MY RESEARCH ON SUBDUCTION ZONES
Subduction zones are locations where one plate (typically oceanic) is
descending under another plate. The cartoon below illustrates how we
envision a subduction zone.
Because we can not see into the Earth directly, we have to rely on indirect observations and theoretical models to understand the
formation, structure, and evolution of regions like subduction zones.
For much of the work I do, I use the long-wavelength gravitational
potential, or geoid, as an observation to constrain models of thermal
convection.
...Section on Convection to be added...
Observed geoid elevations at degrees 2-10: yellow is 100 meters, light blue is -110 meters. |
The geoid of the Earth has a very long wavelength signature, as seen in the image to the left, which is taken from Hager (1984). The longest wavelength part of the geoid correlates very well with tomographic images of the seismic velocity variations in the mantle.
If we assume that the variations in seismic velocity can be directly
related to variations in denisty (i.e., the seismic velocity variations
are controlled by temperature) then we can model the longest wavelength
part of the geoid by the density anomalies in the lower mantle.
The resulting geoid anomalies (left image of the Plate below from Hager (1984) (below) are strongly correlated with the location of subduction
zones. In fact we can model this residual geoid signal by making
reasonable assumptions about the density of the subducting slabs (the
middle and right images the from Plate below).
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(Left) Observed geoid, (Middle) Geoid computed from a Rigid-Earth Slab model, (Right) Geoid computed from a Dynamic Slab model,
all for degrees 4-9. Shading is elevation in meters where yellow is 40 m and light blue is -40 m. |
My work attempted to use the residual geoid over subduction zones to constrain thermal convection models with slab like features.
Below is the temperature field from a 2-D calculation with a slab like
feature in the middle of the box. The color shading is such that blue
is cold material and red is hot.
References
Hagar, Bradford H. Subducted Slabs and the Geoid: Constraints on Mantle Rheology and Flow. Journal of Geophysical Research, v. 89, no. B7, p. 6003-6015, July 10, 1984.
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