Vernon Cormier

1
Small Scale Heterogeneity Seismic Observations
and Wavefield Effects

• Vernon Cormier

2
BODY WAVE EFFECTS
ka lt 1 (2?a/??lt 1)

• Pulse attenuation and broadening
• Pulse postcursors (coda) and precursors
• SPO (shape preferred orientation) long wavelength
  equivalent medium

3
DYNAMIC COMPOSITE ELASTIC MODULI SCATTERING
IMITATES VISCOELASTICITY
V/Vo
Attenuation
Frequency
Kaelin, B., and L.R. Johnson, J. Appl.
Phys.,84(10), 1998
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WAVEFORM EFFECTS OF FORWARD SCATTERING
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Dispersion and Attenuation from Viscoelasticity
Weaker dispersion
Modulus Defect
Note Viscoelastic shear modulus defect lt 25,
implying bounds on width of relaxation spectrum
and viscoelastic attenuation.
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WAVEFORM EFFECTS OF INTRINSIC ATTENUATION
Cormier, V.F., and X. Li, J.Geophys. Res., 107,
2362, doi10.1029/2002JB001796, 2002.
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Q INVERSION WITH SCATTERING MODEL
Inner Core
Cormier, V.F., and X. Li, J.Geophys. Res., 107,
2362, doi10.1029/2002JB001796, 2002.
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Observations of Heterogeneity Power Spectrum
Global Tomography
Well Logs/Exploration
Power
Wavenumber
Note missing information at scale lengths 1000
km to 1 km
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2-D High Frequency Pseudospectral Modeling
Seismogram Record Section
Wavefield Snapshot
85
S
ScS
sScS
sS
65
Distance (deg)
SSS
45
SS
25
S
Figure 1
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SH and SV
Model Near CMB
SKS
S
ScS
DVp/Vp 0.3DVs/Vs
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Apparent Transverse Isotropy
S
ScS
SH
SV
Cormier, V.F., EOS Trans. AGU, 84(46), Abstract
S41E-0129, 2003. Komatitsch, D., L.P. Vinnik, and
S. Chevrot, J. Geophys. Res., doi10.1029/2009JB00
6795, in press.
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Observations of Scattered PKIKP Precursors
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Successful Models for PKIKP Precursors
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Synthetic Seismograms with Rayleigh-Born Approxima
tion in 3-D
Cormier, V.F., Geophys. J. Int., 136, 373-384,
1999.
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A Vanishing D at Short Scale Lengths?
Model 2
Low Pass
High Pass
0.0
0.0
-5.0
5.0
-1.0
1.0
-2.0
2.0
0.0
Figure 6
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Model 3
Figure 11
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Realization that Reproduces Coherent SdS 3.1
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CONCLUSIONS

• Small scale heterogeneity (0.1 to 10 km) can
  mimic viscoelasticty
• Estimated viscoelastic 1/Qs are upper bounds to
  viscoelastic attenuation
• Isotropic distributions of small scale lengths
  can mimic SPO transverse isotropy
• Tests of the seismic wavefield effects of
  realistic mixing models are possible