A Tour of Earth’s Dynamic Mantle: A Synthesis of Seismic Velocity & Quality Factor Presented by: Jesse Fisher Lawrence Institute of Geophysics and Planetary Physics Scripps Institution of Oceanography University of California, San Diego Presented at: University of Wisconsin, Madison February 3 rd

Collaborators: Michael Wysession: Washington University Michael Wysession: Washington University Doug Wiens: Washington University Doug Wiens: Washington University Peter Shearer: Scripps Peter Shearer: Scripps Guy Masters: Scripps Guy Masters: Scripps Andy Nyblade: Penn State Andy Nyblade: Penn State Sridhar Anandakrishnan: Penn State Sridhar Anandakrishnan: Penn State

Talk Outline  Introduction:  Definitions - e.g. Quality Factor & Attenuation  Motivation  Data Measurement:  Case Studies:  The Caribbean lower mantle thermal anomaly  Antarctic lithospheric study  North American upper mantle  3D model of the mantle  Conclusions:

Some Definitions Seismic Velocity ( V ): The speed at which a seismic wave travels through the Earth. Seismic Attenuation ( t* ): The amount of energy a seismic wave looses as it travels through the Earth. Seismic Quality Factor ( Q ): The degree to which the Earth transfers energy without attenuation.

Creep: Diffusion Creep: Reorganization of atoms within a grain or within poor fluids between grains. Dislocation Creep: Through recrystalization, bonds may be broken, moved, and rebuilt without reorganization of the lattice. Vacancy Diffusion Edge Dislocation  Creep: is a slow, time-dependent strain where energy is not recoverable. Most commonly used in viscous flow. Vacancy Attenuation (high temp, low stress, & water) Attenuation (low temp, high stress, & water)

Purely Elastic (Harmonic Velocity)

Elastic and Anelastic (Attenuation & Anharmonic Velocity)

Rational for Studying Attenuation Attenuation & velocity can be used to indicate different sources for anomalies. Attenuation & velocity can be used to indicate different sources for anomalies. WaterWater TemperatureTemperature ChemicalChemical [Lawrence & Wysession., 2005: AGU Monograph in review; Karato, 2003: AGU Mohograph]

Rational for Studying Attenuation Anelasticity is Anelasticity: Anelasticity is Anelasticity: Q(T,H 2 O) n   (T,H 2 O)Q(T,H 2 O) n   (T,H 2 O) [Karato, 2003; Monograph] [Karato, 2003; Monograph] Water increases conductivity. Water increases conductivity. Increases heat flowIncreases heat flow [Li & Jeanloz, 1991; JGR] [Li & Jeanloz, 1991; JGR] Hydrous phases are often anisotropic Hydrous phases are often anisotropic [Wookey & Kendall; 2004 JGR] [Wookey & Kendall; 2004 JGR] Water changes melting temperature Water changes melting temperature [Inoue, 1994; PEPI] [Inoue, 1994; PEPI] [McNamara et al., 2003: JGR]

Talk Outline  Introduction:  Definitions - e.g. Quality Factor & Attenuation  Motivation  Data Measurement:  Case Studies:  The Caribbean small-scale lower mantle thermal anomaly  Antarctic lithospheric study  North American upper mantle  3D model of the mantle  Conclusions:

Differential Measurements Travel-Time Residuals Travel-Time Residuals Seismic VelocitySeismic Velocity Attenuation Attenuation Quality FactorQuality Factor Anisotropy Anisotropy VelocityVelocity Quality FactorQuality Factor Radial Tangential

Travel-Time Measurement Cross- Correlation Cross- Correlation S and ScS Alignment

Attenuation Measurement Cross- Correlation Cross- Correlation Attenuation Operator Attenuation Operator H= ScS/S

Corrected Travel-Time Measurement Cross- Correlation Cross- Correlation Attenuation Operator Attenuation Operator Repeat Cross- Correlation Repeat Cross- Correlation S and ScS Alignment

Talk Outline  Introduction:  Definitions - e.g. Quality Factor & Attenuation  Motivation  Data Measurement:  Case Studies:  The Caribbean lower mantle thermal anomaly  Antarctic lithospheric study  North American upper mantle  3D model of the mantle  Conclusions:

Caribbean Anomaly Fisher et al., [2003] - GRL

Caribbean Anomaly Fisher et al., [2003] - GRL D  : 250 km ScS Path Outer Core

The Caribbean Anomaly [after Tan & Gurnis, 2002; Grand et al., 1997] Thermal Anomaly is expected at the CMB.

