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EPSC 666 Team 3: Olivia
A 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

Andrija Mohorovicic
discovers the
“Moho”, the base of
the geophysical crust
in 1906
Richard Oldham 1906
 Bernard Bruhnes 1906
 Inge Lehmann 1936
 Harold Jeffreys 1936

... 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 geophysics
This 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