3d seismic imaging of the earth’s mantle
TRANSCRIPT
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3D seismic imaging of the earth’s mantle
Barbara Romanowicz
Department of Earth and Planetary ScienceU.C. Berkeley
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Surface waves
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P
Surface waves
P S SS
Surface waves
Loma Prieta (CA) 1989 M 7 earthquake observed at KEV, Finland
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Shearer, 1991
Global Transverse Component Stacks
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After Park et al, 2005After Park et al, 2005
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Sumatra 12/26/04 M9.3 (0.8 to 2.2 mHz)
CAN
UNM 0S7
0S9
3S2
0S6
1S4
0S11
1S5
1S3/3S1
0S8
0S5
0S0 0S10
0S12
mHz x10
0S5
0S13
200 hours starting 10 hours before origin time
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PRELIMINARY REFERENCE EARTH MODEL (PREM)
Dziewonski and Anderson, 1981
Radius [km]
SolidInnerCore
LiquidOuterCore
LowerMantle
Uppermantle
63711210 34800 5700
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(Albarède and van der Hilst, 1999
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Van der Hilst et al., 1998
P-wave travel time tomography
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SH
SV
S wave tomography
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Montagner, 2002
ξ = (Vsh/Vsv)2
Seismic Anisotropy
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Motivation for seismic Q tomography:
Faul and Jackson, 2005
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3D Shear Velocity Models
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“SH models” “SV models”
Gung et al., 2003
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S velocityModel:SAW24B16
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AB CD
“Pacific Superplume”
Q
Hawaii
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MN ST
African “superplume”
ElasticSAW24B16
Q-1
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Panning and Romanowicz, 2004
ISOTROPIC VELOCITY
RADIAL ANISOTROPY
ξ= (VSH/VSV)2
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Wang andWen, 2005
dlnVs ~-3- -12%
Ni and Wen, 2005
AfricanSuperplume
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Vs
Vφ
ρ
Ishii and Tromp, 2000Depth ~ 2800 km
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Garnero, 1998
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Courtillot et al., 2003
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The Earth’s inner core
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Anomalous splitting of core sensitive modes
Data
Model
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Mantle mode
Core mode
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(Tanaka and Hamaguchi, 1995)
Hemispherical dependence of anisotropy
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Garcia and Souriau, 2002
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Innermost Inner Core ?
Ishii and Dziewonski, 2003
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Differential rotation of the Inner Core
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Published by AAAS
J. Zhang et al., Science 309, 1357 -1360 (2005)
Fig. 1. Ray paths of PKP waves and example of waveform doublet used to detect temporal change of travel times through the inner core
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Published by AAAS
J. Zhang et al., Science 309, 1357 -1360 (2005)
Fig. 1. Ray paths of PKP waves and example of waveform doublet used to detect temporal change of travel times through the inner core
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Published by AAAS
J. Zhang et al., Science 309, 1357 -1360 (2005)
Fig. 4. Difference of BC - DF times, d(BC - DF), at station COL as a function of the time separation between the two events of the doublet
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Bréger et al., EPSL, 2000
Map: enhanced tomographic map atThe core-mantle boundary
STRONG MANTLE HETEROGENEITY?
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Current Challenges• Improving resolution of 3D structure:
– Wave propagation in strongly heterogeneous 3D media/waveform inversion
– Address uneven sampling (oceans)– Fine scale structure of major discontinuities
• Attenuation tomography• 3D density structure
• Combining information from seismology, mineral physics, geochemistry and geodynamics
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Cartoon from Cazenave, 2002
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Garnero, Ann. Rev. 2000“Scenario for CMB”
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Cartoon from Hellfrich and Wood, 2001
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“SH models” “SV models”
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Fukao et al., 2001
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175 km
300 km
Transverse isotropy
dln ξ ξ = Vsh/Vsv
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- 0
- 100
- 200
- 300
- 400 km
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Upper mantle:Q - lower mantle: Vsh
Degree 2 only
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QRLW8
Hotspot distribution
Weighted by buoyancy flux
Attenuation tomography
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Anelastic attenuation: QRLW8
Gung and Romanowicz, 2002