Internal Structure of the Earth

11/15/18:
  • Bulk Earth Structure through Seismic Velocities
    Laterally averaged compressional and shear wave velocities and derived density structure through the earth.

  • Mantle Olivine
    • To 410 km:
      Olivine: alpha-phase (Mg,Fe)2Si04
    • 410 - 660 km:
      • First Wadsleyite: beta-phase Olivine (Mg,Fe)2Si04
      • Then around 520 km Ringwoodite: gamma-phase Olivine (Mg,Fe)2Si04
    • Deeper than 660 km separates into:
      • Magnesiowüstite: (Mg,Fe)0
      • Silicate Perovskite: (Mg,Fe)Si03

      • The Slab Graveyard


        A composite view of CMB heterogeneities, suggesting that mantle plumes initiate near these large, probably compositionally distinct 'piles' which may be old lithospheric slabs (source Garnero et al., GSA, 2007).

      • D'': Global topography of the Core-Mantle Boundary: 300 km high mountains?
    • Seismic Shadow Zones

      A dominant 'shadow zone' where no P-wave energy arrives between approximately 120° and 143° from a source. Significant, but non-direct energy P energy diffracts around the core from ~103° to 120°. Direct S energy vanishes near 90°, but does not recover again further away, due to the lack of shear propagation through the outer core. A similar P-wave shadow zone exists just below the lithosphere due to a low-velocity zone created by the relatively weak asthenosphere (this shadow-zone is not universally observed). [Image from the USGS].

11/21/18:
  • Attenuation through the Earth

    Whole-Mantle model of seismic shear-wave attenuation from Lawrence and Wysession (2006). The model includes 90K measurements of attenuation. (image from here).

  • Slabs on Command: An interesting look at Tomographic data used to argue for or against whole mantle convection (sometimes with the same data!).
  • Rheology from Isostasy

    Cumulative estimated uplift [in meters] of Fenoscandia over the past 10,000 years [Flint,Quaternary and Glacial Geology 1971]. Image from here.
  • Ongoing uplift visible in 'bathtub rings' left at this extremely stable inlet near Nunavut, Canada.

  • North American Plate Motion (from Calais et al., 2006)
  • After removing Euler motion, left with residual motion (mostly isostatic rebound) (from Sella_et al.,_2007)
  • 2-Layer viscoelastic rebound model used to describe ongoing deformation (from Sella_et al.,_2007)
11/27/18:
  • Slab Forces

    Major tectonic plates fall into two major classes separated by the fraction of their circumference that is a destructive slab boundary. Those plates with greater than 20% subduction zone move at higher tectonic rates (greater than 5 cm/yr), than those that have little subduction influence.
    Image from here.

Intro. to Geophysics: Supp. | Intro. to Geophysics: Home | Updated: Thu Nov 15 14:49:58 EST 2018