1. Subduction Zone Observatory Big Geodynamics-Related Science Questions Magali Billen Department of Earth & Planetary Sciences UC Davis Collaborators & Students: Ana Negredo-Moreno, Juan Rodriguez- Gonzalez (PD), Katrina Arredondo (GS), John Naliboff (PD), Taras Gerya, Manuelle Faccenda

2. 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?

3. 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?

4. 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, G 3, 2013

5. Asthenosphere & Mantle Wedge  Moving beyond the corner flow…  Affect of melt buoyancy and hydration on flow  Need higher resolution seismic data & EM imaging of all kinds and modeling that includes melt & fluids Gerya & Yuen, EPSL 2003 McGary et al., Nature 2014

6. 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

7. 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

8. 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. Arredondo & Billen AGU 2014 Naliboff et al., AGU 2014

9. Plate Boundary Shear Zone  Physically related to short time-scale seismogenic properties.  Need to devote attention to the properties that link the behavior across time- scales: fluids, mineralogy, grain size, rheology, …? Audet & Burgman, Nature 2014

10. Geodynamics & Other Topics in SZO  Hazards  Faulting & Deformation  Volcanism  The plate boundary shear zone  Deformation of the subducting plate  Affect of/on the overriding plate  Asthenosphere/mantle wedge rheology Geodynamics Other Topics in SZO

11. Conclusions & Suggestions  Recent models illustrate potential deeper insights  More, higher resolution seismic/E-M imaging data & other seismic constraints are needed  More realistic, higher resolution geodynamical models are also needed.  Focus on bridging time-scales of physics from long term tectonics to the earthquake hazards. Li et al., JGR 2014 Liu & Stegman, Nature 2012