Movement of the Earth’s Surface from Within - Southern England - page 31

FIG 29. World map showing the present pattern of the largest lithosphere plates.
Most of the strength difference between the lithosphere and the asthenosphere de-
pends on the temperature difference between them. The lithosphere plates are cooler
than the underlying material, so they behave in a more rigid way when subjected to the
forces generated within the Earth. The asthenosphere is hotter and behaves in a more
plastic way, capable of deforming without fracturing and, to some extent, of 'flowing'.
Because of this difference in mechanical properties and the complex internal forces
present, the lithosphere plates can move relative to the material below. To visualise the
motion of the plates, we can use the idea of lithospheric plates floating on top of the
asthenosphere.
Looking at the surface of the Earth (Fig. 29), the largest plates show up as relat-
ively rigid areas of the lithosphere, with interiors that do not experience as much dis-
turbance as their edges. Plates move relative to each other along plate boundaries , in
various ways that will be described below. The plate patterns have been worked out by