From
http://phoenix.liu.edu/~divenere/gly_511/interior.htm
The Moho
Mohorovicic (1909) discovered a boundary between layers with
differing seismic velocities. He plotted the P wave arrival time
(recorded by seismometers) against distance from an
earthquake. He recognized that out to a couple hundred
kilometers the slope of the line was constant implying that the
seismic waves were travelling through a layer of constant
velocity. At greater distances there was a change in slope of the
plotted time/distance, the seismic waves were arriving sooner
than expected, implying that the waves were passing through a
deeper layer with greater density and higher seismic velocity.
This seismic discontinuity is known as the Mohorovicic
discontinuity or simply the Moho. It is the boundary between the
felsic to mafic crust and the ultramafic mantle.
ยทยทยท
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The Moho reads out as "peaks and troughs," or a region
containng cavities. Some postulate it is a layer of different "rock
density," but there's little to no evidence to support this. It is
demonstrably an area where seismic waves slope sharply and
change course and expected speed. A picture showing the
relative depth of the Moho is here:
http://www.dc.peachnet.edu/~janderso/images/seisvel.jpg
--About twenty miles down, under the continents. A drilling
program to reach the Moho was attempted in the 1960's by NSF,
but it was abandoned (or was it?).
This is one of the most anomalous regions that science
"admits" exists, but really has little to no explanation for.
--Mike