A Tour of Earth’s Dynamic Mantle: A Synthesis of Seismic Velocity & Quality Factor Presented by: Jesse Fisher Lawrence Institute of Geophysics and Planetary

A Tour of Earth’s Dynamic Mantle: A Tour of Earth’s Dynamic Mantle: A Synthesis of Seismic Velocity & Quality FactorA Synthesis of Seismic Velocity & Quality Factor

Presented by: Jesse Fisher LawrencePresented by: Jesse Fisher Lawrence

Institute of Geophysics and Planetary PhysicsInstitute of Geophysics and Planetary PhysicsScripps Institution of OceanographyScripps Institution of OceanographyUniversity of California, San DiegoUniversity of California, San Diego

Presented at: University of Wisconsin, MadisonPresented at: University of Wisconsin, MadisonFebruary 3February 3rdrd

Collaborators:Collaborators:

Michael Wysession:Michael Wysession: Washington University Washington University

Doug Wiens: Doug Wiens: Washington UniversityWashington University

Peter Shearer: Peter Shearer: ScrippsScripps

Guy Masters: Guy Masters: ScrippsScripps

Andy Nyblade: Andy Nyblade: Penn StatePenn State

Sridhar Anandakrishnan: Sridhar Anandakrishnan: Penn StatePenn State

Talk OutlineTalk Outline Introduction:Introduction:

Definitions - e.g. Definitions - e.g. Quality FactorQuality Factor & & Attenuation Attenuation MotivationMotivation

Data Measurement:Data Measurement:

Case Studies:Case Studies: The Caribbean lower mantle thermal anomalyThe Caribbean lower mantle thermal anomaly Antarctic lithospheric studyAntarctic lithospheric study North American upper mantleNorth American upper mantle 3D model of the mantle3D model of the mantle

Conclusions:Conclusions:

Some DefinitionsSome Definitions

• Seismic Velocity ( Seismic Velocity ( V V )):: The speed at which a seismic wave The speed at which a seismic wave travels through the Earth.travels through the Earth.

• Seismic Attenuation ( Seismic Attenuation ( tt* )* ):: The amount of energy a seismic The amount of energy a seismic wave looses as it travels through the Earth.wave looses as it travels through the Earth.

• Seismic Quality Factor ( Seismic Quality Factor ( Q Q )):: The degree to which the The degree to which the Earth transfers energy without attenuation.Earth transfers energy without attenuation.

Creep:Creep:

Diffusion CreepDiffusion Creep:: Reorganization of atoms Reorganization of atoms within a grain or within within a grain or within poor fluids between grains.poor fluids between grains.

Dislocation CreepDislocation Creep:: Through recrystalization, Through recrystalization, bonds may be broken, bonds may be broken, moved, and rebuilt without moved, and rebuilt without reorganization of the lattice.reorganization of the lattice.

Vacancy Diffusion

Edge Dislocation

CreepCreep:: is a slow, time-dependent strain where energy is not is a slow, time-dependent strain where energy is not recoverable. Most commonly used in viscous flow.recoverable. Most commonly used in viscous flow.

Vacancy

Vacancy

Attenuation

(high temp, low stress,& water)

Attenuation

(low temp, high stress,& water)

Purely Elastic Purely Elastic (Harmonic Velocity)(Harmonic Velocity)

Elastic and AnelasticElastic and Anelastic(Attenuation & Anharmonic Velocity)(Attenuation & Anharmonic Velocity)

Rational for Studying AttenuationRational for Studying Attenuation

Attenuation & velocity Attenuation & velocity can be used to indicate can be used to indicate different sources for different sources for anomalies.anomalies.

