Stress guide

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The idea of stress guide is a concept in plate tectonics that appeared in 1967 in a report [1] by Walter Elsasser. A paper with the same title was later published in 1969 in a book edited by S. K. Runcorn [2].

In Elsasser (1969)[2], the Earth is divided into 3 layers based on viscosity: the topmost tectosphere (terminology used in Elsasser,1969; but now known as lithosphere), the asthenosphere, and the mesosphere. The asthenosphere is marked by a pronounced minimum of viscosity.

The lithosphere acts as a stress guide which can transmit stress horizontally over large distances in the lithosphere. In Elsasser’s paper, the lithosphere is not a passive feature whose motion is carried by the mantle convection cells. Instead, the lithosphere slides on top of the asthenosphere due to gravity from the mid-ocean ridges toward the subduction zones.

Isacks and Molnar (1969) estimated the stress state within the subducting plates (known as slabs), by studying the deep earthquake seismic radiation patterns, also known as the focal mechanisms. Isacks and Molnar’s results suggest that downgoing slabs act as stress guide: slabs are stiff and can support large stresses within it, however, the shear stresses along the upper and lower boundaries of the slab are small. As a result, the principal axes of stresses in the slab are parallel and perpendicular to the plate, confirmed by the deep-earthquake focal mechanisms. In the paper by Isacks and Molnar (1969) [3], they cited Elsasser's work.

References

  1. Elsasser, W. M. (1967), Convection and stress propagation in the upper mantle, Princeton University Tech. Report. 5, June 15, 1967.
  2. 2.0 2.1 Elsasser, W. M. (1969), Convection and Stress Propagation in the Upper Mantle, in The Application of Modern Physics to the Earth and Planetary Interiors, edited by S. K. Runcorn,vol. pp. 223-246Vol. Series editor  Wiley, New York.
  3. Isacks, B., and P. Molnar (1969), Mantle Earthquake Mechanisms and the Sinking of the Lithosphere, Nature, 223(5211), 1121-1124.