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Tectonics : the Earth quakes [1]
Tectonique : la Terre tremble [1]
The Earth : Our planet is living - Its quakes [Genista]
By Nicolle Mathé, 'Genista Informations' No. 293, May 2003 (Plate tectonics)
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![the Earth [la Terre]](../../i/globe.gif)
The Etna is turbulent, as are its nearby neighbours, the Stromboli and the Vulcano -- and the Vesuvius gives unrest.
The Earth quakes here and there in the Alps, the Pyrenees, Turkey, Greece...
Lots of questions justle about :
is there a link between all these events ? Can one foresee the places and yimes of these tremblings ? Will our
Mediterranean sea, that we ill-treat so much, exist forever ?
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![section of the Earth from the surface down to the centre [coupe de la Terre de la surface jusqu'au centre]](it/tercrout.gif)
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 naither the same composition, nor the same thickness, depending on the various places :
The oceanic floors are essentially constituted of basalt and are not very think — 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.
![the tectonic plates of our planet Earth [les plaques tectoniques de notre planète Terre]](it/plaqnoms.gif)
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'.
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Tectonics - In this series
TECTONICS : THE EARTH
(1) Our planet is living : its quakes (The present Page)
(2) Drift away, plates : the drift
(3) It folds or it breaks : an active planet
TECTONICS : THE MEDITERRANEAN SEA
(4) The Mediterranean Sea : a jigsaw puzzle
(5) In the Mediterranean Sea : meditate...
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Top of Page • [Haut de Page]
Part 2 : Drift away, plates - The drift • [Deuxième Partie : Voguent les plaques - La dérive]