Advances in Conception about Earthquakes - Earthquake Engineering for Structural Design - page 119

Subduction

Divergence

Figure 4.11 Cross-section of the Earth (modified after Uyeda, 2002)

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Mantle convection is extremely sensitive to changes in the surface conditions.
The collision of two plates can reverse the mantle flow. Both plate tectonics and
balanced convection represent a balance between driving and resisting forces and
the change in any force is immediately transmitted throughout the system, causing
a global reorganization. Therefore, the plate tectonics can be interpreted as a non-
equilibrium process in the sense that a small perturbation in the system can cause a
complete reorganization in the configuration and sizes of plates and in the platform
of mantle convection. Such perturbations include stress changes in a plate and plate
to plate collision or separation. Changes in boundary conditions are transmitted
essentially in instantaneous way throughout the system and new plates with new
boundaries form. These changes in topside system formed by plates and mantle
cause mantle convection to reorganize and the topside is fractured into new plates
due to the extension or compression. Therefore, the plate tectonics, as a very
illustrative example of far-from-equilibrium of a self-organized system, may
respond by evolving to a new state. In the frame of this concept it is clear that the
conformation of plates is not permanent. The actual conformation is a temporary
alliance of major and minor plates. The reorganization process episodically
changes direction and speed of plates and redefines the plate configuration.