EPSC 666 Team 3: OliviaA geophysicist's view

A geophysicist sees Earth through lenses of various physical parameters.

What defines the geophysical crust? That outer “rigid” layer of Earth constrained below by a

sharp increase in the speed of sound waves.

What determines the speed of sound?

α = ( k + 4/3 µ ) / The Mohorovicic crust-mantle boundary

Geophysical structure

... diagram Wikimedia Commons

Seismic discovery

Richard Oldham 1906 Bernard Bruhnes 1906 Inge Lehmann 1936 Harold Jeffreys 1936

Andrija Mohorovicic discovers the “Moho”, the base of the geophysical crust in 1906

... diagram Wikimedia Commons

An inner-inner core?

Xiaodong Song & Xinlei Sun -- 2008

... diagram http://www.physorg.com/news124372414.html

... details upon detail: D''

D'' (D-double-prime) layer is discovered by Keith Bullen, 1950.

The global distribution is difficult to map with seismics or other direct geophysical techniques.

... story: http://www.esrf.eu/news/pressreleases/press_earth/index_html/

Back to the crust...

If we accept the Moho as the base of the crust, crustal thickness varies from 0km at spreading ridges to about 7km in ocean basins and to as much a 70km under the Himalayas.

... diagram: USGS

... beyond geophysicsThis Moho is correlated with mineralogical

differences... Ocean basins: the crust is mafic (basaltic,

gabbroic); the underlying mantle, ultramafic or, perhaps, a high-pressure assemblage of garnet & cpx.

Continents: the crust is largely felsic (granitic, andesitic); the underlying mantle, as above?

... but that is another story