PLANETARY MUSINGS

Lithospheric thermal structure

McKenzie, D, J Jackson, K Priestley, Thermal structure of oceanic and continental lithosphere, EPSL, 233, 337-349, (2005), http://dx.doi.org/10.1016/j.epsl.2005.02.005

McKenzie et al re-examine the problem of what controls the depth of earthquakes in the lithosphere (excluding subducted oceanic lithosphere) primarily by using a more sophisticated thermal model than has been typically used. Until Hofmeister's [1999] paper on the variation of thermal conductivity of mantle materials, no simple model for the variation of thermal conductivity with temperature and pressure really existed. However, with Hofmeister's work, follow-on papers by other workers, and pre-existing data used in the Hofmeister-framework, more realistic thermal models are possible, as was done in this paper. Though the results are certainly reasonable, I was a little surprised at the choice to drop the second term from equation (3) if its effect is about 5 degrees C given some of the other small observational variations that the paper discusses. However, I doubt any major conclusions would be changed.... The choice of a linear interpolation for inital crustal temperature was a surprise since it is pretty much emplaced at the melting temperature; though maybe the intial cooling is more rapid (and hence unresolved) by the time-steps used. Influence would only be near the ridge axis anyway. The inability to accurately reproduce heat flow through old oceanic plates is something that has apparently been known for some time, but is relatively new to me. I suppose there may be a change in the style of convection (small scale) beneath oceanic plates.

Temperature as the primary control on depth of earthquakes is not a surprising idea, but I wonder how much of it has to do with strain-rate?