Strain and stress

Structural analyses of specific features in naturally deformed rock consist of geometric observations (e.g. shape), kinematic measurements (e.g. strain), and dynamic models (e.g. stress). Although analytical definitions clearly distinguish strain and stress, common usage of the terms tends to blur the conceptual difference. Strain and stress do not have a simple cause-and-effect relationship. The fundamental difference between strain and stress is that strain terms reflect descriptive interpretations of what movements produced a structure, while stress terms reflect genetic interpretations of why the structure formed. This descriptive vs genetic distinction has several implications. First, kinematic analysis is less speculative and more directly related to observations than dynamic analysis. Second, kinematic analysis is less computationally and analytically intensive than dynamic analysis. Third, kinematic analysis is amenable to more intuitive, but shallower, understanding than dynamic analysis. The most useful terminology communicates this conceptual framework through clear and accurate use of terms for strain, stress, and related concepts. A variety of examples illustrate the descriptive and genetic usage of strain and stress terminology.