State of stress in the upper part of the Earth's crust based on direct measurements in mines and on tectonophysical and seismological studies

Measurements of the state of stress in the Earth's crust were made in several areas in the U.S.S.R. The orientation of the principal stresses vary from region to region. In some areas, the principal compressive stress is vertical and in others it is horizontal. Usually, the vertical normal stress is approximately equal to the weight of the overburden, but in some places it is larger and in others it is smaller. It may be noted that the horizontal normal stress often exceeds the weight of the overburden. The principal stresses often are not parallel to the stresses that caused deformation earlier in geologic time. Thus, ancient geologic deformation is not always a reliable method for inferring recent stress fields. These stress fields change with time.