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

200 hours starting 10 hours before origin time

0S10

0S12

mHz x10

0S5

0S13

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

= (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-1

Hawaii

MN

ST

African “superplume”

ElasticSAW24B16

Q-1

Panning and Romanowicz, 2004

ISOTROPIC VELOCITY

RADIAL ANISOTROPY

= (VSH/VSV)2

Wang andWen, 2005

dlnVs ~-3- -12%

Ni and Wen, 2005

AfricanSuperplume

Vs

V

Ishii and Tromp, 2000

Depth ~ 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 = 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