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Messages From the Deep: Reviewing Seismic Evidence for Deep Mantle Slabs Thermochemical Piles Post-Perovskite Phase Transition Ultra-Low Velocity Zones. and Uncertainties. Ed Garnero Arizona State Univ. Dept. of Geological Sciences. June 21, 2006 5 th Annual COMPRES Meeting. - PowerPoint PPT Presentation
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Messages From the Deep: Reviewing Seismic Evidence for
Deep Mantle Slabs Thermochemical Piles Post-Perovskite Phase Transition Ultra-Low Velocity Zones
Messages From the Deep: Reviewing Seismic Evidence for
Deep Mantle Slabs Thermochemical Piles Post-Perovskite Phase Transition Ultra-Low Velocity Zones
June 21, 2006 5th Annual COMPRES MeetingJune 21, 2006 5th Annual COMPRES Meeting
Ed Garnero Arizona State Univ. Dept. of Geological Sciences
Ed Garnero Arizona State Univ. Dept. of Geological Sciences
and Uncertainties
Multidisciplinary research conducted in collaboration with:
Avants, Megan (UCSC) Ford, Sean (UCB) Hernlund, John (IPGP) Hutko, Alex (UCSC) Igel, Heiner (U Munich) Lay, Thorne (UCSC) Manga, Michael (UCB)
Multidisciplinary research conducted in collaboration with:
Avants, Megan (UCSC) Ford, Sean (UCB) Hernlund, John (IPGP) Hutko, Alex (UCSC) Igel, Heiner (U Munich) Lay, Thorne (UCSC) Manga, Michael (UCB)
McNamara, Allen (ASU) Rokosky, Juliana (UCSC) Rost, Sebastian (U Leeds) Schmerr, Nick (ASU) Thomas, Christine (U
Liverpool) Thorne, Mike (U Alaska) Williams, Quentin (UCSC)
McNamara, Allen (ASU) Rokosky, Juliana (UCSC) Rost, Sebastian (U Leeds) Schmerr, Nick (ASU) Thomas, Christine (U
Liverpool) Thorne, Mike (U Alaska) Williams, Quentin (UCSC)
-- Today --
Some Seismo Truths: Important modeling uncertainties/trade-offs Outlook: possible things to come
Recent results and interpretations Focus on deep mantle ‘high resolution’ work Draw connections to global scales/processes inferred from long wavelength studies
-- Today --
Some Seismo Truths: Important modeling uncertainties/trade-offs Outlook: possible things to come
Recent results and interpretations Focus on deep mantle ‘high resolution’ work Draw connections to global scales/processes inferred from long wavelength studies
Isaacs, Oliver, Sykes [1969]
Why care? …We’d like to better understand:
Mode/style of mantle convection Depth extent, nature of subduction Source of hot spot magma
Mantle H2O budget/cycle
Transition zone structure, dynamics Nature, structure of fluid and solid cores Thermal evolution/budget of deep interior
Why care? …We’d like to better understand:
Mode/style of mantle convection Depth extent, nature of subduction Source of hot spot magma
Mantle H2O budget/cycle
Transition zone structure, dynamics Nature, structure of fluid and solid cores Thermal evolution/budget of deep interior
Seismology Report CardSeismology Report Card
Structural feature Evidence Constrained?
Transition zone layering/topography
Deep mantle heterogeneity
Deep mantle “piles”
D” Vs discontinuity/layering
D” Vp discontinuity/layering
D” anisotropy
Ultra-low velocity zone
CMB topography
Transition zone layering/topography
Deep mantle heterogeneity
Deep mantle “piles”
D” Vs discontinuity/layering
D” Vp discontinuity/layering
D” anisotropy
Ultra-low velocity zone
CMB topography
B+B+ CC
A+A+ B-B-
CC C-C-
BBA+A+
D-D- D-D-
BB C-C-
AA CC
FF FF
Five reasons for bad “Constraints” gradesFive reasons for bad “Constraints” grades
Seismology Report CardSeismology Report Card
1) Poor constraints regarding where on seismic raypath observables occur (travel time delays, extra arrivals, shear wave splitting, etc)1) Poor constraints regarding where on seismic raypath observables occur (travel time delays, extra arrivals, shear wave splitting, etc)
ao
to
Am
plit
ude
Time
inner
Five reasons for bad “Constraints” gradesFive reasons for bad “Constraints” grades
1) Poor constraints regarding where on seismic raypath observables occur (travel time delays, extra arrivals, shear wave splitting, etc)1) Poor constraints regarding where on seismic raypath observables occur (travel time delays, extra arrivals, shear wave splitting, etc)
Seismology Report CardSeismology Report Card
ao
to
a’
t’
Am
plit
ude
Time
inner
Five reasons for bad “Constraints” gradesFive reasons for bad “Constraints” grades
1) Poor constraints regarding where on seismic raypath observables occur (travel time delays, extra arrivals, shear wave splitting, etc)1) Poor constraints regarding where on seismic raypath observables occur (travel time delays, extra arrivals, shear wave splitting, etc)
Seismology Report CardSeismology Report Card
ao
to
a’
t’
Am
plit
ude
Time
inner
Five reasons for bad “Constraints” gradesFive reasons for bad “Constraints” grades
1) Poor constraints regarding where on seismic raypath observables occur (travel time delays, extra arrivals, shear wave splitting, etc)
2) Modeling trade-off between discontinuity location & isotropic heterogeneity
1) Poor constraints regarding where on seismic raypath observables occur (travel time delays, extra arrivals, shear wave splitting, etc)
2) Modeling trade-off between discontinuity location & isotropic heterogeneity
Seismology Report CardSeismology Report Card
Am
plit
ude
Time
New arrival!