The Story So Far … Small-scale velocity and quality factor anomalies can be isolated in the lower mantle. Small-scale velocity and quality factor anomalies can be isolated in the lower mantle. The Caribbean anomaly is likely thermal due to heat flow perturbations at the CMB. The Caribbean anomaly is likely thermal due to heat flow perturbations at the CMB. But we are are at the surface … And the anomaly is deep in the Earth … Then we have to peel back the layers to really see what is inside

42 stations spanned from the Ross Sea 1300 km into East Antarctica. 42 stations spanned from the Ross Sea 1300 km into East Antarctica. Transantarctic Mountain Seismic Experiement Photos Courtesy of Jen Curtis

Antarctic Lithosphere Velocity & Attenuation are inversely correlated Velocity & Attenuation are inversely correlated 300  C difference between East & West Antarctica 300  C difference between East & West Antarctica Measured crustal thickness Measured crustal thickness Modeled TAMs uplift as flexural response to thermal load Modeled TAMs uplift as flexural response to thermal load Lawrence et al., [2006a -JGR]

Closer to Home: New & improved technique New & improved technique 2 weeks from start to finish not 4 months.2 weeks from start to finish not 4 months. P- waves correlate with S-waves (R 2 > 0.6) P- waves correlate with S-waves (R 2 > 0.6) Attenuation & travel times are less correlated (R 2 < 0.3) Attenuation & travel times are less correlated (R 2 < 0.3) [Lawrence, Shearer, & Masters, 2006: in review at GRL]

The Story So Far … Travel times and attenuation vary significantly for both upper and lower mantle. Travel times and attenuation vary significantly for both upper and lower mantle. Quality factor correlates with velocity indicating thermal anomalies Quality factor correlates with velocity indicating thermal anomalies So, both upper and lower thermal boundary layers possess lateral thermal variations. So, both upper and lower thermal boundary layers possess lateral thermal variations. But we are are at the surface … And we’ve only imaged a small part of the Earth So, what about the Earth as a whole?

VQM3DA V - Velocity V - Velocity Q - Quality Factor Q - Quality Factor M - Whole Mantle M - Whole Mantle 3D - 3 Dimensional 3D - 3 Dimensional A - Anisotropy A - Anisotropy [Lawrence & Wysession, 2006: in review G-cubed]

DATA 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 ,000 Data used: † for Radial Component Only * Uses VanDecar and Crosson, [1990] Tracy Portle Kurt Solander Juliana Rokosky Emily Carter

Tomography Velocity: Quality Factor: Ray Tracing:

Quality Factor & Velocity [Lawrence & Wysession., 2006: in review AGU Monograph] Velocity has poor correlation with seismic velocity. Velocity has poor correlation with seismic velocity. A ring of high velocity high quality factor is clear around the Pacific.A ring of high velocity high quality factor is clear around the Pacific. There is a large, very low Q anomaly between 800 and 1500 km depth.There is a large, very low Q anomaly between 800 and 1500 km depth. Velocity has poor correlation with seismic velocity. Velocity has poor correlation with seismic velocity. A ring of high velocity high quality factor is clear around the Pacific.A ring of high velocity high quality factor is clear around the Pacific. There is a large, very low Q anomaly between 800 and 1500 km depth.There is a large, very low Q anomaly between 800 and 1500 km depth.

VQM3DA v. QRLW8 VQM3DA is more accurate in the lower mantle than in the upper mantle. VQM3DA is more accurate in the lower mantle than in the upper mantle. Even in the upper mantle it has excellent resolution.Even in the upper mantle it has excellent resolution. In the upper mantle, the highest attenuation occurs at subduction zones due to dehydration effects.In the upper mantle, the highest attenuation occurs at subduction zones due to dehydration effects. VQM3DA is more accurate in the lower mantle than in the upper mantle. VQM3DA is more accurate in the lower mantle than in the upper mantle. Even in the upper mantle it has excellent resolution.Even in the upper mantle it has excellent resolution. In the upper mantle, the highest attenuation occurs at subduction zones due to dehydration effects.In the upper mantle, the highest attenuation occurs at subduction zones due to dehydration effects. QRLW8: From surface waves Looses resolution with depth Gung & Romanowicz [2004] VQM3DA: From body waves Gains resolution with depth Lawrence & Wysession [2006]

Upper Mantle Dehydration Melt: Water subducts within hydrous minerals such as serpentine Water subducts within hydrous minerals such as serpentine At km depth the hydrous minerals become unstable At km depth the hydrous minerals become unstable Water is released into the mantle above the slab Water is released into the mantle above the slab Peacock [1990] estimates a net flux of ~6.7  kg/year water into the mantle. Peacock [1990] estimates a net flux of ~6.7  kg/year water into the mantle. +100%-120% dln 1/Q [Roth & Wiens, 1999: JGR]

The Transition Zone Water Filter: Water enters mantle at subduction zones. Water enters mantle at subduction zones. Upper mantle is generally anhydrous. Upper mantle is generally anhydrous. Transition zone sucks up the water. Transition zone sucks up the water. Lower mantle is generally anhydrous. Lower mantle is generally anhydrous. [Bercovici et al., 2003: Nature]

