Earthquakes and Cracks of New Type Complementing the Griffith–Irwin’s Crack

The paper is devoted to the issue on the existence of a new type of cracks, complementing the Griffith–Irwin cracks. These cracks explain one of the mechanisms of fracture of brittle solids, consisting in the appearance of a singular concentration of contact stresses in converging lithospheric plates. The main difference between the Griffith–Irwin cracks and the cracks of new type is that the Griffith–Irwin cracks have a smooth boundary with an apex angle of 180°. Griffith explained their formation as the result of continuous deformation of an unbounded plate with an elliptical cavity into a cavity with rectilinear lateral boundaries resulting from compression of the elliptical cavity from the sides. There are smooth curves at the apices of the cavity. Cracks of new type are formed as a result of compression from the sides of a rectangle instead of an ellipse. The result is a cavity with a piecewise-smooth boundary and an apex angle equal to zero. The study was conducted under the assumption of the absence of friction in the contact area of the lithospheric plates with the base in the first case and the presence of only tangential contact stresses in the second case. In addition, it has been shown that numerous studies of wedge-shaped cavities turning into cracks when the wedge angle tends to zero give rise to a Griffith crack and cannot generate a cracks of new type.