inner
Five reasons for bad “Constraints” gradesFive reasons for bad “Constraints” grades
1) Poor constraints regarding where on seismic raypath observables occur (travel time delays, extra arrivals, shear wave splitting, etc)
2) Modeling trade-off between discontinuity location & isotropic heterogeneity
3) Globally, only very long wavelength structure is retrievable, which involves significant smearing, and may not accurately depict physics of interior
1) Poor constraints regarding where on seismic raypath observables occur (travel time delays, extra arrivals, shear wave splitting, etc)
2) Modeling trade-off between discontinuity location & isotropic heterogeneity
3) Globally, only very long wavelength structure is retrievable, which involves significant smearing, and may not accurately depict physics of interior
Seismology Report CardSeismology Report Card
Five reasons for bad “Constraints” gradesFive reasons for bad “Constraints” grades
1) Poor constraints regarding where on seismic raypath observables occur (travel time delays, extra arrivals, shear wave splitting, etc)
2) Modeling trade-off between discontinuity location & isotropic heterogeneity
3) Globally, only very long wavelength structure is retrievable, which involves significant smearing, and may not accurately depict physics of interior
4) Only fraction of a percent of the globe has been probed at “high resolution”, and hence projection of results to global scales is conjecture
1) Poor constraints regarding where on seismic raypath observables occur (travel time delays, extra arrivals, shear wave splitting, etc)
2) Modeling trade-off between discontinuity location & isotropic heterogeneity
3) Globally, only very long wavelength structure is retrievable, which involves significant smearing, and may not accurately depict physics of interior
4) Only fraction of a percent of the globe has been probed at “high resolution”, and hence projection of results to global scales is conjecture
Seismology Report CardSeismology Report Card
~ 2502 km
~ 200 x 700 km~ 1002 km
Five reasons for bad “Constraints” gradesFive reasons for bad “Constraints” grades
1) Poor constraints regarding where on seismic raypath observables occur (travel time delays, extra arrivals, shear wave splitting, etc)
2) Modeling trade-off between discontinuity location & isotropic heterogeneity
3) Globally, only very long wavelength structure is retrievable, which involves significant smearing, and may not accurately depict physics of interior
4) Only fraction of a percent of the globe has been probed at “high resolution”, and hence projection of results to global scales is conjecture
5) Still using 1-D techniques to get 3-D answers….
1) Poor constraints regarding where on seismic raypath observables occur (travel time delays, extra arrivals, shear wave splitting, etc)
2) Modeling trade-off between discontinuity location & isotropic heterogeneity
3) Globally, only very long wavelength structure is retrievable, which involves significant smearing, and may not accurately depict physics of interior
4) Only fraction of a percent of the globe has been probed at “high resolution”, and hence projection of results to global scales is conjecture
5) Still using 1-D techniques to get 3-D answers….
Seismology Report CardSeismology Report Card
Messages From the Deep: Reviewing Seismic Evidence for Deep Mantle Slabs,
Thermochemical Piles, Post-Perovskite Phase Transition, Ultra-Low Velocity Zones
Messages From the Deep: Reviewing Seismic Evidence for Deep Mantle Slabs,
Thermochemical Piles, Post-Perovskite Phase Transition, Ultra-Low Velocity Zones
A Mineral Physicist’s Guide to Disbelieving Seismologists
A Mineral Physicist’s Guide to Disbelieving Seismologists
IgnoringEmbracingOstracizingCanonizingEnslaving
::
IgnoringEmbracingOstracizingCanonizingEnslaving
::
Unparalleled seismic network seismometer populations (e.g., NSF-funded EarthScope’s USArray)
Enables technique refinement/developmentPermits structural retrieval at smaller scale lengths
Unparalleled seismic network seismometer populations (e.g., NSF-funded EarthScope’s USArray)
Enables technique refinement/developmentPermits structural retrieval at smaller scale lengths
Seismology Report Card: Grades Rapidly Improving !Seismology Report Card: Grades Rapidly Improving !
