Dr. Geoff Abers Examines Subduction Plates "From Thrust Zone to Subarc"

  • Sep 22, 2018

EES is proud to welcome our Distinguished Speaker Dr. Geoff Abers, Professor, Earth and Atmospheric Sciences, Cornell University.

Abers is a geophysicist who uses the tools of earthquake seismology to understand the forces, material cycles, and deep structure of the Earth. He uses modern seismic instrument arrays onshore and offshore to image high-resolution structure in the crust and mantle, and uses those images to understand the material and fluid cycles of the planet.

 

"The Subduction Plate Interface and Mantle Wedge from Thrust Zone to Subarc."

The last two decades have seen a quantum increase in our understanding subduction zones with the advent of dense high-quality seismic imaging arrays. Two primary parts of the subduction system have been particularly well illuminated: the plate interface and the arc/forearc mantle wedge. The plate interface should exhibit a transition in properties downdip from the megathrust fault zone to the region of high-temperature devolatilization that feeds the roots of volcanic arcs. However, the boundary has many characteristics that appear continuous through this transition. At the 1-5 km scale, the teleseismic scattered wavefield indicates a uniformly layered plate interface structure. By contrast, reflections and high-frequency P-S converted waves show complex discontinuous interfaces at the 10-100 m scale that imply much greater heterogeneity, indicating the hierarchical nature of shear zones. This sharply layered zone contrasts strongly with the overlying mantle wedge, which is relatively transparent to seismic waves. The wedge is dominated by a larger-scale transition from a cold forearc “nose” and a hot sub-arc mantle, a transition near 80 km depth that shows up strongly in heat flow and seismic attenuation but not wavespeeds. Within the cold part of the wedge, comparison with wavespeeds suggests relatively dry conditions except for places like Cascadia where young plates subduct. The high seismic attenuation in the hot parts of the wedge far exceeds predictions from temperature sensitivity alone, and requires significant in situ melt to be present. Overall, seismic images of this system are now allowing meaningful integration with geodynamics, geology, petrology, and other related disciplines.

Abers is a Fellow of the American Geophysical Union and the the Geological Society of America, and a member of the Seismological Society of America. He is currently the Vice Chair of the Board of Directors of the Incorporated Research Institutions for Seismology, and former chair of the US MARGINS program.

Come see this new look at subduction plates on Friday, September 28, 2018 at 12:30 PM in Room 204, Natural Science Building on the East Lansing