & elasticity tensor

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Determination of anisotropic ice fabric using seismic data

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  1. Determination ofanisotropicicefabricusingseismicdata Anja Diez, Olaf Eisen, Coen Hofstede, Ilka Weikusat, Ulrich Polom, Thomas Bohlen, Astrid Lambrecht, Christoph Mayer, Heinrich Miller

  2. Overview • Crystal orientation fabric (COF) & elasticity tensor • example: vertical single maximum fabric • connection: eigenvalues – elasticity tensor • Kohnen station • vertical seismic profiling • comparison COF – seismic – radar • ColleGnifetti • velocity analysis • derivation of anisotropy COF & elasticitytensor- Kohnen - Colle Gnifetti

  3. Seismicanisotropy c-axis COF & elasticitytensor- Kohnen - Colle Gnifetti • Ice core: COF eigenvalues: ʎ1< ʎ2< ʎ3 • Radar: linear relationtodielectricconstant ɛ‘ • Seismic: dependence on elasticity tensor Cij

  4. Depthconversion 20% stacking velocity ≠ depth conversion velocity 7% Example: verticalsinglemax NMO-velocities (interval) Thomsen parameterδ, γ COF & elasticitytensor- Kohnen - Colle Gnifetti

  5. Connection Cij for different fabrics Measured Cij Measured eigenvalues Integration uniform distribution (Nanthikesan, 1994) COF & elasticitytensor- Kohnen - Colle Gnifetti

  6. COF → Elasticitytensor Data: Kohnen COF & elasticitytensor- Kohnen - Colle Gnifetti

  7. Kohnen station • Kohnen Station • Dronning Maud Land • ~ 750 km southeastofNeumayer III • EDML (length 2774 m) • Seismic • profile, wideangle, verticalseismicprofiling • explosives, vibroseis • Radar • 60, 600 ns pulse COF & elasticitytensor - Kohnen - Colle Gnifetti

  8. VSP dataset Detonation cord: • depth 2580 - 100 m • 40m intervals COF & elasticitytensor - Kohnen - Colle Gnifetti

  9. VSP-velocities COF & elasticitytensor - Kohnen - Colle Gnifetti

  10. Comparisonelasticitytensors • Best agreement • Gammon (1983) • Jona (1952) • Bennett (1968) • Gusmeroli (2012, JGR) • Boreholesoniclogging 23 kHz • Best agreement: Dantl (1968) Dependencyofseismicwaves on frequency COF & elasticitytensor - Kohnen - Colle Gnifetti

  11. Stackedtraces Englacialreflections? Stackedtrace COF & elasticitytensor - Kohnen - Colle Gnifetti

  12. Core – Seismic – Radar COF & elasticitytensor - Kohnen - Colle Gnifetti

  13. ColleGnifetti • ColleGnifetti • Switzerland • 4500 m a.s.l. • KCI icecore (length 62 m) • Seismicdata • profile • ElViS: P- and SH-wave • Radar data COF & elasticitytensor - Kohnen - Colle Gnifetti

  14. ElViSreflections • stacking = depthconversionvelocity COF measurements COF & elasticitytensor - Kohnen - Colle Gnifetti

  15. Depthshift 7% 1% COF & elasticitytensor - Kohnen - Colle Gnifetti • Seismics:VElViS • KCI: VRMS,P0 VNMO • density • temperature • COF • Bed reflection P-wave depth difference → 4 m

  16. Connecting seismics & radar Seismic VNMO Radar → depth VRMS,P0 COF & elasticitytensor - Kohnen - Colle Gnifetti derive interval δ

  17. Derivinganisotropy COF & elasticitytensor - Kohnen - Colle Gnifetti

  18. Conclusion Seismics& Radar Integration Connection Evaluation Comparison Derivation COF & elasticity tensor - Kohnen - Colle Gnifetti

  19. ThankYou! Thanksto: Pascal Bohleber, Reinhard Drews, Günther Druivenga, Jens Eichler, Sepp Kipfstuhl, Daniel Steinhage andthe Kohnen logisticteam COF & elasticity tensor - Kohnen - Colle Gnifetti

  20. COF & elasticity tensor - Kohnen - Colle Gnifetti

  21. VSP-velocities Temperature correction gradient 2.3 m/s/K COF & elasticity tensor - Kohnen - Colle Gnifetti

  22. Radar COF & elasticity tensor - Kohnen - Colle Gnifetti

  23. COF – Seismic – Radar COF & elasticity tensor - Kohnen - Colle Gnifetti

  24. Vibro COF & elasticity tensor - Kohnen - Colle Gnifetti

  25. Picked velocities VNMO COF & elasticity tensor - Kohnen - Colle Gnifetti

  26. Calculated velocities VRMS,P0 COF & elasticity tensor - Kohnen - Colle Gnifetti

  27. Girdle orientation COF & elasticity tensor - Kohnen - Colle Gnifetti

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