Hello, Guest! The cause of the earthquake is a rapid displacement of the lithosphere (lithospheric plates) at the time of relaxation (discharge) of the elastic deformation of strained rocks. A tectonic earthquake begins by an initial rupture at a point on the fault surface, a process known as nucleation. The possibility that the nucleation involves some sort of preparation process is supported by the observation that about 40% of earthquakes are preceded by foreshocks. Once the rupture has initiated, it begins to propagate along the fault surface. The mechanics of this process are poorly understood, partly because it is difficult to recreate the high sliding velocities in a laboratory.