Using Rock Mechanics Concepts in Tectonic settings

Faulting, folding and subduction zones are the result of forces exceeding the strength of the rock in the earth crust and mantle, hence, if the yield/failure limits can be determined, the maximum value of the acting force is established. The rock strength for various temperatures and stress ratios is defined by the Mohr envelope and accepting that the vertical stress component can either be the minimum or the maximum principal stress, the limits of the maximum or minimum principal stress can be determined. By combining these values with the temperature gradients, thermal models and density variations the yield envelopes are determined and illustrated for a base case, a thermal, collision and subduction model. For verification of the results obtained the yield envelopes are transposed onto pressure temperature values of known metamorphic facies diagrams as well as a comparison between predicted and actual seismicity in subduction zones.