<p>Very important is that the outer core being liquid (and mantle solid), shear waves from earthquakes cannot travel through the outer core. Along with refraction and reflection of <em>P</em>-waves at the core-mantle boundary, this <em>S</em>-wave shadow makes it possible to figure out how far down the boundary is.</p>

CC BY-SA 3.0
2014-04-25T17:00:21.993Z
2014-04-25T17:00:21.993Z
Phil Perry
<p>You are right...noone ever was able to make a borehole that deep. The two deepest boreholes are about. 12.300 m (40.400 ft) - those are the Kola Superdeep Borehole in Russia and the Al Shaheen oil well in Qatar.</p>

<p>So how do we measure the thickness of our subsurface? Think of the earth as an onion with different layers. Each of those layers (lithosphere, asthenosphere, mesospheric mantle, outer core, inner core) contain different mechanical (and chemical) properties. Due to this it is possible to infer indirectly the depth of each layer by using the travel time of refracted/reflected seismic waves (those come from earthquakes).</p>

<p>As mentioned before, each layer contains different mechanical properties, thus making the seismic velocity different in each layer. So on the border of each layer, those changes cause refraction or reflection if large increases in seismic velocity are involved.</p>

<p>Conclusion: no direct measurements possible, only indirectly derived measurements by the speed of travel from seismic waves.</p>

CC BY-SA 3.0
2014-04-25T13:20:08.377Z
2014-04-25T13:20:08.377Z
GeoEki
<p>According to <a href="http://en.wikipedia.org/wiki/Mantle_%28geology%29" rel="nofollow">Wikipedia</a> the earth's mantle is approximately 2900 km (1,800 miles) thick.<br/></p>

<p>How is it possible to achieve such measurements?<br/></p>

<p>Obviously we haven't sent anything down that far to check.</p>

CC BY-SA 3.0
2014-04-25T13:21:55.377Z
Ain't the answer likely to be similar to that given for [your other question](http://earthscience.stackexchange.com/questions/517/how-can-we-guess-the-size-of-the-earths-inner-coreand-what-its-made-of)?
plannapus
CC BY-SA 3.0
2014-04-25T13:25:43.743Z
Likely, but is seismology really the only way?
Ben A. Noone
CC BY-SA 3.0
2014-04-25T13:26:41.497Z
probably not. Do you think there is an alternative way that is valid for the mantle but invalid for the core? (this is not rhetorical, i have no idea myself)
plannapus
CC BY-SA 3.0
2014-04-25T13:46:31.887Z
I don't know either so I asked: http://earthscience.stackexchange.com/questions/557/is-seismology-really-the-only-way-to-measure-the-thickness-of-earths-layers
Ben A. Noone
CC BY-SA 3.0
2014-04-25T18:10:26.393Z
the answer is the same as the question plannapus mentioed.
Neo
CC BY-SA 3.0
2014-04-25T18:44:56.173Z
You don't seem to have done a lot of research for someone who is so interested in the structure of the earth's interior.
Matt Hall
<geophysics><measurements>
How can we measure the thickness of the Earth's mantle?
Ben A. Noone
# How can we measure the thickness of the Earth's mantle?

(Asked by: username_0 on 2014-04-25)

According to [Wikipedia](http://en.wikipedia.org/wiki/Mantle_%28geology%29) the earth's mantle is approximately 2900 km (1,800 miles) thick.

How is it possible to achieve such measurements?

Obviously we haven't sent anything down that far to check.

**Tags:** geophysics, measurements

> **Comments:**
> **username_1**: Ain't the answer likely to be similar to that given for [your other question](http://earthscience.stackexchange.com/questions/517/how-can-we-guess-the-size-of-the-earths-inner-coreand-what-its-made-of)?  
> **username_0**: Likely, but is seismology really the only way?  
> **username_1**: probably not. Do you think there is an alternative way that is valid for the mantle but invalid for the core? (this is not rhetorical, i have no idea myself)  
> **username_0**: I don't know either so I asked: http://earthscience.stackexchange.com/questions/557/is-seismology-really-the-only-way-to-measure-the-thickness-of-earths-layers  
> **username_2**: the answer is the same as the question username_1 mentioed.  
> **username_3**: You don't seem to have done a lot of research for someone who is so interested in the structure of the earth's interior.  

---

## 2 answers

### Answer by username_5 on 2014-04-25. Score: 8 | Accepted answer

You are right...username_0 ever was able to make a borehole that deep. The two deepest boreholes are about. 12.300 m (40.400 ft) - those are the Kola Superdeep Borehole in Russia and the Al Shaheen oil well in Qatar.

So how do we measure the thickness of our subsurface? Think of the earth as an onion with different layers. Each of those layers (lithosphere, asthenosphere, mesospheric mantle, outer core, inner core) contain different mechanical (and chemical) properties. Due to this it is possible to infer indirectly the depth of each layer by using the travel time of refracted/reflected seismic waves (those come from earthquakes).

As mentioned before, each layer contains different mechanical properties, thus making the seismic velocity different in each layer. So on the border of each layer, those changes cause refraction or reflection if large increases in seismic velocity are involved.

Conclusion: no direct measurements possible, only indirectly derived measurements by the speed of travel from seismic waves.


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### Answer by username_4 on 2014-04-25. Score: 4

Very important is that the outer core being liquid (and mantle solid), shear waves from earthquakes cannot travel through the outer core. Along with refraction and reflection of *P*-waves at the core-mantle boundary, this *S*-wave shadow makes it possible to figure out how far down the boundary is.


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