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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

Determination ofanisotropicicefabricusingseismicdata

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

overview
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

seismic anisotropy
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

depth conversion
Depthconversion

20%

stacking velocity

depth conversion velocity

7%

Example: verticalsinglemax

NMO-velocities (interval)

Thomsen parameterδ, γ

COF & elasticitytensor- Kohnen - Colle Gnifetti

connection
Connection

Cij for different fabrics

Measured Cij

Measured eigenvalues

Integration

uniform distribution

(Nanthikesan, 1994)

COF & elasticitytensor- Kohnen - Colle Gnifetti

cof elasticity tensor
COF → Elasticitytensor

Data: Kohnen

COF & elasticitytensor- Kohnen - Colle Gnifetti

kohnen station
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

vsp dataset
VSP dataset

Detonation cord:

  • depth 2580 - 100 m
  • 40m intervals

COF & elasticitytensor - Kohnen - Colle Gnifetti

vsp velocities
VSP-velocities

COF & elasticitytensor - Kohnen - Colle Gnifetti

comparison elasticity tensors
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

stacked traces
Stackedtraces

Englacialreflections? Stackedtrace

COF & elasticitytensor - Kohnen - Colle Gnifetti

core seismic radar
Core – Seismic – Radar

COF & elasticitytensor - Kohnen - Colle Gnifetti

colle gnifetti
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

elvis reflections
ElViSreflections
  • stacking = depthconversionvelocity COF measurements

COF & elasticitytensor - Kohnen - Colle Gnifetti

depth shift
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
connecting seismics radar
Connecting seismics & radar

Seismic

VNMO

Radar

→ depth

VRMS,P0

COF & elasticitytensor - Kohnen - Colle Gnifetti

derive interval δ

deriving anisotropy
Derivinganisotropy

COF & elasticitytensor - Kohnen - Colle Gnifetti

conclusion
Conclusion

Seismics& Radar

Integration

Connection

Evaluation

Comparison

Derivation

COF & elasticity tensor - Kohnen - Colle Gnifetti

thank you
ThankYou!

Thanksto: Pascal Bohleber, Reinhard Drews, Günther Druivenga, Jens Eichler, Sepp Kipfstuhl, Daniel Steinhage andthe Kohnen logisticteam

COF & elasticity tensor - Kohnen - Colle Gnifetti

vsp velocities1
VSP-velocities

Temperature correction

gradient 2.3 m/s/K

COF & elasticity tensor - Kohnen - Colle Gnifetti

radar
Radar

COF & elasticity tensor - Kohnen - Colle Gnifetti

cof seismic radar
COF – Seismic – Radar

COF & elasticity tensor - Kohnen - Colle Gnifetti

vibro
Vibro

COF & elasticity tensor - Kohnen - Colle Gnifetti

picked velocities v nmo
Picked velocities VNMO

COF & elasticity tensor - Kohnen - Colle Gnifetti

calculated velocities v rms p0
Calculated velocities VRMS,P0

COF & elasticity tensor - Kohnen - Colle Gnifetti

girdle orientation
Girdle orientation

COF & elasticity tensor - Kohnen - Colle Gnifetti