Subduction Zone
Observatory
Big Geodynamics-Related Science Questions
Magali Billen
Department of Earth & Planetary Sciences
UC Davis
Collaborators & Students: Ana Negredo-Moreno, Juan RodriguezGonzalez (PD), Katrina Arredondo (GS), John Naliboff (PD), Taras Gerya,
Manuelle Faccenda
Big Geodynamics Science Questions

From the Bottom Up:
 What do we know (or not know) about plate boundary shear
zone coupling?
 What is the role of the overriding plate?
 How does Internal deformation of the slab occur (faulting 
plastic flow)?
 How does the slab couple to the mantle
wedge/asthenosphere?
 What are the mechanisms & controls on intermediate & deep
seismicity?
 What controls slab interaction with the transition zone?
 When do slabs make it to the CMB?
Key Issues for SZO
 From the Bottom Up:

What do we know (or not know) about plate boundary shear
zone coupling?

What is the role of the overriding plate?

How does Internal deformation of the slab occur (faulting 
plastic flow)?

How does the slab coupling to the asthenosphere?

What are the mechanisms & controls on intermediate & deep
seismicity?

What controls slab interaction with the transition zone?

When do slabs make it to the CMB?
Asthenosphere & Mantle Wedge
What is the role of non-
linear rheology?
How can we better use
numerical models to
constrain mantle flow &
dynamics?
Need more seismic
observations beneath the
oceanic side of subducting
plates are needed?
Miller & Becker,
Nature 2012
Faccenda &
Capitanio,
G3, 2013
Asthenosphere & Mantle Wedge
Moving beyond the
corner flow…
Affect of melt buoyancy
and hydration on flow
Gerya & Yuen, EPSL 2003
Need higher resolution
seismic data & EM
imaging of all kinds and
modeling that includes
melt & fluids
McGary et al., Nature 2014
Affect of the Overriding Plate
 Overriding plate motion
 Trench retreat/advance
 Thickness variations can
affect slab shape and dip
 Modifies flow in the mantle
wedge
 Better constraints on present
and past structure are
needed to interpret slab
evolution
 Vary overriding plate structure
in numerical models **
Rodriguez-Gonzalez,
EPSL 2014
Taramon et al.,
submitted
Affect on the Overriding Plate
 Stress state & volcanism depends on
how slab & overriding plate interact
 Compression versus extension
 Transfer of stresses inboard of the
plate boundary
 e.g., Andes, Aleutians…
 Depends on existing structure and
the nature of the plate boundary
shear zone.
 Collect more data on surface
deformation and changes in time
 Predict and compare overriding
plate deformation in numerical
models **
Jadamec et al., EPSL 2013
Plate Boundary Shear Zone
In dynamical models, this is a low viscosity shear zone
or channel.
No strong, independent constraints on value of
effective viscosity
Chosen to get “realistic” rates given rest of model
design.
Important for all other aspects of subduction dynamics
and surface deformation.
Naliboff et al., AGU 2014
Arredondo & Billen AGU 2014
Plate Boundary Shear Zone
Physically related to
short time-scale
seismogenic properties.
Need to devote
attention to the
properties that link the
behavior across timescales: fluids,
mineralogy, grain size,
rheology, …?
Audet & Burgman, Nature 2014
Geodynamics & Other Topics in SZO
Other Topics in SZO
Geodynamics
 Hazards
 The plate boundary shear zone
 Faulting & Deformation
 Deformation of the subducting plate
 Volcanism
 Affect of/on the overriding plate
 Asthenosphere/mantle wedge rheology
Conclusions & Suggestions
 Recent models illustrate potential
deeper insights
 More, higher resolution seismic/E-M
imaging data & other seismic
constraints are needed
Li et al., JGR 2014
 More realistic, higher resolution
geodynamical models are also
needed.
 Focus on bridging time-scales of
physics from long term tectonics to the
earthquake hazards.
Liu & Stegman, Nature 2012