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Convergent Margins Processes National Meeting Summary Report
National Meeting Summary Report
Posted by .(JavaScript must be enabled to view this email address) on 06/29 at 02:30 PM
Key Questions
What are the processes that govern coupling on subduction megathrusts?
- Better characterize ETS in Alaska and compare to emerging results in Cascadia, Puerto Rico, and globally
- Correlate ETS with large earthquakes
- Understand ETS/small earthquake dynamics
- Determine fraction of moment budget that goes into slow slip
- How thick is the slab interface on the megathrust and elsewhere?
- What are its poroelastic properties and how do they correlate with tremor/slip behavior?
- What is the relationship between volcanic eruptions and megathrust behavior?
How do the slab, surrounding mantle and upper plate interact?
- How does mantle flow around the slab compare in Cascadia, Alaska, the Aleutians, and Puerto Rico? Is WNA-style toroidal flow common?
- What are the geochemical/petrological tests of toroidal flow?
- How does subducting plate couple to upper plate deformation?
- How do accreted terranes deform in active convergent margins and in the Appalachians?
- How much of upper plate topography is dynamically vs. isostatically supported?
– Globally compare behavior of “unsubductable” lithosphere, including Yakutat block and Cascadia
What processes govern the cycling of fluids and magma?
- Why does water recycling vary so irregularly along-strike in arcs?
- Why does magma output vary along-strike?
- Temperature, water, magma: What are their implications for rheology, deformation and seismicity?
– Local variations in magma storage depth? – Volcano deformation? – Shallow vs. deep recycling of water?
– Melting processes at depth? – Shallow plumbing? – Need to compare seismic velocities and MT images – Compare to old arcs (e.g.Talkeetna)
Convergent margin questions in the Eastern U.S. – the Ouachitas and Appalachians
- When continental mantles collide, does accretion occur by Himalayan-style sub-horizontal shear vs. New Zealand style mantle shortening?
- How does the style of deformation vary as a function of orogenic age?
- How deeply does localized deformation extend? How wide are deformation zones as a function of depth?
“High risk/reward” Ideas I
What is the rheology of the slab interface through the earthquake cycle, including the ETS cycle?
- Test physical models of interface rheology with ETS, post-seismic deformation, gravitational stressing (tides, glaciers), structural images of interface properties, and pore pressure changes during slip changes.
- Attempt to image a (thin) fluid-rich zone on the subduction mega-thrust in Cascadia.
- Need seismic imaging at wide variety of scales, active and passive.
- Consider adding to OBSs: fluid flux meters to correlate pore fluid output with slip events, accelerometers, pressure gauges, MT, gravimeters
- Instrumentation of an offshore borehole?
“High risk/reward” Ideas II
- Capture a Mw>8 earthquake, looking in subduction zones on a global basis
- Characterize ETS leading up to earthquake
- Did not achieve consensus on instrumentation needs
Thematic Workshop Ideas
- Fluid/magma pathways and storage from subduction to volcano
- Rheological and stress controls on the seismic cycle
- Terrane accretion and continental growth
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