What is the Rate-Limiting Step
In furthering our Understanding
of Subduction Dynamics?
Magali Billen
Katrina Arredondo,
- Juan Rodriguez,
- Erin Burkett,
--Margerete Jadamec
-
Processes in Series are Rate-Limited by
Slowest Sub-Process?
 Visco-elastic Deformation of a
Maxwell Solid
 Rate-limited by the slow
response of the viscous dashpot
 Diffusion of Vacancies Through a
Grain
 Rate-limited by slowest diffusing
species
 Leaving for Work in the Morning
 Rate-limited by my son’s
willingness to cooperate…
Sub-Processes in Subduction Studies
COMPILING
OBSERVATIONS
Two sets of observations:
1. Defining Initial State of Models
geometry, thermal structure, age,
material properties from
experiments
2. Testing/Analyzing Model Results
plate/trench motion, mantle flow,
stress-state, topography, gravity,
magmatism, sedimentary record,
seismicity, tomography
Sub-Processes in Subduction Studies
COMPILING
OBSERVATIONS
DESIGNING
NUMERICAL MODEL
• Equations, model size, mesh,
boundary conditions, initial
conditions, instantaneous, timedependent, material properties,
…
• Necessary simplifications??
Sub-Processes in Subduction Studies
COMPILING
OBSERVATIONS
DESIGNING
NUMERICAL MODEL
• Which parameters will be held
fixed, or varied?
• What is range of uncertainty?
• Which observables are sensitive
to specific parameters?
RUNNING SERIES OF
NUMERICAL
EXPERIMENTS
Sub-Processes in Subduction Studies
COMPILING
OBSERVATIONS
DESIGNING
NUMERICAL MODEL
Two Types of Analysis
1. Generalized fluid dynamics,
mechanics
• What happened?
2. Comparison to observations
• Is this applicable to the Earth?
• What does it tell us about the
parameters and processes?
RUNNING SERIES OF
NUMERICAL
EXPERIMENTS
ANALYSIS OF
MODELING RESULTS
NEW UNDERSTANDING
OF SUBDUCTION
DYNAMICS
What is the rate-limiting step for discovery?
Outline
 Rate-Limiting Process in Subduction Studies?
 Some Outstanding Questions in Subduction Dynamics
 Example Studies: Integrating Observations, Numerical
Modeling and Visualization
 Cyber-infrastructure for Subduction Modeling?
 Accelerating the rate-limiting process.
 Conclusions
Question 1:
How do slabs drive plate motion?
 What are the available driving forces?
 How are forces transmitted to the plate?
 What are resisting forces?
 What are the dynamic feedbacks that regulate plate speeds?
Question 2:
What are the main controls on
non-steady-state evolution of slabs?
 What is the effect of large-scale rheological structure (layered, slab)?
 What are the effects of phase changes & related processes (grain-size
reduction, latent heat, localize torques on slab)?
 How is slab motion reflected in plate boundary motion, structure &
deformation of overriding plate?
Question 3:
How do slabs drive flow
in the surrounding mantle?
 What determines the ratio of toroidal-to-poloidal flow in
subduction zones?
 What conditions are necessary to generate significant
trench-parallel flow?
Example 1:
Snapshot of Flow & Deformation
 How does flow at a slab edge
depend on rheology?
 Observations required to
build model:
 Slab shape
 seismicity, tomography,
tectonic history
 Thermal structure
 subducting plate age,
overriding plate heat flow,
terrane data, volcanism,
magnetic data, crustal
thickness from seismic
reflection/refraction data
Example 1:
Snapshot of Flow & Deformation
 Observation used to test model:
 Seismic anisotropy
 Observed plate motion
 Regions of uplift/subsidence
(dynamic topography)
 Volcanism
 Need non-Newtonian rheology,
sharp slab edge, moderate
plate boundary coupling,
moderate slab yield stress to
match suite of observations.
Example 2:
Ridge-Trench Interaction
 What controls the process of slab detachment and ridge
abandonment?
 Observations to constrain: plate age at trench, ridge-trench
geometry, volcanism & deformation of upper plate, location of
fossil slab beneath Baja.
Example 2:
Ridge-Trench Interaction
 Slab detachment controlled by yield strength of the lithosphere.
 Older plate detaches first.
 Younger plate viscously stretches.
 Upwelling of hot mantle through slab gap.
Example 3:
Slab Flattening & Slab-Parallel Flow
 Can variations in overriding plate thermal structure affect
slab dip & mantle flow?
