Stress observations and driving force models for the South American plate

Stress observations are compared to predictions of driving force models for the South American plate. Stress observations have the potential to give detailed information about the forces driving the plates, in that sets of forces with the same net torque can produce quite different stress patterns. The South American plate has a small slab pull component, amounting to about one-fifth the ridge push force, with the other components reasonably isolated geographically. Thus, the plate balance is largely between ridge push and plate drag. This gives an opportunity of resolving the effects of trench suction or collision at the subduction zones. Most remarkable is the nearly uniform E-W orientation of the regional stress field, SH_max directions, which is extensional in the high Andes; a second feature is the N-S orientations in the Amazon basin. Models with ridge push, slab pull at the Scotia and Caribbean arcs, and trench suction near the west coast, balanced by plate drag, produce similar stress patterns to those observed. -from Authors