• WaterWater

• TemperatureTemperature

• ChemicalChemical

[Lawrence & Wysession., 2005: AGU Monograph in review; Karato, 2003: AGU Mohograph]

Rational for Studying AttenuationRational for Studying Attenuation

Anelasticity is Anelasticity:Anelasticity is Anelasticity:• QQ((T,T,HH22O)O)nn ((T ,T ,HH22O)O)

[[KaratoKarato, 2003; Monograph], 2003; Monograph]

Water increases conductivity.Water increases conductivity.• Increases heat flowIncreases heat flow

[[Li & JeanlozLi & Jeanloz, 1991; JGR], 1991; JGR]

Hydrous phases are often Hydrous phases are often anisotropicanisotropic

[[Wookey & KendallWookey & Kendall; 2004 JGR]; 2004 JGR]

Water changes melting Water changes melting temperaturetemperature

[[Inoue,Inoue, 1994; PEPI] 1994; PEPI][McNamara et al., 2003: JGR]




Case Studies:Case Studies: The Caribbean small-scale lower mantle thermal anomalyThe Caribbean small-scale lower mantle thermal anomaly Antarctic lithospheric studyAntarctic lithospheric study North American upper mantleNorth American upper mantle 3D model of the mantle3D model of the mantle


Differential MeasurementsDifferential Measurements

• Travel-Time ResidualsTravel-Time Residuals• Seismic VelocitySeismic Velocity

• AttenuationAttenuation• Quality FactorQuality Factor

• AnisotropyAnisotropy• VelocityVelocity• Quality FactorQuality Factor

Radial

Tangential

Travel-Time MeasurementTravel-Time Measurement

• Cross- Cross- CorrelationCorrelation

S and ScS Alignment

Attenuation MeasurementAttenuation Measurement

• Cross- Cross- CorrelationCorrelation

• Attenuation Attenuation OperatorOperator

H= ScS/S

Corrected Travel-Time MeasurementCorrected Travel-Time Measurement

• Cross-CorrelationCross-Correlation

• Attenuation OperatorAttenuation Operator

• Repeat Cross- CorrelationRepeat Cross- Correlation

S and ScS Alignment




Case Studies:Case Studies: The Caribbean lower mantle thermal anomalyThe Caribbean lower mantle thermal anomaly Antarctic lithospheric studyAntarctic lithospheric study North American upper mantleNorth American upper mantle 3D model of the mantle3D model of the mantle


Caribbean AnomalyCaribbean Anomaly

Fisher et al., [2003] - GRL

Caribbean AnomalyCaribbean Anomaly

Fisher et al., [2003] - GRL

D: 250 km ScS Path

Outer Core

The Caribbean AnomalyThe Caribbean Anomaly

[after Tan & Gurnis, 2002; Grand et al., 1997]

•Thermal Anomaly is expected at the CMB.

The Story So Far …The Story So Far …

• Small-scale Small-scale velocity and velocity and quality factor quality factor anomalies can be anomalies can be isolated in the isolated in the lower mantle.lower mantle.

• The Caribbean The Caribbean anomaly is likely anomaly is likely thermal due to heat thermal due to heat flow perturbations flow perturbations at the CMB.at the CMB.

But we are are atthe surface …

And the anomaly is deep in the Earth …

Then we have to peel back the layers toreally see whatis inside

• 42 stations 42 stations spanned from the spanned from the Ross Sea 1300 km Ross Sea 1300 km into East into East Antarctica.Antarctica.

Transantarctic Mountain Transantarctic Mountain Seismic ExperiementSeismic Experiement

PhotosCourtesy ofJen Curtis

Antarctic Lithosphere Antarctic Lithosphere

• Velocity & Attenuation Velocity & Attenuation are inversely correlatedare inversely correlated

• 300300C difference between C difference between East & West AntarcticaEast & West Antarctica

• Measured crustal Measured crustal thicknessthickness

• Modeled TAMs uplift as Modeled TAMs uplift as flexural response to flexural response to thermal loadthermal load

Lawrence et al., [2006a -JGR]

Closer to Closer to Home:Home:

New & improved New & improved techniquetechnique• 2 weeks from start to 2 weeks from start to

finish not 4 months.finish not 4 months.

