Tectonics : the Earth quakes [1]

Tectonique : la Terre tremble [1]

The Earth: Our planet is living — Its quakes [Genista]

A slice of globe

Our earthly sphere spreads its two major components in front of our eyes:

 Rocks more or less hard, arranged in layers which we can see, so irregular in shape, in our mountains.
Their erosion gives the thin elements in our soil, which are the basis of our cultures and constructions.
They form a superficial layer, the Earth's crust, called lithosphere —from the Greek lithos = 'stone'.

 Some molten viscous rocks, or lava, at a temperature of 900-1200 °C, which gush out and pour out through cracks made in the underlying layers, until they build up impressivee structures such as aerial or underwater volcanoes.
It comes from a low-viscosity magma, located under the lithosphere and constituting the asthenosphere—from the Greek asthenes = 'weak'.

A heterogeneous crust

The crust, in fact, has neither the same composition, nor the same thickness, depending on the various places :

The oceanic floors are essentially constituted of basalt and are not very thick—6 to 19 miles (10 to 30 km).

The continental blocks are made of varied sedimentary, metamorphic and granitic rocks. Their thickness ranges from 31 miles (50 km) in plains to 62 miles (100 km) in mountain areas.

A discontinuous crust

The crust is not an envelope of one piece.
It is cracked through all its thickness and along impressive distances.
Those cracks encompass pieces called tectonic plates—from the Greek tektonikos = 'which concerns construction'.

Tectonics - In this series