Construire des modèles sphériques de Terre

Ondes P et S

Ondes P et S

Vitesse des ondes de Love

T = 40 s

T = 70 s

T = 150 s

www.geologie.ens.fr/~madariag

Tomographie globale

B. Romanowicz

Grand 2002

Tomoondes Pvd Hilst1998

Tomographie globale

- Séismes enregistrés depuis 1965 (100 000 événements bien localisés)- 3 à 6000 stations utilisées- Découpe de la Terre en cube de 0.5 à 2° (50 à 200 km)- Inversion mathématique de millions d'équations simultanément- Tests de résolution- Visualisation des modèles tomographiques

Velocity

Harvard

Berkeley

Caltech

Isotropic VsDepth = 100 km

Maggi et al., (2005)‏

Interfaces du manteau

Topographie des discontinuités

Les interfaces du manteau

Les précurseurs des ondes SS (S410

S et S660

S) ‏

séisme

station

Précurseurs de SS

Période 20 s résolution latérale : 2000 km

(Tauzin et al., 2007)‏ Flanagan & Shearer, 1998

Topographie des discontinuités

Flanagan & Shearer, 1998

Anisotropie

Graine

Geometry of ray paths for PKP branch. (A) Ray paths for PKPAB (red curve), PKPBC (green curve), and PKPDF or PKIKP (blue curve) at an epicentral distance of 150°. PKPBC (BC for brevity) and PKPAB (AB) turn in the lower and upper outer core , respectively, and do not sample the inner core. Travel times of PKPDF (DF) are referred to as "absolute travel times" in contrast to "differential travel times," which are obtained by subtracting DF travel times from BC (BC – DF) or AB (AB – DF) travel times. Differential travel times are often used in inner-core studies because similarity of the BC or AB path with DF path within the mantle reduces undesirable mantle and earthquake effects from the data. Mantle heterogeneity based on a shear-velocity model of Gu et al. (13) is plotted. Red colors indicate slower than average velocity, and blue colors indicate faster than average velocity. The cross section is made along a great circle between Africa and the southwestern Pacific (crossing under Eurasia). (B) Geometry of the DF ray in the inner core (pale-blue circle), where {xi} is the angle of the ray with respect to the symmetry axis (shown in red). At high values of cos2{xi}, the ray is traveling parallel to the symmetry axis, and when cos2{xi} is small, the ray is traveling perpendicular to the symmetry axis.

Le noyau de la terre change au cours du temps

Zhang et al Science 2005