P- waves correlate P- waves correlate with S-waves (Rwith S-waves (R22 > > 0.6)0.6)

Attenuation & travel Attenuation & travel times are less times are less correlated (Rcorrelated (R22 < 0.3) < 0.3)

[Lawrence, Shearer, & Masters, 2006: in review at GRL]

The Story So Far …The Story So Far …• Travel times and Travel times and

attenuation vary attenuation vary significantly for both significantly for both upper and lower mantle.upper and lower mantle.

• Quality factor Quality factor correlates with correlates with velocity indicating velocity indicating thermal anomaliesthermal anomalies

• So, both upper and So, both upper and lower thermal boundary lower thermal boundary layers possess lateral layers possess lateral thermal variations.thermal variations.


And we’ve only imaged a small part of the Earth

So, what aboutthe Earth as awhole?

VQM3DAVQM3DA

• VV - Velocity- Velocity

• QQ - Quality Factor- Quality Factor

• MM - Whole Mantle- Whole Mantle

• 3D3D - 3 Dimensional- 3 Dimensional

• AA - Anisotropy- Anisotropy

[Lawrence & Wysession, 2006: in review G-cubed]

DATADATA

S-S* >20,000

ScS-S >21,000

SS-S >17,500

sScS-sS ~5000

sSS-sS ~2000

ScS-SS >17000

SKS-S† >3,600

TOTAL 86 - 93,000

Data used:

† for Radial Component Only * Uses VanDecar and Crosson, [1990]

Tracy PortleKurt Solander

Juliana RokoskyEmily Carter

TomographyTomography

Velocity:Velocity:

Quality FactorQuality Factor::

Ray Tracing:

€

Ti = dij V jj=1

M∑

€

t *i = Tij Q jj=1

M∑

Quality FactorQuality Factor&&

VelocityVelocity

[Lawrence & Wysession., 2006: in review AGU Monograph]

Velocity has poor Velocity has poor correlation with seismic correlation with seismic velocity.velocity.• A ring of high A ring of high

velocity high quality velocity high quality factor is clear around factor is clear around the Pacific.the Pacific.

• There is a large, very There is a large, very low low QQ anomaly anomaly between 800 and between 800 and 1500 km depth.1500 km depth.

Velocity has poor Velocity has poor correlation with seismic correlation with seismic velocity.velocity.• A ring of high A ring of high

velocity high quality velocity high quality factor is clear around factor is clear around the Pacific.the Pacific.

• There is a large, very There is a large, very low low QQ anomaly anomaly between 800 and between 800 and 1500 km depth.1500 km depth.

VQM3DAVQM3DAv.v.

QRLW8QRLW8 VQM3DA is more VQM3DA is more

accurate in the lower accurate in the lower mantle than in the mantle than in the upper mantle.upper mantle.• Even in the upper Even in the upper

mantle it has mantle it has excellent resolution.excellent resolution.

• In the upper mantle, In the upper mantle, the highest the highest attenuation occurs at attenuation occurs at subduction zones due subduction zones due to dehydration to dehydration effects.effects.

VQM3DA is more VQM3DA is more accurate in the lower accurate in the lower mantle than in the mantle than in the upper mantle.upper mantle.• Even in the upper Even in the upper

mantle it has mantle it has excellent resolution.excellent resolution.

• In the upper mantle, In the upper mantle, the highest the highest attenuation occurs at attenuation occurs at subduction zones due subduction zones due to dehydration to dehydration effects.effects.

•QRLW8: • From surface waves• Looses resolution with

depthGung & Romanowicz [2004]

•VQM3DA:• From body waves• Gains resolution with

depthLawrence & Wysession [2006]

Upper Mantle Upper Mantle Dehydration Melt:Dehydration Melt:

Water subducts within hydrous Water subducts within hydrous minerals such as serpentineminerals such as serpentine

At 100-400 km depth the hydrous At 100-400 km depth the hydrous minerals become unstableminerals become unstable

Water is released into the mantle Water is released into the mantle above the slababove the slab

PeacockPeacock [1990] estimates a net flux [1990] estimates a net flux

of ~6.7 of ~6.7 10 101111 kg/year kg/year water into water into the mantle. the mantle.

