Advances in Conception about Earthquakes - Earthquake Engineering for Structural Design - page 122

Computed
earthquakes

Rigid
plate

Rigid plate

Plate
boundary

(a)

Figure 4.13 (continues)

(b)

Figure 4.13 Block structure of South American Plate: (a) Model of block and
resulting earthquakes; (b) Produced earthquakes (modified after Rozenberg et al,
2002)

So, after this model, an earthquake is the result of the loss of the block system
equilibrium (Soloviev, 2001, Soloviev and Maksimov, 2001, Digas et al, 2001,
Rozenberg et al, 2002). The motion of a block is defined so that the system is in a
static state of equilibrium, being stressed by the forces resulting from convective
currents in the Earth mantle. When the ratio of the stress to the pressure exceeds a
critical level in some part of a fault zone, a slip between two adjacent blocks
occurs. This slip represents a loss of equilibrium and a jump occurs until a new
position of equilibrium, far from the original one. This new position is reached
when stress and pressure along the fault find a new equilibrium condition. The
jump is a dynamic process and it generates the earthquakes, the oscillations round
the new position producing waves, which propagate in the crust until the surface.
After this stress relaxation and due to the fact that the external forces, produced
by convective currents, continue to exist, a new accumulation of deformation takes