pdf - Centre de recherche sur les innovations sociales

Energy considerations „ „ „ „ „ „ „

Energy = Force x Distance = J Power = Energy /time = J/s = W 1T vehicle at 100km/h ? 1T falling from top of Eifel tower 1 T of Tnt = 108J Hiroshima H bomb

More numbers „ „ „ „ „

Heat loss by Earth? World ennergy consumption? Magnitude 9 quake? All earthquakes in 1 year 20 km radius impacter?

Gross internal structure of the Earth

How do we know the internal structure? „

„ „ „ „ „

Astronomical observations (moment of inertia shows there must be a dense core) Seismology shows major discontinuities Crust-mantle boundary: Moho Core mantle boundary: CMB No shear waves in outer core => it is liquid Seismic discontinuities are compositional

Ondes sismiques „

„

„

„ „ „

Ondes internes: P (de compression ou longitudinales) et S (de cisaillement ou transversales) Ondes de surface (Love, Rayleigh) Mouvement de la surface du sol. Longueur d’onde: λ Periode: T Vitesse de l’onde v = λ /T

Lithospheric temperature profile

Two different regimes At low temperature, brittle regime, stress increases with depth At higher temperature, ductile regime, strength decreases with temperature (i.e. depth) Transition depends on temperature gradient, i.e. heat flux.

Plate Tectonics

Plate tectonics „ „ „

„

Outer shell of Earth made out of rigid plates Tectonic activity at plate boundaries Geological cycles are opening and closing of ocean basins (Wilson cycle) Plate take part in mantle convection

3 types of plate boundaries „ „ „

Divergent (Ridge) Transform Convergent (Deep sea trench-continental collision)

Sea floor spreading „ „ „

„

35000km long mid-oceanic ridge system Volcanic rocks New sea floor forms on mid oceanic ridge system Moves away and cools down

Evidence: Marine magnetic anomalies

„ „ „

Epoch (~1My) Events (