+100% -120%dln 1/Q

[Roth & Wiens, 1999: JGR]

The Transition Zone Water Filter:The Transition Zone Water Filter:

Water enters mantle at Water enters mantle at subduction zones.subduction zones.

Upper mantle is generally Upper mantle is generally anhydrous.anhydrous.

Transition zone sucks up Transition zone sucks up the water.the water.

Lower mantle is generally Lower mantle is generally anhydrous.anhydrous.

[Bercovici et al., 2003: Nature]

Hydrous Phases B & D:Hydrous Phases B & D:

Quench-type experiments:Quench-type experiments: Pressure: Pressure: 20-53 GPa20-53 GPa

Temperature:Temperature: 800-1800°C800-1800°C

Results:Results: Phase D is stable to 42 GPa Phase D is stable to 42 GPa or ~1400km depth.or ~1400km depth.

[adapted from Shieh et al., 1998: EPSL]

The East Asian The East Asian AnomalyAnomaly

Water Anomaly

[Lawrence & Wysession., 2006c: in review AGU Monograph]

Anomaly Volume:Anomaly Volume:1.8 1.8 10 101111 km km33

Water Volume:Water Volume:> 5.5 > 5.5 10 1088 km km33

(0.1 wt% (0.1 wt% water)water)

Water in the Oceans:Water in the Oceans:1.3 1.3 10 1099 km km33

Anomaly Volume:Anomaly Volume:1.8 1.8 10 101111 km km33

Water Volume:Water Volume:> 5.5 > 5.5 10 1088 km km33

(0.1 wt% (0.1 wt% water)water)

Water in the Oceans:Water in the Oceans:1.3 1.3 10 1099 km km33

Consequences:Consequences:

Anelasticity is Anelasticity:Anelasticity is Anelasticity:• QQ((T,T,HH22O)O)nn ((T ,T ,HH22O)O)

[[KaratoKarato, 2003; Monograph], 2003; Monograph]

Water increases conductivity.Water increases conductivity.• Increases heat flowIncreases heat flow

[[Li & JeanlozLi & Jeanloz, 1991; JGR], 1991; JGR]

Hydrous phases are often Hydrous phases are often anisotropicanisotropic

[[Wookey & KendallWookey & Kendall; 2004 JGR]; 2004 JGR]

Water changes melting Water changes melting temperaturetemperature

[[Inoue,Inoue, 1994; PEPI] 1994; PEPI][McNamara et al., 2003: JGR]

Megaplumes:Megaplumes:

? ?

Shear Velocity Quality Factor

[Masters et al., 2001: AGU Monograph]

Pacific

Africa

ConclusionsConclusions• Quality factor & velocity are highly heterogeneous throughout the mantle Quality factor & velocity are highly heterogeneous throughout the mantle

on very large and very small scales.on very large and very small scales.

• Velocity and Quality Factor are often positively correlated indicating Velocity and Quality Factor are often positively correlated indicating thermal anomalies.thermal anomalies.

• Velocity and Quality Factor are often poorly correlated, requiring other Velocity and Quality Factor are often poorly correlated, requiring other sources for the anomalies.sources for the anomalies.

• Water likely plays a key role in shaping the anelastic Earth.Water likely plays a key role in shaping the anelastic Earth.• There is a second dehydration cycle in the mantle related to subduction.There is a second dehydration cycle in the mantle related to subduction.

• Vertical profiles through VQM3DA are consistent with core-to-surface Vertical profiles through VQM3DA are consistent with core-to-surface communications for spreading ridges and subduction zones.communications for spreading ridges and subduction zones.

So, What is the Anomaly?So, What is the Anomaly?

Temperature:Temperature:• V & Q change a lotV & Q change a lot• High T is unlikely above High T is unlikely above

a slab.a slab.

Grain Size:Grain Size:• Hard to reconcile with Hard to reconcile with

size & magnitude of size & magnitude of anomalyanomaly

Composition:Composition:• Velocity variation?Velocity variation?• dln Q is less than dln Q is less than

observedobserved

Water:Water:• V doesn’t change much.V doesn’t change much.