Better computational capabilities
2- and 3-D wave propagation computations doableWe are approaching capabilities of benchmarking solution structures
Better computational capabilities
2- and 3-D wave propagation computations doableWe are approaching capabilities of benchmarking solution structures
Advances in mineral physics, geodynamics, & geochemistry
Provides significant guidance of our research targets and goals
Advances in mineral physics, geodynamics, & geochemistry
Provides significant guidance of our research targets and goals
Recent Seismic ResultsRecent Seismic Results
Some short seismic modeling vignettes relating to:
-Slabs in the lower mantle
-Post-perovskite phase transition
-Ultra-low velocity zone
-Deep mantle piles?
Recent Seismic ResultsRecent Seismic Results
200-800 km depth
Upper mantle, transition zone structure in the central Pacific
400-1000 km depth
Slab detection fromseismic reflections
between
2800-2900 km depth
Ultra-low velocityzone structure
2400-2800 km depth
D” discontinuitytopography
2400-2800 km depth
D” fine-scalelayering
Recent Seismic ResultsRecent Seismic Results
200-800 km depth
Upper mantle, transition zone structure in the central Pacific
400-1000 km depth
Slab detection fromseismic reflections
between
2800-2900 km depth
Ultra-low velocityzone structure
2400-2800 km depth
D” discontinuitytopography
2400-2800 km depth
D” fine-scalelayering
Long wavelength suggestion:Some slabs continue to CMB.
dVs: Grand [2002]Hutko, Lay, Garnero, Revenaugh [Nature, 2006]
Fine-Scale D” Structure Beneath the Cocos PlateFine-Scale D” Structure Beneath the Cocos Plate
Thomas, Garnero, Lay [JGR, 2004]
200-300 km above CMB
0.5-3% velocity increase
consistent with onset of post- perovskite phase
A few % discontinuous dVs increase is consistent with the post-perovskite phase transition
Lay et al. [EOS, 2005]Lay et al [PEPI, 2004]
e.g., Murakami et al. [Science, 2004]
Observations:
Fine-Scale D” Structure Beneath the Cocos PlateFine-Scale D” Structure Beneath the Cocos Plate
Hutko, Lay, Garnero, Revenaugh [Nature, 2006]
Results: Vertical Step in D” Discontinuity:Height of D” increases by 100 km over >200 km horizontally
Hutko, Lay, Garnero, Revenaugh [Nature, 2006]
Fine-Scale D” Structure Beneath the Cocos PlateFine-Scale D” Structure Beneath the Cocos Plate
After Crampin [1981]
D” anisotropy
After Crampin [1981]
D” anisotropy
D” anisotropy
Rokosky, Lay, Garnero [EPSL, 2006, in press]
The apparent step in the The apparent step in the D” layer coincides with a D” layer coincides with a change in D” anisotropy change in D” anisotropy parametersparameters
S, SdiffS, SdiffScSScS
Garnero, Maupin, Lay, Fouch [Science, 2004]Maupin,Garnero,Lay,Fouch [JGR, 2005]
Hutko et al. [Nature, 2006, in press]
Recent Seismic ResultsRecent Seismic Results
200-800 km depth
Upper mantle, transition zone structure in the central Pacific
400-1000 km depth
Slab detection fromseismic reflections
between
2800-2900 km depth
Ultra-low velocityzone structure
2400-2800 km depth
D” discontinuitytopography
2400-2800 km depth
D” fine-scalelayering
Raw array data: Fiji EQ recordedon the Canadian Yellowknife Array
Rost,Garnero,Williams [in prep., 2006]
Array processed data:Each trace = stack at a different Incoming angle to the YKA array
Rost,Garnero,Williams [in prep., 2006]
Back projecting along determinedback azimuth and slowness of eachprecursor permits estimation of reflection location that matches differential time between precursor and the direct PP wave
Rost,Garnero,Williams [in prep., 2006]
Rost,Garnero,Williams [in prep., 2006]
Recent Seismic ResultsRecent Seismic Results
200-800 km depth
Upper mantle, transition zone Structure in the central Pacific
400-1000 km depth
Slab detection fromseismic reflections
between
2800-2900 km depth
Ultra-low velocityzone structure
2400-2800 km depth
D” discontinuitytopography
2400-2800 km depth
D” fine-scalelayering
Williams and Garnero [Science, 1996]
Ultra-low velocity zones at Earth’s core mantle boundaryUltra-low velocity zones at Earth’s core mantle boundary
ULVZ Thickness
(km)
Thorne and Garnero [JGR, 2004]
Not detected globally
Isolated anomalous zones
Best attempt at global coverage ( ~40 % )
Thickness depends of several assumptions
Uncertainties in global ULVZ details quite large
