The Moho

Have you ever heard of the Moho? I know I haven’t, so I thought this would be an interesting article to do. The moho is the boundary between the crust and the mantle.

Moho is short for Mohorovicic Discontinuity. Discontinuity refers to “a surface at which seismic waves change velocity.” It has been found that there is one about 8 kilometers beneath the ocean basin, which is about 32 kilometers under land. At this location, seismic waves accelerate. Remember that a seismic wave is, according to dictionary.com, “an elastic shock wave that travels through the earth, as from an earthquake or explosion; also, one of four distinct waves generated by an earthquake.” That’s far down to have seismic waves. It’s amazing that scientist have been able to figure this out!

Andrija Mohorovicic , a Croatian seismologist, discovered the Mohorovicic Discontinuity in the year 1909. (This is where they get the name of the “moho” from.) He figures out that the velocity of a seismic wave is related to the density of the material that it moves through. Mohorovicic took what he knew about seismic waves and then observed them within Earth’ s  outer shell as a compositional change within the earth. From that, he figured that the acceleration of the seismic waves had to be from a higher density material that was available at the depth. The lower density material right below the surface is now known as “Earth’s crust”. And the higher density beneath the earth’s crust is now refferred to as “Earth’s mantle”.” Mr. Andrija Mohorovicic used density calculations that lead him to the conclusiont aht the ” basaltic oceanic crust and the granitic continental crust are underlain by a material which has a density similar to an olivine-rich rock such as peridotite.”

“Mohorovičić was able to use his discovery to study thickness variations of the crust. He discovered that the oceanic crust has a relatively uniform thickness while continental crust is thickest under mountain ranges and thinner under plains.”

There has not been any successful attempt to  go down to that level.  No one has been that far deep into the Earth in order to get to the moho. There has not been any drilling that goes that far down. But through careful research and calculations, scientist are  pretty sure it’s there.

 

 

http://dictionary.reference.com/browse/seismic+wave

http://geology.com/articles/mohorovicic-discontinuity.shtml

 

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One Response to The Moho

  1. emilyhartman says:

    I always find it interesting how scientists come up with different layers of the Earth even though no one has ever been down that far. It makes since that the seismic behavior changing could mean a different layer.

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