[Lawrence & Wysession., 2006: in review AGU Monograph;

Karato, 2003: AGU Mohograph]

The East Asian The East Asian AnomalyAnomaly

Anomaly

[Lawrence & Wysession., 2006: in review AGU Monograph]

3D Rendering of VQM3DA3D Rendering of VQM3DAModel: Isotropic Velocity

View: South: = 30

Contour: 0.5 %

Compare Compare QQ((rr) to Temperature) to Temperature

Q(z) = e[/TH(z)]

= 2.14 1

= 3.45 0.6

• and are controlled by chemical composition and may have some pressure dependence

Lawrence and Wysession [2005a]

Anisotropic VelocityAnisotropic Velocity

= VSH2/VSV

2

Anisotropic Quality FactorAnisotropic Quality Factor

= QSH2/QSV

2

TomographyTomography

: No net perturbation

: Smoothing constraint

€

Gm = d

€

G'm =

G

α Θ

β Λ

⎡

⎣

⎢ ⎢ ⎢

⎤

⎦

⎥ ⎥ ⎥m =

d

0

0

⎡

⎣

⎢ ⎢ ⎢

⎤

⎦

⎥ ⎥ ⎥= d'

€

m = G'−1 d'

Inversion:

Velocity:Velocity:

Quality FactorQuality Factor::

€

Ti = dij V jj=1

M∑

€

t *i = Tij Q jj=1

M∑

€

m = G−1d

What is Anelasticity?What is Anelasticity?

AnelasticityAnelasticity:: The property of a solid indicating that The property of a solid indicating that deformation depends on the time and stress.deformation depends on the time and stress.

AnelasticElastic

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Spring Silly Putty

Purely Elastic AnisotropyPurely Elastic Anisotropy

Fast DirectionSlow Direction

Anelastic AnisotropyAnelastic Anisotropy

Elastic DirectionAnelastic Direction

SAW16B16AN v. VQM3DASAW16B16AN v. VQM3DA•SAW16B16AN

• Uses surface & body waves• Spherical Harmonics

Gung et al., [2003]

•VQM3DA:• Uses only body waves• Gains resolution with

depthLawrence & Wysession [2006b]

VSH-FastVSV-Fast

1D Quality Factor Structure1D Quality Factor Structure• Measured 30,000 Measured 30,000 dt*dt*ScS-SScS-S

• Excellent global data Excellent global data coveragecoverage

• SS and and ScSScS reach greater reach greater depth with distancedepth with distance

Lawrence and Wysession [2006 EPSL]

Attenuation vs. DistanceAttenuation vs. Distance

~27,000 Data Points ~3,000 Data Points


Previous WorkPrevious Work


1D Models1D Models

9-Layer Model: QLM9 21-Layer Model


dt*dt*ScS-SScS-S((rr))


Compare Compare QQ((rr) to Viscosity) to Viscosity


Temperature ConstraintsTemperature Constraints

Using theoretical Using theoretical calculations of calculations of KaratoKarato [1993], Jackson et al., [1993], Jackson et al., [1992, 2002] we [1992, 2002] we compute a theoretical compute a theoretical temperature profile.temperature profile.

Our model fits the Our model fits the rough expectation rough expectation


The Story So Far …The Story So Far …• Upper and lower mantle Upper and lower mantle

quality factor varies quality factor varies significantly significantly laterally as well as laterally as well as with depth.with depth.

• Quality factor Quality factor correlates with both correlates with both observed viscosity and observed viscosity and velocity.velocity.

• So far, the Earth So far, the Earth appears to be largely appears to be largely thermally driven.thermally driven.


And the Earth is not 1D …

So, what doesthe Earth look like?

Other ResearchOther Research

Documents

A Tour of Earth’s Dynamic Mantle: A Synthesis of Seismic Velocity & Quality Factor Presented by: Jesse Fisher Lawrence Institute of Geophysics and Planetary