 Observations: some regions with colder overriding plate
also have shallow slab dips – which came first?
Example 3:
Slab Flattening & Slab-Parallel Flow
 3D Model Set-up
 Proto-slab
 Generic subduction zone set-up
 Create proto-slab with kinematic boundary conditions, then let run
fully dynamically.
 Vary geometry and temperature structure of “cold” portion of
overriding plate.
Example 3:
Slab Flattening & Slab-Parallel Flow
 Variation in overriding
plate thermal structure
 Causes shallowing of slab




beneath colder
overriding plate.
 20 degree shallower
Small initial slab-parallel
flow
Slab-parallel flow as
strengthens as slab
shape changes
Slab-parallel flow
beneath slab & in mantle
wedge
Result of non-steadystate deformation & flow.
 Compare with location of
seismic anisotropy.
Outline
 Rate-Limiting Process in Subduction Studies?
 Some Outstanding Questions in Subduction Dynamics
 Example Studies: Integrating Observations, Numerical
Modeling and Visualization
 Cyber-infrastructure for Subduction Modeling?
 Accelerating the rate-limiting processes.
 Conclusions
What do these
examples have in common?
 State-of-the-art numerical modeling software
 3D models
 very large model output (gigabytes per time-step!!)
 Visualization of data & model results is key to
 model analysis
 communication of results
 Observations
 inform model design
 used to test/analyze model results
Cyber-infrastructure
for Subduction Modeling?
 What do we need? Access To And Sharing Of:
NUMERICAL
MODELING
SOFTWARE
VISUALIZATION/
ANALYSIS TOOLS
DATA
Cyber-infrastructure
for Subduction Modeling?
 What do we need? Access To And Sharing Of:
NUMERICAL
MODELING
SOFTWARE
VISUALIZATION/
ANALYSIS TOOLS
DATA
A few years ago, I would have said that new/better
software is the rate-limiting process.
Computational Infrastructure for Geodynamics
• Share and support existing community-developed codes
• Develop new cutting-edge codes
• Train next generation of geodynamicists
Cyber-infrastructure
for Subduction Modeling?
 What do we need? Access To And Sharing Of:
NUMERICAL
MODELING
SOFTWARE
VISUALIZATION/
ANALYSIS TOOLS
DATA
Encourage science-driven
development of visualization
/analysis tools
Generic
Specialized
Maps/2D
3D
Cyber-infrastructure
for Subduction Modeling?
 What do we need? Access To And Sharing Of:
NUMERICAL
MODELING
SOFTWARE
VISUALIZATION/
ANALYSIS TOOLS
DATA
Data Access is the rate-limiting step for furthering
understanding of subduction dynamics.
3D Volume/Point/Tensor Data
2D Map/Line/Point Data
Removing the “re”
from Data Research
 The beginning of each modeling project is a hunt for data...
 Scour the literature for most recent data.
 Is data available?
 Yes – excellent - download!
 No - try to contact PI – willing/ready to share data??
 ... followed by a lot of data combining and processing.
 What format is this data in?
 How can I combine this with N other data sets?
 What is best way to visualize data to look for patterns related to
different processes?
 How do I extract derived quantities (e.g., surfaces) to use as
input into numerical model?
Infrastructure for
Data Access and Sharing
 How is Data Used in Model Design & Analysis?
 How is Data Accessed/Extracted?
 Need Up-to-date Data and Data Options.
Enable flexiblity, but anticipate how scientific questions require data.
Need to make contributing “data” EASY.
 Success depends on making EarthCUBE THE place to
contribute data:
 Motivation for PIs contributing “data” :
 Need to know that data accessed here will lead to referencing
of related published papers.
 How can you make data contributing easy when there are
so many different types of data?
 Point sets
 Maps
 Volumes
 Vectors
 Tensors
Create a framework for the
community to develop and
share this infrastructure.
Conclusions
 Modeling of subduction dynamics is motivated by a range
of scientific questions:
 How do slab drive plate motions?
 What are the main controls on slab evolution?
 How slabs drive surrounding mantle flow?
 Modeling subduction dynamics requires
 Cutting-edge modeling software (CIG)
 Flexible 2D/3D visualization tools (support science-motivated
development)
 Data, lots-of, lots-of data (EarthCUBE)
 Acquiring and manipulating data into a useful form can be
the rate-limiting sub-process
 Facilitate grass-roots development of visualization and data
infrastructure that is driven by how the science is actually being
done.