Geotectonic relevance of rock-stress determinations

Abstract

An analysis of in-situ rock-stress measurements shows that the variation of average horizontal stress with depth depends on the tectonic environment. Although the scatter is very large, Precambrian shield rocks usually show average horizontal stress in excess of the overburden pressure, whereas sedimentary cover rocks show average horizontal stress less than the overburden pressure at depths larger than approximately 500 m. Principal horizontal stress directions are sometimes consistent over large regions, but the geographic distribution of observations leaves many areas of the world uncovered. Interpretation of in-situ stress determinations is complicated by the influence of many factors (depth, topography, erosion, geologic structure) on the results. It generally appears that large near-surface horizontal stresses can be generated by factors other than the tectonic stress field. Another source of complexity is the influence of remanent stress. Quantitative evaluation of the factors affecting the measurements is necessary before unequivocal inferences on global tectonics can be drawn from the available evidence.