Hydrous Phases B & D: Quench-type experiments: Quench-type experiments: Pressure: Pressure: GPa GPa Temperature: Temperature: °C °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 Anomaly Water Anomaly [Lawrence & Wysession., 2006c: in review AGU Monograph] Anomaly Volume: 1.8  km 3 Water Volume: > 5.5  10 8 km 3 (0.1 wt% water) Water in the Oceans: 1.3  10 9 km 3 Anomaly Volume: 1.8  km 3 Water Volume: > 5.5  10 8 km 3 (0.1 wt% water) Water in the Oceans: 1.3  10 9 km 3

Consequences: Anelasticity is Anelasticity: Anelasticity is Anelasticity: Q(T,H 2 O) n   (T,H 2 O)Q(T,H 2 O) n   (T,H 2 O) [Karato, 2003; Monograph] [Karato, 2003; Monograph] Water increases conductivity. Water increases conductivity. Increases heat flowIncreases heat flow [Li & Jeanloz, 1991; JGR] [Li & Jeanloz, 1991; JGR] Hydrous phases are often anisotropic Hydrous phases are often anisotropic [Wookey & Kendall; 2004 JGR] [Wookey & Kendall; 2004 JGR] Water changes melting temperature Water changes melting temperature [Inoue, 1994; PEPI] [Inoue, 1994; PEPI] [McNamara et al., 2003: JGR]

Megaplumes: ?? Shear VelocityQuality Factor [Masters et al., 2001: AGU Monograph] Pacific Africa

Conclusions Quality factor & velocity are highly heterogeneous throughout the mantle on very large and very small scales. Quality factor & velocity are highly heterogeneous throughout the mantle on very large and very small scales. Velocity and Quality Factor are often positively correlated indicating thermal anomalies. Velocity and Quality Factor are often positively correlated indicating thermal anomalies. Velocity and Quality Factor are often poorly correlated, requiring other sources for the anomalies. Velocity and Quality Factor are often poorly correlated, requiring other 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 communications for spreading ridges and subduction zones. Vertical profiles through VQM3DA are consistent with core-to-surface communications for spreading ridges and subduction zones.

So, What is the Anomaly? Temperature: Temperature: V & Q change a lotV & Q change a lot High T is unlikely above a slab.High T is unlikely above a slab. Grain Size: Grain Size: Hard to reconcile with size & magnitude of anomalyHard to reconcile with size & magnitude of anomaly Composition: Composition: Velocity variation?Velocity variation? dln Q is less than observeddln Q is less than observed 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 Anomaly Anomaly [Lawrence & Wysession., 2006: in review AGU Monograph]

3D Rendering of VQM3DA Model: Isotropic Velocity View: South:  = 30  Contour:  0.5 %

Compare Q(r) to Temperature Q  (z) =  e [  /T H (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 Velocity  = V SH 2 /V SV 2

Anisotropic Quality Factor  = Q SH 2 /Q SV 2

Tomography  : No net perturbation  : Smoothing constraint Inversion: Velocity: Quality Factor:

What is Anelasticity? Anelasticity: The property of a solid indicating that deformation depends on the time and stress. Anelasticity: The property of a solid indicating that deformation depends on the time and stress. AnelasticElastic SpringSilly Putty

Purely Elastic Anisotropy Fast DirectionSlow Direction

Anelastic Anisotropy Elastic DirectionAnelastic Direction

SAW16B16AN v. VQM3DA SAW16B16AN Uses surface & body waves Spherical Harmonics Gung et al., [2003] VQM3DA: Uses only body waves Gains resolution with depth Lawrence & Wysession [2006b] V SH -FastV SV -Fast

1D Quality Factor Structure Measured 30,000 dt* ScS-S Measured 30,000 dt* ScS-S Excellent global data coverage Excellent global data coverage S and ScS reach greater depth with distance S and ScS reach greater depth with distance Lawrence and Wysession [2006 EPSL]

Attenuation vs. Distance ~27,000 Data Points~3,000 Data Points Lawrence and Wysession [2006 EPSL]

Previous Work Lawrence and Wysession [2006 EPSL]

1D Models 9-Layer Model: QLM921-Layer Model Lawrence and Wysession [2006 EPSL]

dt* ScS-S (r) Lawrence and Wysession [2006 EPSL]

Compare Q(r) to Viscosity Lawrence and Wysession [2006 EPSL]

Temperature Constraints Using theoretical calculations of Karato [1993], Jackson et al., [1992, 2002] we compute a theoretical temperature profile. Using theoretical calculations of Karato [1993], Jackson et al., [1992, 2002] we compute a theoretical temperature profile. Our model fits the rough expectation Our model fits the rough expectation Lawrence and Wysession [2006 EPSL]

The Story So Far … Upper and lower mantle quality factor varies significantly laterally as well as with depth. Upper and lower mantle quality factor varies significantly laterally as well as with depth. Quality factor correlates with both observed viscosity and velocity. Quality factor correlates with both observed viscosity and velocity. So far, the Earth appears to be largely thermally driven. So far, the Earth appears to be largely thermally driven. But we are are at the surface … And the Earth is not 1D … So, what does the Earth look like?

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