The state of stresses in the upper part of the earth's crust

The measurement of the absolute stresses in the earth's crust was begun in Sweden in 1951, is still proceeding in Scandinavia and has been extended to other parts of the world. The presence in the earth's crust in these areas of a general horizontal stress field has been established, which at any point is usually several times the dead weight of the overlying rock, and highly directional. The sum of the horizontal principal stresses,σ₁ + σ₂, is 180 kgf/cm² at the crust surface and increases linearly with depth; for instance at 1,000 m it is 1,000 kgf/cm².The existence of horizontal fissuring of the bedrock down to great depth is discussed, as is the reason for their appearance. The upper part of the earth's crust seems to be in a state of dynamic but not static equilibrium. The stability of wide underground openings is discussed. An account is given of the technique for measuring the absolute rock stress.