<p>This is a good observation. The reason we can measure S-wave (transverse) propagation in the inner core is because <strong>P-waves can set up S-waves and vice versa.</strong> When an S-wave hits the mantle-outer core boundary at an angle it has a vibration component which is normal to the boundary and this sets up a P-wave in the liquid inner core. The opposite happens at the outer core-inner core boundary, where the P-wave at the boundary sets up an S-wave in the solid inner core. In this way, we can measure S-wave transmission through the inner core.</p>

CC BY-SA 3.0
2016-12-03T21:50:06.663Z
Is this also applicable to the Moon? It is said that the Moon rings like a bell:
https://www.nasa.gov/exploration/home/15mar_moonquakes.html
Apparently, the earthquake that triggered the tsunami in Thailand in 2004 had the Earth ringing like a bell too. Therefore I would say that we have little knowledge what is down there.
Snake Sanders
CC BY-SA 3.0
2016-12-04T11:48:56.240Z
@SnakeSanders I don't quite understand what your point is. The 'ringing like a bell' refers to very large earthquakes (or moonquakes) exciting the normal modes of oscillation of the Earth.
bon
CC BY-SA 4.0
2019-03-29T19:18:35.590Z
@bon For the moon the "ringing like a bell" was for the impact of a lunar module from the Apollo mission
jean
CC BY-SA 3.0
2016-05-23T08:28:55.533Z
2016-05-23T08:28:55.533Z
bon
<p>As I know, the Earth core is solid. This is known, because it conducts also transverse waves, while liquids conduct only longitudinal waves.</p>

<p>But, how was it found? The inner core is in the outer core, which is liquid. Thus, it is inpermeable for the transverse waves.</p>

<p>So, any transverse wave originating in the crust, shouldn't be able to reach the core and vice versa.</p>

<p>How could it been measured?</p>

<geophysics><seismology><core>
How is known that the Earth core is solid?
peterh
# How is known that the Earth core is solid?

(Asked by: username_0 on 2016-05-23)

As I know, the Earth core is solid. This is known, because it conducts also transverse waves, while liquids conduct only longitudinal waves.

But, how was it found? The inner core is in the outer core, which is liquid. Thus, it is inpermeable for the transverse waves.

So, any transverse wave originating in the crust, shouldn't be able to reach the core and vice versa.

How could it been measured?

**Tags:** geophysics, seismology, core


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## 1 answers

### Answer by username_1 on 2016-05-23. Score: 13 | Accepted answer

This is a good observation. The reason we can measure S-wave (transverse) propagation in the inner core is because **P-waves can set up S-waves and vice versa.** When an S-wave hits the mantle-outer core boundary at an angle it has a vibration component which is normal to the boundary and this sets up a P-wave in the liquid inner core. The opposite happens at the outer core-inner core boundary, where the P-wave at the boundary sets up an S-wave in the solid inner core. In this way, we can measure S-wave transmission through the inner core.

> **Comments:**
> **username_2**: Is this also applicable to the Moon? It is said that the Moon rings like a bell: https://www.nasa.gov/exploration/home/15mar_moonquakes.html Apparently, the earthquake that triggered the tsunami in Thailand in 2004 had the Earth ringing like a bell too. Therefore I would say that we have little knowledge what is down there.  
> **username_1**: @username_2 I don't quite understand what your point is. The 'ringing like a bell' refers to very large earthquakes (or moonquakes) exciting the normal modes of oscillation of the Earth.  
> **username_3**: @username_1 For the moon the "ringing like a bell" was for the impact of a lunar module from the Apollo mission  

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