3d seismic imaging of the earth’s mantle
TRANSCRIPT
3D seismic imaging of the earth’s mantle
Barbara Romanowicz
Department of Earth and Planetary ScienceU.C. Berkeley
Surface waves
P
Surface waves
P S SS
Surface waves
Loma Prieta (CA) 1989 M 7 earthquake observed at KEV, Finland
Shearer, 1991
Global Transverse Component Stacks
After Park et al, 2005After Park et al, 2005
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
PRELIMINARY REFERENCE EARTH MODEL (PREM)
Dziewonski and Anderson, 1981
Radius [km]
SolidInnerCore
LiquidOuterCore
LowerMantle
Uppermantle
63711210 34800 5700
(Albarède and van der Hilst, 1999
Van der Hilst et al., 1998
P-wave travel time tomography
SH
SV
S wave tomography
Montagner, 2002
ξ = (Vsh/Vsv)2
Seismic Anisotropy
Motivation for seismic Q tomography:
Faul and Jackson, 2005
3D Shear Velocity Models
“SH models” “SV models”
Gung et al., 2003
S velocityModel:SAW24B16
AB CD
“Pacific Superplume”
Q
Hawaii
MN ST
African “superplume”
ElasticSAW24B16
Q-1
Panning and Romanowicz, 2004
ISOTROPIC VELOCITY
RADIAL ANISOTROPY
ξ= (VSH/VSV)2
Wang andWen, 2005
dlnVs ~-3- -12%
Ni and Wen, 2005
AfricanSuperplume
Vs
Vφ
ρ
Ishii and Tromp, 2000Depth ~ 2800 km
Garnero, 1998
Courtillot et al., 2003
The Earth’s inner core
Anomalous splitting of core sensitive modes
Data
Model
Mantle mode
Core mode
(Tanaka and Hamaguchi, 1995)
Hemispherical dependence of anisotropy
Garcia and Souriau, 2002
Innermost Inner Core ?
Ishii and Dziewonski, 2003
Differential rotation of the Inner Core
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
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
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
Bréger et al., EPSL, 2000
Map: enhanced tomographic map atThe core-mantle boundary
STRONG MANTLE HETEROGENEITY?
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
Cartoon from Cazenave, 2002
Garnero, Ann. Rev. 2000“Scenario for CMB”
Cartoon from Hellfrich and Wood, 2001
“SH models” “SV models”
Fukao et al., 2001
175 km
300 km
Transverse isotropy
dln ξ ξ = Vsh/Vsv
- 0
- 100
- 200
- 300
- 400 km
Upper mantle:Q - lower mantle: Vsh
Degree 2 only
QRLW8
Hotspot distribution
Weighted by buoyancy flux
Attenuation tomography
Anelastic attenuation: QRLW8
Gung and Romanowicz, 2002