Ultra-low velocity zones at Earth’s core mantle boundaryUltra-low velocity zones at Earth’s core mantle boundary
Rost,,Garnero,Williams,Manga [Nature, 2005]
Best-fit model properties:
Thickness : 8.5 (1) km DVP : -8 (2.5) % DVS : -25 (4) % D : +10 (5) %
Ultra-low velocity zones at Earth’s core mantle boundaryUltra-low velocity zones at Earth’s core mantle boundary
5 to 30 vol.% melt
no spreading along CMB
trapped intercumulus liquid
incompatible-element
enriched liquid
crystals are initially overgrown
and trap residual
requires large overlying thermal anomaly
downward percolation of melt
correlation to dynamic instabilities/upwellings
probably a fixed base for mantle upwellings
Conceptual model possibility
Rost, Garnero, Williams, Manga [Nature, 2005]
Ultra-low velocity zones at Earth’s core mantle boundaryUltra-low velocity zones at Earth’s core mantle boundary
Recent Seismic ResultsRecent Seismic Results
200-800 km depth
Upper mantle, transition zone structure in the central Pacific
400-1000 km depth
Slab detection fromseismic reflections
between
2800-2900 km depth
Ultra-low velocityzone structure
2400-2800 km depth
D” discontinuitytopography
2400-2800 km depth
D” fine-scalelayering
Lay, Hernlund, Garnero, Thorne [Science, 2006, in review]Avants, M., T. Lay, S. Russell, and E.J. Garnero [JGR, 2006]Avants, M., T. Lay, and E.J. Garnero [GRL, 2006]
dVs [Grand, 2002]
Central Pacific D” LayeringCentral Pacific D” Layering
Lay, Hernlund, Garnero, Thorne [Science, 2006, in review]
Central Pacific D” LayeringCentral Pacific D” Layering
Bin1 Bin2 Bin3
Central Pacific D” LayeringCentral Pacific D” Layering
~ 1000 km
~ 50
0 km
Lay, Hernlund, Garnero, Thorne [Science, 2006, in review]
Recent Seismic ResultsRecent Seismic Results
200-800 km depth
Upper mantle, transition zone structure in the central Pacific
400-1000 km depth
Slab detection fromseismic reflections
between
2800-2900 km depth
Ultra-low velocityzone structure
2400-2800 km depth
D” discontinuitytopography
2400-2800 km depth
D” fine-scalelayering
Schmerr and Garnero[2006, JGR, in press]
SS waves and precursors
Probing the Transition Zone Regionally: Central Pacific Probing the Transition Zone Regionally: Central Pacific
Schmerr and Garnero[2006, JGR, in press]
- Thinning of the TZ ( ~ 15 km average)
- 410 disc slightly depressed
- 660 disc upwarped
Probing the Transition Zone Regionally: Central Pacific Probing the Transition Zone Regionally: Central Pacific
Thorne, Garnero, Grand [2004, PEPI]
Slabs: at least to 1000 km
Step in D” discontinuity:consistent w/ slab piling/folding
Very localized ULVZ:dense, partial melt,base of upwelling
D” stratification:LLSVP, pPv, ULVZ
Thinnedtransition
zone
What about chemically distinct piles in the deep mantle?
Pacificanomaly
Africananomaly
South pole
Caribbeananomaly
corecore
mantle
Sharp top
Ni and Helmberger [2003,2005, Science, EPSL]Ford, Garnero,McNamara [2006, JGR]
Sharp “edges” to low velocities inferred from seismic waveforms
Thorne, Garnero, Grand, PEPI., 2004
red: lowest velocities for S20RTS
green: strongest lateral VS gradients
Indirect evidence from global tomographyIndirect evidence from global tomography
Model: Grand 2002Iso-velocity contour: - 0.7%Hotspots:
Deep mantle shear velocity and hot spots
Thorne, Garnero, Grand [2004, PEPI]
Summing upSumming up
Topic More constrained Less constrainedDeep mantle heterogeneity
Long wavelength dVs patterns
Short scale structure, Vp
Deep mantle anisotropy It exists, it laterally varies
Strength, depth distribution, geometry
D” discontinuity dVs reflector strength, location
Sharpness, height above CMB, dVp disc, deeper disc assoc. w/ pPv phase
ULVZ It exists, it laterally varies
Except for one spot: internal properties, geographical distribution, sharpness
Deep mantle slabs Existence in upper half of lower mantle
Structure/behavior in lower half of the mantle
Deep mantle piles Abrupt transition between low velocities and mantle
Density, internal structure
Today: lots of seismically imaged short scale details in just a few spots of the volume of the interior
“there are known unknownsand unknown unknowns”
Point: Where we’re afforded the ability to image in great detail, richness in complexity is apparent
Garnero [Ann. Rev. , 2000]Garnero, Maupin, Lay, Fouch [Science, 2004]
[email protected]://garnero.asu.edu